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ORGANIC EVOLUTION 
 
ORGANIC EVOLUTION 
 
 AS THE RESULT OF THE 
 
 INHERITANCE OF ACQUIRED CHARACTERS 
 
 ACCORDING TO THE 
 
 LAWS OF ORGANIC GROWTH 
 
 BY 
 
 Dr. O. H. THEODOE EIMEE 
 
 PROFESSOR OF ZOOLOGY AND COMPARATIVE ANATOMY IX TUBINGEN 
 
 TRANSLATED BY 
 
 J. T. CUNNINGHAM, M.A., F.E.S.E. 
 
 LATE FELLOW OF UNIVERSITY COLLEGE, OXFORD 
 
 Hontion 
 
 MACMILLAN AND CO. 
 
 AND NEW YORK 
 1890 
 
 All rights resci-ved 
 
TEANSLATOE'S PEEFACE 
 
 Before I became acquainted with this work of Professor 
 Eimer, I had been for some time growing more and more 
 dissatisfied with the uncritical acceptance accorded to Pro- 
 fessor Weismann's theories of heredity and variation by 
 many English evolutionists. Even before I studied Weis- 
 mann's writings, I had become convinced that selection, 
 whether natural or artificial, could not be the essential 
 cause of the evolution of organisms. I was inclined to 
 attach more importance to the problem of the causes of 
 variation than to any of the other problems considered by 
 Darwin, and among these causes it seemed to me that the 
 most powerful were functional activity and external condi- 
 tions. I was thus led to believe that a deeper insight into 
 the phenomena of evolution would ultimately be obtained by 
 pursuing the line of inquiry suggested by Lamarck, than by 
 continually searching for new instances of adaptation to be 
 explained by the Darwinian formula. When I saw that many 
 of the ablest British biologists accepted Weismann's dogma 
 that acquired characters are not inherited, it seemed to me that 
 they were abandoning the richest vein of knowledge under a 
 mistaken guide, and I cherished the hope of finding time 
 and opportunity to add by my own researches to the evidence 
 
vili TRANSLATOR'S PREFACE 
 
 that the effects of the conditions of life extend beyond a 
 single generation. I was therefore delighted to find that Weis- 
 mann had to contend with a formidable opponent in his own 
 country, and concluded that I could not for the present oppose 
 the progress of his views in England more effectively than 
 by publishing a translation of Professor Elmer's arguments. 
 
 I have endeavoured as far as lay in my power to express 
 my author's ideas and reasoning in language which should 
 be English in w^ords, construction, and style. I am well 
 aware that my object has not been perfectly attained, that 
 the book contains in almost every page internal evidence of 
 its German origin. But I hope nevertheless that the transla- 
 tion is sufficiently English to be readable, and that I have pre- 
 served the full force and the exact significance of Professor 
 Elmer's exposition. I have not in any way presumed to 
 intrude myself between my author and the reader in the 
 text of the work, but I will take the present opportunity of 
 expressing some of the reasons of my uncompromising 
 opposition to Weismann's theories and views. 
 
 One of the fundamental assumptions of Weismann's 
 theories is that acquired characters are not inherited. Only 
 this year he has published an essay on this subject under 
 the title JJeher die, Hypothese einer Vei^erbung von Verletzungen. 
 In this paper he criticises cases which have been adduced as 
 evidence that scars or artificially-produced malformations are 
 sometimes inherited. One case to which he draws parti- 
 cular attention is that of a peculiar cleft in the lobe of a 
 certain man's ear, which was interpreted by Dr. Emil 
 Schmidt as evidently due to the inheritance of a similar 
 cleft in the ear of the man's mother. The cleft in the ear 
 of the mother was known to have been caused by an injury. 
 
TRANSLATOR'S PREFACE ix 
 
 When the mother was between six and ten years old, her 
 ear-ring was accidentally torn out, and the lobe of the ear 
 was split from the hole through which the ring passed down 
 to its edge. After the two divided surfaces liad healed 
 together, a cleft was left round the external edge of the 
 wound. Weismann gives a woodcut of each ear, taken 
 from a photograph, indicating by reference letters the corre- 
 sponding parts in the two figures, and then proceeds to argue 
 that the cleft in the son's ear has really nothing to do witli 
 the lobe at all, but is situated between the true lobe and 
 the termination of the helix. I do not require to appeal to 
 experienced human anatomists to support my contention that 
 Weismann has made an erroneous identification of the parts 
 of the son's ear in order to suit his own arciument. His own 
 figures are sufficient to prove this to any fair-minded man 
 who knows something of anatomy. In the first place, the 
 line of attachment in the figure of the mother's ear is inclined 
 downwards to the left, in the son's to the right, in consequence 
 of which, of course, the apparent difference between the two 
 clefts is increased. Secondly, the lower end of the helix, 
 marked iS^. H in the mother's ear, is not marked at all in 
 the son's, the same letters in the latter pointing to the right 
 half of the lobe of the ear, separated from the left half by a 
 cleft closely corresponding to that in the mother's ear. The 
 only difference between the shape of the lobe in the son's 
 ear and that in the mother's is that in the former the outer 
 half of the lobe is shorter and smaller than the inner, while 
 in the mother's ear they are about equal : a difference wliich 
 I present to Professor Weismann to make what use of he 
 
 pleases. 
 
 I mention this merely to show to what straits Professor 
 
X TRANSLATOR'S PREFACE 
 
 Weismann is reduced to find a reply to the evidence against 
 him. For my own part, I do not think it is of very great 
 importance whether artificial malformations are inherited or 
 not. I think it probable that in the higher animals such 
 inheritance does sometimes take place. Professor Weismann 
 mentions the feet of Chinese ladies, which he says are still 
 when uncompressed as large as if the practice of artificially 
 compressing them had not been practised for centuries. But 
 he does not tell us whether lie ever saw a Chinese young 
 lady, or if he has made any observations on the feet of 
 Chinese women. The fact that artificial malformations are 
 not usually inherited is no argument against the inheritance 
 of acquired characters. In all animals, from the lowest up 
 to reptiles, recrescence of lost parts takes place, and the 
 reappearace of lost parts in the next generation in mammals 
 and birds seems to me to be simply recrescence slightly 
 postponed. 
 
 Weismann says that the faculty of speech and skill in 
 pianoforte-playing are not inherited. It is true that babies 
 are not born in the act of playing pianofortes, and no one 
 would expect that they should be. But that particular 
 kinds of musical skill run in particular families is admitted. 
 It is true also that children have to be taught to speak, as 
 they have to be taught to walk upright. But no amount of 
 teaching would cause a young monkey to speak. The 
 capacity for learning to speak and for speaking is inherited 
 by children, and it is making too great a demand on our 
 faith to ask us to believe that the peculiarities of vocal 
 organs and nervous system on which this capacity depends 
 are due to sexual mixture and selection. 
 
 Does Professor Weismann believe that birds inherit the 
 
TRANSLA TOR 'S PREFA CE xi 
 
 faculty of flight ? Many of them are certainly unable to 
 fly when they are flrst hatched, and have to practise for some 
 little time, even when fully fledged, before they can sustain 
 themselves in the air for any length of time. If sucli Ijirds 
 were never allowed to use their wings at all for several 
 generations, would they not gradually lose the faculty of 
 flight altogether? The answer is given by our domestic 
 ducks and fowls which, although not altogether prevented 
 from using their wings, have almost lost the power of flight. 
 
 But it may be urged that the wings of birds are 
 certainly inherited. Quite true ; and is Professor Weismann 
 in a position to assert that no structural modifications are 
 produced by constant pianoforte -playing during several 
 generations, or that such structural modifications are pro- 
 duced but not inherited ? I think it may be safely assumed 
 that neither he nor any one else knows what changes in 
 the muscles and nerves of the hands are produced by tlie 
 practice of pianoforte-playing : although it is certain that 
 extraordinary skill in the art is connected with peculiarities 
 in the condition of those muscles and nerves. 
 
 Moreover, it can be shown by actual facts that all modi- 
 fications, all progressive development of a structural character, 
 are not due to " sexual mixture," that is, to the combination 
 of the hereditary characters of the parents. I possess a 
 female cat with six toes on every foot. One of the kittens 
 of this cat has six toes on each hind foot, five on the left fore 
 foot, and seven on the right fore foot. But the left foot is 
 not normal, the inner toe or pollex is as large as two of the 
 others. It is practically certain that tlie father of this 
 kitten was an ordinary cat with the usual number of toes, 
 and the abnormal number of toes on the right fore foot lias 
 
XU TRANSLA TOR 'S PREFA CE 
 
 therefore been increased in the kitten, although the action of 
 " sexual combination " is entirely excluded. 
 
 Again, another of the assumptions on which Weismann 
 builds is that " everything depends on adaptation." He 
 confesses himself that this is a conviction of his own, not a 
 demonstrated truth. In fact, it is obviously an assumption 
 necessary to the main proposition of his theory. For Weis- 
 mann means to say that every part of every animal, every 
 structural relation, is either an advantage to its possessor 
 under the present conditions of its life, or was once an 
 advantaQ;e to its ancestors. Xo feature or character which 
 was not at one time or other of advantage to its possessor 
 in the stru<:j£jle for existence could have been selected. 
 Therefore, if some things were not adaptations, congenital 
 variation and natural selection could not be the necessary 
 and sufficient explanation of organic evolution, as Weismann 
 and his disciples maintain them to be. 
 
 It is evident, on Weismann's own admission, that it has 
 not yet been proved that everything is adapted, that is, that 
 every character or structural feature in every animal has its 
 use in the struggle for existence. It is a mere supposition, 
 therefore, that everything has been selected. In direct 
 opposition to Weismann, I am j^i'epared to maintain, first, 
 that many structural features can be pointed out which are 
 not useful to their possessors ; and secondly, that all adapta- 
 tions are due to the inheritance of acquired characters. 
 
 What is the use of the coiling of the shell and the torsion 
 of the organs in the greater number of Gasteropods ? Professor 
 Lankester has admitted recently in the j)ages of Nature that 
 he has been teaching for many years that this torsion was 
 due to a mechanical cause, namely, the weight of the shell 
 
translator's preface 
 
 Xlll 
 
 leaning over to one side, without realising that the explana- 
 tion was Lamarckian. N'ow that it has been pointed out to 
 him that such an explanation is inconsistent with the theory 
 of natural selection, he admits that he can at present find no 
 explanation of the phenomenon which would be consistent 
 with that theory. 
 
 What is the use of the scrotum in Mammalia ? In what 
 way is it better for the male mammal that its testes should 
 descend from their original position at the back of the 
 abdominal cavity into a membranous sac, where they are 
 constantly liable to injury ? 
 
 What is the use of phosphorescence to pelagic animals ? 
 
 What are the different conditions of life to which the 
 different structural characters of the classes of Echinoder- 
 mata are adapted ? The star-fishes have bodies consisting of 
 five, eleven, or thirteen, or some other number of radiatino- 
 arms connected by a central disc. In the Ophiuroidea the 
 arms are long, slender, and so brittle as to break at the 
 least resistance ; while in the Echinoidea the body has the 
 form of a hollow sphere. Are these differences adaptations ? 
 
 It is generally assumed that the mechanism by which 
 flat fishes change their colour so as to assimilate it to that 
 of the ground on which they happen to lie is a beautiful 
 instance of adaptation. And yet the specific marking of 
 each species is perfectly distinct. A large number of 
 different species belonging to different genera live within the 
 same area on ground of uniform colour ; to this colour they 
 all have to assimilate their general tint, and yet eacli species 
 has its own permanent characteristic marking. As these 
 markings are all different, they cannot all aid equally in the 
 protective resemblance ; some of them at least must either 
 
XIV TRA NSLA TOR 'S PRE FA CE 
 
 be indifferent or disadvantageous to the attainment of the 
 useful result. As far as we can judge, all the specific mark- 
 ino's are indifferent. And the chanoje of colour is far less 
 important than is generally supposed. The soles in aquaria 
 are nearly always buried in the sand on which they live : 
 they come out most at night, when to our eyes at least no 
 colours can be distinguished ; and when they move about to 
 seek food in the day-time, they are almost always covered by 
 a thin layer of sand sprinkled over their upper sides, by 
 which tlieir colour is concealed. 
 
 Again, the lower sides of flat fishes are, except in rare 
 abnormal specimens, of a uniform opaque white, and it is 
 impossible to conceive any advantage which they could 
 derive from this, since the lower sides are usually concealed. 
 It is true that plaice and flounders often rise a short distance 
 from the bottom to seize food ; and in this condition their 
 wdiite lower sides are very conspicuous. 
 
 The peculiar structural condition of the flat fishes as 
 compared with symmetrical fishes is admitted on all sides to 
 be one of the most striking cases of adaptation that exist. 
 Yet so obvious is the conclusion that the evolution of the 
 asymmetry is due to the habits of the fishes, that Mr. 
 Wallace, in his new book on Darwinism, attributes the 
 distortion of the orbits to the efforts of the ancestral flat 
 flshes during innumerable generations, at the very moment 
 when he is repudiating with Weismann the inheritance of 
 acquired characters. When it is pointed out that he is thus 
 using the very principle which he denies, lie justifies himself 
 by the sophistry that what was selected in successive genera- 
 tions of flat fishes was the power in the skull of retaining 
 the distortion which the efforts of the muscles produced. 
 
TRANSLATOR'S PREFACE xv 
 
 In the same way we might argue that the structural cou- 
 ditions coimected wdth the upright position in man are not 
 themselves inherited, but that what is inherited is the 
 power in the body of retaining the changes caused by the 
 assumption of the upright position in the child. 
 
 According to Mr. Wallace's argument, the distortion of 
 the skull in flat fishes and the peculiar asymmetry of the 
 eyes are not inherited at all, but are due in every generation 
 entirely to the efforts of each individual young fish actinc^ 
 on a peculiarly sensitive skull. But in the young turbot 
 and brill the metamorphosis is very nearly or quite com- 
 pleted long before the little fish have abandoned their pelagic 
 mode of life and retired to the sea-bottom. In these species 
 the young have a large air-bladder, although in the adults 
 that organ is completely wanting. In consequence of this 
 the young fish swim at the surface of the water until they 
 have reached a considerable size, long after the right eye has 
 migrated to the left side. These young fishes swim at the 
 surface in a horizontal position, as do adult flat fishes when 
 they swim up a short distance from the sea -bottom. Mr. 
 Wallace evidently means by the " efforts of the young fish," 
 the efforts which it makes to use its lower eye after it has 
 assumed the habit of lying on its side on the bottom. Now 
 these young turbot and • brill do not lie on the bottom, and 
 do not therefore need to make efforts to bring their right eye 
 up to the edge of the body, yet the eye migrates all the same. 
 It may be urged that they assume the horizontal position, 
 and therefore have to twist their right eye round : but wliy 
 do they assume the horizontal position ? The reason cannot 
 lie in the great depth of the body, as Mr. Wallace suggests 
 with reo-ard to flat fishes in general, for in the John Dorey 
 
XVI TRANS LA TOR 'S PRE FA CE 
 
 (Zeus faber), which swims in a vertical position, the vertical 
 depth of the body is as great in proportion to the length as 
 in the yonng turbot, and greater than in the young brill. 
 
 It may be thought that these facts are as much in 
 opposition to the view that the asymmetry of flat fishes was 
 evolved in consequence of the efforts of the ancestral fish to 
 use its lower eye after it had assumed the habit of lying flat 
 on the bottom. But it must be remembered that those who 
 believe in the inheritance of acquired characters also believe 
 that the modification caused by the habits of the adult is 
 inherited at an earlier and earlier age, until it may appear 
 long before the habits of the adult are assumed. 
 
 To some extent the controversy concerning the inheritance 
 of acquired characters is due to an ambiguity of language. 
 The Neo-Lamarckians do not assert that a change produced 
 in an individual by functional activity or external conditions 
 is inherited at once and completely by that individual's 
 offspring ; in this sense acquired characters are not usually 
 inherited. But what they do maintain is, that when a 
 certain functional activity produces a certain change in one 
 generation it will produce it more easily in the next, and so 
 on ; so that if a certain constant exercise of functional activity 
 is continued for a great number of generations, ultimately 
 structural modifications will appear in the young even before 
 the function which has produced them has commenced to be 
 exercised ; and this process may go on indefinitely, so that 
 at last the structural character in question will be inherited 
 for many generations after the exercise of the particular 
 function has altogether ceased. 
 
 JSTothim? can test better the claims of the two theories, 
 the Neo-Lamarckian and the J^eo-Darwinian, to be accepted 
 
TRANSLATOR'S PREFACE xvii 
 
 in explanation of the origin of adaptations than tlie case of 
 the woodpecker. This bird lives entirely on insects, and 
 only catches insects in one way — a very peculiar way. It 
 probes the holes in the bark of trees made by insects, or 
 makes holes itself, and then inserts its long pointed tongue, 
 whose tip is provided with recurved papillce, like a narrow 
 bottle -brush, and with this extracts the maggots. The 
 rapid protrusion of the tongue to a considerable distance, 
 and its sudden retraction, are rendered possible by tlie 
 elongation of the processes of the hyoid bone to which tlie 
 tongue is attached. These processes are bent upwards and 
 forwards over the back of the skull and inserted near the 
 orbits. Now, in all birds the tongue is attached to the 
 hyoid bone and moved by the muscles connected with that 
 bone : in nearly all birds the tongue is muscular and mobile. 
 It is admitted even by Weismann's adherents that the size 
 and shape of bones, the size and shape of muscles, are in 
 the individual modified by the use which is made of them 
 It will also probably be admitted that the modification is 
 such as to facilitate the operations in which they are used. 
 Therefore in every generation of woodpeckers — which birds, 
 in the struode for existence, had to be content to pick up 
 a livino- on tree-trunks or starve — the constant use of the 
 tongue in extracting insects from holes in trees must liave 
 elongated the tongue and hyoid bone, and increased tlie 
 power of protrusion of the organ in each individual. TIr' 
 Neo-Lamarckians believe that these individual modifications 
 were inherited in some degree, so that a greater moditicati«ui 
 in the same direction was produced in the oftspring, and m 
 this way it is easy to understand how the degree of special- 
 isation we now see was produced. 
 
 h 
 
xvii i TRANS LA TOR 'S PRE FA CE 
 
 The Neo-Darwiuiaus say that it is quite true that such 
 modifications were produced by the functional activity in the 
 individuals, but these modifications were never inherited : 
 other modifications of the same kind arose by congenital 
 variation in some of the same individuals, and the indi- 
 viduals that had these survived ; and then the favoured 
 individuals pairing together, some of their offspring, inherit- 
 ing from both parents, had the modification in a greater 
 degree, and so on. Which is very much like the argument 
 that the Iliad and the Odyssey were not written by Homer, 
 but by another man of the same name who lived at the 
 same time. 
 
 Professor Weismann's view of heredity is not, as he seems 
 to think, in any sense an explanation or an approach to it. 
 We are unable to comprehend how the individual impresses 
 upon the germ the power of growing into another individual 
 like itself, supposing that we regard heredity in this way. 
 But even if it were perfectly certain that heredity had 
 nothing to do with the influence of the " soma," but con- 
 sisted entirely in a fixed tendency of the germ -plasm to 
 develop into a certain type of adult organism, this fixed 
 tendency would be as absolutely unexplained as the influ- 
 ence of the body on the germ-cells on the other hypothesis. 
 Moreover, we have no evidence in support of the assumption 
 of such a fixed tendency. It is a known fact that the 
 development of an individual depends to a very great degree 
 on the conditions under which that development takes 
 place. The very occurrence of the process of development 
 from the ovum to the adult is dependent upon certain con- 
 ditions ; outside a certain minimum and maximum of 
 temperature, food, light, moisture, etc., the Qgg or embryo 
 
TRANS LA TOR 'S PRE FA CE xi X 
 
 dies. Within those limits the result of the development 
 varies to a very great degree with the variations of tlie 
 conditions. In the cultivation of domesticated animals and 
 plants, no degree of skill or patience in selection will pro- 
 duce improvement in a race, or even maintain its valuable 
 qualities, unless favourable conditions are provided. Every- 
 body knows that in a given district, even on a given farm, 
 certain varieties of animals and plants cannot be produced 
 in perfection. Individuals can be procured, the most perfect 
 in existence, but in a particular district or on a particular 
 farm they do not " thrive " ; that is to say, the qualities for 
 which they are valued disappear in the individuals, or, as is 
 more often the case, in a few generations, in spite of all 
 care and selection. Thus English races of dogs have been 
 shown by Darwin (Domestication, vol. i. p. 37) to degenerate 
 in India in a few generations, losing entirely the peculiarities 
 of form and mental character which distinguish their race, 
 and this in spite of the greatest care in selection and the 
 prevention of crossing. According to Weismann's assump- 
 tions, these degenerated dogs if removed back to Enghnul 
 would in the next generation recover entirely their lost 
 qualities ; but I do not think any sportsman would purchase 
 one of them on Weismann's guarantee. What I wisli to 
 emphasize here is, that it is a fact that characters are only 
 constant under approximately the same conditions; and that, 
 when under new conditions new characters appear constantly 
 in successive generations, we have exactly the same grounds 
 for asserting that these new characters are inherited as for 
 saying that the old characters under the old conditions weix' 
 inherited. The very fact that characters are acquired proves 
 that heredity is not a fixed and constant tendency independ- 
 
XX TRANS LA TOR 'S PRE FA CE 
 
 ent of conditions ; the fact that " acquired " characters 
 disappear when the conditions to which they are due are 
 removed is no more evidence against the inheritance of 
 such characters than the fact that the oricjinal characters 
 disappear under the new conditions is evidence against the 
 heredity of those original characters. We know nothing 
 more about heredity than that it is a name which we give 
 to the generalisation that organisms remain constant in their 
 characters within narrow limits of variation so long as the 
 conditions of life remain unchanged, and retain their char- 
 acters for a time after those conditions are changed. 
 
 Whether it can be proved that adaptations are due to 
 the inheritance of acquired characters or not, it is at least 
 certain that the Lamarckian view explains the evolution of 
 adaptations as perfectly as Weismann's theory. Nay, more 
 perfectly, for the theory of selection can never get over the 
 difficulty of the origin of entirely new characters. It may 
 be said that the necks of the giraffe's ancestors were of 
 different lengths, and the selection of the longest produced 
 the striking? length of neck we now see. But how can it 
 be said that the horns of ruminants arose ? No other 
 mammals have ever been stated to possess two little 
 symmetrical excrescences on their frontal bones as an 
 occasional variation ; what then caused such excrescences 
 to appear in the ancestors of horned ruminants ? Butting 
 with the forehead would produce them, and no other cause 
 can be suggested which would. 
 
 There is evidence that physiological change precedes 
 morphological. There is a climbing kangaroo in Papua 
 which shows so little adaptation of structure to the climbing 
 habit, that no naturalist would believe from the mere study 
 
TRANSLA TOR \S RREFA CE 
 
 XXI 
 
 of its body that it lived in trees. But as a matter of fact 
 it does live entirely in trees. 
 
 Variation and survival are the explanation of adaptations, 
 but the struggle for existence does not merely ^ive rise to 
 natural selection — it is the cause of the variations ^iiicli 
 survive. 
 
 Selection, whether natural or artificial, is perfectly analo- 
 gous to the process of denudation in geology. It explains 
 the extinction of innumerable forms and the consequent 
 gaps and intervals which separate species, families, ordere, 
 etc., just as denudation explains the want of continuity in 
 the stratified rocks. But geologists have never been blind 
 enough to suppose that the evolution of the structure of a 
 given rock was due to denudation ; they have always believed 
 that the structure of each rock was due to the effects of tlie 
 forces which have acted upon it since its formation, and 
 they have devoted their energies to tracing by observation 
 and experiment the effects of the various forces. It lias 
 been the distinction of biologists to maintain the paradox 
 that matter in a certain condition, namely, in the form of 
 living organisms, is not subject to the action of physical 
 forces. 
 
 But the following argument, which I recently attempted 
 to publish in a letter to the Editor of Nature, seems to me to 
 be stronger than any I have yet used. The letter containing 
 it never appeared in the journal, which professes to represent 
 natural science in this country. Its suppression was the 
 more surprising because the controversial correspondence to 
 which it belonged arose originally from a letter of mine, 
 which was published in the same journal, on the explanation 
 of the eyes of flat-fishes given in Wallace's Darwinian. 
 
xxii TRANSLATOR'S PREFACE 
 
 Nature has embraced the principles of Weismaiin's Neo- 
 Darwinism, and while willing to devote plenty of space to 
 favourable reviews of Weismann's essays written by under- 
 graduates, suppresses without a word of explanation or apology 
 contributions which argue against the fashionable creed. The 
 argument rejected is as follows : According to the followers 
 of Weismann, evolution is due to the selection and " sexual 
 mixture " of congenital variations, that is to say, of variations 
 themselves due to sexual mixture, and having nothing to do 
 with the physiological effects of conditions or stimuli or 
 functional activity. These congenital variations, in animals 
 which are hatched or born, must either be present at 
 hatching or birth, or must appear at a later period of life. 
 If they are supposed to be present at hatching or birth, 
 then they can have nothing to do with any of the most 
 important and most interesting modifications which w^e know 
 to have taken ]3lace in the evolution of animals. For such 
 modifications do not begin in individual development until 
 long after birth or hatching. For instance, flat-fishes when 
 first hatched are perfectly symmetrical, and their metamor- 
 phosis does not begin till they are some weeks old. On 
 the other hand, if the disciples of Weismann say that 
 congenital variations appear at later periods of life after 
 birth or hatching, how are such variations to be distinguished 
 from acquired characters due to stimulus and functional 
 activity ? Can it be proved, for example, that the first 
 slight asymmetry of the eyes of the ancestral flat-fish which 
 appeared long after hatching, in a fish which crouched on 
 the ground on one side, was not due to the use that 
 particular fish made of its eyes ? Is there any criterion 
 by which we can distinguish among variations appearing 
 
TRANSLATOR'S PREFACE xxiii 
 
 cU novo at a post-embryonic period of life, those which are 
 acquired, and those which are due to variations ol' the 
 germ-plavSm ? There is none; and therefore it woiiM be 
 as true to assert that there is no evidence of the inheritance 
 of any individual variations, as to say there is no evidence 
 of the inheritance of acquired variations. 
 
 J. T. Cunningham. 
 
 Plymouth, 31s^ Januanj 1890. 
 
CONTENTS 
 
 Introduction 
 
 I'AGE 
 
 SECTION I 
 
 THE NEWEST THEORIES CONCERNING EVOLUTION 8 
 
 SECTION II 
 
 THE ORGANIC GROWTH OF THE LIVING WORLD 20 
 
 Fundamental Causes of the Manifold Variety of Organic Forms 22 
 
 Eeproduction as Organic Growth . . . .2-1 
 
 Individual Development as Organic Growth . 
 
 Separation of the World of Organic Forms into Species — 
 Genepistasis ...... 
 
