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MATERIALS 
 
 FOR THE 
 
 STUDY OF VARIATION 
 
 TREATED WITH ESPECIAL REGARD TO 
 
 DISCONTINUITY 
 
 IN THE 
 
 ORIGIN OF SPECIES. 
 
 BY 
 
 WILLIAM BATESON, M.A. 
 
 FELLOW OF ST JOHN'S COLLEGE, CAMBRIDGE 
 
 Pontoon : 
 MACMILLAN AND CO. 
 
 AND NEW YOKE. 
 1894 
 
 [All Eights reserved.] 
 
Cambridge : 
 
 PRINTED BY C. J. CLAY, M.A., AND SONS, 
 AT THE UNIVERSITY PRESS. 
 
PREFACE. 
 
 This book is offered as a contribution to the study of the 
 problem of Species. The reasons that have led to its production 
 are as follows. 
 
 Some years ago it was my fortune to be engaged in an investi- 
 gation of the anatomy and development of Balanoglossus. At the 
 close of that investigation it became necessary to analyze the 
 meaning of the facts obtained, and especially to shew their bear- 
 ing upon those questions of relationship and descent which modern 
 morphology has attempted to answer. To this task I set myself 
 as I best might, using the common methods of morphological 
 argument and interpretation, and working all the facts into a 
 scheme which should be as consistent as I could make it. 
 
 But the value of this and of all such schemes, by which each 
 form is duly ushered to its place, rests wholly on the hypothesis 
 that the methods of argument are sound. Over it all hung the 
 suspicion that they were not sound. This suspicion seemed at that 
 time so strong that in preface to what I had to say I felt obliged 
 to refer to it, and to state explicitly that the analysis was under- 
 taken in pursuance of the current methods of morphological 
 criticism, and without prejudging the question of possible or even 
 probable error in those methods. 
 
 Any one who has had to do such work must have felt the same 
 thing. In these discussions we are continually stopped by such 
 phrases as, " if such and such a variation then took place and was 
 favourable/' or, " we may easily suppose circumstances in which 
 such and such a variation if it occurred might be beneficial," and 
 the like. The whole argument is based on such assumptions as 
 these — assumptions which, were they found in the arguments of 
 Paley or of Butler, we could not too scornfully ridicule. " If," say 
 we with much circumlocution, " the course of Nature followed the 
 
 p 
 
 S J^- 
 
VI PREFACE. 
 
 lines we have suggested, then, in short, it did." That is the sum 
 of our argument. 
 
 Were we all agreed in our assumptions and as to the canons of 
 interpretation, there might be some excuse, but we are not agreed. 
 Out of the same facts of anatomy and development men of equal 
 ability and repute have brought the most opposite conclusions. 
 To take for instance the question of the ancestry of Chordata, the 
 problem on which I was myself engaged, even if we neglect 
 fanciful suggestions, there remain two wholly incompatible views 
 as to the lines of Vertebrate descent, each well supported and 
 upheld by many. From the same facts opposite conclusions are 
 drawn. Facts of the same kind will take us no further. The 
 issue turns not on the facts but on the assumptions. Surely we 
 can do better than this. Need we waste more effort in these vain 
 and sophistical disputes ? 
 
 If facts of the old kind will not help, let us seek facts of a new 
 kind. That the time has come for some new dej)arture most 
 naturalists are now I believe beginning to recognize. For the 
 reasons set forth in the Introduction I suggest that for this new 
 start the Study of Variation offers the best chance. If we had 
 before us the facts of Variation there would be a body of evidence 
 to which in these matters of doubt we could appeal. We should 
 no longer say " if Variation take place in such a way," or " if such 
 a variation were possible ; " we should on the contrary be able to 
 say " since Variation does, or at least may take place in such a way," 
 ''' since such and such a Variation is possible," and we should 
 be expected to quote a case or cases of such occurrence as an 
 observed fact. 
 
 To collect and codify the facts of Variation is, I submit, the 
 first duty of the naturalist. This work should be undertaken if 
 only to rid our science of that excessive burden of contradictory 
 assumptions by which it is now oppressed. Whatever be our 
 views of Descent, Variation is the common basis of them all. As 
 the first step towards the systematic study of Variation we need a 
 compact catalogue of the known facts, a list which shall contain as 
 far as possible all cases of Variation observed. To carry out such a 
 project in any completeness may be impossible ; but were the plan 
 to find favour, there is I think no reason why in time a consider- 
 able approach to completeness should not be made. 
 
PREFACE. Vll 
 
 Difficulty has hitherto arisen from the fact that Variation is 
 not studied for its own sake. Each observer has some other object 
 in view, and we are fortunate if he is good enough to mention in 
 passing the variations he has happened to see in following his own 
 ends. From the nature of the case these observations must at 
 first be sporadic, and, as each standing alone seems to have little 
 value, in the end they are unheeded and lost. If there were any 
 central collection of facts to which such observations might from 
 time to time be added, and thus brought into relation with cognate 
 observations, their value would at once appear and be preserved. 
 To make a nucleus for such a collection is the object of the present 
 work. 
 
 The subject treated in this first instalment has been chosen for 
 the reasons given in the text. Reference to facts that could not 
 be included in this section of the evidence has as far as possible 
 been avoided, but occasionally such reference was necessary, 
 especially in the Introduction. 
 
 It was my original purpose to have published the facts with- 
 out comment. This course would have been the most logical and 
 the safest, but with hesitation it was decided to add something of 
 the nature of analysis. I do this chiefly for two reasons. First, 
 in starting a method one is almost compelled to shew the way in 
 which it is to be applied. If it is hoped that others may interest 
 themselves in the facts, it is necessary to shew how and why their 
 interest is asked. In the old time the facts of Nature were 
 beautiful in themselves and needed not the rouge of speculation 
 to quicken their charm, but that was long ago, before Modern 
 Science was born. 
 
 Besides this, to avoid the taint of theory in morphology ' is 
 impossible, however much it may be wished. The whole science 
 is riddled with theory. Not a specimen can be described without 
 the use of a terminology coloured by theory, implying the accept- 
 ance of some one or other theory of homologies. If only to avoid 
 misconception matters of theory must be spoken of. 
 
 It seemed at first also that the meaning of the facts was so 
 clear that all would read it alike ; but from opportunities that 
 have occurred for the discussion of these matters I have found 
 that it is not so, and reluctantly I have therefore made such com- 
 ments as may serve to bring out the chief significance of the 
 
Vlll PREFACE. 
 
 phenomena, pointing out what they shew and what they do not 
 shew, having regard always to deficiencies in the evidence. 
 
 That this is a dangerous course I am aware. But in any 
 discussion of a problem in the light of insufficient knowledge the 
 real danger is not that a particular conclusion may be wrong, for 
 that is a transient fault, but rather that the facts themselves may 
 be so distorted as to be valueless to others when the conclusions 
 that they were used to shew have been discarded. This danger I 
 have sought indifferently to avoid by printing the facts as far as 
 possible apart from all comment, knowing well how temporary the 
 worth of these comments is likely to be. I have thus tried to 
 avoid general statements and have kept the descriptions to 
 particular cases, unless the number of similar cases is great and 
 an inclusive description is enough. 
 
 Each separate paragraph relating a fact has been as far as 
 possible isolated and made to stand alone ; so that if any one may 
 hereafter care to go on with the work he will be able to cut out 
 the discarded comments and rearrange the facts in any order 
 preferred, inserting new facts as they come to hand. Most of 
 these facts are numbered for reference. The numbers are distrib- 
 uted on no strict system, but are put in where likely to be useful. 
 
 For almost every fact stated or mentioned one reference at lea>t 
 is given. When this is not the case the fact is either notorious, 
 or else the result of my own observation. In collecting evidence I 
 have freely used the collections of former writers, especially those 
 of Geoffroy St Hilaire, Ahlfeld, and Wenzel Gruber, but unless 
 the contrary is stated, each passage referred to has been seen in 
 its original place. By this system I hope I have avoided evidence 
 corrupted by repetition. Several well known conceptions, notably 
 that of the presence of order in abnormality, first formulated by 
 Isidore Geoffroy St Hilaire, have been developed and exhibited 
 in their relation to recent views. 
 
 The professed morphologist will note that many of the state- 
 ments are made on authority unfamiliar to him. I have spared no 
 pains to verify the facts wherever possible, and no case has been 
 admitted without remark if there was reason to doubt its authen- 
 ticity. So long as skilled zoologists continue to neglect all forms 
 that are abnormal the student of Variation must turn to other 
 sources. 
 
 This neglect of the Study of Variation may be attributed in 
 
PREFACE. IX 
 
 great measure to the unfortunate circumstance that Natural History 
 lias come to be used as a vehicle for elementary education, a 
 purpose to which it is unsuited. From the conditions of the case 
 when very large classes are brought together it becomes necessary 
 that the instruction should be organized, scheduled, and reduced to 
 diagram and system. Facts are valued in proportion as they lend 
 themselves to such orderly treatment ; on the rest small store is 
 set. By this method the pupil learns to think our schemes of 
 Nature sufficient, turning for inspiration to books, and supposing 
 that by following his primer he may master it all. In a specimen 
 he sees what he has been told to see and no more, rarely learning 
 the habit of spontaneous observation, the one lesson that the 
 study of Natural History is best fitted to teach. 
 
 Such a system reacts on the teacher. In time he comes to 
 forget that the caricature of Nature shewn to his pupils is like 
 no real thing. The perspective and atmosphere that belong to 
 live nature confuse him no more. Two cases may be given in 
 illustration. Few animals are dissected more often than the 
 Crayfish and the Cockroach. Each of these frequently presents 
 a striking departure from the normal (see Nos. 83 and 625) in 
 external characters, but these variations have been long unheeded 
 by pupil and by teacher; for though Desmarest and Brisout 
 published the facts so long ago as 1848, their observations failed 
 to get that visa of the text-books without which no fact can 
 travel far. 
 
 It is especially strange that while few take much heed of the 
 modes of Variation or of the visible facts of Descent, every one is 
 interested in the causes of Variation and the nature of " Heredity,'" 
 a subject of extreme and peculiar difficulty. In the absence of 
 special knowledge these things are discussed with enthusiasm. 
 even by the public at large. 
 
 But if we are to make way with this problem special know- 
 ledge is the first need. We must know what special evidence each 
 group of animals and plants can give, and this specialists alone 
 can tell us. It is therefore impossible for one person to make any 
 adequate gathering of the facts. If it is to be done it must be 
 done by many. At one time I thought that a number of persons 
 might perhaps be induced thus to combine ; but though I hope 
 hereafter some such organized collection may be made, it is 
 perhaps necessary that the first trial should be single-handed. 
 
X PREFACE. 
 
 As I have thus been obliged to speak of many things of which 
 I have no proper knowledge each section must inevitably seem 
 meagre to those w 7 ho have made its subject their special study, 
 and I fear that many mistakes must have been made. To any one 
 who may be willing to help to set these errors right, I offer thanks 
 in advance, " humbly acknowledging a work of such concern- 
 ment unto truth did w T ell deserve the conjunction of many heads." 
 
 In the course of the work I have had help from so many that 
 I cannot here give separate thanks to each. For valuable criticisms, 
 given especially in connexion with the introductory pages, I am 
 indebted to Mr F. Darwin, Dr C. S. Sherrington, Dr D. MacAlister, 
 Mr W. Heape, Mr G. F. Stout, Dr A. A. Kanthack and particularly 
 to Mr J. J. Lister. I have to thank the authorities of the 
 British Museum, of the Museum of the Royal College of Surgeons, 
 of the Musee d'Histoire Naturelle in Paris, and of the Museums 
 of Leyden, Oxford, Rouen, New T castle-upon-Tyne, of the Ecole 
 Veterinaire at Alfort, and of the Dental Hospital for the great 
 kindness that they have shewn me in granting facilities for the 
 study of their collections. In particular I must thank Mr Oldfield 
 Thomas of the British Museum for much help and advice in con- 
 nexion with the subject of Teeth. I am also greatly obliged to 
 Messrs Godman and Salvin for opportunities of examining and 
 drawing specimens in their collections. To many others who have 
 been good enough to lend specimens or to advise in particular 
 cases my obligations are acknowledged in the text, but I must 
 especially express my gratitude to Dr Kraatz of Berlin, to Dr L. 
 von Heyden of Frankfurt, and to M. H. Gadeau de Kerville of 
 Rouen for the large numbers of valuable insects wuth which they 
 entrusted me. 
 
 My best thanks are due to Dr A. M. Norman for many useful 
 suggestions, for the loan of specimens and for the kindly interest 
 he has taken in my work. 
 
 My friend Mr H. H. Brindley has very kindly given me much 
 assistance in determining and verifying several points that have 
 arisen, and I am particularly indebted to him for permission to 
 give an account of his very interesting and as yet unpublished 
 observations on the variation and regeneration of the tarsus in 
 Cockroaches. 
 
 Through the help of Dr David Sharp I have been enabled to 
 introduce much valuable evidence relating to Insects, a subject of 
 
PREFACE. XI 
 
 which without his assistance I could scarcely have spoken. It is 
 impossible for me adequately to express my obligation to Dr Sharp 
 for his constant kindness, for the many suggestions he has given 
 me, and for the generosity with which he has put his time and 
 skill at my service. 
 
 It is with especial pleasure that I take this opportunity of 
 offering my thanks to Professor Alfred Newton for the encourage- 
 ment and sympathy he has given me now for many years. 
 
 As many of the subjects treated involve matters of interpret- 
 ation it should be explicitly declared that though help has been 
 given by so many, no responsibility for opinions attaches to anyone 
 but myself unless the contrary is stated. 
 
 The blocks for Figs. 18, 19, 25, 13:3, 161 and 185 (from Proc 
 Zool. Soc.) were very kindly given by the Zoological Society of 
 London; that for Fig. 28 (from Trans. Path. Soc.) by the Pathological 
 Society; and for Fig. 140 which is from the Descent of Man I am 
 obliged to the kindness of Mr F. Darwin. Figs. 5 B, 5 c, and 77 were 
 supplied by the proprietors of Newman's British Butterflies, and 
 Figs. 5 A, 82 and 84 by the proprietors of the Entomologist. The 
 sources of other figures are acknowledged under each. Those not 
 thus acknowledged have been made from specimens or from my 
 own drawings or models by Mr M. P. Parker, with the exception 
 of a few specially drawn for me by Mr Edwin Wilson. 
 
 The work was, as I have said, begun in the earnest hope that 
 some may be led thereby to follow the serious study of Variation, 
 and so make sure a base for the attack on the problems of 
 Evolution. Those who reject the particular inferences, positive 
 and negative, here drawn from that study, must not in haste 
 reject the method, for that is right beyond all question. 
 
 That the first result of the study is to bring confusion and 
 vagueness into places where we had believed order established 
 may to some be disappointing, but it is best we deceive ourselves 
 no longer. That the problems of Natural History are not easy but 
 very hard is a platitude in everybody's mouth. Yet in those days 
 there are many who do not fear to speak of these things with 
 certainty, with an ease and an assurance that in far simpler 
 problems of chemistry or of physics would not be endured. For 
 men of this stamp to solve difficulties may be easy, but to feel 
 
Xll PREFACE. 
 
 difficulties is hard. Though the problem is all unsolved and the 
 old questions stand unanswered, there are those who have taken 
 on themselves the responsibility of giving to the ignorant, as a 
 gospel, in the name of Science, the rough guesses of yesterday 
 that tomorrow should forget. Truly they have put a sword in the 
 hand of a child. 
 
 If the Study of Variation can serve no other end it may make 
 us remember that we are still at the beginning, that the com- 
 plexity of the problem of Specific Difference is hardly less now 
 than it was when Darwin first shewed that Natural History is a 
 problem and no vain riddle. 
 
 On the first page I have set in all reverence the most solemn 
 enuntiation of that problem that our language knows. The priest 
 and the poet have tried to solve it, each in his turn, and have 
 failed. If the naturalist is to succeed he must go very slowly, 
 making good each step. He must be content to work with the 
 simplest cases, getting from them such truths as he can, learning 
 to value partial truth though he cheat no one into mistaking 
 it for absolute or universal truth; remembering the greatness 
 of his calling, and taking heed that after him will come Time, 
 that "author of authors," whose inseparable property it is ever 
 more and more to discover the truth, who will not be deprived 
 of his due. 
 
 St John's College, Cambridge. 
 29 December, 1893. 
 
CONTENTS. 
 
 INTRODUCTION. 
 
 SECT. 
 
 1. The Study of Variation 
 
 2. Alternative Methods ..... 
 
 3. Continuity or Discontinuity of Variation 
 
 4. Symmetry and Meristic Eepetition 
 
 5. Meristic Variation and Substantive Variation 
 
 6. Meristic Repetition and Homology 
 
 7. Meristic Repetition and Division . 
 
 8. Discontinuity in Substantive Variation : Size 
 
 9. Discontinuity in Substantive Variation : Colour and Colour-Patterns 
 
 10. Discontinuity in Substantive Variation : Miscellaneous Examples 
 
 11. Discontinuity in Meristic Variation: Examples .... 
 
 12. Parallel between Discontinuity of Sex and Discontinuity in Variation 
 
 13. Suggestions as to the nature of Discontinuity in Variation . 
 
 11. Some current conceptions of Biology in view of the Facts of Variation 
 
 1. Heredity. 2. Reversion. 3. Causes of Variation. 4. The 
 Variability of "useless" Structures. 5. Adaptation. G. Natural 
 Selection. 
 
 PAGE 
 
 1 
 
 6 
 13 
 17 
 22 
 28 
 33 
 36 
 42 
 r,i 
 GO 
 66 
 68 
 75 
 
 PART I. 
 
 MERISTIC VARIATION 
 
 Linear Series ..... 
 Radial Series ..... 
 Bilateral Series ..... 
 Secondary Symmetry and Duplicity . 
 
 CHAPTER I. Arrangement of Evidence 
 CHAPTER II. Segments of Arthhopoda 
 
 87—422 
 jj;5_447 
 
 448—473 
 
 171— 56G 
 
 83 
 
 91 
 
XIV 
 
 CHAPTER 
 CHAPTER 
 CHAPTER 
 CHAPTER 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 CHAPTER VII 
 
 CONTENTS. 
 
 Vertebra and Ribs 
 
 Spinal Nerves 
 
 Variation in Arthropoda 
 
 Cpletopoda, Hirudinea and Cestoda 
 
 Branchial openings of Chordata and struc- 
 tures IN CONNEXION WITH THEM . 
 
 1. Ascidians. 2. Cyclostomi. 3. Cervical Fistula? and Super- 
 numerary Auricles in Mammals 
 
 CHAPTER VIII. Mammjs 
 
 CHAPTER IX. Teeth 
 
 Preliminary. Primates. Canidae. Felidas. Viverridas. Muste 
 lidae. Pinnipedia. Marsupialia. Selacbii. Radulse of Buccinum 
 
 CHAPTER X. Teeth— Recapitulation 
 
 CHAPTER XI. Miscellaneous Examples .... 
 
 Scales. Kidneys; Renal Arteries; Ureters. Tentacles and Eyes 
 of Mollusca. Eyes of Insects. Wings of Insects. Horns of 
 Sheep, Goats and Deer. Perforations of shell of Haliotis. 
 
 CHAPTER XII. Colour-Markings 
 
 Ocellar Markings. Simultaneity of Colour-Variation in Parts 
 repeated in Linear Series (Larvae of Lepidoptera : Chitonidae) 
 
 CHAPTER XIII. Minor Symmetries: Digits . 
 
 Cat. Pp. 313—324. 
 
 Man and Apes. Pp. 324—360. 
 
 Increase in number of digits, p. 324. 
 
 Cases of Polydactylism associated ivith change of Symmetry. A. 
 
 Digits in one Successive Series, p. 326. B. Digits in two 
 
 homologous groups forming "Double-hands," p. 331. Complex 
 
 cases, p. 338. 
 Polydactylism not associated ivith change of Symmetry, p. 344. (1) 
 
 A. Single extra digit external to minimus, p. 345. (1) B. 
 
 Single extra digit in other positions, p. 349. (2) Duplication of 
 
 single digits, p. 349. (3) Combinations of the foregoing, p. 352. 
 
 (4) Irregular examples, p. 353. 
 Reduction in number of phalanges, p. 355. Syndactylism, p. 356. 
 
 Absence of digits and representation of two digits by one, p. 358. 
 
 Horse, pp. 360 — 373. Extra digits on separate metacarpal or meta- 
 tarsal, p. 361. More than one digit borne by metacarpal III., 
 p. 369. Intermediate cases, p. 371. 
 
 Artiodactyla, pp. 373—390. Polydactylism in Pecora, p. 373. Poly- 
 dactylism in Pig, p. 381. Syndactylism in Artiodactyla, p. 383. 
 
 Birds, pp. 390—395. 
 
 Possibly Continuous numerical Variation in digits : miscellaneous 
 examples, pp. 395 — 398 (Chalcides. Cistudo. Rissa. Erinaceus. 
 Elephas.) Inheritance of Digital Variation. Association of 
 Digital Variation with other forms of Abnormality. 
 
 PAGE 
 
 102 
 129 
 146 
 156 
 
 171 
 
 181 
 195 
 
 265 
 
 274 
 
 288 
 
 311 
 
CONTEXTS. 
 
 XV 
 
 CHAPTER XIV. Digits: Recapitulation 
 
 CHAPTER XV. Minor Symmetries: Segments in Appendages 
 
 CHAPTER XVI. Radial Series 
 
 Coelenterata. Pedicellariae of Echinoderms. Cell-Division. 
 
 CHAPTER XVII. Radial Series: Echinodermata 
 
 CHAPTER XVIII. Bilateral Series 
 
 CHAPTER XIX. 
 
 Further Illustrations of the Relationship 
 between Right and Left Sides 
 
 CHAPTER XX. Supernumerary Appendages in Secondary 
 
 Symmetry 
 
 Introductory. — The Evidence as to Insects. 
 
 CHAPTER XXI. 
 
 The Evidence 
 
 CHAPTER XXII. 
 CHAPTER XXIII. 
 
 CHAPTER XXIV. 
 CHAPTER XXV. 
 
 Appendages in Secondary Symmetry . 
 as to Crustacea. 
 
 Duplicity of Appendages in Arthropoda . 
 
 Secondary Symmetry in Vertebrates. Re- 
 marks on the Significance of Repetition 
 in Secondary Symmetry : Units of Repe- 
 tition 
 
 Double Monsters 
 
 Concluding Reflexions 
 
 PAGE 
 
 400 
 410 
 423 
 
 432 
 448 
 
 4G3 
 474 
 
 525 
 
 539 
 
 553 
 559 
 567 
 
 INDEX OF SUBJECTS, p. 576. 
 
 INDEX OF PERSONS, p. 593. 
 
CORRIGENDA. 
 
 p. 23, line 5. For " and that in " read " and in." 
 
 p. 27, line 29. For " appear" read " appears." 
 
 p. 37, line 18. For " their " read " the." 
 
 p. 54. Note 2. For "xxviii" read "xx." 
 
 p. 55. Parra is now known not to have affinities with the Eallidae. 
 
 p. 141. In description of Fig. 15 insert "After Solgee." 
 
 p. 151, line 2 and p. 153, Note. For "W. B." read "G. B." 
 
 p. 198. For " Pinnipediae" read "Pinnipedia." For "Dent." read "Deuf." 
 
 p. 212. In description of Fig. 40 delete " p l of the left side is in symmetry with 
 two teeth on tbe right side." The figure is correct. 
 
 p. 281, 15th line from bottom. Delete " and perhaps all." 
 
 p. 382. For "W. H. Benham" read "W. B. Benham." 
 
 p. 429. For " Banyul's " read " Banyuls." 
 
 p. 473, 4th and 6th lines from bottom. For " Tornaria" read " Balanoglossus" 
 
 p. 526. Delete the heading " (1) Clear cases of Extra Parts in Secondary 
 Symmetry." 
 
 Note to p. 461, Note 718. As to union of eyes in Bees, see further, Ditteich, 
 Zeit. f. Ent., Breslau, 1891, xvi. p. 21, and Cook, A. J., Proc. Amer. Ass., 1891, 
 p. 327. 
 
 Note to p. 468, Note 2. In connexion with Giard's observation the following 
 fact should be given. Since this Chapter was printed I have had an opportunity of 
 examining a sample of Flounders taken in the shallow water off Bournemouth. Of 
 23 specimens seen alive, all but about half a dozen were more or less blotched with 
 shades of brown on the " blind " side. In five the brown was more extensive than 
 the white. The eyes and dorsal fins were normal. The fishmonger who shewed 
 them to me said that the Flounders in that place were generally thus blotched, and 
 that those seen were a fair sample. In estimating the significance of Cunningham's 
 experiment (p. 467) this fact should be remembered. 
 
INTRODUCTION. 
 
 All flesh is not the same flesh : but there is one kind of flesh of men, another 
 flesh of beasts, another of fishes, and another of bird?. 
 
 SECTION I. 
 
 The Study of Variation. 
 
 To solve the problem of the forms of living things is the aim 
 with which the naturalist of to-day comes to his work. How 
 have living things become what they are, and what are the laws 
 which govern their forms ? These are the questions which the 
 naturalist has set himself to answer. 
 
 It is more than thirty years since the Origin of Species was 
 written, but for many these questions are in no sense answered 
 yet. In owning that it is so, we shall not honour Darwin's 
 memory the less ; for whatever may be the part which shall be 
 finally assigned to Natural Selection, it will always be remem- 
 bered that it was through Darwin's work that men saw for the 
 first time that the problem is one which man may reasonably 
 hope to solve. If Darwin did not solve the problem himself, he 
 first gave us the hope of a solution, perhaps a greater thing. 
 How great a feat this was, we who have heard it all from child- 
 hood can scarcely know. 
 
 In the present work an attempt is made to find a way of 
 attacking parts of the problem afresh, and it will be profitable 
 first to state formally the conditions of the problem and to examine 
 the methods by which the solution has been attempted before. 
 This consideration shall be as brief as it can be made. 
 
 The forms of living things have many characters: to solve the 
 problem completely account must be taken of all. Perhaps no 
 character of form is common to all living things; on the 
 contrary their forms are almost infinitely diverse. Now in those 
 attempts to solve the problem which have been the best, it is this 
 diversity of form which is taken as the chief attribute, and the 
 attempt to solve the general problem is begun by trying to trace 
 the modes by which the diversity has been produced. In the 
 shape in which it has been most studied, the problem is thus the 
 
 Fftor * AFY l 
 
 B. 
 
 ii n n i\\\\ooo 
 
2 THE PROBLEM OF SPECIES. [ixtrod. 
 
 problem of Species. Obscurity has been brought into the treat- 
 ment of the question through want of recognition of the fact that 
 this is really only a part of the general problem, which would still 
 remain if there were only one species. Nevertheless the problem 
 of Species is so tangible a part of the whole that it is perhaps the 
 best point of departure. For our present purpose we cannot 
 begin better than by stating it concisely. 
 
 The forms of living things are diverse. They may neverthe- 
 less be separated into Specific Groups or Species, the members of 
 each such group being nearly alike, while they are less like the 
 members of any other Specific Group. [The Specific Groups may 
 by their degrees of resemblance be arranged in Generic Groups 
 and so on.] 
 
 The individuals of each Specific Group, though alike, are not 
 identical in form, but exhibit differences, and in these differences 
 they may even more or less nearly approach the form characteristic 
 of another Specific Group. It is true, besides, that in the case of 
 many Specific Groups which have been separated from each other, 
 intermediate forms are found which form a continuous series of 
 gradations, passing insensibly from the form characteristic of one 
 Species to that characteristic of another. In such cases the 
 distinction between the two groups for purposes of classification is 
 not retained. 
 
 The fact that in certain cases there are forms transitional 
 between groups which are sufficiently different to have been 
 thought to be distinct, is a very important fact which must not 
 be lost sight of; but though now a good many such cases are 
 known, it remains none the less true that at a given point of 
 time, the forms of living things may be arranged in Specific 
 Groups, and that between the immense majority of these there 
 are no transitional forms. There are therefore between these 
 Specific Groups differences which are Specific. 
 
 No definition of a Specific Difference has been found, perhaps 
 because these Differences are indefinite and hence not capable of 
 definition. But the forms of living things, taken at a given 
 moment, do nevertheless most certainly form a discontinuous 
 series and not a continuous series. This is true of the world as 
 we see it now, and there is no good reason for thinking that it has 
 ever been otherwise. So much is being said of the mutability of 
 species that this, which is the central fact of Natural History, is 
 almost lost sight of, but if ever the problem is to be solved this 
 fact must be boldly faced. There is nothing to be gained by 
 shirking or trying to forget it. 
 
 The existence, then, of Specific Differences is one of the 
 characteristics of the forms of living things. This is no merely 
 subjective conception, but an objective, tangible fact. This is the 
 first part of the problem. 
 
sect. I.] INTRODUCTION. 3 
 
 In the next place, not only do Specific forms exist in Nature, 
 but they exist in such a way as to fit the place in Nature in 
 which they are placed; that is to say, the Specific form which an 
 organism has, is adapted to the position which it fills. This again 
 is a relative truth, for the adaptation is not absolute. 
 
 These two facts constitute the problem : 
 
 I. The forms of living things are various and, on the whole, 
 are Discontinuous or Specific. 
 
 II. The Specific forms, on the whole, fit the places they 
 have to live in. 
 
 How have these Discontinuous forms been brought into exist- 
 ence, and how is it they are thus adapted ? This is the question 
 the naturalist is to answer. To answer it completely he must find 
 (1) The modes and (2) The causes by which these things have 
 come to pass. 
 
 Before considering the ways in which naturalists have tried to 
 answer these questions, it is necessary to look at some other 
 phenomena characteristic of Life. We have said that at a given 
 moment, or point of time, the specific forms of living things com- 
 pose a discontinuous series. The element of time thus intro- 
 duced is of consequence, and leads to important considerations. 
 For the condition of the organized world is not a fixed condition, 
 but changes from moment to moment, and that which can be pre- 
 dicated of its condition at one moment may not at any other point 
 of time be true. This process of change is brought about partly by 
 progressive changes in the bodies of the individuals themselves, 
 hut chiefly by the constant succession of individuals, the parents 
 dying, their offspring succeeding them. It is then a matter of 
 observation that the offspring born of parents belonging to any 
 one Specific Group do as a rule conform to that Specific Group 
 themselves, and that the form of the bodv, the mechanisms and 
 the instincts of the offspring, are on the whole similar to those 
 which their parents had. But like most general assertions about 
 living things this is true not absolutely but relatively only. For 
 though on the whole the offspring is like the parent or parents, its 
 form is perhaps never identical with theirs, but generally differs 
 from it perceptibly and sometimes materially. To this pheno- 
 menon, namely, the occurrence of differences between the structure, 
 the instincts, or other elements which compose the mechanism of 
 the offspring, and those which were proper to the parent, the name 
 Variation has been given. 
 
 We have seen above that the two leading facts respecting the 
 forms of living things are first that they shew specific differen- 
 tiation, and secondly that they are adapted. To these we may 
 now add a third, that in the succession from parent to offspring 
 there is, or may be, Variation. It is upon the fact of the exist- 
 ence of this phenomenon of Variation that all inductive theories 
 of Evolution have been based. 
 
 1—2 
 
4 A POSTULATE. [introd. 
 
 The suggestion which thus forms the common ground of these 
 theories is this : — May not the Specific Differences between Species 
 and Species have come about through and be compounded of the 
 individual differences between parent and offspring ? May not 
 Specific Differentiation have resulted from Individual Variation ? 
 This suggestion has been spoken of as the Doctrine of Common 
 Descent, for it asserts that there is between living things a 
 community of descent. 
 
 In what follows it will be assumed that this Doctrine of 
 Descent is true. It should be admitted from the first that the 
 truth of the doctrine has never been proved. There is never- 
 theless a great balance of evidence in its favour, but it finds its 
 support not so much in direct observation as in the difficulty of 
 forming any alternative hypothesis. The Theory of Decent in- 
 volves and asserts that all living things are genetically connected, 
 and this principle is at least not contrary to observation ; while 
 any alternative hypothesis involves the idea of Separate Creation 
 which by common consent is now recognized as absurd. In favour 
 of the Doctrine of Common Descent there is a balance of evidence: 
 it is besides accepted by most naturalists ; lastly if it is not true 
 we can get no further with the problem : but inasmuch as it is 
 unproven, it is right that we should explicitly recognize that it is 
 in part an assumption, and that we have adopted it as a pos- 
 tulate. 
 
 The Doctrine of Descent being assumed, two chief solutions of 
 the problem have been offered, both starting alike from this 
 common ground. Let us now briefly consider each of them. 
 
 A. Lamarck's Solution. So many ambiguities and pitfalls are 
 in the way of any who may try to re-state, in a few words, the 
 theory propounded in the Philosoplvie Zoologique, that it is with 
 great diffidence that the following account of it is given. 
 
 Lamarck points out that living things can in some measure 
 adapt themselves both structurally and physiologically to new 
 circumstances, and that in certain cases the adaptability is present 
 in a high degree. He suggests that by inheritance and perfection 
 of such adaptations they may have become what they are, and that 
 thus specific forms and mechanisms have been produced, as it were, 
 by sheer force of circumstances. On this view it is assumed that 
 to the demands made on it by the environment the organism 
 makes an appropriate structural and physiological response ; in 
 other words, that there is in living things a certain tension, by 
 which they respond to environmental pressure and fit the place 
 they are in, somewhat as a fluid fits a vessel. 
 
 This is not, I think, a misrepresentation of Lamarck's theory. 
 It amounts, in other words, to a proposal to regard organisms as 
 machines which have the power of Adaptation as one of their 
 fundamental and inherent qualities or attributes. 
 
sect, l] introduction. 5 
 
 Without discussing this solution, we may oote that it aims at 
 being a complete solution of both 
 
 (1) The existence and persistence of differing forms, 
 {'!) The fact that the differing forms are adapted fco 
 different conditions ; 
 and (3) The causes of the Variation by which the diversity baa 
 occurred. 
 
 B. Darwin's Solution. Darwin, without suggesting causes of 
 Variation, points out that since (1) Variations occur — which they 
 are known to do — and since (2) some of the variations are in tin- 
 direction of adaptation and others are not — which is a necessil v — 
 it will result from the conditions of the Struggle for Existence 
 that those better adapted will on the whole persist and the less 
 adapted will on the whole be lost. In the result, therefore, there 
 will be a diversity of forms, more or less adapted to the states 
 in which they are placed, and this is very much the observed 
 condition of living things. 
 
 We may note that this solution does not aim at being a com- 
 plete solution like Lamarck's, for as to the causes of Variation it 
 makes no suggestion. 
 
 The arguments by which these several solutions are supported, 
 and the difficulties which are in the way of each, are so familiar 
 that it would be unprofitable to detail them. On our present 
 knowledge the matter is talked out. Those who are satisfied with 
 either solution are likely to remain so. 
 
 It may be remarked however that the observed cases <<t" adap- 
 tation occurring in the way demanded on Lamarck's theory are 
 very few, and as time goes on this deficiency of facts begins to be 
 significant. Natural Selection on the other hand is obviously a 
 • true cause,' at the least. 
 
 In the way of both solutions there is one cardinal difficulty 
 which in its most general form maybe thus expressed. Aco.rding 
 to both theories, specific diversity of form is consequent upon 
 diversity of environment, and diversity of environment is thus 
 the ultimate measure of diversity of specific form. Mere then we 
 meet the difficulty that diverse environments often shade into 
 each other insensibly and form a continuous series, whereas the 
 Specific Forms of life which are subject to them on the whole 
 form a Discontinuous Series. The immense significance of this 
 difficulty will be made more apparent in the course of this work 
 The difficulty is here put generally. Particular instances have 
 been repeatedly set forth. Temperature, altitude, depth of water. 
 salinity, in fact most of the elements which make up the physical 
 environment are continuous in their gradations, while, as a rule, 
 the forms of life are discontinuous 1 . Besides this, forms which 
 
 1 It may be objected that to any organism tbe other organisms coexisting with 
 it are as serious a factor of tbe environment as the strictly physical components; 
 and that inasmuch as these coexisting organisms are discontinuous Bpecies, the 
 
6 METHODS OF ATTACKING THE PROBLEM. [ixtrod. 
 
 are apparently identical live under conditions which are apparently 
 very different, while species which though closely allied are con- 
 stantly distinct are found under conditions which are apparently 
 the same. If we would make these facts accord with the view 
 that it is diversity of environment which is the measure of 
 diversity of specific form, it is necessary to suppose either (1) 
 that our estimate of similarity of forms, or of environment, is 
 wholly untrustworthy, or else (2) that there is a wide area of 
 environmental or structural divergence within which no sensible 
 result is produced : that is to say, that the relation between en- 
 vironment and structure is not finely adjusted. But either of these 
 admissions is serious ; for if we grant the former we abrogate the 
 right of judgment, and are granting that our proposed solutions 
 are mere hypotheses which we have no power to test, while if we 
 admit the latter, we admit that environment cannot so far be either 
 the directing cause or the limiting cause of Specific Differences, 
 though the first is essential to Lamarck's Theory, and the second is 
 demanded by the doctrine of Natural Selection. 
 
 Such then, put very briefly, are the two great theories, and this 
 is one of the chief difficulties which beset them. We must now 
 pass to our proper work. 
 
 We have to consider whether it is not possible to get beyond 
 the present position and to penetrate further into this mystery 
 of Specific Forms. The main obstacle being our own ignorance, 
 the first question to be settled is what kind of knowledge would 
 be of the most value, and which of the many unknowns may 
 be determined with the greatest profit. To decide this we must 
 return once more to the ground which is common to all the induc- 
 tive theories of Evolution alike. Now all these different theories 
 start from the hypothesis that the different forms of life are re- 
 lated to each other, and that their diversity is due to Variation. 
 On this hypothesis, therefore, Variation, whatever may be its cause, 
 and however it may be limited, is the essential phenomenon of 
 Evolution. Variation, in fact, is Evolution. The readiest way, 
 then, of solving the problem of Evolution is to study the facts of 
 Variation. 
 
 SECTION II. 
 
 Alternative Methods. 
 
 The Study of Variation is therefore suggested as the method 
 which is on the whole more likely than any other to give us the 
 kind of knowledge we are wanting. It should be tried not so 
 much in the hope that it will give any great insight into those 
 
 element of discontinuity may thus be introduced. This is true, but it does not 
 help iu the attempt to find the cause of the original discontinuity of the coexisting 
 organisms. 
 
sect, ii.] INTRODUCTION. 7 
 
 relations of cause and effect of which Evolution is the expression, 
 but merely as an empirical means of getting at the outward and 
 visible phenomena which constitute Evolution. On the hypothesis 
 of Common Descent, the forms of living things are succeeding each 
 other, passing across the stage of the earth in a constant proces- 
 sion. To find the laws of the succession it will be best for us to 
 stand as it were aside and to watch the procession as it passes by. 
 No amount of knowledge of individual forms will tell us the laws or 
 even the manner of the succession, nor shall we be much helped by 
 comparison of forms of whose descent we know nothing save by 
 speculation. To study Variation it must be seen at the momenl 
 of its beginning. For comparison we require the parent and the 
 varying offspring together. To find out the nature of the progres- 
 sion we require, simultaneously, at least two consecutive terms of 
 the progression. Evidence of this kind can be obtained in no other 
 way than by the study of actual and contemporary cases of Varia- 
 tion. To the solution of this question collateral methods of re- 
 search will not contribute much. 
 
 Since Darwin wrote, several of these collateral methods have 
 been tried, and though a great deal has thus been done and a vast 
 number of facts have been established, yet the advance towards a 
 knowledge of the steps by which Evolution proceeds has been 
 almost nothing. It will not perhaps be wandering unduly if we 
 consider very shortly the reason of this, for the need for the Study 
 of Variation will thereby be made more plain. 
 
 Before the publication of the Origin of Species the w r ork of 
 naturalists w r as chiefly devoted to the indiscriminate accumulation 
 of facts. By most the work was done for its own sake in the strict- 
 est sense. In the minds of some there was of course a hope that 
 the gathering of knowledge would at last lead on to something 
 more, but this hope w r as for the most part formless and vague. 
 With the promulgation of the Doctrine of Descent the whole course 
 of the study was changed. The enthusiasm of naturalists ran 
 altogether into new channels ; a new class of facts was sought and 
 the value of Zoological discovery was judged by a new criterion. 
 The change was thus a change of aim, and consequently a change 
 of method. From a large field of possibilities the choice fell 
 chiefly upon two methods, each having a definite relation to the 
 main problem. The first of these is the Embryological Method, 
 and the second may be spoken of as the Study of Adaptation. 
 The pursuit of these two methods was the direct outcome of 
 Darwin's work, and such great hopes have been set on them that 
 before starting on a new line we shall do well to examine carefully 
 their proper scope and see whither each of them may reasonably 
 be expected to lead. 
 
 It is besides in the examination of these methods and in ob- 
 serving the exact point at which they have failed, that the need 
 for the Study of Variation will become most evident. 
 
8 THE EMBRYOLOGICAL METHOD. [introd. 
 
 When the Theory of Evolution first gained a hearing it became 
 of the highest importance that it should be put to some test which 
 should shew whether it was true or not. In comparison with this 
 all other questions sank into insignificance. 
 
 Now, the principle which has been called the Law of von Baer, 
 provided the means for such a test. By this principle it is affirmed 
 that the history of the individual represents the history of the 
 Species. If then it should be found that organisms in their de- 
 velopment pass through stages in which they resemble other forms, 
 this would be 'prima facie a reason for believing them to be geneti- 
 cally connected. The general truth of the Theory of Descent 
 might thus be tested by the facts of development, For this reason 
 the Study of Embryology superseded all others. It is now, of course, 
 generally admitted that the Theory has stood this test, and that 
 the facts of Embryology do support the Doctrine of Community of 
 Descent. 
 
 But the claims of Embryology did not stop here. In addition 
 to the application of the method to the general Theory of Descent, 
 it has been sought to apply the facts of Embryology to solve 
 particular questions of the descent of particular forms. It has 
 been maintained that if it is true that the history of the individual 
 repeats the history of the Species, w r e may in the study of De- 
 velopment see not only that the various forms are related, but 
 also the exact lines of Descent of particular forms. In this way 
 Embryology was to provide us with the history of Evolution. 
 
 The survey of the development of animals from this point of 
 view is now complete for most forms of life, and in all essential 
 points; we are now therefore in a position to estimate its value. 
 It will, I think, before long be admitted that in this attempt to 
 extend the general proposition to particular questions of Descent 
 the embryological method has failed. The reason for this is 
 obvious. The principle of von Baer was never more than a 
 rough approximation to the truth and was never suited to the 
 solution of particular problems. It is curious to notice upon how 
 very slight a basis of evidence this widely received principle really 
 rests. It has been established almost entirely by inference and 
 it has been demonstrated by actual observation in scarcely a single 
 instance. 
 
 For the stages through which a particular organism passes 
 in the course of its development are admissible as evidence of 
 its pedigree only when it shall have been proved as a general 
 truth that the development of individuals does follow the lines 
 on wmich the species developed. The proof, however, of this 
 general proposition does not rest on direct observation but on 
 the indirect evidence that particular organisms at certain stages 
 in their development resemble other organisms, and hence it 
 is assumed that they are descended from those forms. Thus the 
 truth of the general proposition is established by assuming it 
 
sect. II.] INTRODUCTION. 9 
 
 true in special cases, while its applicability to special cases rests 
 on its having been accepted as a general truth. 
 
 Probably however the apologists of this method would main- 
 tain that the principle of von Baer, though its truth has nol 
 been demonstrated directly, yet belongs to the class of "True 
 Hypotheses." To establish the truth of a hypothesis in a case 
 like the present in which the number of possible hypotheses is 
 not limited, it should at least be shewn that its application in all 
 known instances is so precise, so simple, and in such striking 
 accordance with ascertained facts, that its truth is felt to be 
 irresistible. 
 
 Nothing like this can be said of the principle of von Baer. 
 Even if it be generally true that the development of a form is 
 a record of its descent, it has never been suggested that the record 
 is complete. 
 
 Allowance must constantly be made for the omission of stages. 
 for the intercalation of stages, for degeneration, for the presence 
 of organs specially connected with larval or embryonic life, for 
 the interference of yolk and so forth. But what this allowance 
 should be and in what cases it should be made has never beeD 
 determined. 
 
 More than this: closely allied forms often develop on totally 
 different plans; for example, Balanoglossus Kowalevskii has an 
 opaque larva which creeps in the sand, while the other species of 
 the family have a transparent larva which swims at the surface of 
 the sea; the germinal layers of the Guinea-pig when compared with 
 those of the Rabbit are completely inverted, and so on. These are 
 not isolated cases, for examples of the same kind occur in almost 
 every group and in the development of nearly all the systems of 
 organs. When these things are so, who shall determine which de- 
 velopmental process is ancestral and which is due to secondary 
 change ? By what rules may secondary changes be recognized as 
 such? Do transparent larvae swimming at the surface of the sea 
 reproduce the ancestral type or does the opaque larva creeping in 
 the mud shew us the primitive form? Each investigator has 
 answered these questions in the manner which seemed best to 
 himself. 
 
 There is no rule to guide us in these things and there is no 
 canon by which we may judge the worth of the evidence. It is 
 perhaps not too much to say that the main features of the de- 
 velopment of nearly every type of animal are now ascertained, 
 and on this knowledge elaborate and various tables of phylogeny 
 have been constructed, each differing from the rest and all plau- 
 sible; but it would be difficult to name a single case in which 
 the immediate pedigree of a species is actually known. 
 
 The Embryological Method then has failed not for want of 
 knowledge of the visible facts of development but through ignor- 
 ance of the principles of Evolution. The principle of von Baer. 
 
10 THE STUDY OF ADAPTATION. [ixtrod. 
 
 taken by itself, is clearly incapable of interpreting the phenomena 
 of development. We are endeavouring by means of a mass of 
 conflicting evidence to reconstruct the series of Descent, but of the 
 laws which govern such a series we are ignorant. In the inter- 
 pretation of Embryological evidence it is constantly necessary to 
 make certain hypotheses as to the course of Variation in the 
 past, but before this can be done it is surely necessary that w r e 
 should have some knowledge of the modes of Variation in the 
 present. When we shall know something of the nature of the 
 variations which are now occurring in animals and the steps by 
 which they are now progressing before our eyes, w 7 e shall be in 
 a position to surmise what their past has been ; for we shall then 
 know what changes are possible to them and what are not. In 
 the absence of such knowledge, any person is at liberty to pos- 
 tulate the occurrence of variations on any lines which may suggest 
 themselves to him, a liberty which has of late been freely used. 
 Embryology has provided us with a magnificent body of facts, 
 but the interpretation of the facts is still to seek. 
 
 The other method which, since Darwin's work, has attracted 
 most attention is the study of the mechanisms by which organisms 
 are adapted to the conditions in which they live. This study of 
 Adaptation and of the utility of structures exercises an extra- 
 ordinarv fascination over the minds of some and it is most 
 important that its proper use and scope should be understood. 
 
 We have seen that the Embryological Method owed its import- 
 ance to its value as a mode of testing the truth of the Theory 
 of Evolution: in the same way the Study of Adaptation was 
 undertaken as a test of the Theory of Natural Selection. 
 
 Amongst many classes of animals, complex structures are pre- 
 sent which do not seem to contribute directly to the well-being of 
 their possessors. By many it has been felt that the persistent 
 occurrence of organs of this class is a difficulty, on the hypothesis 
 that there is a tendency for useful structures to be retained and 
 for useless parts to be lost. In consequence it has been antici- 
 pated that sufficient research would reveal the manner in which 
 these parts are directly useful. The amount of evidence collected 
 with this object is now enormous, and most astonishing ingenuity 
 has been evoked in the interpretation of it. A discussion of the 
 truth of the conclusions thus put forward is of course apart from 
 our present purpose, which is to examine the logical value of this 
 method of research as a means of attacking the problem of Evo- 
 lution. W T ith regard to the results it has attained it must suffice 
 to notice the fact that while the functions of many problematical 
 organs have been conjectured, in some cases perhaps rightly, there 
 remain w r hole groups of common phenomena of this kind, which 
 are still almost untouched even by speculation, and structures and 
 instincts are found in the best known forms, as to the " utility " of 
 
sect, ii.] INTRODUCTION. 1 1 
 
 which no one has made even a plausible surmise. All this is fa- 
 miliar to every one and every one knows the various answers that 
 have been made. 
 
 It is not quite fair to judge such a method by the imperfection 
 of its results, but in one respect the deficiency of results obtained by 
 the Study of Adaptation is very striking, and though this has 
 often been recognized it must be again and again insisted on as a 
 thing to be kept always in view. The importance of this consider- 
 ation will be seen when the evidence of Variation is examined. 
 The Study of Adaptation ceases to help us at the exact point at 
 which help is most needed. We are seeking for the cause of the 
 differences between species and species, and it is precisely on the 
 utility of Specific Differences that the students of Adaptation are 
 silent. For, as Darwin and many others have often pointed out, 
 the characters which visibly differentiate species are not as a rule 
 capital facts in the constitution of vital organs, but more often 
 they are just those features which seem to us useless and trivial, 
 such as the patterns of scales, the details of sculpture on chitin or 
 shells, differences in number of hairs or spines, differences between 
 the sexual prehensile organs, and so forth. These differences are 
 often complex and are strikingly constant, but their utility is in 
 almost every case problematical. For example, many suggestions 
 have been made as to the benefits which edible moths may derive 
 from their protective coloration, and as to the reasons why unpalat- 
 able butterflies in general are brightly coloured ; but as to the 
 particular benefit which one dull moth enjoys as the result of his own 
 particular pattern of dullness as compared with the closely similar 
 pattern of the next species, no suggestion is made. Nevertheless 
 these are exactly the real difficulties which beset the utilitarian 
 view of the building up of Species. We knew all along that Species 
 are approximately adapted to their circumstances; but the diffi- 
 culty is that whereas the differences in adaptation seem to us to 
 be approximate, the differences between the structures of species 
 are frequently precise. In the early days of the Theory of Natural 
 Selection it was hoped that with searching the direct utility of 
 such small differences would be found, but time has been running 
 now and the hope is unfulfilled. 
 
 Even as to the results which rank among the triumphant suc- 
 cesses of this method of study there is need for great reserve. 
 The adequacy of such evidence must necessarily be a matter for 
 individual judgment, but in dealing with questions of Adaptation 
 more than usual caution is needed. No disrespect is intended 
 towards those who have sought to increase our acquaintance with 
 these obscure phenomena: but since at the present time the con- 
 clusions arrived at in this field are being allowed to pass unchal- 
 lenged to a place among the traditional belief's of Science, it is 
 well to remember that the evidence for these beliefs is far from 
 being of the nature of proof. 
 
12 FUTILITY OF THIS METHOD. [introd. 
 
 The real objection however to the employment of the Study of 
 Adaptation as a means of discovering the processes of Evolution is 
 not that its results are meagre and its conclusions unsound. Apart 
 from the doubtful character of these inferences, there is a difficulty 
 of logic which in this method is inherent and insuperable. This 
 difficulty lies in the fact that while it is generally possible to 
 suggest some way by which in circumstances, known or hypothe- 
 tical, any given structure may be of use to any animal, it cannot on 
 the other hand ever be possible to prove that such structures are 
 not on the whole harmful either in a way indicated or otherwise. 
 There is a special reason why the impossibility of proving the 
 negative applies with peculiar force to the mode of reasoning we 
 are now considering. This is due to the fact that whereas the 
 only possible test of the utility of a structure must be a quan- 
 titative one, such a quantitative method of assessment is entirely 
 beyond our powers and is likely to remain so indefinitely. The 
 students of Adaptation forget that even on the strictest applica- 
 tion of the theory of Selection it is unnecessary to suppose that 
 every part an animal has, and every thing which it does, is useful 
 and for its good. We, animals, live not only by virtue of, but also 
 in spite of what we are. It is obvious from inspection that any 
 instinct or any organ may be of use : the real question we have to 
 consider is of how much use it is. To know that the presence of a 
 certain organ may lead to the preservation of a race is useless if we 
 cannot tell how much preservation it can effect, how many indi- 
 viduals it can save that would otherwise be lost; unless we kn<»w 
 also the degree to which its presence is harmful ; unless, in fact, we 
 know how its presence affects the profit and loss account of the 
 organism. We have no right to consider the utility of a structure 
 demonstrated, in the sense that we may use this demonstration as 
 evidence of the causes which have led to the existence of the struc- 
 ture, until we have this quantitative knowledge of its utility and are 
 able to set off against it the cost of the production of the structure 
 and all the difficulties which its presence entails on the organism. 
 X<> one who has ever tried to realize the complexity of the relations 
 between an organism and its surroundings, the infinite variety of 
 the consequences which every detail of structure and every shade of 
 instinct may entail upon the organism, the precision of the correla- 
 tion between function and the need for it, and above all the mar- 
 vellous accuracy with which the- presence or absence of a power or 
 a structure is often compensated among living beings — no one can 
 reflect upon these things and be hopeful that our quantitative 
 estimates of utility are likely to be correct. But in the absence of 
 such correct and final estimates of utility, we must never use the 
 utility of a structure as a point of departure in considering the 
 manner of its origin ; for though we can see that it is, or may be, 
 useful, yet a little reflexion will shew that it is, or may be, harmful, 
 but whether on the whole it is useful or on the whole harmful, 
 
sect, in.] INTRODUCTION. 1 3 
 
 can only be guessed at. It thus happens that we can only gel 
 an indefinite knowledge of Adaptation, which for the purposes of 
 our problem is not an advance beyond the original knowledge 
 that organisms are all more or less adapted to their circumstanc< -. 
 No amount ot" evidence of the same kind will can-)' us beyond this 
 point. Hence, though the Study of Adaptation will alwaysremain 
 a fascinating branch of Natural History, it is not and cannot be a 
 means of directly solving the problem of the origin of Species. 
 
 SECTION III. 
 Continuity oh Discontinuity of Variation. 
 
 What is needed, then, is evidence of a new kind, for do 
 amount of evidence of the kinds that have been mentioned will 
 take us much beyond our present position. We need more know- 
 ledge, not so much of the facts of anatomy or development, as of 
 the principles of Evolution. The question to be considered is how 
 such knowledge may be obtained. It is submitted that the 
 Study of Variation gives us a chance, and perhaps the only one, of 
 arriving at this knowledge. 
 
 But though, as all will admit, a knowledge of Variation lies at 
 the root of all biological progress, no organized attempt to obtain it 
 has been made. The reason for this is not very clear, but it 
 apparently proceeds chiefly from the belief that the subject is ton 
 difficult and complex to be a profitable field for study. However 
 this maybe, the fact remains, that since the first brief treatment of 
 the matter in Animals and Plants under Domestication do serious 
 effort to perceive or formulate principles of Variation has been 
 made, and there is before us nothing but the most meagre ami 
 superficial account of a few of its phenomena. Darwin's firsl 
 collection of the facts of Variation has scarcely been increased. 
 These same facts have been arranged and rearranged by each 
 successive interpreter: the most various and contradictory pro- 
 positions have been established upon them, and they have been 
 strained to shew all that it can possibly he hoped that they will 
 shew. Any one who cares to glance at the works ot' those who 
 have followed Darwin in these fields mav assure himself ot' 
 this. So far, indeed, are the interpreters of Evolution from adding 
 to this store of facts, that in their hands the original -t<><k 
 becomes even less until only the most striking remain. It is 
 wearisome to watch the persistence with which these are revived 
 for the purpose of each new theorist. How well we know the 
 offspring of Lord Morton's mare, the bitch 'Sappho,' t he Sebright 
 Bantams, the Himalaya Rabbit with pink eyes, the white Cats 
 with their blue eyes, and the rest! Perhaps the time has come 
 
14 THE PHYLOGENETIC SERIES I [introd. 
 
 when even these splendid observations cannot be made to shew 
 much more. Surely their use is now rather to point the direction 
 in which we must go for more facts. 
 
 The questions which by the Study of Variation we hope to 
 answer may be thus expressed. In affirming our belief in the 
 doctrine of the Community of Descent of living things, we declare 
 that we believe all living things to stand to each other in definite 
 genetic relationships. If then all the individuals which have 
 lived on the earth could be simultaneously before us, we believe 
 that it would be possible to arrange them all, so that each stood 
 in its own ordinal position in series. We believe that all the 
 secondary series together make up one primary series from which 
 each severally arises. This is the fundamental conception of 
 Evolution and is represented figuratively by the familiar image of 
 a genealogical tree. If then all the individual ancestors of any 
 given form were before us and were arranged in their order, we 
 believe thev would constitute a series. This view of the forms of 
 organisms as constituting a series or progression is the central idea 
 of modern biology, and must be borne continually in mind in the 
 attempt to apply any principle to the Study of Evolution. 
 
 Each individual and each type which exists at the present 
 moment stands, for the moment, therefore, as the last term of 
 such a series. The problem is to rind the other terms. In the 
 case of each type the question is thus stated in a particular 
 form, and it is a somewhat remarkable circumstance that it is in 
 its particular forms that this problem has been most studied. 
 The same problem is nevertheless capable of being stated in the 
 general form also. Instead of considering what has been the 
 actual series from which a specified type has been derived, we may 
 consider what are the characters and attributes of such series in 
 general. It may indeed be contended that it is scarcely reason- 
 able to expect to discover the line of descent of a given form, for 
 the evidence is gone ; but we may hope to find the general 
 chararacteristics of Evolution, for Evolution, as we believe, is still 
 in progress. It is really a strange thing that so much enterprise 
 and research should have been given to the task of reconstructing 
 particular pedigrees — a work in which at best the facts must be 
 eked out largely with speculation — while no one has ever seriously 
 tried to determine the general characters of such a series. Yet if 
 our modern conception of Descent is a right one, it is a pheno- 
 menon now at this time occurring, which by common observations, 
 without the use of any imagination whatever, we may now see. 
 The chief object, then, with which we shall begin the Study of 
 Variation will be the determination of the nature of the Series by 
 which forms are evolved. 
 
 The first questions that we shall seek to answer refer to the 
 manner in which differentiation is introduced in these Series. 
 
sect, in.] INTRODUCTION. 15 
 
 All we as yet know is the hist term of the Series. By the 
 postulate of Common Descent we take it that the hist term 
 differed widely from the last, which nevertheless is its lineal 
 descendant: how then was the transition from the first term to 
 the last term effected? If the whole series were before us, should 
 we find that this transition had been brought about by very 
 minute and insensible differences between successive terms in the 
 Series, or should we find distinct and palpable gaps in the Series 
 In proportion as the transition from term to term is minimal and 
 imperceptible we may speak of the Series as being Continuous, 
 while in proportion as there appear in it lacunae, filled by no 
 transitional form, we may describe it us Discontinuous. The 
 several possibilities may be stated somewhat as follows. The 
 Series may be wholly continuous; on the other hand it may be 
 sometimes continuous and sometimes discontinuous; we know how- 
 ever by common knowledge that it is never wholly discontinuous. 
 It may be that through long periods of the Series the differences 
 between each member and its immediate predecessor and successor 
 are impalpable, while at certain moments the series is interrupted 
 by breaches of continuity which divide it into groups, of which the 
 composing members are alike, though the successive groups are 
 unlike. Lastly, discontinuity may occur in the evolution of par- 
 ticular organs or particular instincts, while the changes in other 
 structures and svstems may be effected continuous] v. To decide 
 which of these agrees most nearly with the observed phenomena of 
 Variation is the first question which we hope, by the Study of 
 Variation, to answer. The answer to this question is of vital con- 
 sequence to progress in the Study of Life. 
 
 The preliminary question, then, of the degree of continuity 
 with which the process of Evolution occurs, has never been 
 decided. In the absence of such a decision there has never- 
 theless been a common assumption, either tacit or expressed, that 
 the process is a continuous one. The immense consequence of a 
 knowledge of the truth as to this will appear from a consideration 
 of the gratuitous difficulties which have been introduced by this 
 assumption. Chief among these is the difficulty which has been 
 raised in connexion with the building up of now organs in their 
 initial and imperfect stages, the mode of transformation of organs, 
 and, generally, the Selection and perpetuation of minute variations. 
 Assuming then that variations are minute, we are met by this 
 familiar difficulty. We know that certain devices and mechanisms 
 are useful to their possessors; but from our knowledge of Natural 
 History we are led to think that their usefulness is consequent on 
 the degree of perfection in which they exist, and thai if they were 
 at all imperfect, they would not be useful. Now it is clear that in 
 any continuous process of Evolution such stages of imperfection 
 must occur, and the objection has been raised that Natural 
 Selection cannot protect such imperfect mechanisms so as to lift 
 
16 CONTINUOUS, OR DISCONTINUOUS? [iNTBOD. 
 
 them into perfection. Of the objections which have been brought 
 against the Theory of Natural Selection this is by far the most 
 serious. 
 
 The same objection may be expressed in a form which is more 
 correct and comprehensive. We have seen that the differences 
 between Species on the whole are Specific, and are differences of 
 kind, forming a discontinuous Series, while the diversities of en- 
 vironment to which they are subject are on the whole differences 
 of degree, and form a continuous Series ; it is therefore hard to 
 see how the environmental differences can thus be in any sense 
 the directing cause of Specific differences, which by the Theory of 
 Natural Selection they should be. This objection of course in- 
 cludes that of the utility of minimal Variations 
 
 Now the strength of this objection lies wholly in the sup- 
 posed continuity of the process of Variation. We see all organ- 
 ized nature arranged in a discontinuous series of groups differing 
 from each other by differences which are Specific ; on the other 
 hand we see the divers environments to which these forms are 
 subject passing insensibly into each other. We must admit, then, 
 that if the steps by which the divers forms of life have varied 
 from each other have been insensible — if in fact the forms ever 
 made up a continuous series — these forms cannot have been 
 broken into a discontinuous series of groups by a continuous en- 
 vironment, whether acting directly as Lamarck would have, or 
 as selective agent as Darwin would have. This supposition has 
 been generally made and admitted, but in the absence of evidence 
 as to Variation it is nevertheless a gratuitous assumption, and 
 as a matter of fact when the evidence as to Variation is studied, 
 it will be found to be in great measure unfounded. 
 
 In what follows so much will be said of discontinuity in Varia- 
 tion that it will not be amiss to speak of the reasons which have 
 led many to suppose that the continuity of Variation needs no 
 proof. Of these reasons there are especially two. First there 
 is in the minds of some persons an inherent conviction that all 
 natural processes are continuous. That many of them do not 
 appear so is admitted: it is admitted, for example, that among 
 chemical processes Discontinuity is the rule ; that changes in the 
 states of matter are commonly effected discontinuously, and the 
 like. Nevertheless it is believed that such outward and visible 
 Discontinuity is but a semblance or mask which conceals a real 
 process which is continuous and which by more searching may 
 be found. With this class of objections we are not perhaps con- 
 cerned, but they are felt by so many that their existence must not 
 be forgotten. Secondly, Variation has been supposed to be always 
 continuous and to proceed by minute steps because changes of 
 this kind are so common in Variation. Hence it has been inferred 
 that the mode of Variation thus commonly observed is universal. 
 That this inference is a wrong one, the facts will shew. 
 
sect, iv.] INTRODUCTION. 17 
 
 To sum up : 
 
 The first question which the Study of Variation may be ex- 
 pected to answer, relates to the origin of that Discontinuity of 
 which Species is the objective expression. Such Discontinuity 
 is not in the environment; may it not, then, be in the living 
 thing itself? 
 
 The Study of Variation thus offers a means whereby we may 
 hope to see the processes of Evolution. We know much of what 
 these processes may be: the deductive method has been tried, 
 with what success we know. It is time now to try if these things 
 cannot be seen as they are, and this is what Variation may shew 
 us. In Variation we look to see Evolution rolling out before our 
 eyes. In this we may foil wholly and must fail largely, but it. 
 is still the best chance left. 
 
 SECTION IV. 
 Symmetry and M eristic Repetition. 
 
 Having thus indicated some of the objects which we may 
 hope to reach by the Study of Variation, we have next to consider 
 the way in which to set about this study. 
 
 The Study of Variation is essentially a study of differences 
 between organisms, so for each observation of Variation at Leasl 
 two substantive organisms are required for comparison. It is 
 proposed to confine the present treatment of the subject to a 
 consideration of the integral steps by which A^ariation may pro- 
 ceed ; hence it is desirable that the two organisms compared 
 should be parent and offspring, and if, as is often the case, the 
 actual parent is unknown, it is at least necessary that the normal 
 form of the species should be known and that there must be 
 reasonable evidence that the varying offspring is actually de- 
 scended from such a normal. For this reason, evidence from a com- 
 parison of Local Races, and other established Varieties, though a 
 very valuable part of the Study, will for the most part not be here 
 introduced. For the belief that such races are descended from i ln- 
 putative normal scarcely ever rests on proof, and still more rarely 
 is there evidence of the number of generations in which the 
 change has been effected. 
 
 For our purpose we require actual cases of Variations occurring 
 as far as possible in offspring of known parentage: and if, foiling 
 this, we make use of cases occurring in the midst of normal indi- 
 viduals of known structure, it must in such cases be always 
 remembered that we cannot properly assume that the varying form 
 is the offspring of such individuals, though special reasons may 
 make this likely in special cases. 
 
 Since the structure of the offspring is perhaps in no case 
 b. 2 
 
1 8 HETEROGENEITY. [introd. 
 
 identical with that of the parent, observation of any parent and 
 its offspring is to the point ; but such a field as this is plainly too 
 wide to be studied with profit as a whole, and it is necessary from 
 the first, that attention should be limited to certain classes of such 
 phenomena. With this object certain limitations are proposed, 
 and though confessedly arbitrary, they will be found on the whole 
 to work well. 
 
 The first limitation thus introduced concerns the magnitude 
 of Variations. We have seen above that the assumption that 
 Variation is a continuous process lands us in serious difficulties 
 in the application of a hypothesis which, on general grounds, 
 we nevertheless are prepared to receive. If then we can shew 
 that Variation is to some extent discontinuous, a road will be 
 opened by which these difficulties may perhaps be in part avoided. 
 
 Species are discontinuous ; may not the Variation by which 
 Species are produced be discontinuous too ? It may be stated at 
 once that evidence of such Discontinuous Variation does exist, 
 and in this first consideration of the subject attention will be con- 
 fined to it. The fact that Continuous Variation exists is also none 
 the less a fact, but it is most important that the two classes of 
 phenomena should be recognized as distinct, for there is reason to 
 think that they are distinct essentially, and that though both may 
 occur simultaneously and in conjunction, yet they are manifesta- 
 tions of distinct processes. The attempt to distinguish these two 
 kinds of Variation from each other constitutes one of the chief 
 parts of the study. It will not perhaps be possible to find any 
 general expression which shall accurately differentiate between 
 Variations which are Discontinuous and those which are Con- 
 tinuous, but it is possible to recognize attributes proper to each 
 and to distinguish changes which are or may be effected in the one 
 way from other changes which are or may be effected in the other. 
 
 For the present w r e shall treat only of the evidence of Dis- 
 continuous Variation. 
 
 In order to explain the second limitation w T hich is to be intro- 
 duced it is necessary to refer to some phenomena which are 
 characteristic of the forms of organisms, and to separate from them 
 the group with which we shall deal first. 
 
 It was stated above that perhaps no character of form is 
 common to all living things, but nevertheless there is one feature 
 which is found in the great majority. 
 
 In the first place, the bodies of organisms are not homo- 
 geneous but heterogeneous, consisting of organs or parts which 
 in substance and composition differ from each other. This 
 heterogeneity in composition is of course an objective expression 
 of the process of Differentiation, and it is further recognized 
 that such structural heterogeneity of material corresponds with 
 a physiological Differentiation of function. This Differentiation 
 
-sect, iv.] INTRODUCTION. 19 
 
 or Heterogeneity is found in the bodies of all organisms, even 
 in the simplest. 
 
 Now in a wide survey of the forms of living things there is 
 a fact with regard to the presence of this Heterogeneity which bo 
 the purpose of our present consideration is of the highest con- 
 sequence. This may perhaps be best expressed by the state- 
 ment that in the bodies of living things Heterogeneity is generally 
 orderly and formal ; it is cosmic, not chaotic. Not only are the 
 bodies of all organisms heterogeneous, but in the great majority 
 the Heterogeneity occurs in a particular way and according to 
 geometrical rule. This character is not peculiar to a few 
 organisms, but is common to nearly all. We will now examine 
 this phenomenon of geometrical order in Heterogeneity and try 
 to see some of the elements of which it is made up. 
 
 Order of form will first be found to appear in the fact that in 
 any living body the Heterogeneity is in some degree symmetri- 
 cally distributed around one or more centres. In the great 
 majority of instances these centres of symmetry are themselves 
 distributed about other centres, so that in one or more planes the 
 whole body is symmetrical. 
 
 The idea of Symmetry which is here introduced is so familiar 
 that it is scarcely necessary to define it, but as all that follows 
 depends entirely on the proper apprehension of what is meant by 
 Symmetry it may be well to call attention to some of the phenomena 
 which the term denotes. 
 
 In its simplest form the Symmetry of a figure depends on the 
 fact that from some point within it at least two lines may be 
 taken in such a way that each passes through parts which are 
 similar and similarly disposed. The point from which the lines 
 are taken may be called a centre of Symmetry and the lines may 
 be called lines of Symmetrical Repetition. 
 
 Commonly the parts thus symmetrically disposed are related 
 to each other as optical images [in a plane mirror passing through 
 the centre of Symmetry and standing in a plane bisecting the 
 angle which the lines of Symmetrical Repetition make with each 
 other]. For a figure to be symmetrical, in the ordinary sense of 
 the term, it is not necessary that the relation of optical images 
 should strictly exist, and several figures, such as spirals, &c., 
 are accordingly described as symmetrical. But since the relation 
 of images exists in all cases of bilateral and radial symmetry, which 
 are the forms most generally assumed in the symmetry of organ- 
 isms, it is of importance to refer particularly to this as one of 
 the phenomena often associated with Symmetry. 
 
 In the simplest possible case of Symmetry there is a series 
 of parts in one direction corresponding to a series of parts in 
 another direction. Perhaps there is no organism in which such an 
 arrangement does not at some time and in some degree exist. 
 For even in an unsegmented ovum or a resting Amoeba there is 
 
20 MERISTIC REPETITION. [introd. 
 
 little doubt that Symmetry is present, though owing to the slight 
 degree of Differentiation, its presence may not be clearly 
 perceived. In the manifestations, however, in which it is most 
 familiar, Symmetry is a decided and obvious phenomenon. 
 
 Symmetry then depends essentially on the fact that structures 
 found in one part of an organism are repeated and occur again in 
 another part of the same organism. Symmetrical Heterogeneity 
 may therefore be present in a spherical body having a core 
 of different material, and it is possible that in an unsegmented 
 ovum for example a Symmetry of this simple kind may exist. 
 But Symmetry, as it is generally seen in organisms, differs from 
 that of these simplest cases in the fact that the organs repeated 
 are separated from each other by material of a nature different 
 from that of the organs separated. Repetitions of this kind are 
 known in almost every group of animals and plants. The parts 
 thus separated may belong to any system of organs. There is no 
 known limit to the number of Repetitions that may occur. 
 
 This phenomenon of Repetition of Parts, generally occurring 
 in such a way as to form a Symmetry or Pattern, comes near to 
 being a universal character of the bodies of living things. It will 
 in cases which follow be often convenient to employ a single term 
 to denote this phenomenon wherever and however occurring. 
 For this purpose the term Merism will be used. The introduc- 
 tion of a new term is, as a practice, hardly to be justified; but in 
 a case like the present, in which it is sought to associate divers 
 phenomena which are commonly treated as distinct, the employ- 
 ment of a single word, though a new one, is the readiest way of 
 giving emphasis to the essential unity of the phenomena comprised. 
 
 The existence of patterns in organisms is thus a central fact 
 of morphology, and their presence is one of the most familiar 
 characters of living things. Anyone who has ever collected 
 fossils, or indeed animals or plants of any kind, knows how in 
 hunting, the eye is caught by the formal regularity of an organized 
 being, which, contrasting with the irregularity of the ground, is 
 often the first indication of its presence. Though of course not 
 diagnostic of living things, the presence of patterns is one of their 
 most general characters. 
 
 On examining more closely into the constitution of Repetitions, 
 they may be seen to occur in two ways ; first, by Differentiation 
 within the limits of a single cell, as in the Radiolaria, the sculpture 
 of egg-shells, nuclear spindles, &c, to take marked cases ; and 
 secondly, by, or in conjunction with, the process of Cell-Division. 
 The Symmetry which is found in the Serial Repetitions of Parts in 
 unicellular organisms does not in all probability differ essentially 
 from that which is produced by Cell-Division, for, though suffi- 
 ciently distinct in outward appearance, the two are almost cer- 
 tainly manifestations of the same power. 
 
sect, iv.] INTRODUCTION. 21 
 
 Such patterns may exist in single cells or in groups of cells, in 
 separate organs or in groups of organs, in solitary tonus or in 
 colonies and groups of forms. Patterns which arc completed in the 
 several organs or parts will be referred to as Minor Symmetries. 
 These may be compounded together into one single pattern, which 
 includes the whole body: such a symmetry will be called a Major 
 Symmetry. In most organisms, whether colonial or solitary, 
 there is such a Major Symmetry ; on the other hand organisms 
 are known in which each system of Minor Symmetry is, at least 
 in appearance, distinct and without any visible geometrical relation 
 to the other Minor Symmetries. Examples of this kind are not 
 common, for, as a rule, the planes about which each Minor 
 Symmetry is developed have definite geometrical relations to 
 those of the other Minor Symmetries. It is possible, even, that in 
 some if not all of these, the planes of division by which the tissues 
 composing each system of Minor Symmetry are originally split off 
 and differentiated, have such definite relations, though by sub- 
 sequent irregularities of growth and movement these relations are 
 afterwards obscured. 
 
 The classification of Symmetry and Pattern need not now be 
 further pursued. The matter will be often referred to in the 
 course of this work, when facts concerning Variations in number 
 and patterns are being given, for it is by study of Variations in 
 pattern and in repetition of parts that glimpses of the essential 
 phenomena of Symmetry may be gained. 
 
 That which is important at this stage is to note the almost 
 universal presence of Symmetry and of Repetition of Parts among 
 living things. Both are the almost invariable companions of divisi- m 
 and differentiation, which are fundamental characters without which 
 Life is not known. 
 
 The essential unity of the phenomenon of Repetition of Parts 
 and of its companion-phenomenon, Symmetry, wherever met with, 
 has been too little recognized, and needless difficulty has thus been 
 introduced into morphology. To obtain a grasp of the nature of 
 animal and vegetable forms, such recognition is of the first eon 
 sequence. 
 
 To anyone who is accustomed to handle animals or plants, and 
 who asks himself habitually — as every Naturalist must — how they 
 have come to be what they are, the question of the origin and 
 meaning of patterns in organisms will be familiar enough. They 
 are the outward and visible expression of that, order and complete- 
 ness which inseparably belongs to the phenomenon of Life. 
 
 If anyone will take into his hand some complex piece of living 
 structure, a Passion-flower, a Peacock's feather, a Cockle-shell, or 
 the like, and will ask himself, as I have said, how it has come to 
 be so, the part of the answer that he will find it hardest to give, is 
 that which relates to the perfection of its pattern. 
 
 And it is not only in these large and tangible structures that 
 
22 VARIATION MERISTIC AND SUBSTANTIVE. [introd. 
 
 the question arises, for the same challenge is presented in the most 
 miuute and seemingly trifling details. In the skeleton of a Diatom 
 or of a Radiolarian, the scale of a Butterfly, the sculpture on a 
 pollen-grain or on an egg-shell, in the wreaths and stars of nuclear 
 division, such patterns again and again recur, and again and again 
 the question of their significance goes unanswered. There are 
 many suggestions, some plausible enough, as to why the tail 
 of a Peacock is gaudy, why the coat of a pollen-grain should be 
 rough, and so forth, but the significance of patterns is untouched 
 by these. Nevertheless, repetitions arranged in pattern exist 
 throughout organized Nature, in creatures that move and in those 
 that are fixed, in the great and in the small, in the seen and in 
 the hidden, within and without, as a property or attribute of Life, 
 scarcely less universal than the function of respiration or meta- 
 bolism itself. 
 
 Such, then, is Symmetry, a character whose presence among 
 organisms approaches to universality. 
 
 SECTION V. 
 Meristic Variation and Substantive Variation. 
 
 It is to the origin and nature of Symmetry that the first 
 section of the evidence of Variation will relate. That a knowledge 
 of the modes of Variation of so universal a character is important 
 to the general study of Biology must at once be evident, but to 
 the particular problem of the nature of Specific Differences this 
 importance is immense. This special importance comes from two 
 reasons. As it is the fact first that Repetition and Symmetry are 
 among the commonest features of organized structure, so it will be 
 found next that it is by differences in those features that the various 
 forms of organisms are very commonly differentiated from each other. 
 Their forms are classified by all sorts of characters, by shape and 
 proportions, by size, by colour, by habits and the like ; but perhaps 
 almost as frequently as by any of these, by differences in number 
 of parts and by differences in the geometrical relations of the parts. 
 It is by such differences that the larger divisions, genera, families, 
 &c. are especially distinguished. In such cases of course the 
 differences in number and Symmetry do not as a rule stand 
 alone, but are generally, and perhaps always, accompanied by 
 other differences of a qualitative kind ; nevertheless, the differ- 
 ences in number and Symmetry form an integral and very definite 
 part of the total differences, so that in any consideration of the 
 nature of the processes by which the differences have arisen, 
 special regard must be had to these numerical and geometrical, 
 or, as I propose to call them, Meristic, changes. 
 
sect, v.] INTRODUCTION. 23 
 
 In the present Introduction I do not propose to forestall the 
 evidence more than is absolutely necessary for the purpose of 
 making clear the principles on which the facts are grouped, but 
 it will do the evidence no wrong if at the present stage it is stated 
 that Meristic Variation is frequently Discontinuous, and that in 
 the case of certain classes of Repetitions is perhaps always so. 
 
 The nature of Merism and the manner in which Meristic 
 Variations occur will be fully illustrated hereafter, but it Is 
 necessary to say this much at the present stage, since it is from 
 this Discontinuity in the occurrence of Meristic Variations that 
 the phenomena of Symmetry and Repetition derive their special 
 importance in the Study of Variation. 
 
 The importance of the phenomena of Merism to the Study of 
 Variation is thus, in the first instance, a direct one, for the Varia- 
 tions which have resulted in the production of Meristic Systems 
 are a direct factor in Evolution. In addition to this direct relation 
 to the Study of Variation, the phenomena of Merism have also an 
 indirect relation, which is scarcely less important ; for they are a 
 factor in the estimation of the magnitude of the integral steps by 
 which Variation proceeds. This will be more evident after the 
 second group of Variations has been spoken of. 
 
 We have thus far spoken only of the processes by which the 
 living body is divided into parts, and we have thus constituted a 
 group which is to include Variations in number, Division, and geo- 
 metrical position. From these phenomena of Division may be 
 distinguished Variations in the actual constitution or substance 
 of the parts themselves. To these Variations the name Substan- 
 tive will be given. Under this head several phenomena may be 
 temporarily grouped together, which with further knowledge will 
 doubtless be found to have no real connexion with each other. 
 For the present, however, it will be convenient to constitute such 
 a temporary group in order to bring out the relative distinctness of 
 Variations which are Meristic. 
 
 These two classes of Variation, Meristic and Substantive, may 
 be recognized at the outset of the study. There can be no doubt 
 that they are essentially distinct from each other, and the proof 
 that they are thus distinct will be found in the evident f Varia- 
 tion, for it will be seen that either may occur independently of the 
 other. An appreciation of this distinction is a first step towards 
 a comprehension of the processes by which the bodies of organisms 
 are evolved. 
 
 A few simple illustrations may make the nature of these two 
 classes of Variations more clear. For example, then, the flower of 
 a Narcissus is commonly divided into six parts, but through 
 Meristic Variation it may be divided into seven parts or into only 
 four. Nevertheless there is in such a case no perceptible change 
 
24 ILLUSTRATIONS. [introd. 
 
 in the tissues or substance of which the parts are made up. All 
 belong to and are recognizable as belonging to the same sort of 
 Narcissus. On the other hand many Narcissi, i\ r . corbularia, for 
 example, are known in two colours, one a dark yellow and the other 
 a sulphur-yellow, though the number of parts and pattern of the 
 flowers are identical. This is, therefore, an example of a Sub- 
 stantive Variation. 
 
 Again, the foot of a Pig may, through Meristic Variation, be 
 divided into five or six toes instead of into four ; or, on the other 
 hand, the number may, by absence of the median division between 
 the digits III and IV, be reduced to three, though the tissues 
 composing the toes may not in structure differ from the normal. 
 
 Again, the tarsus of a Cockroach (Blatta) may, through Me- 
 ristic Variation, be divided into only four joints instead of into 
 five, the normal number, but the joints are still in substance or 
 quality those of a Cockroach. 
 
 I am aware that Meristic and Substantive Variations often 
 occur together, and that there is a point at which it is not possible 
 to separate satisfactorily the changes which have come about by 
 the one process from those which have come about by the other. 
 Instances of this kind occur especially in the case of series of 
 parts such as Teeth or Vertebrae, in which individual members 
 or groups of members of the series are differentiated from the 
 others. For example, we may see that it is through Meristic 
 Variation that the vertebral column of a Dog may be divided into 
 a number of Vertebra? greater or less than the normal ; and 
 though in such cases all the Vertebrae have distinctively canine 
 characters, yet there are nearly always Substantive Variations 
 occurring in correlation with the Meristic Variations, manifesting 
 themselves in a re-arrangement of the points of division between 
 the several groups of Vertebrae, and causing individual Vertebrae 
 to assume characters which are not proper to their ordinal 
 positions. 
 
 Further inquiry into the questions thus raised cannot at this 
 stage be profitably undertaken, though when the evidence has 
 been considered it will perhaps be advisable to recur to them ; all 
 that is now intended is to indicate broadly the general scope of 
 Meristic and Substantive Variation respectively. 
 
 As has already been stated, it is proposed to begin the Study 
 of Variation by an examination of Variations which are Meristic, 
 leaving the consideration of Substantive Variation to be under- 
 taken hereafter. But nevertheless in the consideration of Meristic 
 Variation it will be necessary to refer to phenomena of Substantive 
 Variation in so far as their occurrence or distribution in the body are 
 affected by Meristic phenomena. For in the determination of the 
 magnitude of the integral steps by which Variation proceeds, the 
 existence of Merism plays a conspicuous part, and it is in con- 
 
 ;. 
 
 M 
 
sect, v.] INTRODUCTION. 25 
 
 sequence of this that the subject of Symmetry and Repetition of 
 Parts has a second and indirect bearing on the Study of Variation 
 which is scarcely less important than the direct bearing of which 
 mention has been made above. 
 
 This indirect bearing on the manner of origin of Specific 
 Differences arises from a circumstance which in treatises on 
 Evolution is commonly overlooked. In comparing a species in 
 which parts are repeated, with an allied species in which the same 
 parts are repeated, it commonly occurs that each of the repeated 
 parts of the one have some character by which they are dis- 
 tinguished from the like parts of the other. This differentiating 
 character may be a qualitative one, or a numerical one, or both. 
 In such cases it very frequently happens that this character occurs 
 in each member of the series of Repetitions. For example, the 
 tarsi of the Weevils have only four visible joints, while those 
 of the majority of beetles have five ; but the characteristic 
 division into four joints occurs in each of the legs. Before the 
 four-jointed character as seen in the Weevils could be produced 
 it was necessary that not one but all of the legs should vary from 
 the five-jointed form, and in this particular way. The leaves on a 
 beech tree are all beech leaves, and if the tree is a fern-leaved 
 beech, they may, and generally speaking do, all shew the charac- 
 ters of that variety; and so on with other particular species ami 
 varieties. 
 
 The limbs of a bilaterally symmetrical animal, in which the 
 right side is the image of the left, are of course alike, and any 
 specific character which is present in the limbs of the one side 
 must in such an animal be normally present in those of the other 
 side. 
 
 The same is true of many forms in which appendages are 
 repeated in series, as for example, the fore-legs and hind-legs 
 of the Horse, the fore- and hind-wings of the Brimstone Butterfly 
 (Gonepteryx rhamni); of the patterns on several segments of many 
 caterpillars ; of the patterns of the segmental setae of many worms, 
 and so forth. In series whose members are differentiated from each 
 other, it of course frequently happens that the same specific 
 characters are not present in all the members of the series, and in 
 nearly all such cases these characters are not presented by all in 
 equal degree; nevertheless substantially the phenomenon remains 
 that similar characters often are presented by the several members 
 of a series of repeated organs. 
 
 To many this will seem little better than a truism, neverthe- 
 less I offer no apology for its introduction; for though, as a 
 common and obvious fact, it is a truism, it is besides a truth, I la- 
 far-reaching significance of which is scarcely appreciated For, in 
 the consideration of the magnitude of the integral steps by which 
 Variation proceeds, we shall have this to remember : that to 
 produce any of the forms of which we have spoken, by V ariation 
 
26 SIMILAR VARIATION OF PARTS IN SERIES, [introd. 
 
 from another form, it is not enough that the particular Variation 
 should occur and become fixed in one member of the series, but it 
 is necessary that the character should sooner or later be taken on 
 by each member of the series which exhibits it. In such cases 
 therefore, this question is raised. Did the Variation come in first 
 in one member of the Series and then in another ? Did it occur, 
 for example, simultaneously on the two sides of the body? Did 
 the right and left fore-legs of the Horse cease to develop more 
 than the present number of digits simultaneously or separately? 
 Was the similar form of the hind-legs assumed before, after, or 
 simultaneously with that of the fore-legs ? Were the orange 
 markings which are present on both fore- and hind- wings of the 
 Brimstone, or the ocellar markings of the Peacock ( V. Io), and of 
 the Emperor (Saturnia carpini), assumed by both wings at once? 
 Were the four w r ings of the Plume Moths split simultaneously into 
 the characteristic " plumes " ? Did the brown spots on the three 
 leaflets of Medicago, the fimbriation of the petals of Ragged Robin 
 (Lychnis flos-cuculi), the series of stripes on the Zebra, the pink 
 slashes on the segments of Sphinx larvae, the eyes on the scutes 
 of Chitons, and the thousand other colour-marks, sense-organs, 
 appendages and structural features, w T hich throughout organized 
 Nature occur in Series, vary to their present state of similarity 
 by similar and simultaneous steps, or did each member of 
 such Series take these characters by steps which were separate 
 and occurring independently? To this question, which lies at 
 the root of all progress in the knowledge of Evolution, the 
 Study of Variation can alone reply. That in the facts which 
 follow, the answer to this question will be found, cannot of course 
 be said ; but these facts, few though they are, do nevertheless 
 answer it in part, and they suggest that more facts of the same 
 kind would go far towards answering it completely. But beyond 
 this, the facts are of value as an indication of the part w r hich the 
 phenomenon of Merism may play in determining the magnitude of 
 Variations and the manner of their distribution among the several 
 parts of the body. On examining the evidence it will be found 
 that between parts related to each other in the w r ay that has been 
 described, there is a certain bond or kinship, by virtue of which 
 they may and often do vary simultaneously and in similar ways, 
 though the fact that they may also vary independently, and in 
 different ways, will of course also appear. 
 
 The phenomenon of the Similar Variation of parts which are 
 repeated Meristically in Series is a fact which will be found to 
 have important bearings on several distinct departments of 
 biological study. 
 
 As was shewn above, it is by recognition of the existence 
 of such similar and simultaneous Variation that the manner of 
 origin of the similar complexity of several organs belonging to the 
 same system or series becomes comparatively comprehensible ; for 
 
sect, v.] INTRODUCTION. 27 
 
 it is not then necessary to conceive a separate origin for the com- 
 plexity of each member of the series. For example, it is difficult 
 to conceive the manner of evolution of an eye of a vertebrate ; 
 nevertheless, for each vertebrate tiuo eyes have been evolved. If 
 it were necessary to suppose that each arose by separate selections 
 of separate variations, the difficulty would be thus doubled. If, 
 however, it is recognized that the complexity of both arose simul- 
 taneously, the phenomenon becomes the more intelligible as the 
 number of integral variations and selections demanded is reduced. 
 
 The case chosen, of paired organs in bilateral symmetry, ifi 
 a very simple one, but it will be found that similar relations hold 
 between other parts repeated in series. For in the same way it is 
 not necessary to suppose an independent evolution for each of the 
 tail-feathers of the Peacock, for the legs of the Horse, and the like, 
 since in the light of the facts of Variation it is as easy for all t«> 
 take on the new characters as for one. 
 
 If the manner of development of Repeated Parts is considered, 
 this fact will not seem surprising. For all these parts arise from 
 the undifferentiated tissues by a process of Division, and what- 
 ever characters were potentially present in the undifferentiated 
 tissues may appear in the parts into which it subsequently divides. 
 A somewhat loose illustration will perhaps make this more clear. 
 Everyone knows the rows of figures which children cut out from 
 folded paper. There are as many figures as folds, each figure being 
 alike if the folds coincide. If the paper is pink, all the figures are 
 pink ; if the paper is white, all the figures are white, and so on. 
 If blotting-paper is used, and one blot is dropped on the folded 
 edges, the blot appears symmetrically in all the figures. So also 
 any deviation in the lines of cutting appear in all the figures ; 
 a whole row of soldiers in bearskins may be put into helmets by 
 one stroke of the scissors. Of course it is not meant to suggest 
 that the process of division by which parts of the body are pro- 
 duced bears any resemblance to that by which the figures are cul 
 out, but merely to illustrate the fact that since it is by a proc- ss 
 of Division of an undifferentiated mass that the Repeated Parts 
 are produced, so the characters of these Repeated Parts depend 
 upon the characters which were present in the original mass and 
 upon the modes by which the parts were divided out from it. 
 
 Summary of Sections I to I 
 
 r 
 
 At this point it will be well briefly to recapitulate the pre- 
 ceding Sections. 
 
 We are proposing to attack the problem of Species by studying 
 the facts of Variation. Of the facts of Variation in general we have 
 selected a particular group upon which to begin this study. The 
 group of variations thus chosen are those which relate to Number 
 of parts, Division, Repetition, and the other phenomena which are 
 
28 METAMERIC SEGMENTATION. [introd. 
 
 to be included under the term Meristic. With variations in 
 quality and Substance it is not at present proposed to deal, except 
 in so far as it is necessary to refer to them in their relation to the 
 phenomena of Merism, and in illustration of the structural possi- 
 bilities or necessities which in the body follow as corollaries upon 
 the existence of Meristic Repetition. 
 
 It has also been proposed to limit the consideration to Varia- 
 tions which are Discontinuous. As has been already stated, Dis- 
 continuous Variations may belong to the Meristic Group or to the 
 Substantive, but it is to the former that attention will first be 
 directed. 
 
 SECTION VI. 
 Meristic Repetition and Homology. 
 
 In what has gone before, the two conceptions now introduced, 
 namely the distinction of Variations into Meristic and Substan- 
 tive, and into Continuous and Discontinuous, have been sketched 
 in outline. The significance of the facts which follow will be 
 made more evident if these two conceptions are now more fully 
 developed in some of their aspects. 
 
 Under the name Merism I have proposed to include all pheno- 
 mena of Repetition and Division, whenever found and in whatever 
 forms occurring, whether in the parts of a body or in the whole. 
 The consequences of the admission of this proposition are con- 
 siderable and should be fully realized ; for on recognition of the 
 unity of these phenomena it is possible to group together a number 
 of facts whose association will lead to simplification of some 
 morphological conceptions, and to other results of utility. 
 
 That the phenomena of Merism form a natural group is in 
 some respects a familiar idea, but in its fullest expression it is as 
 yet not generally received, still less have the consequences which 
 it entails been properly appreciated. Every one who has gone 
 even a little way into morphological inquiry has met some of the 
 difficulties to which we shall now refer. 
 
 It is with respect to the phenomena of Segmentation that 
 these difficulties are most familiar, and it is in this connexion that 
 they may be best discussed. Segmentation is a condition which 
 reaches its highest development in Vertebrates, the Annelids, 
 and the Arthropods, and it is in these groups that it has been 
 most studied. In them it appears as a more or less coincident 
 Repetition of elements belonging to most of the chief systems 
 of organs along an axis corresponding to the long axis of the body. 
 To segmentation of this kind the name ' Metameric ' has been 
 given, and by many morphologists the attempt has been made, 
 either tacitly or in words, to separate such Metameric Segmen- 
 tation from other phenomena of Repetition elsewhere occurring. 
 
sect, vi.] INTRODUCTION. 29 
 
 It has thus been attempted to distinguish the Repetitions which 
 occur along the long axis of the body from those occurring 
 along the long axis of appendages, such as for example the joints 
 of antennae or of digits, and some have even gone so far as to 
 regard the Segmentation of the Vertebrate tail as a thing different 
 in kind from that of the trunk itself. It would be apart from our 
 present purpose to recur to these subjects, were it not that this 
 suggestion of the existence of a difference in kind between Meta- 
 meric Segmentation and other Repetitions has led to several 
 notable errors in the interpretation of the facts of morphology and 
 in the application of these facts to the solution of the problems of 
 Descent. In order to lay a sound foundation for the study of 
 Meristic Variation these errors must be cleared away, and to do 
 this it is necessary to break down the artificial distinction between 
 the phenomena of Metameric Segmentation and other cases of 
 Repetition of Parts, so that the whole may be seen in their true 
 relations to each other. When this is done, the mutual relations 
 of the facts of Meristic Variation will also become more evident. 
 
 The first difficulty which has been brought into morphology 
 by the suggestion that Metameric Segmentation is a phenomenon 
 distinct in kind, is one which has coloured nearly all reasoning 
 from the facts of Morphology to problems of phylogeny. For the 
 existence of Metameric Segmentation in any given form is thus 
 taken to be one of its chief characters, and, as such, is allowed pre- 
 dominant weight in considering the genetic relations of these 
 forms. By the indiscriminate though logical extension of this 
 principle the conclusion has been reached that Vertebrates are 
 immediately connected with, or have arisen by Descent from 
 Annelids, or from Crustacea and the like, for the Repetition in 
 these forms is closely similar. Others again, being struck with 
 the resemblance between the Repetition of Parts along the radial 
 axes of Starfishes and those which occur along the long axes ot" 
 Annelids have hazarded the conjecture that perhaps this resem- 
 blance may indicate the actual phylogenetic history of these 
 Repetitions. Though such speculations as these are little better 
 than travesties of legitimate theory, some of them still command 
 interest if not belief. 1 All alike are founded on the assumption 
 that resemblances between the manner and degree in which Repe- 
 tition occurs are unlikely to have arisen save by community oi 
 Descent. A broader view of Meristic phenomena will shew that 
 
 1 These modern "Instances" recall many that once were famous but are now- 
 forgotten. For example : Item non absurda est similitudo et conformitas ilia, ut 
 homo sit tanquam planta inversa. Nam radix nervorum et facultatum animalium 
 est caput; parte* autem seminales sunt infima, nan computatis < .rtremitatibus tihi- 
 arum et brachiorum. At in planta, radix [qua irutar capitis est) regulariter infimo 
 loco collacatur ; scmitia autem supremo. BACON, Nov. Org. Lib. II. 27. In «0fl 
 computatis extremitatibus, amateurs of Instantije Confohmes may still find matter 
 for warning. 
 
30 HOMOLOGY. [istrod. 
 
 this assumption is unfounded ; for so far are the expressions of it 
 which are called Metamerism from standing alone, that it is 
 almost impossible to look at any animal or vegetable form without 
 meeting phenomena of Repetition which differ from Metamerism 
 only in degree or in extent. Between these Repetitions and 
 Metameric Repetitions it is impossible to draw any line, and the 
 Meristic Variations of all will therefore be treated together. 
 
 This error in the estimate of the value of Metamerism as a 
 guide to phylogeny is one by which the evidence of Variation is 
 only indirectly affected. The other errors now to be mentioned 
 are of a much more serious nature, for they concern the general 
 conception of the nature of Homology which is the basis of all 
 morphological study. 
 
 In introducing the method of the Study of Variation I have 
 said that it can alone supply a solid foundation for inquiry into 
 the manner by which one species arises from another. The facts 
 of Variation must therefore be the test of phylogenetic possibility. 
 Looking at organs instead of species, we shall now see that the 
 facts of Variation must also be the test of the way in which organ 
 arises from organ, and that thus Variation is the test of Homo- 
 logy. For the statement that an organ of one form is homologous 
 with an organ of another means that there is between the two 
 some connexion of Descent, and that the one organ has been 
 formed by modification of the other, or both by modification of a 
 third. The precise way in which this connexion exists is not 
 defined, and indeed has scarcely ever been considered, though 
 such a consideration must sooner or later be attempted. We 
 must for the present be content with the belief that in some un- 
 defined way there is a relationship between ' homologous ' parts, 
 and that this is what we mean when we affirm that they are 
 homologous. 
 
 We have however assumed that the transition from one form 
 to another takes place by Variation. If therefore we can see the 
 variations we shall see the precise mode by which the descent is 
 effected, and this must be true of the parts or organs as it is true 
 of the whole body. In like manner then as the Study of Variation 
 may be hoped to shew the way by which one form passes into 
 another, so also may it be hoped that it will shew how r the organs 
 of one form take on the shape of the homologous organs of 
 another. 
 
 In the absence of the evidence of Variation reasoning as 
 to Homology rests solely on conjecture, and assumptions have 
 thus been made respecting the nature of Homology which have 
 coloured the whole of morphological study. Of these, two demand 
 attention now. 
 
 I. As to Homology between the Members of one Series. We 
 saw above (page 29) how the resemblance between Repetitions 
 
sect, vi.] INTRODUCTION. 31 
 
 occurring in divers forms has led to the belief that those forms 
 had a common descent: in a somewhat similar way it has hap- 
 pened that the resemblance between individual members of a 
 series of Repeated Parts has led to the belief that they must 
 originally have been alike, and that they have been formed by 
 differentiation of members originally similar. Many who would 
 hesitate thus to formulate such a belief nevertheless have taker 
 part in inquiries which can succeed only on the hypothesis that 
 this has been the history of such parts. Of this nature are the 
 old attempts to divide the skull into vertebrae, recognizing the 
 several parts of each ; the modern disquisitions on the segmenta- 
 tion of the cranial nerves ; the attempts to homologize the several 
 phalanges of the vertebrate pollex and hallux with the several 
 phalanges of the other digits ; similar attempts to trace the 
 precise equivalence of the elements of the carpus and tarsus, and 
 many other quests of a like nature. In all these it is assumed 
 that there is a precise equivalence to be found with enough 
 searching, and that all the members of such series of Repetitions 
 were originally alike. If the series of ancestors were before us it 
 is expected that this would be seen to have been the case. In the 
 light of the facts of Variation this assumption will be seen to be a 
 wrong one, and these simple views of the Repetition and Differen- 
 tiation of members in Series must be given up as inadequate and 
 misleading, even though there be no other to substitute. 
 
 II. As to the individuality of Members of Series. In seeking 
 to homologize a series of parts in one form with a series of parts in 
 another, cases often occur in which the whole series of the one is 
 admittedly homologous with the whole series of the other. In 
 such cases the question arises, can the principle of Homology be 
 extended to the individual members of the two Series? If the 
 two Series each contain the same number of members this question 
 is a comparatively simple one, for it may be assumed that each 
 member of the Series is the equivalent or Homologue of the 
 member which in the other Series occupies the same ordinal 
 position. If however the number of members differs in the tw<> 
 Series, how is the equivalence to be apportioned ? This is a 
 question again and again arising with regard to Meristic Series 
 such as teeth, digits, phalanges, vertebrae, nerves, vessels, mammae, 
 colour-markings, the parts of the flower, and indeed in almost every 
 system whether of animals or plants. To decide this question 
 there are still no general principles. But though we yel know 
 nothing as to the steps by which Meristic Variation proceeds, 
 there is nevertheless a received view by which the interpretation 
 of the phenomena is attempted, and though in the case of each 
 system of organs the application of the principle is different, yel 
 the principle applied is essentially the same. 
 
 Thus to compare the members of Series containing different 
 members it is first assumed that the series consisted ancestrally of 
 
32 INDIVIDUALITY OF MEMBERS OF SERIES, [introd. 
 
 some maximum number, from which the formula characteristic of 
 each descendant has been derived by successive diminution. Here, 
 again, I do not doubt that many who employ this assumption 
 would hesitate to make it in set terms, but nevertheless it is the 
 logical basis of all such calculations. 
 
 Now this hypothesis involves a definite conception of the 
 mode in which Variation works, and it is most important that 
 this should be realized clearly. For if it is true that each member 
 of a Series has in every form an individual and proper history, it 
 follows that if we had before us the whole line of ancestors from 
 which the form has sprung, we should then be able to see the 
 history of each member in the body of each of its progenitors. In 
 such a Series the rise of an individual member and the decline of 
 another should then be manifest. Each would have its individual 
 history just as a Fellowship in a College or a Canonry in a 
 Cathedral has an individual history, being handed on from one 
 holder to his successor, some being suppressed and others founded, 
 but none being merged into a common fund. In other words, 
 according to the received view of the nature of these homologies, 
 it is assumed that in Variation tlie individuality of each member 
 of a Meristic Series is respected. 
 
 The difficulty in applying this principle is notorious, but when 
 the evidence of Variation is before us the cause of the difficulty 
 will become evident. For it will be found that though Variation 
 may sometimes respect individual homologies, yet this is by no 
 means a universal rule; and as a matter of fact in all cases of 
 Meristic Series, as to the Variation of which any considerable 
 body of evidence has been collected, numerous instances of Varia- 
 tion occur, in which what may be called the stereotyped or tra- 
 ditional individuality of the members is superseded. 
 
 This error in the application of the principle of Homology to 
 individual members of Meristic Series has arisen almost entirely 
 through want of recognition of the unity of Meristic Repetition, 
 wherever found. In the case of a series of parts among which 
 there is no perceptible Differentiation, no one would propose to 
 look for individual Homologies. For example, no one consid* rs 
 that the individual segments in the intestinal region of the Earth- 
 worm have any fixed relations of this kind ; no one has proposed 
 to homologize single leaves of one tree with single leaves on 
 another ; it is not expected that the separate teeth of a Roach 
 have definite homologies with separate teeth of a Dace, for such 
 expectations would be plainly absurd. But in series whose mem- 
 bers are differentiated from each other the existence of such in- 
 dividuality is nevertheless assumed. To take only one case: a 
 whole literature has been devoted to tin- attempt to determine 
 some point in the vertebral column or in the spinal nerves from 
 which the homologies of the segments may bo reckoned. This is a 
 problem which in its several forms has been widely studied. Some 
 
sect, vi.] INTRODUCTION. 33 
 
 have attempted to solve it by starting from the lumbar plexus, 
 while others have begun from the brachial. In the case of Birds 
 this question is reduced to an absurdity. Which vertebra «>f a 
 Pigeon, which has 15 cervical vertebrae, is homologous with the 
 first dorsal of a Swan which has 26 cervicals ? To decide these 
 questions the only possible appeal is to the facts of Variation, and 
 judged by these facts the whole inquiry comes to an end, for it is 
 seen at once that the expectation is founded on a wrong con- 
 ception of the workings of Variation. No one, as has been said 
 above, would attempt such an inquiry if the series were un- 
 differentiated, for this individuality would not be expected in such 
 a Series ; but to suppose that it does exist in a differentiated 
 Series of parts, is to suppose that with Differentiation the ordinal 
 individuality of the members has become fixed beyond revision. 
 This supposition the Study of Variation will dispel. 
 
 Here, as in the preceding case of the theoretical doctrine of 
 Serial Homology, the current view is far too simple and far too 
 human. Though the methods of Nature are simple too, yet 
 their simplicity is rarely ours. In these subjective conceptions of 
 Homology and of Variation, we have allowed ourselves to judge 
 too much by human criterions of difficulty, and we have let our- 
 selves fancy that Nature has produced the forms of Life from each 
 other in the ways which we would have used, if we had been 
 asked to do it. If a man were asked to make a wax model of the 
 skeleton of one animal from a wax model of the skeleton of 
 another, he would perhaps set about it by making small additions 
 to and subtractions from its several parts; but the natural process 
 differs in one great essential from this. For in Nature the body 
 of one individual has never been the body of its parent, and is no1 
 formed by a plastic operation from it; but the new body is made 
 again new from the beginning, just as if the wax model had gone 
 back into the melting-pot before the new model was begun. 
 
 SECTION VII. 
 Meristic Repetition and Division. 
 
 Before ending this preliminary consideration of ftferism it is 
 right that we should see other aspects of the matter. What fol- 
 lows is put forward in no sense as theory or doctrine but simply as 
 suggesting a line of thought which should be in the minds of any 
 who may care to pursue the subject further or to study the 
 evidence. It is perhaps only when it is seen in connexion with its 
 possible developments that the magnitude of the subject can be 
 fully felt. 
 
 b. 3 
 
34 ASEXUAL REPRODUCTION. [introd. 
 
 Iii the treatises on Comparative Anatomy which belong especi- 
 ally to the beginning of this century, the idea constantly recurs that 
 the series of segments of a metamerically segmented form do in 
 some sort represent a series of individuals which have not detached 
 themselves from each other. Seen in the light of the Doctrine 
 of Descent this resemblance or analogy has been taken as a pos- 
 sible indication that the segmented forms may actually have had 
 some such phylogenetic history as this. By similar reasoning the 
 Metazoa have been spoken of as " Colonies " of Protozoa. Now 
 though we need not allow ourselves to be drawn away into these 
 and other barren speculations as to phylogeny, we may still note 
 the substance of fact which underlies them. For it is now 
 recognized that between the process by which the body of a Kais 
 is metamerically segmented, and that by which it divides into a 
 chain of future " individuals," no line can be drawn : that the 
 process of budding, or of stabilization, by which one form gives 
 rise to a number of detached individuals, is often indistinguishable 
 from the process by which a near ally gives rise to a connected 
 colony, and that the two processes may even be interchangeable in 
 the same form; finally that the process of division of a fertilized 
 ovum by the first cleavage plane may be in some essentials com- 
 parable with the division of a Protozoon into two new individuals. 
 All these are now commonplaces of Natural History. 
 
 With what justice these considerations may have been applied 
 to the problems of phylogeny we need not now inquire, but to the 
 interpretation of the facts of Variation they have an application 
 which ought not to be neglected. 
 
 If, then, as is admitted, there is a true analogy between the 
 process by which new organisms may arise asexually by Division, 
 and the process by which ordinary Meristic Series are produced, it 
 follows that Variation, in the sense of difference between offspring 
 and parent, should find an analogy in Differentiation between the 
 members of a Meristic Series. Applied to the case of asexual re- 
 production there seems no good reason for denying this analogy. 
 It is of course an undoubted fact that in the asexual reproduction 
 of many forms Variation is rare, though the sexually produced 
 offspring of the same forms are very variable. In plants this is 
 familiar to everyone, though the extension of the same principle 
 to animals rests chiefly on inference. Nevertheless in plants bud- 
 variation, both Meristic and Substantive, happens often, and the 
 division of a plant into two dissimilar branches may well be coin- 
 pared to the production of dissimilar offspring by one parent : in- 
 deed, if the processes of Division are admitted to be fundamentally 
 the same, this conclusion can scarcely be escaped. 
 
 In one more aspect this subject may be considered with profit. 
 It is, as we have seen, believed that the division of an ovum into 
 two segmentation-spheres is not a process essentially different 
 
SECT, vii.] INTRODUCTION. 35 
 
 from the division of certain Protozoa into two " individuals." In 
 conceiving the manner of Variation in such Protozoa we have 
 little or no fact to guide us, but this much is obvious : that for the 
 introduction of a variety as the offspring of a given species, ii La 
 necessary either that the two parts into which the unicellular 
 organism divided should have varied equally, and that the 
 division should thus be a symmetrical division (in the full sense of 
 qualitative as well as formal symmetry); or that the division 
 should be asymmetrical, the resulting parts being dissimilar, in 
 which case one may conceivably belong to the type and the other 
 be a Variety. If Variation has ever occurred in the reproduction 
 of animals of this class it must have occurred on one or both of 
 these plans. 
 
 Returning to the segmentation of the Metazoan ovum we have 
 the well-known results of Roux and others, shewing that, in 
 certain species, the first 1 cleavage-plane divides the body into the 
 future right and left halves. In such cases then on the analogy 
 of the Protozoon, the right and left halves of the body are in a 
 sense comparable with the two young Protozoa, and though each 
 half is hemi-symmetrical, it is in this way the equivalent of a 
 separate organism. This suggestion, which is an old one. receives 
 support from many facts of Meristic Variation, especially from the 
 mode of formation of homologous Twins and "double Monsters 
 which are now shewn almost beyond doubt, to arise from the 
 division of one ovum 2 . But besides the evidence that each 
 half of the body may on occasion develop into a whole, evidence 
 will be given that one half may vary in its entirety, independently 
 of the other half. Such Variation may be one of sex. taking the 
 form of Gynandromorphy, so well-known among Lepidoptera, in 
 which the secondary sexual characters of one side are male, those 
 of the other being female; or it may happen that the difference 
 between the two sides is one of size, the limbs and organs of one 
 side being smaller than those of the other; or lastly the Variation 
 between the two sides may be one that has been held characteristic 
 of type and variety or even of so-called species and species 3 . 
 
 These matters have been alluded to here as things which a 
 student of the facts of Variation will do well to bear in mind. I' 
 is difficult to see the facts thus grouped without feeling the 
 
 1 Often it is the second cleavage-plane (if any) which corresponds with the 
 future middle line. 
 
 - The well-known evidence relating to this subject will be spoken of later. The 
 view given above, which is now very generally received, finds BUpporl in the striking 
 observations of Diuesch, lately published (Zt. f. w. ZooL, L891, Lin. p. 160). 
 Working with eggs of Echinus, Driesch found that if the first two segmentation- 
 spheres were artificially separated, each grew into :i Beparate Pluteut; if tin- 
 separation was incomplete, the result was a double-monster, united by homologous 
 surfaces. Similar experiments attended by similar results have since been made on 
 Ampkioxus by E. B. Wilson, Anat. An:., vn. 1892, p. 732. 
 
 :} Evidence of such abrupt Variation between the two sides of the body belongs 
 for the most part to the Substantive group. 
 
 3—2 
 
36 SUBSTANTIVE VARIATION : EXAMPLES. [introd. 
 
 possibility that the resemblance between the two sides of a 
 bilaterally symmetrical body may be in some essentials the same 
 as the resemblance between offspring of the same parent, or to 
 use an inclusive expression, that the resemblance between the 
 members of a Meristic Series may be essentially the same as the 
 resemblance and relationship between the members of one family ; 
 that the members of a row of teeth in the jaw, of a row of peas 
 in a pod, of a chain of Salps, or even a litter of pigs, all resulting 
 alike from the processes of Division, may stand to each other 
 in relationships which though different in degree may be the 
 same in kind. 
 
 If reason shall appear hereafter for holding any such view as 
 this, the result to the Study of Biology will be profound. For 
 if it shall ever be possible to solve the problem of Symmetry, 
 which may well be a mechanical one, we shall thus have laid a 
 sure foundation from which to attack the higher problem of 
 Variation, and the road through the mystery of Species may thus 
 be found in the facts of Symmetry. 
 
 SECTION VIII. 
 Discontinuity in Substantive Variation: Size. 
 
 From the subject of Merism and the thoughts which it suggests, 
 we now r pass to another matter. The first limitation by which we 
 proposed to group Variations was found in the characters which 
 they affect : the second relates to the magnitude, or as I shall call 
 it, the Continuity of the variations themselves. And though 
 for many a conception has no value till it be cast in some finite 
 mould, my aim will be rather to describe than to define the 
 meaning of the term Continuity as applied to Variation. In 
 dealing w r ith a subject of this obscurity, where the outlines are 
 doubtful, an exact mapping of the facts cannot be made and 
 ought not to be attempted; but I trust that from the present 
 indications, vague though they are, some larger and more definite 
 conception of Discontinuity in Variation may shape itself hereafter 
 by a process of natural growth. For this reason I shall as far as 
 possible avail myself of examples rather than of general expres- 
 sions, whether inclusive or exclusive. 
 
 To those who have studied the recent works of Galton, the 
 conceptions here outlined will be familiar. In the chapter on 
 " Organic Stability " in Natural Inheritance, the matter has been 
 set forth with charming lucidity, and what follows will serve 
 chiefly to illustrate the manner in which the facts of Natural 
 History correspond with the suggestions there made. 
 
 In the ease of most species it is a matter of common knowledge 
 
sect, viii.] INTRODUCTION. 37 
 
 that though no two individuals are identical, there are many which 
 in the aggregate of their characters nearly approach each other, 
 constituting thus a normal, from which comparatively few differ 
 widely. In such a species the magnitude of these differences is 
 proportional to the rarity of their occurrence. Now this, which is 
 a matter of common experience, has been shewn by Galton to be 
 actually true of several quantities which in the case of Man are 
 capable of arithmetical estimation. In the cases referred to it has 
 thus been established that these quantities when marshalled in 
 order give rise to a curve which is a normal curve of Frequency of 
 Error. Taking for instance the case of stature, Galton's statistics 
 shew that for a given community there is a mean stature, and the 
 distribution of the statures of that community around the mean 
 gives rise to a Curve of Error. In this case the individuals of that 
 community in respect of stature form one group. Now in the case 
 of a collection of individuals which can be separated into two 
 species, there is some character in respect of which, when arranged 
 by their statistical method, the individuals do not make one group 
 but two groups, and the distribution of each group in respect of 
 that character cannot be arranged in one Curve of Error, though 
 it may give rise to two such curves, each having its respective 
 mean. For example, if in a community tall individuals were 
 common and short individuals were common, but persons of medium 
 height were rare, the measurements of the Stature of such a 
 community when arranged in the graphic method would not form 
 one Curve of Error, though they might and probably would form 
 two. There would thus be a normal for the tall breed, and a 
 normal for the short breed. Such a community would, in respect 
 of Stature, be what is called dimorphic. The other case, in which 
 the whole community, grouped according to the degrees in which 
 they display a given character, forms one Curve of Error, may 
 conveniently be called monomorphic in respect of that character. 
 By considering the possible ways in which such a condition of 
 dimorphism may arise in a monomorphic community, one of the 
 uses of the term Discontinuity as applied to Variation will be 
 made clear. 
 
 Considering therefore some one character alone, in a specie 
 which is monomorphic in respect to that character, individuals 
 possessing it in its mean form are common while the extremes 
 are rare; while if the species is dimorphic the extremes are 
 common and the mean is rare. Now the change from the mono- 
 morphic condition to the dimorphic may have been effected with 
 various degrees of rapidity: for the frequency of the occurrence of 
 the mean form may have gradually diminished, while that <>f the 
 extremes gradually increased, through the agency of Natural 
 Selection or otherwise, in a long series of generations; or on the 
 other hand the diminution in the relative numbers of the mean 
 individuals may have been rapid and have been brought about in 
 
38 
 
 HORNS OF BEETLES. 
 
 [iNTROD. 
 
 a few generations by a few large and decisive changes, whether of 
 environment or of organism. 
 
 Referring to the curve of Distribution formed in the graphic 
 method of displaying the statistics, during the monomorphic period 
 the curve has one apex corresponding with the greatest frequency 
 of one normal form, but in the dimorphic period the curve has two 
 apices, corresponding with the comparative frequency of the two 
 extremes, and the comparative rarity of the mean form. The 
 terms Continuous or Discontinuous are applicable to the process 
 of transition from the monomorphic to the dimorphic state according 
 as the steps by which this change was effected are small or large. 
 
 The further meanings of Discontinuous Variation will be 
 explained by the help of examples. The first cases refer to Sub- 
 stantive Variation 1 , and we may conveniently begin by examining 
 a case of Variation in a character which is easily measured arith- 
 metically. 
 
 Among beetles belonging to the Lamellicorn family there are 
 numerous genera in which the males may have long horns arising 
 from various parts of the head and thorax 2 . These horns may be 
 
 n 
 
 in 
 
 Fig. 1. Side-views of the Lamellicorn beetle, Xylotrupe* gideon. Legs not 
 represented. I, High male, II, Medium male, III, Low male. 
 
 1 In referring thus to evidence as to Substantive Variation, I find myself in tin- 
 difficulty mentioned in the Preface. For it is necessary to allude to matters which 
 cannot be properly treated in this first instalment of facts. In order, however, that 
 the one introductory account may serve for all the evidence together, such allusion 
 is inevitable and I can only trust that full evidence as to Substantive Variation may 
 be produced before long. 
 
 2 For particulars of this subject with illustrations, see Descnit of Man, 1st ed.. 
 vol. i. pp. 309 — 372. A detailed account of this and the succeeding example in the 
 case of the Earwig was given by Mr Brindley and myself in P. Z. N.. 1893. 
 
SECT. VIII.] 
 
 INTRODUCTION. 
 
 39 
 
 of very great size, as in the well-known Hercules beetle ( Dynastes 
 here ales) and others. The females of these forms are usually 
 without horns. In such genera it is commonly found that the 
 males are not all alike, but some are of about the size of the 
 females and have little or no development of horns, while others 
 are more than twice the size of the females and have enormous 
 horns. These two forms of male are called " low ' and " high ' 
 males respectively. 
 
 In many places in the Tropics such beetles abound, both 
 " high ' : and "low" males occurring in the same locality. An 
 admirable example of this phenomenon is seen in Xylotrujpes 
 gideon, of which a " high," " low," and medium male are shewn 
 in profile in Fig. 1. Of this insect a very large number were 
 kindly given to me by Baron Anatole von Hiigel, who collected 
 them at one time, in one locality, in Java. In this species there is 
 one cephalic and one thoracic horn, placed in the positions shewn 
 in the figure. Fig. 1, I shews a "high' male, II is a medium, 
 and in a "low' : male. In the gathering received there were 
 342 males. My friend, Mr H. H. Brindley, has made careful 
 measurements of the lengths of the horns of these specimens and 
 has constructed the diagram, Fig. 2. In this each dot represents 
 an individual, and the abscissae shew the measurements of the 
 length of the cephalic horn. For clearness these measurements 
 are represented as of twice the natural size. So far as the 
 numbers go the result shews that the most frequent forms are 
 
 Fig. 2. Diagram representing the frequency of the lengths of cephalic horn in 
 male Xylotrupea gideon. M, the mean case ; M' the mean value. The abscissas 
 give lengths of cephalic horn in lines. 
 
40 FORCEPS OF EARWIGS. [introd. 
 
 the moderately low and the moderately high, the forms of mean 
 measurement being comparatively scarce. It is true that the 
 numbers are few, but so little heed is paid to phenomena of this 
 kind that material is difficult to obtain and the present oppor- 
 tunity was indeed wholly exceptional 1 . But taking the evidence 
 for what it is worth, the comparative scarcity of " medium " males 
 in that particular sample is clear, and so far the form is dimorphic, 
 and has two male normals. 
 
 Now such a condition may have arisen in several ways. First, 
 in the past history of the species there may have been a time 
 when the males were horned and were monomorphic, the " medium" 
 form being the most frequent, and the present dimorphic condition 
 may have been derived from this, either continuously or discon- 
 tinuously as described above for the case of Stature. Secondly, 
 the dimorphism may date from the first acquisition of the horns, 
 and this character may perhaps have always been distributed in 
 the dimorphic way. In this case the term Discontinuous would 
 be applicable to the Variation by which the groups of "high" and 
 "low' males have been severally produced. I am not acquainted 
 with evidence as to the course of inheritance in these cases, and I 
 do not know therefore whether both " high" and " low" males may 
 be produced by one mother. If this should be shewn to be the 
 case, it would suggest that the separation of the males into two 
 groups was a case of characters which do not readily blend, 
 and are thus exempt from what Galton has called the Law of 
 Regression 2 . 
 
 In the case of a somewhat similar structure found in the Common 
 Earwig (Forjicula auricularia) the dimorphism is 
 still more definite. In the autumn of 1892 on a 
 visit to the Fame Islands, a basaltic group off the 
 coast of Northumberland, it was found that these 
 islands teem with vast quantities of earwigs. The 
 abundance of earwigs was extraordinary. They 
 lay in almost continuous sheets under every stone 
 and tussock, both among the sea-birds' nests 
 1 * and by the light-keepers' cottages. Among them 
 
 Fig. 3. I, High were males of the two kinds shewn in Fig. 3 ; the 
 
 male, II, Low male one or high male having forceps of unusual length, 
 of Common Earwig th Qther Qr j j b - the common f orm . 
 
 {horticula auricu- x . . . . ' . ° . , P 
 
 laria) from the It appears that the high male is known trom many 
 
 Fame Islands. places in England and elsewhere and that it was 
 
 made into a distinct species, F. forcipata, by 
 
 1 In the Lucanidffi, of which the Stagbeetle (L. cervus) is an example, a similar 
 phenomenon occurs, the "high" and "low" males being distinguished by the 
 degree of development of the mandibles. No suihcient number of male Stagbeetles 
 has yet been received to warrant any statement as to the frequency of the various 
 types of males. 
 
 2 Natural Inheritance, pp. 88 — 110. 
 
SECT. VIII.] 
 
 INTRODUCTION. 
 
 41 
 
 Stevens 1 though by later authorities* 2 the species has not been 
 retained. A large sample of Earwigs collected in a Cambridge 
 garden contained 163 males of which 5 would come into the 
 high class, but the great abundance of high males at the Fames 
 seems to be quite exceptional. 
 
 With a view to a statistical determination of the frequency of 
 the high and low forms 1000 of these Earwigs were collected 1»\ 
 Miss A. Bateson, the whole being taken at random on one day 
 from three very small islands joined to each other at low tide. 
 Of the 1000 specimens 583 proved to be mature males with elytra 
 fully developed, no specimen with imperfect elytra being included 
 in this number 3 . On measuring the length of the forceps to the 
 nearest half mm. and grouping the results in the graphic method 
 the curve shewn in Fig. 4 was produced. The figures on the 
 
 Fig. 4. Curve shewing frequency of various lengths of forceps of male Earwigs 
 {F. auricularia) from the Fame Islands. Ordinate*, numbers of individuals \ 
 abseissie, lengths of forceps in mm. 
 
 ordinates here shew the numbers oi individuals, those on the 
 abscissae giving the length of the forceps in millimetres. As there 
 
 1 Stevens, Brit. Ent. 1835, vi. p. 6, PI. xxvm. fig. 4. 
 
 2 Fischer, Orthop. Euro})., 1853, p. 74; Bkunnek von Wattinwyj, Prodr. d. 
 europ. Orthop., 1882, p. 12. 
 
 1 For particulars in evidence of the maturity of these specimens see /'. '/.. Sf., 
 1893. 
 
42 COLOUR. [iNTROD. 
 
 shewn the smallest length of forceps was 25 mm., and the greatest 
 9 mm., the greatest frequency being grouped about 3*5 mm. and 
 7 mm. respectively. The mean form having forceps of moderate 
 length is comparatively rare. The size of the forceps of the 
 females scarcely varies at all, probably less than 1 mm. in the 
 whole sample. 
 
 The number of cases is enough to fairly justify the acceptance 
 of these statistics and it is not likely that a greater number of 
 cases would much alter the shape of the curve. Here, therefore, 
 is a group of individuals living in close communion with each 
 other, high and low, under the same stones. No external circum- 
 stance can be seen to divide them, yet they are found to consist 
 of two well-marked groups. 
 
 Before leaving these examples special attention should be di- 
 rected to the fact that the existence of a complete series of indivi- 
 duals, having every shade of development between the "lowest" and 
 the " highest " male, does not in any way touch the fact that the 
 Variation may be Discontinuous ; for we are concerned not with 
 the question whether or no all intermediate gradations are possible 
 or have ever existed, but with the wholly different question 
 whether or no the normal form has passed through each of these 
 intermediate conditions. To employ the metaphor which Gal ton 
 has used so well — and which may prove hereafter to be more than 
 a metaphor — we are concerned with the question of the positions 
 of Organic Stability; and in so far as the intermediate forms are 
 not or have not been positions of Organic Stability, in so far is 
 the Variation discontinuous. Supposing, then, that the "high" and 
 " low " males should become segregated into two species — a highly 
 improbable contingency — these two species would have arisen by 
 Variation which is continuous or discontinuous according to the 
 answer which this question may receive. 
 
 SECTION IX. 
 
 Discontinuity in Substantive Variation : Colour 
 
 and Colour-Patterns. 
 
 From the consideration of Discontinuity in the Variation of a 
 character, size, which may be readily measured arithmetically, we 
 pass to the more complex subject of Discontinuous Variation in 
 qualities which are not at once capable of quantitative estimation. 
 In this connexion the case of colour- variation may be profitably 
 considered. Nature abounds with examples of colour-polymor- 
 phism, and in numerous instances such Variation is discontinuous. 
 Of such discontinuous Variation in colour I shall speak under two 
 heads, considering first variations in colours themselves and 
 
sect, ix.] INTRODUCTION. }:> 
 
 secondly variations in colour-patterns. As it is not proposed to 
 give the evidence as to Substantive Variation in this volume, a 
 few examples must suffice to shew the use of the term Dis- 
 continuity as applied t<> these Colour- variations. 
 
 I. Colours. The case of the eye-colour of Man may well be 
 mentioned first, as it has been studied statistically by Galton In 
 this case the facts clearly shewed that certain types of eye-colour 
 are relatively common and that intermediates between th< se 
 types are comparatively rare. The statistics further shewed that 
 in this respect inheritance was alternative, and that the different 
 types of eye-colour do not often blend in the offspring. " If one 
 parent has a light eye-colour and the other a dark eye-colour, 
 some of the children will, as a rule, be light and the rest dark ; 
 they will seldom be medium eye-coloured, like the children of 
 medium eye-coloured parents. 1 " 
 
 Colour dimorphism of this kind is very common among animals 
 and plants. It is well known, for example, among beetles. Several 
 metallic blue beetles have bronze varieties of both sexes, living 
 together in the same locality. A familiar instance of this dimor- 
 phism occurs in the common Pliratora vitellince. Again in the 
 Elaterid beetle, Corymbites cupreus, there is a similar dimorphism 
 in both sexes, the one variety having elytra in larger part yellow- 
 brown, while the elvtra of the other are metallic blue. This blue 
 variety was formerly reckoned a distinct species, G. ceruginosus. 
 In the latter case I am informed by Dr Sharp, who has had a 
 large experience of this species, that no intermediate between 
 these two varieties has been recorded, and in the case of the 
 Phratora the occurrence of intermediates is very doubtful. An- 
 other common example of colour dimorphism is seen in Telephorus 
 livid us y the "sailor" of "soldiers and sailors." This beetle inav 
 be found in large numbers, about half being slaty in colour ( var. 
 disj)ar), while the remainder have the yellowish colour which 
 coleopterists call "testaceous." Such instances may be multi- 
 plied indefinitely. When the whole evidence is examined it will 
 be found that different colours are liable to different discontinuous 
 variations; as instances may be mentioned black and tan in dogs ; 
 olive-brown or green and yellow in birds, &c.' J ; grey and cream- 
 
 1 Natural Inheritance, p. 1H9. 
 
 2 A specimen of the green Ring Parakeet [PaUeornU torquatua) at the Zoological 
 Society's Gardens was almost entirely canary-yellow in 1890. Since that date it 
 has become more and more "ticked" with green feathers. A Green Woodpecker 
 (Picas riridis) is described, having the feathers of the runi]> edged with red instead 
 of yellow, the normally green feathers of the three lower rows of wing-coi 
 and the back were pointed with yellow. J. H. Gubnby, Zoologist, xi. p. •"■- 
 
 I am indebted to Mr Gnrney for the loan of a coloured drawing of this specimen. 
 Another example is described as being entirely canary-yellow, with the exception <>t 
 a few feathers on the cap, which were purple-red. Dk Bktta, Mater. i<> r una fauna 
 Veronese, p. 174. For this reference I am indebted to Prof. Newton. Specimen <>f 
 Common Bunting whitish yellow. Edwabo, ZawL, 6492 ; Sedge Warbler canary- 
 yellow. Bird, Zool., 3G32. The Canary itself is a similar case. An Eel gamb<> 
 yellow. Gurnet, Zool., 3599. 
 
44 RED AND YELLOW. [introd. 
 
 colour in mice and cygnets 1 ; red and blue in the eggs of many 
 Copepoda 2 , the tibiae of Locusts 3 , the hind wings of the Crimson 
 Underwing (Catocala nupta) 4 , &c. Another case of blue as a 
 variety of scarlet is the familiar one of the flower of the Pim- 
 pernel (Anagallis arvensis). Discontinuous colour-variation of 
 this kind is one of the commonest phenomena in nature, but to 
 advance the subject materially it is necessary for a large mass of 
 evidence tc^be produced. This cannot now be attempted, but in 
 order to bring out the close relation between these facts and the 
 problem of Species I propose to dwell rather longer on one special 
 section of the evidence which must serve to exemplify the rest. 
 The case which I propose to take is that of certain yellow, orange, 
 and red pigments. For brevity I shall present the chief facts in 
 the first instance without comment. 
 
 1. Colias edusa (Clouded Yellow) is usually orange-yellow, having 
 a definite pale yellow female variety, helice, which is not recognized as 
 occurring in the male form. A specimen is figured having the right 
 side helice and the left edusa. Fitch, E. A., Entomologist, 1878, xli. 
 p. 52, PI. fig. 11. This was an authentic specimen, for Mr Fitch tells 
 me that it was taken by his son and seen alive by himself. 
 
 A specimen having one wing white and the rest orange is recorded 
 by Morris, Brit. But., p. 13. 
 
 Intermediates between edusa and helice must be exceedingly rare. 
 Oberthur records two such specimens and says that Staudinger took 
 a similar one at Cadiz. For this intermediate he proposes a new name, 
 helicina. Bull. Soc. Ent. Fr. (5), x. p. cxlv. 
 
 1 In this case I can affirm the alternative character of the inheritance. For 
 several years a pair of swans kept by St John's College, Cambridge, have produced 
 cygnets, some of which have been of the normal grey, while others have been fawn- 
 colour, a condition which Prof. Newton tells me has been thought characteristic of 
 the " Polish " swan, a putative species. None of these cygnets are intermediate in 
 colour, and all accmire the full white adult plumage, but the feet of the fawn-coloured 
 cygnets remain pale in colour. Now the father of these has pale feet and was 
 doubtless himself a fawn-coloured cygnet ; the hen is normal. The cock formerly 
 belonged to Dr Clifford, who kindly told me that the cygnets of this bird by a different 
 hen were also thus diverse. A pair of these were given to Sir John Gibbons, who 
 informs me that "from these there has been a brood every year, and always I think 
 one of the cygnets has been white or nearly so, the others being of the usual colour." 
 One of Dr Clifford's birds was also given to the late Mrs Gosselin of Blakesware, 
 to whom I am indebted for descriptions of and feathers from several fawn-coloured 
 cygnets which were its offspring. A similar case on the Lake of Geneva is re- 
 corded by Fauvel, Rev. ZooL, 1869, p. 334, and another in the Zool. Gardens at 
 Amsterdam, by Newton, Zool. Rec, 1869, p. 99. 
 
 2 This is well known to collectors of fresh-water fauna, and I have repeatedly 
 seen the same phenomenon in species of Diaptomue, especially D. asiaticus, in the 
 lakes of W. Siberia. Among thousands of individuals with red-brown egg-sacs, will 
 often occur a few specimens having the egg-sacs of a brilliant turquoise-blue. In 
 this connexion compare the case of the Crayfish [Astacus fluviatilis), which turns 
 scarlet on being boiled, and which, like the Lobster, not uncommonly appears in a 
 full blue variety. 
 
 3 Caloptemu spretus with hind tibia? blue instead of red, Dodge, Can. Ent., 1878, 
 x. p. 105 ; Melanoplus paekardii, having hind tibia? red instead of bluish, Bruner, 
 Can. Ent., 1885, xvn. p. 18. For reference to these observations I am indebted to 
 Cockereel, Ent. , 1889, xxii. p. 127. 
 
 4 Win ik. Ent., 1889, xxn. p. 51. Compare the fact that in another species of 
 Catocala (C. fraxini), the Clifden Nonpareil, the hind wings are normally bluish. 
 
sect, ix.] INTRODUCTION. 45 
 
 A curious specimen, apparently a male, having the colour of hdice 
 was kindly shewn me by Mr F. H. Waterhouse. The light marks 
 which in the female are present on the dark borders of the fore-wing 
 are only represented by one minute light mark on each fore-wing. 
 
 In most if not all of the edusa group of Colias, there is a pale 
 aberration of the female, corresponding to the helice variety of < zdusa. 
 Elwes, Tr. Ent. Soc, 1880, p. 134. In the same paper is a full account 
 of the geographical distribution of the several species and colour-varieties 
 of Colias. 
 
 Colias hyale (Pale Clouded Yellow) is normally sulphur-coloured. 
 Nearly white varieties and a variety with the field rich sulphur colour, 
 and the apical marginal patches red, are recorded in several works. 
 
 2. Gonepteryx rhamni (The Brimstone) is sulphur-yellow in the 
 male, and greenish-white in the female. There is a spot in each wing, 
 and the scales covering this on the upper side are bright orange. 
 
 Gonepteryx cleopatra, a S. European species, is like the above 
 in the hind-wings, while the field of the fore-wings is flushed with 
 orange of exactly the tint of that on the spots of G. rhamni. 
 
 There are several records in entomological literature alleging the 
 capture of "G. cleopatra" in Britain, e.g. Proc. Ent. Soc., 1887, p. xliii. 
 
 In addition to these there are records of specimens of G. rhamni 
 more or less flushed with orange ; e.g., a specimen at Aldershot with 
 orange spots on fore-wings as in cleopatra, Proc. Ent. Soc, 1885, 
 p. xxiv. Mr Jenner "Weir said he had seen a specimen in Ingall's 
 collection, intermediate between rhamni and cleopatra. ibid. 
 
 A male of G. rhamni taken at Beckenham had the costal margin 
 of each fore-wing broadly but unequally suffused with bright rose- 
 colour or scarlet, and the right posterior wing was marked in like 
 manner. The insect was thus marked when captured. Bicknell, 
 Proc. Ent. Soc, 1871, p. xviii. 
 
 3. Anthocharis (Euchloe) cardamines (The Orange Tip), in the male 
 has the fore-wings tipped with orange on both sides, while in the 
 female these orange tips are absent. The field in both is white In 
 entomological literature are many records of variations in the extent 
 and depth of the orange markings on upper or under side, or both 
 (cp. Zoologist, xiii. 4562; Proc Ent. Soc, 1S70, p. ii. ; Mosley, 
 Illustrations of British Lepidoptera ; Haworth ; Boisduval ami many 
 others), but with these we are not immediately concerned. 
 
 A specimen is figured in which the orange spots were completely 
 represented by yellow. Mosley, Illustrated Brit. Lep. 
 
 The white of the field is replaced by primrose or lemon yellow in 
 several Continental forms. These have been described as species 
 under the names eupheno, belia, euphenoides, gruneri, &c. 
 
 A local variety of A. eupheno is described from Mogador, where it 
 was found common at a little distance from the town. The female 
 was much larger than the type, resembling the male in markings and 
 in shape of the fore-wings. The orange blotch, instead of being con- 
 fined to tip of the fore-wing as normally, extends to the discoidal spot 
 and is usually bounded by a black band, sometimes suffusing the whole 
 tip of the wing. The colour of the field varies from pure white to pale 
 lemon: the hind-wings are always yellower than in the type, in some 
 
46 RED AND YELLOW. [ixtrod. 
 
 specimens being nearly as yellow as those of the male. Mr M. C. 
 Oberthiir supplied a specimen from Central Algeria which was inter- 
 mediate between the type and this variety. Leech, J. H., P. Z. S., 
 1886, p. 122. 
 
 4. Amongst Lepidoptera the change from red to yellow is very 
 common. A case of Vanessa atalarda, having the red partially replaced 
 by yellow, is figured in Entom., 1878, xi. p. 170, Plate. Varieties of 
 Arctia caja, Callimorpha dominula, C. hebe, C. hera, C. jacoboece, 
 Zygcena filipendulce, Z. minos, tfcc, with yellow instead of red, are to 
 be seen in many collections. See especially Ochsexheimer, Schm. 
 v. Europa, 1808, n. p. x, also p. 25, and many other authors. A 
 chalk-pit at Madingley, Cambridge, has long been known to collectors 
 as a locality for the yellow Z. filipendulce (Six-spot-Burnet); see Eat. 
 Mo. Mag. xxv. p. 289. In some of these the yellow is tinged with 
 red, but it is commonly a very distinct variety. A variety of the Red 
 Underwing (Catocala nupta) with brownish-yellow in the place of the 
 red, is figured by Exgramelle, Papill. d'Eur., PL cccxxn. The evidence 
 relating to this subject is very extensive, and concerns many genera and 
 species besides those named above. 
 
 5. Pericrocotus flammeus (an Indian Fly-catcher) is grey and 
 yellow in the female, and black and orange-red in the male. The young 
 male is grey and yellow like the female. An adult male is described in 
 which the grey had been fully replaced by black, but the yellow 
 remained, not having been replaced by red. R. G. "Wardlaw Ramsay, 
 P. Z. S., 1879, p. 765. See also Legge, Birds of Ceylon, I. p. 363, for 
 description of male in transitional plumage. 
 
 Curiously enough the change from red to yellow and from light 
 yellow to dark is no less common among plants, though it can 
 scarcely be supposed that the substances concerned are similar. 
 
 1. y<ircissus corbularia and other species are known in sulphur- 
 yellow and in full yellow 1 . 
 
 2. The Iceland Poppy (P. nudicaule) is very common in gardens 
 under three forms, white, yellow and orange. Intermediate and flaked 
 varieties occur, but are less common than the three chief forms. 
 Respecting this species Miss Jekyll of Munstead, who first brought 
 out the varieties, kindly gives me the following information. She 
 writes : — " I began with one plant of the yellow colour that I take to 
 be the type-colour. It was then new as a garden plant, so I saved the 
 seed. The first sowing gave me various shades of orange, as well as the 
 type, in different shades. In the 3rd and 4th years I got buffs, whites, 
 and very pale lemon colourings. As there was only one plant to begin 
 with there was no question of cross-fertilization. A white appeared in 
 
 the 3rd year of sowing and I kept on selecting for 2 or 3 years and 
 
 gave it to a friend in Ireland, who returned it to me 2 years later still 
 more improved. This strong white seems now to be fixed and quite 
 unwilling to revert to the yellow colourings, and is a rather stouter and 
 
 1 Mr P. Barr, who has collected these forms in Portugal, tells me that he believe3 
 the pale (" citrina") varieties of N. ajax and X. corbularia to be confined to 
 calcareous soils. 
 
SECT. IX.] INTRODUCTION. 47 
 
 handsomer plant altogether." In seedlings from the orange or yellow 
 
 form grown in separate beds the proportion of seedlings true to their 
 parent colour would not be nearer than about 60 or 70 per cent., but 
 in the case of the white form Miss Jekyll considers that 95 per cent. 
 may be expected to come true. 
 
 The yellow Horned Poppy (Glauciiun hUcinn) is normally of a 
 lemon yellow very like that of P. nudicaule. Of this species also 1 here 
 is an orange cultivated variety. The varieties of the tomato offer a 
 similar series of colour- variations. 
 
 3. Fruits of many kinds are known in red and yellow forms. 
 For instance the yellow berried Yew is well known. It is described 
 under the name Taxus baccata fructu-luteo. Loud. "It appears to 
 have been discovered about 1817 by Mr Whitlaw of Dublin, growing 
 in the demesne of the Bishop of Kildare, near Glasnevin; but it 
 appears to have been neglected till 1833 when Miss Blackwood dis- 
 covered a tree of it in Clontarf churchyard near Dublin. Mr Mackay 
 on looking for this tree in 1837 found no tree in the churchyard, but 
 several in the grounds of Clontarf Castle, and one, a large one, with its 
 branches overhanging the churchyard, from which he sent us specimens. 
 The tree does not differ, either in its shape or foliage, from the common 
 yew, but when covered with its berries it forms a very beautiful 
 object, especially when contrasted with yew trees covered with berries 
 of the usual coral colour." Loudon, Arb. et Frut JJrif., iv. 1S38, 
 p. 2068. 
 
 4. The Raspberry {Rub us idceus) is another fruit which is known 
 wild in both the red and yellow forms, though the latter is less common. 
 According to Babington, it has pale prickles, and leaflets rather obovate. 
 Brit. Rubi, p. 43. (See Rivers, Gard. Chron., 1867, p. 516.) 
 
 Any person who has opportunities of handling animals and 
 plants in numbers can add many similar cases. These few are 
 taken more or less at random, as illustrations of the frequency 
 with which red, orange, and yellow may vary to each other. It is 
 of course not necessary to say that in numerous instances both 
 among animals and plants, the same parts which in one species 
 are yellow, in an allied species or in a geographically distinci race 
 are represented by orange or by red. To an appreciation of the 
 rapidity with which such changes may have come about, facts like 
 the foregoing contribute. 
 
 The frequency of such variations suggest that many of these 
 yellow and red pigments are either closely allied bodies or dim' lent 
 forms of the same body. Until the chemistry of these substances 
 has been properly investigated nothing can be definitely stated 
 as to this, but the fact that vegetable yellows are very sensitive to 
 reagents is familiar. The lemon variety of the Iceland Poppy 
 treated with ammonia turns to a colour almost identical with 
 that of the orange variety, while the white variety so treated g< 
 primrose yellow. The lemon variety when boiled, ( »r treated with 
 alcohol yields an orange solution, which is of the same tint. This 
 returns to lemon-colour if treated with ammonia or acids. The 
 
48 COLOUR-PATTERNS. [introd. 
 
 wings of G. rhamni when boiled yield a soluble yellow, which 
 according to Hopkins (Proc. Chem. Soc, reported Nature, Dec. 31, 
 1891) is a derivative of mycomelic acid, allied to uric acid. This 
 substance turns orange with reagents. The wings of G. rhamni 
 turn orange-red when exposed to wet potassium cyanide {Proc. 
 Ent. Soc, 1871, p. xviii) as may be easily seen. 
 
 When these facts, meagre though they are, are considered 
 together with the evidence of variability, the suggestion is very 
 strong that the discontinuity between these several charac- 
 teristic colours is of a chemical nature, and that the transitions 
 from one shade of yellow to another, or from yellow to orange or 
 red is a phenomenon comparable with the changes of litmus and 
 some other vegetable blues from blue to red or of turmeric from 
 yellow to brown. If such a view of these phenomena were to be 
 accepted, it would, I think, be simpler to regard the constancy of 
 the tints of the several species and the rarity of the intermediate 
 varieties as a direct manifestation of the chemical stability or 
 instability of the colouring matters, rather than as the con- 
 sequences of environmental Selection for some special fitness as 
 to whose nature we can make no guess. For we do know the 
 phenomenon of chemical discontinuity, whatever may be its ulti- 
 mate causes, but of these hypothetical fitnesses we know nothing, 
 not even whether they exist or no. 
 
 II. Colour-patterns. Thus far I have spoken only of dis- 
 continuous variations in colours themselves, but there are no less 
 remarkable instances of discontinuous variations in the distri- 
 bution of colours in particoloured forms. By a combination of 
 these modes, variations of great magnitude may occur. 
 
 One of the most obvious cases of this phenomenon is that of 
 the Cat. In European towns cats are of many colours, but they 
 nevertheless foil very readily into certain classes. The chief of 
 these are black, tabby, silver-grey and silver-brindled, sandy, tor- 
 toiseshell, black and white, and white. Of course no two cats 
 have identical colouring, but the individual variations group very 
 easily round these centres, and intermediate forms which cannot at 
 once be referred to any of these groups are immediately recognized 
 as something out of the common and strange. Yet it is almost 
 certain that cats of all shades breed freely together, and there is 
 no reason to suppose that the discontinuity between the colour- 
 groups is in any way determined by Natural Selection. 
 
 Another example may be seen in the Dog-whelk {Purpura 
 I a pill us). This animal occurs on nearly the whole British coast, 
 wherever there are rocks or even clay hard enough to form 
 definite crevices. Like most littoral animals, the Dog-whelks of 
 each locality differ more or less from those of other localities, and 
 these differences may be differences of size, texture of shell, 
 degree of calcification, amount of " frilling," kc. The peculiarities 
 
SECT, ix.] INTRODUCTION. 49 
 
 may be so striking that each individual can at once 1>'' n -cognized 
 as belonging to a given locality, or they may be trifling, and 
 appreciable only when a large number of individuals arc gathered 
 But apart from these differences of form and texture there are a 
 great number of colour-varieties of which the following are the 
 three chief whole-coloured forms, viz. white, dark purple-brown, 
 and yellow. In addition to these there are banded forms, and the 
 bands may be coloured with any two of the three colours men- 
 tioned above. Among the banded forms there are two distinct 
 sorts of banding, in the one there are very many fine bands and in 
 the other there are a few broad bands. In most localities these 
 colour- varieties may all be found ; though in some places, especi- 
 ally where the water is foul, as at Plymouth, the shells are greatly 
 corroded and the colours, if originally present, are obscured. 
 Speaking however of localities in which colour- varieties are to be 
 seen at all, several may generally be found together. If any one 
 will take the trouble to gather a few hundreds of these shells and 
 will set himself to sort them into groups according to their 
 colours, he will find that the majority fall naturally into groups of 
 this kind ; and that those which cannot be at once assigned to 
 groups but fall intermediately between the groups are com- 
 paratively few. I have seen this at many places on the English 
 coast; in Yorkshire, Norfolk, Suffolk, Kent, Sussex, Dorsetshire. 
 Devonshire, Cornwall, &c. In several localities I have found 
 pairs belonging to different colour-varieties breeding together, 
 and there is therefore no reasonable doubt that these colour- 
 variations do not freely blend, but are discontinuous. 
 
 The statements here made with regard to P. lapillus hold in 
 almost the same way for Littorina rudis, but in this case the 
 number of colour-types is larger. In L. rudis I have occasionally 
 seen specimens of which the upper part belonged to one colour- 
 type, and the lower to another, the transition occurring sharply at 
 one of the varices. In these cases the shell appears to have been 
 injured and is possibly renewed. 
 
 One of the commonest British Lady-birds (Coccuwlla decern - 
 ■punctata) is an extremely variable form. A great number <>f its 
 varieties may be found together, ranging from forms with small 
 black spots on a red field to forms in which the field is black with 
 a few red spots. But in spite of the great diversity there are 
 certain types which are again and again approached, while the 
 intermediates are comparatively scarce. 
 
 The following case, well known to entomologists, may he mentioned here. The 
 Painted Lady (Pyrameis cardui) is found in the typical form over the i utile extent 
 of every continent, with the exception of the Arctic regions and possibly 8. America. 
 A special form of it (var. kerakawi) is found in Australia an 1 New Zealand, bnt the 
 other large islands south of Asia possess the normal type. The Latter is also found 
 in the Azores, Canaries, Madeira and St Helena. This butterfly lias been taken on 
 the snowdevel in the Alps; and in X. America, though it may he regarded as one 
 of the commonest butterflies in the elevated centra] district, it is most abundant at 
 a level of 7000—8000 feet. It has been taken on Arapahoe Teak, between 11,000 
 
 B. 4 
 
50 
 
 COLOUR-PATTERNS. 
 
 [INTEOD. 
 
 and 12,000 feet (from Scxdder, Butterflies of X. America, i. pp. 477 — 480). Of this 
 insect, which is a very constant one, a certain striking aberration has been found, 
 always as a great rarity, in many lands. In this aberration the markings are 
 almost entirely rearranged. It is said to have been first described by Eambur under 
 the name var. Elymi, but this description I have never found. (The reference 
 quoted is Annales des Sci. d' observation, Paris, 1829, Vol. n. PL v.) As often happens 
 with Variation, without coloured figures description is almost useless, but tbe 
 figures referred to are very accessible. In a British specimen of this aberration 
 the white bars are absent from the anterior costae and a series of white fusiform 
 blotches are present along the marginal border; two abnormal white spots are 
 also present near the anal angle, thus continuing the series down the wing (fig. 
 5, a.). The hind- wings are equally aberrant. The two large dark spots which are 
 usually on the disk between the median nervure and the inner margin are altogether 
 wanting. Between each of the nervures of the hind-wing is a white spot, whereas 
 in the normal form there is no white spot at all on the hind-wings. These white 
 spots on the hind-wings form a row parallel to the border of the wing and, as it 
 
 Fig. 
 
 5. 
 
 A. Clark's specimen of P. cardui, var. ehjmi from I'.ut. 1880. 
 
 B. Newman's specimen. Brit. But., p. 64. 
 
 C. P. cardui, normal, also from Newman, Brit. But., p. 64. 
 
SECT, ix.] INTRODUCTION. 51 
 
 were, continue the series of white spots borne by the anterior rings. [Underside 
 not described.] This specimen was reared from a larva found near the river I 
 Clapton Park. Clark, J. A., Entomologist, 1880, xm. p. 73, fig. A coloured 
 figure of the same specimen, Mosley, S. L., PI. 8, fig. H. 
 
 A form very closely similar to the above is figured in black and white by 
 Newman from a specimen in IngalFs collection (fig. 5, n). [This is apparently the 
 specimen given in Zoologist, p. H304.] Newman, British Butterflies, p. 01, liji. A 
 British specimen which nearly approaches this aberration in the absence of the 
 white bars on the costae and in the absence of the black transverse bar i- recorded. 
 In it each of the sub-marginal rows of black spots on the posterior wings is drawn, 
 containing a white spot. In this specimen the In-own-red of the type v. 
 presented by rose-colour. Newman, Entomologist, 1*73, p. 345, fig. 
 
 Another specimen closely resembling this aberrant form is described from New 
 South Wales. Olliff, A. S., Proc. Linn. Hoc, N. 8. W., S. 2, in. p. L250. 
 
 Another specimen closely resembling the above was taken at Graham's Town, 
 S. Africa, and is mentioned by Jenner Weir, Entomologist, 1889, xxn. p. 7:;. 
 
 Another specimen is figured in which the hind-wings are marked as in tie- 
 above, but the anterior wings, though strongly resembling this aberration in the 
 general disposition of the colours, yet differ in details, the chief points of difference 
 being that the white costal bar is only partially obliterated and the white spots on 
 the anal angles of the fore- wings are not developed. 
 
 [This specimen was in Kaden's collection and was presumably European. J 
 Heurich-Schaffer, Bd. i. p. 41, PI. 35, tigs. 157 and 158. 
 
 A description is given of an aberrant form taken at King William's Town, 
 S. Africa, which " closely resembled that figured by Herrich-Schaffer."' Tbimen, 
 R., South-African Butterflies, i. p. 201. 
 
 A specimen (British) resembling the above, but lacking the white spots on the 
 anal angles of the fore- wings and having the marginal row on the hind-wing light- 
 coloured, but not quite white, is figured by Mosley, Pt. in. PI. 3, fig. 3. 
 
 Two specimens were taken in New Jersey, U.S.A., which are stated to have 
 conformed to this aberration. Si'reckkr, Cat. N. Amer. Macrolepidop., p. 187. 
 
 Another British specimen generally resembling Herrich-S chaffer's figure is 
 represented by Mosley, PI. 8, fig. 4. 
 
 In all the above specimens the resemblance, as far at least as the upper surface 
 is concerned, is considerable. With the exception of Herrich-Schaffer's example, 
 the undersides are not figured, but from the descriptions it may he gathered that 
 they also resembled each other though probably not so closely as the upper surfaces. 
 The resemblance between the underside of the Australian specimen an I that figured 
 by Herrich-Schaffer must have been very close. 
 
 "Intermediate between these extreme sports and the normal form are tin 
 examples taken at Cape Town in 1866, 1878 and 1874 — the first by myself in 
 which the fore-wing markings are scarcely affected, hut the hind-wing spots are 
 minutely ocellate and externally prolonged, so as to be confluent with tie 
 ing row of lunules." Tkimen, ibid. pp. 201, 202. 
 
 Another aberration, a Belgian specimen, resembles •* Elijmi" in kind but differs 
 from it in degree. In it also the while bars are absent from the costflB, and tin- 
 brown and black markings of the anterior wings are rearranged in almost exactly 
 the same manner. The posterior wings are modified u> a much less extent and the 
 normal row of black spots between the nervines remains, while only the first and 
 second of the series of white spots is present, the former being very slight. In this 
 individual the markings of the underside also resemble the alienation generally, 
 but it retains the four ocelli of the type. Die DoNCEEL, II. Doni kikk. Ann. S 
 oVEnt. Beige, 1878, xxi. p. 10, Plate. 
 
 A specimen, also Belgian, is described in which the two anterior win J8 n -liihle 
 Herrich-Schaffer's figure in lacking the white bars on the costal and in the arran 
 nient of the black and ground colour. In neither of them are the whit. of the 
 
 anal angles (found in the British ami Australian sp scimens) present. The white 
 markings at the apex of the anterior wings differ on the two sides, being in both 
 of them unlike the type and an approach v> the aberrations in question, hut the 
 degree to which they are developed differs markedly, being greatesl on the right si 
 The left posterior wing resembles the aberration in having the -ix abnormal white 
 spots, but less emphasized than in the figures quoted above; in general colour this wine 
 is darker than the type. The right posterior wing, however, has Qone of the white 
 spots of the aberration, and differs from the type only in being more suffused with 
 
 4- 2 
 
52 COLOUR-PATTERNS. [iNTBOD. 
 
 black. To recapitulate, the two anterior and the left posterior wing resemble generally, 
 though not entirely, the aberration, while the right posterior wing is nearly normal. 
 A specimen is described from Ekaterinoslav, S. Russia, which resembles this 
 aberration in wanting the black transverse band and in the disposition of the apical 
 white spots. A trace of the white costal bar remains on the costal border. On the 
 underside of this specimen the ocelli were placed in a pale rose-coloured band. 
 (Name proposed, aberration, inornata). Bramsox, K. L., Ann. Soc. Ent. France, 
 S. 6, vi. 1886, p. 284. 
 
 Besides the rare aberration " var. Elymi" there is a variety sometimes found in 
 Europe, which in Australia is so constant and definite that it has been regarded as 
 a species. The following may be quoted respecting its occurrence in Australia, 
 where it is common : 
 
 " There is in abundance about Melbourne and in many other parts of Australia 
 a Cynthia with the general appearance and habit of G. cardui, so closely represented 
 that every entomologist I know refers it to that species. The Australian species 
 differs from the European one constantly, however, in having the centres of the 
 three lower round spots on the posterior wings bright blue, and having two other 
 blue spots on the posterior angles of the same wings, the corresponding parts of 
 the European form being black." For this form the name C. kershawi is proposed. 
 M'Cot, F., Ann. and May. of Nat. Hist., Ser. 4, i. 1868, p. 76. See also Olliff, 
 A. S., Proc. Linn. Soc, N. S. W., Ser. 2, in. p. 1251. The notices of its occurrence 
 in Europe are as follows. In 1884 Mr Jenner Weir exhibited a specimen of P. 
 cardui, taken in the New Forest. Three of the five black spots in the disk of the 
 upper side of the hind-wings had blue pupils ; he pointed out that the specimen 
 thus approached the Australian form, P. kershawi. Proc. Ent. Soc, 1884, 
 p. xxvii. 
 
 Olliff, loc. cit., states that he has taken a specimen having these blue 
 markings at Katwijk, in Holland. 
 
 In the case given, the evidence certainly suggests that these 
 various forms of aberration are grouped round a normal form of 
 aberration, just as the individuals of the type are grouped round 
 its normal. 
 
 One example of a similar discontinuity in a melanic varia- 
 tion may profitably be given. I have taken this opportunity 
 of referring to such a case, as the general evidence of melanic 
 variations goes on the whole to shew that they are not commonly 
 discontinuous, and further evidence on this point would be most 
 valuable. To appreciate the evidence Butler's coloured plate 
 should be referred to. 
 
 Terias. A well-marked group of butterflies of this genus allied to 
 T. hecabe, is found in Japan. It contains forms of great diversity in 
 amount of black border which occurs on the outer margins of the fore- 
 and hind-wings. The remainder of the wings is lemon-yellow. The 
 black border may be confined to the tip of the fore-wings, or may there 
 occupy a considerable area and be extended along the whole outer 
 margin of both wings. The form with the least black is called T. man- 
 ihirina, that with the most, is called T. mariesii, and the intermediate 
 form is called T. anemone. Upwards of 150 specimens, all from Nikko, 
 were examined; these ranged between the two extremes, and were 
 found to form a continuous series. Butler states that "the absence of 
 six of them, referable only to two gradations, would at once leave the 
 three species as sharply defined as any in the genus." 
 
 [In the case of these butterflies, there are thus three groupsof va net ies, 
 two extreme groups and one mean group ; intermediates between these 
 
sect, ix.] INTRODUCTION. 53 
 
 are comparatively rare. Butler suggests that these intermediate forma 
 should be regarded as hybrids, even in the absence of experimental 
 evidence. This view is of course dependent on the truth of the belief 
 that such a discontinuous occurrence of variations is anomalous.] 
 
 Twenty specimens of the species T. bethesaba and thirty-nine of 
 T. jaegeri (both from Japan), were also examined. The former pre- 
 sented no variations whatever, and the latter only vary in the yellower 
 or redder tint on the under surface of the secondaries. Butler, A. G., 
 Trans. Ent. Sob, 1880, p. 197, PL vi. 
 
 Compare the following : 
 
 Terras constantia. Twenty-five pupae, all found together on the same 
 twigs at Teapa, Tabasco, Mexico, by Mr H. H. Smith. The butterflies 
 from these are in Messrs Godman and Salvin's collection, who kindly 
 allowed me to examine them. The amount of black border on both wings 
 varies much, nearly though not quite so much as in the cases figured 
 by Butler. In the lightest the apex of the fore-wing alone is black, 
 and there is no black on the hind-wing in 9 specimens ; of the remaining 
 16 some have a well-defined black border to the hind-wing, while in 
 the rest (about 6) this border is slight. This case is a particularly 
 interesting one, as the specimens were associated and presumably 
 belonged to one brood. 
 
 ev 
 
 For another beautiful case of discontinuous Variation in 
 pattern I am indebted to Dr D. Sharp. The Cambridge Univer- 
 sity Museum lately received a series of 38 specimens of Kallima 
 inachys, the well-known butterfly whose folded wings resemble a 
 dead leaf with its mid-rib and veinings. The underside of this 
 butterfly is sometimes marked with large blotches and flecks of 
 irregular shape, which, as has often been noted, resemble the 
 patches of discoloration caused by fungi in decaying Leaves. 
 Dr Sharp pointed out to me that the specimens examined fell 
 naturally into four groups according to the coloration of the 
 underside. In the first group the field is nearly plain, though 
 the tint varies in individuals. The "mid-rib" is strongly marked 
 in this and all the groups, but the "veinings" are absent or very 
 slightly marked in the first group : 18 specimens. In the second 
 group the ground is almost plain, but it bears numerous strongly 
 marked black-speckled spots, of forms which though irregular in 
 outline are closely alike, and occupy the same positions in all the 
 six specimens, being scarcely if at all represented in any of the 
 others. In the third group the dark bars representing "veins' 
 are strong, but the field is nearly uniform : 10 specimens. In the 
 fourth group, of four specimens, the ground-colour is darkened in 
 such a way as to leave large and definite blotches of light colour 
 in particular places. Of these specimens three have the veinings 
 very strongly marked, while the fourth is without them. 
 
 Into these four groups the specimens could be unhesitatingly 
 separated, though in each group many individual differences 
 
54 MISCELLANEOUS EXAMPLES. [iNTBOD. 
 
 occurred. Xo marked variation in the upper-sides was to be seen. 
 These specimens were all from the Khasia hills, Assam, but there 
 was of course no evidence that all were flying together. 
 
 One of the most interesting examples of discontinuous Variation in 
 colour-patterns is the case of ocellar markings or eye-spots. Upon 
 this subject nothing need here be said as the evidence will be given in 
 detail in the course of this volume (see Chap. XIII.). 
 
 SECTION X. 
 
 Discontinuity in Substantive Variation. — Miscellaneous 
 
 Examples. 
 
 Of the discontinuous occurrence of Substantive Variation, the 
 manifestations are many and diverse. We have seen that in such 
 features as size, colour, and colour-patterns, Variations may be 
 discontinuous, and a form may thus result, differing markedly 
 from the type which begot it. Variation in the proportions or 
 the constitution of essential parts may no less suddenly occur. 
 The range of these phenomena is a large one, but for the purposi - 
 of this Introduction a few examples must suffice in general 
 illustration of their scope. 
 
 A discontinuous variation which is familiar to all is that of 
 " reversed" varieties, especially of Molluscs and Flat-fishes. Such 
 varieties are formed as optical images of the body of the type. In 
 both of the groups named, some species are norm ally right-handed, 
 others being normally left-handed, while as individual variations 
 reversed examples are found. In Molluscs this is not peculiar to 
 Gasteropods with spiral shells, but may occur also both in Lima- 
 cidse (slugs) 1 and in Lamellibranchs" 2 . Such variation is commonlj 
 discontinuous, and the two conditions are alternative. The fact 
 that the reversed condition may become a character of an estab- 
 lished race is familiar in the case of Fnsus antiquus. This shell 
 is found in abundance as a fossil of the Norwich Crag, such 
 specimens being normally left-handed, though the same species at 
 the present day is a right-handed one. Of the left-handed form a 
 colon)- was discovered by MacAndrew on the rocks in Vigo Bay 8 . 
 It was there associated with certain ether shells proper to the 
 Norwich Crag. This discovery seemed to Edward Forbes to be so 
 remarkable that he looked on it as corroborative evidence of a 
 special connexion between the fauna of Vigo Bay and the Crag 
 fossils 3 . Jeffreys had the same variety from Sicily 4 . 
 
 1 For example, a sinistral Avion, Baudon, Jour. <!<■ Conch., xxxn. 1884, p. 320, 
 and many otheis. 
 
 - Sinistral Tellina, Fischbb, P., Jour, dc Conch., xxvm. 1880, p. 234. The 
 same is recorded in several other genera. 
 
 ; < Seven specimens, Ann. X. H., 1849, p. 507. 
 
 4 Brit. Conch., i. p. 3'2»i. 
 
SECT. X.] INTRODUCTION. 55 
 
 That they may the better serve to bring out the significance 
 of Discontinuity in Variation to the general theory of Descent, it 
 may be well to choose some examples with reference to characters 
 which when seen in domestic animals are looked on as especially 
 the result of Selection. 
 
 In exoskeletal structures several of this kind are known. 
 From time to time there have been records of captures of the 
 " hairy variety " of the Moorhen (Gallinula chloropus), in which the 
 feathers were destitute of barbules and consequently had a hairy 
 texture, greatly changing the general appearance of the bird. 
 
 Of the " hairy " variety twelve specimens were recorded, five from 
 Norfolk, and the rest from Cambridgeshire, Hampshire, Sussex (2), 
 Suffolk, Nottinghamshire and Athlone in Ireland. The tips of the 
 barbs and shafts of the feathers have been broken off and the barbules 
 are entirely wanting, giving a hairy appearance. This appearance was 
 found in the whole of the plumage. Owing to the absence of barbules, 
 the general coloration is tawny. A few feathers of this kind have 
 been found in Hawks and Gulls, and in the case of a Parra (a bird 
 which bears considerable resemblance to a Moorhen), lent to Mr Gurney 
 by Professor Newton, a great portion of the body feathers were in this 
 condition. The feathers of the Apteryx and Cassowary are also partially 
 destitute of barbules. Mr Gurney was informed of a single case of a 
 Grey Brahma hen which shewed the same peculiarity which appears 
 otherwise to be without parallel. The case of the Silky Fowl is 
 similar in the absence of most of the barbules, but in it the point of 
 the shaft is produced to a delicate point, and the barbs are tine and 
 sometimes bifid or tritid at the apex. From J. H. Gurney, Trans. 
 Norwich Nat. Soc, in. p. 581, Plate. [Bibliography given.] [Tf 
 another " hairy " Moorhen is found, note of the colour of the skin and 
 bones should be made, for, as is well known, in the Silky Fowl they are 
 purplish blue.] 
 
 The following may be compared : " Cochins are now and then met 
 with in which the webs of the feathers having no adhesion, the whole 
 plumage assumes a silky or flossy character like that of the Silky Fowl. 
 It usually occurs quite accidentally, and in every case we have met 
 witli, the variety has been Buff. By careful breeding the character 
 can be transmitted, but we have only known <>,<>> case in which there 
 had been this hereditary character, the others having been of accidental 
 occurrence. Such bircls are sometimes called 'Emu' fowls." Lkwis 
 Wright, IllvM. Book of Poultry, 1886, p. 230. 
 
 Of many domestic animals, for example, the goat, eat and 
 
 rabbit, varieties with long, silky hair are familiar under the name 
 
 of "Angoras." Very similar breeds of guinea-pigs are kept, to 
 
 which the name " Peruvian " is given. In this connexion the 
 
 capture of a mouse {Mm musculus) with long, black, silk-like hair 
 
 is interesting 1 , as shewing that such a total variation may occur 
 
 as a definite phenomenon without Selection. 
 
 1 Cocks, W. P., Tram. Cornwall Polytech. Soc, L852. Like other animals, 
 mice have of course often been found black. For instance, a number of black mice 
 were found in Hampstead-down Wood. Hkwktt, Y\\. '/.oo\. Jour. iv. p. 348. 
 
56 HAIR. [iNTROD. 
 
 As to the partial nakedness of the skin of many animals 
 (Man, &c.), several suggestions have been made. It has been 
 variously supposed that the covering of hair has been gradually 
 lost by Man, in correlation with the use of clothes ; with the heat 
 of the sun ; for ornamental purposes under sexual selection l ; or 
 perhaps as a protection from parasites 2 . Various suggestions 
 Have also been made to explain the persistence of hair at the 
 junction of the limbs and on the head and face. To a con- 
 sideration of the origin of nakedness, the evidence of Variation in 
 some measure contributes, and though the bearing is not very 
 direct, it may illustrate the futility of inquiries of this kind made 
 without regard to the facts of Variation. 
 
 Mouse (Mus musculus) : male and pregnant female found in a 
 straw-rick at Taplow ; both were entirely naked, being without hairs 
 at all, excepting only a few dark-coloured whiskers. The skin was 
 thrown up into numerous prominent folds, transversely traversing the 
 body in an undulating manner. This condition of the skin obtained 
 for them the name of " Rhinoceros mice." The ears were dark or 
 blackish, the tail ash-coloured, and the eyes black, indicating that they 
 were not albinos. The exfoliations from the skin were examined 
 microscopically but no trace of hair-follicles was found, nor any 
 suggestion of disease. The animals were active and healthy. 
 
 The young ones, when born, were similar to the parents. The 
 teeth were normal. 
 
 In the Museum of the College of Surgeons is a precisely similar 
 specimen which was found in a house in London. Gaskoix, Proc. 
 Zool. Soc, 1856, p. 38, Plate. 
 
 Three specimens of the common Mouse ( Mus musculus) were caught 
 in the town of Elgin. The whole bodies of these three creatures "were 
 completely naked — as destitute of hair and as fair and smooth as a 
 child's cheek. There was nothing peculiar about the snout, whiskers, 
 ears, lower half of the legs and tail, all of which had hair of the usual 
 length and colour. They had eyes as bright and dark as in the common 
 
 variety At least two others were killed in the same house where 
 
 these were found." Gordon, G., Zoologist, 1850, viii. p. 2763. 
 
 Shrew. (Sorex sp.) "whole of upper surface of head and body 
 destitute of hair, and skin corrugated like that of Naked Mice figured 
 in P. Z. S., 1856 ;" sent to Brit. Mus. by Mr P. Garner. Gray, J. E., 
 Ann. and Mag. of X. II., 1869, S. 4, iv. p. 360. 
 
 In connexion with these cases, the following fact is interesting : 
 Heterocephalus is a genus of burrowing rodent from S. Africa. It contains two 
 species, of which one is about the size of a mouse and the other is rather larger. 
 They are characterized by possessing an apparently hairless skin which is on the 
 head and body of a wrinkled and warty nature. On closer inspection the skin is 
 seen to be furnished with tine scattered hairs, but there is no general appearance of 
 a hairy covering. There is no external ear in these animals. Oldfikld Thomas, 
 P. Z. S., 1885, p. 845, Plate LIV. 
 
 Naked horses have often been exhibited. Such a horse caught in a 
 
 1 C. Darwin, Descent of Man, i. p. 142. 
 
 2 Belt, Naturalist in Nicaragua; see also Hudson, Naturalist in La Plata, 1892. 
 
sect, x.] INTRODUCTION. 57 
 
 semi-feral herd in Queensland was described by Tegetmeikr, Field, 
 xlviii. 1876, p. 281. The skin was black and like india-rubber. Careful 
 examination shewed no trace of hair, or any opening of a hair-follicle. 
 In Turkestan, in the year 1886, I heard of one thus travelling, but failed 
 to see it. ' Hairless' dogs in S. America remain distinct (Belt, I. c. ). 
 
 Of discontinuous Substantive Variation in bodily proportions a 
 single example must suffice. Among domestic animals of many 
 kinds, races are known in which the bones of the face do not grow 
 to their full size, while the bones of the jaw are, or may be, of 
 normal proportions. Familiar examples of this are the bull-dog, 
 the pug, the Japanese pug, the Niata cattle of La Plata 1 , some 
 short-faced breeds of pigs, and others. In the case of these 
 domestic animals the part which Selection has taken in their pro- 
 duction is unknown, and the magnitude of the original variations 
 cannot be ascertained. It is nevertheless of interest to notice 
 that parallel variations have occurred in distinct forms, and I 
 think that this is to some extent evidence that the variations 
 were from the first definite and striking. As regards the dogs 
 even, there is a presumption that the short face of at least the 
 Japanese pug arose independently from that of the common, or 
 Dutch pug (as it used to be called), but as to this the evidence is 
 insufficient. Among the dogs' skulls found in ancient Inca inter- 
 ments, a skull was found having the form of the bull-dog. 
 Nehring, Kosmos, 1884, xv. As these remains belong to a 
 period before the European invasion, it is most probable that 
 this bull-dog breed arose independently of ours. 
 
 Apart however from domestic animals there is evidence as to 
 the origin of short-faced breeds. This evidence, which is not so 
 well-known as it deserves to be, is provided by the occurrence of a 
 similar variation in fishes. Darwin in speaking of the evidence as 
 to Niata cattle makes allusion to the case of fishes in a note 2 , 
 quoting Wyman as to the cod, which occurs in a form known to 
 fishermen as the " bull-dog " cod. The interest of this obser- 
 vation is increased by the fact that it does not stand alone, but 
 similar variations have been seen in the carp, chub, minnow, pike, 
 mullet, salmon and trout. In the last-named there is even 
 evidence of the establishment of a local race having this singular 
 character. 
 
 Carp (Ci/prinus carpio). " Bull-dog"-headed Carp have often boon 
 described. The face ends more or less abruptly in front of the eyes, 
 while the lower jaw has almost its normal length. The front part of 
 the head is bulging and prominent, giving the fish an appearance which 
 several authors compare to that of a monumental dolphin. A u f ood 
 figure of such a specimen is given by G. St Hilaibe, Hist, des Anom., 
 ed. 1837, i. p. 9G, where a full account of the older literature of the 
 
 1 C. Darwin, Animals and Plants under Domestication, 2nd edition, i. p. 92. 
 - Ibid., p. 93, note. 
 
58 
 
 BULL-DOG HEADS. 
 
 [iNTROD. 
 
 subject may be found. Inasmuch as carp are largely bred in ponds on 
 the continent, there is in this case some suggestion that unnatural 
 conditions may be concerned, but this suggestion does not apply to other 
 cases of the same Variation. Otto, Lehrb. path. Anat., I. § 129, states 
 that in the ponds of Silesia such fish are not rare. See also Voigt, 
 Mag. f. d. Naturk., ill. p. 515. 
 
 Cyprinus hungaricus : specimen from the Danube similarly formed. 
 The forehead was protuberant and bulged in front of the eyes so that 
 its anterior border was almost vertical. The attachments of the 
 mandible are carried forward in such a manner that the mandible 
 itself was directed upwards almost at right angles to the body. [Good 
 figure.] Steindachner, Verh. zool.-bot. Ges. Wien, 1863, xm. p. 485, 
 Plate. 
 
 [Several other types of Variation in the heads of Cyprinoids occur, 
 but cannot be described here.] 
 
 Chub {Leuciscus dobula = cephalus) : specimen having anterior part 
 of head rounded "like a monumental dolphin/' The body was normal, 
 measuring 33 cm. in length. Landois, Zoo/. Garten, 1883, XXIV. 
 p. 298. 
 
 Minnow (Phoxinus ton's) specimen having a snout like a pug 
 ("mnsratt <ln mopsp,' y ) [no description]. LuNEL, Pois*. du lac Lemon, 
 p. 96. 
 
 Mullet (Mugil capito) : specimen having both jaws directed 
 upwards, and the upper and anterior parts of the skull greatly 
 elevated and protuberant : the appearance of the head was like that 
 of a pug dog. Full measurements given. Canestrini, R., Atti deUa 
 soc. Ven. — Trent, di. sci. vat. in Padova, 1884, ix. p. 117 [Bibliography 
 given]. 
 
 Pike (Esox lucius) described as like a pug, ibid., p. 124; see also 
 Vrolik's Atlas, 1849, Tab LXI. Jiff. 6. 
 
 Salmon (Salnio solar) : specimen having front part of face little 
 developed, the supi •a-maxillaries being asymmetrical. Lower jaw 
 projects far in front of upper jaw. Animal of fair size, and not 
 meagre. Van Lidth di-: Jeude, Notes from Leyden Mus., vn. p. 259, 
 Plate. [Curious malformation of S. trutta ibid], see also Jahrb. Ver. 
 vaterl. Nat. Wiirtt. xlii. p. 345. 
 
 Trout (*S f . fario) : several specimens having bull-dog heads were 
 taken in Lochdow, near Pitmain, Inverness-shire. Heads short and 
 round ; upper iaw truncated like a bull-dog. This variety does not 
 
 Fig. 6. Bull-dop-headed Trout after Caklet. 
 
sect, x.] INTRODUCTION. 59 
 
 occur in neighbouring lochs. None weighed more than \ 11». Yarbell, 
 Brit. Fishes, i. p. 286, figure given. 
 
 Another specimen (Fig. G), agreeing closely with Yarn-ll's figure, 
 was taken in a lake at an altitude of over 6000 ft. in the valley of 
 Sept-Laux (Isere). Saving the head it was in all respects normal. 
 This specimen is described and figured by CARLET, M. G., Journ. 
 de VAnat. et Phys., 1879, XV. p. 154. [It is declared that the 
 fishermen who took it, having previously met with similar speci- 
 mens, supposed that they had found a new species, but it is nut 
 expressly stated that these other specimens were from the same 
 locality.] 
 
 Before ending this preliminary glance at Discontinuity in 
 Substantive Variation, allusion must be made to a case which is 
 at once more famous and more instructive than any other. I refer 
 to the celebrated phenomenon of the production of nectarines Im- 
 peaches, or conversely. Upon the subject of almond, peach and 
 nectarine, Darwin produced a body of facts which, whether as an 
 example of a method or for the value of the facts themselves, 
 form perhaps the most perfect and the most striking of all that he 
 gave. 
 
 The evidence which is there collected is known to all. and 
 though similar observations have been made since by many, there 
 is I believe nothing of importance to add to Darwin's statement. 
 The bearing of these phenomena on the nature of Discontinuity in 
 Variation is so close that Darwin's summary may with profit be 
 given at length. 
 
 'To sum up the foregoing facts; we have excellent evidence <>f 
 peach-stones producing nectarine-trees, and of nectarine-stones 
 producing peach-trees — of the same tree bearing peaches and 
 nectarines — of peach-trees suddenly producing by bud-variation 
 nectarines (such nectarines reproducing nectarines by seed), as 
 well as fruit in part nectarine and in part peach, — and, lastly. of 
 one nectarine-tree first bearing half-and-half fruit and subsequent ly 
 true peaches" 1 . After disposing of alternative hypotheses he 
 concludes that "we may confidently accept the common view 
 that the nectarine is a variety of the peach, which may be pro- 
 duced either by bud- variation or from seed." 
 
 In this case the evidence is complete. The variation from peach 
 to nectarine or from nectarine to peach may be total. If less than 
 total, the fruit may be divided into either halves or quarters 
 so that for each segment the Variation i> total -till. Of inter- 
 mediate forms other than these divided ones, we have in this case 
 
 1 Animals and Plants under Dom€8tication t cd. 2, i. p. 362. 
 
 2 Ibid., p. 362, quoting from Loudon's Hard. Mag, L828, p. •">:>. The case of a 
 Royal George peach which produced a fruit. " three parts of it being peach and one 
 part nectarine, quite distinct in appearance as well a< in flavour." The lin« ~ of 
 division were longitudinal. 
 
60 RADIAL REPETITION. [introd. 
 
 no evidence : it is therefore a fair presumption that they are 
 either rare or non-existent; and that the peach-state and the 
 nectarine-state are thus positions of " Organic Stability," between 
 which the intermediate states, if they are chemical ami physical 
 possibilities, are positions of instability. 
 
 These examples of Discontinuity in Substantive Variation 
 must suffice to illustrate the nature of the phenomena. It will be 
 seen that the matters touched on cover a wide range, and the 
 evidence relating to them must be considered separately and at 
 length. Such a consideration I hope in a future volume to 
 attempt. 
 
 SECTION XI. 
 
 Discontinuity ix Meristic Variation: Examples. 
 
 Inasmuch as the facts of Meristic Variation form the substance 
 of this volume, it is unnecessary in this place to do more than refer 
 to the manner in which they exhibit the phenomenon of Dis- 
 continuity. One or two instances must suffice to give some sug- 
 gestion of this subject, detailed consideration being reserved. 
 
 Parts repeated meristically form commonly a series, which is 
 either radial or linear, or disposed in some other figure derived 
 from or compounded of these. For the purpose of this preliminary 
 treatment an instance of Discontinuous Variation in each of these 
 classes may be taken. 
 
 1. Radial Series. 
 
 Variations in the number of petals of actinomorphic flowers 
 exhibit the Discontinuity of Meristic Variation in perhaps its 
 simplest form. 
 
 Phenomena of precisely similar nature will hereafter be de- 
 scribed in animals, but such variations in flowers are so common 
 and so accessible that reference to them may with profit be made. 
 In Fig. 7 such an example is shewn. 
 
 It represents a Tulip having the parts of the flower formed in 
 multiples of four, instead of in multiples of three as normally. 
 Variation of this kind may be seen in any field or hedgerow 1 . 
 
 Meristic Variation is here presented in its greatest simplicity. 
 Such a case may well serve to illustrate some of the phenomena of 
 Discontinuity. 
 
 1 For full literature and lists of cases see especially Masters, Vegetable 
 Teratoid;/ //. s. v. PolyphyUy. It is perhaps unnecessary to refer to the fact tbat 
 the numerical changes here spoken of are quite distinct from those which result 
 from an assumption by the members of one series or whorl of the form and 
 characters proper to other whorls. 
 
SECT. XI.] 
 
 INTRODUCTION. 
 
 61 
 
 A form with four segments occurs as the offspring of a form 
 with three segments. Such a Variation, then, is discontinuous 
 
 Fig. 7. Diagram of the flower of a Tulip having all the parts in -4. 
 
 because a new character, that of division into four, has appeared in 
 the offspring though it was not present in the parent. This new 
 character is a definite one, not less definite indeed than that of 
 division into three. It has come into the strain at one step of 
 Descent. Instances in which there is actual evidence of such descenl 
 are rare, but there can be no question that these changes do 
 commonly occur in a single generation, and, indeed, in many 
 plants, as for example Lysimachia (especially L. nemorum), flowers 
 having all the parts in -4 or in -6 may be frequently seen on 
 plants which bear likewise normal flowers with the parts in -5. 
 
 Now such a variation as this of the Tulip illustrates a pheno- 
 menon which in the Study of Variation will often be met. 
 
 We have said that the variation is discontinuous, meaning 
 thereby that the change is a large and decided one, but it is more 
 than this ; it is not only large, it is complete. 
 
 The resulting form possesses the character of division into four 
 no less completely and perfectly than its parent possessed the 
 character of division into three. The change from three to four is 
 thus perfected : from the form with perfect division into three La 
 sprung a form with perfect division into four. This is a case of a 
 total or perfect Variation. 
 
 This conception of the totality or perfection of Variation is one 
 which in the course of the study will assume great importance, 
 and it may be best considered in the simple case of numerical and 
 Meristic Variation before approaching the more complex questioo 
 of the nature of totality or perfection in Substantive Variation. 
 
 The fact that a variation is perfect at once leads to the (pus- 
 
62 RADIAL REPETITION. [introd. 
 
 tion as to what it might be if imperfect. Between the form in -3 
 and the form in -4 are intermediates possible? and if possible, do 
 they exist ? Now by choosing suitable species of regular flowers, 
 individual flowers may no doubt be found in which there are three 
 large segments and one small one ; or two normal segments and a 
 third divided into two, making four in all. Such flowers are firstly 
 rare, while cases of perfect transformation are common. But be- 
 sides their rarity there is, further, a grave doubt whether they are 
 in any true sense intermediate between the perfect form in -3 and 
 the perfect form in - 4. After this again it must be asked whether 
 or no they do as a matter of fact occur as intercalated steps in the 
 descent of the form in -4 from the form in -3 '. To the last ques- 
 tion a general negative may at once be given ; for though there is 
 abundant evidence that Meristic Variations of many kinds and in 
 several degrees of completeness may be seen in the offspring of the 
 same parent, yet any one member of such a family group may 
 shew a particular Variation in its perfection, and the occurrence of 
 an}- intermediate in the line of Descent is by no means necessary 
 for the production of the perfect Variation. 
 
 To answer the former question, whether or no forms imperfectly 
 divided into four parts are in reality intermediate between those 
 in -3 and those in -4, a knowledge of the mechanics of the 
 process of Division is required. Such knowledge is as yet entirely 
 wanting, and discussion of this matter must therefore be prema- 
 ture. With much hesitation I have decided to make certain 
 reflexions on the subject, which will be found in an Appendix to 
 this work. These may perhaps have a value as suggestions to 
 others, though from their theoretical nature they can find no place 
 here. 
 
 There is however another class of cases which are intermediate 
 in a different way. In the Tulip described above the quality of 
 division into 4 was present in all the floral organs. This is not 
 always the case, for a Meristic Variation may be present in one 
 series of organs, though it is absent in some or all of the others, 
 and this is a phenomenon frequently recurring. Nevertheless, 
 though only partially distributed, a Variation may still be dis- 
 played in its totality in the parts wherein it is present. The 
 parts of a single whorl, the calyx for example, may undergo a 
 complete Variation, while the corolla and other parts are un- 
 changed. In the same way single members of a radial series, as a 
 petal for example, may undergo a complete Variation while the 
 other members of the series are unchanged. The same will be 
 shewn hereafter to be true of animals also. 
 
 For instance, the normal number of the parts in the disc of 
 Aurelia is four, but the whole body may be divided instead into 
 Bix or some other number of parts. Examples are also found in 
 which the parts of one-half or of one quadrant are arranged in the 
 new number, while the remainder is normal; and. as in flowers, 
 
SECT. XI.] 
 
 INTRODUCTION. 
 
 <;:; 
 
 this new Dumber may prevail in some or in all of those systems of 
 organs which are disposed around the common centre. 
 
 2. Linear Series. 
 
 Before speaking further of the totality or perfection of Varia- 
 tion it will be well to give an illustration of Discontinuous Meristic 
 Variation as it occurs in the case of a linear series of parts. AlS 
 such an illustration the case of the variation in the number of 
 joints in the tarsus of the Cockroach (Blatta) may be taken. This 
 variation has been the subject of very full investigation l>v Mr 
 H. H. Brindley. The tarsus of the Cockroach is normally divided 
 into five joints, but in about 25 per cent, of B. americana (and in 
 a smaller proportion of several other species) the tarsus of one or 
 more legs is divided into only four joints, though the total length 
 may be the same as that of the corresponding leg of the other side, 
 Fig. 8. Between the five-jointed form of tarsus and the four-jointed 
 form no single case in any way intermediate was seen. The whole 
 
 11 
 
 Fig. 8. Tarsi of the third pair of legs in a specimen of Blatta americana, 
 I. the left tarsus, having the normal, or 5- jointed form; II. the right tarsus, 
 
 having the 4-jointed form. 
 
 evidence will be given in full in the proper place and raises many 
 questions of great interest; but that which is important to our 
 present consideration is the fact that the Variation is hero un- 
 doubtedly discontinuous, arising suddenly as a total or perfect 
 Variation, from the rive-jointed form to the four-jointed, ffere 
 the variation, though total as regards the limb in which it is 
 present, is not total as regards all the legs taken together. For 
 commonly only a single leg had a four-jointed tarsus, and only one 
 specimen was met with in which all six legs thus varied, and one 
 specimen only shewed the variation in five legs. 
 
 In speaking of such a Variation as a perfect Variation several 
 things are meant. 
 
 First, it is meant that the tarsus of the new pattern is as 
 distinctly divided into four joints as the normal is into five. In 
 
64 LINEAR REPETITION. [ixtrod. 
 
 addition to this the statement that the varying limb is perfect 
 conveys a number of ideas that cannot be readily formulated ; for 
 example, that the joints are to all appearance properly proportioned 
 and serviceable, shewing no sign of unfitness: they have in fact 
 much the same appearance as they have in those of the Orthoptera 
 in which the tarsus is normally four-jointed. But besides these 
 attributes, which though useful enough for ordinary description 
 are still in their nature formless and of no precise application, 
 there is another which in the case of these varying legs we are 
 entitled to make. We have said that these four-jointed tarsi are 
 to all appearance normal, save for the number of the joints. Now 
 the measurements which, at my suggestion, Mr Brindley has been 
 kind enough to make, entitle us to go beyond this, and to assert 
 that the four-jointed, tarsus has another character bv reason of 
 which it is actuallv in a sense a "normal" form. A brief considera- 
 tion of this will clearly illustrate the meaning of the term "per- 
 fection" applied to Variation. 
 
 We saw above that in a monomorphic form, the frequency with 
 which, in respect of any given character, it departs from its mean 
 condition follows a curve of Frequency of Error. This is, indeed, 
 what is meant by the statement that the mean condition is a 
 normal. 
 
 Taking the five-jointed tarsus, measurements shewed that the 
 ratio of the length of any given joint to the length of the whole 
 tarsus varied in this way about a moan value. Measurement of 
 the joints of the four-jointed form shewed that the ratios which 
 they bear to the total length of their respective tarsi vary in a 
 similar way about their mean values, and that there is thus a 
 "normal" four-jointed condition just as there is a "normal" five- 
 jointed condition. In the same way, then, that the ratio of the 
 length of each of the five joints to that of the whole tarsus is not 
 always identical but exhibits small variations, so the ratios of the 
 several joints of the four-jointed tarsus to the length of the whole 
 tarsus also vary, but in each case the ratio has a mean value 
 which is approached with a frequency conforming to a curve of 
 Error. 
 
 The measurements established also another fact which is of 
 consequence to an appreciation of the nature of totality in 
 Variation. It not only appeared that the departures from the 
 mean value of these ratios in the four-jointed variety were dis- 
 tributed about the mean in the same way as those of the five- 
 jointed form, but it was also shewn that the absolute varia- 
 tions from the mean values of these ratios were not on the 
 whole greater in the four-jointed tarsi than in the five-jointed 
 tarsi. In other words, the four-jointed tarsus occurring thus 
 sporadically, as a variety, is not less definitely constituted than 
 the five jointed type, and the proportions of its several joints 
 are not less constant. It is scarcely necessary to point out that 
 
sect, xi.] INTRODUCTION. 65 
 
 these facts give no support to the view that the exactness or 
 perfection with which the proportions of the normal \m\i\ are 
 approached is a consequence of Selection. It appears rather, that 
 there are two possible conditions, the one with five joints and the 
 other with four, either being a position of Organic Stability. Int.* 
 either of these the tarsus may fall; and though it is still conceivable 
 that the final choice between these two may have been made by 
 Selection, yet it cannot be supposed that the accuracy and com- 
 pleteness with which either condition is assumed is the work of 
 Selection, for the "sport" is as definite as the normal. 
 
 This interesting case of Meristic Variation in the tarsus of the 
 Cockroach illustrates in a striking way the principle which is 
 perhaps the chief of those to which the Study of Variation at the 
 outset introduces us. We are presented with the phenomenon of 
 an organ existing in two very different states, between which no 
 intermediate has been seen. Each of these states is definite and 
 in a sense perfect and complete ; for the oscillations of the four- 
 jointed form around its mean condition are not more erratic than 
 those of the normal form. Now when it is remembered that just 
 such a four-jointed condition of the tarsus is known as a normal 
 character of many insects and especially of some Orthoptera, it is, 
 I think, difficult to avoid the conclusion that if the four-jointed 
 groups are descended from the five-jointed, the Variation by which 
 this condition arose in them was of the same nature as that seen 
 as an individual Variation in Blatta ; that as the modern pheno- 
 menon of the individual Variation which we see, so thai pasl 
 phenomenon of the birth of a four-jointed race, was definite and 
 complete, and that the change whose history is gone, like the 
 change to be seen to-day, was no gradual process, but a Discon- 
 tinuous and total Variation 1 . 
 
 1 Since this Section was written it has seemed possible that the account Riven 
 above may be found to need an important modification. It is well known that 
 Blatta, in common with many other Orthoptera, has the power of reproducing the 
 antennae and legs after amputation or injury, and we have made 80me observations 
 shewing that the tarsi of these regenerated legs sometimes, if not always, contain 
 four joints. The question therefore arises whether the 4-jointed tarsus la a truly 
 congenital variation, and not rather a variation introduced in the process of 
 regeneration, somewhat after the manner of a bad- variation. To determine this 
 point a considerable number of immature specimens were examined, and it was 
 found that the percentage of individuals with 4-jointed tarsi is considerably Less 
 in the young than in the adult. These facts lend support to the view that the 
 4-jointed condition is not congenital. A quantity of individuals were also hatched 
 from the egg-cocoons, and among them there has thus far been found no ease of 
 4-jointed tarsus. On the other hand the total number thus hatched is not yet 
 sufficient to create any strong probability that none are ever batched in the 
 4-jointed state. We have also seen the 4-jointed tarsus in three very young in- 
 dividuals, which, to judge from their total length, must have been newly hatched. 
 The statistics shew besides that the abnormality is distinctly commoner p females 
 than in males, and that it is commoner in the legs of the 2nd pair than in the 1st, 
 and much more common in the 3rd pair of legs than in the 2nd. These facts some- 
 what favour the view that the variation may be congenital. It seems also ex- 
 ceedingly improbable that in the specimen with all the tarsi 4-jointed. the six legs 
 could each have been lost and renewed. There seems on the whole to be a pre- 
 
 B. 5 
 
66 SEX AND VARIETY. [introd. 
 
 SECTION XII. 
 
 Parallel between Discontinuity of Sex and Discontinuity 
 
 in Variation. 
 
 The application of the term Discontinuity to Variation must 
 not be misunderstood. It is not intended to affirm that in dis- 
 continuous Variation there can be between the variety and the 
 type no intermediate form, or that none has been known to occur, 
 and it is not even necessary for the establishment of Discontinuity 
 that the intermediate forms should be rare relatively to the 
 perfect form of the variety, though in cases of discontinuous 
 Variation this is generally the case ; but it is rather meant that 
 the perfect form of the variety may appear at one integral step 
 in Descent, either without the occurrence of intermediate grada- 
 tions, or at least without the intercalation of such graduated forms 
 in the pedigree. 
 
 In the case of the tarsus of Blatta we have seen an example 
 of a total and complete Variation affecting single members of a 
 series of repeated parts, not collectively, but one or more at a 
 time 1 . Such an instance of a Meristic Variation occurring in 
 a state which is total as regards members of a series but not 
 total as regards the whole series finds many parallels among 
 Substantive Variations, as, for example, that of the Crab (Cancer 
 par/ ants) bearing the right third maxillipede fashioned as a chela, 
 while the left third maxillipede was normal. Variations of this 
 nature in plants are of course well known to all. 
 
 At a previous place (Section vn.) allusion was made to the 
 familiar but very curious analogy between members of a series of 
 Meristic parts and separate organisms. The facts of Variation bring 
 out this analogy in many singular ways, and in speaking of the 
 totality of Variation it is necessary to bear these facts in mind. 
 Not only are there abundant instances of independent division 
 or multiplication of single members of Meristic series, but as 
 has been said, single members of such series may thus inde- 
 pendently and singly undergo qualitative or Substantive Variation, 
 being treated in the physical system of the body as though they 
 were separate units. In Variation, therefore, though it will be 
 
 sumption that the variation may at least sometimes be congenital. Supposing 
 however that this shall be found hereafter not to be the case, I do not thiuk that 
 the deductions drawn from the facts will be less valid. The conclusions as to 
 the definiteness of the two types, and the relationships of the several parts of each 
 to the several parts of the other, would still hold good. There are besides in other 
 forms, instances of similar numerical Variation, as for example, in the number of 
 joints in the antennae of Prionidae, where the hypothesis of change on renewal is 
 impossible, from which a similar argument might be drawn ; but on the whole I 
 have preferred to leave the account as it stands, taking the case of Blatta as an 
 example, because it is easily accessible and because, from the fewness of the joints 
 concerned, the issues are singularly clear. 
 1 See Note at the end of Section xi. 
 
sect, xii.] INTRODUCTION. G7 
 
 found that members of Meristic series may vary simultaneously 
 and collectively — and this is one of the most important generaliza- 
 tions which result from the Study of Variation — yet it is also 
 true that in Variation single members of such series may vary 
 independently and behave as though they possessed an " in- 
 dividuality" of their own. If ever it shall be possible to form 
 a conception of the physical processes at work in the division 
 and reproduction of organisms, account must be taken of both of 
 these phenomena. 
 
 I know no way in which the nature of Discontinuity in Varia- 
 tion and the position of intermediate forms may be so well illus- 
 trated as by the closely parallel phenomenon of Sex. In the case 
 of Sex in the higher animals we are familiar with the existence 
 of a race whose members are at least dimorphic, being formed 
 either upon one plan or upon the other, the two plans being in 
 ordinary experience alternative and mutually exclusive. Between 
 these two types, male and female, there are nevertheless found 
 intermediate forms, "hermaphrodites," occurring in the higher 
 animals at least, as great rarities. Now though these inter- 
 mediate forms perhaps exist in gradations sufficiently fine to 
 supply all the steps between male and female, it cannot be 
 supposed that the one sex has been derived from the other, and 
 still less that the various stages of hermaphroditism have been 
 passed through in such Descent. Besides this, even though there 
 is an accurate correspondence or homology between the several 
 organs which are modified upon the one plan in the male and 
 upon another in the female, and though this homology is such 
 as to suggest, were we comparing two species, that the one had 
 been formed from the other, part by part, yet by the nature of 
 the case such a view is here inadmissible: for firstly it is im- 
 possible to suppose that either sex has at any time had the organs 
 of the other in their completeness, and secondly it is clear that 
 any hypothetical common form, by modification of which both 
 may have arisen, must have been indefinitely remote and could 
 certainly not have possessed secondary sexual organs bearing any 
 resemblance to those now seen in the higher forms. All this 
 has often been put, but the application of it to Variation is of 
 considerable value. For in the case of Sex there is an instance 
 of the existence of two normals and of many forms intermediate 
 between them, occurring in a way which precludes the supposition 
 that the intermediates represent stages that have ever occurred 
 in the history of the two forms. 
 
 In yet another way Sex supplies a parallel to Variation. As 
 we know, the sexes are discontinuous and occur commonly in their 
 total or perfect forms. Now just as members of a Meristic seri« - 
 may present total variations independently of each other, so may 
 single members of such a series present opposite secondary sexual 
 characters, which may nevertheless be in each case complete. 
 
68 NATURE OF DISCONTINUITY. [introd. 
 
 The best known instance of this is that of gynandromorphic 
 insects, in which the characters of the whole or part of one side 
 of the body, wings and antennae, are male, while those of the 
 other side are female. Remarkable instances of a similar pheno- 
 menon have been recorded among bees and will be described later. 
 As is well known, the organs and especially the legs of the sex- 
 less females or workers are formed differently from those of the 
 drones, but there are cases of individuals having some of the 
 parts and appendages formed on the one plan arid some on the 
 other. Thus in these individuals, which are in a sense inter- 
 mediate between workers and drones, the characters of the two 
 sexes may still be not completely blended, the male type pre- 
 vailing in some parts, and the female in others. In the Dis- 
 continuity of Substantive Variation will be found examples of 
 imperfect blending of variety and type closely comparable with 
 this case of the imperfect blending of Sex. 
 