 The Particular Causes which determme the Difference of the 
 Directions of Evolution, and which also contribute to 
 bring about the Division into Species . .32 
 
 Sexual Combination — One-sided Inheritance . . .35 
 
 Intermittent Evolution — Kolliker's Hypothesis . . ■i'> 
 
 Constitutional Impregnation . . . • . ol 
 
 Elaboration and Simplification in the Evolution of Species 
 
 25 
 
 27 
 
 52 
 
XXVI CONTENTS 
 
 SECTION III 
 
 PAGE 
 
 INFLUENCE OF ADAPTATION IN THE FORMATION OF SPECIES 63 
 
 Is everytliing adaj^teJ I . . . . .63 
 
 Death as an Adajjtation . . . . . 67 
 
 Further Considerations on the Adaptation and Direction of 
 Evolution of the Markings of Caterpillars, Absence of 
 Sexual Combination in this Evolution . . .72 
 
 Characters which are inessential (indifferent) to the Life of the 
 
 Organism . . . . . .74 
 
 SECTION IV 
 
 ACQUIRED CHARACTERS 78 
 
 Methods of Investigation — The Period of Time to be claimed 
 
 for Evolution . . . . .78 
 
 Acquired Characters due to Direct External Action . . 87 
 
 Experiments on the Influence of Temperature on Lepidoptera . 116 
 
 Further Remarks on the Causes which Change the General 
 
 Colouring of Animals . . . . .135 
 
 Influences of Locality on the Variation of Animals, and thereby 
 
 on the Formation of Species . . . .139 
 
 Importance of the Stimulation of the Nervous System in 
 
 relation to Adaptation and the Origin of Species . 142 
 
 Particular Facts which prove the Influence of Nutrition and 
 other external Conditions on tlie Variation and Formation 
 of Species in Lepidoptera . . . .149 
 
 Characters acquired by Use . . . . .153 
 
 Inheritance of Injuries and Diseases . . . .173 
 
 SECTION V 
 
 DISUSE OF ORGANS DEGENERATION PAMMIXIS 205 
 
 Pammixis . . . . . . .217 
 
CONTENTS 
 
 XXVll 
 
 SECTION VI 
 
 MENTAL FACULTIES AS ACQUIRED AND INHERITED CHARACTERS 
 
 The Function of the Brain .... 
 
 Keflex Action ..... 
 
 Intelligence, Keason, Habit (Automatic Actions), Instinct 
 
 Particular Instances of Intelligence and Reason in Animals 
 
 Experiments and Observations on Instinct in newly-hatched 
 Chickens 
 
 • • • 
 
 The Instinct of the Cuckoo in Laying her Eggs in other Birds' 
 Nests ...... 
 
 Reasoning Instincts ,....' 
 
 Further Remarks on Reasoning Instincts and Intelligent In 
 stincts in Animals 
 
 Reflex Action and Instinct . 
 
 Impulse and Instinct 
 
 Concluding Remarks on Instinct 
 
 Irritability and Sensation — Will 
 
 PA<iK 
 
 221 
 
 221 
 222 
 223 
 231 
 
 245 
 
 256 
 266 
 
 278 
 294 
 301 
 304 
 306 
 
 SECTION VII 
 
 ORGANIC GROWTH : THE MORPHOLOGICAL AND PHYSIOLOGICAL EVOLU- 
 TION OF THE LIVING WORLD AS THE RESULT OF FUNCTION 315 
 
 The Origin of Organisation in Unicellular Animals — The 
 
 Fundamental Biological Law 
 
 The Evolution of Organisation in Multicellular Animals 
 
 Origin of Muscles ..... 
 
 Origin of Striation in Muscles 
 
 Evolution of the various Sense-Cells from a Common Cell 
 Layer ...... 
 
 The Origin of the Central Nervous System 
 
 Vicarious Nerve-Centres .... 
 
 The Cell-Nucleus as a Central Nervous Organ 
 
 315 
 323 
 326 
 328 
 
 331 
 331) 
 343 
 34!) 
 
xxvni CONTENTS 
 
 PAGE 
 
 Origin of Nerve-Fibres and their Vicarious Action . . 353 
 
 The Acquisition and Inheritance of Peculiarities of Voice and 
 
 Speech, and the Speech of Animals . . .362 
 
 Concluding Remarks . . . . .377 
 
 SECTION VIII 
 
 THE IDEA OF ORGANIC GROWTH THE LAW OF ORGANIC FORM 
 
 RECRESCENCE 379 
 
 The Idea of Organic Growth . . . .379 
 
 Crossing and Selection as Indirect Causes of Growth . . 383 
 
 The Law of Organic Form : Its Application to the Form and 
 
 Structure of Plants . . . . .384 
 
 The Recrescence of Lost Parts as an Example of Organic Growth 389 
 Conclusion . . . . . . .409 
 
 APPENDIX 
 On the Idea of the Individual in the Animal Kingdom . 413 
 
INTEODUCTION 
 
 It seemed to me long ago of the greatest importance to under- 
 take an nwestigation of the question whether tlie modification 
 (variation) of the species of animals is not governed by 
 definite laws. 
 
 It had previously been assumed that variation occurred 
 quite irregularly, in the most diverse directions, that it was 
 abandoned completely to chance ; in fact, the origin of species 
 according to the Darwinian explanation is left entirely to 
 chance. It was justly objected to that explanation that it 
 asserted the predominance of chance. If, as I acknowledge, 
 the principles of Darwinism are true because they can be 
 shown to follow from natural laws, then it was to be expected 
 that obedience to laws would also be discovered in that pro- 
 vince which Darwin had surrendered to chance. But if 
 variation were shown to follow certain laws, tlie same 
 demonstration would apply to the origin of species. ¥ov 
 species have, as every evolutionist will acknowledrre of 
 necessity been produced from varieties. They differ, if we 
 can draw a dividing line between tlie two at all, from 
 varieties only in this, that they are separated from related 
 forms both upwards and downwards by the impossibility of 
 unlimited fertile sexual intercourse, or else, as in the case of 
 
 > f B 
 
INTRODUCTION 
 
 forms multiplying asexually, they are defined by conspicuous 
 morphological characteristics. 
 
 But the investigation of the laws of variation included the 
 question of the causes of this variation. In this respect also 
 Darwin had left a great gap in the explanation of the 
 origin of species. It was because he left variation essentially 
 to chance that he was unable to say much on the question 
 why it occurred at all. Indeed, it was the most zealous 
 adherents of Darwin who made, and still make, the great 
 mistake of treating the selection depending on utility as the 
 power which by its own action brings forth those variations of 
 the characters of the organism which afford the possibility of 
 that selection ; or at least, the mistake of not perceiving clearly 
 how far selection, how far Darwinism as a whole, is from being 
 able to explain these variations. 
 
 The Darwinian principle of utility, the selection of the 
 useful in the struggle for existence, does not explain the first 
 origin of new characters. It explains only— and that in my 
 opinion only partially— the progress and the gradually effected 
 pre-eminence of these characters. 
 
 Darwin's assertion that every character occurring in an 
 organism must either be now useful to it, or must once have 
 been useful,— an assertion whichDarwin himself didnotadhere 
 
 to, but from which latterly he withdrew more and more,— has 
 certainly more than anything else led to the false conception 
 we have mentioned, for he set up utility as the only ruler in 
 the organic Idngdom. By the imconditional assumption of 
 this supremacy it was quite overlooked that utility is a purely 
 relative conception, and that therefore it cannot possibly be 
 the fundamental principle of the forms of the organic world. 
 
 Before anything can be useful it must first be. Why, by 
 what means, is it brought into existence ? That is the wider 
 question which I have put to myself. 
 
 But if there are agencies independent of utility wdiich 
 
INTRODUCTION 
 
 influence the forms of the organic world, which indeed 
 primarily condition them, many characters of this organic 
 w^orld must exist \vhich have nothing whatever to do with 
 utility. 
 
 It was a fTiori to be expected that the result of niv 
 investigation would relate principally to such characters, 
 hitherto but little considered. 
 
 If we could know all the natural laws which have operated 
 in the evolution, and which operate in the existence of a sin<de 
 animal or a single plant, w^e should understand the laws of 
 the organic world altogether. 
 
 On this ground alone the biologist may look for a rich 
 reward in giving himself unreservedly for once to the study 
 of a single living being, in order to penetrate into its nature 
 as deeply as possible. The single chosen object soon tells 
 him more than all other animals or plants together whicli he 
 has observed more superficially. For the more an investigator 
 devotes himself to a fruitful object, the richer it appears to his 
 eyes, the more it shows new properties, the more it acquires 
 living interest and importance, and the more do all its 
 characters and the relations of its life show themselves to be 
 governed by law. 
 
 The unreserved study of a single species of animal has 
 led me to the discovery of a whole series of laws, which the 
 extension of the investigation to other species showed to hold 
 good generally. 
 
 As far back as the beginning of the eighth decade of the 
 present century, I had turned my attention to the wall-lizard, 
 wdiose remarkable variability is well known, as the starting- 
 point of my investigation. The circumstance that in tlie 
 spring of 1872 I became acquainted with the dark blue wall- 
 lizard, described by me as Lacerta muralis ccerulea, on one of 
 the Faraglione rocks at Capri determined my final decision. 
 
 In this form of the wall -lizard I had found an animal 
 
INTRODUCTION 
 
 wliicli might be with equal justice described as species or 
 variety, so much does it differ from the original form. Thus, 
 at the conclusion of the paper I published on this lizard,-^ I 
 was able to say : " The remark of some opponents of Darwin- 
 ism that no one has yet observed the conversion of a variety 
 into a species is not, I grant, contradicted by the existence of 
 the blue wall-lizard, for it makes on the adherents of the 
 theory a demand similar to this : we want to hear the grass grow. 
 Besides, every naturalist will always be at liberty, within cer- 
 tain limits, to understand by a ' species ' what he will. But an 
 instance is afforded in this animal of undoubted natural race- 
 production, which has evidently occurred in a relatively short 
 period of time, and this ought to prevent any opposition, which 
 is not expressly one of principle, from attaching any import- 
 ance to the argument above quoted." 
 
 The problem of finding the causes of the modifications 
 which this remarkable variety had undergone led me im- 
 mediately into the midst of the inquiries which I had already 
 proposed to myself The result of my researches, which were 
 extended to various classes of animals, was the recognition of 
 the dominion of laws in the process of variation, not only in 
 the lizard, but also in the most diverse tribes of the animal 
 kingdom : these laws holding firstly in the variations of 
 marking, previouslyregarded as quite indifferent, unimportant, 
 and fortuitous, but also applying to other characters. I was 
 able to demonstrate that variation everywhere takes j)lace in 
 quite definite directions which are few in number, and I was 
 able on the basis of my observations to put forward the view 
 that the causes which lead to the formation of new characters 
 in organisms, and in the last result to their evolution, consist 
 essentially in the chemico-physiological interaction between 
 the material comj^osition of the body and external influences. 
 
 ^ Zoologische Studien av.f Ccqrri, ii. Lacerta muralis cccrulea, Leijizig, 
 Engelniacn, 1874, 
 
INTRODUCTION r 
 
 Finally, I succeeded, through the facts 1 established, in 
 referring the separation into species, of which neitlier Darwin 
 nor any of his successors had given a satisfactory explana- 
 tion, in connection with the rest of my views, to natural 
 causes. 
 
 I have expounded these views at full lengtli in a second 
 paper ^ on the variation of the wall-lizard. 
 
 But it seemed that very few investigators in the province 
 of the doctrine of evolution troubled themselves about the 
 wall-lizard, or about facts obtained from such a conmion 
 animal, or about the conclusions to be drawn from them. It 
 is possible, indeed, that the title of my papers was not very 
 inviting. I ought to have put Darwinism first, and the wall- 
 lizard second. Possibly the latter might then have been 
 honoured too — possibly, for the tendency of the " scientific " 
 zoology of to-day is to neglect the study of entire animals.- 
 Anything that is not teased with the needle, or cut with the 
 microtome, or examined with the microscope, is scarcely 
 noticed at the present day, except by those who are exclusively 
 systematists, — even in C|uestions connected with the evolution 
 theory. For, strange to say, even the doctrine of evolution is 
 left entirely in Germany to the decision of anatomy and em- 
 bryology, that is, of the microscope, or else is given up to mere 
 speculation, although Darwin himself, the reviver of this doc- 
 trine, used neither the former nor the latter, but external 
 
 1 " Researches on the Variation of the Wall-Lizard : a Contrilmtion to tlie 
 Theory of Evolution from Constitutional Causes, and also to Darwinism." Arch. 
 f. Naturgeschichte, Berlin, 1881. 
 
 "2 In the zoological Jahreshericht of the Zoological Station in Naples for 1881, 
 published 1883, p. 219, I read: "Th. Eimer has published a very important 
 paper, well worth reading, on the variation of the wall-lizard. This comprelien- 
 sive memoir is not of a kind to be briefly summarised, and therefore the reader is 
 referred to the original." That is all the favourable acknowledgment of the 
 memoirs in question which I have read up to quite recently, exceptnig n-port-s in 
 the Naturforscher and in the Revue der Naturwissenschaften. But K. Dusinp hxxs 
 just published a report showing complete comprehension of my meaning in vol. u. 
 of Kosmos of 1886. 
 
6 INTRODUCTION 
 
 form, the life and the distribution of plants and animals, for 
 his theory. 
 
 ISTo matter. In any case, since the publication of my 
 papers various theories concerning evolution have appeared, 
 whose authors have not troubled themselves in the least about 
 the facts established by me, have not even mentioned them, 
 although they contradicted their theories. But I will not go 
 so far as to say with Niigeli that this was " because they were 
 unable to use these facts." In an address to the second 
 general meeting of the Congress of German Naturalists and 
 Physicians at Freiburg i.B., which is printed as an appen- 
 dix to this book, I had developed a theory based on facts. 
 Subsequently, in various articles in the Zoologisclier Anzciger, 
 and in the journal HumhokU, as well as in a lecture on the 
 markings of birds and mammals^ delivered as early as 1882, 
 which was afterwards published, and which is reproduced in 
 the present book, I largely added to the number of these 
 facts, and brought forward further irrefragable evidence for 
 my views. But notwithstanding all this, not one of those 
 who have set up theories or hypotheses of their own in our 
 subject took any notice of my facts. 
 
 As we shall see, I have no special reason to complain in 
 this matter. What has happened to me has happened to 
 others. The botanist Nageli makes, as I mentioned, the 
 charge against such writers that they have not referred to 
 the facts brought forward by him because they could not 
 make use of them. 
 
 I might express myself in milder terms thus : The founders 
 of theories of evolution set up since Darwin's time have as a 
 rule deviated from Darwin's path, inasmuch as they have 
 sought to adapt the facts to their ideas and opinions, instead 
 
 ^ Ueber die Zeichnung der Vof/el und Sdwjethiere. Lecture delivered at the 
 Meeting of the " Verein fiir Vaterlandische Naturkunde in Wiirttemberg" at Nagold 
 on 24th June 1882. Wurttemberr/ische'iiatunoissenschaftliche Jahreshefte, 1883. 
 
INTRODUCTION 
 
 of adapting their ideas and opinions to tlie facts. Sucli 
 argument leads naturally, even without any had intention, 
 away from the consideration of the opposing facts hack to 
 its starting-point — revolving in a circle and seeing nr.thin^' 
 which lies without the circle. This method is most surpris- 
 ing in those who, like A. Wagner, with his Lcivj of M'ujm- 
 fion, oppose the whole of Darwinism in order to put in its 
 place an explanation of evolution which can only find its phice 
 in Darwinism itself as a suhordinate of that theorv. Isolation 
 in space, regarded hy Wagner as alone regulating the origin 
 of species, favours and promotes the separation of the gradu- 
 ally produced diverse forms into species ; hut apart from the 
 truth that it does not alone explain the separation, its 
 influence cannot possihly he put in the place of that of 
 the principle of utility. 
 
 The effective influence is not necessarily single — many 
 can be effective together. 
 
 On this standpoint I have placed myself in my inquiries 
 from the first, and their course and their results have full}- 
 justifled me. 
 
 On account of the relations which they bear to others, I 
 have repeated some of the facts already published by me 
 which serve as the foundation of my theory. The last sec- 
 tions of this book are specially devoted to such facts. 
 
 It happens that my views on the question before us do not 
 agree with those of some of my valued friends and honoured 
 teachers, and if I am to uphold my own convictions I must 
 endeavour to refute theirs. 
 
 As this opposition is little pleasing to myself, I am con- 
 vinced that my frank advocacy of scientific opinions will 
 neither by those who are aware of this personal relationship, 
 nor by those who are immediately affected, be stigmatised 
 as unfriendly and ungrateful. 
 
SECTION I 
 
 THE NEWEST THEORIES CONCERNING EVOLUTION 
 
 Before I proceed to the exposition of my own views I must 
 briefly discuss some of those attempts to explain the evolution 
 of organisms which have been made by others in recent years, 
 namely, those of Weismann and Nageli. 
 
 The theory of heredity introduced by AVeismann under 
 the name " Continuity of the Germ-plasm,"^ has recently been 
 widely discussed, partly in a favourable, partly in an adverse 
 spirit.^ 
 
 This theory seeks to explain the fact that the characters 
 of the parents are inherited to so high a degree by the 
 children, and the other fact that characters can be inherited 
 from more remote ancestors, e.g. from the grandparents, 
 
 ^ A. Weismann, Die Kontinuitdt cles Keimplasvm als Grundlage einer 
 Theorie der Vererhung, Jena, G. Fischer, 1885. The same : Z\tr Frage 7iach 
 der Vererhung ei-worhener Eigenschaften, Biolog. Centralhlatty 1886, Bd. vi. 
 No. 2. 
 
 - E.g. Naturforscher, 1886, No. 1. Eimer, Deidscher LitteraturzeiUmg 
 15th May 1886. V. v. Ebner, Ueher Vererhung, Lecture delivered to the So 
 ciety of Physicians of Steiermark, 22d March 1886 {Betz MemoraJjilien, 2 Heft 
 1886). Kulliker, Die Bedexdung der Zellkerne fur die Vorgilnge der Vererhung 
 Zeitsch.f. V). Zool. 1885 ; and Dcts Karyoplasnui und die Vererhung, eine Kritik 
 der Weisma/ans' clien Theorie von der Kontinuitdt des Keim]jlasnia, ihid. 1886 
 Virchdw, Descendenz und Pathologie, Arch. f. patholog. Anat. Bd. ciii. Koll 
 mann, Biolog. Centralhlatt, Bd. v. 1886. Virchow, Verhandlungen der Strass 
 burger Naturforscherversammlung, 1885, Address delivered at the second general 
 meeting of this Congress. 
 
SEC. I CONTINUITY OF GERM-PLASM 9 
 
 one or more generations, e.g. the parents, being passed over 
 (atavism). 
 
 Weismann's attempted explanation rests on the assump- 
 tion that the germ cells, by means of which inheritance must 
 be transmitted, pass over unchanged from the body of the 
 ancestor into that of the descendant ; that they form a whok' 
 which so far contrasts strongly with the rest of tlie body ; 
 that it takes no kind of part in the changes which the Litter 
 experiences during life; that they can therefore be trans- 
 mitted from generation to generation unchanged. G. Jiiger ^ 
 and Nussbaum^ had previously already sought to explain such 
 an immediate connection between the germ-cells of parent 
 and child, by the assumption that the germ-cells of the off- 
 spring separated themselves at the very beginning of embry- 
 onic development, or at all events before any histological 
 differentiation, from the rest of the developing ovum. 
 
 According to Weismann — the assumption of Jager and 
 Nussbaum comes ultimately to the same thing — inheritance 
 would be due to the fact that in every reproduction a part of 
 the germ-plasm of the parental egg-cell is not used up in the 
 construction of the offspring, but remains unchanged to serve 
 for the formation of the germ-cells of the following generation. 
 The inheriting substance lies, according to Weismann, in the 
 contents of the nucleus of the germ-cell. 
 
 " The germ-cells," says Weismann, " arise in their essential 
 and distinctive substance, not by any means from the body 
 of the individual, but directly from the parental germ-cells." 
 " Inheritance," he continues, " takes place wholly and solely 
 because a substance of definite chemical, and above all, 
 molecular composition passes over from the germ -cells of 
 one generation to those of the next. This substance, the 
 
 1 G. Jager, Lehrhuch der allg. Zoologie, Leipzig, 1878, Bd. ii. 
 
 2 M. Nussbaum, Die Differenzimng des Geschlechts im TJiierreich, Arch. f. 
 mikAnat, 1880, Bd. xviii. 
 
10 THE NEWEST THEORIES CONCERNIXG EVOLUTION sec. 
 
 germ-plasm, is located in the cell-nucleus, and possesses, by 
 virtue of its extraordinary complexity of structure, the 
 capacity to develop into a very complex organism." 
 
 According to AVeismann's explanation of heredity, therefore, 
 the germ-cells appear no longer as the product of the body, 
 but rather as something in contrast with the totality of the body- 
 cells. " The germ-cells of successive generations are related 
 in the same way as a series of generations of unicellular 
 beings which are derived one from another by continued 
 division." 
 
 The necessary consequence of such a conception is the 
 proposition that acquired characters are never inherited. If 
 he is riGfht, then no external influences whatever can ever 
 have contributed to the moulding of species. The permanence 
 of forms would be explained by that proposition, but their 
 variability would remain, unless other agencies were brought 
 forward for its explanation, a darker mystery than ever. 
 
 Weismann seeks these agencies in sexual reproduction. 
 
 By the mixture of characters which sexual reproduction 
 brings about, according to him, are supplied at once — and 
 exclusively — the materials for the origin of new species ; 
 among the new forms produced by the mixture, the struggle 
 for existence chooses the fittest for survival and for renewed 
 reproduction.^ 
 
 The great importance of the sexual mixing of characters 
 in modification can be ignored by no one, and was indeed never 
 ignored. But if this were the only cause of modification it 
 would be necessary to assume, supposing the same laws to 
 hold for lower as for higher organisms, that all plants and 
 animals, including the low^est, now reproduce sexually, and 
 always have done so, — an assumption which is known to be 
 
 ^ A. Weismann, T)ie Bedeidnng der geschlechtlichen Fortpflanzung far die 
 SeleUionstheorie, Address to the Congress of Naturalists at Strassburg, 1885, 
 and Jena, G. Fischer, 1886. 
 
VARIABILITY 
 
 11 
 
 unjustifiable on the basis of the facts offered to us by the 
 organic world now living, and which is contradicted by tlie 
 general conception of the gradual development and perfection 
 of organic differentiation. But AVeismann compares the 
 increase of the continually unchanged germ- plasm of the 
 multicellular organism with the reproduction of tlie 
 unicellular; in the latter also the same substance grows 
 continually, and new individuals arise only by its division 
 from time to time. The germ -plasm of the multicellular 
 organisms is to correspond therefore with the whole body 
 of the unicellular. Weismann does not deny that the 
 unicellular beings change in consequence of the direct 
 influence of external agencies ; on the contrary, he ascribes 
 to them explicitly this property. From this inheritable 
 individual diversity once produced he derives " that of the 
 Metazoa and Metaphyta,-^ in that this diversity, through 
 sexual reproduction which has in the meantime become 
 general, is preserved for ever, increased and ever produced 
 in new combinations." Thus, according to Weismann, the 
 difference between the unicellular organism and the germ- 
 plasm of the multicellular is a fundamental one — for the 
 former other laws hold good than for the latter. 
 
 But against Weismann's conception of the importance 
 of the germ-plasm in heredity are to be set the following 
 facts. 
 
 It is known that even highly organised animals and plants 
 have the power of multiplying, by simple division in the case 
 of the former, by cuttings in that of the latter." The new 
 complete individual produced by this method has the same 
 characters as the animal or plant produced at anotlier time 
 from a germ-cell — a proof that the substance possessing the 
 property of heredity is not confined to the germ-plasm, and 
 
 ^ I.e. of the multicellular animals and plants. 
 ' Cf. V. V. Ebner, o'p. cit. 
 
12 THE NEWEST THEORIES CONCERNING EVOLUTION sec. 
 
 that it cannot be somethiucr altof^etlier different from other 
 parts of the organism. 
 
 \^^ien Weismann further expresses the opinion that 
 sexual differentiation itself finds its explanation in his theory 
 alone, he is to be met with the fact that such an explanation 
 is certainly afforded by (1) the importance of preventing in- 
 and-in breeding ; (2) the importance of division of labour. 
 
 Weismann's argument against the inheritance of acquired 
 characters seems to me to be abandoned by himself in his 
 acknowledgment of the inheritance of the tendencies (pre- 
 dispositions) to new characters acquired during life. In an 
 article on this question-^ I have remarked that any such 
 tendency certainly implies a corresponding molecular 
 peculiarity of the germ-plasm. 
 
 " Let us assume," I said, " that all living beings have 
 evolved one out of another, then, on the basis of Weismann's 
 conception itself, it must be acknowledged that the predis- 
 position to the acquisition of characters, and with that the 
 molecular structure of the germ-plasm, has in the course of 
 time experienced great changes ; even with predispositions 
 it is a question of characters acquired in the course of time 
 and inherited." 
 
 Further, Weismann grants a slirjlii degree of inheritable 
 external influence on the germ-plasm. 
 
 The greatest stress, however, is laid by him on the fact that 
 no inheritance of injuries incurred during life has been 
 proved. 
 
 That injuries incurred during life are but seldom trans- 
 mitted to the offspring does not appear to me wonderful : 
 the inheritance of the complete form and complete activities 
 of the organism, which took root such enormously long 
 periods of time ago, and has been strengthened at each 
 generation, will as a rule counterbalance in the offspring any 
 
 ^ Deutsche Litteraturzeltunrjy 15tli May 1886. 
 
NON-INHERITANCE OF INJURIES 
 
 such injuries incurred only once and not repeated. It is true 
 there are injuries which, although they have been always 
 repeated constantly, are yet never inherited. Among these 
 is the rupture of the hymen in women. 
 
 In such cases we must presume a specially effective power 
 of correlative activity,^ directed to the part affected and 
 residing in the whole organism — the same compensating 
 power which leads in lower animals during the life of the 
 individual to the regeneration of parts which have been lost 
 or artificially removed.^ But these cases do not prove the 
 general proposition that injuries are not inherited ; they do 
 not prove that even injuries which have been repeated during 
 a considerable period are not inherited. Hitherto little 
 importance has been attached to the demonstration of the 
 inheritance of injuries. Yet single cases of the inlieritance 
 of injuries only once incurred seem to me to be thoroughly 
 authenticated. To these I shall refer subsequently. 
 
 For the rest, it can I believe be proved as a fact that 
 acquired characters are inherited. 
 
 The germ -plasm cannot possibly, in my view, remain un- 
 touched by the influences which are at work on the whole 
 organism during its life. Such an immunity would be a 
 physiological miracle, merely on account of the morphological 
 relations of the animal ovum and spermatozoon, and their 
 dependence on the nutritive processes of the body,^ — a miracle 
 
 ^ Correlation = the principle that the characters of the living being are so 
 connected with one another that one determines the other. 
 
 2 The more imperfect the structure of animals, i.e. the lower their organisation, 
 the less degree to which division of labour is carried out, so much the greater the 
 facility with which injuries are repaired, so that many of the lower animals can 
 be even cut into pieces with the residt that each piece grows again into a perfect 
 animal, just as in many plants. (Cf. on this point the Appendix : On the Idea 
 of the Animal Individual.) The inheritance of injuries is thus of but slight 
 importance in the discussion of heredity in general. 
 
 3 I have myself described arrangements of quite surprising character for the 
 nutrition of animal ova. Cf. my memoirs on the ova of Keptiles, Birds, and Fishes, 
 in Arch. f. mik. Anat. Bd. viii. 1872. 
 
14 THE NEWEST THEORIES CONCERNING EVOLUTION sec. 
 
 wliicli would be no less inexplicable than atavism, apart from 
 Weismann's theory, seems to be. 
 
 According to my ideas, it is not that sexual mixing of 
 characters, together with adaptation, determines the modifica- 
 tion of forms, but rather that sexual differentiation itself is 
 due to acquired and inherited characters. 
 
 But it is not my purpose at this point to bring forward all 
 the arguments on which I rest my opposition to Weismann's 
 theory ; these arguments will be further developed in subse- 
 quent pages. 
 
 A theory essentially opposed to Weismann's regarding the 
 causes of the modification of organic forms, in other words, the 
 origin of species, has been set forth by Nageli under the title 
 " Mechanico-physiological Theory of the Doctrine of Descent." ^ 
 
 According to him, internal causes depending on the nature 
 of the oro-anic substance effect the transformation of the 
 " strains " (individuals, species, families, etc.) in definite direc- 
 tions. Such " internal causes " must necessarily be supposed 
 merely on the ground that the modifications or variations of 
 the strains do actually take place in definite directions and 
 are not irregular. The internal causes effect a constant altera- 
 tion of the strains in definite directions "towards greater 
 perfection, that is, towards greater complexity." The strains 
 grow, as it were, towards greater perfection. Accordingly, 
 Niigeli describes his theory of internal causes as the principle 
 of " improvement." " Superficial reasoners," he says, " have 
 pretended to discover mysticism in this. But the principle is 
 one of mechanical nature, and constitutes the law of persist- 
 ence of motion in the field of organic evolution." " Once the 
 motion of evolution is started it cannot cease, but must persist 
 in its original direction." 
 
 By greater perfection, then, iSTageli understands more com- 
 
 ^ C. v.. Niigeli, Mechanisch-physiologische Ahstamvmngslehre, Mlinchen und 
 Leipzig, 1884. 
 
 f 
 
N AGE LPS VIEW . i 
 
 r 
 
 plex structure, greater division of labour. Distinct from this 
 perfection of organisation there is a perfection of adaptation, 
 " which is repeated at every degree of organisation, and whicli 
 consists in the organism having, in relation to the external 
 conditions at the time, the most advantageous structure which 
 is compatible with its degree of complexity and the division of 
 its functions." 
 
 The improvement of structure and the division of labour 
 progress according to this conception within certain lines 
 uninterruptedly, on account of the mechanical activity, 
 following certain laws, of the living organic substance ; and 
 this course of things is only so far affected by other influences, 
 that the external conditions of each particular period by means 
 of adaptation favour those arrangements of structure which are 
 most useful in the struggle for existence. 
 
 Continual advance of its own accord towards perfection is 
 thus, according to ISTageli, a property of living organic substance. 
 
 But as Weismann's germ-plasm, unaffected by all external 
 influence, would have been gradually used up, so it seems to 
 me, according to Nageli's principle of improvement, since it 
 has been constantly at work ever since there have been living 
 beino's at all, the lowest creatures which existed millions of 
 years ago must long ago have changed into higher — there 
 could no longer be any lowly- organised simple living things 
 at all. Nageli explains their existence by the assumption 
 that abiogenesis still takes place at the present day. The 
 origin of the organic from the inorganic, he says, is a con- 
 clusion to be drawn from observation and experiment, a 
 fact which follows from the law of the indestructibility 
 of matter and energy (a sentence which, excepting the 
 words "is a fact," shall not be contradicted). To deny 
 spontaneous generation, he says, would be to proclaim a 
 miracle. "In later times, and now still, abiogenesis must every- 
 where occur where the conditions are the same as in the 
 
16 THE NEWEST THEORIES CONCERNING EVOLUTION sec. 
 
 primitive time . . . Among known living beings there are 
 none which could have arisen by abiogenesis " — the lowest 
 living plants have already a cell-membrane and the ]\Ionera 
 cannot live independently, i.e. without the products of 
 decomposition of other organisms, as must be the case with 
 organisms produced by spontaneous generation. " The beings 
 wdiich are capable of arising by a spontaneous origin are there- 
 fore not yet known to us. They must have a still simpler struc- 
 ture than the lowest organisms which the microscope shows us" 
 — they may be " beneath the low^est size which is visible with 
 the microscope." The organic being due to spontaneous genera- 
 tion can be but a minute drop of homogeneous plasma " which 
 consists of albuminates without admixture of other organic 
 compounds than food materials, without external form and 
 without distinction of parts, and which grows and feeds on 
 the inorganic or simple organic compounds from wdiich itself 
 arose." " Abiogenesis thus presupposes a spontaneous forma- 
 tion of albuminates." Probably the spontaneous albumen 
 production takes place still at the present time " in the moist 
 superficial layer of some porous material (loam, sand), where 
 the molecular forces of solid, liquid, and gaseous bodies are at 
 work together," favoured by a definite degree of warmth, " so 
 that it may still take place in warmer climates as well as in 
 the w^armer part of the year in colder regions." 
 
 Nageli advocates w^ith Weismann the view" that external 
 influences — that, in particular, climatic conditions and changes 
 of nutrition — have no effect on the transformation of species. 
 He supports his argument with experiments wdiich he made 
 upon plants ; placing them nnder such changed conditions 
 and finding that these had no relation wdiatever to the appear- 
 ance of varieties.-^ 
 
 ^ C. Nageli, Ueher den Einjluss der dussern Verhdltnisse avf die Varietdten- 
 hildung im PJlanzenreiche. Sitzxiugsb. d. math.-2^hys. Klasse d. k. hayer. AJcctd. 
 d. Wissensch. zu 3Iunchen, 18th November 1865 ; and Das gesellschaftliche 
 Entstehen neuer Species, ibid. 1st February 1873. 
 
IDIOPLASM 17 
 
 Thus while, according to Nageli, the influences of nutrition 
 have no power to produce change in higher organisms in even 
 very long periods of time, he nevertheless assumes that such 
 a change is produced in the lowest creatures. Since the lowest 
 living beings arise by spontaneous generation under different 
 conditions and in different places, therefore they must be 
 differently constituted. Thus the further conclusion follows, 
 that " the organic kingdoms take their origin not from a single 
 organism but from several, which, however, differ but little 
 from one another." The explanation of this important differ- 
 ence (between higher organisms, and those which are being 
 produced from inorganic matter), by the assumption of which 
 Nageli not merely limits his statement of the non-inheritance 
 of acquired characters but obviously shakes it to its founda- 
 tions, is sought in a further supposition, namely, that the 
 idioplasm of higher forms " obtains stability of structure from 
 improvement during long geological periods, which structure 
 has a relation to those different influences ; while in the intro- 
 ductory period of spontaneous generation the definite order is 
 being sought for the first time, and therefore is determined by 
 the combined effects of all things which modify the molecular 
 attractions and movements."-^ 
 
 Nageli concludes in fact, like Weismann, that it must be 
 a definitely formed firm substance which determines the special 
 character and the specific evolution of an organism, and that 
 this substance impresses its form upon the passive nutritive 
 plasma which is dependent upon it and which forms the 
 principal bulk of the body. To this substance he gives the 
 name "idioplasm." He does not, however, like Weismann with 
 
 1 [If this last quotation from Nageli seems somewhat obscure in its Englisli 
 rendering, I can only say that it is not less so in the original German. This is not 
 to be wondered at very much, for Nageli is describing things wliich neither he nor 
 any one else can really understand. It may be questioned whether such speculations 
 are legitimate in science ; they are scarcely due to a scientific use of imagination. 
 Trans.] 
 
 C 
 
18 THE NEWEST THEORIES CONCERNING EVOLUTION sec, 
 
 his germ-plasm, pack it away in the cell-nucleus alone, but 
 conceives it as a network or framework which permeates the 
 whole body from cell to cell. It is the idioplasm which 
 changes from generation to generation from internal causes, 
 and thus, without being essentially influenced by accidental 
 variation and selection, produces quite new forms. 
 
 Niigeli thus fundamentally takes us back to the concep- 
 tion of the vital force, applying it to the modification of forms, 
 to the doctrine of evolution, and attempts to divest the 
 principle of utility of any considerable importance. 
 
 His principle of improvement therefore effects greater 
 complexity and greater division of labour in organisms in 
 definite directions. When this metamorphosis is once in 
 progress " it continues by mechanical necessity in the direc- 
 tion in which it started. For when, in virtue of the begin- 
 ning made, one generation produces offspring which in one 
 respect are in advance of the parents, then by the law of per- 
 sistence of motion the offspring of these offspring must be 
 altered to a farther degree, and the evolution must go on as 
 far as the nature of the conditions allows." Thereupon 
 adaptation comes into action. 
 
 We have thus, according to Nageli, as the mechanical 
 causes of the evolution of tlie organic kingdoms "the 
 persistent advance towards perfection from the simpler to the 
 more complex, and further, the definite action of the external 
 conditions in adaptation." 
 
 *' Competition, with its consequent crowding out among 
 living beings, has, within the definitely directed changes 
 towards perfection and adaptation, its effect in separating and 
 in defining, but not in forming, the strains : not a single 
 phylogenetic pedigree owes to competition its existence, but 
 the several pedigrees through the extermination of inter- 
 mediate forms stand forth more clearly and more char- 
 acteristically. 
 
PX0GJ!ESS70Ar AND COMPETITION 
 
 "• • . . Still better may we compare the ve^retablnl-in, i 
 to a great tree branching from its Le upwar^of ^ '7 
 
 ■ s::irre=rr:r^-r 
 
 .conMWlop.thontMr:^^^^^^^^^^ 
 
 o.tnuaS\!r ^"^^■'^'^•^ ^ «-*--. Pnu.e.s the tree 
 
 roll * "" "' '""^■^'^^ ^^^^' -^ P-duces 
 
 an oideUy arrangement with clearly distinguishable parts 
 
 Children who see the gardener daily at his task may weS 
 
 suppose that he is the cause of the formation of the branl 
 
 and twrgs. Yet the tree, without the constant prnZ 
 
 the gardener, would have been much greater, not in height 
 
 biTinr"' ^"' "^ '^^ ""^ ^"^ ''-'^-^ °'°^'^ 
 
 "In the perfecting .process (progression) and adaptation 
 
 >e the mechanical impulses which lead to the abundance of 
 
 forms; m competition and extermination, or in Darwinism 
 
 proper, only the mechanical cause of the formation of gaps in 
 
 the two organic kingdoms." 
 
 ThusNageH's theory attempts principally to explain two 
 points which that of Weismann leaves unexplained, namely 
 the beginning of the formation of characters and the fact of 
 variation i„ definite directions. But Nageli's conception 
 seems to me to rest so much more on assumptions acutely 
 thought out than on facts, that it deserves ratlier to be 
 described as a materialistic-philosophical than as a mechanico- 
 physiological theory. 
 
SECTION II 
 
 THE ORGAXIC GROWTH OF THE LIVING WORLD 
 
 For many years I have myself, from researches on the varia- 
 tion of single species of animals, especially with respect to 
 markings of colour, acquired and expressed ^ views upon 
 the ultimate causes of the origin of species. These views are 
 essentially in contradiction to those of Weismann, and to 
 those of Nageli, while in details they agree with those of each. 
 
 The agreement consists in this, that I have from the 
 zoological standpoint, as already remarked, pointed out and 
 emphatically maintained that the variation of species takes 
 place not in all kinds of directions irregularly, but always in 
 definite directions, and indeed in each species in a given 
 time in only a few directions. 
 
 Further, I opposed, as mentioned likewise in the Introduc- 
 
 ^ Th. Eimer, Zoologische Studien auf Capri, ii. Laccrta muralis coerulea, ein 
 Beitrag zur Danoinschen Lehre ; Leipzig, Engelmann, 1874. Untersuchungen uher 
 das Variiren der Mauereidechse, ein Beitrag zur Theorie von der Entvncklung aus 
 constitutionellen Ursachen; Archiv fur Naturgeschichte (and separately), Berlin, 
 Nicolai, 1881. Ueber den Begriff des thierischen Individuuvi, an Address 
 delivered at the second general meeting of the " Versammlung deutscher Natur- 
 forscher und Aerzte," at Freiburg i. B. , 1883. Further, ray articles: Ueber 
 die Zeichnimg der Thiere, in the Zoolog. Anzdger, 1882, 1883, 1884 ; and 
 (with figures) in the journal Huviboldt, 1885, 1886. Also Ueber die Zeich- 
 nung der Vogel und Sdugethiere, Lecture delivered at the meeting of the 
 "Verein fiir vaterlandische Naturkunde in Wiirttemberg " at Nagold, 1882, in 
 Wurttb. natunv. Jahreshefte, 1883. 
 
 Ii 
 
SEC. II THE AUTHOR'S EARLIER VIEWS 
 
 21 
 
 tion, the earlier view of Darwin, tifterwards abandoned by 
 that great naturalist himself, that every character occurring 
 in an organism must either be now useful, or must at some 
 time or other have been useful. I brought forward in opposi- 
 tion to this the great importance of indifferent characters. 1 
 said then,^ at a time when the Darwinian principle of utility 
 still exclusively prevailed among zoologists in Germany : 
 (1) "From internal causes conditions of organisation may arise, 
 may as it were crystalise out, which are just as useful to the 
 organism as if they had been due to the struggle for existence. 
 In this case the claims of the principle of utility are accident- 
 ally satisfied by the results of evolution from internal causes, 
 and the importance of that principle remains therefore 
 undiminished. (2) From internal causes characters which 
 are indifferent for the success of the organism, and (3) even 
 harmful characters may arise. . . . But organisms burdened 
 with harmful characters can only maintain themselves, and only 
 transmit their peculiarities through future generations when 
 such characters are inconsiderable in comparison with the useful 
 ones also present, or when such characters stand in correlation 
 with others whose usefulness is greater than their harmfulness." 
 
 With these words I already at that time (1874) assumed 
 as important agencies in the modification of species causes 
 independent of the Darwinian principle of utility. At the 
 same time I emphatically stated that it was self-evident that 
 no form could continue to exist which unconditionally 
 contradicted that principle. 
 
 Instead of the expression " internal causes " I subsequently 
 employed " constitutional causes," in order to indicate that I 
 sought the causes of the modification of forms not in some 
 fundamental impulse corresponding to vital force, but rather 
 in physical and chemical processes depending on the material 
 composition of the body. 
 
 ^ Lacerta muralis coerulea, 1874. 
 
22 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 The causes I formerly called " iuternal," therefore, have 
 nothing to do with the internal causes of Xiigeli, a fact which 
 is proved without a doubt by his latest exposition, and for the 
 future I shall avoid the expression. 
 
 Fundamental Causes of the Manifold Variety of 
 
 Organic Forms 
 
 According to my conception, the physical and chemical 
 changes which organisms experience during life through the 
 action of the environment, throuc^h li^ht or want of li^ht, air, 
 warmth, cold, water, moisture, food, etc., and which they 
 transmit by heredity, are the primary elements in the pro- 
 duction of the manifold variety of the organic world, and in 
 the origm of species. From the materials thus supplied the 
 struggle for existence makes its selection. These changes, 
 however, express themselves simply as groicth. 
 
 As individuals grow so the whole world of organic forms 
 has grown up from simple beginnings. 
 
 To separate the continuous growing whole into parts, 
 into species, required, and still requires, special means after- 
 wards to be discussed. Let us first of all in what follows 
 exclude the necessity of this separation. 
 
 Warmth, air, light, moisture, food, condition the growth of 
 the individual being — appear before our eyes as the mightiest 
 impulses which determine the manifold variety of the forms 
 of living beings. They condition growth through physical 
 and chemical change of the living organic mass, the plasma, 
 through the formation of new and more complex compounds. 
 
 Since the external conditions have not always remained 
 the same, but have changed in the course of ages upon our 
 earth, and since they are even now locally different, so that 
 one and the same organism at different parts of the earth, in 
 different dwelling-places even of the same region of the earth, 
 
n FORM AND GROWTH 28 
 
 is exposed to different external influences, tlierefore there 
 results, as a quite self-evident consequence of physico- 
 chemical change in the organism, difference of growtli, and 
 therewith, of the shape and form. 
 
 Just as in inorganic nature from different mother lyes 
 different crystals separate, as even simple mechanical shock- 
 can produce dimorphous crystallisation, so crystallise, if i 
 may so express myself, in the course of ages, organic forms, to 
 a certain degree different, out of the same original mass. 
 Only the organism works with much more complex material, 
 with a much greater variety of compounds. The greater 
 delicacy and multiplicity of the organic processes determine 
 other and more manifold forms in the organic world. 
 
 But just because the form of the organism depends upon 
 physico-chemical processes, it is like the form of the inorganic 
 crystal, a definite one, and can, when modification takes place, 
 only change in certain definite directions. 
 
 When such new characters, which are simply to be referred 
 to changed growth, become persistent in a group of individuals 
 by constant and still continuing inheritance, and when this 
 group in any way whatever has lost its connection with the 
 rest of its relatives, by the loss of the intermediate forms, then 
 we speak of a species. 
 
 New, changed form- constituents appear therefore in the 
 variety and species as the expression of changed growth. 
 
 In other words, the origin of species obeys exactly the 
 same laws as simple growth ; it is the consequence of un- 
 ending dissimilar growth of the organic world taking place 
 under changed conditions, with the postulate of permanent 
 separation of dissimilar links of the growing chain of this 
 
 organic world. 
 
 Eeproduction and individual development likewise depend 
 
 upon the laws of growth. 
 
24 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 Eeproduction as Organic Growth 
 Sexiuxl and Asexual Eejirodudion 
 
 The peculiarity of reproduction as compared with individual 
 growth consists only in this, that parts separated from the 
 whole under certain conditions continue to grow. 
 
 It is a fundamental property of the organism that as a 
 whole it wears out, tliat as a wliole it must perish, die ; 
 another, that during its life it must constantly be nourished, 
 repaired, and in part renewed. It continues its race, it trans- 
 mits its life by division, or by separation of parts which go 
 on orowiuGf. 
 
 Thus reproduction is a fundamental property of the 
 organism. 
 
 The necessary repair and renewal finds its most complete 
 expression in sexual combination. For the beginnings of 
 sexual combination must be sought in conjugation^ as it 
 occurs in lower organisms. And these beginnings indicate 
 that each of the organisms in question simply supplies some- 
 thing which makes up a deficiency in the condition of 
 nutrition in the other. 
 
 Gradually from such conjugation, which originally took 
 place between two individuals sexually quite equivalent, 
 sexual separation has developed on the basis of the advantage 
 of division of labour, and the prevention of in-and-in breeding. 
 
 The difference between sexual and asexual reproduction is 
 not more profound than this. 
 
 Indeed, the union of Qg^ and sperm is to be itself regarded 
 as a kind of conjugation, for egg and sperm are parts which 
 separate themselves in an asexual manner from the organism, 
 
 ^ Temporary contact of two unicellular, not externally dissimilar beings — 
 obviously accompanied by exchange of material — or permanent coalescence of two 
 such beings, in each case followed by reproduction. 
 
II CONJUGATION 25 
 
 to be regarded physiologically as buds from it. The sexual 
 union and reproduction which follow exhibit the whole pro- 
 cess of so-called sexual reproduction in this light as a sort of 
 alternation of generations. The sperm-cell as a micro-organisin 
 conjugates with the egg-cell as a micro-organism. And indeed 
 the processes which take place in this conjugation are essen- 
 tially quite similar to those which are known in the conjuga- 
 tion, for example, of Infusoria. Here also the male element 
 (nucleolus = male nucleus, sperm nucleus) unites with the 
 female element (nucleus = female nucleus, egg nucleus) to 
 form a new nucleus, a part of the female nucleus being 
 extruded. This renovation of the Infusorian nucleus, like 
 that of the egg nucleus in sexually reproducing animals and 
 plants, leads to reproduction. For it is now known that 
 fertilisation universally depends upon the renovation of the 
 ^gg nucleus by its union with the sperm nucleus, accompanied 
 as in Infusoria by the extrusion of a part of the former. 
 
 The essential character of ^.gg and sperm is that each 
 contains in homoeopathic dilution the sum of the properties of 
 the body of the female or male respectively which produces 
 it, or, as it might be expressed, contains an extract of that 
 body — just as two cells which in simple asexual division 
 arise from a single one contain the material of the latter 
 divided between them, or as the bud which separates from a 
 Hydra, or the bud which separates from a plant for the 
 propagation of its species, is of exactly the same material 
 composition as the organism that produces it. 
 
 Individual Development as Organic Growth 
 
 Individual development, or ontogeny, is also an abbreviated 
 phylogenetic growth, taking place under special conditions. 
 At the present time the highest living beings still develop 
 from simple cells, grow out of them, repeat in their develop- 
 
26 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 raeut the staf]res of fjrowth of the orgjanic world. The 
 repetition in tlie development of the individual, in ontogeny, 
 of the ancestral development, of phylogeny, consists at the 
 same time in the compressed abbreviated exhibition of the 
 characters acquired by the whole series of ancestors and 
 transmitted to the developing individual. Phylogeny is the 
 mechanical cause of ontogeny. 
 
 If the organic world is a connected whole, the same 
 fundamental laws must liold for all the members as for the 
 whole — therefore also the law of growth. 
 
 If all members of the organic world are either directly or 
 indirectly connected by affinity, have been derived one from 
 another, — if, according to the biogenetic law, the development 
 of each single being consists in its growing on through stages 
 which represent the series of its forefathers (stages of growth 
 from the cell to the vertebrate, for example), — then, on the 
 assumption that this individual development morphologically 
 and physiologically forms a repetition of the ancestral evolu- 
 tion, the proof is afforded by the biogenetic law alone that 
 even the highest organisms, that the organic world in general, 
 in the course of ages, has 'grown up from cells. 
 
 If the organic world is thus a connected whole, as bio- 
 logical research now assumes, and if it has grown up as I am 
 here attempting to prove, then two further important questions 
 have to be faced, namely: (1) What causes have brought 
 about a separation of this organic world (whose forms of 
 their own accord would be in uninterrupted connection, 
 would be united by imperceptible transitions) into different 
 members, into kinships — into species, genera, etc.? (2) To 
 what causes is it due that any given highest species in a 
 group of related species — assuming divergent branching in 
 the tree of descent — is a stacje farther evolved than those 
 next to it ? 
 
 I will first endeavour to answer the first of these ques- 
 
n SEPARA TION OF SPECIES 27 
 
 tions. Neither Darwin nor any other inquirer has done this 
 in a satisfactory fashion, as I remarked in the Introduction. 
 Indeed, this question has hitherto scarcely been seriously taken 
 in hand, and yet it is entitled to as much importance as the 
 general one of the canses of evolution — with its solution alone 
 have we an explanation of the origin of species in the proper 
 sense of the words. 
 
 For the rest, it will be seen from what has been said 
 that my Theory of the Organic Growth of the liviwj World 
 stands in complete accord with other facts and fundamental 
 considerations. Another circumstance in favour of it is that 
 it is as simple as a true principle must be. This simplicity 
 is probably the very reason that hitherto no advocate of the 
 doctrine of evolution has found words to express it. A ques- 
 tion of so extraordinarily wide a bearing seemed to demand 
 extraordinary means for its solution. Very likely, too, my 
 views, after they have overcome the usual first stage of 
 criticism, the assertion that they are unfounded, will be 
 passed on to the second usual stage, and it will be said they 
 have been long ago expressed and known, and then into the 
 third, that they are self-evident. I hope some day to rejoice 
 in the third stage, and shall rejoice even if through their 
 " self-evidence " the recognition of my own work should be 
 diminished. The second stage, however, I may help to shorten, 
 by expressly bringing forward the labours of others, and at 
 the same time discussing the differences between their views 
 and mine.^ 
 
 Separation of the World of Organic Forms into 
 
 Species — Genepistasis 
 
 I have handled this subject in various zoological technical 
 papers, particularly in my memoir " On the Variation of the 
 
 1 Compare in this respect especially the section on Lamarck ism. 
 
28 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 Wall-lizard," also in the addresses " On the Markings of 
 Birds and Mammals," and " On the Conception of the Animal 
 Individual," and have shown principally — 
 
 1. That the progressive evolution of a character in a definite 
 direction — let us take as an example the origin of beautiful 
 ocelli on the skin of an animal ^ — exhibits perfectly regular 
 stages. In the case referred to we have («) longitudinal 
 striping, (6) black spots, (c) formation of black rings, id) the 
 appearance of the coloured nucleus. These stages succeed 
 one another during the growth of the animal. In other words 
 the whole series of modifications is repeated in the develop- 
 ment of every individual. 
 
 2. That wliere new characters appear, the males, and indeed 
 the vigorous old males, acquire them first, that the females on 
 the contrary remain always at a more juvenile lower stage, 
 and that the males transmit these new characters to the 
 species. (Law of male preponderance.) 
 
 3. That the appearance of new characters always takes 
 place at definite parts of the body, usually the posterior end, 
 and during development — with age — passes forwards, while 
 still newer characters follow after from behind. Thus durinsj 
 life, c/j. in lizards, a series of markings pass in succession over 
 the body from behind forwards, just as one wave follows 
 another, and the anterior ones vanish while new ones 
 
 ^ I have liere in my mind an example which Ly no means serves for all cases. 
 It is to be understood that it is not at all essential that I should mention the 
 origin of ocelli rather than of other characters. Of course all, even the most 
 splendid, ocelli can be proved to arise from the simplest markings, the simplest 
 spots. (Compare my remarks on this point at the Berlin Naturalists' Congress, 
 1886, in the published reports of that Congress, and also especially my observa- 
 tions on butterflies now in course of publication.) That the gradual development 
 can be demonstrated even on the feathers of one and the same adult bird has been 
 already shown by Darwin for the Argus-pheasant. Herr Stud. Kerschner de- 
 monstrated very beautifully the same thing in the peacock, showing in accordance 
 with my theory how in that particular case the development can be followed 
 gradually step by step in definite parts of the body. (Compare his paper in the 
 Zeitschr.f. Wissenchaftl. ZooL, 1886.) Unfortunately he has in other respects 
 almost completely misunderstood the laws established by me. 
 
II LAIVS OF VARIATION 
 
 29 
 
 appear behind. (Law of wave -like evolution, or law of 
 undulation.) 
 
 4. That the whole of the varieties and variations of a 
 species represent nothing else but stages of the course of 
 development passed through by the individuals of the species 
 — unless they represent new characters usually appearinf^ 
 first in males. One variety will thus stand at stage a, another 
 at stage &, and so on ; but one or another is possibly dis- 
 tinguished by a new character, e. 
 
 But in the same direction as the peculiarities of the 
 varieties lie those which characterise the related species. The 
 species most nearly related may, for example, present the 
 varieties /, g, h, i. The character e, which occasionally appears 
 in the previous species, is the most characteristic peculiarity 
 of the second species — the variation of the first towards c 
 showed already the direction in which evolution proceeds 
 farther. In the second species appears occasionally a character 
 k, which has the same significance as e had before, and so on. 
 