 SECTION XIII. 
 Suggestions as to the natuke of Discontinuity in Variation. 
 
 The observations at the end of Section XI, regarding the Dis- 
 continuity of Meristic Variation lead naturally to certain reflexions 
 as to the nature of Discontinuous Variation in general. In tin- 
 case of the Cockroach tarsus, there given, it appeared that just as 
 the structure of the typical form varies about its mean condition, 
 so the structure of the variety varies about another mean condition. 
 This fact, which in the given instance of Meristic Variation is so 
 clear, at once suggests an inquiry whether this is not the usual 
 course of Discontinuous Variation, and, indeed, whether Discon- 
 tinuity in Variation does not mean just this, that in varying the 
 organism passes from a form which is the normal for the type to 
 another form which is a normal for the variety. Such transitions 
 plainly occur in many cases of Meristic Variation, and in a consider- 
 able number of Substantive Variations there will be found to be 
 indications that the phenomenon is similar. It is true that at the 
 present stage of the inquiry the evidence has the value rather of 
 suggestion than of proof, but the suggestion is still very decided 
 and it is scarcely possible to exaggerate the importance of even 
 this slender clue. 
 
 In stating the problem of Species at the beginning of this 
 inquiry it was said that the forms of living things, as we know 
 them, constitute a discontinuous series, and it is with the origin 
 of the Discontinuity of the series that the solution of the main 
 problem is largely concerned. Now the evidence of Discontinuous 
 Variation suggests that organisms may vary abruptly from the 
 
sect, xiii.] INTRODUCTION. G9 
 
 definite form of the type to a form of variety which has also in 
 some measure the character of definiteness. Is it not then possible 
 that the Discontinuity of Species may be a consequence and ex- 
 pression of the Discontinuity of Variation \ To declare at the 
 present time that this is so would be wholly premature, but the 
 suggestion that it is so is strong, and as a possible light on the 
 whole subject should certainly be considered. 
 
 In view of such a possible solution of one of the chief parts 
 of the problem of Species it will be well to point out a line of 
 inquiry which must in that event be pursued. If it can be shewn 
 that the Discontinuity of Species depends on the Discontinuity of 
 Variation, we shall then have to consider the causes of the Dis- 
 continuity of Variation. 
 
 Upon the received hypothesis it is supposed that Variation is 
 continuous and that the Discontinuity of Species results from the 
 operation of Selection. For reasons given above (pp. 15 and 1G) there 
 is an almost fatal objection in the way of this belief, and it cannot 
 be supposed both that all Variation is continuous and also that the 
 Discontinuity of Species is the result of Selection. With evidence 
 of the Discontinuity of Variation this difficulty would be removed. 
 
 It will be noted also that it is manifestly impossible to suppose 
 that the perfection of a variety, discontinuously and suddenly 
 occurring, is the result of Selection. No doubt it is conceivable 
 that a race of Tulips having their floral parts in multiples of four 
 might be raised by Selection from a specimen having this character, 
 but it is not possible that the perfection of the nascent variety 
 can have been gradually built up by Selection, for it is, in its very 
 beginning, perfect and symmetrical. And if it may be seen thus 
 clearly that the perfection and Symmetry of a variety is not the 
 work of Selection, this fact raises a serious doubt that perhaps 
 the similar perfection and Symmetry of the type did not owe its 
 origin to Selection either. This consideration of course touches 
 only the part that Selection may have played in the first building 
 up of the type and does not affect the view that the perpetuation 
 of the type once constituted, may have been achieved by Selection. 
 
 But if the perfection and definiteness of the type is not due 
 to Selection but to the physical limitations under which Variation 
 proceeds, we shall hope hereafter to gain some insight into the 
 nature of these limitations, though in the present state of zoological 
 study the prospect of such progress is small. In the observations 
 which follow I am conscious that the bounds of profitable specu- 
 lation are perhaps exceeded, and I am aware that to many this 
 may seem matter for blame; but there is, in my judgment, a 
 plausibility in the views put forward, sufficient at least to entitle 
 them to examination. They are put forward in no sense as a 
 formulated theory, but simply as a suggestion {'or work. It is, 
 besides, only in foreseeing some of the extraordinary possibilities 
 
70 MECHANICAL. [introd. 
 
 that lie ahead in the Study of Variation, that the great value of 
 this method can be understood. 
 
 It has been seen that variations may be either Meristic or 
 Substantive, and that in each group discontinuous and definite 
 variations may occur by steps which may be integral or total. 
 We are now seeking the factors which determine this totality and 
 define the forms assumed in Variation. In this attempt we may, 
 by arbitrarily confining our first notice to very simple cases, recog- 
 nize at least two distinct factors which may possibly be concerned 
 in this determination. Of these the first relates to Meristic 
 Variation and the second to Substantive Variation. 
 
 1. Possible nature of the Discontinuity of Meristic Variation. 
 
 Looking at simple cases of Meristic Variation, such as that of 
 the Tulip or of Anrelia, or of the Cockroach tarsus, there is, I think, 
 a fair suggestion that the definiteness of these variations is deter- 
 mined mechanically, and that the patterns into which the tissues 
 of animals are divided represent positions in which the forces that 
 effect the division are in equilibrium. On this view, the lines or 
 planes of division would be regarded as lines or planes at right 
 angles to the directions of the dividing forces ; and in the lines of 
 Meristic Division we are perhaps actually presented with a map 
 of the lines of those forces of attraction and repulsion which 
 determine the number and positions of the repeated parts, and 
 from which Symmetry results. If the Symmetry of a living bod} 
 wore thus recognized as of the same nature as that oi any sym- 
 metrical system of mechanical forces, the definiteness of the sym- 
 metry in Meristic Variation would call for no special remark, and 
 the perfection of the symmetry of a Tulip with its parts divided 
 into four, though occurring suddenly as a " sport," would be recog- 
 nized as in nowise more singular than the symmetry of the type. 
 Both alike would then be seen to owe their perfection to me- 
 chanical conditions and not to Selection or to any other gradual 
 process. If reason for adopting such a view of the physics of 
 Division should appear, the frequency with which in any given 
 form a particular pattern of Division or of Symmetry recurs, 
 would be found to be determined by and to be a measure of the 
 
 %J 
 
 stability of the forces of Division when disposed in that particular 
 pattern. It will of course be understood that in these remark- 
 no suggestion is offered as to the causes which determine whether 
 a tissue shall divide into four or into three, but merely as to the 
 conditions of perfection of the division in either case. It will also 
 be clear that though the symmetry of a flower or of any other 
 tissue depends also on symmetrical growth, it is primarily dependent 
 on the symmetry of its primary divisions, upon which symmetrical 
 growth and secondary symmetrica] divisions follow. 
 
•sect, xiii.] INTRODUCTION. 71 
 
 It would be interesting and I believe profitable to examine 
 somewhat further the curiously close analogy between the sym- 
 metry of bodily Division and that of certain mechanical systems 
 by which close imitations both of linear and of radial segmentation 
 can be produced ; and though to some this might seem overdaring, 
 the possibility that the mechanics of bodily Division are in their 
 visible form of an unsuspected simplicity is so far-reaching that it 
 would be well to use any means which may lead others to ex- 
 plore it. 
 
 And even if at last this suggestion shall be found to have in it 
 no other element of truth, it would still be of use as a forcible 
 presentation of the fact, which when realized can hardly be 
 doubted, that among the factors which combine to form a living 
 body, the forces of Division may be distinguished as in their mani- 
 festations separable from the rest and forming a definite group. 
 For, already (Section V.) it has been pointed out that the patterns 
 of Division or Merism may be changed, while the Substance of the 
 tissues presents to our senses no difference. The recognition of 
 this essential distinctness of the Meristic forces will, I believe, be 
 found, to supply the base from which the mechanics of growth will 
 hereafter be attacked. 
 
 The problems of Morphology will thus determine themselves 
 into problems in the physiology of Division, which must be 
 recognized together with Nutrition, Respiration and Metabolism, 
 as a fundamental property of living protoplasm. 
 
 To sum up : there is a possibility that Meristic Division may 
 be a strictly mechanical phenomenon, and that the perfection 
 and Symmetry of the process, whether in type or in variety, may 
 be an expression of the fact that the forms of the type or of the 
 variety represent positions in which the forces of Division are 
 in a condition of Mechanical Stability. 
 
 2. Possible nature of the Discontinuity of Substantive Variation. 
 
 Passing from the phenomena of Division and arrangement to 
 those of constitution or substance we are, as has been said, again 
 presented with the phenomenon of discontinuous or total Varia- 
 tion, and we must seek for causes which may perhaps govern 
 and limit this totality, and in obedience to which the Variation 
 is thus definite. Now as in the case of Meristic Variation, by 
 arbitrarily limiting the examination to those cases which seem 
 the simplest it appears that there is at least an analogy be- 
 tween them and certain mechanical phenomena, bo by similarly 
 restricting ourselves to very simple cases there will be seen to 
 be a similar analogy between the discontinuity of some Sub- 
 stantive Variations and that of chemical discontinuity. It is 
 on the whole not unreasonable to expect that the definitem — 
 of at least some Substantive Variations depends ultimately on 
 the discontinuity of chemical affinities. To take but one instance, 
 
72 CHEMICAL. [introd. 
 
 that of colour, we are familiar with the fact that the colours of 
 many organic substances undergo definite changes when chemi- 
 cally acted on by reagents, and it is not suggested that the 
 defmiteness and discontinuity of the various colours assumed is 
 dependent on anything but the defmiteness of the chemical 
 changes undergone. The changes of litmus and many vegetable 
 blues to red on treatment with acids, of many vegetable yellows 
 to brown on treatment with alkalies, the colours of the series 
 of bodies produced by the progressive oxidation of biliverdin are 
 familiar examples of such definite colour-variations. 
 
 With facts of this kind in view, the conclusion is almost 
 forced on us that the defmiteness of colour-variation is a conse- 
 quence of the defmiteness of the chemical changes undergone. 
 No one doubts that the orange colouring matter of the variety 
 of the Iceland Poppy (P. nudicaule) is a chemical derivative 
 from the yellow colouring matter of the type. It is not ques- 
 tioned that in such cases a definite alteration in the chemical 
 conditions in which the pigment is produced determines whether 
 the flower shall be orange or yellow ; and I think it is reasonable 
 to expect that the frequency with which the flowers are either 
 yellow or orange as compared with the rarity of the intermediate 
 shades is an expression of the fact that the yellow and orange forma 
 of the colouring matter have a greater chemical stability than the 
 intermediate forms of the pigment, or than a mixture of the tun 
 pigments. If then it should happen, as we may fairly suppose it 
 might, that the orange form were to be selected and established 
 as a race, it would owe the defmiteness of its orange colour and 
 the precision of its tint, not to the precision with which Selection 
 had chosen this particular tint, but to the chemical discontinuity of 
 which the originally discontinuous Variation was the expression. 
 
 To pass from the case of a sport to that of Species, it is well 
 known that of the man}* S. African butterflies of the genus 
 Euchloe ( = Anthocharis, Orange-tips), some have the apices or 
 tips of the fore-wings orange-red (for example, E. danae), while 
 in others they are purple (for example, E. ione). Upon the 
 view that the transition from orange to purple, or vice verm, 
 had been continuously effected by the successive Selection of 
 minute variations, we are met bv all the difficulties we know so 
 well. Why is purple a good colour for this creature ? If purple 
 is a good colour and red is a good colour, how did it happen that 
 at some time or other all the intermediate shades were also good 
 enough to have been selected ? and so on. These and all the 
 cognate difficulties are opened up at once, and though they have 
 been met in the fashion we know, they have scarcely been over- 
 come. But at the outset this view assumes that every inter- 
 mediate may exist and has existed, an assumption which i- 
 gratuitous and hardly in accordance with the known fact thai 
 chemical processes are frequently discontinuous. When besides 
 
sect, xiil] INTRODUCTION. 73 
 
 this it is known that Variation may be discontinuous, I submit 
 that it is easier to suppose that the change from red to purple 
 was from the first complete, and that the choice offered to Selec- 
 tion was between red and purple ; and that the tints of the purple 
 and of the red were determined by the chemical properties of 
 the body to which the colour is due. This case is a particularly 
 interesting one in the light of the fact that, as Mr F. G. Hopkins 
 has lately shewn me, this purple colour, dissolved in hot water, 
 leaves on evaporation a substance which gives the murexide 
 reaction and cannot as yet be distinguished from the substance 
 similarly derived from the orange or yellow colouring matters 
 of Pieridae in general. As was stated above, Mr Hopkins has 
 shewn that these yellows are acids, allied to mycomelic acid, a 
 derivative of uric acid, and therefore of the nature of excret- 
 ory products. Whether the purple body is related to the yellow 
 or to the orange as a salt is to an acid, or otherwise, cannot yel 
 be affirmed ; but if the difference between them is a chemical 
 difference, which can hardly be doubted, there is at least a pre- 
 sumption that the discontinuity of these colours in the several 
 species, is an expression of the discontinuity of the chemical 
 properties of this body. The possibility that from such bodies 
 a series of substances might perhaps by suitable means be pre- 
 pared in such a way as to represent many or even all intermediate 
 shades, does not greatly affect the suggestion made; for even in 
 such series it is almost certain that points of comparative stability 
 would occur, and Discontinuity would be thus introduced. 
 
 The case of Colour has been taken in illustration because it 
 is the simplest and most intelligible example of the possibility 
 that the Discontinuity of some Substantive Variations is d. 'tor- 
 mined by the Discontinuity of the chemical processes by which 
 the structures are produced. It is true that perhaps no Bpecies 
 has been rightly differentiated by colour alone, but colour is 
 still one of the many characters which go to the distinguishing 
 of a species, and it is precisely one of the characters whi s 
 significance and delimitation by Natural Selection is most 
 obscure. Moreover by the fact that in the case of these yellow 
 and red Pieridye the colours are of an excretory nature, we are 
 reminded that Variation in colour may be an index of serious 
 changes in the chemical economy of the body, and that when an 
 animal is said to be selected because it is red or because it is 
 purple, the real source of its superiority may be not its red colour 
 or its purple colour, but other bodily conditions of which th< 
 colours are merely symptoms. By those who have attempted to 
 reconcile the phenomena of Colour with the hypothesis of Natural 
 Selection this fact is too often overlooked. 
 
 But though it may reasonably be supposed that much of the 
 Discontinuity of Variation and some of the Discontinuity of 
 
74 ANALOGY OF DISEASE. [introd. 
 
 Species arise through discontinuous transition from one state of 
 mechanical or chemical stability to another state of stability, there 
 nevertheless remain large classes of discontinuous variations, and 
 of Specific Differences still more, whose Discontinuity bears no 
 close analogy with these. To these phenomena inorganic Nature 
 offers no parallel. We may see that they are discontinuous and 
 that their course is in some way controlled, but as to the nature 
 of this control we can make no guess. 
 
 Though the resemblance may be misleading, it is neverthe- 
 less true that in living Nature there are other phenomena, those 
 of disease, which present a Discontinuity closely comparable with 
 that of many variations. In problems of disease we meet again 
 the same problem which we meet in Variation, namely, changes 
 which may be complete or specific, though occurring so suddenly 
 as to exclude the hypothesis that Selection has been the limiting 
 cause. All this is familiar to everyone who has considered the 
 problem of Species. 
 
 For though, like discontinuous variations, the manifestations 
 of specific disease are not always identical, but differ in intensity 
 and degree, varying about a normal form, still these manifestations 
 maybe specific in the sense in which the term is used with reference 
 to the characters of Species. If we exclude those diseases whose 
 specific characters are now known to be the result of the invasion 
 of specific organisms, there still remain very many which are known 
 and recognized by definite and specific symptoms produced in the 
 body, though there is as yet no evidence that they are due to 
 specific organisms. [Of course if it were shewn that these diseases 
 also result from the action of specific organisms, they then only 
 present to us again the original problem of Species ; for if the 
 definiteness, or Species, of a disease is due to the definiteness, or 
 Species, of the micro-organism which causes it, the cause of that 
 definiteness of the micro-organism remains to be sought, and we 
 are simply left with a particular case of the general problem of 
 Species.] But in the meantime we can see that the manifestations 
 are specific ; and while we do not know that they result from causes 
 themselves specific, the nature of the control in obedience to which 
 they are specific is unknown. 
 
 The parallel between disease and Variation may be mis- 
 leading, but this much at least may fairly be learned from it : 
 that the system of an organized being is such that the result 
 of its disturbance may be specific. And in the end it may well 
 be that the problem of Species will be solved by the study of 
 pathology ; for the likeness between Variation and disease goes 
 far to support the view which Virchow has forcibly expressed, 
 that " every deviation from the ty pe of the parent animal must 
 have its foundation on a pathological accident 1 ." 
 
 1 E. Virchow, Journal of Pathology, I. 1892, p. 12. 
 
sect, xiv.] INTRODUCTION. 75 
 
 SECTION XIV. 
 
 Some current conceptions of Biology in view of the facts 
 
 of Variation. 
 
 Enough has now been said to explain the aim of the Study 
 of Variation, and to shew the propriety of the choice of the facts 
 of Meristic Variation as a point of departure fur that study. 
 Before leaving this preliminary consideration, reference to some 
 cognate subjects must be made. 
 
 It has been shewn that in view of the facts of Variation, 
 some conceptions of modern Morphology must be modified, while 
 others must be abandoned. With the recognition of the sig- 
 nificance of the phenomena of Variation, other conceptions of 
 biology will undergo like modifications. As to some of these a 
 few words are now required, if only to explain methods adopted in 
 this work. 
 
 1. Heredity. 
 
 It has been the custom of those who have treated the subject 
 of Evolution to speak of " Heredity ' : and "Variation" as two 
 antagonistic principles ; sometimes even they are spoken of as 
 opposing "forces." 
 
 With the Study of Variation, such a description of the pro- 
 cesses of Descent will be given up, even as a manner of speaking. 
 In what has gone before I have as far as possible avoided any 
 use of the terms Heredity and Inheritance. These terms which 
 have taken so firm a hold on science and on the popular fancy, 
 have had a mischievous influence on the development of bio- 
 logical thought. They are of course metaphors from the descent 
 of property, and were applied to organic Descent in a time when 
 the nature of the process of reproduction was wholly mis- 
 understood. This metaphor from the descent of property is 
 inadequate chiefly for two reasons. 
 
 First, by emphasizing the fact that the organization of the 
 offspring depends on material transmitted to it by its parents, 
 the metaphor of Heredity, through an almost inevitable confusion 
 of thought, suggests the idea that the actual body and consti- 
 tution of the parent are thus in some way handed on. No one 
 perhaps would now state the facts in this way, but something 
 very like this material view of Descent was indeed actually de- 
 veloped into Darwin's Theory of Pangenesis. From this sugges- 
 tion that the body of the parent is in some sort remodelled into 
 that of the offspring, a whole series of errors arc derived Chief 
 among these is the assumption that Variation must necessarily 
 be a continuous process; for with the body of the parent to start 
 from, it is hard to conceive the occurrence of discontinuous 
 change. Of the deadlock which has resulted from the attempt 
 
76 REVERSION. [introd. 
 
 to interpret Homology on this view of Heredity, I have already 
 spoken in Section VI. 
 
 Secondly, the metaphor of Heredity misrepresents the essential 
 phenomenon of reproduction. In the light of modern investiga- 
 tions, and especially those of Weismann on the continuity of the 
 germ-cells, it is likely that the relation of parent to offspring, 
 if it has any analogy with the succession of property, is rather 
 that of trustee than of testator. 
 
 Hereafter, perhaps, it may be found possible to replace this 
 false metaphor by some more correct expression, but for our 
 present purpose this is not yet necessary. In the first exami- 
 nation of the facts of Variation, I believe it is best to 
 attempt no particular consideration of the working of Heredity. 
 The phenomena of Variation and the origin of a variety must 
 necessarily be studied first, while the question of the perpetua- 
 tion of the variety properly forms a distinct subject. Whenever 
 in the cases given, observations respecting inheritance are forth- 
 coming they will be of course mentioned. But speaking of dis- 
 continuous Variation in general, the recurrence of a variation 
 in offspring, either in the original form or in some modification 
 of it, has been seen in so many cases, that we shall not go far 
 wrong in at least assuming the possibility that it nun/ nappear 
 in the offspring. At the present moment, indeed, to this state- 
 ment there is little to add. So long as systematic experiments 
 in breeding are wanting, and so long as the attention of naturalists 
 is limited to the study of normal forms, in this part of biology 
 which is perhaps of greater theoretical and even practical im- 
 portance than any other, there can be no progress. 
 
 2. Reversion. 
 
 Around the term Reversion a singular set of false ideas have 
 gathered themselves. On the hypothesis that all perfection and 
 completeness of form or of correlation of parts is the work of 
 Selection it is difficult to explain the discontinuous occurrence 
 of new forms possessing such perfection and completeness. To 
 account for these, the hypothesis of Reversion to an ancestral 
 form is proposed, and with some has found favour. That this 
 suggestion is inadmissible is shewn at once by the frequent occur- 
 rence by discontinuous Variation, of forms which though equally 
 perfect, cannot all be ancestral. In the case of Veronica and 
 Liiuiria, for example, a host of symmetrical forms of the floral 
 organs may be seen occurring suddenly as sports, and of these 
 though any one may conceivably have been ancestral, the same 
 cannot be supposed of all, for their forms are mutually exclusive. 
 On Veronica buxbaumii, for instance, are many symmetrical 
 tlowers, having two posterior petals, like those of other Scrophu- 
 larinese : these may reasonably be supposed to be ancestral, but 
 
sect, xiv.] INTRODUCTION. 77 
 
 if this supposition is made, it cannot be made again for the 
 equally perfect forms with three petals, and the rest 1 . 
 
 The hypothesis of Reversion to account for the Symmetry 
 and perfection of modern or discontinuous Variation is made 
 through a total misconception of the nature of Symmetry. 
 
 There is a famous passage in the Descent of Man, in which 
 Darwin argues that the phenomenon of double uterus, from its 
 perfection, must necessarily be a Reversion. 
 
 "In other and rarer cases, two distinct uterine cavities are formed, each 
 
 having its proper orifice and passage. No such stage is passed through during the 
 ordinary development of the embryo, and it is difficult to believe, though perhaps 
 not impossible, that the two simple, minute, primitive tubes could know how (if 
 such an expression may be used) to grow into two distinct uteri, each with a well- 
 constructed orifice and passage, and each furnished with numerous muscles, nerves, 
 glands and vessels, if they had not formerly passed through a similar course of 
 development, as in the case of existing marsupials. No one will pretend that bo 
 perfect a structure as the abnormal double uterus in woman could be the result 
 of mere chance. But the principle of reversion, by which Long-lost dormant 
 structures are called back into existence, might serve as the guide for the full 
 development of the organ, even after the lapse of an enormous interval of time-." 
 Descent of Man, vol. I. pp. 123 and 124. 
 
 This kind of reasoning has been used by others again and 
 again. It is of course quite inadmissible; for by identical reason- 
 ing from the perfect symmetry of double monsters, of the si ugh- 
 eye of the Cyclopian monster, and so on, it might be shewn th.it 
 Man is descended from a primitive double vertebrate, from a 
 one-eyed Cyclops and the like. For other reasons it is likely 
 enough that double uterus was a primitive form; but the per- 
 fection and symmetry of the modern variation to this form is 
 neither proof nor indication of such an origin. Such a belief 
 arises from want of knowledge of the facts of Meristic Variation, 
 and is founded on a wrong conception of the nature of symmetry 
 and of the mechanics of Division. The study of Variation shews 
 that it is a common occurrence for a part which stands in the 
 middle line of a bilaterally symmetrical animal, to divide into 
 two parts, each being an optical image of the other: and thai 
 conversely, parts which normally are double, standing as optical 
 images of each other on either side of such a middle line may 
 
 1 For a full account of such facts, see a paper by Miss A. Bateson and myself 
 On Variations in Floral Symmetry. Journ. Linn. Soc, xxvui. p, 386. 
 
 2 This extraordinary passage is scarcely worthy of Darwin's penetration. If 
 read in the original connexion it will seem strange that it should have been allowed 
 to stand. For in a note to these reflexions on Reversion [Descent, i. i>. L25) Darwin 
 refers to and withdraws his previously expressed view that supernumerary digits 
 and mamma? were to be regarded as reversions. This view had been based on I 
 perfection and symmetry with which these variations reproduce the structure of 
 putative ancestors. It was withdrawn because Gegenbaur had shewn that poly* 
 dactyle limbs often bear no resemblance to those of possible ancestors, and I 
 extra mammae may not only occur symmetrically and in places where they are 
 normal in other forms, but also in several quite anomalous situations. In the light 
 of this knowledge it is strange that Darwin should have continued to regard the 
 perfection and symmetry of a variation as evidence that it is a Reversion. 
 
78 CAUSES OF VARIATION. [introd. 
 
 be compounded together in the middle line forming a single, 
 symmetrical organ. 
 
 It would probably help the science of Biology if the word 
 'Reversion' and the ideas which it denotes, were wholly dropped, 
 at all events until Variation has been studied much more fully 
 than it has yet been. 
 
 In the light of what we now know of the process of repro- 
 duction the phrase is almost meaningless. We suppose that a 
 certain stock gives off a number of individuals which vary about 
 a normal ; and that after having given them off, it begins to 
 give off individuals varying about another normal. We want 
 to say that among these it now and then gives off one which 
 approaches the first normal, that shooting at the new mark it 
 now and then hits the old one. But all that we know is that 
 now and then it shoots wide and hits another mark, and we 
 assume from this that it would not have hit it if it had not 
 aimed at it in a bygone age. To apply this to any other matter 
 would be absurd. We might as well say that a bubble would 
 not be round if the air in it had not learned the trick of round- 
 ness by having been in a bubble before : that if in a bag after 
 pulling out a lot of white balls I find a totally red one, this 
 proves that the bag must have once been full of red balls, or that 
 the white ones must all have been red in the past. 
 
 Besides the logical absurdity <»n which this use of the theory 
 of Reversion rests, the application of it to the facts of \ a nation 
 breaks down again and again. I have already mentioned some 
 cases of this, but there are manv others of a different class. For 
 instance, it will be shewn that the percentage of extra molars 
 in the Anthropoid Apes is almost the highest reached among 
 mammals. On the usual interpretation, such teeth are due to 
 Reversion to an ancestral condition with 4 molars, and on less 
 evidence it has been argued that a form frequently shewing such 
 " Reversion " is older than those which do not. From this reason- 
 ing it should follow that the Anthropoids are the most primitive 
 form, at least of monkeys. It is surely time that these brilliant 
 and facile deductions wore no more made in the name of science. 
 
 3. Causes of Variation. 
 
 Inquiry into the causes of Variation is as yet, in my judgment, 
 premature. 
 
 4. The Variability of" useless" Structu?*es. 
 
 The often-repeated statement that "useless" parts are 
 especially variable, finds little support in the facts of Variation, 
 except in as far as it is a misrepresentation of another principle. 
 The examples taken to support this statement are commonly 
 organs standing at the end of a Meristic Series of parts, in which 
 
sect, xiv.] INTRODUCTION. 79 
 
 there is a progression or increase of size and degree of development, 
 starting from a small terminal member. In such cases, as that of 
 the last rib in Man, and several other animals, the wisdom-teeth of 
 Man, etc., it is quite true that in the terminal member Variation is 
 more noticeable than it is in the other members. This is, I 
 believe, a consequence of the mechanics of Division, and has no 
 connexion with the fact that the functions of such terminal parts 
 are often trifling. Upon this subject something will be said later 
 on, but perhaps a rough illustration may make the meaning more 
 clear at this stage. If a spindle-shaped loaf of bread, such as a 
 " twist," be divided with three cuts taken at equal distances, in 
 such a way that the two end pieces are much shorter than the 
 middle ones, to a child who gets one of the two large middle 
 pieces the contour-curves of the loaf will not matter so much ; but 
 to a child who gets one of the small end bits, a very slight altera- 
 tion in the curves of the loaf will make the difference between a 
 fair-sized bit and almost nothing, a difference which the child will 
 perceive much more readily than the complementary difference in 
 the large pieces will be seen by the others. An error in some 
 measure comparable with this is probably at the bottom of the 
 statement that useless parts are variable, but of course there are 
 many examples, as the pinna of the human ear, which are of a 
 different nature. It is unnecessary to say that for any such case 
 in which a part, apparently useless, is variable, another can be 
 produced in which some capital organ is also variable ; and 
 conversely, that for any case of a capital organ w r hich is lit t If 
 subject to Variation can be produced a case of an organ, which 
 though trifling and seemingly "useless," is equally constant. 
 With a knowledge of the facts of Variation, all these trite generali- 
 ties will be forgotten. 
 
 o. 
 
 Adaptation. 
 
 In examining cases of Variation, I have not thought it neces- 
 sary to speculate on the usefulness or harmfulness of the variations 
 described. For reasons given in Section II, such speculation, 
 whether applied to normal structures, or to Variation, is barren and 
 profitless. If any one is curious on these questions of Adaptation, 
 he may easily thus exercise his imagination. In any case of 
 Variation there are a hundred ways in which it may 1»' beneficial, 
 or detrimental. For instance, if the " hairy" variety of the moor- 
 hen became established on an island, as many strange varieties 
 have been, I do not doubt that ingenious persons would invite us 
 to see how the hairiness fitted the bird in some special way tor life 
 in that island in particular. Their contention would he hard t<> 
 deny, for on this class of speculation the only limitations are those 
 of the ingenuity of the author. While the only test of utility is 
 the success of the organism, even this does not indicate the utility 
 
80 NATURAL SELECTION. [ixtrod. 
 
 of one part of the economy, but rather the nett fitness of the 
 whole. 
 
 6. Natural Selection. 
 
 In the view of the phenomena of Variation here outlined, 
 there is nothing which is in any way opposed to the theory of the 
 origin of Species " by means of Natural Selection, or the preserva- 
 tion of favoured races in the struggle for life." But by a full and 
 unwavering belief in the doctrine as originally expressed, we shall 
 in no way be committed to representations of that doctrine made 
 by those who have come after. A very brief study of the facts will 
 suffice to gainsay such statements as, for example, that of Claus, 
 that "it is only natural selection which accumulates those altera- 
 tions, so that tliey become appreciable to us and constitute a varia- 
 tion which is evident to our senses 1 ." For the crude belief that 
 living beings are plastic conglomerates of miscellaneous attributes, 
 and that order of form or Symmetry have been impressed upon 
 this medley by Selection alone ; and that by Variation any of these 
 attributes may be subtracted or any other attribute added in 
 indefinite proportion, is a fancy which the Study of Variation does 
 not support. 
 
 Here this Introduction must end. As a sketch of a part of the 
 phenomena of Variation, it has no value except in so far as it may 
 lead some to study those phenomena. That the study of Variation 
 is the proper field for the development of biology there can be no 
 doubt. It is scarcely too much to say that the study of Variation 
 bears to the science of Evolution a relation somewhat comparable 
 with that which the study of affinities and reactions bears to the 
 science of chemistry: for we might almost as well seek for tin- 
 origin of chemical bodies by the comparative study of crystallo- 
 graphy, as for the origin of living bodies by a comparative study of 
 normal forms. 
 
 1 Text-book of Zoology, Sedgwick and Heathcote's English translation, vol. i. 
 p. 148. In the original the passage runs: " erst die naturliche Zuchtwahl haufi 
 und verstarkt jew Abweichungen in dem Masse dass sie fur mis wahmehmbar 
 werden und eine in die Augen fallende Variation bewirken." C. Claus, Lehrb. d. 
 Zool., Ed. 2, 1883, p. 127, and Grundztige der Zoologie, 1880, Bd. i. p. 90. The 
 italics are in the original. 
 
PART I. 
 
 MERISTIC VARIATION. 
 
 B. 
 
CHAPTER I. 
 
 ARRANGEMENT OF EVIDENCE. 
 
 The cases of Meristic Variation, here given, illustrate only a 
 small part of the subject. The principles upon which these have 
 been chosen may be briefly explained. It was originally intended 
 to give samples of the evidence relating to as many different 
 parts of the subject as possible, so that the ground to be eventual lv 
 covered might be mapped out, leaving the separate sections of 
 evidence to be amplified as observations accumulate. This plan 
 would be the most logical and perhaps in the end the most useful, 
 but for several reasons it has been abandoned. I have chosen ;i 
 different course, first, because during the progress of the work 
 opportunities occurred for developing special parts of the evidence; 
 secondly, since isolated observations have no interest for most 
 persons, it is more likely that the importance of the subject will 
 be appreciated in a fuller treatment of special sections, than in a 
 general view of the whole ; and lastly, because as yet the attempt 
 to make an orderly or logical classification of the phenomena <>f 
 Merism, however attractive, must be so imperfect as to be alm<»M 
 worthless. For these reasons I have decided to treat more fullv a 
 few sections of the facts, hoping that in the course of time similar 
 treatment may be applied to other sections also. The sections 
 have been chosen either because there is a fairly large body <>t 
 evidence relating to them, or on account of the importance or 
 novelty of the principles illustrated. 
 
 As far as possible I have described each case separately, in 
 terms applicable specially to it, deductions or criticism being kepi 
 apart. The descriptions are written as if for an imaginary cata- 
 logue of a Museum in which the objects might be displayed 1 . This 
 system, though it entails repetition, has, I believe, advantag - 
 which cannot be attained when the descriptions are given in a 
 comprehensive and continuous form. In speaking of subjects, such 
 as supernumerary mamma 1 , or cervical Rstulse, where the evidence 
 has been exhaustively treated by others, and upon which 1 can 
 add nothing, it has not seemed necessary to follow this system, and 
 in such cases connected abstracts are given. 
 
 1 Cases of special importance are marked by an asterisk. 
 
 6—2 
 
84 MERISTIC VARIATION. [part i. 
 
 As the evidence here presented consists, as yet, only of speci- 
 men chapters in the Natural History of Meristic Variation, and 
 does not offer any comprehensive view of the whole subject, no 
 strict classification of the facts is attempted. The evidence of 
 Meristic Variation relates essentially to the manner in which 
 changes occur in the number of members in Meristic series. Such 
 numerical changes may come about in two ways, which are in some 
 respects distinct from each other. For instance, the number of legs 
 and body-segments in Peripatus edivardsii varies from 29 to 34 1 : 
 here the variation in number must be a manifestation of an 
 original difference in the manner of division or segmentation in 
 the progress of development. The change is strictly Meristic or 
 divisional. On the other hand, change in number may arise by 
 the Substantive Variation of members of a Meristic series already 
 constituted. For example, the evidence will shew that the 
 number of oviducal openings in Astacus may be increased from one 
 pair to two or even three pairs. Here the numerical variation has 
 come about through the assumption by the penultimate and last 
 thoracic appendages, of a character typically proper to the append- 
 ages of the antepenultimate segment of the thorax alone. Now 
 there is here no change in the number <»f segments composing the 
 Meristic series, but by Substantive Variation the number of 
 openings has been increased. 
 
 The case of the modification of the antenna of an insect into a 
 foot, of the eye of a Crustacean into an antenna, of a petal into a 
 stamen, and the like, are examples of the same kind. 
 
 It is desirable and indeed necessary that such Variations, 
 which consist in the assumption by one member of a Meristic 
 series, of the form or characters proper to other members of the 
 series, should be recognized as constituting a distinct group of 
 phenomena. In the case of plants such Variation is very common 
 and is one of the most familiar forms of abnormality. Masters, in 
 his treatise on Vegetable Teratology 2 , recognizes this phenomenon 
 and gives to it the name "Metamorphy," adopting the word from 
 Goethe. As Masters says, so long as it is only proposed to use the 
 word in Teratology, no great confusion need arise from the fact 
 that the same term and its derivatives are used in a different 
 sense in several branches of Natural History. But if, as I hope, 
 the time has come when the facts of what has been called '"Tera- 
 tology" will be admitted to their proper place in the Study of 
 Variation, this confusion is inevitable. In this study, besides, this 
 particular kind of variation will be found to be especially impor- 
 tant and I believe that in the future its significance and the mod,' 
 of its occurrence will become an object of high interest. For this 
 reason it is desirable that the term which denotes it should not 
 lead to misunderstanding, and I think a new term is demanded. 
 
 1 Sedgwick, A., Quart. Jour. Micr. Sri., 1888, xxvm. p. 467. 
 
 2 Masters, M. T., Vegetable Teratology, p. 239. 
 
chap. I.] ARRANGEMENT OF EVIDENCE. 85 
 
 For the word 'Metamorphy' I therefore propose to substitute the 
 term Homoeosis, which is also more correct; for the essential 
 phenomenon is not that there has merely been a change, but that 
 something has been changed into the likeness of something else 
 
 In the cases given above, the distinction between Homceotic 
 Variation and strictly Meristic Variation is sufficiently obvious, 
 but many numerical changes occur which cannot be referred with 
 certainty to the one class rather than to the other. Such cas 
 are for the most part seen in Vertebrates: for in them what may 
 be called the fun da mental numbers of the segments are not consti- 
 tuted with the definiteness found in Arthropods or in the Annelids, 
 and several Meristic series of organs are disposed in numbers and 
 positions independent of, or at least having no obvious relation bo 
 those of the other Meristic series. The number and positions of 
 mammae, or stripes, for instance, need not bear any visible relation 
 to the segmentation of the vertebrae &c. The repetition of mem- 
 bers of such a series may thus not coincide with, or occur in mul- 
 tiples of the segmentation of other parts in the same region. When 
 such is the case, when the segmentation of one series of organs 
 bears no simple or constant geometrical relation to the segmenta- 
 tion of other systems, it is not always possible to declare whether 
 a numerical change in one of the systems of organs belongs properly 
 to the first or the second of the classes described abow. It is 
 likely enough that in such a case as that of mammas there may 
 sometimes be an actual Meristic division and subsequent separation 
 of the tissues already destined to form the mamma?, occurring in 
 such a way that each comes to take up its final position, and 
 indeed the numerous cases in which such division has been 
 imperfectly effected go far to prove that this is the case. But, on 
 the other hand, it is not possible to know that the division did no1 
 occur before any tissue was specially differentiated off to form 
 mammae, and that the separation may be as old even as the 
 division of the mamma? of the right side from those of the left, a 
 process which almost beyond question occurs in the segmentation 
 of the ovum. The distinction between these two alternatives is 
 thus one rather of degree than of kind, and it is only in such forms 
 as the Arthropods, the floral organs of some Phanerogams and the 
 like, where the members of the several Meristic series have definite 
 numbers, or coincide with each other, that this distinction is easily 
 recognized. For this reason 1 do not think it well to at tempt 
 to carry out any classification of the evidence based on this dis- 
 tinction. 
 
 In the foregoing remarks I am aware that a very large question, 
 which lies at the root of all accurate study of Meristic Variation, 
 has been passed over somewhat superficially, but I scarcely think 
 a fuller treatment possible in the present state of knowledge of 
 the physics of Division, and in the absence of thorough observation 
 of the developmental history of those tissues which ultimately 
 
86 MERISTIC VARIATION. [PABT I. 
 
 become differentiated to form members of such non-coincident or 
 independent Meristic series. 
 
 Some years ago 1 , in the course of an argument that Balanoglossus 
 should be considered as representing some of the ancestral characters 
 of Chordata, I had occasion to refer to some of these difficulties, and 
 especially to the different characters of the two kinds of segmentation ; 
 that of the Annelids, in which the repetitions of the organs belonging 
 to the several systems are coincident, and, on the other hand, that 
 of the Chordata, for example, in which this coincidence may be 
 irregular or partial. At that time I was of opinion that these two 
 sorts of segmentation may, in certain cases, have had a different 
 phylogenetic history, and have resulted from processes essentially 
 distinct. It appeared to me that we should recognize that, in the 
 Annelids on the one hand, segmentation of the various systems of 
 organs had been coincident from the beginning, while in the Chordata 
 the segmentation had been progressive and had arisen by segmentation 
 or repetition of the organs of the several systems independently. The 
 reasons for this view were derived chiefly from the fact that it is 
 possible to arrange the lower Chordata in order of progressive segmen- 
 tation of the several systems. In particular such treatment was shewn 
 to be applicable to the central nervous system, the vertebral column 
 and the mesoblastic somites, and in these cases it was maintained that 
 the evidence of the lower forms of Chordata goes to shew that segmen- 
 tation had occurred in these systems one after another, and that their 
 segmentation was not derived from a form having a complete repetition 
 of each part in each segment : that these forms, in fact, shewed us tin- 
 history of this progress from a less segmented form to one more fully 
 segmented. 
 
 The views then set forth have met with little acceptance. Those 
 who are occupied with the search for the pedigree of Vertebrates still 
 direct their inquiries on the hypothesis, expressed or implied, that in 
 the ancestral form there was a series of complete segments, each 
 containing a representative of each system of those organs which in 
 the present descendants appear in series. It is thus supposed that each 
 segment of the primitive form must have been a kind of least common 
 denominator of the segments of its posterity. The possibility that the 
 segmentation of Vertebrates may have arisen progressively is, indeed, 
 scarcely considered at all. 
 
 Though in the light of the study of Variation, it now seems to 
 me that the discussion of these questions must be indefinitely post- 
 poned, and that there are radical objections to any attempt to interpret 
 the facts of anatomy and development in our present ignorance of 
 Variation, I have seen no reason to depart from the view expressed 
 in the paper referred to : that interpreted by the current methods of 
 morphological criticism, the facts go to shew that the segmentation of 
 the Chordata differs essentially from that of the Annelids drc, and 
 that it has arisen by progressive segmentation of the several systems of 
 an originally unsegmented form. T<> those who hold as Dohrn, Gaskell. 
 Marshall and others have done, that the evolution of Vertebrates has 
 
 1 Quart. Jour. Micr. Set, 1886. 
 
chap. I.] ARRANGEMENT OF EVIDENCE. 87 
 
 been a progress from a more fully segmented form to forms less seg- 
 mented, I would again point out that this view is in direct opposition 
 to the indications afforded by the lower Chordata, which are less and 
 not more segmented than the higher forms. 
 
 The hypothesis of an ancestor made up of complete segments is 
 resorted to because it is felt to be difficult to conceive the progressiva 
 building up of a segmented form, but on appeal to the facts of Variation 
 the evidence will clearly shew that Repetition of parts previously (wilt- 
 ing is a quite common phenomenon; that such repetition may occur in 
 almost any system of organs; and lastly that such new repetitions may 
 be coincident in the several systems. To argue moreover that these 
 repetitions, for instance that of oviducal apertures in Astacus, of 
 mammas or cervical ribs in mammals are "reversions," leads to ab- 
 surdity, for on the same reasoning, the occurrence, in the Crab, of a 
 third maxillipede formed as a chela, would shew that these appendages 
 had been originally chehe, that the occurrence of petaloid sepals shews 
 that the sepals had originally been petals, and so forth. 
 
 These considerations will suffice to illustrate the great difference 
 of degree, if not of kind, which probably exists between these two 
 kinds of segmentation, that which arises by the repetition of bud- 
 like segments, each containing parts of many systems on the one 
 hand, and the progressive and separate segmentation of the several 
 systems on the other. For reasons already given, however, I shall 
 not attempt in this first collection of evidence to separate the facts 
 on these lines. Though some cases can at once be seen to be 
 strictly Meristic while others are plainly Homceotic, many cannot 
 be affirmed to belong to the one group rather than to the other. 
 There is, besides, a serious doubt whether perhaps after all, 
 Homceotic Variation even in its most marked forms, may Dot 
 ultimately rest on and be an expression of a change in the pro- 
 cesses of Division, and be thus, at bottom, strictly Meristic also. 
 In our present ignorance of the physics of Division, this doubt 
 cannot be satisfied, and therefore it will be best to make no 
 definite separation between the two classes of variations, though 
 whenever the nature of a given variation is such that it may at 
 once be recognised as Homceotic, it will be well to specify this. 
 
 In the absence of a more natural classification, the material 
 has been roughly arranged with reference to the geometrical 
 disposition and relations of the structures concerned. In the 
 Introduction, Section IV. p. 21, reference was made to the (aft 
 that the Symmetry of an organism may be such as to include all 
 the parts into one system of Symmetry, and for such a system the 
 term Major Symmetry was proposed. Systems of this kind are 
 seen in the Vertebrates and Echinoderms, for example. On the 
 other hand systems of Symmetry occur in limbs and other separate 
 parts of organisms, in such a way that each such system is either 
 altogether or partially geometrically complete and symmetrical in 
 itself. For example, the toe of a Horse, the arm of a Starfish, the 
 
88 MERISTIC VARIATION. [part I. \ 
 
 eye-spots of some Satyrid butterflies, &c, are each in themselves 
 nearly symmetrical. To these separate systems of Symmetry the 
 term Minor Symmetry will be applied. Minor Symmetries may 
 or may not be compounded into a Major Symmetry. Between 
 these there is of course no hard and fast line. 
 
 In each class of Symmetry, Meristic Repetition may occur, and 
 the repeated parts then stand in either 
 
 I. Linear or Successive Series. 
 
 II. Bilateral or Paired Series. 
 
 III. Radial Series. 
 
 Parts meristically repeated may thus stand in one or more 
 geometrical relations to each other, and the first part of the 
 evidence of Meristic Variation will be arranged in groups according 
 as it is in one or other of these relations that the parts are affected. 
 In each group cases affecting Major Symmetry will be given first, 
 and those affecting Minor Symmetries will be taken after. 
 
 As it is proposed to arrange the facts of Meristic Variation in 
 groups corresponding with these three forms of Meristic Repetition, 
 it will be useful to consider briefly the nature of the relation in 
 which the members of such series stand to each other, and the 
 characters distinguishing the several kinds of series. Reduced to 
 the simplest terms, the distinction may be thus expressed. 
 
 In the Linear or Successive series the adjacent parts of any 
 two consecutive members of the series are not homologous, but the 
 severally homologous parts of each member or segment form a 
 successive series, alternating with each other. For example, the 
 anterior and posterior surfaces of such a series of segments may 
 be represented by the series 
 
 A ,AP, AP, AP, P. 
 
 The relation of any pair of organs in Bilateral Symmetry differs 
 from this, for in that case each member of the pair jwesents to its 
 fellow of the opposite side parts homologous with those which it* 
 fellow presents to it, each being, in structure and i>osition, an 
 optical image of the other. The external and internal surfaces of 
 such a pair may therefore be represented thus : 
 
 E 1,1 E. 
 
 If the manner of origin of these two kinds of Repetition be 
 considered, it will be seen that though both result from a process 
 of Division, yet the manner of Division in the two cases is very 
 different. For in the case of division to form a paired structure, 
 the process occurs in such a way as to form a pair of images, 
 of which similar and homologous parts lie on each side of the 
 plane of division ; while, in the formation of a chain of successive 
 fluents, each plane of division passes between parts which are 
 dissimilar, and whose homology is alternate. The distinction 
 between these two kinds of Division is of course an expression of 
 the fact that the attractions and repulsions from which Division 
 
chap. I.] ARRANGEMENT OF EVIDENCE. 89 
 
 results are differently disposed in the two cases. It is further to 
 be observed that the distinction, though striking, is nevertheli & 
 one of degree, for the two kinds of Division pass gradually into 
 each other. By one or other of these two modes, or by a combin- 
 ation of both, all Meristic Series of Repetitions are formed 
 
 In Radial series, the Major Symmetry is built up by radial 
 divisions of the first kind, producing segments whose adjacent 
 parts are homologous, and related to each other as images. Each 
 of these segments is therefore bilaterally symmetrical about a 
 radial plane. There is no succession between the segments, and 
 in a perfectly symmetrical series, Successive or Linear repetitions 
 can only occur in Minor Systems of Symmetry. 
 
 The considerations here set forth, though well known, have an 
 importance in the interpretation of the evidence, for the connexion 
 between the geometrical relations of organs and their Meristic 
 Variations is intimate. 
 
 An arrangement of the facts with reference to these geometrical 
 relations cannot, of course, be absolute, for it is clear that a Bilateral 
 Symmetry, containing Linear Repetitions may be derived from a 
 Radial Symmetry, and that these figures cannot be precisely 
 delimited from each other; nevertheless this plan of arrangement 
 has still several advantages. Chief among these is this : that it 
 brings out and emphasizes the fact that the possible, or at least 
 the probable Meristic Variations of such parts depend closely on 
 the r/eometrical relation in which they stand. This is, perhaps, in a 
 word, the first great deduction from the facts of Meristic Variation. 
 The capacity for, and manner of Meristic Variation appear to 
 depend not on the physiological nature of the part, on the system 
 to which it belongs, on the habits of the organism, on the Deeds 
 or exigencies of its life, but on this fact of the geometrical position 
 of the parts concerned. Linear series are liable to certain sorts of 
 Variation, Bilateral Series are liable to other sorts of Variation, 
 and Radial Series to others again. As 1 have ventured to hint 
 before, the importance of all this lies in the glimpse which is thus 
 afforded us of the essential nature of Meristic Division and 
 Repetition. Such interdependence between the geometrical re- 
 lations, or pattern, in which a part stands, and the kinds of 
 Variation of which it is capable, is, I think, a strong indication 
 that in Meristic Division we are dealing with a phenomenon 
 which in its essential nature is mechanical. Since this is a thing 
 of the highest importance, it will be useful to employ a system 
 which shall give it full expression. 
 
 Evidence as to Meristic Variation in cell-division and in the 
 segmentation of ova will bespoken of in connexion with the Varia- 
 tion of Radial and Bilateral series. 
 
 The second section of evidence is less immediately relevant to 
 the problem of Species; nevertheless it bears bo closely on the 
 nature of Merism and on the mechanics of Physiological Division, 
 
90 MERISTIC VARIATION. [part i. 
 
 that in any study of this subject reference to it cannot be omitted. 
 The evidence in question relates first to abnormal repetition of 
 limbs or other peripheral structures, (which in the normal form are 
 grouped into and form part of a system of Symmetry,) such ab- 
 normal repetitions occurring in such a way as to lie outside tin's 
 normal system of Symmetry and unbalanced by any parts within 
 it. This phenomenon occurs in many forms, especially in bilateral 
 animals, and may be exceptionally well studied in the case of 
 supernumerary limbs in Insects and in supernumerary chelte in 
 Crabs and Lobsters. It will be shewn that such extra parts 
 generally, if not always, make up a Secondary system of 
 Symmetry in themselves ; and the way in which such a 
 Secondary system is related to the normal or Primary system 
 of Symmetry of the body from which they spring, constitutes 
 an instructive chapter in the study of Meristic Variation. 
 
 More extensive repetitions of this class, when affecting the 
 axial parts of the body, give rise to the well-known Double and 
 Triple Monsters, which, as has often been said, reproduce in tin- 
 higher animals phenomena which, under the name of fission, 
 are commonly seen in the lower forms. The general evidence as 
 to these abnormalities is so accessible and familiar that it need 
 not be detailed here, and it will therefore be enough to give an 
 outline of its chief features and to point out the bearing of this 
 class of evidence on the subject of Meristic Variation in general. 
 
CHAPTER II. 
 
 meristic variation of parts repeated in linear ob 
 
 successive series. 
 
 Segments of Arthropoda. 
 
 Individual Variation in the fundamental number of members 
 constituting a Linear Series of segments can only be recognized in 
 those forms which at some definite stage in their existence cease 
 to add to the number of the series. Hence in a large proportion 
 of the more fully segmented invertebrates this phenomenon cannot 
 be studied, for in many of these, as for instance in Chilognatha 
 and in most of the Chaetopoda the formation of new segments is 
 not known to cease at any period of life, but seems to continue in- 
 definitely. On the other hand, while in Insecta, and in Crustacea 
 excepting the Phyllopods, the fundamental numbers are definite, 
 no case of individual Variation in them has been observed. 
 
 Between these two extremes, there are animals in certain 
 classes, for example, Peripatus, some of the Chilopoda among 
 Myriapods, Aphroditidae among Annelids, and sonic of tin- Hran- 
 chiopoda among Crustacea, in which the number of segments do< a 
 not increase indefinitely during life, but is nevertheless not so 
 immutable as in the Insects and the majority of Crustacea. In 
 the forms mentioned, certain numbers of segments, though not the 
 same for the whole family, are characteristic of certain genera, as 
 in the case of the Chilopoda (excepting I reophilidae), or of certain 
 species, as in some of the Peripati. But besides this, in some oi 
 the forms named, e.g., the Geophili and Peripatus edwardsii, indi- 
 vidual Variation has been recorded among members of the same 
 species. It is unfortunate that for many of the forms in which 
 Variation of this kind possibly takes place no Bufficienl observa- 
 tion on the point has been made, but as examples of a phenomenon 
 which, on any hypothesis, must have played a chief part in the 
 evolution of these animals, the few available instances are oi in- 
 terest. 
 *1. Peripatus. The number of segments which have claw-bearing 
 ambulatory legs differs in different species of this genus. Y\ hile, 
 
92 MERISTIC VARIATION. [part i. 
 
 moreover, in some of the species the number appears to be very 
 constant for the species, in the case of others, great individual 
 variation is seen to occur. Sedgwick's observations in the case of 
 P. edwardii shew conclusively that these variations cannot be 
 ascribed to difference in age. There is besides no ground for sup- 
 posing that increase in the number of legs occurs in any species 
 after birth, and it is in fact practically certain that this is not the 
 case. In Peripatus capensis, which was exhaustively studied by 
 Sedgwick, the appendages arise in the embryo successively from 
 before backwards, the most posterior being the last to appear, and 
 the full number is reached when the embryo arrives at Sedgwick's 
 Stage G. The following is taken from the list constructed by 
 Sedgwick from all sources, including his own observations. As 
 the bibliography given by him is complete and easily accessible 
 it is not repeated here, and the reader is referred to Sedgwick's 
 monograph for reference to the original authorities. 
 
 Sedgwick, A., Quart. Jour. Micr. Sci. xxviii., 1888, pp. 431 — 
 493. Plates. 
 
 South African Species. 
 
 P. capensis : 17 pairs of claw-bearing ambulatory legs (Table 
 Mountain, S. Africa). 
 
 P. balfouri : 18 pairs of legs, of which the last pair is rudiment- 
 ary (Table Mountain, S. Africa). 
 
 Sedgwick has examined more than 1000 specimens from the 
 Cape, and has only seen one specimen with more than 18 pairs of 
 legs. This individual had 20 pairs, the last pair being rudiment- 
 ary. It closely resembled P. balfouri, but differed in the number 
 of legs and in certain other details (q. v.); Sedgwick regarded this 
 form provisionally as a variety of P. balfouri. 
 
 P. mosleyi : 21 and 22 pairs of legs: near Williamstown, S. 
 Africa. The specimens with 22 legs were two in number and were 
 both females. They differed in certain other particulars from the 
 form with 21 legs, but on the whole Sedgwick regards them as a 
 variety of the same species. 
 
 P. brevis (DE Blainville): 14 pairs of legs. (This species not 
 seen by Sedgwick.) 
 
 Other species from S. Africa which have been less fully studied 
 are stated to have 19, 21 and 22 pairs of legs respectively. 
 
 In all South African forms, irrespective of the number of legs, 
 the generative opening is subterminal and is placed behind the 
 last pair of fully developed legs (between the 18th or rudimentary 
 pair in P. balfouri). Sedgwick, pp. 440 and 451. 
 
 Australasian Species. 
 
 P. v one- Zealand ice. 15 pairs of legs. New Zealand. 
 P. leuckartii. 15 pair of legs. Queensland. 
 In both of these species the generative opening is between the 
 last pair of legs. (Sedgwick, p. 486.) 
 
chap, il] SEGMENTS OF ARTHROPOD A. 93 
 
 Neotropical Species. 
 
 In all the Neotropical Species which have been at all fully ex- 
 amined, the number of legs varies among individuals of the same 
 species. 
 
 P. edward&ii: number of pairs of legs variable, the smallest 
 number being 29 pairs, and the greatest number being 34. Males 
 with 29 and 30 pairs of legs. The females are larger, and have a 
 greater number of legs than the males. 
 
 The new-born young differ in the same way. From 4 females 
 each having 29 legs, seven embryos were taken which were practi- 
 cally fully developed. Of these, 4 had 25) legs, 2 had 34, 1 had 32. 
 An embryo with 29 and one with 30 were found in the same mother. 
 An embryo, quite immature, but possessing the full number of legs, 
 was found with a larger number of legs than one which occupied 
 the part of the uterus next to the external opening. (Caracas. | 
 
 Peripatus demeraranus : 7 adult specimens had 30 pairs of 
 legs; 6 had 31 pairs; 1 had 27 pairs. Out of 13 embryos ex- 
 amined, 7 have 30 pairs and 6 had 31. (Demerara.) 
 
 Peripatus trinidadensis : 28 to 31 pairs of ambulatory legs. 
 (Trinidad.) 
 
 Peripatus torquatus : 41 to 42 pairs. (Trinidad.) 
 
 Specimens of other less fully known species are recorded as 
 having respectively, 19, 28, 30, 32, 36 pairs of legs, &c. 
 
 In the Neotropical Species, irrespective of the number of legs, 
 the generative opening is placed between the legs of the penulti- 
 mate pair. (Sedgwick, p. 487.) 
 
 Peripatus (jidiformis?) from St Vincent: six specimens ex- 
 amined. Of these, 1 specimen had 34 pairs of legs, 2 had 32 pairs. 
 1 had 30 pairs, and 1 had 29 pairs. Pocock, R. I., Nature } 1892, 
 xlvi. p. 100. 
 
 In connexion with the case of Peripatus, the following evidence 
 may be given, though very imperfect and incomplete. 
 
 2. Myriapoda. Chilognatha. Variation in the number of segments 
 composing the body in this division of Myriapoda cannot be observed 
 with certainty; foritisnotpossibletoeliniin.it.' changes in number due 
 to age, nevertheless the manner in which this increase occurs has a 
 bearing on the subject. 
 
 In Jidus terrestris the number of segments is increased al each 
 moult by growth of new segments between the lately formed antepen- 
 ultimate segment and the permanent penultimate segment At each 
 of the earlier moults six new segments are here added: in Blaniulua 
 the number thus added is four, and in Polydesmus? two fresh segments 
 are formed at each of the earlier moult-. In each of these forms the 
 number added is the same at each of the earlier moults. Newport, 
 G., Phil. Trans., 1841, pp. 129 and 130. 
 
 Chilopoda. The number of Leg-bearing Begments differs in the 
 several genera of Chilopoda, but except in the Gkophilidse the number 
 proper to each genus is a constant character. For instance in Lithobiw 
 
94 MERISTIC VARIATION. [part i. 
 
 this number is 15; in Scolopendra it is 21; in Scolopendrops, 23; in 
 Cryptops 21, &c. 
 
 In Geophilidse, however, the total number of moveable segments is 
 much larger, ranging from about 35 to more than 200. Though not 
 characteristic of genera, the number seems within limits to mark each 
 particular species. It was found that male Geophili have fewer segments 
 than the female. The males of Arthronomalus longicornis have 51 or 
 52 leg-bearing segments, while females usually have 53 or 54. Full- 
 grown females of Geophilus terrestris have 83 or 84 pairs of legs and 
 segments, and the males of the same species have 81 or 82. In a 
 large Neapolitan species, Geophilus Icevigatus Bruhl. 1 the variation 
 is rather greater. In eight males the number varied between 96 
 and 99; in eleven females, between 103 and 107. Of two female 
 Geophilus sulcatus one individual had 136 and the other 140. Newport, 
 G., Trans. Linn. Soc, xix. 1845, p. 427, &c. 
 
 [In some of the Chilopoda 1 an increase in the number of segments 
 takes place after the larva hatches, but the variations mentioned above 
 are recorded as occurring in fully formed specimens independently of 
 changes due to age.] 
 
 In the foregoing cases, a fact which is often met in the Study 
 of Variation is well seen. It often happens that in particular 
 genera or in particular species, a considerable range of Meristic 
 Variation is found, while in closely allied forms there is little or 
 none. Examples of this are seen in the variability of the Geophi- 
 lidae as compared with the other Chilopoda, and in the neo-tropical 
 species of Peripatus which vary in the number of legs, while P. 
 balfouri, for instance, is very constant. It will !».• noticed that in 
 both these cases, the absolute numbers of parts repeated are con- 
 siderably higher in the variable than in the constant forms. But 
 though such cases have given rise to general statements that series 
 of organs containing a small number of members are, as such, less 
 variable than series containing more members, these statements 
 require considerable modification ; for it is not difficult to give 
 instances both in plants and in animals, where series made up of 
 a small number of members, shew great meristic variability. 
 
 The bearings of these cases on the nature of Meristic Repetition 
 and the conception of Homology will be considered hereafter. 
 Here, however, it may be well to call attention to the fact that we 
 have now before us cases in which various but characteristic num- 
 bers of legs or segments differentiate allied species or genera ; that 
 in assuming the truth of the Doctrine of Descent, we have ex- 
 pressed our belief that in each case the species with diverse num- 
 bers are descended from some common ancestor. In the evolution 
 of these forms, therefore, the number has varied : this on the one 
 hand. On the other hand, in GeopJtilus and in Peripatus, we see 
 
 1 According to Newport (Trans. Linn. Soc. xix. 1845, p. 268), all Myriapoda 
 .acquire a periodical addition of segments and legs, but according to later observi i a 
 this is not true of all the Chilopodu. 
 
chap. II.] SEGMENTS OF ARTHROPODA. 95 
 
 contemporary instances of the way in which such a change at its 
 origin may be brought about. Though there are several things to 
 be gained by study of these instances, one feature of them calls for 
 attention now, namely, the definiteness of the variations recorded. 
 The change from a form with one number to a form with another 
 number here shews itself not as an infinitesimal addition or sub- 
 traction, but as a definite, discontinuous and integral change, pro- 
 ducing it may be, as in Peripatus edwardsti, a variation amounting 
 to several pairs of legs, properly formed, at one step of Descent. 
 This will not be seen always to be the case, but it is none the less 
 to be noted that it is so here. 
 
 Among Insects I know no case of such individual variation in 
 the fundamental number of segments composing the body. Among 
 Crustacea two somewhat remarkable examples must be mentioned, 
 though it will be seen that both of them belong to categories very 
 different from that with which we are now concerned. But in- 
 asmuch as they relate to the general subject of Meristic Variation 
 they should not be omitted. 
 
 3. Carcinus maenas. The abdomen of these crabs consists normally of seven 
 segments, including the last or telson. In the female the divisions between all 
 these seven are very distinct. The abdomen of the normal male is much narrower 
 than that of the female, and in it the divisions between the 3rd, 4th and 5th 
 segments are obliterated. Males, however, which are inhabited by the Rhizo- 
 cephalous parasite Sacculina do not acquire these sexual characters, and in them 
 there are distinct divisions between the 3rd, -4th and 5th segments. (Fig. '.• c. I 
 
 Fig. 9. A. Abdomen of Carcinus mamas, female, normal. 
 
 B. Abdomen of male, normal. 
 
 C. Abdomen of male infested by Sacculina. After Giabb and 
 
 Bonnier. 
 
 In male Carcinus mamas inhabited by the Entoniscian parasite, Fori union, a similar 
 deformity may occur, but is often very much less in extent, sometimes being only 
 apparent in a slight alteration in the contour of the sixth abdominal Bomite. In 
 specimens of Portunus, Platyonyckus, Pilummu and Xantho inhabited by Knto- 
 niscians, no change was observed. Giahd and Bonne b comment on the remarkable 
 fact that the change in the sexual characters effected by Sacculina is greater than 
 that resulting from the presence of Entoniscian- ; for since the latter are more 
 internal parasites, preventing the growth of and actually replacing generative 
 entirely or in part, it might have been expected that the conseqnenoes of their 
 presence would be more profound. <im:i>. A., and Bonnibb, J., Contrib. a L'e'tnde 
 des Bopyriens, Travaux de Vinst. zool. de Lille et <lu laboraioire tool. </<■ Wimereux, 
 1887, torn. V. p. 184. 
 
96 MERISTIC VARIATION. [PART i. 
 
 4. Branchipus and Artemia. As it has been alleged that variation may be pro- 
 duced in the segmentation of the abdomen of these animals by changes in the 
 waters in which they live, it is necessary here to give the facts on which this state- 
 ment rests. The further question of the relation of Artemia salina to A. mil- 
 hausenii is so closely connected with this subject, that though not strictly cognate, 
 some account of the evidence on this point also must be given. 
 
 Some years ago Schmankewitsch 1 published certain papers on variations of 
 Artemia salina induced by changes in the salinity of the water in which the animals 
 lived. The statements there made excited a great deal of interest and have often 
 been repeated botb by scientific and popular writers. The facts have thus at times 
 been somewhat misrepresented, and so much exaggeration has crept in, that before 
 giving any further evidence it will be well to give Schmankewitsch's own account. 
 It is frequently asserted that Schmankewitsch observed the conversion of Branchipus 
 into Artemia and of Artemia salina into A. milhausenii following upon the pro- 
 gressive concentration of the waters of a salt lake. Strictly speaking however this is 
 not what was stated by Schmankewitsch. His story is briefly this: That the Bait 
 lagoon, Kuyalnik, was divided by a dam into an upper and a lower part; the waters 
 in the latter being saturated with salt, while the waters of the upper part were less 
 salt. By a spring flood in the year 1871 the waters of the upper part of the lake 
 swept over the dam and reduced the density of the lower waters to 8° Beaume 
 ( = about sp. g. 1-051), and in this water great numbers of A. salina then appeared, 
 presumably having been washed in from the upper part of the lake, or from the 
 neighbouring salt pools. After this the dam was made good, and the waters of the 
 lower lake by evaporation became more and more concentrated, being in the summer 
 of 1872 14° B (about sp. g. 1-103) ; in 1873, 18° B (about sp. g. 1-135); in August 1874, 
 23-5° B (about sp. g. 1-177) and later in that year the salt began to crystallize out. 
 In 1871 the Artemia had caudal fins of good size, bearing 8 to 12, rarely 1 5, l'Hstles, 
 but with the progressive concentration of the water the generations of Artemia 
 progressively degenerated, until at the end of the summer of 1871 a large part of 
 them had no caudal fins, thus presenting the character of A. miliums, mi Fischer 
 and Milne Edw. The successive stages of the diminution of the tail-fins and of the 
 numbers of the bristles are Bhewn in the figures, with which all are now familiar. 
 
 A similar series was produced experimentally by gradual concentration of water, 
 leading to the extreme form resembling A. milhausenii. It was found also that if 
 the animals without caudal tins were kept in water which was gradually diluted, 
 after some weeks a pair of conical prominences, each bearing a single bristle, ap- 
 peared at the end of the abdomen. 
 
 It is further stated that the branchial plates- of the animals living in the more 
 highly concentrated water were materially larger than those of animals living in 
 water of a less concentration. 
 
 Schmankewitsch next goes on to say that by artificially breeding Artemia salina 
 in more and more diluted salt water he obtained a form having the characters of 
 Si ii a i Fi'.n's genus Branchipus, and that he considers this form as a new species of 
 Branchipus. He explains this statement thus: In the normal Artemia, the last 
 Begment of the post-abdomen is about twice as long as each of the other segments, 
 while the corresponding part in Branchipus is divided into two segments. He states 
 that in his opinion the condition of the last segment of the post-abdomen consti- 
 tutes the essential difference between Artemia and Branchipus, and that such 
 division of the last segment occurred in the third generation of the form produced 
 by him from Artemia by progressive dilution of the water. A second distinction 
 between the genera is found in the fact that Artemia is reproduced partheno- 
 genetically, while Branchipus is not known to be so reproduced. As to the 
 condition of his new form in this respect, Schmankewitsch had no evidence. 
 
 In a subsequent paper, '/.. f, w. '/.. . 1877, further particulars are given, re- 
 specting especially the natural varieties of A. salina. Of these he distinguishes two, 
 var. a and var. b. The first of these i^ distinguished by its greater size (8 lines 
 instead of 6 lines, the average for the type) and by the greater length of the post- 
 abdomen. In the type the bristles on each caudal fin are generally 8 — 12, and in 
 
 1 Z. f. w. Z., xxv., 1875, 2, p. 103 and xxix., 1*77. p. 42«J ; also in several 
 Russian publications, to which references will be found /. <•. 
 
 Upon this point a good deal of interesting evidence is given in Schmanke- 
 witsch's papers, but as it does not bear immediately on the question of the specific 
 differences, it has not been introduced here. 
 
chap, ii.] SEGMENTS OF ARTHHOPODA. 97 
 
 var. a, 8 — 15, rarely more. Amongst specimens of var. a, as also among those of 
 the type, specimens maybe found having three, two, or even only one bristle on the 
 caudal fin. The second antennae of the male are less wide in var. a than in the 
 type, and the knobs on the inner border are rather larger than in the type. 
 
 The variety b was found in pools of a concentration of 4° Beaume. It differs 
 from the type in having the post-abdomen shorter in proportion, though the whole 
 length is about the same. The number of bristles on the caudal fins is greater in 
 the variety. The second antenna? of the male are narrower in the variety than in 
 the type, and bear a tooth and a thickening of the skin internal to the rough knob- 
 like projections. But the most important difference characterizing var, b is the 
 appearance of transverse segmentation in the last (8th) post-abdominal segment. 
 This, according to Schmankewitsch, does not amount to an actual segmentation, 
 but is really a transverse annulation, which may be more or less conspicuous, and 
 suggests an appearance of segmentation. Schmankewitsch looks on this second 
 variety as a transitional form between Artemia and Branchipus, 
 
 Before going further it may be remarked that Schmankewitsch gives no figures 
 of these varieties, except in so far as they are represented in the well-known Beriefl 
 of sketches of the caudal forks with varying numbers of bristles. No analysis of the 
 waters is given. 
 
 It will be seen that two principal and distinct statements are made : 
 
 (1) That A. milhausenii may be reared from A. salina by gradually raising the 
 concentration of the water. 
 
 (2) That by diluting the water a division is produced in the last (8th) segment 
 of A. salina: that this is a character, or, as Schmankewitsch says, the chiei 
 character, of the genus Branchipus. 
 
 First as to the relation of A. salina to A. milhausenii. The species milhausi nix 
 was made by G. Fischer de Waldheim 1 on spirit specimens sent to him, and the 
 absence of caudal fins and bristles was taken as the diagnostic character. Fischi 
 figures are very poor, and indeed are scarcely recognizable : they are also incorrect 
 in several points, giving for instance 12 pairs of swimming feet instead of 11. The 
 description is also very imperfect. In the course of this he speaks of the malt-. 
 saying that its second antennae are larger than those of the female, in which he 
 declares the second antennae may be sometimes absent. From Fischer's account it 
 is quite clear that his material was badly preserved, and indeed, as Schmankewitsch 
 says, specimens of these animals preserved with spirit only are of little use. 
 
 In 1837 Rathke 2 gave a better figure of A. milhausenii l from the original 
 locality of Fischer's specimens. The tail, ending in two plain lobes, is shown. Tin- 
 male is not mentioned. The following analysis of the water is given : 
 
 Potassium Sulphate 0*7453 
 Sodium Sulphate 2*4439 
 
 Magnesium Chloride 7*5500 
 Calcium Chloride 0*2760 
 
 Sodium Chloride 16*1200 
 
 271352 
 
 in 100 of the water. 
 
 Other authors mention A. milhausenii, but there i-. so far as 1 am aware, no 
 special account of the male, or any material addition to the above. 
 
 I will now give an abstract of such further evidence on this subject a- I have 
 been able to collect. 
 
 In the course of a journey in Western Central Asia and Western Siberia 
 I collected samples of Branchiopods from a great variety of localities, of tl. 
 two consist of Branchipus ferox (Milne Edwards), one of Branchipus spinostu .Milne 
 Edwards), three of a species of Branchipus not dearly corresponding with any >p. . 
 of which a description is known to me, and the remainder of Artemia. All the sp* 
 of Branchipus collected are quite clearly defined both in the male and the female, 
 and have certainly nothing to do with the Artemia. Of the latter some preliminary 
 account may now be given, as the tacts bear on Schmankewitsch'a problem. 
 Omitting those which were badly preserved and those which do not contain adults, 
 there remain twenty-eight samples, satisfactorily preserved with corrosive Bublima 
 from as many localities. Of these, eight contain males, all of them having the 
 
 1 Bull. Imp. Soc. Sat. Moscou, 1834, vxx. p. 152. 
 
 2 Mem. Ac. Sci. P€t. t 1837. in. p. 395. 
 
 B. 7 
 
98 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 distinctive characters of A. salina. It is difficult to speak with confidence as to the 
 species of an Artemia from the female alone, but by careful comparison I can find 
 no point of structure which differentiates any of the remainder from the females 
 found with males, and I therefore regard them as all of the same species, A. salina. 
 The waters were of many kinds, some being large salt lakes, while others were small 
 salt ponds or even pools. The specific gravities of these waters varied from 1-030 to 
 1-215, and judging from the results of the analysis of six samples, the composition of 
 the waters is also very different. The specific gravities were measured in the field 
 with a hydrometer reading to -005, and on comparing these readings with the de- 
 terminations of the Sp. G. of the samples brought home it appears that they were 
 approximately correct, and I think therefore that these rough readings are fairly 
 trustworthy. As to the composition of the waters not analyzed, nothing can be said 
 with much confidence. As the analyses shew, some of these lakes contain chiefly 
 chlorides, others chiefly sulphates, and so on. In a few {e.g. xxix) there is a great 
 quantity of sodium carbonate, so much that the water was strongly alkaline and 
 felt soapy to the hands. This can generally be recognized on the spot in various 
 ways. 
 
 The first point raised by Schmankewitsch's work is that of the caudal fins. 
 Among my samples I have every stage between the large fins with some twenty 
 bristles, down to the condition with no distinct fin or bristles. The following table 
 gives the results as regards the number of bristles on the caudal fins, and this 
 
 
 
 Bristles 
 
 
 
 
 on single 
 
 
 No. in 
 Catalogue 
 
 Sp. G. 
 
 caudal fin. 
 
 Eggbearing 
 
 ? ? only 
 
 Remarks 
 
 XXIX. 
 
 1-030 
 
 10 to 24 
 
 Analyzed. Strongly alkaline. <? s present. 
 
 LI. 
 
 1 
 
 050 
 
 11—13 
 
 
 XXXIV. 
 
 1 
 
 056 
 
 9—17 
 
 SS present. 
 
 XXV. 
 
 1 
 
 065 
 
 2— 7 
 
 Si present. 
 
 XLII. 
 
 ?1 
 
 070 
 
 
 
 XXXVII. 
 
 1 
 
 075 
 
 8—13 
 
 
 XXXIX. 
 
 1 
 
 075 
 
 5— 7 
 
 
 XLI. 
 
 1 
 
 085 
 
 13—15 
 
 
 IV. 
 
 1 
 
 095 
 
 20—28 
 
 SS present. This and III. both pools in 
 one dry stream -bed. 
 
 XIV. 
 
 1 
 
 100 
 
 8—14 
 
 Analyzed. 
 
 XLV. 
 
 1 
 
 100 
 
 8—12 
 
 
 XXVII. 
 
 1 
 
 100 
 
 4—10 
 
 
 XXXI. 
 
 1 
 
 105 
 
 5— 9 
 
 <T<? present. 
 
 XXXV. 
 
 1 
 
 105 
 
 4— 8 
 
 
 XLIII. 
 
 1 
 
 115 
 
 1— 6 
 
 Analyzed. 
 
 XIX. 
 
 1 
 
 115 
 
 5— 9 
 
 
 XL. 
 
 about 1 
 
 130 
 
 12—16 
 
 Pool in a stream-bed. <?<? present 
 
 LII. 
 
 1 
 
 140 
 
 3— 7 
 
 
 XXXVI. 
 
 ?1 
 
 150 
 
 4—10 
 
 
 XLIV. 
 
 1 
 
 150 
 
 7— 8 
 
 Analyzed. 
 
 XVI. 
 
 1 
 
 150 
 
 0— 1 
 
 
 III. 
 
 1 
 
 160 
 
 16—19 
 
 <? $ present. This and IV. both pools in 
 one dry stream-bed. 
 
 XII. 
 
 1 
 
 165 
 
 1— 3 
 
 
 XXII. 
 
 1 
 
 165 
 
 1— 5 
 
 
 XVIII. 
 
 1 
 
 170 
 
 6— 8 
 
 
 XXIII. 
 
 1 
 
 175 
 
 1— 5 
 
 
 XXVI. 
 
 1 
 
 179 
 
 4— 9 
 
 Analyzed. 
 
 XXIV. 
 
 1 
 
 204 
 
 2— 5 
 
 Analyzed. 
 
 XXXII. 
 
 1 
 
 215 
 
 2— 4 
 
 
 XXXIII. 
 
 1-215 
 
 2— 7 
 
 
CHAP. II.] 
 
 SEGMENTS OF ARTHROPODA. 
 
 99 
 
 number is a fair guide to the size of the fins, large fins for the most part havin» 
 many bristles and small fins having few. In the third column the range of this 
 number in several individuals is shewn, and for this purpose only adult females 
 bearing eggs in the ovisac are reckoned, as with sex and age there are changes in 
 respect of the number of bristles. 
 
 ANALYSIS OF WATER FROM SIX LOCALITIES CONTAINING 
 
 ARTE MIA SALINA. 
 
 Catalogue Number 
 
 Chlorine Cl 2 
 
 Sulphuric 
 
 anhydride S0 3 . . . 
 Carbonic 
 
 anhydride C0 2 ... 
 
 Lime CaO 
 
 Magnesia MgO 
 
 Soda and Potash 
 
 Na 2 0, K,0 
 
 Total" 
 
 Oxygen equivalent 
 
 to the Chlorine... 
 Total solids in 1000 
 
 grams 
 
 Sp. G. compared 
 
 with Water at 20° 
 
 XXIX. 
 
 2-6950 
 
 5-9105 
 
 7-0125 
 •0311 
 •0384 
 
 16-7471 
 32-4346 
 
 •6082 
 
 31-8264 
 
 1-03074 
 
 XIV. XLIII. 
 
 24-8646 
 
 13-3585 
 
 •3185 
 
 •2256 
 
 3-3561 
 
 27-4589 i 
 69-5822 
 
 5-6112 
 
 63-9710 
 
 1-05196 
 
 54-7793 
 
 30-3797 
 
 •3926 
 
 •0678 
 
 6-0367 
 
 63-6088 
 155-2649 
 
 12-3620 
 
 142-9029 
 
 1-11787 
 
 XXVI. 
 
 70-8130 
 
 53-8150 
 
 •2398 
 
 •2266 
 
 4-7514 
 
 96-7906 
 226-6364 
 
 15-9804 
 
 210-6560 
 
 1-17999 
 
 XLIV. 
 
 57-6653 
 
 71-8775 
 
 •3231 
 
 •1466 
 
 4-5115 
 
 100-0803 
 234-6043 
 
 13-0133 
 
 221-5910 
 
 1-19586 
 
 XXIV. 
 
 61-0830 
 
 74-4463 
 
 •2451 
 
 •5175 
 
 9-8394 
 
 97-2084 
 243-3397 
 
 13-7846 
 
 229-5551 
 
 1-20441 
 
 These analyses were undertaken for me by Mr H. Robinson, of the Cambridge 
 University Chemical Laboratory, and my best thanks are due to him for the care 
 -with which he has conducted them. 
 
 The table shews the great variability in the development of the tails and bristles. 
 In specimens from the same locality there is generally great difference, and even the 
 numbers on the two fins of the same individual are rarely the same. It will be seen 
 that on the whole the forms with few bristles came from waters of high specific 
 gravity, thus generally agreeing with Schmankewitsch's statement. This relation 
 to the salinity is not however very close, but Schmankewitsch never asserted 
 that it was. He fretmently refers to the existence of individuals with tails in several 
 conditions of degeneration in the same water, and especially (Z. f. w. Z., 1877, 
 p. 482) he expressly states that in the original locality of A. milhausenii he found 
 this form and with it several others intermediate between it and A. salina. 
 
 It will also be seen in the Table, that the three samples, IV, XL and III stand 
 •out as having far more bristles than other samples from waters of ecpial specific 
 gravity. Each of these localities was exceptional, and all belong to one class. 
 Ill and IV were pools in the dry bed of a stream in the Kara Kum, near the Irghiz 
 river. They were close together, and must be joined in each spring. XL. was a 
 pool in a somewhat similar dried stream-bed, coming down to the lake Tulu Bai in 
 the district of Pavlodar. The conditions in these pools must be very different from 
 those of the large, shallow, permanent salt lakes from which the other samples 
 mostly came, and it is only fair to Schmankewitsch's case to remember that the 
 water in such pools must be almost fresh during the early part of each summer. 
 
 On the whole, then, it seems satisfactorily shewn that the tailless form is con- 
 nected by intermediate stages with the fully-tailed A. salina, and that this transition 
 is at all events partly connected with the degrees of salinity of the water in which 
 it lives. Almost each locality has its own pattern of Arte mi a, which differs from 
 those of other localities in shades of colour, in average size, or in robustness, and 
 in the average number of spines on the swimming feet, but none of these differences 
 seem to be especially connected with the degree of salinity. 
 
 7—2 
 
100 MERISTIC VARIATION. [part I. 
 
 Passing now to the question of the distinctness of A. milhausenii, it seems clear 
 that, as Eathke said, it should never have been considered a distinct species. The 
 character of the finless tail, which is now seen to be one of degree, does not differ- 
 entiate it satisfactorily, and, as Schmankewitsch found, it is to be seen swimming 
 with tin-bearing individuals. It has never been shewn that there is a male A. mil- 
 hansenii, with distinctive sexual characters, and among the Branchiopoda the 
 various sexual characters of the second antennas in the male are most strikingly 
 distinctive of the several forms. While being in no sense desirous of disparaging 
 the value of Schmankewitsch's very interesting observation, I think it is misleading 
 to describe the change effected as a transformation of one species into another. 
 Schmankewitsch himself expressly said that he did not so consider it, and it is- 
 unfortunate that such a description has been applied to this case. 
 
 The question of the division of the 8th post-abdominal segment of Artemia, 
 stated to occur on dilution of the water, directly concerns the subject of Meristic 
 Variation. As to the facts, there is no doubt that the tail of Branchipus appears to 
 be made up of seven segments besides the two which bear the external generative 
 organs, in all, nine, while in the commonest forms of A. salina there are only 
 eight such segments ; and that the difference lies in the fact that in the long 
 terminal segment of A. salina there is generally no appearance of division. But as 
 Claus 1 has shewn, the last apparent division in Branchipus is of a different 
 character from that of the other abdominal segments. This is indeed easily seen 
 in B. ferox, B. stagnalis, B. spinosus, &c, in which the appearance of the last 
 division is very different from that of the other divisions. It appears, in fact, to be 
 rather an annulation than a segmentation. In longitudinal sections the distinction 
 is quite clear. Such a division, according to Schmankewitsch, appears in the third 
 generation of A. salina bred in diluted salt water. 
 
 Among my own specimens an appearance of division in the last segment occurs 
 in a considerable number, and these are not by any means from the most dilute 
 waters alone, some of them being from waters of great concentration. For instance, 
 the specimens in XXIX, LI, XXXVII, XXXIX and XIV, all have no trace of such 
 division. On the other hand, it was found in several specimens from XXVI (Sp. G. 
 1*179) and XLIII (Sp. G. 1'115), while others from these localities did not shew it. 
 These facts relate to adult females bearing eggs. I do not think, therefore, that the 
 relation of this appearance of division to the salinity of the water is a constant one. 
 
 Lastly, as regards the relation of Artemia to Branchipus, Schmankewitsch has 
 maintained that the division of the last abdominal segment is the only structural 
 character really differentiating Branchipus. Claus (I. c.) pointed out that there are 
 many other points of difference, and that the supposed division is not a structural 
 character of great moment. But above all these, it should be remembered that by 
 the sexual characters of the males, Branchipus is absolutely separated from Artemia. 
 No Branchipus has any structure at all resembling the great leaf-like second antennae 
 of the male A. salina or A. gracilis- Verrill. Schmankewitsch remarks (Z. f. iv. Z.,. 
 1877, p. 492) that there are species of Branchipus (e.g. B. ferox) without the 
 appendages characterizing the second antennas of B. stagnalis s , &c, and that the 
 males of Artemia bear on the second antennas a knob, which is possibly the repre- 
 sentative of the appendages of Branchipus, but nevertheless there is no resemblance 
 whatever between the males of B. ferox or of any other Branchipus and those of 
 Artemia, and there is no reason to suppose that these sexual characters are modified 
 by the degree of concentration of the water. The statement that the descendants 
 of an Artemia can be made to assume the characters of Branchipus Schaffer, depends 
 entirely on the acceptance of Schmankewitsch's criterion of that genus, which is set 
 iip in practical disregard of the far more distinctive sexual characters. It is, besides, 
 as has already been stated, only an irregular and possibly misleading relation which 
 subsists between this appearance of segmentation and the salinity of the water 3 . 
 
 1 Anz. Ak. Wiss. Wien, 1886, p. 43 ; see also idem, Abhandl. Gdttingen, 1873, 
 Taf. in. Fig. 10, Taf. v. Fig. 16. 
 
 2 For two samples of this American form I am indebted to Dr A. M. Norman, 
 who received them from Professor Packard. 
 
 3 I cannot leave this subject without expressing astonishment at the com- 
 paratively slight and evasive differences in the structure of Artemice and other 
 Crustacea inhabiting waters of different salinity and composition. It is not a little 
 
chap.il] segments of arthropoda. 101 
 
 surprising that the animals living in No. XIV, for example, are scarcely dis- 
 tinguishable from those in No. XXIX, though the water in the latter was so strongly 
 alkaline as to feel soapy. The conditions of animal life in these two waters must 
 surely be very different, and yet no visible effect is produced. It is of course certain 
 that there are great differences in the physiology of these forms, for, as I have often 
 seen, animals (Copepoda, Cladocera, &c.) transferred from one water to another of 
 materially different composition, die in a few minutes, though the second water may 
 be inhabited by the same species; but in visible structure, the differences are for the 
 most part trifling and equivocal. 
 
CHAPTER III. 
 
 Linear Series — continued. 
 Vertebrae and Ribs. 
 
 The Meristic Variations of the vertebral column constitute a 
 subject of some complexity. In considering them it must be 
 remembered that numerical change may be brought about in the 
 series of vertebrae by two different processes : first, by Variation in 
 the total number of segments composing the whole column, in which 
 case the variation is truly Meristic ; and secondly by Variation in 
 the number or ordinal position of the vertebra? comprised in one 
 or more regions of the column, not necessarily involving change in 
 the total number of segments forming the whole series, and in this 
 case the variation is Homceotic. Though Homceotic Variation is 
 often associated with change in the total number of segments, 
 from the nature of the case it is rarely possible in any given 
 instance to distinguish clearly whether such change has occurred 
 or not. This arises largely from the fact that while to find the 
 total number of vertebra? it is necessary to know the exact number 
 of caudal vertebra?, in many specimens these are incomplete, and 
 even if present their number cannot often be given with con- 
 fidence. For these reasons the chief interest of this section of the 
 facts arises in connexion with Homceotic Variation, and the modes 
 in which it occurs ; but it must be constantly borne in mind that 
 in almost any given case there may be Meristic Variation also, though 
 the evidence of this may be obscured. 
 
 True Meristic Variation in Vertebrae and Ribs. 
 
 I. Vertebrce. 
 
 True Meristic Variation, that is to say, change in the total 
 number of segments composing the whole column, may neverthe- 
 less be plainly recognized in certain animals. Among some of the 
 
CHAP. III.] 
 
 VERTEBRAE AND RIBS. 
 
 103 
 
 5. 
 
 lower vertebrates, Fishes and Snakes, for example, the range of 
 such Variation may be very great. Among Mammals the following 
 may be given as an example of considerable Variation in the 
 number of presacral vertebrae in a wild animal, and such evidence 
 may be multiplied indefinitely. 
 
 Erinaceus europaeus (the Hedgehog). 
 
 No. 1 
 
 C 
 
 D 
 
 L 
 
 S 
 4 
 
 C 
 
 Total 
 
 7 
 
 14 
 
 6 
 
 11 
 
 42 
 
 2 
 
 7 
 
 15 
 
 6 
 
 3 
 
 10 + 
 
 
 3 
 
 7 
 
 16 
 
 6 
 
 3 
 
 9 + 
 
 
 4 
 
 7 
 
 15 
 
 6 
 
 4 
 
 12 
 
 44 
 
 5 
 
 7 
 
 15 
 
 6 
 
 4 
 
 11 
 
 43 
 
 6 
 
 7 
 
 14 
 
 6 
 
 3 
 
 9 + 
 
 
 7 
 
 7 
 
 15 
 
 6 
 
 3 
 
 11 or 12 
 
 
 8 
 
 7 
 
 15 
 
 6 
 
 3 
 
 13 
 
 44 
 
 9 
 
 7 
 
 15 
 
 6 
 
 3 
 
 12 or 13 
 
 
 Nos. 1—5 in Mus. Coll. Surg., see Catalogue, 1884, pp. 645 and 646; No. 6 in 
 Cambridge Univ. Mus. ; Nos. 7 — 9 in British Museum. 
 
 6. Man. The simplest form of true Meristic Variation in the 
 total number of vertebrae may occur in Man by the formation of 
 an extra coccygeal vertebra, making five coccygeals in addition to 
 five sacrals, i.e. ten pelvic vertebrae in all. Instances of this are 
 rare (Struthers), though in many tailed forms such Variation 
 is common. Two cases, in both of which the sixth piece (1st 
 coccygeal) was partially ankylosed to the sacrum, are fully de- 
 scribed by Struthers, J., Journ. Anat. Phys., 1875, pp. 93 — 96. 
 
 In the presence of cases like that last given, there is a strong 
 suggestion that the number of vertebrae has been increased by 
 simple addition of a new segment behind, after the fashion of a 
 growing worm : the variation of vertebrae thus seems a simple 
 thing. But there is evidence of other kinds which plainly shews 
 this view of the matter to be quite inadequate. Some of these 
 facts may now be offered, and in them we meet a class of fact 
 which will again and again recur in other parts of the study of 
 Repeated Parts. 
 
 Imperfect Division of Vertebrae. 
 
 *7. Python tigris K This is a case of great importance as illus- 
 trating several phenomena of Meristic Division. In a skeleton of 
 Python in the Mus. Coll. Surg., No. 602, the following peculiarities 
 of structure are to be seen. Up to the 147th inclusive the ver- 
 tebrae are normal, each having a pair of transverse processes and a 
 
 1 This and the following cases of Pelamis and Cimoliasaurus are discussed by 
 Baur, G., Jour, of Morph., iv. 1891, p. 333. 
 
104 
 
 M ERISTIC VARIATION. 
 
 [part i. 
 
 pair of ribs. The appearance of the next vertebra is shewn in the 
 figure (Fig. 10, I.). Anteriorly, and as far as the level of the 
 posterior surface of the transverse processes, it is normal, save that 
 its neural spine is rather small from before backwards. The trans- 
 verse processes bear a pair of normal ribs. But behind this pair 
 of transverse processes the parts, so to speak, begin again, rising 
 again into a neural spine, and growing outwards into a second pair 
 of transverse processes, with a second pair of normal ribs. Poste- 
 riorly again the parts are normal. This specimen is described 
 in the Catalogue of 1853, as " 148th and 149th vertebrae anky- 
 losed," but upon a little reflexion it will be seen that this account 
 misses the essential point. For the bone is not two vertebrae 
 simply joined together as bones may be after inflammation or the 
 like, but it is two vertebrae whose adjacent parts are not formed, 
 
 K 
 
 Fig. 10. Two examples of imperfect division of vertebrae in one specimen of 
 Python tigris. I. The vertebras 147 — 150 seen from the right side, shewing the 
 imperfect division between the 148th and 149th. The condition on the left side is 
 the same. II. View of dorsal surface of vertebra? 165 — 167, shewing duplicity of 
 166th vertebra on the right side. On this side it bears two ribs. The left side is 
 normal. (From a skeleton, in Coll. Surg. Mus., No. 602.) 
 
chap, in.] VERTEBRAE AND RIBS. 105 
 
 and between which the process of Division has been imperfect. 
 With more reason it may be spoken of as one vertebra partly divided 
 into two, but this description also scarcely recognizes the real 
 nature of the phenomenon. 
 
 Further on, in the same specimen, at the 166th vertebra, there 
 is an even more interesting variation. This vertebra is represented 
 in Fig. 10, II. As there seen, it is normal on the left side, bearing 
 one transverse process and one rib, while on the right side there 
 are two complete transverse processes and two ribs. The 185th 
 vertebra is also in exactly the same condition, being double on the 
 right side and single on the left. 
 
 8. Python sebs : a precisely similar case (Brussels Museum, No. 
 87, I. G.), in which the 195th vertebra is single on the right side 
 and double with two ribs on the left, is described by Albrecht, P., 
 Bull. Mies. Nat. Hist. Belg., 1883, n. p. 21, Plate II. 
 
 9. Python sp.: a precisely similar case of duplicity in the 168th 
 vertebra, on the left side, in a mounted skeleton in the Camb. 
 Univ. Mus. 
 
 It is to be especially noticed that in each of these four cases of 
 lateral duplicity, the degree to which the process of reduplication 
 has gone on is the same. 
 
 10. Pelamis bicolor [ = Hydrophis]. The 212th vertebra simple 
 on the left side, and double on the right. It bears one rib on the 
 left side and two ribs on the right side. Yale Univ. Mus., No. 763. 
 Batjr, G., Jour. ofMorph., IV. 1891, p. 333. 
 
 11. Cimoliasaurus plicatus (a Plesiosaur). " Centrum of a small 
 and malformed cervical vertebra from the Oxford Clay near Oxford. 
 This specimen is immature, and on one side is divided into two 
 portions, each with its distinct costal facet." Lydekker, R., Cat. 
 Fossil Rept. and Amph. in Brit. Mus., Pt. II. 1889, p. 238, No. 
 48,001. 
 
 A case somewhat similar to the above is recorded in the Rabbit by Bland Sutton, 
 Trans. Path. Soc, xli., 1890, p. 3-41. See also certain cases of a somewhat com- 
 parable variation in Man, considered in connexion with the variations of Bilateral 
 Series. 
 
 II. Bibs. 
 
 12. Man. Partial division of ribs is more common than that of 
 vertebras. Five cases are given by Struthers. 1. Fourth rib 
 becoming broad, and bifurcated in front. Male, aged 93. From 
 about middle of shaft these ribs gradually increase in length from 
 7 lines to 1^, inch on the left side, 1} on right. They then fork, 
 the left 1^ inch, the right J inch from where they join their 
 cartilages. Cartilage of right forks close to rib, enclosing a space 
 which admits little finger ; cartilage of left lost, but the diverging 
 bony divisions, each of good breadth for a rib (6 to 7 lines) enclose 
 an intercostal space 1^ inch long, attaining a breadth of J inch, 
 which was probably continued forwards by the division of the 
 
106 MERISTIC VARIATION. [part i. 
 
 cartilage or by two cartilages. The cartilage of the left 7th rib is 
 also double for H inch, all the others are normal. 2. Left fourth 
 rib becoming very broad and bifurcating in front ; two large spaces, 
 one in the bone, one at the bifurcation. 3. Left fourth rib becoming 
 broad towards sternal end, where it joins bifurcated cartilage. In 
 these three cases the division affected the 4th rib. Three others 
 are given in which the rib affected was probably the 4th or 5th. 
 Struthers, J., Jour. Anat. Phys., Ser. 2, VIII. 1875, p. 51. Such 
 cases are often recorded and preparations illustrating them may 
 be seen in most museums. 
 
 Besides these cases of obviously Meristic Variation, there are 
 many which are combined with Homceosis so as to produce far 
 greater anatomical divergence. Though in some of these examples 
 there may be change in the total number of vertebra? shewing 
 that true Meristic change has occurred, they cannot well be treated 
 apart from the more distinctly Homceotic cases. 
 
 Homceotic Variation in Vertebrae and Ribs. 
 
 Homceosis in vertebrae may be best studied in Mammals, 
 and the following account in the first instance relates chiefly to 
 them. Before considering the details of such variations in vertebrae, 
 it may be useful to describe briefly the ordinary system of nomen- 
 clature which is here followed. In treating this subject it is im- 
 possible to employ a terminology which does not seem to imply 
 acceptance of the view that there is a true homology between the 
 individual vertebrae of two spines containing different total num- 
 bers, for all the nomenclature of Comparative Anatomy is devised 
 on this hypothesis. This difficulty is especially felt in regard to 
 vertebrae, and at this point it should be expressly stated that in 
 using the ordinary terms no such assent is intended. This matter 
 has already been referred to in Section VI. of the Introduction, 
 and will be discussed in relation to the facts to be given. 
 
 The vertebral column 1 is divided into five regions: — cervical, dorsal, lumbar, 
 sacral and caudal. None of these regions can be absolutely defined, but the following 
 features are generally used to differentiate them. 
 
 Cervical vertebrae are those of the anterior portion of the column, which either 
 have no moveable ribs, or else have ribs which do not reach the sternum. Dorsal 
 vertebrae are those which lie posterior to the cervicals and have moveable ribs. 
 Lumbar vertebras are those which succeed to the dorsals and have no moveable ribs. 
 Sacral vertebrae cannot be defined in terms applicable even to the whole class of 
 mammals, but, for the purpose of this consideration, it will be enough to use the 
 term in the sense ordinarily given to it in human anatomy, to mean those vertebra? 
 which are ankylosed together to form a sacrum. Caudal vertebrae are vertebra? 
 posterior to the sacrum. 
 
 The characters thus defined are distributed among the several 
 vertebrae according to their ordinal positions. Among mammals 
 the number of vertebrae which develop the characters of each re- 
 
 1 Abridged from Flower, W. H., Mammals, Living and Extinct, 1891, p. 41. 
 
chap, in.] VERTEBRA AND RIBS: MAN. 107 
 
 gion, though differing widely in different classificatory divisions, 
 are as a rule maintained with some constancy within the limits of 
 those divisions, which may be species, genera or larger groups, so 
 that vertebral formulae are often of diagnostic importance. Changes 
 in the numbers of vertebrae composing the several regions must 
 therefore have been an important factor in the evolution of the dif- 
 ferent forms. 
 
 Homceotic Variation in the spinal column consists in the as- 
 sumption by one or more vertebrae of a structure which in the 
 type is proper to vertebrae in a different ordinal position in the 
 series. Examples of this are seen in the case of the development 
 of ribs on a vertebra which by its ordinal position should be lum- 
 bar ; or in the occurrence of a vertebra, normally lumbar, in the 
 likeness of a sacral vertebra, having its transverse processes modi- 
 fied to support the pelvic girdle, &c. Variations of this kind have 
 one character in common, which though at first sight obvious, will 
 help us in interpreting certain other cases of Homoeosis. In all 
 cases of development of a vertebra normally belonging to one region, 
 in the likeness of a vertebra of another region, this change always 
 takes place in vertebrae adjacent to the region whose form is as- 
 sumed. For example, if one vertebra, normally cervical, bears ribs, 
 it is always the last cervical ; if two cervicals bear ribs, they are the 
 last two, and so on. No gaps are left. 
 
 Homceotic Variation in the spinal column may occur by the 
 assumption of 
 
 (1) dorsal characters by a vertebra in the ordinal position of a 
 cervical, 
 
 (2) lumbar characters by a vertebra in the ordinal position of a 
 dorsal, 
 
 (3) sacral characters by a vertebra in the ordinal position of 
 a lumbar, 
 
 (4) coccygeal characters by a vertebra in the ordinal position of 
 a sacral, 
 
 or by the reverse of any of these. Since almost any of these 
 changes may occur either alone or in conjunction with any of the 
 others, it is not possible to group cases of such Homoeosis under 
 these heads, but the consideration of the more complex cases will 
 be made easier if simple examples of each class are first described 
 as seen in Man. 
 
 I. Simple cases. — Man. 
 
 (1) Homoeosis between cervical and dorsal vertebrce. 
 
 (a) From cervical towards dorsal type. 
 
 The chief character distinguishing dorsal vertebrae is the pos- 
 session of moveable ribs. This character may to a greater or less 
 extent be assumed by cervicals. 
 
108 MERISTIC VARIATION. [part i. 
 
 13. Cases of the development of ribs on the 6th cervical seem 
 to be extremely rare. One is given by Struthers in a young 
 spine, set. 4. The ribs were present as rudiments only, being 
 the same on both sides in the 6th vertebra, and on the left side 
 in the 7th. Each of these rib-elements was -^ inch long. In the 
 6th the ribs rested on the body of the vertebra, but in the 7th the 
 rib did not reach so far. Full details, q. v., Struthers, J. Anat. 
 Phys., 1875, p. 32. 
 
 Cervical ribs on the 7th vertebra are comparatively common, 
 being sometimes moveable and sometimes fixed. The literature of 
 this subject up to 1868 is fully analyzed by Wenzel Gruber, 
 Mem. Ac. Sci. Pet, Ser. vn. T. xiil, 1860, No. 2, who refers to 76 
 cases of such ribs, occurring in 45 bodies, being all that were known 
 to him in literature or seen by himself. In addition to these 12 
 cases are described (10 in detail) by Struthers (I. c.\. Some of 
 the results of an analysis of these cases are important to the study 
 of Variation. 
 
 Of 57 cases, the ribs were present on both sides in 42 cases 
 and on one side only in 15. 
 
 According to the degree of completeness with which the cervi- 
 cal ribs are developed, Gruber divided them into four classes \ 
 
 1. Lowest development. Cervical rib not reaching beyond the 
 transverse process ; corresponding to the vertebral end of a true 
 rib with capitulum and tnberculum, and articulating by both of 
 them. Rare form. 
 
 2. Higher development. Cervical rib reaching beyond the 
 transverse process for a greater or less extent, either ending freely 
 or joining with the first true rib. Commonest form. 
 
 3. Still higher development. Cervical rib reaching still further, 
 and joining the cartilage of the first true rib either by its cartila- 
 ginous end or by a ligament continued from this. Hardest form. 
 
 4. Complete development. Cervical rib resembling a true rib, 
 having a cartilage (generally for a greater or less part of its length 
 united with the cartilage of the first true rib) connecting it with 
 the sternum. Less rare form. 
 
 Gruber states, as the result of an analysis of 47 cases, that the 
 third of these states is very rare, that the second condition is the 
 common one, and that the fourth or complete condition is commoner 
 than the first or least state of development, which is also rare. 
 Of Struthers' cases the majority seem to belong to Gruber's second 
 class, while that on the left side in Struthers' Case 4 must have 
 approached Class 1, and that on the left side in Case 10 belonged 
 to Class 3. 
 
 Two features in this evidence are of especial consequence : first 
 
 1 Gruber considered that cervical ribs in Man are probably of two kinds, the 
 one arising by development of an "epiphysis" on the superior transverse process, 
 and the other by development of the "rib-rudiment" contained in the inferior 
 transverse process. It is of cases of the latter kind that he is here speaking. 
 
chap, in.] VERTEBRAE AND RIBS: MAN. 109 
 
 that the variation is more common on both sides than on one side ; 
 secondly, that it is not in its lowest development that it is most fre- 
 quent, but rather in a condition of moderate completeness, having 
 the proper parts of a true rib. 
 
 (b) From dorsal towards cervical type. 
 
 14. Reduction of ribs in the first dorsal is described by Struthers 
 in a specimen in the Path. Mus. of Vienna. " The whole of the 
 cervical vertebrae being present 1 there is no doubt as to the case 
 being one of imperfect first rib. On left side rib goes about § 
 round, and articulates with a process of the second rib. On right 
 side it joins second rib at from -J- to 1 inch beyond tubercle, but 
 again projects as a curved process where the subclavian artery has 
 passed over it. The manubrium sterni first receives a broad car- 
 tilage, as if from one rib only, and secondly a cartilage at the junc- 
 tion of the manubrium and body which is the cartilage of the third 
 thoracic rib." Struthers, J. Anat. Phi/s., 1875, p. 47, Note. (See 
 also Nos. 24 and 25.) 
 
 (2) Homoeosis betiveen dorsal and lumbar vertebras. 
 
 15. (a) From dorsal towards lumbar type. The characters chiefly 
 distinguishing dorsal vertebras from lumbars are the presence of 
 ribs attached to the former, and of long, flat transverse processes in 
 the latter. Secondly, the articular processes of lumbar vertebrae 
 generally differ from those of most of the dorsal series, each pair of 
 articular surfaces facing inwards and outwards respectively instead 
 of upwards and downwards as they do in the dorsal region. The 
 transition from the one type of process to the other, in passing down 
 the column, is generally an abrupt and not a gradual one. In Man 
 it occurs between the 12th dorsal and 1st lumbar, but in most 
 Mammals it takes place more or less in front of the last dorsal. 
 leaving several dorsal vertebrae with articular processes of the 
 lumbar type. (Struthers, /. c, p. 59.) 
 
 Cases of rudimentary 12th rib in Man are not rare. When the 
 last dorsal in this respect approaches to the lumbar type, the 
 change of the articular process from dorsal to lumbar may take 
 place higher than normally, as in Struthers' Cases 1 and 2 (/. c. 
 p. 54 and p. 57). In both of these the change was symmetrical, 
 and in the first case it was abrupt and completed between the 11th 
 and 12th dorsals, but in the second it was less complete. Though 
 the place at which the change of articular processes takes place 
 here varies in correlation with the diminution of the last ribs, bo1 li 
 being higher than usual, such correlation is not always found, 
 change in respect of either of those characters sometimes occurring 
 alone. 
 
 1 Struthers points out that unless the cervical vertebras above the rudimentary 
 ribs are counted there can be no certainty that in any given case these ribs are not 
 extra cervical ribs. 
 
110 MEMSTIC VARIATION. [part i. 
 
 (b) From lumbar towards dorsal type. 
 
 16. The formation of moveable ribs upon vertebrae normally be- 
 longing to the lumbar groups is in Man rarer than reduction of the 
 12th ribs. In these cases the ribs may or may not coexist with 
 transverse processes of considerable size. In a case of 13th rib in 
 Man, given by Struthers (I. c, p. 60), the change of articular pro- 
 cesses occurred a space lower than usual, being thus correlated with 
 the appearance of ribs at a lower point. 
 
 (3) and (4). Homoeosis between lumbar, sacral and coccygeal 
 
 vertebrae. 
 
 17. The differences between the vertebrae of these regions are far 
 more matters of degree than those between the members of other 
 vertebral regions. By detachment of the 1st sacral (25th vertebra) 
 the lumbars may become 6, and in this case the 2nd sacral wholly 
 or partially takes the characters proper to the 1st sacral, but this 
 change is not necessarily accompanied by union between the last 
 sacral and the 1st coccygeal (see, for example, Struthers, I.e., 
 p. 68). On the other hand, the last lumbar may unite with the 
 1st sacral, and such union may be either symmetrical or unilateral 
 only. The amount to which the ilium articulates with these ver- 
 tebrae and the degree to which their processes are developed to 
 support it also present many shades of variation. Similarly the 
 last sacral may be free, or the 1st coccygeal may be united to the 
 sacrum. 
 
 Since all these changes are manifestly questions of degree it 
 would be interesting to know whether any particular positions in 
 the series of changes are found more frequently than others, but I 
 know no body of statistics from which this might be determined. 
 In the absence of such determination there is no reason to suppose 
 the existence of Discontinuity in these variations. 
 
 Homceotic Variation, Vertebrae and Ribs. 
 
 II. More Complex Cases. — Man. 
 
 From examples of the occurrence of Homoeosis between mem- 
 bers of the several regions we have now to pass to the more 
 interesting question of the degree to which Homoeosis in one part 
 of the column may be correlated with similar Homceotic variation 
 in the other parts. For, though each of the particular changes in 
 the various regions may occur without correlated change in other 
 regions, such correlation nevertheless often occurs, and in any con- 
 sideration of magnitude of Variation it is a factor of importance. 
 In several of the examples to be given it will be seen that the re- 
 distribution of regions is also associated with Meristic change in 
 the total number of segments in the column. It is obvious that in 
 
* 
 
 chap, in.] VERTEBRA AND RIBS : MAN. ] 1 1 
 
 the present place only the most summary notice of the various cases 
 can be given. 
 
 Amongst them can be recognized two groups, the first in 
 which the Homceosis is from before backwards, the second in 
 which it is from behind forwards. 
 
 A few words in explanation of the use of these terms are perhaps 
 needed. 
 
 In describing cases of such transformation in the series, it is 
 usual to speak of structures, the pelvis for example, as " travelling 
 forwards" or "travelling backwards." These modes of expression 
 are to be avoided as introducing a false and confusing metaphor 
 into the subject, for there is of course no movement of parts in 
 either direction, and the natural process takes place by a develop- 
 ment of certain segments in the likeness of structures which in 
 the type occupy a different ordinal position in the series. In 
 using the expression, Homceosis, we may in part avoid this con- 
 fusion, and we may speak of the variation as occurring from before 
 backwards or from behind forwards, according as the segment to 
 whose form an approach is made stands in the normal series 
 behind or in front of the segment whose variation is being con- 
 sidered. The formation of a cervical rib on the 7 th vertebra is 
 thus a backward Homceosis, for the 7th vertebra thus makes an 
 approach to the characters of the 8th. On the other hand de- 
 velopment of ribs on the 20th vertebra (1st lumbar), is a forward 
 Homceosis, for the 20th vertebra then forms itself after the pattern 
 of the normal 19th 1 . 
 
 A. Backward Homososis. 
 
 If each segment in the series of vertebras were to be developed 
 in the likeness of that which in the normal stands in the position 
 next posterior to its own, we should expect the whole series to be 
 one less than the normal. The following case makes an approach 
 to this condition. 
 18. Skeleton of old woman. C 7, D 11, L 5, S 5, C 4 (5th and 6th 
 cervicals partially ankylosed). The 7th cervical bore a pair of cervical 
 ribs [of Gruber's class 2, see p. 108], that on the left being ankylosed 
 to the 7th cervical. There were only 11 pairs of thoracic ribs. 
 The 1st lumbar was a true lumbar. Gruber, Wexzel, Mem. Ac. 
 Set. Pet, 1869, Ser. vil, xiil, No. 2, p. 23. Here the 7th vertebra 
 resembles a dorsal in having ribs, the 19th, which in the type is 
 the last dorsal, resembles a lumbar in all respects, the 24th is the 
 1st sacral, and there is no 33rd vertebra. 
 
 1 The same terminology may conveniently be adopted in the case of the parts of 
 flowers. Development of petals in the form of sepals being an outward Homceosis, 
 while the formation of sepaloid petals would be thus called an inward Homoeosis, 
 and so forth. 
 
112 MERISTIC VARIATION. [part i. 
 
 Male, in Cambridge Univ. Mus., No. 78. Preparation shews 
 C 7, D 11, and the 19th vertebra formed as the 1st lumbar: re- 
 mainder not preserved, but Professor A. Macalister kindly informs 
 me that there were 5 lumbars and 5 sacrals, giving C 7, D 11, L 5, 
 S 5. The 7th vertebra has cervical ribs, the left being large and 
 articulating with a tuberosity on 1st thoracic rib, the right being 
 considerably smaller, but now broken at the end. Only 11 pairs 
 of thoracic ribs. Change of articular process from dorsal to lumbar 
 begins partially on the left side between 17th and 18th vertebra 
 (instead of between 19th and 20th) and is complete on both sides 
 between 18th and 19th. The 19th bears no rib. [Backward 
 Homoeosis, greater on left side than on right, as seen in the 
 greater size of the left rib on the 7th vertebra, and in the change 
 of processes beginning at a higher level on this side. As the 
 coccyx is not preserved it cannot be seen whether there is one 
 segment less in the whole column, which would be the case were 
 the backward Homoeosis complete.] 
 
 Female, cet. 40. C 7, D 12, L 5, S 6, C 3. The 7th vertebra bore 
 cerv. ribs, free on left, ankylosed to vertebra on right. Change of 
 artic. processes partially on left side between 18th and 19th (instead of 
 between 19th and 20th). Twelfth thoracic ribs short, being l^in. long 
 on left, If in. on right. Struthers, J., J. Anat. Phys., 1875, pp. 53 
 and 35. [There is therefore backward Homoeosis, greater on the left 
 side than on the right.] 
 
 Vertebrae C 7, D 11 or 12, L 5 or 4, S 6, C lost. Eleven pairs of ribs. 
 The 19th vertebra having a transverse process on the left side re- 
 sembling that of the vertebra next below it, as regards place of origin 
 and its upward slope, but is longer than it by iin. and is nearly a 
 third broader and also thicker. On right side corresponding part is in 
 two pieces. Change of articular processes complete between 18th and 
 19th (instead of between 19th and 20th). The 24th vertebra is united 
 to sacrum, but is of unusual shape, differing greatly from a normal 
 1st sacral (25th vertebra). The 29th vertebra is nevertheless not 
 detached from sacrum. Struthers, I. c, pp. 70 and 57. 
 
 Adolescent subject. 7th cervical, 12 dorsals and ribs, and 3 lumbars 
 preserved. 11th ribs reduced, 4 in. long, 4^- in. with cartilage. 12th 
 ribs rudimentary, left 1 in., right f in. long, breadth of each about |-in. 
 Artic. processes change chiefly between 18th and 19th vertebrae. 
 Struthers, I. c, p. 55. 
 
 Male, cet. 47. C 7, D 12, L 5, S 5, C 4. Twelfth ribs very unequal; 
 right scarcely 2 in., left 34 in. The 5th lumbar ankylosed to sacrum 
 by its right transverse process. Struthers, I. c, p. 57. [Backward 
 Homoeosis on right side in respect of reduction of 12th rib and union 
 of 24th vertebra to sacrum on that side.] 
 
 B. Forward Homoeosis. 
 
 As was remarked in the case of backward Homoeosis, if each 
 vertebra were to be developed in the likeness of the one which in 
 
* 
 
 chap, in.] VERTEBRAE AND RIBS: MAN. 113 
 
 the normal stands next behind it in ordinal sequence, we should 
 expect such backward Homoeosis to be accompanied by reduction 
 in the total number of vertebrae ; so, conversely we should expect 
 forward Homoeosis to be accompanied by an increase in total 
 number. This will be found to be sometimes the case (e.g. 
 No. 26). 
 
 24. Male. C 7, D 13, L 5, S 5 [C not recorded]. 13 ribs on each 
 side. The right side differed considerably from the left. 
 
 Right side. 1st rib resembled the usual supernumerary cervical, 
 being moveable and extending j- in. from its tubercle. Greater 
 part of ixth nerve crossed the neck of the rib ; just before doing so 
 it was joined by large branch of xth. The 2nd rib, borne by ninth 
 vertebra, in all respects resembled a normal 1st rib. The 3rd rib 
 articulated with sternum like a normal 2nd rib. In all, 8 ribs 
 articulated with sternum on right side, as usual. The 13th rib 
 (on 20th vertebra) was 4^ in. long. 
 
 Left side. The 1st rib articulated with body and transverse 
 process of 8th vertebra, connecting with sternum in normal position, 
 but differing much from a normal 1st rib, being nearly straight 
 with very slight horizontal curve. 2nd rib normal in form and 
 direction; articulates with sternum J in. higher than right 3rd rib, 
 owing to the lower margin of manubrium being directed slightly 
 obliquely upwards and to the left. In all, 8 ribs articulated with 
 sternum, all below the first being at a level slightly higher than 
 that of the right ribs. ■ The 13th rib (on 20th vertebra) was 4f in. 
 long. Lane, W. Arbuthnot, J. Anat. Phys., 1885, p. 267 [full 
 description and discussion]. 
 
 In this remarkable case, by the reduction of the 1st rib on the 
 right side, the 8th vertebra shews a forward Homoeosis so far as 
 that side is concerned. The 20th vertebra, bearing a pair of 13th 
 ribs, also shews a forward Homoeosis, but this seems to have been 
 a little greater on the left than on the right (cp. No. 20), the right 
 rib being a \ in. less in length. The fact that a large branch of 
 the xth nerve on the right side joined the brachial plexus instead 
 of the usually minute fibre is specially noteworthy, as shewing a 
 forward Homoeosis in the brachial plexus on the right side in 
 correlation to the similar Homoeosis appearing in the reduction of 
 the 1st rib on the same side. (Compare Nos. 14 and 25. ) 
 
 25. Skeleton C 7, D 12, L 6 [S and C not recorded]. First pair 
 of ribs rudimentary, about 1|- in. long, exactly alike, as small 
 horns attached to 8th vertebra. Scalene muscles were inserted 
 into 2nd rib. The 25th vertebra was free, but the first lumbar 
 (20th vertebra) had no trace of a rib. Bellamy, E., J. Anat. Phys., 
 1885, p. 185. 
 
 [In this case there is forward Homoeosis in the reduction of 
 the first ribs and in the formation of the 25th vertebra as a 
 lumbar, but there were no ribs on the 1st lumbar, which would 
 
 B. 
 
 8 
 
114 MERISTIC VARIATION. [part i. 
 
 have been expected had there been an even Homceosis throughout 
 the dorso-lumbars.] 
 
 Male, cet. 50. C 7, D 12, L 6, S 5, C "3 or 4, probably 4." 
 Thirteen pairs of ribs, 13th ribs on 20th vertebra, nearly sym- 
 metrical, right 2 in. long; left 1J, and in breadth a little less than 
 the right. The 6th lumbar, 25th vertebra, had the characters of 
 a normal last lumbar (sc. 24th vertebra), including normal trans- 
 verse processes. Coccyx in 3 moveable pieces, the 3rd apparently 
 composed of two. There is therefore probably one more than 
 the normal number in the whole series. Struthers, J. Anat. 
 Phys., 1875, p. 62. 
 
 27. Male, cet, 56. C 7, D 12, L 6, S 5, C 3. Dorsal vertebrae and 
 ribs normal. 20th vertebra normal, except that it has no trace 
 of transverse processes ; ribs have perhaps been present on it. 
 25th vertebra quite free from sacrum, but articulating with ilium 
 by small facet on each side. The 1st coccygeal joined to sacrum. 
 Struthers, I. c, p. 66 and p. 91. [Homceosis in absence of trans, 
 processes in 20th vertebra, in separation of 25th from sacrum, and 
 in union of 30th with sacrum.] 
 
 28. Skeleton C 7, D 12, L6, S 5, C lost. The 25th vertebra is separate 
 from the ilium and the sacrum, but the 30th is united to the latter. 
 Struthers, I.e., p. 69. 
 
 29. Male, cet. 29. C 7, D 12, L6 (1st bearing ribs — 6th partially joined 
 to sacrum), S 5 (exclusive of 5th lumbar), C 4. 20th vertebra bearing 
 ribs ; 25th partially free from sacrum but partly supporting the ilium, 
 and one extra vertebra in the series. Struthers, I. c., p. 64 and p. 92. 
 
 30. Skeleton D 12, L 6, S 4, C 4. The 25th vertebra by right trans- 
 verse process articulates with sacrum and on the same side with the 
 ilium ; the 30th, however, though moveable on the sacrum, has charac 
 ters transitional between those of a 5th sacral and a 1st coccygeal. 
 Struthers, I.e., p. 68 and p. 91. 
 
 31. Male. C 7, D 13, L 5, S and C ankylosed together of uncertain 
 number. Articular processes change between 20th and 21st, i.e. a space 
 lower than usual, but the processes between 19th and 20th are smaller 
 than those higher up and are not quite symmetrical. The 20th vertebra 
 bore rib on left side and rib has apparently been present on right, but 
 probably not so much developed. Struthers, /. c., p. 64, note. [For- 
 ward Homceosis in development of ribs on 20th and in detachment 
 of 25th.] 
 
 But though the variations of the vertebrae may thus in great 
 measure be reduced to system, there remain other cases, rare in 
 Man but not very uncommon in lower forms, which cannot be 
 brought into any system yet devised. Such cases shew that the 
 limits imposed by a system of individual homologies, between which 
 we conceive the occurrence of Variation, are not natural limits, 
 and that they may be set aside in nature. In the following case it 
 may be especially noted that Variation in the segmentation of the 
 
chap, in.] VERTEBRAE AND RIBS : MAN. 115 
 
 spinal nerves does not necessarily coincide with that of the ver- 
 tebrae. This fact will be more fully illustrated in the section of 
 evidence respecting the spinal nerves. 
 '32. Female, cet. 40. As it stands, the grouping is C 6, D 12, L 6, 
 S 5, C 3; in all 32, viz. one less than usual. The vertebral artery 
 did not enter till 5th cervical (instead of 6th) on left side. The 
 7th vertebra bore a pair of ribs, left small, ceasing at middle of 
 shaft ; right has been sawn off, but has all the appearance of a rib 
 that would have reached the sternum. The 19th vertebra bore 
 no ribs, and has transverse processes like those of a normal 1st 
 lumbar. 23rd has transverse processes triangular and sloping 
 upwards, like those of normal last lumbar but one (sc. 23rd), 
 though in a less degree : pedicle thicker than usual for this 
 vertebra. 
 
 The articular processes change in the normal space, between 
 19th and 20th vertebrae. Sacrum 5 ; Coccyx represented by 3 
 pieces ankylosed together. 
 
 Two entire lumbar nerves went down from the lumbar region 
 to the sacral plexus. [Bones described in detail, q. v.] Struthers, 
 J. Anat. Phijs. 1875, p. 72 and p 29. 
 
 Here then the 7th vertebra shews backward Homceosis, im- 
 perfect on left side, but more complete on right. 19th having no 
 ribs, shews the same, and this also appears in the absence of a 
 4th coccygeal. The fact that two entire lumbar nerves join the 
 sacral plexus is also a variation of the same kind. But if the 
 backward Homceosis were complete, the 24th vertebra should be 
 the 1st sacral, and the 29th should be joined to the coccygeal. 
 The change of articular processes moreover is in the normal place. 
 
 An example like this brings out the difficulty that besets the 
 attempt to find an individual homology for each segment. If the 
 characters proper to each segment in the type may be thus re- 
 distributed piecemeal amongst a different total number of seg- 
 ments, the question, which in this body corresponds to any given 
 vertebra, say the 25th, in a normal body, cannot be answered. 
 The matter is thus clearly summed up by Struthers (I. c. p. 75): 
 
 " The variation in this case presents some complexity. To which 
 region is the suppression of the vertebra to be referred 1 The lumbo- 
 sacral nerves would seem to indicate that the lowest lumbar vertebra 
 is the usual 1st sacral set free, thus accounting for the seemingly 
 deficient pelvic vertebra, and leaving 23 instead of 21 vertebrae above. 
 The appearance of suppression of a vertebra in the neck, is met by 
 the consideration that the 7th vertebra carries ribs, imperfectly de- 
 veloped on one side, like cervical ribs. 
 
 "Then, although only 11 ribs remain, the next vertebra below, 
 
 though rib-less, has the normal articular processes of a 12th dorsal 
 
 (19th vertebra). If it is to be regarded as such, and not as the 
 
 1st lumbar, then the suppressed vertebra would be really a lumbar, 
 
 .although there are six free vertebrae between the thorax and the 
 
 8—2 
 
116 MERISTIC VARIATION. [part r. 
 
 pelvis. Whichever view be taken, this case is an interesting one, 
 as exhibiting variation in every region of the spine, and as shewing 
 the importance of examining the entire spine before deciding as to 
 a variation of any one part of it." 
 
 To the question, which vertebra is missing, there is no answer ; 
 or rather the answer is that there is no segment in this body 
 strictly corresponding to the normal 7th, 20th, 25th, &c; that the 
 characters of these several segments are distributed afresh and 
 upon no strict, consistent plan among the segments of this body, 
 and that, therefore, there is no one segment missing from the 
 body. Surely further efforts to answer questions like these can 
 lead to no useful result. 
 
 Attempts to interpret Variation by the light of simple arith- 
 metic serve only to obscure the real nature of Repetition and 
 segmental differentiation ; for by constantly admitting to the 
 mind the fancy that this simple, subjective representation of these 
 processes is the right guide, and that the tangible complexity in 
 which they present themselves is a wrong one, we only become 
 used to an idea which is not true to the facts and the real difficulty 
 is shirked. 
 
 Anthropoid Apes. 
 
 Though adding little that is new in kind to the foregoing speci- 
 men-cases occurring in Man, the following instances of Variation 
 in the vertebrae of the Anthropoid Apes are of some interest if only 
 as illustrations of the fact that the frequency of such Variation 
 has no necessary relation to the conditions of civilization or domesti- 
 cation. (On the subject of Variation in the vertebrae of Anthropoids, 
 see especially Rosenberg's list, Morph. Jahrb. I. p. 160.) 
 
 Troglodytes niger (the Chimpanzee). 
 
 [In considering cases of variation in the Chimpanzee it should 
 be borne in mind that there are several races and perhaps species 
 included under this name, which have not been clearly distinguished. 
 It is possible, therefore, that some of the variations recorded may 
 be characteristic of these races and not actually individual varia- 
 tions.] 
 
 C 7, D 13, L 4, S 5. 
 
 This is the formula in the great majority of Skeletons (v. auctt.). 
 33. An adult female having C 7, D 12, L 4, S 5, C 5, viz. one 
 vertebra and one pair of ribs less than usual. This is a specimen 
 of du Chaillu's T. calvus. It was received united by the natural 
 ligaments and no vertebra therefore is lost. Gat. Coll. Surg., 1884, n. 
 No. 4. 
 34 # Specimen having rudimentary ribs unequally developed on the 
 21st vertebra. The 25th vertebra was transitional or lumbo-sacral in 
 character. The 26th — 30th formed the sacrum and there were 6 
 caudals, while other specimens had from 2 to 4. For the lumbo- 
 sacral plexus of this specimen, see No. 71. Rosenberg, Morph. 
 
chap, iil] VERTEBRAE AND RIBS: GORILLA. 117 
 
 Jahrb., I. p. 160. Tables, Note 19. This case therefore shews forward 
 Homoeosis in the presence of ribs on the 21st, also in the transitional 
 character of the 25th, together with increase in total number. This 
 increase is however not always found when the 25th is lum bo-sacral, 
 for, on the contrary one such case quoted by Rosenberg had only 
 4 caudals (q.v.). 
 
 In this form the number of vertebrae articulating with the ilium 
 varies, and the number uniting with the sacrum is also liable to 
 alterations probably connected with age. Rosenberg, I. c. : Cat. Coll. 
 Surg., 1884, n. p. 3. 
 
 Gorilla savagii. C 7, D 13, occur in all skeletons of which I 
 have found descriptions, making therefore one pair of ribs more 
 than in Man 1 . 
 
 The number of vertebra? articulating with the ilium and the 
 number joining with the sacrum vary, perhaps with age. Cf. 
 Rosenberg, I.e.; Cat. Coll. Surg.; Struthers, J.Anat. Pliys., 1875, 
 p. 79 note, &c. 
 '35. Adult female. C 7, D 12, L 4, S 5, C 3. This is a remarkable 
 case. There is one rib-bearing vertebra less than usual, while the 
 number of lumbo-sacrals is nine, as in the normal cases collected 
 by Rosenberg. In a normal skeleton in the Camb. Mus. the 
 articular processes change from the dorsal to the lumbar type 
 between the 20th and 21st, but in this abnormal specimen the 
 change is completed on the right side between the 19th and 20th 
 as in Man, and on the left side, though the change has there also 
 taken place, there is a curious irregularity in the fact that the 
 posterior zygapophysis of the 19th is divided to form two processes 
 which fit into two similar processes of the left anterior zygapo- 
 physis of the 20th vertebra. The rest is normal. Cambridge Univ. 
 Mas., 1161, F. [There is here, therefore, a backward Homoeosis of 
 all vertebrae from the 19th onwards; perhaps also an absolute 
 diminution in the total number of segments. The simultaneous 
 variation of both the number of ribs and the position of the 
 
 1 Since this account was written, Struthers has published a valuable paper 
 (Journ. Anat. Phys., 1892, xxvn. p. 181), giving particulars of twenty Gorilla 
 skeletons. Of these the following are especially remarkable. 
 
 Female, C 8, D 13, L 3. The seventh cervical is formed like a sixth, and the eighth 
 is formed as a seventh, bearing no rib. The vertebrre 9 to 21 bear ribs, those of the 
 21st being well formed and coming close to iliac crest. The change of articular 
 processes from dorsal to lumbar type occurred between 21st and 22nd, namely, one 
 vertebra lower than usual. There is thus a forward Homoeosis in absence of ribs on 
 8th, in presence of ribs on 21st, and in the variation of position of the articular 
 change. 
 
 Out of 20 skeletons 3 have 11 pairs of ribs (on 8th to 21st) instead of 13 pairs. 
 In one of these the articular change also occurred one vertebra lower than usual. 
 On p. 136 a case is described in which there was a remarkable asymmetry in the 
 structure of the articular processes, which as Dr Struthers lias pointed out to me, is 
 in some respects like that here described as No. 35 in the text. 
 
 Struthers points out that it would be better in all cases to speak of the change of 
 processes as from lumbar to dorsal instead of from dorsal to lumbar. I regret that 
 this suggestion comes too late for me to adopt. 
 
118 MEMSTIC VARIATION. [part I. 
 
 change of articular processes to the human numbers is especially 
 worthy of notice.] 
 
 * Simia satyrus (Orang-utan). Out of eight skeletons in the 
 Mus. Coll. Surg., C 7, D 12, L 4 occurs in seven. In young 
 specimens the distinction between the last lumbar and the first 
 sacral is clearly shewn by presence of pleurapophysial ossifications in 
 the transverse processes of the latter. Thus though Simia resembles 
 Man in the number of ribs, it differs in the total number of prae- 
 sacral vertebra?. Cat. Mus. Coll. Surg., 1884, n. p. 10. 
 
 The arrangement C 7, D 12, L 4, S 5 occurs in a great number 
 of specimens (for cases quoted, see Rosenberg, Morph. Jahrb., i. 
 p. 100, Tabellen ; Cat. Mus. Coll. Surg, ttc.) 
 
 36. Adult male, Sumatra. C 7, D 11, L 5, S 5, C 2. Mus. Coll 
 Surg.f No. 37. 
 
 37. Foetal skeleton. C 7, D 11, L 5, S 5, C 2. Trinchese, S., 
 Ann. Mus. civ. Storia nat. Genova, 1870, p. 4. 
 
 38. Adult. C 7, D 11, L 4, S + C, ankylosed together, containing 
 8 ? pieces. Camb. Univ. Mus., 1160, a. 
 
 39. Adult, C 7, D 12, L 4, S 4, C 3. The last lumbar shared 
 in supporting iliac bones, de Blainville, Osteogr., Primates, Fsc. I. 
 p. 29. 
 
 40. A young specimen, well preserved : there were certainly L 4, S 3. 
 C 4, but in the adult mentioned above, one of the coccygeal was 
 joined to the sacrum, de Blainville, ibid. 
 
 41. Young specimen in spirit, C 7, D12, L 4, So, C 2. Rosenberg, 
 E., Morph. Jahrb. I. p. 160. 
 
 42. Specimen in spirit, not full grown, C 7, D 12, L 4, S 5, CI. 
 There was no doubt that only one coccygeal was present. Rosenberg, 
 ibid. 
 
 43 [Hylobates. Considerable differences in the number of vertebrae 
 and ribs found in this genus are recorded in the Catalogue of the 
 Museum of the College of Surgeons, &c. ; since however the specific- 
 divisions of the genus are very doubtful (see Catalogue, II. p. 15), 
 it is not possible to consider these as necessarily individual variations. 
 See also Rosenberg, I.e., Tables.] 
 
 Bradypodid^e. 
 
 To the study of Variation of the vertebral regions the pheno- 
 mena seen in the Sloths are of exceptional importance, and in 
 attempts to trace the homologies of the segments special attention 
 has always been paid to them. The following table contains brief 
 particulars of 11 specimens of Brady pus and 11 of Cholcepus seen 
 by myself in English museums, and of a few others of which 
 descriptions have been published. To these is added a summary 
 of 40 specimens of Bradypus and 9 of Cholcepus in German 
 museums 1 examined by Welcker. His account is unfortunately 
 not given in detail, but I have tabulated his results so far as is 
 
 1 viz. Gottingen, Tubingen, Marburg, Leipzig, Frankfurt, Berlin, Giessen, Jena 
 and Halle. 
 
CHAP. III.] 
 
 VERTEBRA AND RIBS : BRADYPUS. 
 
 119 
 
 * 
 
 possible. Welcker's list does not, I believe, include any of the 
 specimens separately given in No. 44. 
 
 The determination of the species is quite uncertain. Welcker 
 in his analysis does not divide the species of Brady pas. In the 
 other cases I have simply taken the name given on the labels. As 
 regards Gholoepus the confusion of species is much to be regretted, 
 for according to the received account 1 the more northern species, 
 G. hoffmanni, has only 6 cervicals, while G. didactylus has 7. In 
 the table it will be seen that four specimens in different places 
 have C 6, though generally marked G. didactylus. Possibly 
 some or all of these are G. hoffmanni, and I have therefore entered 
 them as Gholoepus sp. In the case of Bradypus it has not been 
 alleged that the number of cervicals characterizes particular 
 species, so the fact that the species are confused is of less con- 
 sequence. 
 
 44. Bradypus. 
 
 B. tridactylus 
 
 5» 
 ) > 
 
 5 > 
 
 sp. 
 
 5 > 
 5 > 
 
 sp.? 
 
 B. cuculliger 
 B. torquatus 
 
 ditto 
 Bradypus sp. 
 
 sp. 
 
 sp. 
 
 C 
 
 9 
 
 9 
 9 
 9 
 9 
 
 9 
 
 9 
 9 
 
 8 
 
 9 
 
 9 
 9 
 
 9 
 9 
 
 8 
 8 
 8 
 
 D 
 
 L 
 
 15 
 
 4 
 
 15 
 
 4 
 
 15 
 
 4 
 
 15 
 
 4 
 
 15 
 
 4 5 
 
 14 
 
 4 
 
 14 
 
 4 
 
 16 
 
 3 
 
 15 
 
 3 
 
 15 
 
 4 
 
 s 
 
 6 
 
 6 
 6 
 5 
 5 
 
 5 
 
 6 
 
 7 
 
 Struthers 3 
 
 6 
 
 6 
 
 15 
 
 4 
 
 14 
 
 4 
 
 
 5 
 
 15 
 
 
 15 
 
 
 C 
 
 5 + 
 
 8 + 
 9? 
 12 
 10 
 
 11 
 
 9 
 
 11 
 
 9? 
 
 11 
 
 Coll. Surg. 3428. 
 
 9 
 10 
 
 C 8 minute c. r. rt. 
 
 C 9 large c. r. both sides (one lost). 
 
 jD 15 moveable r. rt., fixed on 1. 
 
 Camb. Mus. 
 C 9 no rib. Coll. Surg. 3427. 
 Brit. Mus. 919 a. 
 Brit. Mus. 52. 9. 20. 5. 
 C 9 c. r. h in. long. Univ. Coll. Loud. 
 
 frt. ^ n 
 Oxford Mus. 
 Coll. Surg. 3422. 
 7th sacral onlv ankylosed in part. 
 
 Brit. Mus. 46. 10. 16. 14. 
 C 9 small rib-like horn on 1. Mus. 
 
 Med.-Chir. Acad. Petersb. Gruber 2 . 
 Gruber's private collection' 2 . 
 C 8 may have borne rib on rt. 
 
 il. free c. r. 1st thoracic complete, 
 rt. c. r. ankylosed. 1st thor. A in. 
 long, like a c. r. ; ankylosed. 
 C 9 has pair short c. r. Brit. Mus. «>21 b. 
 Gruber 2 . 
 
 Brit. Mus. 47. 4. 6. 5. 
 j 3 specimens from Brazil said to have 
 8 cervicals. No detailed account 
 
 \ 
 
 given. 
 
 I)E BliAINVILLE 4 . 
 
 1 Flower, W. H., Mammals, Living and Extinct, 1891, p. 183. 
 
 2 Gruber, Mem. Imp. Ac. Sci. Pet. Ser. vn., xiii. 1869, no. 2, p. 31. 
 
 3 Struthers, Jour. Anat. Phys., 1875, p. 48 note. 
 
 de Blainville, Osteogr., Psc. v., pp. 
 
 27, 28 and 64. In the place cited, 
 
 de Blainville gives C 9, D 16, L 3, S 6, C 9—11 as the normal, but he does not say 
 in how many specimens this formula was seen. I have therefore been unable to 
 tabulate this observation. It will be seen that D 16 is quite exceptional, but as it 
 occurred in the Coll. Surg, specimen no. 3422 it was described by Owen as the 
 normal, and this statement has been copied by many authors, perhaps by de Blainville. 
 5 Fourth lumbar ankylosed to sacrum by tr. proc. 
 
120 
 
 MERISTIC VARIATION. 
 SUMMARY OF 40 CASES: Welcker 1 . 
 
 [part i. 
 
 Brady pus 
 
 C 
 
 D 
 
 L 
 
 
 
 10 
 
 14 
 (14 
 
 4 
 4 ) 
 
 C 10 no c. r. 2 cases 2 , * 
 
 
 
 10 
 
 < or 
 
 or > 
 
 C 10 with c. r. of fair size. 
 
 On C 9 c. r. very 
 
 
 
 (15 
 
 3 ) 
 
 3 cases. 
 
 y small or absent. 
 
 
 
 (15 
 
 4 ) 
 
 
 29th is 1st sacral. 
 
 
 9 
 
 1 or 
 
 or } 
 
 9 cases. 
 
 
 
 
 16 
 
 3 ) 
 
 / 
 
 
 
 9 
 
 15 
 
 3 
 
 15 cases, j C° usually with) 28th fa x L 
 
 
 9 
 
 14 
 
 4 
 
 o cases. \ c. r. 21 cases. \ 
 
 
 9 
 
 14) 
 
 s i 
 
 C 9 has either large c. r. or complete r. ) 27th 
 
 
 or 
 
 or > 
 
 5 cases. (This normal in B. tor- > is 1st 
 
 
 8 
 
 15) 
 
 i 
 
 quatus: once in B. cuculliger.) ) sacral. 
 
 (c. r., cervical rib. C 6 , C 7 , &c, sixth, seventh cervical vertebra, &c.) 
 
 45. Choloepus. 
 
 
 C 
 
 7 
 
 D 
 23 
 
 L 
 
 3 
 
 S 
 8 
 
 4 
 
 
 C. didactylus 
 
 CoZi. Surg. 3435. 
 
 it 
 
 7 
 
 24 
 
 3 
 
 7 
 
 
 Oxford. 
 
 ii 
 
 7 
 
 23 
 
 4 
 
 5 
 
 
 CoZZ. Swrp. 3427 {Catalogue). 
 
 ii 
 
 7 
 
 23 
 
 3 
 
 7 
 
 6 
 
 Coll. Surg. 3424. 
 
 sp. 
 
 6 
 
 24 
 
 3 
 
 6 
 
 5 
 
 Cambridge. 
 
 sp. 
 
 6 
 
 23 
 
 3 
 
 9 
 
 3or4 
 
 Brit. Mm. 65. 3. 4. 5. 
 
 sp. 
 
 6 
 
 22 
 
 4 
 
 8 
 
 5 
 
 CZmv. CoZZ. Bond. 
 
 sp. 
 
 6 
 
 21 
 
 3 
 
 8 
 
 5? 
 
 Brit. Mm. 1510 o. 
 
 C. hoffmanni 
 
 6 
 
 22 
 
 5 
 
 8 
 
 5? 
 
 JBrZf. Mus. 1510 c. 
 
 ii 
 
 6 
 
 21 
 
 4 
 
 7 
 
 5 
 
 CoZZ. S»r#. 3439. 
 
 C. hoffmanni ? 
 
 6 3 
 
 23 
 
 2 
 
 7 
 
 4? 
 
 Brit. Mus. 80. 5. 6. 84. 
 
 SUMMARY OF 9 CASES: Welcker 4 . 
 
 
 C 
 
 D + L 
 
 
 C. didactylus 
 
 ii 
 C. hoffmanni 
 
 ii 
 
 7 
 7 
 6 
 6 
 6 C 
 
 27 
 26 
 27 
 26 
 25 
 
 1st sacral is the 35th. 2 cases. 
 1st sacral is the 34th. 2 cases. 
 1st sacral is the 34th. 1 case. 
 1st sacral is the 33rd. 1 case. 
 1st sacral is the 32nd. 3 cases. 
 
 1 Welcker, Zool. Anz. 1878, i. p. 294. 
 
 2 This includes the celebrated specimen (in natural ligaments) described by 
 Rapp, Anat. Unters. d. Edent., Tubingen, ed. 1843, p. 18. 
 
 3 This specimen is labelled C. didactylus, but coming from Ecuador and having 
 this formula is probably C. hoffmanni. (Compare Thomas, O., P. Z. S., 1880, p. 492.) 
 In it C 6 bears cervical rib articulating with shaft of the first thoracic rib. 
 
 4 Zool, Anz. 1878, i. p. 295. 
 
 5 In a specimen in Leipzig Museum, no. 459, the 6th cervical bears large ribs, of 
 which the right nearly reaches the sternum, so that Welcker says that there are 
 only 5 true cervical vertebras. In another of these specimens there is a cervical rib 
 on C 6 measuring 19 mm. 
 
chap, iil] VERTEBRA AND RIBS : BRADYPODID^E. 121 
 
 On this evidence several comments suggest themselves. First 
 it should be noted that the Bradypodidae strikingly exemplify the 
 principle which Darwin has expressed, that forms which have an 
 exceptional structure often shew an exceptional frequency of 
 Variation. Among Mammals the Sloths are peculiar in having a 
 number of cervicals other than 7, and from the tables given it will 
 be seen that both the range and the frequency of numerical 
 Variation is in them very great, not only as regards the cervicals, 
 but as regards the vertebra? generally. 
 
 As concerning the correlation between Variation in the several 
 regions, Welcker points out that his results go to shew that there 
 is such a relation, and that when the sacrum is far back, the ribs 
 also begin further back, or at least are less developed on the 
 cervicals. As he puts it. with a long trunk there is a long neck. 
 This is a very remarkable conclusion, and it must be admitted 
 that it is, to some extent, borne out by the additional cases given 
 above. The connexion, however, is very irregular. For instance, 
 the Cambridge specimen of Brady pus, though the 29 th is the 1st 
 sacral, has had cervical ribs of good size on the 9th vertebra, and 
 even has a small one on the 8th. But taking the whole list 
 together, Welcker's generalization agrees with the great majority 
 of cases. Expressed in the terms defined above, we may therefore 
 say that backward Homoeosis of the lumbar segments is generally, 
 though not quite always, correlated with backward Homoeosis of 
 the cervicals, and vice versa. 
 
 It will be seen further that this Variation concerns every region 
 of the spine, and that even in the total number of prae-sacral 
 vertebrae there is a wide range of variation, viz. from 27 to 29 in 
 Bradypus (52 specimens) and from 30 to 34 in Cholozpus (20 
 specimens). Perhaps no domestic mammal shews a frequency 
 of variation in the fundamental number of segments com- 
 parable with this. In this connexion it may be observed that the 
 absolute number of dorso-lumbars in Clwl&pus (25 — 27) is ex- 
 ceptionally large amongst mammals ; but this is not the case in 
 Bradypus. 
 
 If the case of Bradypus stood alone, some would of course 
 recognize the occurrence of cervical ribs on the 9th and 8th ver- 
 tebrae as an example of atavism, or return to the normal mam- 
 malian form with 7 cervicals. The occurrence of normal ribs on 
 the 7th in Gholoepus and the occasional presence of cervical ribs on 
 the 6th vertebra in this form, even reaching nearly to the sternum 
 as in Welcker's Leipzig case, obviate the discussion of this hypo- 
 thesis. 
 
 We have, then, in the Bradypodidae an example of mammals in 
 which the vertebrae undergo great Variation as regards both their 
 total number and their regional distribution. As the tables shew 
 this is no trifling thing, concerning merely the number of the 
 caudal vertebrae, the detachment of epiphyses which may then be 
 
122 MERISTIC VARIATION. [part i. 
 
 called ribs, or some other equivocal character, but on the contrary 
 it effects besides changes in the number of pras-sacral segments, 
 that is to say, of large portions of the body, each with their proper 
 supply of nerves, vessels and the like, producing material change 
 in the mechanics and economy of the whole body : this moreover 
 in wild animals, struggling for their own lives, depending for their 
 existence on the perfection and fitness of their bodily organiz- 
 ation. 
 
 Carnivora. 
 
 The following cases, though few, have an interest as exemplifying 
 vertebral Variation in another Order. 
 
 Felis domestica. In all the skeletons of Felidje that I have 
 examined the formula is C 7, D 13, L 7, S 3. A specimen of the 
 domestic Cat having C 7, D 14, L 7 is described by Struthers. The 
 change of articular processes from dorsal to lumbar was completed 
 between the 18th and 19th vertebra? but the posterior zygapophyses of 
 the 17 th, though of the dorsal type, have to some extent the characters 
 of a transition-joint. As is stated below, the change in the domestic 
 Cat normally occurs between the 17th and 18th. In this case therefore 
 with increase in numbers of ribs the position of the articular change 
 has varied. This case is described by Struthers, J. Anat. Phys., 1875, 
 p. 64, Note, but the description there given differs in some respects 
 from that stated above, which is taken from a letter kindly written 
 by Professor Struthers in answer to my inquiries. 
 
 There is here forward Homceosis in the development of ribs on the 
 21st vertebra, in the alteration in position of the articular change, 
 and in the fact that the 28th is not united to the sacrum. 
 
 As seen in some other cases, therefore, with forward Homceosis the 
 number of presacral vertebrae is increased ; but as usual owing to the 
 equivocal nature of caudal vertebra? it is not possible to state that 
 the total number of vertebra? is greater. 
 
 Canis vulpes. Normally, C 7, D 13, L 7 ; articular change from 
 dorsal to lumbar between 17th and 18th. 
 
 Specimen having C 7, D 14, L 6, in which further the articular 
 change occurs partly between the 17th and 18th. and partly between 
 the 18th and 19th. In Mus. Coll. Sure/. Edin. Information as to 
 this specimen was kindly sent me by Professor Struthers. 
 
 Jackal. Specimen having C 7, D 13, L 8 instead of 7. Articular 
 change as usual between 17th and 18th. Struthers in litt. 
 
 Canis familiaris. Case of cervical rib on left side borne by 7th 
 
 cervical. This rib was lh in. long and articulated with a tubercular 
 
 elevation on the 1st thoracic rib of the same side. The remaining 
 
 ribs and vertebra? were normal, [fully described] Gruber, W., Arch. 
 
 f. Anat. Phys., u. wiss. Med., 1867, p. 42, Plate. 
 
 [In connexion with the foregoing observations it may be mentioned 
 that the articular change does not take place in the same place in all 
 Felida?. In 4 specimens of F. leo, 2 of F. tigris and 2 of F. pardus, in 
 Edinburgh, and in one Lion and one Tiger in Cambridge the lumbar 
 type begins between the 18th and 19th as in Struther's abnormal Cat 
 
chap, in.] vertebrae: reptilia. 123 
 
 above described ; but in 4 F. domestica, and 2 F. catus in Edinburgh, 
 
 I F. domestica, 1 F. catus, 1 F. concolor and 1 Cyncelurus jubatus 
 in Cambridge the change is between the 17th and 18th. For informa- 
 tion as to the Edinburgh specimens, I am indebted to Professor 
 Struthers.] 
 
 50. Galictis vittata. Specimen from Parana had 16 pairs of ribs, 
 
 I I true and 5 false ; 5 lumbar, 2 sacral and 2 1 caudal vertebra?. 
 
 A specimen from Brazil had only 15 pairs of ribs and the same 
 number of lumbar and sacral vertebra?. Burmeister, Heise durch d. La 
 Plata-Staaten, Halle, 1861, II. p. 409. 
 
 [This is therefore another case of forward Homceosis, (as manifested 
 in the presence of an additional pair of ribs) associated with an increase 
 in the number of pra?sacral vertebra?.] 
 
 51. Halichcerus grypus. Phocida? generally have C 7, D 15, L 5. 
 Specimen of H. grypus having C 7, D 15, L 6 at Berlin. The an- 
 terior of the six lumbars bears a rudimentary rib about 5 cm. in length 
 on the left side. The 28th vertebra is here detached from the sacrum 
 giving S 3, but generally it is united to it, giving S 4. Nehring, A., 
 Sitzb. naturf. Fr. Berlin, 1883, pp. 121 and 122. There is here 
 therefore a forward Homceosis in the development of a rib on the 
 23rd, and also in the detachment of the 28th from the sacrum. 
 
 Reptilia. 
 
 52. Mr Boulenger kindly informs me that though the number of 
 ventral shields (which is the same as that of the vertebra?) is as a 
 rule very variable in the several species of Snakes as a whole, there 
 is nevertheless great difference in the degree of variability. A case 
 of maximum variation is that of Polyodontophis subpunctatus, in 
 which the number of ventral shields has been observed to vary from 
 151 to 240 (Boulenger , Fauna of Brit. India; Reptilia ko,. 1890, 
 p. 303). 
 
 53. On the other hand the range of variation in Tropidonotus natrix 
 is unusually small. Among 141 specimens examined the number of 
 ventral shields varied from 162 to 190 (Straucii, Mem. Ac. Sci. Pet., 
 1873, xxl, No. 4, pp. 142 and 144). 
 
 *54. Gavialis gangeticus. In this animal there are normally present 
 24 presacral vertebra? and 2 sacrals, the first caudal being the 27th. 
 This vertebra has a peculiar form, being biconvex. Specimen de- 
 scribed having 25 presacrals, 2 sacrals, the 28th being the first 
 caudal. Baur, G., J. of Morph., IV., 1891, p. 334. In this case 
 Baur argues that since the first caudal is clearly recognizable by 
 its peculiar shape, this vertebra must be "homologous" in the 
 two specimens and he considers that a vertebra must have been 
 "intercalated" at some point anterior to the first caudal by a process 
 similar to that seen in Python (see No. 7). In liis judgment this 
 has occurred between the 9th and 10th vertebra 1 , but no reason for 
 this view is given. On the system here adopted, this would be spoken 
 of as a case of forward Homoeosis. 
 55. Heloderma. The first caudal in the normal form may be dis- 
 tinguished by having a perforation in the small rib connected with 
 
124 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 it. In this it is peculiar. Four specimens shewed the following 
 arrangements : — 
 
 II. horridum Xo. 1. First caudal is the 36th vertebra (Troschel). 
 
 ditto No. 2 37th (Baur). 
 
 //. suspectum No. 1 38th (Shufeldt). 
 
 ditto No. 2 39th (Baur). 
 
 Baur, G., J. of Morph. iv. 1891, p. 335. 
 
 Batrachia. 1 
 
 Rana temporaria. In the normal frog there are nine 
 separate vertebrae in addition to the urostyle. A specimen is 
 described by Bourne having 10 free vertebras (Fig. 11, III.). The 
 axis and third vertebra bore tubercles upon the transverse pro- 
 cesses, perhaps representing a partial bifurcation of the kind 
 described in No. 58. The ninth vertebra was abnormal in having 
 zygapophyses, and in that its centrum presented two concavities 
 
 Figure 11. Vertebral columns of Frog (Rana temporaria), after Bourne. 
 
 I. Specimen having transverse processes borne by the atlas, together with 
 other abnormalities described in text No. 58. 
 
 II. Normal Vertebral Column. 
 
 III. Specimen having ten free vertebra?, described in text, No. 56. 
 
 1 I regret that the paper bearing on this subject lately published by Adolphi, 
 Morph. Jahrb., 1892, xix. p. 313, appeared too late to permit me to incorporate 
 the valuable facts it contains. 
 
chap, ill.] VERTEBRAE: BATRACHIA. 125 
 
 for articulation with a tenth vertebra. The right zygapophysis 
 was well formed and articulated with the tenth, but the left was 
 rudimentary. The tenth vertebra itself had an imperfect centrum 
 and the neural arch though complete was markedly asymmetrical. 
 Posteriorly its centrum presented two convexities for articulation 
 with the urostyle. [For details see original figures.] Bourne, 
 A. G., Quart. J. Micr. Sci., xxiv. 1884, p. 87. 
 
 This is a case of some importance as exhibiting Meristic 
 Variation in a simple form. Of course, as Bourne says, we may 
 say that in this specimen the end of the urostyle has been 
 segmented off and that it is composed of " potential " vertebra?, 
 and as he also remarks, it is interesting in this connexion to 
 notice that some Anura, e.g. Discoglossus, present one or two pairs 
 of transverse processes placed one behind the other at the proximal 
 end of the urostyle. But this description is still some way from 
 expressing all that has happened in this case ; for beyond the 
 separation .of a tenth segment from the general mass of the 
 urostyle there is Substantive Variation in the ninth vertebra in 
 correlation with this Meristic Variation. For the ninth has devel- 
 oped a zygapophysis and has two concavities behind, like the 
 vertebra? which in the normal frog are anterior to the ninth. 
 There is therefore a forward Homoeosis, associated with an increase 
 in number of segments, just as there is in such a case as that of 
 Man (No. 20) or in that of Galictis vittata (No. 50). 
 
 It is also interesting in this case to see that the actually last free 
 vertebra here, though it is the 10th, has two convex articular sur- 
 faces behind like the 9th, which is the last in the normal frog, thus 
 shewing a similar forward Homoeosis. Now applying the ordinary 
 conception of Homology to this case, we may, as Bourne says. 
 prove that the 9th in it is homologous with the 9th in a normal 
 frog for its transverse processes are enlarged in the characteristic 
 manner to carry the pelvic girdle. But similarly we may prove 
 also that the tenth in this case is homologous with the ninth of the 
 normal, for its centrum has the peculiar convexities characterizing 
 the last free vertebra. Baur's proof that the first caudal was 
 homologous in the two specimens of Gavialis (see No. .54) rested 
 on the same class of evidence, and for the moment is satisfying, 
 but as here seen this method though so long established leads 
 to a dead-lock. Upon this case it may be well to lay some stress, 
 for the issues raised are here so easily seen. Besides this the 
 imperfect condition of the extra vertebra enables us to sec the 
 phenomenon of increase in a transitional state, a condition rarely 
 found. In the instances recorded in Gavialis (No. 54), owing to 
 the perfection and completeness of the variation, the characters of 
 the 1st caudal are definitely present in the 28th though normally 
 proper to the 27th, and therefore it may be argued that the 28th 
 here is the 27th of the type. The frog here described shews that 
 in this conclusion other possibilities are not met. On the analogy 
 
126 MERISTIC VARIATION. [part i. 
 
 of several cases already given, it is not impossible that if the 
 variation seen in this frog had gone further, the 10th vertebra 
 might alone support the ilium (cp. Nos. 57 and 60) and thus 
 present the characters of the normal 9th in their completeness. If 
 this change had taken place, we should have a case like that of 
 Gavialis, and there would be nothing to shew that the new 10th 
 vertebra was not the 9th of the normal. The truth then seems to 
 be that owing to the correlation between Meristic Variation pro- 
 ducing change in number, and simultaneous Substantive Variation 
 producing a change of form or rather a redistribution of characters, 
 the attempt to trace individual homologies must necessarily fail ; 
 for while such determination must be based either on ordinal 
 position or on structural differentiation, neither of these criterions 
 are really sound. As I have tried to shew, the belief that they are 
 so depends rather on preconception than on the facts of Variation. 
 
 '57. A male specimen of It. temporaria <£ with ten free vertebras is 
 described by Howes. In this case the 9th had a posterior 
 zygapophysis on the left side only. Upon the left side the 
 transverse process of the 9th w r as not larger than that of the 8th 
 and did not support the ilium, which on the left side was entirely 
 borne by the large transverse process of the 10th. On the light 
 side the transverse processes of both 9th and 10th were developed 
 to support the ilium, neither being in itself so large as that of the 
 10th on the left side. The 9th was concave in front instead of 
 convex as usual, and thus the 8th which is normally biconcave is 
 convex behind. The posterior faces of both 9th and 10th bore two 
 convexities such as are normal to the 9th. The urostyle was 
 normal, having well-developed apertures for exit of the last pair 
 of spinal nerves. Howes, G. B., Anat. Ariz., I. 1886, p. 277, 
 figures. 
 
 In this case the departure from the normal, exemplified by 
 No. 56, has gone still further, and the new 10th vertebra bears the 
 ilium wholly on the left side and in part on the right. The con- 
 dition is thus again intermediate between the normal and a com- 
 plete transformation of the 9th into a trunk vertebra and the 
 introduction of a 10th to bear the ilium (as in No. 60). As 
 regards the homologies of the vertebras, the same issues are 
 ao-ain raised which were indicated in regard to No. 56. 
 
 58. Rana temporaria: Case in which transverse processes were present 
 in the atlas vertebra and the transverse processes of several of the 
 vertebra? were abnormal (Fig. 11, I.). The atlas possessed well- 
 developed transverse processes. 
 
 In the axis the transverse processes are directed forwards instead 
 of backwards, and that of the left side presents an indication of bifur- 
 cation at its extremity. 
 
 The third vertebra possessed two pairs of transverse processes 
 which are joined together for two-thirds of their length. The fourth 
 
chap, in.] vertebrae: recapitulation. 127 
 
 vertebra presents a transverse process on the right side which is bifur- 
 cated at its extremity. 
 
 The remaining vertebra, though slightly asymmetrical, present no 
 special peculiarity, except that the neural arch of the ninth vertebra is 
 feebly developed. Bourne, A. G., Quart. Jonrn. Micr. Sci., 1884, xxiv., 
 p. 86, Plate. 
 
 There is here backward Homoeosis of the atlas, the only case 
 of the kind I have met with 1 . The reduplication of the transverse 
 processes of the third vertebra should be studied in connexion with 
 the cases of double vertebrae in Python (No. 7) and the cases of 
 bifid rib (in Man, No. 12), for they present a variation perhaps inter- 
 mediate between these two phenomena. 
 
 Bombinator igneus. In this form there is a considerable range 
 of variation in the development of the transverse processes for the 
 attachment of the pelvic girdle. 
 59. Gotte figures a specimen in which the flat expanded transverse 
 processes have a similar extent on the two sides, but while that on 
 the right side is made up of the processes of the 9th and 10th vertebne 
 (in about the proportions of two to one), that on the left side is 
 entirely formed by the transverse process of the 10th vertebra. Gotte, 
 Entiv. d. Unke, Atlas, PI. xix., fig. 346. 
 *60. Sardinian specimen figured in which the processes for the attach- 
 ment of the pelvic girdle seem to be composed entirely by those 
 of the 10th vertebra while those of the 9th are not developed. Gene, J., 
 Mem. Reale Ac. cli Torino, S. 2, i., PI. v., fig. 4. 
 
 61. Specimen figured in which both transverse processes of 9th and 
 of the 10th are almost equally developed to carry the pelvic girdle. 
 Camerano, L., Atti R.Ac. Sci. Torino, 1880, xv.,fg. 3. 
 
 62. Specimen in which the left transverse process of the 9th bears 
 the pelvic girdle on the left side, and the right transverse process 
 of the 10th bears it on the right side, while the corresponding processes 
 of the opposite sides were not developed. Similar case recorded in 
 Alytes obstetricans by Lataste, Rev. int. des Sci., m., p. 49, 1879 
 [not seen, W.B.] ; ibid. Jig. 4. 
 
 63. Specimen in which the transverse processes of the 9th alone 
 were developed to carry pelvic girdle, but the proximal end of the 
 urostyle was laterally expanded more than usual, ibid. p. 7, Jig. 3. 
 
 [Case of hypertrophy of coccyx, ibid. Jig. 6; ad hoc v. Bedriaga. 
 Zool. Anz., 1879, il, p. 664; Camerano, Atti R. Ac. Sci. Torino, xv„ 
 p. 8.] 
 
 Recapitulation of important features of Variation as seen in the 
 vertebral column. 
 
 I. As regards fact. 
 
 1. The magnitude of the variations. 
 
 2. The rarity of imperfect vertebne. 
 
 3. The phenomenon of imperfect Division of vertebras and 
 
 ribs. 
 
 Adolphi, I. c, p. 352, PI. xn. fig. 3 gives an account of a specimen of Bufo 
 variabilis in which the atlas bore a transverse process on the left side only. In 
 this specimen the first two vertebrae were united and their total length was reduced. 
 
128 MERISTIC VARIATION. [part i. 
 
 4. The frequency of substantial if imperfect bilateral sym- 
 
 metry in the variations, but the occasional occurrence 
 of asymmetry also. 
 
 5. The special variability of some types, e.g. Simia satyrus ; 
 
 the Bradypodida? ; Bombinator igneus. 
 
 6. The evidence that this variability may occur without 
 
 the influence of civilization or domestication. 
 
 II. As regards principle. 
 
 1. The occasional, though not universal, association of for- 
 
 ward Homceosis with increase in number and of back- 
 ward Homoeosis with reduction in number. 
 
 2. The frequent correlation between Variation in several 
 
 regions, such correlated Variation being sometimes 
 unilateral. 
 
 3. The impossibility of applying a scheme of Homology 
 
 between individual segments. 
 
CHAPTER IV. 
 
 Linear Series — continued. 
 Spinal Nerves. 
 
 The spinal nerves compose a Meristic Series in many respects 
 similar to that of the vertebrae. As between the vertebra*, so 
 between the spinal nerves, there is differentiation according to the 
 ordinal succession of the members, certain distributions and func- 
 tions being proper to nerves in certain ordinal positions. The study 
 of the way in which Variation occurs in this series is one of great 
 interest, but unfortunately it is extremely complicated. For while 
 as regards vertebrae the distribution of structural differentiation 
 can be recognized on inspection, in the spinal nerves to obtain a 
 true knowledge of the arrangement in any one case physiological 
 investigation or at least elaborate and special methods of dissection 
 are needed. Though it is therefore impossible to introduce any 
 account which should at all adequately represent the great diver- 
 sity of possible arrangements, it is nevertheless necessary to refer 
 briefly to the chief results attained by these methods and to the 
 principles which have been detected in the Variation of the nerves. 
 It must of course be foreign to our purposes to examine the many 
 diversities of pattern produced by the divisions and anastomoses of 
 nerve-cords in the formation of plexuses, &c, and we must confine 
 our consideration to cases of Variation in the distribution of dif- 
 ferentiation among the spinal nerves, that is to say, in the segmen- 
 tation of the nervous system in so far as it may be judged from 
 the arrangement of spinal nerves. 
 
 Some conception of the magnitude and range of Variation found 
 in single species of Birds may be gained by reference to the beau- 
 tiful researches of Furbringer 1 . A table is given by Fiirbringer, 
 shewing the number and serial position of the spinal nerves which 
 take part in the formation of the brachial plexus in 07 species of 
 
 1 Fiirbringer's memoirs are of such magnitude and completeness that I have felt 
 it to be somewhat of an impertinence to attempt to make selection from them : and 
 it must be remembered that from the isolated and typical cases here given, only 
 a distorted view of the evidence can be gained. As regards this subject, therefore, 
 reference to the original work is especially needed. 
 
 B. 9 
 
130 
 
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132 MERISTIC VARIATION. [part l 
 
 Birds investigated by himself. He also gives particulars of the 
 individual variations which were found in certain cases. From 
 this table the following statement is compiled, shewing the most 
 important diversities met with and the instances of individual Va- 
 riation. In the majority of cases the most posterior spinal nerve 
 of the cervical region was the most posterior nerve of the brachial 
 plexus, but in a certain number of cases it does not join the plexus 
 at all ; in some other cases the anterior spinal nerve of the dorsal 
 region also takes part in forming the plexus. As the table shews, 
 each of these plans has been likewise met with as an individual 
 variation. 
 
 Fiirbringer's table shews 3 as the minimum number of spinal 
 nerves found taking part in the formation of the plexus of any bird 
 (Bucoi'vus abyssinicus) : the same number has been found as a 
 minimum by other observers in other birds (v. Furbrixger, p. 242, 
 note). The maximum number w T as 6, found in Gharadrius and 
 some specimens of Columba. The plexus is generally formed by 4 
 or 5 spinal nerves. 
 
 In cases where several individuals were examined, individual 
 variation w r as generally found, as in Anser, Podargus, Picas, Geci- 
 nus and Garrulus ; in these cases the number of spinal nerves 
 which took part in forming the brachial plexus varied between 4 
 and 5, while in Columba, the number even varied between 4 and 6. 
 
 Variations also occurred in this respect between the two sides 
 of the body. For example, in a specimen of Anser cinereus the 
 plexus was formed on the right side by the nerves XVI, XVII, 
 XVIII and XIX. while on the left side it received a strand from 
 the XXth nerve in addition to these. 
 
 As has been stated, the last cervical nerve is generally the last 
 nerve supplying the brachial plexus but deviations from this plan 
 occur in both directions. These deviations may occur as individual 
 variations and they may even be unilateral, owing to the transition 
 between the cervical and dorsal vertebras being effected at different 
 points on the two sides of the body. 
 
 Particulars are given respecting the average proportions of the 
 several roots in the different arrangements, but the arrangement 
 or size of the roots relatively to each other was not found to bear 
 any constant relation either to the systematic position of the bird, 
 or to its size, or to its capacity for flight. It was however generally 
 found that there was a certain relation betw r een the relative size of 
 the roots and the length of the neck in birds with a plexus com- 
 posed of four roots. In this case the greatest thickness was gener- 
 ally either in or anterior to the middle roots of the plexus in short- 
 necked birds, but posterior to the middle of the plexus in long- 
 necked birds, but even this rule was not at all closely observed and 
 many exceptions occurred. Furbrixger, I. c. p. 243. 
 
 In Variation in the ordinal positions of the spinal nerves com- 
 posing the plexus, the pattern of the plexus as newly constituted 
 
CHAP. IV.] 
 
 SPINAL NERVES : BIRDS. 
 
 133 
 
 commonly bore a resemblance to the original pattern of the plexus, 
 a phenomenon which Furbuinger has called "imitatory Homo- 
 dynamy" or u Parhomology " of the plexus 1 (I. c. p. 245). 
 
 Correlation between the constitution of the brachial plexus and 
 the position and number of moveable cervical ribs. 
 
 Anser cinereus, var. domestica. Upon this point Furbrin- 
 ger has made a series of important observations, especially in the 
 Goose, which enabled him to state that there is, within limits, a 
 certain correlation between the composition of the brachial plexus 
 and the development of the ribs of this region. Speaking gener- 
 ally, those individuals in which the plexus was formed in a more 
 anterior position usually shewed a fairly developed cervical rib on 
 the 18th vertebra (Anser) t and even as in Fig. 12, I, a very short 
 but moveable rib on the 17th vertebra ; and in such cases the 19th 
 vertebra generally bore the first true sternal rib. On the other 
 hand, examples with a more posterior development of the brachial 
 plexus shewed not only an entire absence of moveable ribs on the 
 17th, but even a considerable reduction in the size of the ribs of 
 the 18th and 19th vertebrae, so that these became "transitional' 
 in character, leaving the 20th vertebra as the first vertebra bearing 
 
 xv xv7 xMic^^CrXisst 1 xx x\i xvn xwcrXixcr xx 
 
 Fig. 12. Diagrams of brachial plexus and cervical ribs in two Geese {Anser 
 cinereus, var. domestica) after Furbringer (being his specimens D, left, and G, right). 
 
 I. Case in which the 17th and 18th vertebrae bear cervical ribs and the 19th 
 bears the first sternal rib. II. Case in which the 17th and 18th vertebra bear 
 cervical ribs, and the 20th bears the first sternal rib. 
 
 ax axillaris, bri brachialis longus inferior, brs brachialis longus superior, 
 cbri coraco-brachialis internus, ci cutaneus brachii inferior, c-x cutaneus brachii 
 superior, ic intercostals, Id latissimus dorsi, p pectoralis, rh rhomboideus, sbse sub- 
 scapulars, srpr nerves to levator scapula? and serratus profundus, srsp nerves to 
 serratus superficialis, stc sterno-coracoideus. 
 
 1 The principle denoted by these expressions is nearly the same as that here 
 expressed in the term Homceosis, which is perhaps more convenient as being a more 
 inclusive expression. 
 
134 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 true sternal ribs (Fig. 12, II.). The measurements are given by 
 Furbringer for 7 specimens, of which those relating to two ex- 
 treme cases (here figured) are appended. 
 
 
 Eibs of 
 
 17th vert., 
 
 length in mm. 
 
 Eibs of 
 
 18th vert., 
 
 length in mm. 
 
 Eibs of 
 
 19th vert., 
 
 length in mm. 
 
 Eibs of 
 20th vert. 
 
 I. { rt. 
 23 cm. long \ 1. 
 
 II. 1 rt - 
 51 cm. long 1 . 
 
 2-5 
 2-75 
 
 20 
 21 
 
 7 
 12-5 
 
 23-5 (sternal) 
 23-75 (sternal) 
 51 + 13-5 ligt. 
 and cartilage 
 51 + 15-5 ligt. 
 and cartilage 
 
 (sternal) 
 (sternal) 
 
 59 (sternal) 
 
 60 (sternal) 
 
 Furbringer, M., Morph. Jahrb., 1879, v. pp. 386 and 387. 
 
 66. By comparison of specimens of the Pigeon, Columba livia, var. 
 domestica, a similar correlation was found to occur, as shewn in 
 Fig. 13, 1, and II. (Furbringer's specimens A and E). 
 
 XI XV Cr XW Cr XI\ r Cr XV St' 
 
 XB XW Cr XIV Cr XV Cr 
 
 Fig. 13. Diagrams of brachial plexus and cervical ribs in two Pigeons (C. livia, 
 var. domestica) after Furbringer. 
 
 I. Case in which the 12th, 13th and 14th vertebrae bore cervical ribs. II. Case 
 in which the 13th, 14th and loth bore cervical ribs. Letters as in Fig. 12. 
 
 The measurements of the ribs of these individuals were as fol- 
 
 lows 
 
 
 
 Eibs of 
 
 Eibs of 
 
 Eibs of 
 
 
 
 
 
 12th vert., 
 
 13th vert., 
 
 14th vert., 
 
 Eibs of 
 
 Eibs of 
 
 
 
 length in 
 
 length in 
 
 length in 
 
 15th vert. 
 
 16th vert. 
 
 
 
 mm. 
 
 mm. 
 
 mm. 
 
 
 
 I. 
 
 ( rt. 
 
 3 
 
 18 
 20 
 
 25 
 26 
 
 1st sternal 
 1st sternal 
 
 2nd sternal 
 2nd sternal 
 
 II. 
 
 1 rt. 
 (1- 
 
 — 
 
 3 
 
 18 . 
 18 
 
 (damaged) 
 23 
 
 1st sternal 
 1st sternal 
 
CHAP. IV.] 
 
 SPINAL NERVES : MAN. 
 
 135 
 
 67. The same correlation was established in the case of the Jay 
 Garrulus glandarius, but an actual variation in the number of 
 moveable cervical ribs is not recorded in this species (see Fig. 14, 
 I. and II., Furbringer' s specimens A and D). Furbringer, M., 
 Morph. Jahrk, 1879, v. p. 375. 
 
 XI 
 
 XII Xm Cr XTV Cr XV St 1 X* XU XW CrXIVCr xv st' 
 
 Fig. 14. Diagrams of the cervical ribs and brachial plexus in two Jays 
 (Garrulus glandarius) after Fiirbringer. 
 
 I. Case in which the brachial plexus began from the xith nerve, the cervical 
 ribs of 13th and 14th vertebra? being longer than in II, a case in which the xnth is 
 the first nerve contributing to the brachial plexus. Letters as in Fig. 12. 
 
 The measur 
 follows : 
 
 ements of the two specimens here figured were 
 
 as 
 
 
 Ribs of 13th vert., 
 length in mm. 
 
 Ribs of 14th vert., 
 length in mm. 
 
 Ribs of loth vert. 
 
 (with sterno-costal parts), 
 
 length in mm. 
 
 I- If 
 
 5 
 7 
 
 3-5 
 3-5 
 
 18-5 
 20-5 
 17-25 
 16-5 
 
 24-5 
 26 
 22 
 23 
 
 Furbringer, M., Morph. Jahrb., 1879, v. p. 363. 
 
 But though this correlation between the nerves and the ribs is 
 on the whole decided and unequivocal, it should be explicitly 
 stated that it only occurs within certain limits and is not universal, 
 and this statement of correlation is far from covering the whole 
 ground. Furbringer, I c. p. 387. 
 
 Brachial Plexus. 
 
 *68. Man and other Mammals. By minute dissection of the 
 brachial plexus in fifty-five subjects (32 fcetal and 23 adult) 
 Herringham obtained important evidence as to the parts sup- 
 plied by the fibres of the several spinal roots forming the plexus, 
 and as to the considerable variation which occurs in respect of this 
 supply. Of the facts thus arrived at, two examples may be quoted 
 
136 MERISTIC VARIATION. [part r. 
 
 in illustration, concerning the composition of the median and ulnar 
 nerves respectively. 
 
 The median is formed by two heads from the plexus ; into the 
 outer head the Vlth and Vllth spinals enter, while the inner is 
 formed by branches of the Ylllth and IXth, sometimes with the 
 addition of some bundles of the Vllth. The presence of fibres 
 from the Vllth depends on whether the anterior branch of the 
 Vllth bifurcates, or goes wholly to the anterior (outer) cord of the 
 plexus. In order to see whether both Vlllth and IXth contribute 
 to the median, twenty-eight dissections were made, fourteen in 
 infants, fourteen in adults. In one foetus and in one adult no 
 branch from the IXth was found, these being the only exceptions 
 to the rule that both Vlllth and IXth send fibres to the median 
 nerve. The median is then made of the Vlth, Vllth, Vlllth and 
 IXth, but these roots do not send to it a constant proportion. The 
 bundle from the Vlth varies little, that from the Vllth varies 
 considerably, that from the Vlllth is sometimes equal to, some- 
 times smaller, and sometimes larger than the bundle from the IXth. 
 
 The origin of the ulnar nerve was traced in thirty-two cases, 
 fourteen being adults. It was found to arise in four different ways. 
 Most commonly it arose from the Vlllth and IXth : this occurred 
 in twenty-three cases. With the Vlllth and IXth is sometimes 
 combined a strand from the Vllth, as shewn in five cases (four 
 foetal, one adult). In three foetal cases it arose from the Vlllth 
 only, and in one foetal and one adult case from the Vllth and 
 Vlllth. The Vllth is only added to the ulnar in some of those 
 cases in which it gives a branch to the posterior (inner) cord of the 
 plexus. In several cases the branch from the Vlllth was much 
 larger than that from the IXth, but the reverse w 7 as never met 
 with. 
 
 Evidence similar to the above is given respecting other nerves 
 from the brachial plexus. 
 
 From the results of the investigation generally, it appeared that 
 the range of Variation though considerable was not extravagant, 
 and that when parts, usually supplied by some given nerve root, 
 are supplied by some other root, this other root is then either the 
 one anterior or the one posterior to the root from which the supply 
 normally comes. Some muscles seemed to bear definite relations 
 to each other and their nerve supply seemed also " to vary solidly," 
 their nerve supplies remaining the same relatively to each other, 
 though derived from a different root. " The best example of this 
 is in the three muscles which are attached along the inner side of 
 the bicipital groove, the subscapularis, teres major, and latissimus 
 dorsi. The first is usually supplied by the Vth and Vlth, the 
 second by the Vlth, and the last by the Vllth, and however much 
 they may vary above and below their typical place, they do not 
 change their relations to each other. A similar relation exists 
 between the two supinators and the two radial extensors. These 
 
chap, iv.] SPINAL NERVES: MAN. 137 
 
 last are sometimes supplied by the Vlth, sometimes by the Vllth, 
 but they are never in any case placed above the supinators. These 
 are always supplied by the Vlth alone. The flexor group in the 
 forearm show a similar fixed relation." Herringham concludes 
 that " the nerve roots are not always composed of the same fibres, 
 but that what is in one case the lower bundle of the Vth may be 
 in another the upper bundle of the Vlth, and what is now the 
 upper bundle of the VHIth will at another time be the lower of 
 the Vllth root." Hence the following principle is enuntiated : 
 " Any given fibre may alter its position relative to the vertebral 
 column, but ivill maintain its position relative to other fibres." 
 
 Herringham, W. P., Proc. Boy. Soc, xll, 1886 pp. 423, 427, 
 430, 435. 
 
 By physiological methods, Sherrington working chiefly on 
 Macacus, but on other animals also, found that this principle sub- 
 stantially holds good for the outflow of fibres throughout consider- 
 able regions of the cord, but that it is not always applicable to 
 great lengths of the cord, for the brachial plexus may be consti- 
 tuted in a region which is near the head end in comparison with 
 the place of origin in other individuals, while in the same individual 
 the sciatic plexus may be constituted in a region which is for it 
 comparatively far back. No exception to the principle was found 
 in the sense that a given efferent fibre which in one individual is 
 anterior to some other particular fibre is ever in any individual of 
 the same species posterior to it. Sherrington, C. S., Proc, Boy. 
 Soc, LI. 1892, p. 76. This principle of Herringham's is analogous 
 to that which in the much simpler case of Variation in vertebrae 
 was pointed out on p. 107. It was stated that in such Homceotic 
 variation no gaps are left. If a vertebra assumes a cervical cha- 
 racter, it is the 1st dorsal, and so on. 
 
 *09, The following noteworthy case is described by Herringham in 
 an infant. It should be borne in mind that to a normal brachial 
 plexus the I Vth nerve gives a small communication, the Vth, Vlth, 
 Vllth, VIII th and IXth give large cords, while the Xth (or Hnd 
 dorsal) gives a minute fibre only. In this abnormal specimen, on 
 the left side the part from the Xth was as large as that from the 
 IXth, and this was as large as the Vlllth, whereas the natural 
 proportion of VIHth to IXth is about 2 to 1. The musculo-cuta- 
 neous received from the Vllth, instead of from the Vth and Vlth 
 only as more commonly found ; the median received no Vlth ( v. 
 supra); the teres major was supplied by the Vllth alone, instead 
 of by the Vlth; the circumflex received from the Vllth, instead 
 of Vth and Vlth alone as seen in' 43 cases without any other ex- 
 ception; the musculo-spiral was formed by the Vllth, VIHth and 
 IXth, instead of by the Vlth, Vllth and VIHth (and sometimes 
 even Vth) ; the deep branch in the hand received from both VIHth 
 
138 MERISTIC VARIATION. [part i. 
 
 and IXth (instead of Vlllth alone, as seen in five cases out of six). 
 But though in all these respects the nerve-supply of the plexus was 
 in ordinal position posterior to the normal, nevertheless the IVth 
 sent a communication to the Vth (as it does normally) and the 
 suprascapular and subscapular were given off normally. Here, then, 
 the supply to the plexus began at the normal place, though it ex- 
 tended further back than it normally does. On the right 'side the 
 branch from the Xth was slightly bigger than usual, but otherwise 
 the only abnormality noted was that the IXth sent a branch to the 
 musculo-spiral. Herrixgham, W. P., Proc. Boy. Soc, 1886, xli. 
 p. 435. In view of Furbrixger's evidence (see Nos. 65 and 67), 
 it might be expected that the first rib would be reduced in corre- 
 lation with the irregular forward Homceosis of the nerves. In 
 reply however to a question on the subject, Dr Herringham has 
 kindlv informed me that no abnormality in the ribs was seen, but 
 that this point was not specially considered. 
 
 Compare also Laxe's case, No. 24, in wdiich similarly a large 
 branch from the Xth joined the plexus on the right side and the 
 first rib was rudimentary, both structures thus shewing a correla- 
 ted forward Homoeosis. 
 
 Lumbo-sacral Plexus. 
 
 '70. By physiological methods Sherrixgtox found that the supply 
 to the lumbo-sacral plexus varied considerably with regard to its 
 origin from the spinal nerves. This w r as seen in Macacus, in the 
 Cat and in the Frog. In none of these animals was any one ar- 
 rangement found sufficiently often to justify its selection as a "nor- 
 mal " type. In each case it was found convenient to divide the 
 different forms of arrangement into two classes, the one in which 
 the supply to the plexus was in ordinal position more anterior 
 (" pre-axial," Sherrington), the other being more posterior (" post- 
 axial," Sherrington). Particulars respecting the distribution of the 
 several nerves and the movements resulting from their stimulation 
 in the two classes, are given in detail (q. v.). In Macacus, 31 in- 
 dividuals belonged to the more anterior class, and 21 to the more 
 posterior. In the Cat the number of individuals in the two classes 
 was 22 and 39 respectively. It is stated generally that 
 
 " The distribution of the peripheral nerve-trunks is not obviously 
 different, whether, by its root-formation the plexus belong to the 
 pre-axial class, or to the post-axial. The peripheral nerve-trunks are, 
 as regards their muscles, relatively stable in comparison with the spinal 
 roots. When the innervation of the limb-muscles is of the pre-axial 
 class, so also is that of the anus, vagina and bladder ; and conversely." 
 Sherrington, C. S., Proc. Roy. Soc, 1892, li. pp. 70 — 76. 
 
 71. Primates. Since in examining the facts of Variation we are 
 seeking for evidence as to the modes in w r hich specific differences 
 
chap, iv.] SPINAL NERVES: APES. 139 
 
 originate, allusion may therefore be made to some facts of normal 
 structure in differing forms in illustration of the nature of such 
 differences, and for comparison with the differences which are seen 
 to occur by Variation. The arrangement of the lumbo-sacral plexus 
 in the Primates well exemplifies some of these points. In Man, 
 Chimpanzee and Gorilla the 1st sacral vertebra is the 25th ; in 
 the Orang it is the 26th ; in the Baboons, e.g. Macacus inuus 
 (= Inuus pithecus Is. Geoff, the Barbary Ape) it is the 27th. 
 Now, as Rosenberg says, seeing that in Man the sacral plexus 
 receives one whole prae-sacral root, the XXVth, and part of the 
 XXIVth, it might be supposed that this plexus in the Orang 
 would receive two whole prse-sacral roots and part of a third, or 
 that in Macacus it would receive three prse-sacral roots and part 
 of a fourth. But, as a matter of fact, in each of these forms, 
 Chimpanzee, Orang and Macacus, according to Rosenberg, only 
 one whole prse-sacral root and part of the next above it enter 
 the sacral plexus, just as in Man, though the ordinal positions 
 of the nerve-roots are different. 
 
 The Chimpanzee, however, which Rosenberg examined, was 
 the specimen described (No. 34), having the 25th as a trans- 
 itional lumbo-sacral vertebra, and rudimentary ribs on the 21st. 
 In this specimen the prse-sacral nerves received by the sacral 
 plexus were the XXVIth and part of the XXVth, thus bearing 
 the same ordinal relations to the sacrum that the nerves of the 
 lumbo-sacral cord do in the other forms and in Man, though each 
 is ordinally one lower in the whole series than it is in Man. The 
 same was true of the spinal roots composing the obturator and 
 crural. Rosenberg, E., Morph. Jahrb., I. 1876, pp. 148, 149 and 
 Tables, note 19. 
 
 This case is interesting as an example of forward Homu'osis 
 in the vertebrae associated with forward Homceosis in the sacral 
 plexus. When compared with the following case of a Chimpanzee 1 
 having normal lumbo-sacral vertebrae, several discrepancies will 
 be seen beyond those which can be accounted for by the 
 single change of one in the ordinal position of the roots. No 
 doubt for the larger nerves Rosenberg's account is correct, but 
 as he states that the specimen was so badly preserved that 
 the nerves could not be satisfactorily traced, it is possible that 
 some of the branches may have been missed. However this may 
 be, the specimen dissected by Champneys had important features 
 of difference, notably that the sacral plexus received from the 
 XXIInd spinal, while the highest recorded as entering it in 
 Rosenberg's case was the XXVth, a greater difference than can 
 be accounted for on the simple hypothesis of a change of one 
 place throughout. Though, speaking generally, Rosenberg is 
 right in saying that the evidence of the normal condition in 
 Macacus and Orang as compared with each other and with Man 
 1 Champneys, F., Joum. Anat. Phys., Ser. 2, v. 1872, p. 17G. 
 
140 MERISTIC VARIATION. [part I. 
 
 suggests that the variation of the vertebral regions goes hand 
 in hand with that of the plexus, and though a comparison be- 
 tween Rosenberg's abnormal Chimpanzee with that dissected by 
 Champneys largely bears out this suggestion, yet it is also clear 
 that this correlation is not a precise one, as indeed has already 
 appeared in several instances. 
 
 In giving the compositions of the several nerves of the lumbo- 
 sacral plexus in Man and Chimpanzee, I have given the num- 
 bers of the nerves in the whole series for simplicity of comparison. 
 It will be remembered that a Chimpanzee has one pair of ribs 
 more than Man, the XXIst nerve is the 1st lumbar in Man, but 
 is the 13th dorsal in Chimpanzee, the XXVIth nerve being the 
 1st sacral in both forms. The table given shews, as Champneys 
 says, that the general arrangement of the nerves of the lower 
 limb and lumbar and sacral plexuses was in Chimpanzee very 
 similar to that in Man, but that the nerves are very differently 
 composed. 
 
 MAX. CHIMPANZEE. 
 
 Iliohypogastric} m m 
 
 llio-mgumal J 
 
 Genito-crural XXL— XXII XXI. 
 
 External cutaneous XXII. XXIII XXL, XXII. 
 
 Obturator XXIII. XXIV XXL— XXIII. 
 
 Anterior crural XXIL— XXIV XXL— XXIV. 
 
 Superior gluteal XXIV.— XXVI XXIV.— XXVI. 
 
 Sacral plexus XXI V.— XXIX XXIL— XX VII. 
 
 Small sciatic XXI V.— XXIX XXI V.— XXVI. 
 
 (From Champneys, I.e. p. 210.) 
 
 The origin of the nerves is therefore in several cases lower 
 in Man than in the Chimpanzee, although in the absence of ribs 
 on the 20th vertebra Man shews a character which, as compared 
 with the presence of ribs in this position in the Chimpanzee repre- 
 sents a backward Homceosis. 
 
 Man. With the foregoing, compare the case mentioned above 
 (No. 32) in which two entire lumbar nerves joined the sacral 
 plexus in a human subject having no ribs on the 19th vertebra, 
 &c. Struthers, J. Anat. Phi/*., 1875, p. 72 and p. 29. 
 
 72. For information as to the variations of the lumbo-sacral plexus in 
 the Primates see also Rosenberg, Morph. Jahrb., i. 1876, p. 147 et seqq.; 
 and as to cases in Primates and in other vertebrates compare von 
 Jhering, Das peripherische N ervensystem der Wirbelthiere, &c, Leipzig, 
 1878. Of these, two cases of partial backward Homceosis in the 
 lumbo-sacral plexus of the Dog are perhaps noteworthy, as being 
 represented and described in greater detail than many of von Jhering's 
 cases. In one of these the rib of the 13th dorsal (20th vertebra) was 
 not developed, this vertebra being formed as a lumbar and thus itself 
 shewing a backward Homceosis in correlation to that of the nerves 
 
CHAP. IV.] 
 
 SPINAL NERVES : BRADYPODID^. 
 
 141 
 
 (von Jhering, I. c. p. 182, pi. iv. fig. 2). Descriptions and diagrams 
 of similar cases are given throughout the work, but as some of them 
 represent specimens described by others (e.g. Strutiiers and Rosen- 
 berg) originally without diagrams, it is difficult to know how far the 
 
 accounts given are schematic, 
 work must be made. 
 
 For this reason reference to the original 
 
 * 
 
 73. Bradypodidae. Brachial plexus. As examples of normal differ- 
 ences the Sloths are especially interesting, but unfortunately an 
 extended investigation of the nerves in several individuals has not 
 been made. The results found by Solger relate to one specimen of 
 B. tridactylus and one of C. didactylus. The latter was a perfect 
 specimen, but the former had been partially dissected and the details 
 of the nerves were largely imperfect. The Cholcepus was a specimen 
 with seven cervicals, and the Bradypus had nine, the last bearing rudi- 
 
 i n 
 
 Fig. 15. Diagrams shewing the composition of the brachial plexus in 
 I. a Cholcepus, II. a Bradypus. v l — 11 , the vertebras. IV, VII, X, XII, fourth, 
 seventh, tenth and twelfth cervical nerves. A, dorsal cord. B, ventral cord. 
 a, phrenic, b, dorsalis scapulas, c, suprascapular, d, subscapular. 
 
 mentary ribs. As the figure shews (Fig. 15), there was a close but not 
 a perfect resemblance between the composition of the plexus in the 
 two cases, that of Bradypus being in nearly each case two roots lower 
 than that in Cholcepus. In the latter the IVth nerve gave a branch 
 to the Vth, but whether in Bradypus the Vlth gave a branch to the 
 Vllth was not determined with certainty owing to the condition 
 of the specimen. [For details see original paper] Solger, B., Morph. 
 Jahrb., 1875, 1. p. 199, PI. vi. 
 
 One more case may be given in illustration of the kind of 
 difference which normal forms may present. 
 
 74. Pipa (the Surinam Toad). In the majority of the Batrachia, the 
 most anterior pair of spinal nerves leaves the vertebral column between 
 the first and second vertebrae, no sub-occipital being present. The 
 
142 MERISTIC VARIATION. [part I. 
 
 second pair leaves between the second and third vertebrae, and the 
 third pair leaves between the third and fourth vertebrae. The brachial 
 plexus is formed by the whole of the second pair together with parts of 
 the first and third pairs. (The details of the arrangement are compli- 
 cated and vary greatly in different forms.) In Pipa a different arrange- 
 ment exists. The most anterior pair of nerves leaves the spinal 
 column by perforating the first vertebra, and the pair which leaves 
 between the first and second vertebra? is therefore ordinally the second 
 pair of spinal nerves in this form; the pair which leaves between the 
 second and third vertebrae is the third, and so on. The brachial plexus 
 is made up of the whole of the second nerve, nearly the whole of the 
 third nerve and of a branch of the first. 
 
 If then it were to be supposed that the pair of nerves which leaves 
 the column between the first and second vertebrae in Pipa is homo- 
 logous with the pair of nerves which leaves in the same place in Rana, 
 ifcc, it is clear that between the skull and the 2nd vertebra of Pipa, 
 there is an extra pair of nerves not found in Rana. The number of 
 free vertebrae in Pipa is however less than in Rana. For in the former 
 there are only seven of these, making with the united sacral vertebra 
 and urostyle eight pieces in all ; but in Rana there are eight pre- 
 sacrals, one sacral, and counting the urostyle, ten pieces in all. In 
 Rana only one spinal nerve, the 10th, leaves the urostyle, while in 
 Pipa two pairs, the 9th and 10th, pass out through the terminal piece 
 of the vertebral column, suggesting that the diminution in the 
 number of vertebrae is due to the absence of separation between the 
 9th vertebra and the urostyle. The whole number of spinal nerves 
 is therefore- the same in both Rana and Pipa, but in the latter the 
 1st pair perforate the 1st vertebra in addition to the 2nd pair 
 which pass out between the 1st and 2nd vertebrae. Furbringer 1 , 
 M., Jen. Zt., 1874, vm. p. 181 and Note, PL vn. fig. 37 ; also Jen. 
 Zt., 1873, vii. PI. xiv. figs. 5 and 6. 
 
 It was suggested by Stannius (Lehrb. d. vergl. Anat., p. 130, Note) 
 that perhaps the 1st vertebra of Pipa represents two coalesced verte- 
 brae, but in an anatomical examination of two specimens of Pipa, 
 Furbringer (I.e. 1874, p. 180), found no confirmation of this suggestion, 
 and developmental evidence also went to shew that no such fusion 
 occurs in the ontogeny at least 2 . Kolliker, A., Verh. phys.-med. 
 Ges. Wilrzburg, 1860, x. p. 236. 
 
 As Furbringer says there is no satisfactory way of bringing this case 
 of Pipa into accord with the condition seen in Rana. In the Urodela 
 there is of course a suboccipital nerve between the skull and the 1st 
 vertebra which is not present in Rana, and some resemblance to Pipa 
 is thus suggested; but in the Urodela the 1st spinal does not actually 
 
 1 Compare von Jhering, H., Morph. Jahrb., 1880, vi. p. 297. The statement 
 made by von Jhering that the nerves of Pipa and Rana correspond nerve for nerve, 
 though in different positions relative to the vertebras, if established would be 
 important ; but from the want of detailed description it is not clear whether this 
 conclusion was arrived at by actual dissection. 
 
 2 This is questioned by Adolphi, Morph. Jahrb., xix. 1892, p. 315, note. The 
 same paper contains much important matter bearing on the variation of the nerves 
 of Amphibia. I regret that this paper did not appear in time to enable me to 
 incorporate the facts it contains. 
 
chap, iv.] SPINAL NERVES: BATRACHIA. 143 
 
 anastomose with the plexus, though it gives off the superior thoracic 
 which in both Rana and Pipa comes off at a point peripheral to the 
 formation of the plexus (Fiirbringer). 
 
 If the two spinal nerves which come out of the urostyle in Pipa 
 may be taken to shew that this bone contains n + 2 vertebrae while the 
 single pair in liana shews the urostyle to consist of n + 1, there is in 
 Pipa (as compared with liana), a diminution of one in the total 
 number of vertebra?, together with a backward Homoeosis, which is 
 seen in the fact that the 8th vertebra bears the pelvic girdle. Turning 
 now to the nervous system, the fact that the last spinal nerves to join 
 the brachial plexus in Pipa are the Illrd, while in Hana they are the 
 IVth, is again an evidence of backward Homceosis. But if this process 
 were completely carried out, the pair of nerves which in Pipa pass out 
 through the 1st vertebra should pass out between this vertebra and the 
 skull, i.e. in the position of the suboccipital of the Urodela. Beyond 
 this analysis cannot be carried, and this case is a good illustration of 
 the fact that the hypothesis of an individual homology between the 
 segments does not satisfy all the conditions of the problem. 
 
 Relation between the ordinal position of spinal nerves and 
 their distribution to the limbs. 
 
 This subject is introduced partly because it further illustrates the 
 nature of the relations which the spinal nerves maintain towards each 
 other, and thus bears indirectly on the phenomena of their Variation ; 
 but chiefly because it presents a view of some of the complexities which 
 arise in the apportionment of organs centrally disposed in Meristic 
 Series, to the parts of peripheral appendages having no clear or co- 
 incident relation to the primary or fundamental segmentation of the 
 body. The facts have thus a value as furnishing a kind of commentary 
 on the nature of Meristic Repetitions in vertebrates. In any attempt 
 to interpret or comprehend Meristic Repetition as a whole, they must 
 be taken into account. 
 
 The principles of the distribution of the spinal nerves to the muscles 
 of the fore-limb have been thus enuntiated by Herrixoiiau. 
 
 1. "Of two muscles, or of two parts of a muscle, that which is 
 nearer the head-end of the body tends to be supplied by the higher, 
 that which is nearer the tail-end by the lower nerve. 
 
 2. "Of two muscles, that which is nearer the long axis of the 
 body tends to be supplied by the higher, that which is nearer the peri- 
 phery by the lower nerve. 
 
 3. "Of two muscles, that which is nearer the surface tends to 
 be supplied by the higher, that which is further from it by the lower 
 nerve." Herringham, \V. P., Proc. Roy. Soc, xli. 1886, p. 437. 
 
 Details are given shewing- the manner in which the innervation of 
 the muscles in Man bears out these principles. 
 
 Forgue and Lanxegrace \ who worked with dogs and monkey* 
 by physiological methods, arrived at conclusions identical with those 
 which Herringham came to by human dissection. 
 
 1 Distrib. cles racines motrices, &c, Montpellier, 1883, p. 45 [quoted from 
 Herringham: not seen, W. B.]; also Comptes Rendu*, 1884. cxvm. p. 087. 
 
144 MEBJSTIC VARIATION. [part i. 
 
 As regards the sensory nerves in the fore-limb, the following principles 
 were similarly established by dissection in Man. 
 
 1. "Of two spots on the skin, that which is nearer the pre-axial 
 border tends to be supplied by the higher nerve. 
 
 2. "Of two spots in the pre-axial area the lower tends to be 
 supplied by the lower nerve, and of two spots in the post-axial area the 
 lower tends to be supplied by the higher nerve." 
 
 "Thus, if the limb be seen from the front, the two highest nerves 
 on the outer and inner sides respectively are the IVth and Xth. 
 Lower than these the Vth and Vlth take the outer, the IXth and 
 Xth the inner side. Below the elbow the Vlth alone takes the outer, 
 and the IXth alone the inner. In the hand, while the Vlth and IXth 
 continue their positions, the Vllth and Vlllth for the first time join 
 in the supply." Particulars from which this general statement is made 
 are given. Herringham, I.e. p. 439. 
 
 According to subsequent investigations of Sherrington's on the 
 hind-limb, the innervation of the muscles of the posterior aspect of the 
 thigh and leg do not follow the third of Herringham's principles, for in 
 their case the deep layer of muscles is innervated by roots anterior to 
 those which innervate the superficial muscles. The same experiments also, 
 though clearly shewing that the nerve-supply of the skin of the hallux 
 is anterior to that of the 5th digit, gave only equivocal evidence that 
 the same was true of the musculatures of these two digits; and in the 
 thigh the gracilis is not supplied before the vastus externus, whose 
 relation is rather that of ventral to dorsal than of anterior to posterior. 
 Sherrington, C. S., Proc. Roy. Soc, 1892, li. p. 77. 
 
 Recapitulation. 
 
 Some features in the Meristic Variation of the spinal nerves, 
 as illustrated by the foregoing evidence, may be briefly sum- 
 marized. 
 
 In the first place, as might be anticipated from the compound 
 nature of a spinal nerve, when Homoeotic Variation takes place, it 
 does not commonly occur by the transformation of entire nerves, 
 but rather by change in the distribution and functions of parts of 
 nerves. In this respect, therefore, there is a difference between 
 Homceosis in spinal nerves and that in vertebrae, for in the latter, 
 Homceosis is often complete. 
 
 A rough illustration may make this more clear. 
 
 Just as in making up the chapters of a book into volumes, 
 whole chapters may be put into one volume or into the next, and 
 the following chapters renumbered, so it may be with the Varia- 
 tion of vertebras, for these inay belong wholly to one region of the 
 spine or to another. But the nerves are like chapters made up of 
 sections ; particular sections or groups of sections may come in an 
 earlier chapter or in a subsequent one, and the places of those that 
 have been moved on may be filled up consecutively, but it seldom 
 happens that whole chapters are renumbered. Nevertheless it is 
 clear from such a case as that of Brady pus and Choloepus, on the 
 
chap, iv.] SPINAL NERVES! RECAPITULATION. 145 
 
 hypothesis that both forms are descended from a common ancestor, 
 that such changes and renumbering of whole nerves must have 
 happened, though there is evidence to shew that this may happen 
 piecemeal, as in cases given. 
 
 Of course in speaking of such changes among the vertebrae it 
 will not be forgotten that partial changes occur too, but there 
 is still greater Discontinuity in their case than in that of the 
 nerves. 
 
 But that there is Discontinuity in the case of nerves also is 
 clear ; for a given fibre, supplying a given muscle, must leave the 
 spinal cord either by one foramen and one spinal nerve, or by 
 another. Conversely the ?ith motor nerve must supply either one 
 muscle or another, and the transition between the two, however 
 finely it may be subdivided, must ultimately be discontinuous in 
 the case of individual fibres. It would be interesting to know to 
 what extent fibres vary in bundles, but this can hardly be deter- 
 mined. 
 
 There is, however, some evidence that the group of fibres 
 supplying a limb does to some extent vary up and down the series 
 as a group, though much rearrangement may occur also within the 
 limits of the group itself. 
 
 Lastly, there is important evidence that Variation in other 
 parts may be correlated with change in the ordinal positions at 
 which nerves with given distributions emerge from the spinal 
 cord. With Variation in the ordinal positions at which the nerves 
 come out, change in other parts, notably in the ribs, may happen 
 too ; so that we may say that in a sense there may be, at least 
 within the limits of single species (see cases Nos. 24, 65 and 
 71), a correlation between the apportionment of their functions 
 among the nerves and the contour of the body, both changing 
 together, the ribs rising and falling with the rise and fall of the 
 brachial plexus. The nerves do not merely come out through the 
 foramina like stitches through the welt of a shoe, the shape of the 
 shoe remaining the same wherever the threads pass out. The 
 arrangement is, rather, like that of the strings of such an instru- 
 ment as a harp or piano, in which there is a correlation between 
 the curves of the frame and the positions of the several notes: so 
 long as the frame is the same, the strings cannot be moved up or 
 down, the instrument still retaining the same compass and the same 
 number of notes. 
 
 B. 
 
 10 
 
CHAPTER V. 
 
 linear series — continued. 
 Homceotic Variation in Arthropoda. 
 
 The occurrence of Homceosis among the appendages of Ar- 
 thropoda is illustrated by a small but compact body of evidence. 
 To this evidence special value may be attached, not because it 
 is likely that in the evolution of the Arthropods variations have 
 really taken place, in magnitude comparable with those now to 
 be described, but rather because these cases give a forcible illus- 
 tration of possibilities that underlie the common and familiar 
 phenomena of Meristic Repetition. Of these possibilities they 
 are indeed " Instances Prerogative," salient and memorable ex- 
 amples, enuntiating conditions of the problem of Variation in 
 a form that cannot be forgotten. Facts of this kind, so common 
 in flowering plants, but in their higher manifestations so rare 
 in animals, hold a place in the study of Variation comparable 
 perhaps with that which the phenomena of the prism held in the 
 study of the nature of Light K They furnish a test, an elenchus, 
 which any hypothesis professing to deal with the nature of organic 
 Repetition and Meristic Division must needs endure. 
 
 Insecta. 
 
 *75. Cimbex axillaris (a Saw-fly), having the peripheral parts 
 of the left antenna developed as a foot. The right antenna is 
 normal, ending in a club-shaped terminal joint. In the left an- 
 tenna the terminal joint is entirely replaced by a well-formed 
 foot, having a pair of normal claws and the plantula between 
 them (Fig. 16). This foot is rather smaller than a normal foot, 
 but is perfectly formed. The rest of the antenna, so far as the 
 point at which the club should begin is normal in form, but is 
 a little smaller and thinner than the same parts in the right 
 antenna. Kraatz, G., Lent. ent. Ztschr., 1876, xx., p. 377, PL 
 
 1 See the well-known passage in Nov. Org., u. xxii. 
 
chap, v.] HOMCEOSIS IN ARTHROPOD A. 147 
 
 This specimen was most kindly lent to me for examination by 
 Dr Kraatz, but to this description I am unable to add anything 1 . 
 
 HE 
 
 ^V^ 
 
 Fig. 16. Cimbex axillaris: right antenna normal; left antenna bearing a foot. 
 II. the left antenna seen from in front. III. the same from above. After Kraatz. 
 
 It should be noted that the plantar surface of the foot was turned 
 rather forwards as shewn in the figure, and not downwards like 
 the normal feet. 
 *76. Bombus variabilis J 1 (a Humble-bee). A specimen taken 
 beside the hedge of a park in Munich, having the left antenna 
 partially developed as a foot. The first two joints were normal. 
 They were followed by two joints which were rather compressed 
 and increased in thickness and breadth. Of these the first was 
 oblong and somewhat narrowed towards its apex by two shallow 
 constrictions, giving it an appearance as of three joints united 
 into one ; below it presented a projecting and tooth-like point. 
 This joint was only slightly shiny. The next joint to it was al- 
 most triangular, and was reddish-brown, shiny, and having hairs 
 on its lower surface. Posteriorly it was prolonged inwards, cover- 
 ing the previous joint so that both seemed to form one joint : 
 the posterior edge was somewhat thickly covered with hairs. The 
 upper part of the first of these two joints and the prolongation 
 of the second were together covered by a hairy, scale-like third 
 joint, which seemed to be only attached at its base. From the 
 apex of the second joint arose a shortened claw-joint, like the claw- 
 joint of a normal foot. This joint was reddish-brown and shiny, 
 bearing a pair of regularly formed claws, like the claws of the 
 foot. Kriechbaumer, Entom. Nadir., 1889, xv. No. 18, p. -281. 
 
 1 Some to whom I have spoken of this specimen, being unfamiliar with entomo- 
 logical literature, and thus unaware of the high reputation of Dr Kraatz among ento- 
 mologists, have expressed doubt as to its genuineness. I may add therefore that 
 the specimen, when in Cambridge, was illuminated as an opaque object and submit- 
 ted to most careful microscopical examination both by Dr D. Sharp, F.R.S., and 
 myself, and not the slightest reason was found for supposing that it was other than 
 perfectly natural and genuine. The specimen was also carefully relaxed and washed 
 with warm water, but no part of it was detached by this treatment. 
 
 10—2 
 
148 MERISTIC VARIATION. [part I. 
 
 The two following cases must be given here, inasmuch as 
 they relate to Homoeosis of the appendages in Insects ; but in 
 the case of the first the evidence is unsatisfactory, and in the 
 case of the second there is considerable doubt whether the varia- 
 tion is really of the nature of Homoeosis. 
 
 77. Prionus coriarius £ : having elytra represented by legs. 
 The following is a translation of an announcement in the 
 
 Stettin er Ent. Ztg., 1840, vol. I. p. 48, which is copied from the 
 original communication to the Preussische Provinzial-BloMer, Bd. 
 XX. [The latter journal not seen, W. B.] : — " One of my pupils 
 brought me to-day a male Prionus coriarius, Fbr., the thorax of 
 which is remarkably constructed. The horny covering of the 
 meso thorax is absent, and in place of the elytra is a pair of 
 fully developed legs which are directed upwards and backwards. 
 These legs are inserted at the points of articulation of the elytra. 
 The metathorax supports the wings as usual and the abdomen 
 is not hardened more than it usually is. In trying to fly, the 
 creature moved these upwardly directed legs simultaneously 
 with its wings. The scutellum is absent and the prothorax has 
 only two spines ; other parts normally developed." Dr Saage, 
 Braunsberg, 1839 : — Hagen, in quoting this case, mentions that 
 the specimen was afterwards seen by von Siebold, but gives no 
 reference to any writing of von Siebold on the subject. 
 
 [If this specimen still exists, it is to be hoped that a de- 
 scription of it may be published. In the absence of further in- 
 formation there seems to be no good reason for accepting the case 
 as genuine.] 
 
 78. Zygaena filipendulae £ . Specimen possessing a supernumerary 
 wing arising in such a position as to suggest that it replaced a leg. 
 This specimen was originally described by Richardson, N. M., 
 
 Fig. 17. Zygcena Jilipendulce, <? , having a supernumerary wing on the left side. 
 The upper figure shews the neuration of the supernumerary wing. From drawings 
 by Mr N. M. Richardson. 
 
 Proc. Dorset Field Club, 1891, and was exhibited at a meeting of 
 the Entomological Society of London, 1891, Proc. p. x. The extra 
 wing was in general form and appearance like a somewhat folded 
 
chap, v.] HOMCEOSIS IN ARTHROPOD A. 149 
 
 hind wing but its colour was rather yellower, though it was more 
 red than yellow. I have to thank Mr Richardson for allowing me 
 to examine this specimen in company with Dr Sharp. In compliance 
 with Mr Richardson's wish we did not strip the wing or remove the 
 thick hairs which surrounded its base, and it is therefore not 
 possible to speak with certainty as to its precise point of origin. 
 The following description of it was drawn up for me by Dr Sharp : 
 " The supernumerary wing projects on the under side of the body, 
 and at its base there intervenes a space between it and the dorsal 
 region of the body about equal to the length of the metathoracic 
 side-piece. The exact attachment of the base of the supernumerary 
 wing cannot be seen owing to the hairiness of the body, but so far 
 as can be seen it is to be inferred that the wing is attached along 
 the length of the posterior coxa, the outer edge of the point of 
 attachment may be inferred to extend as far as the suture between 
 the coxa and thoracic side-piece ; if this view be correct the 
 abnormality may be described as the absence of the hind femur 
 and parts attached to it, and the addition of a reduced wing to the 
 hind-margin of the coxa. It is, however, just possible that if the 
 parts could be clearly distinguished it might be found that the 
 real point of attachment of the abnormal wing is the suture 
 between the metathoracic side-piece and the hind coxa." 
 
 It should be distinctly stated that there is no empty socket or 
 other suggestion that the rest of the leg had been lost, and it was in 
 fact practically certain that it had never been present. There is 
 thus a strong prima facie case for the view that the leg has been 
 developed as a wiug, however strong may be the theoretical 
 objections to this conclusion. On the other hand, as will be shewn 
 in a later chapter, supernumerary wings are known in specimens 
 having a full complement of legs, and it is conceivable that one of 
 these supernumerary wings may have arisen in such a way as to 
 prevent the proper development of the leg from the imaginal disc. 
 If the specimen were carefully stripped of hairs some light might 
 perhaps be thrown on this question. The figure (Fig. 17) is from 
 a drawing kindly lent me by Mr Richardson. 
 
 Crustacea. 
 
 Cancer pagurus. Specimen having the right third maxilli- 
 pede developed as a chela. This animal was brought by a fisher- 
 man to the Laboratory of the Marine Biological Association at 
 Plymouth. It is a male, measuring five inches from one side of 
 the carapace to the other. All the parts appear to be normal with 
 the exception of the third maxillipede of the right side. This 
 structure, however, has the form shewn in Fig. 18, A, differing 
 entirely from the ordinary condition of the appendage. Fig. 18, B, 
 is taken from the third maxillipede of the left side and shews the 
 ordinary structure of the same parts. On comparing the two 
 figures it will be seen that the protopodite does not differ in the 
 
150 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 limbs of the two sides; that the exopodite of the right side is 
 
 B 
 
 Fig. 18. Cancer pagurus $ ; the right and left third rnaxillipedes, that of the 
 right side having the endopodite in the likeness of the endopodite of a chela. 
 bp. basipodite, cp. carpopodite, dp. dactylopodite, ep. epipodite, g. groove between 
 parts representing ischiopodite and meropodite, g'. groove representing the suture 
 at which a normal chela is thrown off if injured. From P. Z. S., 1890. 
 
 essentially like that of the left, but that it lacks the inner process 
 and the flagellum which are borne by the normal part. There was 
 some indication that this branch of the limb had been injured, and 
 perhaps the flagellum may have been torn away, but the appear- 
 ances were not such as to warrant a conclusion on this point. The 
 branchial epipodites (not shewn in the figures) were normal in 
 both cases. The endopodite of the right side was entirely peculiar, 
 and was, in fact, literally transmuted into the likeness of one of 
 the great chelae. It consists of a single joint (mi), articulating 
 with the basipodite centrally and bearing the carpopodite. This 
 single joint represents, as it were, the ischiopodite and meropodite 
 of an ordinary chela, but these two parts are ankylosed together 
 and the articulation between them is only represented by a groove 
 (g). Another groove (g') represents the groove upon the ischiopo- 
 dite of the chela, at which the limb is commonly thrown off by 
 the animal if it is injured. The carpopodite, propodite and dactylo- 
 podite are freely moveable on each other and hardly differ, save 
 in absolute size, from those of the normal chelae. The shape, pro- 
 portions and texture are all those of the chela. Batesox, W., 
 Proc. Zool. Soc, 1890, p. 580, fig. 1. 
 80. A similar case 1 of Cancer pagurus $ . 4 inches across carapace, 
 mature, right pedipalp [i.e. 3rd maxillipede] normal, left pedipalp 
 modified into a chela having all the joints clearly defined, Coknish, 
 T., Zoologist, S. 3, vm. p. 349. 
 
 *81. Palinurus penicillatus. The left eye bearing an antenna- 
 like flagellum, growing up from the surface of the eye as shewn 
 in the figure (Fig. 19). The eye-stalk and cornea, as represented, 
 appear to have been of the normal shape but reduced in size. 
 
 1 Similar cases since published by Eichaed, Ann. Sci. Nat., Zool., 1893. 
 
CHAP. V.] 
 
 HOMCEOSIS IN ARTHROPODA. 
 
 151 
 
 Milne-Edwards, A., Comptes Rendus, lix. 1864, p. 710 ; described 
 and figured by Howes, W. B., Proc. Zool. Soc, 1887, p. 469. 
 
 Fig. 19. Palinurus penicillatus, the left eye bearing an antenna-like flagellurn. 
 After Howes. 
 
 82. Hippolyte fabricii differs from other species of the genus in 
 being usually without epipodites at the bases of all the cephalo- 
 thoracic legs except the first pair, while in the other species these 
 appendages are usually present upon the bases of the first and 
 second, or upon the first, second and third pairs, and on this 
 character it was placed by Kroyer in a separate section of the 
 genus. 
 
 Of 52 individuals (18 males varying in length from 27 mm. to 
 39 mm. and 34 females varying from 16'5 mm. to 50 mm.), from 
 various localities on the New England coast, 47 had the normal 
 number of epipodites, while 5 had epipodites on one or both of the 
 second pairs of legs. Of the latter 3 were from the Bay of Fundy ; 
 one </, 35 mm. long, has well-developed epipodites on each side of 
 the 2nd pair of legs ; another J 1 , 36 mm. long, has a short epipodite 
 on the left side and none on the right ; the other, $ , 47 mm. long, 
 has a well-developed epipodite on the left side and none on the 
 right. The two others were from Casco Bay: a $,36 mm. long, 
 with a short epipodite on the left side, and a </\ 28 mm. long, with 
 a rudimentary one on the right side. As the measurements shew, 
 the presence of these epipodites is not characteristic of the young. 
 Smith, S. J., Trans. Connecticut Acad., v. 1879, p. 64. 
 
152 MERISTIC VARIATION. [part i. 
 
 Variation in the number of generative openings in Crayfishes. 
 
 Astacus fluviatilis. A female having the normal pair of 
 oviducal openings on the bases of the antepenultimate pair of 
 walking legs, and in addition to them another pair of similar 
 openings placed upon the corresponding joints of the penultimate 
 pair of walking legs. On dissection it was found that the ovary 
 was normal, and that from each side of it a normal oviduct was 
 given off; but each of these oviducts divided a little lower down 
 to form two smaller oviducts, one of which went to each of the 
 four oviducal openings. Desmarest 1 , E., Ann. Soc. Ent. France, 
 1848, Ser. 2, vi. p. 479, PI. 
 
 Astacus fluviatilis $ , having a supernumerary pair of ovi- 
 ducal openings placed on the last pair of thoracic legs. The normal 
 oviducal openings were in the usual position and of the usual 
 shape and size, but in addition to them there was an extra pair 
 placed on the last thoracic legs. It should be remarked that 
 though these are the appendages upon which the openings of the 
 male organs are placed, the oviducal openings were not in this 
 case situated at the posterior surface of the joint as the male 
 openings are, but were placed relatively to the leg in the same 
 situation as the female openings on the antepenultimate legs. The 
 penultimate legs and the abdominal appendages were normal. On 
 dissection it was found that each oviduct after passing for the 
 greater part of its course as a single tube, divided into two parts, 
 one of which went to each oviducal opening. The ovary itself 
 was normal. Benham, W. B., Ann. Mag. N.H., 1891, Ser. 6, vn. 
 p. 256, PI. ill. fl am greatly obliged to Mr Benham for an oppor- 
 tunity of examining this specimen. Attention is called to the 
 fact that in this specimen Homoeosis occurs in an unusual way, 
 leaving a gap in the series ; for the openings are on the ante- 
 penultimate and last thoracic legs respectively.] 
 
 Desmarest's observation stood apparently alone until lately, when 
 the specimen just described and several others presenting the same 
 or similar variations were observed by Benham. Mr Benham was 
 
 %J 
 
 kind enough to send me the following specimens for examination : 
 one female having a single extra oviducal opening on the left side 
 upon the penultimate thoracic leg (Fig. 20 C), and two females 
 having a similar extra opening in the same place on the right 
 (Fig. 20, B) ; in both of these the normal oviducal openings were 
 unchanged. Together with these Mr Benham also sent a female 
 having only one oviducal opening on the right side and another 
 having only the left oviducal opening (Fig. 20, A), the correspond- 
 ing leg of the other side having no trace of an opening. 
 
 1 Desmarest had this specimen from Rousseau {I. c, p. 481 note): Faxon 
 quoting the case (Harv. Bull., viii.) accidentally represents it as two cases, but the 
 note to Desmarest's paper shews that the description referred to a single specimen 
 only. 
 
CHAP. V.] 
 
 HOMCEOSIS IN ARTHROPODA. 
 
 153 
 
 *85. After receiving these specimens I made an attempt to ascer- 
 tain the degree of frequency with which such variations occur in 
 
 b.n 
 
 ambM 
 
 Right. 
 
 Left. 
 
 Fig. 20. Females of Astacus fluviatilis having an abnormal number of oviducal 
 openings. N.B. The form with three pairs of openings is not figured. 
 
 A. Right oviducal opening absent. B. Extra opening in right penultimate 
 leg. C. Extra opening in left penultimate leg. 
 
 the Crayfish, and though the total number examined is too small 
 to give a percentage of much value it may be well to record the 
 result. 
 
 In all, 586 female A. fluviatilis have been examined : of these 
 563 were normal in respect of the number of oviducal openings, 
 and 23 were abnormal, as follows : 
 
 1. Extra oviducal opening on left penult, leg 7 
 
 2. ditto right 10 
 
 3. ditto on both penult, legs 1 
 
 4. ditto on both penult. & last legs 1 
 
 5. Single oviducal opening on left side only 3 
 
 6. ditto right 1 1 
 
 Total abnormal specimens 2-'> 
 
 1 Mr R. Assheton sends me word of a similar specimen found among 80 of both 
 sexes; Prof. W. B. Howes of another among 144 of both sexes. 
 
154 MERISTIC VARIATION. [part i. 
 
 In all cases of supernumerary oviducal openings the normal open- 
 ings were also present. 
 
 These cases are in addition to those received from Mr Benham. 
 So far, therefore, the cases of extra opening amount to over 3 per 
 cent, of females examined. 
 
 Of 714 males examined, only one was abnormal, having no 
 trace of a generative opening on the right side, the vas deferens 
 ending blindly and hanging free in the thoracic cavity. There 
 was no female opening in this specimen, and the abdominal appen- 
 dages had the form characteristic of the male on both sides. The 
 base of the last thoracic leg on the right side bore no enlargement 
 for the genital opening, but was plain and like that of the pen- 
 ultimate leg 1 . 
 
 In cases of females which lacked one of the openings, the basal 
 joint for the leg which should have been dilated and perforated 
 for the opening, was undilated and resembled the basal joint of a 
 penultimate leg. The oviduct upon the imperforate side was 
 more or less aborted and hung loosely in the thoracic cavity. 
 
 In the abnormal females with extra oviducal openings, the 
 oviduct divides generally into two just before it enters the legs, 
 the fork being placed at the level between them. In some few 
 cases no branch of the oviduct could be traced to the extra open- 
 ing. In one specimen the extra opening led into a short tube 
 which ended blindly, not communicating with the oviduct. The 
 specimen (4) with extra openings on the penultimate and last legs 
 had thus in all six oviducal openings. Those in the normal position 
 on the antepenultimate legs were of normal size, those on the next 
 pair were smaller but still of fair size, while those on the last pair 
 of thoracic legs were very small, that on the left side being the 
 smallest and admitting only a fair-sized bristle. In this specimen 
 the single oviduct of each side forked in its peripheral third, 
 giving a duct to each of the first two pairs of openings, but I failed 
 to find any connexion between it and the openings on the last 
 thoracic legs, which were very short blind sacs. 
 
 In all cases of extra oviducal opening the basal joint of the leg 
 is expanded like those of the normal antepenultimate legs, the 
 degree of expansion being proportional to the size of the opening. 
 The normal openings are always the largest, but the extra ones 
 are sometimes almost as large and would easily allow the passage 
 of ova, but occasionally they are too small to let an egg through. 
 
 As regards principles of Homoeotic Variation illustrated by 
 these cases, three points should be especially remarked : 
 
 1 Compare the following : Astacus fluviatilis. Amongst 1500 specimens 3 were 
 found in which the tubercle through which the green gland opens was entirely- 
 absent. The opening itself was not formed and the green gland of the same side 
 was absent. In another specimen the opening was deformed, probably owing to 
 some mutilation. In this and the previous cases the green gland of the other side 
 was considerably enlarged. Strahl, C, Midler's Archiv fiir Anat. u. Phys., 1859, 
 p. 333,^. 
 
chap, v.] HOMCEOSIS IN ARTHROPOD A . 155 
 
 1. That this Variation may be bilaterally symmetrical, 
 but that the evidence goes to shew that it is more often uni- 
 lateral. 
 
 2. That there is a clear succession between the several 
 oviducal openings, those of the antepenultimate legs being 
 the largest, the penultimate the next, and those of the last 
 legs the smallest. 
 
 3. That Homceosis may occur between segments which 
 are not adjacent, as in the case of extra oviducal openings on 
 the last thoracic legs, none being formed on the penultimate 
 (No. 84). 
 
 4. That the Variation may be perfect. 
 
 With the foregoing, the following evidence may be compared, 
 though it is very doubtful whether it properly belongs here 1 . 
 
 86. Cheraps preissii [an Australian freshwater Crayfish, nearly allied 
 to Astacusj. Of seven specimens received one was a normal male 
 and three were normal females. The other three had on the basal 
 joint of the third [antepenultimate] pair of legs a round opening, 
 having the size and shape and situation of the normal female openings. 
 These apertures were closed with soft substance. The fifth legs bore 
 the usual male openings, from which the ends of the ductus ejacula- 
 torius protruded. The coiled spermatic ducts were normal ; but no 
 ovary was found and no internal structure was connected with these 
 female openings, von Martens, E., Sitzb. Ges. naturf. Fr. Berlhi, 1870, 
 p. 1. 
 
 87. Astacus pilimanus J, a single specimen, and A. braziliensis J, 
 a specimen collected by Hensel in Southern Brazil, a similar opening 
 was found on the third pair of legs ; but in other specimens of these 
 forms there was only a slight though sharply defined depression in 
 the chitinous covering at this point, von Martens, E., I.e. 
 
 1 See also Nicholls, ~R.,Phil Trans., 1730, xsxvi. p. 290, figs. 3 and 4 describing 
 a Lobster {Homarus vulgaris) having male organs on the left side and female organs 
 on the right. 
 
CHAPTER VI. 
 
 linear series — continued. 
 
 Ch^etopoda, Hirudinea and Cestoda. 
 
 Imperfect Segmentation \ 
 
 Though from the circumstance mentioned at the beginning of 
 Chapter n, that the total number of segments in the Annelids is 
 generally indefinite, true Meristic Variation cannot be easily re- 
 cognized in this group, there is nevertheless a remarkable group of 
 cases of imperfect segmentation, in which by reason of the incom- 
 pleteness of the process of Division, the occurrence of Variation is 
 at once perceived. The following cases were all originally described 
 by Cori, who speaks of them as instances of "intercalation" of 
 segments. For reasons sufficiently explained in the Chapter on 
 Vertebras, there are objections to the use of this term, if only as a 
 mode of expression, and the evidence concerning these cases has 
 therefore been re-cast. 
 
 *88. Lumbricus terrestris : the 46th segment having the form 
 shewn in Fig. 21, I. being normal on the right side, but double on 
 the left. Internally a septum divided the two parts a and a from 
 each other. Each of them contained a nephridium, setae, &c. 
 Cori, C. J., Z.f. w. Z. t liv. 1892, p. 571, fig. 1. 
 
 *89. Specimen having, in the region close behind the clitellum, 
 three consecutive segments, each resembling that just described. 
 Of these the first was double on the right side, the second on the 
 left, and the third on the right again. Fig. 21, II. shews the 
 internal structure, the nephridia and other jmrts having doubled 
 in each of the doubled half-segments. Cori, /. c, p. 572, fig. 2. 
 
 90. Lumbriconereis : case similar to the first case in Lumbricus, 
 Fig. 21, III. Cori, C. J., I c, p. 572, fig. 4. 
 
 91. Halla parthenopeia. A specimen 50 cm. long presented 
 numerous abnormalities of which two are represented in Fig. 21, IV. 
 At the point marked a the lines of division between the segments 
 
 1 Numerous facts illustrating this subject are given in a recent paper by 
 Buchanan, F., Q. J. M. S., 1893. 
 
CHAP. VI.] 
 
 ANNELIDS. 
 
 157 
 
 enclose a small spindle-shaped island of tissue. Three segments 
 lower a wedge-shaped half-segment is similarly formed. At 
 
 Fig. 21. Examples of imperfect segmentation in Annelids (after Com). 
 
 I. Lrimbricus terrestris (No. 88). II. L. terrestris (No. 89), as seen when laid 
 open on the dorsal side. III. Lumbriconereis (No. 90). IV. Halla parthenopeia 
 (No. 91). 
 
 N, nephridium ; Np, nephridial pores; D, alimentary canal; dG, dorsal vessel; 
 vG, circular vessel. 
 
 The letters a, b, c, &c. indicate the parts belonging to the respective segments. 
 
 another point in the same animal (not shewn in Fig. 21) one 
 of the segments was partly divided into two in the right dorso- 
 lateral region. Com, p. 572, figs. 8 and 9. 
 
 Spiral Segmentation \ 
 
 92. Lumbricus terrestris. Fig. 22, I. A shews a part of an 
 Earthworm seen from the dorsal side, the ventral side being- 
 normal in appearance. By following the groove indicating the 
 plane of the septum between b and c on the right side to the 
 ventral surface, it could be traced to the left side between b and c, 
 so across the dorsal surface, between c and d on the right side, 
 across the ventral surface and between c and d on the left, reach- 
 ing nearly to the middle dorsal line again. This is shewn dia- 
 grammatically in Fig. 22, I. B. 
 
 93 A simpler case affecting one segment only is shewn in Fig. 
 ' 22, II. 
 
 94. Another specimen exhibited a similar arrangement near the 
 tail-end (Fig. 22, III.). The lettering of the figure sufficiently 
 explains the course of the spiral septal plane. [Cori does not 
 state that the septa internally formed a spiral division, but it can 
 scarcely be doubted that they did so, following the external groove, 
 
 1 Further observations on this subject have been lately published by Morgan, 
 T. H., Journ. of Morph., 1892, p. 245, and by Buchanan, F., Q. J. M. S., 1893. 
 
158 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 like the spiral valve of an Elasmobranch's intestine.] Cori, 
 Z.f. w. Z. t Liv. 1892, p. 573, figs. 5, 6 and 7. 
 
 * 
 
 I B 
 
 Fig. 22. Spiral segmentation in Lumbricus terrestris. 
 
 I, A, the case No. 92 ; I, B, diagrammatic representation. 
 
 II, A, the case No. 93 ; II, B, diagrammatic representation. 
 
 III, the case No. 94. (After Cori.) 
 
 Two other cases described by Cori may be mentioned here, though 
 there is a presumption that they are not really examples of Variation 
 in the segmentation along the axis of a Primary Symmetry, but rather 
 belong to the class of Secondary Symmetries. They are alluded to 
 here as it is convenient to illustrate this distinction by taking them 
 in connexion with the examples just given. 
 95. Hermodice carunculata. (Fig. 23, III.) Between two normal 
 segments is what seems at first to be a segment double on the left 
 side with two complete sets of parapodia, but imperfectly divided 
 on the right (left of figure), the septal groove stopping short before 
 it reaches the parapodial region. The lower half on this side is re- 
 presented with a normal ventral ramus of the parapodium, but the 
 ventral ramus in the upper was itself partially doubled, having in 
 particular two cirri Cv. I. and Cv. II. and two branches of setae. The 
 condition of the dorsal ramus is not described. Of course without 
 seeing this specimen it is impossible to say more than this, but the 
 figure strongly suggests that the division between the two halves of 
 this parapodium was a division into images and not into successive 
 segments. The figure represents the lower cirrus Cv II. as standing 
 in the normal position for the cirrus, on the posterior limb of the 
 parapodium, but the anterior cirrus is distinctly shewn as placed on 
 the anterior limb of the elevation and anterior to the bristles. If 
 this were actually the case, this double parapodium must be looked 
 on as a kind of bud, with a distinct Secondary Symmetry of its 
 own. Described afresh from Cori, C. J., Z.f. w. Z., liv. 1892, p. 574, 
 fig. 3. 
 
CHAP. VI.] 
 
 ANNELIDS. 
 
 159 
 
 96. Diopatra neapolitana. In the middle of a specimen 35 cm. long 
 was an arrangement somewhat similar to the above. The part marked 
 
 ci 
 
 CM 
 
 TIT 
 
 Fig. 23. I. The case of Diopatra neapolitana (No. 96) from the side. II, the 
 same looking upon the parapodia. C I. C II, the two supernumerary cirri. 
 
 III. The case of Hermodice carunculata No. 95. Cv, cirrus of ventral branch 
 of parapodium ; Cd. dorsal cirrus ; Cv. I, Cv. II, the two cirri borne on the super- 
 numerary parapodium. (After Cobi.) 
 
 V was cut off as shewn in Fig. 23, I., it bore a normal cirrus, and 
 the other part of the segment, marked b, bore two cirri and two 
 bunches of bristles. The figure does not indicate that there was any 
 relation of images between these two parts, but this would scarcely 
 appear in this case unless specially looked for. Described afresh from 
 Com, C. J., I.e., p. 573, figs. 10 and 11. 
 
 In considering the evidence as to Secondary Symmetries reference 
 to these cases will again be made. 
 
 Generative organs of Earthworms 1 . 
 
 The number and ordinal positions of the primary and accessory 
 generative organs and of their ducts differ in the several classifi- 
 catory groups of Earthworms. In the evolution of these forms it 
 may therefore be supposed that Variation in these respects has 
 occurred. To this subject the following evidence relates. The 
 difficulty which was mentioned in the case of Variation in ver- 
 tebrae, that there is no. clear distinction between Homceotic and 
 strictly Meristic Variation, will here also be met, inasmuch as the 
 total number of segments in these forms is indeterminate ; but 
 
 1 For information and references on this subject I am indebted to Mr F. E. 
 Beddard and Mr W. B. Benham. 
 
160 MERISTIC VARIATION. [part i. 
 
 probably we shall be right in regarding the majority of these 
 variations as Homceotic. 
 
 Lumbricus. Throughout this genus there is normally a 
 single pair of ovaries, placed in the 13th segment, on the posterior 
 surface of the septum between the 12th and 13th segments. The 
 following cases of supernumerary ovaries are recorded : 
 
 97. Lumbricus turgldus : specimen having an extra pair of ovaries 
 in the 14th 1 segment. 
 
 98. Specimen having an extra ovary on the right side in the 14th 
 segment. 
 
 99. L. purpureus: specimen having an extra ovary on the left 
 side in the 14th segment. 
 
 In all these cases the extra ovaries were in size, form and 
 position like the normal ovaries. There was no extra oviduct or 
 receptaculum ovorum, but the normal ovaries and oviducts were 
 present as usual. Bergh, R. S., Zeit. f wiss. ZooL, XLiv. 1886, 
 p. 308, note. 
 
 100. Allolobophora sp. [partly = Lumbricus, the common Earth- 
 worm] : specimen having, in all, seven pairs of ovaries ; viz. a pair 
 in the 12th, 13th, 14th, 15th, 16th, 17th and 18th segments. Of 
 these all except the pair of the 13th segment are supernumerary. 
 Each of these ovaries was placed on the posterior face of a septum 
 in the usual position. The three anterior pairs in shape, structure 
 and position closely resembled the normal structures. Of these 
 the most anterior were slightly the largest. The four posterior 
 pairs were smaller and resembled the ovaries of a very young or 
 immature worm, but on examination all were found to contain 
 ova. The normal pair of oviducts were present and no extra ovi- 
 ducts could be found, though carefully sought for. Woodward, 
 M. F., P. Z. S. } 1892, p. 184, Plate xiil 
 
 •101. Lumbricus herculeus, Savigny (= L. agricola, HofTmeister), 
 having an asymmetrical arrangement of the generative organs, &c. 
 On the left side the arrangement was normal ; the ovary being in 
 the 13th segment, the oviducal opening in the 14th, and the open- 
 ing of the vas deferens in the 15th segment (Fig. 24). 
 
 On the right side each of these structures was placed in the 
 segment anterior to that in which it is normally found : the right 
 ovary was in the 12th, the external opening of the right oviduct 
 was in the 13th, and the external opening of the right vas deferens 
 was in the 14th segment. The spermathecse were normal on the 
 left side, being placed in the 9th and 10th segments, but on the 
 right side one spermatheca only was present, that of the 9th 
 segment. The vesiculse seminales were present as usual in the 
 9th and 11th segments, but there was no vesicula in the 12th 
 
 1 In Bergh's enumeration the ordinal number of these segments is one less than 
 in that commonly used : the latter system is adopted above. 
 
CHAP. VI. 
 
 ANNELIDS. 
 
 161 
 
 segment on the right side, while that of the left side was fully 
 
 Right 
 
 Left (normal) 
 
 Fig. 24. Lumbricus herculeus, having the generative organs of the right side one 
 segment higher than usual. A, external view from below. B, view of the organs 
 from above, spth, sperrnathecae ; ov, ovary; as, oesophagus ; cat, calciferous 
 glands. After Ben ham. 
 
 formed. It is remarkable that in this case, the calciferous gland 
 of the 12th segment was absent on the right side. [I am indebted 
 to Mr Benham for an opportunity of examining this specimen.] 
 Benham, W. B., Ann. & Mag. N. H., 1891, Ser. 6, VII. p. 257, 
 PI. in. 
 
 Another specimen presented the same variations as the fore- 
 going, both as regards the asymmetrical arrangement of the genital 
 pores and the absence of the calciferous gland : but in it there 
 were vesiculae seminales on the right side in segments 10 and 11, 
 but none in segment 9 ; and there was a spermatheca on the right 
 side in segments 8 and 9. [In the normal form the spermatheca? 
 are in segments 9 and 10, so that, in this individual in the matter 
 of the spermathecse as well as of the genital pores, structures were 
 formed in particular segments which are normally found one 
 segment lower down.] Bexham, W. B., in litt., March, 1891. 
 
 11 
 
 B. 
 
162 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 103. Table shewing position of ovaries in forms having two or more 
 pairs of ovaries, and in the Variations found (slightly altered from 
 M. F. Woodward, P. Z. S., 1892): 
 
 Segments 
 
 A canthodrilus 
 
 Kclipidrilus 
 
 Eudrilus 
 
 Lumbricus terrestris (normal) 
 
 L. herculeus (? = teirestris) Benham's \ 1. 
 
 2 specimens (rt. 
 
 I., turgidus Bergh's spec, (abnorm.) 
 
 do. do. do. (abnorm.)... J ' 
 
 L. purpureus do. do. (abnorm.)... J .' 
 
 AUolobophora sp. (Common Earthworm, 
 
 abnorm.) 
 
 Perionyx (two pairs, varying from 9 — 16).. 
 
 Phreodrilus 
 
 Ph reoryctes l 
 
 Vrochceta 
 
 9 
 
 10 
 
 11 
 
 12 
 
 13 
 
 14 
 
 15 
 
 
 
 
 
 X 
 
 X? 
 
 
 X 
 
 X 
 
 X 
 
 X 
 
 ! 
 
 I 
 
 X 
 X 
 
 X 
 
 X 
 X 
 X 
 X 
 X 
 
 X 
 
 X 
 
 X 
 X 
 
 
 
 
 
 X 
 
 X 
 
 X 
 
 X 
 
 16 1 17 
 
 
 
 X 
 
 X 
 X 
 X 
 
 X 
 X 
 
 
 
 18 
 
 x 
 
 104. AUolobophora sp. [</ pores normally in 15th and $ pores in 
 14th, as in common Earthworm] : specimen having on the right 
 side £ pore in 20th and % pore in 19th ; on the left side, <£ pore in 
 17th and $ pore in 16th. Michaelsen, W., Jahrb. Hamburg, 
 wiss. Anstalt, 1890, VII. p. 8. In each case the £ pore is in the 
 segment behind the % pore, as normally. The position of ovaries 
 not given. 
 
 105. Lumbricus agricola Hoffm. (= terrestris L.) : amongst 230 speci- 
 mens in which the position of the male pores are determined, 6 speci- 
 mens were found in which these openings were not normally placed (viz. 
 one on each side in the 15th segment). In two of these specimens, 
 both pores were in the 14th segment; in one case the left pore 
 was in the 14th segment and the right was in the 15th: these three 
 worms were German. One specimen was found in Savigny's collection 
 in Paris which had two pores on the left side [and none on the 
 right (?)]. In one English specimen the " vulva" [sc. the two male 
 pores] was in the 14th segment and in another it was in the 16th. 
 [The author speaks sometimes of both pores as the " vulva," and at 
 other times he uses this term for one pore only, but the meaning is 
 plainly that given above.] Hoffmeister, W., Uebersicht alter bis 
 jetzt bekannten Arten a. d. Familie Begenvnirmer, Braunschw., 1845, 
 p. 7. 
 
 1 Phreoryctes, a N. Zealand Oligochast, has 2 pairs of testes and 4 vasa deferentia 
 opening separately; 2 pairs of ovaries and 4 oviducts. Beddard, F. E., Ann. and 
 May., 1888, i. p. 339, PI. 
 
CHAP. VI.] 
 
 ANNELIDS. 
 
 163 
 
 Perionyx excavatus. In this earthworm a very remarkable 
 series of variations has been observed by Becldard. The accompany- 
 ing table shews the varieties in number of spermatheca? and position 
 of the generative openings which were found. The spermathecae 
 are generally 4, and are placed in the 7th and 8th segment, but in 
 several specimens there were 8 and their position varied from the 
 6th to the 11th segment. In all the varieties, however, they were 
 in segments adjacent to each other. In four specimens the sper- 
 mathecse were in the 8th and 9th segment on the right side and in 
 the 9th and 10th on the left. In normal specimens the male pores 
 are 2, but individuals with 4 (and perhaps 6) were found. There 
 are generally 2 pairs of ovaries and oviducts. In Var. No. 11 an 
 additional ovary was found on the right-hand side in the 11th 
 segment and in Var. No. 10 there were three pairs of ovaries. 
 
 Table of Variations seen in P. excavatus (from Beddard). 
 
 
 Spermatbecfe 
 
 ? pores 
 
 j pores 
 
 Clitellum 
 
 Normal (412 specs.) 
 
 8, 9 
 
 14 
 
 18 
 
 14—17 
 
 Var. 
 
 1 (1 spec.) 
 
 7,8 
 
 11 
 
 16 
 
 12—15 
 
 ,, 
 
 2 
 
 
 13, 14 
 
 18 
 
 
 
 3 
 
 8, 9 
 
 13, 14 
 
 17 
 
 13—17 
 
 5, 
 
 4 
 
 
 15, 16 
 
 20 
 
 
 1 J 
 
 5 (2 specs.) 
 
 8,9 
 
 14, 14 
 
 18 
 
 13—17 
 
 ,, 
 
 6 (1 spec.) 
 
 6,7 
 
 10 
 
 14,15 
 
 
 5, 
 
 n 
 
 < 11 
 
 7, 8, 9, 10 
 
 15, 16 
 
 18 
 
 
 ,) 
 
 8 
 
 
 14, 15 
 
 18 
 
 
 11 
 
 9 
 
 7,8,9 
 
 14 
 
 17 
 
 
 
 10 
 
 8, 9, 10, 11 
 
 15, 16 
 
 19 
 
 15-18 
 
 >> 
 
 11 „ . 
 
 6,7,8 
 
 13, 14 
 
 16 
 
 
 
 12 (2 specs.) 
 
 8, 9, rt. ; 9, 10, 1. 
 
 14 
 
 18 
 
 
 1) 
 
 13 
 
 8, 9, rt.; 9, 10, 1. 
 
 14, 15 
 
 18 
 
 
 >> 
 
 14 (1 spec.) 
 
 8, 9 
 
 15, 17 
 
 21 
 
 
 1) 
 
 15 
 
 
 15, 16 
 
 18 
 
 
 Though the position of both varied greatly, the male pores 
 were always posterior to the female ones. 
 
 In some specimens certain of the segments were only divided 
 from each other on one side of the body, being confluent on the 
 other. For example in Var. No. 14, segments 11 and 12 and also 
 segments 18 and 19 were only divided from each other on the left 
 side (cp. Nos. 88—91). 
 
 Out of 430 individuals 15 variations in these structures were 
 seen; of 12 of these variations single specimens only were found, 
 but two specimens occurred with each of the other three forms oi 
 variation. In a single case a nephridium was found nearer to the 
 dorsal line in one segment than in the adjacent segment. Many 
 of the conditions here occurring as variations are found normally 
 
 11—2 
 
164 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 in other genera and species. 
 1886, p. 308, figs. 
 
 Beddard, F. E., Proc. Zool. Soc, 
 
 
 A 
 
 
 _2 
 
 A. 
 
 5 
 j8 
 
 _8_ 
 
 12. 
 n_ 
 
 12 
 
 13 
 
 11 
 15 
 
 16 
 17 
 18 
 10 
 
 20 
 
 
 '^ 
 
 \-v 
 
 
 ^ 
 
 
 
 
 
 Fig. 25. Perionyx excavatus. Diagrams shewing some of the variations in 
 respect of the number and positions of the openings of the spermathecre and 
 generative pores. From Beddard, P. Z. S., 1886. 
 
 Perionyx griinewaldi, Michaelsen. Normally a pair of male 
 genital pores on the 18th segment, and a single oviducal opening 
 for the two oviducts in the middle line of the 14th segment. 
 
 107. In two specimens a different arrangement was found. One of 
 these had the oviducal opening in the 15th segment [position of male 
 openings not specified and presumably normal]. 
 
 108. The other had two oviducal openings, one in the 13th and one 
 in the 14th segment [not stated whether these openings were median 
 or lateral, nor whether each of them was a double structure as of 
 course the normal female opening is]. In this specimen the male 
 openings also were placed anteriorly to their normal position, being 
 in the 17th segment. Michaelsen, Jahrb. d. Hamburg, wiss. Anstalt, 
 1891, viii., p. 34. 
 
 Allurus. In Terricolse generally, the £ pores are on the 15th, 
 and the $ pores on the 14th, as in the common Earthworm. 
 
 109. Allurus tetraedrus, a widely distributed form, has £ pores on 
 the 13th and $ pores on the 14th, the £ pores being thus in front of 
 the ^ pores as a specific character. Under the name Allurus dubius 
 Michaelsen described two specimens having the male pores on the 
 14th instead of on the 13th, and the £ pores on the 15th instead of 
 on the 14th, each being thus one segment in advance of its normal 
 place [backward Homceosis]. Michaelsen, W., Jahrb. Hamb. wiss. 
 Anst., 1890, vie, p. 7 ; see also Arch. f. Naturg., 1892, lviii., 
 p. 251. Compare No. 111. 
 
 110. Besides these is a batch of 8 specimens of A. tetrdedrus, loc. un- 
 known, 6 specimens had both £ and $ pores in the 14th. Clitellum 
 began in 23rd, tuberc. pubert. in 24th. These specimens are thus 
 intermediate between A. hercynius, which has the pores as in Lum- 
 
CHAP. VI.] 
 
 HIRUDINEA. 
 
 165 
 
 bricus, and A. tetraedrus. Michaelsen, W., Arch. f. Naturg., 1892, 
 
 lviil, p. 251, 
 
 Allurus putris : specimen having J 1 pores on 13th (instead of 
 15th) as an abnormality; in it the other external generative organs 
 (and doubtless the internal also) were 2 segments higher than usual, 
 the J pore being on the 12th instead of 14th. Tuberc. pubert 
 26 — 28. Michaelsen, Jahrb. Hamburg, wiss. Anst., 1891, vin., 
 p. 8. Compare No. 109. 
 
 Allurus sp. : specimen having 1. side normal ; right side, £ pore 
 in 12th, % in 11th, clitellus and tuberc. pubert. one segment higher 
 than usual. Ibid. 
 
 Enchytrceid^e. J 1 pore generally in the 12th segment. In 
 Buchholzia appendicidata (Buch.) it is on the 8th, as a specific 
 character. In Pachydrilus sphagnetorum (Vejd.) it is either 
 on the 8th or on the 9th, according to individual variation, the 
 other parts being then disposed as follows : 
 
 
 cf pore on 8th 
 
 S pore on 9th 
 
 Ovaries on dissep 
 
 Vas def. in front of dissep. 
 
 c? pore 
 
 7/8 
 8/9 
 8/9 
 
 9 
 
 9/10 
 
 10 
 
 9 and \ 10 
 
 6/7 
 
 7/8 
 7/8 
 
 8 
 
 8/9 
 9 
 
 8 and \ 9 
 
 Oviduct on dissep 
 
 ? pore 
 
 Clitellum 
 
 Michaelsen, W., Arch./, mikr. Anal, 1888, xxxr. p. 493 ; see 
 also Jahrb. Hamb. wiss. Ansl, vii. p. 8. 
 
 Perichaeta hilgendorfi, n. sp. Mich. 7 specimens. Variation in number of 
 spermathecal openings, as follows. 5 specimens had 2 pairs in the groove between 
 segments 6/7 and 7/8; 1 specimen had 3 pairs, between 5/6, 6/7 and 7/8; 1 specimen 
 had only one, on the left side between 6/7, which corresponded internally to a single 
 spermatheca [other variations also observed in these specimens, q.v.]. Michaelskn, 
 W., Arch. f. Nature/., 1892, lviii. p. 236. 
 
 Perichaeta fortoesi (an Earthworm from New Guinea). In this animal a pair 
 of spermatheca? is placed in the 8th segment and another pair in the 9th. Two 
 specimens only have been examined and in both of these an additional spermatheca 
 was found on the left side, internal to the other. In one individual the 5th sperma- 
 theca was in the 8th segment, and in the other it occurred in the 9th. Beddaki>, 
 F. E., Proc. Zool. Soc, 1890, p. 65, Plate. 
 
 Aiiolobophora lissaensis. Similar variation in spermatheca 1 , Michaelsen, 
 W., Jahrb. Hamb. wiss. Anst., vin., 1891, p. 19. 
 
 HlRUDINEA. 
 
 Hirudo medicinalis. The number of pairs of testes is 
 variable, but 9 pairs most often found. Of 31 specimens of this 
 species, 21 had 9 pairs, 6 had 10 pairs, and 4 had 9 on one side 
 and 10 on the other. Chworostansky, C, Zool. Anz., 1886, 
 p. 4-AG. 
 
166 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 118. Hirudo officinalis : of 7 specimens, 5 had 9 pairs of testes, 
 
 1 had 10 pairs, and though in the 7th specimen there were 
 
 2 pairs, the vas deferens of the last pair of testes ended blindly. 
 Ibid. 
 
 119. Hirudo medicinalis, Fairly often the vas deferens is prolonged beyond the 
 9th testis, and having passed through rive annuli, ends in a glandular mass of 
 irregular form. Case given in which the 7 last testes of right side were absent or 
 only represented by amorphous material, the testes of the left side being abnormally 
 large. Ebrard, Nouv. monopr. des Sangsues vied., Paris, 1857, p. 9'.). 
 
 *120. Hirudo officinalis : an individual having a supernumerary 
 penis, and vesicula seminalis of the right side, in the 5th somite. 
 
 vs 2 
 
 Fig. 26. Case of Hirudo officinalis, No. 120. 
 
 p l , penis in normal position ; p 2 , supernumerary penis ; vs, the usual vesicula? 
 seminales ; vs' 2 , supernumerary vesicula seminalis. (From a diagram sent to me by 
 Mr Gibson.) 
 
 The normal penis in the sixth segment was fully formed and 
 into it opened on either side a vas deferens, provided with a 
 vesicula seminalis as usual. But the vesicula of the right side 
 gave off in addition a vas deferens, which passed forwards into 
 the fourth segment and there enlarged into another vesicula 
 seminalis. This additional vesicula was connected by a duct 
 with a supernumerary penis placed and opening in the middle 
 of the fifth segment. The parts of the left side as well as the 
 female organs were normal. [I have to thank Mr Gibson for 
 furnishing me with a diagram (Fig. 26) supplementing the 
 published account.] Gibson, R. J. Harvey, Nature, 1887, xxxv., 
 p. 392. 
 
 Aulastoma gulo (Horse Leech). In this form as is usual 
 among the Gnathobdellidce there are from 9 to 12 pairs of tes- 
 
chap, vi.] ANNELIDS : RECAPITULATION. 167 
 
 ticular sacs which communicate with a tortuous vas deferens 
 on each side which together enter a single penis. The paired 
 ovaries are placed behind this and the oviducts unite to form 
 a common vagina. 
 121. In a specimen found amongst a large series investigated, each 
 vas deferens opened by a separate penis, of which the most an- 
 terior opened in the 20th annulus and the posterior in the 25th. 
 The female apparatus was similarly divided. One ovary was 
 placed near the penis in the 25th annulus and from it a vagina 
 passed down to open with the penis. The other ovary, with a 
 similar vagina, lay in the 30th annulus. Asper, G., Zool. Anz., 
 1878, I, p. 297. 
 
 Recapitulation of evidence as to Oligoch^eta and Hirudinea. 
 
 Variation in these two groups appears in such similar modes 
 that points of special consequence in both may conveniently be 
 spoken of together. 
 
 1. As elsewhere seen, so here, there are forms, e.g., Perionyx 
 excavatus or Pachydrilus sphagnetorum, shewing great variability, 
 while others, the common Earthworm for instance, rarely vary. 
 
 2. Both forward and backward Homceosis may occur ; a form 
 normally having the </ pores, for instance, on the 15th segment, 
 may as an individual variation have them on the 16th (No. 105), 
 while an individual of another genus, starting from the same 
 normal, may have them on the 13th (No. 111). 
 
 3. As in other cases of Homceosis, when a member of a 
 Meristic Series, in this case a segment, develops an organ proper 
 to another segment, this organ is formed in a place serially 
 homologous with its normal place. (To this principle certain 
 limitations must hereafter be introduced.) 
 
 4. Variation may, or may not, be simultaneous and cor- 
 related in the several systems. The position of the J openings 
 for example, may or may not vary similarly and simultaneously 
 with that of the £ openings, though on the whole the evidence 
 suggests that such correlation is not uncommon. The facts seen 
 in the genus Allurus, in which one species (A. tetrdedrus) has the 
 c/ 1 pore normally in front of the $ pore, sufficiently indicate that 
 the variation in the position of these two openings is not always 
 so correlated. It may be further mentioned that variation in 
 number of ovaries seems to occur generally without correlated 
 variation in the number of oviducts. 
 
 5. Such Variation may or may not be simultaneous on the 
 two sides of the body. When not thus bilaterally symmetrical, 
 there may nevertheless be a full correlation between the parts 
 of the same side. 
 
 6. The evidence does not indicate any limit to the number 
 of segments which may take on a certain character, or approxi- 
 
168 MERISTIC VARIATION. [part i. 
 
 mate to a given pattern. The highest number of ovaries, for 
 instance, recorded, is 7 pairs ; but there is nothing to shew that 
 more segments might not undergo similar Homceosis. (The pro- 
 gressive diminution in size of these ovaries from before back- 
 wards in this case is worth noticing.) 
 
 7. The principle so often manifested in the evidence of 
 Variation, that the magnitude, completeness, and symmetry of 
 a variation bears no necessary proportion to the frequency of 
 occurrence of that variation, is here strikingly exemplified. 
 
 8. The evidence as to the existence of two varieties of 
 Paclnjdrilus sphagnetorum, the one with all the organs a segment 
 higher than their place in the other variety may be well com- 
 pared with Sherrington's observation, that in the Frog and 
 in several Mammals (see No. 70) the individuals could be 
 roughly divided into two classes according as the lumbo-sacral 
 plexus was formed more anteriorly (" preaxial class ") or more 
 posteriorly (" postaxial class "). 
 
 9. In the evidence as to Perionyx, it was seen that many 
 of the arrangements found occurred in single specimens only, 
 suggesting the inference that the systems do not fall into one 
 of these conditions more easily than into others ; nevertheless 
 of each of three abnormal arrangements two examples were found, 
 a circumstance hardly to be expected on the hypothesis of for- 
 tuitous Variation. 
 
 10. It is perhaps unnecessary to point out that the examples 
 of Variation given are in their several degrees Discontinuous, and 
 that by the nature of the case the Variation by which the several 
 specific forms have attained their particular numbers and charac- 
 teristic disposition of organs, must almost of necessity have been 
 thus Discontinuous. 
 
 Cestoda. 
 
 The following facts respecting Variation in Cestoda are chiefly 
 taken from Leuckart, Parasiten des Menschen 1 . 
 
 Besides the variations here enumerated, abnormalities of several 
 other kinds (variation in number of suckers, prismatic segments, 
 bifurcation, &c.) are known in this group, but as these do not directly 
 illustrate the Variation of Linear Series, consideration of them must 
 be deferred. 
 
 The degree to which the parts bearing sexual organs are 
 separated from each other differs greatly in the various groups 
 of Cestodes. In some (Trice nophor us) the segmentation amounts 
 to an inconsiderable constriction, while in Ligula the generative 
 organs are repeated several times in a common body. L., p. 347. 
 
 1 In what follows the letter L. is used in reference to this work. 
 
chap, vl] CESTODA. 169 
 
 122. Even in the groups whose segmentation is commonly perfect, 
 variations in the degree of separation between the proglottides 
 are not rare. It frequently happens that specimens of Tcenia 
 are found in which the external segmentation is partial, being 
 only found on half of the contour. This abnormality, which 
 does not affect the internal organs, occurs several times in the 
 same chain. Moniez, R, Bull. Sci. du Nord, x., p. 200. 
 
 123. Taenia saginata. Cases of the "intercalation" of a triangular, 
 wedge-like segment between two proglottides are recorded. In 
 such cases the generative opening is on the same side as in an 
 adjacent segment, not taking part in the alternation. L., p. 572. 
 Compare with similar phenomena in Chaetopoda (p. 156). 
 
 The evidence of abnormal repetition of parts occurring in 
 single proglottides bears on the question of the relationship of 
 the perfectly segmented forms to the less fully segmented. 
 124 Taenia saginata: a specimen 128 mm. long, wanting the 
 head, without any division into segments. The longitudinal 
 vessels were seen, but no transverse vessels were discovered. On 
 the margins were numerous genital openings, of which 41 were 
 counted, each leading from a genital organ. There was no regular 
 lateral alternation between the genital papillae, but they were 
 disposed without uniformity of pattern, and several were closely 
 approximated to each other. In no part was there any trace of 
 division into proglottides. From the characters of the genital 
 openings and from the number and size of the calcareous bodies 
 together with other histological details, the specimen was deter- 
 mined without much doubt as Taenia saginata. Grobbex, C, 
 Verh. zool.-bot. Ges. Wien, 1887, Bd. xxxvu., p. 679, fig. 
 
 Such repetition of the generative openings in single segments 
 is very common, especially in Tcenia saginata, and indeed examples 
 of it may be seen in most chains of segments. Usually such 
 repetition is confined to one segment and is not striking. Five 
 generative papillae have been seen by L. in one segment, and 
 Colin [ref. not found, W. B.] described 25 — 30 genital pores in 
 an unsegmented piece measuring 15 cm. L, p. 571. 
 
 125. Repetitions are not confined to the generative openings, but 
 the generative organs themselves are also thus abnormally re- 
 peated. In cases in which several sets of generative organs occur 
 in the same segment it is found that those near the middle of 
 the segment are the least developed. In these cases, though 
 the different organs frequently cross each other, Leuckarl Pound 
 no anastomoses between them, but the number of distinct sets 
 of generative organs was the same as the number of pores. 
 
 It was not found that the length of the segments increased 
 in the same ratio as the number of the pores they contain. I- 1 >r 
 example, a segment with two pores measured IS mm. in Length 
 
170 MERISTIC VARIATION. [parti. 
 
 [instead of about 20 mm.), and one with five pores measured 
 28 mm. (instead of 50 mm.). L., p. 571. 
 
 120. T.-rnia. < [noted by Leuckart from ELelueb of a Tan i a having generative 
 
 on the *ur/ace of the Begments. Leuckart himself has never seen 
 :ui example of this variation. [Original reference not found] L., p. 570, Note. 
 
 127. Taenia solium and T. saginata. Specimens are known 
 having two generative pores opposite each other at the same level. 
 In such cases each l<a«ls to ;i male and a female duct with cirrus- 
 Bac and receptaculum seminis; but the organs for preparing the 
 a are aormal in construction, as the two vaginae lead to a 
 ommon uterus and shell-gland. Two cases only have been seen 
 by Leuckakt and he cites another from Werner. L., pp. 529 
 
 and ">7 I . 
 
 12 s . TaDnia solium in which the pores are normally alternating, 
 may be found with symmetrically developed pores; and on the 
 contrary, T. elliptica in which they are normally symmetrical, 
 may occur with an asymmetrical arrangement. L., pp. 353 and 
 529. 
 
 [29 T. saginata: in a chain of about 6'5 metres in length, and 
 
 containing some (150 joints, there was found a single, heart- 
 Bhaped, supernumerary joint like those described; a single joint 
 was found with two genital pores, one being on each lateral border 
 about the same level. 
 The largest number of consecutive joints having the genital 
 pores on the same side was six. Tuckermax, F., Zool. Anz., xi., 
 L888, p. ( .»4. 
 
 [30 Taenia coenurus. Specimen observed by Leuckart in which 
 the last s or 10 segments shewed a transposition of the generative 
 organs, those which usually lie at the distal end being placed 
 at the proximal. This change of position was especially seen in 
 the case of organs engaged in the preparation of the ova. The 
 proximal proglottides of this individual were normal. The trans- 
 ition segment between these two regions contained two simple 
 vesiculae Beminales and two marginal papillae which were on 
 opposite Bides; but in spite of the resemblance of these structures 
 to genital pores, neither opening, nor cirrus, nor vasa deferentia 
 could be distinguished. L., p. 504. 
 
 131. A.mongst chains of normal proglottides it is not rare to find 
 a segment containing male organs only. L., p. 504. 
 
 Speaking generally, slight abnormalities are far more common 
 than great ones. Nearly every specimen of Tapeworm has in- 
 dividual peculiarities, and these generally repeat themselves in 
 the same chain of proglottides. This repetition of the same 
 abnormality in different parts of the chain is also the rule for 
 the greater abnormalities also. L.. pp. 529, 572 and 573. 
 
CHAPTER VII. 
 
 linear series — continued. 
 
 BRANCHIAL OPENINGS OF CHORDATA AND STRUCTURES IN 
 
 CONNEXION WITH THEM. 
 
 Under the general heading of Variation of branchial openings 
 facts will be given relating to the following subjects. 
 
 I. Variation in the patterns formed by the bars, vessels and 
 stigmata of the branchial sac in Ascidians. 
 
 II. Variation in the number of gill-sacs in Cyclostomi. 
 
 III. Abnormal openings in the cervical region of Mammals, 
 known as " cervical fistula 3 ," and external appendages called " cer- 
 vical auricles," or " supernumerary ears," present sometimes in 
 connexion with such openings. 
 
 With reference to the two first subjects the evidence is only 
 fragmentary, but the instances recorded seem to be of sufficient 
 consequence to warrant their introduction in illustration especially 
 of the magnitude and definiteness of Variation. 
 
 Variations affecting the opercular opening in Amphibia are mentioned in 
 connexion with Bilateral Series. 
 
 I. Ascidians. 
 
 Transverse vessels of Branchial Sac. 
 
 132. Ascidia scabra. Branchial sac in one specimen shewing abnormal 
 and irregular structure owing to branching of transverse vessels. The 
 resulting appearance is entirely peculiar. Herdmax, W. A., J. Linn. 
 Soc. (Zool.), 1881, xv., p. 284, PI. xvii., fig. 3; also p. 330. 
 
 133. Ascidia virginea (O. F. Miiller): a case of great irregularity 
 exactly similar to the above. Ibid., p. 330. 
 
 134. Ctenicella lanceplani. Branchial sac may present characters due 
 to variations in disposition of transverse vessels etc., which assume three 
 distinct patterns or marked varieties. Lacaze-Duthieks, Arch, Zool. 
 Exp., S. 1, Vol. vi., p. 619, Vol. xxxiii., rigs. 9 — 11. 
 
172 MKIMSTIO VARIATION. [part i. 
 
 '13"). Ascidia plebeia (Alder): branchial sac has very characteristic 
 appearance and Lb very constant in the size of meshes, papillae &c. 
 One point La liable to variation: as a rule the transverse vessels are of 
 the same calibre, but in several specimens every fourth vessel is much 
 wider than the intervening three. Herdmax, p. 331. 
 
 Stiqmata and Meshes. 
 
 136. Ciona intestinalis : meshes vary but according to no apparent 
 method: 5 Btigmata in ;i mesb normal; 4 and G met with frequently; 
 10 the utmost seen. Herdman, p. 332. 
 
 1 ;> >7. Ascidia aspersa. In typical specimens, transverse vessels all same 
 size, the meshes being square and undivided, but individuals occur in 
 which many (not all) of these square meshes are divided by delicate 
 transverse vessels into pairs of oblong areas. Herdmax, p. 332. 
 
 L38. Styela grossularia. The genus Styela is characterized by the 
 presence of branchial folds, normally four on each side, but in this 
 3pecies the folds are almost obsolete, being entirely wanting on the 
 left side and reduced to a single slight inward bulging on the right 
 side, bearing internal longitudinal bars. This fold is separated from 
 the dorsal lamina by a broad space without internal longitudinal bars. 
 A similar wide space is present on the left side of the dorsal lamina, 
 and two others on the vertebral edcje of the sac, one on each side of the 
 endostyle. These spaces vary in size in individuals. They commonly 
 contain 1G stigmata, but numbers down to 12 were frequent and in one 
 case 10 only were present: only once more than 16 observed, and in 
 that case tliere were 28. Number of internal longitudinal bars on fold 
 varies from 6 to 9, generally 8 or 9. Herdmax, p. 330. 
 
 Id considering the significance of these cases with reference to 
 the origin of Species it is to be remembered that the characters of 
 the branchial sac, the sizes of the transverse vessels, shape of 
 meshes and the number of stigmata they contain are held to be of 
 the first importance for the classification of Ascidians; but Herd- 
 man finds that while they are highly characteristic in some species 
 they are qoI so in others 1 . 
 
 II. Cyclostomi. 
 
 L39. Myxine glutinosa. In this genus there are normally six 
 pairs of branchial pouches. I am indebted to Professor Weldon 
 for an account of a specimen dissected by him in which there were 
 seven pairs of these pouches. On the left side all the seven 
 pouches were distinct and separate, each having a separate open- 
 
 1 The olfactory tubercle in Ascidians may have a different form and position in 
 different individuals of the same species, but the range of variation changes 
 according to the species. Molgula was found to be the most constant, Ascidia 
 virginea and A. plebeia the most variable forms. Herdman, Pwc. R. Phys. Soc. 
 Edin., vi., p. 267, figs.; also id., Proe. Lit. Phil. Soc. Liverpool, xxxvm. p. 313, 
 Pis. i. and ii. Variation respecting the atrial pore will be considered in connexion 
 with Bilateral Repetition. 
 
CHAP. VII.] 
 
 CYCLOSTOMT. 
 
 173 
 
 ing from the oesophagus and a separate aortic arch supplying it. 
 On the right side the sixth and seventh pouches were practically 
 
 * 
 
 r D asu 
 
 Fig. 27- Myxine glutinosa ; specimen having seven pairs of branchial sac-. 
 Diagram shewing branchial sacs, heart and aortic arches from the dorsal surface. 
 On the right side the sixth and seventh branchial sacs were partially confluent. 
 
 D. oes., ductus cesopJiageus. 
 
 (From a drawing kindly lent by Prof. Weldon.) 
 
 confluent though each had a separate oesophageal opening and a 
 separate arch from the aorta. In the drawing, for which I am also 
 indebted to Professor Weldon, the oesophageal openings are not 
 shewn. 
 40. Bdellostoma. In this genus the number of branchial sacs is 
 variable, different numbers being found in different species and 
 individual variation also occurring. 
 
 The generic name Heptatrema was originally given by Dum£ril 
 from the presence of seven gill-sacs. In 1834 Joh. MtJLLER, finding 
 that this character is not constant proposed the name Bdellostoma. 
 Of three Cape specimens examined by him one had seven gill-sacs 
 on each side, one had six on each side, and one had six on the right 
 side and seven on the left. To these he gave the names B. hepta- 
 trema, B. hexatrema and B. heterotrema respectively (Abh. k. Ah 
 Wiss. Berlin, 1834, pp. 66, 67 and 79, Taf. VII.). Further observa- 
 tion has shewn that the number of gill-sacs in the Cape Bdello- 
 stoma is liable to individual variation, some specimens having six 
 while others have seven. The name B. cirrhatum (GtJNTHER, Gat. 
 Brit Mus., viii. 1870, p. 511) includes these and the New Zealand 
 specimens. As to the relative frequency of specimens with six or 
 seven pairs or with an asymmetrical arrangement I have no in- 
 formation. A collection lately brought from the Cape by Sedgwick 
 includes one specimen with six pairs and several with seven pairs. 
 
174 MEKISTIC VARIATION. [part i. 
 
 141. B. polytrema : single specimen from Chili, badly preserved 
 but apparently having fourteen pairs of gill-openings. GuNTHEJt 
 I. c, p. 512. 
 
 Specimen having 14 gill-openings on left side and 13 on right. 
 Sciinkii.ki:. A., Arch. f. iWaturg., xnvi. 1S80, p. 115 (cp. Putnam, 
 Proc. Bost X. 11. &, xvi. L873, p. 1G0). 
 
 /;. bischoffii: single specimen, 10 gill-openings on each side. 
 ibid. 
 
 Ammoccetes : having eighl branchial openings on each side instead 
 of Beven, the normal number. The shape of the mouth of this specimen 
 was also abnormal, being described as somewhat square. [No satis- 
 factory description.] Eowabo, Thomas, Zoologist, xvi., p. 60D7. 
 
 142. In connexion with individual Variation in the number of gill- 
 sacs in Myxinoids it should be borne in mind that in Petro- 
 myzon there are normally seven pairs of gill-sacs. The case of the 
 Notidanidse may also be mentioned in this connexion. Among 
 Selachians the Notidanidse are peculiar in having a number of gill- 
 slits other than rive, and of them liexanchits has six pairs, while 
 Heptanchus has seven 1 . 
 
 III. Cervical Fistula and Supernumerary Auricles ix 
 Mammals. 
 
 Though the evidence of this subject is well known and has 
 often been collected, it may be convenient to give here some 
 abstract of the facts in so far as the phenomena of Variation are 
 illustrated by them. Since cervical fistula? have been believed to 
 result from the persistence of the embryonic branchial clefts, they 
 may properly be considered in relation to the general question of 
 Variation in the number of gill-slits, while the development of 
 external appendages, perhaps serially homologous with the external 
 ears, directly concerns the subject of Meristic Variation. 
 Man. The subject has been studied by many observers, espe- 
 cially by Aschersox 2 , and by Heusixger 3 , who brought together 
 and abstracted 4(i cases, being all that had been described in Man 
 up to LS(j4. G. Fischer 4 gives a full list of the literature of the 
 subject up to 1870, with an analysis of 65 cases. A further paper 
 by Heusixger 5 contains a general account of these structures as 
 they are found in Man and in the domestic animals. Additional 
 cases, together with a general discussion of the subject, especially 
 in relation to fistula? on the external ears, were given by Sir James 
 
 1 Balanoglossus. In five species with which I am acquainted, the number 
 of pill-bars and slits varies in proportion to the size of the body, and as it is not 
 unlikely that these animals continue to grow throughout life, it is probable that the 
 number of branchiae is always increasing by formation of new gill-slits at the 
 posterior end of the branchial region. The same is probably true of Amphioxus. 
 
 2 Ascherson, BefistulU colli congenitis, Berlin, 1832. 
 
 3 Heusinger, Anh. f. Path. Anat. u. Phys., 1864, xxix. 
 
 4 Fischer, G., Dent. Ztsch.f. Chirurg., 1873. 
 8 Heusinger, Deut. Ztsch. f. Thierm., 1878. 
 
* 
 
 chap, vil] CERVICAL FISTULA. 175 
 
 Paget 1 in 1878. Lastly, the whole evidence as to cervical fistulas 
 and the structures associated with them has been fully collected 
 up to 1889 and tabulated by Kostanecki and Mielecki-, who 
 also discuss in detail the relations of these abnormalities to the 
 facts of development. The following account is taken from these 
 sources. For figures the reader is referred to the original memoirs. 
 
 143. Cervical fistuke are generally known as orifices placed in the region 
 of the neck, leading into a sinus of greater or less extent, varying in 
 size from a mere pit to a duct some inches in length. In the greater 
 number of cases the sinus ends blindly, but in about a third of recorded 
 cases (K. and M.) it passes inwards to open into the pharynx, forming 
 thus a communication between the pharyngeal cavity and the exterior. 
 Such passages are spoken of as complete cervical fistulas, those which 
 have an external but no internal opening being external incomplete 
 fistuke. Besides these there are cases of diverticula from the pharynx 
 or oesophagus which do not reach the exterior, and these are known as 
 internal incomplete fistula?. 
 
 Cervical fistuke are more commonly present on one side only, but 
 in a good many cases they have occurred on both sides. According to 
 Fischer they are more common on the right side than on the left. 
 The following statistics are given by him. 65 persons had 79 fistuke : 
 51 unilateral, 14 bilateral: 20 complete, 53 without an opening to the 
 pharynx: of the unilateral cases 33 were on the right and 13 on the 
 left : 34 in males, 30 in females. There was evidence of heredity in 
 21 cases. 
 
 The external opening is very small and may either be on the 
 surface of the skin or elevated on a minute papilla. Sometimes it is 
 covered by a small flap of skin as with a valve, in other cases it is 
 placed as a fissure between two lips. The positions in which the ex- 
 ternal openings of cervical fistula? are found are very variable, but in 
 the great majority of cases the opening is close to the middle line 
 in the neighbourhood of the sterno-clavicular articulation, generally 
 from a few lines to an inch above it, on either the inner or the outer 
 border of the sterno-cleido-mastoid muscle. In rarer cases the external 
 opening is placed at the level of the middle of the cricoid cartilage, and 
 is sometimes just behind the angle of the jaw. These positions are not 
 however at all precisely maintained, but vary a good deal in different 
 cases. When the external opening is in the higher situation and the 
 fistula is complete, a sound may then be passed into the pharynx, but 
 when the external opening is low, the duct when present passes 
 upwards covered by skin only, in a straight line so far as the upper 
 limit of the larynx, at which point it turns at a sharp angle upwards 
 and inwards. For this reason it is not possible in such cases to follow 
 the course to the pharynx by means of a sound, but in some of them 
 the presence of an internal opening has been proved by the injection of 
 fluids having colour or taste. The position of the internal openings is 
 also variable, and from the nature of the case has been accurately 
 
 1 Paget, Sir J., Trans. Med. Ghir. Soc, lxi., 1878. 
 
 - Von Kostanecki und Yon Mielecki, Arch. f. path. Anat. u. Phys., cxx. 
 and csxi. 
 
176 MEIilSTIC VARIATION. [part i. 
 
 determined in comparatively few instances. In a case dissected by 
 Neuhopek 1 there was a fistula on each side, the external opening 
 of the right was \ in. from the middle line and 7 lines above the 
 clavicle, that of the left was 3 — 4 lines higher and further from the 
 middle line. The right internal opening was on the posterior border of 
 the pharyngo-palatine muscle, behind the cornu of the hyoid near the 
 tonsil, tin- left internal opening being rather higher than the right. 
 Internal openings ol such fistulas have also been seen on the edge of 
 the areas pharyngo-palatinus, also in the neighbourhood of the root of 
 the tongue. Seidel 9 gives a case in which there were two fistulas, the 
 one on the right side in the upper position, and the other in the middle 
 line at about the same level, but whether either of these communicated 
 with the pharynx could not be made out. The twin-brother of the 
 -ante infant had a single minute fistula. 
 
 The ducts of cervical fistulas are usually of greater calibre than the 
 external openings but they are rarely wider than a fine quill. The 
 walls are tough and the lining epithelium is sometimes flat and some- 
 times ciliated. The degree to which the walls are sensitive differs in 
 different cases. The external opening is described in several instances 
 as having a reddish colour. In three cases of the presence of branchial 
 fistulas in female patients, it is recorded that the external openings 
 became inflamed during the menstrual periods. 
 
 From the point of view of the naturalist the chief interest of 
 cervical fistula? arises in connexion with the question of their mor- 
 phology. Since the time of Ascherson the view has been commonly 
 accepted that these structures arise by persistence of embryonic gill- 
 clefts, and some of the recent writers 3 on the subject have gone so far 
 as to apportion the various forms of cervical fistula? among the several 
 gill-clefts from the first to the fourth, according to the situations of 
 the external openings, giving diagrams shewing the regions occupied by 
 each. As Kostanecki and Mielecki point out, this apportionment is 
 quite arbitrary; for in the development of the neck the external in- 
 vaginations for all the clefts behind the hyoid arch become included in 
 the sinus cervicalis of Rabl (sinus pra?cervicalis of His), which is 
 eventually closed by the growth of the opercular process from the 
 hyoid arch. The external opening of a cervical fistula may thus 
 represent a part of the sinus cervicalis still left open, but it cannot on 
 the ground of its position be referred to any gill-cleft in particular. 
 ►Such reference could only be properly made on the ground of the 
 position of the internal opening and the course of the duct in relation 
 to structures whose relation to the visceral clefts is known. More- 
 over owing to the way in w r hich the 3rd and 4th clefts are shifted 
 inwards by the formation of the sinus cervicalis, Kostanecki and 
 .Mielecki consider that they are practically excluded. The same 
 authors after an analysis of the cases in which the position of the 
 internal opening has been properly ascertained, come to the conclusion 
 that in all these it falls within the region of the 2nd visceral sac 
 
 1 Neuhofer, M., Ueb. d. angeb. Hatefistel, Inaug. Diss., Munich, 1847. 
 
 2 Seidel, J., Defist. colli cungen., Inaug. Diss., Breslau, 1863. 
 
 3 Sutton, J.Bland, Lancet, 1888, p. 308; Cusset, Et ude sur Vappareil branchial, 
 &c, Paris, 1887. 
 
chap, vii.] CERVICAL AURICLES. 177 
 
 (hyo-branchial). Besides they point out that the evidence in the few 
 cases in which the course of the duct has been traced, shewed that it 
 passed between the external and internal carotids. In their judgment, 
 therefore, cervical listuhe are all to be referred to the second (hyo-bran- 
 chial) cleft. 
 
 Next it is to be remembered that according to many observers 
 (especially His) there is at no period a complete connexion between the 
 outer gill-clefts and the evagination from the pharynx or branchial 
 sacs, but the membrane separating these chambers is stated by them 
 never to be broken down. If this account is accepted, it is, as 
 Kostanecki and Mielecki have said, necessary to suppose that in the 
 case of any complete cervical fistula a communication between the 
 exterior and the pharynx has arisen by some abnormal occurrence. 
 This is illustrated by reference to the normal condition of the first or 
 hyo-mandibular cleft. Here the auditory meatus represents an external 
 incomplete fistula, and the Eustachian tube an internal incomplete 
 fistula, the two being separated by the tympanic membrane. In a 
 single case given by Virchow 1 a complete passage existed congenitally 
 in this position, together with great abnormality in position and forin 
 of the external ear. 
 
 From the evidence it may thus on the whole be concluded that 
 incomplete external fistula? result from imperfect closure of the sinus 
 cervicalis, and that incomplete internal fistula? may arise by persistence 
 of one of the branchial sacs, but it is doubtful whether many cases of 
 the latter properly belong to the category of branchial fistula? at all. 
 
 Supernumerary A iwicles. 
 
 144. Abnormal appendages attached to the neck have been described by 
 several observers, and by those who have discussed the subject of 
 cervical fistula? some account of these appendages is generally given. 
 In the neighbourhood of the external ears, especially near the anti- 
 tragus, such structures having the form of small warts or flaps of skin 
 are not very uncommon. Their presence is generally associated with 
 deformity of the external ear, and often with what are known as 
 "aural fistula? 2 ." In the region of the neck, supernumerary auricles 
 
 1 Virchow, Arch. path. Anat. u. Phys.. 1865, xxxn. 
 
 2 Aural fistulae are spoken of by many writers as being of the same nature as 
 cervical or branchial fistulae. Tbey are blind ducts or pits, opening on some part 
 of the external ear and are nearly always associated with other abnormalities either 
 in the form of the ear or defective hearing, <fcc. (Schmitz, De fist, colli congen., 
 Inaug. Diss., Halle, 1873 [not seen, W. B.]; Urbaxtschitsch, MonaUch. f. Ohrenh., 
 1877, transl. Edin. Med. Jour., xxiii. 1878, p. 690.) They may be either unilateral 
 or on both sides of the body. Sir James Paget (Trans. Med. Ghir. Soc, lxi., p. 41) 
 described the occurrence of such fistulae in the ears of several members of a family, 
 many of whom were affected with deafness. The supposed connexion of ti 
 fistulae with cervical fistulae was in this case suggested by the fact that several cases 
 of actual cervical fistula occurred in the same family, several of its members having 
 both cervical and aural fistulae. From the evidence of the not infrequent association 
 of the two kinds of malformation most writers (Paget, Urbaxtschitsch. &o.) con- 
 sider that the aural fistulae must be bianchial in origin and may be taken to 
 represent the first (hyo-mandibular) cleft. 
 
 Kostanecki and Mielecki [1. c), following His, point out that Bince in 
 no case has an aural fistula ever been known to communicate with the auditory 
 meatus or tympanic cavity, this belief is unsupported; and in addition, that from 
 the mode of development of the external ear from a number of tubercles, it is 
 
 B. 12 
 
178 
 
 M ERISTIC VARIATION. 
 
 [part I. 
 
 are much rarer, but in several instances they have attained a considerable 
 development. Of this class of variation the following well-known case 
 is one of the most remarkable. 
 
 145. A healthy female infant was brought to Guy's Hospital in 1851 on account of 
 two projecting growths about the middle of the lateral cervical regions. The 
 growths were not removed until February 1858, when they were found to have 
 increased slightly. Tiny were situated over about the centre of the sterno-cleido- 
 mastoid muscles. To the touch they resembled the tissue of the lobe of the auricle, 
 and they contained within them a firm resisting nucleus like the cartilage of the 
 same organ. They were also covered with peculiarly delicate, soft, downy hairs, 
 like the lobe of the ear. They were excised without difficulty. Each was supplied 
 with a small artery. They appeared to be intimately associated with the fibres of 
 the platysma myoides, not dipping deeper than this structure, and to be entirely 
 cutaneous appendages. (Fig. 28.) 
 
 Fig. 28. Child having a well-developed supernumerary auricle on each side of 
 the neck (from Berkett). 
 
 A vertical section was made in the long axis of each growth; and the tissues of 
 the lobe and of the fibro-cartilage of the auricle were clearly distinguished. The 
 shape of the fibro-cartilage resembled more or less closely in parts, the outline of 
 the proper auricle, and its tissues were the same. Jjirkett, J., Trans. Path. Soc. 
 Loud., ix., 1858, p. 448, fig. 1 . 
 
 sufficient to suppose that aural fistula? arise by the imperfect union of these tubercles. 
 The fact, however, that these various defects in development of the branchial 
 apparatus and its derivatives are frequently associated together is well established. 
 As indicating the frequency of association with disease of the ear, Urbantschitsch 
 mentions that in 2000 aural cases, 12 instances of aural fistula? were seen. The 
 same author gives a remarkable case of the occurrence of aural fistula on the right 
 side only in many members of the same family with other important particulars (/. c). 
 1 In Lancet, 1858, n. p. 309 (quoting Harvey), and in a paper by Virchow 
 (quoting Wilde), Arch. path. Anat. Phys. t 1804, xxx. p. 225, reference is made to a 
 case of Cassebohm, Tract, sextus, de aure momtri hum., Norimb., 1084, pp. 30 
 et scqq., describing a child with "four ears." On referring to the original however 
 it appears that this was merely a double monster, having two incomplete heads, 
 and thus bears no analogy with the present examples. 
 
chap, vii.] CERVICAL AURICLES. 179 
 
 Several cases analogous to the above, though differing in the extent 
 of the development, are on record '. Kostanecki and MlELECKl (I. c), 
 who give references to the literature of the subject, consider together 
 with Virciiow and others, that there is no doubt that these super- 
 numerary auricles may properly be regarded as "heterotopic" partial 
 repetitions of the external ears. According to a view which has been 
 held by the majority of writers- on the subject, and which is in part 
 alternative to that given above, it is suggested that the cartilages 
 contained in these appendages are in reality parts of one or other of the 
 usually undeveloped branchial arches behind the hyoid. As against 
 this suggestion it is to be remembered that in the subsequent develop- 
 ment of the neck these arches are pushed in far from the surface, whereas 
 the cartilages in question are always superficial. The usual histology 
 of these bodies is in favour of the view that they are repetitions of the 
 ear-cartilages, but on the other hand a specimen of cervical auricle 
 in Mus. Coll. Surg. (No. 373, c) contains not only cartilage but also 
 a small bone of convplex form. But whether or not any part of such 
 cervical auricles truly represents any part of the gill-bars, it is clear 
 that these external projections having the structure of the ear, con- 
 sidered from the point of view of Variation must be regarded as partial 
 repetitions of the ears, and there is a considerable probability that they 
 stand to the sinus cervicalis in a relation similar to that which the 
 normal external ear bears to the hyo-mandibular cleft, being according 
 to the terminology here proposed, examples of repetition by forward 
 Homceosis. 
 
 In this connexion the question of correlation between supernume- 
 rary auricles of the neck and cervical fistuhe is especially important. 
 If it is true that such auricles are repetitions of the ears, it might, on 
 the analogy of other cases of repetition, be expected that they would 
 usually be found bounding the external openings of tistuhe. As a 
 matter of fact they have several times been found in such a position, but 
 the connexion between these two variations is by no means a close one, 
 for cervical fistula? are not as a rule accompanied by cervical auricles, 
 nor are cervical auricles generally associated with cervical fistula', such 
 collocation being mi the whole exceptional. It should also be men- 
 tioned that in a few cases small cartilaginous or bony structures have 
 been found imbedded in the neighbourhood of cervical fistula 1 , but that 
 similar structures have also occurred independently of any fistula". 
 
 In many domestic animals both cervical fistula' and auricles art- 
 well known and have been described by Heusinger 3 from whom the 
 following account is chiefly taken. 
 146. Pig- Cervical auricles are not uncommon and have been referred 
 
 1 A figure is given by Sutton, J. B., in III. Med. Xnr.<, 1880 (repeated in 
 "Evolution and Disease," by the same author 1890, p. 83), representing a large 
 supernumerary auricle on the right side of the neck of a girl. The structure 
 is represented as helicoid in form, closely resembling the normal ear. It i< 
 unfortunate that no description of this specimen is given: in the absence of such 
 •description this quite unprecedented case cannot be accepted without reserve. 
 
 2 Dermoids of many kinds occurring in the cervical region of Man and other 
 animals are by many writers considered to arise by modification of tissues occluded 
 from the walls of the branchial clefts. 
 
 3 Heusinger, Deut. Arch. f. Thiermed., 1876, n. 
 
 i — — *j 
 
180 MERISTK VARIATION. [part I. 
 
 to as distinguishing particular local breeds. They are generally paired 
 structures. The following case is exceptional in the fact that the 
 auricle was present on the left only, and that it was associated with an 
 opening possibly of a cervical fistula. A pig having a single appendage 
 about 7 t-ni. long attached under the lower jaw on the left, is described 
 by Eudes-Deslono(H ami's ! . It contained a stalk of cartilage stated 
 to have resembled the cartilage of the ear. To this on either side was 
 attached a small muscle. Unfortunately the appendage had been cut 
 off close to the skin. A small opening (pertuis) was present on the 
 skin near the appendage, and from this opening a small brush or tuft of 
 bristles protruded. 
 
 Fistula? in the neck of swine are well known as giving rise to 
 a tlisease called weisse Borste in Germany (Fr. la Soie or poil pique) 
 from the fact that certain white bristles are found at the opening of the 
 duct. In the popular fancy it is supposed that the bristles themselves 
 In. re the perforation, but according to Zundel" they are congenital and 
 often bilateral. Heusinger agrees with Ziindel in regarding such open- 
 ings as branchial fistula?. 
 
 147. Sheep and Goats. Cervical fistula unknown, but appendages on the neck 
 ' common. The Bheep of the "Wilster marshes are described 3 as having the neck bare 
 of wool, and an appearance as of a fur-collar. Above the collar and below the 
 pharynx they have a pair of appendages about the size of an acorn. Such ap- 
 pendages are said to be not uncommon in Merinos 4 . Among the Kalmuck and 
 Kirghiz sheep and goats such auricles are said by Pallas 5 to be common. In many 
 foreign races of goats these auricles seem to be a constant character. In position 
 they may vary from the angle of the jaw to the middle of the neck. The length is 
 usually about 3 in. but they are recorded as reaching 15 cm. Figures of goats 
 having such auricles are given by Sutton 6 . The anatomy of one of these bodies is 
 described by Goubaux 7 , and it is mentioned that a plate of cartilage was found in the 
 interior. A similar cartilage was found by Stewart 8 together with striped muscular 
 fibre. Goubaux gives a case of two she-goats on a farm, one having cervical 
 appendages, the other having none. Each gave birth to a pair of kids at the same 
 time. Each pair was a male and female, and in the one the male only had the 
 appendages and in the other the female only. The characters of the father of these 
 kids were not known. 
 
 Ox. Neither cervical fistula} nor auricles known. 
 
 ]4 t sj Horse. Cervical auricles unknown. Fistuhe (in the position considered by 
 Heusinger to indicate the first branchial cleft) are common and are recognized by 
 their action in soiling the hair near the external opening. 
 
 Recapitulation. The evidence as a whole goes to shew that 
 structures, sometimes of large size, having several essential features 
 of the external ear, that may in fact be fairly spoken of as repeti- 
 tions of the ear. may by Homoeotic Variation appear on the neck of 
 Man and other animals : further, that these repetitions have been 
 known to occur at the openings of cervical fistulas, suggesting a 
 comparison with the relation of the external ear to the hyo-mandi- 
 bular cleft, but that such a relation to cervical fistulae is exceptional. 
 
 1 .1/////. Soc. Linn, de Norm., 1842, vn. p. 41, PL iv. fig. 3. 
 - Dent. Arch.f. Thierm., i. 1875, p. 175. 
 
 3 Viborg, Samtl. Vet.-Afhandl., i. p. 14S [Heusinger]. 
 
 4 Schmalz, Thierveredlungskunde, p. 223 [Heusinger]. 
 
 5 Spicileg. Z<><>1.. xi. p. 172 (two figures). 
 
 6 Sutton, J. 13., Evolution and Disease, pp. 84 and 85. 
 
 7 Goubaux, Bee. de Med. Veter., Ser. 3, ix. p. 335. 
 
 8 Figured by Sutton, I.e., p. 87. 
 
CHAPTER VIII 
 linear series — continued. MAMMAE. 
 
 Some of the phenomena of Meristic Variation are well seen in 
 the case of mammae 1 , and especially in the modes by which increase 
 in the number of these organs takes place. 
 
 The facts regarding these variations in Man have so often been 
 collected that it is scarcely necessary to detail them again. For 
 our present purposes it will be sufficient to give a recapitulation 
 of the chief observations in so far as they illustrate the pheno- 
 mena of Variation. 
 
 The most important collections of the evidence on this subject 
 are those of Puech 2 , Leichtexstern 3 , and Williams 4 , from whose 
 papers references to all cases recorded up to 1890 maybe obtained. 
 Besides these, Bruce 5 has given a valuable account of a consider- 
 able number of new cases together with measurements and statis- 
 tical particulars. These accounts contain almost all that is known 
 on the subject but additional reference will be made to original 
 authorities in a few special cases. 
 
 In Man supernumerary mammae or nipples nearly always occur 
 on the front of the trunk, being usually placed at points on two 
 imaginary lines drawn from the normal nipples, converging in the 
 direction of the pubes. These lines may thus be spoken of as the 
 :t Mammary lines." It is with reference to supernumerary ma mm* 
 occurring on these lines that the subject of mammary variations is 
 chiefly important to the study of Meristic Variation. In addition 
 to these, however, there are a few well authenticated examples .if 
 mammae placed in parts of the body other than the mammary Lines 
 and of these some mention must be made hereafter. 
 
 1 It will be understood that facts as to variations consisting in absence of 
 mammae or nipples and other such changes do not come within the scope of this 
 volume, but belong rather to the province of Substantive Variation. 
 
 2 Puech, Lea Mamelles et leurs anomalies, Paris, 187<>. 
 
 3 Leichtensterx, Virch. Arch.f.patk. Anat. u. Pin/*., 1878, i.xxin. p. 222. This 
 collection was apparently made independently from that of Puech. 
 
 4 Williams, W. Roger, Jour. Anat. Phys., 1891, xxv. p. 22-"). 
 
 5 Bhuce, J. Mitchell, Jour. Anat. Plnja., lsTK, xin. p. 425. 
 
182 MERIST1C VARIATION. [part i. 
 
 In the great majority of cases (over 90 per cent., Leichten- 
 STERN l ) of mammae placed on the mammary lines, the supernumer- 
 ary structures are below the normal ones, being then as a rule in- 
 ternal to them, while those found above the normal mammae are 
 less common and are external to the normal mammae. The di- 
 stance separating the normal from the supernumerary mammae 
 (lifters greatly in different cases, and most conditions have been 
 - 11 intermediate between a stage in which the nipple is bifid, and 
 that in which completely separate supernumerary mammae are pre- 
 sented. It is of consequence to observe that there appears to be 
 no case in which a supernumerary mamma is so large as the nor- 
 mal mamma of the same individual. 
 
 The degree to which supernumerary structures of this nature 
 are developed is very various. They may be fully formed mammae 
 with nipples, in the female capable of function ; while in other 
 cases, on the contrary, they may either consist of nipples only, 
 having no distinguished glandular tissue of mammary character in 
 connexion with them, or they may be tumours of mammary cha- 
 racter without nipples or even definite ducts. Between these 
 >Mveral conditions there is no sharp distinction. It appears there- 
 fore that there are two rudimentary or imperfect conditions possi- 
 ble : either supernumerary nipples without recognizable mammary 
 glands, shading off into small warty elevations of uncertain charac- 
 ter, and on the other hand redundant portions of mammary gland 
 without nipples. The latter may be partially connected w r ith the 
 normal mammae or quite separate from them. All these states of 
 imperfection are much more common than the complete super- 
 numerary mammae. 
 
 Fully formed supernumerary mammae have been found above 
 the normal mammae and also below them, the latter being the 
 more frequent position. For those found on the mammary lines 
 the axilla is the highest position and the upper part of the abdo- 
 minal wall the lowest. Of the rudimentary forms, the mammary 
 tumours without nipples occur usually if not always above and ex- 
 ternal to the normal mammae, being generally in or near the axilla. 
 The supernumerary nipples however are in the great majority of 
 cases below and internal to the normal ones. 
 
 Small supernumerary nipples are quite common in Man, but 
 the statistics of different observers £ive various results. Bruce 
 found in 2311 females 14 cases ('605 per cent.), and in 1645 males 
 47 cases (2"857 per cent.). These persons were patients at the 
 Brompton Hospital for Consumption and were not specially ex- 
 amined with a view to this inquiry. Among 315 such persons 
 examined for the purposes of these statistics, 24 cases were seen 
 (7'6 per cent.), 1 being male and 5 female. In 8 cases two extra 
 nipples were present, and one doubtful case of three extra nipples 
 
 1 Not including mammary tumours without nipples in the axilke. 
 
CHAP. VIII.] 
 
 MAMMAE. 
 
 183 
 
 was seen. Bruce regards 7*6 as for various reasons rather too hio-h 
 
 o o 
 
 a proportion. In a recent paper Bardelebex however states that 
 among 2736 recruits examined with regard to supernumerary nip- 
 ples, 637 cases (23'3 per cent.) were seen, 219 being on right side 
 248 on left side, and 170 on both sides. The discrepancy between 
 these statistics no doubt arises through want of agreement as to 
 the inclusion of cases in which the extra nipples are very rudimen- 
 tary. 
 
 It seems to be clearly shewn that the abnormality is commoner 
 in men than in women, and there is some evidence that it is more 
 frequent on the left side than on the right (Bruce, Leichtex- 
 sterx and Bardelebex). It is also well established that super- 
 numerary nipples are much more commonly present as single than 
 as paired structures, and that when paired they are by no means 
 always at the same level on the two sides. Cases of the presence 
 of supernumerary mamma? as paired structures symmetrically 
 placed are nevertheless sufficiently numerous. Organs of this na- 
 ture may also occur simultaneously on the same side of the bod}* 
 at different levels. For example in one of Leichtexsterx's cases, 
 a small secreting supernumerary mamma with a nipple was pre- 
 sent in the left axilla, while there was also another supernumerary 
 nipple on the lower border of the left breast. The greatest num- 
 ber of supernumerary nipples occurred in a case described by Neu- 
 GEBAUER 1 , represented in Fig. 29. In this patient there were on 
 each side three supernumerary nipples above the normal ones, and 
 
 Fig. 20. Diagram of a case of four pairs of supernumerary nipples in human 
 female. The normal breasts raised to shew the lowest pair. (After Nedgebaueb.) 
 
 1 Neugebaueb, F. L., Gentralb.f. Gyndk., 1886, p. 729. 
 
184 MERISTIO VARIATION. [part i. 
 
 «»ne on each side below them. The latter were concealed by the 
 pendent breasts. When the child was being snckled milk oozed 
 from each of the uppermost or axillary nipples, but from the 
 remaining six supernumerary nipples milk could only be extracted 
 l>v pressure. The flowing of milk from supernumerary nipples 
 when the child is at the normal breasts, has often been observed. 
 
 A few references to cases exhibiting the several features above 
 mentioned may be of use. 
 
 149. Bifid nipple, the same on each breast [plane of division not 
 specified]. Duval, 1>" Mamelon et de son aureole, Paris 1861, 
 
 P-90. 
 
 150. Two nipples on the same areola, bilaterally symmetrical. The 
 
 two nipples stood in the mammary line defined above. Tiedemann, 
 Ztsck.f Physiol, v.. L833, p. 110, Taf. i. fig. 3. 
 
 151. Cases are given by Charcot and le Gendre, Gaz. vied, de 
 Paris, 1859, p. 773, in which an extra nipple was placed external 
 to the normal one on the same breast. In one of these the extra 
 nipple had no areola. Leichtenstern (p. 253) in quoting these 
 cases, speaks of them as instances of supernumerary nipples on 
 the same level as the normal ones, but this is not expressly stated 
 in the original account, which does not, as I think, exclude the 
 possibility that the supernumerary nipples were above and external 
 to the normal ones. Two functional nipples with separate areolae 
 on the left breast, which nevertheless was not larger than that of 
 the light side, ibid. The same authors mention another case in 
 which such a second nipple had no areola ; the mother of patient 
 stated to have been the same. See also SlNETY, Gaz. wed. de 
 Paris, 1887. p. 317 (full description and measurements). In this 
 ease the supernumerary nipple was placed below 7 the normal one. 
 
 152. A case in which three nipples were placed on each breast is given 
 by PAULLINUS, Miscell. Curios., &c, 1687, Decur. ii. Ann. v. 
 Append, p. 40. The case is given on the authority of Prackel 
 and the three nipples are said to have been arranged in an equi- 
 lateral triangle, the normal being above at the apex, and the two 
 others at the same level below. The description and the figure 
 accompanying it do not however justify complete confidence in 
 this observation, and indeed the contributions of Paullinus to the 
 Miscellanea Curiosa contain so much of the marvellous that they 
 should not be accepted without hesitation. The same may be 
 said of the case of five nipples each having an areola quoted by 
 Percy and Laurent, Diet. Sci. med., xxxiv. p. 517, .9. v. " Multi- 
 mamme." The authority for this case is a letter of Hannseus to 
 Borrichius, dated 1675. I have not found any observation of this 
 class of abnormality later than the seventeenth century, but it is 
 of course quite possible that cases may occur in which the nipples 
 are distributed on the breast otherwise than along the mammary 
 lines. 
 
CHAP. VIII.] 
 
 MAMMAE. 
 
 185 
 
 153. Supernumerary mamma with nipple in axilla, Leichtenstern, 
 p. 245, and others. 
 
 154. Supernumerary mamma above and external to the normal ones. 
 Numerous cases; see especially case of two bilaterally symmetrical 
 mammae in this position, Shannon, Dubl. Med. Jour., 1848, v. p. 
 26Q,Jig. [figure repeated by Ahlfeld, Williams &c.]; also similar 
 case, Quinquaud, Rev. photogr. des hop., 1870, p. 10. 
 
 155. Supernumerary mammae below and internal to normal ones: 
 numerous cases, see Leichtenstern, &c. In nearly all these the 
 
 Fig. 30. Supernumerary nipples and mammae of different sizes in human 
 female. (After Bruce.) 
 
 supernumerary organs are close to the normal mamma'. A few 
 examples of such structures on the upper part of the abdominal 
 wall are known, e.g., Tarnier in his edition of Cazeaux, Traite de 
 Vart des Accouchements, 1870, ed. 8, p. 86. In the male several 
 such cases are recorded, e.g., Bruce, J. Anat. Phys., XIII. 1879, p. 
 446, PL Examples of this kind in the female are shewn in Fig. 
 30 (after Bruce) and in the male in Fig. 31 (after Leichtenstern ). 
 
 156. Mammary tumours in the axilla are described by Champneys, 
 Med. Chir. Trans., 1886, lxix. p. 419, as of common occurrence in 
 lying-in women. These structures are of various sizes and without 
 any nipple, pore, or duct. The secretion was obtained by squeez- 
 ing the lump and oozed through the skin at the situations of the 
 sebaceous follicles. In this manner both colostrum and milk were 
 obtained, following each ether as in the normal mammae. Similar 
 observations in single cases have been made by many writers. 
 
 157. Redundant mammary tissue of this kind connected with, and 
 thus forming an axillary extension of the normal mammae, CAME- 
 RON, Jour, Anat. Phys., 1879, XIII. p. 149; also Notta, Arch, de 
 Tocologie, 1882, p. 108. 
 
186 
 
 MERISTIC VARIATION". 
 
 [part I. 
 
 *1 K 
 
 158. Two pairs of supernumerary mamma- below the normal ones, 
 DE MORTILLET, Bull. Soc. d'Anthrop., L883, Ser. 3, vi. p. 458. An 
 
 Fig. 31. Supernumerary mammae in the male, symmetrical and asymmetrical. 
 (After Leichtenstern.) 
 
 important case of a man having two pairs of supernumerary 
 mammae on the mammary lines. There was a gradual diminution 
 in size from the highest to the lowest, the latter being a little 
 above the level of the umbilicus. Each pair was at the same level. 
 159. Four pairs of supernumerary nipples (ten in all) are recorded 
 only in Neugebaxter's patient, already mentioned. Three of the 
 supernumerary pairs were above the normal ones, and the other 
 pair below them. As seen in Fig. 29 the nipples of each pair did 
 not stand in the case of each pair at precisely the same levels, and 
 between those of the lowest pair there was a considerable differ- 
 ence of level, that on the left side being at some, distance below 
 the normal breast, while that on the right side was on its lower 
 border. 
 
 In a few cases the supernumerary nipple is described as having 
 been perpendicularly below the normal one, and it is likely that 
 such cases must be looked on as exceptions to the general rule 
 that the mammary lines converge posteriorly; but it is not impos- 
 sible that even in some of them the supernumerary nipple might 
 have been found to be rather nearer the middle line if this point 
 had been specially inquired into. 
 
 The foregoing examples are given as selected illustrations of 
 the several facts, and for full lists of cases the reader is referred to 
 the works already mentioned. 
 
 ICO. Of supernumerary mammae placed in parts of the body other than 
 the mammary line some mention must be made, though those of them 
 
chap, viii.] MAMMAE. 187 
 
 tliat are authentic have no close bearing on the subject of Meristic 
 Variation. There are firstly two often quoted cases 1 in the Miscellanea 
 Curiosa in which mammae are said to have been present on the back, 
 but as has already been remarked, many of the stories told in this 
 collection are clearly fabulous, and this is especially true of the contri- 
 butions of Paullinus. Both these records are given at second hand and 
 the first case (Paullinus) is said to have been seen in 1564, more than a 
 hundred years before the date of the account. Helbig's accounts of things 
 seen by himself are generally trustworthy, but in this case lie is only 
 repeating what w T as told to him by a Polish noble about a woman seen 
 in Celebes. There are no modern cases on record. There is however 
 indisputable evidence of the presence of a mammary gland on the 
 thigh (especially Robert's case ; for references to several accounts 
 of this see Leichtenstern, p. 255); on the cheek, Bartii, Arch. f. 
 path. Anat. u. Phys., 188, p. 569; on the acromion, Klob, Ztsch. f. 
 K. K. Ges. d. Aerzte in Wien, 1858, p. 815; in the labium majus, 
 Hartung, Ueb.einen Fall von Mamma Accessoria, Inaug. Diss., Erlangen, 
 1875. In the two last cases the mammary nature of the gland was 
 proved by microscopic examination. In Earth's case of a mamma on 
 the cheek the microscopical investigation did not give a certain result 
 (q. v.). 
 
 As Leichtenstern shewed, the case of inguinal mamma, mentioned 
 by Darwin and others, really related to Robert's case of a femoral 
 mamma. In 1885, however, Blaxchard (Bull. Soc. d'Anthrop., 1885, 
 p. 230) stated that Testut had lately seen such a case and was about 
 to publish an account of it, but this has not yet appeared (1892). 
 
 Most writers on the subject have accepted cases of supernumerary 
 mamma placed anteriorly in the middle line. These are given by Percv 
 and Laurent, Diet. Sci. med., xxxiv., 1819, on the authority of several 
 different persons. One case was seen by themselves (p. 526), and in 
 it the third mamma stood below and between the other, forming a 
 triangle with them. In another case given on the authority of Goi;i:i: 
 there are said to have been a pair of extra mammae below the normal 
 ones, and a fifth between the supernumeraries. In view of the fact 
 that many paired organs may by Variation occur compounded in the 
 middle line, there is nothing incredible in these accounts, nevertheless 
 there is, so far as I know, no recent observation of such an occur- 
 rence in the case of mammse, and with the one exception (which is 
 very briefly described), the accounts given are at second hand". It is 
 moreover not clear that the words used ll ai(-tlr#*nHit et an milieu des 
 deux autres" do not mean simply below and between the other two. 
 The case contributed by Gorre is nevertheless given in great detail 
 and cannot lightly be set aside. 
 
 Before speaking of the bearing of these facts on morphological 
 conceptions it is necessary to refer to some of the phenomena of 
 
 1 Paullinus, Miscell. Curios., &c., Dec. ii., Ann. iv. 1686, p. 203, Appendix, giving 
 a case said to have been seen in 1564; also Otto Helbig, ibid., Dec. i., Ann. ix. and 
 x., pubd. 1693, p. 45(j. 
 
 2 Williams (p. 235) quotes Baktels, Arch. f. Anat, 1872, p. 306, as alluding to 
 
 such a case, but I do not think that the passage is meant to convey this meaning. 
 
188 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 mammary Variation in other mammals. In connexion with the 
 case of Man it may be mentioned that supernumerary mamma 
 below and internal to the normal ones has been seen in Macacus 
 and in Cercopithecus patas, Sutton. J. B., Intern. Jour, of Med. 
 Sci., 1889, XCVII. pp. 2o2 and 253; in the Orang-utan, Owen, 
 Con/p. A nut., iii. p. 780. In many mammals the number of the 
 mammae is very inconstant even within the limits of species and 
 from the facts seen in such cases deductions may be drawn which 
 arc at once instructive as to the nature of mammarv Variation 
 and have an application to the morphology of Meristic Series in 
 general, of these I shall give examples taken from three species. 
 
 '161. The first is that of the cow's udder. Normally the cow has 
 four teats of about equal size. Not unfrequently there are six 
 teats, of which four are large and may be said in the usual parlance 
 t<» be the " normal " ones, and two are small and placed posteriorly 
 to the others. A case of this kind is shewn in Fig. 32, II. Commonly 
 these extra teats give no milk, but in many cases they have been 
 known to do so. Their size and position vary greatly; sometimes 
 they are placed near the other teats as shewn in the figure, but I 
 have seen them very high up, almost in the fold between the 
 udder and the thighs. 
 
 Very frequently, however, there is only one extra teat making 
 five in all, such an extra teat being so far as I know, always on 
 
 Fig. 32. Supernumerary teats in two heifers. I. The third teat is completely 
 separate on the left side, but on the right side is united with the second. (The 
 cleft between the two is incorrectly represented as a sharp line ; there was no such 
 sharp line of demarcation; the skin being very slightly depressed in this place.) 
 II. Teats of the third pair both completely separate. 
 
CHAP. VIII.] 
 
 MAMMAE. 
 
 189 
 
 *162. one side of the udder. The sketch given in Fig. 32, I. was taken 
 from a heifer having an arrangement intermediate between the 
 condition with four teats and that with six. As the figure shews, 
 on the left side there were three complete teats but on the right 
 side the third teat was incompletely separated from the second. 
 This third teat was joined to the second for its whole length but 
 had a separate pore. The animal which belonged to the St John's 
 College Dairy Farm was unfortunately sold before the first calf 
 was born, so 1 had no opportunity of seeing whether milk was 
 given by both these teats. The significance of such a case will 
 afterwards appear. 
 
 In many mammals, such as the pig, rabbits, cats and dogs, 
 the mammae are distributed in two mammary lines along the 
 ventral surface. The number of the mamma? in such cases is noto- 
 riously variable, and in some respects this variation is interesting 
 and has a bearing on questions of the nature of Meristic Repetition. 
 If a number of such animals be examined it will be found that as 
 a rule there are the same number of glands on the two sides, and 
 that they are arranged in pairs, those of each pair standing at the 
 same level or nearly so. Nevertheless departures from this ar- 
 rangement are very frequent. Individuals are in the first place 
 commonlv found with a different number of mammae on the two 
 sides, and in such cases it is interesting to observe that together 
 w T ith the difference in the number of mammas on the two sides 
 
 V 
 
 V 
 
 Fig. 33. Diagram of nipples in a male Bull-dog. On right side, four ; on left, 
 five ; the two anterior and two posterior being almost at the same levels. 
 umb. umbilicus. The dotted line shews the outline of the thorax. 
 
190 MERISTIC VARIATION. [part i. 
 
 there is generally if aot always a disturbance in the paired arrange- 
 1G3. ment. A simple case of t his kind occurring in the dog is represented 
 in Fig. 33. The animal is a male bulldog lately in my possession. 
 On the right side there arc four nipples, while on the left there 
 are five. The most anterior on each side stand almost at the same 
 level on the thorax. The second on each side are almost at the 
 same distance below them, that on the left side being J in. higher. 
 Similarly the most posterior nipples stand on each side at almost 
 exactly the same level od the sheath of the penis, the total length 
 from the first to the last nipple on each side being practically the 
 same. On the left however there are two nipples placed between 
 the second and the last, but on the right there is only one. This 
 one nipple stands at a level not far from the middle between the 
 old and 4th of the other side, making as it were a complement to 
 or balance with them. 
 164. Thirty-five young pigs examined with regard to these questions 
 gave the following results. They belonged to five litters (30 pure- 
 bred Tarn worths ; 5 cross-bred, out of Berkshire sow, sire unknown). 
 These pigs were all quite young, about a fortnight old, and conse- 
 quently there was no displacement due to functional development 
 of the glands. 
 
 M.AMHLM. 
 
 Right. Left. Pigs. 
 
 A. 6 — regular! v arranged in pairs 3 
 
 B. 7 — 7 ditto 10 
 
 C. 7 — 7 ditto 5th rudimentary 1 
 
 D. 8 — (S ditto 4th rudimentary 3 
 
 E. 7 — 8 all paired exc. 1. 4th rudimentary 2 
 
 F. 7 — 8 1. 4th rudimentary, 1. 3rd and 5th displaced... 1 
 
 I 1 . 7 — 8 rt. 2nd balances 1. 2nd and 3rd 1 
 
 H. 8 — 71. 2nd balances rt. 2nd and 3rd 1 
 
 I. 8 - — 7 1. 3rd balances rt. 3rd and 4th 1 
 
 K. 6-7 rt. 1st balances 1. 1st and 2nd 1 
 
 L. 6—7 l.-2nd rudimentary 1. 1st and 3rd displaced... 1 
 
 M. 6 — 7 all paired exc. 1. 4th rudimentary 1 
 
 X. 7 — 7 altogether irregular 4 
 
 O. 6 - - 6 ditto 2 
 
 P. 7 — 6 ditto 1 
 
 Q. 7 — 8 ditto 1 
 
 R. 8 — 7 ditto 1 
 
 Total 35 
 
 The animals in groups D and E, except one of the latter, be- 
 longed to the same litter. In them a small rudimentary nipple 
 stood between the 3rd and 5th, but the latter were not spaced out 
 for it, being no further apart than any of the others. The measure- 
 
chap, viil] MA1DLE : COMMENT. 191 
 
 ments of the distances between the nipples on one side in one of 
 these cases were, in inches, 1^, 1, T %, ^, ji, ±£ , j* , the rudimentary 
 nipple standing ^ in. from either of its neighbours. In the I) 
 
 O i o 
 
 o o 
 
 O I 
 
 Ol Ol 
 
 1 o 
 
 2 j 
 O _> 02 .2 
 
 O O O 3 
 
 O 2 
 
 ■4 O ° " , 30 04 0-5 
 
 °4 3 
 
 3 O 4 O 5 olO O* 
 
 O O .5 O ° 
 
 o 4 
 
 05 O O 
 
 , ~ O O 
 
 O O 5 O 06 OO O O 
 
 7 o o 8 6 o o 7 7 a o 8 6 o o 7 6 o o 7 
 
 E F G K L 
 
 Fig. 34. Diagrams of nipples in very young pigs. Letters refer to groups in 
 No. 164. 
 
 group this was found on both sides, but in the E group on one 
 side only, as in the figure (Fig. 34). 
 
 Comment on foregoing evidence. 
 
 On looking at a series of cases like those roughly illustrated in 
 the diagrams, one is tempted to inquire as to the factors which 
 determine the positions of these mammae and nipples. Though 
 such an inquiry must lead to small definite results it may not be 
 unprofitable to point out some deductions which may be made 
 from the facts. I take this opportunity as a good one for illus- 
 trating the position here adopted with respect to the theory of 
 Reversion, and for discussing certain features of the phenomena of 
 Division. 
 
 The mammary glands form an example of a class of Meristic 
 organs which are distributed in series along a body already seg- 
 mented, but whose positions have no obvious coincidence with the 
 fundamental segmentation. In the case of the pig, for instance, it 
 would doubtless be found that the mamma; bear more or less 
 definite relations to particular vertebrae, but they are not limited 
 to such positions as the ribs or spinal nerves must be. The seg- 
 mentation of the mammae is thus a segmentation, or serial arrange- 
 ment, superadded upon that of the vertebra 1 . The question to be 
 considered is. what determines the points at which mammae are to 
 be formed ? 
 
 In the paper to which reference has been made, Williams has 
 contended for the view that each somite bore originally a pair of 
 mammae; and we may remark that if this were so the problem of 
 the segmentation of the mammae would be the same as that of the 
 
192 MERISTIC VARIATION, [part i. 
 
 general segmentation of the trunk. The same author then argues 
 that the appearance of supernumerary nipples or mammae along 
 the mammarv lines is a reversion to an ancestral condition, and a 
 figure is given, shewing the places at which mamma? are on this 
 view believed to have been placed, definite ordinal numbers being- 
 assigned to each. Against this suggestion may be urged those ob- 
 jections to appeals t<» the hypothesis of reversion which were men- 
 tioned in the Introduction (Section XII.), but in addition to these 
 there are a number of objections applying specially in the case of 
 mammary Variation. The view that supernumerary mammae are 
 reversions rests on the frequency and definiteness with which they 
 occupy certain positions. But though they do occur more often 
 in some positions than in others they are in no sense limited to 
 these positions, for they may stand anywhere, at least upon the 
 mammary lines. To justify the view that the positions of super- 
 numerary mammae are definite it is necessary to exclude the cases 
 of bifid nipple, of multiple nipples on the same breast, and of axil- 
 lary extensions of the mammae, all which phenomena would then 
 be looked on as belonging to a class different from that of actual 
 supernumerary mammae. In the argument referred to, this course 
 is actually adopted. The acceptance of such a view leads to great 
 difficulty. For example, in Neugebauer's case (see Fig. 29), 
 Williams considers that the posterior nipples of the two sides be- 
 long to different pairs, and have consequently different homologies, 
 because they stand at different levels. 
 
 Such distinctions are, I believe, unreal. It is surely impossible 
 to suppose that the Repetition seen in the udders of the two cows 
 in Fig. 32 is a phenomenon different in the two cases. In the one 
 there are two extra teats in symmetrical positions, equally spaced 
 out from the second teats ; in the other there is a third teat on 
 one side and a double second or posterior teat on the other. Surely 
 it is clear that the double condition of this teat represents an im- 
 perfect phase of a process perfected on the other side. If further 
 proof were needed it may be found in the fact already mentioned, 
 that the mammae of the pig and other such animals, may be the 
 same in number even on the two sides, but nevertheless stand 
 quite irregularly and without any visible arrangement into pairs. 
 
 The existence of these cases in which no order of form or regul- 
 arity can be traced may seem at first sight to be an insuperable 
 objection to any attempt at the detection of principles in the ar- 
 rangement of the mammae. There is however the fact that many, 
 and indeed in must forms the majority of individuals do shew an 
 orderly and paired arrangement, and the further fact that of those 
 cases which depart from this, a certain number present appear- 
 ances which suggest that this departure has come about in a regular 
 way. Though the irregular cases remain, something would be 
 gained if we could comprehend any of the elements on which the 
 regularity depends. The case of regularity and symmetry, in a 
 
chap, viil] MAMM.£ : COMMENT. 193 
 
 sense, includes the cases of irregularity. The difficulty is to under- 
 stand the causes of regularity and of symmetry ; but if we could be 
 sure of these it would not be hard to conceive disturbances result- 
 ing in irregularity. 
 
 In the pigs are found, first, cases of six on both sides in pairs, 
 and also of seven on both sides in pairs ; besides these there were 
 cases of 6 — 7 and of 7 — 8. Of these there were some in which two 
 on one side stood in positions which geometrically balanced that 
 of one of the other side, the others being arranged in pairs. In 
 such cases the appearances suggest that there has been a division 
 of one mamma to form two, and that the two have then separated 
 or travelled apart. The division of organs into two is of course a 
 common occurrence, and may naturally be supposed to be a pheno- 
 menon of the same nature as the division of single cells. The case 
 of mamma? is perhaps instructive inasmuch as it bears witness to 
 the fact that such division must take place at a remotely early 
 period in development. For while in cases to be given hereafter 
 of division, for example, between teeth, it may be supposed that 
 the travelling apart of the two resulting teeth is mechanical, in the 
 sense that the two growing teeth may simply push apart from each 
 other just as two cartilage- cells, &c, may separate by the concen- 
 tric deposition of material, the separation cannot be supposed to 
 occur in the mamma? by these late changes, but the process of 
 mechanical separation, though the same in kind as that in the case 
 of teeth, must be conceived as beginning early in the history of 
 segmentation. 
 
 At this point a circumstance, very often to be seen in other 
 cases, should be mentioned. When an organ, single on one side, 
 corresponds geometrically with two organs on the other side, each 
 of the latter is frequently of the same size and developed to a like 
 extent as the single one of the other side. This of course would be 
 expected on the hypothesis that the division of organs is a pheno- 
 menon similar to the division of cells, that is to say, not merely 
 a division, but a reproduction. 
 
 But the supposition of division of single members of the series 
 is not sufficient to account for all the facts of Variation seen. We 
 have to consider not only the case in which one organ of one side 
 balances two of the other. We have to deal also with the cases of 
 six on each side and seven on each side all corresponding in pairs. 
 In these there is no indication that there has been a division of a 
 single member on each side. The spacing is regular in each case 
 and there is no obvious crowding at any part of the series. Even 
 if therefore in the former case there is a suggestion that the genus 
 of single mamma? have divided into two at a period of develop- 
 ment after the series of mamma? was constituted as a series, there 
 is no such suggestion in the present case. We must, I think, in 
 the latter suppose that the existences of all the mamma?, whether 
 
 b. 13 
 
194 MERISTIC VARIATION. [part I. 
 
 six or seven, are determined together. How or at what stage such 
 determination is made, there is no direct evidence to shew. 
 
 The various arrangements seen suggest then that the relative 
 positions occupied by the mammae depend partly on the number 
 that are present, and that the position of each mamma is to some 
 extent dependent on the position of other mamma?, especially of its 
 neighbours. In this connexion the cases F and L are interesting- 
 ones (Fig. 34). In L for example, the 1st on the left is at a higher 
 level than the 1st on the right. It is succeeded by a rudimentary 
 2nd having none on the same level on the other side. The left 
 3rd is behind the right 2nd, but posterior to this point the nipples 
 are approximately paired. These appearances suggest that the dis- 
 placement of the 1st and 3rd on the left are in some way connected 
 with the presence of the rudimentary left 2nd. Similarly in F the 
 left 3rd and 5th are spaced out for the rudimentary 4th. From its 
 position and small size it might fairly be supposed that this is a 
 " supernumerary " organ, for at all events it is visibly different from 
 the others : but in the case of seven on each side in pairs, no one 
 mamma rather than another can be pointed out as obviously 
 supernumerary when compared with a similar series of six. It 
 seems therefore that of the factors determining the relative posi- 
 tions of the mamma? along the mammary lines, the number of the 
 mamma? is one, and that the positions of the mamma? are in some 
 way and to a limited extent correlated with each other. That there 
 are other factors at work, also, is sufficiently shown by the exist- 
 ence of cases of apparently utter irregularity. 
 
 In seeking to go beyond this and inquire as to the way in 
 which this correlation is brought about there is, in the present 
 state of knowledge of the mechanics of Division, not much to be 
 gained. Reference may be made to recent observations published 
 in abstract by O. Schultze 1 . According to him there is in young- 
 embryos of several mammals (Pig 1*5 cm. long; Rabbit 13 — 14 
 days, &c.) a ridge running along the dor so-lateral aspect on each 
 side and at points upon this the mamma? and nipples are even- 
 tually formed. (The formation of the true nipples is preceded by 
 the raising of. the epidermis into small elevations, "primitive 
 teats," which afterwards disappear.) The two mammary lines are 
 by subsequent changes and growth of the body brought into the 
 ventro-lateral position. The question of the position of the mamma? 
 therefore resolves itself into this : what determines the positions 
 at which mammary centres, to borrow the word used in the case 
 of bone, are to be formed on the mammary lines ? In a subse- 
 quent place I shall contend that the facts given are only intelli- 
 gible on the view that the forces determining the points of growth 
 of mamma? are compounded into one system of forces. But to the 
 question what are these forces there is no answer. 
 
 1 0. Schultze, Anat. Anz., 1892, vn. p. 265, since published in full {Verh. d. 
 phys.-med. Gee. zu WUrzburg, xxyi. 1893, p. 171, Pis.). 
 
CHAPTER IX. 
 
 linear series — continued. 
 
 Teeth. 
 
 From the consideration of numerical Variation in mammae we 
 may proceed to an examination of like phenomena in the case of 
 the teeth of vertebrates. The modes of Variation in these organs 
 are, as might be expected, in many ways similar, but several cir- 
 cumstances combine to make the Variations of teeth more com- 
 plicated than those of mammae. 
 
 Teeth arise developmentally by special differentiation at points 
 along the jaws, much as the mammae arise by differentiation at 
 points along the mammary lines ; and as in the case of mammas, 
 so in the case of teeth, we are concerned first with changes in the 
 number of points at which such differentiation takes place, and 
 next with the general changes or accommodations which occur in 
 the series in association with numerical changes. As in mammas, 
 so also in teeth, numerical Variation may occur sometimes by the 
 division of a single member of the series into two, and sometimes 
 by a reconstitution of at least a considerable part of the series. 
 
 Between the case of mammas and that of teeth, there is how- 
 ever an important point of distinction. The series of mamma? is 
 practically an undifferentiated series. There is between mammae 
 standing in one mammary line no obvious qualitative differentia- 
 tion. Though not all identical in structure, the differences between 
 them are of size and of quantity, not of form or quality. If 
 such qualitative difference is present it must be trifling. In con- 
 sidering Variation in mammae we have thus to deal only with 
 changes in number, and with the geometrical and perhaps mecha- 
 nical question of the relative positions of the mammae. The teeth 
 of most Vertebrates, however, are differentiated to form a series of 
 organs of differing forms and functions, and the study of Variation 
 in teeth may thus be complicated by the occurrence of qualitative 
 changes in addition to simply numerical ones. In teeth, in fact, 
 there are not only Meristic variations, but Substantive variations 
 
 13—2 
 
196 MERISTIC VARIATION. [part i. 
 
 also ; and thus, as in the case of vertebrae, for instance, in any 
 given example of a numerical change qualitative changes must be 
 looked for too. 
 
 As a preliminary to the consideration of evidence relating to 
 the Variation of teeth it may be useful to call attention to certain 
 peculiarities of teeth considered as a Meristic Series. In the 
 Introduction, Section V, it was pointed out that in order to get 
 any conception of the Evolution of parts repeated in an animal, 
 the fact of this Repetition must be recognized, and it must be 
 always remembered that we are seeking for the mode in which not 
 one part but a series of similar parts has been produced. The 
 simplest case to which this principle applies is that of organs 
 paired about the middle line, and in the steps by which such parts 
 have taken on a given form it is clear that similar variations must 
 have occurred on the two sides. In the absence of evidence it 
 might be supposed either that such variations had occurred little 
 by little on the two sides independently, or on the other hand, that 
 Variation had come in symmetrically and simultaneously on the 
 two sides. Upon the answer given to this question the success of 
 all attempts to form a just estimate of the magnitude of the 
 integral steps of Variation depends. In many examples already 
 given it has now been shewn that though in the case of paired organs 
 Variation may be asymmetrical, yet it is not rarely symmetrical, 
 and in part the question has thus been answered. 
 
 In the evidence that remains many more cases of such sym- 
 metrical variations will be described, and it may be taken as 
 established that when the organs stand in bilateral symmetry, that 
 is to say, as images on either side of a middle line, their Varia- 
 tion may be similar and symmetrical. 
 
 The teeth present this problem of the Variation of parts stand- 
 ing as images, in an unusual and peculiar w T ay. For in the case of 
 teeth we have to consider not only the steps by which the right 
 and left sides of each jaw have maintained their similarity and 
 symmetry, but in addition the further question as to the relation 
 of the teeth in the upper jaw to those in the lower jaw. There 
 are many animals in which there is very great difference between 
 the upper and lower rows of teeth, and it must of course be 
 remembered that perhaps in no animal are the teeth in the upper 
 jaw an exact copy of those in the lower, but nevertheless there is 
 often a substantial similarity between them, and in such cases we 
 have to consider the bond or kinship between the upper and 
 lower teeth whereby they have become similar or remained so. 
 For it may be stated at once that there is some evidence that the 
 teeth in the upper and lower jaws may vary similarly and simul- 
 taneously, though such cases are decidedly rare, especially in 
 numerical Variation, and are much less common than symmetrical 
 Variation on the two sides of the same jaw. 
 
chap. IX.] TEETH I PRELIMINARY. 197 
 
 In speaking of the relation of the series of the upper jaw to 
 that of the lower jaw as one of images., it must be remembered 
 that the expression is only very loosely applicable. In particular 
 it should be noticed that though in so far as the lower teeth are a 
 copy of the upper ones the resemblance is one of images, yet the 
 teeth which resemble each other do not usually stand opposite to 
 each other in the bite, but members of the upper series alternate 
 with those of the lower. The incisors, as a rule, however, and the 
 back teeth of a certain number of forms do bite opposite each 
 other, and in them the relation of images is fairly close. 
 
 The importance of the recognition of the relation of images as 
 subsisting between the teeth of the upper and lower jaws will be 
 seen when this case is compared with that of the two sides of the 
 body. For ordinary bilateral symmetry is, as has already been 
 suggested, an expression of the original equality and similarity of 
 the two halves into which the ovum was divided by the first 
 cleavage-plane, or by one of the cleavages shortly succeeding upon 
 this. The fact that the two halves of the body are images of each 
 other is thus both an evidence and a consequence of the fact that 
 the forces dividing the ovum into two similar halves are equal and 
 opposite to each other. The bilateral symmetry of Variation is 
 thus only a special case of this principle. 
 
 In view of the fact that the teeth in the upper and lower jaws 
 may vary simultaneously and similarly, just as the two halves of the 
 body may do, it seems likely that the division of the tissues to form 
 the mouth-slit must be a process in this respect comparable with 
 a cleavage along the future middle line of the body. It is difficult, 
 however, to realize the actual occurrence of such a process of 
 division in the case of the slit forming the original stomodoeum, 
 and this difficulty is increased by the recent observations of 
 Sedgwick 1 to the effect that in the Elasmobranchs examined by 
 him the mouth-slit first appears as a longitudinal row of pores. If 
 this is so the relation of images must exist in the case of the 
 mouth, not only in respect of the two sides of the slit, but also in 
 respect of the anterior and posterior extensions of the slit. But 
 whatever may be the processes by which the tissues bounding the 
 mouth of a vertebrate come apart from each other, the result is clearly 
 in many cases to produce an anterior series of organs in the upper 
 jaw, related to a posterior series of organs in the lower jaw, much 
 in the same way that the right side of a jaw is related to the left 
 of the same jaw. This relation may appear as has been stated, 
 not only in the normal resemblances between the upper and lower 
 teeth, but also in the fact that similar and simultaneous Variation 
 is possible to them. 
 
 In another respect the Repetition of teeth may differ from that 
 of other Linear Series already considered. In many animals, the 
 
 1 Sedgwick, A., Quart. Jour. Micr. Sci., 1892, p. 570. 
 
198 MEMSTIC VARIATION. [part i. 
 
 Pike, the Alligator, or the Toothed Whales, for example, the teeth 
 stand in a regular and usually continuous series, differing from 
 each other chiefly in size, ranging from small teeth in front, 
 through large teeth, and often down to small teeth again at the 
 back of the jaw. Such a 'homodont' series as a rule passes through 
 only one maximum. Most mammals, however, are 'heterodont,' 
 that is to say, the teeth can be distinguished into at least two 
 groups, the incisors and canines on the one hand, and the pre- 
 molars and molars on the other ; and in a large number of animals 
 having this arrangement the anterior members of the series of 
 premolars and molars are small, increasing regularly in size from 
 before backwards, reaching a maximum usually in some tooth 
 anterior to the last. Though instances will be given of Variation, 
 and especially of reduplication, occurring in most of the teeth, 
 even in those which stand well in the middle of the series of back- 
 teeth, such as the upper carnassials of the Cat, or the fourth pre- 
 molars of the Seal, yet on the whole Variation in heterodont forms 
 is more common at the anterior and posterior ends of the series of 
 back-teeth. In view of this fact it is of some importance to 
 recognize that the small members at the beginning of the pre- 
 molar series are as regards their relatively small size, in the con- 
 dition of terminal members of series, and exhibit the variability of 
 terminal members almost as much as the last molars. 
 
 With these remarks by way of preface, evidence as to the 
 numerical Variation of teeth in certain groups will be given in full. 
 This account will for the most part be confined to a brief description 
 of the conditions presented by the specimens. In the next chapter 
 the principles which may be perceived to underlie these facts and 
 the general conclusions to which they appear to lead will be 
 separately discussed. 
 
 The evidence here given relates to certain selected groups 1 of 
 Mammals, and chiefly to the Primates (excepting Lemuroidea), Car- 
 nivora (CanidaB, Felidse, Viverridse, Mustelidse and Pinnipedise), and 
 Marsupialia (Phalangerida?, Dasyurida^, Didelphyidas, part of Macro- 
 podidae, &c). 
 
 The facts to be given relate chiefly to increase in number 
 of teeth. In the case of terminal members of series, such as the 
 most anterior premolar or the last molar, some reliable facts as to 
 cases of absence were found, but for the most part the evidence as 
 to the absence of teeth is ambiguous and each case requires 
 separate treatment. 
 
 The evidence is in this chapter arranged according to the 
 
 1 Evidence as to the dental variations of Man is not here introduced. Con- 
 siderable collections of such facts have been made by Magitot {Anom. du syst. 
 dent.), Brscn (Dent. Monats. f. Zahnh. 188fi, iv.), and others, and illustrative 
 specimens are to be found in most museums. I do not know that among these 
 human variations are included phenomena different in kind from those seen in 
 other groups, except perhaps certain cases ot teeth united together, a condition 
 rarely if ever recorded in other animals. 
 
chap, ix.] TEETH ! PRELIMINARY. 199 
 
 zoological position of the groups concerned. In several cases 
 variations of similar nature were seen in different groups ; cases of 
 this kind will be brought into association in the next chapter. 
 
 As regards nomenclature I have in the main followed the 
 common English system, numbering both the premolars and 
 molars from in front backwards. In one respect I have departed 
 from the practice now much followed. It has seemed on the whole 
 better that the premolar which in any given jaw stands first, 
 should be called p 1 , even though in certain cases there may be 
 reasons for doubting whether it is the true homologue of the p 1 of 
 other cases 1 . Theoretical views of this kind can only at best be 
 used as a substitute for the obvious nomenclature in a few re- 
 stricted cases, such as that of the Cat, in which by the application 
 of the methods of reasoning ordinarily adopted in Comparative 
 Anatomy the first upper premolar would be looked on as the 
 equivalent of p 2 in the Dog. There are, however, few who would 
 feel confident in extending this reasoning to many other cases, 
 that of Man, for instance, and I believe it is on the whole simpler 
 to number the teeth according to their visible and actual relations. 
 As I have already attempted to shew in another place 2 , in the light 
 of the facts of Variation, it is to be doubted whether in their varia- 
 tions teeth do follow those strict rules of individual homology by 
 which naturalists have sought to relate the arrangements in dif- 
 ferent types with each other. 
 
 The material examined has consisted chiefly of specimens in 
 the British Museum and the Museums of the College of Surgeons, 
 Leyden, Oxford and Cambridge, the Paris Museum of Natural 
 History, and some smaller collections. I have to thank the 
 authorities of these several museums for the great kindness I 
 have received from them; and in particular I must express my 
 indebtedness to Mr Oldfield Thomas, of the British Museum, for 
 the constant help and advice which he has given me, both as 
 regards the subject of teeth generally and especially in examining 
 the specimens in the British Museum 3 . 
 
 PRIMATES. 
 
 S0111D.E. The Anthropoid Apes (Orang, Chimpanzee, and 
 Gorilla). 
 
 *165. The teeth of the three large Anthropoids arc perhaps more 
 variable, both in number and position, than those of any other 
 
 1 In cases where confusion might arise any change from common nomenclature 
 is notified in the text. 
 
 2 Proc. Zool. Soc, 1892, p. 102. 
 
 :i In the following descriptions B.M. stands for British Museum; C.S.M. lor 
 Museum of the Boyal College of Surgeons; CM., O.M., U.C.M., Leyd. M., P.M., 
 for the Cambridge, Oxford, University College London, Leyden and Paris Museums 
 respectively. 
 
200 MERISTIC VARIATION. [part i. 
 
 group of mammals of which I have been able to examine a con- 
 siderable number. In different collections 142 normal adult skulls 
 were seen and 12 cases of extra teeth. Of these one was a case 
 of extra incisor (Gorilla, No. 186), one of anomalous teeth (Gorilla, 
 No. 187), and the remainder molars. Thus far therefore there are 
 nearly 8 per cent, cases of extra teeth. This figure is remarkable 
 in comparison with the rarity of such cases in Hylobates (51 skulls 
 seen, all normal), and the like rarity in other Old World monkeys 
 (42-S normals and 2 cases of extra teeth). 
 
 Simia satyrus (Orang-utan). 
 
 Normal adult skulls seen, 52. 
 
 Supern itinerary molars. 
 166. Adult male haying additional posterior molar (m 4 ) behind and 
 in series with the normal teeth, on both sides in upper jaws and on 
 left side in lower jaw. In each case the in 4 is rather smaller than 
 ??i 3 , but all are well formed, having each four cusps and the normal 
 complement of fangs, viz., one in front and one behind in the 
 lower jaw, and two on outer and one on inner side in upper jaw. 
 On right side of lower jaw there is no trace of additional molar, 
 though there is almost as much room for it as on the left side. 
 C. M., 1160, D, described by Humphry, G. M., Jour. Anat. Phys., 
 1874, p. 140, Plate. 
 
 16/. Female (Borneo) having six cheek-teeth in each upper jaw and in 
 right lower jaw [doubtless a case like the foregoing] mentioned by 
 Peters, W., Sitzungsb. naturf. Fr. Berlin, 1872, p. 76. 
 
 1G8. Specimen with large alveolus on each side for w\ L. M., 24. 
 
 169. Specimen (Borneo) having m 4 in right lower jaw, behind and in 
 series with the normal teeth. The tooth is of rather small size, but is 
 regular in position and form. B. M., 3, m. 
 
 170. Specimen having a right ^ more than half the size of m :i - U. C. M., 
 E, 253. 
 
 171. Specimen having supernumerary molar on each side in lower jaw. 
 Mayer, Arch. f. Nature/., 1849, 1. xv. p. 356. 
 
 172. Similar case. Fitzinger, Sitzungsb. math. — nat. CI. Ak. Wien, 
 1853, i. p. 436. 
 
 Similar case. Bruhl, Zar Kenntniss des Orangkopfes, Wien, 1856. 
 [] refers to the case described by Fitzinger.] 
 
 Molar absent. 
 
 173. Specimen "remarkable for absence of the upper right third 
 molar and for absence of nasal bones, which are greatly reduced 
 in some other specimens." C. S. M., 44. See Catalogue Mus. Coll. 
 Surg. 1884. The other teeth are all normal and fully formed. 
 
 Variations in position of teeth. Though not directly pertaining 
 to the subject here considered, the following examples of consider- 
 
chap, ix.] TEETH : ORAXG. 201 
 
 able departure from the normal arrangement may be perhaps 
 usefully introduced in illustration of the peculiar variability of 
 the dentition of the group. 
 *174. A skull from Borneo in the Oxford University Museum (num- 
 bered 2043 a) has the following extraordinary arrangement. All 
 the teeth are normal and in place except the second premolar of 
 each side in the upper jaw. On both sides there is a large 
 diastema between p 1 and «^. The diastema on the left side is of 
 about the same size as the normal second premolar, but that on 
 the right side is considerably too small for a normal tooth. The 
 singularity of this specimen lies in the fact that the missing 
 tooth of the right side is present in the skull, but instead of being 
 in its proper place it stands up from the roof of the mouth within 
 the arcade immediately in front of the right canine and almost 
 exactly on the level of the second incisor, being in the premaxilla, 
 at some distance in front of the maxillary suture. 
 
 That this tooth is actually the second premolar which has by 
 some means been shifted into this position there can be no doubt 
 whatever. It has the exact form of the normal second premolar, 
 and is of full size. It stands nearly vertically but is a little 
 inclined towards the outside. The canine is by the growth of 
 this tooth slightly separated from the second incisor, and the first 
 premolar is consequently pushed also somewhat further back. 
 Hence it happens that the diastema for the second premolar on 
 the right side is not of full size. This should be understood, as 
 it might otherwise be imagined that the contraction was due to a 
 complementary increase in the size of the other teeth, of which 
 there is no evidence. 
 
 On the left side of the palate there was a very slight ele- 
 vation at a point homologous and symmetrical with that at 
 which the second premolar of the right side was placed. As it 
 seemed possible that the missing tooth of the left side might 
 be concealed beneath this elevation, a small piece of bone was 
 here cut away, with the result that a tooth of about the same 
 size and formation as f; was found imbedded in the bone. In 
 this case therefore the second premolar of the right side and of 
 the left side have travelled away from their proper positions and 
 taken up new and symmetrical positions in the palate, anterior 
 to the canines. The facts of this case go to shew that the germ 
 of a tooth contains within itself all the elements necessary to 
 its development into its own true form, provided of course that 
 nutrition is unrestricted. This might no doubt be reasonably 
 expected ; but since the forms of organs and of teeth in particular 
 are by some attributed to the mechanical effects of growth under 
 mutual pressure, it may be well to call special attention to this 
 case, which goes far to disprove such a view. 
 
 175. Specimen having the teeth of the two sides in the lower jaw in 
 extraordinarily asymmetrical disposition. The bone of the jaw does 
 
170. 
 
 177 
 
 202 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 not seem to have been broken, but there appears to have been disease 
 of the articulations of the mandibles. B. M., S6, 12, 20, 10. 
 
 Specimen in which "position of the left upper canine is abnormal. 
 It is displaced backwards and lies to the outer side of the first premolar, 
 which it has pushed towards the middle line." C. S. M., 41 (see 
 Catalogue). 
 
 Case in which upper right canine occupies a position within and on 
 a level with the first premolar, which is pushed outwards. C. S. M., 
 40, A. 
 
 Troglodytes niger, calvus, &c. (Chimpanzee). 
 
 Normal adult skulls seen. 35. 
 
 Supernumerary molars. 
 
 *178. Specimen having on right side in upper jaw a very small 
 square tooth behind m*, in the arcade (Fig. 35) ; and in the left upper 
 
 1 
 
 ms 
 
 m 3 V *, 
 
 m 
 
 m.z 
 
 Fig. 35. Posterior right upper molars of Chimpanzee. 
 
 I. The case No. 178 {Coll. Surg. Mus., No. 1). 
 
 II. A normal Chimpanzee of approximately the same size. 
 
 jaw an empty alveolus in the similar place, shewing clearly that 
 a similar tooth has been present : lower jaw normal. C. S. M., 1. 
 
 179. Specimen in which teeth all gone, but alveoli exist behind 
 those of the normal teeth on both sides in upper jaw, and there 
 is little doubt that there was here a fourth molar on each side. 
 C. S. M., 9. 
 
 180. Specimen in which teeth all gone, but alveoli shew clearly that 
 there was a fourth upper molar on right side ; evidence on left 
 side inconclusive : lower jaw gone. C. S. M., 12. 
 
 181. Specimen of T. calvus having an extra mS in lower jaw on 
 right side. This tooth is about one quarter of the size of m z , 
 resembling that in case No. 178. This specimen is in the private 
 collection of Prof. Milne Edwards, who w r as so kind as to shew 
 it to me. 
 
 Gorilla savagei (Gorilla). 
 Normal adult skulls seen, 55. 
 
CHAP. IX.] 
 
 TEETH I GORILLA. 
 
 203 
 
 Supernumerary molars. 
 
 *182. Specimen having m i behind and in series with the others 
 on both sides in lower jaw and on right side in upper jaw. On 
 left side both teeth are square and somewhat worn, but the 
 right m* is a curious conical tooth. Gallery of P. M., A, 505, 
 described by Gervais, P., Journ. de ZooL, in. p. 164. PL 
 
 183. Two cases of four molars in each upper jaw. Magitot, Anom. du 
 syst. dent., p. 100, PL v. tig. 8. [Of these one is in collection of Dr 
 Auzoux; the other is No. 121 in P. M., but as I did not see it when 
 examining the collection it is not reckoned in the statistics given 
 above.] 
 
 Similar case, Hensel, Morph. Jahrb., v. p. 543. 
 
 184. Specimen having supernumerary molar which had not quite pierced 
 bone [no statement as to position]. Wyman, Jeffries, Proc. Boston 
 ]S T . H. S\, v. p. 160. 
 
 185. Specimen having extra molar in crypt on each side in upper jaw 
 behind m 3 . L. M., 3. 
 
 Super n umerary incisor. 
 
 Fully adult male from Congo having an extra incisor in lower 
 , There are thus five incisors in lower jaw (Fig. 36), of which 
 
 * 
 
 186. 
 
 jaw 
 
 Fig. 36. Lower incisors and canines of Gorilla No. 186. .r, y and z are three 
 central incisors. The upper figure shews the tooth y as seen from the side. 
 (Specimen in Coll. Surg. Mus., 21, A.) 
 
 one, presumably the supernumerary, stands almost exactly in the 
 middle line. This tooth is turned half round, so that the plane 
 of its chisel stands obliquely. The teeth are all well formed 
 and none belong to the milk-dentition, for the milk-teeth are 
 much smaller and of different form. I did not succeed in 
 satisfying myself that the central tooth is certainly the super- 
 numerary. The second incisors are in place on each side and 
 are quite distinct, and the right first incisor is similarly normal. 
 
204 MERISTIC VARIATION. [part i. 
 
 But whether the oblique tooth, or the tooth between it and 
 the right i l , should be rather considered supernumerary cannot 
 be declared with certainty. Probably this is one of the cases, of 
 which more will be said hereafter, in which both teeth replace the 
 normally single i 1 . C. S. M. 21, A. 
 
 ^37 Anomalous extra teeth. A lower jaw in the Museum of the Odontological 
 
 Society "having two supernumerary teeth embedded in the hone beneath the coro- 
 noid process and sigmoid notch. Originally only a small nodule of enamel was 
 visible on the inner surface of the right ascending ramus, just external to the upper 
 extremity of the inferior dental canal. On cutting away the bone this nodule was 
 found to be a portion of a supernumerary tooth having a conical crown and a 
 single tapering root. Lying above it, another supernumerary tooth was discovered, 
 of which there had previously been no sign whatever. This was likewise exposed 
 by removing the superjacent bone, and found to be a larger tooth with a conical 
 crown and three long narrow roots. The teeth were lying parallel to each other, 
 with their crowns pointing upwards and backwards, so that they could hardly under 
 any circumstances have been erupted in the alveolar arch." Trans. Odont. Soc, 
 1887, xix. p. 206, fig. 
 
 Specimen having fragment of a tooth imbedded in bone between left lower canine 
 and p 1 ; perhaps a fragment of a milk-tooth P.M., A, 506. 
 
 [Two specimens in the stores of the P.M. shew great irregularities in the 
 arrangement of the teeth; but in both cases so many teeth had been lost during 
 life that a satisfactory description of the abnormalities cannot now be given.] 
 
 Hylobates (Gibbons). 
 
 Normal specimens seen, 51. No abnormal case known to me. 
 
 Old World Monkeys other than Anthropoid Apes. 
 
 188. Of the genera Semnopithecus, Colobus, Nasalis, Cercojnthecus, 
 Cercocebus, Macacus and Cynocephalus ; 419 normal specimens 
 examined. Only two had definite supernumerary teeth, but in one 
 other case it was possible that extra molars had been present. 
 
 Supernumerary molars. 
 
 189. Cynocephalus porcarius, having large extra molar behind 
 and in series in each upper jaw. The two teeth are of the same 
 pattern precisely. In lower jaw there is on each side a large 
 space behind m 3 , but there is no tooth in it. O. M., 2011, b. 
 
 190. Macacus rhesus, old male, having a fourth molar in place in 
 right lower jaw. The tooth does not stand up fully from the 
 bone. On the same side in the upper jaw there is also a fourth 
 molar, but was entirely enclosed in bone and was only found by 
 cutting away the side of the maxilla by way of exploration. B. M., 
 30, c. 
 
 191. Macacus radiatus, having small and fairly definite depression behind m} in 
 each jaw. These depressions seem to be perhaps the alveoli of teeth but it cannot 
 be positively stated that extra molars have been present. C.S.M., 145. 
 
 192. Abnormal arrangement. Only one case of considerable irregularity of arrange- 
 ' ment seen, viz., Cercopithecus lalandii (C. S. M. 113), case in which lower canines 
 
 are recurved and pass behind the upper ones. See Cat. JIus. Coll. Surg. 
 
chap, ix.] TEETH : ATELES. 205 
 
 New World Monkeys. 
 
 *193. In the species of Cebida? and especially in Ateles supernumerary 
 teeth arc rather common, eight cases being found in 284< skulls, 
 or nearly 3 per cent, (in addition to cases recorded by others). Of 
 American monkeys belonging to other genera 92 skulls were seen, 
 all being normal. Some cases of absence of the third molar were 
 seen in Ateles, which are interesting in connexion with the fact that 
 there are normally only two molars in Hapalidse. 
 
 Cebid.e : normal formula i J, c\, p f , m§. 
 
 Chrysothrix, normal adults, 5. 
 
 Cebus, normal adults belonging to about ten species, 66. 
 
 Supernumerary molars. 
 
 194. Cebus robustus : supernumerary molar in each upper jaw 
 giving p f , m 4; de Blainville, Laurent's Annal. d'Anat. etPhys., 
 1837, i. p. 300°, PL viii. fig. 6. 
 
 19o. c variegatus : small tubercular molar in right lower jaw 
 behind m?. The extra tooth is cylindrical and peg-like, having 
 about Jth the diameter m?. Leycl. Mus. 8, Cat. 11. 
 
 Ateles : normal adult skulls, belonging to several species, 60. 
 
 Supern umerary molars. 
 
 *196. A. pentadactylus : extra molar in series behind m d in both 
 upper and lower jaws on right side, in each case a small round 
 tooth. P. M., A, 1505. This specimen described by de Blainville 
 Laurent's Ann. d'Anat, et Phys., 1837, I. p. 300, PL VIII. rig. 5: 
 mentioned also by Geoffroy St Hilaire, Anom. d'Organ., i. 
 p. 660. 
 
 197. A. vellerosus : extra molar on left side in lower jaw behind 
 m 3 , as a fully-formed and well-shaped tooth, but not so large as m<. 
 B. M., 89. 12. 7. 1. 
 
 198. Ateles sp. : extra molar on left side in lower jaw. Magitot, 
 Anom. du syst. dent, p. 101, No. 6. 
 
 Supernumerary premolars. 
 
 *199. Brachyteles hemidactylus [a genus doubtfully distinct from 
 Ateles] : specimen from S. America having 1. upper series and all 
 lower series normal. In place of right upper p l are two teeth 
 (Fig. 37). These two teeth are similar to each other and for 
 want of space they bulge a little out of the arcade. Each is in 
 size and shape very like normal £\ having a sharp cusp and a flat 
 internal part to the crown. Both teeth are slightly rotated in 
 opposite directions, so that the cusp of the anterior is antero- 
 
206 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 lateral instead of lateral, while the cusp of the posterior is postero- 
 
 Fig. 37. Surface view of upper jaw of Brackyteles hemidactylus, described in 
 No. 199. From skull in Brit. Mux., 42, a. 
 
 lateral. These two teeth stand thus in somewhat complementary 
 positions. B. M., 42, a. 
 
 *200. Ateles marginatus : wild specimen from river Cupai, has 
 
 4—4 3—3 
 
 P 
 
 O O ' 
 
 O — O 
 
 m 
 
 3—3' 
 
 ■m? m 3 
 
 Fig. 38. Surface view of upper teeth of Ateles marginatum, specimen described 
 in No. 200, and side view of both jaws together. The specimen is in Brit. 3Ius., 
 1214, b. 
 
chap, ix.] TEETH : ATELES. 207 
 
 that is to say, an extra premolar on each side in the upper jaw, the 
 lower jaw being normal. The four upper premolars are perfectly 
 formed, large teeth, in regular series on both sides. As a conse- 
 quence the lower canines bite on and partly behind the upper 
 canines. There was nothing to suggest that any one of these 
 teeth was supernumerary, rather than another (Fig. 38). B. M.. 
 1.214, b. 
 
 Supernumerary incisor. 
 
 201. Ateles ater : specimen from Peruvian Amazon : in right 
 upper jaw there is a large alveolus for i 2 , which is gone, while a 
 third incisor stands between this and the canine. This third 
 incisor bites on lower canine, and lower p 1 of the same side bites 
 in front of the upper canine. B. M., 1108, d. 
 
 202. Ateles paniscus : extra incisor in upper jaw. Rudolphi, 
 Anat.-phys. Abh., 1802, p. 145. 
 
 Absence of molars (cp. No. 209). Inasmuch as^f, m% is the 
 normal formula for the Hapalidae, the following cases of absence of 
 m 3 in Ateles are interesting. There was in no case any doubt that 
 the skulls were fully adult, and there was no suggestion that the 
 absent tooth had been lost. 
 *203. Ateles marginatus : specimen from the Zoological Society's 
 menagerie, bones rough and unhealthy-looking, but skull well 
 formed and certainly not very young, has no m 3 in either jaw, giving 
 
 3 3 2 2 
 
 the formula p — , m~ — -, as in Hapalidse. There is no space 
 
 in the jaw behind m 2 , and in the upper jaw the bone ends there 
 almost abruptly. 
 
 204. A. melanochir : Caraccas specimen, having no posterior m 2 
 on either side in upper jaw. The lower series normal, but the 
 jaws are somewhat asymmetrical, so that the lower posterior right 
 m 3 is behind the level of its fellow of the other side. B. M., 4s. 
 10. 26. 3. 
 
 205. A. variegatus : wild specimen, having lower m 3 absent on 
 both sides. Left *f is also absent, but has been almost certainly 
 present. CM., 1098, B. 
 
 Mycetes : of various species, adult normals, 81. 
 
 Supernumerary molar. 
 
 206. M. niger : supernumerary molar in the right upper jaw. The 
 arrangement is peculiar. So far as m- the teeth are normal. 
 Behind and in series with m 2 there is a large tooth, a good deal 
 larger than the normal m 3 , and having rather the form of m* than 
 of m 3 . Its form is, however, not precisely that of m 2 , for the 
 middle or fifth cusp is rather anterior to the centre of the tooth. 
 
208 
 
 M ERISTIC VARIATION 
 
 [rART I. 
 
 instead of being posterior to it as usual. Outside this tooth is 
 another, standing out of the arcade, having the size and almost the 
 form of normal m*. B. M., 749, c. (Fig. 39). 
 
 This case may be an example of one of two principles which 
 will be in the next chapter pointed out as operating in the case 
 
 Fig. 39. Mycetes niger, No. 20(i ; right upper molars. Brit. Mus., 7-49, c. 
 
 of dental Variation. Eitlier m 2 may have divided into two, both 
 standing in series, and the normal m s may have been pushed out 
 of the arcade in connexion with this reduplication ; or the tooth 
 standing outside may represent an addition to the normal series, 
 and in that case the tooth standing as m z in the series may be a 
 representation of m z , raised to the normally higher condition of m 2 
 in correlation with the presence of an extra tooth in the series, in 
 the way shewn to occur in other cases (see Chapter x., Section 7). 
 Between these alternative possibilities I cannot decide. 
 
 Super n u merary premolar. 
 
 207. Mycetes niger : between and internal to p}_ and $P on left side there is a 
 premolar. This is probably a supernumerary one, but the jaw is so much diseased 
 that the relations are not distinct. B. M., 749, d. 
 
 208. Callithrix, normal adults, 22. (In B.M., 51, b on both sides rn? is separated 
 by a narrow diastema from m?. The appearances suggest that possibly a small 
 rudimentary tooth may have stood between them, but this is quite uncertain). 
 
 Nyctipithecus : 1 1 normals. 
 
 209. Pithecia : 1 1 normals. 
 
 Specimen having no right m*^, and apparently this tooth was not 
 about to be formed, for the dentition is otherwise complete. C. M., 
 1094, a. (Cp. Xo. 202.) 
 
 Lagothrix, 6, Chiropotes, 1, Ouakaria, 3 normals respectively. 
 
 Hapalid.e. In this group m 3 is normally absent ; and no 
 specimen having this tooth or any other dental abnormality was seen. 
 Of adult normal skulls 33 were seen, belonging to various species. 
 
chap, ix.] TEETH : CAXID^E. 209 
 
 CARNIVORA. 
 
 Canid.e. 
 
 The evidence of the Variation of teeth in Canidae is divided 
 into three groups according as it concerns (1) incisors, (2) pre- 
 molars, (3) molars. No case specially relating to the canines 
 is known. In each of these groups the cases relating to (A) 
 ivild Canidae are taken first, and those relating to (B) domestic 
 Dogs afterwards. 
 
 Of wild specimens of the genus Canis (including the Fox) 
 289 skulls were seen, and amongst them were 11 cases of super- 
 numerary teeth, about 3*5 per cent, (besides many recorded cases). 
 Of 216 domestic Dogs (including Pariahs, Esquimaux, &c.) 10 
 had supernumerary teeth, or 7 "4 per cent, (besides many re- 
 corded cases). I have not included skulls of edentulous breeds, 
 in which the original condition of the teeth cannot be told with 
 certainty. 
 
 Statistics of the occurrence of supernumerary teeth are given 
 by Hexsel, Morph. Jahrb., 1879. Among 345 domestic Dogs 
 in his collection there are 28 cases of one or more extra molars, 
 12 cases of extra premolar, and 5 cases of extra incisor. [If 
 therefore no two of these cases refer to the same skull, there were 
 in all 45 cases of extra teeth in 345 skulls, or 13 per cent. It 
 is not stated that the collection was not strictly promiscuous, 
 but it may be anticipated that this figure is rather high.] An 
 analysis of Hensel's cases will be given in the sections relating 
 to the particular teeth. 
 
 The usual dentition of the genus Canis is if, c\, p\, m%. 
 The Wild Dog of Sumatra, Java and India, C. javanicus and 
 C. primcevus (by some considered as one species) have in': 7 ami 
 have been set apart as a genus under the name Cuon (HODGSON, 
 Calcutta Jour. N. H., 1842, ii. p. 205). The genus Icticijon differs 
 in having normally ??ij. The genus Otocyon on the contrary has 
 usually ??if. 
 
 Of the variations to be described in Canis the most notable are 
 (1) cases of i 4 —^ ; (2) cases of extra premolar, common in upper, very 
 rare in lower jaws ; (3) cases of ^ 3 or m*, and one case of in J giving 
 the formula characteristic of Otocyon. In several instances a con- 
 siderable increase in the size of ȣ or m* is found associated with 
 the presence of ™?_ or m* respectively. An interesting group of 
 cases of extra molars was found in 0. cancrivorus, in which this 
 abnormality seems to be common. 
 
 The frequent absence of p 1 in the Esquimaux dogs is worth 
 notice. Absence of m? is common in Dogs, but absence of «^ is 
 rare. 
 
 In Otocyon one case of m± is recorded, and in let icy on one 
 example has m\ instead of m\. 
 
 b. 14 
 
210 MERISTIC VARIATION. [part I. 
 
 I. Variation in Incisors and Canines. 
 
 A. Wild Caxid^e. 
 
 No case of extra incisor known to me. 
 Two cases of absent incisor, viz. 
 
 210. [Canis] Vulpes pennsylvanica, Brit. Columbia, having 
 ' \ o ' a PP aren tly i l has nut been present on either side. B. M., 
 
 1402, b. 
 
 211. Canis vulpes: only 5 incisors in lower jaw, with no trace 
 of alveolus for the sixth. Schaff, E., Zool, Gart, 1887, xxviil 
 p. 270. 
 
 B. Dogs. 
 
 212. Dog (resembling Bloodhound) : four incisors on each side in 
 upper jaw. The externals, i 3 , normal, but no evidence as to which 
 of the other teeth supernumerary. Leyclen Mus. 
 
 213. Thibetan Mastiff, Nepal: sockets for four teeth on each side in 
 pmx. Teeth all gone. Alveoli of two sides nearly symmetrical. In 
 absence of the teeth it cannot be positively stated that this is not a case 
 of persistent milk-teeth, but this seemed unlikely. B. M., 166, g. 
 
 214. Mastiff: four teeth on each side in front of canines; from form of 
 teeth probably case of persistent milk-canines. Lower jaw gone. O. M., 
 1749. 
 
 215. Dog : on right, sockets for three teeth in addition to ? 3 which is in 
 place. These three sockets all smaller than the normal ones, and socket 
 for upper right canine also slightly reduced in size. Odont. Soc. Mus. 
 
 216. Dog : small skull in my possession, has in place of right & two 
 alveoli, both at the same level, divided by a thin bony septum, the one 
 internal to the other: left &_ is in place and normal: lower jaw gone. 
 
 217. Among 345 Dogs' skulls four had extra upper incisor on one 
 side, and one skull had perfectly formed fourth upper incisor 
 on both sides. This tooth smaller than third incisor. Hensel, 
 I. c, p. 534. Several cases of 7 or 8 incisors in upper jaw, teeth 
 being usually asymmetrical. Nehring, Sitzb. not. Fr. BerL, 1882, 
 p. 67. 
 
 218 In lower jaw such cases much rarer. Supernum. lower in- 
 cisor on one side, one case [? in 650 skulls], Nehring, ibid. ; also 
 a Dog (cJiien chinois-japonais), 4 incisors in each lower jaw. 
 Magitot, An. syst. dent, p. 81. 
 
 Case of divided incisor. 
 
 219. Bulldog : right i~ with very wide crown; main cusp partially 
 bifid, as if intermediate between single and double condition. 
 Morph. Lab. Cambridge. 
 
 Similar case kindly sent to me by Prof. G. B. Howes. 
 
chap, ix.] TEETH: CANIDyE. 211 
 
 3 — 3 
 
 220. Absence of incisor is very rare in Dog. One case of i- — given by 
 
 Hexsel, I. c. p. 534. (Hensel observes that this gives the formula for 
 incisors of Enhydris [Latax]; he also calls attention to fig. of Enhydris 
 with three lower incisors in Owen, Odontogr., PI. 128, fig. 12, but as 
 this is not mentioned as an anomaly in text, it is very doubtful.) 
 
 221. Dog having the upper canine imperfectly divided into two on 
 each side as shewn in Fig. 39. The plane of division was at right 
 
 Fig. 39. Eight and left profiles of Dog having the canines partially divided. 
 
 angles to the line of the alveolus so that the two parts of each 
 canine stood in the plane of the series of teeth. The division was 
 more complete on the right side than on the left. The lower 
 canines were normal. This specimen was kindly sent to me by 
 Mr J. Harrison. 
 
 II. Variation in Premolars. 
 
 Several distinct variations were found in the premolars of 
 Canidse. A number of cases shew five upper premolars instead 
 of four, and the question then arises whether the extra tooth is 
 due to the division of a single tooth, or to reconstitution of the 
 series 1 . The occurrence of a fifth premolar in the lower jaw is 
 much rarer, only three or four cases (Wolf (2) and Greyhound (? 2)) 
 being known to me. The following other forms of Variation oc- 
 curred. In C. mesomelas, No. 228, an extra tooth stood internal 
 to fP, and was perhaps a duplicate of this tooth. One case of 
 bifid p^ was seen, and two cases in which p 2 had apparently 
 divided to form two single-rooted teeth (0. viverrinus, No. 227 
 and a Sledge-dog, No. 237). A few examples of absence of p 1 
 deserve notice. Lastly, though really an example of Substantive 
 Variation, I have included a curious case of possibly Homceotic 
 variation of p^ into the partial likeness of the carnassial (No. 245). 
 
 1 On this point see Chapter x. Sections 3 and 5. 
 
 14—2 
 
212 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Increase in number of Premolars. 
 
 A. Wild Canid^e. 
 
 222. C. dingo : specimen having two closely similar teeth between p* 
 and the canine in each upper jaw 1 . Both the teeth had the form and 
 size of a premolar. This not a case of persistent milk-tooth, Nehring, 
 A., Sitzb. naturf. Fr. Berlin, 1882, p. 66. 
 
 C. dingo : on right side p] is in place, and there is an alveolus for 
 second tooth of about same size. On left side P 1 is rather small. L. M. 
 
 C. lateralis, Gaboon. On 1. side p^ is single, but on rt. side 
 there are two almost identical teeth between P^ and the canine : 
 of these the most anterior is level with, but slightly smaller than, 
 left £. (Fig. 40) B. M., 1689, a, (See Mivart, P. Z. 3., 1890, 
 p. 377.) 
 
 223. 
 
 224. 
 
 225. 
 
 226. 
 
 227. 
 
 228. 
 
 229, 
 
 Fig. 40. Cants lateralis, No. 224. View of canines and front premolars of the 
 upper jaw. p l of the left side is in symmetry with two teeth on the right side. 
 
 C. vulpes : in 142 skulls, one case of two teeth between p z and 
 canine (sc. five premolars) in left upper jaw. Hensel, I. c, p. 548. 
 
 In C. vulpes the root of p 1 is not rarely partly divided into two by 
 a groove of variable depth. The division is sometimes nearly com- 
 plete, as in C. S. M., 651. 
 
 C. mesomelas : two teeth between p 2 and canine in left lower 
 jaw, anterior the larger. Doxitz, Sitzb. naturf. Fr. Berl., 1869, p. 41. 
 
 Division of p' 2 
 
 C. viverrinus : left p? represented by two teeth, each having one 
 root. Of these the anterior is tubercular, while the posterior is rather 
 long from before backwards. Anterior premolars normal. L. M. 
 (Compare Sledge-dog, No. 237.) 
 
 Reduplication of p*. 
 
 C. mesomelas : inside right upper p 3 is a supernumerary tooth 
 which nearly resembles p A , but is a little smaller; lower jaw normal. 
 C. S. M., 643. (See Nos. 226 and 247.) 
 
 C. lupus: in addition to irregularities in position of teeth, there is a doubtful 
 appearance as of an alveolus inside left P^ which is displaced outwards. C. S. M., 624. 
 
 1 Mivart, I.e., by mistake quotes this case as one of extra teeth above and below. 
 
CHAP. IX.] 
 
 TEETH : CANID^E. 
 
 213 
 
 Partially bifid premolar. 
 
 230. ^* vu lP es • right v\ has three roots and a partially double crown 
 with two cusps (Fig. 41). The whole crown is pyramidal, the labial 
 face being parallel to the arcade and the three roots stand each at one 
 angle of the base : left pj normal; lower jaw missing. B. M., 175, o. 
 
 Jh 
 
 Iji 
 
 l [ 
 
 Fig. 41. Teeth of Fox (C. vulpes) described in No. 230. The separate view- 
 shews the right first premolar removed, seen from the labial side. 
 
 Extra premolar in lower jaw. 
 
 231. C. lupus : two teeth between p 2 and canine in lower jaw on right 
 side, one case: and the same on left side also, one case. These two 
 occurred in 27 Wolf skulls seen by Hexsel, Morph. Jahrb., 1879, v. 
 p. 548. 
 
 B. Domestic Dogs. 
 
 *232. Dog : between F 2 and canine on rt. side there are two teeth, 
 each shaped like a normal £\ the anterior being somewhat the 
 larger. This seen in two cases, figured in Fig. 42, II. and III. 
 
 right 
 
 m 
 
 Fig. 42. Profiles of canines and anterior premolars in three dogs having two 
 teeth on one side in symmetry with one tooth on the other. 
 
 I. C. S. M., 570. II. and III. Skulls in Cambridge Univ. Morph. Lab. 
 
 Lower jaws absent. The property of the Zool. Lab., Cambridge 
 (cp. G. lateralis, No. 224). 
 233. Spaniel : similar case, left side, Fig. 42, I. C. S. M,, 570. 
 
214 MERISTIC VARIATION. [part i. 
 
 5 5 
 
 234. Dog : large skull, having^ =--, all the normal teeth being 
 
 o — o 
 
 in place, of proper form and size, standing evenly without crowding. 
 O. M, 1780. 
 
 235. Dogs. In 3 t5 skulls were 1 1 cases of supernumerary premolar in 
 the upper jaw. viz. 
 
 on both sides, 1 case, 
 on right side, 7 cases, 
 on left side, 3 cases. 
 
 These were all cases described by Hensel as instances of the presence 
 of "p b " of his notation, i.e. a tooth between p ] and canine. Hensel, 
 Morph. Jahrb.f 1879, v. p. 546. Out of 650 skulls, including Hensel's 
 ."U">, 18 had two anterior premolars as described, on both sides in upjDer 
 jaw. Nehring, Sitzb. naturf. Fr. BerL, 1882, p. 6Q. 
 
 English Spaniel: outside and anterior to right & is a worn stump, probably of 
 an extra tooth (?). B. M., KJG, j. 
 
 236. Deerhound : tiro alveoli where p~i should be; probably two distinct teeth stood 
 here, but it is possible that the two alveoli were for distinct roots of a single tooth. 
 C. M., 991, B. 
 
 Division of r p~. 
 
 237. Sledge-dog, Greenland : all teeth normal except left upper 
 p 2 . This tooth normally of course has two roots. Here it is 
 represented by two distinct teeth, each having one root. The 
 anterior has a fairly sharp cusp, but the posterior has a rounded 
 crown. The teeth are in perfectly good condition and do not 
 look worn. They are separated from each other by a considerable 
 diastema. It appears clear that instead of the normal p* } two 
 distinct teeth have been formed. 0. M., 1787 (compare C. 
 viverrinus, No. 227). 
 
 Absence of Premolars. 
 
 A. Wild Canid.e. 
 
 236. C corsac : fi absent on both sides without trace. Giebel, 
 Jirouits Kl. u. Orel., Mamm. p. 196, Xote. 
 
 239. c. occidentalis : p absent on both sides. C. S. M., 629. 
 
 240. C. vulpes : in 142 skulls : 
 
 P^ absent from both sides 1 case, 
 do. „ „ left „ 1 „ 
 do. „ ,, right „ 1 ,, 
 p 1 » „ both „ 1 „ 
 
 do. „ „ left „ 2 „ 
 
 do. „ ,, right „ 2 „ 
 
 Hensel, Morph. Jahrb., 1879, p. 548. A doubtful case of absence of 
 left p. B. M., 175, c. 
 
chap, ix.] TEETH : CANID.E. 215 
 
 241. C. (Nyctereutes) procyonoides : p^ absent on both sides with- 
 out trace in B. Ms, 186, e; and absent on right side in B. M., 186, d. 
 On the contrary B. M. 186 a and b and C. S. M., 672, are normal. 
 
 The following cases of absent premolars were doubtful : C. dingo : right v^ and 
 left J^. C. S. M. C. antarcticus: p l above and below on left side. C. S. M., 635. 
 
 B. Domestic Dogs. 
 
 242. From the nature of the case it is not often possible to say with con- 
 fidence that p 1 has not been present in a given skull, but from the 
 material examined this variation appears to be rather rare. In 216 
 skulls, excepting those of Esquimaux dogs, I only saw two clear cases 
 in which the bones were smooth, without trace of alveolus, viz. 
 "Danish" Dog: p~i absent on both sides, O. M., 1786. Terrier: 
 p} absent on both sides. C. S. M., 579. Many others doubtful. 
 
 According to Hensel, however, absence of p l is common, and he 
 states that in 345 skulls the following occurred : 
 
 1^ absent on both sides 5 cases, 
 
 do. ,, ,, one 4 ,, 
 
 pi ,, ,, both frequently, 
 
 do. ,, ,, one 9 cases, 
 
 p 1 absent on both sides and F 1 on one side, 1 case. 
 
 Jforph. Ja/trb., 1879, p. 546. [This is of course a far higher frequency 
 than was found by me, but perhaps discrepancy arises from difference 
 in reckoning the evidence of absence.] 
 
 Two doubtful cases of absence of p were seen in Dogs. 
 
 *243. Esquimaux Dogs: absence of p l quite common, the following 
 skulls being all of the breed that I have seen. 
 
 Normals, withp~, only two specimens. Specimens with nop 1 , above 
 or below, the canines in such cases standing close to p 1 , three cases, 
 viz. B. M., 58. 5. 4. 96; B. M., 166, a; C. S. M., 542. £ absent on left 
 side and pi on both sides, C. M., 1000, c. pi absent both sides and pi 
 absent on left side, L. M. p^ and pi both absent from right side; left 
 normal, O. M., 1789. p~ l absent on left side, B. M., 166, r, 3. p~ l 
 absent on right side, B. M., 166, t, 2. 
 
 The partial establishment of a character of this kind in a 
 breed, which, if selected at all, has been selected for very different 
 qualities, is rather interesting. It need scarcely be remarked 
 that the partial loss of this tooth cannot in the Esquimaux dog 
 have occurred in connexion with an enfeebled habit of life, as 
 might perhaps be supposed by some in the case of the edentulous 
 lap-dogs. 
 
 As will be shewn in the next section, absence of the front 
 premolars is a common character in the dogs of the ancient Incas, 
 but in them the posterior molars are also frequently absent. 
 There is no special reason for supposing that the Esquimaux 
 dogs came originally from America, but it may be worth recalling 
 as a suggestion, that according to anthropologists the relations 
 
•2 1 6 MERISTIC VARIATION. [part i. 
 
 of the Esquimaux are rather with American tribes than with 
 Europeans. If this were established, it would be not unlikely 
 thai the Esquimaux dogs might be descended from dogs domesti- 
 cated in America before the coming of Europeans, and so far belong 
 rathe]- with the Inca dogs than with ours 1 . 
 
 *244. Inca Dogs. The domestic dogs from the Inca interments, be- 
 longing to a period before the coming of the Spaniards, have been 
 investigated by Xehrinr. Of nine skulls not one had the full number 
 of teeth and there was no case of supernumerary teeth. Sometimes 
 the anterior premolar was absent, sometimes a posterior molar, and in 
 soiih' cases both. The formulas were as follows: 
 
 4—4 
 ' ; 4-3' 
 
 m 
 
 2- 
 
 -2 . 
 
 
 
 — o 
 
 4 — 4 
 ^3-3' 
 
 7)1 
 
 2- 
 
 3- 
 
 _9 
 
 — 1 case. 
 
 4—4 
 ' ; 3-3' 
 
 m 
 
 2- 
 3- 
 
 _9 
 
 — ~1 3 cases 
 
 — o 
 
 4 — 4 
 *3-3' 
 
 m 
 
 9 
 
 — 
 
 9 
 
 -J 
 
 -1 , 
 
 — - 1 case. 
 
 -2 
 
 4 — 3 
 
 7)1 
 
 2- 
 
 2- 
 
 -2 - 
 
 — - 1 case. 
 
 -2 
 
 3 — 3 
 ^3—3' 
 
 7)1 
 
 9_ 
 
 3- 
 
 _9 
 
 — 2 cases 
 
 — o 
 
 The dogs were all of moderate size, and none shewed any defects 
 in the form of teeth, which were all strong and sound. Nehring, A., 
 A'osntos, 1884, xv. p. 94. 
 
 Variation (J Homceotic) in form of third Premolar. 
 
 245. Dog : large breed. In the upper jaw on both sides the third 
 premolar, instead of having only two roots, has a third internal root, 
 thus somewhat resembling the carnassial. The crown of the tooth 
 very slightly changed. This is not a case of persistent milk-tooth, which 
 though a three- rooted tooth, is very different. C. S. M., 558. 
 
 III. Variation in Molars. 
 
 Supernumerary molars are not rare in Canidae. In all cases 
 seen by me these teeth are single-rooted, round-crowned, rather 
 tubercular teeth, placed behind m? or m? as the case may be. 
 HENSEL 1 has observed that if m± occurs, then m? which is normally 
 single-rooted, not infrequently has a double root, though the same 
 variation may occur when there is no m 4 present. Conversely, 
 when ///'• is absent, not a rare variation, then rn? is often of a 
 
 1 Bartlett, arguing chiefly from habits, considers the Esquimaux dogs to be 
 domesticated wolves, and says that they often breed with the wolf. P. Z. S., 
 1890, p. 47. 
 
 - Hexsel, Morph. Jahrb., 1879, v. p. 539. 
 
chap, ix.] TEETH : CANIDyE. 217 
 
 size below the normal, having a single root and a crown slightly- 
 developed, like that of m*. This reduced condition of ~m* may 
 also occur in cases in which m Ti is not absent. These observations 
 of Hensel's, which are of great consequence to an appreciation 
 of the nature of Repetition, I can fully attest, and similar cases 
 of Variation in adjacent teeth associated with the presence of a 
 supernumerary were seen in other animals also. 
 
 A. Wild Canid.e. 
 Supernumerary Molars. 
 
 246. CJ. lupus: 26 normals seen. Specimen from Courland having 
 supernumerary m? on left. In this specimen m? is rather ab- 
 normally large on both sides, and the lower third molar, on the 
 left side, viz. that on which the upper jaw has an extra tooth, is 
 larger than right m? } but it is not larger than usual. C. M., 
 976, M. 
 
 Hexsel, I. c, p. 548, saw 27 skulls, none having extra molar, but 
 one specimen known to him had a right m?. 
 
 247. C. mesomelas J (a Jackal): small, bitubercular left w^. Doxitz, 
 Sitzb. naturf. Ft. Berlin, 1872, p. 54. (See Nos. 226 and 228.) 
 
 The S. American Canidce {Lycalopex group) are remarkable 
 for the frequency with which they possess extra molars, as the 
 following cases (C. azarcv, vetulus, magellanicus and cancrivorus) 
 testify. Flower and Lydekker 1 speak of the occasional presence 
 of ™? in G. cancrivorus, but the evidence taken together seems 
 rather to shew that there is a general variability at the end of 
 the molar series in both jaws in these species ; for not only is 
 *J}? found, but in some cases m* also, while in one instance there 
 was an 'odontome,' or rather a complex of 4 small teeth attached 
 to m 3 . 
 
 248. O- vetulus, Brazil : specimen having an extra molar in right 
 lower jaw (Fig. 44, 1.). The posterior part of ^ is slightly pushed 
 outwards and a very small extra tooth stands behind and partly 
 internal to it. Right m 3 is slightly larger than left nfi and differs 
 from it also a little in pattern. The extra tooth has one large 
 and about three smaller blunt cusps on its crown, and might be 
 described as a small representation of the larger m* seen in other 
 cases. B. M., 84. 2. 21. 1 (mentioned by Mivart 2 , Monogr. Canidce). 
 
 *249. Canis azarae : Brazilian specimen having a large super- 
 numerary molar (w 3 ) in each upper jaw placed in series with the 
 others. In this specimen the great enlargement of ȣ is very 
 
 1 Mammals, Living and Extinct, 1891, p. 540. 
 
 2 In the same place Mivart mentions a case of m? in " C. cancrivorus" but I have 
 not seen it. Perhaps this reference is to van der Hoeven's case (No. 249) which was 
 by Burmeister named C. cancrivorus (see Huxley, P. Z. S., 1880, p. 268). 
 
218 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 noticeable on both sides, and this tooth is present as a large tooth 
 with apparently three roots. In the lower jaw there is no extra 
 booth, but the molars are considerably larger than those of a 
 
 2.30. 
 *251. 
 
 2") 2 
 
 Fig. 43. ( 'anis </: ira. I. and II. Right upper and lower jaws of the specimen 
 described in No. 248, shewing the extra upper molar and the correlated enlarge- 
 ment of "I 2 and ,//■'. III. and IV. are taken from a normal specimen of slightly 
 Larger size. C, carnassial teeth. 
 
 This figure was kindly drawn for me by Mr J. J. Lister. 
 
 normal spreimen (Fig. 43). In the figure, side by side with the 
 teeth of the abnormal form, are shewn the teeth of a normal skull 
 which was slightly larger than the abnormal one, for comparison. 
 Leyden Mns. ' 
 
 C. magellanicus : specimen having m* on both sides. B. M., 46. 
 11. 3. (mentioned by Huxley, I. c). 
 
 C. cancrivorus. The only skulls of this species seen by me are 
 those in B. M. Of these one skull with lower jaw, one skull without 
 lower jaw. and one lower jaw without skull, have numerically the 
 normal dentition of Canis, but of these, one has right m 73 much larger 
 than corresponding left tooth. The following were abnormal: small 
 tubercular m* on both sides, upper series normal, B. M., 1033, b, and 
 also B. M., 1033, c, (Fig. 44, II.) mentioned by Huxley, I. c. 
 
 Specimen having upper series and left lower series normal. On 
 inner side of right m z and as it were growing out from this tooth is a 
 
 1 This is no doubt the skull described by van der Hoeven. Verh. k. Ah. Wet., 
 Amst., iii. 1856, PL See Huxlky, P. Z. S., 1880, p. 208. 
 
CHAP. IX.] 
 
 TEETH : CAXID.E. 
 
 219 
 
 large 'odontome' composed of four small tubercular teeth. Each of 
 these has a distinct crown and neck, but apparently the necks join with 
 
 R 
 
 ia 
 
 n 
 
 Fig. 44. Posterior lower molars of S. American Foxes. I. C. vetulus No. 249. 
 II. G. cancrivorus No. 251. III. C. cancrivorus No. 252. In each case the right 
 and left sides are shewn. R, right. L, left. 
 
 each other and with the neck of m 3 , which is displaced (Fig. 44, III.). 
 
 B. M. 5 1033, a. (mentioned by Huxley, P. Z. S., 1880, p. 268; 
 figured by Mivabt, P. Z. S., 1890, p. 377). 
 
 In answer to an inquiry, Prof. Nkhrixg informs me that he has three skulls of 
 
 C. cancrivorus Desm. ( = G. braziliensis Lund.) from the province of S. Paolo, Brazil, 
 which are normal, except that in one pi has never replaced a*, which is in place ; 
 and that another Venezuelan skull of this species is also normal. [Whether 
 the B. M. specimens are really of the same species as these I do not know.] 
 
 60i5. T/he rarity of supernumerary molars in G. vulpes, the common 
 Fox, is remarkable in contrast with the foregoing evidence. In 
 142 cases (to which I can add 37), Hensel, Morph. Jahrh.\ 1879, 
 found no single case. 
 
 Absence of Molars. 
 
 254. mr i s very rarely absent in Canidae, and among the wild forms no 
 case seen in 289 skulls (except a doubtful case in 0. occidentalism right 
 
220 M ERISTIC VARIATION'. [part i. 
 
 side, C. S. M., 628). ,7r ; was observed to be absent in the following : C. 
 lag-opus, from Kamtschatka, absent on both sides in two cases 
 received in same consignment with 4 normal skulls. B. J/., 88. 2. 20. 
 9 and 10; another case from Norway. Leyd. Mus. C. zerda : on left 
 side. C. S. M., 671. C. vulpes : ditto, 2 cases. B. M., 177, a and 
 175, b. C. viverrinus : on right side. Leyd. Mus. C. procyonoi- 
 des : ditto. Leyd. Mus. Hensel, /. c, gives the following : C. vulpes: 
 142 skulls; ,„■'■ absent on both sides, 5 cases; on left side, 3 cases. C. 
 lupus : iit» absent on left side, 2 cases; on right side, 1 case. 
 
 ICTICYON AND OtOCYON. 
 
 * It is remarkable that in each of the two genera Icticyon and 
 
 Otocyon, which are especially distinguished from Canis by the 
 possession of unusual dental formulae, numerical Variation in the 
 th has been recorded, though the number of skulls of these 
 forms in Museums is very small. The two forms, besides, differ 
 from Canis in opposite ways, the one having a tooth less in each 
 jaw while the other has in each jaw a tooth more, so that the 
 presence of extra teeth in the two species is all the more im- 
 portant. 
 
 255. Icticyon venaticus : according to the authorities has p±, m\, 
 viz. a molar less than the Dog in each jaw. The following skulls are 
 all that I have seen. The carnassials did not vary appreciably in the 
 three skulls. Each skull differs from the others, as follows. 
 
 j>\ , m\, B. M., 185, a. 
 
 /<{, m~ i, B. M., 185, b. 
 
 yj, rnf, C. S. M., 533. (See Flower, P. Z. S., 1880, p. 71.) 
 
 25G. Otocyon megalotis [ = lalcmdii and coffer]: the usual formula 
 
 is />;}, m : j, that is, one molar more than the Dog in each jaw. It occurs 
 
 in 4 skulls at B. M. and in 2 at C. S. M. One specimen has in adcli- 
 
 4 — 4 
 tion an extra molar of good size in each upper jaw, giving on — — j. 
 
 4 — 4 
 
 In this case m? is enlarged also on both sides. C. S. M., 675 (see Cat, 
 
 Mus. Coll. Surg., Arc). Three specimens having mf mentioned by 
 
 Doxitz, Sit-.h. naturf. Fr. Berlin, 1872, p. 54. 
 
 B. Domestic Dogs. 
 
 Super n itinerary Mola rs. 
 
 257. Dogs. In 345 skulls the following 28 cases occurred, chiefly in 
 large breed- : 
 
 "^ on both sides and v? on one side, 1 case. 
 
 "^ on both sides 2 cases. 
 
 mP on one side 9 cases. 
 
 '» :: and ]n* on one side only 2 cases. 
 
 m* on both sides 6 cases. 
 
 m 4 on one side only 8 cases. 
 
 Hensel, Morpk. Jahrb., 1879, v. p. 538. 
 
CHAP. IX.] 
 
 TEETH I CANID.E. 
 
 221 
 
 In addition to these, 
 
 wi 3 and m* absent on both sides, 1 case. 
 
 This was the only case in 860 skulls of Canis, of which about 650 
 were Dogs. The formula in it is thus that of Otocyon or the fossil 
 Amphicyon. Nehring, Sitzb. naturf. Fr. Berlin, 1882, p. 66. 
 
 In 216 skulls seen by me there were 8 cases of extra molars, viz. : — 
 
 258. Sheep dog : left m 3 . C. S. M., 587; Bulldog : left m 3 . B. M., 
 166 s; Dog from New Zealand, having left m\ left m* being larger 
 than right m». C. M., 1000; Bhotea Mastiff: m+ on right B. M., 166, 
 f.; Pointer: lefty. C. M., 1000, A; Dog: right Ji? Carnb. Morph. 
 Lab.; Pariah : m 4 has been present on both sides, also a small stump 
 below ^ and p 2 , possibly part of a milk-tooth. B. M., 166, <l. 
 
 259. Mastiff: supernumerary m 4 on right. The right m? materially 
 larger than left ^ (Fig. 45). C. S. M., 555. 
 
 right 
 
 left 
 reversed 
 
 200. 
 
 261. 
 
 Fig. 45. Posterior molars of lower jaw of Mastiff No. 259, having an extra m 4 
 on the right side. Right m? is materially larger than left ^i. 
 
 Dog, large size, supernumerary m* on right side. On both sides 
 m? is two-rooted 1 and of large size. Leycl. Mas., 258. 
 
 Windle and Humphreys, P. Z. S. } 1890, p. 27, give an account of 
 extra molars in the Dog, speaking of upper jaws only, and some of the 
 foregoing are mentioned by them. As they do not specify the collec- 
 tion in which each is found the identity of the cases is not easy to tell. 
 The following cases given by them are, I believe, all in addition to 
 those already specifiecl : — Bulldog, Lurcher, Pointer and Terrier, 
 m? on both sides. Bulldog w 3 on left side; Esquimaux, Pug, 
 Spaniel, West Indian Dog, »f on right side. 
 
 Coach-dog : ?/7 4 on both sides, Magitot, Anom. Syst. dent., p. 103. 
 
 Absence of Molars. 
 
 262. Dog: in 345 skulls the following seen : ?«'- and ^ absent on both sides, 2 cases; 
 ^2 and ^a absent on both sides, 1 case ; ^ absent on both sides, 25 cases ; ^ absent 
 on one side, 9 cases. Hensel, /. c. 
 
 In 216 seen by me the following occurred: ^3 absent on both sides, 7 cases; 
 C. M., 993 and 978; C. S. M. {Store), 65 and 67; two skulls marked " Skye Terrier/' 
 
 1 It generally has a simple, conical root, but not rarely it has an imperfectly 
 divided root, e.g. Newfoundland dog, O. M., 1778. 
 
222 MERISTIC VARIATION. [part i. 
 
 probably both of the same strain, C. M. 991, F and G; and Fox Terrier, C. M., 
 991, K; ^ absent on left side, 2 cases. Irish Wolf-dog, B. M. 82. 11. 11. 1; Fox 
 Terrier, C. S. M., 580, A ; llt i absent on right side, 1 case, Bloodhound, B. M., 166, t. 
 besides a few doubtful cases. 
 
 Inca dogs : for evidence as to absence of molars, see No. 244. 
 
 FELIDAE. 
 
 The following evidence relates to the genera Veils and Cyn- 
 cdurus. The usual formula is /§, c\, />§, ni\. Of wild species, 
 27 8 adult skulls having no extra teeth were seen, and 8 cases 
 of extra teeth (nearly 3 per cent.): of domestic Cats, 35 adults 
 without, and 3 cases with extra teeth (so far, about 9 per cent.). 
 Aj3 in Canidte so in Felidae, there is a remarkable group of cases 
 of variation in the anterior premolars. In the normal a small 
 anterior premolar stands in the upper jaw, and commonly it is 
 oiK'-rooted, sometimes two-rooted (cases given); but there is no 
 small anterior premolar in the lower jaw. 
 
 Cases of variation consisting in the presence of two small 
 premolars above are common 1 , just as there are often two small 
 anterior premolars in the Dog. There are besides a few cases 
 of the presence of a small anterior premolar in the loiver jaw, 
 but they are rather rare, and curiously enough there seems to 
 be no case of the coincidence of these two variations in the same 
 skull. 
 
 As already stated, in describing cases, the small anterior pre- 
 molar in the upper jaw will be here spoken of as p^, though no 
 suggestion that it is the homologue of the Dog's p^_ is meant. 
 
 In a few species p^_ is most commonly absent (cases given). 
 There are some curious cases of duplicates of large premolars (Cat) 
 and one of duplicate canine (Tiger), also a few of supernumerary 
 molar. Though so small, and biting on no tooth of the lower 
 jaw, n& is nearly always in place even in old skulls (Hexsel). 
 
 Variation in Incisors. 
 
 No quite satisfactory case of numerical variation in incisors of Felidae known to 
 me. The following should however be mentioned. 
 203. F - lynx : two extra teeth in premaxillai. Bight incisors normal; sockets for left 
 incisors normal. Outside left f and close to canine is an extra tooth of good size, 
 and in same place on right is a socket for a similar tooth. Since they are in pre- 
 maxillffi these teeth are probably not persistent milk-canines. Lower canines bite in 
 front of the extra teeth. B. M., 1156, a. 
 
 Incisors absent. 
 
 9(34_ F. pardalis: i l and fl absent on left side. As regards the lower jaw the tooth 
 may have been present, and been lost, but left £ has probably never been present. 
 It is especially notable that left f is larger than right f, but there is no indication 
 that £ is compounded with it. B. M., 1068, a. 
 
 F. chate [?= pardalis]: doubtful if i 1 has been present on either side. B. M., 
 55. 12. 26. 178. 
 2Qr>. Cynaelurus jubatus : no trace of right P ; same skull has no p^\ lower jaw 
 ' normal. B. M., 135,/. 
 
 1 For discussion of such cases see Chapter x. Section 5. 
 
CHAP. IX.] 
 
 TEETH I FELID^E. 
 
 223 
 
 Anterior Premolars {supernumerary). 
 
 Upper Jaw. 
 
 266. F. pardus : right P^ single and normal; on 1. side two such teeth, 
 both standing at level anterior to right P 1 . The anterior is of same size 
 as right p^, the posterior is rather smaller. B. M., 87. 4. 25. 1. 
 
 267. F. eyra : two small anterior premolars in left upper jaw, Baird, U. S. and Mex. 
 Bound. Swrv., Pt. 2, PI. xni. figs. 2, a and 2, c [anomaly not mentioned in text]. 
 
 *268. F. catus, Athens. Two small anterior premolars in upper 
 jaw both sides (Fig. 40, I.), small and standing close together. 
 On rt. anterior the larger, on 1. posterior the larger. B. M., 47. 
 7. 22; 2. 
 
 * 
 
 269. 
 
 270. 
 
 271. 
 272. 
 
 Fig. 46. Left-hand figure : upper jaw of F. catus, No. 268. Eight-hand figure : 
 upper jaw of F. inconspicua, No. 269. 
 
 F. inconspicua (= torquata). Rajpootana. Two small an- 
 terior premolars in upper jaw both sides ; both small, diastema 
 between them. Posterior is nearly in contact with "jt) 3 ", while 
 anterior is only a little behind canine (Fig. 46, II.). B. M., 85. 
 8. 1. 26. (Another specimen has p^_ as large single-fanged 
 tooth.) 
 
 F. domestica (out of 38 skulls) : internal to and rather behind left p} is an 
 almost identical copy of it, though rather smaller. Not a milk-tooth. C. S. M., 414. 
 
 Out of 252 skulls two anterior premolars on Ijoth sides, 4 cases ; on right, 2 cases; 
 on left, 1 case [none specially described]. Hensel, Morph. Jahrb., 1879, v. p. 553. 
 
 F. caligata, Socotra : outside right p} t a small extra tooth. In this specimen )j} 
 on each side has two roots. B. M., 857, b. 
 
 Doubtful cases of extra upper anterior premolar, F. pardus, C. S. M. 365 ; F. leo, 
 C. S. M. 308. 
 
 Lower Jaw. 
 
 273. F. concolor : a supernumerary anterior premolar on both sides 
 present, Berl. Anal. Mus., 3678. Hensel, ibid. F. catus or mani- 
 culata : ditto. Frank/. Mils., Hensel, ibid. F. catus : ditto, on 
 left side, closely resembling^ 1 . Two cases, B. M., 1143 and 1143, a. 
 
 274. F. domestica : (in 252 skulls) a supernumerary premolar on both 
 sides, just in front of and nearly same size as the usual "P 2 ," one case ; 
 on left, as a very small tooth midway between canine and "p*" one 
 case; on right, rather larger than in foregoing and nearer to "//-'," 
 one case. Hensel, ibid. 
 
 275. F. tetraodon: alveolus for small anterior premolar in right lower 
 jaw; but as this fossil form very rare, uncertain whether normally 
 
224 MERISTIC VARIATION. [part i. 
 
 present in the species, de Blainville, Osteogr., Atlas, PI. xvi. Feles 
 fossiles. 
 
 Variations- in size of P^. 
 
 27(3. r. pardus : j£ sometimes two-rooted, as C. S. M., 360 (African); more often 
 one-rooted, as C. S. M., 304, Arc: many gradations between these. In B. M., 115, q 
 right i± extraordinarily large, left normal. Minute alveolus external and posterior 
 to each of these ; on left side a small worn stump ['? of milk-tooth] in this alveolus. 
 
 277 r. domestica : />} two-rooted C. S. M. 40'J and B. M., 127, q ; on right side two- 
 
 ' rooted B. M. 127, 8. F. catus C. S. M. 401 and F. minuta (Borneo) B. M., 122,/, 
 P 1 partially two-rooted. F. caligata, see above, No. 272. F. chaus: left p} very 
 small, right p] fair size. B. M. 131, e. F. jaguarondi, ditto, B. M. 
 
 Absence of p 1 . 
 
 In the following cases it appeared that p^ had not been 
 
 present. 
 
 278. F. catus. both sides, a cave-skull, Hexsel, I. c. ; left side only, Caucasus, B. M. 
 1113, m ; F. tigris, Hexsel, F. onca, both sides, B. M. 117, c ; F. xnanul, ditto, 
 
 B. M. 1863, a; F. nebulosa, ditto, two cases [? normal for species] B. M.; F. rubi- 
 ginosa. Malacca, ditto, B. M., 1856, a; F. chaus: both sides in domesticated 
 specimen from India, B. M. ; and in B. M. 58. 5. 4. 69, similar specimen, this tooth is 
 small on left, absent on right; F. brachyurus, absent both sides, B. M. ; F. 
 cbinensis, right absent, B. M., 70. 2. 18. 25; F. javanensis, left absent, B. M. 1641, a 
 (but in B. M. 1309, b, p} is particularly large). F. domestica : in 252 skulls v^ 
 nl Kent both sides 6 times, and one side, once (in 2 cases anterior deciduous tooth 
 remained on both sides in upper jaws of adults) Hexsel, /. c. p. 552; in 38 skulls 
 seen by me, n} absent both sides, 2 cases ; right side in one case (Manx, C. S. M., 
 428, a). 
 
 In the following species the absence of vl was so frequent as to call 
 for special notice. 
 
 279. Cynaelurus jubatus : of 8 skulls 3 (2 African) were like Cat, 
 having 2^ both sides; p 1 absent both sides, 3 cases, B. M., 135,/. 
 and 0. S. M. — ; left p^ absent, right very small, C. S. M., 441; right 
 ;/ absent []]. B. M., 135, c. 
 
 280. F. caracal : out of 8 skulls only 4 had any indication that i^ 1 
 might have been present, and in these it was doubtful. 
 
 281. Lynx : of Lynxes of possibly different species, 17 skulls have no .P 1 , 
 a skull marked "Lynx borealis" B. M., 1230, a has a small, worn stump 
 as p 1 on each side. 
 
 2S2. F- pajeros ( =pampana) i Chili: 2 skulls only known to Hensel, 
 I c, both without^. This tooth absent in B. M. 126 and 126, c; but 
 in one specimen seen, right p^ absent but left p} of good size. 
 
 Partial division (?) of lower premolar. 
 
 Two cases relate to this subject. The first lower premolar 
 of Felidse is a two-rooted tooth of well-known form. In the first 
 of the following cases it bore an extra talon and root ; in the 
 second there w r as a small extra root on the internal face. (Cp. 
 
 C. vulpes, No. 230.) 
 
 283. F. tigris : anterior right lower premolar has a thin supernumerary 
 root on internal side of the tooth at the level between the two normal 
 roots. This tooth in form resembled a milk-carnassial to some extent, 
 but it was certainly not one of the normal milk-teeth. C. S. M., 333. 
 