 So, if one examines numerous individuals of a species with 
 regard to its variation, he can in the clearest manner in many 
 cases show from this variation its relation to other species.^ 
 As I said in my Freiburg address, the evolution — the growth — 
 of species one from another proceeds onwards as though 
 following a plan drawn out beforehand. In the case supposed 
 if all the stages of evolution from aioi were of equal import- 
 ance, we should unite them all together as varieties of a single 
 species ; but if between a and i one stage is altogether wanting, 
 or if one of them, say in the second half of the series, appears 
 suddenly with special prominence, dominant, then we have, 
 
 1 For the clearer comprehension of this compare the details in my paper 
 already cited, Ueber das Variiren, etc., with the figures and the last sections. Also 
 my work with coloured plates shortly to be published by G. Fischer in Jena, 
 Die Schmetterlinge nach ihrer auf die Zeichnung begrilndcie Verwandtschaft 
 dargestellt und heschrieben. Lastly, my illustrated articles, Ueber die Zeichmauj 
 der Saugeihiere, in the last three years of the journal Humboldt. 
 
30 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 granted at the same time the impossibility of sexual inter- 
 course, two species. 
 
 The law of undulation, and the other laws 1 to 4 whicli I 
 have formulated, hold therefore as much for the origin or evo- 
 lution of the variety and the species as for the individual. 
 
 One after another, like waves, the new characters appear as 
 stages of growth in the series of organisms which represent 
 the evolution of species. Or as we may conversely express it, 
 the higher species in the ontogeny of the individuals belonging 
 to them, which represents the evolution of those individuals, 
 briefly repeat the characters (stages of growth) of the lower. 
 The highest animals briefly repeat in their ontogeny the whole 
 series of their ancestors (biogenetic law) as stages of growth. 
 And indeed, I have to add, in general the more briefly and 
 the more incompletely they repeat the individual members of 
 the ancestral series, the older these are, the less important they 
 were, and the shorter the duration they had. 
 
 Every older stage of the phyletic growth is abbreviated for 
 the benefit of the newer — a proposition which may be added 
 as a fifth to the four already formulated. 
 
 Thus the facts established by me afford at the same time 
 a new and complete confirmation of the biogenetic law. 
 Varieties and species are therefore in reality nothing but 
 groups of forms standing at different stages of evolution, 
 that is, at different stages of phyletic gro^\i:h, whether it be 
 that they outstripped their fellows or their fellows them 
 in the progress of evolution, so that connection by inter- 
 mediate forms was lost, or that separation in space favoured 
 separation in character. 
 
 Isolation in space or separation of habitats is obviously of 
 great importance in species formation, but it is not absolutely 
 necessary. 
 
 The same explanation evidently holds good for genera as 
 groups of species, and in general for all divisions of a natural 
 
" GRADUATED EVOLUTION 
 
 31 
 
 system to whicli we may with Nligeli give the general nuine 
 kinships {Sippen). It would therefore be more appropriate 
 in general to speak of the origin of kinships than of the origin 
 of species. 
 
 We have then before us a graduated evolution, and the 
 essential cause of the separation of species is seen to be the 
 persistence of a number of individuals at a definite lower 
 grade of this evolution, while the rest advance farther in 
 modification. This mode of origin of varieties or species, as 
 the case may be, I have named Genepistasis (^ei/o? race, 
 eiTicTTaai'^ stand still). 
 
 With the facts and laws set forth by me in the previous 
 pages as the foundations of my theory of the organic fa-owth 
 of the species, compare Wlirtenberger : A Neio Contribution to 
 the Zoological Proof of the Darivinian Theory, Ausland, 1873, 
 Nos. 1 and 2, and Studies on the History of the Descent of the 
 Ammonites. A Zoologiccil Proof of the Darwinian Thcon/. 
 Leipzig, 1880. 
 
 Wlirtenberger finds that in Ammonites all structural 
 changes show themselves first on the last (the outer) wliorl 
 of the shell — as in living animals, e.g. in my lizards ^ at the 
 tail — and that then such a chanoje in the followimr crenera- 
 tions is pushed farther and farther towards the beginning of 
 the spiral — as e.g. in my lizards towards the head — until it 
 prevails in the greater number of the whorls. 
 
 Then still newer characters may arise again on the most 
 external whorl — just as in lizards at the tail — and drive back 
 the former, and so on. The Ammonites also only at an 
 advanced age, only when they have as exactly as possible 
 gone through the course of development inherited from tlieir 
 parents, acquire the power to vary in a new direction ; l)iit 
 this power can be inherited in such a way that in following 
 
 ^ See my memoirs, Ueber das Variiren der Mauereidechse, and ou tlie markings 
 of mammals and birds of prey. 
 
32 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 generations it appears always a little earlier, until it itself 
 characterises the greatest part of the period of growth. This 
 " law of precocious inheritance " as Wlirtenberger calls it, also 
 holds — for it obviously coincides with the law of abbreviated 
 development — for living animals.^ 
 
 " The agreement of the palseontological facts afforded us 
 by the Ammonites with those supplied by living animals," 
 I have said,- certainly with justice, " is in the highest degree 
 interesting. It places the perfectly general application of the 
 law beyond all doubt." ^ For not only the markings, but all 
 other characters of animals also thus follow the same law. 
 
 The Particular Causes which determine the Difference 
 OF THE Directions of Evolution, and which also 
 
 CONTRIBUTE TO BRING ABOUT THE DIVISION INTO SpECIES 
 
 The ancestral tree of organic forms does not rise in 
 a straight line, but has ramose (forked) branchings. This 
 branching, which is also an important factor in the separation 
 of species, is due to (1) the direct influence of external con- 
 ditions, which, differing at each locality, act upon each stage 
 of evolution, and are able to divert the farther evolution from 
 the former direction; (2) the functional activity of the organism 
 in relation to the external world, which directly strengthens 
 characters in process of development by the exercise of them 
 
 1 Compare TJeher das Variiren, etc., p. 454, separate edition, p. 218, where 
 examples are given. 
 
 - Loc. cit. 
 
 •' Compare also the researches of Weismann, subsequently to be more closely 
 considered, ou the markings of the caterpillars of the Sphingidje in his Shidien 
 zur Descendenztheorie, ii. : Ueber die letzten Ursachen der Transviutationen. 
 Leipzig, 1876. With regard to plants the force of the same law is shown — apart 
 from other facts — by the changes in the form of the leaves on one and the same 
 plant from the lower to the upper part. The upper leaves are often at a new 
 stage of evolution, the lower remaining at or passing through a lower stage — 
 the former indicate the new species, the latter ancestral species. 
 
II THE TERM' ADAPTATION' 
 
 33 
 
 (herein lies the importance of use and disuse) ; (3) the 
 struggle for existence, which will indirectly have a different 
 effect according to the difference of the external conditions ; 
 (4) the sudden appearance of new formations through correla- 
 tion (evolution^crs«^^w?/i.); (5) the principle that an ortranism 
 continually exposed to the same conditions, under the un- 
 interrupted action of the same influences, will after many 
 generations, in consequence of '' constitutional impregnation " 
 ("conservative adaptation"), become different in structure, 
 and have a different relation to the external world than 
 before ; (6) sexual mixing, which may, without any in- 
 fluence of adaptation, lead to the formation of quite new 
 material combinations, that is, to the production of new 
 forms. • 
 
 The expression adaptation is often misapplied. Frequently it is 
 erroneously used in an active sense ; people speak of adaptation 
 as of a spontaneously acting power, and in cases in which there can 
 be no question of the use of a character either for the organism which 
 possesses it or for the external world. Adaptation is, however, ahvays 
 something which has been brought about — indeed, implies a character 
 which is in some way useful to the organism which possesses it in 
 relation to the external world, or which is necessary or useful to 
 other creatures or to the generality of things. The first is a special 
 adaptation, the last can be called general (cosmic). In the latter 
 sense, of course, ultimately everything is adapted, and we ought, as 
 will be done in the following pages, only to speak of adaptation 
 without the expressed qualification " general " when special adaptation 
 is meant. 
 
 On the other hand, I cannot agree to the limitation of the Darwinian 
 idea of adaptation which Weismann makes, when he will only recognise 
 it as applied to characters gained in the life of the species, not to those 
 gained in the life of the individual. Individuals during their life al.^o 
 adapt themselves to the external world — consider only the variety oi 
 the experience which individual animals during life, according to tlieir 
 surroundings and their intelligence, meet with and benefit by, or the 
 special strength of body or any other useful qualities which they 
 acquire in consequence of the external demands upon them. There is 
 a personal adaptation in the Darwinian sense, for Darwin has recog- 
 
 D 
 
34 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 nised, as we shall see, tlie inheritance of characters acquired during 
 the individual life, particularly in emphasising the use and disuse of 
 organs as important in the modification of forms. Kollman certainly 
 goes too far when he supposes that by adaptation we have only to 
 understand the acquisition of definite characters during the individual 
 life under the pressure of external agents.^ For each character which 
 seems adapted in an organism is not necessarily acquired during the 
 individual life. But the closer consideration of this question is con- 
 tained in my discussion of the whole theory of evolution. According 
 to the foregoing, we have in any case to distinguish, besides general 
 (cosmic) adaptation, a special adaptation in the usual sense of the 
 word, and in this again personal (individual) and race (or species) 
 adaptation. 
 
 The characters above classed under (1), those called forth directly 
 by the influence of external conditions on the organism, without other 
 aid from the latter than physiological reaction, I have previously de- 
 scribed ^ arising by impression. Example : the production of a 
 darker skin by light and warmth. Light and warmth are here the 
 ca ^tsfe efficientes (0. Schmidt). Here belong a number of characters which 
 cannot be described as adaptations, which are rather unessential (indif- 
 ferent). Also, however, those which are due to the composition of the 
 organism which has been produced by the action of external conditions, 
 and which may be accidentally useful, but cannot have been increased 
 by selection. A host of characters which seem to have arisen through 
 selection will certainly come into this group of the accidentally useful. 
 If the Ijrilliant mother-of-pearl of the internal surface of the mussel- 
 shell, which is completely hidden under the mantle, were visible on 
 the outer surface, it would certainly be indicated as useful. To the 
 same category belong the black back and bright silvery belly of fishes, 
 etc. Probably also many colours due simply to interference, such as 
 the splendid blue of the wings of the male Calopteryx virgo and others. 
 There can be nothing, indeed, more splendid in colour than the 
 iridescence of Labradorite, and is this useful to the stone? And 
 are colour and brightness useful to gold and countless other minerals ? 
 Are they useful to the soap-bubble ? 
 
 Among the characters described under (2) I place those which have 
 been produced with the aid of the external action of the parts of the 
 organism concerned. Example : the formation of the hard skin of the 
 heel, of the hard skin of the sole of the foot in the barefooted African 
 
 ^ Compare Konniann, loc. cit., and Wei.sniann, loc. cit., Biulvg. Centralhlatt. 
 
" SEXUAL COMBINATION 
 
 35 
 
 negro (cf. Livingstone's Travels, etc.), of the nails and lioofs of men and 
 animals. Here selection may play a part, but no more necessarily so 
 than in the first case. However, most of the characters so produced 
 are certainly useful, are to be described as adaptations. The action of 
 the foot is here the causa agens. 
 
 The first case is direct, the second indirect adaptation ; in the third 
 case, the struggle for existence helps in the acquisition of useful char- 
 acters ; the fourth, correlation, may call forth useful or Inirtful or 
 indifferent characters as it may chance to happen ; the fifth, change 
 of the organism, through long continuance under the same conditions, 
 will in like manner produce partly indifferent, partly useful characters ; 
 the sixth, sexual combination, likewise. 
 
 Even in the fifth case, therefore, there need not be necessarily any 
 question of adaptation, and the usual expression " conservative adapta- 
 tion " is only to be applied to the cases in which some advantageous 
 character has been added to the organism through the constancy of 
 relations. Accordingly, I have both in former works and in the 
 present called the change which takes place on account of persistence 
 of the same conditions constitutional impregnation, without regard 
 to advantage or disadvantage. 
 
 Sexual Combination — One-sided Inheritance 
 
 I take in hand, first, the discussion of the sixtli of the 
 factors in modification just enumerated, on account of the 
 exclusive importance which Weismann ascribes to sexual 
 combination, assisted by selection, in the modification of 
 organic forms in general, not merely in the separation of 
 the forms into species. 
 
 My view, that sexual combination can lead to the 
 production of quite new forms without the assistance of 
 selection, is based upon the fact that from the union of two 
 beings intermediate forms are not as a rule, as is generally 
 assumed, produced, but very frequently forms differing from 
 either of the two. For the characters of the parents and tlie 
 ancestors either strengthen or cancel one another (to this, 
 indeed, is due the harm of close breeding, the danger of 
 marriages between relations), or possibly form in similar 
 
\ 
 
 36 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 manner, either witli one another or with cliaracters of 
 ancestors present in a latent condition, quite new combina- 
 tions, as in the union of different chemical substances or 
 elements. 
 
 But on the other hand, to avoid exaggeration of the effects 
 of sexual combinations, it must be pointed out how often the 
 offspring retain unaltered the characters either of the father 
 or the mother, how often one-sided inheritance takes place. 
 
 Every nursery, especially in South Germany, where blonde 
 and black hair together with blue or gray and black eyes are 
 seen side by side, will show this. I mention, for simplicity's 
 sake, hair and eyes only. But it is often obviously a question 
 of a whole series of correlative characters, colour of the skin, 
 strength of the bone structures, shape of head — in brief, of 
 more Germanic or more Eomance race. 
 
 Dark and fair parents together do not usually produce 
 children which in colour are intermediate between them, but 
 fair and dark again.^ Only when the offspring continue this 
 
 ^ A remarkable confirmation of this is afforded by squirrels. Black and red 
 young ones of the same litter are often found in a nest, but intermediate forms 
 not so often. A similar assertion might be made of black and white sheep, 
 although here artificial selection may contribute to the prevention of mixture ; 
 but I am assured by farmers that the colour of the wool is not so very important, 
 because it is usually, at least in Germany, dyed of a dark colour. In any case, 
 intermediate forms between black and white are very seldom found among sheep. 
 I was particularly struck by this in Bulgaria, and in the Balkan peninsula 
 generally, also in Italy, where one sees, besides the pure white, very many pure 
 black sheep, but scarcely ever a mixed form in the pasturing herds. Such mixed 
 forms are piebald. Landowners skilled in breeding horses tell me that from 
 the union of black and white horses, as a rule, not intermediately coloured, or 
 piebald foals result, but black or white again. 
 
 Very important in this question is of coixrse the result of various inter- 
 breedings of races of men. Here also it would seem that a complete mean is 
 not the rule. Thus Levaillant, 1793, speaks of the number of white slaves at 
 the Cape of Good Hope, which were derived from the crossing between Dutch 
 soldiers and slave negresses (mostly from Madagascar and Mozambique), and 
 which in colour completely resembled Europeans. Likewise the hybrids between 
 Hottentots and Europeans (in which case the Europeans mostly if not exclusively 
 have furnished the male element) resemble the Europeans more than the Hotten- 
 tots (male preponderance). Dr. Bernard Schwarz similarly speaks in his account 
 
n COMPLEXION 37 
 
 intermixture for a long time does an intermediate race 
 gradually arise. 
 
 Dark, however, according to my observations, has a pre- 
 ponderance over fair.^ When it is once there it is not easily 
 eradicated from the blood ; it necessarily has this prepond- 
 erance simply on the ground that it is a positive quality as 
 compared with the mere deficiency of pigment in the fair. 
 Darkness of complexion, therefore, among us under the 
 present conditions will always rather increase than diniinisli 
 in its ratio to fairness. 
 
 The length of time for which the dark and the blonde type 
 can constantly recur separately in the children of light and 
 dark complexioned parents is particularly well shown by 
 several south German villages, like those in the immediate 
 neighbourhood of Tubingen, where a thoroughly dark, almost 
 Eomance, and a purely Germanic race of people appear often 
 enough sharply distinguished in the children of one and the 
 same family — notwithstanding the fact that in these little 
 villages intermixture is continually taking place, for the 
 people usually marry among one another, and seldom outside 
 the village. The dark type will here too gradually become 
 predominant, simply in consequence of the preponderance 
 which it has over the blonde and blue. 
 
 Undoubtedly, in our temperate climate, sexual intermixture 
 has been the essential cause of the extension of darkness of 
 complexion, not the sun. But whether sexual selection gives 
 a preference to darkness is at least doubtful — taste in this 
 matter is very varied. It is possible that the intermixture 
 
 of his journey to the Cameroons of the white child of a Dutch ageut aud his I - / 
 black wife. I should be very grateful for additional accurate facts. I 
 
 1 I first expressed this opinion in 1881 ( Variiren, etc.), aud am rejoiced to find | 
 that M. A. de Candolle in his book, Histoire des sciences et des savants dejjuis 
 dettcc siecles, precedee et sidvie d'autres etudes stir des sujets scie7iii/iiiU4-s, en 
 particidier sicr Vherklite et la selection, published in 1885 (Geneve -Bale, H. 
 Georg), likewise defends the view at p. 81 with regard to the dark colour of the . 
 eyes. He promises to discuss the subject more minutely in a later work. 
 
38 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 of dark and fair, that is to say, the formation therewith 
 connected of other characters, has an advantage in the 
 struggle for existence over the pure original Germanic blonde. 
 In this last case only would the increase of the darker type 
 appear as an adaptation. But I am of the opinion that the 
 simple physiological preponderance of the dark colour 
 principally determines the result ; that the dark complexion 
 in Germany is accordingly to be taken as an example of the 
 principle that modifications resulting from sexual inter- 
 mixture are not necessarily useful to the orcjanism in which 
 they appear, but may be indifferent. 
 
 Wallace, it is true, ascribes to pigment an importance in 
 the production of greater acuteness of the senses.^ ISTeverthe- 
 less, according to him, the blonde possess greater intelligence ; 
 they have, he believes, acquired this because in the struggle 
 for existence, in consequence of their deficiency in acuteness 
 of sense, they were driven to rely upon their intelligence. 
 Perhaps it might be urged on another side in favour of 
 adaptation as explaining the predominance of darkness of 
 complexion, that intermixture of blood is within certain 
 limits an advantage. In Germany, as a matter of fact, the 
 purely Germanic blondes of the north show no less vigour 
 in the struc^frle for existence than the mixed race of the south. 
 
 That darkness of hair and eyes is among us something 
 newly ingrafted and is on the increase is proved by the 
 universally known fact that the children of dark German 
 parents are as a rule, in the earlier years of life, fair, and 
 have blue or gray eyes : here also characters which were 
 dominant in the ancestors are repeated in youth. This 
 biogenetic fact struck me first and very forcibly in the 
 Upper Engadine, where obviously an intermixture of blonde 
 Germans with dark Romans has taken place, and where it is 
 the more surprising because the climate in that region would 
 
 ^ Wallace, Tropical Nature, German translation, Braunschweig, Vieweg, 1879. 
 
II EXTENSION OF THE DARK TYPE 
 
 39 
 
 favour rather lightness of colour. For example, in tlie 
 neighbourhood of Sils-Maria, in villages where tl'ie adults 
 are all perfectly Romance in darkness of complexion, one 
 sees children of such dark parents with quite fair flaxen luiii' 
 and blue eyes. I shall subsequently consider more facts ol' 
 the kind, especially from North Italy. 
 
 Accordingly, statistics intended to serve any really scientific 
 end, in dealing with the relative numbers of fair and dark in 
 Germany, would have to give, besides the age of the children 
 enumerated, the colour of the hair and eyes of their brothers 
 and sisters and parents, and, wherever possible, that of the 
 grandparents. 
 
 It is also to be considered whether male preponderance 
 does not also play a part in the extension of the dark type in 
 our territory, for, in any case, it has been for the most part 
 men who have first introduced it among us. We ought, then, 
 to find, if this preponderance has been at work, that there are 
 more dark men than women among adults. But this must 
 (a further point of view for the statistician) have been the 
 result according to laws already explained in any case, because 
 the dark colour is for us a new character, and female indi- 
 viduals always remain nearer to the stage which corresponds 
 to the condition of the young, that is, nearer to the original 
 condition.-^ 
 
 Moreover, male preponderance has an important bearing 
 on the questions before us from another point of view. It is 
 
 ^ [The author here states that supposing there are more men than women 
 possessing the dark complexion in Germany, this effect might be due (1) to the 
 fact that the type was introduced chiefly by men, not by women, from abroad ; 
 (2) to the mere fact that the dark complexion is a new character, liowever pro- 
 duced, and therefore appears first in the adult males among Germans. The first 
 supposed explanation is said to be a case of male preponderance ; but if we refer 
 to p. 28, where the law of male preponderance is formulated, we shall see that it 
 is the second possible explanation which exemplifies that law. In the statement 
 of the law, p. 28, nothing whatever is said about the effect of introducing a few- 
 males of a somewhat new type among the members of a given race. Trans.] 
 
40 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 certainly also the cause of the fact that we are able to recog- 
 nise family likeness in so great a degree among the earliest 
 male ancestors of a family, as they appear in many a gallery 
 of family portraits ; and further, it also explains why the male 
 line of descent is considered of such great importance, while 
 the female is scarcely regarded. If this prepotency of the 
 male did not exist, if the female element in all unions had 
 exactly the same value as the male, then, after comparatively 
 few generations, by the combination of equally potent male 
 and female types, all similarity to ancestors, excluding cases 
 of one-sided reversion, would be completely effaced. 
 
 A very remarkable example of male prepotency in this 
 connection is afforded by the large under lip of the Habs- 
 burgers. Portraits of Rudolf I. of Habsburg already show it. 
 It was inherited by his descendants up till the last of them, 
 the Emperor Charles VI. (1740), that is, for 500 years. 
 AVith Charles VI. the male line of the Habsburgers became 
 extinct. Its place was supplied by the Thuringian line, 
 derived from the marriage of Francis of Thuringia with the 
 Habsburger Maria Theresia. In the male descendants of this 
 couple the great under lip appeared again, and has been 
 transmitted up to the present day, although the wives of the 
 Habsburgers, coming from various families, could not possibly 
 by chance have generally possessed it, and did not possess it.^ 
 
 At all events, the fact of male prepotency in itself shows 
 that a complete mingling of characters is no more the usual 
 consequence of sexual union than the production of herma- 
 phrodites that of the coalescence of sperm and ovum in 
 animals of separate sexes. Atavism is no greater miracle 
 than these facts which must be explained with it. 
 
 Another factor contributing to the separation of forms into 
 species without selection, to be added to those already mentioned 
 
 ^ Cf. Pinacotheca 2irincipicm Austriae, by Marquard Hergott and R. Heer 
 {Benedictines in St. Blasien), Freiburg, 1770. 
 
II CHANGES IN THE SEXUAL ELEMENTS \\ 
 
 as connected with sexual reproduction, is that any new clmr- 
 acters may produce such a correlative change in the composi- 
 tion, or even in the form of the sexual products, that sexual 
 crossing between the forms concerned is no longer possible.^ 
 
 Often, for example, species quite nearly related show sur- 
 prising differences in their spermatozoa (Rana temporaria and 
 esculenta). 
 
 I have already, years ago, pointed out how inadmissible it 
 is for this reason to base the argument that species are to be 
 considered as independent and isolated from the first, us 
 groups created in their present condition, on the fact that 
 true species are not fertile when crossed with one another. 
 On the contrary, the impossibility, or at least the difficulty, of 
 fertile union, and therewith the separation into species, can 
 be brought about or favoured by any change indirectly or 
 correlatively produced in the sexual products, e.g. the sperma- 
 tozoa, affecting their morphological character, their motion, 
 and material composition. 
 
 The sperm-nucleus and the egg-nucleus must in their 
 physico-chemical properties form with perfect exactness the 
 complements of one another, if through their union a new 
 organism is to be produced.- The form and motion of the 
 
 ^ Compare on this the remarks in my publication, Ueber den Bau nnd die 
 Bewegung der Samenfaden in Verhandlungen der j^hysikcdisch-medicinischen 
 Gcsellschaft zic Wiirzhurg, N, Folge, Bd. vi., and Wiirzburg, Stahel, 1874. 
 
 " I must refer in this connection to a concei^tion to wliich much importance 
 has been attached as a support of Weismann's theory of heredity. The latest 
 researches on fertilisation having shown that sperm - nucleus and egg -nucleus 
 (= germinal vesicle) do not dissolve in the process, that it is effected not by 
 liquid but by solid substance, therefore the inheritance of acquired characters has 
 been declared impossible, and fertilisation a morphological, not a physico- 
 chemical, combination. On this view we have before us, to consider more fully 
 what we have previously touched upon, an unchangeable, never wearing out, 
 eternally living organic substance (changeable only by sexual combination or by 
 disease), which cannot even be nourished like other parts of the body, for if it 
 were it would necessarily be affected by the constitution of the body. And 
 whence did it originally obtain its peculiar properties ? How anil whence has it 
 come to be ? Before we are obliged to ask ourselves these riddles, and before wc 
 
42 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 spermatozoon must be adapted with perfect accuracy to the 
 morphological peculiarities of the egg-envelope if there are to 
 be no morphological hindrances, even the minutest, to fer- 
 tilisation. For the formation of new species in this way 
 it is therefore only necessary that the sperms and the 
 eggs of a given number of individuals should have pecu- 
 liarities of structure corresponding with one another, and 
 not corresponding with those of others. Complete isola- 
 tion of the varying individuals is thus on these grounds 
 also not absolutely necessary for the formation of new 
 species.-^ 
 
 The correlative alteration of the sexual products leads to 
 the consideration of a fact which seems to me to cry loudly 
 against Weismann's assumption that those products remain 
 essentially unaffected by the condition of the body from time 
 to time. I refer to the oreat correlative influence which con- 
 versely the condition of the sexual products, namely, their 
 maturity (puberty) and their artificial removal (castration), as 
 well as the extinction of their powers in old age, has upon the 
 
 go so far as to doubt that the chai-acter of the process of fertilisation is that of a 
 physico-chemical, i.e. physiological, process, let us rather, I say, leave the problem 
 of atavism for the present unsolved. What if the solid nuclear substance had the 
 power to reproduce the condition of the whole body at any given moment because 
 it was definitely and peculiarly adapted to contain an extract, as it were, of the 
 whole body ? Who will undertake to prove that it does not take up such an ex- 
 tract somewhat like a delicate sponge, so that the inheritance of acquired char- 
 acters, as in the older view, can be physiologically explained in spite of its firm 
 structure ? In any case, such a hypothesis is not in contradiction to general 
 physiological principles, as the conception of fertilisation as a purely morpho- 
 logical process seems to me to be. 
 
 Weisniann, moreover, speaks in his more recent paper {Bedentung der 
 sexAiellen Fortpflanzunrj) of an increase of the germ-plasm by assimilation ;"vbut 
 such assimilation merely on the ground of the laws of physiology obviously im- 
 plies that the germ -plasm is influenced by the general nourishment — in other 
 words, by the condition of the body. 
 
 ^ Apart from this I have shown in reference to this question in a very carefully- 
 studied example — in the wall-lizard — that varieties difl'ering to any important 
 degree fight with one another when they live together, as if there was profound 
 antipathy between them ; that, therefore, they do not sexually mingle, while the 
 similar individuals breed together, and so establish their characters more firmly. 
 
II 
 
 CORRELATION OF SEXUAL ORGANS 43 
 
 condition of the whole body. This relation is so well know,, 
 that it is unnecessary for me here to give any proof of it. 
 But it is at the same time one of the most striking examples 
 of correlation, and certainly affords most valuable support to 
 my conclusion that changes in the characters of the body 
 appearing suddenly through correhative frrowth mav lead 
 to the formation of new species without the assistance of 
 selection. 
 