CHAP. IX.] 
 
 TEETH : FELID^E. 
 
 225 
 
 *284. F. fontanieri (see No. 290): anterior premolar of right lower jaw 
 has additional talon on internal and anterior surface (Fig. 47). This 
 
 B 
 
 C 
 
 Fig. 47. Veils fontanieri, No. 284. 
 A. The normal anterior premolar of the left lower jaw. B. The corresponding 
 tooth of the right side from above. C. The same from the lingual side. 
 
 portion has a separate root, and stands somewhat apart from rest of 
 crown, looking like a partially separated tooth. B. M., 90. 7. 8. 1. 
 
 Duplicate Teeth. 
 
 285. F- tigris: on right side, two canines in the same socket, both of 
 large size, the anterior being the smaller; neither is a milk-tooth. 
 Mus. Odont. Soc. 
 
 28C. F. domestica : having a large supernumerary tooth in each 
 upper jaw. The extra tooth was in each case a small but accurate 
 copy of the carnassial tooth (Fig. 48) of its own side. In each 
 
 Fig. 48. The teeth in upper jaw of Cat, No. 286. 
 
 case the extra tooth stood internally to the carnassial tooth, ex- 
 tending from the level of the middle of the carnassial tooth to 
 the level of the middle of the molar. B. M., 83. 3. 10. 1. 
 287. Specimen having a tooth in the upper jaw closely resembling the 
 second premolar ("ju 3 " auctt.) internal to and between it and the 
 carnassial. The internal tooth is slightly smaller than the second pre- 
 molar 1 (Fig. 49). C. S. M., 414. 
 
 1 In this case, it is not possible to say strictly that either of the two teeth " is " 
 the normal second premolar, rather than the other. 
 
 B. 15 
 
226 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 288. Specimen having a small tooth internal to the middle of the lower 
 [?side] carnassial (»?): the extra tooth was here divided into two cusps 
 so that it was a copy of the carnassial. 
 
 Iensel, I. c. 
 
 rK/ 
 
 ^ ~& 
 
 Fig. -49. Plan of teeth in upper jaw of Cat, No. 287. The two teeth marked 
 with crosses are separately shewn, that on the right being the external. 
 
 289. Specimen having a tooth like the last, but not so distinctly divided 
 into two cusps, internal to posterior end of lower carnassial [?side]. 
 ibid. 
 
 Supernumerary Mo lars. 
 
 Cases like the last cannot be clearly separated from cases of 
 true extra molars in series, such as the following. 
 
 It is remarkable that no case of supernumerary upper molar in 
 series seems to be known in Felidas. In the Tiger and other 
 species the upper molar is sometimes single- and sometimes 
 double-rooted. 
 '290. F. fontanieri : a species nearly allied to the Leopard (F. 
 jxirdus), inhabiting the Kiu-Kiang, a geographically isolated region 
 of X. China. Only two skulls are known, and each of them pre- 
 sents an abnormality in dentition (see No. 284). Skull having 
 supernumerary tubercular tooth in series (nfi) behind the left 
 lower molar (m l ). B. M., 1490, a. 
 
 291. r - pardalis: "^2 on left side. Hensel, Morph. Jahrb., 1879, v, p. 541. 
 F. tigrina : tubercular ^2 on left side. Schlegel, P. Z. S., 1866, p. 419. r. lynx : 
 ditto [? side}. Magitot, A nom. syst. dent., p. 103. F. domestica : "supernumerary 
 permanent molar in lower jaw" [no particulars]. Wtman, J., Proc. Boston N. H. S., 
 V, p. 160. F. pardus : doubtful indication that a left m 2 has been present. C. M., 
 933, F. 
 
 Absent Molar. 
 
 F. leo : ml absent on both sides, and there is no space for it behind the upper 
 carnassials. B. M., 3043. The only case seen in all Felidas examined. F. domes- 
 tica : "^ absent [? both sides]. Hensel, /. c, p. 541. 
 
chap, ix.] TEETH : VIVEKRID^E. 227 
 
 VIVERRIDJE. 
 
 Of the Viverrida?, Herpestes and Crossarchus are the only 
 genera represented in collections in quantity sufficient to repay 
 study of their dental variations. In the teeth of these two genera, 
 however, variation is considerable and appears in some interesting 
 forms. 
 
 In Herpestes there is first some evidence of variability in the 
 number of the incisors, including one case of extra incisor. Next 
 the facts respecting the presence or absence of the anterior pre- 
 molar are of some consequence, both as illustrating the general 
 variability and modes of Variation of this tooth, and also be- 
 cause the normal presence or normal absence of the anterior pre- 
 molar is one of the characteristics of different species, which shew 
 a progression in this respect. There is one case which should 
 probably be looked on as an example of duplicate anterior pre- 
 molar. 
 
 There are besides two cases of duplicates of large premolars, 
 but of true supernumerary molars in series only one case was 
 seen. Another specimen shewed what is perhaps partial division 
 of a molar. Of 130 skulls, five had supernumerary teeth, not 
 including cases of unusual presence of anterior premolar. 
 
 Incisors. 
 
 The following cases shewed departure from the normal i 
 
 1 
 
 292. Herpestes gracilis : an extra incisor in lower jaw. ^ and P in 
 place and clearly recognizable on both sides, but between the two 
 second incisors are three small teeth, all of about the same size and 
 shape. Neither of these is a milk-tooth, for the milk-teeth are dis- 
 tinctly different both in size and form. There was no evidence to shew 
 which tooth was the supernumerary one. B. M., 826, a. 
 
 *293. H. nipalensis J" : only four incisors in lower jaws. This is a re- 
 markably clean and sound skull. The four incisors stand close together, 
 filling up the whole space between the two lower canines. There is no 
 reasonable doubt that only four lower incisors have been present. It 
 is difficult to see that any of the four incisors exactly corresponds with ■ 
 any of the normal teeth; for while the two lateral teeth are of about 
 the same size as normal p, they have a different position, arising from 
 the outer sides of the jaw, slightly in front of the roots of the canines, 
 whereas normal P arises internal to the other incisors. To what extent 
 the alteration in position is correlated with the change in number 
 cannot be affirmed. B. M. 146, m. 
 
 *294. H. persicus : only four incisors in lower jaw. Judging from 
 general appearances it seemed that T l was missing from both sides. The 
 teeth stand in a close series between the canines, which are nearer 
 together than in normal specimens. The consequence of this to the 
 arrangement of the bite is curious. The left lower canine bites in its 
 normal place, between the upper canine and &; but the right lower 
 canine bites in front of the upper ^, which is displaced backwards 
 
 15—2 
 
228 MERISTIC VARIATION. [part i. 
 
 towards the right upper canine. The whole anterior part of the lower 
 jaw is thus twisted a little towards the left side. 
 
 Besides these two definite cases of absence of incisors, in the following instances 
 there was a presumption that the absence was due to variation, but a definite state- 
 ment cannot be made. 
 
 H. smithii: only four incisors in lower jaw. B. M., 1435, a. H. gracilis: 
 doubtful casu of absence of p on both sides. B. M., 789, b. H. nyula : doubtful if 
 right £ has been present. B. M. 
 
 Anterior Premolars. 
 
 In the great majority of both Asiatic and African species of Her- 
 pestes the anterior premolar (;/) is normally present in both jaws, and 
 in these species 6 cases of absent ^ were seen. When present it 
 is a tootli of small but still considerable size. It appeared from 
 the specimens that pi in the species H. gracilis (Africa generally), 
 and both l^_ and y in H. galera (E. Africa) are commonly absent. As 
 in other cases of absence of teeth the question arises whether the 
 absence is due to age or accident, or on the other hand to original 
 deficiency. This question cannot be definitely answered, but some 
 considerations touching it should be mentioned. 
 
 First, as has been said, the tooth when present is of moderate size: 
 though small, it is quite large enough to be functional, and is in no 
 sense rudimentary. In his synopsis of the genera, Thomas 1 says of 
 Herpestes, " Premolars ± (if only 3 in either jaw, a diastema always 
 present)." There is however no reason for supposing that the presence 
 or absence of p l is determined by chance. From the fact that a tooth 
 is small, it by no means follows that it is often lost. To any one 
 handling large numbers of skulls, instances of the contrary must be 
 familiar. .A case in the Otters well illustrates this point. In Lutra 
 vulgaris upper p l is a small tooth, and from its singular position internal 
 to the canine, it might be supposed that the development of the canine 
 might easily push it out; yet in 41 skulls of Lutra vulgaris, only 
 1 case of absence of P^ was seen. Of L. cinerea on the contrary six 
 skulls are without p] ; but as in two young skulls it is present on 
 both sides, there is thus a strong presumption that in this species the 
 tooth is lost with maturity. The frequent absence in the one species 
 and the constant presence in the others points to a difference in 
 organization between them. When p 1 is missing in a skull, though we 
 are not entitled to infer that it has not been present, still the fact of 
 its presence in one case and of its absence in another is on the face of 
 it an indication that between the two there is a difference or Variation, 
 but whether the Variation lay in the number of teeth originally 
 formed or in the mode in which they were affected by subsequent growth 
 is uncertain. In the specimens to be described the absence of p l in 
 certain individuals or species is no less definite than its presence in the 
 others, and that which is a variation in one species will be seen to be 
 the rule in others. 
 
 As regards the presence of p x the specimens thus make a progressive 
 series. Most species having^, but p± as a variation; H. gracilis (and 
 
 pulverulentus) having p± normally, but pj as a variation and p 
 
 o — o 
 
 1 Thomas, 0., on the African Mungooses, P. Z. S., 1882, p. 62. 
 
chap, ix.] TEETH I HERPESTES. 229 
 
 also as a variation ; and lastly //. galera having p^ normally but shew- 
 
 3 4 4 4 
 
 ing a case of p-~- and another of p- ~ . Lastly, all specimens of 
 
 Crossarchus seen had p^. 
 
 Of species commonly having p±, 91 such skulls and the following cases of absence 
 of jJ l were seen : 
 *295. H - ichneumon, 9 normals: ^i absent both sides. B. M. ; on left, C. M., 
 965, D. H. griseus, 21 normals : pi absent on right, two cases. B. M., 
 145, k and m. H. smithii. 6 normals: pi absent both sides. B. M., 979, b; on 
 left side, B. M. 84. 6. 3. 13. 
 
 296. H. gracilis on the contrary shewed j^i m 8 specimens, p 1 present both sides 
 once, B. M., 789, a ; left pi absent once. B. M., 789, b. 
 
 H. pulverulentus : p± in 2 specimens. 
 
 297. H. galera : pf in 7 skulls, one being quite young: p 1 is present in all four places, 
 in one young skull making pf, B. M., 148, d; pi and p} both present and well 
 developed on right side in old skull. On the left there is ample room for them. B. 
 M., 79, a, P} present on both sides and alveolus for pi on right. B. M., 148, I. 
 
 Crossarchus : 13 skulls assigned to 4 species, all had pf • 
 
 Case of two Anterior Premolars. 
 
 298. H. microcephalus : on right side two teeth like p^, crowded 
 together, others normal. Leyd. M. Compare JRhinogale melleri (an 
 
 5 Q 
 
 African Mungoose) of which only known skull (in B. M.) has p j -. 
 
 The appearance here is that a tooth unlike and rather larger than p^ 
 stands in front of it on each side (see Thomas, I.e., pp. 62 and 84). 
 
 Supernumerary Large Premolars. 
 
 Taken together the two following cases are important as illustrating 
 the difficulty of drawing any sharp distinction between cases of dupli- 
 cates of particular teeth and cases of extra teeth in series. They 
 should be read in connexion with the cases of F. domestica (No. 286), 
 Helictis orientalis (No. 312), Vison liorsfieldii (No. 311), Ommatophoca 
 7'ossii (No. 320), Plioca grcenlandica (No. 324), &c. 
 *299. Herpestes gracilis: supernumerary tooth in right lower jaw 
 (Fig. 50). On comparing the teeth of this specimen with those of 
 
 Fig. 50. Bight lower jaw of Herpestes gracilis, No. 299. View from labial side ; 
 ground-plan of the jaw ; separate view of the tooth + . C, the canine. 
 
 other Herpestes in which jp is present it is quite certain that no tooth 
 in the abnormal jaw corresponds with p. The foremost of its pre- 
 molars on both sides clearly has the form of $K The next teeth have 
 the correct form of p*. In the left lower jaw the next tooth is p; but 
 
230 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 on the right side immediately in succession to j? but slightly within 
 the arcade is another tooth (marked + in the figure), which is very nearly 
 a copy of p*, though a little smaller. On the outside of the jaw and 
 behind this tooth is a normal p. From its singular position outside 
 the series, this tooth might easily be taken for a supernumerary one 
 though its form clearly shews it to be a natural p* displaced, while two 
 teeth having the form of p* stand in succession. B. M., 63. 7. 7. 18. 
 (mentioned 'by Thomas, P. Z. S., 1882, p. 62). 
 300. H. ichneumon (Andalusia): in one of the upper jaws between 
 and internal to l^ and i^ 3 is a 3-rooted tooth (not a milk-tooth) which 
 in size and shape is about intermediate between P^ and p\ Leyd. M. 
 
 Molars. 
 
 The only cases of noticeable variation in molars were both in 
 the same species, Crossarchus zebra. Of this species six skulls were 
 seen, four normal, and also the two following, the first being a case 
 of extra molar on each side, the next a case of increase in size and 
 complex variation in w 2 , on the left side suggesting a partial divi- 
 sion of this tooth. 
 f 301. Crossarchus zebra : small but well-formed additional molar 
 in upper jaw on each side, making pf, m\. (Fig. 51, III.) Teeth 
 unfortunately all much worn, so that it is not possible to determine 
 whether any of the molars differ from their normal forms in corre- 
 lation with the existence of these extra teeth ; but as far as size is 
 concerned, there was no sign of such change, ^ and ȣ being of 
 the usual size. B. M., 73. 2. 24. 18 mentioned by Thomas, P. Z. 
 S., 1882, pp. 61 and 89. 
 
 Fig. 51. Crossarchus zebra. I. Posterior upper molars of No. 
 II. A normal specimen, right upper jaw. 
 III. Upper jaw of No. 301. 
 
 302. 
 
chap, ix.] TEETH : MUSTELINE. 231 
 
 302. C. zebra: all teeth normal except second molars in the upper 
 jaws on each side, which depart from the normal in the following 
 manner. Right ^ has a small extra cusp (Fig. 51, I.) on its outer 
 side, making four instead of three as usual (cp. figure of normal, 
 Fig. 51, II.). The left ™? is very extraordinary. It is rather less 
 than twice the size of its fellow of the other side (Fig. 51, 1.). The 
 crown is of an irregularly elliptical form, the long axis being oblique. 
 The posterior and anterior faces are marked by a shallow groove, 
 giving an appearance of imperfect division into two teeth. The total 
 number of cusps is greater than twice that borne by the other, but 
 from the irregularity of the surface it is not possible to speak more 
 precisely. For fear of injury the tooth was not extracted, so that 
 the number of roots cannot be specified. B. M., 82. 5. 26. 1. 
 
 303. H. ichneumon (Egypt), having no right m 2 - Leyd. Mus. 
 
 MUSTELIDiE 1 . 
 
 The evidence of dental Variation in this family is at present too 
 small in amount to be of much value. It is chiefly interesting in so 
 far as it relates to cases of the occurrence in one genus or sub-family, 
 of a formula characteristic of another. Variations of this class, con- 
 sisting in the presence of or absence of the anterior premolar or last 
 molar, are in some of the forms very common. As will be suggested 
 in the next chapter, some of these, for example, the variations in p 1 in 
 the Badger, have a certain importance as giving some measure of the 
 magnitude which a tooth may have when the species is, as it were, 
 oscillating between the possession and loss of the tooth in question. 
 
 Amongst Mustelidse there were two cases of supernumerary large 
 premolars, probably reduplicatory. 
 
 A nterior Premo lars. 
 
 Mustela (Martens), normally p±, m%. Seen in adult skulls of various species 
 [M . peunanti, mattes, foina, zibellina, Jlavigula, americana), 62: also the following: 
 3Q4 M. foina <? : pi absent both sides. B. M., 1229, k. M. zibellina: p l absent 
 both sides from both jaws [perhaps lost], B. M., 58. 5. 8. 189. M. flavigula. 
 Madras, p 1 clearly absent from both jaws, B. M., 79. 11. 21. 621. M. martes ? 
 the same. C. S. M., 681. Ufl. melanopus: p 1 absent, probably lost, B. M., 42. 1. 
 19. 100. 
 
 Futorius (Weasels, Stoats, Ferrets and Polecats), normally p% , mh. Seen in 
 
 adult skulls of various species (P. vulgaris, erminea, brasiliensis = xanthogenys f 
 
 fcetidus = eversmanni = sarmaticus, lutreola, nudipes, &c), 105: also the following: 
 
 305. p - erm *nea: 1. ^ absent, B. M., 43. 5. 27. 11. On the other hand, P. foetidus, 
 
 ' B. M., 192 s, has rt. ^ as a two-rooted tooth, standing in a plane at right angles to 
 
 the arcade. 
 
 Gulo : p^, mh 5 specimens. 
 
 1 Totals of normal skulls refer to Brit. Mus. and Cambridge Mus. only. 
 
232 MERISTIC VARIATION [part I. 
 
 Galictis : ;>:], mk. Normal adults (G. barbara 8, vittata 4, alla- 
 mo it'll 2), 14 specimens. 
 *306. Gr. barbara, having minute extra anterior premolar (making 4) in 
 each lower jaw. B. M., 839, f. 
 
 In 28 skulls Hensel found the following variations in premolars, 
 the molars being always ?/*.!• 
 
 p - — , viz. the normal, 12 cases 
 o — o 
 
 3—3 „ 
 
 '■■1=2 6 » 
 
 3—3 , 
 
 ' ; 3-2 3 
 
 53 
 
 3—3 
 * 2-3 
 
 9 
 
 - 1 5) 
 
 2 3 3 2 4 4 2 2 3 4 
 
 ;i]s ° J ' J^2 ,P 3~r3' P 2--r P 2~~3' 7 ' 3^3 ea ° h ™ ° ne CaSG ' 
 Taken together therefore there were 12 normals with j>%, 16 cases of 
 greater or less reduction, and 2 cases of increase. Hensel 1 , Saugethiere 
 Sud-Brasiliens, p. 83. 
 
 307. G - vittata: p 1 may be absent, especially from upper jaw. Bukmeister, Reise 
 durch d. La Plaata-Staten, Halle, 1861, n. p. 409 [this variation not seen by 
 Hensel]. 
 
 Poccilogale: p|, m{. 3 specimens. 
 Mephitis : p!}, mh. 9 specimens. 
 
 308. Conepatus: p$, m$. 12 specimens. Conepatus is the S. American representa- 
 tive of Mephitis, and normally differs from it in having one premolar less in upper 
 jaw. This tooth is sometimes present as a minute tooth making p% . Sometimes 
 on the contrary there is a premolar less in the lower jaw, giving p\. Coues, 
 Fur-bearing Animals of N. Amer., p. 192 and Note. 
 
 In addition to the 12 normals mentioned two cases of pf were seen, viz. 
 C. mapurito, B. M., 88. 11. 25. 8, and C. chilensis, B. M. 829, a. In the former 
 the anterior premolar is of good size, but in the latter it is very rudimentary. 
 Another case mentioned by Baibd, Mamm. of N. Amer., p. 192. 
 
 Mydaus : pf, ml. 4 specimens. 
 
 *309. Meles : commonly pj-, m\. In M. taxus, the common Badger, 
 p } is frequently absent from one or more places. Of 36 skulls only 16 
 had p* in all jaws, 7 have it in each lower jaw and 2 had no such tooth 
 in either jaw. In remaining cases it was sometimes absent on right, 
 sometimes on left, sometimes from above and sometimes from below. 
 Some of these cases may be due to senile changes but this was certainly 
 not so in all. Absence from lower jaw seems the most common. 
 Hensel, Morph. Jahrb., 1879, v. p. 550. 
 
 Of genus Meles the following were seen by myself. + means pre- 
 sence, — absence of p l . 
 
 1 The numbers given by Hensel are the totals of p + m, but he states that 
 the variation always concerned the small anterior premolars next the canines. 
 
CHAP. IX.] 
 
 TEETH : MUSTELID^E. 
 
 233 
 
 
 Upper jaw 
 
 Lower jaw 
 
 
 
 ji. 
 
 i 
 
 Cases 
 
 
 right 
 
 left 
 
 r" 
 
 right 
 
 left 
 
 
 Meles ta.riis 
 
 + 
 
 + 
 
 + 
 
 + 
 
 3 
 
 )> )j 
 
 - 
 
 - 
 
 + 
 
 j- 
 
 16 
 
 >5 »1 
 
 - 
 
 - 
 
 ? 
 
 ? 
 
 1 
 
 ») 11 
 
 — 
 
 — 
 
 — 
 
 — 
 
 1 
 
 )) )J 
 
 + 
 
 - 
 
 4- 
 
 + 
 
 3 
 
 il/. ana kirn ) 
 
 + 
 
 + 
 
 
 + 
 
 1 
 
 25 
 
 2 
 
 Japan ) 
 
 
 
 
 
 
 M. chinensis 
 
 
 
 
 3 
 
 Taxidea : p% , mj. 7 specimens. 
 IVIellivora : p% , m^-. 7 specimens. 
 Helictis: p±, m\. 6 specimens. 
 Ictonyx ( = Zorilla) : p%, m\. 14 specimens. 
 
 310. Lutra. The Otters for the most part have p±, mh. The anterior 
 premolar of the upper jaw is a small tooth standing internal to the 
 canine, but in the common Otter its presence is most constant. In the 
 Oriental L. cinerea, and the Neo-tropical L.feUna on the contrary this 
 tooth appears to be more frequently absent than present. The follow- 
 ing table gives the results of examination of a series of skulls. 
 
 + signifies presence, — absence of p\ 
 
 Lutra vulgaris 
 
 11 11 
 
 ,, macrodus 
 
 11 11 
 
 ,, cinerea 
 
 '» >j 
 
 ,, Sumatra na 
 
 ,, capensis 
 
 ii ii 
 
 ,, maculicollis 
 
 ,, felina 
 
 ii ii 
 
 >) )> 
 
 ,, sp. (S. America) 
 
 »j ii 
 
 ii ii 
 
 right 
 
 left 
 
 Cases 
 
 + 
 
 + 
 
 40 
 
 — 
 
 + 
 
 1 
 
 + 
 
 + 
 
 11 
 
 
 — 
 
 2 (1 old ; 1 young) 
 
 + 
 
 + 
 
 2 (young) 
 
 — 
 
 — 
 
 6 
 
 + 
 
 + 
 
 4 
 
 + 
 
 + 
 
 1 
 
 — 
 
 — 
 
 1 
 
 + 
 
 + 
 
 1 
 
 + 
 
 + 
 
 3 
 
 — 
 
 — 
 
 3 
 
 + 
 
 — 
 
 2 
 
 + 
 
 + 
 
 14 
 
 — 
 
 — 
 
 1 
 
 + 
 
 ~ 
 
 1 
 
 In L. cinerea ( = leptonyx) the absence of l^_ is associated with a 
 more forward position of p^, of which the anterior border is then level 
 with the posterior border of the canines 1 . 
 
 1 See Flower and Lydekker, Mammals, Living and Extinct, p. 568, Fig. 261. 
 
234 
 
 MEBISTIC VARIATION. 
 
 [part I. 
 
 Large Premolars. 
 
 311. Putorius (labelled " Vison Horsfieldii"): at the place in which 
 the right lower posterior premolar ("j7 4 ") should stand there are two 
 such teeth at the same level. They are almost identical, but the inner 
 
 -A 
 
 Fig. 52. Putorius, No. 311, right lower jaw, ground-plan of teeth and profile 
 views of two teeth at the same level. Upper figure is the internal tooth. 
 
 (upper in figure) is slightly the smaller (Fig. 52). B. M., 823, a. 
 312. Helictis orientalis, Java: having supernumerary two-rooted 
 tooth internal to and between p 2 and f£. This extra tooth is almost a 
 copy of if (Fig. 53). B. M., 824, a. 
 
 Fio. 53. Helictis orientalis, No. 312. Surface view of upper jaw and a 
 representation of the right upper teeth as seen from inside. 
 
 Molars. 
 
 313. Putorius: Hensel, Morph. Jahrb., v. 1879, p. 540, states that he 
 has several skulls of Fcetorius putorius with an extra upper molar on 
 one side in a rudimentary condition. Giebel, Bronn's Kl. u. Ord., p. 
 18G, Taf. xv. figs. 1, 2 and 3, figures a specimen of "Putorius typus" 
 having a fairly well developed extra upper molar on each side making 
 m# instead of m\. Probably both these accounts refer to P. fcetidus. 
 
 314. Lutra platensis: supernumerary molar on one side of upper jaw. 
 Such a tooth normally present on both sides in L. valetoni, a fossil 
 form. Von Heuglin, Nov. Act. Leop. Car. Cces., xxix. p. 20. Lutra 
 
* 
 
 chap, ix.] TEETH : PINNIPEDIA. 235 
 
 sp., S. America, B. M., 85. 11. 23. 1, has small alveolus behind?^ on each 
 
 side. 
 315. Mellivora (= Ratelus): similar case. Vox Heuglix, ibid. 
 31(3. Meles taxus has normally m\. Skull from Quarternary diluvium 
 
 of Westeregeln has small alveolus behind right w^ and left m 7 -. Another 
 
 fossil skull has m§. Nehring, Arch. f. Anthrop. x. p. 20. [1 Small 
 
 alveolus behind left m* in B. M., 211, L] 
 
 31/. Lutra: case of absence of ^a; Mustela : ^ may be absent. Hensel, I. c. 
 
 PINNIPEDIA. 
 
 With reference to dental Variation in Otariidae and Phocidse 
 there is a considerable quantity of evidence. Id some of the species 
 the frequency of abnormalities is remarkably great. Among the 
 most interesting examples are two cases of reduction in the number 
 of incisors, both occurring in Phoca barbata. These cases are 
 especially important in connexion with the fact that the Seals are 
 exceptional among Carnivores in having a number of incisors other 
 than §, and that among the different sub-families of Seals there is 
 diversity in this respect. 
 
 Taken together, the cases of Variation in the premolars and 
 molars of Seals illustrate nearly all the principles observed in the 
 numerical Variation of teeth. In both premolars and molars there 
 are examples of the replacement of one tooth by two, and in some 
 of these the resulting teeth stand in series while in others they 
 do not. Besides these there are numerous instances of extra pre- 
 molars and molars belonging to various categories. 
 
 As regards the frequency of extra teeth in Seals it may be 
 mentioned that of Phocidae 139 normals were seen, and 11 cases of 
 supernumerary teeth ; of Otariida? 121 normals and 5 cases of super- 
 numerary teeth. 
 
 From the simplicity of the normal dentition and from the 
 diversity of the variations presented, the evidence as to the teeth 
 of Seals may conveniently be studied by those who are interested 
 in the phenomena of Variation without special knowledge of the 
 subject of mammalian dentition. 
 
 Incisors. 
 
 It will be remembered that of Phocidae the sub-family Phocinae 
 (like Otariidae) has normally if, while the Monachinae have if and 
 the Cystophorinas i \. Of Phocinae of various genera and species 
 105 skulls having if were seen, and in addition the two following. 
 
 318. Phoca barbata. Greenland: skull having i\ on both sides 
 (Fig. 54). This skull is a particularly good one and is neither very 
 old nor very young. The teeth stand regularly together and there 
 is no lacuna between them. There is no reasonable doubt that 
 an incisor is absent from each side of each jaw. The shape of the 
 
236 MERISTIC VARIATION. [part i. 
 
 premaxillae is different from that seen in other specimens of Phoca, 
 and, doubtless in correlation with the absence of the two upper 
 
 Fig. 54. Incisors and canines of Phoca barbata, No. 318. 
 
 incisors, the width of the premaxillae is considerably less than in 
 specimens having the normal dentition. B. M., 90. 8. 1. 6. 
 319. P« barbata: in left upper jaw are three normal incisors; but 
 on the right side the incisors have been lost. The alveoli, however, 
 shew plainly that only two incisors had been present. Of these 
 the outer one in size agrees with P, being a large alveolus equal to 
 that of i"3 of the other side, but the second alveolus, occupying the 
 place of i l and i 2 , is also a large alveolus, scarcely smaller than that 
 for R It appears therefore that in this specimen a single large 
 tooth stood in place of i 1 and %K A lower jaw placed with this skull 
 was normal, but it was not certain that it belonged to the skull. 
 O.M., 1724. 
 
 Premolars and Molars. 
 
 Normal arrangement. In Phocidae there are normally five 
 teeth behind the canines in each jaw, and according to the received 
 accounts, of these teeth 4 are premolars and one is a molar, giving 
 p f> m p T ne Otariidae on the other hand have generally p |, m f , 
 but both the two upper molars stand at a level behind that 
 of the lower molar, so that the posterior molar, w* 2 is placed so 
 far back that it meets no tooth in the lower jaw. Some of the 
 Otariidae, however, as 0. californiana, do not possess such a pos- 
 terior tooth, and have only m {. 0. stelleri is peculiar in the fact 
 that it also has only one upper molar, but this tooth is separated 
 by a large diastema from p 4 , and stands in the position character- 
 istic m 2 of the other Otariidae. Hence it may be supposed that ^ 
 is really absent while »& 2 is present. 
 
 Amongst the cases will be found some of the presence in Pho- 
 cidas, especially Halichoerus, of an extra molar placed in the usual 
 position of ȣ in the Otariidae. But lest any one should think it 
 manifest that this is an example of Reversion to the Otarian con- 
 dition, attention is called to cases of such an extra molar in the 
 Otariidse also. Similarly there are instances of absent molar in 
 those Otariidae which have m f , leaving m -j- ; and of these cases one 
 occurs in such a way as to leave the peculiar diastema between 
 
CHAP. IX.] 
 
 TEETH : PINNIPEDIA. 
 
 237 
 
 * 
 
 P^ and the molar, referred to above as characteristic of 0. stelleri 
 (see No. 342). 
 
 The cases are grouped in an arbitrary collocation, according as 
 it seemed desirable that particular variations should be studied 
 together. In the sections dealing with premolars, Phocidae are 
 not separated from Otariida 1 . 
 
 First Premolar. 
 
 320. Ommatophoca rossii, an Antarctic Seal. Of this form only 
 two skulls are known, both in the British Museum. One of these 
 (B. M., 324, b.) has the arrangement usually found in Phocidae, 
 namely, five teeth behind the canines in each jaw, giving the 
 formula 
 
 .2—2 1 — 1 5—5 
 
 *2ZT2' fl I— I>^ + m 5=5 
 
 (on the analogy of other Seals p|, m\). The other specimen is 
 exceedingly remarkable (Fig. 55). In it the incisors and canines 
 
 Fig. 55. Ommatophoca rossii, No. 320, teeth of the upper jaw. 
 
 are as in the first specimen, but the first tooth behind the canines 
 on both sides in the lower jaw and on the right side in the upper 
 jaw, has a very peculiar form, having a deep groove passing over 
 the whole length of the tooth, on its outer and inner sides. These 
 grooves extend from the tip of the root along both sides of the 
 crown, and thus imperfectly divide each tooth into an anterior and 
 
238 MEBISTIC VARIATION. [part i. 
 
 a posterior half. The cusp of each tooth is also divided by the 
 grooves so as to form two small cusps. Each of these teeth is 
 therefore an imperfectly double structure, and may be described as 
 being just half-way between a single tooth and two teeth. These 
 teeth are shewn in Fig. 56. 
 
 Fig. 56. Ommatophoca rossii, No. 320. The anterior premolars of upper and 
 lower jaws from the side. (The left lower and right upper teeth were not 
 extracted.) 
 
 On the left side in the upper jaw, as the vis-a-vis to one of 
 these double teeth, there are actually two complete teeth, of very 
 similar but not identical form, as shewn in Fig. 56. Each stands 
 in a distinct alveolus, the two being separated by a bridge of bone. 
 The dental formula of this skull, taken as it stands, is therefore 
 
 p' i' m n T> f° r snlce the bigeminous teeth are not com- 
 pletely divided, they must be reckoned as single teeth. 
 
 321. Cystophora cristata : internal to and slightly in front of p 1 on 
 each side in the upper jaws is an extra tooth. These extra teeth are 
 alike in form but are rather smaller than jp\ C. M., 895. 
 
 322. Cystophora cristata (label, Phoca cristata): internal to right 
 upper p^ is an alveolus for a small one-rooted tooth. In the corre- 
 sponding situation in the left lower jaw there is such an extra tooth in 
 place. Leyd. M. 
 
 323. Zalophus lobatus ( = Otaria lobata): left 2^ smaller than right 
 j^, and between the canine and the left F 1 there is a supernumerary 
 tooth, smaller than left P 1 . (The same skull has another extra tooth 
 outside and between F* and i^, see below No. 333.) Leyd. M. 
 
 [P. vituUna: alveolus for left #] much larger than that for rt. v l \ the latter 
 tooth is in place, hut left & is missing. C. M., 902.] 
 
 Large Premolars. 
 
 324. P« groenlandica : in the position in which left upper p*> should 
 stand there are two whole and complete teeth, each as large as normal 
 p^. Fig. 57). The two stand perfectly in series, and owing to the wide 
 
CHAP. IX.] 
 
 TEETH : PINNIPEDIA. 
 
 239 
 
 gaps normally existing between the teeth in this species there is no 
 crowding. Between these two teeth there are slight differences of 
 
 325, 
 
 Fig. 57. Phoca groenlandtca, No. 324. Left and right profiles. 
 This figure was kindly drawn for me by Mr J. J. Lister. 
 
 form, and the posterior is rather the larger. On both sides w^ is in 
 place and at the same level. Both the two teeth in place of p^ bite be- 
 tween p* and ™} of the lower jaw. On the right side F* is normal and m^ 
 is also normal but P^ is a very large and thick tooth, and its main cusp 
 is cloven, giving it the appearance of imperfect division into two. In 
 this case therefore p^ on the one side may be supposed to have divided 
 into two perfect and nearly similar teeth, while on the right side this 
 division is begun but not completed. Leyd. M. 
 
 Otaria ursina £ : supernumerary premolar in left upper jaw. 
 This is a curious case. The right upper and both lower jaws are 
 normal. On comparing the left upper series of 7 teeth with the right 
 series which has 6 normal teeth, it is seen firstly that the two molars 
 of each side are alike in form and stand at their proper levels (Fig. 58). 
 
 Fig. 58. Otaria ursina, No. 325, seen from left side. 1, 2, 3, 4, first to fourth 
 lower premolars ; 5, lower molar. 
 
 Next, the two posterior premolars of each side (f* and F 4 ) agree so 
 nearly that there is no reasonable doubt that they are not concerned 
 in the variation. Anterior to this there is difficulty, for whereas p l 
 and p 2 are normal and in place on the right side, there are three teeth 
 on the left side to balance them. These three teeth moreover are so 
 nearly alike that it is impossible to say that either of them is 
 
240 
 
 MEMSTIC VARIATION. 
 
 [part I. 
 
 * 
 
 definitely the extra tooth. The first premolars of each side are almost 
 exactly alike, and the second and third of the left side are each very 
 like the second on the right side (p 2 ), so that it might be said that p 2 
 was represented by two teeth on the left side; and as seen in Fig. 58 
 the second and third on the left side bite between f- and p of the lower 
 jaw, as the normal p 2 would do. This is however accomplished by the 
 backward displacement of p*. Probably therefore this should be looked 
 on as a case of division of P^, but there is no proof that the three first 
 premolars of the left side are not collectively equivalent to the first 
 two of the right side. C. M., 911, f. 
 
 326. P. grcenlandica : the second upper right premolar is represented 
 by two teeth, each of which has two roots; the two teeth stand at the 
 same level in the arcade, the inner one being rather smaller. On the 
 left side the second upper premolar is incompletely double, the crown 
 being partially divided by an oblique constriction into an anterior and 
 internal portion and a larger posterior and external part. The former 
 has one root and the latter two. P. M., A, 2897. 
 
 327. Otaria jubata : left upper p 3 a bigeminous tooth something like 
 the anterior premolars of Ommatophoca (No. 320). In this animal all 
 the premolars and molars are one-rooted and have single conical 
 crowns. The abnormal tooth is formed as it were of two such simple 
 teeth imperfectly divided from each other through their whole length, 
 the plane of division being transverse to the jaw. The teeth of the two 
 sides are not alike and in particular the posterior lower m} is much 
 smaller than the right. The skull has been much mended and the 
 position of some of the teeth is not very certain, but the above- 
 mentioned facts are correct. C S. M., 975. 
 
 oZo. Otaria cinerea : supernumerary tooth in upper jaw on both sides. 
 The extra tooth in each case stands within the arcade, internal to the 
 
 Fig. 59. Otaria cinerea, No. 328. A diagram of the positions of the upper 
 teeth, and profiles of the teeth standing internal to each m*. 
 
 5th tooth behind the canine (sc. »^), which is pushed outwards by it. 
 The extra tooth of the left side (Fig. 59) is a little larger and at a level 
 rather anterior to that of the left extra tooth. C. M., 911 **. 
 
CHAP. IX.] 
 
 TEETH .* PINNIPEDIA. 
 
 241 
 
 *329. P. vitulina : having a supernumerary tooth in each jaw on the 
 right side. This is a somewhat remarkable case. In both jaws the 
 extra tooth does not stand in series with the others but is placed 
 within the arcade (Fig. 59, + + ). That of the upper jaw is a curved 
 tooth with one large median cusp and a small cusp anterior to and 
 posterior to it, having somewhat the form of p* of the lower jaw. This 
 tooth stands within the arcade at a level between that of l^ and F 5 which 
 are pushed outward by it. The extra tooth of the lower jaw in shape 
 closely resembles that of the upper jaw, but is slightly larger, having 
 very much the size and shape of the lower right jp. In position this 
 extra tooth does not stand between p 2 and p 3 like the upper supernum- 
 erary, but is placed ivithin the arcade and p and p* which are some- 
 what separated by it. C. M., 903. [Judged by the ordinary rules of 
 dental homology, the two extra teeth are not homologous, for the 
 upper one is between p 2 and p-\ while the lower one is between p and 
 p 4 . But when the jaws are put together it appears that the two extra 
 teeth are opposite to each other almost exactly, the large cusp of the 
 lower one being in the bite scarcely at all posterior to the large cusp of 
 the upper. The tooth of the lower jaw is thus almost exactly the 
 image or reflexion of the tooth in the upper jaw.] 
 
 Fig. 60. Phoca vitulina, No. 329 ; view of upper teeth from the surface, and 
 an imaginary profile of the upper and lower teeth of the right side seen from 
 within. 
 
 330. Otaria ursina : this skull in bad condition. The Catalogue 
 (1884) states that between F 2 and l^ on both sides and between P^ and nfl 
 on both sides there was a small supernumerary tooth, in all, four extra 
 teeth in the upper jaw. The anterior supernumeraries are in place and 
 one rather smaller than v\ The posterior supernumeraries are lost, but 
 from the alveoli they must have been of fair size, though not so large 
 
 B. 16 
 
242 MERISTIC VARIATION. [Px^rt i. 
 
 as lA In each case the extra tooth is placed a little within the arcade 
 though the adjacent teeth are also spaced out for it. This skull has 
 been a good deal mended. C. S. M., 990. 
 
 331. Phoca grocnlandica : in right upper jaw p^ is smaller than the corresponding 
 tooth of the left side, though it is two-rooted as usual. Between it and pI there is 
 a small, peg-like, supernumerary tooth. Both p^ and the extra tooth bite between 
 pi and m 1 of the lower jaw. Leyd. M. 
 
 332. P. grocnlandica: supernumerary tooth with two roots placed internally to and 
 between left & and m\ The last molars stand at the same level on the two sides. 
 B. M.,328, i. 
 
 333. Zalophus lobatus: in right upper jaw a supernumerary tooth placed on the 
 outside of the arcade on a level with the interspace between p* and p 4 . This tooth 
 resembles p 4 or m 1 . On the left sidep 1 is smaller than on right side and a supernu- 
 merary tooth which is still smaller stands between p^ and the canine. Leyd. M. 
 [given above, No. 323]. 
 
 334. P. vitulina: in right lower jaw a supernumerary tooth inside the arcade, 
 between pi and pi. In size and form it agrees very nearly with the first premolar 
 of the right lower jaw: other teeth normal. C. M., 903, F. 
 
 335. 3P. vitulina: in front of p* on left side the teeth are all lost but there has been 
 some irregularity, probably a supernumerary tooth level with pi : also behind right 
 nfl there is a small tubercular nodule of bone which may perhaps cover a supernu- 
 merary molar. C. S. 31., 1064. 
 
 Molars. 
 
 336. P. vitulina : on left side there is a small supernumerary molar 
 placed behind »^. This tooth stands in the line of the arcade (Fig. 61) 
 
 Fig. 61. Phoca vitulina No. 336, a profile of the left teeth in the bite as seen 
 from within. 
 
 but is turned so that its greatest width is set transversely to the jaw. 
 In the lower jaw of the same side there is a supernumerary tooth placed 
 internally to m l . This tooth has two roots and three cusps, and is 
 therefore not a copy of m 1 , which has 4 — 5 cusps. C. S. M., 1067. 
 
 '337. Halichoerus grypus : of 47 skulls seen, 12 have one or more 
 supernumerary molars. One case of p% , m§. Nehring, Sitzb. 
 naturf. Fr. Berlin, 1883, p. 110. 
 
 2 2 
 
 Of 34 skulls in Greifswald Museum there were 3 cases of m ^ , 
 
 and five cases of m\ on one side only. Ibid., 1882, p. 123. 
 
 Of 11 skulls seen by myself two individuals (C. M.) have an 
 extra molar on left side. In these cases the extra teeth are 
 placed at a considerable distance behind ȣ as they are in Otaria. 
 [In addition to these Gray figures a skull with m\ but without 
 allusion to this fact in the text. Hand-list of Seals in B. M., 
 1874, PL vil] 
 
chap, ix.] TEETH : UNGULATA. 243 
 
 A skull having left ml two-rooted, right ml being much less so. 
 C. S. M., 1059. 
 
 338. •P- groenlandica : minute supernumerary molar on each side in 
 upper jaw making m'f . P. M., A. 2898. 
 
 339. Zalophus californianus, an Eared Seal not far removed from 
 
 tar la. but having p + mi instead of ~. The five back teeth are arranged 
 as a rule in a continuous series, but sometimes there is a small space 
 between the last molar and the penultimate [cp. 0. stelleri], and occa- 
 sionally they are all slightly and evenly spaced. 
 
 One case of p + m £ on both sides and two cases of p + m£ on one 
 side only. In these the extra teeth were behind the (normally) last 
 molar and smaller than it. being without the accessory cusps seen in 
 that tooth. Allen, J. A., J\\ Amer. Pinnipeds, 1880, pp. 209, 224 and 
 226. 
 
 340. Z. lobatus : one specimen having p + w^f on right and £ on left, 
 Leyd. M. [in addition to 3 specimens with the normal £]. 
 
 7 — 7 
 
 341. Callorhinus ursinus : normally £> + m£; one case having 
 
 o — o 
 
 and one case with - -. Allen, I. c, p. 224 (cp. No. 343). 
 
 o — o 
 
 deduction in numbers of molars. 
 
 q 5 
 
 342. Arctocephalus australis, normally p + mf : one case of „ — . 
 
 General statement made that in cases of absence of a tooth it is the 
 antepenultimate molar which is missing [not described in a specific 
 case]. Allen, I. c, p. 224. 
 
 343. Callorhinus ursinus, normally £; 2 cases of i. Allen, I. c. (cp. 
 No. 341). 
 
 344. Otaria jubata, normally 4: one specimen having 4- on both sides, 
 Leyd. M.; one specimen having right 4 left 4. Leyd. M. 
 
 Cystophora cristata: only one molar, viz. left ^ present; from the state of 
 the bones it seemed possible that the others had not been formed, but this is quite 
 uncertain. C. S. M., 1101. Macrorhinus leoninus: doubtful if the molars had 
 been present. C. S. M. 1109. 
 
 UNGULATA. 
 
 As to the occurrence of Variation in the dentition of Ungulates 
 
 1 have no statistics, but a certain number of miscellaneous cases 
 have been collected from different sources. Most of the cases 
 relate to domestic animals and are given on the authority of 
 Morot and Goubaux. 
 
 Perhaps the most interesting evidence is that regarding the 
 change of form in the "canines" of the Sheep. These teeth of 
 course have normally the shape of incisors, but in the cases 
 described by Morot they had more or less of the character of 
 canines. This evidence, though belonging properly to the Sub- 
 stantive class, is introduced here on account of its close relation to 
 some general aspects of variation in teeth. 
 
 1G— 2 
 
244 MERISTIC VARIATION. [part i. 
 
 * It is noticeable that there is so far no case of an incisor appear- 
 
 ing in the upper jaw of Ruminants. 
 
 The evidence is divided into two groups, the first relating to 
 incisors and canines, the second to premolars and molars. 
 
 Incisors and Canines. 
 
 345. Elephas africanus g : the left tusk imperfectly doubled. The 
 root of this tooth was double 1 , one root being outer and the other inner. 
 The half of the tusk arising from the outer root twisted round and over 
 the other half so that at the other end it lay above and internal to it. 
 The structure of the tusk was essentially double, but the two parts 
 were more or less blended together in the middle third. The ex- 
 ternal ends were separate, but broken and somewhat deformed. 
 Friedlowsky, A., Sitzungsb. d. K. Ak. Wien, 1868, lix. i. p. 333. 
 Plate. 
 
 346. Horse. Supernumerary incisors common. Magitot, Anom. Syst. 
 dent., p. 104, Plates. Numerous specimens in Museum of Veterinary 
 School at Alfort. 
 
 347. Specimen having 12 upper incisors and 12 lower incisors belonging 
 to the permanent dentition. Goubaux, Pec. med. vet., 1854, Ser. 4, I. p. 
 71. Similar observation, Lafosse, Cours Hippiatrique, 1772, p. 32. 
 
 348. Extra teeth of more or less irregular form placed behind upper 
 incisors very common : many specimens in museum at Alfort. Speci- 
 men having left ^ as a double structure, the two halves not being 
 separated. (Alfort Mus.) Magitot, /. c, PI. xix. fig. 25. 
 
 Absence of incisor in Horse is rare. Goubaux, who has largely studied the subject, 
 knew no case of absence of any tooth in Horse, /. c. 
 
 349. Skeleton of Cart-mare in C. M. has only two incisors on the left side in the 
 upper jaw. The teeth stand evenly and without break or trace of any other incisor 
 having been present. There is no sufficient indication to shew which of the incisors 
 is missing, but the two incisors present agree most nearly with i 2 and i 3 . This 
 specimen was first pointed out to me by Mr S. F. Harmer. (See also case given by 
 Kudolphi, Anat.-phys. Abh., 1802, p. 145.) 
 
 *350. Mare of common breed, foaled March, 1876, having in the upper jaw no i 3 in 
 either milk or permanent dentition, and in the lower jaw no permanent P. In the 
 upper jaw there were only 4 milk incisors, which were subsequently replaced by 
 4 permanent incisors. Animal seen by Morot in Apr. 1880 ; it then had 4 per- 
 manent incisors in the upper jaw, but no i 3 . In the lower jaw permanent i 1 and i- 
 were in place, together with i 3 of the milk series on each side. As Morot remarks it 
 is still possible that the other incisors might appear. Dam normal; half-sister 
 abnormal, given in next case. Morot, Bull. Soc. med. vet., 1885, Ser. 7, n. p. 125. 
 
 *351. Mare out of same mother as last case, by another sire, foaled Apr. 1877, had only 
 4 milk-incisors in upper jaw. Seen by Morot at 3 years old, had then the teeth of 
 lower jaw normal, viz. permanent i 1 , and milk i 2 and i 3 all in place. In upper jaw 
 were permanent i 1 and milk i 2 on each side. The right milk /- on the external side 
 had a light groove parallel to the long axis of the tooth, suggesting that it might be a 
 double structure, but the groove was very slight and the crown was single. At five 
 years old this animal had the normal 6 lower incisors, but in the upper jaw left i 3 
 was absent. On the other hand a well-formed supernumerary tooth stood behind 
 right i 3 , right i 2 being partly rotated. Ibid., p. 127. 
 
 1 See also a curious case of "nine tusks " imperfectly described by Chapmax, J., 
 Travels in Interior of S. Africa, n. p. 98. 
 
chap, ix.] TEETH : TJNGULATA. 245 
 
 352. Ass : ( $ some 20 yrs. old) on right side in upper jaw were two 
 canines, one in front of the other in the same alveolus. Morot, Rec. med. 
 vet., 1889, Ser. 6, vn. p. 480. Another somewhat similar case, ibid. 
 
 353. Cow : in j}lace of right p, two third incisors placed side by side. 
 Morot, Bull, et mem. Soc. med. vet., 1886, p. 321. 
 
 Goat, 4 — 5 weeks old ; supernumerary lower incisor placed be- 
 tween the two median incisors which rose above it. This tooth stood 
 transversely so that its edge lay exactly in the long axis of the head. 
 Morot, /. c. 
 
 354. Sheep : extra incisor on left side. (Alfort Mus.). Goubaux, Rec. med. 
 vet., 1854, Ser. 4, I. [Several other cases.] 
 
 Abnormal form of Canines in Sheep. 
 
 355. In the lower jaw of the Sheep there are on each side 4 incisi- 
 form teeth, arranged in close series without any diastema. Of 
 these the outermost, known in veterinary works as " corner teeth," 
 are considered by zoologists as representing canines. 
 
 The corner teeth or canines have been found in a considerable 
 number of cases actually shaped like canines instead of like the 
 incisors as usual. These teeth have been found presenting this 
 modification in several degrees, but in order to gain a fair view of 
 the matter it is necessary to read the evidence in its entirety. 
 
 The facts given were founded on 18 animals, 15 ewes and 3 
 males [whether rams or wethers not stated]. In these 18 cases 
 there were 28 individual teeth of abnormal form. Of these 14 
 were conical with a point either sharp or rounded ; 7 were conical 
 with a bifid point ; 5 were cuneiform ; 1 was cylindrical with a 
 surface shaped like an ass' hoof; 1 was pyramidal. 
 
 In 8 specimens the abnormality was unilateral and in 10 it 
 was bilateral, but in the latter the corner teeth of the two sides 
 were frequently of differing forms [details given]. Morot, Bull. 
 Soc. med. vet., 1887, p. 166. 
 
 Pig". No case of Variation in incisors met with. 
 [This is perhaps singular in connexion with the fact that the 
 Peccaries (Dicotyles) have i -§.] 
 
 356. Dicotyles torquatus (normally £§) : two specimens having 
 
 3 2 
 
 i-= ; in one of them i* of the side having the extra tooth is deformed. 
 
 o — o 
 
 Another young skull of Dicotyles also had 3 incisors on left side. 
 
 Hensel, Sdugetldere Sild-Brasiliens, p. 94. 
 
 Molars. 
 
 357. Horse: supernumerary molars exceedingly rare; case of such a tooth in left 
 upper jaw, behind and in series with the others. Goubaux, Rec. med. vSt. } 1854, 
 Ser. 4, i. p. 71, same case, figured by Magitot, /. c, PI. v. fig. 9. 
 
 * 
 
246 MERISTIC VARIATION. [part i. 
 
 *358. Ass : thoroughbred Spanish she-ass, in the Museum of the Royal 
 College of Surgeons, has a large supernumerary molar on each side in 
 series in the upper jaw, and a similar tooth in the left lower jaw. The 
 same skull has the first premolar also present on each side in the upper 
 jaw, as is not unfrequently the case in Equidse. All four canines are 
 present as minute teeth. The dental formula for this skull is therefore 
 
 ,3_3 l_i 4_4 4 — 1 tK 
 ^3=3 C r=Ti^3=3 m 4^3 =45 ' 
 
 359. Auchenia lama : specimen having a suj>ernumerary (fourth) 
 molar in the lower jaw [? on both sides]. This tooth was fully formed 
 and resembled the normal last molar. In the upper jaw T was a small 
 alveolus behind ?/i 3 , for another tooth which was not present in the 
 specimen. Rutimeyer, L., Vers, einer nattirl. Geschichte des Binder, 
 Zurich, I. p. 55, Note. 
 
 360. Cervus axis $ : specimen having a supernumerary grinder placed 
 on the inside of the normal series on the left side of the upper jaw. 
 In the lower jaw of the same specimen the following supernumerary 
 teeth : (1) a small, compressed accessory tooth on both sides placed 
 internally to m? ; and (2) behind the large three-fold sixth molar was a 
 smaller two-fold tooth which had caused a displacement of the 6th 
 molar. Donitz, Sitzungsb. d. naturf. Fr., Berlin, 1872, p. 54. 
 
 361. Cervus rufus : having supernumerary (4th) premolar on one side 
 in lower jaw. Hensel, Morph. Jahrb., v. p. 555. 
 
 362. Ox : supernumerary upper molar on left side. Magitot, I. <?., p. 
 106. 
 
 Sheep : extra molar in left lower jaw, ibid., p. 105, PI. v. fig. 10. 
 [? some error ; the figure represents a normal jaw.] 
 
 MARSUPIALIA. 
 
 The facts given in illustration of Variation in the dentition 
 of Marsupials relate only to a part of the subject and to selected 
 forms. Some of the cases to be given are however of exceptional 
 importance. Evidence is offered in reference to the following 
 subjects: 
 
 (1) Incisors. 
 
 (2) Premolars, and the "Intermediate" teeth (in the lower 
 
 jaw), of Phalangerida3. 
 
 (3) Premolars and Molars of Dasyuridaa and Didelphyidre. 
 
 (4) Molars of certain Macropodida?. 
 
 (1) Incisors. 
 
 The following cases of Variation in incisors are all that were 
 met with in the Marsupials examined. 
 
 Didelphyid/E : incisors normally f, thus differing from the Dasy- 
 uridpe (i |) with which they have much in common 1 . Of various 
 
 1 Thomas states that the family Didelphyidae "is, on the whole, very closely 
 allied to the Dasyuridae, from which, were it not for its isolated geographical 
 position, it would be very doubtfully separable. " Cat. Marsup. Brit. Mas., 1888, p. 315. 
 
CHAP. IX.] 
 
 TEETH I MARSUPIALIA. 
 
 247 
 
 species 90 adult skulls seen having this number of incisors and three 
 cases of abnormal number of incisors. Of these the first two must not 
 be reckoned in estimating the percentage of abnormalities in a pro- 
 miscuous sample, for Mr Thomas, who kindly shewed me these speci- 
 mens, informs me that they were preserved and brought to the Museum 
 expressly as abnormalities. The existence of these variations is never- 
 theless particularly interesting in connexion with the exceptional 
 number of incisors normal in Didelphys. 
 
 363. Didelphys marsupialis : in right upper jaw six incisors ; left 
 upper jaw and the whole lower jaw missing. B. M., 92. 11. 3. 28. 
 
 364. Another specimen has on the right side |- as usual, but on the left 
 i |-. It appears that i 1 and 7 2 of the two sides correspond, but on the 
 left side three very similar teeth stand in series behind P. B. M., 92. 
 11. 3. 29. 
 
 365. D. turneri (= crassicaudata), Demerara. A single specimen of 
 
 .4 — 4 
 this species in collection. It has i- 7, but there is no evidence to 
 
 4—4' 
 shew which of the upper incisors were missing 
 
 B. M. 
 
 * 
 
 Dasyurid^e : incisors normally ±; of genera other than Myrme- 
 cobius, 63 normal skulls seen. 
 
 Dasyurus sp., having only two incisors in left lower jaw; right lower jaw 
 normal, upper jaws missing [doubtful case]. B. M., 250. 
 
 Myrmecobius fasciatus: with incisors normal 4 whole skulls, 
 
 Right 
 
 n 
 
 Right 
 
 left 
 
 Fig. 62. Myrmecobius fasciatus. 
 
 I. Right and left profiles of upper jaw of No. 366. 
 
 II. Eight and left profiles of the two jaws of No. 367. 
 (Premaxillary teeth alone shewn.) 
 
248 MERISTIC VARIATION. [part It 
 
 5 skulls without lower jaws, and 1 lower jaw without skull ; ab- 
 normals 2, as follows : 
 *3G6. A young skull having in the upper jaw on the left side 
 (Fig. 62, I.) two teeth, both apparently in place of left «?, making 
 
 i%~ . B. M, 314, g. 
 
 *367. A specimen having four incisors in the right lower jaw, the 
 left being normal. Perhaps the two hindmost of the four repre- 
 sent the third lower incisor of the left side in the way suggested 
 by the dotted lines in the figure (Fig. 62, II.). B. M., 314, b. 
 
 Phalaxgerid.e : incisors (neglecting " intermediate " teeth of 
 lower jaw) normally y ; this seen in 209 skulls of various genera and 
 species. 
 
 368. Phalanger orientalis, Solomon Islands: left i 3 as an imperfectly double tooth, 
 having two sub-cylindrical crowns and only one root (Fig. 63). The two crowns 
 
 Fig. 63. Phalanger orientalis. No. 368. 
 
 Upper incisors and canines. The separate figure shews the left P extracted. 
 
 stand in the same transverse plane, the one being internal to the other and rather 
 smaller than it. Lower jaw missing. B.M., 1936, c. [Two other skulls from same 
 locality normal.] 
 
 369. P- maculatus, Port Moresby: only two incisors on each side in the upper jaw. 
 The centrals, £, of each side, are in place; externally to them there is on each side 
 an alveolus for a tooth, which, judging from the size of the alveolus, was probably f . 
 Immediately behind these alveoli the canines follow on each side. In this case it 
 may be said that the missing teeth are & in all probability. Lower jaw normal. 
 B. M., 79. 3. 5. 8. 
 
 370. Specimen having "in each upper jaw two incisors instead of three," [also has 
 no left p}, see No. 377]. Leyd. Mus., 55. Jentixk, F. A., Notes Leyd. Mas., 1885, 
 vii. p. 90. Two specimens, Leyd. Mux., 56 and 61 are without & of right upper 
 jaw, ibid., p. 91. Specimen in which "five of the upper incisors are wanting [only 
 one "intermediate" tooth in left lower jaw, see No. 377]. Leyd. Mas., 63, ibid., p. 91. 
 
 371. Pseudochirus forbesi: of this species only a single skull known; it has no 
 upper P [and no upper first premolar, see No. 379]. B. M., 1943. Thomas, 0., Cat. 
 Marsup. Brit. Mas., 1888, p. 183. 
 
 (2) Premolars, and the "Intermediate" teeth {in the lower jaw) of 
 
 Phalangerid^e. 
 
 The evidence here offered relates to the following genera : — 
 Phalanger, Trichosurus, Pseudochirus, Petauroides, Dactylopsila 
 and Petaurus. Before speaking of the variations seen, a few 
 words are needed in explanation of the nomenclature adopted. 
 
chap, ix.] TEETH : PHALANGERIDJE. 249 
 
 In these forms there is only one tooth having a milk -pre- 
 decessor, and in all the genera here referred to this is a distinct 
 and recognizable tooth, with a chisel-shaped crown. Following 
 Thomas' system I shall call this tooth p 4 throughout. This name 
 is used as being well understood and convenient, but without 
 any intention of subscribing to the principles of homology upon 
 which the system of nomenclature is based. 
 
 In front of p 4 there is great diversity. 
 
 In Thomas' paper 1 a careful and well-considered attempt was 
 made to bring these anterior teeth into a formal scheme of homo- 
 logies, and though the application of this method to the teeth 
 of the lower jaw was avowedly tentative, yet at first sight the 
 results in the case of the upper teeth were fairly satisfactory. 
 Nevertheless it appears to me that in view of the facts of Variation 
 about to be related, the system elaborated by Thomas breaks 
 down; not because there is any other system which can claim 
 to supersede it, but because the phenomena are not capable of 
 this kind of treatment. To anyone who will carefully study the 
 examples given in the following pages, especially those relating 
 to the genus Phalanger, it will, I think, become evident that it 
 is not possible to apply any scheme based on the conception that 
 each tooth has an individual Homology which is consistently 
 respected in Variation. 
 
 The evidence concerns first the premolars of the upper jaw, and 
 secondly the lower " intermediate " teeth. Inasmuch as in several of 
 the cases there was Variation in both these groups of teeth, the evidence 
 relating to them cannot well be separated. As regards the upper 
 teeth, all the cases of importance occurred in Phalanger and Trichosurus, 
 and owing to the similarity between the dentitions of these two genera 
 it is not difficult to emj)loy terms which shall be distinctive, though 
 the question of the homologies of the teeth go unanswered. In all 
 the forms concerned there are three upper incisors, and the tooth 
 immediately succeeding them will be called the canine, though its 
 position and form diner greatly in the various genera ; for while in 
 Phalanger and Trichosurus it is a large caniniform tooth placed on the 
 suture between premaxilla and maxilla, in Pseudochirus, for instance, 
 it is proportionally smaller and stands in the maxilla at some distance 
 behind the suture. 
 
 Upper jaw. As already stated, the large premolar having a milk- 
 predecessor will be called p*. 
 
 In Trichosurus between the canine and p 4 there is usually one 
 large tooth, in shape and size much like the canine : this tooth will be 
 called F 1 as Thomas proposed. Though when present it is large, it is not 
 rarely absent altogether (v. infra). In Phalanger there is a similar^ 1 , 
 though of somewhat smaller size ; but besides X there is usually another 
 premolar, a small tooth, placed between l^_ and jp\ On Thomas' system 
 this is F J and for purposes of description the name will be used here. 
 In the left upper jaw of the skull shewn in Fig. 65 C, if, if and P^ are 
 
 1 Phil. Tram., 1887, clxxviii. and Cat. Marmp. Brit, Mus. 
 
250 MERISTIC VARIATION". [part i. 
 
 shewn in the ordinary stcate. Lastly, in Psendochirus behind the canine 
 there is a very small tooth, presumably p\ and between it and p 4 a 
 tooth of good size, presumably jr. 
 
 Lower jaw. In the front of the lower jaw there is on each side one 
 long incisor. Between it and the tooth corresponding to p 4 of the 
 upper jaw there are several small or "intermediate" teeth, whose 
 number varies greatly throughout the group. Thomas has made a 
 provisional attempt to find homologies for these small teeth, but in 
 view "of the facts of their Variation it seems impossible to attribute 
 individuality to them and they will therefore be here merely numbered 
 from before backwards. 
 
 Phalanger orientalis. In this species evidence will be 
 offered to prove the following facts : — 
 
 (1) That between p-\ and p^_ there may be two small teeth, 
 one or both of which may perhaps represent P^_ (Fig. 65). 
 
 (2) That between p*_ and the small p 3 there may be a 
 large tooth (Fig. 64, C), like the p 3 of Psendochirus. 
 
 (3) That p^ may be absent. 
 
 (4) That in case of absence of p 3 , p 1 may be near to p^_ 
 (Fig. 64, A). 
 
 (5) That between the canine and p*_ there may be on one 
 side the usual large p l , but on the other two teeth, evenly spaced, 
 each of about the proportions of p^ (Fig. 64, B;. 
 
 (6) That in the lower jaw the number of intermediate 
 teeth may vary from none to five, three being the most usual 
 number. 
 
 372. Specimen having left side normal, one small premolar standing be- 
 tween P^ and F 4 . In the right upper jaw F 1 is normal and stands at the 
 same level as left F 1 ; p 4 is also normal in size, form and position (Fig. 
 64 C). In front of F* however there is a two-rooted tooth (marked y in 
 the figure) having somewhat the same shape as F 4 , but about -|rds the 
 size. This tooth has not the form of the milk-predecessor of F 4 . A 
 small peg-like tooth (x in the figure) matching the small premolar 
 ("p 3 ") is also present, but is crowded out of the arcade and stands 
 internal to the tooth y. The lower jaw has three intermediate teetli 
 on each side. B. M., 1780, f. The form and position of the tooth y 
 suggest a comparison with the arrangement in Pseudochirus, in which 
 "/'; : " is in a very similar condition. In Fig. 64, D, a profile of Pseudo- 
 chirus is shewn, the dotted lines indicating the comparison suggested. 
 It will thus be seen that if the tooth y corresponds to p z of Psendo- 
 chirus, the tooth x then has no correspondent. 
 
 *373. Specimen (var. breviceps, Solomon Islands) having in right 
 upper jaw p l and p* but no "p s ": in left upper jaw p 1 stands at 
 a level anterior to that of right p l , and a small peg-shaped 
 tooth, "j/," is present close to and almost touching p 4 . (Fig. 
 64, A) Lower jaw, right side, two intermediate teeth, of which 
 the posterior stands internal to p* ; right side three intermediate 
 teeth. B. M., 1936,/ 
 
CHAP. IX.] 
 
 TEETH : PHALANGERID^E. 
 
 251 
 
 *374. Specimen (var. breviceps $ , Duke of York I.) having in rt. 
 upper jaw p 1 and p 4 , but no "p 8 ": in left upper jaw there are 
 two teeth of the size and shape of p 1 (Fig. 64, B), one of them 
 
 P'[A ..P 3 ( of Thomas.) 
 
 right 
 profile 
 
 IP P 4 p s P c 
 
 B 
 
 left profile 
 
 f'x ettt/pi h ints 
 rt. pis file. 
 
 B 
 
 right pirfihi 
 
 Fig. 64. Dentition of Phalanger orientalis. 
 
 A. P. orientalis, No. 373, having no right ";r { " : left p l in front of right p 1 . 
 
 B. P. orientalis, No. 374 : no right "p s "; on left, two teeth both like p 1 , in 
 symmetry approximately balancing right p 1 . Below are the right and left profiles 
 of the upper jaws of this skull. 
 
 C. P. orientalis, No. 372. The left side normal, lettered on Thomas's system. 
 Bight side described in text. Below is a profile of right side. 
 
 D. Pseudochirvs, profile of normal upper teeth from right side enlarged to 
 compare with C. Teeth lettered on Thomas's system. 
 
 being at a level anterior to right p 1 and the other posterior to 
 it (see figures). On neither side is there any tooth having the 
 
252 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 size and form of "p s ." In lower jaw, right side 3 interm. teeth ; 
 left side no interm. tooth. B. M., 1936,^'. 
 
 *375. Specimen having two small premolars on each side between p} and 
 l£. The two teeth are very small and sharply pointed (Fig. 65). In 
 
 III 
 
 II 
 
 IV 
 
 Fig. 65. Teeth of Phalanger orientalis. No. 375. 
 
 I. Premolars of left upper jaw, surface and side views. 
 
 II. aud III. Eight and left lower jaws as far as p 4 . 
 IV. The same in surface view. 
 
 (From a drawing kindly sent by Dr Jentink.) 
 
 the lower jaw there are on the right side five intermediate teeth be- 
 tween the incisor and p~ 4 , and on the left side /our such teeth (instead 
 of three as usual). Leyd. Mus.,104:, Jextixk, F. A., Notes Leyd. Mus., 
 1885, vii. p. 90. 
 
 * 
 
 Statistics of the occurrence o/ small Premolars and lower 
 
 "Intermediate" teeth in Phalanger orientalis and 
 
 Phalanger maculatus. 
 
 376. Phalanger orientalis. 
 
 Statistics as to the absence of the small "p ;i ," and as to the number of the 
 "intermediate" teeth, may conveniently be given together in tabular form. The 
 species has a wide distribution and is by Thomas divided into a larger var. typicu*, 
 and a smaller eastern var. breviceps. In the latter the small p 3 is usually absent. 
 The Leyden specimens are not thus divided by Jentink, and in order to include the 
 statistics given by him (/. c.) the distinction into two races is not followed in the 
 table. 
 
 When present, "^ 3 " generally stands at an even distance from j; 1 and p 4 , as 
 in the left side of Fig. 64, C, and not as in the left side of Fig. 64, A. The 
 
CHAP. IX.] 
 
 TEETH I PHALANGEEID^E. 
 
 253 
 
 positions of the intermediate teeth are most various, sometimes they are evenly 
 spaced out between p 1 and p 4 , but sometimes they are crowded together. The 
 teeth in corresponding ordinal positions do not always stand at the same levels 
 on the two sides. 
 
 * 
 
 Small upper 
 premolar 
 
 No. of 
 intermediate 
 teeth in 1. j. 
 
 A 
 
 Leyden 
 (Jentink) 
 
 Cases. 
 
 Other 
 Museums 
 
 Total 
 
 (No. 374) 
 
 (One of these is No. 
 372) 
 
 (No. 375) 
 
 r 
 right 
 
 left 
 
 1 
 
 right 
 
 left 
 
 + 
 
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 2 
 
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 2 
 
 1 
 3 
 1 
 2 
 3 
 3 
 4 
 1 
 2 
 2 
 3 
 3 
 3 
 4 
 5 
 
 1 
 
 3 
 3 
 3 
 3 
 3 
 2 
 2 
 3 
 2 
 
 4 
 3 
 4 
 
 1 
 3 
 2 
 1 
 1 
 2 
 1 
 2 
 44 
 1 
 1 
 1 
 
 3 
 
 1 
 1 
 1 
 2 
 
 2 
 
 6 
 
 2 
 
 1 
 1 
 2 
 5 
 2 
 1 
 1 
 4 
 1 
 2 
 50 
 1 
 1 
 1 
 
 
 
 
 
 
 
 76 
 
 377. Phalanger maculatus: in this species the small premolar ("£> 3 ") between upper 
 p 1 and p 4 is generally absent, and in the lower jaw there are usually only two 
 "intermediate" teeth. The following table shews the variations seen in 58 skulls 
 and 7 lower jaws wanting skulls (including 43 1 Leyden skulls described by 
 Jentink, I. c). 
 
 Small upper 
 
 Intermediate 
 
 
 Cases. 
 
 
 
 premolar 
 
 teeth in 1. j. 
 
 A 
 
 
 
 
 
 Leyden 
 
 Other 
 
 Total 
 
 r 
 
 > 
 
 r \ 
 
 right 
 
 left 
 
 right I left 
 
 (Jentink) 
 
 Museums 
 
 + 1 lr. jaw 
 
 — 
 
 — 
 
 1 
 
 1 
 
 2 
 
 1 
 
 3 
 
 — 
 
 — 
 
 1 
 
 2 
 
 2 
 
 
 2 
 
 
 - 
 
 — 
 
 2 
 
 1 
 
 2 
 
 
 3 
 
 + 2 lr. jaws 
 
 — 
 
 — 
 
 2 
 
 2 
 
 27 1 
 
 8 
 
 35 
 
 + 4 lr. jaws 
 
 — 
 
 — 
 
 3 
 
 2 
 
 
 2 
 
 2 
 
 
 - 
 
 - 
 
 3 
 
 3 
 
 2 
 
 
 2 
 
 1 In one of these 1. P l 
 
 + 
 
 - 
 
 2 
 
 3 
 
 1 
 
 
 1 
 
 absent (see No. 370) 
 
 — 
 
 + 
 
 3 
 
 3 
 
 
 1 
 
 1 
 
 
 + 
 
 + 
 
 2 
 
 1 
 
 1 
 
 
 1 
 
 
 + 
 
 + 
 
 2 
 
 3 
 
 1 
 
 
 1 
 
 
 + 
 
 + 
 
 3 
 
 2 
 
 2 
 
 
 2 
 
 
 + 
 
 + 
 
 3 
 
 3 
 
 2 
 
 1 
 
 4 
 
 
 + 
 
 + 
 
 4 
 
 3 
 
 1 
 
 
 1 
 
 
 
 
 
 
 
 
 58 
 
 1 Not including the case, Leyd. Mm., 153 (Jentink, I.e., p. 91), in which the 
 "small" upper premolar is stated to be absent as an abnormality. As p 3 is usually 
 absent in the species, probably this refers to p 1 . 
 
254 
 
 MEEISTIC VARIATION. 
 
 [part I. 
 
 The above includes six skulls from Waigiu, the individual peculiarities of 
 which are given below : 
 
 
 
 3 
 
 3 
 
 1 
 
 
 1 
 
 
 
 
 + 
 
 3 
 
 3 
 
 
 1 
 
 1 
 
 B. M., 61. 12. 11. 18. 
 
 + 
 
 + 
 
 2 
 
 3 
 
 1 
 
 
 1 
 
 
 + 
 
 + 
 
 3 
 
 2 
 
 1 
 
 
 1 
 
 
 + 
 
 + 
 
 3 
 
 3 
 
 
 1 
 
 1 
 
 B. 21. , 61. 12. 11. 17. 
 
 + 
 
 + 
 
 4 
 
 3 
 
 1 
 
 
 1 
 
 
 The great variability of these skulls from the island of Waigiu is 
 very remarkable. The 4 Leyden specimens were described by Jen- 
 TINK 1 . In one of these there was besides no left upper 2nd molar, 
 which was entirely absent without trace, leaving a diastema between 
 m 1 and m 3 . In connexion with the variations of the dentition of P. 
 maculatus in Waigiu the following singular circumstance should be 
 mentioned. In all other localities the male P. maculatus alone is 
 spotted with white, the female being without spots, but in Waigiu the 
 females are spotted like the males 2 . This curious fact was first noticed 
 by Jextixk (I. c, p. 111). 
 
 In the other species of Phalanger no case of special importance met with; but 
 since in P. ursinus p x is normally (4 skulls seen) two-rooted, it may be of interest 
 to note that such a two-rooted condition of p l was seen on both sides as a variation 
 in P. ornatus, B. M., 1317, b (2 other specimens having single-rooted p x ). 
 
 * 
 
 378. Trichosurus vulpecula ( = Phalangista vulpina). The typical 
 form of this species is Australian, while the large variety, fuliginosa, 
 is peculiar to Tasmania. In the typical form no instance of absence of 
 P^ seen in 17 specimens examined. All possessed this tooth on each 
 side, and though varying a good deal in size, it was in every case well- 
 formed and functional, never being in a condition which could be called 
 rudimentary. 
 
 Of the Tasmanian variety fuliginosa, 18 specimens (8 in B. M., 10 
 in C. M.) were examined. 
 
 In 6 F 1 was present on both sides. 
 
 1 right side only. 
 
 1 left. 
 
 2 p 1 was absent altogether. C. M., 14 k and I. 
 Nevertheless in every case in which this tooth is present it is a large 
 tooth of about the size of the canines. In one case P^ is two-rooted on 
 each side, as (Thomas, Cat. Marsup., p. 186) in the Celebesian Phalan- 
 ger ursinus. C. M., 14 a, Hobart Town, Tasmania. 
 
 Of the "intermediate" teeth in lower jaw one only is usually present, being 
 
 1 The small premolar was accidentally described in the paper referred to as 
 being between the canine and p 4 , instead of between the anterior premolar and p A . 
 Jentink, in litt. 
 
 2 Compare the converse case of Hepialus humuli (the Ghost Moth), of which, 
 in all other localities, the males are clear white and the females are light yellow- 
 brown with spots; but in the Shetland Islands the males are like the females, 
 though in varying degrees. See Jenner Weir, Entomologist, 1880, p. 251, PI. 
 
CHAP. IX.] 
 
 TEETH : DASYURIDJE. 
 
 255 
 
 close to the large incisor. In two cases (C. M., 15 p and h, pi-ob. both Australian) 
 there are two intermediate teeth, one near the incisor, the other near fi. 
 
 379. Pseudochirus. Of various species 29 skulls shew no numerical variation in 
 upper series. The number of "intermediate" teeth in lower jaw is very variable, 
 2 on each side being the most frequent, but 1 and 3 being also common. P. pere- 
 grinus, Upper Hunter E., B. M., 41, 1182, has 2 intermediate teeth in left lower 
 jaw, but on the right side one partially double intermediate tooth. (See also No. 371.) 
 
 Petaurus : 25 skulls shew no numerical variation in upper series. 
 In this genus the number of small teeth in the lower jaw is remarkably 
 constant. In addition to p* there were 3 small teeth on each side in 
 
 380. all cases seen except two, viz. — P. breviceps var. papuanus (8 
 normals): right side normal; left lower jaw has 4 teeth besides^ 4 (Fi^. 
 66). B. M. 5 77. 7. 18. 19. 
 
 Bight 
 
 Left 
 
 Fig. 66. Petaurus breviceps, No. 380. Lower jaws in profile: on right side 
 three intermediate teeth, on left side four. 
 
 381. Another specimen has, in addition to ~j?,four small teeth in each 
 lower jaw. There is a small diastema between the 3rd and 4th. B. M., 
 42. 5. 26. 1. [no skull]. 
 
 382. Dactylopsila trivirgata : 3 specimens have upper series normal. 
 In addition one has an extra tooth in left upper jaw between i^ and 
 canine. This tooth somewhat resembles but is rather smaller than the 
 canine, near and slightly internal to which it stands [? reduplicated 
 canine]. B. M., 1197, d. 
 
 (3) Premolars and molars of Dasyuridse and Didelphyidse. 
 
 Thylacinus, 19 normals; Sarcophilus, 9 normals, no abnormal 
 known to me. 
 
 Dasyurus, 37 normals (4 species). 
 
 383. D. geoffroyi : specimen in which p 4 in right lower jaw has its 
 crown partially divided into two, the plane of division being at right 
 angles to the jaw. C. M., 39, a. 
 
256 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 384. D. viverrinus : rigKfc upper m 4 slightly larger than the left, which 
 is normal. C. M., 38, g. 
 
 *385. D- maculatus, Tasmania, having a supernumerary molar 
 in left upper jaw, and on both sides in the lower jaw. The 
 fourth molar in the upper jaws is increased in size in a remark- 
 able manner ( Fig. <>7, B and C). 
 
 This case requires detailed description. In Fig. 67, A, a 
 normal right upper jaw is shewn. It belongs to a specimen 
 considerably larger than the abnormal one, but the latter, 
 Mr Thomas tells me, is a good deal smaller than the normal 
 size of the species. In the normal there are two small pre- 
 molars ( p 1 and p 9 of Thomas), and behind these, four molars. 
 The molars increase in size from the first to the third, which is 
 by far the largest. Behind the third is the fourth molar, which 
 is much smaller than the others, having the peculiar flattened 
 form shewn in the Figure 67, A. 
 
 Fig. 67. A. Eight upper jaw of normal Dasyurus maculatus (shewn as far as 
 the canine) for comparison with the variety. (N.B. The latter is considerably 
 smaller.) 
 
 B. Upper jaw of D. maculatus, No. 385. 
 
 C. Lower jaw of the same specimen. 
 
 On comparing the abnormal skull with a normal one it is 
 seen that the two premolars and first three molars on each side 
 are unchanged. Behind the third molar on the right side there 
 is a single tooth ; but this, instead of being a thin tooth like 
 normal ™ 4 , is considerably larger and the longitudinal measure- 
 ment in the line of the jaw is not very much less than the 
 transverse measurement. In the right upper jaw therefore the 
 number of the teeth is unchanged. 
 
 On the left side, behind the third molar, there is a square 
 tooth (w* 4 ) of good size, about equal in bulk to half w 3 , while 
 behind this again there is another tooth, _^ 3 , which is a thin 
 
CHAP. IX.] 
 
 TEETH : DASYURID^E. 
 
 257 
 
 386, 
 
 and small tooth having nearly the form and size of normal w 4 . 
 The lower series is alike on both sides, each having an extra 
 molar behind m" 4 (Fig. 67, C). The two extra teeth are well formed, 
 being as long but not quite so thick as m*. B. M., 41, 12, 2, 3. 
 
 In Cat. Marsup. Brit. Mus., 1888, p. 265, note, Thomas refers 
 to this skull, and describes it as an instance of an additional molar 
 inserted between m 3 and m 4 on the left side above and on both 
 sides below. This view is of course based on the resemblance 
 that the extra »»? of the left side bears to a normal mt and on 
 the fact that the left w 4 is like no tooth normally present. In 
 the light however of what has been seen in other cases of super- 
 numerary molars a simpler view is possible. For in cases in 
 which a supernumerary molar is developed behind a molar which 
 is normally a small tooth, the latter is frequently larger than 
 its normal size. In the present case it appears that on the right 
 side ™ 4 has been thus raised from a small tooth to be a tooth 
 of fair size, while on the left side the change has gone further, 
 and not only is ««* promoted still more, but a supernumerary 
 ra 5 is developed as well. It is interesting to note that this ft& 
 is a small tooth, very like normal ^_ 4 , and it thus may be said 
 to be beginning at the stage which m^ generally reaches. In 
 the lower jaw wf is added without marked change in ~m± ; for 
 mF is normally a large tooth and has, as it were, no arrears to 
 be made up. Mr Thomas, to whom I am indebted for having 
 first called my attention to this remarkable case, allows me to 
 say that he is prepared to accept the view here suggested. 
 
 Phascologale. In the upper jaw normally 3 premolars, by Thomas 
 reckoned as p\ p 3 and p*. Between the first and second ("p 3 ") there 
 is sometimes, but not always, a small space, and in the following case a 
 supernumerary tooth was present in this position. 
 
 Phascologale dorsalis, (Fig. 68) having an extra premolar 
 between the first and second in the left upper jaw : rest normal. B. M., 
 1868, b. Thomas, O., Phil. Trans., 1887, p. 447, PL 27, figs. 7 and 8. 
 
 In the lower jaw ~jfi is often small and may be absent. As Thomas 
 has observed, the size of p 4 in the upper and lower jaws maintains a 
 
 left 
 
 ri/fht 
 reversed 
 
 Fig. 68. Phascologale dorsalis, No. 386. Teeth of left upper jaw from canine 
 to first molar; below, the teeth of the right side reversed (after Thomas). 
 
 b. 17 
 
258 MERISTIC VARIATION. [part i. 
 
 fairly regular correspondence. Within the limits of one species p* may 
 
 387. shew great variation ; for instance, of Phascologale fiavipes 7 
 specimens were seen ; in 1 jT 1 was absent, in 2 it was small, in 2 mode- 
 rate, and in 2 it was large. 
 
 388. Didelphys : 79 specimens normal. One specimen alone, D. lanigera, Colombia, 
 B. At., 1733, b, was abnormal, having no m 4 in either upper or lower jaws. 
 
 D. opossum (one specimen, B. M.) had right n* larger than the left. 
 
 (4) Molars of certain Macropoclidae. 
 
 The following evidence relates to the genera Bettongia, Potorous 
 and Lagorchestes. In these forms the molars are normally four in each 
 jaw. As Thomas observes (Cat. Marsup. Brit. Mus., p. 105, note), in 
 Bettongia cases of fifth molar occur, but on the other hand cases of non- 
 eruption of m 4 occur also. The variations seen in the three genera 
 were as follows. 
 
 4 4 
 
 Bettongia penicillata : 8 specimens have m . ; in 7 of them 
 
 m 4 is small (in B. M., 279, j, ™^ is very minute; but in B. M., 278, m, 
 
 the lower m* is large). 
 
 *389. 1 specimen °. has m 4 in left lower jaw only, this tooth being small. 
 
 B. M., 279, a. 
 
 *onn i • x. 1.2.3.0.5 — 1.2.3.0.0 _ , ., 
 
 *390. 1 specimen has m = — s — = — - — = = — - — =- — . In both upper laws 
 
 r 1.2.3.4.5 — 1.2.3.4.0 rr J 
 
 there is a small empty crypt behind m 3 , and on right side behind this 
 
 again there is a minute tubercular tooth not represented on the other 
 
 side. B. M., 279, b. 
 
 4 — 4 
 B. cuniculus : 2 specimens have m- - . 
 
 391. 1 specimen has no left v?. B. M., 982, c. 
 
 5 5 
 
 *392. 1 specimen has m— — = ; in upper jaws m 5 very small in crypts, but 
 
 o — o 
 
 in lower jaws they are of good size. B. M. 51. 4. 24. 7. 
 
 4 4 
 
 B. lesueri : 13 specimens have m - (in one of them on 4 very 
 
 small. B. M., 277, g). 
 
 5 5 
 
 393. 1 specimen has m , m 5 being minute and lying in crypts. 
 
 B. M., 41, 1157. 
 
 4 4 
 
 394. Potorous (Hypsiprymnus): mj- in 5 specimens of P. tri- 
 
 dactylus and in 2 of P. platyops. A single specimen of P. gilberti 
 has no right upper m\ B. M., 282, b. 
 
 395. Lagorchestes. In this genus m 4 is present and is a large tooth, 
 not materially smaller than m s . Nevertheless it commonly falls short 
 of the other teeth and remains partly within the jaw. This was the 
 case in 10 skulls of L. leporoides and L. conspicillatus. In one skull 
 of L. leporoides, m 4 stood at the same height as the other teeth. I see 
 no reason to suppose that all the other skulls were young, and it seems 
 more likely that this imperfect eruption of m 4 is characteristic. 
 
chap, ix.] TEETH : RHINOPTERA. 259 
 
 Selachii. 
 
 Some features characteristic of Meristic Variation are well 
 seen in the case of the teeth of Sharks and Rays. Of these fishes 
 there are many having little differentiation between the separate 
 rows of teeth. In these a distinct identity cannot be attributed 
 to the several rows, and numerical Variation is quite common. 
 But besides these there are a few forms whose teeth are differ- 
 entiated sufficiently to permit a recognition of particular rows 
 of teeth in different specimens, and to justify the application of 
 the term "homologous'' to such rows. Nevertheless with such 
 differentiation Meristic Variation does not cease. 
 
 In the following examples it will be seen further that in such 
 Variation there may be not merely a simple division of single 
 teeth but rather a recasting of the whole series, or at least of that 
 part of it which presents the Variation, for the lines of division 
 in the type may correspond with the centres of teeth in the 
 variety. 
 
 These cases also exemplify the fact that variations of some 
 kinds are often only to be detected when in some degree im- 
 perfect ; for if the divisions in No. 396 for instance had taken 
 place similarly on both sides, it would have been difficult to 
 recognize that this was a case of Variation. 
 
 Rhinoptera jussieui (= javanica) : specimen in which the 
 number and arrangement of the rows of teeth is different on 
 the two sides, as shewn in Fig. 69, upper diagram. The dis- 
 position on the right side of the figure is normal, that on the 
 left being unlike that of any known form. Specimen in B. M. 
 described by Smith Woodward, Ann, and Mag. N.H., Ser. 6, 
 vol. i. 1888, p. 281, fig. As Woodward points out, the rows of 
 plates on the left side may be conceived as having arisen by 
 division partly of the plates of the central row and partly from 
 the lateral row, marked I. But if this be accepted as a repre- 
 sentation of the relation of the normal to the abnormal, in the 
 way indicated by the lettering, the plates of the row marked b, 
 for instance, must be supposed each to belong half to one rank 
 and half to a lower rank. The same applies to the plates in the 
 row I b. By whatever cause therefore the points of develop- 
 ment of the teeth are determined, it is clear that the centres 
 from which each of the teeth in the rows I b and b was de- 
 veloped were not merely divided out from centres in the normal 
 places but have undergone a rearrangement also. With change of 
 number there is also change of pattern. 
 
 The tessellation on the abnormal side is so regular and definite 
 that had it existed in the same form on both sides the specimen 
 might readily have become the type of a new species. 
 
 There is indeed in the British Museum a unique pair of jaws 
 in both of which (upper and lower) a very similar tessellation 
 
 17—2 
 
260 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 occurs in a nearly symmetrical way. This specimen is described 
 as Rhinoptera potyodon, but it is by no means unlikely that it 
 
 T Th la Oc Ob 
 wM lL £ HLUL 
 
 Oa 
 
 
 
 M M 
 
 jt m 
 
 Fig. 69. Upper figure ; Rhinoptera jussieui, No. 396, after Smith Woodwakd,. 
 from whom the lettering is copied. 
 
 Middle figure, Rhinoptera, sp., No. 397. 
 
 Lower figure Rhinoptera javanica, No. 398, after Owen. 
 
 is actually a Variation derived from the usual formula of Rhino- 
 ptera. It is figured by Gunther, Study of Fishes, 1880, p. 346. 
 Fig. 133. 
 
 *QQ7 
 
 39/. Rhinoptera sp. incert. : teeth as in middle diagram, Fig. 69. On 
 the left side three rows of small lateral teeth, while on the right side 
 two of these rows are represented by one row, which in one part of the 
 series shews an indication of division. C. S. M. {Hunterian Specimen). 
 
CHAP. IX.] 
 
 TEETH I SELACHII. 
 
 261 
 
 398. Rhinoptera javanica : the row of teeth marked I is one side 
 single, but on the other side is represented by two rows. Fig. 69, 
 lower diagram. Owen, Odontography, PI. 25, Fig. 2. C. S. M. 
 (Hunterian specimen). 
 
 399. Cestracion philippi : an upper jaw having the teeth disposed as 
 in the figure (Fig. 70). C. S. M. 
 
 Fig. 70. Upper jaw of Cestracion philippi, No. 399. 
 
 400, 
 
 On comparing the teeth of the two sides it will be seen first that 
 the rows do not correspond individually, and secondly that they do not 
 at all readily correspond collectively. Assuming that the rows marked 
 4 on each side are in correspondence (which is not by any means cer- 
 tain) several difficulties remain: for right 5th is larger than left 5th, 
 but left 6th and 7th together are larger than right 6th; right 7th is 
 about the same size as left 8th, but right 8th is larger than left 9th. 
 The proportions in the figure were carefully copied from the specimen. 
 
 " Cestracion sp." [so labelled, but probably not this genus] : 
 lower jaw as in Fig. 71. On the right side the second row of large 
 plates is represented by two rows, properly fitting into each other, 
 but on the left side the plates of the inner side are completely 
 
262 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 divided, but the division is gradually lost towards the middle of the 
 jaw and the external plates are without trace of division. C. S. M. 
 
 Fig. 71. The lower jaw of a Selachian, No. 400. The proximal ends shewn 
 (enlarged). The right is reversed for comparison with the left. 
 
 RADUL.E of a Gasteropod. 
 
 * 
 
 The following example of Meristic Variation in the teeth 
 of a Molluscan odontophore may be taken in connexion with 
 the subject of teeth, though the structures are of course wholly 
 different in nature. For information on this subject I am in- 
 debted to the Rev. A. H. Cooke. 
 
 Generally speaking the number and shapes of the radular 
 teeth are very characteristic of the different classificatory divi- 
 sions. There are however certain forms in which a wide range 
 of Variation is met with ; of these the case of Buccinum undatum is 
 the most conspicuous. 
 401. Buccinum undatum. In most specimens the number of 
 denticles on the central plate is 5 — 7 and on the laterals 3 — 4. 
 
 In 27 specimens from Hammerfest and Vardo the teeth were 
 as follows : — 
 
 Lateral plates. Cases. 
 
 4 8 
 
 4 12 
 
 4 2 
 
 4 1 
 
 4 1 
 
 3 & 4 1 
 3& 4 1 
 
 4 & 5 1 
 
 Central plate. 
 5 
 6 
 7 
 6—8 
 9 
 6 
 7 
 8 
 
 from Friele, Jahrb. deut mat. Ges., VI. 1879, p. 257. 
 
CHAP. IX.] 
 
 RADUL^E I BUCCINUM. 
 
 263 
 
 *402. The range of Variation may be still greater than this, the 
 number of centrals being sometimes as low as 3. Fig. 72 shews 
 the different conditions found. In it eight varieties are shewn, 
 
 M/vWV. 
 
 IV 
 
 VI 
 
 Fig. 72. Variations in odontophore of Buccinum undatum. 
 
 I. Three centrals (Labrador). II. Four centrals. III. Five centrals, approxi- 
 mately symmetrical bilaterally. IV. Five centrals, not symmetrical ; the two 
 external centrals on one side almost separate, correspond with a bifid denticle on 
 the other side (Labrador). V. Six complete centrals (Labrador). VI. Seven 
 centrals (Lynn). VII. Nine almost distinct centrals. VIII. Eight centrals ; 
 laterals asymmetrical (4 and 5). 
 
 I. II. IV. — VI. from photographs made and kindly lent by Mr A. H. Cooke. 
 III. VII. VIII. after Friele. 
 
 I. II. IV. — VI. being taken from Mr Cooke's specimens, III. VII. 
 and VIII. from Friele's figures. 
 
 As thus seen, in these variations considerable symmetry may 
 be maintained. This symmetry and defmiteness of the varieties 
 in the cases with 3 and 4 centrals is especially noteworthy, in- 
 asmuch as these are abnormal forms and have presumably arisen 
 discontinuously. As also seen in the figure, e.g. IV. and VI. 
 this symmetry is not universal, and may be imperfect. The 
 specimen shewn in VIII. is remarkable for the asymmetry of the 
 lateral plates, which have 4 and 5 denticles respectively. 
 
 In connexion with the subject of symmetrical division interest 
 attaches to cases like that shewn in Fig. 72, IV. in which on the 
 
264 MEBISTIC VARIATION. [part i. 
 
 outside of the central plate a pair of almost wholly separate 
 denticles on one side correspond with a large, imperfectly divided 
 denticle of the other side. A very similar specimen is figured by 
 Friele, Norske Nordhavs-Exp., viii. PL v. fig. 16. 
 
 The number found in one part of the radula is usually main- 
 tained throughout the whole series, but this is not always so. 
 A case in which the number of centrals at the anterior end of 
 the radula was 6, and at the posterior end 8, is given by Friele, 
 Norske Nordhavs-Exp., 1882, viii. p. 27, Taf. v. fig. 17. 
 
CHAPTER X. 
 
 Linear Series — continued. 
 Teeth — Recapitulation. 
 
 In this chapter I propose to speak of those matters which seem 
 to have most consequence in the foregoing evidence as to the 
 Variation of Teeth. Each of the following sections treats of some 
 one such subject, specifying the cases which chiefly illustrate it. 
 It will be understood that the sections do not stand in any logical 
 collocation but are simply arranged consecutively. The treatment 
 given is of course only provisional and suggestive, being intended 
 to emphasize those points which may repay investigation. 
 
 The subjects which especially call for remark are as follows : 
 
 (1) The comparative frequency of dental Variation in differ- 
 
 ent animals. 
 
 (2) Symmetry in Meristic Variation of Teeth. 
 
 (3) Division of Teeth. 
 
 (4) Duplicate Teeth. 
 
 (5) Presence and absence of Teeth standing at the ends of 
 
 series (first premolars, last molars). 
 
 (6) The least size of particular Teeth. 
 
 (7) Homceotic Variation in terminal Teeth when a new 
 
 member is added behind them. 
 
 (8) Reconstitution of parts of the Series. 
 
 (1) The comparative frequency of dental Variation in different 
 
 animals. 
 
 The total number of skulls examined for the purpose of this 
 inquiry was about 3000. From so small a number it is clearly 
 impossible to make any definite statement as to the relative 
 frequency of Variation in the different orders, but some indications 
 of a general character may be legitimately drawn. 
 
 First, the statistics very clearly shew that while dental Varia- 
 tion is rare in some forms, it is comparatively frequent in others, 
 but there is no indication that this frequency depends on any 
 condition or quality common to these forms. Setting aside 
 examples of the coming and going of certain small and variable 
 
266 MERISTIC VARIATION. [part i. 
 
 teeth, the animals shewing the greatest frequency of extra teeth 
 were the domestic Dogs, the Anthropoid Apes and the Phocidse. 
 
 Attention is especially called to the fact that the variability of 
 domestic animals is not markedly in excess of that seen in wild 
 forms. From the hypothesis that Variation is uncontrolled save 
 by Selection, there has sprung an expectation, now fast growing 
 into an axiom, that wild animals are, as such, less variable than 
 domesticated animals. This expectation is hardly borne out by 
 the facts. It is true that, so far as the statistics go, supernumerary 
 teeth were more common in domestic Dogs than in wild Canidse, 
 and though the number of Cats seen was small, the same is true 
 in their case also as compared with wild Felidse. But though it is 
 true that the domestic Dog is more variable in its dentition than 
 wild Doofs, it is not true that it is much more variable than some 
 other wild animals, as for instance, the Anthropoid Apes or the 
 genus Phoca. The doctrine that domestication induces or causes 
 Variation is one which will not, I think, be maintained in the 
 light of fuller evidence as to the Variation of wild animals. It 
 has arisen as the outcome of certain theoretical views and has 
 received support from the circumstance that so many of our 
 domesticated animals are variable forms, and that so little heed 
 has been paid to Variation in wild forms. To obtain any just view 
 of the matter the case of variable domestic species should be com- 
 pared with that of a species which is variable though wild. The 
 great variability of the teeth of the large Anthropoids, appearing 
 not merely in strictly M eristic and numerical Variation, but also 
 in frequent abnormalities of position and arrangement, is striking 
 both when it is compared with the rarity of variations in the teeth 
 of other Old World Monkeys and the comparative rarity of great 
 variations even in Man. If the Seals or Anthropoids had been 
 domesticated animals it is possible that some persons would have 
 seen in their variability a consequence of domestication. 
 
 When the evidence is looked at as a whole it appears that no 
 generalization of this kind can be made. It suggests rather that 
 the variability of a form is, so far as can be seen, as much a part 
 of its specific characters as any other feature of its organization. 
 Of such frequent Variation in single genera or species some 
 curious instances are to be found among the facts given. 
 
 Of Canis cancrivorus, a S. American Fox, the majority shewed 
 some abnormality. Of Felis fontanieri, an aberrant Leopard, two 
 skulls only are known, both showing dental abnormalities. In 
 Seals only four cases of reduplication of the first premolar were 
 seen, and of these two were in Cystopliora cristata. The number 
 of cases of abnormality in the genus Ateles is very large. Of six 
 specimens of Crossarchus zebra, two shew abnormalities. Of the 
 very few skulls of Myrmecobius seen, two shew an abnormal num- 
 ber of incisors. Three cases of Variation were given in Canis 
 mesomelas, not a very common skull in museums. On the other 
 
chap, x.] TEETH : SYMMETRY. 267 
 
 hand the rarity of Variation in the dentition of the Common Fox 
 (G. vulpes) is noteworthy, especially when compared with the 
 extraordinary frequency of Variation in the molars of S. American 
 Foxes. The constant presence of the small anterior premolar in 
 the upper jaw of Otters (Lutra) of most species, as compared with 
 the great variability of the similar tooth in the Badgers (Meles) 
 and in other species of Otters, may also be mentioned. 
 
 The evidence given in the last chapter should not, I think, be 
 taken as indicating the frequency of dental Variation in Mammals 
 generally. The orders chosen for examination were selected as 
 being those most likely to supply examples of the different forms 
 of dental Variation, and it is unlikely that the frequency met with 
 in them is maintained in many other orders. 
 
 (2) Symmetry in Meristic Variation of Teeth. 
 
 With respect to bilateral Symmetry an examination of the 
 evidence shews that dental Variation may be symmetrical on the 
 two sides, but that much more frequently it is not so. The in- 
 stances both of bilaterally symmetrical Variation, and of Variation 
 confined to one side are so many that examples can be easily 
 found in any part of the evidence. 
 
 Besides these there are a few cases in which there is a variation 
 which is complete on one side, while on the other side the parts 
 are in a condition which may be regarded as a less complete 
 representation of the same variation. Such cases are Ommato- 
 phoca rossii No. 320, Phoca gramlandica No. 324, Dasyurus macu- 
 latus No. 385, Ganis lupus No. 246, G. vetulus No. 248, &c. 
 
 In the remarks preliminary to the evidence of dental Variation, 
 reference was made to a peculiarity characteristic of the teeth 
 considered as a Meristic Series of parts. As there indicated, the 
 teeth are commonly repeated, so as to form a symmetry of images 
 existing not only between the two halves of one jaw, but also to a 
 greater or less extent between the upper and lower jaws. It was 
 then mentioned that cases occur in which there is a similar Varia- 
 tion occurring simultaneously in the upper and lower jaws of the 
 same individual. Such similar Variation may consist either in 
 the presence of supernumerary teeth, or in the division of teeth, 
 or in the absence of teeth. It should, however, be noticed that 
 examples of Variation thus complete and perfect in both jaws are 
 comparatively rare. Speaking generally, it certainly appears from 
 the evidence that similar Variation, (1) on one side of both jaws, 
 or (2) on both sides of one jaw and on one side of the other, or 
 (3) on both sides of both jaws are all rare. Of these three the 
 following examples may be given : — 
 
 Of (1), Macacus rhesus No. 190, Ateles pentadactylus No. 196, 
 Esquimaux dog No. 243, Phoca vitulina No. 329. 
 
268 MERISTIC VAKIATIOX. [part i. 
 
 Of (2), Simla satyrus No. 106, Dasyurus maculatus No. 385, 
 E. asinus No. 352. 
 
 Of (3), Dog Xo. 257, Bettongia cuniculus, No. 392, Ateles margi- 
 natus No. 203, Phoca barbata No. 318, Ommatophoca rossii No. 320. 
 
 Of these, further examples may be seen in the evidence given 
 regarding the anterior premolars of Galictis barbara, Meles, and 
 Herpestes. 
 
 (3) Division of Teeth. 
 
 Among the cases of increase in number of teeth are many in 
 which by the appearances presented it may be judged that two 
 teeth in the varying skull represent one tooth in the normal, and 
 have arisen by the division of a single tooth-germ. 
 
 Of such division in an incomplete form several examples have 
 been given. The plane of division in these cases is usually at 
 right angles to the line of the jaw, so that if the division were 
 complete, the two resulting teeth would stand in the line of the 
 arcade. Incomplete division of this kind is seen in the first 
 premolar of Ommatophoca rossii No. 320, in the fourth premolar of 
 Phoca groenlandica No. 324, in the incisors of Dogs No. 219, 
 in the canine of Dog No. 221, in the lower fourth premolar of 
 Dasyurus geoffroyi No. 383. The plane of division is not however 
 always at right angles to the jaw, but may be oblique or perhaps 
 even parallel to it, though of the latter there is no certain case. 
 Cases of division in a plane other than that at right angles to the 
 jaw are seen in C. vulpes No. 230, Phalanger orientalis No. 368, 
 Phoca groenlandica No. 326 and doubtfully in a few more cases. The 
 existence of the possibility of division in these other planes is of 
 some consequence in considering the phenomenon of duplicate teeth 
 standing together at the same level in relation to that of the 
 presence of duplicate teeth in series. Beyond this also it may be 
 anticipated that if ever it shall become possible to distinguish 
 the forces which bring about the division of the tooth-germ, the 
 relation of the planes of division to the axis of the Series of Repe- 
 titions will be found to be a chief element. 
 
 (4) Duplicate Teeth. 
 
 Teeth standing at or almost at the same level as other teeth 
 which they nearly resemble may conveniently be spoken of as 
 duplicate teeth, though it is unlikely that there is a real distinc- 
 tion of kind between such teeth and those extra teeth which stand 
 in series. Duplicate teeth were seen in Felis domestica Nos. 286 
 and 287, Ganis mesomelas No. 228, Herpestes ichneumon No. 300, 
 [Putorius] Vison horsfieldii No. 311, Helictis orientalis No. 312, 
 Cystop)iora cristata No. 322, and perhaps in some other cases. That 
 these cases are not separable on the one hand from examples of 
 extra teeth in series may be seen from Herpestes gracilis No. 299, 
 Cystophora cristata No. 321 [compare with No. 322], Brachy teles 
 
chap, x.] TERMINAL TEETH. 269 
 
 hemidactylas No. 199 [compare with Ateles rnarginatus No. 200]. 
 PJioca vitulina No. 336 ; and that on the other hand they merge 
 into cases of supernumerary teeth standing outside or inside the 
 series, and whose forms do not correspond closely to those of 
 any tooth in the series, may be seen by comparison with Otaria 
 iwsina No. 325, Phoca vitulina No, 329, Phalanger orientalis No. 
 372. Though in some cases the shapes of duplicate teeth make a 
 near approach to the shapes of normal teeth, yet they are never 
 exactly the same in both, and teeth whose forms approach so 
 nearly to those of other teeth in the series as to suggest that they 
 are duplicates of them and that they may have arisen by multipli- 
 cation of the same germ, cannot be accurately distinguished from 
 extra teeth whose forms agree with none in the normal series. 
 
 (5) Presence and Absence of Teeth standing at the ends of Series 
 (first premolars, last molars): the least size of particular Teeth. 
 
 Of the cases of numerical Variation in teeth the larger number 
 concern the presence or absence of teeth standing at the ends of 
 Series. As was mentioned in introducing the subject of dental 
 Variation, in many heterodont forms the teeth at the anterior end 
 of the series of premolars and molars are small teeth, standing to 
 the teeth behind them as the first terms of a series more or less 
 regularly progressing in size. Not only in teeth but in the case 
 of members standing in such a position in other series of organs, 
 e.g. digits, considerable frequency of Variation is usual. 
 
 Variability at the ends of Series is manifested not only in the 
 frequency of cases of absence of terminal members, but also in the 
 frequency of cases of presence of an extra member in their neigh- 
 bourhood. An additional tooth in this region may appear in 
 several forms. It may be a clear duplicate, standing at the same 
 level as the first premolar (e.g. Cat, No. 270). On the other hand, 
 as seen in the Dogs (Nos. 232 and 233) there may be two teeth 
 standing between the canine and (in the Dog) the second pre- 
 molar. The various possibilities as to the homologies of the teeth 
 may then be thus expressed. The posterior of the two small teeth 
 may correspond with the normal first premolar, and the anterior may 
 be an extra tooth representing the first premolar of some possible 
 ancestor having five premolars; or, the first of the two premolars 
 may be the normal, and the second be intercalated (see No. 224) ; 
 or, both the two teeth may be the equivalent of the normal first 
 premolar ; lastly, neither of the two may be the precise equivalent 
 of any tooth in the form with four premolars, Of these possibili- 
 ties the first is that commonly supposed (Hexsel and others) to 
 most nearly represent the truth. But the condition seen in cases 
 where there is an extra tooth on one side only, as in the Dogs 
 figured (Fig. 42), strongly suggests that neither of the two teeth 
 strictly corresponds with the one of the other side. Seeing that in 
 such cases the single tooth of the one side stands often at the level 
 
270 MERISTIC VARIATION. [part i. 
 
 of the diastema on the other, it seems more likely that the one 
 tooth balances or corresponds to the two of the other side, which 
 may be supposed to have arisen by division of a single germ. On 
 the other hand since the two anterior premolars found in such 
 cases are not always identical in form and size, either the anterior 
 or the posterior being commonly larger than the other, there is no 
 strict criterion of duplicity, and it is clearly impossible to draw 
 any sharp distinction between cases of duplicity of the first pre- 
 molar and cases in which the two small premolars are related to 
 each other as first and second. These two conditions must surely 
 pass insensibly into each other. If the case of the teeth is com- 
 pared with that of any other Linear series in which the number of 
 members is indefinite, as for example that of buds on a stem, the 
 impossibility of such a distinction will appear. A good illustration 
 of this fact may often be seen in the arrangement of the thorns on 
 the stems of briars. For large periods of the stem both the angular 
 and linear succession of the thorns of several sizes may be exceed- 
 ingly regular ; but it also frequently happens that a thorn occurs 
 with two points, and on searching, every condition may sometimes 
 be found between such a double thorn and two thorns occurring 
 in series, having between them the normal distinctions of form or 
 size. Very similar phenomena may be seen in the case of the 
 strong dermal spines of such an animal as the Spiny Shark (Echi- 
 norhinus spinosus). These structures are of course from an anato- 
 mical standpoint closely comparable with teeth. In them, spines 
 obviously double, triple or quadruple, are generally to be seen 
 scattered among the normal single spines, but between the double 
 condition and the single condition, it is impossible to make a real 
 distinction. 
 
 The remarks made as to the first premolars apply almost 
 equally to the last molar. See Phoca vitulina No. 336, Mycetes 
 niger No. 206, Man, Magitot, Anom. syst. dent, PI. v. figs. 4, 5 
 and 6, Canis cancrivorus Nos. 251 and 252, Crossarchus zebra 
 No. 302. 
 
 (6) The least size of 'particular Teeth. 
 
 What is the least size in which a given tooth can be present in 
 a species which sometimes has it and sometimes is without it ? In 
 other words, what is the least possible condition, the lower limit of 
 the existence of a given tooth ? This is a question which must 
 suggest itself in an attempt to measure the magnitude or Dis- 
 continuity of numerical Variation in teeth. 
 
 The evidence collected does not actually answer this question 
 completely for any tooth, but it shews some of the elements upon 
 which the answer depends. 
 
 In the first place it is seen at once that the least size of a 
 tooth is different for different teeth and for different animals. 
 
chap, x.] LEAST SIZE OF TEETH. 271 
 
 Considered in the absence of evidence it might be supposed that 
 any tooth could be reduced to the smallest limits which are histo- 
 logically conceivable ; that a few cells might take on the characters 
 of dental tissue, and that the number of cells thus constituting a 
 tooth might be indefinitely diminished. Indeed on the hypothesis 
 that Variation is continuous this would be expected. Now of 
 course there is no categorical proof that this is not true, and that 
 teeth may not thus occur in the least conceivable size, but there is 
 a good deal of evidence against such a view. The facts on the 
 whole go to shew that teeth arising by Variation in particular 
 places, at all events when standing in series in the arcade, have a 
 more or less constant size on thus appearing. Within limits it 
 seems also to be true that the size in which such a tooth appears 
 has in many cases a relation to the size of the adjacent teeth and to 
 the general curves of the series. For example in the Orang, the 
 series of molars does not diminish in size from before backwards, 
 and extra molars when present are, so far as I know, commonly of 
 good size, not wholly disproportionate to the last normal molar. 
 The same is I believe true in the case of the Ungulates. In the 
 Dogs however the series of lower molars diminishes rapidly at the 
 back, and the extra molars added at the posterior end of the series 
 are of a correspondingly reduced size. As presenting some ex- 
 ception to this rule may be mentioned two cases in the Chimpanzee, 
 Nos. 178 and 181 and the case of Cebus robustus No. 194, in each 
 of which the extra molar is disproportionately small. 
 
 The principle here indicated is of loose application, but speaking 
 generally it is usual for an extra tooth arising at the ends of series 
 to be of such a size as to continue the curves of the series in a 
 fairly regular w T ay. It would at all events be quite unparalleled for 
 an extra tooth arising at the end of a successively diminishing 
 series, as the Dog's lower molars, to be larger than the tooth next 
 to it, and with the exception of cases of duplicate anterior pre- 
 molars (see Dogs Nos. 232 and Cat No. 268) I know no such case. 
 In these besides, the anterior tooth is very slightly larger than its 
 neighbour, and it should be remembered that the first premolar, 
 though the terminal member of the series of premolars, is not 
 actually a terminal tooth. 
 
 Examples have been given of animals which seem to be oscil- 
 lating between the possession and loss of particular teeth, the first 
 premolar of the Badgers, p 1 of some species of Otter, &c. In these 
 cases we are not yet entitled to assume because in a given skull 
 the tooth is absent, that it has never been formed in it, though 
 this is by no means unlikely, but as already pointed out (p. 22<S). 
 the fact of its presence or absence may still indicate a definite 
 variation. Attention should be called to the case of Trichosurw 
 vulpecida, var. fuliginosa No. 378, in which the first premolar is 
 generally of good size if present, and there can be no doubt that it 
 has never been present in those skulls from which it is absent. 
 
272 MERISTIC VARIATION. [part i. 
 
 Variation of unusual amplitude may be seen also in the molars 
 of Bettongia Nos. 389, &c, for while on the one hand the last or 
 fourth molar may be absent, it may on the contrary be large and 
 may even be succeeded by a fifth molar as an extra tooth. All 
 these conditions were seen in looking over quite a small number 
 of specimens. 
 
 (7) Homceotic Variation in terminal Teeth token a new member 
 is added behind them. 
 
 Upon the remarks made in the last Section the fact here 
 noticed naturally follows. We have seen that there is a fairly 
 constant relation between the size of extra teeth and that of the 
 teeth next to which they stand, so that the new teeth are as it 
 were, from the first, of a size and development suitable to their 
 position. We have now to notice also that the teeth next to which 
 they stand may also undergo a variation in correlation with the 
 presence of a new tooth behind them. 
 
 It may be stated generally that if the tooth which is the last 
 of a normal series is relatively a small tooth, as for example m» or 
 ra^ i n the Dog, then in cases of an addition to the series, by which 
 this terminal tooth becomes the penultimate, it will often (though 
 not always) be found that this penultimate tooth is larger and 
 better developed than the corresponding ultimate tooth of a normal 
 animal of the same size. 
 
 Of this phenomenon two striking examples (q.v.) have been 
 given, Canis azarce No. 249 and Dasyurus maculatus No. 385. 
 Besides these are several others of a less extreme kind e.g. Otocyon 
 megalotis No. 256, Mastiff No. 259, Dog No. 260. The same was 
 also seen in the molars of Bettongia, 
 
 This phenomenon, of the enlargement of the terminal member 
 of a series when it becomes the penultimate, is not by any means 
 confined to teeth ; for the same is true in the case of ribs, digits, 
 &c, and it is perhaps a regular property of the Variation of Meristic 
 Series so graduated that the terminal member is comparatively 
 small. This fact will be found of great importance in any attempt 
 to realize the physical process of the formation of Meristic Series, 
 and it may be remarked that such a fact brings out the truth that 
 the members of the Series are bound together into one common 
 whole, that the addition of a member to the series may be cor- 
 related with a change in the other members so that the general 
 configuration of the whole series may be preserved. In this case 
 the new member of the series seems, as it were, to have been 
 reckoned for in the original constitution of the series. 
 
 (8) Reconstitution of parts of the Series. 
 
 Lastly there are a few cases, rare no doubt in higher forms but 
 not very uncommon for example in the Sharks and Rays (see 
 
chap, x.] TEETH : HOMOLOGIES. 273 
 
 pp. 259, &c), in which the members of the series seem to have been 
 so far remodelled that the supposed individuality of the members 
 is superseded. In the Selachians several such cases were given, 
 but in Mammals the most manifest examples were seen in the 
 Phalangers and Ateles marginatus No. 200 (q.v.). In the latter 
 specimen there were four premolars on each side in the upper jaw, 
 and there was nothing to indicate that any one of them was super- 
 numerary rather than any other. In such a case I submit that the 
 four premolars must be regarded as collectively equivalent to the 
 three premolars of the normal. The epithelium which normally 
 gives rise to three tooth-germs has here given rise to four, and I 
 believe it is as impossible to analyze the four teeth and to apportion 
 them out among the three teeth as it would be to homologize the 
 sides of a triangle with the sides of a square of the same peripheral 
 measurement. 
 
 Such a case at once suggests this question : if the four premo- 
 lars of this varying Ateles cannot be analyzed into correspondence 
 with the three premolars of the typical Ateles, can the three pre- 
 molars of this type be made to correspond individually with the 
 two premolars of Old World Primates ? 
 
 In the case of Rhinoptera No. 396, for the reason given in 
 describing the specimen, there is plainly no correspondence be- 
 tween the rows of plates of the variety and those of the type, and 
 the rows are, in fact, not individual, but divisible. 
 
 Though cases so remarkable as that of Ateles marginatus are 
 rare, there are many examples of supernumerary teeth, in the 
 region of the anterior premolars of the Dog or Cat for instance, 
 which cannot be clearly removed from this category. As indicated 
 in the fourth section of this Chapter, it is impossible to distinguish 
 cases of division of particular teeth from cases of the formation of 
 a new number of teeth in the series. Finally, on the analogy of 
 what may be seen in the case of Meristic Series having a wholly 
 indefinite number of members, it is likely that the attempt thus to 
 attribute individuality to members of series having normally a 
 definite number of members should not be made. 
 
 b. 18 
 
CHAPTER XL 
 
 linear series — continued. 
 
 Miscellaneous Examples. 
 
 In this chapter are given some miscellaneous examples. Most 
 of them illustrate the Meristic Variation of parts standing in 
 bilateral symmetry on either side of a median line. 
 
 Here also are included certain cases of Variation concerning 
 the series of apertures in the shell of Haliotis, though probably 
 they are of a wholly different nature. 
 
 Scales. 
 
 Among animals possessing an exoskeleton composed of scales, 
 the number of the scales or of the rows of scales found in par- 
 ticular regions is usually more or less definite. So constant are 
 these numbers in their range of Variation that in both Reptiles 
 and Fishes either actual numbers or certain ranges of numbers are 
 made use of for purposes of classification. 
 
 Considerable Variation in these numbers is nevertheless well 
 known, and many instances are given in works dealing with 
 Reptiles or Fishes. The following cases are given as illustrations 
 of some of the larger changes which may occur. 
 403*. Clupea pilchardus (the common Pilchard). Among the 
 Pilchards brought to the curing factories at Mevagissey, Corn- 
 wall, specimens have from time to time been found by Mr Mathias 
 Dunn, the director, having the scales of one side very many more 
 in number than those of the other side. Two specimens 1 shewing 
 this abnormality were given to me by Mr Dunn in 1889. Owing 
 to the fact that the fresh Pilchards are shovelled wholesale into 
 the brine-vats, it is not until the fish are picked over for packing- 
 after the salting process that any individual peculiarities are 
 
 1 These specimens are now in the Museum of the Royal College of Surgeons. 
 An account of them was published in P. Z. S., 1890, p. 586. Figures of the same 
 variation were given by Day, F., P. Z. S., 1887, p. 129, PI. xv. 
 
chap. XL] PILCHARD: SCALES. 275 
 
 noticed. This was the case with the present specimens, which 
 were given to me as they came salted from the presses. Never- 
 theless when received they were in fairly good condition. 
 
 The first specimen measured 8 in. to the base of the caudal fin. 
 The head and opercula were normal on both sides. The number of 
 scales along the lateral line or the left side is 32 and the number on 
 the right side is 56 or 57. On the left side the scales have the 
 size usually seen in Pilchards of this length, and on the right side 
 for a distance of about an inch behind the operculum the scales 
 are not much smaller than those of a normal Pilchard, but behind 
 this point each scale is of about half the normal size. 
 
 The second specimen has a very similar length. It differs 
 from the first in having the reduplication on the left side in- 
 stead of on the right. Furthermore the scales are normal in 
 size as far as the level of the anterior end of the dorsal fin, behind 
 which place they are of about half the normal size. The transi- 
 tion in this specimen is quite abrupt. The scales had been 
 somewhat rubbed, and the counting could not be very accurately 
 made, but the total number along the left lateral line was 
 approximately 48. 
 
 As these abnormal individuals were taken with the shoal there 
 can be little doubt that they were swimming with it. 
 
 In P. Z. S., 1887, p. 129, PI. xv. Day described a specimen, also 
 obtained from Mr Dunn, exhibiting characters similar to those above 
 described. The number of scales along the lateral line is given as 32 
 on the right side and 51 on the left. In the figure no transition from 
 normal to abnormal scales is shewn, but there is a general appearance 
 of uniformity. 
 
 Mr Day regarded this specimen as a hybrid between the Herring 
 (C. harengus) and the Pilchard, and before adopting the view that the 
 case is one of Variation this suggestion must be discussed. This view 
 was chiefly based on the presence of the small scales on one side, but it 
 is added that the ridges on the operculum, which are characteristic of 
 the Pilchard as compared with the Herring, were better marked on 
 the right side than on the left, though they are stated to have been 
 very distinct on the left side also. In the specimen described, the 
 gill-rakers were 61 in the "lower branch of the outer branchial arch" 
 (viz. the bar consisting of the first hypobranchial and ceratobranchial), 
 and it is mentioned that this number is intermediate between that 
 found in a Pilchard (71) and in a Herring (48); but whether this 
 intermediate number was found on the side shewing the " Herring " 
 characters, or on the other, or on both, is not stated. These gill-rakers 
 are also said to have been intermediate in length between those of a 
 Pilchard and those of a Herring. From these points of structure 
 Mr Day concludes that the specimen was a hybrid between the Herring 
 and the Pilchard. 
 
 As against the theory that these specimens are hybrids it may be 
 remarked that no direct evidence is adduced which points to hybrid 
 parentage. The suggestion is derived from (1) the condition of the 
 
 18—2 
 
276 MERISTIC VARIATION. [part I. 
 
 scales, (2) the number of the gill-rakers, (3) the alleged difference in 
 the opercula of the two sides. In view of the first point, viz. that the 
 number of the scales on one side is intermediate between that of the 
 Pilchard and that of the Herring, it seemed desirable to know whether 
 the resemblance extended to the minute structure of the scales or was 
 restricted to their number only. On comparing microscopically the 
 scales of the Pilchard and the Herring, I find that those of the 
 Herring bear concentric lines which are almost always smooth and 
 without serrations, while those of the Pilchard are marked with lines 
 which are waved into very characteristic crenelated serrations. On 
 comparing the scales which are repeated, it was found that they also 
 shew these characteristic serrations and that in pattern they differ in 
 nowise from the scales of the Pilchard. This evidence appears to tell 
 very strongly against the theory that the small scales are derived from 
 a Herring parent. 
 
 The evidence from the gill-rakers seems to be also unreliable. In 
 a normal Pilchard Mr Day found 71 on the hypo- and cerato-branchials 
 of the first gill-bar, and in a specimen examined by me 72 were present 
 and in normal Herrings 48. But in my two specimens shewing the 
 repeated scales there were present, on the normal sides 79 and 67 
 respectively, and on the abnormal sides 78 in the one fish and 67 in 
 the other. In size and shape the gill-rakers were like those of the 
 Pilchard, being smooth, and unlike those of the Herring, which bear 
 well-marked teeth. 
 
 As it is stated that the serrations characteristic of the operculum 
 of the Pilchard were very distinct on the abnormal side, it is impossible 
 to lay much stress on the circumstance that they were less distinct than 
 those of the other side. 
 
 In addition to the considerations given above, there are several 
 d, priori objections to the hypothesis of the hybrid origin of these 
 forms ; as, for example, that unilateral division of parental characters 
 is certainly not a common phenomenon in hybrids, if it occurs at all, 
 and so on. But since the evidence advanced for the theory of hybrid 
 parentage is already open to criticism, it is perhaps unnecessary to 
 discuss these further difficulties. 
 
 On the whole, therefore, it seems simpler to look on these 
 abnormalities as instances of the phenomenon of Meristic Variation 1 . 
 
 In Ophidia the number of scales occurring in different parts 
 of the body is constant in some genera and species, and variable in 
 others. Variation in the number of rows of scales on the body 
 may be specially referred to as an instance of a change in number 
 occurring at right angles to that just described. The number of 
 such rows in Tropidonotus, for example, is generally 19, but Mr 
 
 404. Boulenger informs me that the Swiss Tropidonotus viperinus 
 has either 21 or else 23 rows. 
 
 405. Tropidonotus natrix is remarkably constant in the posses- 
 sion of 19 rows of body scales. A specimen taken in Switzerland 
 
 1 Compare with an interesting series of cases in Gasterosteus (Stickleback). 
 Boulenger, G. A., Ann. and Mag. N. H., 1893, S. 6, xi. p. 228, see also Zool., 
 1864, p. 9145; Sauvage, Nouv. Arch, du Mus., 1874; Day, Jonrn. Linn. Soc, xm. 
 1878, p. 110 ; &c. 
 
chap, xi.] SNAKES : SCALES. 277 
 
 is described by Studer, Mitth. natur. Ges. Bern, 1869, p. 24, as 
 having 20 rows. This specimen was unusually dark in colour. 
 [The presence of an even number of rows is in itself remarkable, 
 but it is not stated whether this total was reached by duplicity in 
 the median dorsal row or by inequality on the two sides.] 
 406. A specimen of Snake from Morocco closely resembled Macropro- 
 todon mauritanicus Guichenot (= Lycognathus cucullatus Dum. 
 Bibr.), but differed from it in having 23 rows of body-scales 
 instead of 19, being 4 rows in excess of the normal number. 
 Peters, W., Sitzb. Ges. naturf. Fr. Berlin, 1882, p. 27. 
 
 For particulars as to the range of variation in these numbers 
 in different species, see numerous examples given by Botjlenger, 
 G. A., Fauna of Brit. India : Reptilia and Batrachia, 1890. 
 
 Kidneys ; Renal Arteries ; Ureters. 
 
 Meristic Variation in these organs is well known and the 
 principal forms found are described in most text-books of anatomy. 
 Some information as to these is given below. The examples are 
 all from the human subject. 
 
 407. Kidneys. Male having three kidneys. The left kidney was 
 normal in shape, position and consistency but was abnormally 
 large. The right kidney was placed opposite to it and weighed 
 only half as much as the left. From it a ureter with a small 
 lumen arose and passed in a normal course so far as the division 
 of the aorta. At this point its course lay along the surface of the 
 third kidney. This third kidney lay over the whole right iliac 
 artery, a portion of the right crural artery for the space of 9 lines, 
 the right crural vein and the psoas major muscle. It was larger 
 than the upper right kidney and had the form of an oval with its 
 ends cut off. The anterior and posterior surfaces were convex. The 
 anterior surface was grooved for the passage of the ureter men- 
 tioned above, which received the ureter of the second kidney and 
 passed normally into the bladder. The man was a sailor and died 
 of enteritis at the age of 39. Thielmanx, C. H., Midlers Arch, 
 f. Anat. u. Phys., 1835, p. 511. 
 
 408. Renal Arteries. The number of the renal arteries in Man is 
 liable to great variation. In specimens in which the kidneys are 
 normal in position the arteries may be (a) diminished or (b) 
 increased in number. The latter is much more common. 
 
 Multiple renal arteries may be threefold, (a) Most commonly 
 the additional branches spring from the aorta, (b) they may come 
 from other sources ; or (c) there may be a co-existence of additional 
 vessels from both sources. 
 
278 
 
 MERIST1C VARIATION. 
 
 [part I. 
 
 Of the first class, there have been described cases of 
 
 one, 
 
 two, 
 
 or 
 
 three 
 
 r one, " 
 right aortic | two, 
 
 renals -I three i-left aortic renals. 
 associated with or 
 
 , four . 
 
 409. 
 
 In the commonest form, next to the normal condition of one on 
 each side, there are two on the right side and one on the left. In the 
 second commonest condition there are two on the left and one on 
 the right ; but among the forms with larger numbers, the greatest 
 number is more frequently seen on the left than on the right side. 
 In all these cases one vessel arises in the position of the normal 
 renal ; a second commonly springs from the aorta much lower 
 down, generally on the level of, or below the inferior mesenteric ; 
 the third when present, is at a very short distance above the 
 normal renal, very close to the supra-renal and on the level of the 
 superior mesenteric. Cases of five on the right are described by 
 Otto and Meckel, and other multiple forms are recorded by the 
 older anatomists. Macalister, A., Proc. Roy. Irish Ac, 1883, p. 
 624. 
 
 Three renal arteries on each side, symmetrically placed (Fig. 
 73). In this case the posterior ends of the kidneys were united 
 
 Fig. 73. Case of three renal arteries on each side combined with " horse-shoe 
 kidney" (Man). (From Guifs Hosp. Rep.). 
 
 across the middle line in the condition known as " horse-shoe 
 kidney" [see evidence as to Bilateral Series]. Guy's Hosp. Rej)., 
 1883, p. 48, fig. 
 
 410. Ureters. Male. Four ureters emerging from the hilum of 
 each kidney. After proceeding about four inches they became 
 united, forming a pelvis from which sprang the proper ureter. The 
 hilum of the kidney was found to be occupied by a quantity of 
 
CHAP. XI.] 
 
 EYES I MOLLUSCA. 
 
 279 
 
 fat and connective tissue, imbedded in which the ureters could be 
 traced to the infundibula, communicating with the calices and 
 pyramids : thus there was no pelvis within the hilum, but the 
 calices united to form infundibula of which these ureters seemed 
 to be the continuation, and they became united in a pelvis some 
 distance removed from the kidney. There were other signs of 
 abnormal urino-genital development and the author believes that 
 it is almost certain that the abnormality described was congenital 
 and not a sequel of disease. Richmond, W. S., Jour. Anat. Phys., 
 xix. p. 120. 
 411. Two ureters from one kidney are frequent. For an example, 
 see Guys Hosp. Rep., 1883, p. 48. 
 
 Tentacles and Eyes of Mollusca. 
 
 412. Subemarginula : specimen having a supernumerary eye on 
 each eye-stalk (Fig. 74, II.). Author remarks that supernumerary 
 eyes are common in forms having eyes borne on tentacles, but are 
 rare in forms in which the tentacle is reduced as it is in Subemar- 
 ginula. Fischer, P., Jour, de Conch., S. 2, i. p. 330, PL xi. fig. 4. 
 
 413. Patella vulgata : tentacle and eye repeated on left side (Fig. 
 74, I.). Right side normal. Supernumerary eye and tentacle of 
 
 . normal size. Ibid., S. 3, iv. p. 89, PL till. fig. 8. 
 
 n 
 
 v 
 
 in 
 
 Fig. 74. Repetitions of eyes and tentacles in Molluscs. (After Fischer and 
 Moquin-Tandon.) 
 
 I. Patella vulgata, No. 413. II. Subemarqinula, No. 412. III. Helix kermo- 
 vani, No. 416. IV. Clausilia bidens, abnormal, No. 417 ; V. normal of the same. 
 
280 MERISTIC VARIATION. [part I. 
 
 414. Triopa clavigera (a Nudibranch): adult of the usual size, 
 having the lamellar rhinophore of the right side formed of three 
 branches, of which the two anterior were lamellar, borne on a 
 common peduncle, and the posterior was simple, of regular shape 
 and probably representing the normal rhinophore of the right side. 
 The rhinophore of the left side was normal. Ibid., S. 3, XXVIII. p. 131. 
 
 415. Physa acuta: right tentacle bifid, left normal. Moquin- 
 Taxdox, Hist. not. des Moll. terr. et fluv. de France, I. p. 322, PL 
 xxxn. fig. 15. 
 
 416. Helix kermorvani : a second eye present, close to, but 
 separate from the normal eye (Fig. 74, III.) on the left tentacle. 
 Ibid., PL xi. fig. 10. 
 
 417_ Clausilia bidens : supernumerary eye on the right tentacle 
 
 ' as shewn in Fig. 74, IV. Ibid., PL xxm. fig. 24. 
 41 $ Littorina : supernumerary eye on one tentacle. Pelsexeer, 
 Ann. Soc. beige de microscojne, XVI., 1891. 
 
 In examining large numbers of Pecten of several species, Mr Bkindley 
 occasionally found one of the eyes imperfectly divided into two, the division 
 being at right angles to the mantle-edge. 
 
 Eyes of Ixsects. 1 
 
 The following are examples of supernumerary eyes in Insects. 
 They are mentioned as examples of the development of tissues of 
 the same nature as those of the normal eye in abnormal situations. 
 All the cases known to me occur in Coleoptera. 
 
 419. Toxotus ( = Pachyta) 4 — maculatus: a normal female. On 
 the vertex of the margin of the right eye and abutting against it 
 is a small third eye. This third eye is round-oblong in shape. It 
 is separated from the large eye only by the outermost margin of 
 the eye, and though it is more convex than the latter there is 
 nevertheless a considerable depression between the upper surfaces 
 of the two eyes. This supernumerary eye is of a brighter colour 
 than the normal eye, being brownish-yellow, while the latter is of 
 a pitchy black. It is facetted in the same way as the normal eye 
 is. Letzxer, K., Jahresb. d. Schles. Gesell.fur vaterl. Cidtur., 1881, 
 p. 355. 
 
 420. Calathus fuscus : having a third eye. On the left side of the 
 vertex was placed a supernumerary eye. This structure was 
 smaller and less projecting than the normal eye and was separated 
 from it by the usual groove. It did not appear to be a part of the 
 normal eye which had separated from it, for the normal eyes of 
 the left and right sides were exactly alike. The integument of 
 the head was slightly wrinkled around the supernumerary eye. 
 de la Brulerie, P., Ann. de la Soc. Ent. de France, S. 5, v., 1875, 
 p. 426, note. 
 
 421. Vesperus luridus $ : head abnormal and bearing a third 
 
 1 For cases of eyes compounded in the middle line (Bees), see evidence as to 
 Bilateral Series. 
 
chap, xi.] WINGS OF INSECTS. 281 
 
 facetted eye. The consistency of the chitinous covering of the 
 head, its sculpture and hairs, colour, &c. are all normal and of the 
 usual structure. The left side of the head however is rather less 
 developed than the right, and the left eye seems to be smaller and 
 somewhat less convex, but there is no special deformity or altera- 
 tion in the facetting. 
 
 At the left side of the head arises an irregular chitinous loop 
 of unequal thickness and having' a diameter of about 2*5 mm. 
 This loop is attached to the substance of the head before and 
 behind and these two attachments are distant from each other 
 about 1 mm. The height of this loop from the surface of the head 
 is about 1 mm. in the highest part. Upon the upper surface of 
 the loop is a small, irregularly rounded eye. The diameter of this 
 eye is about 2 5 mm. and its convexity is considerable. It is 
 facetted, but its facetting is not quite regular and is finer and 
 slighter than that of the normal eyes. VON Kiesen wetter, Bed. 
 Ent. Ztschr., 1873, xvn. p. 435, Plate. 
 
 [A case is recorded by Reitter (Wiener Ent. Ztg., I v., 1885, 
 p. 276) of a Rhyttirhinus deformis, having a "complete and fully 
 formed facetted eye placed on the left side of the thorax." Upon 
 the request of Dr Sharp, this specimen was most kindly forwarded 
 by Dr Reitter for our examination, when it was found that upon 
 the application of a drop of water, the supposed abnormal eye 
 came off. The eye appeared to be that of a fly, and had no doubt 
 become accidentally attached to the beetle either in the collecting- 
 box or before its capture.] 
 
 Wings of Insects. 
 
 Supernumerary parts having the structure of wings have been 
 occasionally recorded in Lepidoptera, but their occurrence is ex- 
 ceedingly rare. In a subsequent chapter detailed evidence will 
 be given respecting supernumerary legs and other of the jointed 
 appendages of Insects and it will be shewn that in very man)' 
 and perhaps all of these cases the supernumerary parts constitute 
 a Secondary Symmetry within themselves (see p. 90). Extra 
 wings however are of a different nature altogether, and there is 
 so far as I am aware no indication that any of their parts are 
 disposed as a Secondary Symmetry. In other words, an extra 
 wing if on the left side is a left wing, and if on the right side 
 a right wing. 
 
 In some cases the extra wing is a close copy of a normal struc- 
 ture, in others it seems to be more or less deformed. No genuine 
 case of an extra wing present on both sides of the body is known 
 to me. 
 
 From the fact that no specimen of supernumerary wing has 
 ever been properly dissected, it is not possible to make any 
 confident statement as to the attachments or morphology of 
 such parts. (See also No. 78.) 
 
282 MERISTIC VARIATION. [part i. 
 
 The cases of S. carpini, No. 422, and of Bombyx quercus, No. 
 429, nevertheless suggest that Variation in number of wings is of 
 the same nature as that seen in teeth, digits, or other parts 
 standing in a Meristic Series. In the specimen of S. carpini 
 it is especially noticeable that on the side having three wings, 
 both the wings formed as secondaries were smaller than the 
 secondary of the normal side ; but in other cases, G. rhamni 
 (No. 427) for instance, this was not the case, and the wing 
 standing next to the extra wing was normal. Both these con- 
 ditions are frequently found in cases of the occurrence of super- 
 numerary parts in series: for two members of a varying series 
 may clearly correspond jointly with a single member of the 
 normal series, or on the contrary a new member may stand ad- 
 jacent to members in all respects normal as in G. rhamni (No. 427.) 
 *422. Saturnia carpini $ , having a supernumerary hind wing. The 
 specimen is rather a small female. The right wings and the 
 left anterior wing are normal, but in the place of the left posterior 
 wing, there are two rather small but otherwise nearly normal 
 posterior wings. Of these the anterior is rather the larger and 
 to some extent overlaps the posterior. The costal border of the 
 posterior wing is folded over a little so that its width cannot 
 
 be exactly measured. 
 
 Greatest Greatest 
 
 length. width. 
 
 Right hind-wing normal 22'5 mm. 19 mm. 
 First left hind-wing 20*5 „ 14 „ 
 
 Second left hind-wing 15'5 „ 11 „ about. 
 
 From the fact that the bases of these two wings are greatly 
 overgrown with hair, it is difficult to distinguish their exact points 
 of origin from the body, but so far as may be seen, the second 
 arises immediately behind and on a level with the first. The 
 neuration of each of the two small wings is identical with that 
 of a normal hind- wing. The scaling is perfect on both surfaces 
 of both wings, but is perhaps a little more sparse on the anterior 
 of the two abnormal ones. In colour the anterior abnormal wing 
 is rather light, but the posterior one is identical with that of 
 the other side. The markings on each of the wings are normal, 
 but are on a reduced scale in proportion to the size of the wings. 
 This is especially remarkable in the case of the ocelli, which are 
 both of a size greatly less than that of the ocellus of the normal 
 hind wing of the right side. 
 
 The two wings were in every respect true left hind-wings 
 and were in no way complementary to each other. [Specimen 
 in collection of and kindly lent by Dr Masox.] 
 423. Bombyx rubi J : 5th wing on left side. The additional wing 
 was placed behind the left posterior wing. It was of normal 
 structure as regards scaling and coloration. Its length was that 
 of the hind-wing but in breadth it did not exceed 6 mm. The 
 
chap, xl] WINGS OF INSECTS. 283 
 
 insertion of this wing into the body was immediately above that 
 of the normal hind-wing. The extra wing bore 4 nervures, of 
 which 3 reached to the margin but one was shorter. The proper 
 hind-wing of the same side was rather narrower than that of 
 the other side and was not so thickly covered with scales, but 
 its neuration was complete and normal. Speyer, A., Stettiner 
 Ent. Ztg., 1888, xlix. p. 206. 
 
 424. Samia cecropia <£, having a fifth aborted wing. Bred in capti- 
 vity : ordinary size, expanding about 5^ inches : a smoky variety in 
 which red portion of transverse bands on wings is much narrowed. 
 Right primary and both secondaries normal in shape and marking. 
 Left primary in length from base to apex exactly the same as the right, 
 but in width from inner angle across to the costa is y 3 F of an inch less; 
 the markings are the same, but condensed into the narrower space. 
 Neuration normal in all wings. Left primary also somewhat narrower 
 at base, where it joins the body. The inner margin is in exact line 
 with its fellow; hence the costal line of the left primary is somewhat 
 posterior to that of the right primary. The supernumerary wing 
 emerges from the side of the collar and runs parallel to the normal left 
 primary. It consists mainly of the costal and subcostal nervures, a 
 small part of the median nervure and a strip of wing about i inch wide 
 which was much curled in drying. The supernumerary wing is in no 
 way connected with the normal one. 
 
 [The author regards this supernumerary wing as a repetition of the 
 anterior part of the left primary wing.] Strecker, H., Proc. Ac. Sci. 
 Philad., 1885, p. 26. 
 
 425. Limenitis populi, having four normal wings and a fifth wing 
 behind the left posterior one. This supernumerary wing was 20 mm. 
 long and 9 mm. wide. It slightly overlapped the left secondary and 
 was attached to it for a length of 12 mm., but its outer end was free. 
 It is described as exactly resembling the part of the secondary which 
 bears the three anterior nervures, and it is stated that both surfaces 
 were normal as regards scales and colouration. Rober, J., Correspond- 
 enzbl. d. ent. Ver. "Isis" z. Dresden, 1884, I. p. 31. 
 
 426. Vanessa urticae, having an additional hind-wing on the right 
 side. This structure is inserted into the thorax dorsal to and betice/i 
 the two normal wings. It is shorter and of about i the width of the 
 normal hind-wing. In colouring it is a close copy of the anterior third 
 of the hind-wing. Westwood, Trans. Ent. Soc, 1879, pp. 220 and 
 221, Plate. [Now in Brit. Mus.] 
 
 427. Gonepteryx rhamni with additional imperfectly developed hind- 
 wing on the right side. In this case the normal right hind-wing is 
 only about two-thirds of its normal size. It overlies the additional 
 hind-wing. The latter is coloured like the normal wing and bears an 
 orange spot. From the neuration of the two wings Westwood con- 
 sidered that the supplemental wing contained missing parts of the 
 normal wing. 
 
 Only two legs existed on the side of the abnormal wing, but for fear 
 of injury the specimen was not sufficiently examined to shew whether 
 
284 MERISTIC VARIATION. [part i. 
 
 the missing leg had been broken off or whether the extra wing was in 
 its place. Westwood, ibid., p. 220. 
 
 A specimen of G. rhamni having five wings was caught at Brandon, Norfolk, in 
 Aug. 1873 by Mr J. Woodgate, and exhibited to the Ent. Soc. by Prof. Meldola, 
 Proc. Ent. Soc, 1877, p. xxvi. A similar specimen of this species was bought at 
 Stevens's auction-rooms and exhibited to Linn. Soc. by Prof. C. Stewart, in April, 
 1891. This specimen is now in Mus. Coll. Surg. Whether it is the same as that 
 taken by Mr Woodgate, or that described by Westwood, or not, I cannot say, but 
 possibly the references are all to one individual. 
 
 428. Lycaena icarus <£ . A coloured figure is given of a specimen 
 of this form with 5 wings from Taurus, Asia Minor. [No further 
 description is given. The figure is not very clear. It shews 
 however that all the wings are normal except the right anterior. 
 This wing is represented by two wings, which together are about 
 a third wider than the normal wing. The costal portion of the 
 foremost of these wings appears to be nearly normal in neuration, 
 and the posterior part of the hindmost seems to be also normal. 
 The two taken together shew several supernumerary nervures 
 as compared with the normal wing, but the details are not 
 shewn with sufficient clearness to justify a more precise statement.] 
 Honrath, E. G., Berl. Ent. Ztschr , xxxn. 1888, p. 498, To.f. VII. 
 
 429. Bombyx quercus J : specimen having 5 wings figured in 
 colour by Honrath, with statement that the left anterior wing 
 shews a double structure. [No further description given. The 
 figure shews the left anterior wing represented by two wings. 
 Of these the posterior appears to represent a nearly complete 
 anterior wing on a reduced scale. It bears the white ocellar mark 
 of the anterior wing. The pale-yellow submarginal band is 
 curved inwards over the ocellus upon the costal border as in a 
 normal wing and thus shews that the foremost wing is not merely 
 the separated costal part of this wing. The foremost wing is 
 anomalous. Its central half is rather darker in colour than that 
 of the normal wing and its peripheral half is pale in colour, 
 deepening towards the margin. It bears no ocellus. The neura- 
 tions cannot be made out from the figure with precision but the 
 two wings together contain many more nervures than the normal 
 anterior wing. The legs are not described.] Honrath, E. G., 
 ibid., fig. 10. 
 
 430. Zygaena minos, having a fifth wing on the left side, inserted above and between 
 the normal wings. The neuration of this wing is peculiar. The colouring of the 
 supernumerary wing was that of the anterior wing. [Dr Rogenhofer kindly informs 
 me that the legs were normal.] Rogenhofer, A., Sitz.-Ber. d. zool.-bot. Ges. Wien, 
 1883, xxxn. p. 3-4, fig. 
 
 In the same place the following instances of five- winged Lepidoptera are given : 
 431 Orthosia laevis with an additional posterior wing on the left side, in the 
 
 ' Museum of Pesth. Treitschke, Bd. vi. Abth. n. p. 407. 
 
 432. Tygaera anastomosis with a wing-like appendage to the left anterior wing in 
 ' the collection of Ochsenheimer in Pesth. 
 
 433. Naenia typica with an additional posterior wing in the collection of Neustadt 
 at Breslau. 
 
chap, xi.] HORNS. 285 
 
 434. Crateronyx dumi with five wings in the collection of Wiskott in Breslau. 
 
 435 Penthina salicella : left fore-wing about J wider than the normal right fore- 
 
 * wing. The apical border was markedly emarginated, giving it a bilobed appearance. 
 
 The nervures were as in the normal wing, except that the cells between the branches 
 
 of the subcostal nervure were enlarged. Kogenhofek, ibid. [I am indebted to Dr 
 
 Eogenhofer for a sketch of this specimen.] 
 
 [Palloptera UStulata (Diptera): specimen having a large upright 
 scale on the thorax. This abnormal structure is like a third wine in 
 appearance, and is fixed on the thorax, passing from the head, back- 
 wards between the wings. Its upper border is circular, and in all 
 respects it resembles the upper wing-scale of one of the Calypterous 
 Muscidce. Gercke, G., Wiener Ent. Ztg., 1886, v. p. 168.] 
 
 Horns of Sheep, Goats and Deer. 
 
 436. Sheep. Repetition of the horns in sheep is well known. The 
 best account is that of H. von Nathusius 1 of which the following 
 is chiefly an abstract. 
 
 Commonly there is a pair of extra horns placed externally to 
 the usual pair, but there may be three pairs in all, and even 
 higher numbers are recorded, though Nathusius had seen no such 
 case. The numbers on the two sides may be different, two on one 
 side and one on the other, and three on one side and two on the 
 other being sometimes met with. 
 
 It is noticeable that in all cases the horns stand in a trans- 
 verse series, and not in a longitudinal series as they do in the 
 Four-horned Antelope (Tetraceros quadricornis). The bases of 
 the horn-cores are generally in contact, standing one outside the 
 other at the same transverse level on the skull. Nathusius 
 observed that in development the outgrowth for the horns of one 
 side is at first single, but afterwards divides into two or more 
 points, but he surmises that the division may appear earlier in 
 other cases. 
 
 The external horns are generally smaller than the internal 
 ones, but this is not universal. In some cases of two pairs of 
 horns a small fifth horn is placed between the external and internal 
 horns of one side. 
 
 In another form of double horn the horn-core of one side or 
 other may be a double structure, both cores being enclosed in a 
 single horn, which on being separated has a double-barrelled 
 appearance. 
 
 Several examples of permanently four-horned breeds occur in 
 various localities, being described as common in Cyprus and 
 notably in Iceland and other northern islands. Youatt (p. 169) 
 stated that there were two breeds of sheep in Iceland, the one 
 small and the other large, and that the greater part of both breeds 
 
 1 H. von Nathusius, Vortr. iib. Viehzucht u. Rcusenkenntniss, Th. n., Die Schaf- 
 zucht, 1880, p. 177, fig. 47. 
 
286 MERISTIC VARIATION. [part I. 
 
 had more than two horns, some having eight. I am informed 
 however by Mr E. H. Acton, who has spent some time in the 
 country, that many-horned sheep are by no means common in 
 Iceland at the present day. In Kishtwar (district of S.E. Kashmir) 
 a breed of 4-horned sheep is carefully preserved, in which the 
 horns are as a rule very symmetrical, somewhat resembling 
 No. 438 \ 
 
 Xathusius states that a four-horned ram does not always beget 
 four-horned offspring even when the ewe has the same character, 
 and the variation between father and son in respect of horns is 
 frequently considerable. 
 
 The best figures of many-horned sheep are those given by Buffon, Hist, nat., 
 Vol. xi. Pis. 31 and 32 (3-horned and 4-horned); Youatt, The Sheep, pp. 141 and 
 171, copied from Buffon. Numerous other figures are referred to by Nathusius, 
 but few of them are satisfactory. 
 
 437. G-oat. A family of goats on an isolated farm near Bozen had 
 4 horns, which had been inherited for many generations. In most 
 cases the two ordinary horns were typical in shape and direction; 
 and in addition to these there were two lateral ones, which were 
 laterally curved, being sickle-shaped and bent into a semicircle. 
 Gredler, V., Korrespondenzbl. d. zool. min. Ver. Regensburg, 1869, 
 xxiii. p. 35. 
 
 '438. Rupicapra tragus (Chamois) : skull bearing two well-formed 
 and symmetrical extra horns. The cores of these horns were a little 
 outside and posterior to the normal pair. Alston, E. R., P. Z. S., 
 1879, p. 802. 
 
 439 Capreolus caprea (Roebuck) : specimens having a supernumerary 
 beam are probably not very rare, and a number of such antlers were 
 shewn among the hunting-trophies exhibited by H. H. the Duke of 
 Saxe-Coburg-Gotha, and H. S. H. the Prince of Waldeck-Pyrmont at 
 the German Exhibition held in London in 1891. The normal antler of 
 the roebuck has a single beam rising vertically, then bifurcating, the 
 posterior branch again dividing. In the abnormal specimens from the 
 single burr of one side arose a supernumerary beam in addition to the 
 normal one. In one specimen, in which the supernumerary beam was 
 nearly as long as the normal one, the latter bifurcated as usual but 
 was rather more slender than that of the other side (Fig. 75 I.). In 
 another case (Fig. 75 II.), from the left burr, which was much enlarged, 
 arose (1) an innermost beam, in thickness and texture resembling that 
 of the normal right horn, though it was much shorter and bore no tine ; 
 (2) an external beam at once dividing into two almost equivalent 
 branches having about the same length as the innermost beam. In 
 such a case I know no criterion by which one of the three beams can 
 be certified to be the normal to the exclusion of the others. As in the 
 sheep and goats, the several horns resulting from subdivision seem to 
 be generally in or nearly in the same transverse plane. 
 
 1 Godwin-Austen, H. H., P. Z. S., 1879, p. 802. 
 
CHAP. XI.] 
 
 HALIOTIS. 
 
 287 
 
 Fig. 75. Abnormal horns of Roebuck (Capreolus caprea), No. 438. ("When seen 
 by me the horns were fixed upon heads modelled in plaster.) 
 
 Perforations of shell of Haliotis. 
 
 44Q Haliotis gigantea (Japan) having two rows of perforations in the shell. In 
 addition to the ordinary row of perforations, of which 12 were present in this 
 specimen, there was a series of 8 additional perforations which began within an inch 
 of the apex. Of the normal series the last four remained open, but all the perfora- 
 tions in the abnormal row were closed with nacre. Specimen in Brit. Mus. Smith, 
 E. A., Ann. and Mag. of X. H., 1888 (1), p. 419. 
 
 441. Haliotis : two specimens, of different species, in which the perforations were 
 entirely absent, their place being taken by a continued convex, spiral rib, like the 
 second rib of Padollus. "Probably in this individual the mantle was without any 
 slit, and hence the malformation, the water being admitted to the gills by the slight 
 notch in front of the ribs, as in some Emarg inula, or Scuta." Gray, J. E., Proc. 
 Zool. Soc, 1856, p. 149. 
 
 442. H - albicans : several specimens in which the perforations were united to form a 
 continuous slit. The appearances were so uniform that Gray was disposed to think 
 that these specimens might represent a new genus, but on comparison with types 
 they seemed to belong to the species named. In some fossil genera (Scissurella) the 
 perforations are replaced by a more or less continuous slit over the mantle. The 
 specimens in question were greatly eroded and had a diseased appearance, ibid. 
 Plate. 
 
CHAPTER XII. 
 
 linear series — continued. COLOUR-MARKINGS. 
 
 Ocellar Markings 1 , especially those of Lepidoptera. 
 
 Upon the bodies of animals belonging to many classes are 
 markings which consist of a central patch of colour surrounded by 
 a variable number of concentric rings of different colours. Such 
 markings are known as ocelli or eye-spots from their resemblance 
 to the pupil and iris of vertebrates. Eye-spots are perhaps best 
 known in Lepidoptera, but similar markings are not unfrequent in 
 other groups and especially on the feathers of Birds and in Fishes. 
 
 In one of the best known chapters in the Descent of Man 2 the 
 nature and mode of evolution of these markings is the subject of 
 a full discussion, the case of eye-spots on feathers being chiefly 
 taken in illustration. As is well known, Darwin by the compara- 
 tive method, comparing the eye-spots found in different species, on 
 the different feathers of the same bird, or on different parts of the 
 same feather, found that it was possible to construct a complete 
 progression from a plain spot to a fully-formed ocellus. Though 
 no one examining such a series can possibly doubt that the simple 
 spot and the fully-formed ocellus are really of the same nature and 
 that the one represents a modification of the other, there remains 
 nevertheless the difficulty that members of a series of parts cannot 
 be assumed to represent conditions through which the other mem- 
 bers of the same series have passed, and it is of course clear that 
 the conditions found in some forms do not necessarily correspond 
 with phylogenetic phases of other forms. In the present instance 
 however Darwin is not specially urging this view, but brings 
 forward the comparative evidence chiefly in illustration of the 
 possibility that such structures may exist in an imperfect state 
 and so may be conceived of as having had a gradual origin. 
 
 1 The evidence concerning eyespots of Lepidoptera is taken here because eyespots 
 when repeated in series, though borne on appendicular parts, are nevertheless 
 arranged chiefly with reference to the chief axis of symmetry of the body. In some 
 few forms, e.g. Taygetis, there is a conspicuous Minor Symmetry within the limits 
 of a single wing (the posterior), but this is not often the case. 
 
 2 Descent of Man, 1871, n. pp. 132—153. 
 
chap, xii.] EYE-SPOTS. 289 
 
 Though doubtless the eye-spots of Birds are in their nature 
 not different from those of Lepidoptera yet their manifestations in 
 the latter are usually in some respects simpler than they are in 
 Birds. From the abundance of material also the Variation of eye- 
 spots is most easily studied in Lepidoptera and it is to them that 
 the present evidence chiefly relates. 
 
 In preface to the evidence a few remarks are needed to direct 
 attention to certain features in the mode of normal occurrence of 
 eye-spots and in the manner of their Variation. 
 
 On a survey of the facts it is at once seen that eye-spots are 
 extraordinarily variable both in number and size, some of the best 
 formed being occasionally absent, and large and perfect ocelli being 
 sometimes added in situations having normally no trace of such 
 marks. With this fact Darwin was well acquainted and he refers 
 to observations in illustration of it. In speaking of Gyllo leda he 
 concludes that from the great variability of the eye-spots " in cases 
 like these, the development of a perfect ocellus does not require a 
 long course of variation and selection ; ' : and again, that bearing in 
 mind " the extraordinary variability of the ocelli in many Lepi- 
 doptera, the formation of these beautiful ornaments can hardly be 
 a highly complex process, and probably depends on some slight and 
 graduated change in the nature of the tissues." The facts to be 
 given and the circumstances attendant on the variation of ocelli 
 tend to support this conclusion. 
 
 Considered from the point of view of Meristic Variation the 
 chief feature in the manner of occurrence of eye-spots in Lepi- 
 doptera is the frequency with which they are repeated. A single 
 spot may be repeated in homologous places in both pairs 
 of wings ; in other cases there is a series along the margins 
 of one or both wings. Besides the repetitions thus occurring it is 
 especially worthy of notice that ocelli are very commonly repeated 
 on both surfaces of the wing (Satyridse, &c), the centres of the 
 upper and lower ocelli coinciding. It need scarcely be remarked 
 that this effect is not produced by transparency of the wing-mem- 
 branes and scales, but is an actual repetition, the scales of both 
 surfaces being so coloured as to form an eye-spot on each side, the 
 two having their centres coincident. In some cases, e.g. Saturnia 
 carpini (the Emperor Moth), the rings and centres of the upper 
 and lower ocelli have nearly the same colouring, but in the majority 
 e.g. Pararge megcera (The Wall), Erebia blandina, &c, the upper 
 and lower spots, though coincident, have quite different colours. 
 In considering the Variation of the spots these facts as to the 
 repetition of the spots should be remembered, for, as has been often 
 insisted on in other cases of repetitions, we are concerned with the 
 evolution of the seizes and not of one member only. Here there- 
 fore regard must be had to the degree of correspondence between 
 the variations of the eye-spots in the fore and hind wings, on the 
 
 b. 19 
 
290 MERISTIC VARIATION, [part i. 
 
 upper and lower surfaces of the same wing, in the several eye-spots 
 along the margin of the same wing, or in all of these, as the case 
 may be. The evidence will shew that there is sometimes a close 
 correspondence between the variations of eye-spots in these several 
 positions. 
 
 But though these are the matters with which we have now 
 the more direct concern it will be convenient to speak at the same 
 time more generally of eye-spots. It should be remembered first 
 that there are eye-spots of various complexity. In the simplest 
 all the bands are circular, having one centre ; the ocellus is then 
 as a rule complete in one cell of the wing, though sometimes the 
 outer zones of colour overspread parts of the adjacent cells. In 
 some cases the spot is double, having two centres, the bands being- 
 disposed round them in an hour-glass shape. As to the visible 
 structure of eye-spots it can be seen with the microscope that the 
 colour of the eye-spot lies in the colours of the scales. The scales are 
 arranged in parallel rows running (with little crossing or anasto- 
 mosing) as nearly as possible at right angles to the nearest nervures, 
 being disposed in regard to them much as the circular threads of a 
 cobweb are in regard to the radial threads. Across these rows of 
 scales run the colour-zones, in no way limited or guided by them. 
 On the other hand it can be seen that the patterns are almost 
 wholly made up by the colours of single scales, each having its 
 own colour, particoloured scales being exceptional. The effect 
 thus seen is very like that of a mosaic picture made of similar 
 pieces, or of a design worked in cross-stitch on canvas, all the 
 stitches being in rows and each stitch having its own colour. 
 
 As regards the position of eye-spots it should be noticed that 
 the simpler sort, e.g. those of Morpho or of Satyridaa, are usually 
 placed in such a position that each of their centres is on the line of 
 one of the creases or fold-marks of the wing, and it sometimes 
 happens that these creases seem to begin from the centre of an 
 ocellus. From the fact that the creases for the most part run 
 evenly between two nervures, bisecting a cell, it commonly results 
 that the centre of the eye-spot is exactly halfway between two 
 nervures. The large spots on the hind wings of some Pieridas, e.g. 
 Parnassius apollo, are an exception to this rule. 
 
 In that cell of the hind wing which lies between the submedian 
 and first median nervures in many ocellated forms (Satyridse, 
 Morpho, &c.) there are two creases, and it is especially interesting to 
 notice that in this cell there are commonly two ocelli, one on each 
 crease ; but if there is only one ocellus its centre does not corre- 
 spond with the middle of the cell but is nearer to the first median 
 nervure, being placed exactly on the anterior of the two creases. 
 In spite of the excessive variability of ocelli, in for instance Satyr- 
 idse, it appears that they are not formed in situations other than 
 these, being so far as I have seen always on one of the creases \ 
 1 These remarks refer to simple ocelli with one or more definite centres. 
 
chap, xii.] EYE-SPOTS. 291 
 
 On looking at such a series of repeated ocelli as those on the hind 
 wing of Pararge ?negcera, from this fact that the ocelli are on these 
 creases or folds the question naturally arises whether the wing may not 
 have been, in its development, folded along these creases so as to bring 
 the ocelli into contact with each other like the fold-edges of a fan. If 
 this were the case it might be supposed that the repetition of the ocelli 
 was due to the action of some one cause on all the folded edges 
 together. As a matter of fact, however, so far at least as can be 
 judged from the condition of the wings in the pupal state before scales 
 or pigments are excreted, there is no such folding, but each wing is 
 laid smoothly out, and the increase in extent of the wings of the imago 
 is attained, not by a process of unfolding, but by a stretching of the 
 elastic wing-membranes on inflation from the trachea?. On the whole 
 it does not seem likely that the repetition of similar eye-spots on the 
 Lepidopteran wing arises in any way more immediately mechanical 
 than that by which other repeated patterns are elsewhere formed on 
 animals. 
 
 The Variation of eye-spots as already stated may be very great, 
 and examples are to be given both of the total absence of large 
 eye-spots present in the normal, and of the presence of perfect 
 eye-spots in abnormal places. Besides these extreme cases there 
 is immense Variation in the degree to which eye-spots are develop- 
 ed, and such variability is nearly always to be seen in any species 
 possessing simple ringed ocelli. In the manner of Variation of 
 ocelli the following things are noteworthy. 
 
 (1) The tvhole of an eye-spot, centre and various concentric 
 bands together, may be wanting ; conversely a tvhole new eye-spot 
 having the centre and all the bands pertaining to the normal eye- 
 spot of the species may suddenly appear upon a crease normally 
 bearing no eye-spot. Eye-spots therefore may come or disappear 
 in their entirety. 
 
 (2) If a number of specimens of some much ocellated species 
 are taken and compared, examples will be found in which some of 
 the normal ocelli are absent altogether. But besides these there 
 may generally be found specimens having an ocellus in a reduced 
 and imperfect condition. Speaking generally such reduction com- 
 monly occurs by diminution of the diameter of the whole spot ; but 
 if any of its component parts are wanting the centre is the first to 
 disappear, then the next innermost band, and so on. In Fig. 76 is 
 shewn a series of specimens illustrating this fact in the case of 
 Hipparchia tithonus. The eye-spot in its least form is represented 
 by a plain black patch. In the more complete condition a white 
 centre appears. A similar case in Morpho is shewn in Fig. 81. 
 Here on the right side a certain eye-spot is absent altogether, 
 while on the left side it is present in a reduced state ; the white 
 centre and the innermost broad black band are absent, and the 
 actual centre is of the yellow-red colour which in the normal eye- 
 spot of the species is the third colour from the centre. The spots 
 
 19—2 
 
292 MERISTIC VARIATION. [part I. 
 
 on the upper surface of the hind wings of the Wall (P. megcera) 
 are an excellent illustration of these principles of Variation. 
 
 The principle here stated, though generally followed, is not 
 absolutely universal, and in other instances it occasionally happens 
 that even when of very minute size an eye-spot still retains all its 
 bands ; but the statement that the order of disappearance is from 
 the centre outwards and not the reverse is substantially true. 
 Some have expressed a belief that ocelli arise by the breaking up 
 of bands of colour, but this view finds no support in the facts of 
 Variation so far as the simple ocelli of such forms as Morplio and 
 the Satyridse are concerned ; for in its rudimentary condition a 
 circular eye-spot is in them a circular eye-spot still. 
 
 The fact just stated, that in the reduction of a circular ocellus 
 its central parts are the tirst to disappear, recalls phenomena seen 
 in many cases of disturbance propagated from a centre through a 
 homogeneous medium. A whole eye-spot may come, or it may go (as 
 seen in cases of Morpho), leaving the field of the cell plain and 
 without a speck. The suggestion is strong that the whole series of 
 rings may have been formed by some one central disturbance, somewhat 
 as a series of concentric waves may be formed by the splash of a stone 
 thrown into a pool. It is especially interesting to remember that the 
 formation even of a number of concentric rings of different colours 
 from an animal pigment by the even diffusion of one reagent from 
 a centre occurs actually in Gmelin's test for bile-pigments. Bile is 
 spread on a white plate and a drop of nitric acid yellow with nitrous 
 acid is dropped on it. As the acid diffuses itself distinct rings of 
 yellow, red, violet, blue and green are formed concentrically round it 
 by the progressive oxidation of the bile-pigment. 
 
 If the experiment is made by letting a drop of the acid fall on 
 a piece of blotting-paper wetted with bile, a fairly permanent imitation 
 of an ocellar mark can be made. It will be noticed that as in the 
 natural eye-spot, so here, the outermost zone appears first and the central 
 colour last. As also is usually the case in the ocellus, when all the 
 zones are formed, the centre may greatly increase in diameter without 
 any increase in the breadths of the circular zones, which merely get 
 larger in diameter, remaining of the same breadth. 
 
 There is of course no reason whatever for supposing that ocelli are 
 actually formed by the oxidation or other simple chemical change of 
 the pigments of the field, but this example is merely given as an 
 illustration of the possibility that a series of discontinuous chemical 
 effects may be produced in concentric zones by a single central disturb- 
 ance. Indeed, that the formation of an ocellus cannot be in reality of 
 such simplicity is shewn by the fact that the scales of the centres of 
 ocelli generally exhibit interference-colours (usually white or blue) and 
 are then wholly or partially without pigment, while in not a few cases 
 the centres of ocelli are deficient in, or destitute of, scales. It must 
 also be remembered that occasionally the colour of one of the outer 
 zones is repeated in an inner zone, which would scarcely be expected on 
 the analogy of the oxidation of bile-pigments. 
 
 (3) As in the case of Teeth at the ends of series, disappearance 
 of a member of a close series of eye-spots commonly occurs by the 
 
chap, xii.] EYE-SPOTS. 293 
 
 loss of the spot standing at one of the ends of the series. This is 
 easily seen in P. megcera, &c. Likewise as was found in Teeth, 
 disappearance of such a terminal eye-spot is associated with 
 reduction in the size of the other members of the series, and 
 especially of those nearest to the place of the absent member. 
 If as in Satyrus hyperanthus and many others, the series is broken 
 into groups, then as in the case of heterodont dentitions containing 
 gaps, a new member may be added on to the end of either group. 
 
 (4) The condition of the ocelli may vary similarly and simul- 
 taneously in both anterior and posterior wings. In a series of 
 Satumia carpini for example I notice that the size of the ocelli 
 varies greatly, those of a particular female specimen in the Cam- 
 bridge University Museum being nearly a quarter larger than those 
 of the specimen having the smallest ocelli ; but the size of the 
 ocelli in the hind wings of each individual varies with that of 
 the ocelli in the fore wings not less closely than the size of the 
 right ocelli does with that of the left. 
 
 (5) This correlation between the wings of the two pairs is seen 
 also in the presence or absence of ocelli as exhibited for instance 
 in H. tithonus (Fig. 76). It is of course often very irregular, but 
 for our purpose it is even of consequence that such correlation 
 may occur sometimes. 
 
 (6) As mentioned, ocelli are often coincident on the upper and 
 lower surfaces. When this is so, the degree of development of the 
 spots on the one surface is generally an accurate measure of the 
 degree to which they are developed on the other surface. But in 
 species having spots developed thus coincidently on the two sur- 
 faces it can be found that, in varying, an ocellus always first 
 appears in its least condition either on one surface or on the other, 
 and not indefinitely sometimes on one and sometimes on the 
 other. In P. megcera, for example, ocelli of both pairs of wings 
 can be seen on the under surface when not formed on the 
 upper and conversely. Nevertheless there is always a close corre- 
 lation between the degrees of development on the two surfaces. 
 
 (7) Lastly, attention is called to the circumstance that in two 
 cases of great variation in ocellar markings there was a variation 
 in the neuration. In the first case, P. megcera, No. 458, the second 
 median nervure was absent from both fore and hind wings. In 
 the fore wing upon the line where it should be there was an eye-spot: 
 in the hind wing the eye-spots of the two cells which should be 
 separated by the second median were partially coalescent. In the 
 other case, S. carpini, No. 459, the large ocellus was absent from 
 each wing, and it is stated that a nervure was also absent, but of 
 this case no proper description has appeared, and it is uncertain 
 which nervure was absent. When however these facts are con- 
 sidered in connexion with the circumstance that ocelli stand on 
 the creases of the wings it seems likely that in some way unknown 
 the positions and perhaps even the existence of the eye-spots may 
 
294 
 
 MERLSTIC VARIATION. 
 
 [part I. 
 
 be determined by the manner of stretching of the wing-membranes. 
 It must still be remembered that in the great majority of cases of 
 ocellar variation there is no change in the neuration. 
 
 As to the Junction of ocellar markings nothing is known, and I 
 am not aware that any suggestion has been made which calls for 
 serious notice. 
 
 * 
 
 443 
 
 Evidence as to Variation of Ocelli in Lepidoptera. 
 
 General variability of ocelli. 
 
 The following are chosen to illustrate the general variability of 
 ocelli in Satyridse. Any of the common forms, such as C. darus, 
 P. megcera, &c. shew similar variations. Generally speaking the 
 condition is bilaterally symmetrical, but somewhat asymmetrical 
 examples are not rare. 
 
 Hipparchia tithonus : from some 80 specimens taken in one 
 
 Fig. 76. Hipparchia tithonus <? , cases illustrating Variation in number of ocelli. 
 I. In f. w. the upper half of the large ocellus has a pupil, the lower has none : 
 in h. w. no ocellus. II. Both halves of large ocellus of f. w. have pupils, and the 
 h. w. has one ocellus. III. Pupils of large ocellus of f. w. are larger : h. w. has 
 two ocelli. IV. F. w. has a new ocellus and the large double ocellus is half- joined 
 to a second new ocellus. H. w. has two ocelli, one being placed otherwise than in 
 III. V. F. w. has two ocelli without pupils as well as the large double one. H. w. 
 has three ocelli. The wings of the other side corresponded near-ly though not 
 accurately. II. is the most frequent form. 
 
 (This figure was drawn with especial care from the specimens by Mr Edwin 
 Wilson.) 
 
CHAP. XII.] 
 
 EYE-SPOTS. 
 
 295 
 
 f 444. 
 
 ditch in the Cambridgeshire Fens on the same day the individuals 
 shewn in Fig. 76 were selected. These cases especially illustrate 
 the statements numbered (2) and (o), viz. the order of appearance 
 of the colours and the similar Variation of the two pairs of wings. 
 Satyrus hyperanthus : four specimens (Fig. 77) shewing 
 
 ill 
 
 II 
 
 IV 
 
 Fig. 77. Satyrus hyperanthus. Various conditions of ocelli. II. is the most 
 frequent form. 
 
 (From Newman's British Butterflies.) 
 
 different conditions of ocelli in this species from Newman's British 
 Butterflies. A form without ocelli is mentioned by Porritt, Ent. t 
 xvl, 1883, p. 188. 
 
 On one day I have myself taken all the forms shewn in Fig. 77 
 (except III.) and others in Monk's Wood, so that here no question 
 of seasonal or local difference is necessarily involved. 
 
 445 Chionobas. The North- American species of this genus [in general appearance 
 ' somewhat resembling the British Hipparchia semele, the Grayling] are of a brown 
 colour having eye-spots on some or all of the wings. According to Strecker the 
 number of eye-spots varies extremely, and the following instances are given. The 
 species norma may have two spots on fore wings and none on hind wings ; two on 
 f. w. and one on h. w. ; one on f. w. and one on h. w. ; one on f. w. and none on h. w.; 
 three on f. w. and two on h. w. Of the species uhleri one of the types has three on 
 f. w. and four on h. w., the other has four on f. w. and five on h. w., the subapical 
 being very small ; other examples have only one on f. w. and two or three on h. w. 
 The species chryxus may have one on f. w. and none on h. w.; or two on f. w. and 
 one on h. w. Strecker, Cat. Macrolepid., p. 155. 
 
 446. Arge pherusa: a butterfly resembling the British Arge galathea, the Marbled 
 White, has a variety plesaum, in which the eye-spots of hind wing are wanting. ^ 
 
 Specimen figured in which the left hind wing is a third smaller than the right 
 and lacks the eye-spots. Failla-Tedaldi, Nat. Sicil., i. p. 208, PI. xi. lig. 8. 
 
296 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 MORPHO. 
 
 A number of species of this genus, for example, M. achilles, 
 menelaus, octavia, montezuma, &c. are marked upon the under 
 surface of both pairs of wings with large ocelli having four principal 
 zones in addition to the white central spot. Of the zones the 
 outermost is silvery, the next dark brown, the next either red or 
 some shade of yellow. Within this is a band of verv variable 
 width having a deep chocolate colour. When very broad, as in M. 
 montezuma or M. achilles, the inner parts of this band are irregu- 
 larly sprinkled with red scales. The centre is white or bluish- 
 white, some of the scales in its periphery being nearly always 
 distinctly blue. The centre is commonly not circular but is pro- 
 duced (especially in larger ocelli) in a direction at right angles to 
 the crease on which it stands. Fig. 78, I, taken from a normal 
 specimen of M. achilles, shews the usual positions of the eye-spots 
 in all the species whose variations are described below. The ocelli 
 on the fore wing are 3, on the hind wing 4. In speaking of them 
 the letters a, b, c, d, e,f, g are used as shewn in the figure. Between 
 a and b there is a cell normally bearing no ocellus, and between d 
 and e there are two such cells. The spot g as described on p. 90, 
 stands at the anterior side of its cell and not in the middle of it, 
 and a second spot g L may appear behind it in the same cell. 
 
 The following examples are taken from the series in the collec- 
 
 II 
 
 ^-7 
 
 Fig. 78. Morpho achilles. Undersides of left wings. I. Normal. II. Specimen 
 wanting the spots a and c on both sides. 
 
 (From specimens in the collection of Messrs Godman and Salvin.) 
 
CHAP. XII.] 
 
 MORPHO : EYE-SPOTS. 
 
 297 
 
 tion of Mr F. D. Godman and Mr O. Salvin, to whom I am much 
 indebted for permission to examine the specimens 1 . 
 
 447. Morpho achilles £. Specimen having the spots a and c en- 
 tirely absent (Fig. 78, II) and the spot g very small. This specimen 
 occurred together with t\vo normals from Para. Ten other normal 
 males seen, and also a specimen in Camb. Univ. Mus. having no c, 
 the spot a being also greatly reduced. 
 
 448. M. montezuma £ : 15 specimens have all the spots from a to 
 g of fair size. One specimen has a spot in the place a v as shewn 
 
 Fig. 79. Morpho montezuma. Abnormal specimen having an ocellus on both 
 sides in the position a x (where an ocellus normally exists in Si. sulkowskii). 
 (From a specimen in the collection of Messrs Godman and Salvin.) 
 
 in Fig. 79. One specimen has a very faint a 1 and g l : another lias 
 a 1 as a small ocellus, and g indicated as a bulging of the spot g. 
 
 In Camb. Univ. Mus. are 4 normal males and one specimen 
 having both a 1 and g 1 marked somewhat as shewn in the case of 
 the abnormal M. octavia (Fig. 80). 
 449. M. octavia. Mr Salvin tells me that this form has a very 
 restricted distribution and is probably only a local form of M. 
 montezuma. In addition to 12 normal males the following were 
 seen, all being male. Specimen having g x as a spot of moderate 
 size ; another having g 1 very small. In another a 1 and g x were 
 both present as shewn in Fig. 80. Besides these is one having g 
 very small. All are from the Pacific slope of Guatemala. The 
 specimen figured is from El Reposo in this district, one of the 
 normals being from the same place. 
 
 1 In each of the figures the faint lines round the ocelli should be shewn as in 
 Fig. 81 ; they are omitted for simplicity. 
 
298 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Fig. 80. Morpho octavia: abnormal specimen having ocelli on both sides in 
 the positions a 1 and g 1 (where ocelli normally are in M. sulkowskii). 
 (From a specimen in the collection of Messrs Godman and Salvin.) 
 
 *450 M. menelaus </ : ten normals, and two having no a ; one 
 having left a absent and right a very faint, c and g both absent. 
 In addition to these, the specimen shewn in Fig. 81, having no c 
 
 Fig. 81. Morpho menelaus : abnormal specimen having no ocellus c in rt. f. w. 
 In left f. w. there is a small ocellus c, but it wants the two innermost colours of a 
 normal ocellus. Compared with a normal ocellus, as that at b of the same wing, the 
 abnormal has only the zones 1, 2 and 3, the latter colour forming the centre. 
 
 Fig. 78, I. may be taken as approximately shewing the normal for this species 
 also. 
 
 (From a specimen in the collection of Messrs Godman and Salvin.) 
 
chap, xil] COMPLEX EYE-SPOTS. 299 
 
 on right side, while on the left the same spot is reduced as shewn 
 in the figure, the centre being of the colour normally constituting 
 the third band. 
 
 In connexion with the above cases it should be mentioned that 
 in another species, Morpho sulkowskii, one of the more transparent 
 species, the spots a 1 , a,, and g x are all normally present. The spot 
 c is however sometimes absent in this species. In M. psyche the 
 spot c is normally absent, though present in one specimen examined. 
 
 Complex ocelli. 
 
 Besides the simpler ocelli there are other forms of ocelli of 
 more complex structure, having two or more centres around which 
 the coloured zones are disposed without an accurate symmetr} 7 . 
 Such ocelli may be seen in Vanessa io or in Junonia, and it is 
 noticeable that they are no less variable than the simpler forms. 
 The following examples may be given. 
 
 Vanessa io. Looking at the eye-spot on the fore wing of the 
 Peacock-butterfly one can readily see that it is not a structure of 
 the same nature as the other ocelli that have been already con- 
 sidered. The eye-spot of the hind wing does not materially differ 
 from other eye-spots, being essentially a black spot surrounded by 
 a pale band and containing an irregular and incomplete centre of 
 blue. The eye of the fore wing on the contrary is not actually 
 made up of concentric markings but is quite exceptional, being 
 formed of a combination of patches of different colours. But 
 whether the eye of the fore wing is a true ocellus or not it is 
 nevertheless certain that its formation mav vary with that of the 
 eye of the hind wing, as the following examples testify. 
 
 451. Specimen, British; reared from a larva in captivity, having all the 
 eye-spots deficient (Fig. 82). On the fore wings the series of white 
 spots along the margin (on the creases) are present. The three which 
 lie within the field of the normal eye-spot are longer than usual. The 
 costal black mark is extended so as to cover the greater part of the 
 
 Fig. 82. Vanessa io, the Peacock butterfly, having all the four eye-spots 
 deficient (No. 451). (From Newman.) 
 
300 MERISTIC VARIATION. [part I. 
 
 situation of the eye-spot. On the hind wings the eye-spots are entirely 
 obliterated and their place is taken by an ill-defined patch of pale 
 colour. Newman, Ent., 1872, \\ 105, Fig. 
 
 452. Similar specimen described by Goossexs, Bull. Ent. Soc. France, 
 S. 5, v. p. cxlix. 
 
 453 Similar specimen in Lord Walsingham's collection in Brit. Mus. 
 
 Here the blue and black of the eye-spots of the hind wing are altogether 
 absent. The black internal border of the spot is broader than usual, 
 and the place of the spot is lightish in colour. In the spot of the fore 
 wing the blue is deficient, the yellow is largely absent, but the white 
 spots are emphasized. 
 *454. Specimen in which the eye-spots on the hind wings are obliterated, 
 as in the foregoing : those of the fore wings are also similarly modified, 
 but the white spots of the marginal series are enlarged to a much 
 greater extent. Also another specimen in which the eye-spots were 
 partially deficient. These two specimens were from one brood reared 
 in Germany: of this brood none were typical, and several resembled 
 the specimens described. South, P., Ent., 1889, xxn. p. 218, PI. 
 
 455 Specimen figured in which the eye-spots are symmetrically absent 
 
 from both posterior wings. In this case both the greyish yellow 
 bordering of the eye-spots and the blue marks generally contained 
 within them are entirely absent. The ground-colour of the hind wings 
 is greyish brown, and upon this two black marks are placed in the 
 situation of the normal eye-spot and a series of small black lines occurs 
 round the margins of the hind wings. The eye-spots of the anterior 
 wings are modified in a peculiar manner which is not easily described. 
 Mosley, S. L., Varieties of Brit. Lepicl, Pt. m. PI. 2, Fig. 3. 
 
 456. Junonia clelia. Cram. In this species there are normally two ocelli in each 
 fore wing and a similar pair in each hind wing (Trimex, S. Afr. Butterflies, i. p. 
 214). In a series of nine specimens in the Cambridge University Museum very 
 great variations in the size of the ocelli appear. The posterior ocellus of each wing 
 is more constant in size than the anterior. One specimen wants altogether the 
 anterior ocellus of the hind wings, which in most specimens has a diameter of about 
 2*5 mm. In several the anterior ocellus of the fore wings is hardly visible. 
 
 457- Junonia coenia : the degree to which the two eye-spots of each wing are de- 
 veloped varies greatly. In a Californian specimen in Godman and Salvin's collection 
 the spots are all very large, while in a Granada specimen they are almost entirely 
 obliterated. Of four specimens in the same collection from the United States of 
 Colombia (but not from the same locality), one has scarcely a trace of the anterior 
 eye-spot of the fore wing, the second eye being very faint. In the hind wing the 
 anterior eye-spot is very faint and the posterior is absent. 
 
 The two following cases are important from the fact that in 
 each of them there is said to have been abnormality in neuration. 
 
 *458. Pararge megaera ^ (the Wall Butterfly) : specimen in 
 which the second nervure of the median vein is wanting in eacit 
 of the four wings. In the anterior wings the place which should 
 be crossed by this nervure is occupied by an extra ocellus (Fig. 83), 
 which is nearly as large as the normal large ocellus of the wing. 
 The normal ocellus itself is incompletely doubled. In the hind 
 wings, the two ocelli (2nd and 3rd), which in the normal insect 
 are separated by the missing nervure, are elongated towards each 
 
CHAP. XII.] 
 
 EYE-SPOTS AND NEURATIOX. 
 
 301 
 
 other, so that their black borders touch and the usual central white 
 dots join into a line, one- twelfth of an inch long. On the under 
 
 Fig. 83. Pararge megcera, the Wall ; case described in No. 458. [This copy is 
 rather too light, and the banding on the hind wing is too distinct.] 
 
 (From Webb.) 
 
 side, the anterior wings have respectively six and five ocelli and 
 the hind wings five and six. The arrangement of the dark colour 
 on the upper surface of the anterior wing differs somewhat in the 
 direction of the pattern of the female. Webb, S., Entomologist, 
 1889, xxii. p. 289, Fig. 
 
 Saturnia carpini £ ; variety without eye-spots. (Fig. 84.) 
 This specimen was bred from a larva found with many others 
 
 Fig. 84. Saturnia carpini lacking the ocellar marks in each wing (No. 459). 
 
 (From Bond.) 
 
 feeding upon sallow in Sawston Fen, Cambridgeshire. " In the 
 colour and markings of the specimen there was perhaps nothing 
 worth notice excepting the absence of the ocellus in each wing and 
 also of one of the veins in each of the anterior wings." 
 
 About 50 larvae were collected at the same time on one large 
 sallow. One of them, a female, was destitute of scales 1 , but the 
 remainder of the specimens reared were remarkably fine. Bond, 
 F., Entomologist, x., 1877, p. 1, fig. [This is the specimen 
 mentioned by Humphreys, Brit. Moths, p. 20. It is unfortunate 
 that no further description is given, and the figure is not sufficiently 
 clear to enable one to see which nervure was absent. On the fore 
 wings a narrow, elongated patch of light colour was in the place of 
 each ocellus, and on the hind wings there was a somewhat wider 
 
 1 Partial deficiency of scales, occurring evenly over all the four wings, is not very 
 rare in S. carpini. I have myself reared two such specimens. 
 
302 MERISTIC VARIATION. [part i. 
 
 and irregularly shaped patch of pale colour. If this specimen, 
 which was in the collection of the late Mr F. Bond, is still in 
 existence it is greatly to be wished that a proper description of it 
 should be published.] 
 
 460. Saturnia carpini £ : wings yellowish-grey throughout, with 
 the usual markings, save that on the fore wings there is no ocellus, 
 and on the hind wings is only a small black eye, without a border, 
 having a yellowish-grey central spot. Ochsenheimer, F., Schmet. 
 von Europa, 181(3, IV. p. 191. 
 
 From this evidence it is clear that the range of Variation of 
 ocellar markings in Lepidoptera is very great. It is especially to 
 be noticed that this variability affects no one family, or the species 
 of one geographical region, or one kind of ocellus exclusively, 
 though doubtless it is more marked in some than in others ; but it 
 seems rather to be a property belonging to ocelli in general. From 
 the fact that they can bodily come and go, it seems clear that, as 
 was suggested above, each ocellus is as regards its origin one 
 structure made up of parts in correlation with each other. 
 
 RAIIDiE. 
 
 The great variability of ocellar markings is probably not 
 peculiar to Lepidoptera, but I have no evidence sufficient to pro- 
 duce regarding the variability of ocellar markings in other forms. 
 I may however instance the case of the Raiidye, many of which 
 have been found marked with a large ocellar mark on the dorsal 
 surface of each pectoral fin. At different times such a mark has 
 been thought to characterize a certain species, but I believe it is 
 now generally admitted that it may appear as a variation in several 
 species. The best figure of this ocellar mark is that given by 
 Donovan (Brit. Fishes, 1808, v. PL cm.) in a Ray described under 
 
 461. the Linnean name Raid miraletus. On each "wing" was a large 
 spot, having a dark purple centre, surrounded by a zone of silvery 
 green enclosed by a broad dark boundary composed of five equi- 
 distant, contiguous spots of blackish purple. Donovan suspected 
 that the fish might be a variety of the Homelyn (R. maculata), 
 and it has been generally believed by other authors to have been 
 so. Donovan states that a similar eye-spot was seen by him in 
 various degrees of definition in several young Skates. 
 
 462. R. clavata, the Thornback, also sometimes has a large white 
 spot surrounded with black on the " wings." Day, Brit. Fishes, II. 
 p. 344. 
 
 Raia circularis, the Cuckoo Ray, has normally on each " wing " 
 a large black blotch banded with yellow and surrounded by yellow 
 spots. This structure may be absent as a variation. Day, Brit. 
 Fishes, II. p. 349. 
 
chap, xii.] SIMULTANEOUS COLOUR- VARIATION. 303 
 
 Simultaneity of Colour-variation in Parts repeated in 
 
 Linear Series. 
 
 Reference was made (Introduction, Section V.) to that relation 
 subsisting between the several members of a linear series of 
 segments or other repeated parts, by virtue of which they may 
 resemble each other in respect of colour or pattern of colours 
 From the fact that the several members do in such cases often 
 bear the same colours or patterns it is clear that they must at 
 some time or other have undergone similar Variation. In order 
 to measure the possible rapidity of the process of evolution by 
 which such parts may have reached their present condition it is 
 important to ascertain the extent to which their several variations 
 may be simultaneous. 
 
 Variations in colour are of course Substantive variations and a 
 full consideration of their nature cannot be taken here. For the 
 present we are only concerned with the consequences of the fact 
 that the parts are repeated in series. As was pointed out in the 
 Introduction the problem of the resemblance between the colours 
 of such segments is only a special case of the same problem of 
 Symmetry which is again presented in bilateral or other Repetition. 
 
 Simultaneous colour-variation taking place abruptly in a large 
 number of organs, such as hairs, feathers, &c. is a very common 
 occurrence, and the part that repetition of structures plays in 
 producing the total effect is apt to be overlooked. In comparing 
 two varieties of some whole-coloured animal, a bay horse with a 
 chestnut for example, it must be remembered that the difference 
 is really made up of a simultaneous variation in the pigment of each 
 particular hair. Similarly if a caterpillar normally green appears 
 in a uniformly brown variety we may conceive the total change as 
 brought about by variation occurring simultaneously in the skin 
 of the several segments, or in some smaller units. But whatever 
 unit be taken, whether segment, or hairs, or cells, that all or any 
 particular groups of such units should vary together and in the 
 same direction is not a matter of necessity. That such simul- 
 taneity is not universal and that segments may vary independently 
 of each other is a matter of common observation, and indeed is 
 sufficiently proved by the occurrence of differentiation between 
 segments. Nevertheless the evidence goes to shew that between 
 parts repeated in series there may be a relationship of the kind 
 spoken of, though its causes, nature and limitations are unknown. 
 In the case of actual segmentation this relationship may appear 
 either in the simultaneous variation of the colour-patterns of the 
 segments, or of some one colour or patch borne by each, or by the 
 appearance of some unusual mark or patch on several of them at 
 once. 
 
 In some cases it happens that certain of the segments may 
 vary together, the rest remaining unchanged, and, as seen in 
 
304 MEMSTIC VARIATION. [part i. 
 
 Chiton marmoreus, (q.v.), the segments thus undergoing the same 
 variation are not always even adjacent to each other. 
 
 The whole question is a very large one and it is not possible 
 here to do more than refer briefly to a few cases illustrating some 
 of its different aspects. Fuller treatment will be attempted in 
 connexion with the evidence of Substantive Variation. 
 
 463. As examples of a form whose segments in their colour-variations 
 manifest a very close agreement with each other, the Hirudinea may 
 be taken. Figures of numerous varieties of medicinal Leeches are given 
 by Ebrard. Xouvelle monogr. des Sangsues, 1857, and other cases are 
 represented by Moquin-Taxdox, Monogr. de la famille des Hirudinees, 
 1827 (see especially PI. v. fig. 1). As these figures testify, there is a wide 
 diversity both in the ground-colour and in the size, colour and manner 
 of distribution of the lines and spots with which it is decorated, but 
 so far as may be judged from the figures and descriptions the same 
 decorations are repeated on the various segments. It cannot be doubted 
 that a close scrutiny of the specimens would shew points of difference 
 even between adjacent segments but substantially the patterns are the 
 same for the segments of an individual. The patterns of the varieties 
 may thus, like patterns of ribbon, be each represented by a drawing 
 of a short piece of the body in the way adopted by the writers named. 
 
 As regards the larvae of Lepidoptera a good deal of information 
 bearing on this subject exists, and some of these results, especially 
 those relating to Sphingida?, are of interest 1 . 
 
 '464. I n ^he larvae of many species of Sphingidae there is a more or 
 less regular dimorphism in colour. Notable examples of this are 
 Acherontia atropos, Chozrocampa elpenor, C. porcellus and Macroglossa 
 stellatarum, in each of which the larva is known both in a light green 
 and in a dark form 2 . The dark form is the commonest in C. porcellus 
 but in A. atropos it is much rarer than the green form. Judging from 
 the figures, the ground-colour of the segments generally varies as a 
 
 1 The facts which follow are chiefly taken from Wilson, Larvce of Lepidoptera , 
 1880; Weismanx, Studies in Theory of Descent, Eng. Trans., 1882; Poulton, Trans. 
 Knt. Soc, 1884, 1885, 1886, 1887; Buckler, Larva of Brit. Butterf. and Moths, 
 Vol. in. Eay Soc, 1887. 
 
 2 That this dimorphism is 'phytophagie ' is not very likely, but the possibility should 
 be remembered. It seems to be established that in many of the species the colour- 
 varieties are definite and largely discontinuous. Of 21. stellatarum Weismann (p. 
 250) bred 140 from one batch of eggs, and of these 49 were of the green form and 63 
 of the brown form, only 28 being transitional. The discontinuous character of the 
 variation was illustrated by one most remarkable specimen. In it the body was 
 particoloured, being partly of the green and partly of the brown form. The head, 
 prothorax, all the abdominal segments behind the 2nd, and the right side of the 
 remainder were brown, but the left side of the meso- and meta-thorax, of the 1st 
 abdominal, and part of the left side of the 2nd abdominal were green [according to 
 the figure 9 on PI. in., with which the description in the text, p. 249, differs slightly]. 
 In A. atropos I know no account of any intermediate form. In most of the species 
 the dimorphic or polymorphic character appears in the later periods of larval life 
 and especially after the last moult; but in C. porcellus, according to both Weismann 
 (p. 188) and Buckler (p. 117) though the larva are of both kinds in the penultimate 
 state all or nearly all after the last moult turn to the dark form. 
 
CHAP, xii.] LARVAE OF SPHINGID^E. 305 
 
 whole, shewing only slight differences in tint in different parts of the 
 body. To this there are certain exceptions, of which A. atropos is 
 especially remarkable. In the brown variety of this species the 
 abdominal segments have a dark ground-colour composed of shades 
 of brown, while the three thoracic segments in it are white "like linen" 
 (see Wilson, PI. vi.; Buckler, PI. xxi.; Poulton, 1886, p. 149; 
 Hammond, ZooL, 6282; Balding, Ent. Mo. Mag. xxn. p. 279; Girard, 
 Bull. Soc. ent. Fr., 1865, S. 4, v. p. xlix. &c). 
 
 Tn M. stellatarum though the ground-colour of the head and of all 
 the segments varies greatly it appears that the head and prothorax vary 
 in colour simultaneously with each other and are of one colour, while 
 the other two thoracic segments and the abdominal segments also vary 
 together but usually differ from the head and pro-thorax (see Weismann, 
 PI. in.). 
 
 In illustration of the degree to which simultaneity of Variation 
 is possible over considerable areas of the body the varieties in markings 
 are perhaps more important than those in ground-colour. Of such 
 changes simultaneously occurring in several segments there are many 
 examples. 
 
 4(3 5 # In all the varieties of ground-colour in M. stellatarum the pattern 
 of the markings remains the same though of differing intensities 
 (Weismann, p. 248), but in the brown variety of A. atropos the pattern 
 is quite peculiar and cannot even be recognized as a representation of 
 the markings seen in the green form. Even the oblique stripes are 
 absent (Poulton, 1886, p. 149; see also authors quoted above). But 
 as in the ground-colour so in the markings, the abdominal segments 
 have one new pattern while the thoracic segments have another. 
 *466. The figures of larvae of Deiphila euphorbias given by Buckler and 
 by Weismann are especially interesting in this connexion, shewing 
 that in the complex variations of this polymorphic form the particular 
 pattern of the individual is carried out with little difference in each 
 segment behind the prothorax. Some of these changes are extensive, 
 but to be at all appreciated the figures must be referred to. In one 
 case all the triangles at the posterior part of each segment were red 
 instead of green as usual, and this change was found in many speci- 
 mens from one locality (see Weismann, p. 206, PI. v.). This identical 
 variation was known to and figured by Hubner (Weismann). In 
 one specimen from the same place as the last the second row of marks 
 which should occur just below the sub-dorsal mark of each segment 
 was absent throughout the whole line, and the ring-spots of the upper or 
 sub-dorsal row had, as a variation, a red centre or nucleus, well marked 
 in the posterior spots but fading away anteriorly. The occurrence of 
 these considerable changes is still more noteworthy if, as Weismann 
 states, the members of each batch are much alike. He remarks also 
 that the variability is great in some localities but little in others. 
 
 467. The larva of Deilephila hippophaes has a sub-dorsal row of red 
 markings upon a variable number of segments from the 7th abdominal 
 to the 3rd or even 2nd abdominal, increasing in size and distinctness 
 from behind forwards. The size of these markings differs greatly in 
 different specimens, varying from a mere dot to a distinct red spot 
 with a black ring. As the figures shew, there is a considerable cor- 
 
 B. 20 
 
306 M ERISTIC VARIATION. [part i. 
 
 respondence between the segments in the extent to which the spots 
 are developed, though in each case they fade away in the anterior 
 segments (see "Weismann's tigs. 59 and 60). 
 
 468. Another interesting example of considerable uniformity in the 
 colour-variation of a series of segments is to be seen in Saturnia 
 carpini. In this species besides change in the tint of the green 
 ground-colour [two chief tints being found, one dark and one light] 
 there is immense difference in the amount of black pigment deposited, 
 most marked in the last two stages of the larva?. Good figures and 
 descriptions of these are given by Weismann (PI. vin.). Though no 
 two segments are alike and though there are differences perceptible 
 even between the two sides of most segments, yet the general scheme 
 of colour of each individual is carried out with fair constancy over 
 the several segments. As I have myself seen, the lightest and darkest 
 may both be reared from one batch of eggs and in the same breeding- 
 cage or sleeve. 
 
 469. The colour of the tubercles of S. carpini also varies greatly. They 
 may be light yellow, dark yellow, pink, violet, or white, but the yellow 
 and pink forms are the commonest. As I have myself observed, there 
 is generally a close agreement between the different tubercles of each 
 larva in point of colour. In a few specimens I have seen the tubercles 
 of the anterior and posterior segments pinkish, while the remainder 
 were yellow, but this diversity is exceptional. The importance of this 
 case is increased by the fact that Poulton (1887, p. 311) has found 
 that the offspring of a pair whose tubercles had been pink shewed a 
 high proportion of larva? with pink tubercles. The two parents were 
 from a lot of 80 larva? found together, of which only 3 had pink tubercles : 
 but of their 88 offspring 64 had pink tubercles. 
 
 470. The case of the occurrence of red spots on the larva? of Smerinthus 
 ocellatus and S. populi 1 may be quoted as an instance of great irregu- 
 larity in the degree to which the segments agree in their colour- 
 variations. This well-known case is also of great interest as an 
 example of a parallel variation occurring in different species. The 
 larva? of both species are most commonly without any red spots, but 
 not rarely a number of red spots are present. In extreme cases each 
 of the spiracles is surrounded with red, and there is in addition a row 
 of red spots in the sub-dorsal region of all segments from the 1st 
 thoracic to 7th abdominal, and also a red spot on each clasper. The 
 number of spots, number of rows, the size and tint and distinctness of 
 the spots is exceedingly variable. In point of time the spots of the 
 3rd abdominal segment appear first and those of the 2nd thoracic 
 next (Poulton, 1887, p. 285, &c). Though in much spotted specimens 
 the spots may remain till the larva is full-fed, in some cases a few 
 spots appear at an early stage and are afterwards lost. Among the 
 individuals of the same brood there may be great diversity, some 
 having spots and others being without them (Poulton, 1887, p. 287). 
 In several cases a spot present on one side of a segment has been 
 found absent on the other side. As Poulton observes, it is especially 
 
 1 I have not referred to the case of S. tilice, as it is possibly of a different 
 nature. 
 
chap. XII.] COLOURS OF CHITOXS. 307 
 
 remarkable that though there are no spiracular openings on the meso- 
 and meta-thoracic segments, yet in cases of extremely spotted larvae 
 there are red spots at the level of and continuing the spiracular series 
 of spots upon these segments also (S. ocellatus, Buckler, PI. xx. 
 tig. 1 a; Poulton, 1887, PL x. fig. 1. S. populi, Poulton, 1887, p. 286). 
 As an indication of an element of definiteness in this variation may 
 be mentioned the fact that in fully spotted larvae of S. populi the 
 sub-dorsal spot on the 7th abdominal seems to be always the smallest 
 in that row (Poqlton, 1887, p. 285; Wilson, PI. v. fig. 2a; Flemyng, 
 Ent, 1880, p. 243, &c). 
 
 In our present consideration the fact that these very large variations 
 sometimes occur simultaneously over a large range of segments and 
 are sometimes restricted to particular segments is of considerable 
 importance. 
 
 We may note that Weismann (p. 360) is prepared to believe that 
 these spots represent a new variation arising similarly and indepen- 
 dently in the different species of Smerinthus. As however is usual in 
 cases of considerable Variation an attempt has been made to lessen 
 the value of these indications of the magnitude of Variation by sug- 
 gesting that they may be of the nature of " reversion " (Poulton, 
 1884, p. 28). Apart however from a general reluctance to recognize 
 the possibility of the occurrence of large variations there seem to be 
 no special grounds for the suggestion here. It is nevertheless true 
 that in the case of the Smerinthus larvoe a complete disproof of the 
 hypothesis of "reversion" is wanting. This is only to be obtained in 
 cases (like that of D. euphorbice), in which a great number of complex 
 and mutually exclusive variations exist side by side. In the absence 
 of such complete refutation the hypothesis of reversion may still find 
 favour. 
 
 '471. Chitonidae. The following facts observed in certain Chitons 
 are given in illustration of the existence of a similar possibility 
 of simultaneous Variation between parts which are repeated in 
 series but whose repetition is not of the kind commonly included 
 in the term Metameric. Unfortunately the material at hand is 
 very limited and I do not know what might be the result of 
 further examination, but the facts seen suggest that the subject 
 is worth investigating. 
 
 The dorsal plates of Chitons are eight in number. Though 
 the colours and markings in different species are complex and 
 various yet in many species all the plates are alike or nearly so. 
 The question then arises do all the plates change colour together, 
 or do they change one by one, or otherwise ? From the few 
 observations made it seems that in this respect the species differ, 
 but variation uniformly occurring in all the plates seems to be 
 rare. This may perhaps be due to the constitution of such 
 specimens as separate species, but I saw little likelihood of this. 
 On the other hand in several cases the same variation was present in 
 more than one segment, and in particular there was strong evidence 
 that in some species the segments 2, 4 and 7 shew a noticeable 
 
 20—2 
 
308 MERISTIC VARIATION. [part i. 
 
 agreement with each other in colour-variation. The specimens 
 are all in the MacAndrew Collection in the Cambridge University 
 Museum, and I have as usual simply followed the labelling of the 
 specimens. 
 
 C. arhustum, Australia. 10 specimens, of which the plates in 6 are nearly uniform. 
 In one there is a white band in the centre of each plate ; in 2 the plates are irregularly 
 coloured; in one the plates 1 and 6 agree in being broadly marked with white. 
 
 Cliiton hennahi, Peru. 4 specimens. 3 are uniformly dark brown; but in the 
 other specimen there is a strong tohite mark on the centre of plates 2 — 7, and a faint 
 one on plates 1 and 8. 
 
 C. elegans, Chili. 2 specimens. In one, complicated markings are repeated on 
 each plate nearly uniformly ; in the other specimen a much simpler pattern recurs on 
 each segment. 
 
 On the other hand, C. pellis-serpentis, New Zealand, 8 specimens: great di- 
 versity of markings and no uniformity among plates in 4 specimens, but in one 
 specimen plates 2 — 5 were black and the rest light-coloured. Similar want of uni- 
 formity among the plates in 2 specimens of C. incanus, New Zealand. 
 
 The evidence of agreement between segments 2, 4 and 7 in the following cases is. 
 very striking. 
 
 C. (Tonic ia) marmoreus, "Hebrides, &c." 18 specimens, all of a light brown 
 colour marked with dark red. 
 
 In 4 specimens the plates are uniformly marked or nearly so. 
 
 In 6 specimens plates 2, 4 and 7 are much darker than the others, being for the 
 most part of a uniform dark red. 
 
 In 5 specimens plates 2, 4, 7 and 8 are darker than the rest. 
 
 In 1 specimen plates 2, 4, 5 and 7 are darker than the rest. 
 
 In 2 specimens the central parts of most of the plates have dark markings, but 
 no segment is specially distinguished. 
 
 Of 18 specimens therefore 12 have plates 2, 4 and 7 darker than the rest. 
 
 Among 3 specimens of the same species from Gr. Manan (N. America) 2 are nearly 
 uniform throughout, but in one plates 2, 4, 7 and 8 are much darker than the rest. 
 
 C. (Tonicia) lineatus, 2 specimens. In one the markings on all the plates are 
 nearly similar, and the white wavy streaks characterizing the species are almost 
 similarly distributed on the sides of all the plates. In the other specimen these 
 lines are absent on the plates 2, 4 and 7, which are much darker than the rest ; but 
 the lines, though less extensive than in the first specimen, are present on plates 
 1, 3, 5, 6 and 8. 
 
 The preceding evidence may suffice to indicate the nature of 
 this important question of the degree to which the colour-variations 
 of parts repeated in Linear Series may be similar and simultaneous, 
 a question which, as must be evident, is of the highest consequence 
 in estimating the magnitude of the steps by which Evolution 
 may proceed. To the consideration of this matter it will be 
 necessary to return when the evidence of Substantive Variation 
 is considered. 
 
 Meanwhile it will not be forgotten that though we have only 
 spoken of this question in reference to colour and to Linear Series, 
 the same question arises also with regard to other variations and in 
 reference to all parts which are in any way repeated and resemble 
 each other, whether such repetition is strictly serial or not. In a 
 survey of any group of animals cases will be seen in which organs 
 in one region are repetitions of organs in another region though 
 
chap, xil] SIMULTANEOUS VARIATION OF SERIES. 309 
 
 not necessarily in serial homology with them in any sense in 
 which the term is commonly used. Many such cases were spoken 
 •of by Darwin in the chapter on " Correlated Variability 1 " and are 
 now famous. The simultaneous colour- variations of the mane and 
 tail of horses 2 , the correspondence between the large quills of the 
 wings and those of the tail of pigeons 3 and other birds are 
 among the most familiar of such cases. 
 
 When with such facts in mind we turn to some species which 
 differs from an ally in the presence of some characteristic develop- 
 ment or condition common to a number of its parts, in making 
 any estimate of the steps by which it may have been evolved it 
 must be remembered that it is at least possible that the common 
 feature characterizing these several parts may have been assumed 
 by all simultaneously. To take a single instance of this kind, the 
 species of the genus Hippocampus, the Sea-horses, have the 
 shields produced into more or less prominent tubercles or spines. 
 The back of the head is also drawn out into a prominent knob. 
 In^ an allied genus from Australia, Phyllopteryx, many of these 
 spines are provided with ragged looking tags of coloured skin, 
 like the seaweed which the fishes frequent 4 , giving the animal a 
 most fantastic appearance and no doubt contributing greatly to 
 its concealment [probably from its prey]. If in this case it were 
 nece>sary to suppose that the variations by which this form has 
 departejj from the ordinary Hippocampi had occurred separately, 
 and that -each spine had separately developed its tag of skin, the 
 number of variations and selections to be postulated would be 
 enormous ; but probably no such supposition is needed. We are, 
 as I think, entitled to expect that if we had before us the line of 
 ancestors of Phyllopteryx, we should see that many and perhaps 
 all of the spines which are thus modified in different parts of the 
 body had simultaneously broken out, as we may say, into tags of 
 skin, just as the feathers of the Moor-hen (Gallinula chloropus) 5 
 may collectively take on the " hairy " form, or as, to take the case 
 
 1 Animals and Plants under Domestication, ed. 1885, n. chap. xxv. 
 
 2 As D,*$*vin mentions, simultaneity in the variations of the hair may be mani- 
 fested in size and texture as well as in colour. A bay horse was lately exhibited at 
 the Westminster Aquarium standing 16£ hands, having the hair of both mane and 
 tail of prodigious length. The longest hairs of the mane measured 14 ft. and those 
 of the tail 13 ft. It did not appear that the hair of the fetlocks or bo ly was unusual 
 in character, but these were kept closely clipped and nothing could be affirmed on 
 this point. 
 
 3 By the courtesy of Professor L. Vaillant I was enabled to examine a number 
 of specimens of the singular breeds uf Gold-fish from China in the Paris Museum of 
 Natural History. Some of these are characterized by the great length both of the 
 appendicular fins and of the caudal fin also. Measurement shewed that there was 
 a substantial correspondence between the lengths of these parts, those with long 
 appendicular fins having also very long tails. The correlation between these parts 
 is not however universal in Gold-fishes, and in many of the ordinary "Telescope" 
 Gold-fish the tail may be longer than that of a common Gold-fish of the same size, 
 though the length of the appendicular fins be not exceptional (v. infra). 
 
 4 Gunther, Study of Fishes, 1880, p. 682, fig. 309. 
 
 5 See Introduction, p. 55. 
 
310 MERISTIC VARIATION. [part i. 
 
 of Radial Series, the petals of a flower may all together take on 
 the laciniated condition 1 . 
 
 Further study will indeed probably lead to the recognition of 
 a principle which may be thus expressed : that jxtrts which in any 
 one body are alike, which have, that is to say, undergone similar 
 Variation in the past, may undergo similar variations simid- 
 taneously; a principle which, if true at all, is true without regard 
 to the morphological position of the parts in question. 
 
 1 For cases see Masters, Vegetable Teratology, 1869, p. 67. 
 
CHAPTER XIII. 
 linear series — continued. 
 
 Minor Symmetries : Digits. 
 
 All the cases considered in the foregoing chapters have il- 
 lustrated Variation of parts whose repetition is disposed in Linear 
 Series along the chief axis of the body, being thus arranged 
 directly and immediately with reference to the Major Symmetry 
 of the body. We have now to consider cases of the Meristic 
 'Variation of parts which are also repeated in Linear Series but 
 normally possess in some degree the property of symmetry partially 
 completed within the limits of their own series, thus forming a 
 Minor Symmetry. 
 
 Of Linear repetitions thus occurring there is a great diversity, 
 and evidence will here be produced regarding two of the chief 
 examples, namely, the digits of vertebrates and the segmentation 
 of antennae and tarsi of Insects. 
 
 In each of these groups of organs the parts are frequently 
 formed in such a way as to make an approach to symmetry, 
 about one or more axes within the limits of the appendage to 
 which they belong. This fact will be found to lead to conse- 
 quences apparent in the manner in which numerical Variation 
 takes place in limbs of the various types. 
 
 In these Minor Symmetries Linear Repetition may occur in 
 two forms : there may be repetitions of digits or other parts in 
 lines forming an angle with the axis of an appendage ; and there 
 may be repetitions in the form of joints &c. along the axis of the 
 appendage itself. 
 
 The cases of Variation in number of joints in the appendages 
 of Insects are chiefly interesting as examples of manifest Dis- 
 continuity in Variation, and from the conclusions which they 
 suggest as to the supposed individuality of segments. This latter 
 question arises also in considering the relation of the two pha- 
 langes of the pollex and hallux to the three phalanges of the 
 other digits, but the evidence which can be gained from a study 
 
312 MERISTIC VARIATION. [part i. 
 
 of Variation with reference to this question is so intimately con- 
 nected with the subject of the variation of digits in general that 
 it cannot be considered apart. Other cases referring to repetitions 
 in the line of the axis of appendages will be taken in a subsequent 
 chapter. 
 
 In studying numerical Variation in the digits of certain animals, 
 especially the Horse and the Pig, we shall meet with forms of 
 Variation which are peculiar to structures having a bilateral 
 symmetry. In examining the evidence as to Meristic Variation 
 of Bilateral Series further reference to these cases will have to 
 be made, but it appears simplest to describe the facts in the first 
 instance in connexion with the subject of digits. 
 
 From the evidence as to Meristic Variation in digits I propose 
 to make a selection, taking certain groups of cases having a direct 
 and obvious bearing on the general problems of Variation. It 
 will be understood and should be explicitly stated that unless 
 the contrary is declared the principles of form which can be per- 
 ceived as operating in special cases are not of universal appli- 
 cation in the Variation of digits, but are enuntiated as applying 
 only to the special cases in which they are perceived. In the 
 human subject, for example, cases of polydactylism will be quoted 
 which when arranged together form a progressive series illus- 
 trating the establishment of a novel and curious Symmetry ; but 
 though these cases are valuable as illustrations of the way in 
 which the forces of Division and growth can dispose themselves 
 to produce a symmetrical result, yet it must always be borne in 
 mind that very many variations of the digits have been seen in 
 Man, whether consisting in increase in number of digits or in 
 decrease, of which the result is almost shapeless. The case of 
 polydactyle Cats is thus especially interesting from the fact that 
 in this animal the polydactyle condition, though differing in degree 
 of expression in various specimens, yet, in the greater number of 
 cases, occurs in ways which may be interpreted as modifications 
 of one plan, or rather of one plan for the hind foot and of another 
 for the fore foot. 
 
 I arrange the evidence primarily according to the animal con- 
 cerned, Cat, Man and Apes, Equidye, Artiodactyles, &c. To these 
 are added a few facts as to digital variations in Birds, but from 
 the scantiness of the evidence and the difficulty of determining 
 the morphology of the parts I have not found it possible to give a 
 profitable account of these phenomena in other vertebrates below 
 Mammalia. 
 
 In most of the groups increase in number of digits may be 
 seen to occur in several distinct ways ; and, just as in the case 
 of teeth, mammae, &c, it is possible to recognize cases of division 
 of single members of series, and cases of addition to the series 
 
chap, xiil] DIGITS : CAT. 313 
 
 either at one of its ends (often associated with remodelling of 
 other members of the series) or in the middle of the series. 
 
 Reduction in number of digits, or ectrodactylism as it is often 
 called, is usually so irregular in the manner of its occurrence that 
 little could be done as yet beyond a recitation of large numbers 
 of cases amongst which no system can be perceived. For the 
 present therefore the interest of these observations for the student 
 of Variation is comparatively small and they are for the most 
 part omitted. 
 
 To the irregularity of ectrodactylism in general certain cases 
 of syndactylism are a marked exception and of these an account 
 will be given. 
 
 After stating the morphological evidence as to numerical 
 Variation in digits in the several groups, reference will be made 
 to some collateral points of interest concerning such variations. 
 
 There is a good deal of evidence respecting the recurrence 
 of digital variations in those lines of descent wherein they have 
 appeared. Facts of this kind have been frequently seen in the 
 case of Man, and other examples are known in the Cat, the Pig, 
 the Ox, Deer, Sheep, &c. References to these cases will be given. 
 
 It will be seen that the facts contained in this section of 
 evidence are of consequence rather as indicating the limits set 
 on Variation, and from their bearing on the question of the nature 
 of Symmetry and of Homology, than from any more direct appli- 
 cation to the problem of Species, but even this cannot be said 
 with much confidence. 
 
 There are in certain groups limbs such as the pes of Macro- 
 podidse or that of Peramelidae whose appearance forcibly recalls 
 what is seen in some teratological cases and the possibility that 
 they may have had such a sudden origin may well be kept in 
 
 view 1 . 
 
 Cat. 
 
 The apprehension of the chief features in the evidence as to 
 digital variation in the Cat will be made more easy if a general 
 account of the subject be given as a preliminary. In order to 
 understand the peculiar phenomena seen in the limbs of poly- 
 dactyle cats certain points of normal structure are to be re- 
 membered. Of these the most important relate to the claws 
 and their disposition with regard to the second phalanx ; for it is 
 by this character that the relation of digits to the symmetry of 
 the limb may be determined. 
 
 1 In the case named this is all the more likely from the circumstance that 
 according to Thomas, Cat. Marsup. Brit. 2Ius., p. 220, there is reason for supposing 
 that the extraordinary condition of the digits II and III was attained independently 
 in these two groups. 
 
314 MERISTIC VARIATION. [part i. 
 
 Hind foot. 
 
 The phenomena seen in the case of the hind foot are in some 
 respects simpler than those of the variations in the fore foot, and 
 for this reason they may conveniently be described first. 
 
 If the phalanges of the index of the hind foot, for example, be 
 examined, it will be seen that the proximal phalanx is nearly 
 bilaterally symmetrical about a longitudinal axis, but that the 
 second phalanx is deeply hollowed out upon the external or fibular 
 side. Into this excavation the ungual phalanx is withdrawn when 
 the claw is in the retracted position. The retraction is chiefly 
 effected by a large elastic ligament running from the outside of 
 the distal head of the second phalanx and inserted into the upper 
 angle of the last phalanx (see Owen, Anat. and Phys. of Vert., III. 
 p. 70, fig. 36). The same plan is found in the digits II to V both 
 of the fore foot and of the hind foot. By this asymmetrical re- 
 traction of the claw a digit of the right side may be differentiated 
 at a glance from one of the left side, for the claw is retracted to 
 the right side of a right digit and to the left side of a left digit. 
 The importance of this fact will be seen on turning to the evidence, 
 for it is found that with variation in the number of digits there is 
 a correlated variation in their symmetry. 
 
 With respect to the tarsus little need be said. The proximal 
 part of the tarsus contains three bones, the calcaneum, astragalus 
 and navicular. The distal row consists of four bones, the cuboid 
 and three cuneiform bones. In the majority of polydactyle cats 
 that I have seen in which the tarsus is affected, the cuboid is 
 normal and the ecto-cuneiform is also normal and recognizable ; 
 internal to the latter there are three small cuneiforms articulating 
 with the navicular instead of two, making four cuneiforms in all. 
 In some specimens there is no actual separation between the two 
 innermost of these cuneiforms, but the lines of division between 
 them are clearly marked. 
 
 In the normal hind foot of the Cat there are four fully formed 
 toes, commonly regarded as II, III, IV and V, each having 
 three phalanges. In the place where the hallux would be there 
 is a small cylindrical bone articulating at the side of the internal 
 cuneiform. As usually seen, all the four digits are formed on a 
 similar plan, each having its claw retracted to the external or 
 fibular side of the second phalanx, the four digits of a right foot 
 being all right digits and those of left feet being all left digits. 
 The rudimentary hallux has of course no claw. 
 
 Starting from this normal as the least number of digits, it will 
 be found that a large proportion of cases are such that they may 
 be arranged in an ascending or progressive series. In this series 
 the following Conditions have been observed. 
 
 In the schematic representations of the limbs the words 'Eight' or 'Left' 
 signify that a digit is shaped as a right or as a left. The Roman numeral 
 
chap, xiil] digits: cat. 315 
 
 indicates that the digit to which it is assigned has the tarsal or carpal relations of 
 the digit so numbered in the normal. For brevity each is described as a right foot. 
 
 I. The normal, consisting of four three-phalanged digits, each 
 retracting its claw to the external, viz. right side, and a rudimentary 
 hallux with no claw. In this foot therefore the digits enumerated 
 from the external side are 
 
 Eight. Eight. Eight. Eight. Eudiment. 
 
 V IV III II I 
 
 II. Five digits, each with three phalanges. Of these the 
 minimus and annularis borne by a normal cuboid are normal and 
 are formed as right digits. The medius is borne by a normal ecto- 
 cuneiform and is also a true right digit. Internal to this is a full- 
 sized digit having the relations of an index and borne by a bone 
 placed as a middle cuneiform. But the claw of this digit cannot 
 be retracted to the external side of the limb, for the second 
 phalanx is not excavated on this side. There is on the contrary a 
 slight excavation on the internal side of the second phalanx, but 
 this is very incomplete and the claw cannot be fully retracted, 
 being in fact almost upon the middle line of the digit when bent 
 back. This digit is thus intermediate between a right and a left. 
 Nevertheless it is truly the index of this right foot, for it has the 
 tarsal relations of an index. 
 
 Internal to this digit is another, which by all rules of homology 
 should be the hallux, but it has three phalanges and is fashioned 
 as a left digit, retracting its claw to the left (internal) side of the 
 digit. This digit (Fig. 85, II, d 1 ) is borne jointly by two cuneiforms, 
 c 1 and c 2 , as shewn in the figure. There is thus one cuneiform 
 more than there is in the normal. In this foot therefore the digits 
 enumerated from the external side are as follows : — 
 
 Eight. Eight. Eight. Indifferent. Left. 
 
 V IV III II I 
 
 Such a specimen is No. 472, right pes. 
 
 Between this state and the normal I have as yet met no inter- 
 mediate. It might perhaps have been expected that a foot having 
 four three-phalanged digits and a hallux with two phalanges would 
 be a common form of variation. Such a condition has not however 
 been seen, so far as I know. 
 
 III. The foot shewn in Fig. 85, 1 exemplifies the next condition. 
 In it the three external digits, which are structurally the minimus, 
 annularis and medius of a normal foot are normal in form, position 
 and manner of articulation with the tarsus. Internal to the 
 medius are three digits, of which the innermost has two phalanges 
 (Fig. 85, I, d l ) and a claw which cannot be retracted, like the 
 pollex of the normal fore foot. The other digits, d 3 and d 2 , are 
 fashioned as left digits, retracting their claws to the internal or 
 left side of the limb. It will be seen that of them d 3 has the 
 
316 MERISTIC VARIATION. [part I. 
 
 relations to the tarsus which an index should have. The tarsus is 
 as in the last Condition. 
 
 In the specimen seen, c 1 and c 2 were not actually separate from 
 each other, but there was a distinct line of division between them. 
 
 Here then the digits enumerated from the external side are as 
 follows : — 
 
 Eight. Eight. Eight. Left. Left Hallux-like 
 
 V IV III II digit digit 
 
 IV. The stage next beyond the last is shewn in Fig. 87, II. 
 [The drawing is from a left foot.] Here there are six digits, each 
 with three phalanges. The three externals are normal and true 
 rights as before. The other three are all formed as lefts. Tarsus 
 as before. 
 
 This foot may be represented thus : — 
 
 Eight. Eight. Eight. Left. Left Left 
 
 V IV III II digit digit 
 
 As far as I have seen the last or fourth Condition is the com- 
 monest. There are doubtless many variants on these plans. 
 No. 477 is an especially noteworthy modification of the third 
 Condition and the cases of the hind feet in No. 478 must also 
 be specially studied as not conforming truly to either Condition. 
 
 Forefoot. 
 
 I. The normal right fore foot has four digits II — V each with 
 three phalanges all differentiated as rights, and a pollex with two 
 phalanges, the last being non-retractile but bearing a claw. It may 
 be represented thus : — 
 
 Eight. Eight. Eight. Eight. Pollex. 
 
 V IV III II I 
 
 Departures from this normal are more irregular than they are 
 in the case of the hind foot. Those given in this summary being 
 only a selection. For the others the evidence must be examined. 
 
 II. One specimen, No. 474, has the four external digits normal. 
 The pollex however has three phalanges and is formed as a digit of 
 the other side, thus : — 
 
 Eight. Eight. Eight. Eight. Left. 
 
 V IV III II I 
 
 III. The next Condition seen was as follows: — 
 
 Eight. Eight. Eight. Eight. 
 
 V IV III II 
 
 d tj Q 
 
 -2 a 2 
 
 03 it Cj 
 
 rt O CO 
 
 Left Indifferent 
 
 digit digit 
 
 IV. In the majority of polydactyle cats the manus 1ms the 
 digits II — V normal in shape and symmetry. Internal to the 
 digit II are two digits more or less united in their proximal parts ; 
 sometimes the metacarpal only, sometimes the metacarpal and first 
 phalanx are common to both. Of these two digits the external, 
 
chap, xiil] digits: CAT. 317 
 
 that is, the one next to the digit II, is in some degree shapeless 
 and imperfect, but the external branch is as a digit of the other 
 side in form. Internal to this double digit is a seventh digit, 
 sometimes with two phalanges, sometimes with three, but in either 
 case the claw is as a rule non-retractile, and the digit is in this 
 respect not differentiated as either right or left. Such a manus 
 may be thus represented (cp. Fig. 86 a left manus) : — 
 
 Eight. Right. Right. Right. Amorphous Left Indifferent 
 
 V IV III II digit digit digit 
 
 / As regards the carpus its changes are like those of the tarsus. 
 When there are six metacarpals there are three carpals in the distal 
 row internal to the magnum. That next the magnum may be 
 supposed to be trapezoid, and the other two may be spoken of as 
 first and second trapezium. In correspondence the length of the 
 scapho-lunar is increased. 
 
 No comment can increase the interest of these curious facts. 
 In the pes, as has been stated, with change in the number of 
 digits there is change in the grouping and symmetry of the series 
 of digits, and in particular the digit having the relations of the 
 index or digit II is formed as the optical image of its neighbour 
 III instead of forming a successive series with it. There is thus a 
 new axis of symmetry developed in the limb, passing between the 
 parts which form the digits II and III of the normal. 
 
 The evidence of the above statements may now be given. 
 
 r 472. Cat having the digital series of each extremity abnormal, being 
 that preserved in the Coll. Surg. Mus., Teratological Catalogue, 
 1872, Nos. 305 and 306. 
 
 Right pes (Fig. 85, II). Digits III, IV and V normal right 
 digits. Internal to these are two digits each having three phalanges 
 and claws. That lettered d 1 is formed as a left digit but d 2 is al- 
 most indifferent, the second phalanx being slightly hollowed on the 
 inside. Internal to the external cuneiform there are three small 
 bones, of which the inner two together bear the digit d 1 . [This is 
 the Condition II of the pes.] 
 
 Left pes has the same structure as the right so far as can be 
 seen from the preparation (in which the muscles remain). The 
 digits III, IV and V are normal left digits, but internally to them 
 there are two digits each with three phalanges, of which the 
 external is an indifferent digit, while the internal is formed as a 
 right. [Condition II of the pes.] 
 
 Left manus. The digits II, Til, IV and V are normal. But 
 the carpal of the distal series (trapezoid) which bears the digit II 
 is imperfectly separated from a similar bone placed internal to it. 
 This second part of the trapezoid bears a metacarpal which 
 articulates with a full-sized digit of three phalanges formed as a 
 right digit. From the external side of the first phalanx of this 
 
318 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 digit there is given off a rudimentary digit, which has however a 
 complete claw, but its bones do not differentiate it as right or left. 
 
 II 
 
 ect cijl 
 
 Fig. 85. I. Right pes of Cat No. 473, shewing condition III of the pes. 
 
 II. Right pes of Cat No. 472 shewing Condition II of the pes. 
 
 as, astragalus, c 1 , c-, c 3 , three ossifications representing the ento- and meso- 
 cuneiforms of the normal, cb, cuboid, clc, calcaneum. d 1 — cZ 6 , the digits numbered 
 from the inside, ect, cu, ecto-cuneiform. nav, navicular. 
 
 (From specimens in Coll. Surg. Mus.) 
 
 The " pollex", d\ has two phalanges and is rather slender. The 
 trapezium which bears it is not separated from the scaphoid. 
 (Fig. 86). [Condition IV of the manus.] 
 
 Right manus. This is exactly like the left manus so far as can 
 be seen from the dissection, except for the fact that the rudimentary 
 digit borne by the large digit external to the "pollex" is much 
 more reduced than in the case of the left manus. The digit which 
 supports it is fashioned as a left digit. [Condition IV of the 
 manus.] 
 473. Cat having digital series of all feet abnormal, being the 
 specimen in Mus. Coll. Surg., Teratol. Catalogue, 306 B. 
 
CHAP. XIII.] 
 
 DIGITS : CAT. 
 
 319 
 
 Right pes. The digits III, IV and V (Fig. 85, I) are 
 normal and are fashioned as right digits. The cuboid and external 
 
 Fig. 86. Left manus of Cat No. 472, shewing Condition IV of the manus. 
 cu, cuneiform, d 1 — d 7 , digits numbered from the inside, m, magnum, sclu, 
 scapho-lunar. Tp, trapezoid. 
 
 (From a specimen in Coll. Surg. Mus.) 
 
 cuneiform (cb and ect. cu) are also normal. Internally to the ex- 
 ternal cuneiform there is a long flat bone which is grooved in such 
 a way as to divide it into three parts (c 1— 3 ) and each of these bears 
 a digit. 
 
 Of these digits, d 2 and d 3 have each three phalanges, but d l has 
 only two phalanges and may therefore be called a hallux. The 
 digits d 2 and d 3 are fashioned not as right digits but as left 
 digits, and their claws are thus retracted towards the internal side 
 of the second phalanges, which are hollowed out to admit of this. 
 
 The bones of the hallux are not thus differentiated as right or 
 left, for the claw is not retractile. The navicular is enlarged in 
 correspondence with the presence of the fourth cuneiform element 
 and the astragalus and calcaneum are normal. (Fig. 85, 1). [Con- 
 dition III of the pes.] 
 
 Left pes. This foot is almost exactly like the right. As in it, 
 the digits III, IV and V are normal and are left digits. Internal 
 to this are three digits, viz. a hallux and two long digits with three 
 phalanges which are both made as right digits. The bones of this 
 foot have not been cleaned. [Condition III of the pes.] 
 
 Right manus. This is formed on the same plan as the manus 
 of the last animal, differing from it in details of the carpus, chiefly 
 in the presence of two separate trapezial elements. The four digits 
 on the external side, II — V are shewn by their claws to be true 
 
320 MERISTIC VARIATION. [part I. 
 
 right digits. They articulate in a normal way with the trapezoid, 
 magnum and unciform, and are thus clearly II, III, IV and V. 
 The metacarpals of the " pollex " and of the double digit corre- 
 sponding to d' 2 and d 3 of Fig. 86 articulate with two separate 
 carpal bones of the distal row. The external of these bears a 
 rather thick metatarsus which peripherally gives articulation to 
 two digits. Of these the internal is well formed and bears a claw 
 which slides up on its internal side, and thus shews it to be formed 
 as a left digit. The other is misshapen in its proximal phalanx which 
 perhaps contains two phalangeal elements compounded together 
 and aborted ; hence the relation of this digit to the symmetry of 
 the limb is not apparent. The claw and last phalanx are well 
 formed. The innermost carpal bone is nearly normal and bears 
 an almost normal " pollex." [Condition IV of the manus.] 
 
 Left manus. This foot has not been dissected, but from ex- 
 amination it appears that the digits II, III, IV and V are normal 
 like those of the right manus. As in it, there is a " pollex " with 
 two proper phalanges, but the metacarpal of the " pollex " is in its 
 proximal part united with the metacarpal of an imperfectly double 
 digit corresponding to d 2 and d 3 of Fig. 86. The division between 
 the two parts of this double digit is not so complete in the left 
 manus as it is in the right and from external examination it 
 appears that the phalanges of the two are not separate. There are 
 two claws of which one is rudimentary and the pads of the two are 
 separated only by a groove. There is nothing to indicate .whether 
 these digits are formed as right or left digits. [Approaches Con- 
 dition IV of the manus.] 
 *474. Cat having supernumerary digits. This specimen belonged to 
 the strain of polydactyle Cats observed by Mr Poulton (see No. 
 480) and I am indebted to Mr J. T. Cunningham for an oppor- 
 tunity of examining it. 
 
 Left manus. Five digits, the normal number. The " pollex ' 
 however is a long digit, composed of three phalanges, which reaches 
 very nearly to the end of the index. The claw of this digit is not 
 retracted to the outside of the second phalanx, like that of a 
 normal digit, but to the inside, and the chief elastic ligament is on 
 the inside of these joints instead of being on the outside as in 
 a normal digit. This pollex therefore may be said to be fashioned 
 as a right digit, bearing the same relation to the others as a right 
 limb bears to the left. The flexors and extensors of this digit were 
 fully developed. The carpal series was normal. [Condition II of 
 the manus.] 
 
 Right manus. Six digits fully formed, one bearing an additional 
 nail on the third digit from the inside. Beginning from the outer 
 or ulnar side, there are four normal right digits, placed and formed 
 as V, IV, III and II respectively. Internal to these are two 
 digits, the outermost having three phalanges, being shaped as a 
 left digit and bearing a minute supernumerary nail in the skin 
 
chap, xiii.] digits: CAT. 321 
 
 external to the normal nail. The innermost digit has two pha- 
 langes, and is formed like a normal pollex, excepting that its claw 
 was very deep and looked as if it were formed from the germs of 
 two claws united and curving concentrically. The carpus as 
 regards number of elements was normal, but the trapezium and 
 trapezoid were both of rather large size, and the pollex articulated 
 partly with the trapezium but chiefly with the downward process 
 on the radial side of the scapho-lunar. [This approaches Condition 
 IV of the manus, but in it the external of the two united digits is 
 only represented by the minute extra nail.] 
 
 Left pes. Six digits, each having three phalanges. The three 
 outer digits were formed as left digits, but the three inner digits 
 were shaped like right digits. The internal cuneiform is double 
 the normal size, but is not divided into two pieces. It bears the 
 two internal digits, of which the innermost is ankylosed to it. 
 [Condition IV of the pes.] Compare Fig. 87, II. 
 
 Right pes. Same as the left, except for the fact that the two 
 internal digits are completely united in their metacarpals and first 
 phalanges, and the cuneiform series consists of four bones, two of 
 which correspond to the internal cuneiform of double size described 
 in the left foot. (Compare Fig. 85, I, c 1 and c 2 .) [Condition IV of 
 the pes, save for the union of the metacarpals of the two internal 
 digits.] 
 
 475. Kitten belonging to Mr Poulton's strain (see No. 480) and 
 kindly lent by him to me for examination. The specimen was 
 very young and the carpus and tarsus were not dissected. 
 
 Left manus. Six digits, all with three phalanges. The two 
 internal digits are separated by a space from the others so as 
 to form a sort of lobe. The claw of the innermost digit is re- 
 tracted on the top of the second phalanx and not to the side, 
 so that this digit is not differentiated either as a right or a left. 
 The next digit is a right and the four external digits (II, III, 
 IV and V) are normal lefts. [Condition III of manus.] 
 
 Right manus. Same as left. 
 
 Left pes. Same as left pes of No. 474 [sc. Condition IV oi 
 the pes]. 
 
 Right pes : same as the left [Condition IV of the pes]. 
 
 476. Cat having its extremities abnormal, the property of the 
 Oxford University Museum and kindly lent for examination; 
 bones only preserved. 
 
 Right pes. Like the left pes of No. 474, but c 1 not separated 
 from c 2 . [Condition IV of pes.] 
 
 Left pes. Like the right, but c 1 separate from c'\ [Condition 
 IV of pes.] 
 
 Right manus. The four external digits II — V normal. The 
 double digit like that of No. 472. The innermost digit with thn 
 b. 21 
 
322 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 phalanges, but the claw not retracted to one side more than to 
 the other. [Condition IV of the manus.] 
 
 Left manus. The same as the right. [Condition IV of the 
 manus.] 
 
 *477. Cat having all extremities abnormal, also the property of the 
 Oxford University Museum. 
 
 Left pes. Like the left pes of case No. 474 [sc. Condition IV 
 of the pes] represented in Fig. 87, II. 
 
 Right pes a peculiar case (Fig. 87, I). The digits V, IV and 
 III are normal right digits. The digit II marked 3 in the figure is 
 
 e.cu 
 
 Fig. 87. Hind feet of Cat No. 477. 
 
 I. Eight pes not truly conforming to any of the Conditions numbered. 
 
 II. Left pes shewing the ordinary form of Condition IV of the pes. 
 Lettering as in Fig. 85. (From a specimen in Oxford Univ. Mus.) 
 
 very slightly differentiated as a right digit, but the excavation on the 
 external side is very slight, and the claw when retracted is almost on 
 the middle of the second phalanx. The digit 2 of the figure is a left, 
 and internal to it is a three-phalanged digit of which the claw is 
 not retracted into any excavation. [Not conforming to any of the 
 Conditions specified.] 
 
 478. Cat having all feet abnormal, kindly lent to me by Mr Oldfield 
 Thomas. 
 
chap, xiil] digits : cat. 323 
 
 Left pes. Digits V, IV, III normal lefts. The next internally 
 (II) is a three-phalanged digit formed as a right. The next is 
 a thick three-phalanged digit with a partially double nail and 
 double pad. This is not differentiated as either right or left. 
 The innermost digit is a two-phalanged hallux-like digit, not 
 differentiated as right or left. [Not conforming to any condition 
 in my scheme.] 
 
 Right pes. The same as the left except that the digit II is 
 only slightly differentiated as a left. The next has a double nail, 
 and the innermost is hallux-like as described for the other foot. 
 [Not conforming to any condition of my scheme.] 
 
 Right manus. As in No. 472. "Pollex" with two phalanges. 
 [Condition IV of the manus.] 
 
 Left manus. Same as right, but the " pollex ' : is only repre- 
 sented by a single bone not differentiated or divided into meta- 
 carpal and phalanges and bearing no claw. [Approaches Condition 
 IV of the manus.] 
 
 479. Cat. A left pes bearing abnormal digits. The digits II, III, 
 IV and V are normal and are true left digits. Internal to these 
 are two metatarsals which are united centrally and peripherally 
 but are separate in their middle parts. These two metatarsals by 
 their common distal end bear amorphous phalanges belonging to 
 three digits. There are two large claws and one rudimentary one. 
 [For details the specimen must be seen.] The navicular bone is 
 divided into two distinct bones, of which one carries the external 
 cuneiform and a small cuneiform for the digit II, the metatarsal of 
 which is rather slender and compressed in its proximal part. The 
 internal part of the navicular bone bears two cuneiforms, one for 
 each part of the united metatarsals. The digits borne by these 
 metatarsals are so misshapen that it is not possible to say anything 
 as to their symmetry. Mus. Coll. Surg., Terat, Catal., No. 306 A. 
 [This specimen does not conform to any of the Conditions of 
 my scheme.] 
 
 *480. In the case of the Cat the polydactyle condition has been observed 
 by Poulton (Nature, xxix. 1883, p. 20, figs. ; ibid., XXXV. 1887, p. 38, 
 figs.) to recur frequently in the same strain. A female cat had six toes 
 on both fore and hind feet. The mother of this cat had an abnormal 
 number of toes not recorded. The grandmother and great-grandmother 
 were normal. Two of the kittens of the 6-toed cat had seven toes both 
 on the fore and hind feet [no 7-toed pes among specimens examined 1 »y 
 me]. Many families produced by the 6-toed cat, and among them only 
 two kittens with 7 toes on all feet, but between this and the normal 
 numerous varieties seen. The abnormality is not in all cases sym- 
 metrical on the two sides of the body. The pads of the different toes 
 are sometimes compounded together. In some cases an extra pad was 
 present on the hind foot behind and interior to the central pad. The 
 second pad was sometimes distinct from the central pad and sometimes 
 was united with it. [From the figures it appears that the secondary 
 
 21—2 
 
324 MERISTIC VARIATION. [part I. 
 
 central pad in the pes bore to the digits internal to the axis of sym- 
 metry a relation comparable with that which the chief central pad bears 
 to the digits III — V, but the secondary central pad is at a higher level 
 than the primary one.] It was especially noted that the details in the 
 arrangement of the pads were inherited in several instances. 
 
 The history of the descendants of the 6-toed cat was followed and 
 a genealogical tree is given shewing that the abnormality has been 
 present in a large proportion of them. This was observed in five 
 generations from the original 6-toed cat, so that including the mother 
 of the 6-toed cat the family has contained polydactyle members for 
 seven generations. It may reasonably be assumed that in most of these 
 cases the fathers of these kittens have been normal cats and a good deal 
 of evidence is adduced which makes this likely. 
 
 It was observed also that some normal cats belonging to this family 
 gave birth to polydactyle kittens. In the later period of the life of 
 the original 6-toed cat she gave birth to kittens which were all normal. 
 
 I know no case of reduction in number of digits or of syndac- 
 tylism in the Cat. 
 
 Man and Apes. 
 
 Increase in number of Digits. 
 
 Increase in the number of digits occurs in Man in many forms. 
 Among them may be distinguished a large group of cases differing 
 among themselves but capable of being arranged in a progressive 
 series like that described in the Cat. These cases are all examples 
 of amplification or j3roliferation of parts internal to the index of 
 the manus. 
 
 Taking the normal as the first Condition, the next in the 
 progress is a hand having the digits II — V normal, but the thumb 
 with three phalanges, or as the descriptions sometimes say, " like 
 an index." (Condition II.) 
 
 In the next condition a two-phalanged digit is present internal 
 to the three-phalanged " thumb." (Condition III.) In the next 
 Condition the digit internal to the three-phalanged " thumb " has 
 itself three phalanges. (Condition IV.) A variant from this oc- 
 curred in the left hand of a child (No. 488) of parent having hands in 
 Condition IV. In the child the right hand was in Condition IV, but 
 in the left there were the usual four digits II — V, and internal to 
 them two complete digits, each of three phalanges, but of these the 
 external had a small rudimentary digit arising from the meta- 
 carpus. Hence the hand may be described as composed of two 
 groups, the one containing four and the other three digits. 
 
 In one case, No. 490, the right hand was in Condition IV, but 
 the left hand was advanced further. For in it the metacarpal of 
 the innermost digit bore a 2-phalanged digit internally to its 
 3-phalanged digit. This may be considered as a Condition V. 
 
chap, xiil] DIGITS : MAN. 325 
 
 The number of phalanges in the digits in these Conditions 
 may be represented thus. The || marks the metacarpal space. 
 (The hand is supposed to be a right.) 
 
 Condition I 
 
 2 
 
 | 33 3 3 
 
 II 
 
 3 
 
 | 3333 
 
 „ III 
 
 2 3 
 
 | 3 3 33 
 
 n IV 
 
 3 3 
 
 | 3333 
 
 v 
 
 2 3 3 
 
 | 3 33 3 
 
 Distinct from these Conditions are the states sometimes 
 described as " double-hand." In the full form of this there are 
 eight digits, each of three phalanges. The eight digits are 
 arranged in two groups, four in each group. The two groups 
 stand as a complementary pair, the one being the optical image 
 of the other ; or in other words, the one group is right and the 
 other is left. 
 
 Besides the double-hand with eight digits there are also forms 
 of double-hand with six digits, arranged in two groups of three and 
 three. 
 
 Lastly, there are cases of double-hand having seven fingers, 
 an external group of four and an internal group of three. Thus 
 expressed these cases seem to come very near that mentioned as 
 a variant on Condition IV, but in one and perhaps both of these 
 double-hands there was in the structure of the fore- arm and 
 carpus a great difference from that found in the only recorded 
 skeleton of Condition IV. 
 
 At first sight it would naturally be supposed that these double- 
 hands in one or all kinds stand to the other Conditions in the 
 some relation that Condition IV of the pes in the Cat does to the 
 other polydactyle conditions in the Cat. But the matter is 
 complicated by the fact that the evidence goes to shew that in the 
 human double-hands the bones of the arm and carpus may be 
 modified, and in Dwight's example of seven digits (No. 489) at all 
 events, and perhaps in other double-hands, an ulna-like bone takes 
 the place of the radius, or in other words, the internal side of the 
 fore-arm is fashioned like the external side. In the polydactyle cats 
 the bones of the fore-arm were normal, as are they also substantially 
 in cases of the human Conditions III and IV, which have been 
 dissected. Further, in some of the human cases of eight digits 
 the abnormality was confined to one hand, which is never the case 
 in the higher condition of polydactylism in the Cat, so far as I 
 know. These circumstances make it necessary to recognize the 
 possibility that some at least of the human double-hands are 
 of a different nature from the lower forms of polydactylism. 
 This subject will be spoken of again after the evidence as to the 
 variation of digits has been given (Chap. xiv. Section (4).) 
 
326 MERISTIC VARIATION. [part I. 
 
 In addition to cases more or less conforming to schemes that 
 can be indicated are several which cannot be thus included. These 
 will be duly noticed when the more schematic cases have been 
 described. That any of the cases can be arranged in a formal 
 sequence of this kind is perhaps surprising, and the relations of 
 some of the Conditions, II and III for instance, to each other must 
 at once recall the principle seen already in other examples of 
 addition of a member at the end of a successive series of parts, 
 notably in the case of Teeth (see p. 272). It was then pointed out 
 that when a new member is added beyond a terminal member 
 whose size is normally small relatively to that of the normal 
 penultimate, then the member which is normally terminal is 
 raised to a higher condition. Now this same principle is seen in 
 Condition III of the polydactyle manus. 
 
 Attention must nevertheless be forthwith called to the fact 
 that a two-phalanged digit 1 may be present internal to the thumb 
 (usually arising from it) though the thumb has still but two 
 phalanges. But generally these cases may properly be described 
 as examples of duplicity of the thumb ; and as was well seen in 
 the case of Teeth, any member of a series may divide into two 
 though the rest of the series remain unaltered. Duplicity of a 
 member without reconstitution of the series is to be recognized as 
 one occurrence, and change in number associated with reconstitu- 
 tion of other members especially, of adjacent members, is another. 
 In Teeth and other Meristic series these two phenomena are both 
 to be seen, though as was pointed out (p. 270) they pass insensibly 
 into each other. 
 
 Another feature to be specially mentioned in this preliminary 
 notice is the difference in the manner in which the higher forms 
 of polydactylism appears in the human foot from that seen in the 
 human hand. In the hand there is this strange group of cases 
 forming a progress from the normal hand to Condition V, besides 
 the distinct series of double-hands. Polydactyle feet on the con- 
 trary do not in Man, so far as they have been observed (with the 
 doubtful exception of Nos. 499 and 500), develop a new symmetry. 
 
 Cakes of Polydactylism associated with Change of Symmetry. 
 A. Digits in one Successive Series. 
 
 '481. Man having a "supernumerary index" on each hand. Left 
 hand. No" thumb " present. In its stead there is a digit having 
 three phalanges which " performs its office." The middle phalanx 
 was abnormally short. The first intermetacarpal space was not 
 great. [Degree of opposability not stated.] Right hand. In 
 addition to four normal fingers there was a three-jointed digit 
 
 1 A case in which a 3-phalanged digit was placed on the radial side of the pollex 
 is mentioned by Windle, Jour. Anat. Plnjs.. xxvi. p. 440, but has not yet been 
 described. No other such case is known to me. This perhaps should be classed 
 with double-hands. Cp. No. 502. 
 
CHAP. XIII.] 
 
 DIGITS : MAX. 
 
 327 
 
 482, 
 
 which could be opposed to them and could perform all the move- 
 ments of flexion, &c. Internal to this three-jointed digit was a 
 rudimentary thumb having only one phalanx and no nail. [Re- 
 lations of metacarpals to each other not particularly described.] 
 Guermonprez, F., Rev. des mal. de Venfance, iv. 1886, p. 122, figs. 
 [Left hand Condition II; right hand almost Condition III.] 
 
 Girl having a three-jointed thumb, resembling a long fore- 
 finger. Annandale, Diseases of the Fingers and Toes, p. 29, PI. II. 
 fig. 19. [Condition II.] 
 
 483. Man having a thumb with three phalanges on each hand. Feet 
 normal. In the thumbs the metacarpal is 2 j- in. long; the first phalanx 
 If in., being longer than usual. The second phalanx is longer on the 
 radial side than on the external side, causing the distal phalanx to curve 
 towards the index. On the internal it measures J- in., in the middle 
 | in., and on the ulnar side \ in. The distal phalanx is 1 in. long. 
 When the left thumb is straightened it passes \ in. beyond the joint 
 between the 1st and 2nd phalanx of the index. In the right hand the 
 thumb scarcely reaches that joint. The utility of the thumb is not 
 impaired. A maternal aunt had a similar thumb on right hand. 
 Struthers, Edin. New Phil. Journ., 1863 (2), p. 102, PI. n. fig. 6. 
 [Both hands Condition II.] 
 
 *484. Father and three children, each having 3-phalanged thumbs shaped 
 as indices and not opposable. [Full description q.v.~\ Paternal grand- 
 mother had double-thumb. Farge, Gaz. hebd. de med. et chir., Ser. 2. 
 ii. 1866, p. 61. 
 
 *485. Man having the following abnormalities of the digits. (Fig. 
 88). Right hand. The number of digits was normal, but the 
 
 Fig. 88. Right and left hands of No. 485. Right hand in Condition II; Left 
 hand in Condition III. (After Windle.) 
 
328 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 * 
 
 ±86, 
 
 radial digit or thumb had three phalanges in addition to the meta- 
 carpal, all the articulations being moveable. Relatively to the 
 others their digit was placed as a thumb. Left hand. The digit 
 corresponding with the thumb was composed of three phalanges like 
 that of the right side, and though finger-like in form it was 
 functionally a thumb. On the radial side of this 3-jointed digit 
 there was a supernumerary digit composed of two phalanges articu- 
 lating with the metacarpal bone of the 3-jointed thumb. This 
 supernumerary digit had a well-formed nail. The 3-jointed thumb 
 of the left hand was longer than that of the right hand (measure- 
 ments given), Windle, B.C. A., Journ. of Anat. xxvi. 1891, p. 100, 
 PL II. [Right hand, Condition II ; left hand, Condition III.] 
 
 Man having 3 phalanges in the thumb of the left hand together 
 with a supernumerary digit. (Fig. 89.) This case in several 
 respects resembles the left hand of the subject described by Windle. 
 The four fingers were normal. The thumb stood in its normal 
 relations to them, but was finger-like in form, having three 
 phalanges in addition to the metacarpal. On the radial side of 
 
 Fig. 89. 
 
 Bones of left hand of No. 486, shewing Condition III. 
 (After Rijkebusch.) 
 
 this 3-phalanged digit there was a supernumerary digit, having 
 two phalanges and a separate metacarpal, which articulated with 
 the head of the metacarpal of the thumb and the trapezium. In 
 the carpus of this hand there was a supernumerary bone which is 
 described as an os centrale. The bones and muscles of this limb 
 
CHAP. XIII.] 
 
 DIGITS : MAN. 
 
 329 
 
 are described in detail. The thumb and the supernumerary digit 
 were closely webbed together and were very slightly moveable. 
 Specimen first described by Rukebusch, Bijdr. tot de Kennis der 
 Polydactylie, Utrecht, 1887, Plates, and subsequently by Spronck, 
 Arch, neerl, XXII. 1888, p. 235, PL VI. — IX. [Condition III.] 
 
 *487. Woman having 6 digits on each hand and foot as follows. In each 
 hand the thumb has three phalanges, and internal to it articulating 
 with the same metacarpal is an extra digit having two phalanges 
 [measurements given] webbed to the three-phalanged thumb. [Con- 
 dition III of the manus.j Right foot has six complete metatarsals and 
 digits very regularly set, one of them being internal to but longer than 
 the hallux which has two phalanges as usual. The digit internal to it 
 has also two phalanges. Left foot has also an extra digit with two 
 phalanges longer than the hallux, placed internal to and articulating 
 with the metatarsal of the hallux which has two phalanges as usual. 
 Many members of family polydactyle [particulars given]. Struthers, 
 Edin. New Phil. Jour., 1863 (2), p. 93. [Note in this case that in the 
 feet the digits added internally to hallux are greater than it, and they 
 thus stand as the largest terms in the series, the other members being 
 Successive to them. The series thus does not decline from the hallux 
 both internally and externally in the way seen in most other cases of 
 extra digits on the internal side of the limb.] 
 
 488. Man having six digits, each with three phalanges, on each hand. 
 
 d 1 
 
 Fig. 90. Bones of right hand of No. 488 shewing Condition IV. 
 n 1 and n 2 represent the scaphoid, lu, lunar, c, cuneiform, tm, trapezium. 
 td, trapezoid, m, magnum, u, unciform. ac l , ac 2 are supernumerary bones. 
 
 (After Eudinoer.) 
 
330 MERISTIC VARIATION. [part I. 
 
 The digits were arranged in two groups, which were to some extent 
 opposable to each other. The digits II, III, IV and V stood in their 
 normal positions and were properly formed. In the place where the 
 thumb should stand there were two digits, each with three pha- 
 langes. Of these the external (rf 2 ) was of about the length and 
 form of the index finger while the internal, d 1 , was a good deal 
 shorter and more slender. The bones of the carpus are shewn in 
 Fig. 88. The scaphoid was represented in the right hand by two 
 bones n 1 and n 2 , and there were two accessory bones, ac 1 and ac 2 
 placed in the positions shewn. The two hands were almost exactly 
 alike, save for slight differences in the carpal bones [see original 
 figures], and for the fact that in the left hand the internal of the 
 two digits of the radial group was rather more rudimentary. 
 Rudinger, Beitr. zur Anat. des Gehororgans, d. venosen Blutbahnen 
 d. Schddelhohle, sotuie der ilberzdhligen Finger, Miinchen, 1876, 
 Plate. [Both hands in Condition IV.] 
 
 489. A female child born to the last case, No. 488, had the right hand 
 in the same condition as that of the father, while the left hand 
 differed from it in the presence of an additional rudimentary 
 finger arising from the ulnar side of the digit d\ This additional 
 finger bore a nail but it appeared to consist of two joints only and 
 to be attached to the metacarpus by ligamentary connexions. 
 Rudinger, ibid. [Right hand in Condition IV ; left hand depart- 
 ing from the Conditions enumerated. Compare with manus of 
 Cat, Fig. 84] 
 
 490. Man. Rigid hand bore six digits and metacarpals. The most 
 external digit was a normal minimus, succeeded by digits IV and 
 III webbed together. Next to III there was an index. Internal 
 to this and separated from it by a small metacarpal space was a 
 3-phalanged long digit much as in Windle's case, No. 481, and 
 internal to it is a 2-phalanged thumb of nearly normal form like 
 that of No. 485. Left hand bore seven digits but six metacarpals. 
 Minimus normal. IV, III and II webbed together. Internal to II 
 was a 3-phalanged digit much as in the right hand ; but internal 
 to this there was a metacarpal bearing two digits, an external 
 having 3 phalanges and an internal having 2 phalanges. Each 
 foot had six digits and six metatarsals (q. v.). Redescribed from 
 the account and figures given by Gruber, Bull. Ac. Sci. Pet., xvi. 
 1871, p. 359, figs. [Right hand Condition IV, left hand Con- 
 dition V.] 
 
 491. Child having six fingers on each hand. The fingers were united together. In 
 the thumb [? both] there were three phalanges and the length of the thumb was as 
 great as that of the "other fingers." Dubois, Arch, gener. de Med., 1826, Ann. iv. 
 T. xi. p. 148; this case is quoted by Geoffroy St Hilaire, Hist, des Anom., i. p. 227, 
 Note. [? Condition IV.] 
 
 491, d. New-born male child having on the right hand two "thumbs" each with three 
 phalanges. Oberteufer, J. G., Stark's Arch. f. Gebnrtsh., 1801, xv. p. 612. [Con- 
 dition IV.] 
 
 (No more cases known to me.) 
 
 * 
 
CHAP. XIII.] 
 
 DOUBLE-HAND. 
 
 331 
 
 B 1 . Digits in two homologous groups, forming "Double-hands." 
 
 *492. Double-hand I. Seven digits in two groups of four and three. 
 Male : left arm abnormal, having seven digits arranged in two 
 groups, the one an external group of four normal digits, and the 
 other an internal group of three digits 2 . (Fig. 91.) Described 
 from a dried specimen in Mus. of Harvard Med. School. The man 
 was a machinist and found the hand not merely very useful to him 
 in his business, but he also thought that it gave him advantages 
 in playing the piano. 
 
 " The fore-arm consists of the normal left ulna and of a right one in 
 the place of a radius. The left one shews little that calls for comment, 
 excepting that there is a projection outward at the place of the lesser 
 sigmoid cavity to join a corresponding projection from the other ulna. 
 The upper surface of this projection articulates with the humerus. At 
 the lower end the styloid process is less prominent than usual, and the 
 head rather broad. The right or extra ulna is put on hind side before, 
 that is, the back of the olecranon projects forward over the front and 
 outer aspect of the humerus. If the reader will place his right fore-arm 
 on the outer side of the left one he will see that it is necessarv for the 
 
 I 
 
 ; ■ 
 : . . 
 
 . i* ho 
 
 ■ '• 
 
 II 
 
 Fig. 91. I. The left band of No. 492 from the dorsal surface. 
 II. The humerus and two bones of the fore-arm at the elbow of the same c 
 0, olecranon. O 2 , the secondary " olecranon ". I, the inner condyle of the 
 humerus. I 2 , the second or external " inner condyle." 
 
 (After Dwight.) 
 
 ulna to be thus inverted if the thumbs are to toucli and the palms 
 to be continuous. This olecranon is thinner, flatter, and longer than 
 normal. The coronoid process is rudimentary. From the side of this 
 process and from the shaft just behind it arises the projection already 
 
 1 Every case known to me is given. 
 
 2 This is the case reported by Jackson, to Bost. Soc. of Med. hup.. 1852. 
 
332 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 referred to which meets a similar one from the normal ulna [Fig. 89, II]. 
 On the front of this there is a small articular surface looking forward 
 which suggests a part of the convexity of the head of the radius. The 
 upper articular surface shews a fissure separating it from the side of 
 the olecranon which is not found in the normal ulna. These projections 
 which touch each other are held together by a strong interosseous liga- 
 ment. The lower end of this ulna is very like the other, only somewhat 
 broader. The mode of union of the lower ends could not be seen without 
 unwarrantable injury to the specimen. There can hardly have been 
 any definite movement between these bones. Perhaps the ligaments may 
 have permitted some irregular sliding, but it is impossible to know. 
 These bones have been described first because their nature is very clear 
 and, once understood, is a key to the more difficult interpretation of the 
 lower end of the humerus." 
 
 The upper end of the humerus presented nothing noteworthy. A 
 detailed description and figures are given, from which it appears that 
 the lower end of the humerus had such a form as might be produced 
 by sawing off the greater part of the external condyle and applying in 
 place of it the internal condyle of a right humerus. 
 
 The carpus seen from the dorsal side had the structure shewn in the 
 diagram (Fig. 92). The proximal row consisted of three bones besides 
 the two pisiforms (p l and p 2 ). There was a cuneiform at either side of 
 the wrist, and between them a bone evidently composed of a pair of 
 semilunars, having a slight notch in its upper border. At each end of 
 
 Fig. 92. Diagram of the carpal bones in the left hand of No. 492 from the 
 dorsal surface. 
 
 pis 1 , cu 1 , u 1 , m 1 , pisiform, cuneiform, unciform and magnum of the external or 
 normal half of the band consisting of four fingers ; pis*, cu 2 , u 2 , m 2 , the similar 
 bones for the internal group of three fingers. Zu 1+2 , the compounded lunar 
 elements corresponding to the two groups, x, bone placed as trapezoid. 
 
 (After Dwight.) 
 
 the second row is an unciform bearing the middle and ring fingers. 
 Next came two ossa magna very symmetrically placed, each bearing the 
 metacarpal of a medius. Between these is a bone which Dwight states 
 
chap, xiil] double-haxd. 333 
 
 to have clearly represented the trapezoid of the left hand, bearing an 
 index finger. The metacarpals and phalanges needed no description. 
 
 The muscles are described in detail [^.v.]. Some of the features 
 in the distribution of the arteries and nerves are of interest, and 1 
 transcribe Dwight's account in full. It appears that, like the bones, 
 the vessels and nerves proper to the radial side of a normal left arm 
 have in a measure been transformed into parts proper to the ulnar side 
 of a right arm. 
 
 "The Arteries. The brachial divides at about the junction of the 
 middle and lower thirds of the humerus. The main continuation, which 
 is the ulnar proper, runs deeply under the band thought to represent 
 the pronator radii teres, to the deep part of the fore-arm where it gives 
 off the interosseous. Above the elbow there is a branch running 
 backward between the internal condyle and the olecranon. The inter- 
 osseous branches are not easy to trace. There seems to be an anterior 
 interosseous and three branches on the back of the forearm, one running 
 on the membrane and one along each bone. At least two of them share 
 in a network on the back of the carpus. Having reached the hand the 
 ulnar artery runs obliquely across the palm to the cleft between the 
 two sets of fingers, supplying the four normal fingers and the nearer side 
 of the extra middle finger. The other branch of the brachial crosses 
 the median nerve and runs, apparently superficially, to the outer side 
 of the fore- arm. It supplies the little and ring fingers and the corre- 
 sponding side of the middle finger of the supernumerary set. There is 
 no anastomosis in the palm between the superficial branches of the 
 two arteries. Each gives off a deep branch at the usual place, which 
 forms a deep palmar arch from which some interosseous arteries spring. 
 There is also an arterial network over the front of the carpal bones. 
 The arteries of the deep parts of the hand cannot all be seen. 
 
 The Nerves. The ulnar nerve proper pursues a normal course and 
 supplies the palmar aspect of the little finger and half the ring finger of 
 the normal hand. Near the wrist it gives off a very small posterior 
 branch, which is not well preserved, but which seems to have had less 
 than the usual distribution. The median nerve is normal as far as the 
 elbow, running to the inner side of the extra condyle. It is then lost 
 in the dried fibers of the flexor sublimis, from which it emerges in two 
 main divisions near the middle of the fore-arm. The inner of these soon 
 divides into two, of which one supplies the adjacent sides of the ring 
 and middle fingers and the other those of the middle and index fingers 
 of the normal hand. The outer division of the median supplies the 
 outer side of the index and both sides of the extra middle finger and 
 one side of the extra ring finger. One of the branches to the index 
 gives off a dorsal branch, and there is a doubtful one for the extra 
 middle finger. The musculo-spiral nerve passes behind the humerus as 
 usual. A nerve which is undoubtedly continuous with it emerges from 
 the hardened muscles over the fused outer condyles. It seems to be the 
 radial branch changed into an ulnar. It runs with the extra ulnar 
 artery to the hand and sending a deep branch into the palm, goes to 
 the ring linger. There is a detached branch on the other side of the 
 little finger which in all probability came from it. The deep branch 
 sends a twig along the metacarpal bone of the ring finger. It probably 
 
334 MERISTIC VARIATION. [part i. 
 
 supplied the side of the ring linger left unprovided for, but this is 
 uncertain. Assuming this to have been the case, each ulnar nerve 
 supplies the palmar surface of one finger and a half, the median supply- 
 ing the remaining fingers of both hands. Unfortunately no dorsal 
 branches except those mentioned have been preserved." 
 
 Dwight, T., Mem. Boston Soc. of JV. H.. 1892, Vol. iv. No. x. 
 p. 473, Pis. xliii and xliv. 
 
 [This is a case of high significance. We shall come back 
 to it hereafter. Meanwhile it will be noted that in it we meet 
 again the old difficulty so often presented by cases of Meristic 
 Variation. In this fore-arm there is already one true ulna. 
 Internal to it is another bone also formed as an ulna. We 
 may therefore, indeed we must, call it an ulna. But is it 
 an " ulna " ? To answer this we must first answer the question 
 what is an ulna? Similarly, is the second pisiform a "pisiform," 
 or is the second ulnar nerve an c< ulnar " nerve ? These questions 
 force themselves on the mind of anyone who tries to apply the 
 language of orthodox morphology to this case, but to them there is 
 still no answer. Or, rather, the answer is given that an " ulna," a 
 " pisiform " and the like are terms that have no fixed, ideal 
 meaning, symbols of an order that we have set up but which the 
 body does not obey. An " ulna " is a bone that has the form of an 
 ulna, and a " pisiform " is that which has the form of a pisiform. 
 If we try to pass behind this, to seek an inner and faster meaning 
 for these conceptions of the mind, we are attempting that for which 
 Nature gives no warrant : we are casting off from the phenomenal, 
 from the things which appear, and we set forth into the waste of 
 metaphysic] 
 
 493. Boy having abnormalities in the left hand as follows. The four 
 outer fingers II — V are normal in form and proportions. Internal to 
 these is firstly an opposable digit with a single metacarpus and single 
 proximal phalanx but having two distal phalanges side by side webbed 
 together. Internal to this partially double thumb are two digits in 
 series, each with a metacarpal and three phalanges, respectively re- 
 sembling the annularis and minimus of a right hand. Struthers, Edin. 
 New Phil. Jour., 1863 (2), p. 90, PI. n. fig. 5. [Not representing any 
 of the Conditions.] 
 
 494. Male infant, one year and five months, examined alive, having the right hand 
 abnormal, possessing seven digits, arranged in two groups, an ulnar group of 
 four and a radial group of three. Each digit had three phalanges, but the ring 
 and middle fingers of the ulnar group are webbed in the region of the proximal 
 phalanges. The ulnar group seemed to articulate with the carpus in the usual 
 way. The radial group probably formed joints with more than one facet on the 
 trapezium, and possibly also with a surface on the lower end of the radius. It 
 did not seem that the carpal bones were increased in number, for the right wrist 
 had the same circumferential measurement as the left, which was normal. The 
 lower end of the ulna did not seem to articulate normally with the carpus. The 
 elbow was also abnormal, and it seemed "as if the ulna were dislocated inwards." 
 Ballantyne, J. W., Edin. Med. Jour., 1893, cdli. p. 623, fig. [Possibly this 
 condition approached to that found in the last cases.] 
 
495. 
 
 CHAP. XIII.] 
 
 DOUBLE-HAND. 
 
 335 
 
 Double-hand II. Eight digits in two groups of four and four. 
 Woman (examined alive) having eight fingers in the left hand 
 arranged as follows (Fig. 93). With the exception of the left arm 
 the body was normal. The limb was very muscular. The shoulder- 
 joint was natural. The external condyloid ridge of the humerus 
 was strongly defined. The muscles and tendons of the fore-arm 
 were so prominent that it was not easy to decide whether there 
 was a second radius or ulna, but Murray eventually came to the 
 
 Fig. 93. Left hand of No. 495. (After Murray.) 
 
 conclusion that there was no such extra bone. The fore-arm 
 could be only partially flexed. The eight fingers were arranged in 
 two groups of four in each, one of the groups standing as the four 
 normal fingers do, and the other four being articulated where the 
 thumb should be. There was no thumb distinguishable as such, 
 but it is stated that there was a protuberance on the dorsal side 
 of the hand, between the two groups of fingers, and this is con- 
 sidered by Murray to represent the thumbs, for according to his 
 view the limb was composed of a pair of hands compounded by 
 their radial sides. In the figure of the dorsal aspect which is given 
 by Murray taken from a photograph, this protuberance cannot be 
 clearly made out. The four radial fingers in size and shape 
 appeared to be four fingers of a right hand. In the radial group of 
 fingers, the" middle "and" jring " fingers (6 and 7) were webbed as 
 far as the proximal joints, and the movements of the fingers of this 
 group were somewhat stiff and imperfect. Between the t \v< » gn nips 
 of fingers there was a wide space as between the thumb and index 
 of a normal hand, and the two parts of the hand could be opposed 
 to each other and folded upon each other. The power of inde- 
 pendent action of the fingers was very limited. No single finger 
 could be retained fully extended while the other seven fingers 
 were flexed, but if both " index " fingers (4 and 5) were extended, 
 
336 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 the other six fingers could be flexed, or the four fingers of either 
 group together with the " index " of the other group may be 
 extended, while the other three are flexed. The " index " fingers 
 could not be flexed while the other fingers were extended, nor can 
 the " little fingers " be extended while the others were flexed. 
 Murray, J. Jardine, Med. Chir. Trans., 1863, xlvi. p. 29, PL n. 
 
 496. Female child, five weeks, having a hand of eight digits on the right side 
 (Fig. 94). The digits were disposed in two groups of four in each. [No further 
 
 r*0^" 
 
 Fig. 94. Right hand of No. 496. (After Giraldes.) 
 
 description.] Giraldes, Bull. soc. de Chirurg., Paris, 1866, Ser. 2, vi. p. 505, 
 fig. The same case referred to again, Giraldes, Mai. Chir. des Enfants, 1869, 
 p. 42, Jig. 
 49^ Female child having right hand almost exactly like Murray's case, but without 
 ' syndactylism. The two halves could be folded on each other. The four extra digits 
 articulated with an imperfect metacarpal which was annexed to the normal meta- 
 carpal [of the index]. Fumagalli, C, Annal. Univers. di Med. Milano, 1871, 
 vol. ccxvi. p. 305, fig. 
 
 Girl's right hand having eight fingers, represented in a wax model. Langalli, 
 La scienza e lapratica, Pavia, 1875 [Not seen : abstract from Dwight, I. c], 
 
 498. Double-hand III. Six digits in two groups of three and three. 
 Man having abnormalities of left arm as follows (Fig. 95). The 
 left hand was composed of six digits with three phalanges, which 
 were disposed in two groups of three digits in each. The two 
 middle digits were the longest (d 3 and c/ 4 ), and the length of the 
 digits on either side of them diminished regularly. The appear- 
 ance was as of a hand composed of the middle, ring and little 
 fingers of a pair of hands united together. The two groups of 
 fingers were to some extent opposed to each other and all the 
 digits could be flexed and extended. The digit d 3 though single 
 in its peripheral parts articulated with two metacarpals, its proxi- 
 mal phalanx having two heads. Upon the radial side of the 
 
CHAP. XIII.] 
 
 DOUBLE-HAND. 
 
 337 
 
 carpus of this hand there was a soft tumour about 2'5 cm. in 
 height, resembling a cyst with a firm wall. 
 
 Fig. 95. Dorsal and palmar aspects of the left hand of No. 
 are numbered from the inside. 
 
 (After Jolly.) 
 
 498. The digits 
 
 The structure of the bones of the arm and fore-arm could not 
 be made out with certainty in the living subject, but it appeared 
 that the humerus was formed by two bones partially united 
 together. 
 
 As regards the skeleton of the fore-arm an ulna could be felt 
 extending from the upper arm to the processus styloideus. The 
 existence of a radius could not be made out with certainty, but a 
 second bone could be felt which was in very close connexion [with 
 the ulna]. Jolly, Tnternat. Beitr. z. wiss. Med., 1891. 
 499. Male child, three years old, twin with a normal female child, 
 having all extremities abnormal. Right hand. Six metacarpals 
 arranged in two groups of three in each group. Each bore a 
 three-phalanged digit, none resembling a thumb. The first and 
 sixth were alike, resembling a minimus, while the two median 
 fingers resembled middle fingers. On the radial side the three 
 digits were completely united together. The next was five, and 
 the two external to this were also united. Left hand. Like the 
 right, but all the fingers united together in two groups of three in 
 each group. Feet. Each foot had nine metatarsals and nine digit-, 
 the central being like a hallux and having two phalanges perhaps, 
 but thicker than a hallux. The externals were like minimi. The 
 four toes on each side of the " hallux " were united two and two. 
 The tarsus was of about double size. The right leg was shorter 
 than the left. Gherixi, A.,Gaz. med. ital.-lombard., 1874, No. .31. 
 p. 401, figs. 
 
 B. 
 
 22 
 
338 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Complex and irregular cases of Polydactylism associated with 
 
 Change of Symmetry. 
 
 *500. Man (examined alive) having abnormalities in the digits of hands 
 and feet (Fig. 96). The case is very briefly and inadequately described, 
 but the condition was apparently as follows. 
 
 Right hand. Beginning from the ulnar side, there were three 
 normal digits (6, 5, 4). Beyond the third of these, which must be 
 
 ») '/] 
 
 > 
 
 ■i) 
 
 f] / 
 
 > 
 
 si 
 
 1 
 
 ;t 
 
 
 jr 
 
 6 
 
 ft 
 
 loJ 
 
 5 
 
 J J v 
 
 3 
 
 2 ~3 * 
 Fig. 96. Hands and feet of No. 500. (After Kuhnt.) 
 
chap, xiii.] COMPLEX POLYDACTYLISM : MAN. 339 
 
 regarded as the medius, there were two complete digits (3, 2) each 
 having three phalanges : and on the radial side of the innermost of 
 these digits there was a stump-like rudiment (1), apparently representing 
 another digit. [This case therefore differed from those of Win die and 
 Rijkebiisch in the fact that both the digits internal to the medius (m) 
 were disposed as though they belonged to a left hand, and Kuhnt, in 
 fact, states that each hand was, as it were, composed of parts of a pair 
 of hands, thus agreeing with Jolly's case, No. 499.] 
 
 Left hand. In this hand there were only five digits, each of which 
 had three phalanges. None of them was fully opposable, but that on 
 the radial side (1) could to some extent be moved as a thumb. Of 
 these five digits the middle one was the longest, and on each side of it 
 there were two similar digits, those next to the middle finger being the 
 longest and those remote from it being a good deal shorter and having 
 the form of little fingers, which Kuhnt considers them to have been. 
 [This hand is perhaps in Condition II.] 
 
 Right foot. The hallux (2, 3) was of abnormal width and its bones 
 were to some extent double, the ungual phalanx being completely so. 
 [The nail however is drawn as a single structure and the double character 
 of the toe was not apparent in its external appearance.] On the internal 
 (tibial) side of the hallux there were two supernumerary toes (1, 1) 
 having, so far as could be ascertained, a single metatarsus. The 
 number of phalanges in these toes is not distinctly stated. 
 
 Left foot. The hallux (3, 4) was to some extent double, like that of 
 the right foot. Internally to it were two supernumerary toes (1, 2) 
 having apparently a common metatarsal. [Of these the most internal 
 is represented as being very wide and resembling a hallux, but this 
 feature is not mentioned in the description and the number of phalanges 
 is not given]. 
 
 [It is greatly to be regretted that no fuller account of this important 
 case is accessible. According to Kuhnt's view each hand and each foot 
 were structurally composed of parts of a complementary pair of hands 
 and feet. As regards the hands the facts agree witli this description 
 and with what has been seen in other cases, but the condition of tin 1 
 feet is more doubtful, and without more knowledge of the details no 
 opinion can be given. It should be remembered that the original 
 description is very brief and Dr Kuhnt offers an apology for the im- 
 perfection of the figures.] Kuhnt, Virch. Arch, f path. Anat. u. Phy8., 
 lvi. 1872, p. 268, Taf. vi. 
 
 501. Case of a foot with eight toes, stated to have resembled Kuhnt's 
 case (No. 501). Ekstein, Prager Wochens., No. 51, 1891. 
 
 502. Man whose right arm beside the normal hand bore an extra thumb 
 and finger. The two thumbs were united and had a common meta- 
 carpal joint. They were of equal size. They were flexed and extended 
 together and had the power of spreading apart. The extra finger was 
 beyond the extra thumb and was shaped like an index. Besides the 
 radius and ulna of the normal arm there was an extra radius on the 
 outer [1 internal] side of the normal radius. This bone had a joint of 
 its own at its elbow. The wrist was broad, suggesting the presence or' 
 additional bones. Nothing is said of a metacarpal bone for the new 
 index. Carre, Seance publ. de la soc. rog. <1> Mid., Ghir. et Pharm. de 
 
 o 
 
340 MEMSTIC VARIATION. [part i. 
 
 Toulouse, 1838, p. 28. [Not seen by me. Abstract taken from D wight, 
 I.e., vide No. 492. Cp. p. 326, Xote.] 
 503. Girl, new-born, having the left foot "double," bearing eleven toes. 
 The left labium majus was twice as large as the right, and the left 
 leg and thigh were much thinner than the corresponding parts on the 
 right side [measurements given]. The extra parts were all on the planter 
 side of a foot which had toes of nearly normal shapes and sizes. This 
 foot was bent into a position of extreme talipes equino-varus, and the 
 great toe was bent so that it pointed inwards at right angles to. the 
 metatarsal. 
 
 Upon the plantar side of this foot there was a series of six well- 
 formed, small toes, arranged in a series parallel to that of the 'normal' 
 five, and having their plantar surfaces in opposition to those of the 
 latter. Of the series of six toes that facing the normal little toe exactly 
 resembled it. The second was the longest of the six, but did not 
 resemble a great toe. The third and fourth were equal in length, the 
 fifth and sixth being shorter, as are the external toes of a normal foot. 
 None of the toes were webbed. Bull, G. J., Boston Med. and Sury. 
 Jour. 1875, xciii. p. 293, fig. [This figure copied by Ahlfeld. 
 Missb. d. Menschen, PI. xx. fig. 2.] 
 
 [The case described by Graxdix, Amer. Jour, of Obstetrics, 1887, xx. p. 425, 
 Jig., is probably a case of a pair of limbs composing a Secondary Symmetry 
 attached to and deforming the limb belonging to the Primary Symmetry and 
 corresponding with that of the other side. The nature of this case will be better 
 understood when evidence as to the manner of constitution of Secondary Symmetries 
 has been given.] 
 
 "504. Macacus sp. A monkey, full-grown, having nine toes on the 
 left foot ; right foot normal, upper extremities not preserved. The 
 specimen is described as No. 307 in the Catalogue of the Terato- 
 logical Series (1872) in the Mus. Coll. Surg. (Hunterian specimen). 
 Though I am disposed to agree in the main with the view of the 
 nature of the specimen given in the Catalogue it is not in my 
 judgment possible to decide confidently in favour of this view to 
 the exclusion of all others. For this reason the specimen is here 
 described afresh. This is the more necessary as the account of 
 the Catalogue is incorrect in some particulars. 
 
 Extra parts are present in the limb and in the pelvic girdle. 
 (Figs. 97 and 98.) The names to be given to the parts depend on 
 the hypothesis of their nature which may be preferred. In general 
 terms it may be stated that the ventral or pubic border of the 
 girdle and the internal (tibial) border of the limb are nearly normal. 
 The external (fibular) border of the limb is also normal, but between 
 these there are in addition to the normal parts other structures, 
 whose true nature is somewhat uncertain. 
 
 The appearances may be realized best in the following way. Sup- 
 pose that two similar left feet lie in succession to each other, the 
 " posterior " having its hallux next to the minimus of the "anterior/' 
 so that the digits read I, II, III, IV, V, I, II, III, IV, V. Now if 
 the two feet could interjDenetrate so far that the minimus of the 
 " anterior " foot took the place of the hallux of the " posterior," this 
 
chap, xiii.] POLYDACTYLE FOOT : MaCCLCUS. 
 
 341 
 
 second hallux not being represented, the condition of this specimen 
 would be nearly produced. In the same way the left pelvic girdle 
 is just what it would be if two left innominate bones were placed 
 in succession, the ischium of the " anterior " superseding the pubis of 
 the posterior. As in the foot, so in the innominate, of the portions 
 which coincide the parts belonging to the anterior are alone 
 represented. Something very like this was seen in the case, for 
 instance, of the imperfect division of vertebrae in Python, No. 7. 
 
 The chief difficulty attending this view of the nature of the 
 case is the fact that as regards the tarsus the "anterior" foot 
 
 h'- 
 
 .g* 
 
 It- 
 
 4&} 
 
 .fib 1 
 
 Fig. 97. Macacus, No. 50-1, left leg. 
 C. S. M. 307. 
 
 7* 1 , head by which femur articulates. 
 lr, supernumerary head (?). gt, great tro- 
 chanter. gt 2 , " posterior " great trochanter. 
 It, lesser trochanter, t, tibia, fib 1 , " anterior 
 fibula." fib 2 , "posterior" fibula (?). clc, 
 calcaneum. As, astragalus, nav, navicular. 
 nav 2 , supposed second navicular, c 1 — c 6 , 
 six cuneiform bones, c 3 , the ecto-cuneiform 
 of "anterior" foot, cb, cuboid. 
 
 'C3 
 
342 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 lacks the external (fibular) parts of a tarsus, viz. the cuboid and 
 calcaneum. There is a cuboid, cb, and a calcaneum, c, for the 
 "posterior" foot, but none for the " anterior." The bone c 3 might 
 of course be called a cuboid ; but if this is a cuboid there is no 
 ecto-cuneiform for the anterior foot. The account given in the 
 Catalogue avoids these difficulties by the statement that each foot 
 has three cuneiforms and a cuboid, declaring that there is a second 
 cuboid between the two sets of cuneiforms. This is nevertheless 
 incorrect, for the whole distal series in the tarsus contains onlv 
 seven bones and not eight. The mistake has no doubt arisen by 
 counting c s twice over. The Catalogue is also in error in neglecting 
 the fact that the tarsal articulation of the digit 2 is quite abnormal. 
 Similarly in the crus, there is no good reason to affirm that the 
 boney^ 1 is a fibula rather than a tibia. The Catalogue regards it 
 as a second tibia, but I incline to speak of it as the fibula of the 
 ' anterior ' foot following the view already indicated. As I have 
 said, the leg is almost normal in the structure of its external 
 border and almost normal in its posterior border, but between 
 these the nature of the parts is problematical. All that can be 
 done is to describe the parts as they are seen. 
 
 Beginning at the external (fibular) border of the foot there is a 
 nearly normal series of three digits, 9, 8, 7, fashioned as V, IV and III 
 
 I II 
 
 Fig. 98. I. Innominate bone of Macacus, No. 504. i\ p, is 1 , t 1 , of 1 , ilium, 
 pubis, ischium, ischial tuberosity and obturator foramen of the supposed anterior 
 part of the girdle; the parts marked 2 being the corresponding structures of the 
 supposed posterior part. 
 
 II. Details of tarsus of the same. Digits numbered 1 — 9 from the inside. 
 A, astragalus, c, calcaneum. n 1 . navicular of "anterior" foot. n\ navicular of 
 "posterior" foot, cb, cuboid, c 1 — c F ', six bones placed as cuneiforms. 
 
chap, xiii.] POLYDACTYLE FOOT : MoCOCUS. 343 
 
 respectively, the V and the IV articulating with the cuboid (cb) and 
 the III with an external cuneiform, c 6 , as usual. There is a middle 
 cuneiform, c 5 , bearing a digit, 6, which is almost exactly formed as a II. 
 Internal to this point the parts can only be named with hesitation. 
 The tarsal bone, c 4 , of the distal series internal to c 5 is shaped like 
 another c 5 , but the digit which it bears rather resembles a minimus. 
 This is succeeded by a tarsal bone, c 3 , shaped like the external cunei- 
 form, c 6 , but it bears a digit of the length suited to an annularis. 
 Internal to this are two tarsal bones of the distal row, c 2 and c\ which 
 bear three digits, 1, 2, and 3. Of these the most internal is undoubtedly 
 an internal cuneiform ; it bears firstly a slender but otherwise normal 
 hallux with two phalanges, and secondly, it contributes (abnormally for 
 an internal cuneiform) to the articulation of a digit, 2, which is thinner 
 than all the others and resembles rather a minimus than an index. 
 The digit, 2, also articulates with c 2 which chiefly supports the third 
 digit. 
 
 Between the metatarsals of the digits 5 and 6 there is a considerable 
 space, owing to the fact that the head of the metatarsal of 6 is pro- 
 longed upwards like that of a normal metatarsal V. 
 
 In addition to those described are four other tarsal bones : firstly, a 
 calcaneum c, which is rather smaller than that of the normal right 
 leg. It articulates with the cuboid, cb, with the astragalus, A, and 
 with the bone, n 2 . The astragalus is very large in its transverse 
 dimension but its length is less than that of the normal astragalus. 
 Peripherally it bears two bones, firstly, a navicular, n\ and secondly. 
 a bone of uncertain homology, marked n 2 in Fig. 96. The navicular 
 articulates with c\ c 2 and c 3 , together with the bone n 2 . The latter, ri 2 , 
 articulates with c 3 , c 4 , c 5 , c 6 , and also with the cuboid, cb, the astragalus 
 and calcaneum and navicular. From its form and relations it is 
 probably a second navicular. 
 
 The bones of the crus are three. Firstly, a tibia, lib., which is 
 rather thinner than the normal bone and is somewhat bowed inwards. 
 Passing as a chord to the curve of the tibia there is a thin bone, fib . 
 which is tendinous in its upper part. External to this, articulating 
 with the external condyle of the femur there is a third bone. ji/>\ 
 which has nearly the form and proportions of a normal fibula. All 
 three bones articulate with the large astragalus. 
 
 There is a small patella. 
 
 The femur is about half as thick again as that of the right leg. Its 
 head is nearly normal in form, articulating with the rather shallow 
 acetabulum. The lesser trochanter and the internal border of the femur 
 are nearly normal. Anteriorly and externally there are the following 
 parts. Upon the external border there is a projecting callosity, clearly 
 being a great trochanter in its nature. Internal to this there is a knob- 
 shaped, rounded protuberance, which in texture so closely resembles 
 the head of a femur that it is almost certainly of this nature. h is 
 rounded and smooth as though for articulation with an acetabulum, 
 though it stands freely. Between this tuberosity and the real head of 
 the femur there is a third tuberosity, apparently representing the end 
 of the great trochanter of that limb which lias been spoken of as 
 "anterior." The peripheral end of the femur is nearly normal on its 
 inner side, while on the outside it is considerably enlarged. The ex 
 
344 MERISTIC VARIATION. [part i. 
 
 ternal condyle is thus much larger than that of the normal femur, but 
 there is in it only a very slight suggestion of a division into two parts. 
 The innominate bone has an ilium which anteriorly is normal, but 
 which posteriorly enlarges and to some extent divides into two parts, V 
 and i 2 . Of these the ventral part, i\ unites with a nearly normal pubis, 
 p, and bounds the shallow acetabulum with which the femur articu- 
 lates. The rest of this acetabulum is made up by the ischium, is 1 , of 
 the "anterior" limb, which together with the pubis bounds an obturator 
 foramen, of 1 . Dorsal to these parts the ilium has a partly separated 
 portion, i 2 , which forms part of the wall of a cavity apparently repre- 
 senting the acetabulum of the "posterior" limb. Dorsal to this a 
 complete ischium arises which bears a normal ischial tuberosity and 
 curves round a second smaller obturator foramen, of 2 . 
 
 In so far as the foregoing description involves conceptions of 
 homology it is merely suggestive, but the structure of the innomi- 
 nate bone leaves little doubt that the nature of the parts is much as 
 here described. Nevertheless the appearance of the digits 5 and 6 
 and of the tarsal bones c 3 to c 6 somewhat suggests that there is a 
 symmetry about an axis passing between the digits 5 and 6 ; but 
 if 5 were a minimus and if 6 were fashioned as an index, which it 
 is, the appearance of a relation of images would to some extent 
 exist in any case. This appearance is however confined to the 
 dorsal aspect of the foot and is not present on the plantar aspect. 
 
 This case, if the view of it proposed be true, differs from other 
 examples of double-hand (e.g. Nos. 491 to 499) in that the Repe- 
 tition is Successive and is not a Repetition of images ; for the 
 digits stand I, II, III, IV, V, II, III, IV, V, and not V, IV, III, II, 
 [I], II, III, IV, V as in those other cases. In this respect it is so 
 far as I know unique. 
 
 Those who have treated the subject of double-hand generally make reference 
 to the following records. Kueff, De conceptu, Frankfurt, 1587, PI. 41 ; Aldro- 
 vandi, Monstr. Hist., 1642, p. 495 ; Kerckrixg, Obs. anat., Amst. 1670, Obs. xx. 
 PL, but the descriptions are scarcely such as to be useful for our purpose. A case 
 quoted by Dwight, Mem. Bost. Soc.of N. H., iv. No. x. p 474, from du Cauroi, Jour. 
 des Scavans, 161)6, pub. 1697, p. 81 [originally quoted by Mor.vxd and misquoted by 
 many subsequent authors], is probably not an example of double-hand (see No. 522). 
 
 Cases of Polydactylism in Man and Apes not associated with 
 
 definite change of Symmetry. 
 
 From the evidence as to polydactylism in general the foregoing 
 cases have been taken out and placed in association as exhibiting 
 the development of a new system of Symmetry in the limb. It 
 will have been noticed that in all of them the external (ulnar or 
 fibular) parts of the limb remain unchanged, and the parts not 
 represented in the normal are on the internal (radial or tibial) 
 sides. In the remaining cases of polydactylism, which constitute 
 the great majority, there is no manifest change in the general 
 symmetry of the limb. 
 
chap, xiil] DIGITS : MAN. 345 
 
 These general phenomena of polydactylism have been observed 
 from the earliest times and the literature relating to the subject 
 is of great extent. Most cases known up to 1869 [not including 
 Struthers' cases] were collected by Fort, Difformites des Doigts, 
 Paris, 1869, and independently by Grubeu, Bull. Ac. Sci. Pet, 
 xv. 1871, p. 352 and p. 460, and good collections of references have 
 subsequently been published, especially by Fackexheim. Jen. 
 Zeits., XXII. p. 343. Of the whole number of cases the majority 
 fall into a few types, and a great part of the evidence may thus be 
 easily summarized and illustrated by specimen-cases. The forms 
 of polydactylism thus constantly recurring may be dealt with 
 conveniently under the following heads. 
 
 (1) Addition of a single digit, complete or incomplete. 
 
 A. external to minimus, in series with the other digits. 
 
 B. in other positions. 
 
 (2) Duplication of single digits, especially of the pollex and 
 
 hallux. 
 
 (3) Combinations of the foregoing. 
 
 Besides these are a certain number of cases not included in 
 the above descriptions, and of them an account will be given under 
 the heading 
 
 (4) Irregular examples. 
 
 As bearing upon the frequency of the several forms of poly- 
 dactylism it may be stated that in this irregular group are 
 included all cases which I have met with that exhibit any feature 
 of importance in departure from the cases otherwise cited. For 
 the purpose of this list I have examined every record of polydactyl- 
 ism to which access could be obtained. 
 
 (1) A. Single extra digit external to minimus in hand or foot. 
 
 (a) Incomplete form. 
 
 This is one of the commonest forms of extra digit. In the great 
 majority of such cases the extra digit is not complete from the carpus 
 or tarsus but arises from the metacarpal or metatarsal, less often from 
 one of the phalanges, of the minimus. The attachment may be either 
 by a direct articulation upon the side of one of these bones, or they may 
 give off a branch bearing the extra digit. In a not uncommon form 
 of the variation the extra digit has no bony attachment to the hand, 
 but is a rudimentary structure hanging from some part of the minimus 
 by a peduncle. Of these several forms the following are illustrative 
 cases. 
 
 -A' Extra digit hanging from minimus hi/ a peduncle. 
 
 Nanus. Annandale", Diseases of Fingers and Toes, 1865, p. 30, PI. n. fig. 20; 
 Tarnier, Bull. Soc. de Chir., Paris, vi., 1866, p. 487; and numerous other examples. 
 Pes. Bcsch, quoted by Grcber, I.e., p. 470: this form in the pes is rare. 
 
346 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 506. Extra digit arising from one of the phalanges of minimus. 
 
 Axxandale, I.e. ; Otto, Monstr. sexc. Descr., Taf. xxv. fig. 7; Cramer, Wochens. 
 f. d. ges. Heilkunde, 1834, No. 51, p. 809; Gaillard, Gaz. med,, 1862. This form 
 seems to be comparatively scarce. 
 
 507. Extra digit arising from metacarpus or metatarsus of minimus. 
 
 The great majority of cases are of this nature but exhibit many differences of 
 degree. The articulation may be on the side of the metacarpus V (see Morand. 
 Mem. Ac. Sci. Paris, 1770, p. 142, fig. 4; Coll. Surg. Mus., Catal, Teratol. Ser.', 
 1872, No. 308, and numerous other cases), or of the metatarsus V (see Grurer, I. c 
 p. 476, Note 28) but in the pes this is less common. Frequently also the articulation 
 of the extra digit is on the head of the metacarpus V (Gaillard, I. c.) or metatarsus 
 V (Mus. Coll. Surg., Terat. Ser., No. 310). 
 
 In the foregoing cases the extra digit articulates immediately with the side or 
 head of metacarpal or metatarsal, but sometimes in the manus and often in the pes 
 the digit articulates at the end of a branch given off by the metacarpus (Morand. 
 ibid., fig. 3, and numerous other records), or by the metatarsus (Morand, /. c; 
 Struthers, Edin. New Phil. Jour., 1863 (2), p. 89; Meckel, J. F., Handb. d. path. 
 Anat., ii. Abth. 1, p. 36, and many more. 
 5 OS Hylobates leuciscus (Fig. 99) having an extra digit in the left manus arti- 
 
 culating externally with the metacarpus V and in the right manus articulating with 
 a branch from it. Mus. Coll. Surg., Teratol. Ser., No. 307, A. 
 
 Fig. 99. Hylobates leuciscus, No. 508, minimus of right and left manus bearing 
 a supernumerary digit articulating with the metacarpals. 
 
 (From specimen in Coll. Surg. Mus.) 
 
 (b) Complete digit having metacarpus or metatarsus external 
 
 to minimus. 
 
 Extra digits external to the minimus are occasionally complete, 
 having a metacarpal or metatarsal and three phalanges, standing 
 truly in series with the other digits, but to judge from the records 
 this complete form is decidedly rare. In the first of the following 
 examples given it should be noted that the digit standing fifth, 
 
CHAP. XIII.] 
 
 DIGITS : MAX. 
 
 34; 
 
 that is to say, as minimus, was itself rather longer than it should 
 be in the normal, thus illustrating the principle with regard to the. 
 Variation of a small terminal member of a Meristic Series on 
 becoming penultimate which was predicated especially in regard 
 to Teeth (see p. 272). In Morand's case the interesting feet of th< 
 partial assumption by the sixth digit of anatomical characters 
 proper to the minimus is commended to the attention of the 
 reader. 
 
 *i 
 
 .09. 
 
 *r 
 
 510. 
 
 Girl : one extra digit on the external side of each hand. The 
 normal little fingers are rather longer than usual and the extra lingers 
 have nearly the same length. Each has three phalanges. Neither of 
 the extra fingers can be moved separately from the finger adjacent to 
 it. In the left hand the extra finger is borne on a supernumerary meta- 
 carpal which lies parallel with the normal metacarpal V. Each extra 
 digit can be opposed to the pollex. In the right hand the extra finger 
 is borne on the enlarged head of the fifth metacarpal. Beraxger, Bull. 
 Soc. d > A?ithrop., Paris, 1887, Ser. 3, x. p. 600. 
 
 Man (parents normal, one brother had six digits on each extremity, 
 six other members of family normal) having an extra digit external to 
 minimus on both hands (Fig. 100) and both feet, in series with the 
 normal digits. 
 
 Left hand: unciform abnormally large, having two articular facets, 
 one for the metacarpal of the fifth and the other for that of the sixth 
 digit. The sixth metacarpal bears a digit of three phalanges of which 
 the second and third were very short. [It does not appear that V was 
 of increased length.] Bight hand : metacarpals normal in number, but 
 the fifth is very thick, having in its peripheral third on the external 
 
 R L 
 
 Fig. 100. Palmar views of the bones of the hands of No. 510. 
 
 (After Otto and Mokand.) 
 
348 M ERISTIC VARIATION. [part i 
 
 surface an articulation for a short digit of three phalanges, the second 
 and third being very small. Feet : well formed ; cuboid of size greater 
 than the normal, bearing the proximal end of two united fifth and sixth 
 metatarsals. Each of these is separate peripherally and bears a digit 
 [of 3 phalanges to judge from the figure (fig. 6)] in series with the 
 normal toes, but shorter than the minimus. 
 
 Muscles. In the left hand the sixth digit was fully supplied with 
 muscles. There were two extra interossei and the extensor communis 
 sent tendons to the sixth digit. The abductor, the flexor brevis and 
 the flexor ossis metacarpi which in the normal are proper to the minimus 
 were all inserted into the sixth digit instead. 
 
 In the right hand the extensor communis gave a tendon to the sixth, 
 which also possessed a proper abductor, but the fifth had no special 
 extensor. Of the flexors the sublimis gave a tendon to each of the 
 digits index, medius and annularis, none to the fifth, but a small slip 
 to the sixth. The flexor profundus gave four tendons as usual, but 
 from that going to the fifth a small tendon passes off laterally and 
 piercing the sublimis is inserted as usual. 
 
 In both feet the muscles were similar. The extensor longus gave a 
 
 tendon to the sixth digit, and the extensor brevis does not. The flexor 
 
 longus has four tendons as usual, none going to the sixth digit ; the 
 
 flexor brevis has four normal tendons and an extra one for the sixth. 
 
 The two tendons proper to the fifth (minimus) go to the sixth. The 
 
 interossei are normal and there are only two lumbricales, one for the 
 
 second digit and one for the fourth. Morand 1 , Mem. de V Acad. Roy. 
 
 des Sci., Paris, 1770, p. 142, Figs. 1, 2, 4, 5 and 6. [The condition of 
 
 the muscles in regard to the fifth and sixth digits in this case is worthy 
 
 of special attention. If the morphologist will here propose to himself 
 
 the question which is the extra digit, he will find it unanswerable. In 
 
 the right hand, judging from the bones, it may seem evident that the 
 
 fifth with its complete metacarpal is the minimus and that the sixth is 
 
 a new structure ; but the condition of the feet and the right hand taken 
 
 with that of the left, make a series or progression from which the 
 
 similarity of the variation in each of the three states is evident; hence, 
 
 if it is thought that the most external digit in the right hand is the 
 
 extra part, it must also be held that the external or sixth digit in the 
 
 left hand is the extra digit. But this digit in respect of its muscles has 
 
 some of the points of structure peculiar to a minimus, while the fifth 
 
 digit or supposed minimus on the contrary is without these characters. 
 
 Hence neither digit is the minimus. Just as in the Condition III (see 
 
 p. 326) of the hand, we saw that on the presence of a digit internal to the 
 
 pollex, the pollex itself may be promoted to be a fingerdike digit with 
 
 three phalanges, so may the fifth digit be partially fashioned as a more 
 
 1 The .similar descriptions and figures given by Otto, I.e., PI. xxv. figs. 9 — 11, 
 Seerig, Vb. angeb. Verwachs. d. Finger u. Zelien, Ammon, Die angeb. Kr. d. Mensch., 
 all refer, I believe, to this one original case of Morand's, though the fact is not 
 stated and though several authors (Gruber, &c.) quote thern as separate cases. 
 Seerig states that his figures are from preparations in the Breslau Museum. These 
 figures agree exactly with those of Otto, which again agree closely with those of 
 Morand but give more detail as to the carpi, taken no doubt from the actual 
 specimens which had been acquired by the Breslau collection. I have therefore 
 copied Otto's figures, though taking the important descriptions from Morand. 
 
chap. XIII.] DOUBLE-THUMBS : MAX. 349 
 
 central digit on the presence of a digit external to it. If therefore it 
 
 be still called the "minimus" this term can only be applied to it by 
 virtue of its ordinal position. ' 
 
 For other cases of complete digits in this position see Auvard, Arch, de Tocologie 
 xv. 1888, p. 633; Marsh, Lancet, 1889 (2), p. 739. 
 
 (1) B. Single extra digit in other positions. 
 
 Apart from cases of extra digit external to the minimus, cases of duplication of 
 the pollex or hallux (to be considered below), and cases of extra digits internal to 
 the pollex or hallux associated with change of symmetry of the digital Beries, the 
 remaining cases of single extra digit are very few. In other words, it is with digits 
 as with Meristic series in general, when a new member is added, the addition taking 
 place in such a way that homologies may be recognized, it is most often at on* 
 the ends of the series that the addition is made. Cases of extra digits in other 
 positions are in Man and Apes very rare, and even in some of the few recorded < 
 of a new digit arising on the inner side of the minimus (No. 511) it should be re- 
 membered that this inner digit is judged to be the extra one rather than the outer 
 mainly by reason of its smaller size. I can only give particulars of few such cases, 
 and of the remainder no details are available. 
 
 *511. Simia satyrus (Orang-utan), having a rudimentary extra digit arising from the 
 internal side of the minimus of each hand: feet normal. In the left manus the 
 minimus has all joints moveable as usual ; the first phalanx is normal, but the 
 second is bent outwards nearly at right angles, thus making room for an extra digit 
 arising from the first phalanx and directed inwards. This digit is fixed and has no 
 articulation and no nail, but it is in its outer part bent back again towards the 
 minimus with which it is webbed. The structure in the right manus is almost the 
 same but the extra digit is larger and in its outer part free from the minimus, 
 bearing a nail. Bolau, Verh. naturw. Ver. Hamburg, 1879, N. P. in. p. 119. 
 512. Woman: left pes bearing an extra digit articulating by an imperfect metatarsal 
 with outside of metatarsal of IV. The extra digit stands obliquely to the others, 
 sloping outwards and being attached by ligaments to the normal V. [The Cata- 
 logue states that the extra digit resembles a right digit, but I see no sufficient 
 evidence of this.] C. S. M., Ter. Cat. 312. 
 
 [A case perhaps similar to foregoing is briefly quoted by Gruber, I.e., p. 471, 
 note 83, as being in the Vienna Museum of Anatomy.] 
 
 512(2. Child: left metacarpal IV bore a supernumerary digit on external side. This 
 digit was shorter than the digit IV and was completely webbed to it. Broca, 
 
 *ki «)7 <l uoted h J Tort, I.e., p. 66. 
 
 ' DiZb. Foetus (otherwise abnormal) : left hand bore extra digit attached by peduncle to 
 first phalanx of digit IV. The minimus was separated from IV by a metacarpal 
 space, standing almost at right angles to it. Hennig, Sitzb. naturf. Qes. Leipzig, 
 1888. Oct. 9. 
 
 [Ammon (Die angeb. Krankh. d. Hensch. p. 101, PI. xxn. fig. 7) describes a 
 rudimentary finger appended to the "ring-finger" and is so quoted by * rBUBl a; but 
 the figure apparently represents the appendage as attached to the minimus.] 
 
 (2) Duplication 1 of single Digits, especially of the Pollex and Hollas. 
 
 *513. Duplication of the pollex or of the hallux is one of the commonest 
 forms of polydactylism and numerous cases have been described by all 
 who have dealt with the subject. It consists in the development of 
 two digits, complete or incomplete, in the position of the usually single 
 series of bones composing the pollex (or hallux). In the section dealing 
 with polydactylism associated with change of Symmetry (p. 326 we 
 saw how upon the appearance of an extra digit in this position the 
 thumb itself may have three phalanges. In these cases the extra digit 
 may properly be considered as arising in Successive Series with the 
 
 1 A few cases are thought by some to shew triplication of digits, but i: 
 doubtful whether there is a case of division of one digit into three really equivalent 
 
 digits, perhaps excepting the thumb of No. 521. 
 
350 MEMSTIC VARIATION. [part i. 
 
 pollex. But in a large majority of cases of the presence of an extra 
 digit on the radial side, the thumb has two phalanges as usual. Upon 
 a review of the evidence it is I think clear that we shall be right in 
 considering that in most of these cases the extra digit is not really in 
 Succession to the thumb, but that the two radial digits together repre- 
 sent the thumb, the increase in number being achieved by duplication 
 and not by successive addition. 
 
 Most authors (Gruber, etc.) thus speak of these formations as 
 "double-thumbs" and recognize them as examples of duplicity, but it 
 should be remembered that this view of their nature is not consistent 
 with any statement that either of the two digits is the extra one. If 
 these thumbs are instances of duplicity then both together represent 
 the normally single thumb. 
 
 In clear cases of double-thumb the two thumbs are equal or nearly 
 equal in size and development, as commonly happens in cases of true 
 duplicity. Double-thumbs are known in every degree of completeness. 
 The division between the two may occur at any point in their length. 
 Thus the duplicity may be confined to the nail and first phalanx 
 (Otto, Monstr. sexc. Descrip., Taf. xxv. fig. 1 ; Birnbaum, Monatsschr. 
 f. Geburtsk., 1860, xvi. p. 467); or it may include both first and second 
 phalanges (Gruber, Arch. f. path. Anat. Phys. x xxxn. 1865, p. 223); or 
 both phalanges and the greater part of the metacarpal (Gaillard, 
 Mem. Soc. de biol., 1861, p. 325); or even the whole digit and meta- 
 carpus, the two thumbs separately articulating with the trapezium 
 (Joseph, quoted by Gruber, I. c, p. 463, Note 37). It would be 
 interesting to know which of these conditions is the most frequent, for 
 it is likely that between the degrees of this variation there is Dis- 
 continuity, but the point is not easy to determine. As regards records 
 the conditions first and last named are much the rarest, and the double- 
 thumbs with two sets of phalanges articulating with one metacarpal 
 constitute the majority of cases. 
 
 Sometimes the two thumbs are webbed together (Gruber, Bull. Ac. 
 Sci. Pet. xv. p. 480, fig.) sometimes they are separate and may be 
 
 Fig. 101. Eight hand having a thumb double from the metacarpus, shewing the 
 relationship of images between the- two thumbs. (After Annandale.) 
 
CHAP. XIII.] 
 
 DOUBLE-THUMBS : MAN. 
 
 351 
 
 opposed to each other (Fackenheim, Jen. Zts., xxn. p. 358, fi". IV . ■ 
 Axnandale, Diseases of Fingers and Toes, PI. in. fig. 25). This con- 
 dition is important as an indication that between these double-thumb- 
 there may be a relation of images (Fig. 101). 
 
 The duplicity may be and often is very different in decree in the 
 two hands, though it is very commonly present in both. 
 
 514. The description given of duplicity in the pollex applies equally to 
 the hallux, though of duplicity in the latter perhaps fewer cases are re- 
 corded. Here too the duplicity may be in all degrees of completeness. 
 An example from Anxandale (I. c, PL in. fig. 32) is shewn in Fig. 102. 
 
 Fig. 102. Feet of infant, No. 514, having thumb-like supernumerary digits 
 arising from the metatarsi of the great toes. 
 
 (After Annandale.) 
 
 Here a thumb-like extra hallux is borne on the inner side of the meta- 
 tarsal I. Several such cases are known (cp. No. 517). 
 
 5X5. Among the cases called by authors "double-thumb" are a certain 
 number in which the two thumbs are not equally developed, that on 
 the radial side being more rudimentary. In such a case we are entitled 
 to consider the radial thumb as an extra digit formed in Succession to 
 the normal thumb, and not as a double of it. In speaking of other 
 Meristic Series (especially mammae and teeth) we have seen that it is 
 not possible accurately to distinguish between cases of duplicity and 
 cases of change in number of the series by formation of another 
 member in the Succession. This is extremely well seen in digits. For 
 firstly several conditions intermediate between the two are recorded by 
 many authors (e.g. a case in which the radial thumb had two phalanges 
 "ankylosed" together [or rather not completely segmented from each 
 other]. Gruber, I.e., p. 480; cases in which the radial thumb had 
 only one phalanx, ibid., p. 482; Strutiiers, Edin. New Phil. J-->>r., 
 1863 (2), p. 87; Boulian, Rec. de Mem. de Mid. milit., 1865, Ser. 3, 
 xiii. p. 67, jigs.); and besides this there are several examples in which 
 one hand bore a clear pair of double-thumbs, while in the other hand 
 there is an extra radial digit in succession to the normal thumb (e.g. 
 
352 MERISTIC VARIATION. [part i. 
 
 Fackexheim, I.e., p. 359, fig. iv.). Thus do the two conditions pass 
 into each other, though some cases are clearly cases of duplicity and 
 some are clearly cases of extra digit in Succession 1 , 
 
 I know no case of unmistakeable duplicity in any digit but pollex or 
 hallux ; but no doubt a good many cases of extra digit arising from the 
 minimus may be of this nature (e.g. Annandale, PI. ill., fig. 28), though 
 it is more likely that the extra digit is in Succession. 
 
 In digits other than I or V the only case of possible duplicity known 
 to me as occurring in a limb not exhibiting one of the complex conditions 
 of polydactylism, are those of Streng ( Viertelja.hr sschrift f prakt. Heilk.. 
 xlix. 1856, p. 178; original not seen by me; quoted by Gruber, 
 p. 476), being a case apparently of double medius on one metacarpal ; 
 and of Dusseau, Cat. Mus. Vrolik, No. 518, two terminal phalanges on 
 right medius (together with double thumb ; six fingers on left hand 
 and peripheral duplicity of hallux in each foot). Accompanied by 
 numerical Variation in other parts of the digital series such cases 
 of duplicity are known in a few other cases. 
 
 (3) Combinations of the foregoing. 
 
 Limbs not rarely present the forms of polydactylism already named 
 in combination. Such combination may be found in the same limb, or 
 one or more limbs may present one form, while another form may be 
 found in the other limb or limbs. Of these combinations the following- 
 three cases will be sufficient illustration. 
 
 Case of double hallux on each foot, and rudimentary digit attached by 
 peduncle to the minimus of each hand. 
 
 516. A female member of a polydactyle family [particulars given] had an abortive 
 supernumerary finger attached by a peduncle to the little finger of each hand. In 
 the feet the two great toes were each partially double. In the left great toe the 
 individual phalanges could be felt and there were two nails. In the great toe 
 of the right foot the adjacent sets of phalanges were inseparably united by their 
 lateral borders, forming one bone, which was correspondingly broadened. There 
 was only one nail which was notched in the middle of its free border. Mum, J. 
 S., Glasgow Med. Jour., 1884, N. S. xxi. p. 420, Plate. 
 
 Case of each extremity with double pollex or hallux and rudimentary 
 digit attached to minimus. 
 
 517. Female infant having thumb of each hand double, the two sets of bones lying in 
 the same skin and connective tissue. In the right hand the nails and phalanges of 
 each were quite distinct, but it was not certain whether the metacarpals were 
 separate or not. In the left hand the nails were not completely separate and the 
 phalanges of the two thumbs were less distinctly separate. To the first phalanx of 
 the little finger of each hand was appended a rudimentary bud- like finger, hanging 
 by a peduncle. 
 
 The feet resembled the hands. From the inner border of the metatarsal of each 
 great toe there proceeded a well-formed thumb-like toe with two phalanges. This 
 toe was set at right angles to the great toe and could be flexed and to some extent 
 opposed. On the external border of the right foot there was a small extra little toe 
 hanging by a peduncle from the metacarpal V. In the left foot the supernumerary 
 little toe was bound up with the normal little toe for its whole length. Hagenbach, 
 E., Jahrb.f. Kinderheilk., xiv. 1879, p. 234,^*. [Cp. No. 514.] 
 
 1 Compare with the largely similar series of phenomena seen in the foot of the 
 Dorking fowl (v. infra). But in it if the two hallucal digits are not a true pair it is 
 most commonly the inner that is the largest, conversely, to the general rule in 
 the extra digits arising from the pollex in Man. 
 
chap, xiil] IRREGULAR POLYDACTYLISM : MAX. 353 
 
 Case of double hallux in combination ivith extra digits on external 
 side. 
 
 518. Man in Middlesex Hospital, 1834, having on the right foot two 
 toes articulating with the first metatarsal, and ou the left foot two toes 
 articulating with the first metatarsal, and also two toes articulating 
 with the fifth metatarsal. From the ulnar side of one of his hands 
 two fingers had been removed. In each hand the middle and ring 
 fingers were adherent throughout their length, as also were all the toes, 
 except the minimi. Five brothers and three out of four sisters of this 
 man had six toes on each foot and six fingers on each hand. The other 
 sister had seven toes on one foot and six on the other, and had two extra 
 fingers on each hand. London Med. Gaz., 1834, April, p. 65, figs. 
 
 (4) Irregular examples. 
 
 Thus far we have considered cases of polydactylisra that can be in 
 some degree brought into order and included in general descriptions. 
 There remain a small number of irregular cases each presenting special 
 features which make general treatment inapplicable. These cases are 
 instances of extremities, mostly feet, having seven, eight or nine digit-. 
 The descriptions of these cases are for the most part fragmentary, and 
 as the bones have been examined in only one of them (Moraxd) so far 
 as I am aware, the relations of the digits to each other and to the limb 
 are obscure. Speaking generally in these irregular examples there is 
 an appearance of division, possibly of duplication, of several digit-. It 
 should be noticed also that in some of them (e.g. Blasius, No. 520) the 
 digits did not lie evenly in one plane but were in a manner bunched up 
 so as to overlie each other. In such a case it would be interesting 
 to know whether the digits originally grew in one plane and were 
 afterwards shifted during growth, or whether the original Repetition 
 was thus irregular. 
 
 As all these cases differ from each other an adequate account of 
 them could only be given at great length, and by reproducing the 
 original descriptions in full, together with such figures as are attainable. 
 For these reasons it would not be profitable to introduce them here, 
 though in a study of the nature of Meristic Repetition it is important 
 to remember that these irregular cases exist. As illustrative of several 
 cases I have appended an account of two complex cases in the foot and 
 of one in the hand, giving references to such others as I am acquainted 
 with. 
 
 19*. Girl, set. 6, having abnormal toes on the left foot as follows (Fig. 103). The total 
 number of toes on the left foot was nine. From the position and form it appeared 
 that the digits (6—9) representing II, III, IV and V were normal, bat upon th< 
 radial side of these instead of a single hallux there were five toes. ( >f these 1 and 2 
 were imperfectly separated, articulating with the first metatarsal bj their first 
 phalanges, which were united to form a common proximal head. Bach had a 
 distinct second phalanx and in general form resembled a great toe having a separate 
 nail. The second metacarpal bore firstly a pair of toes, 3 and 4, which were still 
 less separate from each other than 1 and 2, the biridity being oonfined to the soft 
 parts. These two toes had one proximal and one distal phalanx in oommon. The 
 second metatarsal also bore an external digit, 5, which in form ratlin reaembli d a 
 normal third digit, being considerably shorter than »'• [and presumably oontaining 
 three phalanges]. The toes 1, 2, 3 and 4 were found alter amputation to be devoid 
 of muscles and presented onlv the terminations of the tlexor and extensor tendons 
 
 b. 23 
 
354 MERISTIC VARIATION. [part i. 
 
 having their normal insertions. The toes 1 and 2 were supplied by the same flexor 
 tendon which bifurcates and passes to be inserted into the ultimate phalanx of each 
 
 / H 
 Fig. 103. Foot of No. 519. (After Athol Johnson.) 
 
 by a separate slip. The vinculum by which it is attached is common to the two 
 bones. Johnson, Athol A., Trans. Path. Soc, ix. 1858, p. 427, fig. 
 
 520. Male infant having supernumerary toes on the left foot, The tarsus and meta- 
 tarsus were abnormally wide. The hallux appeared externally to be divided into 
 two. This duplicity was most marked in the second phalanx and appeared in a 
 slight infolding of the skin. The nail also shewed traces of duplicity. Next to the 
 hallux were two toes which were bent upwards and inwards. Of these the one 
 overlay the other. The uppermost was found after excision to have two sets of 
 phalangeal bones enclosed in the same skin ; these two articulated with a single 
 metatarsal bone. The lower toe was thought by Blasius to represent the digit II. 
 Next to this there was a rudimentary digit with a slightly developed nail. After 
 excision it was found that this toe contained a cartilaginous basis which was partly 
 segmented into two phalanges and articulated with a metatarsal. External to this 
 rudimentary toe were three normal toes, representing as Blasius supposes, the 
 digits III, IV and V. External to the putative V was another digit of the same size 
 and shape. Blasius, v. SiebohVs Jour. f. Geburtsh., xiii. 1834, p. 131, figs. 1 and 
 2 ; figures copied in Ahlfeld, Jlissb. d. Mensch., Taf. xx. fig. 11. [This foot appears 
 to contain parts of ten digits.] 
 
 521. Child having polydactyle hands as follows. In each hand the fingers were 
 webbed to the tips, each minimus having an extra nail. In the right hand the 
 pollex was triplicate, having three sets of phalanges and three nails, the whole being 
 in a common integument. In the left hand the pollex was duplicate, having two 
 sets of phalanges webbed together and two nails. Each member thus formed a 
 prehensile paw. In right foot little toe webbed to next toe. Some (not all) of 
 brothers and sisters had similar hands : father and grandfather had similar hands : 
 mother and grandmother normal. Harker, J., Lancet, 1865 (2), p. 389, ^.g. 
 
 522. The following are other examples of irregular polydactylism : Morand, Mem. 
 Ac. Sci. Paris, 1770, p. 139, figs. 8 and 9. (The same redescribed from Morand's 
 figure by Delplanque, Etudes Teratol., n. Douai, 1869, p. 67, PI. v. ; and again by 
 Lavocat, Mem. Ac. Sci. Toulouse, v. 1873, p. 281, PI. i., who takes a different view.) 
 
 Gruber, Mem. Ac. Sci. Pet., Ser. vn. Tom. n. No. 2 (fig. copied in Bull. Ac. Sci. 
 Pet., xv. 1871, fig. 6, and by Ahlfeld, Missb. d. Mensch., PI. xx. fig. 20). 
 
 Gruber, Bull. Ac. Sci. Pet., xv. 1871, p. 367, figs. 4 and 5. 
 
 Otto, I.e., PI. xxvi. figs. 8 — 11. 
 
 Froriep, Neue Notizen, d)c., Weimar, No. 67, 1838, iv. p. 8, figs. 4 — 8 (very brief 
 account of important case, copied by Ahlfeld and others). 
 
 Du Cauroi, Jour, des Scavans, 1696 (pub. 1697), p. 81 (quoted first by Morand, 
 afterwards wrongly quoted by many writers. Dwight, Mem. Bost. N. H. S., iv. 
 
chap, xiil] REDUCTION OF DIGITS : MAX. 355 
 
 No. x. p. 474, supposes that this is a case of double-hand, palm to palm (as No. 503), 
 but the original probably means that two adjacent thumbs and two adjacent annu- 
 lares were united, the digits being all in one plane). 
 
 Popham, Dull. Quart. J. of Med. Sci., xliv. 1867, p. 481. 
 
 Dusseau, Cat. JIus. Vrolik, 1865, p. 457 (very brief, see p. 352). 
 
 Graxdelemext, Gaz. des hop., 1861, p. 553. 
 
 Lisfraxc (see Schm. Jahrb., xn. 1836, p. 263). 
 
 Eorberg, Jour. f. Kinderkr., xxxv. 1860, p. 426. 
 
 Mabjoltn, Bull. Soc. de Chir., 1866, Ser. 2, vi. p. 505, jig. (probably case of double- 
 hand). 
 
 Annandale, Bis. of Fingers and Toes, 1865, p. 39 (eight metatarsals on a foot 
 possibly associated with change of Symmetry). 
 
 Ibid., p. 35, figs. 41 and 49 (pollex with two sets of phalanges but three nails, 
 together with extra digit external to V). Cp. No. 521. 
 
 Heyxold, Vireh. Arch., 1878, lxxii. p. 502, PL vn. 
 
 Mason, F., Trans. Path. Soc., 1879, xxx. p. 583 (foot having eight metatarsals 
 and nine digits). 
 
 Melde, Ft., Anat. Unters. eines Kindes mit beiders. Befekt d. Tibia u. Poly- 
 dactylic an Hdnden u. Fiisseti, Inaug. Diss., Marburg, 1892 (important). 
 
 REDUCTION IN NUMBER OF DIGITS. 
 
 Though in reduction of digits the course of Variation is generally 
 irregular and the result often largely amorphous there are still features 
 in the evidence which may be of use to us, and a few selected cases are 
 of some interest. These features will be sjDoken of under the three 
 following heads, though for a general view of the subject reference 
 must be made to teratological works. 
 
 (1) Reduction in number of phalanges. 
 
 ( 2 ) Syndactylism. 
 
 (3) Ectrodactylism. 
 
 (1) Reduction in number of phalanges. 
 
 As in certain cases of polydactylism it appeared that increase in the 
 number of phalanges in the thumb could be regarded as a step in the 
 direction of increase in the number of digits, so a reduction may be 
 thought to be a step towards diminution in the number of digits. But 
 though many cases of reduction in number of phalanges are recorded, 
 there is in them nothing which suggests that they may be fitted into a 
 series of gradual reduction comparable with the series of gradual 
 increase already described. It is indeed chiefly as illustrating the 
 possible completeness and perfection of Variation that these phenomena 
 have a direct bearing on the subject of Meristie Variation, The 
 following case is chosen as being especially regular and symmetrical. 
 
 *523. ^ an having only one phalanx in each hallux, and two in each of the other 
 fingers and toes. The hands were almost exactly alike. The thumb had a 
 short metacarpal fin: long, and one phalanx (11 in.), the joint between them 
 being loose as if composed of soft tissue. Uy the length of the metacarpal (Sin.) 
 the index is longer than the other digits. The next two metacarpals have only half 
 that length. The metacarpal of V is l.lin. long, but from its obliquity does not 
 project so far as that of IV. The proximal phalanx of the index measnn I , mediae 
 I:, annularis 1, minimus 1^. The distal phalanx in index and middle |, ring and 
 little | in. In left hand the distal phalanx of index is proportionally short. r. 
 Except the index all the dibits present their usual proportions. The feet are well 
 formed as far as distal ends of metatarsals. The toes are short, pulpy and loosely 
 articulated. Each has two phalanges except the hallux, which has only cue. This 
 case was a twin with a normal male. An elder brother and younger sister have the 
 
 23—2 
 
356 MERISTIC VARIATION. [part i. 
 
 digits similarly formed, but in the last the feet are also turned in. Struthers. 
 Edin. New Phil. Jour., 1863 (2), p. 100. 
 
 As an example of similar and simultaneous Variation in both extremities this is 
 an instructive case. 
 
 (2) Syndactylism. 
 
 Under this name have been described those cases in which two 
 or more digits are to a greater or less extent united together. In 
 their bearing on the morphology of Repeated Parts some of these 
 variations are very instructive. It will be found that the impor- 
 tant considerations in this evidence may be divided into two parts. 
 Of these the first concerns the manner of the variation and the 
 second to the position in which it is most commonly found. 
 
 The manner of union betiveen digits. 
 
 In many cases of union of digits the limb is amorphous ; with 
 these we have now no special concern. In simpler examples the digits 
 may be of normal form but some or all of them may be united by a 
 web of integument for a part or the whole of their length. (For 
 records of such cases see Fort, Axxaxdale, &c). 
 *524. But besides these cases of webbing are many in which the union 
 may be of a much more intimate character. Taking the cases together 
 a progressive series may be arranged shewing every condition, beginning 
 from an imperfect webbing together of the proximal phalanges to the 
 state in which two digits are intimately united even in their bones, and 
 perhaps even to the condition in which two digits are represented by a 
 single digit (see No. 529). That the latter condition represents a phase 
 in this series of variations does not seem to be generally recognized by 
 those who have dealt with the subject but it is impossible to exclude it. 
 
 The lower conditions of this variation are sufficiently illustrated by 
 Fig. 104, I and II (from Anxaxdale, Diseases of Fingers and Toes, 
 figs. 39 and 33), shewing cases of medius and annularis partially com- 
 bined for the whole of their length. A higher condition is shewn in 
 Fig. 104, III, in which the same digits are united so closely that their 
 external appearance suggests that only four digits are present in the 
 hand. In this specimen (Anxaxdale, I. c, p. 14) there were neverthe- 
 less five metacarpals, but the first phalanges of III and IV were united 
 peripherally and bore a second and third phalanx and one nail common 
 to them both. The same author (I. c. fig. 44) gives an illustration of 
 such a set of bones from Otto 1 . 
 
 The following cases are interesting as occurring in Apes. 
 
 *525. Pithecia satanas (Monkey) : young male having the third and fourth digits of 
 the hand on each side completely connected by a fold of nude skin. The remain- 
 ing digits of the hands and feet were normal. Forbes, W. A., P. Z. S., 1882, 
 p. 442. 
 526. Macacus cynomologus : specimen having the fifth finger of the right hand 
 represented by a rudiment only. On dissection the first phalanx of the fifth finger 
 was found to be enclosed with that of the fourth. All the fingers of the abnormal 
 (right) hand were somewhat misshapen and bore several exostoses. [? congenital 
 variation] Fbiedlowsky, A., Verh. zool. hot. Ges. Wien, 1870, xx. p. 1017, Plate. 
 
 1 I have failed to find the original of this figure in Otto's works. 
 
CHAP. XIII.] 
 
 UNION OF DIGITS : MAN. 
 
 357 
 
 Before going further certain points are to be noted. First, the 
 union as shewn in the figures is a union or compounding as of optical 
 
 I 
 
 D 
 
 IV 
 
 Fig. 104. Cases of syndactylism. I, II and III. A progressive series illus- 
 trating degrees in the union of medius and annularis in the hand. IV. Case of 
 union of index and medius of the foot. The union is incomplete peripherally. 
 
 (After Axxandale.) 
 
 images in Bilateral Series, and is not like that of parts in Succc»m\ <■ 
 Series. Next, the union of the bones is more complete /» rxphi rally and 
 less complete centrally. The latter is a rule very commonly observed in 
 cases of the union of the bones of digits both in Man ami other mam- 
 mals. This statement is made without prejudice to the other let that 
 in the least state of syndactylism as manifested by union of the Bofl 
 parts, it is the most central phalanges which are united. Such a case 
 of partial union between II and T FT in the foot' is shewn in Pig. 1" 1. I V 
 (Axnaxdale, /. c, fig. 34). The rule that in the Lowest condition o! 
 syndactylism of the bones it is commonly at the periphery thai the 
 union is most complete is also difficult bo understand in connexion with 
 
 1 Compare several remarkable cases of this variation in one family, lb Clkbo, 
 M€m. hoc. Linn. Normandie, ix. p. xxvi. 
 
358 MERISTIC VARIATION. [part i. 
 
 the fact that the division of digits in the lowest forms of polydactylism 
 appears also first in the peripheral phalanges. These phenomena appear 
 to be in contradiction to each other, and I am not aware that the fact 
 of the appearance of the digits early in the development of the limb 
 throws any light on the difficulty. 
 
 The number of digits which may be thus united is not limited to 
 two, and examples of intimate union between three and even four digits 
 are common. 
 
 The position of union. 
 
 *527. Those who have treated of this subject do not, so far as I am aware, 
 notice the fact that the phenomenon of Syndactylism most frequently 
 affects particular digits. From an examination of the recorded cases 
 it appears that in the hand there is a considerable preponderance of 
 cases of union between the digits III and IV. I regret that I have 
 not material for a good analysis of the evidence on this point, but I 
 may mention meanwhile that in a collection taken at random of some 
 thirty-five cases of hands having only two digits united (chiefly those 
 given by Fort and Annandale) over 25 are cases of union of the digits 
 III and IV ' ; in only one were the digits I and II united ; the digits 
 II and III in 1 4 cases ; the digits IV and V in 1 3 cases. 
 
 *528. On the other hand if two digits in the foot are united they are 
 nearly ahvays II and III. 
 
 If in the hand three digits are joined they may be either III, IV 
 and V, or (perhaps less commonly) II, III and IV. In cases of union 
 of all the digits II to V, the digits III and IV are often much more 
 intimately united than the others, and are often recorded as having a 
 common nail, while II and V have separate nails. 
 
 This question of the comparative frequency of the different forms of 
 syndactylism would probably repay full investigation, and to the study 
 of the mechanics of Division it would clearly be important. In the 
 meantime may be noted the fact that the evidence suggests the possi- 
 bility that we have here to do with a case of union of parts which are 
 related to each other as optical images, and that the digits II to V of 
 the hand constitute an imperfect Minor Symmetry within themselves. 
 The fact that the subjects of most frequent union in the foot are the 
 digits II and III, not the digits III and IV as in the hand, may be 
 connected with the fact that the hallux stands to the foot in a different 
 geometrical relation from that which the pollex bears to the hand and 
 that consequently the axes of Symmetry are different in it. 
 
 (3) Absence of digits (Ectrodactylism). 
 
 In the conditions already described though the digits are not all 
 clearly divided from each other yet no one wdiole digit can be supposed 
 to be absent. Even in the specimen shewn in Fig. 104, II, from the 
 presence of separate metacarpals III and IV the identity of the several 
 digits is still easily recognized. These simplest cases however by no 
 means exhibit all the phenomena. From a large group of cases the 
 three following are chosen as each illustrating a distinct possibility. 
 
 1 Owing to the ambiguity of some records as to the similarity of the condition 
 in the right and left hands I cannot give exact numbers. 
 
chap, xiil] ONE DIGIT STANDING FOR TWO. 
 
 359 
 
 Upon the morphological questions arising out of these facts comment 
 will be made when the whole subject of numerical Variation of digits 
 is discussed. 
 
 *x 
 
 529. 
 
 Representation of digits II and III of the pes by one digit. 
 
 Man having four digits in the right foot as shewn in Fig. 105. The calcaneum. 
 astragalus, navicular, first (internal) cuneiform and cuboid were normal. The 
 navicular had on its peripheral surface three facets as usual. The second and third 
 cuneiforms were completely united to form one bone which bore no traces of its 
 double nature as shewn in the figure (c 2 + c 3 ). The peripheral surfaces of both form 
 one plane. Taking the four digits in order, the minimus has its normal form and 
 tarsal relations. The digit next to it has the normal form and relations of a dijnt IV. 
 
 n+m 
 
 Fig. 105. Bones of the right foot of No. 529. I, 
 apparently representing index and medius. IV, annularis. 
 
 hallux. 11^- III, digit 
 V, minimus, a, astra- 
 c 3 , bone apparently 
 representing the middle and external cuneiforms. (After Gruber.) 
 
 galus. sc, navicular, cb, cuboid, c 1 , internal cuneiform, c 2 
 
 *x 
 
 530, 
 
 Internal to this is a metatarsal of abnormal thickness articulating with the single 
 bone presumably representing the external and middle cuneiforms. This metatar- 
 sus presented no trace of duplicity. It bore a digit of three phalanges of more than 
 normal thickness but otherwise normal. The hallux was normal, having two pha- 
 langes. Each of the other digits had three phalanges, but the 2nd and 3rd phalai. 
 of the minimus were ankylosed. 
 
 Of the muscles, the transversalis pedis, one of the lumbricales, one of the inter- 
 ossei dorsales and one of the interossei plantares were absent. The extensor and 
 flexor longus each had three tendons. [Detailed description of bones and soft parts 
 given.] Gruber, W., Virch. Arch. f. path. Anat. u. PJn/s., 1869, xi.yii. [p. :>04. 
 
 PI. VIII. 
 
 Single digit articulating with the cuboid [probably a ease of representation of 
 
 digits IV and V by one digit]. 
 
 Man having four digits on the left foot as follows. The foot is well form 
 The digits I, II and III are normal and have normal tarsal relations. The fourth 
 digit has a well-formed metatarsal and three phalanges. The hones are perhaps 
 rather more robust than those of a normal fifth digit, but the nit tatarsal has the 
 normal tuberosity at the base strongly developed. This metatarsal articulates with 
 a cuboid of somewhat reduced size having only onv articular facet on it- peripheral 
 surface. The other parts were all normal, and even in the muscular BVstem only a 
 trifling abnormality was found. Parents normal. Stkintiiu.. C. P., Virch. Arch, 
 f. path. Anat. u. Phys., 1887, cix. p. 347. 
 
360 MEMSTIC VARIATION. [part l 
 
 Reduction of digit IV of pes. 
 
 '531. [This case is introduced here for comparison with the last.] A left foot having 
 abnormalities as follows. Calcaneum, astragalus, internal cuneiform normal in size 
 and shape. The second cuneiform is rather broader than usual, but the surface 
 which it presents to the internal cuneiform has all the characters of a middle cunei- 
 form. External to this middle cuneiform is only one large tarsal bone in the distal 
 row. This bone presents no clear sign of duplicity, but from its form and relations 
 it appeared that it represented both the cuboid and the ecto-cuneiform. The hallux 
 and digit II have approximately normal relations. The large cuboid-like bone 
 bears externally a metatarsal agreeing in shape with a metatarsal V ; and internal 
 to this the same tarsal bone bears another metatarsal which upon its external side 
 gives off yet another metatarsal of reduced size. Each of the five metatarsals bore 
 a digit, but the digits of the minimus and of the slender IV were webbed together. 
 [Full details given.] Brenner, A., Virch. Arch. f. path. Anat. u. Phys., 1883, xciv. 
 p. '23, PL ii. 
 
 532. Besides these simpler cases there are very many recorded instances of reduction 
 in number of digits in which the identification of the parts is quite uncertain. From 
 the point of view of the naturalist it is worthy of remark that even in some of the 
 cases departing most widely from the normal form the limb though having only 
 three or perhaps two digits still presents an approach to a symmetry. Examples of 
 this kind are given by Guyot-Daubes {Rev. d' Anthropoid 1888, xvn. p. 541, figs.) 
 and by Fotherby (Brit. Med. Jour., 1886 (1), p. 975 figs. ) and many more. Fotherby's 
 record is interesting as relating to a family among whose members feet bearing only 
 two opposable claw-like digits of irregular form recurred for five generations. Evi- 
 dence relating to limbs of this kind is so obscure that it is not possible as yet to make 
 deductions from it, but there seems to be a general agreement among anatomists 
 that when two digits only remain one of them has the characters of a minimus. 
 
 Reference must be made also to the fact that in cases of absence of radius the 
 pollex is almost always absent. This seems to be established in very many cases. 
 The only examples of a pollex present in the absence of a radius known to me are 
 that of (jruber, Virch. Arch. f. path. Anat. u. Phys. 1865, xxxn. p. 211, and that of 
 Geissendorfer, Zur Casuistik d. congen. Radiusclefectes, Munch. 1890. 
 
 Horse. 
 
 Variation in the number of digits in the Horse 1 has been 
 repeatedly observed from the earliest times. The mode of occur- 
 rence of the change is by no means always the same, but on the 
 contrary several distinct forms of Variation may be recognized. 
 On inspection the cases may be divided into two groups. 
 
 A. Cases in which the extra digit (or digits) possesses a distinct 
 metacarpal or metatarsal. 
 
 B. Cases in which the large metacarpal or metatarsal (III) gives 
 articulation to more than one digit. 
 
 Besides these I have placed together in a third group (C) two 
 very remarkable cases which cannot be clearly assigned to either of 
 the other groups. These instances are of exceptional interest from 
 the fact that in them is exhibited a condition intermediate between 
 those of the other two groups. We have seen repeatedly that 
 
 1 In the Mule two cases have been recorded, but in the Ass I know no instance 
 of polydactylism. Describing a polydactyle horse seen on a journey in Rio Grande 
 von Jhering (Kosjjios, 1884, xiv. p. 99) states that he believes polydactyle horses to 
 be much more common in S. America than in Europe, and that most persons who 
 have travelled much in that country have met with cases. Mules between the 
 jackass and mare are bred in great numbers, but he had heard of no case in a mule. 
 
chap, xiil] digits: horse. 361 
 
 Meristic Variation may take place by division of single members 
 of Series, a phenomenon well seen in the B group ; and we have also 
 seen many cases of numerical Variation by addition to the Series 
 associated with a reconstitution, or more strictly a redistribution 
 of differentiation amongst the members of the series thus newly 
 constituted ; but here in these rare examples of the C group the 
 nature of the parts is such that it cannot be predicated that 
 the change is accomplished by either of these methods exclusively. 
 From such cases it follows that the two processes are not really 
 separable, but that they merge into each other. (Compare the 
 similar facts seen in regard to teeth p. 269, and mammae p. 1.93.) 
 
 A. Extra digits borne by distinct metacarpal or 
 
 METATARSAL. 
 
 The cases in this group may be subdivided as follows : 
 
 (1) Two digits, one being formed by the development of the 
 digit II. 
 
 a. Only three metacarpals or metatarsals (II — IV) as 
 
 usual. Common form : fore and hind limb. 
 
 b. Four metacarpals (? I — IV). Common form : anato- 
 
 mically described in fore limb only. 
 
 c. Five metacarpals (? I — V). Single case in fore limb. 
 
 (2) Tivo digits, one being formed by development of the digit IV. 
 
 Rare. 
 
 (3) Three digits; the digits II and IV both developed. Rare. 
 
 (4) Two digits; the digits II and IV both developed, III 
 
 aborted. Rare. 
 
 It will appear from the evidence that though the same varia- 
 tion is often present in the limbs of both sides this is not always 
 so. The fore and hind limbs also sometimes vary similarly and 
 simultaneously, but in other cases they do not. Different forms of 
 numerical Variation are also sometimes found on the two sides, 
 and not rarely the variation in the fore limb is different from that 
 in the hind limb. 
 
 (1) Two digits, one formed by development of the digit II. 
 
 a. Three metacarpals or metatarsals only. 
 
 To this division and to the next, (1) b, belong the greal majority 
 of cases of polydactylism in the Horse. Unfortunately most of the 
 records have .been made from living animals and contain do 
 anatomical description: in the absence of such particulars it is 
 not possible to know r whether a given case belongs to this division 
 or to the next, and it thus is impossible to determine the relative 
 frequency with which the two forms occur. 
 
 The following are given as specimen cases. 
 
362 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Forefoot 
 
 *533. Horse of common breed, having a supernumerary digit on the 
 inner side of the right fore foot (Fig. 106). 
 
 Humerus and radius: no noticeable variation. Ulna a little 
 more developed than usual ; lower end slightly broken, having 
 probably reached to lower fourth of radius. The part of the 
 inferior and external tuberosity of the radius which is usually 
 supposed to represent the ulna is larger than in the normal form. 
 
 Fig. 106. Right fore foot of Horse, 
 No. 533. 
 
 A. The leg seen from in front. 
 
 B. The carpal bones enlarged. 
 
 M, magnum, sc, scaphoid, u, unci- 
 form. t' 2 , trapezoid, t 1 , supernumerary 
 bone not found in normal, represent- 
 ing trapezium. IV, the metacarpal re- 
 presenting digit IV. Ill and II, meta- 
 carpals bearing those digits respec- 
 tively. (After Arloing.) 
 
 Carpus consisted of eight bones, instead of seven as usual. 
 Scaphoid much larger than normal ; lunar, cuneiform and pisiform 
 normal. In the lower row the magnum and unciform have normal 
 relations, but in the place of the normally single trapezoid are two 
 bones, one anterior (f), the other posterior (t 1 ). These together 
 bear the enlarged inner metacarpal (II). The posterior of these 
 bones had a short pyramidal process lying beside the inner meta- 
 carpal. This process was partially constricted off and is regarded by 
 
chap, xiii.] DIGITS : HORSE. 363 
 
 Arloing as a representative of the metacarpal I, the carpal portion 
 of the bone being the trapezium. 
 
 The outer metacarpal (IV) was perhaps slightly larger than 
 usual. 
 
 The inner metacarpal (II) was greatly enlarged at its central 
 end, articulating with the tw r o bones t 1 and t' 2 , and partly with the 
 magnum. In its central part this metacarpal was fused with the 
 large metacarpal (III) and above is united to it by ligamentous 
 fibres. Below r it again separates from the large metacarpal and 
 is enlarged, bearing an additional digit of three phalanges, the 
 lowest bearing a hoof. [This hoof is not curved towards the large 
 hoof as in many specimens described, but is convex on both sides, 
 resembling the hoof of an ass.] The large central metacarpal was 
 flattened on the side adjacent to the enlarged metacarpal II. The 
 muscles, nerves and vessels are fully described (q. v.). Arloing. 
 M. S., Ann. Sci. Nat, ZooL, Ser. V. T. vm. pp. 61 — 67, PL 
 
 534. Foal having two toes on each fore foot. The father and mother of 
 this foal w r ere both of the "variete chevaline comtoise." The foal in 
 question was the only one which this mare dropped and she died two 
 months afterwards. The foal w T as in nowise abnormal excepting for the 
 peculiarity of the fore feet. The carpus was normal and the external 
 metacarpal was rudimentary as usual and ends in a small knob. The 
 internal metacarpal is thicker than the external one and bears a digit 
 of three phalanges, the terminal phalanx bearing a small hoof. This 
 hoof is curved outwards towards the normal hoof. The ligaments and 
 tendons of the foot did not suffice to keep it stiff, and as the animal 
 walked, it not only touched the ground with the hoof but also with 
 the posterior surface of the phalanges. This led to inflammation of 
 the foot, in consequence of which the foal was killed. CORNEVIN, 
 Nouveaux cas de didactylie chez le chevcd, Lyons (1882?). [Xote that 
 this case differs from the last in the fact that the carpus was normal.] 
 
 A similar case in the right forefoot is given by Kitt. Dent. Ztsch. 
 f. Thiermed., 1886, xn. Jahresb., 1884 — 5, p. 57, Jig. 
 
 Hind foot. 
 
 Among the many accounts of polydactyle horses I know none 
 which gives an anatomical description of a case of a fully developed 
 digit II in the hind foot. The following case, indeed, is the only one 
 known to me in which an}^ facts respecting the condition of the 
 tarsus of a polydactyle horse have been ascertained. In it, as will be 
 seen, the digit II was not fully developed. 
 
 535. Horse having the metatarsal II enlarged and bearing a rudimentary 
 ' digit (Fig. 107 B and C). In the left hind foot the arrangement was as 
 
 shewui in Figs. B and C. The metatarsal II was enlarged an. 1 articulated 
 with "two united cuneiform bones" [presumably one bone with indica- 
 tions of duplicity]. Internal to this digit was a " first cuneiform bone," 
 but the digit I was not developed. The metatarsal II bore peripherally 
 a rudiment of a digit as shewn in the figure. The right hind foot was 
 similar to the left but it is stated that the "three small cuneiform 
 
364 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 bones'' were serjarate 1 , as shewn in Fig. 107 C. The fore feet of the 
 same animal were in the condition described in (1) h. [See No. 537.] 
 
 Marsh, 0. C, Am. Jour. Sci., xliii 
 
 1892, pp. 340 and 345. 
 
 s'l " mr iv 
 
 Fig 
 A. 
 B. 
 C. 
 
 107. Limb bones of a polydactyle horse. 
 
 Left fore foot. No. 537. 
 
 Left hind foot. No. 535. 
 
 Tarsus of right hind foot from the inside. 
 
 three bones placed as 
 m, magnum. 
 
 No. 535. 
 n, navicular, cb, cuboid. 4, ecto-cuneiform. 1, 2, 3, 
 cuneiforms, td, trapezoid, tm, trapezium, u, unciform. 
 
 I, II, III, IV, numerals affixed to the metacarpals on the hypothesis that these 
 are their homologies. Cp. Fig. 108, which is lettered on a different hypothesis. 
 
 (After Marsh.) 
 
 b. Four metacarpals. 
 
 This condition is a higher manifestation of the variation seen 
 in the cases just given. In No. 533 the digit II was developed and 
 in addition the trapezium had appeared ; in the cases now to be 
 
 1 Marsh introduces this case in support of a contention that these variations are 
 of the nature of Reversion. Upon the same page appears the statement that "in 
 every specimen examined, where the carpal or tarsal series of bones were preserved 
 and open to inspection, the extra digits were supported in the usual manner," I. c, 
 p. 345 : this assertion is hardly in agreement with the previously stated fact that 
 the metatarsal II is supported by two cuneiform bones. On p. 349 Marsh comments 
 on the presence of five bones in the distal row of the tarsus, and from the expres- 
 sions used it is implied that five such bones had been met with in other polydactyle 
 hind feet. A number of alternative explanations are proposed ; (1) that the five 
 tarsals correspond "to those of the reptilian foot"; (2) that the first may be a 
 " sesamoid " ; (3) that the first may be a remnant of the first metatarsal, for such 
 a rudiment " apparently exists in some fossil horses." With conjectures of this class 
 morphologists are familiar. Into their several merits it is impossible to inquire, but 
 it may be mentioned that the real difficulty is not the presence of the cuneiform 
 marked 1, but the fact that the tarsal element of the digit II seems to have been 
 double, and that the digits in reality are not supported in the usual manner. 
 
CHAP. XIII.] 
 
 DIGITS : HORSE. 
 
 3G5 
 
 given the digit II is extensively developed and the trapezium 
 bears a splint bone representing the metacarpal I, like that which 
 in the normal represents the digit II. This is a phenomenon 
 illustrating the principle seen in the case of teeth and other parts 
 in series (see p. 272), namely, increase in the degree of development 
 of the normally last member of a series correlated with the appear- 
 ance of a new member beyond it. 
 
 Nevertheless the same cases have sometimes been described 
 (e.g. Gatal. Mus. Coll. Surg.) on a different hypothesis. This is 
 illustrated by the lettering of Fig. 108. On this other view 
 the innermost carpal is considered to be the trapezoid and its 
 splint-bone is regarded as the original metacarpal II. The second 
 digit, ac, and its tarsal bone are supposed to be " accessory ' : or 
 "intercalated." To these terms it is difficult to attach any 
 definite meaning. The proposal that some digits are to be 
 reckoned in estimating homologies and that others are to be 
 omitted is arbitrary, and, if allowed, would make nomenclature 
 dependent on personal choice. It is, as has been often pointed 
 out in foregoing chapters, simpler to number the parts in order as 
 they occur and to accept the visible phenomena as the safest index 
 of the methods and possibilities of Variation. Nevertheless, to 
 illustrate the point at issue I have introduced two cases of the 
 same Variation, the one, No. 536, lettered on the view advocated 
 by the Catalogue of the College of Surgeons, &c, the other, Xo. 537. 
 
 108. 
 
 Eight fore foot of Horse No. 
 
 530 from 
 
 acta 
 
 Fig. 
 behind. The upper surfaces of the carpal bones of the 
 distal row are separately shewn above. Specimen in 
 Coll. Surg. Mus., Ter. Cat., 304. 
 
 T, trapezoid, if, magnum. U, unciform. <u\ ac- 
 cessory carpal bone. II, III, IV, metacarpals, ocm, 
 accessory metacarpal. 
 
 This figure is lettered to illustrate the hypothi 
 adopted in the Catalogue, which is alternative to that 
 adopted in Fig. 107, A. 
 
366 MEMSTIC VARIATION. [part i. 
 
 lettered on the other and in the case of polydactyle horses, more 
 usual method. 
 '536. Horse: right manus with extra digit (Fig. 108). The distal 
 row of the carpus is present. It consists of four bones, the unci- 
 form, magnum and two other bones. Of these that lettered T 
 on the view of the Catalogue must be supposed to be the normal 
 trapezoid, while ac is considered to be an intercalated bone, perhaps 
 an additional os magnum. The unciform bears a splint-bone, 
 namely mcp. IV. The magnum bears a fully-formed mcp. and 
 digit III. With the bone ac articulates a large and substantial 
 metacarpal with a digit of three phalanges and a hoof, while the 
 bone T bears another splint-bone, marked II in the figure on the 
 hypothesis that the digit ac is not to be reckoned. Cat. Mus. Coll. 
 Surg., Terat. Series, 1872, No. 304. As mentioned above, it would 
 be more consistent with fact to count the bone ac as trapezoid with 
 mcp. II and the bone T as trapezium with mcp. I. 
 
 .537. Horse having both fore feet (Fig. 107, A) as in the last case, the 
 hind feet bein^ in the condition described in the last Section, No. 535. 
 Marsh, Am. Jour. Sci., xliii. 1892, p. 3-40, Jigs. 3, 6, and 8. 
 
 538. Foal having right manus closely resembling the above, the other 
 limbs being unknown. The mcp. I was longer than the normal mcp. 
 II. In this case the metacarpal II was partially united to mcp. Ill at 
 the central end but was free from it peripherally. vVehenkel, J. M., 
 La Polydactylie chez les Solipedes, from the Journal de la soc. r. des 
 sci. med. et nat. de Bruxelles, 1872, Jig. 2. 
 
 Probably the feet of a large number of polydactyle horses would be 
 found to be in this condition if examined. Marsh, I.e., mentions three 
 other cases known to him in Yale Museum. 
 
 c. Five metacarpals. 
 
 539. Horse having Jive metacarpals and one supernumerary digit in 
 the left manus, and four metacarpals with a similar supernumerary 
 digit in the right manus. 
 
 In the left manus with the trapezoid there articulated a well- 
 developed metacarpal II bearing the extra digit. Internal to this 
 was a trapezium bearing a splint-bone, 6 cm. long, 1'5 wide at 
 proximal end, representing metacarpal I [as in Section (1) b] 
 coalescing peripherally with III. On the external side of III the 
 splint-bone IV was present as usual. The case is remarkable from 
 the fact that external to the metacarpal IV there was another 
 rudimentary metacarpal, presumably representing V. This bone 
 was distinctly separated from IV at the central end, but was for 
 the most part united with it. Putz, Deut. Ztschr. f. Thierm., 1889, 
 XV. p. 224, figs. [The figures illustrating this paper are 
 carefully drawn. The representation of mcp. I is quite clear, but 
 the condition of the mcp. V cannot be well seen, as the whole foot 
 is represented with its ligaments, &c, which partly conceal the 
 structure. The whole account is very minute and gives confidence 
 in the statements.] 
 
 KKf 
 
CHAP. XIII.] 
 
 DIGITS : HORSE. 
 
 367 
 
 * 
 
 The right manus of the same animal came into the possession 
 of the University of Graz and was described independently. In it 
 also the metacarpal II was developed and bore a well-formed digit. 
 There was also a rudimentary metacarpal I beside it, having a 
 length of 5 '7 cm., and a breadth of 1*5 cm. at the central end. [The 
 description is brief and makes no mention of a mcp. V : further 
 account promised.] Mojsisovics, Anal Anz., 1889, IV. p. 255. 
 
 (2) Two digits, one being formed by development of the digit IV. 
 
 Cases of this variation are ex- 
 ceedingly rare. No. 540 is the only 
 instance known to me in which a 
 proper account exists. Most writers 
 on the subject make a general state- 
 ment that such cases exist, but give 
 no references. 
 540. Horse, having a supernumerary 
 digit on the outside of each fore foot. 
 (Fig. 109.) The animal was from 
 Bagdad. The outer rudimentary 
 metacarpal (IV) was well formed and 
 of nearly even thickness throughout 
 its length. It bore a digit of three 
 phalanges and a well- formed hoof. 
 The hoof was elongated and is de- 
 scribed as being shaped like the hoof 
 of a cloven-footed animal. [The de- 
 scription is very imperfect, but two 
 good figures are given, from which 
 it may be gathered that the inner 
 metacarpal (II) was somewhat more 
 developed than in an ordinary horse; 
 and it appears that both the inner 
 
 and outer metacarpals were separate 
 
 throughout their course, but whether 
 
 they could be detached from the 
 
 large metacarpal or were ankylosed 
 
 with it is not stated. The carpal 
 
 bones are not described, but the 
 
 figure suggests that the unciform 
 
 was larger than it normally is. It 
 
 is not stated that the two feet were 
 
 alike in details. The large hoof 
 
 (III) is represented as of the normal 
 
 shape.] Wood - Mason, J., Proc. 
 
 Asiat. Soc. Bengal, 1871, p. 18, Plate. 
 
 Fig. 100. Right fore foot of Horse, No. 640, the ,.rtu->ci! metacarpal (IV 
 being developed, bearing a digit. 
 
 (After V\'<>"I»-Mason.) 
 
 Ill 
 
368 MERISTIC VARIATION. [part i. 
 
 Wehenkel, I. c, p. 15, mentions a similar specimen in the Museum of the 
 Veterinary School at Berlin described by Gurlt, Mag. f. gesam. Thierh., 1870, p. 
 297 [not seen, W. B.]. 
 
 (3) Three digits [1 the digits II and IV being both developed]. 
 
 Examples of this variation are alluded to by many authors but I 
 know of no anatomical description. The following are all very im- 
 perfectly described. 
 
 541. Foal (foetus): left manus having three sub-equal digits; right 
 manus two digits and rudiments of a third more developed than usual. 
 Hind feet normal. Geoffroy St Hilaire, Ann. Sci. Nat., xi. 1827, 
 p. 224. 
 
 Similar case, Bredin, Froriep , s Notizen, xvm. p. 202. 
 
 542. Horse from Texas, having extra digit on inside of each manus, 
 and an extra digit both on the outside and on the inside of each pes 
 [external view only]. Marsh, Am. Jour. Sci., xliii. 1892, p. 344, 
 
 fig- ~- 
 
 543. Horse with both splint-bones bearing digits in each foot. Franck, 
 Handb. d. Anat., Stuttg., 1883, p. 228. 
 
 (4) Two digits ; the digits II and IV both developed, III aborted wholly or in 
 part. 
 
 Mention of these cases must be made in illustration of the possibilities of 
 Meristic Variation, but the parts were in all three instances so misshapen that the 
 animals could not have walked. 
 
 544. Foal having two toes on each foot, the developed toes belonging to the metacar- 
 pals and metatarsals II and IV, while the normally large III was not developed at 
 all in the fore feet and was in the hind feet represented by a wedge of bone only. 
 
 Hind feet. Left. Bones of leg and tarsus said to have been normal. Metatarsal 
 III represented by a wedge of bone fixed between the greatly developed metatarsals 
 
 II and IV. The wedge-like bone 5 cm. wide at upper end, having usual tarsal rela- 
 tions. Its length about the same as its width. Laterally it is united to the 
 metatarsals II and IV which curved round it till they met, and then curve away 
 from each other again. Each was about 20 cm. long and bears a misshapen digit 
 consisting of a proximal phalanx and a hoof-bearing distal phalanx. A small 
 nodule of bone attached to the proximal phalanx may or may not represent part of 
 a middle phalanx. Bight. Very similar to left, but the wedge-like III was rather 
 broader — [for details see original]. 
 
 Fore feet. More misshapen and less symmetrical than hind feet : metacarpal 
 
 III not developed at all. The metacarpals II and IV curved towards each other and 
 crossed, giving an unnatural appearance to the feet. Eight foot. Cuneiform and lunar 
 united, and upon the surface of the bone formed by their union there was a groove 
 occupied by two parts of the tendon of the anterior extensor metacarpi passing to 
 mcp. II and IV respectively. Pisiform and scaphoid normal [this is not clear from 
 the figure]. Magnum absent. Unciform and trapezoid abnormal only in respect 
 of their relations, for whereas they should articulate with the magnum they do not 
 do so, for both magnum and mcp. Ill are not represented. Metacarpal II was 
 11 cm. long, mcp. IV being 19 cm. long. Each bore a digit with a hoof; the digit 
 
 IV having a proximal and a distal phalanx connected by a fibrous cord instead of a 
 middle phalanx. The digit II had a rudimentary distal phalanx only. Left foot 
 like the right, but with the mcp. and digit II more fully developed. [Muscles fully 
 described. It may perhaps be thought that there is not sufficient proof that the 
 developed digits are actually those normally represented by the splint-bones II and 
 IV, but the condition of the hind feet is practically conclusive that this is the right 
 interpretation.] Wehenkel, La Poly dacty lie chez les Solipedes, from J. de la soc. r. 
 des sci. vied, de Bruxelles, 1872, Plate. 
 
 545. Foal, in which the right anterior leg possessed two metacarpals and digits. 
 
 The radius, ulna and proximal series of carpal bones were normal. In the 
 distal series only two bones were present, viz., an inner bone corresponding to the 
 trapezoid, and a magnum. There was no separate bone corresponding to the 
 
CHAP. XIII.] 
 
 DIVISION OF DIGIT I HORSE. 
 
 369 
 
 546. 
 
 unciform, but in its stead, the head of the outer metacarpal was continued upwards 
 to articulate with the cuneiform. Between the heads of the two metacarpals was 
 an irregularly quadrate bone which articulated with the magnum in the place where 
 the large metacarpal (III) should be. This bone however only extended a little 
 way, articulating at its outer end with a notch in the external metacarpal. [This i- 
 the author's view, but the figure strongly suggests that this quadrate bone may have 
 been originally in connexion with the external metacarpal and that it may have been 
 separated from it by fracture. If this were so, the large metacarpal would then not 
 be represented by a separate bone at all.] The outer metacarpal distally bore three 
 phalanges of irregular shape, flexed backwards and outwards. The inner metacarpal 
 articulated solely with the trapezoid. Peripherally it bore a callosity which was 
 due to the healing of a fracture. The phalanges of the inner metacarpal were three, 
 but the first was reduced in length, while the second was elongated and bent in a 
 sinuous manner. The ungual phalanx of this toe was cleft. [The author 
 regards this case as analogous to the foregoing one, No. 544, that is to say, as an 
 instance of development of the normally rudimentary lateral metacarpals to the 
 exclusion of the large one (III), and he considers therefore that the large metacarpal 
 (III) is only represented by the quadrate ossification which lay between the two 
 developed metacarpals.] Ercolani, G. B., Mem. della Ace. Sci. d. Istituto di 
 Bologna, S. 4, T. in. 1881, p. 760, Tav. i.fig. 11. 
 
 Foal in which the feet were all very abnormal. In the two fore feet the meta- 
 carpal of the normal toe (III) was very little developed, being however somewhat 
 larger on the left side than it was on the right. It bore no digit. The external 
 metacarpal bone (IV) of each fore foot attained a considerable length and bore a 
 small hoof-bone. In the left fore foot the inner metacarpal was present but reduced ; 
 in the right foot it was absent. Bight hind foot also had the external metacarpal 
 developed and bearing three small phalanges, but the central metacarpal (III) was 
 fairly developed, bearing however only two phalanges. Left liind foot was amor- 
 phous. Boas, J. E. V., Deut. Ztschr. f Thiermedecin, vn. pp. 271 — 275. [For full 
 description, measurements and figures see original.] 
 
 B. Cases in which metacarpal III gives articulation to 
 
 MORE THAN ONE DIGIT. 
 
 These cases are clear examples of the representation of a Bingle 
 digit by two. It will be seen besides that the 
 two resulting digits may stand to each other 
 in the relation of optical images (see Fig. 110) 
 and do not form a Successive Series, thus 
 following the common method of division of 
 structures possessing the property of Bilateral 
 Symmetry in some degree (cp. p. 77). All 
 cases of this variation known to me occurred 
 in the fore limb. 
 
 *z 
 
 o47. 
 
 Foal: a right fore foot figured from a specimen 
 in the collection of the Veterinary School of 
 Copenhagen (Fig. 110) has two complete digits 
 articulating with a single normal metacarpal bone. 
 The two digits are symmetrically developed ; each 
 consists of three phalanges and bears a hoof. 
 These two hoofs are well formed and curve to- 
 wards each other like those of Artiodactyles. 
 Boas, J. E. V., Deut. Ztschr. f. Thiermedecin, 
 vii., p. 277, Taf. xi.,jiy. 9. 
 548. Two fore feet of a foal, each being Irregularly 
 and unequally bifid. Boas, ibid., jigs. 7 and ^. 
 
 B. 
 
 t.rt 
 
 inf 
 
 Fio. IK'. Bight 
 for.' foot of Bora No. 
 547. 
 
 Mcp, peripheral 
 cml of metacarpal III. 
 est, external side. int. 
 internal Bide 
 
 i After Boas.) 
 
 24 
 
370 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 549. 
 
 Filly, two-year old, which had been born with left fore foot cleft 
 like that of the Ox. Each of the two toes had three phalanges, which 
 were completely separate as far up as the metacarpophalangeal joint. 
 The division externally was carried to the same extent as in the Ox. 
 The lower end of the great metacarpal III felt as if bifurcated like 
 that of the Ox, so as to give separate articular support to the two toes. 
 Upper parts normal. The lesser metacarpals, II and IV, felt through 
 skin, seemed to terminate rather lower down in left foot than in right, 
 but this was uncertain. Animal examined alive. No attempt at 
 
 shoeing had been made, and hoofs 
 
 * 
 
 550. 
 
 having become elongated forwards 
 
 larger 
 
 was much larger or 
 New Phil. Jour.. 
 
 had had their points sawn off. The whole foot 
 more spread than the other. Struthers, J., Edin 
 1863, pp. 279 and 280. 
 
 Horse: right fore foot having phalanges bifid (Fig. 111). The limb 
 was normal as far as the distal end of the metatarsal, except for some 
 exostoses. The proximal phalanx was short and 
 of great width; in its lower third it divided into 
 two divergent parts, the divergence being more 
 marked on the posterior face than on the anterior. 
 Each of these diverging processes bears a complete 
 second and third phalanx. The third phalanges 
 each bear hoofs, which are convex on the outer 
 sides but lit together on the opposed surfaces, the 
 external hoof being slightly concave on its inner 
 face, while the internal is slightly convex. On 
 the plantar surface, each toe bore a half -frog. 
 The two large sesamoids, normally present in the 
 Horse, are in this specimen united along their 
 inner borders to form a single bone, which was 
 placed behind the upper part of the proximal 
 phalanx. Two small sesamoids lay behind the 
 third phalanx. A good deal of exostosis had 
 taken place in all the phalangeal bones. Arloing, 
 M. S., Ann, Sci. Nat., Ser. V., Tome vin. pp. 
 67—69, PI. 
 
 551. 
 
 Mb 
 
 Sla 
 
 Fig. 111. Right 
 fore foot of Horse No. 
 550, from in front. 
 
 sc, scaphoid, tp, 
 
 552. 
 
 Foal : in right fore foot the large metacarpal divided 
 into two parts, each bearing a separate digit. The proximal 
 row of the carpus consisted of four normal bones, but the 
 distal row was composed of two bones only. The external 
 splint-bone (IV) was of normal proportions, but the internal 
 splint-bone (IIj had almost completely disappeared. The 
 
 large metacarpal (III) divided in its peripheral third into trapezoid. II, III, 
 two equal cylindrical branches, each of which bore a digit IV, metacarpals. Ilia, 
 composed of three phalanges and bearing a crescentic HI 6, internal and 
 hoof. These two digits were bent across each other in a external sets of pha- 
 shapeless way. Delplanque, Mem. Soc. centr. cVAgric. langes representing 
 du Dep. du Nord, s. 2, ix. Douai, 1866—18(37, p. 295, 
 PL III. fig. 5. 
 
 Mule, having two distinct toes on each fore foot. The 
 hoofs were shaped like those of the Ox. They were of 
 unequal length. Jolt, Comptes Eendus, 1860, p. 1137. [Perhaps a case belonging 
 to this section.] 
 
 the digit III of the 
 normal. 
 
 (After Abloing.) 
 
chap, xiii.] DIGITS OF HORSE : SPECIAL CASES. 
 
 371 
 
 C. Intermediate casks. 
 
 m 
 
 trf 
 
 flWml 
 
 i* 
 
 IV T 
 
 We have now seen cases of increase in number of digits oc- 
 curring by addition to the series, and cases occurring by division 
 of III. It may at first sight seem impossible that there can be 
 any process intermediate between these two. Nevertheless the 
 word sufficiently nearly describes the condition of at least the first 
 of the following cases, and is to some extent applicable to the 
 second also. If the condition shewn in Fig. 112 be compared with 
 those in Figs. 106 and 110 it will be seen that it is really inter- 
 mediate between them. 
 *553. Horse (young): right manus with internal supernumerary digit. 
 The bones are not in place, but have been attached with wires. 
 The condition is as follows. The distal series of carpus remains ami 
 is normal or nearly so. Of the splint-bones, the inner (mcp. II) is 
 thicker than the outer mcp. IV, but it is very 
 little longer. The large metacarpal (III) is 
 almost, but not quite, bilaterally symmetrical 
 about its middle line. In the distal epiphysis 
 the asymmetry is distinct, the internal side of 
 the epiphysis being less developed than the 
 external side. This epiphysis bears a large 
 digit of three phalanges, but instead of being 
 bilaterally symmetrical, like the normal toe of 
 the Horse, each of the joints is flattened on the 
 internal side, the flattening increasing from the 
 first to the third phalanx. The hoof is greatly 
 flattened on its inner face. 
 
 Internally to the epiphysis of the digit III 
 there is a separate small bone, representing the 
 distal end of an inner metacarpal. This bone 
 bears a digit with two phalanges, and a hoof 
 which is flat on the side turned towards the 
 •other hoof, like that of a calf, though it only 
 reaches to the top of the larger hoof. The 
 first phalanx of this digit is imperfectly divided 
 by a suture into two parts. This division is not 
 that of the epiphysis from the shaft. This extra 
 digit may be thought to be that of mcp. II, 
 but it is clear that it was in part applied to 
 mcp. III. Note also that mcp. Ill is modified 
 in correlation with its presence. Coll. Surg. 
 Mas., in Terat Cat., No. 301. 
 
 The foregoing case well illustrates the inade- 
 quacy of the view on which an individuality is 
 attributed to members of the digital series. 
 The smaller digit in it is as regards 
 
 Fig, 112, Bight 
 
 maims of :i hoi 
 
 No. ").*)3, from behind, 
 
 m, magnum. I i tra- 
 pezoid. », unciform. 
 
 (From a -inrirnen 
 the Sym- in Coll. Surg. Mus.). 
 
 oi •> 
 
 _ 1 — 
 
372 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 metry of the limb complementary to the larger digit. It is a 
 partial substitute for the inner half of the digit III. If the 
 visible Symmetry of the limb is an index of mechanical relations 
 in which the parts stood to each other in the original division of 
 the manus into digits it is possible that there may have been 
 a mechanical equivalence between the two digits. 
 
 554. Mule (between jackass and mare): foetus of about nine months having super- 
 numerary digits. Hind limbs normal. Fore limbs normal as far as peripheral 
 ends of metacarpals. Each manus consisted of three digits. Eight. Metacarpals 
 II and IV normal splint-bones. Metacarpal III normal as far as line of union with 
 its distal epiphysis. The inner part of the sheath of the epiphysis is continued into 
 a rod of fibro-cartilage which supports an extra toe. This rod of cartilage contains 
 a small ossification which represents, as it were, the proximal phalanx of this 
 internal supernumerary toe. Its outer end bears a small second pbalanx, and this 
 bears a small distal phalanx which was covered by a hoof. This extra toe, therefore, 
 is internal to the main continuation of the leg, commences from the line of union 
 between the large metacarpal and its epiphysis, and has three phalangeal joints. 
 
 The epiphysis of the large metacarpal supports a normal first 
 phalanx with which the second phalanx articulates. This 
 second phalanx is enlarged iuternally [details obscure] to 
 bear a small extra nodule of cartilage which appears to be 
 of the nature of an extra toe. The second phalanx also 
 bears a large third (ungual) phalanx. This ungual phalanx 
 together with the minute supernumerary toe borne by the 
 second phalanx are together encased in a common hoof, but 
 the hoof is divided by a groove into two distinct lobes, 
 corresponding with the division between the two digits 
 which it contains. The whole foot, therefore, has one free 
 internal toe and one large toe bearing a small internal one, 
 which are enclosed in a common hoof. 
 
 Left fore foot. Fig. 113. The small, lateral metatarsals 
 II and IV, and the large central metatarsal III are normally 
 constructed ; but from the inner side of the sheath of the 
 large metatarsal, upon the line of union between the bone 
 and its epiphysis, arises a fibro-cartilaginous rod, which 
 contains an ossification representing the proximal phalanx 
 of a supernumerary toe (lettered II in fig.). This rod of 
 tissue in its proximal portion is represented in the figure as 
 abutting on, but distinct from the end of the inner small, 
 lateral metatarsal. It bears a cartilaginous second phalanx, 
 containing a small ossification, which articulates with a 
 terminal (ungual) phalanx covered by a hoof. 
 
 The distal end of the large metatarsal articulates with 
 
 a large first phalanx, which at its proximal end is of normal 
 
 width. At about its middle point this phalanx bifurcates 
 
 into two parts, of which the inner, Ilia, is short and ends a 
 
 little beyond the point of bifurcation : it bears an ungual 
 
 phalanx only, which is encased in a hoof. The outer iimb 
 
 (III b) of the bifurcated first phalanx bears an elongated 
 
 second phalanx of somewhat irregular shape which carries a 
 
 larger ungual phalanx covered by a separate hoof. In this 
 
 foot, therefore, there is an inner toe consisting of three 
 
 phalanges attached to the inside of the large metatarsal : next, 
 
 the proximal phalanx of the large toe is divided longitudinally into two parts, 
 
 bearing (1) an internal toe having only the ungual phalanx and hoof; (2) an outer 
 
 toe which has a second and third (ungual) phalanx. 
 
 In the case of both feet, the hoof and ungual phalanx of the outer toe are turned 
 inwards, having an external curved edge and an internal straight edge; but the two 
 inner toes in each case are turned outivards, having their outer edges straight and 
 their inner edges curved. Jolt, A. et Lavocat, N., Mem. de VAc. des Sci. de Tou- 
 louse, S. 4, Tome in., 1853, p. 364, Plates. [Authors regard this case as proof of 
 
 Fig. 113. Left 
 fore foot of Mule No. 
 554. 
 
 IV, the external 
 splint-bone. Ill, the 
 chief metacarpal. 
 Ilia, Illb, internal 
 and external rudi- 
 mentary digits borne 
 by HI. II, a super- 
 numerary digit at- 
 tached to the inner 
 side of III. 
 
 (After Joly and 
 Lavocat.) 
 
•chap, xiii.] DIGITS OF HORSE : SPECIAL CASES. 373 
 
 truth of certain views of the phylogeny of the Horse and employ a system of nomen- 
 clature based on these views. This is not retained in the abstract here given.] 
 
 ARTIODACTYLA. 
 
 In the domesticated animals of this order digital Variation is 
 not rare, being in the case of the Pig especially common. Such 
 variation has been seen in the Roebuck and Fallow Deer, but not 
 in any more truly wild form so far as I am aware. These varia- 
 tions may take the form either of polydactylism or of syndactylism. 
 Of the former a few cases are known in Ox, Sheep, Roebuck 
 Fallow Deer, and many cases in the Pig ; syndactylism has been 
 seen only in the Ox and in the Pig. The absence of cases of 
 syndactylism in the Sheep is a curious instance of the caprice 
 with which Variation occurs. 
 
 The phenomena of polydactylism in Pecora may conveniently 
 be taken separately from the similar phenomena in Pigs. 
 
 Polydactylism in Pecora. 
 
 At the outset one negative feature in the evidence calls for 
 notice. It is known that in the embryo Sheep rudiments of meta- 
 carpals II and V exist 1 which afterwards unite with III and IV. 
 In view of this fact it might be expected by some that there would 
 be found cases of Sheep and perhaps Oxen polydactyle by develop- 
 ment of the digits II or V. In the Sheep only one case (No. 
 555) is known that can be possibly so interpreted; and in the I ).\ 
 there is no such case unless Nos. 557, 558, and 559 should be held 
 by any to be examples of the development of II, a view attended 
 by many difficulties. 
 
 The two following examples are the only ones known t<> nit- in 
 which there can be any question of reappearance of a lost digit, 
 but in neither is the evidence at all clear. 
 *555. Sheep. Some specimens of a small Chilian breed had an 
 extra digit on the hind foot. It was not present in all individuals 
 and was not seen to be inherited; but normal parents were 
 observed to have offspring thus varying. [From the description 
 given I cannot tell whether the extra digit was internal or 
 external. Also, though said to have been on the hind foot, in 
 describing the bones the cannon-bone is twice called metacarpus; 
 probably this is a slip for metatarsus.] The digit was only 
 attached by skin. It contained a bent bone, of which the upper 
 segment was 20 mm. long, the lower 13 mm. Proximally the 
 
 1 Rosenberg, Z. f. w. Z., 1873, xxiii. pp. 126—182,^. It. Ac. Sometimes 
 these rudiments remain fairly distinct ;it the proximal end of the eannon-bone, 
 especially of the fore foot. See Xatiicsius, Die Sehafiucht, L880, pp. 187 and 1 13, 
 figs. 
 
374 MERISTIC VARIATION. [part I. 
 
 cartilaginous head of this bone rested in a pit on the tendon of 
 the flexor brevis digitorum at the level of the end of first third of 
 the cannon-bone, and peripherally it bore an end-phalanx and 
 claw-like hoof, properly articulating. No splint-bones present. 
 [Other details given : it was suggested that the bent bone re- 
 presented an extra ' metacarpal ' and first and second phalanx.] 
 Von Nathusius, H., Die Schafzucht, 1880, p. 143. 
 556. Capreolus caprea (Roebuck), 2 yr. old, killed in district 
 of Betzenstein, having a slender fifth digit on the inside of each 
 fore foot. In the left there was a small, conical metacarpal 
 element, bearing a digit with three phalanges. The right extra 
 digit had a longer metacarpal piece with epiphysis, but in it 
 there were only two phalanges. Each bore a hoof of about the 
 size of those of II or V. The hoofs curved outwards. Bau- 
 muller, C, Abh. naturh. Ges. Numb., ix. 1892, p. 53, PL 
 
 Other cases of polydactyle Pecora mostly fall into two groups : 
 
 (1) Examples of limbs having three digits borne by a large 
 cannon-bone made up of three metatarsal or metacarpal elements, 
 grouped in one system of Symmetry. The axis of Symmetry is 
 then deflected from the normal position, and instead of falling 
 between two digits it approaches more or less to the central line 
 of the middle of the three digits. The degree to which this change 
 of Symmetry takes place corresponds irregularly with the extent 
 to w r hich the innermost digit is developed. This form is known in 
 the Ox only [? Goat]. 
 
 (2) Limbs in which the series of digits has two more or less 
 definite axes of Minor Symmetry. Both of the systems of Sym- 
 metry thus formed are in addition arranged about one common 
 axis of Symmetry. The nature of this condition will be discussed 
 later. It occurs in Ox, Sheep, Roebuck and Deer. 
 
 (1) Three digits in one system of Symmetry. 
 
 *557. Calf. Right manus (Fig. 114) having three digits borne by a 
 single cannon-bone. This is an old specimen of unknown history 
 which was kindly sent to me by Mr W. L. Sclater for examination. 
 
 Of the carpal bones only the distal row remains, containing a trap- 
 ezoido-magnum and unciform not differing visibly from the normal. 
 The cannon-bone spreads at about its middle into three sub-equal parts, 
 each ending in a separate articular head bearing a trochlear ridge. 
 Between these articular surfaces the only point of difference was that 
 in that of the middle digit (b), the trochlear ridge was rather nearer to 
 the outer surface of the joint, not dividing it into two halves as usual 
 (see figure). The foramen for entrance of the nutrient vessel was in 
 the channel between the external and middle digits. This channel was 
 very slightly deeper than the corresponding channel between the 
 middle and inner digits. Each articular head bore a digit, well formed, 
 
CHAP. XIII.] 
 
 DIGITS : PECORA. 
 
 375 
 
 of approximately similar lengths, having a hoof. The [hoofs of the 
 outer and inner digits curved to the middle line of the limb, like the 
 
 -n for 
 
 Fig. 114. Eight fore foot of a Calf, No. 537. 
 
 I. The whole foot seen from behind. 
 
 II. The bones from behind. 
 
 tpM. trapezoido-magnum. imc, unciform, n, for., nutrient foramen. J", 
 dotted outline shewing position of supposed rudiment of digit V. Sesamoids not 
 shewn. 
 
 normal hoofs of a cloven-footed animal, but the hoof ol the central toe 
 was convex on both sides. The two accessory hoofs were in place, 
 one on each side as shewn in the figure. The whole manus was very 
 nearly symmetrical about the middle line of this digit. It was notice 
 able that the out^r and inner hoofs were both father narrow in propor- 
 tion to the length of the limb, but the whole width y>i the fool was 
 rather greater than it should be. The small bone considered to repre 
 sent the digit A' articulates with the unciform as usual, being of normal 
 size. Each of the three digits was supplied with flexor and extensor 
 tendons. 
 558. Heifer having three fully developed toes on each hind limb. 
 
 The right hind foot described (Fig. 115). The calcaneum, astragalus 
 and cuboido-navicular presented no special abnormality. The cuneiform 
 
376 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Uc 
 
 559. 
 
 series usually consisting of two pieces in the Ox, were here represented 
 by one piece (c and c 3 ), though externally the bone seemed to be in two 
 pieces. The internal portion (c) approximately corresponding in posi- 
 tion with the normal ento-cuneiform was imperfectly and irregularly 
 divided by a groove into two parts. The metatarsus or cannon-bone at 
 its proximal end was almost normal, but from about its middle it 
 spread out into three parts as shewn in the figure, each part ending in 
 an articular surface and bearing a digit, but the trochlear ridge for the 
 innermost digit (ac) was not quite so large as those for the others. 
 From the skeleton it seems clear that this innermost digit could not 
 have reached the ground. 
 
 Of the three hoofs the middle one was the 
 largest, the other two being nearly equal to each 
 other in size. The outermost hoof curved inwards, 
 and the innermost hoof curved outwards. The 
 middle hoof also curved outwards, but less so than 
 that of a normal digit III, being rather flatter 
 underneath, and having its two edges more nearly 
 symmetrical. The accessory hoofs ('ergots' of 
 French writers) were " in their usual place, on 
 either side of and behind the foot." This speci- 
 men was originally described by Goodman, Ne- 
 ville, Jour. Anat. Phys., 1868, Ser. 2, i. p. 109. 
 
 The skeleton of the foot is in the Cambridge 
 
 University Museum of Pathology. 
 
 In answer to my inquiries Mr G. Daintree of 
 
 Chatteris, the owner of this animal, kindly gave 
 
 me the following information. This cow was 
 
 bought in 1861 and from her a three- toed strain 
 
 arose, of which about ten generations were pro- 
 duced. The three-toed condition appeared in 
 
 both males and females, but no three-toed bull 
 
 was kept, so that the descent was wholly through 
 females. About two in three calves born of this 
 
 strain had three toes. In one case only were 
 
 there three toes on the fore feet. The third toe 
 
 was never walked on. The breed was got rid of 
 
 because it was at last represented only by males, 
 
 the last being sold in 1887. The beasts were as 
 
 good as any other cattle of the same class. 
 
 Calf. 
 
 ally resembling the last case 
 
 is nearly normal. The middle digit is very thick, 
 
 and is somewhat twisted and flexed. Its ungual 
 
 phalanx is not specially curved in either direction 
 
 but it is not truly symmetrical. The innermost 
 
 digit is thin and short and its ungual phalanx is the hypothesis that 
 
 not much curved. In this specimen there is a HI and IV represent 
 
 , . •■ j j, ,. . . . ,, ,. . , . these dibits ot the 
 
 decided appearance or division in the distal epi- norma i and that ac 
 
 physis of the metacarpal of the middle digit is an accessory digit. 
 
 (?III). Coll. Surg. Mus., Terat. Series, No. 300. 
 
 gener- 
 
 Left manus having three digits, 
 
 ?he external digit 
 
 uan 
 
 Km) 
 
 Fig. 115. Right 
 hind foot of heifer, 
 No. 558. 
 
 As, astragalus. 
 clc, calcaneum. c, 
 c s , parts of a large 
 united bone repre- 
 senting cuneiforms. 
 
 Ill, IV, ac, letters 
 affixed to illustrate 
 
chap. XIII.] DIGITS : PECORA. 377 
 
 The following two cases are jjerhaps of the same nature as the foregoing. 
 
 560. Goat having three digits in each manus, described by Geoffroy St Hilaire, 
 Hist, des Anom. i. p. 689. The description states that a supernumerary toe was 
 placed between the two normal toes. The middle toe was one-third of the size of a 
 normal toe, but the lower part of the foot was larger than usual. This case was 
 probably like No. 557 ; for from the shapes of the lateral hoofs that case also might 
 seem to an observer at first sight to be an example of a toe " intercalated " between 
 two normal toes. But in No. 5G0 the middle digit was reduced. 
 
 561. Calf having a small supernumerary toe 'placed between the digits of the 
 right manus.' This toe had a hoof and seemed externally to be perfect, but on 
 dissection it was found to contain no ossification, but was entirely composed of 
 fibrous tissue and fat. Ercolani, Mem. Ac. Bologna, S. 4, in. p. 772. [Probably 
 case like last, the middle digit being still less developed.] 
 
 This case is probably distinct from the others given. 
 
 562. Calf: right fore foot having three complete metacarpals, each bearing a 
 digit of three phalanges. The two outer were disposed as in the normal, but the 
 innermost metacarpal was quite free from the others and its digit stood off from 
 the others [not grouping into their symmetry as in preceding cases] and having 
 
 an ungual phalanx [of ? pyramidal shape]. Delplanque, Etudes Teratol., Douai, 
 1869, n. p. '63, PI. II. Jigs. 2 and 3. [It is difficult to determine the relation of this 
 case to the others and I am not sure that I have rightly understood the form of 
 the inner digit ; but since this digit seems to be outside the Minor Symmetry 
 of the limb it is almost impossible to suppose that it can really be the digit II 
 reappearing. I incline to think that it is more likely that this digit belongs to a 
 separate Minor Symmetry. Compare the similar phenomena in Pigs, No. 570.] 
 
 On the foregoing cases some comment may be made. It may 
 be noted that the two first (Nos. 557 and 558) present two stages 
 or conditions of one variation. In No. 557 all three digits reach 
 the ground and the change of Symmetry is completed ; in No. 558 
 the internal digit is not so large in proportion and the plane of 
 Symmetry is not deflected so far. 
 
 As to the morphology of the three digits in these cases three 
 views are open on the accepted hypotheses. First, the internal 
 digit (if it be admitted to be the supernumerary) may be simply 
 a developed II. The existence of the normal accessory hoofs 
 practically negatives this suggestion, for there can be little doubt 
 that one of them represents II (v. infra, No. 579). The condition 
 of the cuneiforms in No. 558 suggests further that an element is 
 introduced into the cuneiform series between the almost normally 
 formed ento-cuneiform and the ecto-cuneiform. But if this new 
 element is the middle cuneiform, then the internal digit (Fig. 115, 
 ac) may still be II. But the innermost ergot is II in the normal. 
 Or is the inner ergot in this case I, and is this once more a case of tin- 
 development of a normally terminal member, II, and of the addition 
 . of I beyond it in correlation, as we saw in the Horse (see p. 364) ? 
 That such a correlation may exist is unquestionable, and it is not 
 clear that these cases are not examples of it. But even if this 
 principle be adopted here as a means of bringing these cases into 
 harmony with received conceptions it will presently be seen that 
 it still will not reconcile some other cases, notably those of the 
 presence of supernumerary digits in a Minor Symmetry apart from 
 that of the normal series. Yet if the conception of the digits as 
 
378 MERISTIC VARIATION. [part I. 
 
 endowed with individuality be not of universal application, we shall 
 not save it even if by ingenuity we may represent the facts of the 
 present case as in conformity with its conditions. 
 
 On the other hand it may be suggested that there is a division 
 of some one digit, and undoubtedly in No. 559 there is a sugges- 
 tion that the innermost digit and the central digit are both formed 
 by division of III. But in the first place this view cannot so easily 
 be extended to Nos. 557 and 558, for in them there is practically 
 no indication that the digits are not all independent and equivalent. 
 The circumstance that the nutrient vessel enters between the 
 external and middle digits may perhaps be taken to shew that 
 they are III and IV ; but this vessel, if single, must necessarily 
 enter in one or other of the interspaces and there is no reason for 
 supposing that, were there an actual repetition of a digit, the 
 vessel must also be doubled, though doubtless repetition of vessels 
 commonly enough occurs with repetition of the organs supplied. 
 
 Next, the Symmetry of the foot, the development of the middle 
 digit to take a median place, the position of the accessory hoofs, 
 one on either side equidistant from the middle line of the manus, 
 all these are surely indications that this limb was from the first 
 developed and planned as a series of three digits, and not as a series 
 of two digits of which one afterwards divided. The series has a 
 new number of members, and each member is in correlation with 
 the existence of the new number remodelled. 
 
 It is no part of the view here urged to deny that a single digit, 
 like any other single member of a series, may divide into two (or 
 even into three) for this phenomenon is not rare. Probably enough 
 No. 559 is actually a case of such a division of the digit III. But 
 here in digits as in mammae, teeth, &c, the evidence goes to shew 
 that there is no real distinction between the division of one member 
 to form two, and that more fundamental reconstitution of the series 
 seen in No. 557, for the state of No. 558 is almost halfway between 
 them. In it we almost see the digit III in the act of losing its 
 identity. 
 
 (2) Limbs with digits in two systems of Minor Symmetry (Double-foot). 
 
 In dealing with these there are difficulties. The cases are examples 
 of limbs of Calves or Sheep hearing four or rive digits arranged in two 
 groups either of two and two, or of two and three. The members of 
 each group curve towards each other in such a w r ay that each group 
 has a separate axis of Symmetry (Figs. 117 and 118). In several such 
 cases the two groups are related to each other as right and left. Of 
 these facts two different views are possible. For first, a limb of this 
 kind may be a structure like the double-hands seen in Man (pp. 331 to 
 337), for it is certain that an almost completely symmetrical series of 
 parts is in those cases formed by proliferation of a series normally 
 hemi-symmetrical, how r ever unexpected this phenomenon may be. 
 
 On the other hand it might be argued that one of the groups of 
 digits represents the normal, and that the other group is supernumerary. 
 
chap, xiii.] DOUBLE-FOOT I PECORA. 379 
 
 For, as will be hereafter shewn at length in the case of Insects, super- 
 numerary appendages may grow out from a normal appendage and are 
 then a pair, being formed as a right and a left, composing a separate 
 Secondary Symmetry. 
 
 On the first view the digits of each group are in symmetry with 
 each other like those of the normal limb, the two groups also balancing 
 each other like the halves of a double-hand: on the other view one of 
 the groups would be supposed to be made up of a right and a left digit 
 III, or of a right and a left digit IV. The possibility of the second 
 view being true arises of course in the Artiodactyles from the fact that 
 in them the normal digits compose a bilateral Minor Symmetry. 
 
 There is nevertheless little doubt that the former account is the 
 right one and that neither group is a Secondary Symmetry ; for were 
 either of the groups really in Secondary Symmetry the supposed super- 
 numerary group should contain at least parts of four digits. Lastly, 
 some of the cases, as No. 566, are clearly of the nature of double limbs, 
 both groups having a common axis of Symmetry. 
 
 A further difficulty arises from the fact that most of these double 
 limbs are old specimens cut off from the trunk. There is therefore 
 no proof that such a limb is not that of a polymelian in Geoffroy St 
 Hilaire's sense. In other words, though it is practically certain that 
 neither of the groups of digits is itself a system of Secondary Symme- 
 try it is quite possible, and in some cases likely that the whole limb is 
 of this nature. In cases of duplicity, especially of posterior duplicity, 
 the two limbs of one or both of the united bodies frequently form a 
 compound structure somewhat resembling one of the double limbs here 
 under consideration. Hence it is not possible to include with confid- 
 ence great numbers of cases of double limbs described by various 
 writers or preserved in museums, for it is rarely that particulars re- 
 garding the rest of the animal are to be had. This difficulty applies to 
 almost all cases known to me and they are therefore given with this 
 caution. This objection of course does not apply to such a case as No. 
 564. 
 
 The following few cases will sufficiently illustrate the different forms of limbs 
 included in this section. They consist of two chief kinds ; first, limbs like Nos. 563 
 and 566, in which both groups contain two digits, and secondly, cases like No. 567, in 
 which one of the groups contains three digits, recalling the state described in the 
 last section (cp. Nos. 558 and 559). Besides these there are some cases of amor- 
 phous extra digits not here related. 
 563. Cow, full-grown, right fore foot with four digits arranged in two groups of two, 
 as sbewn in fig. 116. The carpus not preserved. No particulars as to the rest of the 
 animal. This specimen is in the Museum of Douai and is described in detail by 
 Dklplanque, Etudes Teratologiques, n. Douai, 1869, p. 30, PI. I. [The possibility 
 that this may be a limb of a pygomelian is not excluded.] 
 
 *564. Cervus dama (Fallow Deer). A female having each hind foot 
 double. The division occurs in the upper part of the tarsus, which 
 gradually diverges into two separate tarsi [? metatarsi] and two 
 separate feet. This doe had for several successive years dropped a 
 fawn with the same malformation, though she had been served by 
 several bucks. Ward, Edwin, Proc. Zool. Soc, 1874, p. 90. 
 565. Two cases, a Roebuck and a Deer, mentioned by Geoffroy St 
 Hilaire {Hist, des Anom., I. p. 697) are probably of this nature. 
 
380 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Fig. 116. Specimen stated by 
 Delplanque to have been the ri^bt 
 foot of a Cow (see No. 563). (After 
 Delplanque.) 
 
 Sheep, having four toes, each having three phalanges, 
 on each posterior limb (Fig. 117). In each case the toes 
 were arranged as two pairs, the hoofs of each pair being 
 turned towards each other. Each foot had four united 
 metatarsals, marked off from each other by grooves on the 
 surface of the bone, the division between the metatarsals 
 of each pair of toes being clearly marked at the peripheral 
 ends of the bones. In the case of each foot there were 
 parts of a pair of tarsi arranged in a symmetrical and com- 
 plementary manuer about the middle line of the limb. 
 In each tarsus there was a large bone having the structure 
 of two calcanea, a right and a left, united posteriorly ; the 
 upward prolongation, proper to the calcaneum, was present 
 on each side of this bone and projected upwards on each 
 side of the tibia. The astragalus of each foot was similarly 
 a bone double in form, uniting in itself the parts of a right 
 and left astragalus. The left foot had a single fiat bone 
 below the astragalus, representing as it were two naviculars 
 fused together ; and four bones in a distal row, representing 
 presumably two cuboids, and two cuneiform elements. In 
 the right foot also there was a single bone below the 
 astragalus, and four other bones arranged in a way slightly 
 different from that of the other foot. Ercolani, ibid., p. 
 773, Tav. n. figs. 7 and 8. 
 
 Fig. 117. Bones of left hindjfoot of a Sheep, No. 566 [q. v.] copied from Ercolani. 
 clc, clc, the two calcanea. a + a 2 , bone representing the two astragali, n + n' 2 , 
 
 tbe two naviculars, cb, cb, the two cuboids. 
 
CHAP. XIII.] 
 
 DOUBLE-FOOT : PECORA. 
 
 381 
 
 [A case given by Ebcolani (I. c, p. 783, Tav. 11., figs. 9 and 10) of similar 
 duplicity in a lamb seems to be very possibly a case of double monstrosity. In this 
 animal the hind limbs were altogether absent.] 
 
 567. Calf, having five digits on one manus. There is nothing to shew positively 
 whether this specimen is a right or a left, and it is even possible that it is part of a 
 polymelian 1 . Carpal bones gone. Metacarpals four, disposed in two pairs. One 
 pair bear the digits d 4 and d 5 (Fig. 110), which 
 
 have a common proximal joint. Their ungual 
 phalanges curve towards each other, forming a 
 Minor Symmetry like those of a normal Calf. 
 The other two metacarpals bear three digits ; two 
 (d 3 and d 2 ) articulate with one metacarpal having 
 a divided epiphysis. The other metacarpal bears 
 a digit (d 1 ) of full size curving towards d' 2 . The 
 ungual phalanges of d 2 and d 3 are nearly straight 
 [cp. Nos. 558 and 559.] C. S. M., Terat. Ser., 
 No. 299. 
 
 568. Calf: left hind foot similar case : inner group 
 of tico toes curving towards each other and an 
 outer group of three toes of which the middle one 
 was almost bilaterally symmetrical while the hoofs 
 of the other two were each turned towards it. Five 
 metatarsals united but marked out clearly by 
 grooves. Tarsus much as in No. 566. Ercolani, 
 7. c, p. 774, Tav. i. fig. 8. 
 
 569. Calf: left hind foot a somewhat different case, 
 Drew, Commercium Litterarium, Nuremberg, 1736, 
 p. 225, Taf. in. fig. 2. [Description meagre, but 
 figure good. Beginning from the inside the five 
 toes turned (1) outwards, (2) outwards, (3) inwards, 
 (4) outwards, (5) inwards, respectively. There were 
 only four metatarsals, (3) and (4) being both borne 
 on one metatarsal.] 
 
 POLYDACTYLISM IX THE PlG. 
 
 Fig. 118. Manus of a Calf. 
 No. 567. d\ d 2 , d 3 , group of 
 three digits [? internal] ; d 4 , d\ 
 group of two digits [? external]. 
 
 570. 
 
 Of the great numbers of feet of poly- 
 dactyle pigs recorded or preserved in 
 museums all I believe are fore feet. No 
 case of a polydactyle hind foot is known to 
 me in the pig. All the cases are examples of proliferation upon the 
 internal side of the digital series. With very few exceptions the 
 variation takes one of two forms, consisting either in the presence of 
 a single digit internal to the digit II, or in the presence of tivo digits, 
 either separate or partially compounded, in this position. A very few 
 cases depart from these conditions 2 . The condition is very usually 
 the same or nearly the same in both fore feet. 
 
 One extra digit, internal to digit II. 
 
 Such a digit may either have a separate bone for its articulation in 
 one or both rows of the carpus (as Ercolani, /. c, PI. I. fig. 3), or it 
 may articulate with a half-separated extension of the trapezoid (as Coll. 
 Surg. Mus., Ter. Ser., 297 A), or with the metacarpal or other part of 
 digit II (very common), sometimes simply branching from this digit 
 without an articulation. In no case of which good accounts are to be 
 
 1 The Catalogue gives no indication on these points. 
 
 2 For example a 1. fore foot in which the -metacarpal of II. bears a rudimentary 
 digit on each side of the digit II, three in all. Ebcolani, Mem. Ac. Bol., 1881, PL 
 I, fig. 1. 
 
38: 
 
 9 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 had does such a digit group itself into the Symmetry of the normal 
 manus ; but it stands apart, or is bent or adducted behind the other 
 digits, having a hoof which is irregularly pyramidal, curving in neither 
 direction especially. Such a digit has generally three phalanges, and 
 is of about the size of digit II, though not rarely it is large in size 
 approaching more nearly to III than to II (as Coll. Surg. Mus., Ter. 
 Ser. t 297). 
 
 Two extra digits internal to digit II % 
 
 This condition is not less common than the last. The two extra 
 digits are borne either by two separate extra carpal bones (Fig. 119, c\ 
 c 2 ), or by one carpal imperfectly divided (Ercolani, I. c, PI. I., Jig. 6); 
 or the metacarpals of the extra digits simply articulate against the 
 carpo-metacarpal joint of II (as in a specimen in my own possession). 
 The extra digits may be double throughout, or the two may be com- 
 pounded in their proximal parts (Ercolani, I. c, PL i., fig. 5 ; also case 
 in Oxford Mus. 1 , 1506, a, in which the two extra digits were ill-formed 
 and of unequal size, having a common metacarpal). Fig. 119 shews 
 such a pair of extra digits in their most complete form. The central 
 part of the metacarpal of II has either never ossified or has been 
 absorbed. As bearing on the question of the relations of parts in 
 Meristic Repetition the fact of most importance is the circumstance 
 that the digits III and IV retain their normal Symmetry, but the two 
 
 • I II 
 
 Fig. 119. Left manus of a Pig, No. 571. 
 
 I. View from in front. II. View from inside to shew the convergence of 
 d 1 and d 2 towards each other. 
 
 d 1 , d 2 , two extra digits placed internally, c 1 , c 2 , two extra carpal bones with 
 which they articulate, sc, scaphoid, lu, lunar, cu, cuneiform, t, trapezoid, 
 m, magnum, u, unciform. d z — d 6 , the digits II, III, IV, V. 
 
 1 For note of this specimen I am indebted to Mr W. H. Benbam. 
 
chap, xiil] DIGITS : PIG. 383 
 
 extra digits form another Minor Symmetry of their own. It is perhaps 
 worth noting that the metacarpal of the digit lettered d a in the form of 
 its head is nearly the optical image of that of III (d*), but this resem- 
 blance may be misleading and must not be insisted on. Coll. Surg. 
 Mus., Ter. Ser., 298. 
 572 Wild Boar. Two cases, apparently resembling the foregoing are 
 
 described, from external examination only, in the wild boar by Geoffroy 
 St Hilaire, Hist, des Anom., 1. p. 696. 
 
 Syndactylism in Artiodactyla. 
 
 This phenomenon is known in the Ox and is common in the 
 Pig. In all cases the variation consists in a more or less complete 
 union or absence of division between the digits III and IV. Among 
 the many records of digital variation in the Pig no case relates to 
 union between a lateral and a chief digit, but it is always the two 
 chief digits III and IV that are united. (Compare the case of 
 Man, p. 358.) In this case there is therefore an absence of a 
 division in the middle plane of a bilateral Minor Symmetry, and 
 the parts that remain united are related to each other as optical 
 images. The phenomenon is thus the exact converse of the 
 variation consisting in a division along a plane of bilateral sym- 
 metry which was seen in the Horses Nos. 547 and 550. As was 
 remarked in speaking of similar variations in Man, it is to be 
 noticed that if the union is incomplete, as it commonly is, the 
 peripJteral parts are the least divided, the division becoming more 
 marked as the proximal parts are approached. 
 
 In the normal Sheep according to Rosenberg 1 the metacarpals 
 II and V are distinct in the embryonic state, afterwards completely 
 uniting with III and IV. The same is presumably true of the Ox ; 
 but whether this be so or not, the digits II and V are in the 
 normal adult not represented by separate bones in the hind foot, 
 and in the fore foot V only is represented by the rudimentary 
 * bone articulating with the unciform. Unusual interest therefore 
 attaches to the observations made by Bo AS and by Kitt of the 
 development of lateral metacarpals and metatarsals (II and V) in 
 Calves having III and IV united. Note also that in two of Kitt's 
 cases there was not only a development of lateral digits but also 
 indications of a division occurring in them. Besides this, in the 
 right fore foot of one solid-hoofed Pig (No. 585) there is a slight 
 appearance of duplicity in the ungual phalanx of the lateral 
 digit V. 
 
 On the other hand the reduction of accessory hoofs {ergots) in 
 Landois' case, No. 582, seems to be an example of a contrary 
 phenomenon ; for the connexion between the developed lateral 
 metacarpals and metatarsals in Kitt's case (No. 579) must be 
 taken as evidence that the accessory hoofs do really represent 
 II and V. 
 