 Finally, some importance is to be attached, as supporting 
 my conclusions in opposition to Weismann's, to the evidence 
 which tends to prove that not only the bodily, but the mental, 
 condition of the parents at the moment of procreation has an 
 influence on the offspring. This evidence is so abundant and 
 comes from so many sides, that it will be difficult to doubt at 
 least its partial trustworthiness.^ But if it is really based on 
 fact, a further important proof is afforded of the inheritance 
 of acquired characters, and of course also of the part played 
 by sexual combination in the alteration of the characters of 
 living beings. But it is sufficiently evident from the fore- 
 going that I place a high value on the latter influence. The 
 divergence of my interpretation from that of Weismann con- 
 sists only in this, that the latter pronounces natural selection 
 to be the indispensable handmaid of sexual combination in 
 the transformation of species ; whilst I, although recognising in 
 the present work and always the importance of selection, 
 
 ^ In this connection may be mentioned tlie fact tliat, according to the belief 
 of breeders, a pnre-bred mare or bitch if only once covered by a worthless male is 
 spoilt for all subsequent breeding — indeed, it is asserted that such females 
 subsequently, even when they were covered by thorough -bred males, produced 
 young which possessed characters of the mongrel with whom they had once 
 bred. (Probably this is essentially a case of nervous influence [troiihic nerves].) 
 Compare my later observations on the influence of the age of the parents on tlie 
 off"spring. It is generally asserted that procreation during drunkenness t-ausos 
 inferiority of mental powers or even idiocy in the child — in this case general 
 influences of nourishment are the probable explanation. Comiiare with respect 
 to the importance for the ofl"spring of the condition of the parents during pro- 
 creation, A. de Candolle, op. cit. p. 49, et seq. , and the literature there referred to. 
 
 ; 
 
44 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 regard it as by no means absolutely necessary to that trans- 
 formation. 
 
 Lastly, although I ascribe to sexual combination, with and 
 without the help of selection, an important influence in the 
 moulding of species, yet it cannot be granted that this 
 influence is essentially paramount, or even that it is thoroughly 
 independent in its action, if we start from the assumption 
 that sexual differentiation is itself at first an acquired 
 character. 
 
 In reality its own beginnings are to be traced to external in- 
 fluences, and obviously it continues to serve as the means for the 
 transmission and distribution of other characters acquired by 
 the body in difterent localities under different conditions. In 
 that it unites, combines different elements, it can engender a 
 new third element (crossing). Without this mixture of what 
 is foreign — different, however, through the continued union of 
 the cognate, it leads ultimately on the contrary to equalisation, 
 not to progress. 
 
 Thus sexual combination, like the principle of utility, can 
 only work with the material which phyletic growth offers to 
 it ; universally something new must first exist before either 
 can commence to operate. 
 
 I years ago expressed my belief that the original directions 
 of evolution are shown by the facts to have been followed with 
 an extraordinary persistence ; let the external influences be 
 what they will, the new directions never seem to radiate from 
 the starting-point of modification — the new lines pass off at 
 an acute anc'le, at first near the original ones — onlv the 
 intermittent deviation caused by correlation forms an excep- 
 tion. But the fact of evolution in a definite direction is 
 explained neither by selection nor by sexual combination by 
 itself 
 
 I proceed now to the closer consideration of one of the 
 most important of the causes to which I have attributed the 
 
" THE AXOLOTL 
 
 separation of species, to the just-mentioned action of correla- 
 tion, to what I have called intermittent evolution. 
 
 Intermittent Evolution— Kolliker's Hypothesis 
 
 It appears, therefore, according to my views, to be pos- 
 sible, that since one character is followed by one or perhaps 
 several others correlated with it, a new form may suddenlv 
 arise, which, if the variation extends to the sexual products, 
 may be no longer capable of crossing with the original form. 
 At the same time, this latter condition is not necessaiy for the 
 production of a new species. For example, hair, horns, and 
 hoofs have been proved to be connected correlatively with 
 one another, and by simultaneous variations in these three 
 organ -systems a very considerable change in the external 
 appearance of an animal may be effected. If only one of the 
 altered systems is more useful to the animal than that of the 
 original form, then, notwithstanding the possibility of crossing, 
 a new species may arise. 
 
 There are of course few examples among living animals 
 which illustrate this mode of origin in so complete a manner 
 as the Axolotl. But if this were the only one it would 
 suffice, and would justify the conclusion that the same meta- 
 morphosis has under similar conditions probably occurred in 
 other allied animals. The metamorphosis of the Axolotl into 
 Amblystoma is clearly the consequence of the transition of 
 the animal from an aquatic to a terrestrial existence. With 
 the. cessation of branchial and the commencement of ex- 
 clusively pulmonary respiration went correlatively hand in 
 hand the appearance of a spotted marking on the skin, of the 
 smoothness of the latter in place of the warty character, 
 especially on the head, of that of the Axolotl, the slight change 
 in the form of the body, and lastly the formation of a more 
 cylindrical tail, while also, in consequence of terrestrial 
 habits, the legs became more powerful. It is highly 
 
46 THE ORGANIC GROWTH OF 7HE LIVING WORLD sec. 
 
 remarkable that tlie same peculiarities distinguish Sala- 
 mandra maculata iu comparison with its aquatic larva. 
 In fact, it is scarcely possible to distinguish a Salamander 
 larva so long as it retains its gills from a young Siredon. 
 Both have the gray colour without large yellow -spots, 
 the laterally compressed swimming tail, and the feeble legs ; 
 and lastly, in comparison witli the adult Salamander or 
 Amblystoma, respectively, a somewhat Hatter, longer, and 
 narrower head, with less prominent eyes. 
 
 Siredon is for the problem of evolution one of the most 
 important of living animals, in that it brings so beautifully 
 before our eyes the transition of a lower sexually mature 
 into a higher sexually mature form, and at the same time 
 shows so clearly the causes of the transformation. We 
 discern these causes simply in the reaction of the organism 
 under external conditions, the increased exertion of an 
 organ already in process of formation (the lung), and the 
 disappearance of another (gills) in consequence of definite 
 demands of the environment, and changes connected with 
 these by correlation.^ 
 
 Amblystoma appears where the Axolotl has too little water 
 to live in, where it is compelled to live on dry land. That this 
 is the case is proved by the possibility of artificially rearing 
 Amblystoma from the Axololt by gradually withdrawing the 
 water. Before this can be possible it must of course be a 
 previous condition that the Axolotl has already a great 
 tendency to transform itself into a land animal. This may 
 be due to the possible fact that it has in its aquatic state 
 already made much use of its lungs ; but the transformation 
 which follows its assumption of terrestrial habits is none the 
 less sudden, and evidently connected with correlative changes. 
 When an Amblystoma is formed, then this is the adult animal, 
 
 ^ These are the essential causes ; I do not pretend to have exhausted the 
 explanation of the metamorphosis. 
 
II THE AXOLOTL 
 
 47 
 
 the Axolotl its larva. If it is not formed, the latter is the 
 adult animal capable of sexual reproduction. 
 
 Since, then, in the spotted Salamander and its allies exactly 
 the same metamorphosis in structure occurs in the passa<^e 
 from larval life to the adult condition as in the transition 
 from the Axolotl to the Amblystoma, we have in these 
 amphibia again clearly revealed definite directions of evolution. 
 
 Weismann has offered another explanation of the develop- 
 ment of Ambly stoma out of Siredon, namely, that it is a 
 reversion to an earlier form. But no cogent reason for this 
 hypothesis seems to me to have been given, any more than 
 there is any reason to suppose that the adult Salamander is 
 to be regarded, as a reversion to an earlier form. AVhat is 
 true in the one case is reasonable in the other. The onlv 
 difference I can see in the two cases, besides the sexual 
 immaturity of the Salamander larva, is that in the spotted 
 Salamander and its nearest allies the metamorphosis into an 
 exclusively air-breathing animal has become the rule, while 
 in Siredon it is only commencing, and occurs at first in rare 
 individual cases. 
 
 If this be so, then, as I have said, the metamorphosis of 
 Siredon pisciformis into Amblystoma is evidently the most 
 perfect example of the occurrence of the evolution ^ptr scdtum 
 of a species of animal now living, in consequence of the action 
 of external conditions. 
 
 My view of the meaning of the metamorphosis of the 
 Axolotl is supported by the experiments of Fralilein von 
 Chauvin. That lady reared larva? which were the progeny 
 of Amblystoma. These larvae were kept under conditions 
 in which larv« begotten by the Axolotl would never have 
 changed into Amblystoma. The larvse thrived well, and their 
 gills attained in abundantly aerated water an unusually great 
 development. In spite of this they came often to the surface 
 of the water to get air, and remained there for hours— a thing 
 
48 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 which in an Axolotl usually occurs only at a more advanced 
 age, and in water but slightly aerated. When the larviie were 
 one year old, the weather continuing warm for some time, a 
 reduction of their <4ills commenced. Fraiilein von Chauvin 
 gave twenty of the larvie an opportunity to quit the water, 
 and to her surprise some of them innnediately crept out into 
 the moss. The metamorphosis began in these after only a 
 few days. One of the larvie completed its change in ten days, 
 and after twenty-three days all the twenty larvae had of their 
 own accord quitted the water. 
 
 Six other Amblystoma larva3 of the same brood were kept 
 from the beginning in very cool rapidly-flowing water, and 
 their tendency to breathe air was thus checked, and these 
 remained in the water.^ 
 
 The Amblystoma larvie had therefore inherited the charac- 
 ters acquired by their parents, and the experiments justify 
 the conclusion that in consequence of this inheritance, after 
 a longer duration of the external conditions, the new form 
 Amblystoma would become the permanent species as truly 
 as the perfect spotted Salamander is the species, and not its 
 f]jill-breathinG[ larva. 
 
 It is supposed that the North American genera Menobran- 
 chus and Menopoma stand in the same relation to one another 
 as Siredon and Amblystoma. 
 
 Further, I may refer to the transformation, shortly to be 
 mentioned, of the crustacean Artemia salina into another 
 species or another genus through the increase or decrease of 
 the saltness of the water in which it lives. Here also a great 
 deal is due to correlative modification. 
 
 On a previous occasion I have endeavoured to describe the 
 physiological causes of this fact of correlation which plays so 
 important a part in the modification of forms, and therewith 
 the ultimate causes of evolution 'per saltum, in the following 
 
 1 M. V. Chauvin in Zeitschr. fur wissensch. Zoologie, xli. , p. 385, 1886. 
 
II KALEIDOSCOPIC E VOL UTION 
 
 49 
 
 words : " As soon as something or other in the original state, 
 in the original arrangement of the parts of the organism, is 
 changed, other parts also are set in motion, all arranges itself 
 into a new whole, becomes — or forms — a new species,"— just 
 *' as in a kaleidoscope, as soon as on turning it one particle 
 falls, the others also are disturbed and arrange themselves in 
 a new figure — as it were recrystallise." ^ 
 
 And these considerations, I added, also throw light on the 
 question of the absence of intermediate forms : in the forma- 
 tion of new species the animals have by no means necessarily 
 passed through all conceivable intermediate stages. 
 
 These sentences also imply the assertion that through 
 correlation, in other words, through jpcr saltum evolution, new 
 species can arise without the aid of selection, however much 
 the latter may facilitate the formation of the first new charac- 
 ter, as indeed was probably the case in the Axolotl. 
 
 I need scarcely point out that this sudden evolution for 
 which I am arguing has nothing to do with the hypothesis of 
 sudden evolution brought forward by Kolliker. 
 
 KoUiker, who has repeatedly argued in opposition to the 
 utility principle, to pure Darwinism, contends for i\\Q evolution 
 of forms from " internal causes " on the basis of a " general 
 law of evolution." In this evolution the ova even of the 
 higher and highest of now living animals play a special part 
 as the " original organisms " : it is supposed that the ova, or 
 the germ-cells of a given form, in consequence of an altered 
 mode of development due to internal causes, could give rise 
 to new forms. If the newly produced forms are widely 
 separated they belong to a new genus, family, or order ; 
 if they are less different from one another, they are related 
 to one another as varieties and species. 
 
 Further, according to Kolliker, there is reason to consider 
 
 ^ Variiren der Mauereidechse. 
 E 
 
50 7'HE ORGANIC GROWTH OF THE LIVIXG WORLD sec. 
 
 whether new forms coiikl not be generated b}^ internal 
 germs or external buds. In support of this the phenomena 
 of alternation of generations are adduced. 
 
 Thirdly, it would have to be- considered whether not onl}^ 
 germs and buds, but free-living young forms of animals are not 
 capable of entering upon a development other than the typical. 
 
 Lastly, the possibility of a " rapid modification of adult 
 organisms into others " is considered. 
 
 In all these cases we should have a sudden evolution, " yet 
 this is essentially to be traced to the embryonic period, and, 
 indeed, to its first stages." 
 
 In addition, a more gradual modification in a less degree is 
 recognised as possible, and some effect is ascribed to it, and 
 this likewise is chiefly to fall within the embryonic period. 
 
 We should have, therefore, I said in my " Variation of the 
 "Wall-Lizard," "an upward evolution towards higher forms, 
 from internal causes. Original organisms — ova — must, ac- 
 cording to this, have developed all at once into higher 
 forms, e.g. into mammals, and they would have succeeded in 
 this just the same wherever they happened to be, no matter 
 what the external conditions in which they lived or were 
 about to live. Adaptation has nothing to do with the 
 question — whether a part newly arising is useful or harmful is 
 of no consequence ; it is as if the whole course which the 
 original organism had to pass through was definitely pre- 
 ordained for it by internal causes, and as if this plan (the 
 w^ords plan of evolution are repeatedly used, and used as if 
 equivalent to * general law of nature ') corresponded from the 
 beqinnin^f to the external conditions." 
 
 Kolliker also explained, although not in his first paper on 
 this subject, yet later, that his internal causes were physico- 
 chemical. 
 
 The facts on which my conception of the modification of 
 species is based show, in harmony with those brought to 
 
n PERSISTEATT CHARACTERS 51 
 
 light by Wiirtenberger in the field of paleontology, that 
 the last, the highest stages in the development of animals 
 govern the modification of the species. The opposite view 
 advocated by Kolliker is no more supported by facts than his 
 other propositions — it rests only on assumptions, on the con- 
 ceivable and the possible. Moreover, Kolliker, as already 
 remarked, opposes Darwinism, the utility principle, altogether.^ 
 
 The rest of the agencies previously mentioned as causes of 
 the division of the organic world into species will be examined 
 in subsequent sections. Here I have only to make the 
 following preliminary remarks on 
 
 Constitutional Impregnation 
 (Constitutional A dajjtation) 
 
 The proposition that a character must establish itself more 
 firmly the longer it remains in an organism exposed to the 
 same conditions, in other words, the longer it is maintained by 
 continually repeated inheritance, scarcely requires any further 
 proof than is given by general physiological considerations. As 
 I have elsewhere expressed it :^ " If a form remains stationary 
 at a low phyletic stage, then, from purely constitutional causes, 
 the longer it remains at that stage the more does it become 
 different, because its characters stamp themselves more and 
 more deeply on the organism (constitutional impregnation). It 
 will, therefore, after a certain time no longer be the same as it 
 was when its relatives diverged from it. The longer it is able to 
 exist with these characters the more it will change in anotlier 
 way while its relatives change by correlation, but the more also 
 
 1 Cf. Kolliker, Ueber die Danvinsche ScMpfungstheorie, Zeitschr. f. w. ZooL, 
 Bd. xiv. Also MoriJhologie unci Entwickhmgsgeschichte des Pennatididen- 
 stcmimes, nebst allgemeinen Betmchtungen zur Descendenzlehre, Frankfurt (Sen- 
 keubergsche Abkaudluugen), 1872. EntwicMungsgeschichte, Second Edition. 1S79, 
 pp. 6, 27. " ^ariiren, etc. 
 
52 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 will it be in a condition to maintain the persistent characters 
 in face of the coercive powers of adaptation, and these latter 
 will be thrown on to other characters with greater modifying 
 effect." 
 
 Elaboration axd SiMrLincATiox in the Evolution of 
 
 Species 
 
 I come now to the second of the questions previously 
 formulated, to the question, On what grounds each species 
 high in the scale of evolution was able to surpass the one 
 next below it — wliat are the causes of increased perfection ? 
 
 This advance in structure in the organic world is most 
 clearly revealed by the examination of the development of 
 some one individual organism — so long as it be not a 
 degenerated form. The individual in this development 
 passes by growth through the series of its ancestors, but it 
 grows a stage farther on to the condition which constitutes 
 its individuality, which distinguishes it from the next lower 
 stage. 
 
 Niigeli calls in the aid of a " principle of improvement." 
 
 I assume with him that the conditions for a progi^ess 
 towards the more complex and towards division of labour 
 exist in the fact that a higher stage once reached can afford 
 a foundation for one still higher, since the former, the 
 existing stage, will necessarily be the starting-point for 
 further modification. 
 
 Nevertheless, my view has certainly nothing to do with a 
 " principle of increasing perfection " in Niigeli's sense. I 
 confess that with respect to the criticism of this foundation 
 of Xageli's theory I count myself among those whom its 
 author describes as the " less far-sighted," at least in so far as 
 I consider the assumption of such a principle acting in 
 accordance with organic persistence of motion as merely an 
 
II CAUSES OF ADVANCE OR RETROGRESSION 
 
 53 
 
 assumption. Although he explains it as a mechanico-physio- 
 logical principle, I hold it to be a kind of striving towards a 
 goal, or teleology, in face of which the recognition of a 
 directing power conceived as personal, existing outside 
 material nature and ruling all things, would seem to me fully 
 justified.^ 
 
 The formation of species is not completely comparable to 
 the sprouting of the twigs of a tree. It depends not only on 
 increased perfection, but just as much on deterioration and 
 simplification, and on retrogression in complexity and in 
 division of labour, i.e. upon growth, with all the changes which 
 growth can undergo through hindrance and through the 
 modifications which are imposed upon it. 
 
 The abundance of the species which have been formed by 
 degeneration, by retrogression, is known to every zoologist. 
 It is self-evident that their origin is to be traced to the action 
 of external conditions, that they have been produced by 
 acquired and inherited changes of growth depending on these 
 conditions. 
 
 My own extensive researches on the variation of animals, 
 
 ^ Here I may be allowed also a remark ;pro domo. Nageli in the introduction 
 to his book speaks very severely of those who without any justification undertake 
 to express opinions upon the question of the origin and the evolution of organisms. 
 He claims this right exclusively for those who are physiologists by profession, 
 and counts among the non-physiologists both Darwin and Haeckel. Against such 
 a close corporation I protest. Investigators who have enjoyed a thorough 
 physiological training, and whose ideas must in consequence of this trainiug have a 
 physiological basis — and among such I would modestly request to be numbered — 
 are surely not to be excluded. But, as every one knows, outsiders have at times 
 larger ideas than the members of a corporation. Besides, we might in accordance 
 with Nageli's argument conversely inquire whether the laws of vegetable physio- 
 logy and the facts at the disposal of this limited branch of science are 
 sufficient to justify the treatment of a matter which concerns the whole 
 morphology and physiology of the animal kingdom ? At all events, the animal 
 kingdom, on account of its greater complexity and the active functions of its organs, 
 affords a wide field for the examination of questions which never come to the 
 notice of the botanist at all. For this reason, the impulse towards a more 
 scientific doctrine of evolution has come from zoologists, or at least, from men 
 zoologically trained, not exclusively from botanists. 
 
54 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 especially Avith regard to colours and markings, only tlie 
 smallest part of ^vllicll are published, show, however, in the 
 most distinct way, that the directions, not only of variation, 
 due, for example, to parasitism, but, as I may express it, of free 
 variation, in very many cases tend towards simplification and 
 not towards greater complexity. How far it is true in such 
 cases that the partial simplification is connected with simul- 
 taneous advance in evolution in another respect, and how 
 much is to be attributed to adaptation, must be ascertained 
 for each individual case ; in my examples these questions 
 have been considered. The facts already published by me on 
 the markings of animals, the transformation of longitudinal 
 striping into spots, then into transverse striping, and the final 
 disappearance of the marking, are sufficient to contradict 
 Nageli's principle of increased perfection. 
 
 But my inquiries on the markings of butterflies will 
 furnish still more striking examples of the fact that variations 
 tending to simplicity as well as those to greater complexity 
 take place with wonderful persistence in direction, as if 
 following a patli previously ordained. Such variation is 
 often in the same definite direction in species nearly related 
 but completely separated in habitat or even belonging to 
 quite different faunse, so that sometimes external conditions 
 appear to be undoubtedly the essential controlling factor. 
 Moreover, in many cases we have simplification alone, un- 
 compensated by greater complexity in another part. Thus 
 these examples also show once more that neither the inferior 
 ToU ascribed to adaptation by Niigeli nor the commanding 
 one given by Weismann are justified. 
 
 The process of evolution is not, as Niigeli believes, to be 
 compared to an eternally growing tree, on which adaptation acts 
 only by cutting branches away and by pruning the whole. 
 Adaptation has also, if only indirectly, a perfecting and 
 strengthening — in any case, a modifying eflect. On the tree 
 
II CAUSES OF PROGRESSIVE EVOLUTION 
 
 55 
 
 many shoots are stunted and many are metamorphosed in 
 manifold ways, but others die away. I have on occasion 
 used another simile for evolution : 
 
 " Thus we may," I said, " compare the whole process of the 
 modification of forms to the results of the migration of a 
 people over an extensive foreign territory. Some tribes, not 
 having the strength to follow, soon, others later, remain behind 
 (genepistasis), others again reach a distant goal. Some 
 retain their characters in their new home or strengthen them, 
 even modify them by correlation, others change under the 
 influence of external conditions and adapt themselves to the 
 environment— all that is not sufficiently capable of endurance 
 is left lying by the way and perishes, and if the struggle for 
 existence is at all severe only the toughest of all survive. 
 The sooner the connection between the separate tribes is lost, 
 the sooner each appears as a new species, as a new genus ; 
 but all bear the stamp of common descent." 
 
 I willingly confess, however, that this simile, like all 
 similes, is incomplete. 
 
 I find, then, the ultimate and the most essential causes of 
 progressive evolution in all the causes of growth in general — 
 therefore in all the influences of the external world upon 
 
 organisms. 
 
 It has been said that it is impossible to comprehend how 
 the varying external conditions should produce a continual 
 advance in evolution (Weismann). In answer to which the 
 first proposition to be emphasised is, that each higher stage 
 of evolution attained is a firmly established condition, — by the 
 previous argument, all the more firmly established, fastening 
 the more upon the new form, the longer it continues; a 
 condition wdiich, therefore, the longer it exists is with tlie 
 greater difficulty disestablished, but which merely through 
 the continual repetition of stimuli, although these have no 
 unusual strength, will undergo a change in the course of 
 
56 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 long periods in tlie direction of more complex (higher) 
 organisation, especially with the aiding action of selection. 
 But such higher development will be in a greater Segree 
 experienced when an unusual increase of stimulation occurs 
 — in both cases as a consequence of modification, that is, 
 intensification of growth. 
 
 For the action of continuous unvarying stimuli the 
 influence of the use of an organ may serve as an example ; 
 further, the effect of cold and other climatic conditions which 
 produce hardiness. For the action of increased stimuli, the 
 influence of warmth on plants as it manifests itself in several 
 of their characters in various warm regions of the earth. 
 
 Similarly, permanent cessation or diminution of the stimuli 
 will be followed by simplification of organisation as a result 
 of change of growth. 
 
 "Whenever the power of growth, be it through persistence 
 of characters, through retrogression, or through progress, has 
 undergone a change in any species under particular external 
 conditions, then the reapplication of a stimulus — even if it 
 be that which was formerlj^ the most usual — will have a new 
 ground for action, will excite a peculiar kind of growth, and 
 lead to new structure. 
 
 We have, however, to answer the question. Why male 
 animals for the most part are in advance of the females in 
 organisation, why, again, the older males first possess the new 
 characters, and why this new formation of characters (advance 
 in organisation) takes place on the body in a constant direc- 
 tion, for the most part from behind forwards ? And since the 
 changes in markings consist principally in the conversion of 
 a longitudinal striping into spots, and these into transverse 
 stripes, Ave have to inquire what are the causes of this con- 
 version. What are in general the causes of the modification 
 
" SHADOWS AND MARKINGS 
 
 57 
 
 of the marking in definite directions in the intermediate 
 stages between longitudinal striping and spotting and trans- 
 verse striping ? 
 
 I have permitted myself to express the supposition ^ " tliat 
 the fact of the original prevalence of longitudinal striping 
 might be connected with the original predominance of the 
 monocotyledonous plants, whose linear organs and linear 
 shadows would have corresponded with the linear stripes of 
 the animals ; and further, that the conversion of the striping 
 into a spot-marking might be connected with the develop- 
 ment of a vegetation which cast spotted shadows.— It is a 
 fact that several indications exist that in earlier periods the 
 animal kingdom contained many more striped forms than 
 is the case to-day." — The American fauna exhibits in many 
 respects a lower stage of evolution in the markings of its 
 members than ours ; it gives, therefore, at the present day an 
 idea of the condition of the ancient world referred to. This 
 supposition of mine is also supported somewhat by the fact 
 " that at present strongly spotted forms mostly occur in places 
 with spotted shadows, the longitudinally striped more in 
 grassy regions. Young slugs and caterpillars are often longi- 
 tudinally striped. Cross-marking is perhaps to be connected 
 with the shadows, for example, of the branches of woody 
 plants, — thus the marking of the wild cat escapes notice 
 among the branches of trees." Others have previously 
 suggested such relations as that of the cross-striping of the 
 tiger with the shadows of the bamboos in which it lives. 
 
 Weismann also has sought in the different markings of 
 the caterpillars of Sphingidse adaptations to their environment. 
 And while he provisionally leaves out of consideration the 
 ultimate causes of the origin of any of these markings he 
 says, " Even the first commencement of striping must have 
 been useful, for it divided at once, to the eye of the observer, 
 
 ^ Variiren, etc. 
 
58 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 the large conspicuous surface of the caterpillar's body into 
 several areas, and so made it less conspicuous." 
 
 In fact, one has only to look at such a light green cater- 
 pillar with long stripes as it rests lengthwise on a grass-stalk 
 or a pine-needle. 
 
 Weismann points out that all caterpillars of the Sphingid^, 
 in which the longitudinal striping is at the present time the 
 permanent marking, live either among grasses or on conifers. 
 
 Oblique striping is regarded by him as adapted to the 
 veins of leaves, the circular or ocellus marking as imitating 
 parts of the plants fed upon, berries, etc., or as means of 
 frightening enemies, or as enabling the possessor to be recog- 
 nised as unpalatable. 
 
 Preponderance of the males, I myself suggested further, 
 might be possibly explained by the fact that the males fight 
 the battle of existence more than the females, and therefore 
 must always be first to respond to new demands. The 
 postero-anterior evolution by the fact that the part of the 
 body farthest from the head is most in need of mimicry, 
 because it is least protected in other ways by the sense- 
 organs, and because it is at a special disadvantage ; that it is 
 the last part to be withdrawn from the pursuit of an enemy 
 (some instances of the opposite condition in caterpillars I 
 endeavoured to trace to special adaptations). The fact that in 
 mammals the new marking appears first on the sides was 
 comprehensible, I thought, because the sides were most 
 exposed to the view of an enemy, certainly more than the 
 marking along the back, which always remains at a lower 
 stagre. 
 