 1 Rosenberg, A., Z.f. w. Z., 1873, xxm. pp. 126 — 132, figs. 14, &c. 
 
384 M ERISTIC VARIATION. [part i. 
 
 *573. Ox. Young ox having the two digits of the right fore foot 
 completely united together. At the lower extremity of the large 
 double metacarpal (III and IV) of the normal limb a deep cleft is 
 present, which separates the two articular extremities of the bone. 
 In this specimen this cleft was represented only by a sort of 
 antero-posterior channel, at the bottom of which there was a 
 slight groove, which was all that remained as an indication of the 
 original double nature of the bone. At the back of this metacarpal 
 there were only three sesamoids instead of four, and in the central 
 one there was not the slightest trace of duplicity. This sesamoid 
 was placed opposite to the channel above mentioned. The two 
 first phalanges were entirely united, but the vestiges of this fusion 
 could be seen both before and behind and also in the two articular 
 surfaces by which the bone was in contact with the metacarpal. 
 The same was true of the second phalanges. The third phalanges 
 however were so completely fused and so reduced in size that they 
 had the appearance of a single bone. The two small sesamoids 
 were similarly united. The general appearance of this limb was 
 remarkably like that of the Horse. Barrier, Rec. mecL veter., 
 1884, Ser. 6, Tome 13, p. 490. [No particulars given as to the 
 condition of the other feet of the same animal.] 
 
 574. Ox having right fore foot with a single large metacarpal and 
 one splint-bone [? Y]. The peripheral end of the metacarpal 
 had two articular surfaces closely compressed together, and these 
 two surfaces bore but one digit of three phalanges and one hoof 
 like that of a Foal. The preparation was an old one, and with 
 regard to the accessory hoofs there was no indication that could be 
 relied on. Kitt, Dent. Ztschr. f. Thierm., XII. 1886, Jahresb., 
 1884—5, p. 62, Case No. III. 
 
 575. Calf: each foot having only one hoof. The phalanges, sesamoids, meta- 
 carpals and metatarsals, were all normal and the hoofs alone were united. The 
 cavity of the hoof was divided internally into two chambers, which were more 
 distinct in front than behind. Externally each hoof was slightly bifid in front, but 
 the soles of the feet were without trace of division. Morot, C, Bull, de la Soc. 
 de vied, vet., 1889, Ser. vn. T. vi. p. 39. Case I. 
 
 576. Calf: killed at 10 weeks old. The left fore foot alone was abnormal, having only 
 one hoof. Viewed from without, this hoof was like that of a young ass, but it bore 
 a slight median depression, which was about 3 cm. wide and only 1 to 2 mm. deep, 
 which was all that remained to shew its double structure. Internally the cavity of 
 the hoof was single, but a horny ridge was present on the inside in the region of 
 the depression. The two unequal phalanges were peripherally united into a single 
 bone, but were separate centrally, and the two parts were not quite symmetrical 
 [details given]. The other parts were nearly normal. Morot, C, I. c, Case 2. 
 
 *577. Ox. In a newly-born calf the following abnormalities were seen. 
 In the right fore foot there was a small well formed metacarpal 
 bone on the outside of the normal paired metacarpals, and a similar 
 but more rudimentary structure was also present on the inside of 
 the limb. The additional outer metacarpal bore two small phal- 
 angeal cartilages, and with them had a length of about 10 cm., 
 but the supernumerary metacarpal on the inner side was more 
 rudimentary and bore no trace of phalangeal structures. The toes 
 
chap, xiii.] syndactylism: ox. 385 
 
 borne by the normal metacarpal of the right fore foot were ab- 
 normal, inasmuch as the second and third phalanges were united 
 together. The first pair of phalanges were separate, but their outer 
 ends were modified so as to articulate with the single second 
 phalanx. The distal (third) phalanx bore a groove indicating its 
 double origin, but the second phalanx was without any such groove, 
 and was to all appearance a single structure. 
 
 The left fore foot also bore an outer and an inner supernumerary 
 metacarpal, but in this case it was the inner supernumerary meta- 
 carpal which attained the greatest size. This inner metacarpal 
 bore two small phalangeal bones, while the outer extra metacarpal 
 was more rudimentary and had no phalanges. The phalanges of 
 the two normal toes were separate in the left foot, but though the 
 bones were of the ordinary formation the two toes were enclosed 
 in a common hoof. Boas, J. E. V., Morph. Jahrb., 1890, p. 530, 
 
 figs- 
 
 Boas also states that in the museum of the Agricultural 
 School of Copenhagen are several instances of united toes in the 
 fore foot of the Ox, and that in all these specimens the outer 
 metacarpals (II and V) are larger than they are in normal 
 specimens, but are not so much developed as in the case just 
 described. Boas, I.e. 
 578. A case [sc. Ox (?)] is also mentioned in which the two normal 
 toes of the hind foot were united, and the median and distal parts 
 of the metatarsals II and V were developed, though they are 
 absent in the normal form. Boas, I.e. 
 
 *579. Calf having the digits of each foot united and bearing a single 
 hoof. The carpus and tarsus were not seen. Fore foot. The chief 
 digits, III and IV, were completely united in the fore limbs and bore 
 a single hoof, but, in addition to this variation, the metacarpals of the 
 lateral digits, II and V, were developed and ossified. The length of 
 metacarpal II was 9 cm. and its thickness at the proximal end was 
 T5 cm. Metacarpal Y had a length of 8 cm. and a maximum thick- 
 ness of 1*3 cm. at the proximal end. The metacarpal of the united 
 digits, III and IV, measured 13 cm. in length. The metacarpal V 
 was slightly bifid at its distal extremity, and here presented two 
 articular surfaces. With the internal of these there articulated a bone 
 measuring 2 cm. by 0-5 cm., and attached by fibrous tissue to the end 
 of this bone there was a cartilaginous nodule. The external end of 
 metacarpal V bore a rod-like piece of cartilage, 1 cm. in length. This 
 and the cartilaginous nodule of the other part of the digit together 
 formed the basis of one of the accessory hoofs (ergots), but the horny 
 covering itself was divided by a deep cleft into two imperfectly separate 
 parts. To the metacarpal of II was loosely articulated a bone 2*5 cm. 
 in length, to which a nodule of cartilage was attached. The end of this 
 digit was covered by an accessory hoof, which was imperfectly double 
 like that of V and contained a second cartilaginous nodule, which was 
 distinct from the first and was not supported by any proximal bone. 
 The union between the digits III and IV was complete, and the re- 
 
 b. 25 
 
386 MERISTIC VARIATION. [part i. 
 
 suiting structure with its hoof was like that of the Horse. The artic- 
 ulations were perfectly mobile. At the ruetacarpo-phalangeal joint 
 there were two sesamoids only. [With this division in the lateral 
 digits on fusion of III and IV compare Pig, No. 585.] 
 
 Hind foot. The digits III and IV were united as in the fore feet, 
 but the single hoof was more pointed. The metatarsals II and V 
 were developed. The latter was 12-7 cm. long, and was united to the 
 large metatarsal above, but was free below, and was joined by a liga- 
 ment to its accessory hoof. That of II began in the middle of the 
 metatarsus, being cartilaginous and of about the thickness of a goose- 
 quill ; it was connected with the accessory hoof by a ligament only. 
 Kitt, Dent. Z. f Thierm., xil, 1886, Jahresb. 1884-85, p. 59, Case 
 No. I, Jin. 
 *580. Calf. Three of the feet had each one large digit (III and IV) 
 formed much as in the last case. But in the dried preparation it 
 could be seen that in each of these feet there were four accessory 
 hoofs, and connected with them several ossicles irregularly placed, re- 
 presenting phalanges 1 and 2 connected by ligaments with lateral 
 metacarpals. The fourth foot [which 1] had only three accessory hoofs, 
 but the phalanges 1 and 2 of the digits III and IV were partially 
 separated from each other, and there were two distal phalanges, 
 one for each digit ; but instead of being side by side, they were placed 
 one behind the other, both being encased in a single hoof. Kitt, I.e., 
 p. 61, Case No. II. 
 
 581. Calf. A right fore foot having the two chief digits (III and IV) 
 represented by one digit with one hoof. The distal end of the common 
 metacarpal had two articular surfaces in close contact which bore a 
 digit in which there were only slight traces of duplicity. The meta- 
 carpal of the digit V was represented by two small bones, one beside 
 the upper and one beside the lower end of the large metacarpal. 
 These two ossicles were connected together by a ligament which is 
 prolonged downwards as far as the accessory hoof, and contains two 
 nodules of cartilage. On the median side of the foot there is no 
 rudiment of the metacarpal II, but the accessory hoof contains a 
 nucleus of partly ossified cartilage. Kitt, I.e., p. 63, Case IV. 
 
 582. Calf having a single hoof on each fore foot. In external appearance, the hoof 
 was a single structure, but its anterior portion shewed two projections which sug- 
 gested that it was really a double structure. The outer accessory hoof was present 
 on the right foot in a very much reduced form, but the corresponding structure of 
 the inner side of the foot was entirely absent, and a marked ' turning-point ' in the 
 hairs (Haancirbel) indicated the place where it should normally have been de- 
 veloped. In the left foot the accessory hoofs were in the same condition as in the 
 right foot, but the ' turning-point ' was not formed at all. There were no skeletal 
 structures corresponding to the accessory hoofs. 
 
 The skeleton of left fore foot was prepared. In it the metacarpal was 125 mm. 
 long, having a deep cleft on its anterior face, indicating the line of union of the two 
 metacarpals. The two articular heads, which in a normal animal of the same age 
 are separated from each other by about 5 mm., are in this specimen united by the 
 inner edges of their anterior borders. The proximal phalanges formed a single 
 bone, 32 mm. long. The division between the two bones was visible as a cleft on 
 the anterior surface, in which place the two ossifications were distinctly separated 
 from each other ; on the posterior surface the union between the two is continued 
 for half the length. The second phalanges formed a typically single bone, as did 
 also the distal phalanges which bore the hoof. The foramina for the two nutrient 
 arteries of the two toes remained double and entered the single bone, one on each 
 
CHAP. XIII.] 
 
 SYNDACTYLISM : PIG. 
 
 387 
 
 583. 
 
 side. Landois, H., Verh. d. naturh. Ver. d. preuss. Rheitil., Bonn, 1881, S. 4, vin. 
 p. 127. 
 
 Pig. " Solid-hoofed " pigs have been mentioned by many 
 writers from the time of Aristotle. The fact that they have 
 been reported as occurring in many parts of the world makes it 
 likely that the variation has often arisen afresh. The first case 
 (No. 583) is the only instance of complete union of III and IV in 
 the pig that is known to me. The variation is most commonly 
 simultaneous in fore and hind feet. As seen, it occurs in many 
 degrees. Several specimens not separately mentioned below are in 
 the Coll. Surg. Mus. and other collections. 
 
 A fore foot and a hind foot of the same individual, in which the 
 two chief digits were completely united, viz. represented by a 
 single series of bones. 
 
 In each case the two chief metacarpals and metatarsals (III 
 and IV) were respectively represented by a single large bone, and 
 with each a single digit of three phalanges articulated. The bones 
 of these digits were straight, and not curved as they are in an 
 ordinary foot in which two toes are present. There was not the 
 slightest trace of duplicity, and the lateral digits were placed 
 symmetrically on either side. The sesamoids were two in number 
 
 A 
 
 B 
 
 Fig. 120. Bones of feet of solid-hoofed Pig, No. 583, from specimens in the 
 Museum at Alfort, described by Barrier. 
 
 A. Left manus from in front. 
 
 B. Left manus from behind. 
 
 C. Left pes from in front. 
 
 The numbers II and V indicate the digits so numbered in the normal. 
 
 25—2 
 
388 MERISTIC VARIATION. [part i. 
 
 instead of four. The carpus and tarsus appear to have also been 
 changed in connexion with this unification of the digits, for in the 
 distal series at least the normal number of bones was not present. 
 [The feet had been cut off across the tarsus and carpus before 
 being received. By kind permission of the authorities at Alfort 
 I examined these specimens and made the sketches in Fig. 118. 
 I could not satisfactorily identify the bones of carpus and tarsus. 
 The proximal parts were covered by a large exostosis.] The 
 extensor of the phalanges ended in three tendons only, and the 
 same was true of the deep and superficial flexors. The central 
 tendon in each case however shewed signs of its double nature. 
 Barrier, Rec. mid. ve'ter., 1884, Ser. 6, Tom. xiii. p. 491. 
 
 584 A skeleton of a solid-hoofed pig exists in the Museum of the Royal 
 College of Surgeons of Edinburgh which was presented by Sir Neil 
 Menzies of Rannoch, Perthshire. Inquiries instituted by Struthers 
 (1863) elicited the following facts. 
 
 " The solid-hoofed pig has been well known and abundant on the 
 estates of Sir Neil Menzies at Rannoch for the last forty years. 
 Most, if not all of them, were black. They were smaller than the 
 ordinary swine, and seem to have had shorter ears. They liked the 
 same food and pasture as the common swine, and showed no antipathy 
 to herd with them. They were more easily fattened, though they did 
 not attain so large a size as the ordinary swine ; their flesh was more 
 sweet and tender, but some of the Highlanders had a prejudice against 
 eating the flesh of pigs which did not " divide the hoof," unaware 
 apparently that the Mosaic prohibition applied to all pigs. A male 
 and female of the solid-hoofed kind w T as brought to Rannoch forty 
 years ago, by the late Sir Neil Menzies, which was the commencement 
 of the breed there ; but I have not been able to learn Avhere they were 
 brought from. Although they did not breed faster than the common 
 kind, they multiplied rapidly, in consequence of being preserved, so 
 that the flock increased to several hundred. 
 
 " At first, care was taken to keep them separate, on purpose to 
 make them breed with each other, but after they became numerous 
 they herded promiscuously with the common swine. As might be 
 expected in a promiscuous flock, some of the young pigs had solid and 
 some cloven feet, but I am unable as yet to say whether any definite 
 result was ascertained as to the effect of crossing ; whether any experi- 
 ments were tried as to crossing ; or whether after the promiscuous 
 herding, some of the pigs of the same brood presented cloven and 
 some solid hoofs. 
 
 " No pig was ever known there with some of its feet solid and 
 some cloven ; nor, so far as is known, was there any instance of young 
 born with cloven feet, when both parents were known to be solid- 
 hoofed. The numbers diminished — for what cause is not apparent ; 
 so that last year there was only one or two — one of them a boar, 
 which died ; and now the solid-hoofed breed appears to be extinct in 
 Rannoch." 
 
 585. " Fore foot. — The distal phalanges of the two greater toes are re- 
 presented by one great ungual phalanx, resembling that of the Horse, 
 
CHAP. XIII.] 
 
 SYNDACTYLISM : PIG. 
 
 389 
 
 but longer in proportion to its breadth. The middle phalanges are 
 also represented by one bone in the lower two-thirds of their length, 
 presenting separate upper ends for articulation with the proximal 
 phalanges. The proximal phalanges are separate through their entire 
 length. The whole foot above the middle phalanges presents the 
 usual arrangement and proportions in the hog." Middle Phalanges. 
 "There is no symphysis or mark indicating a line of coalescence of the 
 two phalanges. The surface across the middle is somewhat irregularly 
 filled up to nearly the level of each lateral part. Each half of the 
 phalanx, as indicated by the notch between the separate upper ends, 
 has the full breadth of the proximal phalanx above it." Distal 
 Phalanx. The middle part of this is raised above the lateral parts, 
 and is partially separated from them by a fissure on each side, giving 
 it an appearance as of the union of three bones. The end of the 
 phalanx is notched like that of the horse ; it bears no trace of 
 symphysis. ' ' The ungual phalanx of one of the lesser internal toes of 
 the fore foot presents a bifurcation reaching half the length of the 
 phalanx." See Fig. 121. 
 
 I. II. 
 
 Fig. 121. I. A right fore foot of a solid-hoofed Pig, No. 585, from in front. 
 The ungual phalanx of the digit V is bifid [cp. Nos. 579 and 580]. 
 
 (After Struthers.) 
 
 II. Middle digits of foot of solid-hoofed Pig, No. 587. .r, an extra ossification 
 wedged in between the phalanges of III and IV. (After Elliott Coues.) 
 
 " Hind foot. In the hind foot only the distal phalanx is single.... 
 There is no trace of double origin to the bone." Struthers, J., Edin- 
 burgh New Phil. Jourii., 1863, pp. 273— 279, Jigs. 
 
 586. A P air of solid-hoofed pigs received by Zoological Society of London from Cuba 
 * in 1876. The sow gave birth to a litter of six [the solid-hoofed boar being presumably 
 the father]. The six young were three males and three females. The hoofs wen 
 solid like those of the parents in two males and one female : in the others the hoofs 
 were cloven as in the normal pig. The feet of one of the solid-hoofed males of thi> 
 litter were dissected, and it was found that "the proximal and second phalanges 
 are separated as usual, whilst at the extreme distal ends of the ungual phalanges 
 
390 MERISTIC VARIATION. [part i. 
 
 these bones are completely fused together ; and, further, a third ossicle was developed 
 at their proximal ends, where they are not completely united, between and above 
 them " [cp. No. 587]. " It might have been imagined that the deformity was simply 
 the result of an agglutination along the middle line of the two completely-formed 
 digits ; but such is not the case, the nail-structure being absent in the interval, 
 where it is replaced by bone with a transverse cartilage below it. The nail is con- 
 tinued straight across the middle line of the hoof, as in the horse." Garbod, A. H., 
 Proc. Zool. Soc, 1877, p. 33. 
 
 587. Domestic pigs having the two central hoofs compounded into a single solid hoof 
 have been known to occur several times in America. The two other toes remain 
 distinct in these cases. A breed of pigs having this character is said to have been 
 established in Texas, which transmits this peculiarity in a definite way. In this 
 breed the peculiarity is said to have been so firmly established that "no tendency to 
 revert to the original and normal form is observable in these pigs." A cross between 
 a solid-hoofed boar and an ordinary sow is said to produce a litter of which the 
 majority shew the peculiarity of the male parent. " On the sole of the hoof, there 
 is a broad, angular elevation of horny substance, apex forward, and sides running 
 backward and outward to the lateral borders of the hoof, the whole structure being 
 curiously like the frog of the horse's hoof. In fact it is a frog, though broad, 
 flattened, and somewhat horseshoe-shaped, instead of being narrow, deep and acute 
 as in the actual frog of the horse. This arcuate thickening of the corneous sub- 
 stance occupies about the middle third of the whole plantar surface of the foot." 
 The terminal phalanges are united together, and above this single bone is another 
 independent ossification lying between the second phalanges of the two digits, which 
 remain distinct. [Cp. No. 586.] Coues, Elliott, Bull. XI. S. Geol. Geogr. Surv., iv. 
 p. 295, fig. 
 
 588. Case resembling the above reported from Sioux City, Iowa, in which these pigs 
 were bred for some time and were advertised for sale, with the statement that they 
 were also of superior quality. Other cases given from different parts of the United 
 States. In one of these it is stated that one hind foot was thus formed [the others 
 being presumably normal]. Auld, R. O, Amer. Nat., 1889, xxiii. p. 447, fig. 
 
 589. Fig. In all four feet the digits III and IV partially united and covered by one 
 hoof. The metacarpals and first phalanges were separate in each case but the 
 second and third phalanges of the two digits were united together. The common 
 hoofs were not compressed laterally, as in some of the cases seen in the Calf, and 
 the small digits II and V were unmodified. Kitt, Deut. Zt. f. Thierm., xn. 1886, 
 Jahresb., 1884-85, p. 64, Case IV, figs. 
 
 POLYDACTYLISM IN BlRDS 1 . 
 
 The whole number of cases of Polydactylism recorded in 
 birds generally is small. The phenomena however seen in the 
 Dorking fowl are well worthy of attention and have scarcely been 
 adequately treated. I propose here to give an account of this 
 case, mentioning instances seen in other birds and indicating so far 
 as may be their relation to the facts of the Dorking. 
 
 Five-toed fowls have been known from very early times. The 
 character is now most definitely associated with the Dorking, though it 
 is also considered necessary in Houdans for show purposes. It is 
 likely that the latter breed derived the fifth toe from the Dorking. 
 Fifth toes may often be seen to occur in other breeds, but I cannot 
 quote a satisfactory record of their appearance in pure strains. 
 
 In the foot of an ordinary four-toed fowl the hallux articulates with 
 the tarso-metatarsus by a separate metatarsal. The hallux in such a 
 foot most often has two phalanges. In its commonest form the five- 
 toed foot departs from this normal in the fact that the hallucal meta- 
 
 1 See also the case of Rissa, p. 396. 
 
chap, xiii.] DIGITS I BIRDS. 391 
 
 tarsus bears two digits instead of one. The morphological nature of 
 these digits is obscure. Some have judged that one of them is .1 
 " prse-hallux ; " Cowper ' sees in the internal toe the true hallux, and 
 argues that the digit commonly called the hallux is really the index ; 
 Howes and Hill 2 consider that the normal hallux has split into these 
 two digits. The diversity of these views comes partly from an insuffi- 
 ciency of the area of fact over which the inquiry has been extended, 
 for it will be found that the conditions are very various and shade off 
 imperceptibly in several directions. As in all cases of Meristic Series, 
 the first question relates to the position of these digits in the system of 
 Symmetry of the limb. Are they in a Successive Series with the 
 other digits, or do they balance them ? Are they in Succession to each 
 other or do they balance each other as images 1 
 
 Turning to the facts with these considerations in view it will be 
 seen that no general answer can be given, but that the condition is 
 sometimes of the one kind and sometimes of the other. For there are 
 not merely two conditions, a four-toed and a live-toed, but there is a 
 whole series of conditions and according to the cases chosen so may the 
 question be answered. By examining a few score of fowls' feet many 
 sorts may be seen. 
 
 590. (1) The most usual five-toed foot is that figured by Cowpeb 
 (I.e., p. 2-19), in which the metatarsal of the hallux bears two digits, an 
 outer one of two phalanges and an inner of three phalanges. For pur- 
 poses of description let us call the outer the hallux. In this foot then 
 the hallux is the least digit, and the members of the digital series 
 increase in size on either side of it. 
 
 591. (2) But not rarely is found a state like the last save that the 
 inner digit is borne by the proximal phalanx of the hallux. This is 
 very common. The two digits may then be about equal in size, or 
 more often the hallux is the smaller. 
 
 592. (3) Hallux more or less perfectly divided into two digits with a 
 common base, having (a) two, or (b) three phalanges (as in Howes' case 
 Fig. 5). This state is practically that of the human "double-thumb" 
 (see p. 350), and, just as in that phenomenon, the duplicity may be of 
 various extent, often affecting only the nail and distal phalanx. f ><•- 
 tween the two parts of such a double digit there is often that relation as 
 of optical images found in human double-thumb, the curvatures of the 
 two parts being equal and opposite. But if both digits are of good - 
 and are separate up to the metatarsal this equality is rarely it ever found, 
 and one of the digits, generally the innermost, is the larger. In this 
 condition therefore there is a Succession from the hallux to the inner 
 digit just as in (1). So the condition of double-hallux, that is to say 
 the representation of one member of a series by two members in bi- 
 lateral symmetry, shades off' imperceptibly into the condition in which 
 a new member is formed in Succession to the terminal member. 
 
 It should be noted that this case presents a remarkable difference 
 from that seen in the like cases of variation on the radial Bide of the 
 hand of Man. In Man the states of true double-thumb are just as in 
 the Fowl; but if there is a difference or Succession between the two parts 
 
 1 Jour. Anat. Phys., xx. p. 593; and xxm. p. 242. 
 - Ibid., xxvi. p. 31)5, jigs. 
 
392 MERJSTIC VARIATION. [pam I. 
 
 it is the external l which is the greater, being in several cases a three- 
 phalanged digit shaped like an index (see No. 486). Nevertheless in the 
 Fowl it is the internal which is the greater. 
 
 The conditions in the following cases are not far removed from those named 
 above. 
 
 593. Archibuteo lagopus (Rough-legged Buzzard): specimen in good condition 
 shot near Mainz, being otherwise normal. The toes of the left foot were placed as 
 usual in a bird of prey, but on the outside 2 of the hind toe was a much smaller 
 accessor}- toe. This accessory toe was attached to the hind toe almost as far as the 
 base of the claw of the latter. The claw of the accessory toe was half the size of 
 that of the hind toe. In the left leg the muscles of the thigh and shank were less 
 developed than usual. Toes of right foot abnormally arranged, being all directed 
 forwards. The three normally anterior toes were on the inside of the series, and 
 the toe which should properly be single and directed posteriorly was double and was 
 directed anteriorly. These abnormally disposed toes were not functional. The 
 right leg was much more developed than the left, and it seemed as if the bird had 
 habitually stood on the right leg. vox Reichenau, W., Kosmos, 1880, vn. p. 318. 
 
 594. Gallinula chloropus (Moorhen): specimen killed in Norfolk in 1846. "Each 
 of the hind toes possessed a second claw, which in the right foot merely springs 
 from about the middle of the true toe, but in the left is attached to a second toe, 
 which proceeds from the original one, about half-way from its junction with the 
 tarsus." Extra toe and claw in each case attached outside 2 of the true hind toe. 
 Guexey, J. H., and Fishek, W. R., Zoologist, 1601. 
 
 Guinea-hen having double hallux ; of the two digits the external 2 was the 
 longer. Geoffroy St Hilaire, Hist, cle Anom., i. p. 695. 
 
 Division of digits II and III. 
 
 595. Anas querquedula, L. (Garganey Teal): wild specimen having the left foot 
 abnormally formed. In it there was no toe occupying the place of the hallux, but 
 the digits II and III [using the common nomenclature] were partially bifurcated. 
 In the digit III, the extremity only was divided, but each part bore a separate nail 
 and there was no web between these secondary digits, which were somewhat irregular 
 in form. The digit II divided in about its middle into two nearly similar digits, 
 which were united by a web. The nails of these digits were hypertrophied. Erco- 
 laxi, Mem. Ace. Bologna, S. iv. T. in. p. 804, Tav. in. fig. 1. 
 
 596. (4) From the condition seen in (3) it might be supposed that 
 duplicity of the hallux is the least possible step in the progress of the 
 four-toed form towards the five-toed. It is only one of the least possi- 
 ble steps. For in a few cases upon the base of the digit recognizable 
 as the hallux, and standing in the normal place of the hallux, may be 
 found a minute rudiment of a digit, sometimes with a nail, sometimes 
 without. Between this and the well-formed fifth toe all conditions exist. 
 
 There are thus, as usual in the numerical variations of Meristic 
 Series, two least conditions, one being found in duplicity of a single 
 member, the other taking the form of addition of a rudimentary 
 member beyond the last member. 
 
 597. Passing now from the simpler conditions of the variation to the 
 more complex, several distinct states may be mentioned. The diverg- 
 ence from the normal may be greater either by the presence of two 
 extra digits, or by change in the position of the extra digit or digits. 
 
 1 The only case to the contrary is that mentioned by Wixdle, Jour. Anat. Phys , 
 xxvi. p. -440, in which a three-phalanged digit stood on the radial side of a pollex. 
 This ease has not been described. See pp. 326 and 352. 
 
 2 In reading these records it should be remembered that owing to the backward 
 direction of the hallux the apparent outside is morphologically inside, and probably 
 this is meant in each case. 
 
chap, xiii.] DIGITS : BIRDS. 393 
 
 Tico extra digits are said to be not uncommon in the Dorking but I have 
 myself seen only one case. A foot of this kind is figured by Cowper 1 , 
 and in it the appearance is as of an extra digit of three joints ( ? all 
 phalanges) arising internally and proximally to the hallucal metatarsal, 
 which already bears two small and sub-equal digits. In the case seen 
 by myself there was one large internal digit with three phalanges sepa- 
 rately articulating with the tarso-metatarsus, and the hallucal metatarsus 
 bore a digit divided peripherally, bearing two nails related as images. 
 Here therefore there was a double hallux, and internal to it a separate 
 digit. 
 
 598. The evidence regarding extra digits in other positions, though small 
 in amount, is of importance as a light on the morphology of these repeti- 
 tions of digits. We have seen that the ordinary extra digit is, with 
 the hallux, borne on the hallucal metatarsal. In one of Howes' cases 
 (I. c. figs. 2 and 3) this metatarsal instead of simply articulating with 
 the shank of the tarso-metatarsal ivas continued up to articulate also 
 with the tibio-tarsus. From this state the condition in which a separate 
 digit (or digits) articulates with the tibio-tarsus only is not far removed. 
 Of this condition I know no detailed account in the Dorking, though it 
 is referred to by Lewis Wright 2 , but I have met with the following 
 cases in other birds. • 
 
 599. Aquila chrysaetos (Golden Eagle): having two extra toes borne by right 
 metatarsus [left foot is not described]. The two extra toes attached to upper part 
 of the back of the metatarsus. Each bears a full-sized claw which was curved 
 backwards and upwards. One of the toes bore six scutella on the morphologically 
 upper surface and four on the plantar surface. The other toe, which was more 
 completely united to the metatarsus along its whole length, bore only a single 
 scutellum on the plantar surface. The rest of the foot was normal. Jackel, A. J.. 
 Zool. Gart., xv. 1874, p. 141, fig. 
 
 600. Pheasant: right foot bearing a thin and deformed digit articulating internally 
 with the distal end of tibio-tarsus. Hallux normal. Left not seen. Specimen 
 received from Mr W. B. Tegetmeier. 
 
 (301. Pheasant: each leg bears a large extra digit of irregular form attached to the 
 middle of anterior surface of tibio-tarsus. The two legs almost exactly alike, but in 
 one the digit is firmly and in the other loosely attached to tibio-tarsus. Specimen 
 kindly sent by Mr Tegetmeier. 
 
 602. Buteo latissimus S , having extra digit on right leg. the toe was well formed, 
 with two phalanges, bearing perfectly formed claw, loosely attached internally 
 to tibio-tarsus just above articulation with tarso-metatarsus. Coale, H. K., Auk, 
 1887, iv. p. 331, fig. [Cp. No. 593.] 
 
 603. Turkey having two imperfectly separate digits [? images] attached to process of 
 tibio-tarsus. Two cases differing in degree: hallux normal. Ercolani, Mem. Ac. 
 Bologna, Ser. iv. in. PI. in. figs. 2 and 3. 
 
 604. Pheasant: somewhat similar case, in which two such digits were similarly 
 placed, but one was large and the otber small. Ibid., fig. 4. 
 
 605. Larus leucopterus. For the following case I am indebted to Professor R. 
 ' Ridgway, Curator of the Department of Birds, in the United States National 
 
 1 Cowper, J., Joum. Anat. Phys., xxm. p. 249. 
 
 2 "Perhaps the most difficult point in judging Dorkings, however, La to watch 
 
 against malformations of the feet which have been fraudulently removed ; for 
 
 the abnormal structure of the Dorking foot is very apt to run into still more abnor- 
 mal forms, which disqualify otherwise fine birds for the show-pen. Birds are not 
 unfrequently produced which possess three back toes, or have an extra toe high ap 
 the leg; or, in the case of the cock, with supernumerary spurs, which have been 
 
 known to grow in every possible direction We have on two occasions seen 
 
 prizes awarded to birds which shewed unquestionable traces of such amputation...." 
 The Illustrated Book of Poultry, 1886, p. 331. 
 
394 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Museum. The specimen is No. 76,221 in that collection, marked "Greenland, 
 Sept. 1877 ; Loc. Kumlien." The accompanying figures were kindly made for me 
 
 A 
 
 B 
 
 Fig. 122. Larus leucopterus, No. 605. 
 
 A. Eight foot seen from in front. 
 
 B. The same from the internal side. 
 
 C. Left foot from in front. 
 
 From a drawing of specimen in U. S. Nat. Mus., kindly made for me by Prof. 
 Eidgway's direction. 
 
 under Professor Eidgway's supervision and sufficiently shew its structure (Fig. 122). 
 [It will be seen that the hallux in A, the right foot, appears on the outside; this I 
 conceive is due to partial rotation to shew the abnormal toes.] 
 
 Besides these there are a few amorphous cases of extensive repetition of digits in 
 birds. 
 
 These facts shew how fruitless a work it is to try to find a 
 general statement which shall include all the cases. There is an 
 almost unbroken series of conditions starting from either duplicity 
 of the hallux, or from the presence of an internal rudimentary 
 
chap, xiii.] DIGITS : LIZARD. 395 
 
 digit, up to a condition somewhat resembling that of " double- 
 hand " in Man. If the first digit behind the hallux is the prae- 
 hallux, what are the digits on the tibio-tarsus ? If on the other 
 hand the appearance of an extra digit internal to the supposed 
 hallux is to be evidence that this " hallux ,: is the index, it may 
 equally be argued that if two digits come up internal to the 
 " hallux " then the supposed hallux is the medius, and so on inde- 
 finitely. Again, though with Howes and Hill we may accept 
 the cases of double-hallux as evidence that an extra digit may 
 appear by division of the hallux, which is indisputable, we must 
 equally accept the cases Nos. 597 and 598 as evidence that extra 
 digits may grow directly from the tarsus or even from the tibia, 
 though the hallux remain single and unchanged. And between 
 these two there is no line of distinction ; they pass into each 
 other. Do not these things suggest that we are looking for an 
 order that does not exist ? Is it not as if we should try to name 
 the branches of a tree in their sequences ? 
 
 Possibly Continuous numerical Variation in Digits : miscellaneous 
 
 examples. 
 
 Under this heading are placed in connexion a few cases of 
 great interest. Whatever may be held as to the relation to the 
 problem of Species of the phenomena hitherto described, it can 
 scarcely be doubted that the following are instances of Variation 
 which at least may be of the kind by which new forms are evolved. 
 
 Great interest would attach to a determination whether the 
 reduction of the digits in these cases is a' continuous or a discon- 
 tinuous process, but unfortunately these phenomena have been 
 statistically studied by no one, and it is not possible to do more 
 than make bare mention of the fact that such Variation is known 
 to occur. There is no statistical evidence as to whether the indivi- 
 duals in any one locality may not fall into groups, dimorphic or 
 polymorphic in respect of the degree to which the digits are 
 developed (compare the case of the Earwig, Introduction, p. 40). 
 As an inquiry into the Continuity of Variation such an investiga- 
 tion would be exceptionally valuable. In the case, for instance, of 
 Cistudo mentioned below, such a statistical inquiry should surely 
 not be hard to make. 
 
 *606. Chalcides. This is a genus of Lizards belonging to the 
 family Scincidse. In several genera of this family the limbs are 
 reduced or absent, differences in this respect being frequent among 
 species of the same genera. (See Boulenger, Catalogue of Lizards 
 in Brit. Mus., 1887, m. pp. 398, &c.) 
 
 Mr Boulenger kindly shewed me a number of Lizards of the 
 
 ..... 
 
 genus Chalcides from the shores of the Mediterranean basin which 
 strongly resemble each other in colour and general appearance, but 
 which contained almost a complete series of conditions in respect 
 
396 MERISTIC VARIATION. [part i. 
 
 of the development of the limbs and digits, ranging from C. ocellatus 
 and C. bedriagce with pentadactyle limbs fairly developed, through 
 C. lineatus (tridactyle) and 0. tridactylus to C. guentheri in which 
 the limbs are minute conical rudiments. Amongst the species of 
 this series great individual variations occur. 
 
 607. Chalcides mionecton : normally four digits on each foot. 
 A specimen in Brit. Mus. kindly shewn to me by Mr Botjlenger 
 has on each hind foot five digits. 
 
 608. C. sepoides : Mr Botjlenger tells me that the normal num- 
 ber of digits on each foot is five, but that specimens occur having 
 four digits on each foot. 
 
 609. Cistudo. This genus includes the North American Box- 
 turtles as defined by Agassiz (N. Amer. Testudinata, Gontrib. to 
 N. H. of U. S., I. p. 444). These animals are widely distributed 
 to the E. of Rocky Mountains. On the hind feet of some of them 
 there are three digits, while others have four. Gray (P. Z. S., 
 1849, p. 16) described two Mexican specimens which agreed in 
 having three large claws on the hind foot with no appearance of a 
 fourth claw, and even scarcely any rudiment of the fourth toe, 
 which was then believed to be present in the other members of 
 the genus. To this three-toed form he gave the generic name 
 Onychotria, but in Brit. Mus. Cat, 1855, he gave up this name as 
 a generic distinction, describing the Mexican form as Cistudo mexi- 
 cana, giving three toes on the hind foot as a definite character. 
 
 Agassiz in 1857 (I.e.) divided Cistudo into four species, giving 
 to the Mexican form the name C. triunguis, and he states that the 
 western and south-western type is remarkable for having almost 
 universally only three toes on the hind feet. The toe which is 
 missing is the outer toe and " it fades away so gradually that the 
 genus Onycliotria cannot stand." The form found from New 
 England to the Carolinas is called by Agassiz G. virginea = C. Caro- 
 lina, and he states that he received a three-toed specimen from N. 
 Carolina which agreed in all other respects with those from New 
 England. 
 
 Putnam (Proc. Boston, N. H. S., x. p. 65) stated that the three- 
 toed form found in the South is only a variety of C. virginea, and 
 that he had seen two specimens which had three toes on one hind 
 foot and four on the other. 
 
 610. Rissa 1 . The common Kittiwake (R. tridactyla) as found in 
 
 1 In illustration of the possible bearing of these facts on the problem of Species 
 reference may be made to the fact that among birds there are several examples of 
 species differing from their near allies by reason of the absence of the hallux. 
 Speaking of this feature in Jacamaraleyon tridactyla, Sclater observes: "In the 
 present bird we meet with another example of the same character [viz. a monotypic 
 form], and with one, perhaps, more isolated in its structure than any of those 
 above mentioned, Jacamaraleyon being notably different from all other members 
 of the Galbulidae in the absence of the hallux. At the same time we must be 
 careful not to put too high a value upon this at first sight seemingly important 
 
chap. xiii. j DIGITS : K1TTIWAKE, ELEPHANT, &C. 397 
 
 this country and in N. Atlantic has no hallux, but only a small 
 knob without a nail in its place. No variation in respect of this 
 digit is recorded 1 . Birds not distinguishable from the Atlantic 
 Kittiwake occur in the North Pacific, but amongst these Pacific 
 specimens birds are found occasionally as rarities having a hallux 
 " as large as it is in any species of Larus " (Coues, p. 640). This 
 feature also exhibits gradatious. Specimens are described by 
 Coues and also by Saunders having the hallux including the 
 nail 2 in. long, with a perfect claw. These are given as extreme 
 examples. Saunders remarks that this hallux is small for the 
 size of the bird, stating that another species of similar size, L. 
 canus, had a hallux '5 in. long. Of these specimens of R. tridac- 
 tyla from Alaska one had the nail of the hallux developed, though 
 less so than in the extreme case. Saunders states further that the 
 variation is not always equal in extent on both feet of the same 
 individual : he considers that the extreme form is probably rare 
 and local. Coues, E., Birds of North-West (U. S. Geol. Surv. 
 Terr.), 1874, p. 646; and Saunders, Howard, P. Z. 8., 1878, pp. 
 162—64. 
 611. Rissa brevirostris : a species from the N. Pacific distinct from 
 R. tridactyla shews a similar variation in the development of the 
 hallux, though in a smaller degree. A specimen has no claw on 
 right hind toe and only minute speck on left ; another has no 
 hind nail whatever ; another has small black nails of unequal size 
 on the two hind toes. Saunders, H., I. c, p. 165. 
 
 (312. Erinaceus. E. europceus has a large hallux, while in E. diadema- 
 tus it is only 4 mm. in length, and in E. albiventris it is normally absent 
 in adults. An adult female S. albiventris had a minute hallux in 
 the left hind foot, represented by a claw and ligamentous structures, 
 the rjhalanges being absent 2 . In a female a few months old a minute 
 hallux with usual number of phalanges was present on both sides. 
 The presence or absence of a hallux has often been considered a suffi- 
 cient ground for the formation of a new genus. Dobson, G. E., 
 P. Z. &, 1884, p. 402. 
 
 613. Elephas. In both the Indian and African elephant the 
 number of digits represented by bones is five, both in the fore and 
 the hind foot. The number of hoofs differs in the two species. 
 The African elephant has normally four on the fore foot and three 
 
 character, as the same feature occurs as is well known, not only in certain genera 
 of other allied families (such as Alcedinidre and Picida}), but even in a genus of 
 Oscines (Cholornis), in which group the foot- structure is generally of a very uniform 
 character." Sclater, P. L., Monograph of t he Jacamars and Puff-Bird* t 1879 -82, 
 p. 50. 
 
 1 Mr A. H. Evaxs has called my attention to a recent paper by Clarke (Ibis, 
 1892, p. 442) giving an account of a minute rudiment of the hallux in embryos of 
 R. tridactyla from Scotland. 
 
 2 Compare facts as to the loss of the hallux in Mungooses (Herpestida 1 ), Thomas. 
 O., P. Z. S., 1882, p. 61. 
 
398 MERISTIC VARIATION. [part I. 
 
 on the hind foot, and I am not aware that variations from this 
 number have been seen. 
 
 In the Indian elephant there is variation, and though I cannot 
 give any complete account of the matter the following particulars 
 may be of interest. 
 
 According to Buffox the ' Elephant ' has generally five hoofs 
 on both fore and hind feet, but sometimes there are four, or even 
 three 1 . He gives a particular case of an Indian elephant with 
 four hoofs on each foot, both fore and hind feet. 
 
 Tachard 2 , to whom Buffon refers, was desired by the French 
 Academy to notice on his journey in Siam, whether elephants had 
 hoofs, and he states that all that he saw had five on each foot. 
 Possibly the four- toed variety does not occur in Siam. 
 
 I am indebted to Mr W. T. Blanford for the information that 
 the natives of India attach importance to the number of hoofs, 
 and also for the following references. Hodgson 3 gives a sketch 
 of elephants with four hoofs on each foot, marked " Elephas 
 Tndicus, var. isodactylus nob., Hab. the Saul forest," together with 
 the following note : " The natives of Nepal distinguish between 
 the breeds with four toes [sic] on all the feet and those with five 
 to four toes." Sanderson 4 speaking of this says that some 
 elephants have but sixteen hoofs, the usual number being five on 
 each fore foot and four on each hind foot ; and that in the native 
 opinion 'a less number than eighteen hoofs in all disqualifies the 
 best animals.' Forsyth 5 also alludes to the same fact. 
 
 Taken together these accounts seem to shew that five on the 
 fore foot and four on the hind foot is the most usual number, but 
 that both the number on the fore foot may diminish to four and 
 that on the hind foot may increase to five. Several text-books 
 mention the subject but I know no statistics regarding it. In 
 view of the different number characteristic of the African elephant 
 this variation has some interest. In particular it would be of use 
 to know whether the variation exhibits Discontinuity, and also 
 to what extent it is symmetrical. 
 
 Inheritance of digital Variation. 
 
 614. Recurrence of digital Variation in strains or families is frequent, 
 but though many observations on the subject have been made no 
 guiding principle has been recognized. To the general statement that 
 digital Variation, whether taking the form of poly dactyl ism or other- 
 
 1 Buffon, Hist. Nat., xxviii. p. 201. The mention of three hoofs must I think 
 refer to the African species, which Buffon does not distinguish from the Indian. 
 In the Cambridge Museum (Catal. 699) is an old preparation of the skin of an 
 elephant's foot having three hoofs. This is declared by the Catalogue to be the 
 fore foot of an Indian elephant. Perhaps this is a mistake. 
 
 2 Tachard, Voy. de Siam, 1687, p. 233. 
 
 3 Hodgson, B. H., Mammals of India, MS. in Zool. Soc. Library. 
 
 4 Sanderson, G. P., Wild Beasts of India, p. 83. 
 
 5 Forsyth, J., Highlands of India, 1872, p. 286. 
 
chap, xiii.] INHERITANCE OF DIGITAL VARIATION. 399 
 
 wise, does very commonly appear in the offspring or kindred of the 
 varying individuals I can add nothing. It should be mentioned that 
 though in families exhibiting digital Variation the forms that the 
 change takes may differ (in some cases widely even among individuals 
 nearly related) yet on the whole the variation, if recurring at all, more 
 often recurs in a like form. This holds good apart from the rarity 
 of the particular form of variation. The facts described by Farge 
 (I.e., infra) are exceptionally interesting in this connexion. In the 
 family described by him duplicity of the thumbs occurred in the 
 paternal grandmother, while the father and three children had their 
 thumbs of the three-phalanged form as in No. 483. This case strikingly 
 illustrates the well-known principle that Meristic variability may 
 appear in the same strain or family under forms morphologically very 
 dissimilar. 
 
 Attention is also called to the circumstance that in the case of the 
 three toes in the ox (No. 558) the descent was wholly through females, 
 and the same was almost certainly true in the polydactyle cats (No. 480). 
 In the case of the syndactyle pigs the evidence of maintenance of the 
 variation in the strain is very clear (No. 584). See also No. 564. 
 
 As regards digital Variation in Man the following are the best 
 genealogical accounts : 
 
 Anderson, Brit. Med. Jour., 1886 (1), p. 1107. Billot, Mem. vied, milit., 1882, 
 p. 371. Boyd-Campbell, Brit. Med. Jour., 1887, p. 154. Fackenheim, Jen. Zte., 
 1888. Fotherby, Brit. Med. Jour., 1886 (1), p. 975. Furst (see Canst. Jahresb., 1881, 
 p. 283). Harker, Lancet, 1855(2), p. 389. Lucas, Gm/s Hosp. Rep., xxv., p. 417. 
 Morand, Mem. Ac. Sci., 1770, p. 140. Muir, Glasg. Med. Jour., 1884. Pott, 
 Jahresb. d. Kinderh., xxi., p. 392. Potton 1 quoted by Gruber from de Bansi . 
 Bull. Soc. d'Anthrop., 1863, iv. p. 616. Struthers, Edin. Neio Phil. Jour., 1863(2), 
 pp. 87 et seqq. Wolf, Berl. klin. Wochens., 1887, No. 32. Farge, Gaz. hebd. de 
 med. et chir., Ser. 2, n. 1866, p. 61. Case given Loud. Med. Gaz., 1834, p. 65. 
 
 Association of digital Variation with other forms of Abnormality. 
 
 (315, In the great majority of cases of polydactylism the rest of the bod} 
 is normal, the limb or limbs varying alone. There are however a cer- 
 tain number of examples of polydactylism in association with other 
 abnormalities ; as for instance with phocomely, cyclopia, double uterus, 
 hare-lip, defective dentition, defect of tibia, <kc, but there is nothing 
 as yet to indicate any special connexion between these several 
 variations. Diminution in number of digits and syndactylism is on 
 the contrary very often associated with general deformity and with 
 many forms of arrested development. To this no doubt is largely due 
 the fact that cases of ectrodactylism are commonly irregular, whereas 
 polydactylism is generally fairly regular in its manifestations, for 
 numerous cases of diminution in number of digits occur in bodies or 
 in limbs otherwise amorphous. 
 
 1 The notorious case of a village in Isere where the majority of the inhabitants 
 are said to have been polydactyle. Most modern writers on the subject quote this 
 statement but I have never found original authority for the fact. By some it is 
 referred to Devat, Du danger des mariages consanguins, 1862, p. 95, but I can rind 
 no mention of the facts in that work. 
 
CHAPTER XIV. 
 Digits : Recapitulation. 
 
 In the remarks preliminary to the evidence of digital Variation 
 it was stated that this group of facts is interesting rather as bearing 
 on morphological conceptions than from any more direct relation 
 to the problem of Species. The indications to be gained from the 
 evidence will be treated under the following heads : 
 
 (1) Comparative frequency of digital Variation in different 
 
 animals. 
 
 (2) Particular forms of digital Variation proper to particular 
 
 animals. 
 
 (3) Symmetry in digital Variation. 
 
 (4) The manus and pes as systems of Minor Symmetry. 
 
 (5) Duplicity of limbs. 
 
 (6) Homceotic Variation in terminal digits when a new 
 
 member is added beyond them. 
 
 (7) The absence of a strict distinction between duplicity of 
 
 a given digit and other forms of addition to the 
 Series. 
 
 (8) Discontinuity in digital Variation. 
 
 (9) Relation of the facts of digital Variation to the problem 
 
 of Species. 
 
 (1) Comparative frequency of digital Variation in different animals. 
 
 In reviewing much of the evidence of Variation and especially 
 in the evidence concerning the variations of teeth it has been seen 
 that the frequency of these variations is immensely greater in some 
 classes or species than in others. This is remarkably clear in the 
 case of the variations of digits. Compare for instance the great 
 frequency of polydactylism in the Horse with the complete absence 
 of recorded cases in the Ass. It is true that the latter is the rarer 
 animal, but it might still be expected that some record would have 
 been found if the variation were as frequent in the Ass as in the 
 Horse. Again polydactyle Cats are certainly not very rare and 
 specimens are in several collections having been acquired at many 
 
chap, xiv.] FREQUENCY OF DIGITAL VARIATION. 401 
 
 dates. On the other hand digital Variation in the Dog seems to 
 be confined to the formation of a hallux in the hind foot, and to 
 duplicity of hallux and pollex \ Similarly though digital Varia- 
 tion is so common in the Pig it is very rare in the Sheep, only 
 one or two clear cases being so far known to me. Note again that 
 polydactylism is common in the Fowl and has been often seen 
 in the Pheasant, while in other birds it is very rare. 
 
 Some one will of course remark that the Fowl is a domesticated 
 bird and the Pheasant is partially so ; but pigeons, ducks - and 
 geese 3 are as much domesticated and in them digital Variation 
 does not seem to be known. The cases in Apes deserve mention 
 in connexion with this matter. One case of syndactylism was 
 quoted in Pithecia No. 525, a case of polydactylism in Macacus No. 
 504?, in Orang No. 511, and in Hylobates No. 508, and a case of 
 ectrodactylism in Macacus No. 526. These five cases surely 
 suggest that Meristic Variation is something more than a mere 
 result of high feeding or of " unnatural " conditions. It is not a 
 little strange that among Apes Meristic Variation should be 
 frequently met with in so many systems of organs. 
 
 (2) Particular forms of digital Variation proper to particular 
 
 animals. 
 
 Of more significance than the frequency with which digital 
 Variation recurs in certain animals is the frequency with which in 
 particular animals it approaches to particular forms, or to particu- 
 lar conditions in a series or progression of forms. This has been 
 seen in the Cat, Man, Horse, Pig, Ox, &c. In each of these the 
 mode of occurrence of Variation has in it something distinctive, 
 something that marks the phenomenon as in some way different 
 from the similar phenomena in other forms. Taking for instance 
 the curious series of cases found in the human manus, ranging 
 
 1 Both these variations are of course very common and may be seen in any 
 walk in the streets. The hallux is very frequently present in the Dachshund and 
 is common in Collies, Mastiffs and other large breeds. In the Mastiff dew-claws 
 (hallux) are not a disqualification (Shaw, Book of the Dog). In the St Bernard the 
 hallux is very often double, perhaps more often than not. This is largely due to 
 the fact that the monks of the Hospice considered the presence of the dew-claw of 
 the utmost importance and preferred it double if possible (Shaw, I.e.). The same 
 writer states that ' the more fully the dew-claws are developed the more the feet are 
 out-turned.' This fact suggests that there may be a change of Symmetry like that 
 in the Cat, but I have no observations on the point. I have several times seen 
 simultaneous duplicity of hallux and of pollex in the same individual (Dachshund, 
 &c). Other digital variations must be rare in dogs as there are hardly any recorded 
 cases. A problematical case of ectrodactylism is given by Baum, Deut. Ztochr. f. 
 TJiierm., xv. 1889, p. 709, Jig. [q. v.]. I once saw a mongrel Fox-terrier with no 
 pollex on either manus, but I was not satisfied that they had not been cut off, 
 though there was no suggestion of this. 
 
 - For an interesting account of a Duck with the webs of the toes almost wholly 
 absent see Mobius, Zool. Gart., xvm. 1877, p. 223. Another case of the same kind 
 Morris, F. 0., Zool., iv. p. 1214. 
 
 3 Pygomelian geese often recorded; e.g. Clelaxd, Proe. Phil. Soc. Glasg., 
 xvm. 1886, p. 193,^.; Wyman, Proc. Bost/N. H. S., vm. 1861, p. 256. 
 
 b. 26 
 
402 MERISTIC VARIATION. [part l 
 
 from the addition of a phalanx to the pollex up to the condition of 
 Nos. 488 or 490, and comparing them with the essentially similar 
 series of cases in the hind foot of the Cat, there is this remarkable 
 difference : that though both progressions lead up to a similar 
 kind of Symmetry in the series of digits, in the human manus 
 an approach is made to a system of Symmetry whose axis lies 
 internal to the index, while in the Cat's feet the axis lies external 
 to the index (see Section (4)). The series of forms in the manus 
 of the Cat is still more peculiar and is not like any case of poly- 
 dactylism in other animals. 
 
 (3) Symmetry in digital Variation. 
 
 From the evidence it will have been seen that digital Varia- 
 tion in most of its manifestations may be similar and simultaneous 
 in the limbs of the two sides of the body, though not rarely it 
 affects the limb of one side only ; and still more frequently the 
 form which it assumes on one side differs in degree from that found 
 on the other side. Considerable difference in kind between Varia- 
 tion on the right side and on the left is much rarer. 
 
 Almost the same statement may be made respecting simul- 
 taneity of Variation between the manus and the pes, though in 
 the pes the manifestation of Variation is rarely identical with that 
 in the manus of the same individual. Some variations, as for 
 instance duplicity of pollex and hallux, or extra digit external to 
 minimus, are not rarely found simultaneously in both pes and 
 manus, but there are many cases in which no such agreement is 
 found. The frequency of this simultaneous variation in the case of 
 syndactylism in the Pig may be specially noticed. 
 
 Certain variations in certain animals seem to be almost or 
 quite restricted either to hind limb or to fore limb. The form 
 taken on by the pes of the Cat upon increase in number of digits 
 is distinct from that assumed by the manus. The development of 
 the digit II in the Horse is much more common in the manus. 
 The extra digit (or pair of digits) in the Pig is so far as I know 
 seen only in the manus. On the contrary the three-toed state in 
 the Ox is found in the manus and also in the pes. Generally 
 speaking, M eristic Variation is much commoner in fore limbs than 
 in hind limbs. 
 
 One fact here calls for special notice. Though general statements 
 are hazardous, we are perhaps justified in affirming the principle 
 that large Meristic Variation, involving great departure from the 
 normal, very rarely affects exclusively one side of a bilaterally sym- 
 metrical body. In cases of variation in vertebra?, in spinal 
 nerves, in teeth, in the oviducts of Astacus, and many more, it is 
 seen that on the occurrence of great variation the change is seldom 
 restricted wholly to one side of the body, though the condition 
 reached by the two sides is frequently of differing degree. Now in 
 
chap, xiv.] SYMMETRY IN DIGITAL VARIATION. 403 
 
 the extreme forms of double-hand as seen in Man there is a curious 
 exception to this principle. For in nearly all the extreme cases 
 the abnormality was on one side only, the other being normal. 
 This was seen in Nos. 492 — 500 and 501 — 503, and also in Macucus 
 No. 504. The case No. 500 is probably an exception to this general 
 statement. As to the significance of this absence of correspond- 
 ence between the right and left sides in extreme cases of digital 
 Variation I can make no conjecture. It has seemed that perhaps 
 in such cases the absence of symmetry between the two sides 
 of the body may be connected with the fact that in these extreme 
 forms of double-hand an approach is made to a bilateral symmetry 
 completed within the series of digits. But against this suggestion 
 must be noticed first the fact that a similar bilateral symmetry is 
 established in the six-toed pes of the Cat (Condition IV of the pes, 
 p. 316), but the variation is nevertheless found on both sides of 
 the body ; and secondly the case of double-foot in the lamb (No. 
 566), though for reasons stated this latter case may perhaps be 
 open to question. 
 
 (4) The manus and pes as systems of Minor Symmetry. 
 
 This is a subject to which it is most difficult to give adequate 
 treatment. Several of the phenomena have as yet been studied in 
 far too small a range of cases to justify sound generalization, and 
 with further knowledge the suggestions arising from the facts now 
 before us may not improbably be found to have been misleading 
 wholly or in part. Besides this there is a serious difficulty in 
 finding modes of expressing with clearness even those principles of 
 form which seem to underlie the phenomena. This difficulty pro- 
 ceeds first from the vague and contradictory character of the 
 indications, and next from the total absence of a terminology by 
 which diversities of symmetry and the form-relations of parts may 
 be expressed. Nevertheless it has seemed best to abstain from 
 the introduction of new terms until the ideas to be expressed 
 shall have been more clearly apprehended. It need scarcely 
 be said that the remarks which follow merely represent an attempt 
 to state some of the lines of inquiry along which the facts point. 
 
 On p. 88 mention was made of the fact that in a Bilateral 
 Symmetry the organs which occur as a pair, one on the right and 
 the other on the left, in so far as they are symmetrical are optical 
 images of each other, this relation of images being what is implied 
 by the statement that these organs are bilaterally symmetrical. 
 The hands and feet of vertebrates are organs of this kind, the 
 right hand and the right foot being approximately images of tin 
 left hand and foot respectively. But beyond their symmetrical 
 relations to each other in the Major Symmetry of the whole body 
 each manus and each pes may exhibit the condition of a Minor 
 Symmetry within the limits of its own series of digits. Not only 
 may each limb geometrically balance the limb of the other sid>- 
 
 26—2 
 
404 MERISTIC VARIATION. [part I. 
 
 but its own external parts may more or less balance its own inter- 
 nal parts. This relation differs greatly in different animals, the 
 Minor Symmetry being nearly complete in the Artiodactyles and 
 in the Horse, but much less so in the human manus and pes, &c. 
 The matter now for consideration is the influence or consequences 
 of the existence of this symmetry in the Meristic Variation of 
 digits ; and conversely the light which the observed phenomena of 
 Variation throw on the nature of that relation of symmetry. It 
 will be seen that in some points the two halves of a bilaterally 
 symmetrical limb behave just as do the two halves of the bilaterally 
 symmetrical trunk, while in other points their manner of Varia- 
 tion is different. 
 
 Thus, the digit III of the Horse may divide into two halves 
 related to each other as images, bearing hoofs flattened on their 
 adjacent edges ; that is to say, the two resulting parts are formed 
 not as copies of the undivided digit, but as halves of it, a condition 
 never seen in division occurring anywhere but in the middle line of 
 a bilateral Symmetry. 
 
 In the syndactyle feet of the Pig or the Ox the converse pheno- 
 menon exists ; for the digits III and IV, which normally stand 
 as images of each other, are here wholly or in part compounded to 
 form a digit to which the uncompounded digits are related as 
 halves. 
 
 Thus far the connexion between the geometrical relations of 
 the digits and the modes of their Variation is clear and simple, 
 and does not differ from that maintained in the Major Symmetry. 
 But in proceeding further there is difficulty. 
 
 If, for instance, the manus or pes of a Horse possesses within 
 itself the properties of a bilateral Symmetry, then the splint-bone 
 II may be supposed to be in symmetry with the similar bone IV. 
 It would therefore be expected that on the occasion of the develop- 
 ment of II to be a full digit, the splint-bone IV would at least not 
 unfrequently develop, thus exhibiting that similarity and simul- 
 taneity of Variation which we have learnt to expect from parts in 
 symmetry with each other. Nevertheless such an occurrence 
 seems to be extremely rare. Then arises a further question: if 
 the digit II develop simultaneously, say in the two fore feet, would 
 the mechanical conditions of which Symmetry is the outward 
 expression be satisfied without a corresponding change in the 
 digit IV of the fore feet ? Is the frequent absence of symmetry 
 in the variation of the halves of the Minor Symmetry in any way 
 connected with the possibility that the two Minor Symmetries 
 together may be maintaining their relations to each other as parts 
 of a Major Symmetry ? Of course as to this we know nothing, but 
 the existence of this double relation should be remembered. 
 
 In several other phenomena of digital Variation the influence 
 of Symmetry is to be suspected. Reference may first be made to 
 the series of changes seen in the Cat's hind foot in correlation with 
 
chap, xiv.] SYMMETRY IN DIGITAL VARIATION. 405 
 
 numerical change. The bones of this pes do not normally exhibit 
 any very clear bilateral symmetry \ Yet on the appearance of new 
 digits the foot is reconstituted and its parts are, to use a metaphor, 
 c deposited ' in a system of bilateral symmetry a whose completeness 
 is proportional to the degree of development of the new digits. 
 What may be the meaning of this extraordinary fact one cannot 
 yet guess. The fancy is constantly presented to the mind that there 
 is in the normal foot a condition of strain, that the balance between 
 the right foot and the left is a condition of imperfect stability, and 
 that upon the introduction of some unknown disturbance this 
 balance is upset and each foot settles down as a separate 
 system. But I see no way of testing this fancy and no way of 
 following it further. 
 
 Still more complex are the facts seen in the human hand. 
 There is here first the fairly complete series of conditions ranging 
 from the normal, through the three-phalanged thumb up to the 
 several Conditions in which extra digits upon the internal side of 
 the limb seem to have sprung up to balance the four normal digits ; 
 but on the contrary there is the exceptional case of the Macacque's 
 foot (No. 504) where the extra parts are, as I believe, external. 
 (Besides these there are the wholly distinct series of "double- 
 hands," which will be spoken of below.) The former cases taken 
 alone would certainly suggest that there is an imperfect balance 
 or system of symmetry subsisting between the thumb and the 
 four fingers of the normal manus, but to this suggestion there 
 are numerous difficulties which need hardly be detailed in this 
 preliminary glance at the phenomena. 
 
 With more confidence it can be maintained that the pollex 
 and perhaps the hallux of Man is in itself a Minor bilateral Sym- 
 metry, apart from the four fingers, for it may divide into equal 
 parts related as images. The same is true of the hallux of the 
 Dorking (p. 390), and probably of the extra digit or digits some- 
 times arising from the tibio-tarsus of the Turkey for example (see 
 No. 603). 
 
 Besides this the facts of the frequent syndactylism between the 
 digits III and IV of the human manus, taken in connexion with the 
 phenomena of the Pig and Ox, suggest that the four fingers may 
 have among themselves again a relation of the nature of Symmetry. 
 
 1 In the normal pes, though all the claws are retracted to the outside of the 
 second phalanges, yet the claws of digits III and IV rest close together, that of III 
 being external to its pad, while that of IV is internal to its pad, forming, so far, a 
 relation of images between these two digits. In the polydactyle foot it is a remark- 
 able feature that, though the bones are in symmetry about an axis passing between 
 II and III, the relation of the claws of III and IV to their pads remains almost 
 normal, still giving a superficial appearance of symmetry between these two digits. 
 (In the polydactyle pes the pads are mostly rather narrower.) 
 
 2 It will be remembered that this symmetry appears not merely in the lengths of 
 the several digits but in the manner of retraction of the claws and in the corre- 
 sponding form of the second phalanges, three digits being fashioned (in the case of 
 six perfect digits) as right digits and three as lefts. 
 
406 MERISTIC VARIATION. [part i. 
 
 It has been mentioned that there is some evidence to shew 
 that in the human pes it is the digits II and III which are most 
 frequently syndactyle, even up to the point of being (in No. 529) 
 apparently represented by a single digit, and in this connexion 
 it will be remembered that in the polydactyle pes of the Cat 
 it is also between these digits that the new axis of Symmetry 
 falls. 
 
 These scanty allusions to the possible influences which Sym- 
 metry may exercise over Meristic Variation of digits will suffice to 
 indicate the nature of the problem to those who may care to 
 examine it. It is with hesitation that so indefinite a matter is 
 spoken of at all. Nevertheless it is likely that if any one can find 
 a way of interpreting these indications the result will be con- 
 siderable. 
 
 (5) Duplicity of limbs. 
 
 In the evidence as to the digits of Man facts were given 
 respecting the state known as Double-hand, and some similar 
 cases were referred to in Artiodactyles. In these instances the 
 digital series, and to some extent the limb, is in its new shape 
 made up of the external parts of a pair of limbs compounded 
 together in such a way that there is a partial duplicity of the limb, 
 the two halves being more or less exactly complementary to each 
 other and related as images 1 . 
 
 This phenomenon in its perfect form must be essentially 
 distinct from the other cases of increase in number of digits ; 
 for in the double-hands the limb developes an altogether new 
 bilateral symmetry (see especially No. 492). Between cases of 
 duplicity in limbs and the other forms of polydactylism confusion 
 can only arise when the nature of the parts is ambiguous. 
 
 As has been stated, in all certain cases of double-limbs the 
 two are compounded by their internal or pneaxial borders, but 
 the case of Macacque No. 504 was peculiar in the fact that there 
 was in it a presumption that the two limbs were not a pair but in 
 Succession. 
 
 In Arthropoda there are a very few cases of true duplicity in 
 appendages comparable with the double-hands. These cases will 
 be dealt with hereafter. 
 
 1 The fact that a structure naturally hemi-syminetrical, needing the limb of the 
 other side to balance it, may on occasion develop as a complete symmetry is most 
 paradoxical, but no other interpretation of the facts seems possible. The phenome- 
 non is of course comparable with that observed by Driesch in the eggs of Echinus, 
 where eacb half-ovum developed into a whole larva on being separated from the 
 other half-ovum (see p. 35, Note). It will be shewn that in almost every case in 
 which such an appearance is found in the extra appendages of Insects this appear- 
 ance is misleading, and that the extra parts have a Secondary Symmetry of their 
 own ; but no such way through the difficulty is here open. 
 
chap, xiv.] DISCONTINUITY IN DIGITAL VARIATION. 407 
 
 (6) Homceotic Variation in terminal digits token a new member 
 
 is added beyond them. 
 
 This is a principle that has been several times seen in Meristic 
 Variation, and in Chapter x. Section 7, it was treated of at length 
 in the case of teeth. Some few illustrations of the same principle 
 occur among the evidence as to digits. It has been seen for in- 
 stance how that, upon the appearance of an extra digit on the 
 radial side, the digit which stands in the position of pollex may have 
 three phalanges and resemble an index (No. 485, &c). Similarly 
 it was found that upon the formation of a large digit externally to 
 the minimus the digit standing in the ordinal position of the 
 minimus may have an increased proportional length (No. 509). 
 Still more important is Morand's case (No. 510), in which the most 
 external digit had muscles proper to a minimus, while the digit 
 standing in the ordinal position of the minimus was without them. 
 
 The cases of extra digit in the Horse (No. 536, &c.) still more 
 clearly illustrate the principle, if the view of the nature of those 
 cases taken in the text be received. 
 
 It should be expressly stated that in digits, as in teeth, it is 
 not always that the terminal member is promoted on becoming 
 penultimate. Such promotion is indeed rather exceptional in 
 digits, but the fact that it may occur is none the less a phenome- 
 non of great significance. 
 
 (7) The absence of a strict distinction between duplicity of a 
 given digit and other forms of addition to the Series. 
 
 This subject has been so often spoken of in connexion with 
 special cases that it is unnecessary here to make more than brief 
 allusion to it. The same principle was shewn to be true of teeth 
 (p. 270) and of mammae (p. 193), and there is little doubt that it is 
 true of Meristic Series generally. Facts illustrating the matter in 
 relation to digits will be found in the evidence as to duplication of 
 pollex and hallux in Man (p. 351), as to duplication of the hallux in 
 the Fowl (p. 391), in the evidence of cases in the Horse of variation 
 intermediate between division of III and development of II (p. 371), 
 and in the cases of three-toed Cows (p. 377). 
 
 In almost all the animals in which any considerable range of 
 digital Variation is to be seen it is possible to find a series of cases 
 making an insensible transition from true duplicity, or division into 
 two equivalent parts whose positions and forms are such that they 
 maybe reasonably looked upon as both representing a normally single 
 member, up to the condition in which while the series contains a 
 greater number of members, each member nevertheless stands in 
 a regular Succession to its neighbour. 
 
 Upon the proper understanding of this proposition and upon 
 the recognition of its truth hang those corollaries before enuntiated 
 
408 MERISTIC VARIATION. [part i. 
 
 touching the false attribution of the character of individuality to 
 members of Meristic Series. 
 
 (8) Discontinuity in digital Variation. 
 
 The evidence that the Meristic Variation of digits may be 
 discontinuous is often rather circumstantial than direct. If for 
 example in the case of the Horse any one chooses to suppose that 
 every polydactyle horse had in its pedigree an indefinitely long- 
 series of ancestors in which the size of the extra digit progressively 
 increased, it would not be easy to produce direct evidence that this 
 was not the fact. But as regards the human examples such evi- 
 dence is abundant, many of the most marked cases being the 
 offspring of normal parents and there can be no reasonable doubt 
 that the same would be found true of other animals. 
 
 But it may fairly be replied that until it shall have been shewn 
 that formations like those described as variations may be estab- 
 lished in a natural race or species the contention that the Varia- 
 tion of digits may be discontinuous is so far weakened. To this I 
 would reply by referring to the case of Cistudo, Chalcides, and the 
 other similar examples ; for though in respect of these forms the 
 evidence is sadly imperfect yet it plainly indicates that very 
 distinct and palpable variation may be found between different 
 individuals. And since it is actually known that there may in 
 these points be considerable differences between the two sides of 
 the body it may safely be assumed that at least the same differ- 
 ences may occur between parent and offspring. 
 
 We may therefore take it that there is in these cases some 
 Discontinuity of Variation, though until some one shall have 
 examined statistically such cases as that of the Box-turtles or of 
 the Kittiwakes, as to the magnitude of the Discontinuity it is not 
 possible to speak. If hereafter Discontinuity shall be shewn to 
 occur in many such cases it will be difficult to resist the sugges- 
 tion that similar numerical diversity elsewhere characterizing the 
 digital series of various forms may have come about by similarly 
 discontinuous Variation. 
 
 (9) Relation of the facts of digital Variation to the problem of 
 
 Species. 
 
 This relation is both direct and indirect : direct, inasmuch as 
 some of the conditions seen to occur as variations are not far 
 removed from those known as normals in other forms ; and indi- 
 rect, since those strange and paradoxically regular dispositions of 
 digits which are found among the variations bear witness to the 
 influence of the principles of Symmetry, and prove that there are 
 modes in which Variation may be controlled and may produce a 
 result which has the quality of regularity and order of form 
 independently of the guidance of Natural Selection. 
 
chap, xiv.] DIGITAL VARIETY AXD SPECIES. 409 
 
 Of actual variations from the arrangement of digits character- 
 istic of one form to that characteristic of another there are as ye1 
 scarcely any examples. The cases given on pp. 395 to 39S being 
 the most evident. 
 
 For the rest, that is to say examples of arrangements happen- 
 ing as variations matching no normal, some may say in haste that 
 with their like Zoology has no concern. It would be convenient if 
 those who make this careless answer (as many do) would mark 
 the point at which it is proposed to begin this rejection of the 
 evidence of Variation. Few perhaps realize how impossible it is to 
 give a real meaning to these distinctions. As regards digits, for 
 instance, I suppose that no one who holds the doctrine of Common 
 Descent would refuse to admit the evidence of Variation as to the 
 hallux of Hedgehogs (No. 612) as exemplifying the way in which 
 species may be built up — if indeed species are built up of varia- 
 tions at all. And if this case is admitted, by what criterion shall 
 we exclude cases of the formation of a hallux in the Dog ? But if 
 these are not excluded it is difficult to shew good reason for 
 not admitting the case of the three-phalanged digit placed as a 
 hallux in the Cat (No. 472) with all the curious series of which that 
 is only the first term. Are we quite sure that because there is no 
 Carnivore with a three-phalanged hallux therefore such a creature 
 could not exist in nature ? Still more difficult is it to shew cause 
 why duplicity of the hallux should be set apart as a variation not 
 capable of being perpetuated or of becoming part of the specific- 
 characters of an animal, seeing that there is actual evidence both 
 in the case of the Dorking fowl and in the St Bernard dog that it 
 may become at least an imperfectly constant character. 
 
 In connexion with the subject of this section many suggestions 
 with special bearing on particular cases, both positive and negative, 
 will strike every reader. In the present imperfect state of the evidence 
 it would be premature to pursue these. It may however be well to 
 mention that several writers, especial ly Joly and Lavocat (No. 554). 
 have seen in the cases of divided digit III in the Horse an indication 
 that the digit III of the Horse corresponds with the digits III and 
 IV of the Artiodactyles. The evidence as to syndactylism between 
 these two digits in Ox and Pig would probably be considered t<» 
 give support to the same view. But while we may note that the 
 relations of the digits with the carpus and tarsus of these forms, 
 were comparative evidence absent, should absolutely prevent any 
 one from seriously maintaining such an opinion, nevertheless the 
 fact that such closely similar systems of Symmetry may thus aris< 
 independently of each other is of interest. 
 
CHAPTER XV. 
 
 linear series — continued. 
 
 Minor Symmetries : Segments in Appendages. 
 
 Meristic Repetition along the axes of appendages is very like 
 that along the axis of the body. Just as particular numbers of 
 segments or repetitions along the axis of Major Symmetry charac- 
 terize particular forms, so particular numbers of joints characterize 
 particular appendages. Such numbers frequently differentiate 
 species, genera, or other classificatory divisions from each other. 
 In the evolution of these forms therefore there must have been 
 change in these numbers. 
 
 Those who are inclined to the view that Variation is always 
 continuous do not perhaps fully realize the difficulty that besets 
 the application of this belief to the observed facts of normal 
 structure. For in those many groups whose genera or species 
 may be distinguished from each other by reason (amongst other 
 things) of difference in the number of joints in some particular 
 appendage or appendages, will any one really maintain that in 
 all these the process by which each new number has been intro- 
 duced was a gradual one ? To take a case : even were evidence 
 as to the manner of such Variation wanting, would it be expected 
 that the Longicorn Prionidae, most of which have the unusual 
 number of 12 antennary joints, did, as they separated from the 
 other Longicorns which have 11 joints, gradually first acquire a 
 new joint as a rudiment which in successive generations in- 
 creased ? Or, conversely, did the other Longicorns separate from 
 a 12-jointed form by the gradual "suppression" of a division or 
 of a joint ? If any one will try to apply such a view to hundreds 
 of like examples in Arthropods, of difference in number of joints 
 in appendages of near allies — forms that by the postulate of 
 Common Descent we must believe to have sprung from a common 
 ancestor — he will find that by this supposition of Continuity in. 
 Variation he is led into endless absurdity. Surely it must be 
 clear that in many such cases to suppose that the limb came 
 through a phase in which one of its divisions was half-made or 
 
chap, xv.] JOINTS OF ANTENNAE. 411 
 
 one of its joints half-grown, is to suppose that in the comparatively 
 near past it was an instrument of totally different character from 
 that which it has in either of the two perfect forms. But no 
 such supposition is called for. With evidence that transitions 
 of this nature may be discontinuously effected the difficulty is 
 removed. 
 
 The frequency of Meristic Variation in appendages is much 
 as it is in the case of body-segments. On the one hand there 
 are series containing high total numbers of repetitions little 
 differentiated from each other (e.g. the antennas of the Lobster), 
 and in these Meristic Variation is common ; on the other hand 
 in series containing few segments much differentiated from each 
 other, such Variation, though not unknown, is rare. Of the 
 latter a few instances are here offered. That the} 7 are so few 
 may perhaps be in part attributed to the little heed that is paid 
 to observations of this class. Records of this kind might indeed 
 be hoped for in the works of those naturalists to whom the title 
 " systematic " has been given ; but unfortunately the attention 
 of these persons has from the nature of the case been drawn 
 rather to features whereby species may be kept apart than to 
 facts by which they might be brought together. 
 
 From the lack therefore of records of such variations their 
 absence in Nature must not lightly be assumed. To quote but 
 one case : in the common Earwig the numbers and forms of the 
 antennary joints are exceedingly variable, but in many special 
 treatises on Orthoptera, I cannot find that this variability is 
 spoken of, and if alluded to at all the only notice is given in 
 the form "antennas 13- or 14-jointed." 
 
 Antennae of Insects. 
 
 Prionid,e. 
 
 I am indebted to Dr D. Sharp for the information that the 
 number of antennary joints in certain Prionidse varies. In Longi- 
 corns generally the number of joints is constantly 11. Dr G. 
 H. Horn of Philadelphia who is specially acquainted with this 
 group, has kindly written to me that of six species of N. 
 American Prioni four species have 12 antennary joints constantly 
 in both sexes. Besides these he gives the following cases of 
 Variation. It will be seen that in both of these the normal 
 number is much greater than it is in the other species 1 . 
 *61G. Prionus imbricornis : females have very constantly 18 joints; 
 males have 18 to 20. A male in Dr Sharp's collection has only 
 17 joints in each antenna. 
 
 1 In Prionus imbricornis and P. fissicornis doubt may be felt whether the trifid 
 apex should be reckoned as one joint or as two, but this applies equally to each 
 individual. I have counted it as one. 
 
412 MEMSTIC VARIATION. [part t. 
 
 *617. Prionus fissicornis: the female has 25, and the male 27 — 
 30, the note on the preceding species applying here. 
 
 618. Polyarthron. A Prionid beetle, in which the male has curious 
 many-jointed feather-like antennae, according to Serville has always 
 47 joints, but Thomson (Syst. Ceramb., 1866, p. 284) says the number 
 varies with the species and individually. A male in Dr Sharp's col- 
 lection has 45 joints in each antenna and a female has 31 in each. 
 
 619. Lysiphlebus is a Braconid (Hymenoptera) parasite on Aphides. 
 From a colony of Aphides on a bush of Baccharis viminalis 121 speci- 
 mens of Lysiphlebus were reared : of these 57 were males and 64 were 
 females. 
 
 The number of joints in the antennae varied as follows : 
 
 Males. 
 
 1 4 joints 18 specimens. 
 
 15 37 
 
 16 1 .... 
 
 15 on one side and 16 on the other 1 
 
 Females. 
 
 12 7 
 
 13 54 
 
 14 1 
 
 12 on one side and 1 3 on the other 2 
 
 In those having a different number of joints in the right and left 
 antenna?, the last joint of the antenna which contained the fewest 
 joints was longer than the last joint of the antenna with the larger 
 number of joints. Nevertheless this relation did not hold throughout : 
 for example in the case of the male with 16 joints, the last joint was of 
 the same length proportionally as that of the males with only 14 joints. 
 As a rule the specimens with fewer antennary joints are smaller than 
 the others. 
 
 Variations were also seen in coloration, in the proportional length 
 of the tarsi, and in the presence or absence of the transverse cubital 
 nervure, but none of the characters divided the sample consistently, it 
 was therefore inferred that the individuals belonged to one species of 
 Lysiphlebus, (L.citraphis, Ashm.) 
 
 From another colony of Aphides living on a rose-bush 58 specimens 
 of Lysiphlebus were bred, and no characters were found by which these 
 could be separated from those bred from the Aphis of Baccharis. In 
 the case of the second sample the joints of antennae were as follows : 
 
 Males. 
 
 14 joints 10 specimens. 
 
 15 19 
 
 14 on one side and 1 5 on the other 2 
 
 Females. 
 
 12 2 
 
 13 25 
 
CHAP. XV.] 
 
 ANTENNAE : BEETLE. 
 
 413 
 
 The number of antennary joints is employed as a specific character 
 in the classification of Lysiphlebus by Ashmead, Proc. U. S. Nat. Mus., 
 1888, p. 664). Coquillet, D. W., Insect Life, 1891, Vol. in. p. 313. 
 
 *620. Donacia bidens. (Phyt.) A female found by Dr D. Sharp 
 at Quy Fen in company with many normal specimens had in each 
 antenna eight joints instead of eleven as in the normal. As shewn 
 in the figure (Fig. 123) the antennae of the two sides were exactly 
 
 Fig. 123. Donacia bidens ? . I. Normal antennae, eleven joints in each. 
 II. Abnormal specimen, having eight joints in each antenna. No. 620. 
 
 alike, and the insect was normal in all other respects. I am much 
 obliged to Dr Sharp for shewing me this specimen. 
 
 Forficula auricularia, the common Earwig. In the various 
 species of Forficula the number of joints in the antenna? differs, 
 the numbers 11, 12, 13 and 14 being all found as normals in 
 different species 1 . As regards F. auricularia most authors give 
 14 as the number of antennary joints. Serville 2 gives 13 or 
 14. A number of adult earwigs examined by myself with a 
 view to this question shewed that there is great diversity in 
 regard to the number of antennary joints. The whole matter 
 needs much fuller investigation but the preliminary results are 
 interesting. 
 
 The commonest number is 14, which occurs in perhaps 70 — 
 80 per cent. The next commonest is 13, which was seen in a 
 considerable number, while 12, and even 11 occur in exceptional 
 cases. Different numbers were frequently found on the two sides. 
 
 1 Brunner von Wattenwyl, Prodr. eur. Orth., 1882. The number in F. auri- 
 cularia is given by Brunner as 15, but I have never seen this number. It is no 
 doubt an accidental error. The same mistake is repeated by Shaw, E., Ent. Mo. 
 Mag., 1888—89, xxv. p. 358. 
 
 2 Suites a Buffon: Orthop., 1839. 
 
414 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 * 
 
 As is usual with appendages the whole length of the antenna? 
 differed a good deal independently of the number of joints. 
 621. On comparing antennas with different numbers it seemed that 
 the proportional length of the first two joints was nearly the 
 same in all, but in the third joint there was great difference, as 
 shewn in Fig. 124. The left antenna in Fig. 124, I may be 
 taken to be the normal form with 14 joints. In it both 3rd and 
 4th joints are small. The right antenna of the same specimen 
 has 13 joints and in most of the 13-jointed antenna? the arrange- 
 
 Fig. 124. Various forms of antennas of adult Earwigs {Forficula auricularia), 
 all from one garden and taken at one time. 
 
 I. Specimen having the left antenna normally 14-jointed, and the right 
 13-jointed. No. 621. 
 
 II. Both antennae 13-jointed. No. 622. 
 
 III. Both antennae 12-jointed. No. 623. 
 
 IV. Bight antenna normally 14-jointed ; left antenna 12-jointed. No. 624. 
 
 Note that the rights and lefts are arranged as marked by letters r and I. The 
 antennae were so fixed for drawing in order to bring them side by side after the 
 bend from the first joint. This figure was drawn with the camera lucida by 
 Mr Edwin Wilson. 
 
 ment was much as shewn in this figure. As shewn, the 3rd joint 
 especially is here rather longer than in the 14-jointed form, but 
 several of the peripheral joints are also a little longer, so that 
 
chap, xv.] antenna: earwigs. 415 
 
 though the 13-jointed antenna is not as a whole so long as the 
 14-jointed antenna of the same individual it is longer than its 
 first 13 joints. 
 
 622. But besides the common 13-jointed form occasional specimens 
 are as shewn in Fig. 124, II. Here both antennae are 13-jointed, 
 the 3rd joint being much longer, and the 4th a little longer than 
 the corresponding joints of the normal with 14 joints. Two 
 specimens were seen having this structure in both antennas, thus 
 presenting a difference which, did it occur in a form known from 
 but few specimens, would assuredly be held to be of classificatory 
 importance. 
 
 623. In another case (Fig. 124, III) each antenna contained only 
 12 joints, the 3rd, 4th and 5th being all of greater length than 
 in the normal. 
 
 624. Fig. 124, IV shews a case in which there was on the right 
 side a normally 14-jointed antenna but that of the left side was 
 12-jointed, agreeing nearly with those in Fig. 124, III. 
 
 In considering these facts the possibility that some or all the 
 abnormal states may result from or be connected with regenera- 
 tion must be remembered ; but from the frequency of the varia- 
 tions, from their diversity, and from the fact that symmetrically 
 varying individuals are not rare, it is on the whole unlikely that 
 all can owe their origin to regeneration. It will besides be 
 noticed that it is in the proximal joints that the greatest changes 
 are seen, and it must surely be rarely that these are lost by mutila- 
 tion. 
 
 The difficulty — indeed the futility — of attempting to adjust a 
 scheme of individuality among such series of segments must here 
 be apparent to all. We can see the change in number and the 
 change in proportions, and we are doubtless entitled to affirm 
 that the differences between these several kinds of antennae are 
 reached by changes occurring chiefly in the neighbourhood of 
 the 3rd and 4th joints ; but not only is there no proof that the 
 changes are restricted to these joints, but the appearances suggest 
 that there are correlated changes in many, and. perhaps in all of 
 the joints. 
 
 Tarsus of Blatta 1 . 
 
 : 625. Among the families of the class Orthoptera the number oi 
 
 tarsal joints differ. In Forficularia the number of tarsal joints 
 
 1 In connexion with variation in the number of joints in legs I may mention the 
 case of Stenopterus rufus ? (Longicorn) described by Gadbatj de Kkkville as having 
 each tibia divided into two parts by an articulation [Le Naturaliste, 1889, B. 2, xi. 
 p. 9, fig.)} but upon examination it proved that each tibia had been sharply bent at 
 each of these points, and there was no real articulation. I have to thank M. Gadeau 
 de Kerville for lending me this insect together with many interesting specimens of 
 which mention will be made hereafter. 
 
416 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 is 3, in Blattodea, Mantodea and Phasmodea 5, in Acridiodea 3, 
 in Locustodea 4, in Gryllodea 2 or 3 1 . 
 
 The fact, originally observed by Brisout de Barneville 58 , 
 that in various species of Blattidse the number of tarsal joints 
 may vary from five to four is therefore of considerable importance 
 in a consideration of the manner in which these several forms 
 have been evolved from each other. The species in which Brisout 
 observed this variation were ten in number and belonged to four 
 genera of Blattidse. 
 
 At my suggestion Mr H. H. Brindley has made an extended 
 investigation of the matter and a preliminary account of the 
 results arrived at was given in the Introduction (p. 63). It was 
 found that of Blatta americana 25% of adults have one or 
 
 Fig. 125. I. Normal five-jointed left tarsus of Blatta americana. 
 tarsus of the same having four joints. 
 
 n 
 
 II. Right 
 
 more tarsi 4-jointed. In Blatta orientalis these cases amounted 
 to 15°/o > an d of 102 B. germanica examined, 16 had one or more 
 4-jointed tarsi. 
 
 The abnormality occurred sometimes in one leg and sometimes in 
 another, being more frequent in the legs of the second pair than in those 
 of the first, and much more frequent in the third pair than in either. 
 In some specimens legs of the two sides were symmetrically affected, 
 but this was exceptional. Only one specimen has hitherto been met 
 with having all the tarsi 4-jointed. There was a slightly greater 
 frequency in females than in males. 
 
 When the examination of these abnormal tarsi was begun it was 
 supposed that the variation was congenital, but as explained in a note 
 to the Introduction (p. 65) doubt subsequently arose as to this. It is 
 well known that Blattidse like many other Orthoptera have the power 
 of renewing the appendages after loss, and Mr Brindley found by 
 experiment that when the tarsus of Blatta orientalis is renewed after 
 mutilation the resulting tarsus is 4-jointed. It was also found that 
 4-jointed tarsi were much more frequent in adults than in the young. 
 The question therefore arises, is the 4-jointed tarsus ever congenital 1 
 
 1 From Bbunneb von Wattenwyl, Prodr. europ. Orthop., 1882. 
 • Ann. ent. soc. France, s. 2, vi. 1848, Bull., p. xix. 
 
CHAP. XV.] 
 
 tarsus of Blatta. 
 
 417 
 
 To this question a positive answer cannot yet be given ; but as about 
 200 young B. orientalis have since been hatched from the egg and no 
 4-jointed tarsus was found among them, while in every instance of 
 regeneration the new tarsus had four perfect joints, there is now a 
 presumption that the variation does not occur congenitally. On the 
 other hand it should be mentioned that the 4-jointed tarsus was seen 
 in 3 specimens, found by Mr Brindley, which by their size would be 
 judged to have been newly hatched. But even if the variation shall 
 hereafter be found to be sometimes congenital it is certain that this 
 occurrence must be very rare, and there can be no doubt that in the 
 majority of cases the 4-jointed tarsus has arisen on regeneration 1 . 
 
 As mentioned in the Introduction, the existence of the 4-jointed 
 tarsus, whatever be the manner of its origin, raises two questions. Of 
 these the first is morphological, relating to the degree to which the 
 joints exhibit the property of individuality, and the second is of a 
 more general nature, relating to the application of the theory of 
 Natural Selection to such a case of discontinuous change. The interest 
 of the case in its bearing on both of these questions arises from the 
 Discontinuity, which was complete. All the tarsi seen were either 
 5-jointed or 4-jointed, and in none of the latter was any joint ever 
 rudimentary, or any line of articulation imperfectly formed (except 
 in a single specimen having a deformed tarsus). There were 5-jointed 
 tarsi and 4-jointed tarsi : between them nothing. 
 
 Following the usual methods of Comparative Anatomy it must be 
 asked which of the 5 joints is missing in the 4-jointed tarsus'? With 
 reference to this question careful measurements of the separate joints 
 were made by Mr Brindley in 115 cases of 4-jointed tarsi occurring in 
 legs of the third pair in B. americana; and for comparison the separate 
 joints of 115 normal 5-jointed third tarsi of the same species were also 
 measured. (It is clear that the legs compared must belong to the same 
 pair, 1st, 2nd or 3rd, for there is considerable differentiation between 
 them. From this circumstance it was comparatively difficult to obtain 
 a large number of cases, and hence the smallness of the whole number 
 measured. But though of course statistics respecting a larger number 
 would be more satisfactory there is no reason to think that by exami- 
 nation of a greater number of cases the result would be materially 
 affected.) 
 
 In the two sets of tarsi the total length of each tarsus was reduced to 1-000, the 
 lengths of the joints being correspondingly reduced. 
 
 The arithmetic means of the ratios of the several joints to the whole lengths of 
 the tarsi to which they belonged was as follows : 
 
 Five-jointed form. 
 
 1st joint 
 •532 
 
 2nd joint 
 •156 
 
 3rd joint 
 •095 
 
 4th joint 
 •019 
 
 5th joint 
 ■168 
 
 Four-jointed form. 
 
 1st joint 
 •574 
 
 2nd joint 
 •183 
 
 3rd joint 
 •061 
 
 4th joint 
 •179 
 
 1 The circumstance that in Mr Brindley's observations the variation was in all 
 species more frequent in females than in males, and that the frequency differed in 
 
 b. 27 
 
418 MEEISTIC VARIATION. [part i. 
 
 The evidence derived from these numbers lends no support to the 
 expectation that any one particular joint of the 5-jointed form is 
 missing from the 4-jointed, or that any one joint of the 4-jointed form 
 corresponds with any two joints of the 5-jointed ; for if the numbers 
 are treated with a view to either of these hypotheses it will be found 
 impossible to make them agree with either. It appears rather that the 
 four joints of the 4-jointed form collectively represent the five joints of 
 the normal. 
 
 The other question upon which the statistics bear has already been 
 stated in the Introduction. In any appendage the ratio of the length 
 of each joint to the whole length of the appendage varies ; but if it 
 varies about one normal form it will be possible to find a normal or 
 mean value for this ratio, and the frequency with which other values 
 of the same ratio occur will be inversely proportional to the degree in 
 which they depart from the normal value. The curve representing the 
 frequency of occurrence of these values will then be a normal Curve of 
 Error. The form of this curve will indicate the constancy with which 
 the normal proportions of the tarsal joints are approached. If the 
 proportional lengths of the tarsal joints vary little then the curve 
 representing the frequency of their departure from their normal value 
 will be a steep curve, but if these proportions are very variable and have 
 little constancy, then the curve will be flatter. The probable error 
 will thus in the case of each value be a measure of the constancy with 
 which it conforms to its normal proportions. As explained in the 
 Introduction, upon the hypothesis that all constancy of form is due to 
 the control of Natural Selection, it would be anticipated that the 
 4-jointed tarsus, if a variation, would be very much less constant in the 
 proportions of its joints than the 5-jointed tarsus. It was however 
 found that as a matter of fact the proportions of the joints of the 
 4-jointed form were very nearly as constantly conformed to as those of 
 the joints of the normal tarsus. 
 
 The evidence of this is as follows. The total length of the 5-jointed tarsus being 
 
 L, and t 1 , t 2 , &c. being the lengths of its several joints, I, T 1 , T 2 , &c. representing 
 
 t l T 1 
 
 the same measurements in the 4-jointed form, the ratios — &c, — &c, represent 
 
 J-J v 
 
 the proportional length of the several joints in each case. The values of these 
 
 ratios were then arranged in ascending order in their own series and the measures 
 
 occupying the positions of the first, second, and third quarterly divisions noted 1 
 
 (indicated hereafter by Q 1 , M and Q 3 respectively). The probable error or 
 
 t 1 T 1 
 variation of each ratio y , — , &c. will then be represented by the expression 
 
 Q3_ Ql 
 
 — - . Inasmuch as the joints are of different lengths, to compare the results 
 
 each must be converted into percentages of the mean length of the joint concerned. 
 These results are set forth in the accompanying tables. 
 
 the different pairs of legs may seem to point to the existence of some control other 
 than the simple chances of fortuitous injury. As regards the latter point it is 
 not unlikely that the legs of the third pair, being longer and less protected, may 
 be more often mutilated than the others. 
 
 1 As described by Galton, F., Proc. Roy. Soc, 1888-9, xlv. p. 137. 
 
CHAP. XV.] 
 
 tarsus of Blatta. 
 
 419 
 
 Five-jointed tarsus. 
 
 
 t l 
 
 «-' 
 
 t* 
 
 t* 
 
 t 5 
 
 
 L 
 
 L 
 
 L 
 
 T* 
 
 L 
 
 Q l 
 
 •521 
 
 •152 
 
 •095 
 
 •046 
 
 •162 
 
 M 
 
 •529 
 
 •156 
 
 •099 
 
 •049 
 
 •168 
 
 Mean error 
 
 as percentage 
 
 of M 
 
 •535 
 1-3 
 
 •160 
 2-6 
 
 •101 
 3-0 
 
 •051 
 5-0 
 
 •174 
 3-6 
 
 Four-jointed tarsus. 
 
 
 T 1 
 
 rp'2 
 
 T i 
 
 T i 
 
 
 I 
 
 I 
 
 I 
 
 I 
 
 Q 1 
 
 •565 
 
 •178 
 
 •060 
 
 •172 
 
 M 
 
 •575 
 
 •183 
 
 •064 
 
 •177 
 
 Q 3 
 
 Mean error 
 
 as percentage 
 
 of M 
 
 •584 
 1-6 
 
 •189 
 3-0 
 
 •068 
 6-2 
 
 •183 
 3-1 
 
 It is thus seen that the percentage variation of the ratios of the 
 several joints to the total length is very little greater in the case of the 
 abnormal than it is in the normal tarsus. 
 
 As regards the longer joints these results are probably a trustworthy 
 indication of the amount of Variation, but in the case of the shorter 
 joints the errors of observation must no doubt be so great in proportion 
 to the smallness of the lengths to be measured that no reliance should 
 be placed on results obtained from them. 
 
 As evidence that in spite of the small number of instances examined 
 the general result is satisfactory it may be mentioned that the mean 
 
 Q 3 + Qi 
 
 obtained as the value of — ^r— agrees fairly well in each case both 
 
 -j 
 
 with the value of M, the middlemost value, and also with the arith- 
 metic mean given above. It may therefore be taken that the curve is 
 regular and the series nearly uniform. 
 
 The correlations between the lengths of the joints and that of the 
 whole tarsus have also been examined by Mr Brindley using the 
 method proposed by Galton I.e., the results closely agreeing with those 
 obtained by the ordinary method here described 1 . 
 
 If the 4-jointed tarsus be a congenital variation the sig- 
 nificance of the fact that the abnormality is in its constancy to 
 its normal hardly less true than the type-form must be apparent 
 
 1 It is hoped that a fuller account of this subject will be given separately. I am 
 indebted to Mr F. Galton for advice kindly given when this investigation was 
 begun, and Mr Alfred Harker has most obligingly given much help in connexion 
 with it. 
 
 27—2 
 
420 MERISTIC VARIATION. [part i. 
 
 to all. Yet even if, as now seems likely, the 4-jointed tarsus 
 be not a congenital variation but is rather a result of regenera- 
 tion, there is still difficulty in reconciling the now established 
 fact that the form of the regenerated part, though different from 
 the normal, is scarcely less constant, with any hypothesis that 
 the constancy of the normal is dependent upon Selection. 
 
 If it were true that the smallness of the mean variation of the 
 
 t 1 ..." 
 
 ratio y , which is ultimately the measure of the constancy and 
 Li 
 
 truth to type of the 5-jointed tarsus, is really due to Selection 
 and to the comparative prosperity of specimens whose tarsal pro- 
 portions departed little from the normal, to what may we ascribe 
 
 T l 
 
 the smallness of the mean variation of the ratio -j- ? Are we 
 
 to suppose that the accuracy of the proportions of the regenerated 
 tarsus is due to the Natural Selection of individuals which in 
 renewing their tarsi conformed to this one pattern ? 
 
 We are told that the struggle for existence determines every 
 detail of sculpture or proportions with such precision that in- 
 dividuals which fall short in the least respect are at a disad- 
 vantage so great as to be capable of being felt in the struggle, 
 and so decided as to lead to definite and sensible effects in Evolu- 
 tion. If this is so, should we not expect that individuals which 
 had suffered such a comparatively serious disadvantage as the 
 loss of a leg or of a tarsus, would be in a plight so hopeless that 
 even though some of them may survive, renew the limb and 
 even breed, yet, as a class, by reason of their mutilation they 
 must rank with the unfit ? Nevertheless we find not only that 
 there is a mechanism for renewing the limb, but that the renewal 
 is performed in a highly peculiar way ; that in fact the structure 
 newly produced differs from the normal just as species differs 
 from species, and is scarcely less true and constant in its pro- 
 portions than the normal itself. 
 
 Now if this exactness in the proportions of the renewed limb 
 is due to Selection, it must be due to Selection working among 
 the mutilated alone ; and of them only among such as re- 
 newed the limb ; and of them only among such as bred. 
 Moreover if the accuracy of the form of the renewed tarsus is 
 due to Selection working on fortuitous variations in the method 
 of renewal, and not to any natural definiteness of the variations, 
 the number of selections postulated is already enormous. But 
 this vast number of selections must by hypothesis have all been 
 made from amongst the mutilated — a group of individuals that 
 would be supposed to be at a hopeless disadvantage 1 . 
 
 1 The same dilemma is presented in all cases where a special mechanism or 
 device exists (and must be supposed to have been evolved) only in connexion with 
 regeneration. An instance is to be seen in the Lobster's antenna. As is well known 
 the antennary filament of the Lobster when lost is renewed not as a straight out- 
 
chap, xv.] RADIAL JOINTS OF COMATUL^E. 421 
 
 One or more of the hypotheses are thus clearly at fault. A 
 natural, and I believe a true comment will occur to every one : 
 that probably the injured insects are not at any serious disad- 
 vantage, and that these mutilations perhaps make very little 
 difference to their chances. But can we admit that the loss of 
 a leg matters little, and still suppose that the definiteness and 
 accuracy of the exact proportions of the tarsal joints makes any 
 serious difference ? 
 
 The hypothesis, therefore, that the smallness of the mean 
 variation in the proportional lengths of the tarsal joints of the 
 4-jointed tarsus has been gradually achieved by Selection is un- 
 tenable, whether that 4-jointed tarsus be a product of regenera- 
 tion or a congenital variation. But if the accuracy with which 
 the abnormal conforms to its type be not due to a gradual Selec- 
 tion, with what propriety can we refer the similar accuracy of 
 the normal to this directing cause ? 
 
 Kadial joints in Arms of Comatul^e. 
 
 The number of radial joints above the basals up to the division of the rays in 
 Crinoids is usually constant in the genera. In Antedon and Actinometra there are 
 normally three such joints, the third radial being the axillary, and none of these 
 bear pinnules. Both increase and decrease in the number of radials has been 
 observed, but variations from this number are rare, more so than variations in the 
 number of rays. Carpenter, P. H., Chall. Rep., xxvi. Pt. lx. p. 27. 
 
 Antedon alternata: specimen having in one ray four radials, none bearing 
 pinnules or united by syzygy. ibid., PL xxxu.fig. 6. 
 
 Encrinus gracilis (fossil) : in one ray four radials. Wagner, Jen. Ztschr., 
 1887, xx. p. 20, PI. ii. fig. 13. 
 
 Antedon remota, A. incerta, Actinometra parvicirra (Fig. 126); one 
 specimen of each of these species had one ray with only two radials. Carpenter, 
 I.e., PL xxix. fig. 6; PL xviii. fig. 4; PL lxi. fig. 1. 
 
 Fig. 126. Actinometra parvicirra, No. 628. Specimen having only two radials 
 in the ray marked x. (From P. H. Carpenter.) 
 
 growth, as the other appendages are, but when formed again it is coiled up in a 
 tight conical spiral which cannot be extended at all, but is kept firmly in place by 
 the shortness of the skin on the inner curvature. (For figure see Howes, Jour. 
 Anat. Phys., xvi. p. 47.) During the process of regeneration the antenna is very 
 soft, and were it extended it would from its great length be much exposed to injury. 
 At the next moult after renewal the new antenna is drawn out as a straight filament 
 like the normal, and its skin then hardens with that of the rest of the body. This 
 strange manner of growth occurs only on regeneration. It is hard to believe both 
 
422 MERISTIC VARIATION. [part i. 
 
 Metacrinus. Some species have normally 5, others normally 8 radials. If there 
 are 5, the 2nd and 3rd are united by syzygy and bear pinnules; but if there are 8, 
 both 2nd and 3rd, and the 5th and 6th are thus united and bear pinnules. In 
 Plieatocrinus the number of radials is two, and this is also the case in one or two 
 fossil Comatulas. Pentacrinus has normally three radials like Antedon. 
 629. Pentacrinus mulleri: specimen having in one ray four radials, the 2nd and 3rd 
 united by syzygy, though bearing no pinnules. Carpenter, I.e.; and Chall. Rep. 
 xi. Pt. xxxii. p. 311, PI. XY.Jig. 2. 
 
 (1) that the number of individuals that have lost antennae — a serious injury one 
 may judge — and have renewed them, and have bred, can have been enough to lead 
 to the establishment by Selection of a distinct and highly special device to be 
 invoked solely on the occasion of mutilation of an antenna ; and also (2) that the 
 least detail of normal form is of such consecpience as to be rigorously maintained by 
 Selection. 
 
CHAPTER XVI. 
 
 Radial Series. 
 
 Little need be said in preface to the facts of Meristic Varia- 
 tion in Radial Series. In them phenomena analogous to those 
 of the Variation in Linear Series are seen in their simplest form. 
 Just as in Linear Series the number of members may be changed 
 by a reconstitution of the whole series so that it is impossible 
 to point to any one member as the one lost or added, so may 
 it be in the Meristic Variation of Radial Series: and again as 
 in Linear Series, single members of the series may divide. Be- 
 tween these there is no clear line of distinction. 
 
 Next, as in Linear Series, Variation, whether Meristic or 
 Substantive, may take place either in single segments (quadrants, 
 sixths, &c), or simultaneously in all the segments of the body. 
 For instance, a single eye may be divided into two, or there 
 may be duplicity simultaneously occurring in all the eyes of the 
 disc (see No. b'34) and so on. 
 
 These phenomena are here illustrated by facts as to the 
 Meristic Variation of Hydromedusae and of Aurelia. The latter 
 is exceptionally variable and in its changes exhibits important 
 features. 
 
 Together with these facts as to Variation in Major Symmetries 
 is given an instance of similar Variation in the pedicellarise of an 
 Echinid, and it will be seen that in this case of a Minor Symmetry 
 the change is perfect and altogether comparable with those found 
 in Major Symmetries of similar geometrical configuration. 
 
 The best field for the study of the variations of Radial Series 
 is of course to be found in plants ; and in the Meristic Variations 
 of radially symmetrical flowers precisely similar phenomena may 
 be easily seen. 
 
424 
 
 MERISTIC VARIATION. 
 
 [part 1. 
 
 I. CCELENTERATA. 
 
 *630. Sarsia mirabilis 1 : normally four radial canals, &c. (Fig. 127. 
 I and III). Out of many hundreds of N. American specimens 
 two were found with six radial canals, six ocelli, and six tentacles, 
 
 Fig. 127. Sarsia mirabilis. I and III, the normal form, with four radii, from 
 below and from above. II and IV, an abnormal form with six radii, from below 
 and from above respectively. (From Agassiz.) 
 
 symmetrically arranged (Fig. 127, II and IV). These specimens 
 were of larger absolute size than the normals. Agassiz, L., Mem. 
 Amer. Ac. Sci., iv. p. 248, PI. v. fig. 5. 
 
 1 Sarsia is the medusa of the Gymnoblastic Hydroid Syncoryne. 
 
chap, xvi.] RADIAL SERIES : JELLY-FISH. 425 
 
 'G31. Sarsia sp. Among many thousands examined on the east 
 
 coast of Scotland one was found having six radial canals, six 
 
 ocelli and six tentacles. Romanes, G. J., Jour. Linn. Soc, Zool., 
 
 xii. p. 527. 
 '632. Sarsia sp. A single specimen having five complete segments: 
 
 the only abnormality met with amoog thousands of naked-eyed 
 
 medusae observed, ibid., xiii. p. 190. 
 
 There is perhaps in the whole range of natural history no 
 
 more striking case of the Discontinuity and perfection of Meristic 
 
 Variation. 
 
 Is it besides a mere coincidence, that the specimens presenting 
 
 this variation, so rare in the free-swimming Hydromedusse, should 
 
 have been members of the same genus ? 
 
 633. Clavatella (Eleutheria) prolifera. This form has a medusa 
 which creeps about on short suctorial processes borne by the tentacles. 
 The number of these tentacles varies from 5 to 8. In the specimens 
 examined by Krohn 1 the number was 6. Most of Claparede's 2 speci- 
 mens had 8. Filippi 3 found that the majority had 6 arms, but 15 per 
 cent, had 7. Those examined by Hincks 4 never had more than 6. 
 Filippi considered that the difference in number was evidence that his 
 specimens were of a species different from Claparede's. I examined 
 many of this form at Concarneau and found six the commonest number 
 in the free medusae, but those still undetached frequently had 5, 
 possibly therefore the number increases with development. [See also 
 Cladonema radiatum, &c. Hincks, I.e., p. 65, &c] 
 
 Claparede states that the 6-armed specimens had 6 radial canals, 
 but the 8-armed usually had four though occasionally six, but never 
 eiidit canals. 
 
 In this case note not only the frequent occurrence of Meristic 
 Variation, but also the suggestion that particular numbers of tentacles 
 are proper to particular localities. 
 
 '634. Normally there is a single eye at the base of each arm. Claparede 
 figures (I.e. p. 6, PL i. fig. 7 a) a case of duplicity of an eye, and says 
 that specimens occur in which each eye is doubled, so that there are 
 two eyes at the base of each arm instead of one. 
 
 635. Stomobrachium octocostatum (.ZEquoridae) : variety found in 
 Cromarty Firth, |rds of size represented by Forbes (Monogr. Br. 
 Naked-eyed Medusce); ovaries bluish instead of orange, and without 
 denticulated margins. Tentacles arranged in double series, long and 
 short alternating, while in the type the series is single. The number 
 of large tentacles same as in type. Each smaller tentacle bears vesi- 
 cular body at base, without pigment or visible contents. The same 
 variety figured by Ehrenberg, Abh. Ah. Berl., 1835, Taf. vin. fig, 7. 
 Romanes, G. J., Jour. Linn. Soc. xn. p. 526. [Simultaneous Variation 
 of the several segments.] 
 
 With Nos. 634 and 635 compare the fact that in Tiarops poly- 
 
 1 Arch. f. Naturg., 1861, p. 157. 
 
 2 Beob. iib. Anat. u. Entw. Wirbelloscr Thiere, 1863, p. 5. 
 
 3 Mem. Ac. Torino, S. 2, xxiii. p. 377. 
 
 4 Brit. Hyd. Zoophytes, 1868, p. 71. 
 
426 MERISTIC VARIATION. [part i. 
 
 diademata there are normally as a specific character four diadems 
 between each pair of radial tubes, making in all sixteen instead of 
 eight, which is the usual number in the genus. Romanes, G. J., 
 Jour. Linn. Soc. Zool., XII. p. 525. 
 
 *636. Aurelia aurita. This form exhibits an exceptional frequency 
 of Meristic Variation. In the normal there are 16 radial canals, 
 4 oral lobes, 4 generative organs and 8 lithocysts. The de- 
 partures from this normal form have been described in detail 
 by Ehrenberg 1 and by Romanes 2 . 
 
 Meristic Variation in Aurelia may occur in two distinct ways, 
 first in the degree to which there is complete separation between 
 the generative sacs, and second in actual numerical change. 
 
 Imperfect division of generative sacs. 
 
 In the commonest form of Aurelia there are four generative organs each 
 distinct from its neighbours, but in some specimens the generative epithelium is 
 continuous all round the mouth, and there is then one continuous generative 
 chamber, though opening by 4 openings as usual. (Such absence of complete sepa- 
 ration between some of the generative organs is not rarely seen in cases of numerical 
 Variation, v. infra.) Though the epithelium is then continuous it does not form 
 a true circle, but is sacculated to form 4 (as normally) 3, 6, or some other number 
 of incompletely separated parts. Ehrenberg (I. c, p. 22) saw a case in which there 
 were 6 such sacculations, three on each side being united and having one generative 
 pouch, but each of these pouches opened by 3 openings. There was thus a bilateral 
 symmetry, each half containing three lobes of ovarian epithelium incompletely 
 separated from each other. Complete union of all the generative organs was 
 very rare. 
 
 The specimens differ greatly with regard to the degree to which the generative 
 epithelium is folded off, and in the shapes of the generative organs. Commonly 
 the generative epithelium is of a horse-shoe form, the two limbs of the horse-shoe 
 not meeting each other; but in some specimens the two limbs may be to various 
 degrees approximated, so that each generative organ is kidney-shaped or even 
 roughly circular. (Cases figured by Ehrenberg, I.e., PI. n.) [Here note the 
 Simultaneous Variation of the single quadrants.] 
 
 Numerical Variations. 
 
 Of these the most striking and also the most frequent are variations 
 consisting in a perfect and symmetrical change in the fundamental 
 number of segments composing the disc. Normally there are four 
 quadrants (Fig. 128, I). Varieties are found having only half the usual 
 number of organs, the disc being made up of two halves, each contain- 
 ing one generative organ (Fig. 128, IV). Other symmetrical varieties 
 having three, and six, as their fundamental numbers are shewn in Fig. 
 128, V, and II. These figures are from Romanes. Symmetrical forms 
 having five segments and eight segments are described and figured by 
 Ehrenberg. As to the comparative frequency of these forms facts are 
 given below. In each of them all the parts normally proper to one 
 quadrant are repeated in each segment of the disc, the number of parts 
 being greater or less than the normal in correspondence with the funda- 
 mental number of the specimen. 
 
 1 Ehrenberg, C. G., Abh. k. Ah. Wiss., Berlin, 1835, pp. 199—202, Plates. 
 
 2 Romanes, G. J., Jour. Linn. Soc., Zool., xn. p. 528, and xm. p. 190, Pis. xv. 
 and xvi. 
 
CHAP. XVI.] 
 
 radial series : Aurelia. 
 
 427 
 
 Next, the number of certain organs may vary independently of 
 other organs. For example as seen in Fig. 128, VI the radial canal 
 
 Fig. 128. Diagrams of various forms of Aurelia aurita, slightly simplified from 
 Eojianes. I. The normal. II. Symmetrical form with 6 radii. III. Two 
 additional chief radial canals in opposite interradii (where manubrial lobes also 
 were bifid) and substitution of two canals for one in another interradius. 
 IV. Form with two generative organs. V. Form with three generative organs. 
 VI. Symmetrical form in which the intergenital canals are all doubled, the others 
 remaining single. VII. Apparently upper half-disc arranged as for a symmetry of 
 four, lower half for a symmetry of six. VIII. One of the quadrants tripled (?). 
 IX. Form resembling VI. except that in one quadrant the intergenital canal is not 
 doubled. The descriptions are not altogether those of Romanes. 
 
 normally lying in a plane between each pair of generative organs may 
 in each quadrant be represented by two canals, and in correspondence 
 with this change the number of marginal organs is proportionately 
 changed in the quadrants affected. 
 
 But besides these changes symmetrically carried out in eacli quadrant 
 or in the whole disc, one or more quadrants or a half-disc may vary inde- 
 pendently. For example Fig. 128, VII, shews a specimen in which the 
 two upper quadrants are normal but the lower half-disc is primarily 
 divided into three. (In the case figured the parts of the lower half-disc 
 
428 MERISTIC VARIATION. [part i. 
 
 are not quite accurately distributed). Similarly a particular quadrant 
 may be represented by two sets of parts or by three sets (Fig. 128, VIII), 
 the other three quadrants being normal or nearly so. I have seen a 
 case also in which the chief symmetry was arranged as for three seg- 
 ments (having 3 oral lobes), but one of the three segments was imper- 
 fectly divided into two. 
 
 In a case of 6 segments, 3 on one side may be large and the other 3 
 small, somewhat as in Fig. 128, VIII, but the whole disc was not circular, 
 the radius on the side of the large segments being the greater. 
 
 In the figures (after Romanes) all the discs are represented as 
 circles, but my own experience was that when there was not a truly 
 symmetrical distribution of the generative organs the half quadrant or 
 other segment in which the number of parts was greatest bulged out- 
 wards, thus exemplifying the general rule that when an organ divides 
 the two resulting parts are together larger than the undivided organ. 
 
 Besides those specified, there are also irregular cases, e.g., specimens 
 with 3 generative organs but 4 oral lobes and other parts in multiples of 
 4, but as Ehrexberg says in such cases it is generally possible to detect 
 that one of the generative organs is larger than the others or even 
 partially double. He also saw cases otherwise arranged in a symmetry 
 of 6, but having 22 chief radial canals instead of 24, &c. Also 14 radial 
 canals (instead of 12) were found in some cases of 3 generative organs. 
 
 As everyone will admit, it is impossible in regular threes, sixes, tfcc. 
 to say that any particular segment is missing or is added rather than 
 another. 
 
 Comparative frequency of the several forms. 
 
 *637. Among thousands of individuals seen by Ehrenberg only two were 
 8-rayed, 15 — 20 were 6-rayed, some 20 — 30 were 5- and 3-rayed, the 
 remainder being 4-rayed. In percentages, 90 are 4-rayed, 3 are 3-rayed 
 3 are 5-rayed, 2 are 6-rayed and 2 have other numbers. 
 
 The result of an attempt to ascertain these percentages in a great 
 shoal of Aurelia washed ashore on the Northumberland coast on 4 Sept. 
 1892 is given below. The radial canals were not counted, and the 
 numbers apply strictly to the generative sacs only. It will be seen 
 that the proportion of abnormals is lower than that given by Ehrenberg. 
 
 2 generative sacs 
 
 symml. : 3 oral lobes in 4 unbroken cases ...10 (O^ /,) 
 
 2 large, 1 small : 3 or. lobes 1 
 
 normal 1735 
 
 3 large, 1 small : 5 or. lobes 1 
 
 3 
 
 4 
 4 
 4 
 5 
 5 
 6 
 6 
 6 
 6 
 6 
 
 2 large, 2 small : 3 lobes 1 
 
 symmetrical 5 lobes in one 2 
 
 not quite symmetrical 1 
 
 sym. : 6 lobes in 2 unbroken cases 7 (0'39°/ o ) 
 
 not symmetrical 1 
 
 4 large, 2 small 1 
 
 4 large, 2 united : 6 lobes in 1 unbroken ... 2 
 
 3 large, 3 small : 6 lobes 1 
 
 1763 
 
CHAP. XVI.] 
 
 RADIAL SERIES : PEDICELLARI^E. 
 
 429 
 
 There were therefore 1735 normals, 19 symmetrical varieties and 9 
 irregulars. It will be noted not only that the symmetrical varieties 
 are comparatively frequent, but also that the several forms of irregu- 
 larity were seen for the most part in single specimens only. 
 
 II. PEDICELLARI.E OF ECHINODERMS. 
 
 The number of jaws in the pedicellarias differs in different 
 forms of Echinoderms, and I am indebted to Professor C. Stewart 
 for information concerning them. 
 
 In Asteroidea the number of jaws is usually two, but in Luidia 
 savignii the normal number of jaws is three. 
 
 In the Echinoidea the number of jaws is usually three, but 
 in Asthenosoma the normal number is four. 
 638. Dorocidaris papillata : number of jaws in pedicellariae 
 
 I I 
 
 Fig. 129. Peclicellariae of Dorocidaris papillata. 
 
 I. Normal form with three jaws. 
 
 II. A pedicellaria with four jaws from the abactinal region. 
 
 (From Prof. Stewart's specimens.) 
 
 normally three as in Fig. 129, I, but occasionally four in pedi- 
 cellarise of the abactinal region, as in Fig. 129, II. [Note that the 
 variety is perfect and symmetrical.] For this fact I am obliged to 
 Professor Stewart, who kindly allowed this figure to be made from 
 his preparations. 
 
 639. Luidia ciliaris : pedicellariae nearly all with three jaws ; but 
 on Roscofif specimens a few having two jaws occur on the borders 
 of the ambulacral groove. In Banyul's specimens none such were 
 found in this position, but there is one in almost all the marginal 
 intervals. CuE"not, Arch. zool. exp., S. 2. V. bis, p. 18. 
 
 640. Asterias glacialis : occasionally ^ree-jawed pedicellariae like 
 those of Luidia are found among the normal two-jawed pedi- 
 cellarise. Cu£not, I. c, p. 23. 
 
430 MERISTIC VARIATION. [part 
 
 III. Cell-Division. 
 
 *G41. It was purposed at this point to have introduced an account 
 of Meristic variations observed in the manner of division of nuclei 
 and cells ; but I have found that, to give adequate representation 
 of these facts even in outline, it would be necessary not only to 
 treat of a very complex subject with which I have no proper 
 acquaintance, but also greatly to enlarge the scope of this work. 
 But were no word said on these matters, indications most useful 
 as comment on the nature of Meristic Variation at large would 
 have to be foregone ; and unwilling that these should be wholly 
 lost I shall venture briefly to allude to so much of the matter as 
 is needful to shew some ways in which the facts of abnormal cell- 
 division can be used in reference to the wider question of Meristic 
 Variation. 
 
 We have been dealing with cases of Radial repetition, and we 
 have seen that with Variation in the number of parts the result 
 may still be radially symmetrical. It therefore becomes of interest 
 to note that in the case of abnormal cell-division the result of 
 numerical change may in like manner be radially symmetrical. 
 Cells which should normally contain two centrosomes and which 
 should divide into two parts have been seen to contain three centro- 
 
 I II 
 
 Fig. 130. Triasters. I. Tripolar division of nucleus in embryonic tissue of 
 Trout (after Henneguy 1 ). II. Triaster from mammary carcinoma. Centrosomes 
 not shewn (from F lemming 2 ). 
 
 somes (Fig. 130) prior to division into three parts, and the tri- 
 angle formed by the three centrosomes may be equiangular just 
 as may be the triangle of the segments of the abnormal Aurelia 
 (Fig. 128, V), or of the jaws of the normal pedicellaria of 
 Dorocidaris (Fig. 129). It is, I imagine, difficult to suppose 
 that the radial symmetry of each of these series of organs is 
 
 1 Heknegut, Jour, de VAnat. et Phys., 1891, p. 397, PI. xix. fig. 9. 
 
 2 Flemming, Zelhubstanz, Kern u. Zelltheilung, 1882, PI. viii. fig. v. after 
 Martin, Virch. Arch., 1881, lxxxvi. PI. iv. 
 
chap, xvi.] SYMMETRY IN TRI ASTERS. 431 
 
 different in its nature, or indeed that it is anything but a visible 
 expression of the equality of the strains tending to part each 
 segment from its neighbours. (The case of the triaster is taken 
 as the simplest and most plainly symmetrical, but examples of 
 cells with greater numbers of centrosomes, sometimes dividing 
 symmetrically, have also been seen.) 
 
 For our purpose this fact is first of use as a demonstration of 
 the absurdity of an appeal to " Reversion " as a mode of escape 
 from the admission that variations in Radial Symmetry may be 
 total and perfect though the new number of segments is one 
 which presumably never occurred in the phylogeny ; for we need 
 scarcely expect that even conspicuous defenders of the doctrine 
 that all perfection must have been continuously evolved, will 
 plead that the cells of every tissue in which a triaster is found 
 did once normally divide with three poles. Yet if it be once 
 granted that the symmetry of these abnormal forms is a sudden 
 and new departure from the normal, it will not be easy to put the 
 other cases on a different footing. 
 
 Though we have repudiated all concern with the causes of ab- 
 normality, mention may be made of the fact that multipolar figures, 
 both regular and irregular, have been observed to result from the 
 action of reagents {e.g. quinine, Hertwig 1 ). Such figures are of 
 course well known especially in the case of carcinomatous growths, and 
 as Hertwig observes, from the resemblance of these figures to those 
 artificially induced by chemical means it seems possible that these 
 pathological appearances may also be the result of some chemical 
 stimulus. But whatever be the immediate or directing causes of 
 abnormalities in cell-division, or of those other abnormalities in the 
 segmentation of Radial Series of larger parts, and whether any of the 
 causes in the several cases be similar or different, we can scarcely 
 avoid recognition that the resulting phenomena are closely alike 2 . 
 
 1 0. Hertwig, Die Zelle u. d. Geivebe, 1893, pp. 192—198. 
 
 2 See also a case of the presence of triasters in two bilaterally symmetrical 
 tracts of the blastoderm of Loligo [v. infra). 
 
CHAPTER XVII. 
 Radial Series: Echinodermata. 
 
 As seen in the majority of adult Echinoderms the repeated 
 parts are arranged with a near approach to a Radial Symmetry 
 and it is thus convenient to consider their Meristic Variations 
 in that connexion. But it must of course always be remembered 
 that in their development these repetitions are in origin really 
 a Successive Series and not a Radial Series. The segments are 
 not all identical (as, in appearance at least, they are in many 
 Ccelenterates &c), but are morphologically in Succession to each 
 other, though there may be little differentiation between them. 
 
 In the case therefore of Variation in the number of segments, 
 resulting in the production of a body not less symmetrical than 
 the normal body, there must be in development a correlated 
 Variation among the several members like that seen in so many 
 cases of additions to the ends of Linear Series. 
 
 This circumstance should be kept in view by those who seek 
 in cases of numerical Variation, in Echinoderms to homologize 
 separate segments of the variety with those of the type, hoping 
 to be able to say that such a radius is added, or such other 
 missing. As in other animals, this has been attempted in Echino- 
 derms, and though I know well that in the complex subject of 
 Echinoderm morphology I can form no judgment, yet it is difficult 
 to suppose that the same principles elsewhere perceived would 
 not be found to hold good for Echinoderms also. 
 
 All that is here proposed is to give abstracts of facts as to 
 Variation in the numbers composing the Major Symmetries. 
 It will of course be remembered that though the fundamental 
 number in Echinoderms is most commonly five, other numbers 
 also occur as normals, {e.g. four in the fossil Tetracrinus, six 
 in some Ophiurids, &c. Examples will be given of total change 
 from five to four and to six, and so on. It is besides not a 
 little interesting that of the normally 4-rayed Tetracrinus both 
 o -rayed and 3-rayed varieties should be known. 
 
 Besides the examples of total Variation there are a few cases 
 of incomplete Variation in which there is a fair suggestion that 
 
chap, xvil] RADIAL SERIES : HOLOTHURIOIDEA. 433 
 
 a particular ray is reduced in size (Nos. 680 and 681, &c). There 
 are also two cases of imperfect division of a ray in an Echinid 
 (Nos. 688, &c), while in Asteroids &c. this condition is common. It 
 is of importance to observe that just as in Linear Series abnormal 
 divisions of members of the series are commonly transverse to the 
 lines of Repetition, so in radial forms the divisions of rays are 
 commonly radial. 
 
 The evidence is complicated by the fact that in many 
 Echinoderms extensive regeneration can occur, and in some 
 genera reproduction by division of the disc and subsequent 
 regeneration is almost certainly a normal occurrence 1 . Never- 
 theless it cannot be doubted that the variation seen in Echini, 
 in Asterina, in the discs and stems of Crinoids, &c, are truly 
 congenital. Similarly, though in Asterias &c. reduction in the 
 number of arms might otherwise be thought to be due to mutila- 
 tion, it cannot be so in Echini &c. 
 
 HOLOTHURIOIDEA. 
 
 Cucumaria planci : among 150 half-grown specimens found 
 at Naples five were 6-rayed. Ludwig, H., Zool. Anz., 1886, IX., 
 p. 472. [These specimens are described in detail.] To determine 
 which is "the intercalated ray" the following ingenious reasoning 
 is offered, and as a good practical illustration of the conception 
 of the individuality of segments as applied to an Echinoderm 
 we may well consider it. 
 
 1 It is likely that several of the Ophiurids and Asteroids which normally have 
 more than 5 arms undergo such fission. Lutken ((Efvers. Dansk. vid. Selsk. 
 Fork., 1872, pp. 108—158 : tr. Ann. and Mag. N. H., 1873, S. 4, xn. pp. 323 and 391) 
 gave an account of this phenomenon. Ophiothela isidicola (Formosa) generally 
 has 6 arms, rarely equal, usually 3 large opposite to 3 small ; specimens common 
 with only 3 arms, with appearance as if corresponding half-disc cut off. There 
 can be no doubt that the animal divides and that the other 3 arms are renewed. 
 The same phenomenon has been seen in other small 6-armed Ophiurids, especially 
 of genus Ophiactis, but Liitken never saw any trace of it in any normally 5- rayed 
 species of the genus. There are indications that the division occurs once when the 
 animal is very small and again when it is adult or nearly so. In Ophiocom<i pumila 
 the small specimens have 6 arms, while the adults have 5. Probably therefore 
 division only occurs in the young, the last division being followed by the pro- 
 duction of 1 or 2 arms instead of 2 or 3. 
 
 Division is probably not a usual occurrence even in Ophiurids having more than 
 5 arms. Ophiacantha anomala has normally 6 arms, and 0. vivipara has 7 — 8, 
 but no such appearances are known in them. 
 
 Similarly there is evidence [figs, given] that certain Asteroids having normally 
 more than 5 arms viz. Asterias problema Stp. [ = Stichaster albulus], A. tenuispina 
 &.c. undergo fission; but there is no reason for believing that other many-armed 
 Asteroids divide. The Solasters have many rays, Asterias polaris has (5, but no 
 signs of division are seen in them. 
 
 An account is also given of the comet-like specimens of Ophidiaster cribrarius. 
 occasionally found, having one long arm, at the adoral end of which are present 
 4 or 5 arms as mere tubercles or as half-grown structures. This phenomenon is 
 well known in Linckia multiflora, in which doubtless the separate arms may break 
 off, each reproducing complete disc and arms. [See also as to Stichaster albulus, 
 Asterina wega, &c, Cuenot, L., Arch. zool. exp., V. bis, 1879—90, p. 128; and as 
 to Linckia, Sarasin, Ergeb. naturw. Forsch. auf Ceylon, 1888, X. lift. 2.] 
 
 b. 28 
 
434 MERISTIC VARIATION. [part i. 
 
 In the normal there are 5 radii and interradii, and 10 tentacles : 
 in the abnormals there are 6 and 12 respectively. In half-grown 
 normals the 3 ambulacra of the ventral trivium have more tube-feet 
 than the 2 ambulacra of the bivium ; also the pair of tentacles corre- 
 sponding to the central radius of the trivium are smaller than the rest. 
 In the abnormals 3 ambulacra have more tube-feet and are separated 
 by narrower interradii than the rest, and of them the central has the 
 least pair of tentacles : therefore these are the 3 radii of the ventral 
 trivium, and of them the central is the central of the normal. The 
 structure of the calcareous ring bears out this correspondence. The 
 central radius of the ventral trivium is therefore not the intercalated 
 radius. 
 
 In the 6-rayed specimens there is thus a ventral trivium and a 
 ' dorsal trivium.' (There were 2 Polian vesicles in 3 specimens, 3 in 
 one and one in the other, but in the normal also these vary in number.) 
 The stone- canal was single in all ; but in one of them it could be seen 
 that the canal arose in the interradius to the left of that which bore the 
 madreporic plate, suggesting that the radius thus crossed was super- 
 numerary ; for in a normal the interradius of the dorsal mesentery is 
 in the centre of the bivium. In a normal there are in the calcareous 
 ring two radials on either side between the dorsal mesentery and the 
 ventral median radius. In 4 of the abnormals (to which alone what 
 follows refers) there were 3 such radii on the left and 2 on the right, 
 while in the 5th specimen there were 3 on the right and 2 on the left. 
 
 The respiratory trees of the normal are in the right interradius 
 of the bivium and in the left interradius of the trivium. In the 6-rayed 
 they are in the left interradius of the ventral trivium and in the lower 
 right interradius of the dorsal trivium, agreeing with the normal and 
 shewing that the right radius of the ventral trivium is not an intercalated 
 one. Next, the mesentery in its course traverses in the 6-rayed form 
 4 radii and 3 interradii, the lower right interradius of the dorsal trivium 
 with its 2 adjacent radii alone being free. In the normal, 3 radii and 
 2 interradii are thus traversed, the right bivial interradius and its 2 
 adjacent radii being free. Therefore the right radius of the dorsal 
 trivium and of the ventral trivium are not intercalated. The central 
 radius of the ventral trivium has already been excluded ; therefore the 
 intercalated segment is either the middle or the left of the dorsal, or 
 the left of the ventral trivium. 
 
 In a normal, the mesentery which is attached to the alimentary 
 canal at that place where its upward portion again turns downwards 
 comes from that interradius which bounds the ventral trivium on the 
 left. This is the case also in the abnormals, and therefore the left 
 radius of the ventral trivium is not intercalated. Of the two remaining 
 radii the left of the dorsal trivium is in nowise abnormal, but the 
 central dorsal radius is abnormal in that it is crossed by the sand-canal, 
 therefore the central dorsal is the intercalated radius. 
 
 And since in four cases there were three radii in the calcareous 
 ring on the left, between the interradius of the stone-canal and the 
 central of the ventral trivium, and two on the right, therefore the new 
 segment is in them intercalated on the left of the median interradius of 
 the bivium ; while in the fifth specimen the intercalation has been made 
 on the rigid of the same interradius. 
 
chap. XVII.] VARIATION IN HOLOTHUKIOIDEA. 435 
 
 Now all this argument rests on the premiss that the several 
 members of a series of differentiated parts cannot undergo a 
 Substantive Variation in correlation with Meristic change in the 
 total number of members constituting the series. It is assumed 
 that there can be no redistribution of differentiation. 
 
 This assumption has now in many cases of Linear Series been 
 shewn to be false. To refer to one of the simplest cases, there 
 is, in the case of the Frog, evidence that the peculiarities of the 
 9th vertebra may be wholly or in part transferred to the 10th 
 vertebra, when by Meristic Variation there are 10 vertebras 
 (Nos. 56, 57 and 60), and the like has been shewn in many other 
 examples (cp. No. 35). The functions (as indicated by the struc- 
 tures) of the vertebras may be redistributed on the occasion of 
 Meristic Variation. 
 
 Will anyone affirm that similar redistribution of differentiation 
 may not happen in the Meristic Variations of Echinoderms ? 
 
 Variations in organs of Holothurioidea. Lampert calls attention to the 
 great variability found in this group and the consequent difficulty in distinguishing 
 specific characters from individual abnormalities. These variations often take the 
 form of alterations in the number of organs. For example, the distribution of 
 the tube-feet is liable to great alterations during the lifetime of individuals. In 
 some forms (as Thyone and Thyonidium) the feet are confined to the ambulacral 
 areas in the young animal, but are distributed over the whole body in more mature 
 individuals ; and in species of the genus Stichopus, though the tube-feet are 
 arranged in rows, yet in old individuals this arrangement may become obliterated. 
 On the contrary, in others, as for example, Holothuria graeffei, the arrangement 
 of the feet in thoroughly mature specimens is still most sharply defined. 
 
 The number of tbe tentacles is generally a multiple of five, and such cases 
 as Amphicyclus and Phyllophorus in which other numbers are found, are rare. 
 In these forms the tentacles are said to vary both in number, position and size, 
 but the number is always about 20. The case of Thyonidium nwlle is cited as 
 an extreme case. Of this species 4 specimens had 20 tentacles arranged in a paired 
 manner as in typical Thyonidia ; other specimens had 20 tentacles of similar 
 length ; others had from 16 to 19 tentacles of nearly equal lengths, and others 
 again had from 19 to 21, which instead of being disposed in pairs were placed 
 irregularly, some being larger and some smaller. 
 
 Of all the organs, the Cuvierian organs are the most variable and they are 
 of little value for purposes of classification. Their number is very inconstant 
 and they may even be absent altogether. It is impossible to distinguish any 
 circumstances whether of locality or of structure in which the individuals without 
 Cuvierian organs differ from the others which possess them. The two chief ap- 
 pendages of the water vascular ring, namely Polian vesicles [cp. No. 642] and the 
 stone- canal are usually constant when they are single, but in rare cases there 
 are exceptions even to this rule. If however more than one of these organs is 
 normally present, it may generally be assumed that there is no constancy in 
 their numbers, and in such cases the number of the Polian vesicles is especially 
 variable. A few species have been recorded in which, from a single Polian vesicle, 
 secondary ones are formed by lateral outgrowths. 
 
 The calcareous plates are of all the organs the least liable to variations, but 
 in certain cases they are stated to change with age. 
 
 Lampert, K., Die Seeivalzen, in Semper's Reisen im Archipel der Philippinen, 
 1885, iv. in. pp. 6, 13, and 174; also in Biol. Centrabl. v. p. 102. 
 
 Crinoidea. 
 
 Variation from the pentamerous condition has been many times 
 observed, though considering the vast number of specimens collected 
 
 28—2 
 
436 MERISTIC VARIATION. [part i. 
 
 it must be a rare occurrence. In Tetracrinus the four-rayed condition 
 is normal, and it is an especially interesting circumstance that in this 
 form Variation to both a five-rayed and to a three-rayed condition has 
 been observed. For nearly all the references to the following facts I 
 am indebted to the useful collection of evidence on the subject given by 
 Bather, F. A., Quart. Jour. Geol. Soc., 1889, p. 149. 
 
 Four-rayed varieties of five-rayed forms 1 . 
 
 044. Holopus rangi. This genus was originally described from a 
 4-rayed specimen by d'Orbigny, Mag. de ZooL, 1837, CI. x., PL in. 
 Subsequently, 5-rayed examples were obtained and this condition was 
 found to be normal (see Carpenter, Chall. Rep., XL, Pt. xxxn., p. 197). 
 
 645. Eugeniacrinus : departure from 5-rayed condition very rare. 
 Among many hundreds of calyces in Brit. Mus. one only is 4 rayed, 
 Bather, I. c., p. 155. 
 
 646. E. nutans : 4-rayed specimen at Tubingen figured in Quenstedt's 
 Atlas to Petrefacteuk. Deutschl. Taf. cv., figs. 179 — 181. Another case 
 Goldfuss, Petrefacta Germanice, I., p. 163, PL I., fig. 4, now in Poppels- 
 dorf Mus., Bour. (Bather). 
 
 647. E. caryophyllatus : 4-rayed specimen seen at Stuttgart. Such 
 a specimen [Hhe same] Rosinus, Tentaminis de Lithozois...Prodr. &c, 
 tab. in. (Hamb. 1719). Another case Goldfuss, I.e., fig. 4: now in 
 Poppelsdorf Mus. (Bather). 
 
 648. Pentacrinus : a 4-rayed stem-joint from the Chalk, Mantell, G. 
 A., Geol. of Sussex, 1822, p. 183 : now in Brit. Mus., E. 5501 (Bather). 
 
 649. Pentacrinus jurensis : 4-rayed specimen. The stalk had only 
 4 sides, one being quite flat. This flat side had an articulation for a 
 cirrus, de Loriol, P., Paleont. Franc. Terr, jur., Ser. 1, Paris, 1886, 
 p. 112, PL cxliv., fig. 6. 
 
 650. P. subsulcatus : 6 joints of a 4-rayed stem, ibid., p. 117, PI. 
 cxlv., fig. 2. 
 
 651. P- dumortieri: 8 joints of a 4-rayed stem, ibid., 1887, p. 186, 
 PL clxii., figs. 6 and 6 a. 
 
 652. P- dubius : 4-sided stem quite regular. Basle Mus., Bather, I.e., 
 p. 168. 
 
 653. Balanocrinus subteres : 4-sided stem quite regular, ibid. 
 (354. B. bronni : "the articular surface shows 4 sectors quite regularly 
 
 disposed ; this peculiar character is continued over the whole series of 
 joints, 26 in number." ibid. 
 
 655. Encrinus fossilis : a 4-rayed calyx, &c, v. Strombeck, A., 
 Ztschr. d. deut. geol. Ges., I., 1849, p. 158 et seqq. See also Palceonto- 
 graphica, 1855, iv., p. 169, PL xxxi. figs. 1 and 2. 
 
 656. E. fossilis : two 4-rayed calyces with mutilated arms, v. Koenen, 
 Abh. k. Ges. d. Wiss., Gottingen, 1887, xxxiv. Phys. Kl., p. 23. 
 
 657. Antedon rosacea : 4-rayed specimen, Carpenter, P. H., Chall. 
 Rep., xxvi. Pt. lx. p. 27. Four-rayed Japanese specimen, ibid. 
 Another in Brit. Mus. ibid. 
 
 1 4-sided stem joints undetermined. Pusch, Polens Palaont., 1837, p. 8, PI. n. 
 fig. 8, a, b, c, d. See also Austin, Ann. and Mag. N. H., 1843, xi. p. 203. 
 
chap, xvil] VARIATIONS IN CRINOIDS. 437 
 
 658. Actinometra paucicirra : 4-rayed specimen, ibid. " In all 
 these [Nos. 657 and 658] the anterior ray (A) is missing, so that the 
 mouth,' instead of being radial in position is placed interradially between 
 the rays E and B." Carpenter, I. c. 
 
 Compare the following case of imperfect change towards the 4-rayed 
 state : 
 
 659. Cupressocrinus crassus : abnormal calyx (now referred to this 
 species, see Bather, I. c, p. 169) has one segment of the calyx reduced 
 in size and bearing no radial plate or arm. This reduced segment is 
 covered in by the adjacent segments so that the calyx as a whole is 
 regularly 4-sided. Goldfuss, Nova Acta Ac. C. L. C, 1839, xix. p. 
 332, PL xxx., figs. 3 a and b [cp. No. 665]. 
 
 Six-rayed varieties of five-rayed forms. 
 
 660. Actinometra pulchella : doubtful case of six rays, Carpenter, 
 I. c. 
 
 661. Antedon sp. Six-rayed specimen. "The additional ray is in- 
 serted between the two of the right side (D and E)." Carpenter, I. c. 
 
 662. Rhizocrinus lofotensis : 6-rayed specimen. Four and six rays 
 stated to be more common in Rhizocrinus than in other recent Crinoids ; 
 seven rays are also found, but very rarely. In Pentacrinus no 6-rayed 
 specimen seen. Carpenter, P. H., Chall. Rep., xi. Pt. xxxn. p. 38, 
 PI. viii. a, figs. 6 and 7. 
 
 f 663. Pentacrinus jurensis (probably) : stalk with 6 sides. [Fig. 
 represents two adjacent lobes of the stalk as smaller and closer 
 together than the rest, suggesting that perhaps these two may cor- 
 respond with one lobe of the normal.] de Loriol, I.e., PL cxliv. fig. 7. 
 
 664. P. jurensis : 6-sided stalk having two adjacent lobes larger than 
 the others, ibid., fig. 10. 
 
 The following is a case of imperfect change towards the six-rayed 
 state : 
 
 665. Sphaerocrinus geometricus : abnormal specimen having the 
 basal plate irregularly six-sided by reason of the flattening of the 
 external angle of an infra-basal piece. Three of the sides are normal 
 and each of these bears a normal parabasal ; but of the other three 
 sides two are rather shorter than the normal sides and each of them 
 bears a somewhat smaller parabasal. Upon the sixth side between 
 these two, is a still smaller parabasal. The radials are five as usual, 
 but one of them articulates with the smallest parabasal and in con- 
 nexion with this its form is changed [for details see original figure]. 
 Sculpture, &c. normal. Eck, H., Verh. naturh. Ver. preuss. RheinL, 
 1888, Ser. 5, v. p. 110,^. 
 
 Three-rayed and five-rayed varieties of a four-rayed forni. 
 
 *666. Tetracrinus moniliformis : normally 4-rayed (as shewn in 
 Fig. 131, I.). A 3-rayed basal from the same locality, Birmensdorf 
 (Fig. 131, II.). A 5-rayed basal from Oberbuchsitten (Fig. 131, 
 
438 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 III.), de Loriol, P., Me'm. Soc. paleont. Suisse, 1877 — 1879, p. 245, 
 PL xix. figs. 39 6, 40 a, 41a. 
 
 E 
 
 III 
 
 Fig. 181. I. Normal four-rayed basal of Tetracrinus moniliformis (from Birmens- 
 dorf). II. A three-rayed basal of the same species from the same locality as I. 
 III. A live-rayed basal of the same species from Oberbuchsitten. 
 
 (After P. de Lokiol.) 
 
 •667. Cupressocrinus gracilis. This form has normally a 5-rayed 
 calyx, and a 5-sided basal plate containing only 4 canals round 
 the central canal (Fig. 132, I.). Varieties have been seen in which 
 
 GOT a. 
 
 Fig. 132. Cupressocrinus gracilis. The normal form of the basal is shewn in 
 I. A form with five canals round the central is represented in II, and in the 
 specimen shewn in III there are three peripheral canals. See No. 667 a. 
 
 (After L. Schdltze.) 
 
 there are 5 (Fig. 132, II.), or 3 (Fig. 132, III.) such peripheral 
 canals. The stalk is normally 4-sided, but in the varieties it is 
 either 3- or 5-sided in correspondence with the number of canals. 
 C. elongatus : stalk may be either 4- or 5-sided. The 
 species G. inflatus has normally 3 canals in the (circular) stalk. 
 Schultze, L., Denkschr. Ah Wiss., Math.-nat, CL, 1867, xxvi. 
 pp. 130 and 136, PI. I. fig. 2 b, and PI. III. figs. 2 c and 2 i [Cp. 
 No. 667.] 
 
 Abnormalities in the manner and frequency of branching in the arms of Crinoids 
 leading to great numerical variation have been often recorded. See Carpentek, 
 Chall. Rep., xxvi. Pt. lx. p. 28; id. Phil. Trans., 1866, Pt. 2, p. 725 PI., also a case 
 of twelve arms in Antedon rosacea, the abnormality not being symmetrical, Dendy, 
 Proc. h. Phy.8. Soc. Edin., ix. p. 180, PL; also case of A. rosacea having abnormal 
 branches in two arms symmetrically placed with regard to the axis. Bateson, W., 
 /'. /.. S. , L890, p. 584, tig. 4 (now in Coll. Surg. Mus.). The abnormal arms were 
 />._. and e x of the usual nomenclature, as shewn in Fig. 133. For details see original 
 description. 
 
 *6G9. Encrinus liliiformis : amongst other abnormalities case 
 given in which one of the radii bore only one arm. V. Strom- 
 beck, Palceont, IV. p. 169, PL xxxi. fig. 3. 
 
 668. 
 
CHAP. XVII.] 
 
 ASTEROIDEA. 
 
 439 
 
 ASTEROIDEA. 
 
 670. Symmetrical change in number of rays is common in some 
 of the forms. Asterias rubens and A. glacialis are frequently 
 seen with 6 or with 7 arms symmetrically arranged, and I have 
 
 , mouth 
 
 anus 
 
 Fig. 133. Antedon rosacea having two arms abnormally divided. Tbe figure A 
 shews the relations of the two abnormal arms, b 2 and e lt to the mouth and anus. B 
 shews the arm b 2 . (From Proc. Zool. Soc.) 
 
440 MEBISTIC VARIATION. [part i. 
 
 seen one with 8. Individuals with 4 arms occur, but are much 
 less common than those with 6. I have seen Asterina gibbosa 
 with 4 rays, and a specimen (Scilly) given me by Mr S. F. Harmer 
 has 6 rays, of which 2 are a little nearer together than the others 
 (suggesting division of a ray). Mr E. W. MacBride tells me that 
 he has seen several 6-rayed specimens of this species. Mr E. 
 J. Bles kindly tells me that he dredged a 4-rayed Porania 
 pulvillus in the Clyde estuary. There appeared to be no trace 
 of a fifth ray and the specimen was as nearly as possible sym- 
 metrical. 
 
 The following cases exhibit special points. 
 
 671. Asterias glacialis : specimen with 8 rays possessed 3 madre- 
 porites. Couch, J., Charlesworttis Mag. of N. R., 1840, iv. p. 34. 
 
 (372. Asterias rubens : G-rayed specimens frequent atWimereux. In 
 several of these there are two sand-canals terminating at a common 
 madreporite. Giard, A., Comptes rendus, 1877, p. 973; cp. id. C. R. 
 soc. bid., 1888, p. 275. 
 
 673. Partial division of an arm is fairly common in Asteroids, but less 
 common I believe than the total variation in number, though I know 
 no statistics on this point. For a figure of Asterias (Hippasterias) 
 equestris L. with a bifid arm, presenting no appearance as of regener- 
 ation see Tiedemann, Zeitschr.f Phys., 1831, iv. p. 123, Plate 1. 
 The two following are peculiar cases. 
 
 6 / 4. Cribrella oculata : one of the arms bearing a branch, not as a 
 radius, but about (in dried specimen) at right angles to the normal arm, 
 the property of Prof. C. Stewart, who kindly shewed it to me. 
 
 675. Porania pulvillus, Gray (a Starfish): Specimen 5 cm. in diame- 
 ter, having five short rays. The ray opposite the madreporite when 
 viewed from the aboral surface is seen to be distinctly bifurcated at 
 
 
 1/ 
 
 v^i.'i\\ & 
 
 
 \ Mm* &*& a *~-s 
 
 
 s. 
 
 
 
 Fig. 134. Porania pulvillus, No. 675, having the arm opposite the madreporite 
 abnormally divided as shewn at x and y. (From a sketch kindly sent by Prof. 
 Hbbdmak.) 
 
chap, xvii.] ECHINOIDEA. 441 
 
 about 1 cm. from its termination. The ambulacral groove of (Fig. 134) 
 this abnormal ray divides into two branches at a distance of 2 cm. 
 from the edge of the mouth. One of these branches runs along one of 
 the forks of the ray to its extremity without further complication ; 
 but the other branch, belonging to the second fork, divides again 2 mm. 
 from the first bifurcation, so as to form two tracts which unite with 
 one another 3 mm. further on, thus inclosing a small piece of the ordi- 
 nary integument in an ambulacral area. Finally, this ambulacral area 
 divides once more close to the tip of the ray. There are no signs of 
 injury or disease in the specimen. Hekdman, W. A., Nature, 1886, 
 xxxi. p. 596. [I am indebted to Professor Herdman for the accom- 
 panying diagram of this specimen.] 
 
 ECHINOIDEA. 
 
 In the Echinoids there are (1) cases of total Variation to a 
 4-rayed form with 4 ambulacra and 4 interambulacra 1 : (2) cases 
 of partial or total disappearance of a definite ambulacrum or 
 interambulacrum, which can be named either because part of 
 it is present, or because two sets of similar plates thus become 
 adjacent: (3) a case of total variation to a 6-rayed form : (4) cases 
 of imperfect reduplication of a radius, thus forming an imperfectly 
 6-rayed form. 
 
 (1) Total Variation to a Grayed form. 
 
 676. Cidarites coronatus?: 4-rayed regular specimen (Fig. 135). 
 Meyer, A. B., Nova Acta G. L. C, xvm. 1836, p. 289, PL xm. 
 
 Fig. 135. Cidarites coronatus ? No. 676, a regularly 4-rayed specimen from 
 oral surface. (From A. B. Meyer.) 
 
 *677 # Echinoconus (Galerites) subrotundus : 4-rayed specimen in 
 Woodwardian Mus. (Fig. 136). The ambulacral and interambulacral 
 areas are relatively wider than in a normal of the same size, the space 
 of the areas that are wanting being as it were shared among those that 
 are present. Apical disc roughly rectangular, and seems to be com- 
 posed of 4 perforated basals (genitals) and 4 perforated radials (oculars). 
 The basal plate corresponding to the posterior unpaired interambulacral 
 area is perforated, though normally imperforate. Statement made that 
 
 1 CuiNOT, Arch, tie Biol., 1891, xi. p. 632, says that Echinoconus vulgaris 
 has been seen with only three radii, but no authority is given. 
 
442 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 the parts missing are those which lie on the left side of a line drawn 
 through the middle of the anterior single ambulacrum and the posterior 
 
 na 
 
 1 
 
 * 
 
 >-// .... 
 
 '^ ■/■':[: 
 
 < vv 1 v- -•■/ •> 
 
 • • 
 
 L 
 
 ' 
 
 -< 
 
 
 r~ 
 
 V 
 
 
 
 
 
 
 -. 
 
 
 Fig. 136. Echinoconus subrotundus having 4 rays, No. 677. (From Roberts, 
 Geol. Mag., 1891.) 
 
 1. View of apical system. 2. Seen from side. 3. From apex. 4. From below. 
 aa, anterior ambulacrum [?]. mp, madreporite. ai, anal interradius. 
 
 The parts are lettered after Roberts. 
 
 unpaired interambulacrum, but it is not possible to say which of the 
 paired areas of this side are wanting, as the pores in the ambulacral 
 plates round the peristome are indistinctly shewn. Roberts, T., Geol. 
 Mag., 1891, Dec. ill., vni. p. 116, figs. 
 678. Discoidea cylindrica : a 4-rayed specimen, absolutely sym- 
 metrical. There are only 4 oculars corresponding with the 4 ambu- 
 lacra. Cotteau, G., Pal. /rang., 1862 — 67, VII. p. 31, PI. 1011, figs. 6 
 and 7. [This is exactly like Roberts' case No. 677 and is illustrated 
 by beautiful figures (q.v.). Cotteau in describing it says that the 
 anterior ambulacrum is wanting. It is difficult to see any sufficient 
 reason for the determination that this ambulacrum in particular is 
 wanting. For in this case there are only 4 sets of interambulacral 
 plates as well as 4 ambulacral areas in perfect symmetry. The anus 
 of course lies between two ambulacra ; and as the whole number is 
 even and the radii are symmetrically arranged, there is thus no ambu- 
 lacrum in the plane of the anus. Hence the suggestion that it is the 
 anterior ambulacrum which is wanting. But if by Variation an 
 Echinid has 4 symmetrical radii it would always seem that the 
 
chap, xvii.] ECHINOIDEA. 443 
 
 anterior ambulacrum was missing, whether it be the anterior ambu- 
 lacrum, or the left anterior, or the left posterior that is wanting, or 
 even if all 4 new ambulacra correspond with all 5 of the normal.] 
 
 (379. Amblypneustes sp. (S. Australia): four specimens, each with four ambulacra 
 [no description or statement as to symmetry]. Haacke, Zool. Anz., 1885, p. 505. 
 (See No. 687.) 
 
 (2) Partial or total disajipearance of a definite ambulacrum or 
 
 inter ambulacrum. 
 
 *680. Echinus melo, having only four complete ambulacral areas (Fig. 
 137). The specimen is not spherical, for the apical system is warped 
 over in one direction and the oral pole is pulled in an opposite direction, 
 while the shell is much higher in the region of the apical system than 
 it is at the opposite side. There are only four ocular plates, which are 
 subequal, the madreporic plate and the plate opposite to it being some- 
 what larger than the other two. The genital plates are also four. 
 Only four ambulacral areas leave the apical system, and at that point 
 they are almost symmetrically disposed. Lower down however a 
 triangular series of plates bearing ambulacral pores is intercalated 
 between the plates of one of the interambulacral systems which it 
 divides into two. This intercalated series is of course the representa- 
 tive of the ambulacral area which is wanting at the apex of the shell. 
 The five ambulacra are nearly symmetrically disposed round the oral 
 surface just as theyb^r ambulacra are round the apical system. This 
 transition from a tetramerous to a pentamerous symmetry is effected 
 by complementary changes in the amount of divergence of the rays as 
 they pass down the shell. Examination shews that the ambulacrum 
 which is thus partially absent is the right posterior. Philippi, Arch. f. 
 Naturg., in. p. 241, Plate. 
 681. Amblypneustes formosus : a 4-rayed specimen having a 
 somewhat asymmetrical test. One of the interambulacral regions is 
 abnormally wide, and at about 9 plates down the side of the test in this 
 region a wedge-shaped piece composed of several partially distinct 
 plates bearing 7 pairs of ambulacral pores. This fragment doubtless 
 represents the deficient ambulacral area. The apical system consists of 
 10 plates. The two genital plates of the abnormal area are reduced in 
 size, and the ocular plate between them is abnormally large. Consider- 
 ing the madreporic plate as indicating the right anterior interambula- 
 crum, it appears that it is the left anterior ambulacrum which is thus 
 deficient. The height of the shell at the abnormal side is less than at 
 the other. Bell, F. Jeffrey, Jour. Linn. Soc, xv. p. 126, Plate. 
 
 In each of the foregoing the missing ambulacrum is actually at some 
 place represented by plates of ambulacral character, and the shape of 
 the test is greatly changed in correlation with the partial disappearance 
 of the radius. The following cases differ, in that in them one ambula- 
 crum is wholly wanting in the affected radius, and the interambulacra 
 are contiguous with each other. Curiously enough in two of these 
 specimens the symmetry is changed little or not at all. The cases in 
 Hemiaster were all Algerian fossils l . 
 
 1 Besides those here given in the text, Gauthier in the same place describes 
 an interesting case of symmetrical reduction in the two posterior ambulacra of 
 Hemiaster africanus. 
 
 * 
 
444 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 II 
 
 Fig. 137. Echinus melo, No. 680, having the right posterior ambulacrum 
 partially absent, a, anterior ambulacrum, ra, la, right and left anterior ambu- 
 lacra, rp, Ip, right and left posterior ambulacra. I. View from apex. II. View 
 from oral surface. (From Philippi.) 
 
chap, xvil] ECHINOIDEA. 445 
 
 g§2 # Hemiaster batnensis : specimen in which the left posterior 
 ambulacrum is not present, and the ambulacral groove is only indicated 
 by a shallow depression, beyond which there are some rounded pores 
 which continue the ambulacral area beyond the fasciole. The corre- 
 sponding ocular seems to be absent. The test is of normal form, but 
 the median suture of the right posterior interambulacrum is not quite 
 straight. Gauthier, M. V., Comptes rendus de I'Ass. pour Vav. des sci., 
 1885, xiii. p. 258, PL vn. fig. 1. ' 
 
 (383. H. batnensis : very similar case of absence of right anterior 
 ambulacrum and corresponding genital and ocular plate, ibid., fig. 3. 
 
 (384. Hemiaster sp. : left anterior ambulacrum wanting and is gone 
 without trace. There are only 4 oculars and 3 genitals. In corre- 
 spondence with this variation there is considerable change in symmetry 
 of the test, which is irregular, the anterior and right anterior ambu- 
 lacra being deflected from their normal courses. [See details.] Ibid., 
 figs. 4 and 4 bis. [Here, where there is a clear differentiation between 
 the several ambulacra, it is doubtless possible to affirm that such a 
 definite ambulacrum is missing, for the two interambulacra are left 
 adjacent to each other.] 
 
 685. Echinus sphaera (O. F. Miiller): specimen described in which 
 the left posterior interambulacral series of plates is almost entirely 
 absent. The details of the structure are as follows : the genital plate 
 which stands at the head of the left posterior interambulacrum is 
 reduced in size in all directions ; but the two ocular plates which should 
 be separated by it are somewhat enlarged, bearing several extra tuber- 
 cles, and meet together peripherally to the genital plate. The series of 
 interambulacral plates which should begin from this genital plate are 
 represented by a rudimentary row of small tubercles : the ambulacral 
 systems which are normally separated by these plates are consequently 
 almost contiguous. The rudimentary interambulacral series widens 
 somewhat at a short distance from the apical series and forms a small 
 island of interambulacral structure bearing 4 large tubercles. Beyond 
 this, viz. at a point placed about ^ the distance from the apex to 
 the oral surface, the two ambulacra again unite and are continued as a 
 single ambulacrum of double width. Doxitz, W., Midler's Arch, f 
 Anat. u. Phys., 1866, p. 406, PI. xi. 
 
 (3) Case of total Variation to a Q-rayed form. 
 
 *686. Galerites albogalerus(P) : a regularly 6-rayed specimen having 
 six symmetrical ambulacra and interambulacra (Fig. 138). Meyer, 
 A. B., Nova Acta Ac. Cces. Leop. Gar., xvm. 1836, p. 224, PI. xiii. 
 
 Fig. 138. Galerites albogalerus, No. 686. A six-rayed specimen. (After 
 Meyer.) 
 
446 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 (387. Amblypneustes (S. Australia): 6-rayed specimen [no description or statement 
 as to symmetry]. Haacke, W., Zool. Anz., 1885, p. 505. (See No. 679.) 
 
 (4) Cases of imperfect reduplication of a radius. 
 
 '688. Amblypneustes griseus : having one of the ambulacra doubled 
 (Fig. 139); the apical system was normal. The width of the anterior 
 ambulacral region was almost double that of the others : it contained 
 two ambulacra lying side by side, each, as usual, composed of a double 
 row of plates with an ambulacral area and two poriferous zones. The 
 
 is.aPca 
 
 
 Fig. 139. Amblypneustes griseus, No. 688. Specimen having the anterior 
 ambulacrum doubled. I. The test seen from the apex. II. Details of anterior 
 ambulacrum shewing combined poriferous zones between A and A. The dotted line 
 bisects the ambulacrum of double width. (After Stewart.) 
 
 areas and external poriferous zones are like those of a normal ambula- 
 crum ; but the poriferous zones which touch one another are fused 
 together, with the pores irregularly arranged. The combined porifer- 
 ous zones are not quite equal to the sum of two normal ones. The 
 whole of this area, formed of the union of two ambulacra, projects as a 
 ridge which is continued down the whole of the side of the shell. 
 Stewart, C, Jour. Linn. Soc, xv. p. 130, PI. 
 
 689. Hemiaster latigrunda : right posterior ambulacrum double, the 
 two resulting ambulacra are closely adjacent peripherally and a small 
 interambulacral area is formed between them in their more central 
 parts. There are 6 oculars but no extra genital. Gauthier, /. c, tigs. 
 5 and 5 bis. 
 
 690. Hemiaster batnensis : right anterior ambulacrum double, the 
 two ambulacra are in contact through all their length. Cotteau, Pal. 
 
 frarig., 1869, p. 150, PI. xx., and Gauthier, I. c. 
 
 [For interesting evidence as to variation in the number of genital pores on the 
 costals in several genera of Echini, see Lambert, Bull. Soc. Yonne, 1890, xliv. Sci. 
 
chap, xvil] ophiuroidea. 447 
 
 nat., p. 34; also Gauthier, Comptes rendus Ass. fr. pour Vav. Sci., Toulouse, 1887, 
 and other references given by these authors.] 
 
 Ophiuroidea. 
 
 Individuals with various numbers of arms are often seen, 
 especially in the genera Ophiothela, Ophiocoma, Ophiacantha and 
 Ophiactis, and in many of the species there are most usually 
 six arms. In these forms the evidence as to Meristic Variation 
 is complicated by the circumstance that in several of them change 
 in the number of arms may take place in the ontogeny, by division 
 and subsequent regeneration (see note on p. 433). 
 
CHAPTER XVIII. 
 Bilateral series. 
 
 Of the organs repeated in Linear Series whose variations have 
 been illustrated, many are bilaterally repeated also ; but thus far we 
 have considered them only in their relations as members of Linear 
 Series. It now remains to examine the variations which they 
 exhibit in virtue of their relation to each other as members of 
 a Bilateral Series. 
 
 Meristic Variation in this respect is manifested in two ways. 
 A normally unpaired organ standing in the middle line of a bi- 
 lateral symmetry may divide into two so as to form a pair of 
 organs ; and conversely, a pair of organs normally placed apart 
 from each other on either side of a middle line may be com- 
 pounded together so as to form a single organ in the middle 
 line. 
 
 In animals and plants nothing is more common than for 
 different forms to be distinguished from each other by the fact 
 that an organ standing in the middle line of one is in another 
 represented by two organs, one on either side. The facility there- 
 fore with which each of these two conditions may arise from the 
 other by discontinuous Variation is of considerable importance. 
 
 Admirable instances of the bearing of this class of evidence upon 
 the question of the origin of Species are to be seen in zygomorphic 
 flowers. Veronica for example differs from the other Scrophulariacea? 
 especially in the fact that it has only one posterior petal, instead of 
 two posterior petals one on each side of a middle line. But there is 
 evidence not only that forms having normally two posterior petals 
 may as a discontinuous variation have only one such petal, placed in 
 the middle line, but also that the single posterior petal of Veronica may 
 as a variation be completely divided into two. Similarly the single 
 anterior petal of Veronica may also as a variation be divided into two, 
 thus giving three posterior and two anterior petals as in for example 
 Salpiglossis 1 . In these cases, which might be indefinitely multiplied, 
 
 1 An account of several discontinuous variations in the structure of zygomorphic 
 corollas was given by Miss A. Bateson and myself. Jour. Linn. Soc, 1892, xxvm., 
 Botany, p. 386. 
 
chap, xviii.] BILATERAL REPETITION. 449 
 
 there is thus a clear proof that so far as the variations in number and 
 symmetry are concerned, the transition from the one form to the other 
 may be discontinuous. 
 
 Analogous phenomena in animals are so familiar that general 
 description of them is for the most part not needed, and an 
 account will only be given of a few less known examples both 
 of union and of division of such parts. Besides these strictly 
 Meristic Variations in the amount of separation between the two 
 halves a few examples are introduced in further illustration of 
 the relationship that subsists between the two halves of a bilateral 
 animal. 
 
 In considering the evidence both of median union and of 
 division it must be remembered that the germs of most of the 
 organs in question are at some time of their developmental history 
 visibly double, and that when organs that should normally unite 
 to form single median structures are found double in older stages, 
 this duplicity is strictly speaking only a persistence of the earlier 
 condition. But to appreciate this comment it should be extended. 
 For, in every animal in which at some period of the segmentation 
 of the ovum, the plane of one of the cleavages corresponds with 
 the future middle line, all median organs must in a sense be paired 
 in origin, and the distinction between paired and median organs 
 is thus seen to be only one of the degree or amount of separation 
 between the symmetrical halves. Nevertheless the evidence of 
 Variation bears out the expectation that would be formed on 
 examination of normal diversities between species or larger groups 
 both in animals and plants, namely that whenever structures are 
 geometrically related to each other as optical images, insta- 
 bility may shew itself as Variation in the degree to which such 
 parts unite with or separate from each other. It is remarkable 
 that this instability appears as much in the case of organs bi- 
 laterally symmetrical about an axis of Minor Symmetry as it does 
 in the parts paired about the chief axis of Symmetry of the 
 whole body. 
 
 Examples of such Variation in bilaterally symmetrical parts 
 of a Minor Symmetry have been already given in the case of 
 the feet of the Horse and of the converse phenomenon in the 
 feet of Artiodactyles (q.v.). 
 
 A good illustration of the way in which duplicity about an 
 axis of Minor Symmetry may pass into the unpaired condition 
 is seen in the case of ocellar markings on bilaterally symmetrical 
 feathers. By comparing different feathers on several species of 
 Polyplectron, Darwin found that it was possible to find most of 
 the gradations between the complete duplicity shewn in Fig. 140, 
 I, where each half of the feather bears an almost symmetrical 
 ocellus, and the partially confluent condition shewn in Fig. 140, II, 
 which is not far removed from the state of the ocellus in the 
 Peacock's tail-coverts, where the whole ocellus has no peripheral 
 
 b. 29 
 
450 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 indentation and is very nearly symmetrical about the rachis of 
 the feather, though each of its halves has no axis of symmetry. 
 
 I II 
 
 Fig. 140. I. Part of tail-covert of Polyplectron chinquis, with the two ocelli of 
 nat. size. II. Part of tail-covert of Polyplectron malaccense, with the two ocelli 
 partially confluent, of nat. size. 
 
 (From C. Darwin, Descent of Man, 1871, n. p. 139, figs. 54 and 55.) 
 
 Attention should be called to the fact that abnormal division along 
 a middle line may in many cases represent one of two different pheno- 
 mena which are not readily distinguishable. For when a normally 
 single organ is represented by two, standing on either side of a middle 
 line it is often possible that there may be not only a division of the 
 organ but a partial duplicity of the axis. These two conditions are of 
 course morphologically distinct ; for in the case of division of the organ 
 only, the two parts are still in symmetry about the original axis of 
 Major Symmetry of the body, but in the case of duplicity of the axis 
 there are two equivalent axes of symmetry, about which each half is 
 separately symmetrical. But though this distinction is in a sense a 
 real one it cannot be applied to cases of duplicity occurring in any 
 organ whose halves assume a bilaterally symmetrical form when sepa- 
 rate. For example in the case of the foot of the Horse, or of the 
 hjemal spines &c. of Gold-fishes (v. infra), when division occurs, each of 
 the two halves is only hemi-symmetrical, and this duplicity is no more 
 evidence that the axis is double than is the ordinary double condition 
 of the vertebrate kidney; but in the case of duplicity of the central 
 neural canal in Man for instance, or in the case of the tail-spine of 
 Limulus described below, it is not clear that there is not a partial 
 duplicity of the axis. 
 
 Division or absence of union in Middle Line. 
 
 Most of the organs which in a vertebrate stand in a median 
 position have been seen more or less often in a divided condition. 
 
chap, xviii.] MEDIAN DIVISION: GOLD-FISHES. 451 
 
 Examples of such division in the middle line were, I believe, first 
 put together by Geoffroy St Hilaire, and a very full collection 
 of the evidence seen in Man is given by Ahlfeld 1 . The organs 
 most often divided are the sternum, neural arches, uterus, 
 penis, &c, and of these, specimens may be seen in any patho- 
 logical collection. Organs more rarely divided are the tongue 2 , 
 epiglottis 3 , uvula 4 , and central neural canal 5 . The following are 
 special cases of variation consisting in a median division. 
 
 Division of caudal and anal fins in Gold-fishes. 
 
 •691. Cyprinus auratus (Gold-fish). The following account of the 
 multiple fins of Gold-fishes in China and Japan is taken chiefly 
 from Pouchet 6 and Watase 7 . There is evidence to shew that these 
 animals were first imported to Japan from China. 
 
 Three distinct breeds of Gold-fishes are kept in Japan. The 
 first, called " Wakin " has a slender body closely resembling that of 
 the common carp. The second "Maruko or Ranckiu" has a very 
 short body, being in some cases almost globular in shape and 
 in it the dorsal fin is generally entirely absent. The head is 
 usually disfigured by rough-looking protuberances of the skin 
 which often attain a considerable size. 
 
 The third or "Riukin" has a short body with a rounded ab- 
 domen. Of all the breeds, this has the most beautiful tail which 
 is very large and often longer than the rest of the body. 
 
 Gold-fish breeders of the present day can freely produce the 
 " Riukin" or "Maruko " from the " Wakin." Various intermediate 
 forms between the above-mentioned breeds exist. 
 
 In all gold-fishes, irrespective of the breed to which they belong, 
 the tail-fin is, above all other parts, subject to the greatest varia- 
 tion. It is to be found in one of the following three states ; 
 
 (1) It is vertical and normal. 
 
 (2) It may consist of two separate halves ; each of these 
 halves is to all appearance a complete tail and the two tails pass 
 backwards side by side, but are united dorsally at the point where 
 they join the body. 
 
 (3) The two tails thus formed are united by their dorsal 
 edges to a variable degree and their lower edges may be bent 
 outwards, so that the two combined tails come to be spread out 
 into a three-lobed, nearly horizontal fin. 
 
 1 Ahlfeld, F., Mush. d. Menschen, 1880. 
 
 2 Partsch, Brest. Arztl. Ztsch., 1885, No. 17 ; Pooley, Amer. Jour., 1872, N.S., 
 cxxvi. p. 385 [from Ahlfeld, p. 119]. 
 
 3 Manifold, W. H., Lancet, 1851(1), p. 10; French, Ann. Anat. Surg. Soc. 
 Brooklyn, N. Y., 1880, ii. p. 271 [not seen], from Cat. Libr. Surg. -gen. U. S. 
 Army. 
 
 4 Trelat, Gaz. des H6p. t 1869, No. 125 [for others v. Ahlfeld, Abschn. n. p. 175], 
 
 5 Wagner, J., Mull. Arch. Anat. Phys., 1861, p. 735, PI. xvn. A. 
 
 6 Pouchet, G., Jour, de Vanat. et phys., vn. p. 561, PI. xvu. 
 
 7 Watase, S., Jour. Imp. Coll. Sci. Tokio, i. p. 217, Plates. 
 
 29—2 
 
452 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Besides the caudal fin, the anal fin undergoes remarkable 
 
 Fig. 141. Caudal and anal fins of Gold-fish (Cyprinus auratus). 
 
 I. Normal tail, seen from side. t>, dorsal lobe, d, ventral lobe. II. Abnormal 
 form divided as far as the notochord. v' v', two ventral lobes, d' d\ two dorsal 
 lobes. III. Abnormal form, the two ventral lobes, v' v', separate. IV. Pen- 
 ultimate vertebra of normal Carp (C. carpio). n.s, neural spine, h.s, haemal spine. 
 V. Penultimate vertebra of a Gold-fish with trilobed caudal fin. h'.s', double 
 haemal spine. VI. Diagram of transverse section through region of anal fin of 
 normal Gold-fish. VII. Similar section through a specimen having the anal fin 
 doubled, i.s, interhaernal spine. /. r, fin ray. n, bony nodule. i.s',f'.r', n', corre- 
 sponding parts doubled. (After Watase.) 
 
 variation. It is either median and normal ; or it may be distinctly 
 paired (Fig. 141, VII). 
 
 There are all stages of caudal and anal fins, intermediate be- 
 tween the normal and the completely paired states. Thus the 
 tail-fin with its lower portion alone in a double state, or the anal 
 fin with either its anterior or posterior portion double and the 
 remainder single, is of quite common occurrence. These different 
 conditions of the two fins combine in various ways in different 
 individuals thus giving rise to manifold varieties of form. 
 
 This doubling of the tail-fin consists essentially in a longi- 
 tudinal splitting of the morphologically lower lobe of the tail. 
 The first step in the process of doubling is seen in the case of 
 gold-fishes in which there is a slight longitudinal groove in the 
 
chap, xviil] MEDIAN DIVISION : GOLD-FISHES. 453 
 
 ventral margin of the tail-fin. This groove may be extended up 
 through all the rays of the lower lobe of the tail, which then 
 consists of two tails side by side. The small dorsal lobe, which 
 lies above the notochord, is never involved in the jwocess, but always 
 remains single. There is therefore in this case no doubling of 
 the axis of the body. Examination of the skeleton shews that 
 in those fishes which have two tails the haemal spines of the last 
 three vertebrae are longitudinally split 1 and diverge to carry the 
 two tail-fins (Fig. 141, V). 
 
 Pouchet lays stress on the fact that the size of each of the 
 paired tails is greater than that of the normal tail of a Gold-fish ; 
 but as Watase states that in the variety "Riukin" the tail may 
 be as long as the body, it is clear that this hypertrophy may exist 
 without any repetition. 
 
 In cases where the anal fin is doubled the process is exactly 
 the same, resulting from a longitudinal splitting of the rays of 
 which it is composed. This may only affect the outermost parts 
 of the fin or may be carried up further so as to divide the inter- 
 hsemal spines, in which case the two anal fins arise from the 
 body wall at separate points and diverge from each other. 
 
 Pouchet, who has extensively studied the history of Gold-fishes 
 in Europe, believes that it is almost certain that those which were 
 brought to Europe in the eighteenth century were all more or 
 less of the double-tailed order. He refers especially to the figure 
 given by Linnaeus 2 representing the double-tailed form as a normal. 
 
 Pouchet states that the evidence goes to shew that this 
 anomalous race is not maintained in China by any rigid selec- 
 tion. He quotes a Chinese encyclopaedia to the effect that the 
 double-tailed Gold-fish is found in running streams, and gives 
 the evidence of Kleyn 3 , a missionary in China during the 
 eighteenth century, who states that "In fluvio Sleyn Gyprini 
 sunt qui caudam habent trifurcam et a piscatoribus Leid-brassen 
 vocantur, quasi diceres aliorum Cyprinoram conductor es." 
 
 Though the duplicity of the hasmal spines may be unaccompanied by other 
 variations it should be noticed that the extraordinary "Telescope ' , Gold-fish not 
 unfrequently has also the double tail-fin. In the Telescope Gold-fish the eyes 
 project from the orbit to a greater or less extent, in the extreme form being 
 entirely outside the head and attached by a small peduncle only. The various 
 forms of abnormal Gold-fishes are generally to be seen in large quantities in 
 the shops of the dealers in aquariums &c. which abound near the Pont Neuf in 
 Paris. One of these dealers told me that he bred considerable numbers of them 
 every year, and that in fish from the same parents there was little uniformity, 
 many normals being produced for one that shewed any of the extreme variations. 
 It is recorded that of the Gold-fish hatched in Sir Robert Heron's menagerie about 
 two in five were deficient in the dorsal fin and two in a hundred or rather more had 
 a "triple" [sc. three-lobed as described above] tail-fin, and as many have the anal 
 
 1 It should be observed that there is no want of original union between the 
 hasmal spine3, for these close in the haemal canal as usual. The phenomenon is 
 thus altogether different from that of spina bifida in the neural spines. 
 
 2 Fauna suecica, 17-15, p. 331, PI. II. 
 
 3 Kleyn, Miss., v. p. 62, Tab. xm. fig. 1 [not seen], quoted by Baster, Opusc. 
 subsec, Harl., 1762, p. 91, note. 
 
454 MERISTIC VARIATION. [part I. 
 
 fin doubled. The deformed fishes were separated from the others but did not 
 produce a greater proportion of varying offspring than the normals (Ann. Mag. 
 N. H., 1842, p. 533). 
 
 For a magnificent series of plates illustrating the various forms of Gold- 
 fishes see Billardon du Sauvigny, Hist. nat. des Dorades de la Chine, Paris, 1780. 
 [In Brit. Mus. copy text wanting ; I do not know if it ever appeared.] 
 
 Division of median structures in Coleoptera. 
 The following list includes every case known to me. 
 
 I. Epistome. 
 
 692. Anisoplia floricola (Lam.): Algerian specimen having the 
 epistome (chaperon) completely divided into two parts in the middle 
 line. Attention is called to the fact that this is a normal character 
 in certain genera of Lamellicorns, for example, Diphucephala and 
 Inca. Fairmaire. L., Ann. Soc. ent. France, 1849, Ser. 2, VII. 
 Bull., p. lx. 
 
 II. Pronotum 1 . 
 
 In Coleoptera the pro-thoracic shield or pronotum is normally 
 a single plate continuous from side to side. The following is a 
 list of cases in which this structure w r as composed of two lateral 
 parts. In Nos. 695 and 706 the division was not completed 
 through the whole length of the shield. The two halves were 
 in most cases symmetrical, but in Nos. 700 and 703 they were 
 unequal. 
 
 As is shewn by No. 704 &c, there is in these variations more 
 than a mere fault of union between two chitinous plates, for in 
 this case the adjacent or inner edges of the plates were beset 
 with yellow hairs such as occur on the anterior and posterior 
 margins of the normal pronotum. In No. 703 again the adjacent 
 edges of the two plates are everted and form definite margins. 
 
 693. Melolontha vulgaris (Lam.), prothoracic shield consists of 
 two symmetrical pieces which do not meet in the dorsal middle 
 line. The prothorax is greatly reduced in length and the head con- 
 sequently is almost in contact with the scutellum (Fig. 142, I). 
 Kraatz, G., Deut. ent. Ztschr., 1880, p. 341.. PL u. fig. 8. 
 
 Fig. 142. Melolontha vulgaris, the Cockchafer, two cases of division of prono- 
 tum. (After Kraatz. ) 
 
 1 With these cases compare the following : Hydrobius fuscipes, specimen 
 having pronotum formed into three lobes, one being central, and two lateral. The 
 lateral lobes projected from each side as considerable expansions. Kraatz, G.,Deut. 
 ent. Ztschr., 1889, p. 222, fig. 21. 
 
chap, xviii.] MEDIAN DIVISION: BEETLES. 455 
 
 694. A male, closely similar case (Fig. 140, II., ibid., 1877, xxr. 
 v .5l,Taf.i.fig.2. 
 
 695. A male in which the pronotum was similarly divided, but 
 the division was not quite complete, de la Chavigxerie, Ann. 
 Soc. ent. Finance, 1846, Ser. 2, iv., Bull., p. xviii., PL II., fig. II. 
 
 696. An almost identical specimen (male). Mocquerys, Coleop. 
 anorm., 1880, p. 140, fig. [Now in the Rouen Museum, where 
 I have examined it.] 
 
 697. Another case ; extent of division not specified. Staxxius, Milll. 
 Arch. Anat. Phys., 1835, p. 304. 
 
 698. Oryctes nasicornis £ (Lam.) : anterior part of pronotum 
 divided into two parts by a longitudinal suture : posterior part 
 of pronotum undivided. Head normal, ibid., PL V. fig. 7. 
 
 699. Onitis bison (Lam.) : pronotum divided in the middle by a 
 longitudinal suture, the lateral pieces being raised up. ibid. 
 
 700. Heterorhina nigritarsis (Lam.) : specimen in the Hope Col- 
 lection at Oxford having the pronotum completely divided into two 
 somewhat unequal halves, of which the left is the largest. The 
 posterior angle of each of the pieces does not occupy its normal 
 position, but lies internal to the outer border of the elytron. 
 Owing to this disposition the mesothorax is exposed for a short 
 distance on each side and for a considerable extent in the 
 centre. 
 
 701. Attelabus curculionides (Rhyn.) : specimen of moderate size ; 
 head, elytra and legs normal. Structure of prothorax peculiar in that 
 the two lateral halves do not meet in the middle line, leaving 
 betwixt them a membranous space. The prothorax is shortened 
 and the head is pushed back into the thorax as far as the level 
 of the eyes. The edges of the plates of the prothorax are well 
 formed and properly finished. Scutellum present, but is not at 
 all concealed by the prothorax. Drechsel, C, Stettiner ent. Ztg., 
 1871, xxxii. p. 205. 
 
 702. Chrysomela fucata (Phyt.) : Pronotum divided centrally into 
 two parts, each of which is triangular. The parts of the head and 
 scutellum which should be covered by the thoracic shield are 
 thus exposed. Krause, Stettiner ent, Ztg., 1871, xxxir. p. 137. 
 
 703. Telephorus nigricans (Mai.) : the pronotum is divided into 
 two unequal halves. The left half is nearly twice as large as the 
 right, and projects beyond the middle line, covering a part of the 
 right side of the prothorax. The right portion is small and very 
 concave. Both of these two parts of the pronotum are everted 
 at their edges to form a definite margin. The margins are con- 
 tinued all round each piece, and thus two margins are adjacent 
 in the contiguous parts of the plates. This specimen was kindly 
 lent to me by M. H. Gadeau de Kerville. 
 
 704. Carabus scheidleri: thorax dorsally covered by two com- 
 pletely separate and symmetrical plates, whose inner edges are 
 beset with yellow hairs [as the anterior and posterior margins 
 
456 MERISTIC VARIATION. [part i. 
 
 normally are]. The rest of the animal was normal. Kraatz, G., 
 Berl. ent. Ztschr., 1873, xvn. p. 430, fig. 
 
 705. Carabus lotharingus : thoracic shield divided in centre to 
 form two triangular pieces which only unite at a single point. 
 The head is drawn back into the thorax. Duponchel, Ann. Soc. 
 ent. France, 1841, S. 1, X., Bull, p. XX., PL 
 
 706. Lixus angustatus (Rhyn.): thoracic shield partially divided, 
 present a deep emargination both before and behind [description 
 not quite clear]. Doue, Ann. Soc. ent, France, 1851, ix. Bull., 
 
 p. LXXXII. 
 
 III. Metasternal plates. 
 
 ~07. Rhizotrogus marginipes $ (Lam.) having the abdomen de- 
 formed in a svmmetrical manner. Looked at from the ventral 
 surface the metasternal plates are seen to be divided in the middle 
 line by a deep depression so that the abdomen consists superficially 
 of two lobes ; these two lobes are united together in the last 
 segment in which the metasternal plate is undivided. The two 
 lobes are of equal size and the longitudinal depression which 
 divides them is shewn in the figure to be regularly and sym- 
 metrically formed. The animal is otherwise normal. [No dis- 
 section was made.] Baudi, L. V., Bull. Soc. Ent. Ital., 1877, ix., 
 p. 220, fig. 
 
 IV. Pygidium. 
 
 708. Melolontha vulgaris (Lam.) : pygidium bifid, two cases. 
 Kraatz, G., Deut. ent. Ztschr., 1880, p. 342, PL II., figs. 4 and 
 4 a; and ibid., 1889, p. 222, PL I., fig. 19. 
 
 ■j-qq A case of "double proboscis 1 ' is recorded in Sphinx ligustri. The specimen 
 was a pupa, and through the pupal skin it could be seen that the two mandibles 
 had not united to form the single proboscis, but were divaricated. Kraatz, Deut. 
 nit. Ztschr., 1880, xxiv., p. 345, rig. 
 
 Miscellaneous cases of doubtful nature. 
 
 T 1 0. Ascidians. Prof. W. A. Herdman tells me that he has several 
 times met with Ascidians having a supplementary lateral atriopore. 
 He regards this as a retention of a larval character, since in the young 
 there are two atriopores which in normal individuals afterwards unite 
 dorsally. 
 
 711, Limulus polyphemus : large specimen found at Fort Macon, N. 
 Carolina, having a forked caudal spine (Fig. 143). This variation is 
 
 Fig. 143. Limulus polyphemus No. 711, having forked caudal spine. 
 
 (After Packard.) 
 
chap, xviii.] MEDIAN DIVISION : MISCELLANEOUS. 
 
 457 
 
 probably very rare. Packard, A. S., Mem. Bost. N. II. S., 1872, n. p. 
 201, .$7. 
 712. Palamnaeus borneensis (Scorpion) : specimen in which the 
 terminal poison-spine was double, as 
 shewn in Fig. 144. The two halves 
 were not quite equal and there was no 
 opening of a poison-gland on the shorter 
 spine. This specimen, which is in the 
 Brit. Mus. was kindly shewn to me by 
 Mr R. I. Pocock. 
 
 Chirocephalus £ : specimen hav- 
 ing the generative sac with two horns 
 instead of one. [Normally there is only 
 one such horn which forms a median 
 downward prolongation of the ovisac. 
 No further description.] Provost, B., 
 Mem. sur les Chirocephales, p. 232 ; in 
 
 71; 
 
 Jurine's 
 1820. 
 
 Hist, des Monocles. Geneva, 
 
 Fig. 144. Double poison-spine 
 of a Scorpion {Palamncem borne- 
 ensis). I. From dorsal side. 
 II. From ventral side. ??, the 
 spine which bore the openings of 
 the poison-glands. 
 
 714. Buccinum undatum. A number of specimens were formerly obtained from 
 Sandgate in Kent 1 , having the operculum double. Sometimes the two opercula 
 were separate, sometimes united. Many specimens of this variation are in the 
 collection of Dr A. M. Norman, who kindly shewed them to me. The shells and 
 opercula alone remain and consequently it is not now possible to determine the 
 position of the line of division relatively to the morphological planes of the animal ; 
 but, from the fact that in several instances the two opercula were related to each 
 other as images, it seems likely that the division was in the longitudinal median 
 plane, though this must be uncertain. Moreover in one of Dr Norman's specimens, 
 from the fragment of dried flesh adhering, it appeared that the apex of the foot 
 might have been bifid. Four cases are shewn in Fig. 145. In two of them (I and 
 II) there is a fairly close relation of images, while in III this relation is less clear 
 and in IV it is practically destroyed, though it is of course quite possible that this 
 may be the result of unequal growth. Several of these opercula are much contorted 
 and without any very definite shape. 
 
 II I 
 
 w. 
 
 HE 
 
 Fig. 145. Cases of duplicity in operculum of Buccinum undatum, from 
 specimens in the collection of Dr A. M. Norman. I and II nat. size. Ill and 
 IV enlarged. Ill and IV were kindly drawn for me by Mr J. J. Lister. 
 
 1 See Jeffreys, J. G., Ann. Mag. N. H., 1860 (2), p. 152. 
 
458 MERISTIC VARIATION. [part i. 
 
 It was intended to have introduced here some account of the 
 curious and very rare cases in which, for a greater or less region of 
 the spine, corresponding half-vertebrae, on either side of the middle 
 line, are not united together in their proper order, but I fear this 
 would be too great a digression. For references on the subject see 
 Leveling, Obs. anat. rarior., Norimb., 1787, Fsc. 1, cap. in. p. 145, 
 Tab. v.; Sandifort, Mils, anat, Leyden, 1835, IV. p. 74. PL 
 clxxviii. ; Reid 1 , Jour, of Anat., 1887, xxi. p. 76, fig.; Guy's 
 Hosp. Rep., 1883, p. 132. 
 
 Union or absence of Division in the Middle Line. 
 
 This phenomenon is the converse of that described above. 
 Examples of median union are found in many organs of different 
 kinds. In vertebrates such union is especially well known in the 
 case of the eyes, the ears, and the posterior limbs, producing the 
 cyclopic, synotic and symmelian conditions respectively. 
 
 Each of these is of some interest to the student of Variation by 
 reason of the symmetry and perfection with which the union takes 
 place. In the cyclopian the degree to which the two eyes are com- 
 pounded presents all shades intermediate between the perfect duplicity 
 of the normal and the state in which the eye-balls are united in the 
 middle line of the forehead and have one circular cornea 2 . These 
 variations are closely comparable with those of the eye-spots on feathers 
 referred to on p. 449 ; for there also all stages are seen between a pair 
 of eye-spots placed one on either side of a middle line and complete 
 union to form one eye-spot bisected by the middle line. There is of 
 course no normal vertebrate having the eyes thus united in the middle 
 line, but as Meckel has remarked, the case of the cyclopian is not 
 essentially different from that of the Cladocera in which the compound 
 eyes, paired in other Crustacea, are united to form a single median eye. 
 The cases No. 718 and 719 of median union of the compound eyes of 
 Bees may also be considered in this connexion. 
 
 A very similar series of variations occurs in regard to the ears of 
 vertebrates, which in the synotic or cephalotic condition are compounded 
 in the middle line to a varying degree 3 . Such union of the ears is 
 especially common in the Sheep, cyclopia being most frequent in the 
 Pig. Dareste 4 states that the first beginning of the cyclopian condi- 
 tion appears in the Chick as a precocious union of the medullary folds 
 in the region of the fore-brain, occurring before the optic vesicles are 
 fully formed from it. The degree to which the union of the eyes is 
 complete then depends on the earliness with which the folds begin to 
 meet relatively to the time of budding off of the optic vesicles. Dareste 5 
 also declares that the cephalotic state is similarly first indicated by a 
 premature union of the folds in the region of the medulla, taking place 
 
 1 A ease in Man, resembling No. 7. 
 
 2 For an extensive collection of cases illustrating the various degrees of cyclopia 
 see especially Ahlfeld, Missb. d. Mensch., Abschn. n. 1882. 
 
 3 For figures see e.g., Otto, Mus. anat. path. Vratisl., PI. i. fig. 5, PI. in. fig. 2 
 (Lambs) ; Guerdan, Monats.f. Geburtsk., x. p. 176, PI. i. (Man) and many more. 
 
 4 Comptes rendus, 1877, lxxxiv. p. 1038. 
 
 5 I. c, 1880, xc. p. 191. 
 
chap, xviil] MEDIAN UNION : KIDNEYS. 459 
 
 before this part of the brain has widened out. In this way the auditory 
 involutions are approximated. This account however cannot apply to 
 all cases of union of ears; for the compounded ears are sometimes on 
 the ventral side of the neck, as in Guerdan's case 1 . 
 
 The body of the symmelian ends posteriorly in an elongated lobe 
 made up of parts of the posterior limbs compounded together by homo- 
 logous parts. The two femora are usually united to form a single bone, 
 the tibiae are separate and the two limbs are again compounded in the 
 tarsal region. The axial parts posterior to the hind limbs are always 
 greatly aborted 2 . 
 
 Union of the kidneys in the middle line (Fig. 146), forming the 
 " horse-shoe kidney " of human anatomists, is a similar phenome- 
 non. As to the mode of development of this variation I know no 
 evidence. Usually the kidneys together form a single horse-shoe 
 shaped mass of glandular tissue, the union being posterior 3 ; very 
 
 Fig. 146. Kidneys united in the condition known as "horse-shoe" kidney 
 (Man). In this specimen there were three renal arteries on each side. 
 
 (From Guy's Hosp. Rep., 1883.) 
 
 1 See note 2, p. 458. 
 
 2 See especially, Meckel. Arch. Anat. Phys., 1826, p. 273; Geoffroy Si 
 Hilaire, Hist, des Anom., ed. 1837, n. p. 23; Gebhard, Arch. Anat. Phys., l^ss, 
 Anat. Abth., p. 164 (good fig.). To the determination of the morphology of the 
 hind limb the structure of the symmelian monster is of unique importance, but I do 
 not know that it has had the notice it deserves from comparative zoologists. 
 From the manner of union of the parts of the two limbs may be obtained a positive 
 proof of the morphological relations of the surfaces of the two limbs to each other. 
 In a symmelian the feet are united by their fibular borders, the minimi being 
 adjacent, the halluces exterior, and the combined plantar surfaces ventral. The 
 great trochanters are dorsal, being often united into one in the dorsal middle line, 
 and the patellae are also dorsal, being also not rarely partly compounded. From 
 these facts, even were other indications wanting, we have a proof that if the hind 
 limbs were laid out in their original morphological relations to each other (as the 
 tail-fins of a Crayfish may be supposed to be) the halluces would be external and 
 anterior, the minimi internal and posterior, the flexor surfaces of the thigh and 
 crus and the plantar surface of the (human) foot would be ventral and the extensor 
 surfaces of the thigh and crus and the dorsum of the (human) foot would be dorsal. 
 This is of course affirmed without prejudice to any question of phylogeny ; but that 
 these must be the ontogenetic relations of the parts is clearly proved by the symmelian. 
 
 3 Sometimes anterior, e.g. Odin, Lyon mid., 1874, No. 12 [from Constat?* 
 Jahresb., 1874, i. p. 19] ; and Freund, Beitr. z. Geburtsh. u. Gyn., iv. 1875 [from 
 Canstatt's Jahresb., 1875, p. 340]. 
 
460 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 rarely the posterior ends of the kidneys are joined by a bridge of 
 ligamentous tissue 1 . 
 
 A remarkable case, in which the union of the two kidneys 
 was very complete and only indications of duplicity remained, is 
 given by Pichaxcourt, Gaz. hebd., 1879, p. 514. 
 
 *7 
 
 715 
 
 Illustrative Cases. 
 
 To these familiar instances are added a few less generally 
 known. 
 
 Capreolus caprea (Roebuck): specimen having the two horns 
 compounded in the middle line, forming a common beam for almost 
 the lower half of the horn (Fig. 147). This specimen was exhibited 
 among a large series of abnormal horns in the German Exhibition 
 beld in London 1891. Casts of it are in the Brit. Mus. and Camb. 
 Univ. Mus. 2 . 
 
 * >v ' 
 
 Fig. 147. A Roebuck (Capreolus caprea) Xo. 705, having the horns com- 
 pounded to form one. 
 
 716. Limax agrestis : specimen having the upper tentacles united 
 into one in the middle line. The eyes were paired as usual. 
 Forbes and Haxley, Hist. Brit. Moll, iv. p. 288 and I. PI. JJJ, 
 fig. 4. 
 
 1 See Gruber, Virch. Arch., 1865, xxxn. p. 111. 
 
 The original is at Darmstadt. 
 
chap, xviii.] MEDIAN UNION: EYES. 461 
 
 717. Helix hispida : specimen in which the tentacles were united 
 together. They were adherent throughout, excepting for a slight 
 cleft at the end, about one line in length. A shallow longitudinal 
 suture was visible between the two. The animal and shell were 
 otherwise normally formed. Roberts, G., Science Gossip, 1886, 
 xxii. p. 259. 
 *718. Apis mellifica (Honey-bee): a worker having the two com- 
 pound eyes continued up so as to unite on the top of the head 
 (Fig. 148). The union between the eyes of the two sides was com- 
 plete. There was no trace of any groove or division between them 
 and the resulting structure was perfectly symmetrical. In a 
 normal the three simple eyes are arranged in a triangle between 
 
 CE~~~^1 
 
 Fig. 148. A worker Bee (Apis mellifica) No. 708, having the two compound 
 eyes united across the middle line, seen from in front, and from the side. 
 CE, the united compound eyes. Oc, a single structure representing the three 
 simple eyes of the normal. (After Stannius.) 
 
 the upper edges of the compound eyes, but in this specimen they 
 were united into a single structure which was symmetrically placed 
 in the middle line in front of the united compound eyes (Fig, 148, 
 Oc). The body thus formed by the union of the simple eyes was 
 a round projection beset with long yellowish hairs. 
 
 In a normal male the compound eyes are much larger and are 
 in contact with each other at the top of the head, but the division 
 between them is sharply defined. In a normal worker, however, 
 the compound eyes are widely separated. 
 
 The facetting and the hairs on these eyes were normal and the 
 animal was in all other respects properly formed. STANNIUS, 
 Muller's Arch, Anal Phys., 1835, p. 297, PI. 
 '719. Apis mellifica having the compound eyes completely and 
 symmetrically fused. This individual was either a young and 
 abnormally developed queen, or else a worker. Its structure was in 
 several respects abnormal. The third pair of legs are like those 
 of the workers, as is shewn by the structure of the first joint of 
 the tarsus, the brush of hairs on the outside of the leg is not so 
 
462 MERISTIC VARIATION. [part i. 
 
 much developed as in the workers, and this feature suggested that 
 perhaps the specimen may be a young and abnormal queen. The 
 abdomen is small and seems to have been arrested in its develop- 
 ment, but its shape is that of the abdomen of the workers. The 
 last segment of the abdomen is elongated, triangular, and slightly 
 grooved in the middle of the posterior border, so as to permit the 
 passage of the sting. The wings are more like those of a queen or 
 worker than those of a male ; for in the latter they generally 
 greatly exceed the abdomen in length. The thorax is small, 
 narrow, and contracted more than in the normal form, being also 
 less convex. The space between the wings is less than in a fully 
 developed bee. The antennas are mutilated, but seem to have 
 been normal ; but their last joints are slightly reddish brown as 
 they are in females, whether workers or queens, and not black as 
 they are in drones. The two compound eyes were completely 
 fused together in the middle line, across the place in which the 
 simple eyes ought to be found. The simple eyes are not present 
 at all. Lucas, H., Ann. Soc. Entom. France, S. 4, viii. 1868, p. 
 7: 37, PI. 
 
CHAPTER XIX. 
 
 bilateral series — continued. 
 
 Further illustrations of the Relationship between 
 
 Right and Left Sides. 
 
 I. Variations in Segmentation of the Ovum of Loligo. 
 
 The following facts, taken from Watase 1 , are introduced in 
 further illustration of the mode of occurrence of bilaterally symme- 
 trical M eristic Variation. 
 *720. Loligo pealei. In the blastoderm the nucleus is placed eccen- 
 trically, being rather nearer to the posterior pole, as shewn in Fig. 
 
 a. v. 
 
 Fig. 149. Diagrams illustrating variations in segmentation of a Squid. 
 (Loligo pealei). 
 
 I. Normal unsegmented ovum, n, the nucleus eccentrically placed. A, anterior. 
 P, posterior. L, left. R, right. II, III, and IV. The shaded portions shew areas 
 in which in some specimens nuclear division was precocious. V. In the two 
 shaded areas triasters occurred in one specimen. VI. The hlastomeres of the 
 shaded areas in one specimen were not divided from each other. 1, 2, 3, successive 
 planes of division, ar, anterior right quadrant, pr, posterior right quadrant. 
 ar', pr', &c. areas separated off by the third segmentation-furrow. (After Watase.) 
 
 1 Watase, S., Jour, of Morph., iv. 1891, p. 247, Plates. 
 
464 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 149, I. The first furrow, 1, 1, divides the blastoderm into two 
 halves and corresponds with the future longitudinal middle line. 
 The second furrow, 2, 2, is at right angles to this, dividing the 
 blastoderm into anterior and posterior halves, and the third 
 furrow, 3, 3, passes as shewn in Fig. 149, V. 
 
 In the subsequent segmentations various irregularities were 
 seen in single eggs, some of the variations being bilaterally sym- 
 metrical while others were confined to a particular half or to a 
 particular quadrant. For example, in some ova the nuclei of the 
 cells formed from the left half of the blastoderm, excepting those 
 next the median axis posteriorly (Figs. 149, II and 150, I), began 
 to divide before those of the right side and reached an advanced 
 stage of karyokinesis while the nuclei of the right half were still 
 resting. The nuclei of each half kept time very nearly (for details 
 see original figures). This curious variation was seen in three 
 (perhaps four) ova all taken from one mother. 
 
 In another the nuclei of the two anterior quadrants al, ar, in 
 their divisions kept ahead of those of the posterior quadrants. 
 Fig. 149, IV. represents an ovum in which the nuclei of the right 
 posterior quadrant on the contrary divided before those of the 3 
 other quadrants. 
 
 Another variation is shewn in Figs. 149, VI and 150, II. There 
 the four blastomeres shaded had either been never fully divided 
 from each other or had subsequently fused together symmetrically 
 on each side. 
 
 / IT 
 
 Fig. 150. Variations in segmentation of ovum of Loligo pealei. I. Case in 
 which the nuclei of cells of the left half of the blastoderm began to divide pre- 
 cociously. II. Case in which the blastomeres of the areas ar' and al' were not 
 distinct from each other. (After Watase.) 
 
 Fig. 149, V, illustrates another remarkable Meristic variation 
 which symmetrically affected the portions shaded. In both of 
 these shaded segments the nuclei divided into three by triple 
 karyokinesis, forming " triasters." 
 
chap, xix.] LATERAL HOMOEOSIS. 465 
 
 II. Homoeosis in cases of normal Bilateral Asymmetry. 
 
 In proportion as an animal is bilaterally symmetrical the right 
 side is an image of the left. Nevertheless in many substantially 
 symmetrical forms there is asymmetry in the condition of some 
 one or more organs present on both sides. (This asymmetry, in 
 the cases to be considered, is of course distinct from that due to 
 asymmetrical disposition of unpaired viscera, such as the heart and 
 liver of vertebrates, &c.) In several of these cases there is evidence 
 that both sides may on occasion assume the form normally proper 
 to one only. 
 
 Some one will no doubt be prepared with the suggestion that 
 these variations are reversions : with this suggestion I shall deal 
 after the facts have been recited. 
 
 Spiracle of Tadpole. 
 
 721. Pelobates fuse us : a tadpole, 7 cm. long, having two spiracles 
 symmetrically placed (Fig. 151), one on the right side and the other on 
 the left 1 . [No details given.] H^ron-Royer, Bull. soc. zool. Fr. t ix. 
 
 Fig. 151. A tadpole of Pelobates fuscus, having, as a variation, two spiracular 
 openings, No. 721. (After Heron-Royek.) 
 
 1884, p. 162, j%. [In the normal there is only one spiracle, that of 
 the left side. In Pipa and Dactylethra two spiracles are normally 
 present. See Wyman, Proc. Bost. N. H. S., ix. p. 155; Wilder, Am. 
 Nat.y 1877, xi. p. 491 ; Boulenger, Bull. soc. zool. Fr., 1881, vi. p. 27. 
 
 Tusk of Narwhal. 
 
 722. Monodon monoceros (Narwhal). In normal males the left tusk 
 alone is developed while the right remains abortive in its alveolus. In 
 the female both tusks are in this rudimentary condition. No reliable 
 record (1871) of a specimen having the right tusk only developed, but 
 in eleven cases from various sources the two tusks were both developed, 
 and in several of these the two were of about equal length. The 
 normal asymmetry of the skull is not affected by the presence or 
 absence of the teeth. Clark, J. W., P. Z. S., 1871, p. 42, figs, (full 
 literature); see also Turner, W., Jour. Anat. Phys., 1871, p. 133 and 
 1874, p. 516. 
 
 Ovary and oviduct of Fowl. 
 
 It might be anticipated that development of the right ovary and 
 oviduct in birds would be a frequent form of Variation, but as a 
 matter of fact very few such cases are recorded. In consideration of 
 
 1 In the same place is recorded a case of a tadpole of this species having the 
 spiracle on the right side instead of the left, perhaps a case of situs inversus. 
 
 b. 30 
 
466 MERISTIC VARIATION. [part i. 
 
 the large numbers of birds, wild and domesticated, annually dissected 
 in laboratories it may perhaps be concluded that these variations are 
 exceedingly rare 1 . 
 
 728. Hen having a small right ovary in addition to the left ovary. The 
 left oviduct was normal, but the left ovary was partially transformed 
 into sacculated tissue. [Full histological details of the structure of 
 both ovaries given.] The hen had partly assumed the plumage of the 
 cock, having four sickle-feathers and other characters proper to the 
 male. Brandt, Z.f. w. Z., xlviii. 1889, p. 134, Pis. 
 
 724. Hen having a normal left oviduct and in addition a partially 
 developed right oviduct which formed a large thin-walled cyst dis- 
 tended with gas. C. S. M., Ter. Cat., 1872, 455. 
 
 Proboscis-pore of Balanoglossus 
 and ivater-pores of larvce of Asterias. 
 
 ♦725. Balanoglossus kowalevskii. The anterior or proboscis-body- 
 cavity is continued backwards into the proboscis-stalk as two hollow 
 horns. In this and most other species the left of these alone acquires 
 an opening to the exterior at the proboscis-pore. In B. kupfferi alone 
 there are two such pores, one opening into each of the two horns 2 . A 
 specimen of B. kowalevskii in which both horns thus opened to the 
 exterior was seen by Morgan, T. H., Jour, of Morph., 1891, v. p. 442. 
 72G. Asterias vulgaris. The Bipinnaria larva as commonly seen 
 resembles the usual Tornaria in having a left water-pore only. In 
 several larvae 3| to 4 days old the presence of two such water-pores, a 
 right and a left, symmetrically placed, has been observed by Field and 
 Brooks. The right pore subsequently closes. This condition is be- 
 lieved by Field to represent not a variation but a normal phase of 
 development [though further confirmation is needed]. Field, G. W., 
 Q. J. M.S., 1893, xxxiv. p. 110, PL xiv. figs. 22 and 23. 
 
 Variations in Flat-fishes. 
 
 A curious series of variations bearing on the relations of the 
 right side to the left occur in Pleuronectidse. The evidence on 
 this subject was collected by Steenstrup 3 in 1863. 
 
 Flat-fishes are normally coloured on the upper side and are 
 without chromatophores in the skin of the lower side 4 . Variations 
 in colour occur in two ways ; the upper side may be white like the 
 lower, or on the contrary the lower side may be coloured like the 
 upper. The former change cannot well be distinguished from 
 other cases of albinism 5 and does not call for special notice here. 
 
 1 In view of the cases of the Crayfish and the Cockroach mentioned in the 
 Preface, much stress cannot be laid on this consideration. 
 
 2 Spengel, J. W., Mitth. zool. Stat. Neap., 1884, v. p. 494, PI. xxx. fig. 2. 
 
 3 Steenstrup, Overs, k. Dansk. vid. Selsk., 1863, p. 145, abstr. by Wyville 
 Thomson, Ann. and Mag. X. H., 1865 (1), p. 361. 
 
 4 In some species the coloured side is normally the right, in others the left, 
 reversed specimens being common in some species (P. Jlesus), rare in others. The 
 reversed condition concerns only the head, skin, muscles, &c, and there is no 
 transposition of the internal viscera. 
 
 5 Evidence collected by Steenstrup. Gottsche (Arch. f. Naturg., 1835, n. p. 
 139) states that P. platessa is not rarely wholly white on both sides. I have never 
 
chap, xix.] FLAT-FISHES. 467 
 
 The converse variation, by which the lower side assumes the 
 colour of the upper side is important in several aspects. 
 
 Interest has of late been drawn to this subject especially through an experiment 
 recently made by Cunningham 1 , who found that of a number of young flat-fishes 
 reared in a vessel illuminated by mirrors from below, some became partially marked 
 with pigmented patches on the lower side. The suggestion was made that this 
 pigmentation was induced by the direct action of light. It is of course impossible 
 here to enter into the theoretical questions raised in connexion with this subject 
 and this account will be confined to description of the colour- variation as seen in 
 nature and of the singular variation in structure commonly associated with it. 
 Mr Cunningham has obligingly advised me in connexion with this subject. 
 
 Pigmentation of the lower side has been seen in Rhombus 
 maocimus, R. Icevis, Pleuronectes flesus, P. platessa, P. oblongus, 
 Solea vulgaris [?] and probably other forms. Attention is drawn 
 to one feature in these changes which from our standpoint has an 
 important bearing. When the underside of a flat-fish is pigmented, 
 it is often not merely pigmented in an indefinite way but it is 
 coloured and marked just as the upper side is. There are, I know, 
 many specimens upon whose undersides a brownish yellow tint is 
 either generally diffused or restricted to patches, but when there 
 is pigment of a deeper shade, as in all the well marked cases of 
 the variation, the colour and markings are closely like those of the 
 upper side. For example, a Plaice (P. platessa) sent to me by Mr 
 Dunn of Mevagissey is fully coloured over the posterior half of the 
 lower side ; but there is not merely a general pigmentation, for the 
 coloured part of the lower side is marked ivith orange markings 
 exactly like those of the upper side. 
 
 More than this : it was found by passing pins vertically through 
 the body that there was in the case of most of the spots a close 
 correspondence in position behveen those of the upper and those of 
 the loiver side. There were 13 spots on the coloured part of the 
 lower side, which extended slightly beyond the line of greatest 
 width. Of these, 13 spots on body and fins coincided exactly with 
 those of the upper side ; 2 coincided nearly ; 2 were not repres- 
 ented on the upper side ; and 2 spots of the upper side were not 
 represented on the lower. From these facts it is clear that in 
 " double " flat-fishes we have an instance of symmetrical variation 
 of one half of the body into more or less complete likeness of the 
 other half, resembling other cases of Homceosis in Bilateral Series 
 already noticed. 
 
 This is made the more evident by the fact that in the two best 
 described specimens of "double" Turbot (No. 727) not merely did the 
 lower side resemble the upper side in point of colour, but upon it were 
 also present the bony tubercles normally proper to the dark side, being 
 only slightly less well developed on the lower side than on the upper. 
 
 succeeded in seeing an entirely white specimen, though individuals partially white 
 on the upper side are not rare. See also Zool, pp. 4596, -1914. Zeugopterus puncta- 
 tus white on both sides, Day, Brit. Fishes, n. p. 19. 
 1 Cunningham, J. T., Proc. Roy. Soc, 1893. 
 
 30—2 
 
468 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 (Such a development of tubercles 1 on the lower side may however occur 
 without any correlated change of colour.) It is also stated that in 
 the " double " turbots the muscles of the lower side are thicker than 
 they normally are, thus approximating to the upper side, a feature 
 that may be taken as an indication that the manner of swimming is 
 different from that of normals. 
 
 A flat-fish having pigmentation on the lower side does not 
 necessarily present any other abnormality' 2 . The Plaice, for in- 
 stance, just mentioned, was, colour apart, quite normal. But 
 some specimens of flat-fishes darkly coloured below present in 
 addition a very singular structural variation. This consists essen- 
 tially in the presence of a notch of greater or less depth occurring 
 below the anterior end of the dorsal fin above the eye (Fig. 1 52). By 
 this cleft the anterior end of the dorsal fin is separated from the 
 back of the head and is borne on a process or horn project- 
 ing anteriorly so as to continue the contour of the body above the 
 
 Fig. 152. Head of a Brill (Rhombus Icevis) having the dorsal fin separated from 
 the head as described in the text. (From Yarrell.) 
 
 1 The literature relating to discontinuous variations consisting in the presence 
 of bony tubercles upon the blind side of Rhombi is extensive. See especially 
 Demidoff, Voy. dans la Russie Merid., 1840, in. p. 534, Pis. 28, 29 and 30. 
 Steixdachner, Sitzb. Ak. Wiss. Wien, 1868, lvii. (1), p. 714. Rathke, Mem. Ac. 
 Sri. P6t. t 1837, in. p. 349. Gunther, Cat. Brit. Mm. Fishes, iv. p. 409. These 
 cases will not be confounded with those of supposed hybrids between R. maximus 
 and R. lavis, which bear upon both sides scales of various sizes. 
 
 - I know no detailed description of a flat-fish wholly pigmented on the underside, 
 having the dorsal fin normal, but numerous authors (Gottsche, Duhamel, &c.) make 
 mention of such cases. Since this chapter was written I have seen two recent papers 
 on the subject by Giard (Comptes rend. Soc. Biol, 1892, S. 9, iv. p. 31 and Nat. Sci., 
 1893, p. 356) contributing further evidence on the subject and giving new cases in 
 the Turbot. According to Giard, of flounders (P.Jiesus) at Wimereux 3 °/ are fully 
 coloured on the blind side, in addition to many that are piebald. This must be a 
 very much higher proportion of abnormal specimens than is found in English 
 fisheries. 
 
chap, xix.] FLAT-FISHES. 469 
 
 head. Steenstrup states that the variation has, he believes, been 
 observed in all flat-fishes 1 except the Halibut (Hippoglossus). 
 
 In several but not all cases of this abnormality the eye belong- 
 ing to the lower side was not placed in its normal position on the 
 upper surface, but stood in an intermediate position on the top of 
 the head, so that it could be partially seen in profile looked at from 
 the " blind " side. It seems possible that the pigmentation of the 
 " blind " side is in some way correlated with some abnormal delay 
 in the shifting of the eye and a consequent continuation of the 
 power of receiving visual sensations from this side. 
 
 The abnormality of the dorsal fin is in accordance with this suppo- 
 sition. To understand the nature of this condition it must be remem- 
 bered that the form of the flat-fish is derived from the usual "round" 
 form by two principal changes. (1) By a twisting of the head the eye 
 is brought over from the blind side to the upper side. (2) The dorsal 
 tin is extended forwards above the eye thus shifted ; for as Steenstrup 
 and Traquair 2 have shewn, this anterior extension of the dorsal fin is 
 not in the morphological middle line. It is in fact an anterior repeti- 
 tion of the series of dorsal fin-rays along the new contour-line of the 
 body, and occurs irrespective of the fact that the tissues with which it 
 is there associated are not median at all. 
 
 Steenstrup and Traquair shewed plainly that it is insufficient to 
 suppose that there is a twisting of the head, for this does not explain 
 the presence of the dorsal fin in the position in which it is found, 
 curving along that which ivas once the side of the head. Traquair sug- 
 gested that these relations could be attained by two processes ; ( 1 ) a 
 twisting of the head so as to bring over the eye from the future 
 "blind" side, and (2) a forward growth of the dorsal fin along that 
 which is then the upper contour-line of the head. These processes 
 have now been actually seen by Agassiz 5 in several Pleuronectidre. 
 The first observation of a specimen at the stage when the eye is on the 
 top of the head and the dorsal fin is not yet extended, seems to be that of 
 Malm 4 and there can be little doubt that the normal development 
 proceeds in this way 5 . It has been pointed out by many writers that 
 if the upper eye were to remain in an intermediate position on the top 
 of the head, and the dorsal fin were then to grow forwards, arching 
 over it, the condition of these abnormal forms would be reached. That 
 this is what has actually occurred in them seems likely. 
 
 A number of difficult questions are thus raised as to the histological 
 
 1 The evidence as to the Sole seems to be doubtful (v. infra). 
 
 2 Traquair, Trans. Linn. Soc, 1865, xxv. p. 2(33. 
 
 3 Agassiz, Proc. Amer. Ac. Sci. 1878, xiv. p. 1, Pis. 
 
 4 Malm, (Efvers. k. Sven. Vet. Ac, 1854, p. 173, see Ann. and Man. N. H. 1865 
 (1), p. 366. 
 
 5 Allusion should be made to the fact that in the genus " Plagusia" the dorsal 
 fin acquires its forward extension at a time before the shifting of the eye occurs. 
 When the time for this change comes the eye of the future bliud side passes under 
 the dorsal fin and above the skull, through the tissues from one side of the head to 
 the other. This was first observed by Steenstrup, and afterwards by Agassiz in 
 great detail and the fact can hardly now be questioned. This mode of development 
 is peculiar to " Plagusia" though when Steenstrup wrote he expected that the same 
 would be found to occur in other Pleuronectidse. 
 
470 MERISTIC VARIATION. [part I. 
 
 processes by which the dorsal fin comes to stand where it does. We 
 are accustomed to think of the repetition of the fin-rays as being an 
 expression of the fundamental segmentation of the trunk, accessory to 
 it no doubt, but still of the same nature and histologically dependent 
 upon it. The extension of this repetition along the morphological side 
 of the face is thus an anomaly. 
 
 Further comment on the nature of the variation will be made 
 after the chief cases have been given. 
 
 *727. Rhombus maximus (Turbot). Two specimens respectively 9 in. 
 9 lines and 7 in. 6 lines in length, 7 in. 6 lines, and 5 in. 6 lines broad. 
 Both sides of a similar coffee-brown colour. The smaller had a 
 yellowish white spot, about 1 in. square, on the operculum of the lower 
 side. The colour was more uniform than usual and the dark spots 
 normally found on the fins of the Turbot were absent. Both sides 
 irregularly beset with horny tubercles, only slightly more developed on 
 the upper than on the lower sides. Fine scales were also found deep 
 in the skin of both sides. All fins except the dorsal were normal in 
 form and position. The dorsal fin was anteriorly detached from the 
 head, being borne on a horn-like projection. The separation between 
 the head and dorsal fin was continued backwards as a semi-circular 
 notch to a level behind the eyes. Upon many of the fin-rays of the 
 dorsal, anal and caudal fins there were 1 — 7 small knotty elevations of 
 the size of poppy-seed. In the smaller specimen these elevations were 
 smaller, and on the caudal fin absent. The left eye had its normal posi- 
 tion, but the right eye [of "blind" side] was placed on the top of the 
 head, but in such a position that it could scarcely have seen any thing 
 not directly over it. [See further details given.] Schleep, Isis, 1829, 
 p. 1049, PL in. 
 
 Similar specimen Couch, Fishes Brit. Isl., in. p. 157. Dried speci- 
 mens in Brit. Mus., Newcastle Mus., &c. 
 
 *728. Very good figures of such a Turbot are given by Duhamel du 
 Monceau (Traite general des Pesches, 1777, III. Sect. ix. p. 262, PI. III. 
 figs. 3 and 4). The under side was of nearly the same colour as the 
 upper and the tubercles generally found on the upper side only were 
 present on the lower side also, though of smaller size. A slight notch 
 separated the dorsal fin from the head ; but the upper eye is figured as 
 in its normal place, not being on the top of the head, and it w T ould of 
 course be invisible from the "blind" side. [This important case is 
 referred to by Steenstrup, but seems to be unknown to others, who 
 attribute the separation of the dorsal fin to the persistence of the eye on 
 the top of the head.] 
 
 729. A young turbot, similarly coloured on both sides, having the eyes 
 still symmetrical, swimming on edge, is figured by McIntosh, Fishes of 
 St. Andrews, 1875, PI. vi. figs. 5 and 6. Prof. Mcintosh kindly 
 informed me that these "double" individuals swim on edge much 
 longer than usual. 
 
 730. Rhombus laevis (Brill). Specimen presenting similar characters. The lower 
 (rt.) side of a uniform dark colour with exception of a white patch on operculum. 
 The right pectoral fin was whitish. The under side was rather darker than the 
 upper and the mottling present on the upper side was entirely absent from the 
 under side, which was without marking or spot. This is very probably a post- 
 
chap, xix.] FLAT-FISHES. 471 
 
 mortem change. Right pelvic fin dark, but the left was whitish, speckled with 
 black. Nostrils normal. The eye of the right (blind) side was placed almost 
 entirely on the left side, but not completely so, for it could be seen to some extent 
 in profile from the right side. The notch separating the dorsal fin from the head 
 was rounded, and extended to about the level of the posterior margin of the left eye. 
 There were about 6 chief fin-rays borne by the prominence above the eye. The fish 
 seemed to be in all respects healthy and well grown. Paris Mils., numbered 
 #90 #310. [This specimen was kindly shewn to me by Prof. Vaillant.] 
 
 Similar specimen, also having white patch on operculum Duhamel du Monceau, 
 7. c. See also Fig. 152, from Yarrell, Brit. Fishes, 3rd ed., i. p. 613. 
 
 The specimen described by Donovan (Brit. Fish., 1806, iv. PI. xc.) under the 
 name " Pleuronectes cy clops" was in Steenstrup's opinion a young Brill having this 
 variation. In this specimen the right eye is seated on the top of the head and is 
 seen in profile from the right side. The right side was coloured like the left, but 
 was not so dark. The dorsal fin began behind the right eye. This specimen was 
 found in a rock-pool "inveloped in a froth" said to have resembled cuckoo-spit. 
 
 731. Zeugopterus punctatus (Muller's Topknot). This fish is very liable to mal- 
 formations of the anterior end of the dorsal fin, causing it to form an arch over the 
 eyes. Yarrell (quoting Couch), Brit. Fish., 3rd ed., i. p. 6-18. 
 
 732 "Platessa oblonga" De Kay (American Turbot) ; specimen having both sides 
 
 darkly coloured; upper eye placed on the top of the head; dorsal fin separated by a 
 notch. Storer, Mem. Amer. Ac. Sci., vm. p. 396, PI. xxxi. fig. 2 b. 
 
 733. Pleuronectes platessa (Plaice) : specimen completely and similarly pigmented 
 on both sides far from rare. In a specimen thus coloured the ' tubercula capitis ' 
 were as strongly marked on the one side as on the other. In several examples the 
 anterior end of the dorsal fin was separated, from the head, Gottsche, Arch. f. 
 Naturg., 1835, n. 1, p. 139. 
 
 734 Pleuronectes nesus (Flounder) : several specimens found at Birkenhead, having 
 ' a deep notch of this kind above the eyes. These fishes were 'very dark brown 
 (almost black) on both sides.' In the length of the fins these examples differed 
 somewhat from the Flounder, Higgins, Zoologist, 1855, p. 4596, fig. Specimen of 
 this kind figured by Traquair, Trans. Linn. Soc, 1865, xxv. p. 288, PI. xxxi. figs. 8 
 and 9. See also Nilsson, Skandin. Fauna: Fiskama, Lund, 1855, p. 621; Couch, 
 Brit. Fishes, 1864, in. p. 198. 
 
 735. Solea vulgaris. Many authors mention Soles coloured on both sides, but I 
 know no good description of one. Yarrell (I. c, p. 669) says "we have not seen 
 the Solea Trevelyani of Ireland (Sander's News-letter, 16th April, 1850). It is 
 dark-bellied and is described as bearing a projection on the head like the monstrosity 
 figured on p. 643." Duhamel du Monceau (/. c, PL I. figs. 3 and 4) represents a 
 sole darkly coloured on both sides. The dorsal fin is shewn in its normal state, 
 not separated from the head. No special description is given, and as the author 
 does not state that he had himself seen such a sole the figure was perhaps not 
 drawn from an actual specimen. A sole with the under side piebald is described in 
 Zool. x. p. 3660. 
 
 In connexion with this evidence Steenstrup refers to a small flat- 
 fish, Hippoglossus pinguis, found in a few localities in Scandinavian 
 waters, having a form almost intermediate between a "flat" and a 
 "round" fish. The eye of the "blind" side is exactly on the top of 
 the head and can be seen in profile from the blind side. The blind side 
 is nearly as muscular as the upper side, and its skin is yellowish-brown 
 in colour and is only slightly paler than that of the upper side. The 
 dorsal fin begins behind the eye, not arching over it. Steenstrup 
 looked on this creature as representing in a normal form the "double 
 condition presented as a variation in the cases we have been speaking 
 of. See description and figures in Smit's edition of Fries, Ekstrom 
 and Sundevall's Hist, of Scand. Fishes, 1893, pp. 416 and 417. 
 Smit makes a new genus, Platysomatichthys, for this animal. 
 
472 MERISTIC VARIATION. [part i. 
 
 Comment on the foregoing cases. 
 
 In the cases preceding many will no doubt see manifest examples of 
 Reversion. There is a sense in which this view must be true, for it can 
 scarcely be questioned that if we had before us the phylogenetic series 
 through which the Flat-fishes, the Narwhal, &c. are descended, it would 
 be seen that each did at some time have a bilaterally symmetrical 
 ancestor. But, for all that, in an unqualified description of the change 
 as a reversion the significance of the facts is missed. By the state- 
 ment that a given variation is a reversion it is meant that in the vary- 
 ing individual a form, once the normal, reappears. The statement more- 
 over is especially intended to imply that the definiteness and magnitude 
 of the step from normal to variety is due to the circumstance that 
 this variety was once a normal. It is meant, in fact, that the great- 
 ness of the modern change can be explained away by the suggestion 
 that in the past, the form now presented as a variation, was once built 
 up by a gradual evolution, and that though in its modern appearance 
 there is Discontinuity, yet it was once evolved gradually. 
 
 Now the attempt to apply this reasoning, especially to the case of 
 the "double " Flat-fishes, leads to difficulty. "We may admit that in so 
 far as the varieties are bilaterally symmetrical they represent a normal. 
 Their bilateral symmetry, as a quality apart, may be an ancestral 
 character, if any one is pleased so to call it. But that in the contem- 
 porary resumption of a bilateral symmetry we have in any further sense 
 a reappearance of an ancestral form is very unlikely. 
 
 First it might be fairly argued that it is improbable that there was 
 ever a typical flat-fish having ori'both sides the peculiar pigmentation 
 of the present upper sides of the Pleuronectidse of our day. Such a 
 creature would be highly anomalous. But even if in strictness we 
 forego the assumption that since the evolution of Flat-fishes there has 
 never been an ancestor fully pigmented on both sides, there still 
 remains the difficulty that each species may in the "double" state have 
 upon its lower side the specific colour proper to its own upper side. A 
 notable instance of this has been mentioned in the Plaice (p. 467); and 
 here not only was the pigmentation of the lower side, as far as it went, 
 like that of the upper, but the spots were even almost bilaterally 
 symmetrical. It is true that the lower side does not in every case copy 
 the upper in colour, but it may do so ; and, in proportion as it does so 
 in different species, so far at least are the changes not simply revers- 
 ions ; for the several patterns of Turbot, Plaice &c. are mutually ex- 
 clusive and it can hardly be supposed that each species had separately 
 a "double" ancestor having the present specific pattern on both sides. 
 
 The outcome of this reasoning is to shew that the hypothesis of 
 Reversion in the strict sense is an insufficient account of the actual 
 variation in these Flat-fishes, and in the production of these varying 
 forms there is thus a Discontinuity over and above that which can be 
 ascribed to Reversion. The facts stated in connexion with the Plaice 
 (p. 467), especially the symmetry of the spots, probably indicate the real 
 nature of this Discontinuity, and raise a presumption that in the new 
 resemblance of the lower side to the upper we have a phenomenon of 
 Symmetry resembling that Homceosis shewn to occur between parts in 
 
chap, xix.] LATERAL HOMCEOSIS : COMMENT. 473 
 
 Linear Series. In the Flat-fish the right side and the left have been 
 differentiated on different lines, as the several appendages of an Ar- 
 thropod have been, but on occasion the one may suddenly take up all 
 or some of the characters, whether colour, tubercles or otherwise, in 
 the state to which they have been separately evolved in the other. 
 
 What may be the cause leading to this discontinuous change we do 
 not know. That it is often associated with a delay in the change of 
 position of the eye of the " blind " side seems clear from the frequent 
 detachment of the dorsal fin in these cases. But it should be borne in 
 mind that even in such examples the eye may still eventually get to 
 its normal place, though probably it was delayed in the process and so 
 led to detachment of the fin. Taken with the fact that the young 
 " double " turbots swim on edge longer than the normals it must be 
 concluded that the bilateral symmetry of colour is associated with 
 reluctance or delay in the assumption of the asymmetrical state, but 
 more than this cannot be affirmed. 
 
 I do not urge that the same reasoning should be applied in other 
 cases, but the possibility must be remembered. In the Narwhal, for 
 instance, it is perhaps unlikely that there was ever an ancestor which 
 had two tusks developed to the extent now reached by the left tusk of 
 the male ; but if there ever were any such form, it is hard indeed to 
 suppose that it could have been connected with the present species 
 by a series of successive normals in which the right tusk gradually 
 diminished while the left was of its present size. On the whole it 
 seems more likely that when the right tusk now develops to be as 
 long as the left, it is taking up at one step the state to which the left 
 has been separately evolved. 
 
 However this may be, the fact that such Homoeosis is possible 
 should be kept in view in considering the meaning of such cases as that 
 of a Tornaria with two water-pores. For while on the one hand we 
 may suppose that Balanoglossus kupfferi with its normal pair of water- 
 pores is the primitive state and that the varying Tornaria is a revers- 
 ion, on the other hand B. kupfferi may be a form that has arisen by a 
 Homceotic variation from the one-pored form, and of this variation 
 Balanoglossus No. 725 may be a contemporary illustration 1 . 
 
 1 The following interesting example of a similar Variation has appeared since 
 these pages were set up. Eledone cirrhosa : specimen having not only the third 
 left arm developed as a hectocotylus, as usual, but the third right arm also. The 
 right had 57, the left 66 suckers, but otherwise they were alike. Appellof, A., 
 Bergens Museums Aarbog, 1893, p. 14. 
 
CHAPTER XX. 
 
 Supernumerary Appendages in Secondary Symmetry. 
 
 Introductory. — The Evidence as to Insects. 
 
 Of all classes of Meristic variations those consisting in repeti- 
 tion or division of appendages are by far the most complex and 
 the most difficult to bring into system. There is besides no 
 animal which normally presents the condition seen in the varia- 
 tions about to be described, though there may be a true analogy 
 between them and phenomena found in colonial forms. It has 
 nevertheless seemed well to introduce some part of this evidence 
 here for two reasons. First the subject is a necessary continuation 
 of the evidence as to digits, which would otherwise be left incom- 
 plete ; secondly it will be shewn that though many of the cases are 
 irregular and follow no system that can be detected, there remain 
 a large number of cases (being, indeed, the great majority of those 
 that have been well studied) whose form-relations can be put in 
 terms of a simple system of Symmetry. Thus not only are we 
 introduced to a very remarkable property of living bodies, but also 
 the way of future students of Variation may be cleared of a mass 
 of tangled facts that have long been an obstacle ; for on apprehen- 
 sion of the system referred to it will be seen that cases of repeti- 
 tion in Secondary Symmetry are distinct from those of true 
 Variation within the Primary Symmetry and may thus be set 
 apart. 
 
 Arrangement of evidence as to Repetition of Appendages. 
 
 In the first instance I shall give the evidence as to Secondary 
 Symmetries in Insects and Crustacea, prefacing it with a prelimin- 
 ary account of the system of Symmetry obeyed by those cases 
 which I shall call regular, and explaining the scheme of nomen- 
 clature adopted. Besides the regular cases of extra parts in 
 Secondary Symmetry there are many irregular examples which 
 cannot be shewn to conform to the system set forth. Of all but a 
 few of these, details are not accessible, and of the rest many are 
 
chap, xx.] SECONDARY SYMMETRY: PRELIMINARY. 475 
 
 mutilated or so amorphous that the morphological relations of the 
 surfaces cannot be determined. 
 
 Over and above these there remain a very few cases of 
 Repetition of parts of appendages where the arrangement is cer- 
 tainly not in Secondary Symmetry, but is of a wholly different 
 nature, exemplifying in Arthropods that duplicity of limbs already 
 seen in the human double-hands (p. 331) and in the double-feet of 
 Artiodactyles (p. 378). Genuine cases of this kind are excessively 
 rare ; but owing to hasty examination great numbers of cases have 
 been described as instances of duplicity, though in reality the 
 supernumerary parts in them can be shewn to be of paired struc- 
 ture. To emphasize the distinctness of these cases they will be 
 made the subject of a separate consideration. Logically they should 
 of course be treated before the Secondary Symmetries ; but their 
 essential features may be understood so much more readily if the 
 latter are taken first that I have decided to change the natural 
 order. 
 
 In continuation of the evidence as to Secondary Symmetry in 
 Arthropods will be given a brief notice of similar phenomena in 
 vertebrates. This evidence is comparatively well known and 
 accessible and I shall attempt no detailed account of it, referring to 
 the facts chiefly with the object of shewing how the principles 
 found in Arthropods bear on the vertebrate cases. 
 
 It will then be necessary to consider how repetitions in Second- 
 ary Symmetry are related to other phenomena of Repetition. 
 Lastly something must be said with regard to the bearing of these 
 facts on the general problems of Natural History. 
 
 Preliminary account of paired Extra Appendages in 
 Secondary Symmetry (Insects). 
 
 Supernumerary appendages in Insects are not very un- 
 common, perhaps 120 cases of this kind being recorded 1 . Nearly 
 all known examples are in beetles, but this may be due to the 
 greater attention paid to the appendages in that order. They 
 do not seem to appear more often in one family than in another, 
 but perhaps the rarity of instances in Curculionidye is worth 
 noting. They are found in both sexes, in all parts of the world, 
 and in species of most diverse habits. 
 
 Supernumerary parts may be antenna?, palpi or legs. (Extra 
 wings are probably in some respects distinct. They have al- 
 ready been considered. See p. 281.) Extra appendages may 
 be either outgrowths from the body in the neighbourhood of 
 the part repeated, or, as in the great majority of cases, they 
 occur as outgrowths from an appendage, extra legs growing from 
 normal legs, extra antenna: from antenna 1 , &c. In every case 
 there are two essentials to be determined : first the constitution 
 
 1 Not including some 110 cases of alleged duplicity of appendages given later. 
 
476 MERISTIC VARIATION. [part L 
 
 of the extra parts, and secondly the symmetry or relation of form 
 subsisting on the one hand between the extra parts themselves, 
 and on the other between the extra parts and the normal parts. 
 
 In few cases of extra appendages arising from the body 
 itself have these essentials been adequately ascertained. 
 
 For brevity I shall describe the phenomena as seen in extra 
 legs. The same description will apply generally to the antennae. 
 Recorded cases of extra palpi are very few, but probably are not 
 materially different. 
 
 Structure of Paired Extra Legs. 
 
 The parts composing extra legs do not as a rule greatly differ 
 from those of the normal legs which bear them. Though in 
 many instances extra legs are partially deformed, they are 
 more often fairly good copies of the true leg. Not rarely the 
 extra parts are more slender or a little shorter than the normal 
 appendage, but in form and texture they are real appendages, 
 presenting as a rule the hairs, spurs, &c. characteristic of the 
 species to which they belong. 
 
 The next point is especially important. The parts found in 
 extra legs are those parts which are in the normal leg peripheral 
 to the point from which the extra legs arise, and, as a rule no 
 more. Though in extra legs parts may be deficient or malformed, 
 structures which in the normal leg are central to the point of 
 origin of the extra legs are not repeated in them 1 . For instance, 
 if the extra legs spring from the trochanter they do not contain 
 parts of the coxa, if from the second tarsal joint, the first tarsal 
 joint is not represented in them, and so on. 
 
 Extra legs may arise from any joint of the normal leg, and 
 are not much commoner in the peripheral parts than in the 
 central ones, but there is a slight preponderance of cases be- 
 ginning from the apex of the tibia. It is rather remarkable that 
 cases of extensive repetition are not much less rare than others, 
 the contrary being for the most part true of the limbs of vert- 
 ebrates. 
 
 It does not appear that extra legs arise more commonly 
 from either of the three normal pairs in particular. 
 
 Supernumerary legs of double structure are sometimes found 
 as two limbs separate from each other nearly or quite from the 
 point of origin, but in the majority of cases their central parts 
 may be so compounded together that they seem to form but one 
 limb, and the essentially double character of the limb is not then 
 conspicuous except in the periphery. For example it frequently 
 happens that the femora of two extra legs are so compounded 
 together that they seem to have only a single femur in common, 
 
 1 Particular attention is therefore called to one case of extra antennas, which 
 did actually contain parts normally central to the point of origin. (See No. 804.) 
 
chap, xx.] SECONDARY SYMMETRY I PRELIMINARY. 477 
 
 and careless observers have often thus declared them to be two 
 legs with one femur. Similarly the two tibiae or the two tarsi 
 may be more or less compounded. In the case of Silpha nigrita 
 (No. 769), the two extra legs which arose from a femur were 
 compounded throughout their length, having a compound tibia 
 and tarsus (see Fig. 167). Even in cases when the two extra 
 legs appear to arise separately it will generally be found that 
 they articulate with a double compound piece of tissue which 
 is supernumerary and is fitted into the joint from which they 
 appear to arise. This is especially common in cases of two extra 
 tarsi, which seem to spring directly from a normal tibia. As a 
 matter of fact in all such cases these extra tarsi articulate with 
 a supernumerary piece of tissue, as it were let into, and com- 
 pounded with, the apex of the normal tibia. These bodies are 
 themselves double structures, composed of parts of two tibiae. 
 In determining the morphology of the limbs they are of great 
 importance, but unfortunately they are not generally mentioned 
 by those who describe such formations. But though extra parts 
 are generally present in the leg centrally to the point from which 
 the extra legs actually diverge, it should be expressly stated 
 that if this point is in the periphery of the leg, the central 
 joints are normal : if for example, there are two extra tarsi, 
 there may be parts of two extra tibial apices, but the base of 
 the tibia, the femur, &c. are single and normal. 
 
 Symmetry of Paired Extra Legs. 
 
 To appreciate what follows it is necessary to have a distinct 
 conception of the normal structure of an insect's leg, and to 
 understand the use of the terms applied to the morphological 
 surfaces. 
 
 If the leg of a beetle, say a Carabus, is extended and set at right 
 angles to the body, the four surfaces which it presents are respectively 
 dorsal, ventral, anterior and posterior. In the femur, tibia and tarsus 
 the dorsal is the extensor, and the ventral is the flexor surface. The 
 anterior surface is seen from in front and the posterior from behind. 
 (The terms ' internal ' and ' external ' are to be avoided as they de- 
 note different surfaces in the different pairs.) Difficulty as to the use 
 of terms arises from the fact that as the beetle walks or is set in 
 collections, the legs are not at right angles to the body but are rotated 
 on the coxa?, so that the plantar surface of the first pair of legs is 
 turned forwards, but the plantar surfaces of the second and third pairs 
 are turned backwards 1 . 
 
 1 Attention is directed to the fact that in a beetle there is a complementary 
 relation not only between the legs of the right and left sides but also imperfectly 
 between the legs of the first pair and those of the second and third pairs, which are 
 in some respects images of the first leg of their own side. For instance, in Gerambyx 
 (see Fig. 160) the trochanter of the fore leg is kept in place by a process of the coxa 
 which goes down behind it, but the corresponding process in the second and third 
 legs is in front of each trochanter. Again in Melolontha &c. the tibial serrations of 
 
478 MERISTIC VARIATION. [part I. 
 
 Extra legs may arise from airy one of the morphological 
 surfaces, but more often their origin is in a position intermediate 
 between them, e.g., antero-ventral, or postero-dorsal. 
 
 The next question is that of the determination of parts which 
 are extra from the parts which are normal. Two extra legs 
 spring from a normal leg. The appearance is often that of a 
 leg single proximally, but triple peripherally. All three limbs 
 are often equally developed and at first sight it might well be 
 supposed that the three collectively represent the single leg of 
 the normal. 
 
 In many cases of Meristic Variation I have contended that the 
 facts are only intelligible on the view that there has been such 
 collective representation. But in these Secondary Symmetries 
 this supposition is [? always] inadmissible. On closer examination 
 it is generally more or less easy to see that the three legs do not 
 arise in the same way, but that one arises as usual while the 
 other two are, as it were, ingrafted upon it. It is thus possible 
 in all but a very few cases to determine the normal leg from 
 the others by tracing the surfaces from apex to base, when it 
 will be found that some surface of the normal is continuous 
 throughout the appendage while those of the extra legs end 
 abruptly at some part of the normal leg. 
 
 Nearly always besides, as has been mentioned, the extra legs 
 are more or less compounded together at their point of origin 
 even if separate peripherally. In a few very exceptional cases 
 it happens that one of the extra appendages is compounded 
 with the normal and not with the other extra appendage. A 
 remarkable case of this in an antenna may be seen in Melolontha, 
 No. 800, and in a leg in Platycerus caraboides, (q.v.) 
 
 We have now to consider the positions of the paired extra 
 legs in regard to the normal leg and in regard to each other. At 
 first sight their dispositions seem entirely erratic ; but though it is 
 true that scarcely two are quite identical in structure, yet their 
 divers structures may for the most part be reduced to a system. 
 This system, though far from including every case, still includes a 
 large proportion and even the remainder do not much depart from 
 it except in very few instances. The comprehension of the general 
 system will also greatly help to make the aberrant cases appreciated 
 with comparatively few words. For simplicity therefore, the con- 
 sideration of exceptional cases will be deferred and the principles 
 stated in a general form. It will be remembered that we are 
 as yet concerned only with doable extra legs. 
 
 When extra appendages, arising from a normal appendage, are 
 thoroughly relaxed and extended, the following rules will be 
 
 the first legs curve backwards, but those of the other legs curve forwards. This 
 circumstance is mentioned lest it might be thought to have been neglected in what 
 follows, but this complementary relation has nothing to do with that which will be 
 shewn to exist between the extra legs. 
 
chap, xx.] SECONDARY SYMMETRY : RULES. 479 
 
 found to hold good with certain exceptions to be hereafter 
 specified. 
 
 I. The long axes of the normal appendage and of the 
 
 two extra appendages are in one plane : of the two 
 extra appendages one is therefore nearer to the axis 
 of the normal appendage and the other is remoter 
 from it. 
 
 II. The nearer of the two extra appendages is in structure 
 
 and position formed as the image of the normal 
 appendage in a plane mirror placed between the 
 normal appendage and the nearer one, at right angles 
 to the plane of the three axes; and the remoter append- 
 age is the image of the nearer in a plane mirror 
 similarly placed between the two extra appendages. 
 
 Transverse sections of the three appendages taken at homo- 
 logous points are thus images of each other in parallel mirrors. 
 
 As the full significance of these principles may not be at once seen 
 it may be well to add a few words of general description. The relation 
 of images between the extra legs is easy to understand. They are a 
 complementary pair, a right and a left. This might indeed be pre- 
 dicted by any one who had considered the matter. 
 
 The other principles, which concern the relations of the extra legs 
 to the normal leg, are more novel. For first it appears not that either 
 of the extra legs indifferently may be adjacent to the normal, but that 
 of the extra pair the adjacent leg is that which is formed as a leg of 
 the other side of the body. If therefore the normal leg bearing the 
 extra legs be a right leg, the nearer of the extra legs is a left and the 
 remoter a right. This principle holds in every case of double extra 
 appendages of which I have any accurate knowledge, where the struc- 
 ture of the parts is such that right limbs can be distinguished from 
 left. 
 
 But perhaps of greatest interest is the fact that the inclination of 
 the surfaces of each extra leg to those of its fellow and to those of the 
 normal are determined with an approach to uniformity in the manner 
 described. 
 
 These principles of arrangement may be made clear by a simple mechanical 
 device (Fig. 153). A horizontal circular disc of wood has an upright rod fixed in its 
 centre. This rod passes through one end of a vertical plate of wood which can be 
 turned freely upon it as an axle, so as to stand upon any radius of the horizontal 
 circle. The head of the axle bears a fixed cog-wheel. In the vertical wooden plate 
 are bored two holes into which two rods each bearing a similar cog-wheel are 
 dropped, so that each can rotate freely on its own axis. The three cog-wheels are 
 geared into each other. They must have the same diameter and the same number 
 of teeth. Three wax models of legs are fixed on the head of each wheel as shewn in 
 Fig. 153. In that figure, R represents the apex of the tibia and tarsus of a normal 
 right leg. The anterior surface is dark, and the posterior is white. The anterior 
 and posterior spurs of the tibia are shewn at A and P. SL and SR represent the 
 two supernumerary legs, SL being a left, SR a right. (They are supposed to arise 
 from the leg R at some proximal point towards which they converge.) When the 
 wooden plate is put so that the arrow points to the word "Posterior" on the disc, 
 the models will then take the positions they would have if they arose from the 
 posterior surface, all the ventral surfaces coming into one plane. If the arrow be 
 
480 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 set to "Ventral" the two supernumeraries will turn their dorsal surfaces to each 
 other, and so on. The model SL thus rotates twice on its own axis for each 
 
 Fig. 153. A mechanical device for shewing the relations that extra legs in 
 Secondary Symmetry bear to each other and to the normal leg from which they 
 arise. The model R represents a normal right leg. SL and SR represent respect- 
 ively the extra right and extra left legs of the supernumerary pair. A and P, the 
 anterior and posterior spurs of the tibia. In each leg the morphologically anterior 
 surface is shaded, the posterior being white. R is seen from the ventral aspect and 
 SL and SR are in Position VP. 
 
 revolution round R, but the surfaces of the model SR always remain parallel to those 
 of the model R. In every possible position therefore each model is the image of its 
 neighbour in a mirror tangential to the circle of revolution. In the figure the models 
 have the position they should have if arising postero-ventrally. Here the plantar 
 surface of SL is at right angles to the plantar surfaces of the other two legs. 
 
 Since at each radius the relative position of the legs differs, it is 
 possible to define these positions by naming the radius. This will be 
 done as shewn in Fig. 154. In this diagram imaginary sections of the 
 legs are shewn in the various positions they would assume at various 
 radii. The central thick outline shews a section of the normal leg, a 
 longer process distinguishing the anterior surface from the posterior. 
 The radii are drawn to various points D, A, V, P, representing 
 the dorsal, anterior, ventral and posterior positions respectively. In- 
 termediate positions may be marked by combinations, DA, VVP, 
 &c, using the system employed in boxing the Compass. 
 
 On several of the radii ideal sections of the extra legs are shewn in 
 thin lines, the shaded one being the nearer and the plain one the 
 remoter. M 1 and M 2 shew the planes of the imaginary mirrors. 
 
 The manner in which the pair of extra limbs are compounded with 
 each other in their proximal parts, and with the normal limb at their 
 
chap, XX.] SECONDARY SYMMETRY : SCHEME. 
 
 481 
 
 point of origin is most extraordinary. It does not appear that the 
 surfaces compound together along any very definite line or that the 
 
 II 
 
 Fig. 154. Diagrams of the relations of extra legs in Secondary Symmetry at 
 various positions relatively to the normal leg from which they arise. 
 
 The legs are represented in transverse section, the morphologically anterior side 
 of each heing indicated by the longer spur. The section of the normal leg, in 
 which the radii converge, is shewn with a thick black line. The section of the 
 nearer extra leg in Diagram I is shaded, while the remoter is blank. The radii 
 shew them in various positions, anterior, posterior, dorsal, ventral, iv/c. relatively to 
 the normal leg. 
 
 M 1 , the plane of reflexion between the nearer extra limb and the normal. 
 M' 2 , plane of reflexion between the nearer and the remoter extra limbs. 
 
 Diagram II is constructed in the same way to illustrate special cases of extra 
 legs arising anteriorly or posteriorly. If the two extra legs diverge from each other 
 centrally to the tibial apex each tibial apex is then complete, as on radius A of 
 Diagram I. In Diagram II are shewn two degrees of composition of the two 
 tibial apices, illustrating how, in cases of complete composition, the extra parts may 
 consist wholly of two morphologically posterior or anterior surfaces according as 
 they arise posteriorly or anteriorly to the normal leg. (See for instance Nos. 
 750 and 764.) 
 
 line of division between the several limbs is determined by the normal 
 structure of the limbs. The homologous parts seem to be compounded 
 at any point, almost as an object partly immersed in mercury com- 
 pounds with its image along the line to which it is immersed, where- 
 ever that line may be. 
 
 b. 31 
 
482 MERISTIC VARIATION. [part i. 
 
 From this some curious results follow. For instance, if two extra 
 limbs arise anteriorly and are separate at their tibial apices, they 
 bear four spurs as shewn at radius A in the upper diagram of Fig. 154. 
 But if the two are fully compounded at the tibial apices in the anterior 
 position the compounded limb will only have two spurs, both being 
 shaped as anterior spurs (as shewn in the lower diagram) and con- 
 versely for the posterior position (see No. 764). The parts, in fact, 
 where the pair may be supposed to interpenetrate (dotted in the diagrams) 
 are not represented. 
 
 Those who have described these phenomena have in consequence 
 often made the following error. Observing a limb giving off' a morpho- 
 logically double limb with a common proximal part subsequently sepa- 
 rating into its two components, they speak of this as a "primary 
 and secondary dichotomy." When the facts are understood it is clear 
 that there is no dichotomy between the extra legs and the normal, for 
 the parts are not equivalent and the normal is undivided. 
 
 Such are the principles followed. It ivould not be true to 
 assert that these rules are followed with mathematical jyrecision, 
 but in the main they hold good. Special attention will be given 
 to cases departing from them, bat the number of such cases is 
 small. The cases of slight deviation from the schematic positions 
 are besides mostly those of extra limbs in the Positions A and P, 
 and generally the deviation in them takes the same form, causing 
 the ventral surfaces of the extra parts to be inclined to each 
 other downwards at an obtuse angle instead of forming one 
 plane. 
 
 In all cases possible I have examined the specimens myself, 
 and I am under obligation to numerous persons who have very 
 generously given me facilities for doing so. Amongst others I 
 am thus greatly indebted to M. H. Gadeau de Kerville, Dr G. 
 Ivraatz and Dr L. von Heyden for the loan of many valuable 
 insects, and also to Messrs Pennetier, Giard, Dale, Mason, West- 
 wood, Waterhouse, Janson, Harrington, Bleuse, &c. In this part 
 of the work I am under especial obligation to Dr D. Sharp, for 
 without his cooperation it would not have been possible for me 
 to have undertaken the manipulations needed. He has most 
 kindly given up his time to the subject, and in the case of almost 
 every one of the specimens examined at Cambridge I have had 
 the benefit of his help and advice. 
 
 Of cases not seen by me few are described in detail sufficient 
 to warrant a statement as to the planes in which the parts stood, 
 but sometimes the figures give indications of this. Some of the 
 accounts are quite worthless, merely recording that such an 
 insect had two extra legs : in such cases I have thought it 
 enough to give the reference and the name of the insect for 
 statistical purposes. But every case known to me is here re- 
 corded : there has been no rejection of cases. 
 
 The cases will be taken in order of the Positions, beginning 
 
CHAP. XX.] 
 
 EXTRA LEGS : POSITION V. 
 
 483 
 
 with the Position V and taking the other radii in order, going 
 round against the hands of a watch. 
 
 Cases of Extra Legs in Secondary Symmetry. 
 
 (1) Position V. 
 
 *736. Carabus scheidleri % : pair of extra legs having a common 
 femoral^ portion arising from the trochanter of the right fore leg 
 (Fig. 155). This case is of diagrammatic simplicity. The troch- 
 
 Fig. 155. Carabus scheidleri, No. 736. The normal right fore leg, R, bearing 
 an extra pair of legs, SL and SR', arising from the ventral surface of the coxa, C. 
 Seen from in front. (The property of Dr Kraatz.) 
 
 anter bears a normal leg (R) articulating as usual. Immediately 
 ventral to this articulation there is a second articulation upon a 
 small elevation. This bears a double femur made up of jDarts 
 of a pair of femora compounded by their dorsal borders. The 
 double femur has thus two structurally ventral surfaces opposite 
 to each other. 
 
 The apex presents two articular surfaces in the same plane 
 as that of the normal leg, each bearing a tibia, both tibiae flexing 
 in the same vertical plane. 
 
 Since the double femur of the extra legs stands vertically 
 downwards at right angles to the normal femur, it will be seen 
 that both the extra tibiae flex upwards, but one of them is a 
 left leg (SL), bending to meet the normal leg, while the other 
 is a right (SR') } bending towards the ventral surface of the body. 
 The tibia of the left extra leg is a little shorter than that uf 
 the normal, and the tibia of the right extra leg is a little longer 
 than it. All three tarsi are thinner than a normal tarsus; and 
 the claws are a good deal reduced in the case both of the normal 
 and the right extra leg, while in the left extra leg they are absent 
 altogether. This is an example of a pair of extra legs arising 
 
 31—2 
 
484 MERISTIC VARIATION. [part i. 
 
 in the position marked V in the Scheme and having precisely 
 the relations there shewn. Specimen first described by Kraatz, 
 G., Berl. ent. Zt., 1873, p. 432, fig. 9. I am greatly indebted to 
 Dr Kraatz for an opportunity of examining it. 
 
 737. Carabus marginalis : penultimate joint of left hind tarsus is en- 
 larged and presents two articular surfaces, a proximal one on the 
 ventral surface, and another at the apex. The latter bears the normal 
 last joint with its claws. From the proximal articular surface arises a 
 thick joint shorter than the normal last joint, bearing at its apex two 
 pairs of claws set back to back, as in the Position "V. Specimen rede- 
 scribed from Kraatz, G., Deut. ent. Zt., 1880, xxiv. p. 344, PI. n. fig. 29. 
 
 738. Carabus granulatus <f , left posterior tibia bearing an amor- 
 phous rudiment of two extra tarsi arising from the ventral surface of 
 its apex. The apex of the tibia is produced at the dorsal border to 
 form an irregular process which bears a tarsus of normal form but 
 reduced size and immediately ventral to this tarsus is a pair of tibial 
 spurs. Ventral to these spurs is another deformed pair of spurs and 
 below them again is a deformed 3-jointed rudiment which probably 
 represents two tarsi. Ventral to the rudiment of the extra tarsi is 
 a third deformed pair of spurs. It was not possible to recognize the 
 surfaces of the tarsal rudiment, but the presence of tvw extra pairs of 
 spurs indicates plainly that the extra parts are morphologically of double 
 structure ; and as the spurs indicate the morphologically ventral sur- 
 faces, it follows that the surfaces adjacent in the extra tarsi are 
 dorsal. This specimen was originally described by Dr L. Von Heyden, 
 who was so good as to lend it to me for examination, see Deut. ent. Zt.. 
 1881, xxv. p. 110, fig. 26. 
 
 739. Prionus coriarius (Longicorn) : three legs in region of right 
 posterior leg. The proximal relations not quite clear and hence it is 
 not easy to distinguish the normal. Presumably it was the most dorsal. 
 This le<2r was of normal form but of reduced size and it wanted the 
 claw-joint. Internal to it, arising by a double coxa, trochanter and 
 femur, were the other two legs. The remoter w r as a normal right, but 
 the nearer was a left leg of reduced size, slightly crooked and lacking 
 three apical tarsal joints. The compound femur was just as in No. 736. 
 The normal leg must either have been the most dorsal or the most 
 ventral. If the former, the extra parts are in the Position V ; if the 
 latter, they are in the Position D, but in this event the normal would 
 be compounded with one of the extra legs. [Kedescribed from descrip- 
 tion and figure given by Krause, Sitzb. nat. Fr. Berl., 1888, p. 145, y?^.] 
 
 740. Melolontha vulgaris ? (Laraellicorn) : right posterior femur bears a super- 
 numerary pair of limbs having a double tibia in common. The supernumerary 
 parts are rather smaller than the normal ones. [The position of origin and 
 symmetry, according to the figure, must have been approximately V.] Kolbe, H. 
 J., Naturic. Wochens., 1889, iv. p. 169, fig. 
 
 741. Carabus perforatus <? : from the ventral or plantar surface of the 5th tarsal 
 joint of left hind leg project an extra pair of claw-joints compounded in Position V, 
 each bearing a pair of claws, set back to back. This is a diagrammatic case, well 
 and clearly described by Asmuss, Monstr. Coleop., 1835, p. 54, Tab. IX. 
 
CHAP. XX.] 
 
 EXTRA LEGS : POSITION VAA. 
 
 (2) Position VAA. 
 
 485 
 
 742. Feronia (Pterostichus) miihlfeldii % (Carabidse) : left 
 middle tibia bearing two supernumerary tarsi arising by a 
 common proximal joint (Fig. 156). As in other cases of super- 
 numerary tarsi arising from the tibia, the apex of the tibia 
 itself is really a triple structure, containing parts of the apices 
 of a pair of tibiae in addition to the normal apex. This is shewn 
 by the presence of three pairs of spurs, &c. The additional 
 parts are in this case anterior and ventral to the normal apex 
 and a complementary pair. All three are completel}* blended 
 together, forming in appearance a single apex. The relations of 
 the three component parts are almost exactly those indicated 
 in the Scheme for the Position VAA. 
 
 743, 
 
 Fig. 156. Pterostichus miihlfeldii, No. 742. Semidiagrammatic representation 
 of the left middle tibia bearing the extra tarsi upon the antero-ventral border of the 
 apex. L, the normal tarsus; R, the extra right; L' the extra left tarsus. (The 
 property of Dr Kraatz.) 
 
 The two extra tarsi (R, L') arise by a common proximal joint 
 of double structure having two complete ventral surfaces inclined 
 to each other as in the Position VAA. Peripherally to this the 
 two tarsi are separate. The tarsus which is nearer to the normal 
 tarsus is perfect, and stands in the schematic position. The 
 second joint of the remoter arises in the position shewn for VAA, 
 but its apex is slightly shrivelled and in consequence the re- 
 mainder of this tarsus, though perfect in size and form is thrown 
 a little out of position. This specimen was kindly lent to me 
 by Dr Kraatz, and was originally described and figured by him 
 in Dent, ent. Zt, 1877, xxi. p. 56, fig. 21. 
 
 Aromia moschata J (Greece) (Longicorn) : right anterior 
 tibia enlarged at apex bearing anteriorly a supernumerary pair 
 
486 MERISTIC VARIATION. [part i. 
 
 of tarsi. The widened apex bears three supernumerary spurs of 
 which the middle one is thicker than a normal posterior spur. 
 This is no doubt a double spur representing the two posterior 
 spurs of the extra tibia?. The other two extra spurs are ordinary 
 anterior spurs. The relative positions of these spurs are exactly 
 those marked VAA in the Scheme. Of the extra tarsi 3 joints 
 only remain and the two tarsal series are so closely compounded 
 that superficially they seem to form one tarsus only. In their 
 first joints the inclination of the ventral surfaces to each other 
 is at an acute angle, thus departing from the Scheme, but in 
 the second and third joints, where they are more separate from 
 each other, the inclination is at approximately the same angle 
 as that of the lines joining their respective spurs. Specimen 
 in General Collection of the British Museum. 
 
 744. Carabus graecus ^ : trochanter of right middle leg bears a super- 
 numerary pair of legs having trochanter, femur, tibia and 1st tarsal 
 joint common. The coxa of the normal leg is enlarged and the trochan- 
 ter has two heads, of which the anterior belong to the extra pair of legs. 
 The femur of the extra pair is a single piece but is morphologically 
 double, presenting two structurally anterior surfaces and two structurally 
 ventral surfaces, the latter being inclined to each other at an angle of 
 about 120°. From the apex of this femur there arises a double tibia, 
 also composed of two anterior and two ventral surfaces. This fact is 
 especially clear in the case of the tibia and is proved by the arrange- 
 ment of the spines and spurs. In a normal tibia there are two spurs, 
 one posterior and one anterior, and the posterior spur is longer than 
 the anterior. Now in this tibia there are three spurs, two shorter ones 
 at either margin of the apex, and one longer one with a bifid point 
 between them, which is clearly therefore a pair of "posterior spurs not 
 completely separated from each other. This view of the structure of 
 the double tibia is equally evident from the arrangement of the 
 remainder of the spines on its surfaces. In it the inclination of the ven- 
 tral surfaces is about the same as in the femur, but is perhaps rather 
 more acute. The 1st tarsal joint is similarly a double structure. Its 
 apex presents two articulations, but while the posterior bears a com- 
 plete 4-jointed continuation, the anterior bears only a single aborted 
 joint, from which possibly some portion has been detached, but this is 
 not certain. 
 
 The relations of the parts are a little obscured by the fact that the 
 normal tibia is slightly bent. The double part of the trochanter lies 
 very nearly anterior to the single part but it is also somewhat dorsal 
 to it. This gives to the base of the double femur a trend dorsal wards: 
 but from the base the femur curves ventralwards so that the nett 
 result is that its apex is actually ventral to the apex of the single 
 femur when both limbs are extended. This curve of course gives the 
 femur an abnormal form which is increased by the fact that it is 
 perceptibly shorter than the single femur. Now the relative position 
 of the pair of extra limbs is that marked VAA, and as it stands when 
 extended the apex of the double femur and the peripheral parts of the 
 double limb stand in the Position VAA with regard to the single limb ; 
 
CHAP. XX.] 
 
 EXTRA LEGS : POSITION A. 
 
 48' 
 
 * 
 
 but as has been mentioned, by the curvature of the double femur its 
 base is somewhat dorsal to the single limb. This specimen was very 
 kindly lent to me by Dr L. Yon Heyden and was first described and 
 figured by him in Deut. ent. Zt., 1881, xxv. p. 110, fig. 25. 
 
 (3) Position A. 
 
 745. Eurycephalus maxillosus (Longic): right anterior femur 
 divides at base into two parts, of which the posterior bears ;i 
 normal leg. The other part of the femur is bilaterally sym- 
 metrical, being made up of the anterior surfaces of two femora, 
 for both sides present the same convexity (Fig. 157), neither 
 being flattened as the posterior surface of a normal first femur 
 is. With the apex of this joint ar- 
 ticulates a bilaterally symmetrical 
 tibia of extra width, bearing a 1st 
 and 2nd tarsal joint, each of nearly 
 double width. 
 
 The 2nd tarsal joint bears two 
 3rd tarsal joints, which are both 
 much wider than the normal 3rd 
 joint of the tarsus. (This is exag- 
 gerated in the diagram.) One of 
 these in 1891 bore a perfect ter- 
 minal joint with a pair of claws ; but 
 the terminal joint and claws of the 
 other side were gone, though Moc- 
 querys' figure shews that they were 
 originally present. Mocquerys' state- 
 ment that "la cuisse anterieure du 
 cote droit se bifurque des son origine 
 en deux branches ayant chacune le 
 volume dune cuisse normale" is mis- 
 leading, as suggesting that the two 
 femora are similar, while upon closer 
 examination they are seen to be 
 dissimilar. Here a pair of extra legs 
 arising from the anterior surface of 
 the normal limb, are compounded 
 together as in the position marked 
 A in the Scheme. Specimen origin- 
 ally described by Mocquerys, Col. 
 anorm., 1880, p. 54, fig. 
 
 '746. Eros minutus (Malacoderm): 
 
 divided at apex, forming two apices (Fig. 158). The posterior 
 apex bears a normal tarsus. The anterior apex bears a double 
 tarsus having the first three joints simple (3rd being enlarged). 
 The 4th joint is of nearly double width and bears peripherally 
 two claw-joints each with a pair of claws. From the structure 
 
 Fig. 157. Eurycephalus maxil' 
 
 losus. Right anterior leg bearing 
 an extra pair arising from the 
 femur. 22, the normal right. SL, 
 supernumerary left. SB, super- 
 numerary right, p, posterior sur- 
 face, a, anterior surface of normal 
 femur, a', <i'\ the two structurally 
 anterior surfaces of the extra le^ r -. 
 (In Rouen Mus.) 
 
 right 
 
 anterior 
 
 tibia slight lv 
 
488 MERISTTC VARIATION. [part i. 
 
 of these it was clear that they are a pair. When extended the 
 three plantar surfaces are not truly in a horizontal plane, as they 
 
 Fig. 158. Eros minutus, No. 746. The right fore leg seen from dorso-posterior 
 aspect. P, posterior face. A, anterior face. This figure was drawn from the 
 microscope and has been reversed. (From a specimen the property of Dr Mason.) 
 
 should be in Position A, but they are nearly so. This deviation 
 is exaggerated iu the figure. Specimen very kindly lent by 
 Dr Mason. 
 
 747. Aleochara msesta (Staph.) : middle left tibia has two articulations at apex. 
 The posterior bears a tarsus normal in form but without claws. The anterior bears 
 an extra tarsal series with a pair of rudimentary terminal joints, each having a pair 
 of claws. Of this double tarsus the 3rd and 4th joints are not distinctly separated. 
 The parts are in Position A. Specimen kindly lent by Dr Mason*. 
 
 748. Meloe proscaraba-:us <? (Heteromera). The apex of the femur of right hind 
 leg is extended on the anterior side so as to form a second apex in the same hori- 
 zontal plane. With this second apex articulates the common head of a pair of extra 
 tibiae each bearing a complete tarsus. As usual they are a right and a left respectively. 
 The two extra legs are twisted out of their natural position so that they turn their 
 ventral surfaces upwards. The tibia which in origin is remoter from the normal 
 tibia is moreover bent over the nearer tibia so that it stands actually nearer to the 
 normal tibia. In this way the morphological relations are obscured, but nevertheless 
 on tracing the ventral surfaces up to the point of articulation with the femur it is 
 clear that they arise in the normal position and that they have the relations marked 
 in the Scheme for the Position A, which is their position of origin. As this case is 
 a somewhat obscure one, I may add that Dr Sharp, who has kindly examined this 
 specimen, gives me leave to state that he concurs in the above description. This is 
 the specimen described by von Heyden, Isis, 1836, ix. p. 761 and by Mocquerys, 
 Col. A norm. p. 52, Jig., and was kindly lent to me by Dr L. von Heyden in whose 
 possession it remains. 
 
 749. Cetonia opaca (Lamell.): [right fore leg bears a pair of extra terminal tarsal 
 joints very nearly in Position A, arising from 4th tarsal joint. All the claws are 
 turned ventralwards, but those of the extra joints are turned away from each other 
 as well as downwards]. Mocquerys, I.e., p. 61, fig. 
 
 r 750. Prionus coriarius % (Longicorn), having parts of a super- 
 numerary pair of tarsi arising from the middle right tarsus, 
 and also a similar double structure arising from the posterior 
 
CHAP. XX.] 
 
 EXTRA LEGS : POSITION A. 
 
 489 
 
 right tarsus (Fig. 159). This is a very important case as a clear 
 
 II I 
 
 Fig. 159. Prionus coriarius, No. 750. I. Apex of tibia of right hind leg with 
 its tarsus. II. Similar parts of right middle leg. (The property of Dr von Heydeu.) 
 
 PS, AS, posterior and anterior tibial spurs belonging to the normal leg. A'S', 
 A"S", the spurs of the extra legs, all structurally anterior spurs. A, anterior 
 surface. V, ventral surface. (The property of Dr von Heyden.) 
 
 illustration of the mode in which double supernumerary limbs 
 may be compounded together so as to closely simulate a single 
 limb. Each of the extra parts in this case in the original account 
 was described as a single extra limb, but as will be shewn, each 
 is really composed of parts of a complementary pair. Cases of 
 this kind suggest very strongly that other cases of supposed single 
 extra limbs are really instances of double extra limbs in which the 
 duplicity is disguised. 
 
490 MERISTIC VARIATION. [part I. 
 
 Right hind leg (Fig. 159, I), the tibia is dilated towards the 
 apex which presents dorsally two emarginations instead of one 
 as usual. On the ventral aspect of the apex there are two whole 
 spurs PS, A"S" and a double one AS, A'S', between them. 
 
 These spars give the key to the nature of the structure. The 
 proximal tarsal joint gives off a process on its anterior side and 
 is then continued to bear a normal termination as shewn in the 
 figure. The process from the first tarsal bears a second tarsal 
 from which the termination has been broken off. The extra parts 
 are as in the figure, being covered ventrally from edge to edge 
 with papillae, and having no longitudinal cleft in the middle line 
 like the normal tarsus. 
 
 Looking at these tarsal joints alone, the real nature of the 
 extra parts does not appear, for the anterior and posterior surfaces 
 of the normal tarsi are not differentiated from each other, and 
 hence it is not possible to say of what parts the supernumerary 
 limb is made up. Fortunately, however, the tibial spurs are 
 normally distinguishable from each other, for the anterior spur 
 is a short spur while the posterior is a long thin spur. Now the 
 spurs present in this case are firstly one long posterior spur PS, 
 and then three short anterior spurs, of which two are united for 
 part of their length .4$, A'S'. The extra spurs are thus both 
 anterior spurs, that of the extra tarsus which is nearer to the 
 normal being united to the normal anterior spur. Hence this 
 case is a case of a supernumerary pair of appendages compounded 
 together in the Schematic Position A, having the posterior sur- 
 faces adjacent and suppressed. 
 
 Right middle leg. (Fig. 159, II.) In this case there would 
 have been more difficulty in making out the real nature of the 
 parts ; for in the normal middle leg the anterior spur is not so 
 much differentiated from the posterior one as it is in the hind 
 leg : but having this case for comparison it is easy to see that 
 this also is a case of a pair of appendages similarly compounded 
 in Position A. This case differs from that of the hind leg in 
 the fact that the parts are not so fully formed, and especially 
 the anterior spur of the nearer extra tarsus is scarcely separated 
 from the anterior spur of the normal. By turning the specimen 
 over in the light however, its form can be made out to be that 
 shewn in the figure. When the specimen was received by me 
 the parts present were as shewn in the figure, but when originally 
 described by vox Heydex there was a third joint in the extra 
 appendage which was small and elongated, and to all appearance 
 it was the original termination and nothing had been broken off. 
 For the loan of this specimen I am indebted to Dr L. VON Heydex, 
 who originally described and figured it in Dent. ent. Zt., 1881, 
 xxv. p. 110, Jigs. 27 and 28. 
 
 In the two following cases there was nothing to differentiate 
 
chap. xx.J EXTRA LEGS: POSITION DA A. 491 
 
 the normal limb from the two supernumeraries, and the Position 
 may either have been P or A. 
 
 751. Foenius tarsatorius (Ichneumon): tibia of left posterior leg bears a pair of 
 supernumerary limbs. This is rather a remarkable case by reason of the k'reat 
 similarity in the modes of origin of the three limbs, whence it is difficult to 
 determine positively which is the normal one. The tibia divides into three parts 
 which lie in a horizontal plane and are separate from each other for about ^ of the 
 length of the tibia. Of these the anterior is a good deal more slender than the other 
 two which are similar and about of normal size. The middle of the three is shewn 
 by its spurs to be a right limb. Each bears a complete tarsus The ventral surface 
 of the most anterior tibia is horizontal while those of the other two are not quite so, 
 but converge downwards at a very obtuse angle. From this fact, and from the 
 equality in size between them, it seems probable that the two posterior limbs are 
 the supernumerary pair. The Position is therefore very nearly P or perhaps A. 
 This specimen was described by Mr Harrington in Can. Ent., 18U0, p. 124, 
 who was so kind as to lend it to me. 
 
 752. Agestrata dehaanii (Lamellicorn) : the coxa of the right anterior leg has two 
 articulations, one anterior and the other posterior. With the anterior there articulates 
 a single trochanter, bearing a normal right leg. The posterior articulation bears a 
 large structure which is composed of two trochanters united together. This double 
 trochanter bears two legs and is placed in such a way that the two do not lie in the 
 same horizontal plane ; but the posterior extra leg is in the same horizontal plane 
 as the normal leg while the anterior extra leg is wedged out towards the ventral 
 surface, between the normal leg and the posterior extra leg. The posterior extra 
 leg is a normally shaped right leg having its structurally anterior surface forwards 
 as normally. The anterior extra leg is fashioned as a left leg and the surface of it 
 which is structually anterior faces backwards towards the other extra leg. These 
 two are therefore a complementary pair, having their structurally anterior surfaces 
 adjacent: all three legs are normal and similar in form, size and colour. [Specimen 
 kindly lent by Mr E. W. Janson.] 
 
 (4) Positions DA A and DA. 
 
 *753. Cerambyx scopolii (Longicorn.) : pair of extra legs arising 
 from the coxa of the right anterior leg. As this is a remarkably 
 simple and perfect case it will be well to describe it in some 
 detail, as it will serve to illustrate the arrangement of such cases 
 in general. 
 
 A normal leg of such a beetle as Cera/mhyx consists of coxa, tro- 
 chanter, femur, tibia and four tarsal joints. To a proper understanding 
 of the mode of occurrence of the extra legs in this case it is essential 
 that the forms of these parts and their mode of movement with regard 
 to the body and to each other should be accurately known. 
 
 Of the large, irregularly pear-shaped coxa only the hemispherical face 
 is seen from the exterior. It is chiefly enclosed by embracing out- 
 growths from the sternum, forming a socket in which it can be rotated 
 like a ball. Upon its broad, exposed surface it is itself hollowed out 
 to form a socket for the ball of the trochanter. For our purposes it is 
 necessary to find some means of distinguishing the anterior face of the 
 coxa from the posterior face. The structure which at once enables us 
 to do this is the process (Fig. 160, p), which goes down from the coxa 
 to embrace the neck of the ball of trochanter and lock it into its socket. 
 Now in the case of an anterior leg, this process is posterior to the 
 trochanter (but in a middle or hind leg it is anterior to the trochanter). 
 The next point to be considered is the position of the femur. The 
 
492 
 
 MERJSTIC VARIATION. 
 
 [part I. 
 
 femur itself is flattened antero-posteriorly, having two broad surfaces, 
 morphologically anterior and posterior, and two narrow surfaces which 
 are extensor and flexor surfaces, or morphologically dorsal and ventral. 
 By rotation of the coxa the whole leg may assume a great variety 
 of positions, and it is thus of the utmost consequence that the nature of 
 the surfaces be truly recognized. If the front leg be placed with the 
 
 III 
 
 SL< m 
 
 Fig. 160. Cerambyx scopolii. No. 753. I. The whole beetle seen from ventral 
 surface. II. Details of right anterior coxa bearing extra trochanters and legs. 
 In this figure the legs are rotated so as to shew that SB is an image of SL. 
 III. The same, placed so as to shew that SL is an image of R. 
 
 p, process of coxa locking in the trochanter, srp, sip, corresponding processes 
 for the extra trochanters. (From a specimen belonging to M. H. Gadeau de 
 Kerville.) 
 
chap, xx.] EXTRA LEGS : POSITION DA A. 4.93 
 
 femur at right angles to the body it may either be placed so that the 
 ventral surface is downwards, or by rotation of the coxa through 90 J 
 the broad posterior surface may be downwards. The rotations of the 
 middle and hind legs are complementary to this. 
 
 In the abnormal specimen the extra pair of legs arise from 
 the anterior side of the normal coxa, forming with it a solid mass 
 and preventing its free rotation in its socket, so that the normal 
 leg can scarcely be moved from the first position with the 
 ventral surface downwards. The common coxal piece is about 
 half as large again as the normal. Posteriorly it bears the tro- 
 chanter of the normal leg, which is of full size and of proper pro- 
 portions. The process of the coxa locking in the ball of the 
 trochanter is posterior, as in the normal front leg. 
 
 Anteriorly the legs SL and SR articulate with the coxa by 
 separate trochanters. Each is separately closed in by a process 
 of the coxa, sip and srp, respectively. Of these processes that 
 of the leg SR is posterior, but that of SL is anterior. Hence 
 the two legs are complementary to each other, and SR is a right 
 leg while SL is a left. This complementary relation is main- 
 tained in all the other parts of these legs. In size the two extra 
 legs are rather more slender than the normal leg. 
 
 It was explained in the introduction to the subject of super- 
 numerary legs that the relations of form between them depend 
 upon the surface of the normal leg from which they arise. Here 
 the point of origin is chiefly anterior to the normal leg, but is 
 also slightly nearer to the extensor or dorsal surface of the coxa. 
 This is not at first sight evident owing to the rotation of the 
 normal leg due to the great outgrowth from its anterior surface ; 
 but nevertheless if the plane of the ventral surface of the normal 
 femur were produced, it would pass ventrally to the ventral 
 surface of the remoter extra leg SR, and therefore this leg is 
 morphologically dorsal to the leg R. The positions of the extra 
 legs are approximately those of the Scheme for the radius marked 
 DAA, and while the surfaces of SR are parallel to those of R 
 when both are extended, the surfaces of SL are inclined slightly 
 to them as in position DAA. In the enlarged Figure III the 
 coxa is rolled forwards so as to exhibit the relation of images 
 between R and SL, and the figure II shews the coxa rolled 
 back to shew the similar relation between SR and SL. 
 
 For the loan of this beautiful specimen I am great!}* obliged to 
 M. Henri Gadeau de Kerville. 
 
 754. Harpalus rubripes (Carabidte) : left posterior tibia bears a supernumerary pair 
 of tarsi. The apex of the tibia is widened and presents two articulations, of which 
 the posterior bears a normal tarsus. The anterior articulation bears a pair of complete 
 tarsi having proximal joints compounded. The two extra tarsi are a complementary 
 pair, the posterior being fashioned as a right. The surfaces adjacent in these two 
 tarsi are structurally posterior surfaces, but they are a little supinated, so that the 
 ventral surfaces are also partly turned towards each other. The position of origin 
 and the relations of the surfaces to each other are almost exactly those which are 
 
494 MERISTIC VARIATION. [part I. 
 
 indicated in the Scheme for the position DAA. This specimen was described by M. 
 A. Fauvel (Rev. (VKtit., 188 ( J, p. 331) and was kindly lent by him for further 
 examination. 
 755. Chrysomela banksii iPhytophagi) : right hind tibia bearing an extra pair of 
 tai-si. The border of the tibia which corresponds in position to the ventral or flexor 
 border of the normal tibia is covered with the hairs which characterize it in the 
 normal limb; but the ojjposite border of this abnormal tibia is similarly covered 
 with hairs, shewing that the anterior parts of at least two tibiae are included in it. 
 A rigid process projects from the wide apex of the tibia. Upon the inner side of 
 this process is the articulation for the tarsus, which from its direction and position 
 appears to be the normal tarsus of the limb. Outside the process articulates a 
 slightly smaller tarsus, which from its form and from the plane in which it moves 
 is a left tarsus, flexing away from the normal one. At a point slightly external to 
 this is the third tarsus, which is again a right tarsus and moves in a plane comple- 
 mentary to the middle one. The two are therefore a pair. The position of origin 
 lb anterior and dorsal, being nearly that marked DA, but the relative positions of 
 the extra tarsi are approximately DDA. As to the nature of the tibial process I can 
 make no conjecture. (Fig. 161.) 
 
 Fig. 161. Chrysomela banksii, No. 755. View of right hind tibia from posterior 
 surface. A normal right hind tibia is shewn for comparison. (From Pruc. Zuol. 
 Soc, specimen the property of Dr D. Sharp.) 
 
 This specimen is the property of Dr Sharp, who was good enough to lend it to 
 me. It was briefly described and figured by me P. Z. S. , 1890, p. 583, but 1 was not 
 at that time aware of the complementary relation existing in these cases and failed 
 to notice the somewhat inconspicuous differences which are evidence of it in this 
 case. 
 756. Hylotrupes bajulus (Longic): right middle tibia bears a suj^ernumerary 
 pair of limbs having proximal parts in common. From the antero-dorsal surface of 
 the base of the normal tibia, there arises a slender tibial piece which is not so long 
 as the normal tibia and bears no spurs. At the apex of this supernumerary tibia, 
 which is doubtless a double structure, articulate a pair of tarsi having their 
 first and second joints compounded together. After the second joint the tw r o tarsi 
 separate from each other and each bears a pair of claws. The relative position of 
 the two tarsi when they separate from each other is almost exactly that marked DA. 
 It should be mentioned that the supernumerary parts central to the 3rd tarsal joints 
 are not fully formed, being deficient in thickness, and the transverse separation 
 between the 1st and 2nd tarsal joints is incomplete. Specimen first described by 
 Mocquerys, Col. anorm., 1880, p. 53, fig. I am indebted to Dr L. vox Heydex 
 for an opportunity of examining it. 
 
 (5) Position D. 
 
 *757. Aphodius contaminatus <£ (Lamellicorn.) : left middle tibia 
 bearing two supernumerary tarsi which stand very nearly in the 
 position DDP, being rather nearer to D. The relative positions 
 are shewn in Fig. 162. The articular surface at the apex of the 
 tibia is extended along an elongated process which projects on 
 the dorsal side of the tibia. Upon this extension of the apex 
 articulate two extra tarsi. They stand with their ventral or 
 
CHAP. 
 
 XX.] 
 
 EXTRA LEGS : POSITION D. 
 
 495 
 
 758. 
 
 LT. 
 
 plantar surfaces facing each other, and the tarsus RT is placed so 
 that its dorsal surface is 
 very nearly opposed to the 
 dorsal surface of the normal 
 tarsus LT, and the three 
 tarsi thus flex almost in the 
 same vertical plane. It is 
 to be observed, however, 
 that the tarsus LT is not 
 actually in the same plane 
 as the other two, but is a 
 little deflected from it so as 
 to flex rather more towards 
 the posterior surface of the 
 line than it would do if it 
 stood actually as L'T stands. 
 This may be made clear by 
 reference to the Scheme 
 (p. 481) : for while the two 
 extra tarsi are placed re- 
 latively to each other as if 
 they were in the position 
 D, the position of RT to 
 LT is that which it would 
 have if it stood in DDP. 
 
 In this species the mid- 
 dle tibia in the male bears 
 one large spur, namely, the 
 posterior one, while the an- 
 terior spur is rudimentary. 
 PS in the figure represents Fm 162 AphoMug containinatuSf No . 757> 
 
 the large posterior spur of left middle tibia bearing extra parts. LT, 
 
 EPS & LPS. 
 
 singh 
 of suture 
 b is seen 
 (Specimen the 
 
 iding posteriorly i u± ana jlt correspo 
 and between the two extra s P ur Fs of normal, x, x, line 
 
 tarsi represents their two between these two spurs The limb is 
 
 . i ill from the posterior surface - 
 
 posterior spurs. 1 he double property of Dr Kraatz.) 
 
 nature of this spur is seen 
 
 when it is examined from the anterior side, for upon that surface 
 
 it is marked by a longitudinal ridge-like suture. This specimen 
 
 was first described by Kraatz, JJeut. ent. Zt, 1876, xx. p. 378, 
 
 fig. 13, and I am indebted to Dr Kraatz for an opportunity of 
 
 examining it. 
 
 Galerita africana (Carab.) : (Fig. 163) right middle leg normal as far as the last 
 tarsal joint, which bears three additional claws arising dorsally to the normal pair. 
 The extra claws are three in number, two of them being small and standing at the 
 anterior border of the limb, while at the posterior border there is one claw of larger 
 size. This larger claw is really a double structure, which is clearly shewn by the 
 
496 MERISTIC VARIATION. [part i. 
 
 presence of two channels on its concave surface. Position of origin is therefore D, 
 while the inclination of the extra pairs of claws to each other is about that required 
 
 A. 
 
 Fig. 163. Galerita africana, No. 758. Apex of right middle tarsus. A, 
 anterior. P, posterior. V, ventral. (Specimen in Rouen Mus.) 
 
 for the position DDA ; for the planes of the two pairs are not parallel but incline 
 to each other at an acute angle. Specimen originally described by Mocquerys, Col. 
 unarm. , p. 64, fig. 
 
 (6) Position DP. 
 
 759. Pyrodes speciosus (Longic.) ; having two supernumerary legs 
 articulating with the thorax by a common coxal joint, which is 
 distinct from the coxa of the left middle leg, but is enclosed in 
 the same socket with it. In this remarkable case the normal 
 leg is complete, though slightly pushed towards the middle line. 
 The socket in the mesothorax is enlarged posteriorly and dorsally 
 so as to form an elongated, elliptical articulation, which lies ob- 
 liquely, so that its ventral end is anterior to its dorsal end. The 
 anterior and ventral end is occupied by the coxa of the normal 
 leg, while the coxal joint of the two extra legs fills the space 
 dorsal and external to it. Both are capable of being moved 
 independently in the relaxed insect. The extra legs articulate 
 with their coxa by a common double trochanter which has two 
 apices, from which point the legs are distinct. Their position 
 is dorsal and posterior to the normal leg, being practically that 
 marked DP in the Scheme, and the relative positions of the 
 extra legs are very nearly those indicated for the Position DP. 
 The leg nearest the normal leg is of course a right leg in structure, 
 and its plantar and a little of its structurally anterior surfaces 
 are turned posteriorly. On the other hand, the remoter leg is 
 a true left leg and the ventral surface of its femur is placed 
 almost exactly horizontally. All three legs are complete, but 
 they are a little shorter and more slender than the middle leg 
 of the other side. 
 
 This specimen is in the Hope Collection at Oxford. 
 
CHAP. XX.] 
 
 EXTRA legs: position dp. 
 
 497 
 
 * 
 
 7 gO. Carabus irregularis J ; left middle leg and right hind leg bear- 
 ing supernumerary tarsal portions. In the left middle leg, Fig. 164, I, 
 the 2nd tarsal joint is short and thick ; the 3rd joint is partially double, 
 as shewn in the figure. One of its apices bears a tarsus of reduced 
 size, and the other apex, which is postero-dorsal, bears a double tarsus 
 having common 4th and 5th joints. The 5th joint of the latter bears 
 two pairs of claws which curve ventrally and partly towards each 
 other. The figure I shews the appearance from the ventral or concave 
 side of the claws, while the figure II is drawn from the convex or 
 dorsal side. The disposition and small number of the spines on the 
 ventral side of the extra 5th joint shew that the ventral surfaces are 
 partly suppressed, and in fact that the surfaces which are adjacent in 
 the extra tarsi are in part ventral surfaces. This view is also borne 
 out by the direction and curvature of the claws. Eelatively to each 
 other and to the normal the extra parts have nearly the Position DP. 
 
 7-° 
 
 III 
 
 Fig. 164. Carabus irregularis. I. Semi-diagrammatic view of left middle leg 
 from antero-ventral surface. I 1 , the claws of normal left tarsus, r, I 2 , claws of extra 
 tarsi compounded together. lh l , hair marking the dorsal surface between the claws. 
 A, anterior. P, posterior. II. Dorsal view of apex of extra tarsus rh, Ur, two hairs 
 marking dorsal surfaces. III. Dorsal view of right hind leg. c'c', c"c", claw-like 
 spines, perhaps representing extra claws. (Specimen the property of Dr Kraatz.) 
 
 The right hind tarsus has the form shewn in Fig. 164, III. The 3rd, 
 4th and 5th joints are not fully separated from each other. Both the 
 4th and 5th joints bear extra parts, but their nature is obscure. The 
 5th joint is partly double, and the anterior part bears two shapeless 
 claw-like spines (c'c). The 4th joint bears a similar pair of claw-like 
 
 b. 32 
 
498 MEBTSTIC VARIATION. [part i. 
 
 structures of smaller size (c"c"). Probably these should be considered 
 as rudiments of extra tarsi ; but if this view is correct, it appears that 
 two extra tarsi are present, arising from different joints. For the loan 
 of this specimen I am indebted to Dr G. Kraatz, who first described 
 and figured it in Deut. ent. Z&, 1877, XXI. pp. 57 and 63, tig. 27. 
 
 •rgj Chrysomela graminis (Phy tophagi) : the femur of the right middle leg bears a 
 
 supernumerary pair of legs attached to the posterior and dorsal side of its apex. 
 At this point' there is an articulation with which the single proximal part of the 
 extra pair of tilme articulates. This- piece, which is common to the two super- 
 numerary tibia?, is a sub-globular, amorphous mass from which the two tibia? 
 diverge. " Each of the two tibia? bears a complete tarsus, except that the most 
 posterior has only one claw. In colour the two supernumerary tarsi differ from the 
 normal, being brown instead of metallic green, but the tibia? are normal in colour. 
 From the shape of the articulations and the arrangement of the pubescence, it is 
 clear that the surfaces of the legs which are naturally adjacent are constructed as 
 posterior surfaces, and the forms of the two are complementary to each other, the 
 hindmost of the extra legs being formed as a left leg, while the foremost is a right 
 leg. As the}' stand, however, the two tibia? are not in the same position relatively to 
 the body, for the foremost is placed normally, having its plantar surface turned 
 downwards, but the hindmost is rotated so that its plantar surface is partially 
 turned forwards. The relative positions are nearly those marked DP in the Scheme, 
 but the most posterior tarsus is more rotated than it should be according to that 
 diagram. This condition may be to some degree connected with the presence of the 
 amorphous growth at the base of the extra tibia?. This specimen was kindly lent 
 for description by Dr Mason. 
 
 762. Fimelia interstitialis (Tenebrion.) : left posterior femur bears two super- 
 numerary tibia? arising from the postero-dorsal surface of its apex. These two are 
 a pair, for the tibia nearest to the normal tibia is a right tibia, the remoter being a 
 left. The adjacent surfaces are chiefly anterior surfaces in structure, but the 
 ventral surfaces are inclined to each other at an obtuse angle. The position of the 
 extra legs is almost that marked DP in the Scheme, but the inclination of the 
 ventral surfaces of the extra legs is rather more acute than it would be in the 
 Position DP. The tarsi are all broken off. Specimen originally described by 
 Mocqvekys, Col. anorm., p. 44, fig. 
 
 7Q3 Acinopus lepelletieri (Carab.): two extra legs arising from posterior surface 
 
 of base of femur of /. middle leg. From position it seems that the most anterior is 
 the normal, but this is doubtful. The arrangement is nearly that of Position DP, 
 but as one of the femora is constricted and bent, the relations are rather irregular. 
 Specimen first described by Mocquerys, Col. anorm., p. 41, Jig. 
 
 (7) Position P. 
 
 *764. Silis ruficollis^ (Malacoderm) : right anterior femur bearing 
 a supernumerary limb (Fig. 165). The coxa and trochanter normal. 
 The femur is of about twice the antero-posterior thickness of a 
 normal femur and at its apex presents two articulations in the 
 same horizontal plane. Of these the anterior bears a normal 
 tibia and tarsus, but the posterior bears an extra tibia which 
 appears at first sight to be a single structure. This tibia is more 
 slender than the normal one and is provided with four tarsal 
 joints, the terminal one being withered and without claws. Upon 
 closer examination it is found that this extra tibia is in reality 
 made of the posterior surf aces of a paii; of tibice not separated from 
 each other. In this case the morphological duplicity of the extra 
 tibia is capable of proof. For, as shewn in Fig. 165, II, the 
 normal tibia is not bilaterally symmetrical about its middle line. 
 On the contrary the anterior surface is differentiated from the 
 
CHAP. XX.] 
 
 EXTRA LEGS : POSITION P. 
 
 499 
 
 posterior by several points. This may be seen in the spurs at 
 the apex of the tibia, for the anterior spur (a) is long, but the 
 
 a- 
 
 II 
 
 II 
 
 III 
 
 Fig. 165. Silts ruficollis, No. 764. I. The right anterior leg seen from ventral 
 surface, a, anterior, p, posterior. This figure was drawn with the microscope 
 and is reversed. II. Detail of apex of tibia of the anterior or normal tibia, 
 shewing a, the anterior, and p, the posterior sjjurs. III. Similar detail of apex of 
 the tibia of the extra limb, shewing p' and p", two structurally posterior spurs. 
 
 posterior (p) is short (as is usual in the front leg of many beetles). 
 The hairs on the surface of the tibia are also directed asymmetri- 
 cally and the parting or division between them is not median, 
 but is nearer to the anterior border (see figure). 
 
 But in the extra part there is no such differentiation, and botli 
 surfaces are structurally posterior surfaces. The hairs part in the 
 middle, and both spurs (p, p") are formed as posterior spurs. This 
 extra structure is therefore made up of the two posterior borders 
 of a right and a left tibia compounded together in Position P. 
 (See diagram, Fig. 165, II.) 
 
 This specimen was found by Dr Sharp amongst a number 
 of insects collected by myself in his company at Wicken Fen on 
 Sunday 1 , July 26, 1891. 
 
 Such a case taken in connexion with others {e.g. Xo. 801 ) 
 makes it certain that many cases of supposed " single ' : extra 
 appendages are really examples of double extra parts. 
 
 1 A day or two before, the manuscript of this part of the subject had been put 
 by with the remark that no good opportunity of thoroughly investigating a case 
 of " single" extra leg had occurred, but that it could scarcely lie doubted that traces 
 of duplicity would be found in them. Considering the great rarity of extra ap- 
 pendages in Insects, and remembering that even of the whole number very few are of 
 the supposed " single " order, I have thought the occurrence of this capture a 
 coincidence of sufficient interest to be worthy of mention. Dr Sharp tells me thai 
 amongst all the beetles that have gone through his hands only one case of extra 
 appendage (No. 755) was seen. 
 
 32—2 
 
500 MERISTIC VARIATION. [part I. 
 
 765. Scarites pyracmon (Carab.). At base of posterior face of the 
 trochanter of left normal front leg, immediately above the cotyloid 
 articulation was implanted an elongated lanciform joint. This joint 
 was directed backwards and represented a pair of trochanters com- 
 pounded by their anterior surfaces. With each of the two apices of 
 this double trochanter was articulated a complete leg, in all respects 
 formed as an anterior leg. The two moved as a complementary pair. 
 [Details given. This is one of the earliest and best described cases. 
 AsMUSS 1 in quoting it points out that the description and figure plainly 
 shew that the two extra legs were a pair, a right and a left, respect- 
 ively. They were in fact a pair, arising from the posterior surfaces of 
 the normal leg, and presenting their anterior surfaces to each other.] 
 Lefebvkk, A., Gu&rin's Mag. de ZooJ., 1831, Tab. 40. 
 
 766. Geotrupes mutator (Lainellicorn) : two supernumerary limbs arising from 
 femur of right anterior leg. Femur greatly widened, upon posterior border giving 
 off a large prominence which divides into two processes at right angles to each 
 other. Each of these processes bears a normal tibia and tarsus, but the foremost of 
 these tibiae is shaped as a left tibia, having its serrated border placed anteriorly, 
 while the other extra tibia is formed as a right tibia, having its serrated border 
 placed 'posteriorly. [The pair of limbs arise from the posterior surface of the normal 
 limb and have their anterior surfaces adjaceut, as in Position P.] FRiVALDsm:, J., 
 Term. Fuzetek., 1886, x. p. 79, PI. 
 
 76/. Pterostichus lucublandus ? (Carabidre): third tarsal joint of left middle leg 
 at apex presents wide articular surface. On this stands a triple 4th joint, made up 
 of a single anterior portion, bearing the rest of the normal tarsus and a posterior 
 portion, double in structure, the two parts being completely united. The single 
 anterior part of this 4th joint bears a normal 5th joint with claws. The double 
 posterior part of the 4th joint bears a pair of separate 5th joints, each having a pair 
 of claws. Of these the anterior is perfect, but the peripheral part of the posterior 
 5th joint is crumpled, so that its claws are twisted out of position, but at its base it 
 stands exactly as the normal 5th joint, and as the 5th joint of the anterior extra 
 tarsus, all three being in the same horizontal plane. These extra parts, therefore, 
 are in the Position marked P in the Scheme and have the relations there indicated 
 for that position. This specimen was kindly lent to me by Mr Harrington, who 
 first described it Can. Ent., 1890, xxn. p. 124. 
 
 (8) Positions VPP to VVP. 
 
 *768. Ceroglossus valdiviae, Chili (Carabidse): left anterior tibia 
 bearing a pair of supernumerary legs. The tibia widens, and in 
 its middle part gives off posteriorly and ventrally a wide branch 
 having the form of a pair of tibial apices compounded together. 
 The double tibia bears two tarsi (Fig. 166, B! , L') having a common 
 proximal joint, but these have unfortunately been broken, two 
 joints being missing from the one and three from the other. The 
 legs are a right and left as usual, and they stand in the relative 
 positions marked VPP in the Scheme. This is a very simple 
 and striking case, for the animal is of good size and the parts 
 are well formed. The two tibial spurs which are adjacent in 
 the two extra tibiae are compounded so as to form a double spur 
 with two points as shewn in the figure. As shewn for the Position 
 
 1 Monstrositates Goleopterorum, 1835, p. 44, PI. 
 
chap, xx.] EXTRA LEGS : POSITION VPP. 501 
 
 VPP in the Scheme, the compounded parts of the extra ap- 
 pendages, viz., the double tibia and the double first tarsal joint 
 have two complete ventral surfaces inclined to each other at an 
 obtuse angle, while there are only two halves of dorsal surfaces. 
 
 Fig. 166. Ceroglossw valdivia, No. 768. Left 
 anterior tibia with extra parts seen from the 
 ventral surface. L, the normal left tarsus. R' and 
 L', the extra tarsi, compounded in their proximal 
 joint. A, anterior. P, posterior. 
 
 Xote that the anterior spur of the normal is 
 curved and that the double spur representing the two 
 anterior spurs of the extra tibial apices has thus a 
 bifid point. (Specimen the property of Mr E. W. 
 Janson.) 
 
 Similarly there are two structurally posterior surfaces, but no 
 structurally anterior surfaces, for these are adjacent and un- 
 developed. This specimen was kindly lent by Mr E. \V. Janson. 
 
 769. Silpha nigrita (Heteromera): from right middle femur arises a 
 
 pair of legs which are completely united as far as the apex of the last 
 tarsal joint. The point of origin of the supernumerary limbs is on the 
 anterior and ventral border of the femur. The form of the extra limbs 
 is shewn in Fig. 167. The surfaces V and V are structurally ventral 
 surfaces. They are turned chiefly forwards, but are inclined to each 
 other at an acute angle. The surfaces, therefore, which arc adjacent 
 in this pair of legs, and which are consequently obliterated, arc chiefly 
 the morphologically anterior surfaces and to some extent the dorsal 
 surfaces. The plantar or ventral surfaces of the last tarsal joints are 
 inclined to each other rather more obtusely than those of the tibiae, 80 
 that the curvatures of the two pairs of claws are very nearly turned 
 forwards as well as away from each other. This is not fully brought 
 out in the figure. The position of origin is about VP, but the claws are 
 in Position VPP. Specimen first described and figured by MoCQUERYS, 
 Col. anorm., p. 43, fig. 
 
502 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Fig. 167. Silpha nigrita, No. 769. Right middle femur bearing a compounded 
 pair of extra legs. V, ventral surface of nearer extra leg. V, ventral surface of 
 the remoter extra leg. (In Rouen Mus.) 
 
 770. Tenthredo solitaria (Sawfly): tibia of right middle leg divides 
 in peripheral third to form two branches, of which the anterior bears 
 the normal tarsus. The posterior branch arises from the postero-ven- 
 tral surface of the normal and bears a double tarsus consisting of the 
 posterior parts of a pair compounded in Position VP, almost exactly. 
 Tibial spurs as in Fig. 166. The compound tarsus has only 4 joints, the 
 5th being apparently broken off. In Cambridge Univ. Mus., history 
 unknown. 
 
 771. Telephorus rusticus (Malacoderm) : tibia of left middle leg dilated 
 and somewhat deformed in its peripheral portion. It presents two 
 apical processes, the one anterior and the other posterior. The anterior 
 of these bears a normal, backwardly directed tarsus, but the posterior 
 process bears two tarsi by separate articulations. The anterior of these 
 two tarsi is directed forwards to face the tarsus of the other apex, but 
 the posterior tarsus is backwardly directed. [From its attitude it is 
 clear that the middle of these tarsi is a structure complementary to one 
 of the others, but there is no evidence to shew whether it is a pair to 
 the anterior or to the posterior. Position either VPP, or DAA, pro- 
 bably the former.] Kraatz, Deut. ent. Zt., 1880, p. 344, fig. 33. 
 
 772. Anthia sp. (Carabidae) : left posterior tibia bearing two supernumerary tarsi. 
 The postero-ventral side of the apex of the tibia is dilated so as to form a triangular 
 projection, causing the point of articulation of the normal tarsus to be raised 
 upwards. The projection bears two tarsi of which the posterior curves downwards 
 and backwards, being fashioned as a left tarsus while the anterior curves forwards 
 and slightly upwards being a right tarsus. These two tarsi have unfortunately been 
 broken but were presumably complete. The whole apex of the tibia bears five spurs 
 instead of two, but the relation of the spurs to the separate tarsi was not clear. The 
 
chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 503 
 
 tarsi are very nearly in the Position VPP. Specimen very kindly lent by Mr E. W. 
 Janson. 
 773. Julodis aequinoctialis (Buprestida?) : the extra legs arise from the posterior and 
 ventral side of the base of the tibia of left middle leg. They are a pair, and are 
 compounded together by their lateral and dorsal surfaces in such a way that the 
 morphologically ventral surfaces of the two are almost in contact along the anterior 
 border of the compound limb. The ventral surfaces here converge at an acute 
 angle. The two extra legs are compounded together throughout the tibiae and first 
 4 tarsal joints. The 5th tarsal joints are free, but only one of them remains. The 
 former presence of the other is only shewn by a socket. The normal tibia is con- 
 stricted and bent at one point so that it does not stand in its normal position. The 
 femoro-tibial articulation is rigid. 
 
 This is a case of a pair of legs compounded as in the position marked VVP in 
 the Scheme but the point of origin is more nearly that of VPP. Specimen originally 
 described by Mocquerys, Col. anorm., p. 47 Jig. 
 
 774 Metrius contractus (Carab.) Esch.: specimen in which the middle left femur 
 ' bears an incomplete pair of legs in addition to the normal one. The femur is of 
 
 normal length. The tibia of the normal leg is articulated with the end of the femur 
 as usual, but is somewhat shorter, stouter and more curved than the tibia of the 
 corresponding leg of the other side. A supernumerary tibia arises from the posterior 
 [and ventral ?] side of the femur a short distance within the apex, and is articulated 
 with it by a separate cotyloid cavity ; the two articular cavities for the two tibia? 
 are confluent, being connected by a groove. The end of this tibia is dilated at its 
 outer end, and bears two articular surfaces, one on each side ; with each of these 
 surfaces, a complete tarsus is articulated, nearly normal in form but somewhat 
 stouter than a normal tarsus. There are four terminal spurs to this tibia, two being 
 below the outer tarsus and two being below the inner tarsus. [It therefore seems 
 that this tibia is made up of parts corresponding with the ventral side of a right 
 tibia and the ventral side of a left tibia, and it is hence probable that if the dis- 
 position of the claws of the tarsi had been examined, it would have been found that 
 they too were a pair, one being a right foot and the other a left. Position probably 
 VVP.] Jayne, H. V., Trans. Amer. Ent. Soc, 1880, vin. p. 156, PL iv. figs. 3 
 and 3 a . 
 
 775 Aromia moschata ? (Longicorn) : right anterior coxa bearing a pair of super- 
 numerary legs having trochanter and the proximal half of the femur in common. 
 The normal leg and the extra ones were all somewhat reduced in size but were 
 complete. The extra leg adjacent to the normal is a left leg. [From the figure it 
 appears that the legs arose in the Position P, or VPP, and their relative positions 
 seem to have been those indicated in the Scheme. Of course it is not possible to 
 state this definitely without examination, but it is clear that there was at least no 
 great departure from the position shewn in the Scheme.] It is remarked that in 
 this specimen the right mandible was abnormally small. Kolbe, H. J., Naturw. 
 Wochens., 1889, iv. p. 169, Jigs. 
 
 (9) Two cases not conforming to the Scheme. 
 
 Two cases of double supernumerary tarsi require separate con- 
 sideration. The arrangement in both of these cases departs from 
 chat which is usually followed, but it will be seen that there is 
 considerable though imperfect agreement between the two ex- 
 ceptions. Both of these occur in the anterior legs of males of 
 the genus Galathus, and it happens that in the normal form the 
 apex of the tibia presents a considerable modification from the 
 simple structure of other beetles. This modification affects the 
 anterior legs only, and is found in several genera of Carabidae, 
 being especially pronounced in Calathus. 
 
504 MERISTIC VARIATION. [part i. 
 
 In order to appreciate the nature of these cases it is necessary 
 that the anatomy of the parts should be understood. 
 
 The apex of the tibia in the simple form, e.g. the second or 
 third leg in Carabus, bears two large articulated spurs. The two 
 spurs are ventral to the articulation of the tarsus, and one of 
 them is placed at the anterior border of the tibial apex while 
 the other is posterior. In these unmodified legs both spurs are 
 placed at the same level in the limb, so that the bases of both 
 are in the same transverse section (cp. Fig. 166). In the forms 
 presenting the sexual modification, the anterior spur is of some- 
 what small size but occupies the same position relatively to the 
 other parts that it does in a simple leg. 
 
 The posterior spur however, which is large, does not stand 
 at the same level on the tibial apex, but has, as it were, travelled 
 up the tibia so that it stands at a considerable distance central 
 to the apex, and instead of marking the posterior border of the 
 limb it is placed nearly in the middle of the actual ventral surface. 
 A long channel runs from the posterior spur to the anterior one, 
 and the appearances suggest that the modified form is reached 
 by a deformation of the original apical surface, which is twisted 
 so that the posterior spur is thus drawn up into the secondary 
 position. In the fore leg of a male Carabus the beginning of 
 such a change can be seen, but in Pterostichus and especially in 
 Calathus it reaches a maximum. The change may be briefly 
 described by saying that a section to include the two spurs must 
 be taken in a plane which is oblique to the long axis of the limb 
 instead of transverse to it. 
 
 As a result of this modification the morphological surfaces 
 of the anterior tarsus of Calathus &c. have a peculiar disposition 
 relatively to the same surfaces of the tibia when compared with 
 other forms. Commonly the ventral surface of the tarsus is 
 parallel to a line taken through the bases of the spurs, but owing 
 to the rotation of the posterior spur into its secondary position 
 this plane is here oblique to the ventral surface of the tarsus. 
 These points will be at once evident if the front leg of a male 
 Calathus is examined. 
 
 It was laid down as a principle generally followed in cases of 
 double extra appendages, that the three terminations, when ex- 
 tended, stand in the same plane, and the chief feature which 
 distinguishes the two following cases is that the three termina- 
 tions are not in one plane. 
 
 Moreover, though the two supernumerary tarsi are a com- 
 plementary pair, and together with the normal tarsus are arranged 
 as a series of images, yet in order to produce the arrangement of 
 the present cases the planes of reflexion would not be parallel to 
 each other (as in Fig. 154) but inclined in the manner to be 
 described. 
 
CHAP. XX.] 
 
 EXTRA LEGS : CALATHUS. 
 
 505 
 
 g a 
 
 *77G. Calathus graecus g (Carabiclre) : left anterior tibia bearin 
 
 pair of supernumerary tarsi compounded together. The diagram, 
 Fig. 169, I, shews, in projection, the relations of the parts round the 
 tibial apex. As lias been explained, the posterior spurs P 1 , P 2 and P 3 
 are really much central to the apex, but they are here represented as it* 
 they were projected upon the apex. The head of the tibia is produced 
 posteriorly into a long and narrow process which is formed of the united 
 parts of the two extra limbs and bears the articulation common to the 
 two extra tarsi. The two tarsi stand with their ventral surfaces almost 
 at right angles to each other, but the united dorsal surfaces are almost 
 in a continuous plane. The fifth joints alone are separate, that of RT 
 being small (Fig. 168). 
 
 RT, 
 
 Fig. 168. Calathus gracus, No. 776. Left anterior tibia bearing a double extra 
 tarsus. L2\ normal tarsus. RT, L'T, extra pair of tarsi. LAS, LPS, normal 
 anterior and posterior spurs. L'A'S', L'P'S', anterior and posterior spurs belonging 
 to L'T. RAS, RPS, anterior and posterior spurs belonging to RT. x, .v, dotted 
 line indicating plane of morphological division between extra tarsi, .r.v, .vx, plane 
 of division between the normal and RT. (Specimen the property of Dr Kraatz.) 
 
 In studying this case one source of confusion should be specially 
 referred to. It is seen that though the origin of the extra tarsi is 
 posterior to the normal tarsus, the extra tarsi are as a fact united along 
 their morphologically posterior borders. Nevertheless the position of the 
 spurs shews that it is the anterior surfaces which are morphologically 
 adjacent to each other, for the spurs are arranged in the series A'P', 
 PA 2 , A 3 P 3 , and the union of the posterior borders of the tarsi is a 
 result of the modification in the form of the tibia consequent on the 
 rotation of the posterior spur. 
 
 To produce the arrangement here seen, the planes of reflexion would 
 be M 1 and M 2 respectively, and these are almost at right angles to each 
 
506 
 
 MEBJSTIC VARIATION. 
 
 [part t. 
 
 other. The present case therefore is very different from those hither- 
 to described, for in them the planes of reflexion were nearly or quite 
 parallel. Whether this difference in the Symmetry of the extra parts 
 may be connected with the departure of the normal tibia from its own 
 customary symmetry cannot be affirmed, but such a possibility should 
 be borne in mind. 
 
 This specimen was kindly lent to me by Dr G. Kraatz, who first 
 described it in Deut. ent. Zt., 1877, xxi. p. 62, fig. 23. 
 
 Dorsal 
 
 t 3 Posterior 
 
 A/2 I 
 
 II 
 
 Posterior 
 
 Anterior 
 
 
 Fig. 169. I. Ground-plan of tibial apex of Calathus grams, No. 776. 
 II. Similar ground-plan of the tibial apex of Calathus cisteloides, No. 777. 
 
 In each case the spurs are conceived as projected upon one plane, t 1 , the 
 normal tarsus. A 1 , P 1 , its anterior and posterior spurs, t 2 , A 2 , P 2 , similar parts 
 of nearer extra tarsus, t 3 , A 9 , P s , similar parts of remoter extra tarsus. M 1 , 
 plane of reflexion between t 1 and t 2 . M 2 , plane of reflexion between i 2 and t 3 . 
 
 Calathus cisteloides ^ (Carabidae): right anterior tibia bearing 
 a pair of supernumerary tarsi compounded together. In this case the 
 extra parts were anterior to the normal tarsus. The parts were 
 arranged as in the diagram, Fig. 169, II, which is a projection of the 
 tibial apex. The apex is produced anteriorly so as to form a wide 
 expansion which bears the common articulation for the double tarsus. 
 This produced portion is of course formed by the composition of parts 
 of a pair of tibiae. It is noticeable that the three tibial apices which 
 enter into the formation of the general apex are in one respect not 
 actually images of each other. For the angular distances between A 1 
 and P 1 , and between A 2 and P 2 , are exceedingly small, being far less than 
 in a normal tibia of the species, and in fact the grooves running from 
 each anterior spur to the corresponding posterior one are almost paral- 
 
chap, xx.] EXTRA LEGS I UNCONFORMABLE CASES. 507 
 
 lei to each other and to the long axis of the tibia. The tarsi f and f' 
 separate in the first joint. 
 
 The relative positions are shewn in the diagram, and it is thus seen 
 that the planes of reflexion M x and M 2 are inclined to each other at an 
 acute angle. 
 
 This specimen was kindly lent to me by Dr L. von He yd ex and 
 was first described and figured by Mocquerys, Col. anorm., 1880, p. 
 65, Jig. 
 
 It is difficult to observe the two foregoing cases without sus- 
 pecting that the fact that they deviate from the normal symmetry 
 of extra parts may be connected with the normal modification 
 of the anterior tibia in these Carabidw. It should be remembered 
 that the tibia and tarsus of the unmodified leg of a beetle are 
 very nearly bilaterally symmetrical about the longitudinal median 
 plane of the limb, but in this leg of these forms the symmetry 
 is lost. Possibly then the upsetting of the ordinary rules for 
 the Symmetry of extra parts may follow on this modification. 
 The difference between the two cases moreover is possibly due 
 to the fact that in one the extra parts are on the posterior surface 
 of the leg, while in the other they are on the anterior. Since the 
 normal limb is not bilaterally symmetrical it is reasonable to expect 
 that the results would differ in the two cases. One other case 
 of a pair of extra tarsi in the fore leg of a male Calathus is re- 
 corded (No. 777 a), but insufficiently described. It is to be hoped 
 that a few cases of extra tarsi in the fore leg of male Calathus 
 or Pterostichus may be found, and it is very possible that such 
 a case even in Carabus would help to clear up these points. 
 
 777 a. Calathus fulvipes 3 (Carabidre) : tibia of right fore leg bears pair of extra tarsi. 
 [Fig. and description inadequate.] Perty, Mitth. not. Ges. Bern, 1866, p. 307, Jig. 5. 
 
 (10) Nine other cases departing from the Schematic Positions. 
 
 Each of these needs separate consideration. 
 
 *778. Platycerus caraboides (Lucan.) : left hind tarsus has form 
 shewn in Fig. 170. The terminal joint had only one 
 claw. R and L' are presumably the extra pair, but it 
 will be seen that they arise at separate places from the 
 3rd tarsal joint. Otherwise, they stand approximately 
 in Position V. Described originally by Mocquerys, 
 Col. anorm., p. 67, Jig. 
 779. Philonthus ventralis (Staphylinidse): third joint 
 of right posterior tarsus bearing supernumerary termi- 
 nation of double structure. The apex of the third joint 
 is enlarged, and at a point anterior and slightly dorsal 
 to the articulation of the normal fourth joint the super- 
 
 raboides, No. 778. Left bind tarsus from posterior surface. 
 L, the presumably normal apex, has only one median claw. R 
 and L', arise separately from the 3rd joint. (In Houen Mus.) 
 
508 MEMSTIC VARIATION. [part i. 
 
 numerary parts arise. The fourth and fifth joints of the supernumerary 
 tarsi are of double structure, but are not separated from each other. 
 The double fifth joint bears two pairs of claws, of which the two adja- 
 cent members are compounded together at their bases. The plane in 
 which one pair of claws stands is about at right angles to the plane in 
 which the other pair is placed, the opposed surfaces being ventral 
 surfaces. Stated in terms of the Scheme on p. 481, the supernumerary 
 tarsi are placed as in the position DDA, whereas their position of 
 origin is DA A. It is noticeable that the normal fifth joint does not 
 stand quite in its usual jDosition, but is a little twisted so that it par- 
 tially turns its ventral surface in an anterior direction. This specimen 
 was described and figured by Fauvel, Rev. d'Fnt., 1883, n. p. 93, PI. 
 ii. No. l'. It was kindly lent to me by M. Bleuse, to whom it belongs. 
 
 780. Alaus sordidus (Elateridae) : Ceylon, femur of right middle leg 
 bears two supernumerary legs arising from its postero-dorsal surface. 
 All three legs are somewhat abnormal in form and the principal femur 
 is partly shrivelled at its base. At a point on the postero-dorsal sur- 
 face about halfway from the apex there is a large, irregular boss from 
 which the two extra femora diverge. Of these that wdiich is nearest 
 to the normal leg may be distinguished as a left leg by the planes of 
 movement of its tibia and tarsus, while the remoter leg is a right leg. 
 The tarsus of the latter is broken but was probably complete. The 
 surfaces which the extra legs present to each other are structurally 
 anterior surfaces, but the relative positions of the three legs do not 
 correspond with any of the positions shewn in the Scheme. It should 
 however be noticed that this fact may be connected with the presence 
 of the amorphous thickening at the point of origin of the extra femora. 
 Specimen in Hope Collection first described and figured by AVestwood, 
 Oriental Entomology, PL XXV. fig. 9, and mentioned Proc. Linn. Soc. 
 1847, p. 346. 
 
 781. Clythra quadripunctata (Phyt,): left anterior trochanter bears 
 two supernumerary legs. Both the normal leg and the two extra ones 
 are complete. The position of the latter is very peculiar ; for, arising 
 from the anterior surface of the trochanter, they turn their structurally 
 dorsal surfaces towards the anterior surface of the normal leg, which 
 thus stands between them, one of them being above it and the other 
 ventral to it. Of these that which is placed dorsally is structurally a 
 right leg, while the lower one is a left, like the normal one. Both the 
 extra legs are also partly rotated so that their ventral surfaces are 
 partially directed upwards. From these facts it appears that the 
 position of these extra legs relatively to the normal one does not 
 correspond with any of the positions indicated in the Scheme, and it 
 did not seem to be possible to refer this deviation from the usual 
 arrangement to any special malformation of any of the parts. Speci- 
 men originally described by Mocquerys, Col. anorm., p. 42, fig. 
 
 782. Clytus liciatus (Long.) : right tibia reduced and thickened, being- 
 shapeless and bent. Its apex presents two articulations, the one anterior 
 and the other posterior, the latter bearing a normal, 4-jointed tarsus. 
 The anterior articulation bears a slender double tarsus, the two parts 
 of which are compounded in the 1st, 2nd, and 3rd joints but separate 
 in the 4th or terminal joints. The supernumerary tarsi are very 
 
chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 
 
 509 
 
 slender and the whole thickness of their common proximal joint is 
 even less than that of the proximal joint of the normal tarsus. The 
 
 ac 
 
 Fig. 171. Clytus liciatus, No. 782. I. View of right tibia. II. Detail of the 
 extra parts, from plantar surface, ac, ac, claws supposed to be morphologically 
 anterior, pc, rudiments supposed to represent posterior claws. III. Enlarged 
 view of the end of the normal tarsus. (The property of Dr Kraatz.) 
 
 terminal joints of the extra tarsi are well formed, but they each bear 
 only one fully developed claw, the claw of the adjacent side of each 
 being only represented by a rudimentary knob. It appears at first 
 sight that these extra tarsi are at their origin from the tibia only a 
 single appendage and that their double nature only begins from the 
 third joint. This however is not the case, for there are five spurs on 
 the tibia, together with a small brown knob which perhaps represents 
 the sixth spur. The tibia is greatly misshapen and the arrangement of 
 the spurs is so amorphous that I did not succeed in determining their 
 morphological relations. This specimen was kindly lent by Dr Kraatz, 
 having being first described by him in Berl. ent. Zt., 1873, xv r n. p. 433, 
 figs. 1 7 and 17 a. 
 
 783. Cryptohypnus riparius (Elater.). The tibia of the right anterior le<j is 
 enlarged at its apex and bears one very large tarsal joint: this joint has two apical 
 articulations, of which the posterior bears the remaining 4 joints of what is pre- 
 sumably the normal tarsus. The other articulation bears a large tarsal joint, connn< in 
 to a pair of complete extra tarsi. This pair of tarsi stand with their lateral parts 
 closely adjacent and their plantar surfaces downwards, but the other tarsus which 
 is posterior to them, and is presumably the normal, stands with its plantar surface 
 turned backwards. This disposition differs considerably from that indicated in the 
 Scheme. For the place of origin of the extra tarsi and their position relatively to 
 each other is A; but the normal tarsus is twisted so that it turns its dorsal surface 
 forwards, towards the posterior surface of the nearer extra tarsus. For this specimen 
 I am obliged to Dr Mason. 
 
 784. Taurhina nireus (Lamell.) : right middle tibia bearing two extra tarsi. [In 
 the normal leg of this beetle the tibia is like that of many other Lamellicorns, 
 presenting at its apex two sharp processes, the one anterior and the other dorsal : 
 and ventrally two articulated spines, one anterior and the other posterior to the 
 tarsus. The abnormal tibia of this specimen is considerably widened at its apex, 
 and bears in addition to the normal two processes two other processes of a similar 
 kind separated from each other by a pair of articulated spines. Instead of a single 
 
- 
 
 5 1 MEMSTIC VARIATION. [part l 
 
 pair of articulated spines, this tibia bears five such spines, of which a pairstand 
 between the two extra processes. The disposition of these spines could not be made 
 clear without several figures. There are two complete tarsi and both have their ventral 
 surfaces turned downwards. The anterior tarsus is somewhat the smaller. I did 
 not succeed in definitely determining the homologies of the parts in this specimen. 
 It should be specially observed that while the tarsi are only two in number, suggesting 
 that the supernumerary part is sinr/le, the spines indicate that there are here at 
 least some elements of further repetition.] Specimen figured by Kkaatz, Deut. ent. 
 Zt., 1889, xxxiii, p. 221, fig. 18, and kindly lent by him. 
 7g5 Ranzania bertolonii (Lamellicorn) : in the right posterior foot the last joint of 
 
 the tarsus is curved outwards and bears six claws instead of two, and three onychia 
 instead of one. The arrangement of the parts is somewhat complex and could not 
 well be made clear without elaborate figures. Speaking generally, the last (fifth) 
 tarsal joint presents at its apex a large articular surface of irregular shape. This 
 surface bears four large claws disposed in the same direction as the normal pair of 
 claws. Of the four claws the two adjacent ones are in solid continuity for a part of 
 their length, being joined together by chitin much as the extra dactylopodites are in 
 l''i^ r . 184, in. It is clearly shewn that the conjoined claws are respectively the fellows 
 of the two free claws, for the two extra onychia stand one upon either side of and 
 opposite to the curvature of the conjoined claws. Terminally the fifth tarsal joint 
 bears also a small pair of somewhat deformed claws with which an enlarged and 
 misshapen onychium corresponds. This specimen was kindly lent to me by M. 
 Henri Ctadeau de Kerville and was mentioned by him in Bull. Soc. Ent. France, 
 Ser. 6, vi. 1886, p. clxxx. 
 
 786. Rhizotrogus aestivalis $ (Lamellicorn), bearing supernumer- 
 ary parts of double structure upon the right posterior 5th tarsal 
 joint (Fig. 172). The structure found in this case is very re- 
 markable and is, I believe, in some respects unique. The tarsus 
 is normal as far as the extremity of the terminal joint, and the 
 abnormality consists entirely in repetition of claws and pulvillus. 
 The normal formation is shewn from the ventral surface in 
 Fig. 172, A. There is an anterior claw, a posterior claw T and a 
 small pulvillus, placed ventrally to the claws, bearing two hairs. 
 Fig. 172, B, shews the abnormal foot from the ventral side. Each 
 claw gives off from its base a ventrally-directed supernumerary 
 claw, and each supernumerary claw is bifid at its point. Ex- 
 amined from below each of these extra claws is seen to bear 
 two grooves separated by a ridge, and is therefore morphologically 
 a double structure. The next structure of importance is the 
 pulvillus. The normal pulvillus (pid) is in place and of the usual 
 form, but dorsally to it there is a supernumerary pulvillus (pid-) 
 of cylindrical form and rather longer than the normal pulvillus. 
 At its apex this extra pulvillus bears a median bifid hair with 
 another hair on each side of it ; these hairs thus prove that the 
 extra pulvillus is morphologically double. 
 
 In this foot, therefore, a supernumerary pair of claws and a 
 supernumerary double pulvillus are intercalated between the 
 normal claws and the normal pulvillus. Hence though the repet- 
 ition affects both claws and pulvilli, and the structures found 
 are sufficient for an incomplete pair of extra feet, yet the extra 
 parts are disposed in the system of symmetry of the normal foot, 
 forming, all taken together, one foot only. Specimen very kindly 
 lent by Dr G. Kraatz. 
 
chap, xx.] EXTRA LEGS : MISCELLANEOUS CASES. 
 
 511 
 
 A 
 
 B. 
 
 A 
 
 a'and 
 
 p'andp' 
 
 D. 
 
 K ,.P 
 
 pul -/ 
 
 Fig. 172. Ehizotrogus cestivalis, No. 786. A, normal hind foot from ventral 
 surface. B, right hind foot of No. 786 from ventral surface. C, enlarged view of 
 pulvilli. D, inside view of the claws at the anterior border of the apex. E, inside 
 view of the claws of the posterior border of the apex. A, anterior. P, posterior. 
 a, normal anterior claw of abnormal foot, p, normal posterior of the same. 
 a', a", the two points of extra claw of anterior side. p' s p", the two corresponding 
 posterior points. In D the posterior group of claws is supposed to be cut off at P. 
 pul, normal pulvillus. pul 2 , extra double pulvillus. 
 
 (11) Cases in which the legs were either mutilated, or in part 
 amorphous, or insufficiently described. 
 
 '87. Want of space prevents me from giving more than a list of refer- 
 ences to these cases. Most of them besides are imperfectly known. Of 
 those seen by myself the case of Ulster would, I think, be interest 
 ing, but I regret that my notes of this case are imperfect. In the 
 following list the letters R and L shew the leg affected ; the " means 
 that the case probably did not agree with the Scheme, the , that it 
 probably did agree ; the J means that the parts were either mutilated, 
 or imperfect, or deformed. Of those unmarked, the accounts are 
 inadequate. 
 
 E 3 Tischbeix, Stet.ent. Ztg., 1861, xxn. p. 128. 
 Kraatz, Deut. eut. Zt.. 1889, xxxni. p. 222, 
 fig. 17. 
 Lj Gkkdlkh, Korresp. zool.-min. Ver. Regetuo., 
 
 1877, xxxi. p. 139. 
 Ro LANDOis, Zool. dart., 1**1. xxv. p. 2SS[q.v.J 
 L." Kraatz, Berl. ent. Zt., 1873, xvn. p. 432. 
 
 Ichneumon luctatorius 
 Carabus auratus 
 
 C. auronitens 
 
 C. cancellatus 
 
 ditto <? 
 
512 
 
 MEBISTIC VARIATION. 
 
 [part I. 
 
 B„ 
 B" 
 
 1 
 
 C. catenulatus 
 C. italicus 
 Dyschirius globulosus 
 
 (Car.) 
 
 Calopus cisteloides (Het.) 
 Pterostichus prevostii L 3 
 
 (Car.) 
 Chl.-rnius nigricornis (Car.) L. { 
 Agra catenulata (Car.) L 3 
 
 Prionus coriarius (Long.) B 3 
 
 Prionus sp. ? 3 
 
 Aromia moscliata (Lam.) L x 
 
 Dorcadion rufipes (Long. ) L 3 
 
 Blaps sp. (Het.) 
 
 B, 
 
 Ptinus latro (Plin.) L x 
 
 Dytiscus marginalis (Dyt.) B x 
 
 Colymbetes sturmii (Dyt.) L x 
 Strategus antaeus (Lam.) L 2 
 Rutela fasciata (Lam.) B 3 
 
 Hister cadaverinus (Clav.) B x 
 Cetonia morio- (Lam.) L x 
 
 ivielolontha vulgaris (Lam.) L 3 
 ditto B x 
 
 ditto L, 
 
 ditto 
 
 * 3 
 
 La 
 
 Ri 
 
 Li 
 
 and 
 
 B 3 
 Oryctes nasicornis (Lam.) P^ 
 
 Enema pan. (Lam.) L 3 
 
 + % ditto 
 
 || Rhizotrogus castaneus 
 (Lam.) 
 
 t H- aestivalis 
 
 Brit. Mm. 
 
 Baudi, Nat. Sicil., vni. No. 9, p. 199. 
 Jaynk, Trans. Amer. Ent. Soc., 1880, vm. 
 
 p. 157, PI. ix. jigs. 6, 6a. 
 vox Heyden, Isis, 1836, ix. p. 761. 
 Muller, A., Proc. Ent. Soc, 1869, p. xxviii. 
 
 Mocquerys, Col. anorm., 1880, p. 62, Jig. 
 Stannius, Miill. Arch. f. Anat. Phys., 1835, 
 
 p. 306, fig. 13. 
 Perty, Mitth. not. Ges. Bern, 1866, p. 308, 
 
 fig- 11. 
 
 Ann. and Mag. N. H., 1841, p. 483. 
 Kraatz, Dent. ent. Zt., 1877, xxi. p. 56, PI. 
 
 i,2,^.ll. 
 Perty, I.e. 
 Laroulrene, Bull. Soc. Ent. Fr., S. 4, v. 
 
 1865, p. xlix. 
 von Fricken, Ent. Nachr., 1883, ix. p. 44. 
 Bitzema Bos, J., Tijds. v. Ent., 1879, xxn. 
 
 p. 206, PI. 
 Stannius, I.e., p. 307, fig. 9. 
 Jayne, I.e., p. 159, fig. 10. 
 Spinola, A nn.Soc. ent.Fr. 1835,iv.p.587,P7. 
 Mocquerys, I.e. , p. 59, fig. 
 Sartorius, Wien. ent. Monats., 1858, 11. p. 50. 
 Treuge, Ent. Nachr., vin. 1882, p. 177. 
 Doumerc, Ann. Soc. cut. Fr., 1834, in. p. 171, 
 
 PI. 1 a, fig. 1. 
 Boulard, Bull. Soc. ent. Fr., 1846, S. 2, iv. 
 
 p. xwin.fig. 
 Tiedemann 3 , MeckeV s Arch. f. Phys., 1819, 
 
 v. p. 125, PI. 11. fie. 1. 
 Mocquerys, I.e., p. ii8, fig. 
 Bassi, Ann. Soc. ent. Fr., 1834, in. p. 373, 
 
 PI. VII A. 
 
 /Perroud, Ann. Soc. Linn. Lyon, 1854, n. 
 ( p. 325. 
 
 Audouin, Bull. Soc. ent. Fr., 1834, in. p. iv. 
 Taschenrerg, Zts. f. ges. Naturiv., 1861, 
 xviii. p. 321. 
 
 1 As Kraatz suggests, this is presumably the case given by Sartorius, /. c. 
 
 2 Probably same specimen as that of Gredler, Korresp. zool.-min. Ver. Begensb., 
 1869, xxiii. p. 35. 
 
 3 Tiedemann's grave comment is of interest as recalling past phases of thought. 
 He says: " Was die Entstehung der oben beschriebenen Missbildung betrijf't, so lasst 
 sich wohl annehmen, dass die Phantasie der Mutter des Maikdfers durch ein voraus- 
 gegangenes Versehen aufgeregt, hier nicht als Ursache beschuldigt werden kann, theils 
 weilwir iiberhaupt keine Beiveise filr eine lebhafte Phantasie der Maikdfer haben,und 
 theih weil die Bildung des Embryo ausserhalb des Leibes der Mutter nur sehr langsam 
 geschieht, und die Mutter ohnehin gleich nach Legung der Eier stirbt " I. c, p. 126. 
 
chap, xx.] EXTRA ANTENX.E : PRELIMINARY. 513 
 
 Paired Supernumerary Antenna 
 
 In dealing with extra antennae there is more difficulty in de- 
 termining the true nature of the parts than there is in the case 
 of extra legs. We have seen that the real duplicity of com- 
 pounded extra parts often appears only in the fact that they 
 have a bilateral symmetry, while in the normal appendage one 
 side is differentiated from the other. Now in very many species 
 of Insects the antenna seems to be a bilaterally symmetrical fila- 
 ment, having joints cylindrical or elliptical in section. When from 
 such an antenna there proceeds an extra filament, itself bilaterally 
 symmetrical, it is almost impossible to determine whether the 
 extra filament is really a single repetition of the normal or 
 whether it is made up of two homologous borders of a pair. 
 (Cp. Nos. 801 and 764.) In speaking of actual cases of 
 duplicity in Arthropodan appendages we shall have to return 
 to this subject. 
 
 Meanwhile evidence will be given as to examples of obvious 
 duplicity in extra antennae. It will be seen that in species having 
 normally a marked differentiation between the anterior 1 and 
 posterior borders of the antennae (Lainellicorns, Lucanidae, &c. ). 
 and the case has been really studied, there is often clear proof 
 not only of the duplicity of the extra parts but also that they 
 are arranged as images, almost as described for legs. 
 
 We shall moreover meet cases where of the paired extra 
 parts one springs free from the normal at a point proximal bo 
 the point of origin of its fellow. Among extra legs there is scarcely 
 any certain example of this phenomenon, Platycerus caraboides No. 
 778 being perhaps the clearest case. But among antennae there 
 are several where no other interpretation seems possible. These 
 cases I have set in a separate section. 
 
 Of the remainder, little can be said with confidence. Probablv 
 if they were carefully examined microscopically it would be found 
 that differentiation between the two sides exists in respect of 
 the distribution of sense-organs or hairs, and that thus the du- 
 plicity and symmetry might be traced. 
 
 After giving the clear cases I have thought it enough bo give 
 a list of those of this doubtful order. As has been said, there is 
 little doubt that with careful study of the specimens many 
 of the cases now included in the list of supposed single extra 
 appendages might be shewn to be cases of extra parts in 
 Secondary Symmetry. 
 
 1 This term is used, as in the case of legs, to denote the border which ia anterior 
 when the appendage is extended horizontally at right angles to the body. The 
 upper surface will then be dorsal, the lower ventral. These terms are thus applied 
 without any intention of affirming that they are morphologically correct. 
 
 b. 33 
 
5 1 4 MERISTIC VARIATION. [part i. 
 
 (1) Clear cases of Supernumerary Antennce in Secondary 
 
 Symmetry. 
 
 (a) The extra ixirts arising together. 
 
 f 788. Phyllopertha horticola (Lamellicorn) : specimen in which 
 the right antenna bears a supernumerary pair of clubs. This 
 specimen may conveniently be described in detail as it furnishes 
 a good example of the mode in which repetition of the antenna^ 
 occurs in the Lamellicorns. The left antenna is normal and 
 possesses nine joints (Fig. 173, L). The first is a large pear- 
 shaped joint, articulating with the head by its narrow end. The 
 
 L R 
 
 Fig. 173. Phyllopertha horticola, No. 788. L, the normal left antenna. E, 
 the normal right antenna. /, r, extra left and right clubs. 
 
 second joint is also a pear-shaped joint, of about half the size 
 of the first. The third, fourth and fifth joints are elongated and 
 cylindrical. The sixth is short and wide. The seventh, eighth 
 and ninth are each expanded into a lamella. These three la- 
 mellae are generally kept firmly closed together and form the 
 sensory organ, or " club." In Melolontha (v. infra) and several 
 other genera of Lamellicorns, there are ten joints, of which seven 
 are developed as lamellae, forming the club. 
 
 In the right antenna (Fig. 173, It), which bears the extra 
 pair of clubs, the basal joint is rather thick. The second joint 
 is longer than it normally is, and curves slightly backwards and 
 downwards. At its apex it bears the rest of the normal antenna, 
 which is in all respects well formed. In addition to the normal 
 antenna, the second joint upon its anterior surface gives attach- 
 ment to a large joint which is imperfectly constricted into two 
 parts in a vertical plane at right angles to the general direc- 
 tion of the normal antenna. Each of these half-joints bears a 
 structure containing in itself all the parts proper to an antenna 
 peripherally to the third joint, the clubs being well-formed and 
 normal. In absolute size they are equal, but are a little smaller 
 than the normal antenna. 
 
CHAP, xx.] EXTRA ANTENNAE ARISING TOGETHER. 515 
 
 These two antennae curve in opposite directions and arc in 
 all respects complementary to each other, forming a true pair. 
 The most anterior of them, r, is disposed as a rir/ht antenna, 
 while the posterior, I, is disposed as a left. This specimen 
 was taken by M. Albert Mocquerys, and was kindly lent to me 
 by M. Henri Gadeau de Kerville. 
 
 789. Melolontha vulgaris $ (Lamellicorn) : left antenna bearing a 
 pair of supernumerary clubs. The extra pair arises from the second 
 joint of the normal antenna, and they have their third joints united at 
 the base. The relative positions of the extra clubs and the normal one 
 are those marked VP in the Scheme. All these three clubs are perfect 
 and of the same size, but each is a little smaller than a normal club. 
 At the thoughtful suggestion of Prof. Howes this specimen was 
 very kindly lent to me by Mr E. E. Green, and has been placed in the 
 Museum of the Royal College of Surgeons. 
 
 790. Melolontha vulgaris : [right antenna bearing a supernumerary 
 pair of clubs in Position P. For details see original, where a different 
 and I think untenable view is taken] Lereboullet, Rev. et Mag. de 
 Zool., S. 2, in., 1851, Jig. 
 
 791. Melolontha vulgaris £ , with a pair of supernumerary antenna? 
 arising from the left antenna. [The figure shews that the proximal joint 
 or scape was of abnormal thickness and had two peripheral articulations 
 in the same horizontal plane. The anterior articulation bore a normal 
 antenna. The posterior articulation bore a single large first funicular 
 (2nd) joint which in its turn bore a pair of clubs in the same horizontal 
 plane, the anterior being a right club and the posterior a left, having 
 their anterior surfaces adjacent : they are therefore a complementary 
 pair in Position P.] Kraatz, G., Ueut. ent. Zt., 1880, XXIV. p. 341, 
 figs. 7 and 7 a. 
 
 792. Amphimallus solstitialis (Lamellicorn): left antenna bearing a 
 supernumerary pair of imperfect antenna? articulating by a common 
 stalk on the anterior surface of the second joint. The two extra clubs 
 are an imperfect pair, complementary to each other, being set on bark 
 to back, in Position A. The most anterior of the clubs has only two 
 lamellar joints, one small and one large. The posterior has three 
 lamella?. The normal club has three lamella? as usual. Originally 
 described by Mocquerys, /. c, p. 15, Jig. 
 
 793. Anomala junii (Lamellicorn) : left antenna bears 3 clubs, each having 3-jointed 
 stem articulating with elongated 2nd joint of antenna. [Symmetry not clear: 
 possibly Position DPP.] Kraatz, Ueut. cut. /A., 1881, xxv. p. Ill, PI. in. fig. 4. 
 
 *794. Geotrupes typhaeus ^ (Lamellicorn): left antenna bearing 
 a pair of supernumerary clubs compounded together. The an- 
 tenna is normal up to the 7th joint which is dilated. The 8th is 
 still more dilated and bears posteriorly the normal club com- 
 posed of three lamellae; and anteriorly by a separate articulation 
 a supernumerary structure (Fig. 174, mr,ml) consisting of three 
 joints, each of which has the form of a complementary pan oi 
 lamellae joined by their morphologically posterior (so. external) 
 edges. The whole supernumerary structure is thus morphologic- 
 
 33—2 
 
516 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 ally a pair of clubs, a right and a left, compounded together. 
 The histology of the supernumerary lamellae is just the same as 
 
 Fig. 174. Geotrupes typhous, No. 794. Left antenna bearing a compounded 
 pair of clubs, ml, mr, morphological left and right of the extra parts. (The 
 property of Dr Kraatz.) 
 
 that of the normal lamellae, all being covered with pubescence. 
 The form of the compound eleventh joint is somewhat irregular. 
 The extra parts are in the Position A of the Scheme. Specimen 
 kindly lent by Dr Kraatz, and first described and figured by 
 him in Dent, ent Zt, 1889, xxxni. p. 221, fig. 13. 
 795. Melolontha hippocastani <£ having supernumerary parts of 
 double structure upon both the right and the left antenna. 
 
 Right Antenna. Third joint elongated, thickened and pre- 
 senting two articular surfaces ; of these one is terminal and bears 
 a normal autennary club, while the other is dorsal and bears a 
 supernumerary double club. This structure has the form shewn 
 in the drawings. Fig. 175, A, shews its appearance when looked 
 at from above, B shews the structure when seen from below and 
 externally. It consists of seven pieces shaped like half-funnels, 
 fitted into each other. 
 
 Fig. 175. Melolontha hippocastani, No. 795. D, view of the whole head and 
 antennae after von Heyden. C, view of right antenna. B, detail of right antenna 
 from below. A, detail of the same from above. 
 
chap, xx.] EXTRA ANTENNAE ARISING TOGETHER. 517 
 
 The morphological nature of this supernumerary organ may 
 be determined thus. The upturned edges of the folds bear 
 hairs as shewn in the figure A; since in the normal antenna 
 the dorsal edges of the lamellae alone bear hairs, these edges 
 are in this case dorsal morphologically as well as by position. 
 
 Since the outermost lamella (marked 4) is articulated into 
 the third joint of the funiculus, it is therefore the 4th joint, or 
 proximal lamella, and the remaining lamellae are therefore 5th, 
 6th, 7th, 8th, 9th and 10th respectively. Next, the surface ////• 
 is structurally like that of the internal (sc. anterior) surface of 
 the proximal lamella of a normal club, and the surface ml is a 
 similar surface : but ml, being an internal surface, faces towards 
 the right and is therefore morphologically a left; while mr, being 
 an internal surface and facing towards the left, is a right ; hence 
 this club consists of two clubs compounded together by their 
 external or posterior borders, and the two are a right and a left, 
 the left being next the normal right club. 
 
 Lastly, since the upper free edges of the lamella* are structur- 
 ally dorsal, it follows that their lower edges are structurally 
 ventral: but these lower edges do not exist as free edges, f'« >r 
 the lamellae are continuous upon their ventral aspect : therefore 
 the surfaces which are adjacent in the extra right and left clubs, 
 and by which they are compounded together, are partly ventral 
 surfaces. This is approximately Position DP of the Scheme. 
 
 Left Antenna. Second joint thickened and presenting three 
 articulations as follows. 1. a peripheral articulation bearing the 
 normal club ; 2. a ventral articulation bearing a 4th joint and 
 club composed of 3 formless lamellae ; 3. a dorsal articulation 
 bearing a small cylindrical joint only. The shape and formation 
 of these extra parts is so indefinite that their morphology could 
 not be determined. 
 
 For the loan of this specimen I am indebted to Dr L. v< »x 
 Heyden, who first described it in Deut ent. Zt. y 1881, XXV, p. 10"), 
 fig. 1. 
 
 796. Rhizotrogus aequinoctialis (Lain.) : 4-th joint of right antenna 
 bears a supernumerary structure projecting forwards and lying in the 
 same horizontal plane as the normal club. This structure is lanceolate 
 in form and its outer surface is in texture similar to the external surfaces 
 of a normal club. On the ventral aspect it presents a simple ridge, but 
 on the dorsal side its outer coating is divided by a spindle-shaped slit 
 through which part of the internal structure protruded. The edges of 
 this opening and the protruding portion of the interior bear a few 
 hairs. There can be little doubt that this supernumerary body repre- 
 sents an imperfectly formed pair of cluhs, and that it is in fact a more 
 rudimentary condition of the parts found in No. 795. Specimen origi- 
 nally described and tigured by Mocquerys, Col. anorm., p. 1 •>,./?'#. 
 
 797. Llchnanthe vulpina (Lam.) : right antenna bears in addition to normal club a 
 small spherical club made up of three joints, arising from posterior border of a l<>n^ 
 
518 MERISTIC VARIATION. [part i. 
 
 joint apparently representing the normal 4th, 5 th, and 6th joints not segmented from 
 each other. [As this supernumerary part is in itself symmetrical it probably con- 
 tains within itself parts of a pair of clubs compounded in Position P. Cp. No. 
 795.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm. p. 158, PI. iv. fig. 8. 
 798. Polypbylla decemlineata (Lamellicorn). A specimen in which the right 
 antenua bears a partially double supernumerary branch in addition to the normal 
 antenna. This additional structure articulates with the second joint of the antenna 
 by means of a single large joint. This joint carries a double club consisting of two 
 sets of lamellae, seven being in each set. The two sets of lamellae are united at 
 their bases at an angle of forty-five degrees. The plane of the normal club is per- 
 pendicular to that of the abnormal ones. The normal club itself is Ath shorter than 
 that of the other side. [The details of the structure of this specimen are difficult 
 to follow and the reader is referred for further particulars to the description and 
 figures given in the original.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm. 
 p. 158, Ji(]s. 
 
 (b) The extra parts arising from the normal at separate points. 
 
 99. Odontolabis stevensiij (Lucanidae). As the repetition in 
 this specimen is almost complete and the relations of the parts 
 fairly clear though in some respects peculiar, a detailed account 
 will be useful. 
 
 The body, legs, &c. are normal, save that the back of the 
 head and thorax have been crushed by some accident. The 
 antennae are both abnormal in the way shewn in Fig. 176. The 
 condition will be better understood if the normal antenna is first 
 described. 
 
 *7 
 
 r i 
 
 Fig. 176. Odontolabis stevensii, No. 799. The liead seen from below, and 
 
 enlarged views of the two antennae. R, right. L, left. There is some doubt as 
 
 to which of the branches is the normal and which the supernumeraries. See 
 description in text. 
 
 The normal antenna of Odontolabis is much like that of its 
 ally Lit can us cervus, the Stag-beetle. It is made up of 10 joints 
 composing three parts differentiated from each other. 
 
 The first, or " scape, ' : is a single joint as long as the rest 
 of the antenna. It widens a little from its central end or base 
 towards the apex, and is slightly flattened from above downwards. 
 The second part, or " funiculus," has six simple joints. The last 
 three joints form the club. They are flattened from above down- 
 wards and lie in a horizontal plane. The anterior (" inner ") 
 border of each of these three joints is produced into flat ex- 
 pansions, covered with sensory pores, which together form a series 
 of serrations along the anterior border. When in its natural 
 
chap, xx.] EXTRA ANTENNAE ARISING TOGETHER. 519 
 
 position the serrated border of the right antenna faces towards 
 the left side, and that of the left is turned towards the right. 
 The structure of the abnormal specimen is as follows. 
 
 Left Antenna. Scape normal. Its plane however is not quite 
 horizontal as usual, but is a little oblique, the anterior border being 
 slightly higher than the posterior. In the funiculus the 1st and 
 2nd joints (2nd and 3rd of the whole antenna) are a little thicker 
 than usual but otherwise normal. The 3rd joint of the scape 
 is enlarged and presents at its apex two sockets, each bearing 
 a continuation as shewn in the figure. The two sockets are not 
 in a horizontal plane, but their plane is oblique and nearly at 
 right angles to the plane of the scape, the socket bearing the 
 branch l l being the higher. It is important that the precise re- 
 lations of these parts should be clearly understood. 
 
 This outer socket of the 3rd funicular joint bears the branch l\ 
 made up of three more funicular and three club-joints, turning 
 their serrated border in the direction of the rigid antenna : I 1 is 
 therefore structurally a left antenna. Its surface is of the same 
 nature as that of a normal antenna, but its size is a little smaller. 
 It is in an oblique plane inclined to the horizontal at about 45 . 
 the posterior (outer) border being the higher. 
 
 The inner socket of the 3rd funicular joint bears a cylindrical 
 joint not quite fully segmented off from the next joint peripheral 
 to it. These two are 4th and 5th funiculars. The 5th again 
 presents two sockets, bearing respectively the branches I 2 and 
 I 3 . The branch I 2 has one small joint (6th funicular) and three 
 club-joints, turning their serrated border towards I 1 . This branch 
 is therefore structurally a right antenna. It stands in the same 
 oblique plane as I 1 , the serrated border being the higher. In 
 size it also agrees with l\ being rather smaller than the normal. 
 The branch I 3 is a normal left in size and shape, and it lies in 
 a horizontal plane. 
 
 Here therefore there is a left antenna and a pair, one a right 
 and the other a left. Which then is the normal, I 1 or I 3 ? Inas- 
 much as I 3 and P arise by a common stalk it may seem that 
 they are the extra pair and that I 1 is the normal. We have 
 now seen in many cases that extra parts in Secondary Symmetry 
 are compounded together as P and I 2 are here. But considering 
 the fact that I s is of normal size and in the normal horizontal 
 plane, whereas I 1 and I- are both smaller and are in an oblique 
 plane complementary to each other, I incline to the view thai 
 if one branch is the normal, it is I 3 , and that / l and I- are the 
 extra pair in Secondary Symmetry, though tlieij do not arise to- 
 gether. They are then nearly in Position DPP, but depart from 
 that position in the fact that I 1 is not horizontal (cp. No. 757). 
 
 If I 1 and I 2 are really the extra parts, in the fact that they 
 do not arise together, but spring separately from different points 
 on the normal, w r e meet with a condition rarely seen, but that 
 
520 MERISTIC VARIATION. [part t. 
 
 this is a possible condition is proved beyond doubt by the 
 succeeding case. 
 
 Right Ante)i int. Scape precisely as in left antenna. The 
 1st funicular (2nd antennary) has two sockets at its apex, placed 
 like those on the 3rd funicular of the left side, the anterior socket 
 being the lower and the posterior socket being the higher. The 
 anterior socket bears a normal right antenna, ?- 3 . The posterior 
 bears the structure shewn in the figure. This appendage has 
 unfortunately been broken, but enough remains to suggest the 
 original structure. It consists of five funicular and a 1st club- 
 joint. The 5th joint of the whole funiculus bears a large socket 
 looking downwards and forwards, its other socket looking back- 
 wards and upwards. From the former the original continuation 
 has been lost. The latter bears the 6th funicular and its 1st 
 club-joint, this again having an empty socket. 
 
 The plane of the two sockets of the 5th funicular is oblique 
 to the horizon, like that of I 1 and I' 2 . Though it is clearly im- 
 possible to shew how this antenna was in its unbroken state, 
 we may note that if it were continued in the way suggested 
 by the dotted lines it would have borne a complementary pair 
 of clubs, r 1 and r 2 , like I 1 and I' 2 of the other side, placed like 
 them in an oblique plane nearly corresponding with DPP of the 
 Scheme. 
 
 This specimen was kindly entrusted to me by M. Henri 
 Gadeau de Kerville. He tells me that he believes a description 
 of it has already appeared, but this I have failed to find. I 
 have therefore ventured to describe it again, with apologies to 
 the original describer. The specimen bears a label in the hand- 
 writing of the late Major Parry and was no doubt in his cele- 
 brated collection of Lucanidse. 
 
 800. Melolontha vulgaris : right antenna bearing a pair of incomplete 
 supernumerary antennae (Fig. 177). The first joint is normal ; it bears a 
 second joint of singular form, consisting of a long anterior branch, and 
 a short posterior branch i the length of the anterior. The anterior 
 bears two clubs in the manner shewn in the figure (Fig. 177). Of these 
 
 Fig. 177. Melolontha vulgaris, No. 800. Lettered according to the view that R 
 is the normal right club. L, the supernumerary left, and R' the supernumerary 
 right. (From Wesmael.) 
 
* 
 
 801, 
 
 chap, xx.] EXTRA ANTENNA ARISING SEPARATELY. 521 
 
 one (E) is inwardly directed and is as wide as, but only | the length of 
 a normal club. The posterior of the two clubs (L) is directed back- 
 wards and has only four lamellae which are apparently united together. 
 The other small club (R') is also composed of only four lamella? which 
 are similarly united together. In both L and R the middle lamellae shew 
 traces of further subdivision. The figure represents the three clubs as 
 being all in one plane, but the club R' is really below /,, which stand- 
 up from the normal antenna. It is mentioned that some of the tarsi 
 were mutilated or defective. [Here L and R' are clearly a complement- 
 ary pair, though separately arising from the normal. It will be 
 observed that as in Lereboullet's case (No. 790) the second joint, which 
 is common to two clubs, is greatly elongated.] Wesmael, Bull. Ac. 
 Belg., 1850, xvi. 2, p. 382, fig. 
 
 Navosoma sp. (Longic.) Left antenna abnormal. The joints of 
 the normal are a little flattened from above downwards and are nearly 
 elliptical in section. But the anterior border is differentiated from the 
 posterior by the presence of two elongated patches of tissue covered 
 with sensory pores. The two patches are both on the anterior border, 
 one being* on the dorsal surface and one on the ventral, separated from 
 each other by a chitinous ridge. Upon the general surface of the 
 peripheral joints of the antennae are several other such patches, but 
 none are so distinct as those of the anterior border. The abnormal left 
 antenna has the form shewn in Fig. 1 78. So far as the 8th joint it does 
 
 L'*R 
 
 L'+R' 
 
 Fig. 178. Navosoma, No. 801. Left antenna seen from below. Lettered on 
 the view that R and L' are the extra parts. S, sensory patch. (In Hope 
 Collection.) 
 
 not differ from the normal. The 9th and 10th joints have besides their 
 chief patches of sensory pores (S) on the anterior border, an additional 
 patch (L' + R') posterior to the chief patch. But up to the 10th joint 
 there is no vertical division. The 10th joint however has two articular 
 surfaces, anterior and posterior, in the same horizontal plane. The posterior 
 bears an apical (11th) joint of normal form, having anteriorly a sensory 
 patch. But the apical joint borne by the anterior articular surface has 
 two such sensory patches, an anterior and a posterior. This joint 
 therefore contains in itself parts of a pair of joints. It is not quite 
 fully segmented off from the 10th joint. 
 
 Nevertheless it is difficult to suppose that the anterior joint is the 
 extra pair in Secondary Symmetry, for its anterior patch, Ls, seems to 
 continue the normal series of patches, S, S, etc. Therefore the patches 
 R and L' seem to be the patches of the extra pair, though one of them 
 is on a separate joint and the other is applied to the normal. Taken 
 with the case of Odontolabis No. 799 and Mehlontha No. 800, this 
 
522 MERISTIC VARIATION. [part i. 
 
 must, I think, be judged to be a possible account, and in this case R 
 and L' are, as regards symmetry, in Position P. It is of course possible 
 that Ls and R are really the extra pair in Position A, but the presump- 
 tion is rather the other way 1 . Specimen in Hope Collection at Oxford. 
 
 (2) Cases of double extra antennce, Symmetry unknown. 
 
 802. In none of the following can any confident statement be made 
 as to the symmetrical relations of the parts, Several of the 
 cases I have myself seen, but I noticed no clear indications as 
 to their symmetry. A good many of them however were ex- 
 amined before I was fully alive to the importance of these matters 
 in the case of filamentous antennae, and perhaps if they were 
 studied with proper regard to the question of symmetry more 
 might be made of them. Many cases that follow r are mutilated 
 or partly amorphous, and of almost all the descriptions are very 
 imperfect. For our purpose some value attaches to these records 
 as evidence of the distribution of such abnormalities, and to 
 any person who may hereafter pursue the subject a fairly com- 
 plete list of the references may be of use. To this therefore I 
 shall confine myself; for on reviewing the abstracts that I have 
 made of these examples it is clear that they only give the results 
 of superficial examination. 
 
 Speaking generally, in these cases, from some one joint of an 
 antenna there arises either a pair of extra antennae compounded 
 for a greater or less extent of their proximal parts, or two extra 
 antennae distinct from their point of origin. 
 
 The letters R and L indicate the side affected, and the number 
 following is approximately that of the joint from w r hich the extra 
 parts spring. In the greater number of sound cases the three 
 branches lie in or nearly in a horizontal plane and are, I anticipate, 
 in Positions A or P. 
 
 Cases which seem from the indications to conform to the 
 Scheme are marked ||. Mutilated or partially amorphous cases are 
 
 marked J. 
 
 
 
 Blaps attenuata (Het.) 
 
 R3 
 
 Mocquerys, Coleopteres anormaux, 1880, 
 p. 5, Jig. 
 
 ' || Malachius marginellus 
 
 L2 
 
 ibid., p. 7, fig. 
 
 (Mai.) 
 
 
 
 Timarcha tenebricosa 
 
 R9 
 
 ibid., p. 13, fig. 
 
 (Phyt.) 
 
 
 
 Clytus tricolor (Long.) 
 
 L7 
 
 ibid.' 2 , p. 19, fig. 
 
 * X C. arcuatus 
 
 LI 
 
 ibid., p. 20, fig. 
 
 Calopteron reticulatum 
 
 LI 
 
 ibid., p. 25, fig. 
 
 (Mai.) 
 
 
 
 Carabus monilis (Car.) 
 
 L3 
 
 ibid., p. 3, fig. 
 
 ' C. auronitens 
 
 L7 
 
 ibid., p. 9, fig. 
 
 ■ Ftinus latro (Ptin.) 
 
 L5 
 
 ibid., p. 8, Jig. 
 
 Elater murinus (Elat.) 
 
 L2 
 
 Ann. and Mag. of N. H., 1831, iv. p. 476. 
 
 Zonites praeusta (Het.) 
 
 E3 
 
 Stannius, Mull. Arch. f. Anat. Phys., 1835, 
 
 p. 303. 
 
 1 This is perhaps too strongly put. 
 
 2 Description and figure incorrect. Apical joint of extra branch is bifid. 
 
chap, xx.] EXTRA ANTENNA : OBSCURE CASES. 
 
 523 
 
 Helops cacruleus (Het.) R5 
 
 Dendarus hybridus (Het.) L 4 
 
 : Scraptia fusca (Het.) L 5 
 
 : Carabus sacheri (Car.) R7 
 
 Fimelia scabrosa (Het.) R 2 
 Anchomenus sex punctatus L 6 
 
 (Car.) 
 
 Calosoma investigator R 5 
 
 (Car.) 
 
 Dromrcolus barnabita L 5 
 
 (Eucn.) 
 
 Carabus arvensis L 4 
 
 Shringe, Ann. Soc. Linn, de Lyon, 1836, PI. 
 Romano, Atti Ac. sci. Palermo, 1845, N. S., 
 
 i. fig. 
 Rouget, Ann. soc. ent. France, 1849, S. •_'. 
 
 vii. p. 437. 
 Letzner, Jahresb. schles. Ges. f. vaterl. 
 
 Kultur, 1854, p. 86. 
 Blackmore, Proc. Ent. Soc, 1870, p. xxix. 
 Kraatz, Dent. ent. Zt., 1877, xxi. p. 56, 
 
 fig. 19. 
 ibid., 1889, xxxm. p. 221, fig. 
 
 von Heyden, ibid., 1881, xxv. p. 108, jig. 16. 
 
 Specimen kindly lent by M. A. Fauvel. 
 
 803. Meloe violaceus ? : between rigbt eye and tbe base of the right antenna arise 
 two supernumerary antenna from the head. Of these one has 3 joints and the other 
 has one. Kraatz, Bent. ent. Zt., 1877, xxi. p. 57, PI. i.fig. 22. 
 
 804. 
 
 The following example is mentioned here, though its nature 
 is quite obscure. In it there is a suggestion that parts of two 
 extra antennae are present, but the extra parts seem to be peri- 
 pheral to the parts which they repeat. 
 
 As my stay in Rouen was short I was not able to give as much 
 time to this specimen as I should have wished \ 
 
 Melolontha vulgaris ^ : left antenna abnormal. This case 
 differs wholly from any other that I know of. I can only describe 
 it in a most tentative way. The appearance when the lamella' 
 were cleaned and separated was as shewn in Fig. 179. Joints 
 1 — 8 are fairly normal, but peripheral to this place there were 
 
 Fig. 179. Left antenna of Melolontha vulgaris, No. 804. The numbers air 
 set in tentative suggestion of the possible nature of the parts. (In Rouen Mas.) 
 
 1 This antenna was when I saw it covered with mould and dirt. In washing it 
 I accidentally detached it from the head, but I mounted it again carefully with the 
 specimen. 
 
524 MERISTIC VARIATION. [part i. 
 
 a number of lamellae, some like normal lamellae, others quite 
 irregular. As far as I could make out, the divisions were as 
 shewn in the figure, and I have affixed numbers to the several 
 parts in illustration of their possible nature. The appearance 
 suggests that there is an irregular repetition of a pair of clubs 
 peripheral to the normal antenna, but I can form no opinion 
 as to the morphology of the parts. Originally described by 
 MoCQUERYS, Col. an arm., 1880, p. 12, fig. [Description and 
 figure altogether misleading.] 
 
 Paired extra Palpi. 
 
 805. Bembidium striatum (Carabidae) : left maxillary palp arises by a 
 first joint enlarged towards its apex, bearing three separate terminal joints 
 instead of one. Of these joints one stands apart on a small process of 
 the first joint, but the other two are placed close together, on either 
 side of the apex of the first joint, and diverge from each other at about 
 a right angle. Jacquelix-Duval, Ann. Soc. Ent. France, 1850, Ser. 2, 
 viii. p. 533, Plate xvi. 
 
 806. Helops sulcipennis (Het. ): supernumerary, partially double 
 apical joint arises from the 2nd joint of right maxillary palp. It is 
 set on at right angles to the plane of the normal palpus. Jayxe, H. F., 
 Trans. Amer. Ent. Soc., 1880, viii. p. 1QI, jig. 14. 
 
 807. Euprepia purpurea (Arctiidse): a specimen in which the right wings and 
 antenna were male and the left wings and antenna female, is declared to have 
 possessed an extra pair of palpi. [No sufficient description of this extraordinary 
 occurrence is given; and as the repetition of the palpi is only incidentally mentioned, 
 it may be doubted whether a full examination was made.] Freyer, C. F., Beitr. 
 zur Schmetterlingshunde, 1845, Vol. v, p. 127, Tab. 458, Jig. 4. 
 
CHAPTER XXL 
 
 Appendages in Secondary Symmetry — continued. 
 
 The Evidence as to Crustacea 1 . 
 
 The facts as to Secondary Symmetries in Crustacea are so 
 similar to those already detailed in Insects that, were it not for 
 their value as confirmation of the principles indicated, it would 
 be scarcely necessary to describe them at large. Some few of 
 the cases have besides a special interest, as in them may be seen 
 rudimentary or bud-like structures apparently presenting the 
 lowest condition of paired parts in Secondary Symmetry. 
 
 Precisely as in Insects there are a number of cases (including 
 those last mentioned) where it would at first sight be supposed 
 that the extra parts are single, but on inspection most of them 
 prove double. Nevertheless there remain some few where this 
 cannot be shewn, and strange as it may seem, these must be 
 admitted to be genuine examples of duplicity of limbs. Of them 
 a special account will be given in another chapter. 
 
 There are besides, as in Insects, a considerable number of 
 cases in which the nature of the parts is not clear, though the 
 majority of such cases are not examples of extra parts, but are 
 normal appendages mutilated or deformed. 
 
 One specimen (No. 821) is the only case known to me in 
 which tivo pairs of supernumerary parts arise from one append- 
 
 a s e - 
 
 Another (No. 827) is unique in the fact that according to the 
 description three separate appendages are repeated upon a single 
 appendage. It is not clear that this is in any strict sense an 
 instance of Secondary Symmetry, but for convenience it is taken 
 in this chapter. 
 
 1 Useful bibliography given by Faxon, Harv. Bull., 1880—1, vm. p. 271. 
 
526 MERISTIC VARIATION. [part i. 
 
 Of the whole number, two affect antennas, four are in non- 
 ehelate ambulatory legs, one is in a chelate ambulatory leg and 
 the rest, being the great majority, are all in chelae. 
 
 With reference to these extra parts several false views have 
 from time to time been held. For example, in some of the 
 commonest cases there is an extra pair of dactylopodites, or of 
 indices, curving towards each other. The extra parts may then 
 greatly resemble the dactylopodite (or " pollex ") and index of 
 a normal chela, and many authors have not unnaturally supposed 
 that the extra parts were actually an extra pair of forceps re- 
 peating those of the normal chela. This may easily be shewn 
 to be an error, from the fact that it is often possible by some 
 slight structural difference between the pollex and the index to 
 detect that both extra parts are either both pollices or both 
 indices. 
 
 But the fullest disproof of this supposition is found in the 
 fact that the great majority of the phenomena will be readily 
 seen to conform to the principles enuntiated for Secondary Sym- 
 metries in Insects (p. 479). 
 
 A good many authors from the time of Rosel vox Rosexhof 1 
 onwards have said that these cases are a result of injury, or of 
 regeneration after injury. For this belief I know no ground. 
 It should be remembered as an additional difficulty in the way 
 of this belief, that when the limb of a Crab or Lobster is injured 
 it is usually thrown off bodily, while the extra parts most often 
 spring from the periphery of the chela. But since, according to 
 Heixekex 2 , such mutilated parts are sometimes retained, this 
 must not be insisted on. 
 
 In the case of an ambulatory leg the surfaces may be named 
 as in an insect (without any suggestion that these names denote 
 true homologies between the surfaces so named). In describing 
 chelae I propose to use the following arbitrary terms. The border 
 upon which the dactylopodite articulates is the pollex-border, the 
 opposite border being the index-border. It should be noted that 
 in the Crab the pollex-border is superior, but in a Lobster 3 it 
 is internal. 
 
 (1) Clear cases of Extra Parts in Secondary Symmetry. 
 
 A. Legs. 
 
 *808. Palinurus vulgaris : left penultimate ambulatory leg bore 
 two supernumerary legs (Fig. 180). Coxopodite of great width. 
 The basipodite had three articular surfaces as shewn in Figure 180, 
 
 1 Eosel von Rosenhof, Insekten-Belustigung ', 1755, in. p. 344. 
 
 2 Heineken, Zool. Jour. 1828—29, iv. p. 284. 
 
 3 It is worth noticing that in the chela of a Scorpion though a close copy 
 of that of a Decapod, the arrangement is reversed, the articulated pincer being 
 external. 
 
chap, xxl] SECONDARY SYMMETRY : CRUSTACEA. 
 
 527 
 
 each bearing a complete leg. When seen by me the leg marked L' 
 was lost. 
 
 Normal tytl 
 
 Fig. 180. Palinurus vulgaris, No. 808. Left penultim ate walking leg. (After 
 
 Leger.) 
 
 * 
 
 I could not quite satisfy myself as to which of the three was 
 the normal, but it was clear that R' was in form a right leg and 
 that the other two were lefts. If the leg L' is the normal, it 
 has been pushed out of place by a pair of extra legs in Posi- 
 tion DAA, but if R' and U be the extra legs, then the most 
 anterior leg is the normal and has been pushed out of place by a 
 pair in Position VPP. For an opportunity of examining this 
 specimen, I am obliged to the courtesy of Prof. A. MlLNE EDWARDS. 
 Originally described and figured by Leger, M., Ann. Sci. Nut., 
 ZooL, 1886, S. vii. I, p. Ill, PI. 6. 
 
 809. Lithodes arctica : 2nd leg on right side has terminal joint as 
 shewn in Fig. 181, II. If E be the normal then K and L are a pair in 
 Position Y, but if B! be the normal then R and L' are a pair in Position 
 D. Attention called to the sreat diminution in size of all three termi- 
 nations as compared with the normal (Fig. 181, I). Original description, 
 Herklots, J. A., Bijdr. tot J. h. Genootsch. Sat. Art is Mag., 1852, iv. 
 p. 37, PI. ; repeated Arch, neerl., 1870, v. p. 410, PI. xi. 
 
 810. Cancer pagurus : last left leg closely like last case [in Position 
 D]. Richard, Arch. Zool. exp., 1893, p. 102, fy. 
 
 811. Carcinus maenas : 2nd amb. leg as in Fig. 181, III. A pair of 
 
528 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 compounded extra points in Position J). Duns, Proc. jR. PJiys. Soc. 
 Edin., ix. p. 75, PL 
 
 Fig. 181. I. Lithodes arctica, normal terminal joint of ambulatory leg. 
 II. Second right leg of No. 809. (Both after Herklots.) III. Carcinus mcenas, 
 No. 811, second ambulatory leg. (After Duns.) P, normal terminal point. P', 
 P", extra terminal points in Position D. 
 
 B. Chelate Appendages. 
 
 (a) Two extra dactylopodites and double extra index. 
 
 812. Eriphia spinifrons $ : specimen of unusually large size, 
 normal but for left chela shewn in Fig. 182, I and II 1 . The 
 chela bore normal left dactylopodite, LD, and index, LI ; also, 
 upon pollex-border the structures shewn. These consisted of two 
 dactylopodites, R'D, L'D, working opposite each other on a com- 
 pounded double index, R'l\ L'l, which had two toothed borders, 
 one for each of them. This is therefore a pair of chelae repeated 
 in Position D [if indeed the dactylopodite mark the dorsal surface]. 
 Taken from Herklots, Arch, neerl., 1870., v. p. 412, PL XI. 
 
 1 In connexion with this case Herklots states that the rt. chela in the normal 
 is the larger and otherwise differs from the left (1 in 8 being reversed in this 
 respect). It does not seem from the figure that there was such differentiation 
 between the extra pair, but in future cases this point should be looked for. 
 
chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA. 
 
 529 
 
 813. Astacus fluviatilis : about 3 years old according to Sou- 
 beiran's (Camp. Rend. 1865, lx. p. 1249) account. Right chela ap- 
 parently deformed by injury or disease. Left chela had all normal 
 
 Fig. 182. I and II. Eriphia spinifrons, No. 812. I. A view of the left chela. 
 II. An enlarged view of the extra parts from the other side. LD, LI, normal lift 
 dactylopodite and index. R'D, L'D, right and left extra dactylopodites. R'l, LI, 
 right and left extra indices not separated from each other. (After Herklots.) 
 
 III. Cheliped of Homarus americanus, No. 811. (After Faxon.) I), I. normal 
 dactylopodite and index. D', D", extra dactylopodites. I', I", perhaps an 
 indication of double extra indices. 
 
 IV. Astacus fluviatilis, No. 813, left chela. L, normal left dactylopodite. 
 R'D, L'D, right and left extra dactylopodites. L'l + R'I, left and right extra 
 indices not separated from each other. (After Maggi.) 
 
 parts and in addition the structure shewn in Fig. 182, IV upon the 
 pollex-border of propodite. Here was a boss, separated by a 
 groove. It was observed that the structure was that of a rt. 
 and 1. dactylopodite working upon a double index [as in last 
 case]. Structure of muscles, fully described, was also in agree- 
 ment with the view that the extra parts were a complementary 
 
 B. 
 
 3-1 
 
530 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 814 
 
 815. 
 
 pair [similarly in Position D]. Maggi, L., Rend. R. 1st. Lomb., 
 1881, xiv. p. 333,^5. 
 
 Homarus americanus : small cheliped as shewn in Fig. 182, 
 III. It bears normal dactylopodite (D) and index (7), but this 
 part is bent almost at rt. angles. From the outer angle arise 
 the parts shewn. Apparently U and D" are a complementary 
 pair of extra dactylopodites in Position D. The piece I' + I' 
 is not described ; from the figure it seems possible that it may 
 represent parts of the indices proper to D' and D". Case given by 
 Faxon, Harv. Bull, 1880—1, vm. p. 261, PI. II. fig. 2. 
 
 Cancer pagurus : right chela as shewn in Fig. 183. This is a case 
 of some complexity. The figure will best make it clear. The dactylo- 
 podite D' is single and so also is the index P. D is a double dactylo- 
 podite, and F having teeth on two sides may be judged to be a double 
 index. But if D' and P are the normal chela they each stand opposite 
 
 Fig. 183. Cancer pagurus, No. 815. Eight chela seen from the apex, and 
 from the outside. The lettering is arranged on the hypothesis that 1)' is the 
 normal dactylopodite, P the normal index. D, the double extra dactylopodite, 
 P', small double extra index. (From Proc. Zool. Soc.) 
 
 the pincers to which they do not belong. Nevertheless I see no other 
 interpretation possible. (This case is curiously like that of the tarsal 
 claws in Rhizotrogus No. 786.) Specimen incorrectly described by 
 myself, P. Z. S., 1890, p. 581, fig. 2. C. 
 
 816. Cancer pagurus : right chela in a condition not far removed from r 
 that of the last case, le S£n£chal, Bull. Soc. Zool. France, 1888, p. 123, 
 
 figs- 
 
 817. Uca una: a chela having complex repetition of parts somewhat 
 
 as in No. 815. Jaeger, G., Jahresh. d. Ver. vaterl. JVaturk, 1851, xvn. 
 
 p. 35, PL i. figs. 12 and 13. 
 
 Perhaps of this nature is the case in Astacus fiuviatilis, Eoesel v. Kosenhof, 
 Ins.-Belust., in. Tab. L.x.fig. 28. 
 
 (b) Two extra dactylopodites arising from normal dactylo- 
 podite. 
 *818. To this and the next division belong the great majority of 
 
chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA. 
 
 531 
 
 cases of repetition of parts in Crustacea. Including examples 
 recorded by various authors and specimens in different Museums 
 there are nearly fifty cases of this class known to me. 
 
 Indjpx 
 
 Fig. 184. Three cases of two extra dactylopodites arising from a normal 
 dactylopodite. I. Left chela of Carcinus mamas in Brit. Mus. II. Left chela of 
 C. mcenas after Lucas, Ann. Soc. ent. France, S. 2, n. p. 42, PL I. Jig. 2. III. Right 
 chela of Homarus, after van Beneden, Bull. Ac. Belg., S. 2, xvn. p. 371. 
 
 Fig. 185. Cancer pagurus. Two chela? of the kind specified in No. 818, 
 described by myself in Proc. Zool. Soc, 1890, p. 581, whence figs, are taken. 
 
 34—2 
 
532 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 The various simple forms taken are illustrated by the eight 
 cases shewn in Figs. 184, 185 and 186. It will be seen that when 
 such extra processes arise on the toothed border of the dactylo- 
 podite they turn their smooth borders to each other, but when 
 
 819 
 
 Fig. 186. Homarus americanus. Three chela whose dactylopodites bear double 
 extra dactylopodites. I. A left. II. A left. III. A right. R, normal right. 
 L, normal left. R', extra right. L\ extra left. (From Faxon.) 
 
 they arise on the smooth border they turn their toothed borders 
 to each other, thus fulfilling the conditions of the Scheme given 
 at p. 481. Though from the close agreement between the three 
 prongs in some of the specimens it is not always possible to 
 tell the normal dactylopodite with certainty, it will be seen that 
 in these the rules hold whichever of the two possible prongs be 
 supposed to be the normal. 
 
 Astacus leptodactylus : left chela has dactylopodite as 
 shewn in Fig 187, II. Presumably D is the normal pushed out 
 of place, and D' and D" are the two extra dactylopodites. They 
 are so placed that none meets the index. Karoli, J., Term. 
 Filzetek, 1877, i. p. 53, PI. II. 
 
chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA, 
 
 533 
 
 7? 
 
 I Jl 
 
 Fig. 187. I. Cancer pagurus, No. 820, right chela. Specimen in Coll. Surg. 
 Mus. II. Astacus leptodactylus, left chela, after Karoli. 
 
 820. Cancer pagurus : somewhat similar case in rt. chela (Fig. 187, 
 I) ; but here the normal, R, stands in its normal place. In Coll. 
 Surg. Mus. 
 •821. Homarus americanus : dactylopodite only of right chela 
 preserved. It is bent sharply downwards, out of the plane of 
 the " hand," and bears upon its upper surface two pairs of blunt, 
 toothed processes [probably being rudiments of two pairs of extra 
 dactylopodites]. Faxon, I.e., p. 261, PL II. fig. 1. 
 
 822. Homarus americanus : dactylopodite {a) bent upwards and 
 outwards, crossing index without meeting it (Fig. 188). From 
 the smooth border of dactylopodite arise two toothed processes 
 
 Fig. 188. Homarus americanus, No. 822, left chela, a, normal point of 
 dactylopodite. b, c, extra points. (After Faxon.) 
 
 (b and c) curving towards index. [I take it that this is some- 
 thing like the cases of Position A in Insects (p. 4M) but from 
 the original figure the relations cannot be quite decided.] Faxon. 
 I.e., p. 260, PI. I. fig. 15. 
 
534 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 (c) Two extra indices arising from a normal index. 
 *823. This again is a fairly common form, though much less frequent 
 
 pi 
 
 Fig. 189. I. Right chela of Homarus americanas. R', L', right and left extra 
 indices not separated from each other. (After Faxon.) II. Homarus vulgaris, 
 right chela in Brit. Mus. III. H. vulgaris, right chela bearing extra double index. 
 R' and L', not separated. (After Lucas, I. c.) 
 
 R' V 
 
 i. n 
 
 Fig. 190. I. Left chela of Carcinus mcsnas, indices only shewn, d, place of 
 articulation of dactylopodite. In Coll. Surg. Mus. II. A similar case in 
 Homarus americanus, after Faxon. L, normal left index. R', L' y extra right and 
 left indices. 
 
chap, xxi.] SECONDARY SYMMETRY [ CRUSTACEA. 
 
 535 
 
 than the last. The cases known to me amount to about ten 
 or fifteen. Seven cases are illustrated in Figs. 189, 190, and 191. 
 
 Fig. 191. Two cases of extra indices in Cancer pagurus. I. In Coll. Surg. 
 Mus. II. After le Senechal. R, normal right index. L, normal left. R', L', 
 extra rights and lefts. 
 
 (d) Simple processes, probably being rudimentary extra pairs 
 
 of indices or of dactylopodites. 
 
 *824. Many such are described, but of 
 few can anything be said with confid- 
 ence. A comparatively simple case 
 is shewn in Fig. 19:2, where there is 
 a decided suggestion that the process L' 
 + R' is morphologically a pair of indices 
 that have not separated from each other 
 but stand compounded by their toothed 
 borders. On comparing this case with 
 for instance, Fig. 191, II, it will be seen 
 that the two conditions might readily 
 pass into each other in the way so often 
 seen in Insects. 
 
 Other cases of a more doubtful cha- 
 racter are shewn in Fig. 193. Though 
 in each the nature of the extra part is 
 obscure, it is probable that they are all 
 rudimentary states of the repetitions 
 described. The alternative view that 
 
 they are single repetitions certainly can- 
 
 ,i i- j . n £ • ' ji„ mu puber from le Senechal. Bull. 
 
 not be applied to all, for m many the Soc / XlluL ,,,.„„,,, l88 8, m... p. 125. 
 
 extra process, though in the plane ot the L , normal index. L' + ll\ ?pair 
 
 index and dactylopodite, is similar on of extra indices in Position V. 
 
 Fig. 192. Left chela of Porta- 
 
536 
 
 MEKISTIC VARIATION. 
 
 [part I. 
 
 m 
 
 Fig. 193. I. Eight chela of C. pagurus in Coll. Surg. Mus. E, right index. 
 II. Similar specimen whose dactylopodite bears x, a supernumerary process. In 
 Coll. Surg. Mus. III. Astacus fluviatilis, left chela bearing ,r, a supernumerary 
 process. EI, ED, right index and dactylopodite. (After Lucas.) 
 
 both its faces in this plane. There is however no doubt that the 
 distinction between these cases and true duplicity is hard to trace 
 and possibly enough it is not really absolute. 
 
 825. -A- s eac h case differs from the others I give a list of those not in private col- 
 lections 1 . The ? indicates that the case perhaps approaches the condition of 
 true duplicity. 
 
 D, dactylopodite. I, index. 
 
 Tiedemann, Meckel's Arch., 1819, v. p. 127, 
 PL u. Jig. 2. 
 
 Jaegek, G., Jahresh. Ver. vaterl. Naturk., 
 1851, xvn. p. 35, PL i. fig. 7. 
 
 id., Meckel's Arch., 1826, p. 95, PL n. fig. 3. 
 
 Eosel v. Eosenhof, Ins.-Belust., in. p. 314, 
 fig. 31. 
 
 ibid., fig. 30. 
 
 Lucas, Ann. soc. ent. Fr., 1814, Ser. 2, n. 
 p. 45, PL i. fig. 6. 
 
 Faxon, Harv. Bull., vm. p. 259, PL i. fig. 11. 
 
 ibid., PL i. fig. 6. 
 
 Eichard, Ann. sci. nat., 1893, p. 106. 
 
 Coll. Surg. Mus. 
 
 Coll. Surg. Mus. 
 
 E, right. L, 
 
 left. . 
 
 Astacus fluviatilis 
 
 EI 
 
 ? A. fluviatilis 
 
 EI 
 
 A. fluviatilis 
 A. fluviatilis 
 
 LD 
 EI 
 
 '.' A. fluviatilis 
 A. fluviatilis (Fig. 193, in.) 
 
 LI 
 LI 
 
 Homarus americanus 
 H. americanus 
 '? Cancer pagurus 
 C. pagurus (Fig. 193, i.) 
 C. pagurus (Fig. 193, n.) 
 
 LI 
 
 ED 
 LD 
 LI 
 LD 
 
 (e) Exceptional Gases. 
 
 *826. Homarus americanus : Right chela. Meropodite sub- 
 cvlindrieal instead of flattened ; peripherally divides into two 
 parts each bearing an articulated appendage as shewn in Fig. 194. 
 [The appendage R is a normal chela. What is B! + 1/ ? Faxon, 
 carefully describing the case, thinks that R! + U is a rudimentary 
 and reversed copy of R, and that the case is one of duplicity. 
 But from the particulars given, and especially from the circum- 
 stance that the carpopodite was " much more spiny ,; than the 
 normal, I think it likely that R' + U is morphologically a double 
 structure formed of a pair of carpopodites compounded together. 
 
 1 With these may perhaps be mentioned the following : Apus cancriformis, 
 having upon the 40th foot a second small flabellum shaped like the normal flabellum. 
 The bract was greatly reduced in size. Lankestek, E. E., Q.J. M.S., 1881, xxi. p. 
 350, PL xx. fig. 12. [In explanation of Plate the abnormal foot is called the 30th.] 
 
chap, xxi.] CRUSTACEA : EXCEPTIONAL CASES. 
 
 537 
 
 Without having seen the specimen it is impossible to say much, 
 but the parts should be examined with a view to this possibility. 
 I conceive that the large spine marked by Faxon &p' stands on 
 
 1B' + L' 
 
 Fig. 194. Homarus americanus, No. 826. A right chela. (After Faxon.) 
 
 the morphologically middle line between the two extra half- 
 
 meropodites.] Faxon, Harv. Bull VIII. p. 262, PI. II. fig. G. 
 
 *827. Astacus fluviatilis $ : large adult. /. 
 
 Abdomen wide in comparison with 
 
 slender chelae: otherwise normal except 
 
 left chela. This was formed as in Fig. 
 
 195. All normal except carpopodite, 
 
 from which arose a fixed piece seeming 
 
 to be an extra misshapen carpopodite, 
 
 bearing three extra chelce, L', R and x. 
 
 [R! and L' are a clear pair of images L' 
 
 being right and left respectively. But 
 
 between R' and the normal L there is 
 
 the third extra chela x. As to the 
 
 nature of this nothing can be said. 
 
 Whether it is a left or a right cannot 
 
 be told from fig. So far as I know, Fk;. 195. A$tacu» fluviatilis $Ho. 
 
 this case is unique. Full description 82 ?, 1(,ft chela. /.. the normal. 7/ . 
 on j w,^nm,^,.^v,4.„ • • • • i L>', presumaMv extra right and lelt 
 
 and measurements given in original, oh ^ *, exta-a chela of uncertain 
 
 q. V.] CANTONI, Rend. R. 1st, Lomb., nature. (After Cantoui.) 
 
 1883, xvi. p. 771,^. 
 
538 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 C. Antenna}. 
 
 *82S. Palinurus vulgaris : right antenna bore three complete 
 filaments. So far as last spiny joint (merocerite) normal. Of 
 this joint the peripheral portion 
 much enlarged, presenting two 
 articulations. The most posterior 
 bore a normal carpocerite and fila- 
 ment (Fig. 196, 1). The anterior 
 articulation bore a double carpo- 
 cerite with two filaments (II and 
 III). As author points out, II is 
 structurally a left antenna. [By 
 the kindness of M. Alphonse Milne 
 Edwards I have been allowed to 
 examine this specimen. I am not 
 sure that I succeeded in correctly 
 determining the surfaces of the 
 extra antennae, for the basal parts 
 were not veiy fully formed ; but 
 according to my determination 
 
 their relations differed markedly „,«„„., . , 
 
 r ,1 r f»j_i o l- j.* Fig. 196. Proximal parts of the right 
 
 from those of any of the Schematic antenna of Pa Unurm vulgaris, No. 828. 
 
 positions, for while the position I, the normal. II, extra left. Ill, extra 
 of origin is VVA the two extra ri g ht - ( After L eg er 
 antennae stand very nearly in the Position DA.] 
 sci. nat, ZooL, 1886, S. 7, i. p. 109, PI. 6. 
 *829. Astacus fluviatilis : exopodite of left 
 antenna (Fig. 197) bears two supernumerary 
 points, R' and L', which seem to have been 
 inserted upon the internal border of the 
 normal exopodite. Stamatt, G., Ball. Soc. 
 Zool. France, 1888, xm. p. 199,^. 
 
 Amorphous Cases. 
 
 As has been stated, there are many cases, 
 recorded or preserved, in which the nature of 
 the parts cannot be made out. The majority 
 of these are, I believe, injured or deformed 
 limbs, and not cases of repetition of parts. 
 
 Nevertheless of the latter class there are un- tiUs paving extra points to 
 
 , exopodite of left antenna. R, 
 
 doubtedly some amorphous cases, though they normal right. L, normal left. 
 
 are far less common than regular ones, even R', L', extra right and left. 
 
 as normal structures are more common in their (After Stamati.) 
 
 regular shapes than in a deformed state. I mention the following as 
 
 being, I think, the earliest record of abnormalities of this class. 
 
 830. Homarus : left chela having irregular process on inner border of 
 
 dactyl opodite, and two irregular processes on inner border of index. 
 
 [No description.] Bernhardus a Berniz, Miscell. Curios., Jena, n. 
 
 1671, p. 175, Obs. ci. PI. 
 
 L£ger, A 
 
 nn. 
 
 
 Fig. 197. Astacus fiuvia- 
 
CHAPTER XXII. 
 Duplicity of appendages in Arthropoda. 
 
 That there should be such a thing as a limb double in the 
 sense in which the following are double, has always seemed to 
 me most strange. We know that a segment of an Annelid, or 
 a vertebra, may be on one side of the body divided to form 
 two segments or two vertebrae (as in No. 88 or No. 7) while 
 on the other side of the middle line the segment is single. This 
 is in keeping with all that we know of Division of parts in Linear 
 Series. So might we suppose that a parapodium, or a rib, or 
 perhaps a limb-bud might divide into two ; but the two half- 
 segments or half- vertebrae are in Succession to each other, and 
 are not complementary images of each other as these double- 
 limbs are. 
 
 That a parapodium may divide into two Successive para- 
 podia is possible enough, though, apart from division of the 
 segment bearing it, I know no clear case. But it may be stated 
 at once that in Arthropods and Vertebrates such a phenomenon 
 as the representation of one of the appendages by two identical 
 appendages standing in Succession is unknown. No right arm 
 is ever succeeded on the same side of the body by another arm 
 properly formed as a right, and no Crustacean has two right 
 legs in Succession, w T here one should be. The only cases at all 
 approaching this state are those of Macacus No. 504 (q. r.), a case 
 that must be interpreted with great hesitation ; and of the Frogs 
 described by Cavanna and by Kingslev, also doubtful cases 
 (see Chapter xxm). 
 
 But though such repetition is probably unknown and is perhaps 
 against Nature, there are still these strange double-limbs: fcwo 
 limbs, always I believe imperfect, placed not in Succession, but as 
 complementary images of each other, more or less exact. These 
 we have seen in the hand of Man and in the feet of Artiodactvles; 
 we have now to study them in Insects and in Crustacea 1 . 
 
 1 With mistrust I name cases in Amphibia and Fishes, perhaps of tin's nature. 
 Lissotrjton punctatus (Newt): left pes having 10 digits in two groups, ('» and 4. 
 Coll. Surg. Mas., Ter. Sei\. 293, a [not dissected]. Protopterus annectens : rt. 
 
540 MERISTIC VARIATION. [part i. 
 
 On the morphology or significance of duplicity in limbs I can 
 make no comment beyond the few remarks given on p. 406. 
 It is just possible that in Nos. 832 to 834 the duplicity of the 
 chela or of the index is a division in the middle line of a Bilateral 
 Minor Symmetry ; for some chelae are peripherally very nearly 
 symmetrical about the plane of the dactylopodite and index. 
 
 In Arthropods double-limbs are no less rare than in Vert- 
 ebrates, for though in various works there are some scores of 
 cases to be found, the great majority may be safely rejected as 
 being almost certainly cases of double extra parts in Secondary 
 Symmetry having their duplicity disguised as we saw it in 
 Nos. 750, 764, or 801. By most of those who have dealt with 
 these things the possibility of disguised duplicity in the extra 
 part has been unheeded ; and ignorant of the special difficulties 
 of these cases they have thus set down specimens as examples 
 of duplicity of appendages at a casual glance. For this reason 
 therefore I shall only give particulars of those few cases which 
 are better established or otherwise of special interest, letting the 
 rest follow as a list of references. 
 
 It will not be forgotten that whenever an extra part is in 
 itself symmetrical it always may be a double structure, and the 
 special application of this fact to cases of extra filamentous an- 
 tennas must in particular be borne in mind. 
 
 Crustacea. 
 
 *831. Hyas araneus : a left chela having the form shewn in 
 Fig. 198, II and III. Fig. 198, I shews a normal left chela of 
 this species from the outside in the same position as II. In 
 the abnormal specimen the dactylopodite D is normal save that 
 
 pectoral fin double, the division being in a horizontal plane, so that the two filaments 
 
 were dorsal and ventral to each other [cp. No. 503]. Albrecht, Sitzb. Ak. Wiss. 
 
 Bed., 1886, p. 545, PL vi. Silurus glanis : extra fin attached to pelvic girdle and 
 
 partly to rt. pelvic fin. Warpachowski, Anat. Anz., 1888, in. p. 379, fig. Rana 
 
 esculenta : left hind foot double ; rt. not seen [a very clear case]. Ercolani, 
 
 Mem. Ace. Bologna, 1881, S. 4, in. p. 812, PI. iv.fig. 11. ' 
 
 In Kaiidae a group of cases of extra fin are known. They are upward projections 
 
 from the dorsal surface near the middle line. They are often spoken of as " dorsal ' : 
 
 7902 
 fins, but in the only case I have seen (Paris Mus. N. H., —^ , kindly shewn me by 
 
 Prof. L. Vaillant) the attachment is not really median but is slightly oblique, and 
 seems, from external examination, to spriug from some part of the pectoral girdle 
 ('? left scapula). See Lacepede (who named such a fish "Raja cuvieri"), Hist. not. 
 des Poiss., 1798, i. p. 141, PL vn.; Neill, Mem. Wern. Soc., 1808, i. p. 554; 
 Moreau, Poiss. de la France, 1881, i. p. 206. In these fishes the real dorsal fins 
 were in the proper place (though in some species they may be far forward, Forskal, 
 Descr. Anim. in itin. Orient., 1775, i. p. 18). This repetition is of course quite 
 distinct from that other curious and also Discontinuous variation in which the 
 pectorals are partly divided into two lobes (R. clavata, Yarrell, Brit. Fish., eel. 
 Richardson, 1859, ii. p. 585) ; or are separated from the head so as to project like 
 horns on either side, as in last case ; and also in R. clavata, Yarrell, ibid. ; p. 384 ; 
 Day, Brit. Fish., n. p. 345, PL clxxi. fig. 2; in R. batis, Day, l. c., p. 337; in 
 R. asterias, Bureau, Bull. soc. zool. France, 1889, xiv. p. 313, fig. 
 
chap, xxn.] DOUBLE APPENDAGES : ARTHROPODA. 
 
 541 
 
 its point is rather worn. Where the index should be, there is 
 a great eminence, bearing apically a second articulated dactylo- 
 podite D\ complementary to D. Between the two dactylopodites 
 
 Fig. 198. Hyas araneus. I. A normal left chela. II. The left chela of 
 No. 831 from the outside. III. The same from the inside. D, normal dactylo- 
 podite. D', extra dactylopodite. j, normal index, f, a small index toothed on 
 both sides. (In Brit. Mus.) 
 
 at the inner side of the eminence there is a fixed short process, 
 j', which is toothed upon both the edges which it presents to 
 the two dactylopodites. Round the articulation of 1)' are setae 
 like those round the place of articulation of D. Specimen in 
 Brit. Mus., kindly shewn to me by Mr R. I. Pocock. 
 
 832. Cancer pagurus : right chela. 
 Dactylopodite and index each double 
 in the way shewn in Fig. 199. Each is 
 toothed on the side presented to the 
 other half-pincer. Note that there is 
 no proof that one or other of these 
 points is not a pair compounded in 
 Position A or P, but since both seemed 
 equally to diverge from the normal plane 
 of the propodite this is most unlikely. 
 Specimen in Museum of Newcastle- 
 upon-Tyne. 
 
 833. Homarus americanus : right chela 
 shewn in Fig. 200, I. Two dactylo- 
 podites separately articulating. Index 
 bifid at apex and bearing two rows of 
 teeth, one on each edge. Dactylopod- 
 ites did not meet index. Faxon, Harv. 
 Bull, vin. p. 260, PL I. fig. 13. 
 
 834. ? Hyas sp. Right chela. Dactylopodite single and in normal 
 plane. Two separate and similar indices, each toothed as usual, 
 
 Fig. l'J'.l. Ki-ht i-h. hi of 
 Cancer pagurus, No. 832. I>\ 
 D 2 , two partially Beparate 
 dactylopodites. I 1 , 1-, two 
 partially separate indices. (In 
 Newcastle Mus.) 
 
542 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Fig. 200, I. Homarus americanus, right chela, No. 833. (After Faxon.) 
 II. Lupa dicantha, left chela, No. 836. LI), LI, left dactylopodite and index. 
 x, supernumerary index. (After Lucas.) 
 
 making angle of about 45° with each other. This angle almost 
 exactly bisected by the plane in which dactylopodite moves. 
 Bell Collection, Oxford. 
 
 835. Maia squinado : from inner side of base of 
 index of right chela arises a second index as 
 shewn in Fig. 201. It is about half as large as 
 the supposed normal index. The latter is dis- 
 placed outwards. Dactylopodite moves in ap- 
 proximately normal plane, missing both indices 
 and falling between them. Specimen kindly lent 
 by Prof. C. Stewart. 
 
 Fig. 201. Right chela of Maia squinado, No. 835. 
 The following are cases very similar to Nos. 834 and 835. 
 
 836. Lupa dicantha, left chela (Fig. 200, II). Lucas, Ann. Soc. eat. 
 ' France, 1844, S. 2, II. p. 43, PI. i. fig. 1. 
 
 837. C. pagurus, right chela, 2 cases, le Sknechal, Bull. Soc. Zool. 
 France, 1888, xm. p. 125, Jig. 2. 
 
 838. Xantho punctulatus, left chela (Fig/ 202) in which the index 
 divided at about its middle to form two similar and equally diverging 
 blunt processes. Herklots, Arch, neerl, 1870, v. p. 410, PI. x. 
 
 839. Homarus americanus : right chela bearing an extra index. 
 Dactylopodite does not meet the normal index. [Very doubtful if of 
 same nature as foregoing cases.] Faxon, I.e., PL I. fig. 14. 
 
 The following cases are exceptional. 
 
 840. Homarus vulgaris : right chela has coxopodite single ; but basi- 
 
chap, xxil] DOUBLE APPENDAGES : ARTHROPODA. 
 
 543 
 
 Fig. 202. Xantlw punctulatw. Two views of left chela of No. 838, shewing the 
 division of the index. (After Herklots.) 
 
 podite is wrinkled and has two apical articulations, each bearing a small 
 chela ; both are soft and not calcined, having articulations indicated 
 by furrows only. [No information as to planes.] Richard, Ann. Sci 
 Nat., 1893, p. 106. 
 
 841. Homarus americanus : right chela having a short articulated 
 process below the dactylopodite moving in plane at right angles to it. 
 [?a double structure]. Faxox, Haw. Bull., viii. PI. i. fig. 12. 
 
 842. H. americanus : toothless process articulating beloiv dactylopo- 
 dite, moving in plane at right angles to its plane of motion. It articu- 
 lates upon a separate process given by the propodite. [It is difficult 
 to suppose that this extra process can be double.] Faxon, I. c , PI i 
 fig. 16. 
 
 Mr G. Dimmock of Canobie Lake, N. H. has kindly sent rue word of a Gelasimus 
 having a chela of very anomalous form. Both index and dactylopodite are said to 
 have been bifid, but the plane of division was at right angle* to the plane of the 
 dactylopodite and index, so that all four points were in one plane. This specimen 
 has unfortunately been destroyed ; but Mr Dimmock tells me that the arrangement 
 was certainly thus, and that the unusual difficulty of bringing this case into agree- 
 ment with others was recognized in examining it. 
 
 INSECTS. 
 
 Among the following 110 cases which all either have been 
 or might be called cases of " duplicity ,J of legs, antenna-, or 
 palpi, there is, I think, not one clear case of unmistakeable 
 duplicity, such as for instance those of the chela? in Nos. 831 
 or 832. They should thus be considered as cases in which bhe 
 extra parts have not been or cannot be shewn to be double, 
 rather than as examples of proved duplicity of normal appendag 3. 
 In every case that I have myself properly examined, it is either 
 possible to prove the duplicity of the extra parts; or else essential 
 features {e.g. spurs &c.) by which a right appendage may be 
 told from a left are wanting. Nevertheless the few straight- 
 forward cases of double-limbs in Crustacea k«-i-j» one alive to the 
 possibility that some of these also may be the same. The most 
 probable cases of true duplicity of limbs are Nos. 844, JS40 and 85 I . 
 
544 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 *843. 1. Legs. 
 
 Prionus californicus (Longic.) : each femur bore two tibiae 
 and tarsi : both maxillary palps and also the left labial palp were 
 partially double (Fig. 203). [No statement as to right labial 
 palp. This shewn in fig. much thicker than left, but on com- 
 
 S44. 
 
 Fig. 203. 
 Jayne.) 
 
 Prionus californicus, No. 843, having extra legs and palpi. (After 
 
 paring with a specimen it seems to be of normal thickness.] 
 In some of the legs the two tibise are compounded at their bases, 
 in others they articulate separately. [Several details given ; and 
 in particular, enlarged views of the palpi and of the bases of 
 the tibiae. But as no details are given regarding the apices and 
 apical spurs of the tibia3 nothing can be said as to symmetry. 
 
 It will be remembered that we have already had a case of 
 a Prionus, No. 750, which similarly was supposed to have two 
 of its legs double ; but there by means of the tibial spurs it was 
 shewn that the extra part was in Secondary Symmetry. Possibly 
 enough the same could here be shewn. It is much to be hoped 
 that this specimen can be traced.] Jayne, H. F., Trans. Anier. 
 Ent. Soc. y 1880, viii. p. 159, fig. 12. 
 
 Allantus sp. (Tenthred., Sawfly) : extra leg borne by coxa 
 of right middle leg. This coxa is imperfectly double, bearing 
 two separate trochanters. Of these the anterior bears a small 
 leg which, though ill formed, is complete in all its parts, but 
 has the tarsal joints of abnormally small size. The posterior 
 trochanter bears a leo; of full size. Its femur curves forwards 
 
 and then backwards. The femur of the smaller 
 
 
 curves 
 
 for- 
 
chap, xxil] DOUBLE APPENDAGES : INSECTS. 
 