 " The preponderance of age," I said, " is due, in the first 
 place, to the fact that those individuals which are most 
 adapted to the environment as a rule also live longest, and 
 have the longest time to transmit their peculiarities. 
 
 " Since, moreover, the individuals provided with the new 
 
II GROWTH IN DEFINITE DIRECTIONS 59 
 
 marking live longest— in other words, bear the new markin^r 
 for the longest time, this becomes, as it were, most firmly 
 inoculated in the organism, and is therefore with greater 
 certainty transmitted to the offspring. The longer it is borne 
 by the possessors the more completely from constitutional 
 causes will it be inherited, and as the duration of its existence 
 in the posssessorwill be proportional to its usefulness, the degree 
 of its heredity will also be proportional to its usefulness, so that 
 an important share must be ascribed in the process to the con- 
 servative adaptation which depends on constitutional causes." 
 
 But all this does not explain the first occurrence of the 
 new characters, nor the undeviating course of the evolution 
 in a particular direction. 
 
 Tor when a number of varying individuals are compared 
 it is seen that the variations of all tend to a definite end, and 
 that the majority of the intermediate forms show stages in 
 the development of the characters which are absolutely with- 
 out use to them. 
 
 Tliis cannot be explained except by natural growth, whose 
 operations are changed, intensified, or diminished to a certain 
 extent by the stress of adaptation, and may also at times be 
 entirely restrained. 
 
 That this growth proceeds in definite directions and begins 
 at definite spots is not more wonderful than the same processes 
 in individual growth, which are of course more evident in 
 plants than in animals ; in the latter, on account of the more 
 active life, they are more altered and obscured by adaptation 
 than in the former. 
 
 Some important ultimate causes of the direction of growth 
 must, however, be sought in the general physiological mechan- 
 isms of the body — for example, in the distribution of the blood, 
 etc. In particular, the tendency to symmetrical, and even to 
 metameric development in the marking, for instance, depends 
 obviously on such mechanisms. 
 
60 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 
 
 That the male outstrips the female in phyletic growth is 
 comprehensible apart from the importance of adaptation in 
 this process, from the greater strength developed in the 
 former ; and that the growth of new characters shows itself 
 first in the later period of life, in the period of most complete 
 development, at the end of the ordinary and general develop- 
 ment, is comprehensible, again apart from the importance of 
 adaptation, merely from my theory of growth. 
 
 This view of mine is, however, further supported by the 
 fact that an essential cause of male preponderance consists in 
 the appearance of characters during the breeding period, at 
 the time of maximum vigour, many of which are subsequently 
 transmitted by heredity first as constant male characters, and 
 finally to the whole race. These characters include not merely 
 colour and strongly developed markings, — a long series of 
 male characters could be mentioned which were evidently 
 only present originally as such sexual distinctions in the 
 male. And we know many instances in which such characters 
 are intensified to a surprising degree in the males at the 
 breeding period, as, for instance, the dorsal crest of many 
 water newts (Tritonidas), the hook-shaped prolongation of the 
 lower jaw in salmon and trout. In this sense it is an interest- 
 ing fact that the latter formation becomes permanent in old 
 male salmon, so that such hook-jawed specimens have been 
 considered as forming an independent species. 
 
 The facts referred to in the preceding : (1) the definite 
 directions of evolution ; (2) the appearance of new characters 
 at definite regions of the body, and their progress in an un- 
 varying direction during individual life ; (3) the symmetrical 
 or in some cases metameric occurrence of characters ; (4) the 
 first occurrence of characters at a late period of life, as it were 
 at the end of the stage of evolution previously attained ; (5) 
 their first occurrence at the time of the maximum develop- 
 ment of vigour — these facts I might point to as not merely 
 
II FIRST APPEARANCE OF NEW CHARACTERS 
 
 61 
 
 in complete harmony with my theory of growth but as very 
 clear evidence of its truth. They may be compared with 
 processes which can be recognised in the, so to speak, more 
 transparent individual growth of any plant. Such comparison 
 holds especially for the 2d and 4th of these facts ; plants 
 grow from the apex; and from the terminal point of the 
 evolution which has previously taken place, that is, of the 
 structure already formed, from the so-called vegetating point, 
 new characters arise. 
 
 Thus the proper permanent leaves arise after the appear- 
 ance of the seed-leaves ; after the foliage-leaves, the flowers, 
 with their parts formed of modified leaves, and among the 
 foliage-leaves, again, sometimes various successive forms or 
 even colours. 
 
 As in plants, the new characters show themselves also in 
 the shells of Ammonites at the youngest part, as it were at 
 the growing point. For in these shells, as in snail shells, the 
 parts near the aperture are the newest. The growth of 
 these shells takes place, as we may observe still in the shell 
 of the Nautilus, in an intermittent manner ; it becomes more 
 vigorous at each period of maximum vigour in the animal, 
 which probably coincides with the most favourable season of 
 the year, again to decrease and come to a standstill, just as 
 the growth wdiose results are seen so beautifully in the shells 
 of our vineyard snails, and the annual rings of any tree-trunk. 
 That this j)ei'ioclical growth results in the formation of 
 characters appearing successively more strongly or more 
 feebly is not to be wondered at. A high degree of symmetry 
 or metamerism may be produced by it. 
 
 These considerations seem to me also to afford an explana- 
 tion of the origin of the symmetrically, i.e. metamerically 
 arranged characters of segmented animals, and to enable them 
 to be included in the same class of phenomena. That in such 
 segmented animals each somite should have the same 
 
62 THE ORGANIC GROWTH OF THE LIVING WORLD sec. ii 
 
 characters ought not to surprise us. These somites have 
 arisen by the subdivision of a whole, and the first has the 
 same relation to the second as the second to the third, and so 
 on. Now, since in lizards, as in caterpillars {yid. subsequent 
 sections), and also in mammals and birds, new peculiarities of 
 marking first arise on the hinder part of the body and extend 
 thence forwards, the question at once occurs whether this fact 
 harmonises with the explanation given for plants and 
 Ammonites, i.e. whether the hinder part in these animals is to 
 be regarded as the youngest. It is to be noted that a ver- 
 tebrate is segmented, and that there is much to be said for 
 the supposition that the vertebrates were once forms similar 
 to segmented worms ; on various grounds they are regarded 
 by many as descended from the latter. The Arthropoda, 
 including caterpillars, have similar relations to the segmented 
 worms (Annelids). But in the latter the most anterior 
 segments obviously as a matter of fact are composed of the 
 oldest tissues. Tliis is proved by the fact of ontogeny : so far 
 as sj^ecial attention has hitherto been paid to the commence- 
 ment and succession of ses^mentation in Annelid larv«, it has 
 shown that the process begins in the anterior part of the 
 body and is continued thence backwards ; the worm must 
 therefore grow at the posterior end. Exactly the same thing 
 is observed in our fresh-water worm, Xais probescidea. In 
 the young worms produced by division the new head always 
 consists of the oldest material — growth takes place at the 
 posterior end. 
 
 At present, my only intention in referring to this subject 
 is to indicate a definite point of view from wiiich to investigate 
 a question which requires a work to itself. Moreover, I am 
 not at present in a position to explain in a similar way the 
 infero-superior modification of the marking wliich takes place 
 in many mammals. 
 
SECTION III 
 
 INFLUENCE OF ADAPTATION IN THE FORMATION OF SPECIES 
 
 Is everything adapted ? 
 
 From the preceding considerations it appears to me, therefore, 
 that leaving aside Kolliker's hypothesis, neither Niigeli's view, 
 which ascribes to the principle of utility an almost infini- 
 tesimal effect, nor Weismann's, which regards adaptation as 
 all-powerful, can be unreservedly accepted. The truth lies 
 between them. Weismann in his latest paper explains every- 
 thing as adaptive. As an example of such complete adapta- 
 tion he describes the whale. 
 
 He alludes to Nageli in his remark that he can perfectly 
 understand that it is more natural to a botanist than to a 
 zooloo'ist to take refugee in internal forces of evolution. " Tlie 
 relations of form to function, the adaptation of the organism 
 to the internal and external conditions of life, are less con- 
 spicuous in plants, less easily observed, indeed — are often only 
 to be discovered by the most careful and acute investigation. 
 The temptation is therefore greater to regard everything as 
 due to causes actinsj from within." And he savs further : 
 " In any case, animal biology cannot point out too empliatically 
 how exactly and to the minutest detail form and function go 
 together, how completely adaptation to definite conditions of 
 
64 EFFECTS OF ADAPTA TION sec. 
 
 life prevails in the animal body. There nothing is indifferent, 
 nothing could be otherwise than it is ; every organ, nay, every 
 cell and every part of a cell, is as it were tuned to the part 
 which it has to play in relation to the outer world. True, we 
 are not able to demonstrate all these adaptations in any one 
 species, but wherever we succeed in fathoming the significance 
 of a structural feature, it always turns out to be another adap- 
 tation, and any one who has ever attempted to study profoundly 
 the structure of any one species, and to give an account to 
 himself of the relation of its parts to the function of the 
 whole, will be much inclined to say with me, everything 
 depends on adaptation." Of course Weismann adds : " These 
 are convictions, I grant it, not absolutely proved facts." 
 
 " If then," he continues, " the organism consists only of 
 adaptations based upon the constitution of its ancestors, it is 
 impossible to see what remains for any phyletic force to do, 
 even if it be conceived in the refined form of Nacreli's idio- 
 plasm." 
 
 Weismann then describes the whale in order to show the 
 completeness of adaptation, and concludes : " And now I 
 repeat my former question with regard to this special case. 
 If all that is characteristic in the animal depends on adapta- 
 tion, what is there left to represent the action of an internal 
 force of evolution ? " 
 
 I also repudiate any special internal force of evolution. 
 According to my view, everything in evolution is due to 
 perfectly natural processes, to material, physical causes. 
 
 I also have investigated the phenomena in question in 
 single forms of animals ; but I have arrived at a conclusion 
 which does not acjree with AVeismann's — "that evervthino^ 
 depends on adaptation." 
 
 But when AVeismann says : Even where we cannot 
 recognise the purpose of a character at present, it will 
 ultimately prove to be adaptive, then I feel justified in revers- 
 
Ill IMPERFECT ADAPTATION 6S 
 
 ing his assertion with respect to his own example, and sav- 
 ing : We do not know the numerous relations and conditions 
 of the life of the whale with anythinj.^ like sufficient accuracy 
 to enable us to conclude that it is so perfectly adapted to 
 them as Weismann believes. Our own conditions and rela- 
 tions of life we do know accurately, and although it is a 
 matter of taste with us whether we think our adaptation 
 greater or less, it must surely be conceded that in an}- case 
 this adaptation cannot be called perfect, even in the prime 
 of life, not to speak of childhood and gray old age. 
 
 What would be the total, to take only one instance, if we 
 were to add up the number of men in vigorous life who perish 
 miserably every year simply in consequence of the entrance 
 of fruit-stones or similar bodies into the useless vermiform 
 appendix of the caecum ? 
 
 Besides, it is self-evident that adaptation must be more 
 perfect in highly-organised forms much exposed to the dangers 
 of life than in many of a lower order ; in those which have 
 and had more enemies much greater than in others which 
 have fewer, and whose ancestors had fewer. And I do not 
 dispute the fact that there are forms which seem to be adapted 
 to external conditions in as high a degree as Weismann 
 supposes. But that only proves that those particular forms 
 are possibly so adapted. But with respect to all forms which 
 vary in a high degree, the assumption of perfect adaptation is 
 a 'priori improbable. And there are forms of which we can 
 say with all the required certainty, that their bodily shape 
 must depend not on adaptation, but on a " crystallisation," 
 resulting from the physical and chemical action of external 
 agents on the material of the organism subjected to them. 
 
 In my essay on " The Variation of the AVall-Lizard " I ex- 
 pressed, with reference to adaptation, the view that the in- 
 dividual is not necessarily constructed entirely in accordance 
 with its own requirements : " Only an inconceivably gross 
 
 F 
 
'66 EFFECTS OF ADAPTATION sec. 
 
 egoism could seriously make tins assumption — the individual 
 is notlnncr but a wheel in the clock-work of the universe : to 
 the universe its characters must be subordinated, must be 
 adapted ; for the wheel, for the individual itself, only such a 
 proportion of advantage is possible as the order of the whole 
 allows, as in this order belongs to it." It is certainly no 
 adaptation in organic beings that they cannot live without 
 nourishment ; and to the lamb devoured by the wolf the 
 deficiency of adaptation is particularly palpable, as it is to us 
 in death itself, our gradual extinction just when the highest 
 degree of knowledge and experience has been obtained. But 
 both hunger and death are conditioned by the substance of 
 which we are composed, and this again is conditioned by the 
 circulation between orc^anic and inoriranic nature. 
 
 ''Wherefore," I said, " have the calcareous or siliceous bodies 
 which crystallise out from the cells of a sponge, wherefore 
 have the calcareous spicules of the coral skeleton, wherefore 
 have the spicules of the Holothurian's skin, just this or that 
 exquisite form and no other ? Surely on the same grounds 
 on which a crystal has its definite form, and not on the 
 ground of utility. To what end the exquisite shapes of the 
 Radiolaria, the exquisite sculpture, markings, and colours of 
 the mollusc's shell, which latter are, moreover, generally 
 covered throughout life by mud and dirt, and whose beauty 
 of line and colour often only appears after polishing ? To 
 what end the black colour of the peritoneum of many verte- 
 brates ? To what end the various delicately- wrought patterns 
 of the leaves of our foliaqe trees ? To what end the whiten- 
 ing of the hair and all the other chanoes of old aoe in animals 
 and in man ? To what end the necessity of material meta- 
 bolism, of death following the acquirement of the highest 
 degree of capacity and knowledge, of the highest adaptation 
 to the environment? Surely not for the advantage of the 
 individual, nor that of the species — at most their use is to 
 
in UTILirV OF DEATH 
 
 67 
 
 maintain the circulation of life upon the earth ; and to place a 
 higher value upon this than upon the continuance of vigorous, 
 joyful bodily existence must be difficult even for the most 
 consistent advocate of the principle of immediate utility." ^ 
 
 Death as an Adaptation 
 Immortality 
 
 Weismann, we know, explains death itself as an advantage, 
 as an adaptation.^ 
 
 The unicellular animals, the Protozoa, which multiply by 
 simple division, are, he says, immortal. The multicellular, 
 however, the Metazoa, are mortal. Originally the latter were 
 also immortal, but after they had differentiated their germ- 
 cells from their body-cells (somatic cells), so that reproduc- 
 tion could only be carried out through the former, they 
 became necessarily more and more imperfect, because they 
 were no longer able to repair the damages incurred during 
 life. Hence the utility of their death. 
 
 The direct opposite of this is held by Gotte.^ According 
 to him, all animals are mortal, and reproduction is itself the 
 cause of death. Eeproduction in Protozoa is preceded by 
 encystation. In this condition the organism passes into a 
 non-livino; condition, from which it revives with renewed 
 youth and renewed life ; a similar condition occurs in the egg 
 of the Metazoa, during a certain period in which it forms an 
 unorganised, non-living body composed of organic substance. 
 The idea of " death " is here conceived as the stand-still of the 
 organic life of the whole — the idea of a corpse is not included. 
 
 ^ For botanical instances compare Askenaz, Beitrdge zur Kriiik der Darwin- 
 schen Lehre, Leipzig, 1872. 
 
 - A. Weismann, Ueher die Bauer des Lehens, an Address delivered at the 
 Salzburg Naturalists' Congress, 1881 ; and Ueher Leben und Tod, eine hioloyische 
 Untersuchung, Jena, G. Fischer, 1884. 
 
 ^ Ueher den Ursxrrung des Todes, Hamburg, Voss, 1SS3. 
 
68 EFFECTS OF ADAPTATION sec. 
 
 Weismann replies, in his latest essay, such an arbitrary 
 definition of the term death is unjustifiable. The process of 
 encystment is by no means comparable with death, and does 
 not even occur in all I'rotozoa — a view which is certainly 
 correct. Weismann says further : " The gradual evolution 
 of death is to be explained in this way, that at the first differ- 
 entiation of the body of the JNIetazoon into somatic and germ- 
 cells, tlie life of all cells was limited to one generation, that of 
 the somatic, therefore, to a short duration. The somatic cells 
 first bej^an to last for several cjenerations amonoj the hidier 
 Metazoa, and life was prolonged. This change was brought 
 about by processes of selection, on the basis of the principle 
 of division of labour. The shorter or longer duration of life 
 depends entirely on adaptation. Death is not due to an 
 original property of living substance, nor is it necessarily con- 
 nected with reproduction. Eeproduction, on the other hand, 
 is an original property of living matter. Life is continuous, 
 not, as Gotte would have us believe, interrupted, discon- 
 tinuous." 
 
 With rei]fard to the different views of Weismann and 
 Gotte, I have elsewhere ^ expressed myself as follows : " On 
 account of the definite evolution of science, certain ideas are 
 not far to seek. I have for years discussed the immortality 
 of the Protozoa in my lectures,^ but in consideration of the 
 action of metabolism, and the necessity of the renewal of 
 the organs of even these forms in consequence of wear, w^ould 
 place some limitations on its acceptance. 
 
 " In the Metazoa, according to my opinion, the germ-cells 
 are immortal like the Protozoa (with the same limitations as 
 hold for the immortality of these) ; only the soma dies. 
 
 " The latter is not really an end in itself,^ but rather its 
 
 ^ In a report in the Deutsche Literaturzeitunfj, 18S4, No. 19. 
 ^ Cf. also Blitschli, Zool. Anzeiger, 1882, p. 64. 
 
 2 [It would be just as true to say that the germ-cells are not an end in them- 
 selves, but serve only to produce the soma. Trans.] 
 
in EXPLANATION OF DEATH 69 
 
 principal function is to ensure the maintenance of organic 
 life by favouring reproduction, by sheltering the genii-cell> 
 till their maturity, and in order to deposit them repeatedly ; 
 further, by the dispersal of the same in space, by incubation 
 in the widest sense, and so on. Further, it has the function 
 of strengthening the power of endurance of the species by 
 the inheritance of acquired characters. 
 
 " Eeproduction is unending growth. Not reproduction is 
 the essential cause of death, but the differentiation of the 
 constituent parts of the soma resulting from division of 
 labour, in the last result division of labour itself, to which the 
 soma owes its very existence : the germ-cells alone are still 
 individually complete elementary organisms, and as such 
 retain still the general complete combination of matter which 
 in them as in Protozoa ensures endless growth. To the soma 
 such growth is impossible because these fundamental condi- 
 tions in it are wanting ; it dies in consequence of the exhaus- 
 tion of the organs. 
 
 " Separation of the sexes is likewise due to division of 
 labour, and sexual reproduction finds its explanation in this 
 very necessity of the complete combination referred to as a 
 condition of endless growth. And thus at the same time 
 parthenogenesis would explain itself." 
 
 This conception is in some measure completed and 
 developed in the preceding and following pages. I have to 
 add here at once : there are also Metazoa whose bodies (soma), 
 in that they divide or multiply by budding, maybe immortal. 
 Amonojst these are instances in which division of labour in 
 the organisation has not yet attained any considerable 
 development (many Zoophytes, e.g. Hydra), and others in 
 which the body consists of equivalent parts, into which it 
 may separate {e.g. Annelids, like Nais). In both cases sucli a 
 reproduction (possibly unending) of the soma without the aid 
 of the germ-cells can only occur because the parts have all 
 
70 EFFECTS OF ADAPTATION sec. 
 
 the properties, because they have the complete combination 
 of the Avliole. The liigher animals, with more advanced 
 division of labour, cannot reproduce by division, because each 
 part does not contain the properties, the complete combination, 
 of the whole. In this sense the germ-cells alone are still in- 
 dividually complete elementary organisms, in relation to the 
 present question. 
 
 Further, the Blastozoa,^ which reproduce only by germ- 
 cells, are only distinguished with respect to immortality from 
 the Protozoa, inasmuch as we are accustomed to regard their 
 soma as the essential part. But let us place ourselves at the 
 point of view indicated above, " that the soma is not really an 
 end in itself, but rather its principal function is to ensure the 
 maintenance of organic life by favouring reproduction," — let us 
 reflect a moment while we picture to ourselves the unbroken 
 chain of organic nature, its unity, and look upon the in- 
 dividual animals and plants as merely seed-vessels, — then the 
 Blastozoa appear as immortal as the Ablastozoa.- 
 
 If we philosophise about nature at all, the naturalist who 
 desires to be thorough must not halt half-way. 
 
 Thus the above way of regarding the matter is perfectly 
 justifiable — if the multicellular animals have really been 
 evolved little by little from the unicellular, it is a mere 
 self-evident consequence. 
 
 Although, however, we may be willing to reason with as 
 much self-abnegation as is demanded by this conception, yet 
 by the above we are not compelled to go so far as to consider 
 death as useful, as an adaptation. 
 
 Besides, Weismann himself speaks concerning the relation 
 between the germ-plasm of the multicellular organism on one 
 hand and of the unicellular on the other, and concerning the 
 significance of the body (soma) of the former, as follows : — 
 
 1 Animals witli germinal layers = Metazoa = multicellular animals. 
 - Animals without germinal layers = Protozoa = unicellular animals. 
 
Ill THE UNICELLULAR AND THE MULTICELLULAR 
 
 After lie lias stated that his notion of the continuity of the 
 germ-plasm reduces heredity to simple growth, and parallels 
 it with the reproduction of unicellular forms in which tin- 
 same substance grows on and on, and new individuals are 
 only produced by its division, he continues : " Tlie distinction 
 between the unicellular and the multicellular consists only in 
 this — that in the latter every division of the 'germ-substance' 
 is followed by a process of development which leads to the 
 formation of a multicellular individual. This, then, exceeds in 
 mass by an enormous amount the unused remnant of the 
 germ-plasm, but yet it is only a by-product of the eternal 
 germ-substance, is abandoned to death, must die after a time, 
 while the germ-substance, under the shelter and nurture of 
 the multicellular body (soma), continues to grow, increases in 
 mass, and produces new germ-cells, which possess the power 
 of forming another generation of bodies (somata), in which the 
 same process again takes place. The germ-plasm may there- 
 fore be conceived under the simile of a long creeping root, 
 from which at intervals separate plants arise, the individuals 
 of the successive generations." 
 
 If the body of the multicellular organism is thus, even 
 according to Weismann's ideas, of secondary importance in 
 comparison w4th the germ-plasm, if the latter corresponds to 
 the unicellular organism, it follows that the multicellular is 
 just as immortal or mortal as the unicellular. And thus it is 
 impossible to see why, between the germ-plasm of the multi- 
 cellular on the one hand, and that of the unicellular on the 
 other, there should exist this profound difference, that tlie 
 latter acquire characters during life and transmit them by 
 heredity, the former not,— how the former any more than the 
 latter can nourish itself and grow without being influenced in 
 its nature by its nurture. 
 
72 EFFECTS OF ADAPTATION sec. 
 
 Further Considerations on the Adaptation and Direc- 
 tion OF Evolution of the Markings of Cater- 
 pillars. Absence of Sexual Combination in this 
 Evolution 
 
 I much rei^ret that Weismann's views and mine with recjard 
 to the causes of evohition are now so divergent, after the 
 great agreement between us, which I felt myself entitled to 
 assume in my publication on the variation of the wall-lizard, 
 judging from AVeismann's researches on the markings of the 
 Sphingidie caterpillars, which demonstrate definite directions 
 in the modifications of these markings. 
 
 I was rejoiced to be able to appeal to the fact that the re- 
 sults of these researches of Weismann admitted of an explana- 
 tion in accordance with my views, and thought I had good 
 grounds, therefore, for believing that we agreed. I was the 
 more pleased at this supposed harmony because I had 
 arrived at my results quite independently of Weismann's 
 paper. 
 
 Weismann was one of the first who insisted that variation 
 takes place in constant directions ; he also recognised the 
 truth that simply from the fact of the given constitution of 
 the body it could not occur in any direction at random. 
 Formerly, moreover, he did not allow such exclusive dominion 
 to adaptation as now. Thus he says in his work on season- 
 dimorphism : ^ " Little as I am inclined to talk of an unknown 
 transmutation force, I w^ould as emphatically insist here again 
 that the modification of a species depends only in part on ex- 
 ternal conditions, and in the other part on the specific consti- 
 tution of the species." 
 
 ^ a. Weismann, Studien zicr Descendenz-TheoHe. I. Ueber den Saison Di- 
 morjihismus der Schvietterlinr/e, Leijizig, Engelmann, 1875. 
 
ni MARKINGS OF CATERPILLARS 
 
 73 
 
 Weismann discovered in his caterpillars a regular series of 
 steps in the marking from longitudinal lines °to transverse 
 lines and spots, and came to the conclusion : '' That among 
 species which are ornamented with oblique streaks or with 
 spots there are many whose young stages are streaked length- 
 wise, but the converse never occurs; never do the young 
 caterpillars exhibit spots or oblique streaks when tlie adult 
 caterpillar has only longitudinal streaks. The first and most 
 ancient marking of the Sphingida3 caterpillars was therefore 
 the longitudinal striping." A derivation of the oblique from 
 the longitudinal striping is not demonstrated; both occur 
 together, but the former appears later than the latter, and re- 
 mains when this has vanished. 
 
 I thought it possible that the longitudinal streaks broke 
 up first into small spots and dots, and that these, spots 
 and dots formed the oblique streaks. If so, complete agree- 
 ment with my laws of marking would be proved in this 
 case. 
 
 In caterpillars also, as already mentioned, the new charac- 
 ters arise mostly at the posterior end of the body. 
 
 Weismann endeavours, as before remarked, to explain the 
 markings of caterpillars as adaptations to the conditions of 
 the environment. Nevertheless, he comes to the conclusion 
 that these markings have phyletically developed extremely 
 gradually, according to certain laws, and in quite definite 
 directions. And he further says : " The evolution of the 
 species of Deilephila shows that the evolution of the marking 
 follows throughout a certain law, that it proceeds in all 
 species in the same manner. All the species seem to steer 
 towards the same point, and this gives the impression that there 
 is an internal law of evolution which, like an impelling force, 
 determines the future phyletic modification of the species." 
 This conclusion seems to be supported also by the fact that in 
 caterpillars there is a tendency for the same characters to be 
 
74 EFFECTS OF ADAPTATION sf.c. 
 
 repeated in succession on all segments; and further, tliat 
 characters which have newly arisen appear afterwards at 
 an earlier and earlier ai:je, althoucrh no advantage is to be 
 discovered in this. 
 
 Although Weismann, even at that period, showed the 
 greatest repugnance to recognising a special force of evolution. 
 and, in my opinion, was quite right in his opposition, yet how 
 can he explain by his theory of the action of sexual reproduc- 
 tion the facts established by himself concerning caterpillars ? 
 And how is it possible to explain definite directions at all in 
 evolution by sexual reproduction, unless every step in the 
 process of modification is demanded by adaptation ? 
 