 545 
 
 wards, but its tibia curves backwards. The femora are so twisted 
 that I failed to determine the symmetry of these 1<-l;s ; and while 
 it was clear that neither was a normal left it was equally doubtful 
 whether either was shaped as a right. Of all cases in Insects 
 this is one of the nearest to the condition of true duplicity. Hope 
 Collection, Oxford. 
 
 845. Carabus intricatus : middle right femur is partially bifid, pre- 
 senting two apices in the same horizontal plane. The anterior apex 
 bears a tibia and tarsus of nearly normal form. The other apex bears 
 a tibia and tarsus of full length but much more slender than a normal 
 one. This leg was ill-formed. The tibia bore no spurs, and there 
 was no indication as to its symmetry, and nothing shewed that it was 
 a right or a left leg. It is stated in the original description that the two 
 legs could be separately moved and that both assisted in locomotion. 
 Originally described by Mocquerys, Col. anorm., p. 45, ^y. 
 
 f 846. Melolontha vulgaris : right anterior leg divided to form two 
 legs. The femur dilates in peripheral third to form two apices, each 
 bearing a tibia. These two tibiae are at right angles to the femur and 
 are together in the same straight line, the one pointing forwards and 
 the other backwards, each tibia turning its ventral or flexor surface 
 towards the femur. The anterior tibia carries a tarsus of 4 joints 
 with claws, while the posterior tibia lias a normal tarsus of live joints. 
 For a figure of this specimen and particulars concerning it I am in- 
 debted to Professor Alfred Giard. 
 
 847. Leptura testacea (Longic.): in tarsus 
 of left middle leg the 2nd joint presents two 
 apices (Fig. 204). The posterior bears normal 
 3rd and 4th (terminal) joints with a proper 
 pair of claws. The anterior apex bears a 
 narrow 7 3rd and 4th joint, the latter having 
 only a single median claw [cf. No. 848]. 
 Kraatz, Deut. ent. Zt., 1876, xx. p. 378, 
 fig. 14. 
 
 848. Tetrops praeusta (Longic.) : right 
 anterior femur widened towards apex, which 
 presents two articulations in same horizontal 
 plane. Each of these bears a tibia. The post- 
 erior tibia and tarsus are complete in all 
 respects, but they flex downwards and back- 
 wards. The anterior tibia has a normally 
 4-jointed tarsus, but the apical joint bears 
 only one claw, and there is no sign of muti- 
 lation [cp. No. 847]. Were it not for the 
 closely similar case of Silis No. 764 there 
 would be no reason to doubt that this is 
 a true case of duplicity, but that example 
 
 shews how masked may be the doubleness of extra parts ; and though 
 I could not prove either of these legs to be double I feel no certainty 
 that one of them is not double. Specimen very kindly lent for descrip- 
 tion by Mr F. H. YVateruouse. 
 
 b. 35 
 
 Fig. 204. Leptura tes- 
 tacea, No. SIT. Tarsus of 
 left middle Leg from the 
 plantar surface. (The pro- 
 perty of Dr Kraatz.) 
 
546 MERISTIC VARIATION. [part i. 
 
 849. Chlaenius holosericus (Carab.): left anterior tibia enlarged and 
 dividing close to base into two branches of similar form and length 
 [curving towards each other], botli equally furnished with hairs and 
 bearing spines characteristic of the species. Anterior branch bears a 
 complete tarsus like that of a leg of the other side, but posterior branch 
 bears only one tarsal joint. Camerano, Atti Ac. Sci. Torino, 1878, 
 xiv. fig. 
 
 850. Brachinus crepitans (Carab.): 3rd joint of right posterior tarsus 
 enlarged ; 4th joint divides to form two apices (Fig. 205), each bearing- 
 separate 5th joint in same horizontal plane. Each of these has a pair 
 
 *.Q^ 
 
 Fig. 205. Eight hind foot of Brachinus crepitans, No. 850. A, anterior. 
 P, posterior. E, the supposed normal right apex. (In Rouen Mus.) 
 
 of claws curving ventralwards. The two apical joints are not identical, 
 the anterior being the shorter and continuing the general direction of 
 the tarsus. I could not determine the symmetry. When examined by 
 me the specimen was intact, but in cleaning it I broke this abnormal 
 leg. First described by Mocquerys, Col. anorm., 1880, p. 63, fig. 
 
 The two following cases differ from the rest in that the extra 
 leg arose from the body separately from the normal leg. Among 
 the cases of extra limbs in Secondary Symmetry were a few in 
 which the coxa of the extra limbs was in the same socket as 
 the coxa of a normal leg, though not united to it ; but in the 
 first, and perhaps in both of the two cases that follow, the extra 
 leg was wholly separate. The first case, No. 851, is the only one of 
 the kind that I have seen. 
 
 *»^ 
 
 851. Tenthredo ignobilis (Tenthred., Sawfly) : extra leg arising from 
 2?rothorax, on the left side of the body, at some distance behind the 
 proper left anterior leg. Behind the anterior legs the prothorax of a 
 normal specimen presents ventrally an elevation on each side of the 
 middle line ; the point of origin of the extra leg is about halfway 
 between this elevation and the socket of the coxa of the normal left 
 anterior leg. The specimen had been a good deal injured by being- 
 pinned very nearly through the point of origin of the extra leg, and on 
 relaxing the specimen and attempting to restore the parts to their 
 former positions I unfortunately broke off the extra leg from the 
 body 1 . The leg is fairly well formed, but is a little shorter and a good 
 
 1 The specimen has been mended as nearly as possible in the position originally 
 occupied by the leg. As it may pass hereafter into other hands, it may be well to 
 
chap, xxii.] SUPPOSED CASES OF DOUBLE LEG. 
 
 54' 
 
 deal more slender than the normal anterior leg. Owing to the slighl 
 degree to which the anterior legs of this insect are structurally differen- 
 tiated from the middle legs, it cannot be positively stated that the 
 extra leg is in form an anterior or a middle leg, but in size and general 
 conformation it approaches very nearly to that of an anterior leg. It 
 is complete in all its joints, having normal ciliation and claws, but the 
 spurs are entirely absent from the apex of the tibia and probably have 
 never been formed. This is an unfortunate circumstance; for, ina 
 much as the anterior spur of a normal anterior tibia in this specie- is 
 markedly differentiated from the posterior spur, it would have been 
 easy to determine the surfaces of this leg had the spins been present. 
 As it is, the matter cannot be positively decided, and it must sutlice to 
 say that the general form of the leg and the shape and curvat are of its 
 joints are such as to make it appear to be fashioned as an anterior leg 
 and as a leg of the side upon which it occurs, namely, the left. This 
 specimen was most kindly lent for description by Mr C. W. Dale, of 
 Glanville's Wootton, Dorsetshire. It is the specimen mentioned in 
 Ann. and Mag., 1831, iv. p. 21. 
 352. Elater variabilis (Elat.): complete extra leg articulating by 
 separate coxa close to right anterior leg. Germar, E. F., May. cU r 
 Ent., II. p. 335, PI. i. fig. 12. [This case has been copied by many 
 authors. The figures represent the right fore leg and the extra one as 
 normal right legs, but they are not sufficiently detailed to give con- 
 fidence that this was so. If the specimen still exists it is to be hoped 
 that it may be properly described.] 
 
 o ko This is a list of all remaining cases in which it is in any way possible that there 
 
 is duplicity of a leg. The point of origin is shewn approximately. 
 
 * , seen by myself. J, partly amorphous or mutilated. 0, no description. 
 
 R, right. L, left, tr., trochanter, f, femur, tb, tibia, ts, tarsus. 
 
 * % Osmoderma eremita 1 (Lamell.) L 1. c. 
 
 Mallodon sp. (Longic.) R 3. c. 
 
 Pasimachus punctulatus (Carab.) L 2. tr. 
 
 Broscus vulgaris (Carab.) R 1. tr. 
 
 Agonuxn sexpunctatum (Carab.) R 3. f. 
 
 % Carabus septemcarinatus £ R3. f. 
 
 J Carabus nemoralis L 3. f. 
 
 Carabus creutzeri ? L 1. f. 
 
 Procrustes coriaceus' 2 (Carab.) R3. f. 
 
 IVIeloe coriaceus (Het.) L 1. f. 
 
 Carabus helluo R 1. f. 
 
 Trichodes syriacus (Cleriche) R 1. f. 
 
 X Chrysomela haemoptera (Phyt.) ? 3. f. 
 
 1— ii. 
 
 Mocquerys, Col. anorm., 
 
 p. 40, fig. 
 ibid., p. 50, fig. 
 Jayne, Trans. Amer. Ent. Soc., 
 
 1880, yiii. p. 150, PI. iv. fig. I. 
 Imhoff, Ber. Vale nut. Get. 
 
 Basel, 1838, in. p. 3. 
 Schneider. Jahresb. scJdes. (?< -. 
 
 vaterl. Kultur, I860, p. L29. 
 Kraatz, Dent. cut. Zt., 1*77. xxi. 
 
 p. 57, PI. i.fig. 32. 
 Otto, Herm., Term.fuzetek, 1*77, 
 
 i. p. 52, PI. ii. 
 Kk.vatx, /. c, fig. 31. 
 MOCQUEBYS, /. «'., )'. ">■">. fig. 
 Staxnius, Mail. A n-li. . I wit.I'h >/■<.. 
 
 1835, i>. 3( >!'>,. //'.</. 11. 
 Rey, Ann. Soc. Linn. <l, Lyon, 
 
 1882, xxx. p. 123. 
 ibid. 
 Curtis, Brit. Ent., PI. 111,.//'//. 5*. 
 
 state explicitly that there was no conceivable doubt as to the genuineness of the 
 abnormality. When received by me it was absolutely natural an. I had not been in 
 any way mended. 
 
 1 Probably this is the specimen mentioned byBELLiER DB LA Ohavionebie, lUill. 
 Soc. ent. France, 1851, S. 2, ix. p. lxxxii. 
 
 2 See also Klingelhofer, Stet. cut. At., 1844, v. p. 330. 
 
 35—2 
 
548 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 Jayne, I.e., p. 157, PI. vr.fig. 7. 
 Krause, Stet. ent. Zt., 1871, 
 
 xxxn. p. 136. 
 Perty, Mitth. not. Ges. Bern, 
 
 1866, p. 307, fig. 6. 
 
 MOCQUERYS, I.C., p. iS,jig. 
 
 Kraatz, Dent. ent. Zt., 1877, xxi. 
 
 p. 56, PI. i. Jig. 11. 
 Otto, Herm., I. c., 1877, i. p. 52, 
 
 PI. ii. 
 Kraatz, Dent. ent. Zt., 1880, xxiv. 
 
 p. 344. 
 Mocquerys, I.e., p. 49, Jig. 
 Lent by M. H. Gadeau de Ker- 
 
 ville 1 . 
 Ragusa, Nat. Sicil., i. p. '281, 
 
 fig. 
 
 Lent by Dr Mason. 
 Mocquerys, I.e. , p. 60, Jig. 
 Ann. and Mag. N. H.,'l829, n. 
 
 p. 302, fig. 
 Bassi, Ann. Soc. ent. France, 1834, 
 
 S. 1, m. p. 375. 
 von Heyden, Isis, 1836, ix. 
 
 P. 761. 
 ibid. 
 
 X CMaenius diffinis (Carab.) L 2. tb. 
 
 Rhagium mordax (Longic.) R 2. tb. 
 
 Agabus uliginosus (Dytisc.) R 3. tb. 
 
 * J Acanthoderes nigricans (Longic.) L 2. tb. 
 
 Colymbetes adspersus (Dytisc.) <? L3. tb. 
 
 $ Procrustes coriaceus (Carab.) R3. tb. 
 
 J Carabus melancholicus <? R3. tb. 
 
 * £ Tenebrio granarius (Het.) L 3. tb. 
 
 * j Calosoma auropunctatum (Carab.) Rl. tb. 
 
 Silpba granulata (Clav.) R3. tb. 
 
 * Philonthus succicola (Staph.) R 3. ts. 
 
 * J Telephorus excavatus (Mai.) R 2. ts. 
 
 Chlacnius vestitus (Carab.) L2. ts. 
 
 Telephorus fuscus (Mai.) ? 2 ? 
 
 Prionus coriaceus (Longic.) ? 
 
 Prionus sp. (Longic.) ? ? f. 
 
 2. Antennae. 
 
 The remarks made in preface to the last section apply here 
 also, and with additional force from the consideration pointed out 
 (p. 513), that many antennae are without obvious differentiation 
 between their anterior and posterior surfaces. As Kraatz has 
 pointed out, it is especially in such forms as Lamellicorns or 
 Lucanidae that extra antennas are found double, and I think there 
 is an obvious inference that this greater frequency in them is due 
 to the fact that the two borders are so markedly differentiated 
 that the duplicity cannot easily be disguised. I have sometimes 
 fancied too that perhaps the existence of this great differentiation 
 between the two borders may actually contribute to the physical 
 separation of the two extra parts in the Positions A and P and 
 thus prevent that masking of the duplicity which is seen for 
 instance in Navosoma No. 801. 
 
 However this may be, special importance must be attached to 
 the few cases in Lamellicorns, Lucanidas and the like, where there 
 seems to be a single extra part, making that is to say a duplicity 
 of the antenna. Cases of this kind that I have myself seen I 
 therefore treat more fully, and it may be stated that in none of 
 them is there anything that can be called clear duplicity. In 
 many on the contrary the extra part is nearly cylindrical, and 
 thus symmetrical in itself. Hence it may possibly be morpho- 
 logically double. Of the remainder I can give no confident 
 account. For as has been said, though many, e.g., Zonabris 
 ^-punctata (in No. 858), do look very like cases of true duplicity 
 
 1 Originally described by Fleutiaux, Rev. d'Ent., 1883, p. 228. 
 
chap, xxii.] SUPPOSED CASES OF DOUBLE ANTENNA. 54'.) 
 
 I feel no certainty that they are so. Nothing but careful micro- 
 scopical examination can shew this, and it would in every case 
 be necessary to begin by fixing upon some definite character 
 differentiating the anterior from the posterior border in the 
 
 normal antenna. 
 
 In the majority of cases one of the branches has Less than the 
 normal number of joints. 
 
 Special attention is called to No. 854, for in it is seen not only 
 an extra branch, but an extra joint in the course of the chief 
 antenna. 
 
 N.B. At the end of this list I have set three cases of extra 
 antenna arising from the head. 
 
 *854. Lucanus cervus g (Lucanidae) : left antenna normal, practi- 
 cally same as that described for Odontoiatria No. 799. I light 
 antenna shews a rare condition. Scape and 2nd joint normal. 
 Then follows a piece as long as the 3rd, 4th and 5th joints of a 
 normal, together. This joint has a complex form. It has no trans- 
 verse division and is clearly one segment from base to apex, but 
 the posterior border is divided from the anterior by an irregular, 
 crescentic suture, giving it the look of two joints spliced together. 
 The posterior portion gives origin to a small, backwardly directed 
 branch made up of two nearly spherical joints, the apical having 
 a minute depression whence a fragment may have been broken. 
 
 The long third joint just described bears at its apex the rest 
 of the antenna, which is abnormal in structure and diverges a 
 little forward of the normal direction. In the normal there are 
 only 7 joints peripheral to the 3rd, making 10 in all: here 
 there are 8, making 11 in all. The four apical flattened joints 
 are normal, but the joint preceding them (7th in this antenna) 
 is more produced on the anterior border than in the normal, 
 and it is thus in form almost intermediate between a funicular <ni</ 
 a lamellar joint. The other three are simple funicular joints. 
 For this singular specimen I am indebted to the kindness of 
 M. Henri Gadeatj de Kerville. 
 
 855. Nigidius sp. (Lucanidae) New Guinea: the second joint of 
 the right antenna bears a small supernumerary three-jointed 
 branch directed forwards and upwards. The terminal joint of the 
 branch, which morphologically stands fifth from the body, bears 
 a long hair of the kind which is borne in the normal antenna only 
 by the seventh and subsequent joints. 
 
 There appears to be no deformation in the normal antenna in 
 correspondence with the presence of this extra branch. The (tui- 
 tion of the antenna with reference to the second joint is a little 
 altered, but it is not in any other way changed. This specimen 
 was kindly lent to me by M. Henri Gadeau de Kerville. 
 
 856. Lucanus cervus J* : the second (1st funicular) joint of the 
 left antenna bears a four-jointed, pointed filament. The lower 
 
550 
 
 MERISTIC VARIATION. 
 
 [part I. 
 
 parts of the head on the left side are also greatly deformed. 
 Vox Heydex, Deut. ent. Zt, 1881, xxv., p. 110, fig. 24. 
 
 857. Melolontha vulgaris (Lamell.) : from ventral surface of 
 2nd joint of left antenna a separate joint projects vertically down- 
 wards. This joint bears a forward ly-directed process which is 
 about as long as a normal club and is imperfectly divided into 
 lamellae. Nothing could be definitely determined as to the 
 symmetry of this structure. Originally described by MoCQUERYS, 
 Col. anorm., p. 22, Jig. 
 
 858. In this list * means that 1 have seen the specimen, $ that it is partly amorphous 
 or mutilated, that there is no description. The number is a rough indication of 
 the joint from which the extra part arose. 
 
 113. 
 
 * J Cicindela sylvatica (Cicind. ) 
 
 Cararid^e 
 
 Carabus sylvestris <? 
 
 C. auratus 
 
 ditto 
 
 ditto 
 
 C. italicus 
 
 C. exaratus 
 
 C. intricatus 
 
 C. emarginatus ? 
 
 C. cancellatus 
 
 C. catenulatus <? 
 Pterostichus planipennis ? 
 Procrustes coriaceus J 
 
 ditto ? 
 
 Harpalus calceatus ? 
 Calosoma sycophanta 
 C. triste 
 
 Anchomenus albipes 
 
 Mus. H. Gadeau de Keryille. 
 
 + 
 
 * A. angusticollis 
 Nebria sp. 
 Agonum viduum 
 
 J Ditomus tricuspidatus 
 
 Colymbetes coriaceus (Dytisc.) 
 
 Thylacites pilosus (Rhyn.) 
 
 * Rhynchitcs germanicus (Rhyn.) 
 
 Cryptophagus scanicus ? (Clav.) 
 C. dentatus 
 
 Monotonia quadricollis (Clav.) 
 
 Chrysomela cacalicc «J (Phyt.) 
 
 Adimonia tanaceti (Phyt.) 
 
 R8. 
 
 L8. 
 
 8. 
 
 L5. 
 
 9. 
 
 L2. 
 
 Kraatz, Dent. ent. Zt., 1877, xxi. 
 p. 55, fig. 9, and Sartorius, Wien. 
 ent. Monats., 1861, v. p. 31. 
 R2. ibid., fig. 8. 
 
 R5. Doumerc, Ann. Soc. ent. Fr., 1834, 
 S. 1, in. p. 174, PI. i. 
 Perty, Mitth. nat. Ges. Bern, 1866, 
 
 p. 307, fig. 4. 
 Gredler, Corr.-Bl. zool.-min. Ver. 
 
 Regensb., 1877, xxxi. p. 139. 
 ibid. 
 
 Ann. and Mag. N. H., 1841, p. 483. 
 von Heyden, Deut. ent. Zt., 1881, 
 xxv. p. 109,^. 
 R 10. 1 Sartorius, Wien. ent. Monats. , 1858, 
 LlO.j ii. p. 49. 
 L 8. Brit. Mus. 
 
 Kraatz, I.e., p. 56, fig. 17. 
 ibid., fig. 10. 
 ibid., 1881, xxv. p. 112. 
 ibid., 1877, xxi. p. 57, fig. 24. 
 Gredler, /. e. , 1858, xn. p. 195. 
 R 6. Jayne, Trans. Amer. Ent. Soc., 1880, 
 
 viii. j3. 155, PI. rv. fig. 1. 
 L 10. Mocquerys, Col. anorm., 1880, p. 17, 
 
 fig. 
 
 ibid., p. 10, fig. 
 
 Gredler, 1. c., 1869, xxiii. p. 35. 
 
 von Heyden, Deut. ent. Zt., 1881, 
 
 xxv. p. 109, fig. 19. 
 ibid., fig. 18. 
 
 R9. 
 L7. 
 5. 
 R9. 
 L9. 
 
 R8. 
 
 ? 
 
 R6. 
 
 R8. 
 R5. 
 
 L. 
 R10. 
 L 9. 
 
 R9. 
 
 L3. 
 
 R. 
 
 L7. 
 
 L5. 
 
 Lucas, Ann. Soc. ent. Fr., 1843, 
 
 S. 2, i. p. 55, PL 
 Kraatz, I. c, 1876, xx. p. 378, fig. 
 
 Lent by Dr Mason. 
 
 Kraatz, /. c. , 1877, xxi. p. 57, fig. 25. 
 Sartorius, Wien. ent. Monats., 
 
 1861, v. p. 31. 
 Rey, C., Ann. Soc. Linn, de Lyon, 
 
 1882, xxx. p. 424. 
 liKrz~SER,Jahresb.schles. Ges. vaterl. 
 
 Kultur, 1855, p. 106. 
 Schneider, ibid., 1860, p. 129. 
 
chap, xxii.] SUPPOSED CASES OF DOUBLE ANTENNA, 551 
 
 Heteromera 
 
 X Sepidium tuberculatum 
 Zonabris quadripunctata 
 
 Eleodes pilosa 
 * Blaps chevrolati 
 B. cylindrica 
 B. similis 
 Akis punctata 
 
 LONGICORNIA 
 
 Prionus 1 sp. 
 Aromia moschata 
 
 ditto 
 
 * ditto 
 
 X Cerambyx cerdo ? 
 X C. scopolii ' 
 X Lamia textor 
 
 * X Strangalia atra 
 
 S. calcarata 
 
 * X Solenophorus strepens- 
 
 Clytus arcuatus 
 Hammaticherus heros 
 
 Callidium variabile 
 
 L5. Pebty, /. e., jig. 10. 
 
 LG. Kbaatz, l.c, L889, xxxm. p. 221, 
 
 fig. 14. 
 
 B 9. Jayne, /. <■., p. 161, fig. 13. 
 
 L 7. Miimh i.k, s, /. <•., p. 11, jig. 
 
 L 3. i6fd., p. 6, fig. 
 
 II H. von HeYDEN, /. c, p. lO'.t. fig, 22. 
 
 L3. Baudi, /.'////. Sioc. ent. //<//., 1877, 
 ix. p. 221, fig. 
 
 10. J/o/. and Man. N. II., 1841, S. 1, 
 
 p. 483. 
 6. Kbaatz, /. c, 1889, xxxm. p. 221, 
 
 fig. 15. 
 
 R2. Mocquebys, /. c, p. 18,.//'//. 
 
 L 5. Lent by Mr Janson. 
 
 L6. von Heydkn, /. c, p. 10!), .//'</. 23. 
 
 R3. Kraatz, /. c, 1877, xxi. p. 56, fig. 
 
 L 1. Smith, P., Zuol., vi. p. 2245. 
 
 LI. Mocquerys, /. c, p. 14, fig. 
 
 ? Gredler, /. c, 1858, xii. p. 195. 
 
 K2. Mocquerys, /. c, p. I'd, jig. 
 
 R5. von Heydkn, ////. 21. 
 
 L 7. Klingelhofi.i;, Stef. ent. Zt., 1844, 
 
 v. p. 330. 
 
 L3. Mocquerys, I. c, p. 24, j'uj. 
 
 Lycus sp. (Mai.) 
 * Telephorus lividus (Mai.) 
 
 T. rotundicollis 
 E later hirtus (Elat.) 
 
 LI. von Heyden, I. c, p. 109,.////. 17. 
 L2. Lent by Mr F. H. Watebhouse. 
 R2. Jayne, I. c, p. 159, fig. 11. 
 9. Eassi, Ann. Sue. cut. Er., 1*34, 
 S. 1, in. p. 375. 
 R6. Kawall, Stet. ent. Zt., 1858, xix. 
 
 p. 65. 
 L6. Westwood, Proc. Linn. Soc., 1847, 
 i. p. 34(3. 
 IVIacrognatlius nepalensis (Lucan.) R3. Kraatz, /. c, 1880, xxv. p. 342. 
 
 fig. 10. 
 Julodis clouei (Bupr.) R5. Buquet, Ann. Soc. ent. Fr., 1843, 
 
 S. 2, i. p. 97, PI. iv. 
 
 Extra antenna arising from the head. 
 
 Ampedus ephippium (Elat.) 
 Chiasognathus grantii (Lucan.) 
 
 * 
 
 859. Callidium violaceum ? (Longic.) li. 
 
 Saperda carcharias (Longic.) L. 
 
 * Cerambyx cerdo (Longic. ) L. 
 
 von Roder, /•.'///. Sarlir., 1888, xiv. 
 
 p. 219. 
 Bitzema Bos. Tijds. r. Ent., 1879, 
 
 xxii. p. 208, PL 
 Kbaatz, Pent. ent. Zt., lss«», xxxm. 
 
 p. 222,.////. 23. 
 
 3. Palpi. 
 
 Subject to the reservations made in regard to instances of 
 duplicity in antennae, &c, the following examples of supposed 
 duplicity in palpi are given. 
 *860. Nebria gyllenhalli £ (Carab.) : maxillary palps abnormal. 
 
 1 I suspect that this is Navosoma No. 801. 
 
 2 Doubtless the specimen mentioned by Ltcas. Hull. Soc. ent. France, 1848, 
 S. 2, vi. p. xix. 
 
552 MERISTIC VARIATION. [part i. 
 
 Fig. 206, I, shews the normal form of a right maxillary palp. 
 Fig. 206, II, represents the right palp of this specimen. The 1st 
 and 2nd joints are much thickened and the latter has 8 hairs 
 (instead of 4) and two apical articulations, the anterior bearing 
 
 Fig. 206. Nebria gyllenhalli, No. 860. I. Normal right maxillary palp. 
 II. Right palp of this specimen. III. Left palp of the same, m, terminal 
 membrane. (The property of Dr Kraatz.) 
 
 an apparently normal terminal joint, the posterior bearing a 
 symmetrical piece ending in a sharp point with no membrane like 
 that at the apex of the normal. The left palp of this specimen is 
 shewn in Fig. 206, III. In it the 2nd joint has 8 hairs instead of 
 4, and the terminal joint though very much enlarged is not 
 divided at all. For the loan of this specimen I am indebted 
 to Dr G. Kraatz who first described it in Bed. ent, Zt, 1873, 
 xvii. p. 4s33,fig. 12. 
 
 861 . Carabus splendens : penult, jt. of 1. labial palp enlarged, and bearing two nearly 
 similar jts. [broken before seen by me]. Mocquerys, /. c, p. 29, fig. 
 
 862. C. auratus : 1st. jt. of 1. maxillary palp bears two similar branches at rt. angles 
 to each other, each with two jts. [Specimen not seen.] Mocquerys, /. c, p. 30, Jig. 
 
 863. C. purpurascens : extra labial palp on 1. side. [Specimen not seen.] Moc- 
 querys, I.e., p. '62, fig. 
 
 4. Mandibles. 
 
 864. Lucanus. Three cases are recorded in which one of the 
 mandibles bore an extra process of considerable size. Whether 
 any of these are examples of duplicity, or whether the jaw, mor- 
 phologically single, has in them varied towards a state of greater 
 complexity, cannot well be said. The cases are L. cervus ^ , 
 Mocquerys, I. c, p. 106 [figure fairly true]: L. cervus J, 
 Kraatz, Beat. ent. Zt,, 1881, xxv. p. Ill, fig. ; L. capreolus J y 
 id., I. c, 1876, xx. p. 378, fig. 
 
CHAPTER XXIII. 
 Secondary Symmetry in Vertebrates. 
 
 Remarks on the Significance of Repetitions in Secondary 
 
 Symmetry: Units of Repetition. 
 
 The evidence as to repetition of appendages in vertebrates 
 is of great extent and has been studied by many, but in tin- 
 morphology of these repetitions there is still much that is ob- 
 scure. Speaking generally, the phenomena are similar to those 
 seen in Arthropods, but there is no approach to the same regu- 
 larity. Nevertheless when two extra limbs are present, it is 
 usually possible to recognize that they are together a comple- 
 mentary pair; and if the extra part is apparently a single limb 
 it is, I believe, never a normal limb and may very often be 
 shewn to contain parts of a pair of limbs. The fact that the 
 geometrical relations of the parts are less regular than they are 
 in Arthropods may probably be ascribed in some measure to the 
 circumstance that the surfaces of the vertebrate limbs do not 
 maintain their original relations but are more or less rotated in 
 the course of their development. 
 
 In Insects it appeared that repetition of the peripheral parts in 
 Secondary Symmetry was not much more common than repetitions 
 of whole limbs, but apparently this is not the case in vertebrates. 
 Perhaps it would be more true to say that in vertebrates it i^ 
 only in those extensive repetitions which include the greater 
 part of the limbs beginning from the girdles, that the parts 
 are clearly in Secondary Symmetry. From this circumstance 
 doubt suggests itself whether some of the phenomena of poly- 
 dactylism, at present regarded as repetitions »»i' digits in Series, 
 may not really be of the nature of Repetitions in Secondary 
 Symmetry (see p. 378). But however this may be, there are, 
 with the exception of some Artiodactyle cases, no examples of 
 paired repetitions of digits or phalanges at all suggesting a 
 comparison with the double extra tarsi &c. of Insects, or the 
 double extra dactylopodites of Crustacea. 
 
554 MERISTIC VARIATION. [part i. 
 
 In the most usual forms of extra limbs in vertebrates a more 
 or less amorphous pair of limbs, compounded together for a great 
 part of their length, are attached to a supernumerary piece fitted 
 into some part of the shoulder-girdle, or more often into the 
 pelvic girdle. 
 
 It is important to notice that though, as many (especially 
 Ercolaxi) have shewn, a complete series can be constructed, 
 ranging for instance from the ordinary pygomelian up to com- 
 plete posterior duplicity, yet repetition of limbs may be and often 
 is wholly independent of any axial duplicity, being truly a repe- 
 tition of appendicular parts only. 
 
 The question naturally arises whether there is ever an extra 
 limb placed as a single copy of a normal limb of the same side 
 as that on which it is attached. As to this the evidence is not 
 wholly clear, but I incline to think that no case known to me 
 can properly be so expressed. Perhaps the condition which comes 
 nearest to this is exemplified by a case of a Frog fully described 
 by Kingsley 1 , where a single extra left hind leg is said to have 
 been attached to the left side of the pelvis. It is difficult to 
 question that this was actually the fact, for the figure clearly 
 represents the extra limb as a left leg; but though the muscles 
 are fully described, the bones are not ; and it still seems possible 
 that there was in reality some duplicity in the limb. The leg 
 was admittedly abnormal in its anatomy and the naming of the 
 muscles must in part have been approximate. 
 
 But though perhaps it should not be positively stated that 
 no single extra limb is ever formed in a vertebrate in Succession 
 to the normal limb of the same side of the body, it is certainlv 
 true that in the enormous majority of polymelians the extra 
 repetition consists of parts of a complementary pair. These phe- 
 nomena are thus of interest as bearing upon the morphology of 
 repetitions in Secondary Symmetry, but in all probability are 
 not of the nature of variations in the constitution of the Pri- 
 mary Symmetry. 
 
 A just view of the details of these phenomena can only be gained 
 from the specimens or from numerous drawings. The cases of extra 
 limbs in Batrachia may be conveniently studied as exhibiting most of the 
 different kinds of Secondary Symmetries both in the fore and hind 
 limbs. In all, some fifty cases are recorded. These may be found 
 from the following references. The evidence up to 1865 was put 
 together by Dum^ril, and an abstract of it is given also by Lunel, 
 and by Kingsley. A fuller bibliography is given by Ercolaxi. The 
 best papers on the subject are marked with an asterisk. I have added 
 a few references of less importance not included in the other biblio- 
 graphies. 
 
 * Dumeril, Nouv. Arch. Mus. Paris, 1865, i. p. 309, PI. xx. 
 
 * Lunel, Mem. soc. phys. d'hist. not. de Geneve, 1868, xix. p. 305, PL 
 
 1 Proc. Bost. N.H.S., 1881—2, xxi. p. 169, PI. n. 
 
chap, xxiil] SIGNIFICANCE OF SECONDABT? SYMMETRY. 55 
 
 * Kingsley, Proc. Boston N.H.S., 1881—2, xxi. p. 169, PL n. 
 
 * Cavanna, G., Pubbl. del J!. 1st. di Studi super, in , 1879, p. 8, Tav. i. 
 Four important cases; one, jig. 2, apparently resembling Km in somen -p- 
 
 * Mazza, Atti Soc. ital. sci. nat., 1888, xxxi. p. I 15, PI. i. 
 
 TUCKERMAN, JOW. Alldt. I'ln/s., 1886, p. 517, PI. X\ I. 
 
 Cat. Terat. Ser. Coll. Surg. Mus., 1872, No. 23. 
 Heron-Koyer, Bull. soc. Zool. France, 1884, ix. p. 165. 
 Bergendal, Bihang k. svensk. vet. Ah., 1889, xiv. Aid. iv. PI. i. 
 
 * Ercolaxi, Mem. Ace. Bologna, 1881, iv. p. 810, PI. iv. Four important ca 
 and very good bibliography. 
 
 Sutton, Trans. Path. Soc., 1889, xe. p. 161, fig. 
 
 [Three cases in Newts: Triton cristatus, Jackei,, /.<»,!. Cart., lssl. xxn. p. l.'.f,. 
 Triton tceniatus, Landois, H., ibid., 1884, xxv. p. ( J4; Cabiebano, Atti Soc. ital. 
 nat., 1882, xxv]. 
 
 From these Batrachian cases most of the chief features of the 
 phenomena may be learnt. To those wishing to get a general view of 
 the subject of repetition of Vertebrate limbs in a comparatively small 
 compass the valuable memoir of Ercolaxi quoted above is especially 
 recommended. 
 
 Before proceeding to a consideration of the significance of the 
 phenomenon of Repetition in Secondary Symmetry it must be 
 expressly stated that there are in vertebrates a certain number 
 of cases, perhaps even classes of cases, which it is likely differ 
 widely from the rest ; but as was said above, the chief difference 
 between the Vertebrate and Arthropod cases lies in the com- 
 parative simplicity of the latter. It may be stated further that 
 this greater simplicity of the Arthropod cases consists especially 
 in the maintenance of the relation between the extra pair and 
 some normal limb. 
 
 Remembering always the existence of unconformable cases we 
 may, I think, safely gather up from the simple cases several 
 points relating to the problems of Natural History at large. I 
 only propose here to make allusion to those considerations which 
 are not developed in the ordinary teratological treatise-. 
 
 Of the fact that any regularity can be discerned in thes< 
 strange departures from normal structure, and of the bearings 
 of this fact on current conceptions of the causes determining the 
 forms of animals it is now hardly necessary to speak further. 
 Other points not before noticed remain. 
 
 In the Arthropod cases that were spoken of as 'regular' it 
 was seen that the polarity of the Secondary Symmetries has a 
 definite relation to that of the body which bears them. This 
 is quite in harmony with the supposition that they are related 
 to the normal body somewhat as buds are related to a colony, 
 for in most colonial forms the morphological axes and planes 
 of the buds are definitely related to those of the stock. 
 
 But in the Vertebrate cases though there is generally a re- 
 lation of images between the extra pair, a definite geometrical 
 relation between them and a normal limb is seen more rarely. 
 
556 MERISTIC VARIATION. [part I. 
 
 That this is so may, I think, be in part at least attributed to 
 the normal twisting of the vertebrate limb, especially of the hind 
 limb, from its original position (see Note on p. 459). 
 
 A question brought into prominence by facts of this kind 
 is that of the nature of the control which determines how mucli 
 of a body shall be repeated, or be capable of repetition, in a 
 Secondary Symmetry. 
 
 What is a unit of repetition ? 
 
 With repetition of a whole body we are familiar. Apart from 
 the processes of sexual reproduction, we know this total repetition 
 in the many forms of asexual reproduction, whether occurring 
 by budding, or by division either of adult bodies or of embryos 1 , 
 and we thus commonly look on the whole body of any organism 
 as in a sense a unit, capable of repetition or of differentiation — the 
 latter especially in gregarious and colonial forms. Again, we 
 familiarly use the conception of cells as units of repetition or of 
 differentiation. Besides these we have come to recognize that 
 members of series of segments are, in their degree, similar units. 
 And generally, the same attribute of separateness may in un- 
 defined senses be properly attached to all organs that are re- 
 peated in Series, and to appendicular parts especially. 
 
 The attribution of some of the undefined properties of "unity 2 " 
 to some at least of these various groups is very ancient, and there 
 can be no doubt that it is in the main a right and useful in- 
 duction. 
 
 The chief interest of repetitions in Secondary Symmetry lies 
 in the fact that they give a glimpse of new light upon the nature 
 of this unity, shewing a new form in which it may appear. 
 
 For in Secondary Symmetry there is not a simple repetition 
 of a part in Series, taking its place as a member of that series, 
 but an addition of paired parts, whose intrinsic relation to each 
 other is the same as that of any pair of parts occurring in the 
 Primary Symmetry. 
 
 The addition is thus a unit, is in form complete in itself, and 
 seems to have no place in the Primary Symmetry of the whole 
 body any more than a late side-chapel — also a unit with its own 
 focus and polarity — had a place in the design of t lie original archi- 
 tect of the Cathedral. 
 
 From analogy, and from general knowledge of vital processes 
 it would I think have been impossible to foresee the very curious 
 indeflniteness of the quantity of the parts repeated in systems 
 of Secondary Symmetry. It seems, especially in Arthropod cases, 
 
 1 As a normal occurrence notably in the case of Cyclostomatous Polyzoa of the 
 genus Grisia described by Harmer, S. F., Q. J. M. S., 1891, p. 127, Plates. 
 
 2 This somewhat incorrect term is used here to express some of the meanings 
 commonly still more incorrectly rendered by the word "individuality" — a word 
 etymologically most unhappy in this application to things endowed with divisibility 
 as a conspicuous attribute. 
 
chap, xxiii.] UNITS OF REPETITION. 557 
 
 that the repetition may begin from any point in an appends 
 and include all the parts peripheral to the poinl of origin. Seeing 
 that the repeated parts are, in their degree, comparable with a 
 whole organism, this indefmiteness is remarkable. We have thus 
 to recognize that the property of morphological "unity" may 
 attach not only to a pair of appendages beginning from the 
 body, or from some definite surface of articular segmentation, bu1 
 also to a pair of parts having no semblance of morphological dis- 
 tinctness. 
 
 Strangest of all is the repetition of the index of Crabs and 
 Lobsters in Secondary Symmetry. The dactylopodite is of course 
 a separate joint. Double extra dactylopod it es in Secondary Sym- 
 metry present no feature different from double extra tarsi, &c. 
 But the index we think of as merely a large spine or tubercle. 
 It is in no sense a joint or segment. Yet a pair of indices may 
 be added to a normal body. The interest of this fact is in it-- value 
 as a comment on the principle given on p. 476 that extra parts 
 in Secondary Symmetry contain the structures peripheral to their 
 point of origin. The case of extra indices shews that tin- term 
 peripheral, if it is to include the case of indices, must be inter- 
 preted as meaning not morphologically but geometrically peri- 
 pheral \ 
 
 We have spoken of parts in Secondary Symmetry as having 
 no place in the Primary Symmetry of the body. This is on 
 the whole a true statement, but there are a few cases which 
 make it uncertain whether it is absolutely true. These e.-^es 
 are those few where repetitions in Secondary Symmetry were 
 present on appendages of both sides of the body. 
 
 Cases of this class were Odontolabis stevensii, No. 7!>l), and 
 Melolontha hippocastani, No. 795, where such extra parts were 
 present on both antennae, suggesting that the similarity of the 
 repetition of the two sides is due to the relation of Symmetry 
 between the right side and the left. But against this view may 
 be mentioned the cases Prionus coriarius, No. 750, and Carabus 
 irregularis, No. 760, where two legs of the same side each bore 
 extra parts, and the Lobster, No. 821, having two pairs of extra 
 points on one dactylopodite. These cases suggest that bilateral 
 simultaneity in such repetition may perhaps represent merely 
 a general capacity for this form of repetition. The case of 
 Prionus calif orm'c us, No. 843, would no doubt bear on this 
 question, but unfortunately the facts in that case are scarcely well 
 enough known to justify comment. 
 
 1 A case is given by Faxon {llarv. Bull., vin. PI. n. fig. 8) of Callinectes has- 
 tatus in which the left lateral horn of the carapace, instead of being simple as in 
 normal specimens, had three spines. It is just possible that two of these may have 
 been in Secondary Symmetry. All other cases known to me arc in appendicular 
 parts. 
 
558 MERISTIC VARIATION. [part i. 
 
 One further point remains to be spoken of. We have said 
 that a system of parts in Secondary Symmetry is in a sense 
 analogous with a bud, but in one respect the condition of these 
 parts differs remarkably from all phenomena of budding or 
 reproduction that are seen elsewhere. In a bud the various 
 organs always present the same surfaces to each other, or in 
 other words, the planes of division always pass between similar 
 surfaces. In Secondary Symmetries this is not the case. As 
 illustrated by the diagram on p. 481, the extra parts may present 
 to each other, or remain compounded by any of their surfaces, 
 whether anterior, posterior, or otherwise. This seems to be 
 altogether unlike anything ever met with in animals and plants. 
 It is as if in a bud on a plant two leaves on opposite sides of the 
 axis could in their origin indifferently present any of their surfaces 
 to each other. 
 
 It will be remembered that the symmetry cannot be the result 
 of subsequent shiftings, but must represent the original manner of 
 cleavage of the two extra limbs from each other. We must there- 
 fore conceive that in the developing rudiment of the two extra 
 limbs either surface may indifferently be external, the polarity 
 being ultimately determined by the relation of the bud or 
 rudiment to the limb which bears it. 
 
CHAPTER XXIV. 
 Double Monsters. 
 
 Of the evidence as to double and triple " monstrosity ' and 
 
 of the classification of the various forms no account can be given 
 here. This may be found in any work on general teratology. In 
 this chapter are put together a few notes on points respecting 
 these formations of interest to the naturalist, and having relation 
 to what has gone before. 
 
 It is now a matter of common knowledge that in animals [and 
 plants] division may occur in such a way that two or more bodies 
 may be formed from what is ostensibly one fertilized ovum (cp. 
 multipolar cells). But by a similar division, imperfectly effected, 
 the resulting bodies instead of being complete twins or triplets 
 may remain united together, frequently having a greater or less 
 extent of body in common. In other words, speaking of simple 
 cases in bilateral animals, the whole body, resulting from the 
 development, may contain more than one bilaterally complete 
 group of those parts which normally constitute the Primary Sym- 
 metry of an " individual." 
 
 If well developed, the component groups are most often united 
 by homologous parts, so that there is a geometrical relation <>t' 
 images between the groups together, forming the compound struc- 
 ture, the whole being one system of Symmetry. Concerning the 
 relations of the several parts of such a system to each other 
 numerous questions of interest arise, but with these it is not now 
 proposed to deal. 
 
 To those unacquainted with facts of this class it may be of use to point out in 
 the fewest words the direction in which this importance lies. It arises, briefly, from 
 the fact that in the resemblance between a pair of homologous twins, win fcher wholly 
 or partially divided, there is once again an illustration of the phenomenon of Sym- 
 metry, and of the simultaneous Variation of structures related to each other as sym- 
 metrical counterparts. 
 
 The frequency of close resemblance between twins is a matter of common know- 
 ledge. If it be true that such twins may result from the development of one ovum— 
 a fact that cannot be doubted in face of the complete series of stages intermediate 
 between total and partial duplicity — the resemblance between these twins is then of 
 the same nature as that subsisting between the two halves of any other bilaterally 
 symmetrical system. A wide field of inquiry is thus opened up. for, as suggested 
 in the Introduction (p. 30) if the very close resemblance of twins to each other is a 
 phenomenon dependent on Symmetry of Division, the less close resemblance betw een 
 members of families may be a phenomenon similar in kind. 
 
560 MERISTIC VARIATION. [part i. 
 
 It will be remembered that the resemblance between twins is a true case of 
 similar and simultaneous Variation of counterparts. This is clearly proved by the 
 fact that when distinct Meristic Variations are exhibited by one twin they are not 
 rarely present in the other also. Cases of this simultaneous Variation are familiar 
 to all who have studied this subject. A useful list of examples in completely separate 
 twins is given by Windlk 1 . One of the best known cases in twins incompletely 
 separated, is that of the Siamese Twins-, who had each only eleven pairs of ribs 
 (instead of twelve). 
 
 Reference must lastly be made to a particular corollary which may naturally be 
 deduced from the fact that the bodies of incompletely separated twins are grouped 
 as a single system of Symmetry. If the whole common body were bilaterally sym- 
 metrical, one twin must be the optical image of the other. But if the organs of one 
 twin be normally disposed, the organs of the other must be transposed in completion 
 of the Symmetry. This theoretical expectation is in part borne out by the facts. 
 With a view to this question Eichwald 3 examined the evidence as to thoracopagous 
 double monsters (including xiphopagi, &c), and found that in almost every case one 
 of the bodies shewed some transposition of viscera, though to a varying extent 4 . 
 
 There are nevertheless a few cases even of thoracopagi where neither body ex- 
 hibits any transposition 5 . Moreover, contrary to natural expectation, it does not 
 appear that in ordinary cases of completely separate twins either twin has its 
 viscera transposed; and conversely, of 152 cases of transposition collected by 
 Kuchenmeister only one could be shewn to have been a twin 6 . It seems therefore 
 that the frequency of transposition in double monstrosity depends in some way upon 
 the maintenance of the connexion between the twins; and that if the separation be 
 completed early, as it must be supposed to be in cases of homologous twins born 
 separate, then both bodies as a rule develop upon the normal plan, like the bodies 
 of multiple births of other animals. But as the evidence now stands there is no 
 reason to suppose that individuals with transposition of viscera, born as single births, 
 have ever had a counterpart any more than individuals whose viscera are normally 
 placed, tempting as it is to imagine that both may have had some counterpart which 
 in the ordinary course does not develop. 
 
 For the present we need not go beyond the fact that between 
 complete duplicity resulting in " homologous twins," and the 
 least forms of axial duplicity, consisting in a doubling of either 
 extremity of the longitudinal axis almost all possible degrees 
 have been seen 7 . By persons unfamiliar with abnormalities it 
 
 1 Windle, B. C, Jour. Anat. Phys., xxvi. p. 295. 
 
 2 For full abstracts of all evidence relating to this case, see Kuchenmeister, 
 Die angeb. Verlagerung d. Eingeweide d. Menschen, Leipzig, 1883, p. 201. 
 
 3 Eichwald, Pet. med. Ztsch., 1870, No. 2, quoted from abstr. Virch. u. Hirsch, 
 Jahresb., 1871, p. 167. 
 
 4 Eichwald supports the view that in these cases it is the right twin which shews 
 the transposition. As Kuchenmeister (I. c.) points out, this cannot by the nature 
 of the case be a universal rule ; for the relative position of xiphopagous twins may 
 result singly from the way in which they happen to be laid by the mother or the 
 midwife. Of the Siamese Twins, besides, it was Chang, the left twin, in whose body 
 there were indications of transposition. The twins may also remain face to face. 
 The expression " right twin " must always need further definition, and it should be 
 qualified as the right when the livers are adjacent, or when the hearts are adjacent, 
 as the case may be. Whether the rule is wholly or partially true for either of these 
 positions seems to be very doubtful. 
 
 5 For example, Bottchee, Dorpater med. Ztschr., n. p. 105, quoted from V. u. 
 II., Jahresb., I. c. In the specimen Terat. Cat. Coll. Surg. Mus., 1872, No. 114, there 
 is no transposition, but here the hearts were not separate. 
 
 6 1. c., p. 268. One, however, was a child of a mother who had before borne 
 twins, I. c, p. 313. 
 
 7 The fact that some of the degrees are much more common than others has an 
 obvious bearing on the question of Discontinuity, which might with profit be pur- 
 sued. A statistical examination as to the angles at which the bodies are most 
 frequently inclined to each other would also probably lead to an interesting result. 
 
chap, xxiv.] AXIAL DUPLICITY: BEPTILES. 561 
 
 is sometimes supposed that axial duplicity is a phenomenon more 
 or less peculiar to Man and to domesticated animals [and plants], 
 and the occurrence is looked on as a part of thai Meristic in- 
 stability which is ascribed to absence of the control of a Btrict 
 and Natural Selection. This view is far from Bound Such 
 phenomena have on the contrary been found in many classes of 
 animals, vertebrate and invertebrate, and the unquestionable 
 frequency in domesticated animals may in great measure be 
 fairly attributed to the comparative ease with which the births 
 of these creatures can be observed. As considerations of tin- 
 kind have weight with many it has seemed worth while to give 
 references to examples taken from a variety of different groups, 
 shewing not only that such compound bodies may be produced 
 in wild animals, but also that they may sometimes be able to carry 
 on the business of life without artificial help. 
 
 In Mammals and Birds I do not know an authentic case of a double 
 monster that had grown up in the wild state. 
 *865. In Reptiles many such cases are known and are referred to by 
 most of the older writers. Of Snakes having complete or partial 
 duplicity, nearly always of the head, some twenty cases are recorded. 
 Several of these were animals of good size, and must have had aD 
 independent existence for some considerable time. 
 
 Some of the cases have special points of interest, but into these it 
 is not now proposed to enter. As bearing on the question of the 
 frequency of Meristic Variation in families and strains attention is 
 called to the circumstance that Mitchill's three specimens were all 
 found in one brood of 120 which were taken with the mother. The 
 following is a list of records of snakes having the head whollv or 
 partially double. 
 
 Coluber constrictor. Wyman, J., Proc. Bost. X. II. S., 1862, 
 ix. p. 193, fg. 
 
 Coluber constrictor. Mitchill, S. L., Amer. Jour, of Sri., x. 
 1826, p. 48, PI. (3 specimens). 
 
 Ophibolus getulus. Yarrow, Amer. Xat., 1878, xn. p. 470. 
 
 Pityophis. ibid., p. 264. 
 
 Pelamis bicolor. [Remarkable case 1 : the duplicity appearing 
 only in the fact that there were 4 nasal plates instead of 2, each with a 
 nostril] Boettger, 0., Per. iib. d. Seuck. nat. Ges. in Frank/, a. J/., 
 1890, p. lxxiii. 
 
 In the remainder the species is not clear. Redi, Osserv, int. agli 
 anim. viventi, &c, 1778, p. 2, Tav. i. [very good account]; LaceVkde, 
 Hist. nat. des Serpens, n. 1789, p. 482; Bancroft, Nat Hist, of 
 Guiana, 1769, p. 214, PL; Laxzoxi, Miscell. curios., 1690, Obs. « i.wi. 
 p. 318, Fig. 36; Boston Soc. Med. Imp., Catal. of Mas.. No. 856, 
 quoted from Wyman, /. c. ; Edwards, Nat. Hist, of Birds, dfcc, Pt. iv. 
 1751, p. 207, PI. ; Dorxer, Zoo!. Gart., 1873, xiv. p. 407 : Coll. Surg. 
 Mus., Terat. Cat, 1872, Nos. 24—27. 
 
 1 Compare with Mitchill's two last cases, and also with a case ill Alytes ob- 
 stetricans. Herox-Royer, Bull. Soc. Zool. France, 1884, ix. p, 164, 
 
 B. 
 
 36 
 
562 
 
 MERIST1C VARIATION. 
 
 [part I. 
 
 EC 
 
 TV 
 
 Fig. 207. Chrysemys picta, 2 or 3 days old. I, II, normal. Ill and IV, two- 
 headed specimen. In the latter the nuchal and two pygal plates are normal. Be- 
 tween them are 12 plates on each side, 11 being the most usual number. Among 
 the costals an extra plate is wedged in on the rt. First vertebral divided by suture ; 
 fifth is made up of 4 irregular plates. In the plastron there is a doubling of the 
 gular plate. The rt. femoral has a suture. (From Barbour.) 
 
chap, xxiv.] AXIAL DUPLICITY: IX VERTKIiKATKS. 563 
 
 See also, Geoffroy St. Hilaire, Hist, des a num., ed 1838, 11. p. 
 197; Dumeril et Bibron, Erpdt generate, 1884, vi. p, 209. 
 
 866. Duplicity of the head is less common in Lizards, but several 
 examples are known. See Geoffkoy St. HlLAlBB, I c, p. 195: Con 
 Paris, 1869, S. 3, v. p. 136, etc. 
 *867. In Chelonia also are several such instances. See Edwards, N<U. 
 
 Hist, of Birds, d/c, Pt. IV. 17">1, p. lMm 1 , ; .Mnniii.i, /. ,-. ; BaBBOUB, 
 E. H., Amer. Jour, of $ci., 1888, S. 3, xxxvi. p. 227, PL v. The lasi i 
 particularly interesting case from the circumstance that the behaviour 
 during life was observed to some extent, though only a popular account 
 is given. The two heads seemed to act independently, and it is said 
 that there was no concerted action between the feet of the two sides. 
 Barbour's figures are reproduced in Fig. 207. 
 
 In fish-hatching establishments double monstrosity is of frequent 
 occurrence among young Salmon and Trout. A two-headed embryo of 
 a Shark is preserved in Coll. Surg. Mus. {Terat. Cat. 1 s 7l', No. 22 
 
 The following cases relate to invertebrates. 
 
 Chaetopoda. Duplicity in this Class has been often seen, but 
 that any of the cases are truly congenital cannot be stated. There is 
 evidence that in many Annelids regeneration 1 both of head or tail may 
 freely occur, and it is quite possible that the second head or second tail 
 may have grown out from an injured place, though of this there is no 
 actual proof. In cases of posterior bifurcation each tail generally 
 contains all the parts proper to the normal, but in Xo. S71 one of the 
 tails was without the terminal cirri usual in the species. So far as can 
 be gathered from the evidence it does not appear that the two con- 
 tinuations of the body have always the same number of segments, 
 which might perhaps be expected were both the result of a natural 
 division of the developing body. On the other hand, they do seem 
 generally to have a nearly equal development, and are almost always 
 (in cases of double tails, at least) fairly equal in length, which would 
 not be anticipated if one only were a new growth. Moreover, if the 
 double tail is in some way due to regeneration one would expect to 
 find such duplicity in its minor conditions much more commonly. 
 
 Into the details of the structure it is not now proposed to enter, 
 and indeed of most of the cases there is little to be told. The evidence 
 is mentioned here simply in further proof of the power of these indiv- 
 iduals, thus greatly departing from the normal of their species, to 
 maintain themselves with no apparent difficulty. It will be noticed that 
 the species concerned are most various, and include not only Errant ia, 
 but two cases also in Serpulida?. 
 
 The literature of the subject was collected by Collin ', and a list of 
 the references was independently collected and published with abstracts 
 by Andrews 3 . This list, with a few additions, was republished by 
 Friend 4 . Though many of the accounts are imperfect they are referred 
 
 1 The evidence on this point does not come within the scope of this work. 
 References to it may be obtained from Akdbbws, Zeppelin, <ic (r. infra). 
 3 Collin, A., Naturw. Wochens., 1891, No. 12, p. 113. 
 
 3 Andrews, E. A., Amer. Nat., 1892, xxvi. p. 729. 
 
 4 Friend, H., Nature, 1893 (1), p. 397. 
 
 36—2 
 
564 
 
 MERISTIC VARIATION. 
 
 [part l 
 
 *S6S. 
 
 to below, in evidence that the total number of cases is considerable. 
 There are only two certain cases of double head (see Typosyllis, No. 868, 
 and Allolobophora, No. 873). 
 
 POLYCH.ETA. 
 
 Typosyllis variegata : individual having two small heads, as 
 shewn in Fig. 208. Heads of unequal size, that od the left having 4 
 segments behind the eyes, while that on the right had two. The 
 
 869. 
 870. 
 
 871. 
 872. 
 
 Fig. 208. Typosyllis variegata, No. 868, having two small heads. 
 
 (After Langerhans.) 
 
 appearance suggested that the original head had been broken off and 
 that two new ones had grown in its place. Langerhans, P., Nova 
 Acta Ac. C. L. C, xlii. p. 102, PL 
 
 Nereis pelagica : bifid posteriorly. Bell, F. Jeffrey, Proc. Zool. Soc., 1886, p. 3. 
 
 Salmacina incrustans (Serpulida?) : posterior end double. [Two tails shewn in 
 figure as of equal length and in the same straight line, at right angles to the body. 
 The arrangement of the segmentation at the junction is not clearly shewn.] 
 Claparede, Mem. soc.phys. et dltist. nat. Geneve, xx. 1869 — 70, p. 177, PI. xxx. fig. 5 f. 
 
 Proceraea tardigrada (Syllid*) : tail double; two specimens. In one of these 
 the tails were nearly equal, but one had no anal cirri. Andrews, E. A., Proc. U. S. 
 Nat. Mus., 1891; xiv. p. 283, and Amer. Nat., 1892, xxvi. p. 729, PI. xxi. 
 
 Branchiomma sp. (Sabellidre) : two posterior ends, one being rudimentary. 
 Brunette, Trav. Stat. Zool. de Cette, 1888, p. 8 [quoted from Andrews, I. c] 
 
 [With these conditions compare Syllis ramosa, a form found by the Challenger 
 in two localities, inhabiting a HexactineUid Sponge. The body of this creature con- 
 sisted of vast numbers of branches, about as thick as thread, passing off at right angles, 
 coiling upon each other and forming inextricable masses. In some specimens no 
 head was found, but a single head was afterwards discovered. It seemed likely that 
 large tracts of the body have no head, but there was no evidence to shew how many 
 heads occur in the colony. Many female buds were found, and a single complete 
 male. McIntosh, Chall. Rej)., xn. p. 198, PI. xxxi.] 
 
chap, xxiv.] AXIAL DUPLICITY : INVBRTEBBATES. oG5 
 
 Oligoch^ta, 
 
 *873. Allolobophora longa : specimen represented as bearing a Becond 
 head on the right side of the first segment behind the peristomium. 
 The second head is represented with prostomium, peristomium and one 
 more segment which rests on the peristomium of the normal body. 
 Friend, H., Science-Gossip, 1892, July, p. 161, fig, 
 
 874. Ctenodrilus monostylos : double tail; in many hundreds 
 examined, three cases seen, Zeppelin, Z.f, //•. Z., 1883, xxxix. ]». 621. 
 PI. 36, figs. 18 and 19. 
 
 875. Lumbriculus variegatus : similar cases, von Bulow, A rch, f 
 Naturg., 1883, xlix. p. 94. 
 
 876. Acanthodrilus sp. : case of two tails arising from a much thicker 
 anterior portion. Such worms were believed or alleged to be common 
 in a particular district in New Zealand. Kirk, T. ^Y., Trans. N. Zeal. 
 Inst., xix. p. 64, PL 
 
 877. Earthworms generally, belonging to genera Lumbricus, or 
 Allolobophora : cases of double tail recorded, as follows : Robertson, 
 C, Q. J. M. S. } 1867, p. 157, fig.; Horst, Notes Legd. Mu8. t vn. p. 42 : 
 Thompson, W., Zool, xi. p. 4001 ; Bell, F. Jeffrey (2 cases), Ann. <v 
 Mag. N. H., 1885 (2), p. 475, fig.; Friend, H., Sci.-Gossip, 1892, p. 
 108, figs.; Marsh, C. D., Amer. Nat, xxiv. 1890, p. 373; Fitch, A., 
 Eighth Rep. upon Insects of State of X. Y., Append., 1865, p. 204 [from 
 Andrews, I.e.]; Terat. Cat. Mus. Coll. Surg., 1872, No. 20. Breese, 
 West Kent N. H. S., 1871; Broome, Trans. N. II. S. Glasgow, 1888, p. 
 203 ; Foster, Hull. Sci. Club, 1891; [the last three quoted from Friend, 
 Nature, 1893 (1), p. 397]; Collin, A., Naturw. Wochens., 1891, No. 12, 
 figs. I have also a specimen with two nearly symmetrical tails kindly 
 sent by Mr W. B. Beniiam. 
 
 Arthropoda. 
 
 Three cases. 
 *878. Chironomus (Gnat): larva with two heads, duplicity beginni 2 
 from the 5th segment behind the head [important details given, g. v.]. 
 Weyenbergh, H., Stet. ent. Ztg., 1873, xxxiv. p. 452, fig. 
 
 879. Euscorpius germanicus (Scorpion): tail double from 4th prse- 
 abdominal segment [figure represents each abdomen with one segment 
 too few, presumably an error]. Pavesi, P., Rend. R. 1st. Lmib., S. II., 
 xiv. 1881, p. 329, fig. 
 
 880. [Scorpio africanus :] specimen with two tails. Skba, Rerum 
 Naturalium Thesaurus, 1734, i. p. 112, PI. lxx. fig. 3. This example 
 was kindly sent me by Mr R. I. Pocock, who tells me that the figure 
 shews the animal to be of the species named. 
 
 Cestoda. 
 
 Conditions, perhaps akin to duplicity, have been seen to occur 
 under three forms. 
 
 881. > Taenia ccenurus : specimen whose head had 6 suckers instead of 
 4, and 32 hooks instead of 28. Proglottides were 3-sided prisms, in 
 section triangular. Longitudinal vessels 6 instead of 4, two being in 
 each angle. Absolute size of head greater than normal. This abnormal 
 
566 MERISTIC VARIATION. [part i. 
 
 form is known to occur in many kinds of Tapeworms, and especially in 
 Cysticerci. Leuckart, Parasiten d. Menschen, pp. 501 — 2, cp. p. 577. 
 [Case withfii'e suckers mentioned, ibid., p. 578.] 
 
 In another form of abnormality the chain of segments has three 
 longitudinal flanges, formed, as it were, by the union of two chains of 
 proglottides having one edge in common. Head not found, but several 
 cases known. Genital openings in one case all upon the common edge. 
 Leuckart, ibid., p. 574. Cp. Cobbold, Trans. Path. Soc, xvn. p. 438; 
 Levacher, Comptes Yendus, 1841, xm. p. 661. 
 882 Bifurcated chains of proglottides have also been seen, e.g. specimen 
 
 of TaBnia (cysticerci) tenuicollis, which bifurcated several times in 
 terminal portion, though normal in front of this. Momez, Bull. >Sci. du 
 No rd, x. p. 201. See also Taenia saginata ? Leuckart, I. c, p. 573. 
 
 Brachiopoda. 
 883. Acanthothyris spinosa (Rhynchonellida^): case of duplicity 
 
 I u 
 
 Fig. 209. Acanthothyris spinosa, No. 883. Case of duplicity. (From P. Fischer.) 
 I. Seen from ventral valve. II. Looking between the valves. 
 
 as shewn in Fig. 209. Fischer, P., Jour, de Conchyl. S. 3, xix. p. 
 343, PL xm. figs 4—7. 
 
 HOLOTHURIOIDEA. 
 
 884. Cucumaria acicula : specimen made up of two individuals 
 cohering laterally at posterior ends. Schmeltz, Verh. d. Ver. f. 
 naturw. Unterhaltung, Hamb., 1877, iv. p. XV. 
 
 885. Cucumaria planci : case of second mouth and ring of tenta- 
 cles borne on a lateral bud-like projection. Ludwig, H., Z.f. w. 
 Z., liii. Supp. p. 21, PI. v. 
 
 886. Ccelenterata. Forms which are commonly simple, such as Actinia or Sagartia, 
 are rarely found with two discs seemingly due to incomplete division, which in 
 these forms may take place longitudinally [?] as well as by ordinary budding. 
 Gosse, P. H., Sea-Anemones, p. xxi., &c. See also Guyon, Zoologist, p. 7026, fig. 
 
 Similar occurrences, not distinguishable from budding, have been seen in 
 Medusas, e.g., Phialidium variabile, Davidoff, Zool. Anz., iv. p. 620, fig.; Gastro- 
 blasta raffaeli, Lang, A., Jen. Ztseiir., xix. p. 735. An interesting case of this kind 
 * was seen in Cordylophora lacustris. Several polystomatous specimens were found 
 on a particular mass of Cordylophora, but were not found on all colonies gathered 
 with this mass and had not been seen previously in specimens from the same 
 locality. [Further particulars.] Price, H., Q. J. M. S„ 1876, p. 23, figs. 
 
 Protozoa. Double and triple monstrosity has been seen in several 
 Foraminifera, see e.g., Dawsox, Canad. Nat., 1^70, p. 177, figs.; Balkwit>l 
 and Wright, Trans. B. Irish Ac, 1885, xxviii. p. 317, PL xiv., &c. 
 [As to cases in Stentor, see Balbiani, J. de Vanat., 1891, No. 3, but these 
 are doubtless examples of regeneration and duplicity following injury.] 
 
CHAPTER XXV. 
 
 Concluding Reflexions. 
 
 To attempt at this stage any summary of conclusions would be 
 misleading. The first object of this work is not to set forth in 
 the present a doctrine, or to advertise a solution of the problem of 
 Species, but rather to bring together materials that may help 
 others hereafter to proceed with the solution of that problem. A 
 general enumeration of particular conclusions is therefore to be 
 avoided. Indeed, from the scantiness of the evidence, its present 
 value is chiefly in suggestion, and the facts must therefore be 
 themselves still studied in detail. The reader must interpret as 
 he will. 
 
 But, as often happens, that which may not shew the right road 
 is enough to shew that the way taken has been wrong, and so is it 
 with this evidence. Upon the accepted view it is held that the 
 Discontinuity of Species has been brought about by a Natural 
 Selection of particular terms in a continuous series of variations. 
 Of the difficulties besetting this doctrine enough was said in the 
 introductory pages. These difficulties have oppressed all who have 
 thought upon these matters for themselves, and they have caused 
 some anxiety even to the faithful. And if in nice of the difficulties 
 reasonable men have still held on, it has not been that the obstacles 
 were unseen, but rather that they have hoped a way through them 
 would be found. 
 
 Now the evidence, of which a sample has been here presented, 
 gives hope that though there be no way through the difficulties, there 
 is still perhaps a way round them. For since all the difficulties grew 
 out of the assumption that the course of Variation is continuous, 
 with evidence that Variation maybe discontinuous, for the present 
 at least the course is clear again. 
 
 Such evidence as to certain selected forms of variations has 
 I submit, been given in these chapters, and so tar a presumption 
 is created that the Discontinuity of which Species is an expression 
 has its origin not in the environment, nor in any phenomenon of 
 Adaptation, but in the intrinsic nature of organisms themselves, 
 manifested in the original Discontinuity of Variation. 
 
 But this evidence serves a double purpose. Though some may 
 
568 MERISTIC VARIATION. [part I. 
 
 doubt whether the variations here detailed are such as go to the 
 building of Specific Differences (a doubt which, it must be granted, 
 does fairly attach to some part of the evidence), yet the existence 
 of sudden and discontinuous Variation, the existence, that is to 
 say, of new forms having from their first beginning more or less of 
 the kind of perfection that we associate with normality, is a fact 
 that disposes, once and for all, of the attempt to interpret all per- 
 fection and definiteness of form as the work of Selection. The 
 study of Variation leads us into the presence of whole classes of 
 phenomena that are plainly incapable of such interpretation. 
 
 The existence of Discontinuity in Variation is therefore a final 
 proof that the accepted hypothesis is inadequate. If the evidence 
 went no further than this the result would be of use, though its 
 use would be rather to destroy than to build up. But besides this 
 negative result there is a positive result too, and the same Discon- 
 tinuity which in the old structure had no place, may be made the 
 framework round which a new structure may be built. 
 
 For if distinct and "perfect" varieties may come into existence 
 discontinuous!)', may not the Discontinuity of Species have had a 
 similar origin ? If we accept the postulate of Common Descent 
 this expectation is hard to resist. In accepting that postulate it 
 was admitted that the definiteness and Discontinuity of Species 
 depends upon the greater permanence or stability of certain terms 
 in the series of Descent. The evidence of Variation suggests that 
 this greater stability depends primarily not on a relation between 
 organism and environment, not, that is to say, on Adaptation, but 
 on the Discontinuity of Variation. It suggests in brief that the 
 Discontinuity of Species results from the Discontinuity of Variation. 
 
 This suggestion is in a word the one clear and positive indica- 
 tion borne on the face of the facts. Though as yet it is but an 
 indication, there is scarcely a problem in the comparison of 
 structures where it may not be applied with profit. 
 
 The magnitude and Discontinuity of Variation depends on 
 many elements. So far as Meristic Variation is concerned, this 
 Discontinuity is primarily associated with and results from the fact 
 that the bodies of living things are mostly made up of repeated 
 parts — of organs or groups of organs, that is to say, which exhibit 
 the property of "unity," or, as it is generally called, "individuality." 
 Upon this phenomenon depends the fact that Meristic Variation in 
 number of parts is often integral, and thus discontinuous. 
 
 The second factor that most contributes to the Discontinuity of 
 Variation is Symmetry, manifesting its control in the first place 
 directly, leading often to a result that we recognize as definite and 
 perfect because it is symmetrical. 
 
 But besides this direct control that we associate with Symmetry, 
 other erfects greatly contributing to the magnitude of Variation 
 
chap, xxv.] CONCLUDING REFLEXIONS. 569 
 
 can be traced to a factor not clearly to be distinguished from 
 Symmetry itself. For, as has been explained, Symmetry, whether 
 Bilateral or Radial, is only a particular case of that phenomenou of 
 
 Repetition of Parts so universally characteristic of living bodies ; 
 and that resemblance between two counterparts, which we call 
 Bilateral Symmetry, is akin to the resemblance between parts 
 repeated in Series, though, as is shewn by their geometrical re- 
 lations, the processes of division by which the parts were originally 
 set off, must be in some respects distinct. Bilateral Symmetry <>t 
 Variation is thus only a special case of the similar and simul- 
 taneous Variation of repeated parts. 
 
 The greatness of the observed change from the normal is often 
 largely due to this possibility of simultaneity in Variation, the 
 change thus manifesting itself not in one part only, but in many 
 or all of the members of a series of repeated parts. Instances of 
 such similar and simultaneous Variation of serial parts in animal- 
 have now been given. Examples still more marked may be seen 
 abundantly among plants. A variation, for example, in the form or 
 degree of fission of the leaf, slight perhaps by itself, when taken up 
 and repeated in every leaf in its degree, constitutes a definite and 
 conspicuous distinction. Everyone has observed this common fact. 
 Few illustrations of it are more evident than that of the common 
 Hawthorn. In a quickset hedge soon after the leaves begin to 
 unfold almost each separate plant can be recognized even at a 
 distance, and its branches can be traced by their special character-, 
 by the shapes and tints of the leaves, by the angles that they make 
 with the stem, by the manner of unfolding of the buds, and - 
 forth. These variations, sometimes slight in themselves, by their 
 similarity and simultaneity build up a conspicuous result. 
 
 The phenomenon of serial resemblance is in fact an expression 
 of the capacity of repeated parts to vary similarly and simul- 
 taneously. In proportion as in their variations such parts retain 
 this capacity the relationship is preserved, and in proportion as it 
 is lost, and the parts begin to vary independently, exhibiting 
 differentiation, the relationship is set aside. It will be noticed 
 that to render the converse true we must extend the conception of 
 Serial Homology in special cases to organs not commonly regarded 
 as serially homologous with each other, but which having assumed 
 some common character thereafter may vary together (cp. p. :*()!»). 
 
 In the power of independent Variation, members of series once 
 more exhibit the property of "unity" that we have already noticed 
 as appearing in the manner in which the number of the members 
 is changed. ' The fact that members of series should hi' capable of 
 varying as "individuals" is paradoxical. Such members, teeth, 
 digits, segments of Arthropods, and the like, are each made up of 
 various tissues endowed with miscellaneous functions and d i ss imil ar 
 in their morphological nature. Nevertheless each group is capable 
 
570 MERISTIO VARIATION. [part I. 
 
 of independent division and of separate Variation. Single digits for 
 instance may thus be independently hypertrophied as a whole, single 
 segments or single appendages or pairs of appendages may be differ- 
 entiated in some special way, and so forth. 
 
 At this point reference may again be made to that extraordinary 
 Discontinuity of Variation appearing in what I have called Ho- 
 mceosis, so strikingly seen in the few Arthropod cases given (p. 146), 
 and so common in flowering plants. In these changes a limb, 
 a floral segment, or some other member, though itself a group of 
 miscellaneous tissues, may suddenly appear in the likeness of some 
 other member of the series, assuming at one step the condition to 
 which the member copied attained presumably by a long course of 
 Evolution. 
 
 Many times in the course of this work we have had occasion to 
 consider the modifications in the conception of Homology demanded 
 by the facts of Variation. It is needless to speak further of this 
 matter here, and the reader is referred to pp. 125, 191, 269, 394 
 and 417, where the subject is discussed in relation to Linear Series 
 of several kinds, and to the facts given in Chapter XVI and at 
 p. 433 bearing on the same questions in their application to Radial 
 Series. The outcome of these considerations shews, as I think, 
 that the attribution of strict individuality to each member of a 
 series of repeated parts leads to absurdity, and that in Variation 
 such individuality may be set aside even in a series of differentiated 
 members. It appears that the number of the series may be in- 
 creased in several ways not absolutely distinct, that a single 
 member of the series may be represented by two members, that 
 a terminal member may be added to the series, and also that the 
 number of the members may change, no member precisely corre- 
 sponding in the new total to any one member of the old series : in 
 short, that with numerical change resulting from Meristic Variation 
 there may be a redistribution of differentiation. 
 
 But though this is, in my judgment, a fact of great consequence, 
 its relation to the Study of Variation is merely incidental. It is 
 not so much that to enlarge the conception of Homology so as to 
 include the phenomena of Meristic Variation is a direct help, as 
 that to maintain the old view is a hindrance and keeps up an 
 obstacle in the way of any attempt to apprehend the real nature 
 of the phenomena of Division, and hence of Meristic Variation. 
 So long as it is supposed that each member of a series of repeated 
 parts is literally individual, it is impossible to form any conception 
 of Division that shall include the facts of Meristic Variation, for in 
 Variation it is found that the members are divisible. 
 
 It is an unfortunate thing that the study of Homology has been 
 raised from its proper place. The study of Homologies was at first 
 undertaken as a means of analyzing the structural evidences of 
 relationship, and hence of Evolution. This is its proper work and 
 
chap, xxv.] CONCLUDING REFLEXIONS. 571 
 
 use ; but the pursuit of this search as an aim in itself has led to 
 confusion, and has tended to conceal the fact that there are pheno- 
 mena, to which the strict conception of individual Homology is not 
 applicable. 
 
 This exaggerated estimate of the fixity of the relationship of 
 Homology has delayed recognition of the Discontinuity of Meristic 
 Variation, and has fostered the view that numerical Variation 
 must be a gradual process. 
 
 This view the evidence shews to be wrong, as it was also im- 
 probable. 
 
 Brief allusion may be made to three separate points of minor un- 
 importance. 
 
 It is perhaps true that, on the whole, series containing large num- 
 bers of undifferentiated parts more often shew Meristic Variation than 
 series made up of a few parts much differentiated, but throughout the 
 evidence a good many of the latter class are nevertheless to be seen. 
 
 Reference may be made to a point that might with advantage be 
 examined at length. The fact that Meristic Variation may take place 
 suddenly leads to a deduction of some importance bearing on the expect- 
 ation that the history of development is a representation of the course of 
 Descent. In so far as Descent may occur discontinuously it will, I 
 think, hardly be expected that an indication of the previous term will 
 appear in the ontogeny. For example, if the four-rayed Tetracrinus 
 may suddenly vary to both a five-rayed and also to a three-rayed form 
 (see p. 437) it is scarcely likely that either of these should go through 
 a definitely four-rayed stage; and if the origin of the four-rayed form 
 itself from the five-rayed form came similarly as a sudden change, it 
 would not be expected that a five-rayed stage would be found in its 
 ontogeny. Similarly, if a flower with rive regular segments arise as a 
 sport from a flower with four, it would not, I suppose, be expected that 
 the fifth segment would arise in the bud later than the other four. I 
 suggest these examples from Radial Series, as in them the question is 
 simpler, but similar reasoning may be applied to many cases of Linear 
 Series also. 
 
 It will be noted that the attempt to apply to numerical variations 
 the conception of Variation as an oscillation about <>n> mean is not 
 easy, difficulty arising especially in regard to the choice of a unit for 
 the estimation of divergence. In few cases can facts be collected in 
 quantity sufficient even to sketch the outline of such an investigation : 
 but, to judge from the scanty indications available, it seems that in 
 cases of numerical change variations to numbers greater than the 
 normal number, and to numbers less than it are not generally of equal 
 frequency. Probably no one would expect that they should be so. 
 
 As was stated in the Introduction, wo arc concerned here with 
 the manner of origin of variations, not with tin- manner of their 
 perpetuation. The latter forms properly a (list ind subject. We 
 may note however, in passing, how little do the lew known facta 
 bearing on this part of the problem accord with those ready-made 
 
572 MERISTIC VARIATION. [part i. 
 
 principles with which we are all familiar. Upon the special 
 fallacy of the belief that great Variation is much rarer in wild than 
 in domesticated animals we have often had occasion to dwell. As 
 was pointed out in the discussion of the evidence on Teeth (p. 266) 
 this belief arises from the fact that domesticated animals are for 
 the most part variable, and that w r e have every opportunity of ob- 
 serving and preserving their variations. To compare rightly their 
 variability with that of wild animals choice should be made of 
 animals that are also variable though wild. Taken in this way the 
 comparison is fair, and as I have already said, if we examine the 
 variation in the vertebrae of the Sloths, in the teeth of the Anthro- 
 poid Apes, in the colour of the Dog-whelks {Purpura lapillus), &c, 
 we find a frequency and a range of Variation matched only by 
 the most variable of domesticated animals. 
 
 It is needless to call attention to the fact that in hardly any 
 cases even of extreme variations in wild creatures is there evidence 
 that the animal was unhealthy, or ill nourished, or that its economy 
 was in any visible way upset ; but in almost every example, save 
 for the variation, the body had the ajDpearance of normal health. 
 
 After all that has been said few perhaps will still ask us to 
 believe that the fixity of a character is a measure of its importance 
 to the organism. To try to apply such a doctrine in the open air 
 of Nature leads to absurdity. Let one more case be enough. I go 
 into the fields of the North of Kent in early August and I sweep 
 the Ladybirds off the thistles and nettles of waste places. Hun- 
 dreds, sometimes thousands, may be taken in a few hours. They 
 are mostly of two species, the small Coccinella decempunctata .or 
 variabilis and the larger C. septempunctata. Both are exceedingly 
 common, feeding on Aphides on the same plants in the same places 
 at the same time. The former (G. decempunctata) shews an ex- 
 cessive variation both in colours and in pattern of colours, red- 
 brown, yellow-brown, orange, red, yellowish-white and black, in 
 countless shades, mottled or dotted upon each other in various 
 ways. The colours of pigeons or of cattle are scarcely more variable. 
 Vet the colour of the larger G. septempunctata is almost absolutely 
 constant, having the same black spots on the same red ground. 
 The slightest difference in the size of the black spots is all the 
 variation to be seen. (It has not even that dark form in which 
 the black spreads over the elytra until only two red spots remain, 
 which is to be seen in C. bipunctata.) To be asked to believe that 
 the colour of G. septempunctata is constant because it matters to 
 the species, and that the colour of C. decempunctata is variable 
 because it does not matter, is to be asked to abrogate reason. 
 
 But the significance of the facts does not stop here. When, 
 looking further into the variations of 0. decempunctata it is found 
 that most of its innumerable shades of variation are capable of 
 being grouped round some eight or ten fairly distinct types, surely 
 
chap, xxv.] CONCLUDING REFLEXIONS. 57 3 
 
 an expectation is created in the mind that the distinctness of these 
 forms of varieties, all living [and probably breeding] together, may 
 be of the same nature as the distinctness of Species : and since it 
 is clear that the distinctness of the varieties is not the work of 
 separate Selection we cannot avoid the suspicion that the same 
 may be true of the specific differences too. 
 
 An error more far-reaching and mischievous is the doctrine 
 that a new variation must immediately be swamped, if I may use 
 the term that authors have thought fit to employ. This doctrine 
 would come with more force were it the fact that as a matter of 
 experience the offspring of two varieties, or of variety and normal, 
 does usually present a mean between the characters of its parents. 
 Such a simple result is, I believe, rarely found among the facts of 
 inheritance. It is true that with regard to this part of the problem 
 there is as yet little solid evidence to which we may appeal, but in 
 so far as common knowledge is a guide, the balance of experience 
 is, I believe, the other way. Though it is obvious that there are 
 certain classes of characters that are often evenly blended in the 
 offspring, it is equally certain that there are others that are not. 
 
 In all this we are still able only to quote case against case. 
 No one has found general expressions differentiating the two 
 classes of characters, nor is it easy to point to any one character 
 that uniformly follows either rule. Perhaps we are justified in the 
 impression that among characters which blend or may blend evenly, 
 are especially certain quantitative characters, such as stature : while 
 characters depending upon differences of number, or upon quali- 
 tative differences, as for example colour, are more often alternative 
 in their inheritance. But even this is very imperfectly true, and 
 as appeared in the case of Earwigs (p. 40) there may be a definite 
 dimorphism in respect of a character which to our eye is simply 
 quantitative. Nevertheless it may be remembered that it is 
 especially by differences of number and by qualitative differences 
 that species are commonly distinguished. Specific differences are 
 less often quantitative only. 
 
 But however this may be, whatever may be the meaning of 
 alternative inheritance and the physical facts from which it results, 
 and though it may not be possible to find general expressions to dis- 
 tinguish characters so inherited from characters that may blend, it 
 is quite certain that the distinctness and Discontinuity of many 
 characters is in some unknown way a part of their nature, and is 
 not directly dependent upon Natural Selection at all. 
 
 The belief that all distinctness is due to Natural Selection, and 
 the expectation that apart from Natural Selection there would be 
 a general level of confusion, agrees ill with the facts of Variation. 
 We may doubt indeed whether the ideas associated with that 
 flower of speech, "Panmixia," are not as false to the laws of Hie as 
 the word to the laws of language. 
 
574 MERISTIC VARIATION. [part I. 
 
 But beyond general impression, in this, the most fascinating 
 part of the whole problem, there is still no guide. The only way 
 in which we may hope to get at the truth is by the organization of 
 systematic experiments in breeding, a class of research that calls 
 perhaps for more patience and more resources than any other form 
 of biological inquiry. Sooner or later such investigation will be 
 undertaken and then we shall begin to know. 
 
 Meanwhile, much may be done to further the Study of Varia- 
 tion even by those who have none of the paraphernalia of modern 
 science at command. Many of the problems of Variation are pre- 
 eminently suited for investigation by simple means. If we are to 
 get further with these problems it will be done, I take it, chiefly 
 by study of the common forms of life. There is no common shell 
 or butterfly of whose variations something would not be learnt were 
 some hundreds of the same species collected from a few places and 
 statistically examined in respect of some varying character. Any- 
 one can take part in this class of work, though few do. 
 
 At the present time those who are in contact with the facts and 
 material necessary for this study care little for the problem, or at 
 least rarely make it the first of their aims, and on the other hand 
 those who care most for the problem have hoped to solve it in 
 another way. 
 
 These things attract men of two classes, in tastes and tempera 
 ment distinct, each having little sympathy or even acquaintance 
 with the work of the other. Those of the one class have felt the 
 attraction of the problem. It is the challenge of Nature that 
 calls them to work. But disgusted with the superficiality of 
 "naturalists" they sit down in the laboratory to the solution of 
 the problem, hoping that the closer they look the more truly will 
 they see. For the living things out of doors, they care little. Such 
 work to them is all vague. With the other class it is the living 
 thing that attracts, not the problem. To them the methods of 
 the first school are frigid and narrow. Ignorant of the skill and of 
 the accurate, final knowledge that the other school has bit by bit 
 achieved, achievements that are the real glory of the method, the 
 "naturalists" hear onlv those theoretical conclusions which the 
 laboratories from time to time ask them to accept. With senses 
 quickened by the range and fresh air of their own work they feel 
 keenly how crude and inadequate are these poor generalities, and 
 for what a small and conventional world they are devised. Dis- 
 appointed with the results they condemn the methods of the 
 others, knowing nothing of their real strength. So it happens 
 that for them the study of the problems of life and of Species 
 becomes associated with crudity and meanness of scope. Beginning 
 as naturalists they end as collectors, despairing of the problem, 
 Turning for relief to the tangible business of classification, account- 
 ing themselves happy if they can keep their species apart, caring 
 
chap, xxv.] CONCLUDING REFLEXIONS. 575 
 
 little huw they became so, and rarely telling ns how they may be 
 brought together. Thus each class misses that which in the 
 other is good. 
 
 But when once it is seen that, whatever be the truth as to the 
 modes of Evolution, it is by the Study of Variation alone that the 
 problem can be attacked, and that to this study both classes of 
 observation must equally contribute, there is mice more a place 
 for both crafts side by side: for though many things spoken ..f in 
 the course of this work are matters of doubt or of controversy, of 
 this one thing there is no doubt, that if the problem of Species i^ 
 to be solved at all it must be by the Study of Variation. 
 
INDEX OF SUBJECTS. 
 
 Acanthoderes nigricans, double (?) leg, 
 
 548 
 Acanthodrilus, double tail, 565 
 Acanthothyris, double monster, 566 
 Accessory hoofs of Ox, connected with 
 
 supernumerary digits, 285 
 Acherontia atropos, colours of larva?, 304, 
 
 305 
 Acinopus lepelletieri, extra legs, 498 
 Actinometra, variation in number of 
 
 radial joints, 421; 4-rayed specimen, 
 
 437 ; 6-rayed, 437 
 Adaptation, Study of, as a method of 
 
 solving problems of species, 10; 
 
 logical objection to the method, 12 ; 
 
 speculations as to, avoided, 79; of 
 
 species, approximate only, 11 
 Adimonia tanaceti, double (?) antenna, 
 
 550 
 Agabus uliginosus, double (?) leg, 548 
 Agestrata dehaanii, extra legs, 491 
 Agonum sexpunctatum, double (?) leg, 
 
 547; riduum, double (?) antenna, 550 
 Agra catenulata, extra legs, 512 
 Akis punctata, double (?) antenna, 551 
 Alans sordidus, extra legs, 508 
 Aleochara mcesta, extra legs, 488 
 Allantus, extra appendage, 544 
 Allolobophora, generative organs of, 160, 
 
 162, 165 ; duplicity of head and tail, 
 
 565 ; lissaensis, spermathecae, 165 
 Allurus, generative organs of, 164, 165; 
 
 putris, 165; hercynius, tetraedrus, 164 
 Alytes, vertebras, 127; axial duplicity, 
 
 561 
 Amblypneustes, 4-rayed, 443; 6-rayed, 
 
 446; partial reduction of a ray, 443; 
 
 partial duplicity of a ray, 446 
 Ammoccetes, alleged case of eight pairs 
 
 of gill-openings, 174 
 Ampedus ephippium, double (?) antenna, 
 
 551 
 Amphicyclus (Holothurian), tentacles 
 
 not in multiples of five, 435 
 Amphimallus solstitialis, extra antenna?, 
 
 515 
 Amphioxus, number of gill- slits, 174. 
 Anagallis arvensis, colour- variation, 44 
 Anas querquedula, division of digits, 392 
 Anchomenm sexpunctatus, extra antenna?, 
 
 523; double (?) antenna, albipes, an- 
 
 gusticollis, 550 
 Angora breeds, 55 
 Anisoplia floricola division of epistome, 
 
 454 
 Annelids, segmentation compared with 
 
 that of Chordata, 86; imperfect seg- 
 mentation, 156; spiral segmentation, 
 
 157 ; variation in generative organs, 
 159 ; axial duplicity, 563 
 Anomala junii, extra antenna?, 515 
 A user, spinal nerves, 130, 133 
 Antedon, variation in number of radial 
 joints, 421; 4-rayed specimen, 436; 
 6-rayed specimen, 437; abnormal 
 branching, 438 
 Antenna developed as foot, 146, 147 
 Anteuna?, variation in number of joints, 
 Prionida?, 411; Polyarthron, 
 412; Lyriphlebus, 412; 
 Donatio,, 413; Forficuhi, 
 413 
 extra, in Secondary Symmetry, 
 513-522 ; symmetry un- 
 known, 522; arising from 
 head, 551 
 supposed double, 548 
 Anthia, extra legs, 502 
 Antkocharis cardamines, colour-varia- 
 tion, 45 
 eupheno, 45 ; ione, 72 
 Anthropoid Apes, Variation in Verte- 
 bra?, 116; teeth, 199; digits, 349 
 Aphodius, extra legs, 494 
 Apis mellifica, union of compound eyes, 
 
 461 
 Appendages, joints of, 410 
 
 supernumerary, arrange- 
 ment of evidence, 474 
 in Secondary Symmetry, 
 475 ; mechanical model 
 illustrating relations, 
 480; duplicity of, 406, 539 
 Apteryx, brachial plexus, 130 
 Apus, extra fiabellum, 536 
 Aquila chrysaetos, extra digits, 393 
 Archibuteo lagopus, extra digit, 392 
 Arctia, colour-variation, 46 
 Arctocephalus australis molars, 243 
 Arge pherusa, eye-spots, 295 
 Avion, sinistral, 54 
 
 Aromia moschata, extra legs, 485, 503, 
 512 ; double (?) antenna, 3 cases, 551 
 Artemia, salina and milhausenii, 96; 
 gracilis, 100; relation to Branchipus, 
 96 ; segmentation of abdomen, 100 
 Arteries, renal, 277; in a case of double- 
 hand, 333 
 Arthronomalus, number of segments, 94 
 Arthropoda, variation in number of 
 segments, 87; Homoeosis in append- 
 ages, 146; axial duplicity, 565 
 Articular processes, change from dorsal 
 to lumbar type, 109 ; variations in 
 position of change, 110, 112, 114, 117, 
 122 
 
INDEX OF SUBJECTS. 
 
 577 
 
 Artiodactyla, polydactylism, 373; syn- 
 dactylism, 383 ; teeth, 245, 246 
 Ascidia plebeia, specimens having every 
 fourth vessel of branchial sac dilated, 
 172 
 Ascidians, variation in branchial struct- 
 ures, 171, 172; extra atriopore, 456 
 Ass, canines, 245 ; molars, 246 ; absence 
 
 of digital variation in, 360 
 Astaeus fluvidtilis, colour-variation, 44 
 
 variation in number 
 of oviducal open- 
 ings, 84, 152 
 absence of male open- 
 ing, 154 
 absence of oviducal 
 
 opening, 152, 153 
 
 absence of opening 
 
 from green gland, 
 
 154 
 
 extra chela?, 529, 537 
 
 extra processes from 
 
 chela?, 536 
 repetition of exopod- 
 ite of antenna, 538 
 A. leptodactylus, extra dactylopodites, 
 
 532 
 A. pilimanus and braziliensis, apparent 
 presence of female opening in males, 
 155 
 Aster ias, variation of pedicellariae, 429; 
 arms, 439 
 with 8 rays and 3 madreporites, 
 
 440; extra water-pore, 466 
 polaris, normally 6-rayed, 433 
 problema, tenuispina, undergo 
 fission, 433 
 Asterina, 4-raved and 6-rayed specimens, 
 
 440 
 Asteroidea, arms, 439-441 
 Ateles, teeth, 205, 206, 207 
 Atriopore, extra, in Ascidians, 456 
 Attelabus, division of pronotum, 455 
 Aulastoma gulo, asymmetrical variation 
 
 in generative organs, 167 
 Aurelia aurita, Meristic Variation of, 
 
 426 ; statistics as to, 428 
 Auricles, cervical, in Man, 177; in Pig, 
 179; in Sheep and Goats, 180; are 
 repetitions of ears, 180 
 
 Baer, von, Law of, 8; its proper scope, 
 9; probably not applicable to cases 
 of Discontinuous Meristic Variation, 
 571 
 
 Balance between mamma?, 189 ; between 
 teeth, 213 
 
 Balanocrinus, 4-rayed specimens, 436 
 
 Balanoglossus, two methods of develop- 
 ment, 9 ; number of gill-slits, 174 ; 
 extra proboscis-pore, 466 ; supposed 
 relation to Chordata, 86 
 
 Batrachia, extra limbs, 554; spinal 
 nerves, 141; vertebra?, 124; extra 
 
 B. 
 
 atrial opening, 465; axial duplicitv, 
 561 
 Bdell08tQma t individual and specific 
 variations in number of 
 gill-sacs, 173, 174 
 cirrhatum, heptatrema, 
 heterotrema, hexatrema, 
 173; btichoffi,polytrema, 
 174 
 Beech, fern -leaved, 25 
 Bees, hermaphrodite, 68 ; union of 
 eyes, 461 ; antenna modified as foot, 
 147 
 Beetles, variation of horns, 38; an- 
 tenna?, 411, 413; extra ap- 
 pendages in Secondary Sym- 
 metry, 475; legs, 483; an- 
 tenna?, 513; palpi. 524; di- 
 vision of pronotum. 455 
 supposed double leg.-,, 544 ; sup- 
 posed double antennas, 51s ; 
 supposed double palpi, 551 
 Benibidium striatum, extra palpi, 524 
 Bettontjia, variation in molars, 258; 
 
 cuniculus, lesueri, penicillata, 258 
 Bilateral asymmetry, Homceosis in cases 
 
 of, 465 
 Bilateral Series, nature of. 88; Bieristic 
 
 Variation of, 448 
 Bilateral Symmetry. 19 ; in variation of 
 vertebra?, 128; in variation 
 of Annelids, 167 ; in varia- 
 tion of mamma, 183; in 
 variation of teeth, 267; in 
 cervical fistula. 175; in 
 variation of ocelli, 292; in 
 variation of digits, 402; in 
 variation in antennae <>f /•'<</•- 
 fieula, 414; in variation of 
 Radial Series, 427; in ab- 
 normal branching of Ante- 
 don, 438; in distribution of 
 triasters in segmenting egg, 
 464 ; in abnormal union of 
 blastomeres, 164 
 as found in manna and p< -. 
 
 369, 403 
 influence on Secondary Sym- 
 metries doubtful, 5 7 
 Bipinnaria, extra water-pore, (66 
 Birds, spinal nerves, 129; digital Varia- 
 tion, 390, 396 
 Blaniulus, mod.' of increase in uum 
 
 of segments, 93 
 Blaps, extra legs, 512; extra antennae, 
 attenuate, 522; double antenna, ehev- 
 rolati } cylindrica, similis, •">•"> 1 
 Blatta, variation in number ><( tarsal 
 joints, discussion of, 63; facts, 1 1 5 : 
 regeneration of tarsus with 4 joint-. 
 
 116 
 
 Blue, as variation of i. .1. 1 1 
 Boar, Wild, extra digits, 38 
 Bombinator, vertebra . 127 
 
 37 
 
578 
 
 INDEX OF SUBJECTS. 
 
 Bomlms variabilis, antenna developed as 
 
 foot, 147 
 Borribyx, extra wing, quercus, 284, rubi, 
 
 282 
 Box-turtle, digital variation, 396 
 Brachial plexus, birds, 129; Man, 113, 
 
 135 ; Bradypodidae, 141 
 Brachinus crepitans, double (?) leg, 546 
 Brachiopod, double monster, 566 
 Bradypodidae, vertebrae, 118; brachial 
 
 plexus, 141 
 Brachy teles, teeth, 205 
 Branchiae, variations in number, 172 
 Branchiomma, double tail, 564 
 Branchipus, segmentation of abdomen, 
 97; relation to Artemia, 
 96 — 101 ; species dis- 
 tinguished by sexual 
 characters of male, 100 
 ferox, xpinosus, 97, 100; 
 stagnalis, 100 
 Brill, pigmentation of blind side, 468, 
 
 470 
 Brimstone butterfly, variation in colour, 
 
 45 ; nature of pigment, 48 
 Broseus vulgaris, double (?) leg, 547 
 Buccinum, teeth, 262 ; double operculum, 
 
 457 
 Bucorvus, brachial plexus, 131, 132 
 Bulldog, teeth, 210, 221 
 Bulldog-headed races of Dogs, 57: of 
 
 Fishes, 57 
 Buteo latissimus, extra digit, 393 ; vul- 
 garis brachial plexus, 131 
 Buzzard, extra digit, 392, 393 
 
 Calathus fuscus, extra eye, 280; extra 
 legs, cisteloides, 506, fulvipes, 507, 
 grceeus, 505 
 
 Callidium variabile, double (?) antenna, 
 
 551; ciolaceum, extra antenna arising 
 
 from head, 551 
 Call into rpha, colour-variation of species 
 
 of this genus, 46 
 Callinectes hastatus, extra spines on 
 
 lateral horn of carapace, 557 
 Callithrix, teeth, 208 
 Callorhinus ursinus, teeth, 343 
 Caloptenus «]>retus, colour-variation, 44 
 Calopteron reticulatum, extra antennae, 
 
 522 
 Calopus cisteloides, extra legs, 512 
 Calosoma investigator, extra antennae, 
 
 523; auropunctatum, double (?) leg, 
 
 548; double (?) antenna, sycophanta, 
 
 triste, 550 
 Cancer pagurus, maxillipede developed 
 
 as chela, 149, 150 ; extra parts of 
 
 limbs, 527 ; variations in chelae, 530 — 
 
 536 
 Canidje, digits, 401; mammae, 189 
 
 teeth, 209—222; incisors, 210; 
 canines, 210; premolars, 211; 
 molars, 217 
 
 CaxidjE, teeth, 
 
 Canis antarcticus, 215; azarce, 
 217; cancrivorus, 218; corsac, 
 214; dingo, 212, 215; javan- 
 icns, 209; lacjopus, 220; later- 
 alis, 212; lupus, 212,213,217, 
 220; magellanicus, 218; me- 
 somelas, 212, 217 ; occidentalis, 
 214,219 ipennsylvanicus, 210 ; 
 prinuevus, 209; procyonoides, 
 215,220; vetulus, 217 ; viver- 
 rinus, 212; vulpes, 210, 212, 
 213, 214, 219, 220 ; zerda, 220 
 vertebras, 122; cervical rib, 122 
 Canines, supernumerary, Tiger, 225 ; 
 
 Ass, 245; divided in Dor. 211 
 Capreolus, horns, 286; union of horns, 
 
 460; polydactylism, 371, 379 
 Caprimulgus, brachial plexus, 131 
 Carabus, antenna, supposed cases of 
 double, auratus, cancellatus, 
 catenulatus, emarginatus, ex- 
 aratus, intricatus, italicus, 
 sylvestris, 550 
 antennae, paired extra, arv en- 
 sis, 523; auronitens, 522; 
 monilis, 522; sacheri, 523 
 leg, supposed cases of double, 
 creutzeri, 547; helluo, 547; 
 intricatus, 545; melanckoli- 
 cus, 548; nemoralis, 547; 
 septemcarinatus, 547 
 legs, extra in Secondaiy Sym- 
 metry, auratus, 511; auro- 
 nitens, 511 ; cancellatus, 511; 
 catenulatus, 512; grcecus, 
 486; granulatus,48£; irregu- 
 laris, 497; italicus, 512; 
 marginalis, 484; perforatus, 
 484; sche idler i, 4 V 3 
 palpi, supposed cases of double, 
 auratus, purpurascens, splen- 
 dens, 552 
 pronotum, division of, lothar- 
 ingus, 456; scheidleri, 455 
 Carcinomata, multipolar cells in, 431 
 Garcinus nucnas, external segmentation 
 of abdomen changed by parasites, 95 ; 
 extra parts in limbs, 527, 531, 534 
 Carnivora, teeth, 209; vertebrae, 122 
 Carp, bulldog-headed, 57 
 Cassowary, feathers partially without 
 
 barbules, 55 
 Castration, parasitic, of crabs, 95 
 Cat, variation in colours of, 48 
 
 digits, 312, 313; porydact3*lism in- 
 herited, 323 
 spinal nerves, 138 
 teeth, 222 
 vertebrae, 122 
 Caterpillars, segmental Repetition of 
 
 pattern in, 25 
 Catocala nupta, colour-variation in hind 
 wings, 44, 46 
 
INDEX OF SUBJECTS. 
 
 579 
 
 Caudal fin, division of, in Gold-fishes, 
 
 451 
 Cebida), teeth, 205 
 Cebus, teeth, 205 
 Cell-division, variations in, 430 
 Centrosomes, variations in number of, 
 
 480 
 Cephalotia, 458 
 Cerambyx, extra legs, 491; double (?) 
 
 antenna, cerdo, scopolii, 551; extra 
 
 antenna arising from head, cerdo, 551 
 Cercocebus, teeth, 204 
 Cercopithecus, teeth, 204; abnormality 
 
 in, 204 
 Ceroglossus valdivice, extra legs, 500 
 Cervical vertebrae, assumption of dorsal 
 
 characters, Man, 107 
 Cervus axis, molar, 246 
 
 rufus, premolar, 246 
 darna, extra digits, 379 
 Cestoda, variation in segmentation of, 
 
 168; bifurcation and other conditions 
 
 allied to duplicity, 565 
 Cestracion, teeth, 261 
 Cetonia, extra legs, opaca, 488, morio, 
 
 512 
 Chalcides, digital variation in the genus, 
 
 395 
 Chamois, extra horns, 286 
 Charadrius, brachial plexus, 130, 132 
 Chela?, extra parts in Secondary Sym- 
 metry, 528 ; amorphous cases, 
 538; duplicity of, 540 
 developed from third maxillipede 
 in Cancer, 149 
 Chelonia, axial duplicity, 563 
 Gheraps preissii, apparent presence of 
 
 female openings in males, 155 
 Chiasognathus grantil, double (?) anten- 
 na, 551 
 •Chilognatha and Chilopoda, variation in 
 
 segmentation of, 93 
 Chirocephalus, sujaernumerary horn to 
 
 generative sac, 457 
 Chimpanzee, vertebrae, 116 
 
 spinal nerves, 139 
 teeth, 202 
 'Chionobas, eye-spots, 295 
 Chironomw, double head, 565 
 Chiropotes, 208 
 
 Chitons, repetition of eyes in, 26; vari- 
 ation in colours of scutes, 307 
 ChUenius nigricornis, extra legs, 512; 
 
 double (?) leg, holosericus, 546, dijli- 
 
 nis, 548, vestitus, 548 
 Cheerocampa, colours of larva 3 , 304 
 Cholapus, vertebrae, 118, 120; brachial 
 
 plexus, 141 
 Cholornis, hallux absent, 397 
 Chordata, segmentation of, 86 
 Chroicocephalus, brachial plexus, 130 
 dhrysemys, axial duplicity, 563 
 Chrysomela, division of pronotum,/HCt7f(i, 
 455 
 
 Chry8omela, extra legs, banksii, 194; 
 graminis, 198 
 double (?) leg, hcemoptera, 
 
 517 
 double (?) antenna, eacalia , 
 550 
 
 Chub, bulldog-headed, 58 
 
 Cicindela sylvatica, double (?) antenna, 
 
 550 
 Cidarite8, 4-rayed specimen, 411 
 Clmbex axillaris", antenna developed as 
 
 foot, 146 
 Cimoliasaurus, imperfect division of ver- 
 tebra?, 103 
 Ciona intestinal is, variation in number 
 
 of stigmata, 172 
 Cistudo, digital variation in, 396 
 Cladocera of salt lakes, 101 
 Clausilia bidens, extra eye, 280 
 Clavatella, variation in number of s< g 
 ments, 425 ; in number of eyes in each 
 segment, 425 
 Clupea pilchardus, scales, 274 
 Glythra quadripunctata, extra legs. 5os 
 Clytus liciatus, extra legs, 508; extra 
 antenna?, arcuatus, 522, tricolor, 522; 
 double (?) antenna, arcuatus, 551 
 Coccinclla decempunctata, bipunctata 
 and septeiupunctata, colour-variation, 
 49, 572 
 Cochin fowls, "silky" variety, 55 
 Cockroach, variation in number of tarsal 
 
 joints, 63, 415 
 Coelenterata, imperfect division, 566 
 Colias, colour-variation, 44 ; interme- 
 diates between ediua and helice, 14; 
 varieties of hyale, 45 
 Colobns, teeth, 204 
 Colour and Colour-patterns, variations 
 
 in, 42, 288, 572 
 Colour-variation, discontinuity of, per- 
 haps chemical, 72; simultaneous, in 
 segments, <\c, 303 
 Coluber, double monster, 561 
 Columba, brachial plexus, 131, 134 
 Colymbetes sturmii, extra legs, 512; ad- 
 spersus, double (?) leg, 548; coriaceut, 
 double (?) antenna, 550 
 Col y tubus, brachial plexus, 130 
 Conepatus chilensti and mapurito, teeth, 
 
 232 
 Continuity, use of term as applied to 
 Variation. 15; of differences in En- 
 vironment, 5 
 
 Copepoda, Of salt lakes, 101 
 
 Cordylophora lactutris, porystomatous 
 
 specimens, 566 
 Correlation, between variations of nerves 
 
 and vertebra, 145; between Keristic 
 
 and Substantive Variation, L96 
 
 CorvtU, brachial plexus, 131 
 Corymbitet cupretu, colour-variation. 18 
 Counterparts, simultaneous variation of, 
 500 
 
 M7— 2 
 
580 
 
 INDEX OF SUBJECTS. 
 
 Cow, variation in number of teats, 188 
 
 Crab, extra parts of appendages, 527 — 
 536 ; variation in segmentation of ab- 
 domen, 95 
 
 Crateronyx, extra wing, 285 
 
 Crayfish, variation in number of gene- 
 rative openings, 152 ; repetition of 
 parts of chelae, 529, 532, 537; extra 
 parts in antennas, 538 
 
 Cribrella, abnormal branching of an arm, 
 440 
 
 Crinoids, radial joints, 421; variation in 
 number of rays, 435 ; 4-rayed varieties, 
 436 ; 6-rayed varieties, 437 ; 3-rayed 
 and 5-rayed varieties of a 4-rayed 
 form, 437; variation in number of 
 canals in stems, 438; abnormal 
 branching, 438 
 
 Crista, division of embryos, 556 
 
 Crossarchus, teeth, 227—231 ; zebra, 230, 
 231 
 
 Crustacea, theory of descent of Yerte- 
 brata from, 29 ; of salt lakes, 100 ; 
 Secondary Symmetry in, 525; Homce- 
 osis in, 149 
 
 Cryptohypnus riparivx, extra legs, 509 
 
 Cryptophagus scanicus, dentatus, double 
 (?) antenna, 550 
 
 Ctenodrilus, double tail, 565 
 
 Cucumaria planei, with six radii, 433; 
 double monster, 566 
 aciculi, double monster, 566 
 
 Cnon, one lower molar absent, 209 
 
 Cupressocrinus, imperfect variation to 
 4-rayed state, 437 ; variation in num- 
 ber of canals in stalk, 438 
 
 Curve of Frequency of Variations, 37, 64 
 
 Cuvierian organs, variation in number of, 
 435 
 
 Cj'clopia, 458 
 
 Cygnus olor, cervical vertebras, 33 ; colour- 
 variation of young, 44 ; atratus, 
 brachial plexus, 130 
 
 Cyllo leda, variability of ocelli, 289 
 
 Cyncelurus, teeth, 222, 224 
 
 Cynocephalus jyorcarius, extra molar, 204 
 
 Cyprinus carpio, bulldog-headed varie- 
 ties^?; hungaricus, ditto, 58; auratus, 
 division of fins, 451 
 
 Cyprus, 4-horned sheep, 285 
 
 Cypselus, brachial plexus, 131 
 
 Cystophora cristata, premolars, 238; 
 molars, 243 
 
 Dachshund, hallux in, 401 ; duplicity of 
 
 hallux and pollex, 401 
 Dactylopodites. extra, 528 
 Dactylopsila, premolars, 255 
 Darwin's solution of problem of Species, 
 
 5; views on Reversion, 77; on sudden 
 
 Variation in eye-spots, 289 
 Dasyuridas, incisors, 247 
 Daayurua, incisors, 247 ; premolars, 255 ; 
 molars, 256 
 
 Dasyurus, viverrinus, variation in molars,. 
 256 
 maculatus, molars, 256 
 Deilephila euphorbia*, colours of larvae, 
 
 305; hippophaes, 305 
 Dendarus hybridus, extra antennas, 523 
 Descent, Doctrine of, assumed to be 
 
 true, 4 
 Diaptomus, colour-variation of eggs, 
 
 44 
 Dicotyles torqaatus, incisors, 245 
 Didolphyidae, incisors, 246 
 Didelphys, teeth, 246, 258 
 Digits, Variation of 
 
 Mammals. Capreolus, 374 ; Cat, 
 
 313; Cervus, 379; Dogs, 401; 
 
 Erinaceus, 397; Elephas, 397; 
 
 Goat, 377; Herpestidas, 346; 
 
 Horse, 360; Hylobates, 346; 
 
 Macacus, 340; Man, 324; Mule, 
 
 360, 370; Ox, 374, 383; Pig, 
 
 381, 387; Sheep, 373, 380 
 
 Birds. Anas, 392; Aquila, 393; 
 
 Archibuteo, 392; Buteo, 393; 
 
 Fowl,390;La/'us,393; Pheasant, 
 
 393; Rissa, 396; Turkey, 393 
 
 Reptiles. Chalcides, 395 ; Cis- 
 
 tudo, 396 
 
 Reduction in number, Man, 355, 
 
 358 ; Artiodactyla, 383 
 Union of, Ox, 383; Pig, 387 ; Man, 355 
 Variation in, associated with other 
 
 variations, 399 
 Inheritance of Variation in, 398 
 Recapitulation of evidence, 400 
 Dimorphic condition, its relation to the 
 
 monomorphic condition, 37 
 Dimorphism in Spinal nerves, 138; in 
 position of generative openings in 
 Pachydrilus, 165, 168 ; in secondary 
 sexual characters, 38 
 Diopatra, abnormal repetition, 159 
 Discoidea (Echinid), 4-rayed specimen, 
 
 442 
 Discontinuity of Species, 5 
 
 in Variation, a possibility, 
 17 ; suggestion as to its 
 nature, 68, 568 
 in chemical processes, ] 6, 
 
 48, 72 
 in colour-variation, 43, 48, 
 72; in colour-patterns, 
 48 
 in states of matter, 16 
 of Meristic Variation per- 
 haps mechanical, 70 
 of Substantive Variation 
 perhaps in part chemi- 
 cal, 71 
 in the Variation of spinal 
 
 nerves, 145 
 in the Variation of the 
 generative organs of 
 Annelids, 168 
 
INDEX OF SUBJECTS. 
 
 581 
 
 Discontinuity in the Variation of digits, 
 •407 
 in Meristic Variation of 
 
 Radial Series, 423 
 partly dependent upon 
 Symmetry, 568 
 Discontinuous Variation, use of the term, 
 
 15 
 Disease, analogy with Variation, 74 
 Ditomus tricuspidatux, double (?) an- 
 tenna, 550 
 Division of organs, a process of repro- 
 duction, 193 
 of teeth, 268; of mamma?, 193; 
 of digits, 349, 369; of ten- 
 tacles, 280 ; of radius of 
 Echinid, 446; median, 454 
 Dog, cervical rib, 122; hairless, 57; bull- 
 dog, 210, 221; digits, 401; nipples, 
 189 
 teeth, 209—222; incisors, 210; 
 canines, 211 ; premolars, 213, 
 215; molars, 220; deficiencies in 
 Esquimaux, 215; in Inca, 216 
 Dog-whelk, colour-variation, 48 
 Domestication, variability falsely ascrib- 
 ed to, 266, 401 
 Dunacia bidens, Variation in antennre, 
 
 413 
 Dorcadion rufipes, extra legs, 512 
 Dorking Fowl, digital variations, 390 — 
 
 395 
 Dorocidaris papillata, variation in pedi- 
 
 cellaria?, 429 
 Double-foot, Artiodactyles, 378; Frog, 
 
 540; Macacus, 340; Man, 337, 338 
 Double-hand, 325, 331 
 Double Monsters, 559 
 Double-thumb, 349 
 Dromceolus barnabita, extra antennae, 
 
 523 
 Duck, no variation in number of digits 
 recorded, 401 ; cases of absence of 
 webs between toes, 401 
 Duplicity of single members of series not 
 distinct from other modes 
 of addition, 193, 407 
 of appendages, 406 ; in Arthro- 
 poda, 539; in Vertebrata, 
 539 
 axial, 559 
 Dutch pug, 57 
 
 DyscJiirim globuloxus, extra legs, 512 
 Dytiscus marginalis, extra legs, 512 
 
 Eagle, extra digits, 393 
 
 Ears, repetitions of, known as cervical 
 auricles, 180 
 
 Earthworms, variation of generative 
 organs, 159 ; of segmentation, 157 ; 
 asymmetrical arrangement of genera- 
 tive organs, 160, 161 ; table of arrange- 
 ment of ovaries, 162; duplicity of 
 head, 565, of tail, 565 
 
 Earwig, variation of forceps, 40 ; of 
 antennary joints, 413 
 
 Echinocomu, 4-rayed specimen, 441 ; 
 alleged case of 3 rays, 411 
 
 Echinodermata, Meristic Variation in, 
 432; variations of pedicellaria-, 429; 
 duplicity, 
 
 Echinoidea, Meristic Variation of, 411 ; 
 4-rayed specimens, 441; partial dis- 
 appearance of a ray, 413; partial 
 duplicity of a ray, 446; 6-rayed speci- 
 men, 445; pedicellariae, 429; variation 
 in number of genital pores, 446 ; sym- 
 metrical reduction of two rays, 4 13 
 
 Echinus melo, partial reduction of an 
 ambulacrum, 443 
 
 EcJtinus sphcera, partial reduction of an 
 interambulacrum, 445 
 
 Ectrodactylism, Man, 355, 358 
 
 Elater murinus, extra antennas, 522 ; 
 variabilis^ extra leg, 547 ; hirtus, 
 double (?) antenna, 551 
 
 Elcdone, supernumerary hectocotylus. 
 473 
 
 Eleodex pilosa, double (?) antenna, 551 
 
 Elephas, tusks, 244; hoofs, 397 
 
 Elytra, said to have been replaced by 
 legs in Prionus, 148 
 
 Embryology, as a method of investigating 
 problems of Descent, 7 
 
 Emperor moth, ocelli absent, 289, 301; 
 colour- variations of larva, 306 
 
 Emu fowls, 55 
 
 Enchytr&'idae, generative openings, 165 
 
 Encrinus, variation in number of radial 
 joints, 421 ; 4-rayed calyces. 436 ; 
 radius bearing only one arm, 438 
 
 Enema pan, extra legs, 512 
 
 Entoniscians, alter segmentation of 
 some crabs but not of all, !'"> 
 
 Enhydris, incisors, 211 
 
 Epiglottis, division of, 451 
 
 Epipodites, variation of in Hippolyte, 
 151 
 
 Epistome (of Beetle), division of, 1">1 
 
 Erebia bland inn, ocelli, 289 
 
 Erinaceus, variation in hallux, 3'.i7 
 
 Eriphia spinifrom, extra chela . 528 
 
 Eros minutus, extra Legs, 487 
 
 Enox Indus, bulldog-headed, 58 
 
 Esquimaux Dog, absi ace of first pre- 
 molars, 214, 215, •-'•-'}_ 
 
 Euchloe, pigments of, 72 
 
 Eugeniacrinus, 4-rayed specimens, i 
 
 Euprepia puipurea, extra palpi (alleged), 
 524 
 
 Eurycephahu maxillosus^ extra legs, 1^7 
 
 Euscnrpius, double tail, 565 
 
 Eve of Palinurtu developed as antenna, 
 160 
 
 Eye-colour of Man. 43 
 
 Eye-spots, 288; Variation as a whole. 
 
 291; outer /.one- first to appear, 291; 
 
 analogy with chemical phenomena. 
 
582 
 
 INDEX OF SUBJECTS. 
 
 292; in Linear Series, 288, 293; 
 simultaneous Variation of, 293 ; corre- 
 lated with variation of neuration, 293, 
 
 301 
 
 Arge, 295; Chionobas, 295; Hip- 
 parchia, 294; Satyrus, 295; 
 Morpho, 296 ; Vanessa, 299 ; 
 Junonia, 299, 300; Pararge, 300; 
 Saturnia, 301, 302; Raiidae, 302; 
 Polyplectron, 450 
 Eyes of Clavatella, variation in number, 
 
 425 
 Eyes of Molluscs, 279; of Insects, 280; 
 union of, 458, 461 
 
 Feathers, of "hairy" Moorhen, without 
 
 barbules, 55 
 Felid.e, digits, 313 
 
 teeth, 223—226 
 
 Felis brachyurus, 224; cali- 
 gata, 223 ; caracal, 224 
 catus, 224; chaus, 224; chi 
 nensis, 224 ; concolor, 223 
 domestica, 223, 224, 225, 226 
 eyra, 223; fontanieri, 225 
 226 ; inconspicua, 223 ; ja 
 guarondi, 224 ; javanensis 
 224; jubata, 224; leo, 226 
 /;//(.r, 226; manicirfata, 223 
 manul, 224; minuta, 223 
 nebulosa, 224; cwca, 224 
 pajeros, 224; pardalis, 226 
 pardus, 223, 226; tetraodon 
 223; tigrina, 22G; tigris, 224, 
 225 
 vertebrae, 122 
 Feronia muhlfeldii, extra legs, 485 
 Fins, division of, in Gold-fish, 451 
 Fishes, undifferentiated teeth in certain, 
 32 ; bulldog-headed, 57 
 
 division of caudal fins, 451 ; 
 scales, 274 ; flat-fishes, 466 
 Fistulae, cervical, 174; morphology of, 
 176 ; aural, 177 
 
 in Man, 175; in Pig, 179; in 
 Horse, 180; unknown in Sheep, 
 Goats and Oxen, 180 
 Flat-fishes, reversed varieties, 54, 466 ; 
 
 "double" varieties, 466 
 Fcenius tarsatorius, extra legs, 491 
 Foot, double, Artiodactyla, 378 ; Frog, 
 
 540; Macacus, 340; Man, 337, 338 
 Foraminifera, duplicity, 566 
 Forfieula auricularia, variation of for- 
 ceps, 40; of antennary joints, 413 
 Fowls, silky variety of, 55 
 
 digital variation in, 390; ovary 
 and oviduct, 465 
 Frog, vertebrae, 124; extra legs, 554; 
 double foot, 540 ; Secondary Sym- 
 metry, 554 
 Fusus antiquus, sinistral, 54 
 
 Galerita africana, extra legs, 495 
 
 Galerites albogalerus, 6-raved specimen, 
 445 
 
 subrotiuidus, 4-rayed specimen, 
 441 
 Galictis, teeth, barbara, vittata, 232 
 
 vertebrae, 123 
 GaUinula chloropus, hairy variety, 55 ; 
 
 extra digits, 392 
 Gallus, brachial plexus, 130; digits, 
 
 390; oviduct, 465 
 Garganey Teal, division of digits, 392 
 Garrulus, brachial plexus and ribs, 135 
 Gasteroxteu*, scales, 276 
 Gavialis, change in number of vertebrae, 
 
 123 
 Gecinus, brachial plexus, 131 
 Generative openings, repetition of, in 
 Astacus, 152; absence of, in Astacus, 
 152, 154; of Earthworms, 159; of 
 Hirudo, 166 
 Generative organs of Earthworms, varia- 
 tions in, 159; of Leeches, 165 
 Genital pores, variation in number in 
 
 Echini, 446 
 Geophilus, variation in number of seg- 
 ments, 94 
 Geotrupes mutator, extra legs, 500 : 
 
 typhcvus, extra antennae, 515 
 Gill-slits, of Ascidians, 171; of Hyxine, 
 172; of Bdellostoma, 173; of Ammo- 
 coctes, 174 ; of Notidanidae, 174 ; of 
 Balanoglossus and Amphioxus, 174 
 Glaucium luteum, colour-variation, 47 
 Gmelin's test for bile-salts, 292 
 Goat, incisor, 245 ; horns, 286 ; digits, 
 
 377 ; cervical auricles, 180 
 Gold-fish, simultaneous variation in 
 length of tail and fins, 309; division 
 of anal and caudal fins, 451; "Tele- 
 scope," 453 
 Gonepteryx rJiamni, similarity of fore 
 
 and hind wings, 
 25 
 colour - variation, 
 45 ; nature of 
 the yellow pig- 
 ment, 48 
 extra wing, 283 
 Goose, brachial plexus, 133; pygomelian. 
 
 401 
 Gorilla, vertebrae, 117; spinal nerves, 
 
 139; teeth, 202 
 Goura, brachial plexus, 130 
 Grits, brachial plexus, 130 
 Guinea-hen, double-hallux, 392 
 Guinea-pig, inversion of layers in, 9 
 Gido, teeth, 231 
 
 Haemal spines, division of, in Gold- 
 fishes, 453 
 Hair, absence of, in Mouse, Horse, 
 
 Shrew, 56 ; silky in Mouse, 55 ; 
 
 excessive length in mane and 
 
 tail of a horse, 309 
 
INDEX OF SUBJECTS. 
 
 583 
 
 "Hairy" Moorhen, 55 
 Halichoerus, vertebras, 123; molars, 242, 
 243 
 
 Haliotis, extra row of perforations, 287; 
 perforations occluded, 287; perfora- 
 tions confluent, 287 
 Halla, imperfect segmentation in, 156 
 Hallux, duplicity in Man, 349; Fowl, 
 390; variations in Kittiwake (Rissa), 
 396; Erinaceus, 397; Herpestidae, 397, 
 normally absent in certain birds, 396 
 Hammaticherus hews, double (?) an- 
 tenna, 551 
 Hand, digital variations in, 324; double, 
 325, 331 
 progressive series of Conditions, 
 324 
 Hapalida?, teeth, 208 
 Harpalus, rubripes, extra legs, 493; cal- 
 
 ceatus, double (?) antenna, 550 
 Hawthorn, variation of, 569 
 Hectocotylus, supernumerary, in Ele- 
 
 done, 473 
 Helictis orientalis, teeth, 233, 234 
 Helix kermovani, extra e3'e, 280 
 
 hispida, union of tentacles, 461 
 Heloderma, vertebrae, 123 
 Ilelops ceeruleus, extra antennae, 523 
 
 sulcipennis, extra palpi, 524 
 Hemiaster ; cases in which one ambula- 
 crum wanting, 445 ; two ambulacra 
 reduced, 443 ; duplicity of ambulacra, 
 446 
 Hepialus humuli, males like females in 
 
 Shetland, 254 
 Heptanchus, seven gills, 174 
 Heredity, objection to use of term, 75 ; 
 
 in digital variation, 398 
 Hermaphroditism, 67 ; in bees, 68 
 Hermodice carunculata , abnormal seg- 
 mentation, 158 
 Herpestid.e, hallux, 397 
 teeth, 227-231 
 
 Herpestes galera, 229; gracilis, 227, 
 228, 229; griseus, 229; ichneu- 
 mon, 229, 230, 231 ; microcephalus, 
 229; nipalcnsis, 227; nyula, 228; 
 persicus, 227; pulverulentus, 228, 
 229; smithii, 228, 229 
 Herring, supposed hybrid with Pilchard, 
 
 275 
 Heterocephalus, a naked Eodent, 56 
 Heterogeneity, universal presence of in 
 living things, 18 
 symmetrically distributed 
 around centres or axes, 
 19 
 Heterorhina nigritarsis, division of pro- 
 
 notum, 455 
 Hexanchus, six gills, 174 
 Hipparchia tithonus, eye-spots, 293, 294 
 Hippocampus compared with Pliyllo- 
 
 pteryx, 309 
 Hippoglossus pinguis, 471 
 
 Hippolyte fabricii, variation in epipo- 
 
 dites of legs, 151 
 Hirudinea, variation in generative 
 organs, 165 
 in colours, 304 
 Hirudo medicinalis, variation in numbei 
 
 of testes, 165, L66 
 officinalis, supernumerary penis, 
 166 
 HUter cadari rinus, extra legs, 512 
 Holopus rangi, 4-rayed specimen, 436 
 Holothurioidea, variation in number of 
 radii, 433; variations in numbers of 
 organs, 435; double monsters, 5C6 
 Homarus, repetition of parts in cheliped, 
 530; in chela , 531-538 ; colour varia- 
 tion, 44; hermaphrodite, 155 
 "Homodynamy," 133 
 Hornceosis, use of the term, 85 
 
 between vertebra;, 106-127 : 
 backward and forward, use 
 of terms, 111; forward in 
 vertebra?, 112; backward in 
 vertebra, 111 ; in spinal 
 nerves, 144 ; of appendages 
 in Arthropoda, 146; in Beg- 
 ments of Annelids with re- 
 spect to genital organs, 162, 
 163, 167, eve; in teeth, 272; 
 in bilateral asymmetry, 465; 
 in parts of flowers, 111 
 Homology between members of Series 
 of Repetitions, 30 
 individual, not attributed if 
 series is undifferentiated, 
 32; attempt to trace in 
 mammas, 191 ; discuss* J 
 in the case of teeth, 269; 
 in the case of digits, 351, 
 391, 371, 377; in the case 
 of joints of tarsus of Blatta , 
 418 ; in the case of radii of 
 Holothurioidea, 433 
 Horns, Sheep, 285 ; Goat, 286; Boebuok, 
 286, 460 ; Chamois, 286 ; of EU A ■ 
 buck united in middle line, 4»ii» 
 Horse, similarity of fore and hind L< 
 25, 26 
 naked variety, 56 ; teeth, 244, 2 !•"> 
 cervical fistula?, 180 
 simultaneous variation of mane 
 
 and tail, 309 
 extra digits, 360; by development 
 
 of digit ii. 
 ;stil 367 
 by development 
 ofdigit iv,367 
 by development 
 of digits n 
 and iv, 368 
 by division of 
 digit in, 369 
 by intermediate 
 process, 371 
 
584 
 
 INDEX OF SUBJECTS. 
 
 Hyas, double chela, 540; double index, 
 
 541 
 Hybrids, supposed, between Herring and 
 
 Pilchard, 274 ; supposed, between Tur- 
 
 bot and Brill, 468 ; supposed, in genus 
 
 Terias, 52, 53 
 Hydrobius fuscijjes, pronotum having 
 
 three lobes, 454 
 Ilylobates, vertebrae, 118; teeth, 204; 
 
 leuciscus, extra digit, 346 
 Hylotrupes bajulus, extra legs, 494 
 Hypsiprymnus, teeth, 258 
 
 Iceland, 4-horned sheep, 285 
 Ichneumon luctato^•ius, extra legs, 511 
 Ichueumonidae, extra legs, 491, 511 
 Icticyon venations, teeth, 220 
 Ictonyx, teeth, 233 
 
 Images, relation of, the basis of Symme- 
 try, 19 
 between upper and lower jaws, 
 196, 267; between right and 
 left sides, 88; in the case of 
 the manus and pes, 404 
 division and union of parts re- 
 lated as, 449 
 principles of, followed in the 
 structure and position of parts 
 in Minor Symmetry, 479 
 Inca Dogs, a bulldog found amongst, 
 57 ; variation of premolars and molars, 
 216, 222 
 Incisors, supernumerary, Gorilla, 203 ; 
 Ateles, 207; Canidae, 210; 
 Felidae,222; Herpestidas,227; 
 Pecora, 245; Licotyles, 245; 
 Horse, 244 
 division of, Canidse, 210; Ele- 
 
 phas, 244 
 absence of, Canidse, 211 ; Feli- 
 dae, 222; Herpestidae, 227; 
 Phocida?, 235 ; Horse, 244 
 Index of crabs and lobsters, peculiarity 
 
 in repetition of, 557 
 Individuality, attributed to members of 
 Meristic Series, 31 ; such individuality 
 not respected in Variation, 32; cases 
 illustrating the absence of supposed 
 individuality in Members of Meristic 
 Series, 104, 115, 124, 191, 269, 407, 
 433; an unfortunate term, 556 
 
 Jacamaralcyon tridactyla, distinguished 
 
 by absence of hallux, 396 
 Jackal, vertebrae, 122; teeth, 217 
 Japanese pug, probable independent 
 
 origin of, 57 
 Jaws, relation of upper to lower, 196 
 Julodis cequinoctialis, extra legs, 503; 
 
 clouei, double (?) antenna, 551 
 Julus tevrestris, mode of increase in 
 
 number of segments, 93 
 
 Kallima inachys, colour- variation, 53 
 
 Karvokinesis, symmetry in, 20; varia- 
 tions in, 430; bilaterally symmetrical 
 variation of, in the segmentation of 
 an egg, 464 
 
 Kidney, supernumerary, 277 ; horse- 
 shoe, 278, 459 
 
 Kittiwake, variations in hallux, 396 
 
 Laciniation, simultaneous, of petals, 310 
 
 Lady-birds, colour-variation, 49 
 
 Lagorchestes, teeth, 258 
 
 Lagothrix, teeth, 208 
 
 Lamarck's solution of problem of Species, 
 
 4 
 Lamellibranchs, sinistral, 54 
 Lamia textor, double (?) antenna, 551 
 Larus leucopterus, digits, 393 
 Larvae of Lepidoptera, variations in 
 
 colours of, 304 
 Leaf-butterfly, colour-variation, 53 
 Leeches, variation in generative organs 
 
 of, 165 ; in colours, 304 
 Legs, extra, in Secondary Symmetry, 
 general account, 475, cases in 
 Insects, 483; in Position V, 
 483 ; in Position VAA, 485 ; in 
 Position A, 487; in Position DA, 
 491; in Position D, 494; in 
 Position DP, 496; Position P, 
 498 ; Position VP, 500. Uncon- 
 formable cases, 503; miscel- 
 laneous cases, 511 ; in Crus- 
 tacea, 526 ; in vertebrates, 554 
 supposed double in Insects, 544 
 Leopard, two cases of dental variation 
 
 in a Chinese, 225, 226 
 Lepidoptera, colour-variation of larvae, 
 
 304; ocellar markings, 288; nature of 
 
 yellow pigments, 73 
 Leptura testacea, double (?) leg, 545 
 Leuciscus dobula, bulldog-headed variety, 
 
 58 
 Lichnanthe vulpina, extra antennae, 517 
 Ligula, absence of segmentation in, 168 
 Limax, union of tentacles, 460 
 Limenitis populi, extra wing, 283 
 Limulus, division of caudal spine, 450, 
 
 456 
 Linaria, many symmetrical variations 
 
 of, 76 
 Linckia multijiora, fission, 433 
 Linear Series, Meristic Variation in, 63 ; 
 
 simultaneity in colour-variations of, 303 
 Lissotriton, supposed double limb, 539 
 Lithobius, number of segments, 93 
 Lithodes arctica, extra legs, 527 
 Littorina rudis, colour- variation, 49 
 Littorina, sp. , extra eye, 280 
 Lixus angustatus, division of pronotum, 
 
 456 
 Lizards, digital variation in, 395, 396 
 Lobster, colour-variation, 44 ; herma- 
 phrodite, 155; variations in chelae, 
 
 530—538 
 
INDEX OF SUBJECTS. 
 
 585 
 
 Local Races, evidence as to, not a direct 
 contribution to Study of Variation, 17 
 Locusts, variation in colour of tibia?, 44 
 Loligo, variations in segmentation of 
 
 egg, 4(i3 
 Lucanus cervus, extra antennary branch, 
 2 cases, 549 ; extra branch on man- 
 dible, 2 cases, 552 ; capreolus, ditto, 552 
 Luidia ciliaris, variation of pedicellariae, 
 
 429 
 Lumbo-sacral plexus, 138 
 Lumbriconercis, imperfect segmentation, 
 
 156 
 Lumbriculus, double tail, 565 
 Lumbricus, undifferentiated segments in, 
 82 ; imperfect segmenta- 
 tion, 156 ; spiral segmen- 
 tation, 157 ; repetition of 
 ovaries, 160; asymmetrical 
 arrangement of organs, 160, 
 161 ; variation of genital 
 openings, 162 ; duplicity, 
 565 
 agricola, 162; herculeus, 160; 
 pvrpurens, 160; terrestris, 
 156, 157 ; turgidus, 160 
 Lupa dicantha, extra index, 542 
 Lurcher, teeth, 221 
 Lutra, teeth, 228, 233, 234, 235 
 
 constancy of p l in L. vulgaris, 
 228 
 Lyccena icarus, extra wing, 284 
 Lycalopex group of Foxes, frecpuency of 
 
 extra molars in, 217 
 Lychnis, repetition of fimbriation in 
 
 petals, 26 
 Lycus, double (?) antenna, 551 
 Lynx, teeth, 224 
 Lysimaehia, Meristic variation in flower 
 
 of, 61 
 Lysiphlebus, variation in number of an- 
 tennary joints, 412 
 
 Macacus cynomologus, syndactylism, 356 
 inuus, spinal nerves, 137, 139 
 teeth, 204 
 radiatus, doubtful extra molars, 
 
 204 
 rhesus, extra molar, 204 
 Macroglossa, colours of larvae, 304, 305 
 Macrognathus nepalensis, double (?) an- 
 tenna, 551 
 Macropodidae, teeth, 259 
 Macrorhinus leoninus, teeth, 243 
 Madreporites, repetition of, 440 
 Maia squinado, extra index, 542 
 Major Symmetry, 21, 87 
 Malachius marginellus, extra antenna, 
 
 522 
 Males, high and low, 39 
 Mallodon, double (?) leg, 547 
 Mammae, numerical Variation in, 181 ; 
 along mammary lines, 181 ; 
 in other positions, 186 ; in 
 
 axilla, 185 ; below and inter- 
 nal to normal mamma, 186; 
 above and external, 185 
 Mammae, variation in Cow, 101 ; Dog. 
 189; Pig, 190; Man, 181; 
 A]h -. L88 
 comment on facts, 191 
 development of, 191 
 Mammary extensions to axilla, 185 
 lines, 181 
 tumours. 185, 187 
 Man, cervical fistula;, 174; cervical auri- 
 cles, 177 
 digits, increase in number, 324 : 
 reduction in number, 355; poly- 
 dactyliam in general, 344; double- 
 hand, 331 ; symmetry of manna 
 and pes, 403 
 kidneys, union of, 459; renal arte- 
 ries, 277 ; ureter-. 27> 
 mammae, 181 
 
 nerves, spinal, 135; brachial plexus. 
 135 ; notable variation in, 137, 
 113 ; lumbo-sacral plexus com- 
 pared with that of Chimpanzee, 
 etc., 138 
 teeth, 198 
 
 transposition of viscera, 559 
 uterus, double, Darwin's comment 
 
 on, 77 
 vertebrae, Meristic and Homceotic 
 variation in, 103, 106 — 116, 458 
 Mandibles, supposed duplicity of, in 
 
 Lucanus, 552 
 Manns, variations in, compared with 
 those of pes, 405 ; as a system of 
 Minor Symmetry. 4(>:-i 
 Marsupialia, teeth. 2 16 — 258 
 Mastiff, teeth, 210, 221 ; hallux per- 
 mitted in, 401 
 Maternal impressions and extra Legs in 
 
 a beetle, 512 
 Maxillipede developed as a chela, 149, 
 
 150 
 Median nerve, variations in composition 
 
 of, 136 
 Medicago, repetition of brown Bpol in 
 
 leaflets, 26 
 Medusas, Meristic Variation i>i\ [23 ; 
 
 duplicity in, 666 
 Melanopliu packardit, colour-variation, 
 
 44 
 Meles, teeth, 2:52, 233, 236 
 Mellivora, teeth, 233, 235 
 Meloe coriaceus, double (?) I , 547 j 
 pro8carabau8i extra 1. 188; viola- 
 a us, extra antenna 
 HJelolonthavulgarii, division ol pronotum 
 
 i .". . . i ."> \ 
 
 division of pygi- 
 dium, : 
 
 tra legs, 184, 512 
 extra antennas, 515, 
 520, 533, 550 
 
586 
 
 INDEX OF SUBJECTS. 
 
 Melolontha vulgaris, double (?) leg, 545 
 hippocastani, extra antennae, 
 510, 557 
 Mephitis, teeth, 232 
 
 Merism, 20; importance of, to Study of 
 Variation, 23 
 indirect bearing of, on the 
 magnitude of Variations, 
 25 
 Meristic Repetition, 20 ; kinship of parts 
 so repeated, 26 ; similar Variation of 
 parts in, 27, 310, 46-4; compared with 
 asexual reproduction, 34 
 Meristic Variation, distinguished from 
 Substantive Variation, 22 ; compared 
 with Hoinceotic Variation, 84 
 Metacarpals, development of lateral, in 
 Artiodactyla in correlation with syn- 
 dactylism of metacarpals III and IV, 
 383 
 Metameric Segmentation, not distin- 
 guishable from other forms of Repe- 
 tition, 28 ; errors derived from such 
 distinction, 30 
 Metasternal plates, division of, 456 
 Metazoa, comparison with Protozoa, 35 
 Metritis contractus, extra legs, 503 
 Middle Line, division by images in, 404, 
 
 450 ; union of images in, 383, 458 
 Minnow, bulldog-headed specimen, 58 
 Minor Symmetry, 21, 88 ; Meristic Varia- 
 tion in, 311, 410 ; in manus and pes, 
 403 
 Molars, supernumerary, Simla, 200 ; 
 Troglodytes, 202; Gorilla, 
 203; Cynocephalus, 204; Ma- 
 cacus, 204 ; Cebus, 205 ; Ateles, 
 205 ; Mycetes, 207 ; Canidae, 
 217, 220 ; Felidae, 226 ; Her- 
 pestidae, 230; Mustelidae, 234; 
 Phocidse, 242; Ungulata, 245, 
 246; Dasyurus, 256; Bet- 
 tongia, 258 
 
 special frequency in Anthro- 
 poid Apes, 200; in Lycalopex 
 group of Foxes, 217 
 absent, Sirnia, 200; Ateles, 207 ; 
 Pithecia, 208; Canidae, 219, 
 221; Felidae, 226; Herpes- 
 tidae, 231; Mustelidae, 235; 
 Phocidse, 243; Bettongia, 258 
 division of, Canis cancrivorns, 
 
 219 ; Crossarchus, 230 
 Variation in form, Crossarchus, 
 
 231 ; Dasyurus, 256 
 in Icticyon and Otocyon, 220 
 Monkevs, Old World, teeth, 204; New 
 
 World, 205 
 Monodon, development of right tusk, 465 
 Monomorphism, 33 
 
 Monotonia quadricollis, double (?) an- 
 tenna, 550 
 Moorhen, hairy varietv, 55; extra digits, 
 392 
 
 Morpho, eye-spots, 296—299 
 
 achillcs, 297; menelaus, 298; 
 montezuma, 297; psyche, 299 ; 
 sulkoicskii, 299 
 
 Mouse, colour-variation, 44 ; with silky 
 hair, 55 ; black variety, 55 ; naked, 
 56 
 
 Mugil capito, bulldog-headed, 58 
 
 Mule, rarity of digital variation in, 360 ; 
 case of, 370 
 
 Mullet, bulldog-headed varietj-, 58 
 
 Multipolar cells, 430 
 
 Mustelidae, teeth, 231, 235; premolars in 
 M. foina, martes, melanojnis, zibellina, 
 231 
 
 Mycetes, teeth, 207, 208 
 
 Mycomelic acid, relation to yellow 
 colouring matters, 73 
 
 Mydaus, teeth, 232 
 
 Myriapoda, variation in number of seg- 
 ments, 91, 93 
 
 Myrmecobius, incisors, 247, 248 
 
 Myxine, variations in number of gill- 
 sacs, 172 
 
 Ncenia typica, extra wing, 284 
 Narcissus, Substantive and Meristic 
 Variation in, 23 ; colour- variation, 40 
 Narwhal, development of tusks, 465 
 Nasalis, teeth, 204 
 
 Natural Selection, chief objection to 
 
 theory of, 5 ; misrepresentations of 
 
 the theory, 80 ; difficulty in connexion 
 
 with regeneration, 420 
 
 Navosoma, extra antennae, 521 
 
 Nebria, double (?) antenna, 550; gyllen- 
 
 halli, double (?) maxillary palp, 551 
 Nectarine, discontinuous variation in, 
 
 59 
 Nereis, double tail, 564 
 Nerves, spinal, Birds, 129 — 135; Man, 
 
 135; Apes, 138; Cat, 
 138; Dog, 140; Brady - 
 podidae, 141; Pipa, 
 141 
 attempt to homologize, 
 
 32 
 variations, 129-145 
 correlation with verte- 
 brae, 145 
 relation to limbs, 143 
 Neural canal, division of, 451 
 Neuration of wings varying with eye- 
 
 spots, 293 
 Nigidius, extra branch on antenna, 549 
 Nipples, supernumerary, on normal 
 breast, 184; on normal areola bifid, 
 184; on mammary lines, 186; in Pig, 
 190; in Dog, 189 
 Notidanidae, number of gills, 174 
 Nuclei, multipolar division, 430, 464; 
 
 precocious division, 464 
 Nyctcreates procyonoides, teeth, 215 
 Nyctipithecus, teeth, 208 
 
INDEX <)F sriUKcTs. 
 
 .W 
 
 Ocellar markings, 288, 449 
 
 Lepidoptera, 288 ; Raiida , 
 302 ; Birds, 449 
 Odontolabis stevensii, extra antennae, ">18, 
 
 557 
 Oligochseta, axial duplicity, 503 ; ge- 
 nerative organs, 159; segmentation, 
 156 
 Ommatophoca rossii, premolars, 237 
 Onitis bison, division of pronotum, 455 
 Operculum, double in Buccinum, 457 
 Ophiacantha anomala, normally arms, 
 
 not known to divide, 433 
 Opkiactis, fission, 433 
 Ophibolus, double monster, 561 
 Ophidia, vertebra, 103, 123 
 Ophidiaster cribrarius, fission, 433 
 (Jphiocoma pumila, young with 6 arms, 
 
 adults witb 5 arms, 433 
 Ophiothela isidicola, fission, 433 
 Ophiuroidea, variation in number of arms, 
 
 447; fission, 433 
 Opisthocomus, brachial plexus, 130 
 Orang, vertebrae, 118; spinal nerves, 13'J ; 
 teeth, 200 ; extra digit, 349 ; extra 
 mamma, 188 
 Organic Stability, 36 
 OrtUosia Icevis, extra wing, 284 
 Oryctes nasicornis, division of pronotum, 
 
 455; extra legs, 512 
 Osmoderma eremita, double (?) leg, 547 
 Otaria cinerea, molars, 240 
 
 jubata, premolars, 240, 243 
 ursina, premolars, 239, 241 
 Otocyon, teeth, 220, 221 
 Ouaharia, teeth, 208 
 Ovaries, variations in number and posi- 
 tion in Earthworms, 160, 162 
 not always correlated with 
 variations in oviducts, 167 
 Ovary, right, developing in Fowl, 466 
 Oviduct, right, case of, in Fowl, 466 
 Oviducts of Astacu*, variation in number, 
 
 152; in Earthworms, 167 
 Ox, incisors, 245; molar, 246; poly- 
 dactylism, 374-381 ; syndactylism, 
 384-387; syndactylism together with 
 development of digits II or V, 385 ; 
 with duplicity of II and V, 386; cer- 
 vical auricles and fistula? unknown, 
 180 
 
 Pachydrilus sphagnetprum, dimorphic in 
 respect of position of generative open- 
 ings, 165, 168 
 Painted Lady butterflv, colour-variation, 
 
 49 
 Palaornis torquatus, colour-variation, li-i 
 Palamnaus borneensis, division of poison- 
 spine, 457 
 Palinurus penicillatus, eye developed as 
 
 antenna, 150 
 vulgaris, extra legs, 527 ; extra 
 antennae, 538 
 
 Palloptera ustulata, abnormal growth 
 
 from thorax, 285 
 Palpi, paired extra, in Insects, 524 
 
 supposed doable, 551 
 Pangenesis, 75 
 " Panmixia," 573 
 Papaver nudicaule, colour-variation, 16; 
 
 pigment of, 17, 72 
 Parakeet, colour- variation, 13 
 Pararge megara, eye-spots, 289, 800 
 " Parhomology," 133 
 Pariah dog. teeth, 221 
 Parnassius, ocelli. 292 
 Parra, feathers, 55 
 Pasimachus punctulatus, double (?) . 
 
 547 
 Patella, extra tentacle and eye, 279 
 Pattern, universal presence of, in organ- 
 isms, 19-21; difficulties arising from, 
 21 
 Peach, discontinuous variation in. 59 
 Peacock, ocelli, 449 
 Peacock butterfly, repetition of i 
 
 spots in, 26; variation of, 299 
 Pecora, polydactylism, 'M'> 
 Pecten, double eye-, 280 
 Pedicellariae, Meristio Vaiiatiou of, 4 J '. * 
 Pelamis bicolor, imperfect division of 
 
 vertebrae, 105; axial duplicity, 561 
 Pelecanus, brachial plexus, I'M 
 Pelobates fuscus, extra spiracle, 165 
 Penis, supernumerary, in Hirudo, 166; 
 
 in Aulastoma, 167 
 Pentacrinus miilleri, increase in nun: 
 
 of radial join 
 4-rayed >p< cim< 
 dubius, dumorti- 
 i r/, jurensis, tub- 
 tulcatus, 436 
 6-rayed specimens, 
 jurensis, I 
 Penthina salicella, extra wing, 285 
 Peramelidee, digits of pes, 313 
 Perichata, variation in number of -i 
 
 mathecse, 165 \forbesi, hilgendorfi, 165 
 PeHcrocotus Hammeus, oolour-vanati 
 
 16 
 Perionyx, generative organ watus, 
 
 163, 167, L68 
 griim waldi, 164 
 l\ ripatus, variation in nnmbei i 
 
 ments, 84, 91, 94 
 l\ taurus, premolars, 26*5 
 Puai.ani.i Kin.v.. incisors, 248; premo 
 
 Lars, 248 256 
 Phalanger maculatus, incisors, 248; | 
 
 molars, 258; females Bpot- 
 t. i in Waigiu, 2 
 orientalis, incisors, 248, 250; 
 
 premolars, 250 
 ornatus, first pn molar two 
 
 root* d as \;n tation, 25 i 
 ursinus, first premolar nor- 
 mallv two-root* d. 254 
 
588 
 
 INDEX OF SUBJECTS. 
 
 Phalanges, reduction in number, 355 
 
 Phascologale dorsal is, teeth, 257 
 
 Pheasant, digits, 393 
 
 Philonthus succicola, double (?) leg, 548 
 ventralis, extra legs, 507 
 
 Phoca barbata, incisors, 235, 236 
 cristata, premolars, 238 
 groenlandica, premolars, 238, 2-40, 
 
 242; molars, 243 
 vitulina, premolars, 238, 241, 
 242; molars, 242 
 
 PJuvnicopterus, brachial plexus, 130 
 
 Phoxinus Icevis, bulldog-headed, 58 
 
 Phratora vitellines, colour-variation, 43 
 
 Phreoryctes, generative organs, 162 
 
 Phyllopertha horticola, extra antenna?, 
 514 
 
 Phyllophorus, tentacles not in multiples 
 of live, 435 
 
 Phyllopteryx, compared with Hippo- 
 campus, 309 
 
 Physa acuta, tentacle bifid, 280 
 
 Picua uiridis, colour-variation, 43; me- 
 dius, brachial plexus, 131 
 
 Pieridae, colours of, 73; eye-spots in, 
 292 
 
 Pig, digits, 381; syndactylism. 387; 
 syndactylism with division of digit V, 
 389 ; cervical auricles, 179 ; cervical 
 fistulas, 180 
 
 Pigeon, cervical vertebras, 33 ; brachial 
 plexus, 134 
 
 Pigments, definite variations proper to 
 certain, 43; nature of yellow, in Pie- 
 ridae, 48. 
 
 Pike, bulldog-headed, 58 
 
 Pilchard, variation in scales, 274 ; sup- 
 posed hybrid with Herring, 275 
 
 Pilumnus, not altered by Entoniscians, 
 95 
 
 Pimelia inter stitialis, extra legs, 498 
 scabrosa, extra antennae, 523 
 
 Pinnipedia, Teeth, 235—243 
 
 Pipa, spinal nerves, 141 
 
 Pithecia, absent molar, 208 
 
 sa tanas, syndactylism in, 356 
 
 Pityophis, axial duplicity, 561 
 
 Plaice, symmetrical spotting of blind 
 side, 467 
 
 Plant, compared to the body of Man, 29 
 
 Platycerus caraboides, extra legs, 507 
 
 Platyonychus, not altered by Entonis- 
 cians, 95 
 
 Platysomatichthys, 471 
 
 Pleuronectes, pigmentation of blind side, 
 467, 471 
 
 Plume moths, repetition of pattern in 
 wings, 26 
 
 Pluteus, double, 35 
 
 Podargus, brachial plexus, 131 
 
 Pcecilogale, 232 
 
 Pointer, teeth, 221 
 
 Polian vesicles, variation in number of, 
 434, 435 
 
 Pollex, duplicity in, Man, 349 ; Bogs, 
 
 401 
 Polyarthron, variation in number of an- 
 
 tennary joints, 412 
 Polychaeta, axial duplicity in, 564 
 Polydactylism, Cat, 312; Man, 324; 
 Macacus, 340; Hylobatcs, 346; Simia, 
 349; irregularcasesinMan,353 ; Horse, 
 360—371 ; Artiodactyla, 373 
 Polydesmus, mode of increase in number 
 
 of segments, 93 
 Pohjodontophis, vertebrae, 123 
 Polyphylla decemlineata, extra antennae, 
 
 518 ' 
 Polyplectron, eye-spots, 449, 450 
 Polyzoa, division of embryos, 556 
 Poppy, Iceland, colour- variation, 46; 
 
 Horned, colour- variation, 47 
 Porania, 4-rayed specimen, 440; irregu- 
 lar division of an arm, 440 
 Portunion, change in Carcinus produced 
 
 by, 95 
 Portunus puber, extra parts on chela, 
 
 535; not altered by Entoniscians, 95 
 Potorous, teeth, 358 
 Premolars, nomenclature, 199 
 
 supernumerary, Brachy teles, 
 205; Ateles, 206; Mycetes, 
 208; Canidae, 212—214; 
 Felidae, 225 ; Herpestidae, 
 229; Mustelidae, 231—234; 
 Phocidae, 237—242; Cer- 
 vus, 246; Phalangeridae, 
 248; Phascologale, 257 
 absence of, Canidae, 214 — 
 216 ; Felidae, 224 ; Herpes- 
 tidae, 229; Mustelidae, 231 
 —234 ; Phocidae, 237—242 
 apparent division, Brachy- 
 teles, 205; Canidae, 213; 
 Dasyurus, 255; Phocidae, 
 237 
 displacement and other va- 
 riations, Simia, 201 
 Pbionus, supposed development of elytra 
 as legs, coriarius, 148 
 variation in number of anten- 
 nary joints, imbricomis, 411, 
 Jissicornis, 412 
 extra legs, coriarius, 488, 512, 
 califomicus, 544, 557, cori- 
 aceus, 548 
 double (?) antenna, 551 
 double (?) legs, califomicus, 544 
 Procercea, double tail, 564 
 Protozoa, sujjposed relation to Metazoa, 
 
 35 ; duplicity, 566 
 Pseudochirus, premolars, 250, 255; in- 
 cisors, 248 
 Pterostichus, extra legs, lucublandus, 512; 
 miihlfeldii, 485; prevostii, 512; dou- 
 ble (?) antenna, planipennis, 550 
 Ptinus latro, extra legs, 512; extra an- 
 tennae, 522 
 
INDEX OF SUBJECTS. 
 
 .>:> 
 
 Pujinus, brachial plexus, 130 
 
 Pug, breeds of, 57; teeth, 221 
 
 Purpura lapillus, colour-variation, 48 
 
 Putorius, teeth, 231, 234 
 
 Pygara anastomosis, extra wing, 284 
 
 Pygidium, division of, in Melolontho, 456 
 
 Pygoinelian geese, 401 
 
 Pyrameis cardui, aberrations of, 49, 52 ; 
 
 var. kershawi, 49, 52; var. <'l>/>ui, 50, -51 
 Pyrodes speeiosus, extra legs, 490 
 Python, imperfect division of vertebra?, 
 
 103, 105 
 
 Radial joints of Crinoids, 421 
 Radial Series, Meristic Variation in, 60 ; 
 evidence, 422; in Echinodermata, 432 
 Radii, variations in number, Holo- 
 thurioidea, 433 ; Crinoidea, 435 ; As- 
 teroidea, 439; Echinoidea, 441; Ophi- 
 uroidea, 433, 447 
 Radius, absence of, 360 
 Radula? of Buccinum, 262 
 Raiidre, eye-spots, 302: extra fin, 540; 
 division of fin into lobes, 540; separa- 
 tion of fin from head, 540 
 Rana, vertebrae, 124, 126; double foot, 
 540 ; spinal nerves, 142 ; extra limbs, 554 
 Ranzania bertolonii, extra legs, 510 
 Raspberry, yellow variet}', 47 
 Red, variations of, 44 — 48 ; as variation 
 
 from blue, 44 
 Renal arteries, 277 
 Repetition of Parts, association of these 
 
 phenomena, 21 
 Repetition, Linear, Bilateral or Radial, 
 distinctions between, 88 
 Units of, 556 
 Reptilia, vertebra?, 103, 123 
 Reversion, hypothesis made in order to 
 escape recognition of Discontinuity in 
 Variation, 76 
 Rhagium mordax, double (?) leg, 548 
 Rhea, brachial plexus, 130 
 Rhinoptera, teeth, 259 — 261, javanica, 
 
 261, jussieui, 259 
 Rhizocrinus, 6-rayed specimen, 437 
 Rhizotrogus, extra legs, aestivalis, 510; 
 castanius, 512 
 extra antennae, aquinoc- 
 
 tialis, 517 
 division of metasternal 
 plates, 456 
 Rhombus, pigmentation of blind side, 
 467—471 ; Usvis, 467, 468, 
 470; maximus, 467, 470 
 variations in scales, 468 
 RJupichites permanicus, double (?) an- 
 tenna, 550 
 Rhyttirhinus, supposed case of extra 
 
 eye, 281 
 Ribs, division of, in Man, 105 
 
 cervical, in Man, 108, 112, 115; in 
 Dog, 122; Bradypodids, 119: on 
 6th vertebra in Man, 108 
 
 Ribs, variations in dorso-lumbar region, 
 Man, 109—116; Anthropoid Ap< s, 
 116— lis; Bradypodide, Vi\ ; 
 Felis, 122; Canis, 122; Galietis, 
 123; Halichams, 123; eleven in 
 
 Siamese Twins. ."> t , « i 
 
 Rissa, variations of hallux in the genus 
 
 396, 397 
 Roebuck, horns, 286 ; polydactylism, 
 
 374,379; union of horns, 160 
 Rubus idaus, colour-variation, 17 
 Rupicapra tni<itt.<, horns, 286 
 Rutela fasciata, extra Legs, 512 
 
 Sacculina, effect of, on segmentation of 
 Carciniu and other Crabs, 93 
 
 St Bernard dog, duplicity of hallux in. 
 401 
 
 Salinity, doubtful relation of variations 
 of Crustacea to changes in, 100 
 
 Salmo fario, salar, trutta, 58 
 
 Salmon, bulldog-headed variety, 58; axial 
 
 duplicity, :>f>:i 
 
 Salmacina, double tail. 564 
 Salt lakes, Crustacea of. 96, LOO 
 Samia cecropia, extra wing, 28 
 Sand-canals, repetition of, in Aster 
 
 440 
 Saperda carcharias, extra antenna ariai 
 
 from head, 551 
 SarcophiluS) teeth, 255 
 Sarsia, Meristic Variation in. 424; with 
 
 six segments, 424 ; with five Begments, 
 
 425 
 Saturnia carpini, repetition ofeye-8] 
 
 in wings, 26; extra wing. 282; varia- 
 tion of eye-spots, 289, 301, 302; 
 
 colours of Larva, 306 
 Satyrus hyperanthus, eye-spots, 294 
 Sawfiy, extra legs, 502, 546 
 Scales of Pilchard, 271; of GasUi 
 
 276; of Snakes, 276 
 Scarites pyraemon, extra legs, 500 
 « Scheme, shewing the relations ^i parts in 
 
 Secondary Symmetry, 1M 
 Scolopendra, numlx r of w jm< nts. 94 
 Scorpion, double poison-spine, r~ 
 
 double tail, 565 
 Saraptia fusca, extra antenna?, 523 
 Is, variations in dentition. 235 
 Segmentation, metameric, not in 1. 
 distinol from other foi i 
 of Repetition, 28; two 
 way- by which a full s. 
 
 mentation mayhavi l>< . □ 
 achieved in phyiogeny, 
 
 of Axthropoda, variation 
 
 in. 91 ; impi if. ct in An- 
 nelids. L56 : spiral in 
 Annelids, L57 : variation 
 of in Cestoda, L68, 17" 
 
 of mamma . I'M 
 
 of ovum, variations in. , 
 
590 
 
 IXDEX OF SUBJECTS. 
 
 Selachians, teeth in, 259 
 
 Semnopithecus, teeth, 204 
 
 Sepidium tuberculatum, double (?) an- 
 tenna, 551 
 
 Sex, analogy with Discontinuous Varia- 
 tion, 66 
 
 Sexual characters, statistics as to, in 
 Beetles, 38; Earwigs, 40 
 of Hepialus in Shetland, 254 
 of Phalanger in Waigiu, 254 
 
 Sheep, cervical auricles, 180; incisors, 
 245 ; change in form of canines, 245 ; 
 molar, 246; extra horns, 285; poly- 
 dactylism, 373, 380 
 
 Sheep-dog, teeth, 221 
 
 Shetland, variety of Hepialus in, 254 
 
 Shrew, naked variety, 56 
 
 Siamese Twins, 560 
 
 Siberia, Crustacea of salt lakes, 97, 100 
 
 Silis rvficollis, extra"legs, 498 
 
 Silky fowls, 56 
 
 Silpha nigrita, extra legs, 501 ; granu- 
 lata, double (?) leg, 548 
 
 Silurus, extra fin, 540 
 
 Simia, vertebrae, 118; teeth, 200; extra 
 digit, 349 ; extra mamma, 188 
 
 Simultaneity of Variation, possibilities 
 of, 25, 26, 308 ; in fore and hind 
 wings of Lepidoptera, 293; in counter- 
 parts, 569; in colours of segments of 
 Lepidopterous larvae, 303 ; in Chiton 
 idffi, 307; in limbs, 402; in homo- 
 logous twins, 559 ; in radial segments, 
 423; not clearly distinguishable from 
 Symmetry, 569 
 
 Sinistral varieties, 54 
 
 Situs transversus, 465, 560 
 
 Sledge-dog, absence of first premolar, 
 215; division of premolar, 214 
 
 Smerinthus, colours of larvae, ocellatus, 
 pojnili, tilice, 306, 307 
 
 Snakes, vertebrae, 103, 123; axial du- 
 plicity, 561 
 
 Solea, pigmentation of blind side, 471 
 
 Solenophorus strepens, double (?) an- 
 tenna, 551 
 
 Sore.r, naked variety, 56 
 
 Spaniel, teeth, 221 
 
 Species, the problem of, 2. Methods of 
 attacking, 6 
 Discontinuity of, a fact, 2 
 
 Specific Differences, indefinite, 2 
 
 Spermathecae of Earthworms, variation 
 in number, &c. of, 160, 165 
 
 Spharocrinus, imperfect variation to 6- 
 rayed state, 437 
 
 Sphingida?, repetition of markings in 
 larvae of, 26 ; variation in, 304 
 
 Sphinx Ugustri, division of proboscis, 456 
 
 Spinal nerves, 129; Birds, 130; Man, 
 
 135; Primates, 138; Bra- 
 
 dypodidre, 141 ; Pipa, 
 
 141; Rana, 142 
 
 dimorphism in respect of, 
 
 138 ; distribution to 
 
 limbs, 143 ; Homeeosis, 
 
 144; recapitulation, 144 
 
 Spinal nerves, principles of distribution, 
 
 143 
 Spiracle, extra in tadpole of Pelobate*, 
 
 465 
 Stability, Organic, 36 
 Starfishes, theory of origin of repetition 
 in, 29; variations in number of rays, 
 439 ; multiplication by fission, 433 
 Stentor, duplicity, 566 
 Sticlioj)us, arrangement of tube-feet 
 
 changes with age, 435 
 Stickleback, variation in number of 
 
 bony plates, 276 
 Stomobrachium octocostatum, variety 
 having tentacles in double series, 
 425 
 S trau galia, double (?) antenna, atra, 
 
 551, calcarata, 551 
 Strategns antceus, extra legs, 512 
 Struthio, brachial plexus, 130 
 Styela, variations in branchial sac, 172 
 Subemarg inula, extra eye, 279 
 Substantive Variation, distinguished 
 from Meristic, 23; cor- 
 related with Meristic in 
 vertebra?, 125 
 in size, 38, 40; in colour, 
 43 — 48; in colour-pat- 
 terns, 48 — 54 ; miscel- 
 laneous, 54 — 60 
 Swan, cervical vertebrae, 33; colour- 
 variation of young, 44 ; brachial 
 plexus, 130 
 Symmelian "monster," 459 
 Symmetry, the conception of, 19, 569 
 
 a relation between optic- 
 al images, 19 
 almost universal pre- 
 sence of in living or- 
 ganisms, 21 
 of mammae, 191 
 in dental Variation, 267 
 in digital Variation, Man, 
 324,402; Cat, 314; in 
 manus and pes, 4U3 
 in nuclear division, 430; 
 in variations in seg- 
 mentation of ovum, 
 463 
 in variations of homo- 
 logous twins, 559, 560 
 in double monstrosity, 
 
 559 
 Bilateral, characters of, 
 88; as appearing in 
 variations of flat- 
 fishes, 467 
 Major and Minor, 21, 86 
 Primary and Secondary, 
 
 90 
 Kadial, characters of, 89 
 
INDEX OF SUBJECTS. 
 
 591 
 
 Symmetry, Secondary, preliminary ac- 
 count, 475; principles, 
 479 
 Scheme of relations of 
 parts in, 481; parts 
 repeated in, geometri- 
 cally peripheral to 
 points of origin, 557; 
 relation to Primary, 
 556, 557 
 in Insects, 475; Crus- 
 tacea, 525 ; Verte- 
 brates, 553 ; Batra- 
 chia, 554; Triton, 555 
 Syndactylism, Man, 355, 356; Pithecia, 
 356; Macacus, 356; Ox, 384—387; 
 Pig, 387—390 
 
 Tadpole, extra Bpiracle in, 465 
 Tcenia coznurus, transposition of genera- 
 tive organs, 170 ; case of six 
 suckers and segments pris- 
 matic, 565 
 elliptica, asymmetrical arrange- 
 ment of genital pores, 170 
 
 saginata, "intercalated 
 
 seg- 
 
 ments, 169; repetition of gene- 
 rative organs in proglottides, 
 169 ; two genital pores at the 
 same level, 170; consecutive 
 genital pores on same side, 
 170; bifurcation of chain, 566 
 solium, changes in position and 
 alternate arrangement of geni- 
 tal pores, 170 
 tenuicollis, bifurcation of chain, 
 566 
 Tail-fin, division of, in Gold-fish, 451 
 Tail-spine, division of, Limulus, 456; 
 
 Scorpion, 457 
 Tapeworms, variations, 168 — 170; du- 
 plicity in, 565 
 Tarsus, in some beetles with only four 
 joints appearing, 25 ; variation in 
 number of joints, Blatta, 63, 415; 
 various numbers of joints in families 
 of Orthoptera, 415 
 Taurhina nireus, extra legs, 509 
 Taxidea, teeth, 233 
 Ta.vus baccata, colour-variation, 47 
 Teal, Garganey, division of digits, 392 
 Teeth, in undifferentiated series not 
 credited with individuality, 32 
 numerical Variation, 195 ; di- 
 vision of, 268 ; duplicate, 268 ; 
 statistics of Variation, 200, 
 209, 222, 235 
 relation of upper to lower, 196 
 of Primates, 199—208; Canidae, 
 209—222; Felidae, 223—226; 
 Viverridee, 227—231; Mus- 
 telidae, 231—235 : Pinnipedia, 
 235—243 ; Ungulata, 243— 
 246; Marsupialia, 246—258; 
 
 Selachians, 259—262; 7.v 
 
 a a in, 262 
 Teeth, terminal, least size of, 270; pn - 
 sence and absence of, 269; 
 Homteotic Variation in, 272 
 Recapitulation, 265 
 Telephorus, colour-variation, lividus, 43 
 division of pronotum, nigri- 
 cans, 455 
 double (?) antenna, lividus, 
 rotundicollis, 551 
 
 double (?) leg, <.ff,ir,itii-. 
 
 fuscus, 5 18 
 extra Legs, rusticus, 502 
 " Telescope " Gold-fish, 453 
 Tellina, sinistral variety. 54 
 Tenebrio granarius, double (?) leg, 548 
 Tentacles of Molluscs united, Helix 
 hispida, 461 ; Limazagn -• 
 tie, 460 
 repeated, Patella vulgata, 27$ 
 bifid, Phy8a acuta, 280 
 of Holothurians, 4.;~< 
 Tenthredo solitaria, extra legs, 502 
 ignobilis, extra leg, 546 
 Terias, colour-variation, 52, "»:5 ; am - 
 mone, hecabe, mandarina, mariesii, 52 ; 
 betheseba, constantia, jaegeri, 53 
 Terminal members of Series, variation 
 of, 79, 269, 271. 272. 407 
 teeth, 269, 272; digits, 107 
 Terrier, absence of premolar, 21"< 
 Testes, variation in number in Hirudo, 
 
 165, 166 
 Tetraceros, horns not as in 4-horned 
 
 Sheep, 285 
 Tetracrintu, normally 4-rayed, 5-r;r 
 
 and 3 -rayed varieties, 137 
 Tetrops prceusta, double (?) It-}.'. ">1"> 
 Thoracopagous twins, transposition in. 
 
 560 
 Thumb, variation in number of phalan- 
 ges, 324 
 double, 349 
 Thylacinus, teeth, 255 
 Thylacites pilosus, double (?) antenna, 
 
 550 
 Thyonidium, variation in number of 01 
 
 gans, 435 
 Tiaraps polydiademata, specific charad 
 
 of, 426 
 Timarcha tenebricosa, extra anteni 
 
 522 
 Tomato, colour-variation. 47 
 Tonicia, variation in colour of BOUfc 
 
 308 
 Tongue, division ^i. L51 
 ToxotUS, extra « \. . 280 
 Transposition of viscera. 560 
 Triasters, symmetry of. ISO; found in 
 bilaterally symmetrica] areas "t" a 
 menting ovum, 164 
 Trichodet syriacus, double i?. 1 leg, 547 
 Trichosurus vulpecula, premolars, 254 
 
592 
 
 INDEX OF SUBJECTS. 
 
 TricenopJwrus, segmentation of, 168 
 Triopa clavigera, rhiuophore trifid, 280 
 Triton, legs repeated, 555 
 Troglodytes, vertebra?, 116; teeth, 202 
 Trupidonutus, vertebrae, 123 ; scales, 276 
 Trout, bulklog-headed, 58, 59; axial du- 
 plicity, 563 
 Tulip, Meristic Variation in, 60 
 Turbot, pigmentation of lower side, 467, 
 
 470 
 Turdus, brachial plexus, 131 
 Turkey, digits, 31)3 
 
 Twins, homologous, 559 ; Simultaneous 
 Variation of, as a case of Bi- 
 lateral Symmetry, 559 
 Siamese, peculiarities of, 560 ; 
 thoracopagous, 560 
 in Echinoderms and in Amphi- 
 oxus, 35 
 Typosxjllis, double head, 564 
 
 Uca una, extra parts in chela, 530 
 
 Ulna, a second, 331 
 
 Ulnar nerve, variations in composition 
 of, 136; a second, 333 
 
 Ungulata, teeth, 243 ; digits, 360—390, 397 
 
 Union, mediau, 458; of horns of Roe- 
 buck, 460; of eyes of Bee, 461; of 
 kidneys, 459; of tentacles of Umax, 
 460; of tentacles of Helix, 461; of 
 posterior limbs of Vertebrates, 459 ; of 
 digits in Ox, 383, 386; of digits in 
 Pig, 387—390 
 
 Units, of Repetition, 556 
 
 I'metos, brachial plexus, 131 
 
 Ureters, supernumerary, 278 
 
 "Useless'' parts, supposed variability of, 
 78 
 
 Uterus, double, Darwin's comment on, 
 77; is a case of median division, 451 
 
 Utility, fallacies of reasoning from, 12 
 
 Uvula, division of, 451 
 
 Vanessa atalanta, colour-variation, 46 
 urticce, extra wing, 283 
 io, eye-spots, 299, 300 
 Variation, defined, 3 
 
 the Study of, as a method 
 
 of attacking the problem of 
 
 Species, 6 
 Continuous and Discontinu- 
 ous, 15 
 Meristic and Substantive, 
 
 distinguished, 23, 24 
 magnitude of integral steps 
 
 affected by Merisrn, 25 
 about a Mean form, 37 
 perfection in, 60, 64 
 causes of, 78 
 Homoeotic, 85, in vertebras, 
 
 106; in Arthropoda, 146; 
 
 in teeth, 272 
 Simultaneity of, in repeated 
 
 parts, 303, 402, 425, 464 
 
 Variations, minimal, questionable uti- 
 lity of, 16 
 Vertebras, Meristic Variation in, 102 
 imperfect division, 103, 458 
 Homceotic Variation, 106 
 reduction in numbers, Man, 
 
 111 
 numerical variation, 102 
 Man, 103, 106—116; Anthro- 
 poid Apes, 116; Bradypodi- 
 dae, 118; Carnivora, 122; 
 Reptilia, 123 ; Batrachia, 
 124; features of Variation 
 recapitulated, 127; correla- 
 tion with spinal nerves, 113, 
 115. 139, 145 
 Vesper us luridus, extra eye, 280 
 Veronica buxbaumii, numerous symme- 
 trical variations in, 76 ; illus- 
 trating variations of Bila- 
 teral Series, 448 
 Viverridae, teeth, 227 — 231 
 
 Waigiu, female Phalanger maculatus 
 coloured like male in island 
 of, 254 
 Wall butterfl}', variation in ocelli and 
 
 neuration, 300 
 Water-pore, extra, in Bipinnaria, 466 
 Webs, between toes of Duck, absent, 401 
 Weevils, four visible joints in tarsus, 25 
 Wing, supposed to replace a leg in Zy- 
 
 gcena, 148 
 Wings, supernumerary in Insects, 281 
 fore and hind, varying simul- 
 taneously in Lepidoptera, 293 
 quills of, varying with quills of 
 tail in Pigeons, 309 
 Woodpecker, Green, colour-variation, 43 
 
 Xantho punctulatus, duplicity of index, 
 542 
 
 Xiphopagous twins, transposition of 
 
 viscera in, 560 
 Xylotrupes gideon, variation of horns in, 
 
 38 
 
 Yellow, variations of, 43-48, 73 
 Yew, yellow-berried, 47 
 
 Zalophus calif or nianus, molars, 243 
 
 lobatus, premolars, 238, 242; 
 molars, 243 
 Zebra, repetition of stripes in, 26 
 Zeugopterus, white varieties, 467; varia- 
 tion in dorsal fin, 471 
 Zonabris quadripunctata, double (?) an- 
 tenna, 551 
 Zonites prausta, extra antenna?, 522 
 Zyyana filipenduUc, colour variation, 46 
 
 supernumerary wing, 
 148 
 minos, colours, 46; extra wing, 
 284 
 
IXDKX OF PERSONS. 
 
 Acton, 286 
 
 Adolphi, 124, 127, 142 
 
 Agassiz, A., 469 
 
 Agassiz, L., 396, 424 
 
 Ahlfeld, 840, 354, 451, 458 
 
 Albrecht, 105, 540 
 
 Aldrovandi, 344 
 
 Allen, J. A., 243 
 
 Alston, 286 
 
 Ammon, 348, 349 
 
 Anderson, 399 
 
 Andrews, 563, 564 
 
 Annandale, 327, 345, 346, 350-352, 355- 
 
 358 
 Appellor", 473 
 Arloing, 363, 370 
 Ascherson, 174 
 Ashmead, 413 
 Asmuss, 484, 500 
 Asper, 167 
 Assheton, 152 
 Audouin, 512 
 Auld, 390 
 Austin, 436 
 Auvard, 349 
 Auzoux, 203 
 
 Babington, 47 
 
 Bacon, 29, 146 
 
 Baird, 223, 232 
 
 Balbiani, 566 
 
 Balding, 305 
 
 Balk will, 566 
 
 Ballantyne, 334 
 
 Bancroft, 561 
 
 Barbour, 563 
 
 Bardeleben, 183 
 
 Barr, P., 46 
 
 Barrier, 384, 388 
 
 Bartels, 187 
 
 Barth, 187 
 
 Bartlett, 216 
 
 Bassi, 512, 548, 551 
 
 Baster, 453 
 
 Bateson, Miss A., 77, 468 
 
 Bather, 436 
 
 Baudi, 456, 512, 551 
 
 Baudon, 54 
 
 Baum, 401 
 
 Baumuller, 374 
 
 Baur, 103, 105, 123, 124 
 
 Beddard, 159, 162, 163, 165 
 
 B. 
 
 Bedria^a, 127 
 
 Bell, P. J., 443, 564, 565 
 
 Bellamy, 113 
 
 Belt, 56, 57 
 
 Beneden, van, 531 
 
 Benham, 152, 15i>, 161, 565 
 
 Beranger, 347 
 
 Bergendal, 555 
 
 Bergh, 160 
 
 Bernhardus a Berniz. 5j - 
 
 Betta, de, 43 
 
 Bibron, 563 
 
 Bicknell, 45 
 
 Billardon de Sauvigny, 454 
 
 Billott, 399 
 
 Birkett, 178 
 
 Birnbaum, 350 
 
 Blackinore, 523 
 
 Blainville, de, 118, 119, 205, 224 
 
 Blanchard, 187 
 
 Blanford, W. T., 398 
 
 Blasius, 354 
 
 Bles, 440 
 
 Bleuse, 482, 508 
 
 Boas. 369, 383, 385 
 
 Boettger, 5<il 
 
 Boisduval, 45 
 
 Bolau, 349 
 
 Bond, 301 
 
 Bonnier, 95 
 
 Bottcher, 560 
 
 Boulard, 512 
 
 Boulenger, 123, 276, 277. 16, 165 
 
 Boulian, 351 
 
 Bourne, A. G. 12">. 127 
 
 Boyd-Cainpbell, 399 
 
 Bramson, 52 
 
 Brandt, 466 
 
 Bredin, 31M 
 
 Breese, 565 
 
 Brenner, 3ti0 
 
 Brindley, 38, 39, 63, 280, 416 
 
 Brisout de Barneville, 116 
 
 Brooks, 466 
 
 Broonir. 565 
 
 Bruce, 181, 185 
 
 Brulerie, de la, 280 
 
 Brum r, I * 
 
 Brunette, 56 l 
 
 Brunner von Wattenwyl, 11, 113, 116 
 
 Buchanan, Mi^s P., 156, 1 57 
 
 Buckler, 304, 305, 307 
 
 38 
 
594 
 
 INDEX OF PERSONS. 
 
 Buffon, 286, 398 
 Bull, 340 
 Biilow, von, 565 
 Buquet, 551 
 Bureau, 540 
 Burmeister, 123, 232 
 Busch, 198, 345 
 Butler, A. G., 52, 53 
 
 Cauierano, 127, 546, 555 
 
 Cameron. 1S5 
 
 Canestrini, 58 
 
 Cantoni, 537 
 
 Carlet 59 
 
 Carpenter, P. H., 421, 422, 436-438 
 
 Carre, 339 
 
 Cassebohm, 178 
 
 Cauroi, du, 344, 354 
 
 Cavanna, 539, 555 
 
 Cazeaux, 185 
 
 Champneys, 139, 185 
 
 Chapman, J., 244 
 
 Charcot, lsl 
 
 Chavignerie, de la, 455, 547 
 
 Chworostansky, 165 
 
 Claparede, 425, 564 
 
 Clark, J. A., 51 
 
 Clark, J. W., 465 
 
 Clarke, E., 397 
 
 Claus, 80, 100 
 
 Cleland, 401 
 
 Coale, 393 
 
 Cobbold, 566 
 
 Cockerell, 44 
 
 Cocks, 55 
 
 Colin, 169 
 
 Collin, 563, 565 
 
 Cooke, A. H., 262, 263 
 
 Coquillet, 413 
 
 Cori, 156, 157, 158 
 
 Cornevin, 363 
 
 Cornish, 150 
 
 Cotteau, 446 
 
 Couch, 440, 470, 471 
 
 Coues, 232, 390 
 
 Cowper, 391, 393 
 
 Cramer, 346 
 
 Cuenot, 429, 433, 441 
 
 Cunningham, 320, 467 
 
 Curtis, 547 
 
 Cusset, 176 
 
 Daintree, 376 
 
 Dale, 482, 547 
 
 Dareste, 458 
 
 Darwin, C, 1, 5, 13, 56, 57, 59, 77, 121, 
 
 288, 449 
 DavidofT, 566 
 Dawson, 566 
 
 Day, 275, 276, 302, 467, 540 
 Delplanque, 354, 370, 377, 379 
 Demidoff, 468 
 Dendy, 438 
 Desmarest, 152 
 
 Devay, 399 
 
 Dimmock, 543 
 
 Dobson, 397 
 
 Dohrn, 86 
 
 Donceel, de, 51 
 
 Donitz, 212, 217, 220, 246, 445 
 
 Donovan, 302, 471 
 
 Dorner, 561 
 
 Doue, 456 
 
 Doumerc, 512, 550 
 
 Drechsel, 455 
 
 Drew, 381 
 
 Driesch, 35 
 
 Dubois, 330 
 
 Duhamel du Monceau, 470, 471 
 
 Dumeril, 554, 563 
 
 Dunn, 374 
 
 Duns, 528 
 
 Duponchel, 456 
 
 Dusseau, 352, 355 
 
 Duval, 184 
 
 Dwight, 325, 334 
 
 Ebrard, 166, 304 
 
 Eck, 437 
 
 Edward, T., 43, 174, 563 
 
 Ehrenberg, 425, 426, 428 
 
 Eichwald, 560 
 
 Ekstein, 339 
 
 Ek strom, 471 
 
 Elwes, 45 
 
 Engramelle, 46 
 
 Ercolani, 369, 377, 380, 381, 392, 393, 
 
 540, 554, 555 
 Eudes-Deslongchamps, 180 
 
 Fackenheim, 345, 351, 352, 399 
 
 Failla-Tedaldi, 295 
 
 Fairmaire, 454 
 
 Farge, 327, 399 
 
 Fauvel, 44, 494, 508, 523 
 
 Faxon, 152, 530, 532, 533, 536, 537, 
 
 541, 542, 557 
 Field, 466 
 Filippi, 425 
 Fischer, 41 
 Fischer, Or., 174 
 Fischer, P., 54, 279, 566 
 Fischer de Waldheim, 97 
 Fisher, W. K., 392 
 Fitch, 565 
 
 Fitch, E. A.,'44 
 
 Fitzinger, 200 
 
 Flemming, 430 
 
 Flemyng, 307 
 
 Fleutiaux, 548 
 
 Flower, W. H., 106, 119, 217, 220, 233 
 
 Forbes, E., 54, 425, 460 
 
 Forbes, W. A., 356 
 
 Forgue, 143 
 
 Forskal, 540 
 
 Forsyth, 398 
 
 Fort, 344, 356, 358 
 
 Foster, 565 
 
INDEX OF PER80N8. 
 
 
 Fotherby, 360, 399 
 
 Franck, 368 
 
 French, 451 
 
 Freund, 459 
 
 Freyer, 524 
 
 Fricken, von, 512 
 
 Friedlowsky, 244, 356 
 
 Friele. 262, 264 
 
 Friend, 563, 565 
 
 Fries, 471 
 
 Frivaldsky, 500 
 
 Froriep, 35 1 
 
 Fumagalli, 336 
 
 Fiirbringer, 131, 133, 135, 142 
 
 Fiirst, 399 
 
 Gadeau de Kerville, 415, 455, 4s2, 510, 
 
 548, 549 
 Gaillard, 346, 350 
 Galton, F., 36, 40. 43, 418, 419 
 Garrod, 390 
 Gaskell, 86 
 Gaskoin, 56 
 
 Gautbier, 443, 445—447 
 Gebhard, 459 
 Gegenbaur, 77 
 Geissendbrfer, 360 
 Gene, J., 127 
 Geoffroy St Hilaire, I., 57, 205, 330, 
 
 368, 377, 379, 383, 392, 451, 459, 563 
 Gercke, 285 
 Gervais, 203 
 Gherini, 337 
 
 Giard, 95, 440, 468, 482, 545 
 Gibbons, Sir J., 44 
 Gibson, 166 
 Giebel, 234 
 Gifford, 44 
 Giraldes, 336 
 Girard, 305 
 Godman, 53, 297 
 Godwin-Austen, 286 
 Goldfuss, 436, 437 
 Goodman, 376 
 Goossens, 300 
 Gordon, 56 
 Gorre, 187 
 Gosse, 566 
 Gosselin, Mrs, 44 
 Gotte, 127 
 Gottsche, 466, 471 
 Goubaux, 180, 244, 245 
 Grandelement, 355 
 Grandin, 340 
 
 Gray, J. E., 56, 242, 287, 396 
 Gredler, 286, 511, 512, 550, 551 
 Green, 515 
 Grobben, 169 
 Gruber, W., 108, 111, 119, 122, 330, 345, 
 
 346, 350, 352, 354, 359, 360 
 Guerdan, 45H 
 Guermonprez, 327 
 Giinther, 173, 174, 260, 309, 468 
 Gurlt, 368 
 
 Gurney, .1. H.. 1 
 
 ( in\. i| 1 1 in .•-, B60 
 
 Baacke, 1 13, L46 
 Bagen, I L8 
 Bagenbaoh, B52 
 Hammond, 805 
 
 I I;, 111. v. 160 
 
 Bannams, 1 84 
 
 Bark( r, A., 119 
 Barker, .1., 354, B 
 Barmer, i M), 556 
 Harrington, 182, 191, "00 
 
 Harrison, 211 
 
 Bartung, 1-7 
 
 Harvey, 178 
 
 Haworth, L5 
 
 Heincki n. 526 
 
 Hell.i-, 1*7 
 
 Heller, 170 
 
 Henne^ny, 430 
 
 Hennig, 349 
 
 Hensel, 203, 20n. 212 216, 220, 223, 
 
 226, ->w>. 244, 246, 269 
 Herdman, 171, 172, 139, 156 
 Herkluts. 527, 528, 529, 542 
 Heron, Sir R., 453 
 Heron-Rover, 465, 55.1. 56] 
 HerrichSchiilY.]', 51 
 Herrin^hain, 137, 138 
 Hertwig, O., 431 
 Heuglin, von. 234. 235 
 Heusinger, 174, 179 
 Hewett. 55 
 
 Hevden, H. von. 4s*. 512. 5 1* 
 Heyden, L. von. 484, 187—490, 194, 
 
 517, 523, 550, 551 
 Heynold, 355 
 Higgins, 471 
 Hill, 391 
 Hincks. 425 
 His, 177 
 
 Hodgson, 209, 398 
 Hoeven. van der, 21 s 
 Hoffmeister, 162 
 Honratli. 284 
 Hopkins. 48, 73 
 Horn, 411 
 Horst. 565 
 
 Howes, 126, 153, 210, 891, 121, 515 
 Hubner,&05 
 Hudson, 56 
 
 Hiigel, Huron A. von, 89 
 Humphreys, 221 
 Humphreys, 11. N.. 801 
 Humphry, 200 
 Huxley, 217, 218, 219 
 
 Imhoff, -")47 
 
 .Tiiekrl. 393 
 
 Jackson, '-531 
 Jaequelin-Duval, 524 
 
596 
 
 INDEX OF PERSONS. 
 
 Jaeger, G., 536 
 
 Janson, 482, 491 
 
 Jayne, 503, 512, 518, 524, 544, 547, 548, 
 
 550, 551 
 Jeffreys, G., 54, 457 
 Jekyll, Miss, 46 
 Jentink, 248, 252, 253 
 Jhering, von, 140, 142, 300 
 Johnson, Atbol, 354 
 Jollv, 337 
 Joly, 370, 372 
 Joseph, 350 
 
 Karoli, 532 
 
 Kawall, 551 
 
 Kerckring, 344 
 
 Kiesen wetter, von, 281 
 
 Kingsley, 539, 554 
 
 Kirk, 565 
 
 Kitt, 363, 383, 384, 386, 390 
 
 Kleyn, 453 
 
 Klingelhofer, 547, 551 
 
 Klob, 187 
 
 Koenen, von, 436 
 
 Kolbe, 484, 503 
 
 Kolliker, 142 
 
 Kostanecki, von, 175 
 
 Kraatz, 146, 454, 456, 484, 485, 494, 
 498, 502, 506, 509—511, 515, 516, 
 523, 545, 547, 548, 550, 551, 552 
 
 Krause, 455, 548 
 
 Kriechbaumer, 147 
 
 Krohn, 425 
 
 Kroyer, 151 
 
 Kuchenmeister, 560 
 
 Kuhnt, 339 
 
 Laboulbene, 512 
 
 Lacaze-Dutbiers, 171 
 
 Lacepede, 540, 561 
 
 Lafosse, 244 
 
 Lamarck, 4 
 
 Lambert, 446 
 
 Lampert, 435 
 
 Landois, 58, 383, 387, 511, 555 
 
 Lane, 113 
 
 Lang, 566 
 
 Langalli, 336 
 
 Langerhans, 564 
 
 Lankester, 536 
 
 Lannegrace, 143 
 
 Lanzoni, 561 
 
 Lataste, 127 
 
 Laurent, 184 
 
 Lavocat, 354, 372 
 
 Le Clerc, 357 
 
 Leech, J. H., 46 
 
 Lefebvre, 500 
 
 Le Gendre, 184 
 
 Leger, 527, 538 
 
 Legge, 46 
 
 Leichtenstern, 181 — 185 
 
 Lereboullet, 515 
 
 Le Senechal, 530, 535, 542 
 
 Letzner, 280, 523, 550 
 
 Leuckart, 168—170, 566 
 
 Levacher, 566 
 
 Leveling, 458 
 
 Lidth de Jeude, van, 58 
 
 Linnams, 453 
 
 Lisfranc, 355 
 
 Lister, 218, 457 
 
 Loriol, P. de, 436, 437, 438 
 
 Loudon, 47 
 
 Lucas, 399 
 
 Lucas, H., 462, 536, 542, 550, 551 
 
 Ludwig, H., 433, 566 
 
 Lunel, 58, 554 
 
 Liitken, 433 
 
 Lydekker, 105, 217, 233 
 
 Macalister, A., 112, 278 
 
 MacAndrew, 54 
 
 MacBride, 440 
 
 McCoy, 52 
 
 Mcintosh, 470, 564 
 
 Maggi, 530 
 
 Magitot, 198, 203, 205, 210, 221, 244, 
 
 245, 270 
 Malm, 469 
 Manifold, 451 
 Mantell, 436 
 Marjolin, 355 
 Marsh, 349 
 Marsh, C. D., 565 
 Marsh, O. C, 364, 366, 368 
 Marshall, 86 
 Martens, von, 155 
 Martin, 430 
 
 Mason, 282, 488, 498, 509, 548, 550 
 Mason, F. , 355 
 Masters, 60, 84, 310 
 Mayer, 200 
 Mazza, 555 
 
 Meckel, 278, 346, 458, 459 
 Melde, 355 
 Meldola, 284 
 Meyer, A. B., 441, 445 
 Michaelsen, 162, 164, 165 
 Mielecki, von, 175 
 Milne-Edwards, 151, 202, 527 
 Mitchill, 561, 563 
 Mivart, 212, 217, 219 
 Mobius, 401 
 Mocquerys, 455, 487, 488, 494, 496, 498, 
 
 501, 503, 507, 508, 512, 515, 517, 522, 
 
 545—548, 550—552 
 Mojsisovics, 367 
 Moniez, 169, 566 
 Moquin-Tandon, 280, 304 
 Morand, 346, 348, 354, 399 
 Moreau, 540 
 
 Morgan, T. H., 157, 466 
 Morot, 245, 384 
 Morris, F. O., 44, 401 
 Mortillet, de, 186 
 Mosley, S. L., 45, 300 
 Muir, 352, 399 
 
INDEX OF PERSONS. 
 
 597 
 
 Miiller, A., 512 
 
 Miiller, J., 17.5 
 Murray, 330 
 
 Nathusius, H. von, 285, 373, 374 
 Nehring, 57, 123, 210, 212, 216, 221, 2 
 
 242 
 Neill, 540 
 
 Neugebauer, 183, 186 
 Neubofer, 170 
 Newman, 51, 205, 300 
 Newport, 04 
 Newton, A., 44, 55 
 Nicbolls, 155 
 Nilsson, 471 
 Norman, 100, 457 
 Notta, 185 
 
 Oberteufer, 330 
 
 Oberthiif , 44 
 
 Ocbsenbeimer, 40, 284, 302 
 
 Odin, 450 
 
 Olliff, 51, 52 
 
 Otto, 58, 278, 340, 348, 350, 354, 350, 
 
 458 
 Otto, H., 547, 548 
 Owen, 119, 188, 211, 261 
 
 Packard, 100, 457 
 
 Paget, Sir J., 175, 177 
 
 Pallas, 180 
 
 Parry, 520 
 
 Partsch, 451 
 
 Paullinus, 184, 187 
 
 Pavesi, 565 
 
 Pelseneer, 280 
 
 Pennetier, 482 
 
 Percy, 184, 187 
 
 Perroud, 512 
 
 Perty, 512, 548, 550, 551 
 
 Peters, 200, 277 
 
 Pbilippi, 443 
 
 Pichancourt, 400 
 
 Pocock, 93, 457, 565 
 
 Pooley, 451 
 
 Popham, 355 
 
 Porritt, 295 
 
 Pott, 399 
 
 Potton, 399 
 
 Pouchet, 451 
 
 Poulton, 304—307, 320, 321, 323 
 
 Prackel, 184 
 
 Prevost, 457 
 
 Price, 500 
 
 Puecb, 181 
 
 Pusch, 436 
 
 Putnam, 174, 396 
 
 Piitz, 366 
 
 Quenstedt, 430 
 (juinquaud, 185 
 
 Rabl, 176 
 Ragusa, 548 
 
 Rambur, 50 
 
 Ramsay, l;. <i. \\\. L6 
 
 R;m-. . d( . 899 
 
 Rapp, L20 
 
 Rathke, '.i7. K 
 
 I;, di, 561 
 
 !;• ichenan, iron, 392 
 
 Reid, i 9 
 
 Ri itter, 281 
 
 Rey, "'IT. 550 
 
 Richard, L50, 586, 543 
 
 Richardson, 1 1^ 
 
 Richmond, 279 
 
 Ridgway, 393 
 
 Rijkebusch, 329 
 
 Ritzema Bos, 512, 55] 
 
 Rivers, 17 
 
 Rober, 283 
 
 Roberts, (r., 401 
 
 Roberts, 1.. t (•_' 
 
 Robinson. II.. O'J 
 
 Roder, von, 551 
 
 Rogenhofer, 284, 286 
 
 Romanes, 125 128 
 
 Romano, 523 
 
 Rorberg, 355 
 
 Rose! von Rosenhof, 526, 530, 536 
 
 Rosenberg, 116—118, 138, 373, 383 
 
 Rosinus, 136 
 
 Rouget, 523 
 
 Rousseau, 152 
 
 Roux, 35 
 
 Riidinger, 330 
 
 Rudolphi, 2(>7. 244 
 
 RuefE, 344 
 
 Riitimeyer, 246 
 
 Saage, 1 L8 
 
 Salvia, 53, 2:17 
 
 Sanderson, 398 
 
 Sandifort, 458 
 
 Sarasin, 433 
 
 Sartorius, 512, 550 
 
 Saunders, Howard, 897 
 
 Sauvage, 276 
 
 Schaff, 210 
 
 Scbleep. 470 
 
 Schlegel, 220 
 
 Schmankewitsch, 96 
 
 Bchmeltz, 566 
 
 Schmitz, 177 
 
 Schneider, "'17. 550 
 
 Schneider, A.. 17 1 
 
 Schultze, L., 138 
 
 Schnltze, 0., 194 
 
 Sdater, P. L., 396 
 
 Sclater, W. L., 37 1 
 
 Scndder, "»0 
 
 Seba, 566 
 
 Sedgwick, 84, 92, 93, 173. 197 
 
 Seerig, 3 18 
 
 Seidel, L76 
 
 Seringe, 523 
 
 Serville, 412, 413 
 
598 
 
 INDEX OF PERSONS. 
 
 Shannon, 185 
 
 Sharp, D., 43, 53, 149, 411, 482, 494, 499 
 
 Shaw, E., 413 
 
 Shaw, V., 401 
 
 Sherrington, 137, 138, 144, 168 
 
 Siebold, von, 148 
 
 Sinety, 184 
 
 Smit, 471 
 
 Smith, E. A., 287 
 
 Smith, F., 551 
 
 Smith, S. J., 151 
 
 Solger, 141 
 
 Soubeiran, 529 
 
 South, 300 
 
 Spengel, 466 
 
 Speyer, 283 
 
 Spinola. 512 
 
 Spronok, 329 
 
 Stamati, 538 
 
 Stannius, 142, 455, 461, 512, 522, 547 
 
 Staudinger, 44 
 
 Steenstrup, 466, 469 
 
 Steindachner, 58, 468 
 
 Steinthal, 359 
 
 Stevens, 41 
 
 Stewart, C, 180, 429, 440, 446 
 
 Storer, 471 
 
 Strahl, 154 
 
 Strauch, 123 
 
 Strecker, 51, 283, 295 
 
 Streng, 352 
 
 Strombeck, von, 436, 438 
 
 Struthers, 103, 105—119, 122, 140, 327, 
 
 329, 334, 346, 351, 356, 370, 389 
 Studer, 277 
 Sundevall, 471 
 Sutton, 105, 176, 179, 180, 188, 555 
 
 Tachard, 398 
 
 Tarnier, 185, 345 
 
 Taschenberg, 512 
 
 Tegetmeier, 57, 393 
 
 Testut, 187 
 
 Thielmann, 277 
 
 Thomas, O., 56, 120, 199, 228, 230, 246 
 
 —249, 254, 257, 258, 313, 322, 397 
 Thompson, W., 565 
 Thomson, 412 
 Thomson, Wyville, 466 
 Tiedemann, 184, 512, 536, 540 
 Tischbein, 511 
 Traquair, 469 
 Treitschke, 284 
 Trelat, 451 
 
 Treuge, 512 
 Trimen, 51, 300 
 Trinchese, 118 
 Tuckerman, 170, 555 
 Turner, Sir W., 465 
 
 Urbantschitsch, 177 
 
 Vaillant, 309, 471 
 
 Viborg, 180 
 
 Virchow, 74, 177, 178, 17 
 
 Voigt, 58 
 
 Vrolik, 58 
 
 Wagner, 421 
 
 Wagner, J., 451 
 
 Walsingham, Lord, 300 
 
 Ward, E., 379 
 
 Warpachowski, 540 
 
 Watase, 451, 463 
 
 Waterhouse, F. H., 45, 545 
 
 Webb, S., 301 
 
 Wehenkel, 366, 368 
 
 Weir, J. Jenner, 45, 51, 52, 254 
 
 Weismann, 76, 304—307 
 
 Welcker, 118, 120 
 
 Weldon, 172 
 
 Werner, 170 
 
 Wesmael, 521 
 
 Westwood, 283, 284, 508, 551 
 
 Weyenbergh, 565 
 
 White, 44 
 
 Wilde, 178 
 
 Wilder, 465 
 
 Williams, 181, 185, 191 
 
 Wilson, 304, 305, 307 
 
 Wilson, E. B., 35 
 
 Windle, 221, 326, 328, 392, 560 
 
 Wiskott, 285 
 
 Wolf, 399 
 
 Woodgate, 284 
 
 Wood-Mason, 367 
 
 Woodward, M. F., 160, 162 
 
 Woodward, Smith, 259 
 
 Wright, 566 
 
 Wright, L., 55, 393 
 
 Wyman, 57, 203, 226, 401, 465, 561 
 
 Yarrell, 59, 469, 471, 540 
 Yarrow, 561 
 Youatt, 285, 286 
 
 Zeppelin, 565 
 Zundel, 180 
 
 FWPCT7T UBtAItT 
 
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