 Chaeacteks which are inessential (indifferent) to the 
 
 Life of the Organism 
 
 I once devoted myself for a long time to the study of the 
 siliceous sponges. As is well known, we find in these a 
 degree of variation which is extremely troublesome to the 
 investigator. One form passes into the other, and almost in- 
 numerable, often in the highest dec^ree insicrnificant, divert- 
 ences are met with in the parts on which diagnosis depends — 
 the siliceous spicules and particles of the skeleton. It cannot 
 possibly be of importance for the success of a given variety 
 whether the spicules have this or that minute character or 
 not. That this is true is proved by the occurrence of many 
 such varieties side by side. As there can be therefore no 
 question here of useful adaptation, the variations under the 
 circumstances can be only ascribed to an extreme sensi- 
 tiveness of the protoplasm to external influences. The " cry- 
 stallisation " in these sponges of the siliceous parts, often so 
 graceful in shape, from the protoplasm is, to an extent most 
 favourable to my ideas, comparable to processes of form- 
 production in inorganic nature, where there can be no question 
 
"I USELESS CHARACTERS 
 
 of special adaptation. It is known, for example, that in cal- 
 careous sponges the variation and disappearance of one axis 
 of the spicule actually forms a transition from one of the 
 principal divisions of the order into another, a subject wliicli 
 will subsequently be discussed fully in connection with a 
 particular case. 
 
 And of what use was the gradual modification of tlie 
 Ammonite's shell in such a way that new characters, some of 
 a very beautiful kind, arose always round the aperture, and 
 extended in the descendants more and more over the whole 
 structure, so as to form new species, as Wiirtenberger has 
 shown ? How can these characters, especially at their first 
 origin, have been useful ? 
 
 And what demand upon the organism could entirely 
 exclude the development of such indifferent characters? 
 Certain it is that this one or that among such characters was 
 once useful to the ancestors — as, for example, possibly the 
 traces still occurring of marking in Canidre^ (dog, wolf, 
 jackal), or possibly the stripes on the shell of our garden 
 snails. Helix hortensis and nemoralis. But it is equally 
 certain that this does not hold for all. 
 
 I mentioned the garden snails as an example intentionally. 
 It is the less easy to discern any use in the striping of the 
 shells of these snails ; not only does the striping vary greatly, 
 but it is about as often absent as present. The striping 
 might be regarded as an ornament which acted as an advan- 
 tage in sexual selection. But such an assumption is incon- 
 sistent with the following facts : I have observed for years in 
 my garden that striped and unstriped individuals of Hdix 
 hortensis unite without any selection. And what makes this 
 case particularly noteworthy as a support for my view of the 
 comparatively slight effect of sexual crossing in the production 
 of intermediate forms (one-sided heredity) is this, that the 
 
 ^ Cf. my articles iu Ilumholdt. 
 
76 EFFECTS OF ADAPTATION sec. 
 
 offspring of these striped and unstriped parents are again 
 striped or unstriped — in spite of constant crossing (pammixis) 
 these two forms appear everywhere side by side with no con- 
 nectiusij forms between them. 
 
 If everything were adapted, there would be no characters 
 at present useless, representing either rudiments of formerly 
 useful or the benfinninGjs of new characters. There would be 
 no gradual transitions, and, more particularly, no change of 
 function, and also there would be no correlative char- 
 acters — there could be no striking variability in forms 
 at all 
 
 The universal dominion of adaptation is finally also con- 
 tradicted by the reflection, that from the given materials only 
 instruments of a certain quality can be produced in organic 
 nature^ — that these instruments might be many times better 
 for their purpose, more perfect, less easily damaged — that they 
 are not in all cases completely adapted to the requirements 
 seems to me beyond a doubt. 
 
 Xevertheless, what great importance, in spite of my refusal 
 to recognise its exclusive dominion, I ascribe to adaptation in 
 the modification of forms \vill be best gathered from the 
 section on the adaptation of lizards. 
 
 It was not my purpose in this place to exhaust the question 
 of non-essential characters, as it is discussed elsewhere in this 
 work, both in preceding and following pages. I wished 
 merely to mention here the existence of such characters as an 
 argument against the assumption that adaptation rules ex- 
 clusively in all cases. 
 
 If this exclusive dominion did belong to it, if everything 
 
 ^ Compare here my remarks, reproduced in a later passage, on the formation 
 of sense-organs, in my monograph Die Medusen, anatomisch vncl physioJogisch 
 auf ihr Nerven-system v.ntersucht, Tiibingen, Laupp, 1878. I there showed how 
 clearly the structure of sense-organs, especially of the optic and auditory organs 
 of various animals, indicated that the given material permits only the formation 
 of instruments constructed on certain few principles, which instruments satisfy 
 the requirements, but are obviously often very imperfect. 
 
Ill ADAPTATION NOT SUPREME 77 
 
 were adapted, all evolution of the living world would be also 
 excluded — there would be stagnation. 
 
 The chief evidence for my view of the organic growth of 
 the living world as yet withheld is now to be given : (1) The 
 evidence that external conditions modify organisms, and (2j 
 that characters so acquired are inherited. 
 
SECTION IV 
 
 ACQUIRED CHARACTERS 
 
 ^Methods of Investigation — The Period of Time to be 
 
 claimed for Evolution. 
 
 Nageli says in the introduction to his book, when he is 
 objecting to the discussion of the doctrine of descent from 
 the standpoint of descriptive natural history, and arguing for 
 the " exact physiological method " : " As the ' descriptive 
 naturalist' is accustomed to attain in his progress to only 
 disputable hypotheses, not to certain laws, he regards every- 
 thinsj, even the results of exact observation and ric^id 
 criticism, not as matter of fact, but as matter of oj^iniou. 
 This was the case, for instance, with the fact of the promiscu- 
 ous evolution of species of plants, and with that of the insig- 
 nificance of the influence of climate and nutrition in the 
 production of varieties, both of which I believe I have 
 adequately established, and which an unprejudiced and 
 conscientious observer can easily test and confirm. These 
 facts inflict a very heavy blow on the whole fabric of the 
 doctrine of descent as it now exists, and could not therefore 
 be considered unless the existing doctrine were abandoned. 
 . . . ' I cannot make use of that,' they say." 
 AYitli regard to the promiscuous evolution of species of 
 
SEC. IV NAG ELI'S EXPERIMENT 
 
 plants, all that need be said from my standpoint is, tliat it is 
 by no means in contradiction to my view, but rather lielps to 
 confirm the correctness thereof : Nageli shows, for instance 
 that the crossing of nearly related plants living tof^ether 
 (Hieracium species) does not, as might It priori be expected, 
 lead to the production of intermediate forms, but ratlier ol" 
 varieties which possess the characteristics of the one or the 
 other parent forms intensified — a result which harmonises 
 completely with the process described by me as one-sided 
 heredity, and with the points of view indicated in tliat 
 description.-^ 
 
 Against ISTageli's supposition that the influences of climate 
 and nutrition are of no consequence in the formation of 
 varieties, it is, however, to be urged that isolated negative 
 examples prove nothing. This is especially the case when 
 the observations are made only on one distinct kind of 
 objects, only to a limited extent, and only during a limited 
 period of time. Such experiments prove only that in the 
 given cases the result was negative. A single positive 
 example on the other side is, however, sufficient for complete 
 proof. I have adduced here such examples, and will bring 
 forward more. ISTageli's arbitrary general application of his 
 results, be it remarked in passing, is sufficient to show his 
 misuse of the word fact, and also to prove the injustice of his 
 charges against the " descriptive naturalist." 
 
 When, therefore, this inquirer believes he has by his ex- 
 periments quite settled in the negative the question of the 
 influence of external conditions on the permanent modification 
 of species in general, and that he has shattered the whole 
 structure of the doctrine of descent hitherto held, I cannot 
 agree with him, actively as I am endeavouring myself to alter 
 that doctrine. 
 
 1 Cf. ante p. 39, and Nageli, Bas gesellschaftliche Entstehung neuer Species, 
 Sltzungsherichte der Miinchener Akademie, 1873. 
 
80 ACQUIRED CHARACTERS sec. 
 
 Against the validity of the evidence afforded by Niigeli's 
 exj)eriments I would further, above all, bring into the field the 
 circumstance that thev are artificial throughout, and that 
 they cannot therefore claim to be held as complete evidence 
 for the processes which occur under unrestricted natural 
 conditions. Not that I would attach no value at all to 
 artificial experiments, but they must certainly be employed 
 with great caution. Their relatively slight importance depends 
 in my opinion on the fact that definite directions of evolution 
 become fixed in living beings by extremely long continu- 
 ance, and these can only be changed by continuous ex- 
 ternal influences acting for a long time. Thus an organism 
 is restricted lonf,^ beforehand to a certain direction of modi- 
 fication. If an artificial experiment chance to promote 
 change in this direction, it soon results in the appearance of 
 permanent modifications : these will persist even after the 
 artificial external conditions have ceased to act. But not so 
 when art is in opposition to nature — then the organism will 
 rather return to its former condition immediately after the 
 cessation of the artificial action, or its descendants will do so. 
 This last seems to have been the case in Niigeli's experiments 
 with plants, which he placed under different and more favour- 
 able conditions of nutrition, and which were modified by the 
 change, but whose seeds sown in poorer soil again produced 
 plants of the old kind. 
 
 An Alpine plant, for example, is necessarily covered with 
 snow for a long time in winter, and in summer is exposed to 
 strong heat from the sun and to intense light, and has acquired 
 through its peculiar conditions of life the power of very rapid 
 development and also special morphological characters. If 
 this plant is placed where these conditions are intensified, in 
 the far North for instance, these characters ought to be still 
 more strongly developed, and the advance ought to remain 
 permanent even in the offspring which are reared from their 
 
IV SIGNIFICANCE OF EXPERIMENTS 81 
 
 seeds in the Alps again — this on the additional ground that 
 the advance would be useful also in the Alps. But it is 
 otherwise when, as was done by Nageli, plants growing on 
 the Alps (Hieracium) are transplanted to the Botanical Garden 
 of Munich, and their offspring are reared in gravelly soil (as 
 a substitute for the conditions of their Alpine home). That 
 these offspring, deprived of the rich garden soil, revert to the 
 original form seems to me less surprising than the reversion 
 of all the garden plants everywhere artificially cultivated for 
 a much longer time as soon as they grow in a wild condition ; 
 and thus Nageli's experiments, on which he lays so nuicli 
 stress, seem to me to prove nothing new against the modifica- 
 tion of forms by external influences. 
 
 The effect of the gradual withdrawal of water upon the 
 Axolotl is a case in which art hits upon and hastens the 
 movement of evolution already in progress. Likewise, un- 
 doubtedly, the action of water of greater or less saltness on 
 the crustacean Artemia salina, shortly to be considered more 
 closely. It is of course also possible that one part of this 
 latter case is an instance of reversion, for examples show that 
 when animals are transferred to the life-conditions of their 
 nearest ancestral form, or retained in those conditions from 
 the young state onwards, they retain the characters of the 
 ancestral form which they possess as larva3. Thus we are 
 able to prevent Salamanders from losing their gills and giving 
 up branchial respiration by compelling them to remain in water 
 all their lives, and so cause them to remain similar to their 
 ancestors the Perennibranchiata, because their other characters 
 also, through correlation, remain permanently at the lower stage. 
 
 Very pretty experiments in relation to this point have been 
 made by Fraulein von Chauvin ^ upon the Alpine Salamander, 
 Salamandra atra. The gill-bearing larva? of this animal 
 were taken out of the oviduct of the mother and put into 
 
 1 Zeitschr. filr loiss. Zoologie, Bd. xxix. 
 G 
 
82 ACQUIRED CHARACTERS sec. 
 
 water. It is well known that these larvie under the usual 
 conditions at a later time, while still within the mother's 
 body, lose their gills, and, what is very rare among Amphib- 
 ians, are born as completely terrestrial animals. The gills of 
 the larvic placed in water at so early an age were dispropor- 
 tionately large, and hindered the animals in their movements, 
 and in some cases they were cast off, whereupon new smaller 
 organs arose in their place. These new gills persisted in one 
 case for a surprisingly long time (fourteen weeks), and then 
 atrophied. This larva, like the rest, ultimately developed into 
 a land animal. But the remarkable fact remains that on ac- 
 count of the peculiar conditions of life artificially produced, 
 after the original gills, which were unadapted for use in a free 
 state of life, had perished, new and suitable gills were formed, 
 not in the struggle for existence against competitors with the 
 cumulative effect of selection, but, as I believe, directly from 
 purely physiological causes. These causes must, to my think- 
 ing, be sought in this, that as the pulmonary respiration was 
 not allowed to develop, and the original relations of the 
 branchial circulation therefore continued, new outg^rowths of 
 the skin, i.e. gills, were formed in consequence of the unchanged 
 distribution of nutrition at the place which that distribution 
 made most favourable ; yet in the end the phylogenetic ten- 
 dency which had been for a long time established got the 
 upper hand. 
 
 In thousands of cases, on the other hand, we are unable 
 by changing the external conditions to bring about any 
 change at all in the organism, even of temporary duration — 
 the animals or plants perish rather than adapt themselves ; 
 we succeed by experiments only in killing them very rapidly. 
 It is clear that from this most sim})le physiological effect to 
 those of Niigeli's experiments an unbroken chain of transitions 
 must exist, and that therefore the latter are in reality as 
 little surprising as the former. 
 
IV TENACITY OF HEREDITY 83 
 
 But ill addition to tliis an important considuration lias 
 been entirely left out of consideration in Njigeli'.s ai\anneiit— 
 the length of time necessary for the production of important 
 modifications. 
 
 When the external change favours completely the process 
 of evolution in progress, then the modification may— apart 
 from the possibility of the aid of adaptation— Ije brouglit 
 about very rapidly. In most cases, on the contrary, (jvun 
 when the external change is perfectly natural, the result must 
 evidently be very gradual. Leaving aside the very gradual 
 disappearance of unused organs, uj. parts of the skeleton, this 
 is proved by the obstinacy with which, as I have pointed out, 
 traces of primitive markings are inherited in animals. 
 
 These facts prove the extreme tenacity of heredity. In 
 other words, they show how difficult it is to divert forms 
 from their usual direction of evolution, to conquer their vis 
 inertia:, and with what difficulty they can in general be led 
 into new paths of evolution. 
 
 And this whole argument of mine shows also, to recur 
 again to the sul^ject of the previous sectiou, how unjustifiable 
 it necessarily is to talk of universal adaptation, for this very 
 tenacity of heredity is sufficient surety for the existence in 
 animals and plants of innumerable inessential characters 
 which have gone out of use or which belong to a deserted 
 path of evolution. 
 
 Even natural science has found it hard to recognise the 
 effects of long periods of time. Only a few decades back 
 the 5000 years of the Bible were accepted even in 
 Geology. Now Geology reckons merely in the history of 
 living beings with endless time, and Darwin required a long 
 period of time to explain the modification of a single form. 
 But that the conviction is even at the present time far i'rom 
 forming part of the mental constitution of the naturalist, is 
 shown by the fact that so eminent and talented an iiKiuirer 
 
84 ACQUIRED CHARACTERS sec. 
 
 as Xiioeli can fomet its claims, and believe himself entitled 
 to draw conclusions as to the evolution of organic nature from 
 cultivation experiments, carried out during a few years with 
 negative result, and to deduce from them a " fixed law." 
 
 Yet more : it is only a few years since we have reached 
 the conviction that tlie Egyptian civilisation stretches l)ack 
 more than 6000 years behind us. A few years ago, after Darwin 
 had proposed his theory of the origin of species, his conserva- 
 tive opponents believed themselves justified in urging against 
 the doctrine of the modifiability of species, that the species 
 of cereals and other plants and also animals known from the 
 ancient Egyptian times had not changed up to the present 
 day, for the period of time in question seemed to them 
 eternal. The Darwinians explained in reply that demon- 
 strably the external conditions have not changed in Egypt 
 since that time, and that therefore in the particular case no 
 inducement, no necessity has existed for the new adaptation 
 of tlie livincj beinojs, and therewith for their modification. 
 But quite recently AVeismann employs the fact cited by 
 Darwin's opponents to prove that the germ -plasm is a 
 substance of extreme power of persistence, a substance, he 
 says, "which is nourished and grows to an enormous ex- 
 tent without changing thereby in tlie slightest degree its 
 complicated molecular structure. We ought," continues 
 Weismann, " to maintain this with all certainty, like Ntigeli, 
 although we can get no direct perception of this structure. But 
 when we see that many species have reproduced themselves 
 for thousands of years without change — I mention merely the 
 sacred animals of ancient Egypt, whose embalmed bodies 
 must in some cases be 4000 years old — this proves to us that 
 their germ-plasm possesses still to-day the same molecular 
 structure which it had 4000 years ago. And since, further, 
 the amount of germ -plasm which is contained in a single 
 germ -cell must be supposed very small, and since of this 
 
IV IVEISMANN ON THE GROWTH OF THE GERM- PLASM S5 
 
 again only a very small fragment can remain unchanged 
 when the germ-cell develops into an animal, tlierefore, even 
 within a single individual, a quite enormous growth of germ- 
 plasm from this fragment must occur. In every indivi(huil, 
 as a rule, thousands of germ-cells are produced. It is thus 
 not too much to say that the growth of the germ-plasm in 
 the Egyptian Ibis or the crocodile in those 4000 years nuist 
 have been utterly immeasurable. In the plants and animals, 
 however, which inhabit equally the Alps and the Polar Regions, 
 we have examples of species which have continued unchanged 
 for much longer periods, namely, since the ice age, in whicli, 
 therefore, the growth of germ -plasm must have been much 
 greater. 
 
 " Since, nevertheless, the molecular structure of the germ- 
 plasm has remained exactly the same, it must be very hard 
 to modify, and there is little prospect that tlie slight 
 temporary differences in nutrition which will of course 
 happen to the germ-cells as well as to every other part of the 
 organism, will bring about any change, however small, in its 
 molecular structure. Its growth will proceed now faster now 
 more slowly, but its structure will be affected tlierel)y all the 
 less that these influences are mostly of an alternating 
 character, and act now in one direction now in another." 
 
 The hereditary individual differences Weismann infers 
 must therefore have another root— they are to be derived 
 from sexual reproduction.^ 
 
 Against the above exposition, which reproduces once more 
 Weismann's whole theory of the continuity of the germ- 
 plasm, I must repeat that I cannot conceive how the germ- 
 plasm grows, grows to an enormous extent, without being 
 influenced by the conditions of nutrition, by the composition 
 of the body. What is the cause of its growth, and why is it 
 sometimes faster sometimes slower ? 
 
 1 Die Bedentunrj cler sexuellen Fortpjlanzxmg, etc., p. 27 ct seq. 
 
86 ACQUIRED CHARACTERS sec. 
 
 The objection against the influence of external conditions, 
 that these are of variable nature, tending now in this now in 
 that direction, is discussed in the preceding pages. The 
 view, liowever, tliat the variations in nutrition to which the 
 body, and as Weisniann acknowledges tlie germ -cells also, 
 are subjected, must be regarded as transitory and minute, 
 I cannot admit. 
 
 The fundamental difference between "Weismann's view 
 and mine seems to me to lie just in this point. I grant 
 entirely that the permanent action of external conditions on 
 the body of the organism in most cases is not immediately 
 perceptible. From physiological principles this is not in 
 general possible. The question essentially depends on what 
 ideas we possess of the time occupied by organic evolution. 
 It is my opinion that we must accustom ourselves to a much 
 less limited conception than even that introduced by Darwin. 
 
 ^ly theory of the progressive growth of the living world 
 and of the origin of species demands for the modification of 
 a form, according to physiological principles, to the extent 
 shown in an}^ given case, enormous periods of time — periods 
 compared with which the few thousand years of the history 
 of Egyptian civilisation may be but as a moment in com- 
 parison with the individual growth of a plant or an animal. 
 
 My evidence of the importance of external conditions for 
 the origin of species requires that this demand shall be borne 
 in mind. None the less, I am able, as shown already in 
 preceding pages, to bring forward cases in which influences 
 show themselves in their effects in a short time. I proceed 
 now to produce further evidence. 
 
 Every character which must have been formed through 
 the activity of the organism, is an ac(|uired character. All 
 characters, therefore, which have been developed by exertion 
 are acquired, and these characters are inherited from genera- 
 
^^ PRODUCTION OF PIGMENT 87 
 
 tion to generation. The same holds for all organs atrophied 
 through disuse— the degree of atrophy is acquired and 
 inherited. In the first class we see especially tlie action of 
 direct adaptation, in the second the results of the cessation of 
 this action. A third class of acquired characters are to be 
 traced simply to the immediate action of the environment on 
 the organism, and originally, at the commencement of their 
 appearance, all characters must have belonged to this class. 
 Let us take first an example of the last class. 
 
 Acquired Characters due to Direct External Action 
 
 The formation of pigment is universally subject to the 
 influence of light and warmth. Numerous species of animals 
 living in the dark have become completely colourless; the 
 deficiency of pigment due to external influences has been 
 inherited and becomes at length a constant character. Everv- 
 one who like myself has undertaken, with his eyes open on 
 such questions, a journey from Germany directly to the South, 
 to Africa, as far as the tropics, will acknowledge the gradually 
 increased darkness of colouring even in one and the same 
 race of men, and must ascribe it to the gradual increase in 
 the power of the sun. The result of this action of the sun, 
 however, has been inherited and has become a constant 
 character. We meet near and in the tropical regions oi' 
 Africa tribes of men who are almost as black as ebony, and 
 who, as for instance the nomadic Bischari, have features, 
 skulls, and general form of body of perfectly Caucasian type ; 
 and the nesjresses give birth to lio-ht skinned children — a 
 proof, for those who take their stand upon the biogenetic law, 
 that their forefathers were light-skinned. 
 
 That I allow special importance to sexual admixture in 
 relation to the distribution of dark colouringof theskin,liair,and 
 eyes, I have already shown, since I pointed out that dark liair 
 
88 ACQUIRED CHARACTERS sec. 
 
 and eyes in Germany must be principally referred to this 
 process. But that tlie dark colour of the inhabitants of 
 hot countries cannot be explained by sexual admixture, any 
 more than the light colour of cave animals (see below), needs 
 no elaborate argument. 
 
 To me it is utterly incomprehensible, not so much that 
 views opposed to tlie relation of the sun to tlie dark colouring 
 of the skin are expressed, but that, without further investiga- 
 tion and reflection, any scientific importance is given to 
 them. To form a decisive judgment on the question one 
 must travel through a region like the Xile valley, which 
 forms a uniform, continuous, isolated, whole — not over 
 mountain and valley, which not only separate different tribes, 
 l)ut also afford sudden transitions in climatic conditions, and 
 with them in the habits of life of the inhabitants. The 
 perfectly gradual transition in the colour of the inhabitants 
 from brownish yellow to black in \X\^ Nile valley in passing 
 from the Delta to the Soudan is particularly conclusive as 
 evidence for my contention, for the very reason that various 
 races originally of various colours dwell there. The Berbers, 
 who live from the First Cataract southwards to Nubia, are as 
 a race much darker tlian the Egyptians. The anthropo- 
 logical separation of the two races is at the present day 
 perfectly distinct, and the difference between the languages, 
 except for one or two interchanges of words, is well-marked. 
 The traveller accustomed to the sound of Arabian, who has 
 learnt to make himself understood in that tongue, beyond 
 Assouan no longer understands a word of the language of the 
 natives. And yet the colour of the neighbouring Egyj^tians 
 passes into that of the Berbers, that is, the former at Assouan 
 are scarcely lighter than the latter, whose colour again towards 
 Wadi-Halfa is still blacker than at Assouan. Crossing between 
 the two peoples has of course to be considered, but it is not 
 the most important cause of the facts described. On this 
 
IV COLOUR OF INHABITANTS OF THE NILE VALLEY 89 
 
 subject I agree entirely with E. Hartmaun, who says, in his 
 book on The Races of Africa (Internat. Bibliothek, 1879, p. 
 9) : " Our travellers make too much of the contrast between 
 the light- coloured Egyptians and the dark Nubians. It 
 always seemed to me as if these gentlemen slept away the 
 time of the journey between Kene and Syene (Assouan). In 
 this district one sees transitions enough betw^een the two 
 types of people. This is not merely a result of the immigra- 
 tion and settling of Nubian families in Said (Upper Egypt), 
 but the inhabitant of Said as he gradually approaches the tropic 
 becomes darker, darkened by the sun, but also in consequence 
 of marriages with Berbers. So also the Nubian settlers in 
 the Nile valley possibly become gradually lighter under the 
 mild sun of Middle Egypt, partly also of course in conse- 
 quence of marriages with people originally lighter. But that 
 in such processes a certain adaptation to the physical and 
 climatic conditions of the district takes place, seems to me a 
 fact in natural history wliich cannot be denied." 
 
 That the black Berbers under the slightly greater mild- 
 ness of the Egyptian sun become lighter I should consider 
 not very probable. But I have traced step by step the 
 quite gradual increase in darkness in one and the same race, 
 in the Nile valley up to Dongola, as clearly as it can be 
 traced from Germany to Calabria. 
 
 Such observations on dark peoples, and on the intlu- 
 ence of the sun on colour, bring the significance of tlie 
 peculiarity of our Germanic race prominently into the fore- 
 round. There is no race among all the peoples of the eartli 
 wdiich is nearly as peculiar in the absence of dark colour in 
 the body-surface, and this to me is evidence that we Germanic 
 people had our original home in a very moderate climate, 
 indeed in quite northern regions.^ 
 
 1 It is true that the greater action of light in the north has favoured the 
 development of pigment in plants and in many animals, but this does not api-ly 
 
 or 
 
90 ACQUIRED CHARACTERS sec. 
 
 The physical cause of the dark colouring of tlie integument is 
 obviously that in consequence of the greater flow of blood to the 
 skin under the action of light and warmth, of their stimulation, 
 pigment is deposited there. I'ossibly in some cases greater 
 moisture has contributed to the result. An increased supply 
 of blood can etl'ect the deposition of pigment in particular 
 parts of tlie skin without the influence of light. This happens, 
 as Ave know, in woman round the nipples, in man on tlie 
 scrotum, in both sexes in the arm-pits and round the anus. 
 Dr. Passavant, known for his travels in the Cameroons, states 
 in his doctorate dissertation that in the negroes just those 
 parts which are least exposed to light are darkest, e.g. the 
 arm-pits, and he argues from this fact against tlie conclusion 
 that liLiht is the cause of darkness of colour in man. This 
 apparent contradiction finds a very simple explanation in the 
 above considerations. 
 
 Like the pigmentation of the human skin, and pigmenta- 
 tion in general, the formation of leaf-green (chlorophyll), the 
 green colour of plants, depends also on the influence of light. 
 But here the colour is not inherited by the offspring, for when 
 these are reared in the dark they remain colourless. 
 
 The profound action of light on the whole physical 
 constitution of the plant-body, on the whole physiology of 
 plants, is shown by the fact that many tropical plants, as for 
 example the South American species of Bougainvillea, in 
 European hothouses either do not bloom at all or only 
 incompletely in spite of all application of warmth, on account 
 of the deficiency of light.^ 
 
 And who would deny that action when he only thinks of 
 the influence which light exercises on the direction of growth 
 of plants, and therewith on their whole form ? 
 
 to northern races of mankind, ■who are not constantly exposed to this 
 action. 
 
 ^ Cf. Charles Martin's edition of the Philosophic Zoologique of Lamarck. 
 German, Jena, 1876. (In the biographical introduction by Martin.) 
 
IV ABSENCE OF COLOUR IN CAVE ANIMALS 91 
 
 To tliis cause I also ascribe the first commencement of the 
 vivid colours in the skin of many animals, e.(j. of reptiles, 
 which, clearly in consequence of the increased circulation of 
 blood, appear under a warm sun, and disappear under a low 
 temperature, and which with the aid of selection have 
 developed into the permanent brilliant colours in the skin of 
 southern animals. All the animals that pass their lives in 
 darkness must have become colourless in consequence of the 
 absence of light, since their nearest relatives which live in the 
 daylight are coloured. Absence of pigment is indisputably 
 an acquired and inherited character. No one will seriously 
 maintain that male and female individuals which chanced to 
 be slightly pigmented have everywhere crept into caves, and 
 there, in consequence of sexual mixture and selection, have 
 given rise to colourless races. 
 
 Weismann advocates the view that the absence of colour 
 in cave animals is due to pammixis, to indiscriminate sexual 
 mixture consequent upon the cessation of selection. But 
 how can selection have contributed to the evolution of the 
 oriojinal dark colourins; — what use can this have had ? Sexual 
 selection on the ground of beauty is out of the question in the 
 gloom of the caves. And the principal question is. Why is a 
 colourless race evolved everywhere in darkness by pammixis, 
 and not one of some other colour, green, yellow, blue, or red ? 
 Since we know that light is favourable to pigmentation as it 
 is to the development of chlorophyll, since we know that 
 pigmentation like chlorophyll universally vanishes in the 
 absence of light, we need, it seems to me, no other 
 explanation than that which lirst offers for the absence of 
 pigment in cave animals. Animals are in general more or 
 less colourless in the early stages of development, and ^•e^y 
 many are born light-coloured or colourless, and only sub- 
 sequently develop a dark colouring. This circumstance 
 evidently facilitates the loss of colour in cave animals : since 
 
92 ACQUIRED CHARACTERS sec. 
 
 the first offspring of tlie individuals which have betaken 
 themselves to caves are born with liizht skins and are no 
 longer exposed to the action of light, the later descendants 
 will very soon remain jDcrmanently light coloured. 
 
 Further, liow immense is the direct effect of warmth on 
 the vegetable world, and how obvious the inheritance of this 
 effect. Consider merely the characters of the flora in the 
 different zones of the earth. Quite different forms of plants 
 have been developed in the tropics than with us — yet 
 obviously in part essentiall}' through the direct influence of 
 the climate. Warmth and moisture have always, as at present, 
 stimulated tlie growth {i.e. the multiplication) of cells beyond 
 the limit which it reaches in colder climates, and this growth 
 necessarily produces new and more luxuriant developments. 
 
 The following example shows to what a degree increased 
 growth results directly in change of form : the luxuriant 
 slioots wdiich spring from the stumps of trees, e/j. elms and 
 other forest trees, which have been cut dowai, often bear leaves 
 wliicli have a quite different shape from those the tree usually 
 bears, so that they have quite a strange appearance. This is 
 the immediate effect of unusually increased nutrition; the same 
 roots which previously supplied nourishment to the whole 
 tree have now only to provide for a few shoots. If such a 
 shoot grows into a tree, this again bears the ordinary leaves. 
 And if most of the roots of the stump were cut away so that 
 the shoot was reduced again to the usual supply of nutrition, 
 then likewise the new leaves would revert to the ordinary 
 form. Certain characters wliich are directly conditioned by 
 better nutrition, and others connected with them by correla- 
 tion, must obviously again disappear with the cessation of the 
 condition — thus certainly hunger causes leanness and feeble- 
 ness, over-feeding fat and laziness. In any case, experiments 
 continued for a year or two prove nothing. It is another 
 question whether specially abundant nutrition continued 
 
i^' EFFECTS OF CLIMATE ON PLANTS 
 
 93 
 
 through several thousands of years does not produce constuni 
 characters in a species of plant, so that the species could no 
 longer exist if brought again under conditions more unfavour- 
 able to nutrition. 
 
 The directly modifying influence of climate is exliibited 
 most distinctly in our common plants. The resistance, for 
 example, of the plants of a single species to the influence of cold 
 or warmth is very variable. It is very surprising at what diff^er- 
 ent times trees of the same species in a wild state under tlie 
 same conditions develop their foliage in spring — for instance, 
 beeches growing close together in a wood. Years ago this 
 struck me particularly in the garden of the castle of Yeit- 
 shochheim, near Wurzburg, which is laid out in the rococo 
 style. The straight walks are there enclosed between hedges 
 of cut beeches like walls. In the spring, parts of the hedges 
 formed by certain beeches are already green, while parts 
 formed of others which stand between the former, and are 
 even mingled with them, have not begun to open their buds. 
 
 Every gardener knows that individual plants are more able 
 to endure cold than others of the same species under tlie same 
 conditions. Darwinism is satisfied with making use of such 
 differences to explain how they render selection possible, and 
 how they are increased by its means, but does not inquire into 
 their causes. Yet these differences cannot be due to chance. 
 There must be a peculiar condition of the tissues underlying 
 them, which peculiarity must ultimately depend on external 
 influences which have acted on the plants themselves or their 
 ancestors. For that such powers of endurance are inherited 
 no one, in the face of so many facts known to every fruit- 
 grower, will deny. 
 
 Perhaps the above difference in beeches, considering tliat 
 nearly every beech-wood with us is more or less artificially 
 planted, is due to the fact that the ancestors of the trees wliich 
 come into leaf at different times were derived from different 
 
94 ACQUIRED CHARACTERS sec. 
 
 stations in wliicli they had accustomed themselves to the pre- 
 vailing external conditions. That the trees themselves — even 
 in the ""arden of Veitshocldieini — came from different stations 
 is a less probable supposition. 
 
 "We can observe every spring in our gardens that the shrubs 
 Avliich belong to the south begin to l)ud later than our own — 
 thev are so accustomed to a certain sli^lit degree of warmth 
 that it has no effect upon them ; their tissue is indifferent 
 towards this degree of warmth, is not stimulated by it. It 
 may thus be assumed that plants whose ancestors grew in cold 
 stations have become accustomed to cold, whicli means in 
 physiological terms that tlieir tissues have gradually been 
 modified simply by the influence of climate. 
 
 In this manner many of our cultivated plants have ac- 
 climatised themselves in a high degree. There cannot well 
 be any doubt that the different kinds of summer and winter 
 corn are forms which, originating from one and the same 
 species, have not only gradually accustomed themselves to 
 ripen at different times, but have also acquired new mor- 
 phological characters. Very remarkable instances of such 
 acclimatisation are described by F. C. Schlibeler in Scandi- 
 navian plants, especially species of cereals.^ Schlibeler finds 
 that — 
 
 1. When various cereals in Scandinavia (Norway and 
 Sweden) are gradually transplanted from the plains to mount- 
 ain districts, they can be accustomed not only to develop in 
 the same, or even in a shorter time than in their native region, 
 but even at a lower average temperature. When sucli grain 
 after it has Ijeen grown for several years in the mountain 
 regions is again sown in its native soil, it ripens at first earlier 
 
 •■ F. C. Schlibeler, Virularlviii Xorceglcum. — Xorrjes ViLdrirjc. Et BUlrdjj til 
 Nord-Europas Naiur- off Kidturhistorie. Bd. i. Universitets-Programni. With 
 inunerous woodcuts in the text, and four maps. Christiania (Dybwad) 1885. Tlie 
 above extracts according to Foslie (Tromsu), Botanisches Centralhlatt, 1886. Bd. 
 xxviii. p. 205. 
 
IV OBSERVATIONS ON CEREALS 
 
 95 
 
 than other grain of the same kind which has been cultivated 
 uninterruptedly in the plains. 
 
 2. The same thing occurs when species of cereals are 
 gradually transplanted from south to north, even when tlic 
 warmth is less and the sky more cloudy than in tlie native 
 
 region. 
 
 3. The seeds of various plants increase up to a certain 
 degree in size and w^eight when the plants are transplanted to 
 the north, provided that they have attained their full develop- 
 ment. But they return to their original size when the plants 
 are again grown on their native southern soil. Similar relations 
 hold for the leaves of several trees and other plants. 
 
 4. Seeds wdiich have ripened in northern regions produce 
 larger and more vigorous plants, able to endure severe 
 weather better than those of the same species or forms which 
 are reared from seeds brought from southern districts. 
 
 5. The formation of pigment in flowers, leaves, and seeds 
 is greater (at least up to a certain degree) in the same 
 vspecies and varieties in northern than in southern lati- 
 tudes. 
 
 6. In plants in which certain organs are aromatic tliis 
 property increases as we go northward, provided that the 
 plants attain their full development, while the proportion of 
 sugar lip to a certain degree decreases. 
 
 From these facts, of which 3 and 4 are probably to be 
 explained by natural selection, it follows amongst other tilings 
 that my view, namely, that an organism is altered by the 
 continued action of definite external conditions, is fully 
 justified ; for the longer it is exposed to this action the less 
 will be its tendency to reversion. Thus also the Egyptian 
 varieties of wheat are certainly not exactly the same as tliey 
 were 4000 years ago, even although the change is not 
 expressed in their external form but only in tlieir constitu- 
 tion and their powers of life. For it is a proposition of special 
 
96 ACQUIRED CHARACTERS sec. 
 
 importance to my argument, as well as in itself self-evident, 
 that physiological changes must always precede morphological 
 changes of structure in the organic world, because the former 
 determine the latter. 
 
 T would draw particular attention to two results of 
 Schiibeler's experiments. 
 
 It is generally known that the formation of pigment, i.e. 
 the brilliancy of colour in plants, is greater in elevated regions 
 and in the north. Alpine plants afford evidence of this. This 
 phenomenon is to be explained in part by selection, for it is 
 clear that in the brief flowering period those plants will be 
 soonest fertilised by insects which have the most striking 
 colours witli wliich to attract them. But in consequence of 
 the shortness of the nights and the clearness of the sky, sun- 
 light has a more continuous and more powerful action on the 
 heifdits of mountains and in the nortli, notwithstandins; the 
 shorter duration of the summer, and there can be no doubt 
 that this directly contributes to the development of the more 
 vivid colouring. It has alwaj^s struck me how much the garden 
 and window-flowers of the houses in mountain districts surpass 
 the same kinds among ourselves in splendour of colour, and 
 this is a difference not due to insect selection. 
 
 But it is also a known fact that many species of animals, 
 especially of insects, which are found at a high level on 
 mountains have a darker colourincj tlian their allies at a loAver 
 level Thus tliere are remarkably dark species and varieties 
 of beetles occurring at high levels. 
 
 The great variation in colour of our common wayside slug, 
 Arion empiricorum, is universally known. The colour varies 
 from light yellowish red to deep black. In my publication 
 on the variation of the wall-lizard, in discussing the question 
 of the causes of darkness of colouring in lizards, I have 
 minutely considered this peculiarity, and I reproduce the 
 passage here because it contains references to other conditions 
 
IV MOISTURE AND DARKNESS OF COLOUR 97 
 
 which produce this character and further examples of the 
 inheritance of acquired characters in general. 
 
 "Leydig has pointed out that variation towards greater 
 darkness of colouring, the tendency to become black, is con- 
 nected with the action of moisture in the environment, liavin^r 
 observed this connection in the case of the dark variety of 
 Lacerta vivipara, of Amphibia/ and above all, of Arion 
 empiricorum.^ He observed that, besides Arion empiricorum, 
 other molluscs, e.g. Helix arbustorum, Succinea Pfeifferi, 
 Helix circinata, become darker than usual in moist localities. 
 In Arion the colour even changes in this way according to 
 the dampness or dryness of the weather : ' In early spring, 
 when the ground and the air are still very moist, all the slugs, 
 in places where later on in the year only reddish-yellow 
 specimens are seen, have a dark brown colour.' For instance, 
 in the cool and rainy May of 1873 and in June with cold 
 weather and heavy rains the slugs in the saturated forest 
 of the Spitzberg (near Tubingen) were of a deep black. 
 Numerous other instances of the dark colour of xVrion 
 empiricorum in moist places are given by Leydig. I can 
 confirm his statement that this slug under otherwise similar 
 conditions exhibits a dark colour in moist localities ; I found 
 that in the extremely damp summer of 1870 all specimens 
 were dark in places where at other times they were rather 
 light." 
 
 "Some years ago, however, I pointed out a relation be- 
 tween elevation of habitat and darkness of colour in Arion 
 which is inconsistent with the supposition that moisture has 
 an absolute influence in producing this character." ^ I observed, 
 for instance, that Arion empiricorum on the heights of the 
 
 ^ Leydig, Die anuren Bairachier, Bonn, 1877. 
 
 2 Leydig, Die Hautdecke und Schale der Gasteropoden, Arch.f. Naturgcschichte 
 
 von Troschel, 1876. 
 
 3 Wurttemhergische natiiric. Jahreshefie, Vortrcuj fjehalten im Vcrdn fur 
 
 vaterl. Naturkunde zit TiXbingen, 1878. 
 
 H 
 
«8 ACQUIRED CHARACTERS sec. 
 
 Eaiihe Alb {e.g. above Uracil), "where there is little water, 
 was generally darker than at its base in the well -watered 
 valleys. Down tlie descent into the latter the animals 
 became lighter and lighter ; and I found afterwards that 
 on all mountains on which I examined this species the 
 greater number of the specimens, or even all, were dark, 
 almost black, e.g. on the Schwarzwald, on the Harz, on the 
 Eigi, etc. 
 
 Ley dig states, on the contrary, that he found almost ex- 
 clusively Arion rufus on the dry heights of the Alb,^ but my 
 observations are confirmed by another excellent observer of 
 molluscs — Weinland, who found that Arion on the heights of 
 the Alb near his own home was usually dark, and never 
 reddish yellow as it so often is in the valley. " It might 
 be said," adds AVeinland, " that darker pigment is always 
 produced on mountains as in Vipera prester, the black 
 mountain variety of Vipera berus, as in the black rattle- 
 snake of the AVhite Mountains in North America." " But," 
 he continues, " the law does not always hold : near the 
 Hohe Neuften I found almost exclusively light -red speci- 
 mens." He attributes, therefore, the difference of colour to 
 adaptation, in which I am unable to agree with him.^ The 
 explanation of the contradictions is probably that both 
 moisture and elevation produce darkness of colour — both 
 causes may act together, and probably often do on mount- 
 ains, or great dryness may partially counteract the in- 
 fluence of elevation. More dark sIug^s ouoht to be found on 
 the heights in wet than in dry summers.^ It must also be 
 pointed out that in many localities all colours occur side by 
 side, which can only be explained by the individuality, and 
 
 ^ Op. cit. separate copy, p. 60. 
 
 2 Weinland, Zur Weichthierfauna der Schwcibischen Alb, Jahreshefte des 
 Verehis far vaterl. Xaturkundein Wurttemherg , 1876. 
 
 ^ Only black specimens of Arion are said to occur at Hamburg. Perhaps the 
 moisture always i^roduces this colour on the sea-coast. Compare the following. 
 
IV LOSS OF AROMA IN SOUTHERN FRUITS 
 
 99 
 
 the particular habits, the special liirkiug-places of the diilerent 
 specimens. 
 
 It seems to me, therefore, certain that moisture and eleva- 
 tion promote dark colouring directly and without tlie aid of 
 adaptation. Adaptation, in my opinion, in the case of our 
 native slugs is out of the question, for they are to be numbered 
 among the animals which, creeping over road and patli, 
 expose themselves openly and freely to the view of all the 
 world, as if exposing themselves intentionally in order to 
 proclaim : I am an uneatable, loathsome thing, touch me not. 
 
 But what is it that causes darkness of colour at hi'^li 
 levels ? Only tw^o causes, apart from moisture, seem to me 
 possible, either light or decreased atmospheric pressure. 
 Since the latter facilitates the flow of blood to the skin, it 
 might also promote the deposition of dark pigment. 
 
 In any case, elevation and moisture in various animals have 
 determined a permanent change of colour, which serves as one 
 of the characters by which species are distinguished.-^ 
 
 A second point to which I wdsh to refer in connection witli 
 Schlibeler's results is the increase in the aromatic flavour of 
 fruits towards the north. Pleasant to the taste as oran^jes 
 and figs are in Southern Europe, they do not, in my opinion, 
 by any means compensate for the loss in aromatic flavour 
 wdiich our native fruits undergo in the south. The wild 
 strawberries, equally with the cherries and apples, are in 
 South Italy almost absolutely tasteless. This is certahily 
 a change brought about simply by climate and soil, — just 
 as there is no wine in the world which equals good lihine 
 wine in fine aroma. 
 
 With regard to the acclimatisation of plants transferred to 
 new regions, and the modifications shown by Scliiibek'r 
 to be caused by the process, similar facts, as I have already 
 mentioned, are known in abundance to every fruit-grower, 
 
 1 Additioual proofs of tliis are given farther ou. 
 
100 ACQUIRED CHARACTERS sec. 
 
 indeed to every agriculturist. Cultivated plants of the most 
 difterent species are gradually accustomed to new stations, to 
 rich or poor soil, by being transplanted themselves or by the 
 planting of their progeny. The fruit-grower of a district 
 where the climate is severe will import his trees, no matter 
 of what species, not from a warm, but from a similar region, 
 if he wishes to make sure of their success. 
 
 Hundreds of examples supporting Schlibeler's conclusions 
 could be obtained in all directions. 
 
 The objection will be urged that in these artificial experi- 
 ments there is no formation of new species. In the preceding 
 pages I have already recognised the justice of this criticism 
 as a statement of fact. But I do not acknowledge it as a 
 valid basis for the proposition : that the fact that external 
 influences, that artificial cultivation, effect changes in animals 
 and plants which last as long as the influences themselves 
 proves nothing with regard to the action of external con- 
 ditions, to the inheritance of acquired characters, to the 
 modification of species. 
 
 All the results of cultivation which man successfully pro- 
 duces in plants and animals, and for thousands of years has 
 produced, prove rather most incontestably the fact that 
 acquired characters are hereditary. 
 
 Why permanent species have not been produced by such 
 results of cultivation, is a question by itself which I have 
 attempted to answer in the preceding. 
 
 In my opinion, to expect that effects which have been 
 obtained and maintained by artificial conditions continued 
 during a relatively short period should persist after the sudden 
 cessation of those conditions is to expect what is perfectly 
 unnatural and unphysiological. 
 
 Only by gradually bringing the organism slowly, step by 
 step, during a very long period of time, into new conditions 
 — if moreover the new conditions harmonised with the direc- 
 
IV EFFECTS OF TROPICAL CLIMATE 
 
 101 
 
 tioii given to the evolution— could the artificially produced 
 characters ^Dossibly be maintained. In Schiibeler's experi- 
 ments, by attention to the necessary requirements, artificial 
 characters were to a certain degree maintained. But nature 
 alone can completely satisfy these requirements. If we had 
 in our artificial experiments command of the measureless 
 periods of time which have been employed by nature, we 
 should be able perhaps in many cases to imitate artificially, 
 or even to surpass, her success in producing permanent 
 modification. 
 
 The facts, however, which are brought to light by study 
 of the gradual transformation in plants and animals seen in 
 passing from north to south, or from high to low elevations, 
 afford the clearest proof that climatic conditions have pro- 
 moted, i.e. have helped to produce that transformation ; and 
 the gradual transformation of extinct plant and animal forms 
 also points in the most definite way to such external causes. 
 
 This gradual transformation is in many ways so obvious 
 that its explanation becomes of secondary importance com- 
 pared with the problem of the causes of the separation of the 
 organic chain into species. That the chain was originally 
 continuous is proved by the fact that it can be actually traced 
 without interruption between widely separated limits among 
 extinct organic forms. 
 
 The tropical climate, however, certainly has exercised, 
 sometimes in a very short time, a direct influence on particular 
 characters of animals, especially on the integument, on the 
 thickness of the coat of hair, on the nature of the wool, etc. 
 This is demonstrated by authentic instances. 
 
 In India our races of dogs after only two generations lose 
 their distinc^uishino; characteristics ; thus, for example, in 
 pointers the nostrils become more contracted, the snout mure 
 pointed, the size smaller, the limbs more slender (Everest). 
 On the Guinea coast the ears of dogs become long and stiff, 
 
102 ACQUIRED CHARACTERS sec. 
 
 as in foxes, to wliicli they also approximate in colouring, so 
 that in three or four years they deteriorate into very ugly 
 creatures, and after three or four generations their bark 
 becomes a howl (Bosmann). In Paraguay the domestic cat 
 has become one-fourth smaller, its body is slender, its hair 
 short, shiny, thin, and pressed closely to tlie skin, especially 
 on the tail, which is almost naked (Rengger). 
 
 In the ]\Ialay Archipelago, and in Further India, the cats 
 have a stumpy tail of only half the usual length, and often a 
 kind of knol;) at the end of it (Crawfurd). 
 
 Also dogs in the tropics, according to several authorities, 
 often become thin haired. 
 
 The recrular summer and winter chano-es of the hair in 
 mammals are supposed by Darwinian reasoning to have been 
 gradually acquired by selection, no thought being given to 
 the ultimate causes of the phenomenon. But the facts above 
 stated seem to indicate that these causes are to be found in 
 the direct influence of climate, or rather in the changes in the 
 physiological condition of the skin produced by climate. 
 
 The fact that our mammals acquire a thinner coat of hair 
 in spring, a thicker coat in autumn, miglit also be due to 
 another cause, namely, that they are as a rule in a better 
 condition of nutrition in autumn than in spring. In that 
 case the changes of hair in our domesticated animals would 
 be an inherited acquired character. 
 
 In Porto-Santo the rabbits which have there run wild have 
 on the back red hair only occasionally mixed A\*ith black, or 
 black tipped hair. The throat and certain parts of the lower 
 surface are, instead of pure white, pale gray or lead 
 colour, the upper side of the tail reddish brown instead 
 of dark gray, the ears without a blackish border. In less 
 than four years a specimen imported into England from 
 Porto-Santo almost entirely lost the peculiarities of the race 
 (Darwin). 
 
IV EFFECTS OF IMPROVED NUTRITION 
 
 103 
 
 In New Zealand the climate is said directly to favour the 
 formation of a longer and stronger wool. 
 
 In more southern regions animals and plants have in 
 general better conditions of nutrition than in \\\q nortli, and 
 to these also, not alone to the effect of climate, must be 
 attributed the changes of form which they underf^o wlien 
 transferred from north to south. Of the importance of tlie 
 influence of nutrition on growth and change of form I have 
 already spoken.^ 
 
 I have only to add here that the increase in size of animals 
 of the same genus, and even of the same species, in passing 
 from north to south is sometimes in the highest de<"Tee 
 conspicuous. It is often then most clearly evident that where 
 this increase in size has been accompanied by the develop- 
 ment of other characters, the formation of new species has 
 become possible, and it is often a debated question in such 
 cases whether the changed forms are to be called new^ species 
 or not. I may mention in illustration the species of the 
 genus Scorpio, which in its smallest form as Scorpio germanus 
 occurs as far north as the Tyrol. I may mention further the 
 wonderful increase in size of the species of Julus and Scolo- 
 pendra towards the Equator. 
 
 I have minutely investigated and described an example of 
 such increase in size and change in colour, and of the char- 
 acters connected with these by correlation, in the common 
 lizard (compare below). 
 
 The acquired and inherited characters depending on nutri- 
 tion in our domestic animals are so well known and so obvious 
 that nothinfT further need be said about them. 
 
 A little careful consideration, however, will also show tliat 
 a large number of these characters must have arisen without 
 
 1 With reference to the effect of nutrition in the modification of forms, compare 
 especially what is said below on bees as an example of the importance of acquired 
 and inherited characters. 
 
104 ACQUIRED CHARACTERS sec. 
 
 any assistance from selection : ultimately, in fact, all of these 
 characters owe their oric^in either to the direct influence of 
 changed conditions of life, or to correlation. 
 
 I will mention some examples in which selection is excluded. 
 A particularly striking one has recently been communicated 
 to me bv a German landowner who is a laro-e breeder of 
 cattle and sheep. He assures me that by feeding the lambs 
 with powdered bones he has obtained in a few years a race of 
 sheep of much greater weight, more massive skeleton, and 
 larger in size than the original form. In this case selection 
 was not emj^loyed. 
 
 Another similar example is this, that the feathers of 
 domesticated ostriches, according to the statements of experts, 
 are heavier than the wild, and for this reason that the quills are 
 thicker. In consequence of this a given weight of the feathers 
 of domesticated ostriches fetches a smaller price than of 
 the wild. 
 
 Other examples of characters acquired and inherited 
 through cultivation without the assistance of adaptation I 
 shall brino- forward in the next section. 
 
 We have to consider next the already mentioned case of 
 the crustacean Artemia salina, as a proof of the change of 
 one species into another in a state of nature through a change 
 in the saltness of the water. 
 
 The little crustacean Artemia salina, which occurs in our 
 salt inland waters, acquires, through diminution of the saltness 
 of the water in which it lives, the characters of the fresh-water 
 genus Branchipus, among them a nine-jointed instead of an 
 eight-jointed abdomen; but through increase in the saltness it 
 becomes transformed into the species Artemia Milhausenii, 
 which lives in the Crimea, and this on diminution of the 
 saltness conversely into Artemia salina. 
 
 As with the Axolotl this single example alone speaks 
 forcibly in favour of the view I am advocating. 
 
IV TRANSFORMATIONS OF ARTEMIA 105 
 
 
 
 Herr Schmaiikewitsdi ^ observed that the transformation 
 into A. Milhausenii, M. Edw., in a lake in South Paissia, in 
 consequence of the increase of saltness, was completed after 
 an interval of three years. The latter animal differs from 
 A. salina chiefly by the absence of the caudal lobes. 
 Schmankewitsch has also produced the A. Milliausenii 
 through artificial cultivation, i.e. by rearing several genera- 
 tions of A. salina in water of increasing saltness. 
 
 The species of Branchipus into which Artemia salina is 
 transformed in consequence of the dilution of the salt water 
 in which it lives is Branchipus spinosus Grb. We have 
 here, therefore, a transformation not into a form which is 
 described merely as a distinct species, but into one which is 
 ascribed to another genus. 
 
 Branchipus has more somites than Artemia. It must be 
 regarded, compared with Artemia, as the phylogenetically 
 older form, and thus the transformation from Artemia into 
 Branchipus can be considered as a reversion. But not so the 
 transformation from Artemia salina into A. Milhausenii, for 
 the latter stands hioiier in evolution than the former. 
 
 o 
 
 Moreover, it is most remarkable that the saltness of the 
 water has also an effect on the duration of the development : 
 a higher proportion of salt retards, a lower accelerates it. 
 
 In other Crustacea also, in minute Daphni^, Schmankewitsch 
 observed similar changes as a consequence of the increase or 
 decrease of saltness. In my opinion, there can be no doubt 
 that, among other cases, the nature of the waters in which 
 they live has governed the evolution of new forms among 
 our fresh -water fishes. The species of Salmo in our fresh 
 waters, which are so nearly related to one another, are 
 evidently in part local forms, or they are obviously inlhi- 
 enced by the character of the water in which they live. 
 Especially noteworthy in this connection is tlie lake trout, 
 
 1 Zeitsch.f. wiss. Zoologie, Bd. xxv. Suppl. aud xxix. 
 
106 ACQUIRED CHARACTERS sec. 
 
 Salmo lacustris, as compared with the brook trout, Sahiio 
 fario. The epicure easily distinguishes the one from the 
 other. The hake trout has coarser flesh than the brook trout, 
 and also tastes somewhat peaty. The two forms also show 
 differences in the colour and marking of the skin, but the 
 specific distinction is generally founded principally on the 
 dentition of the vomer. Quite recently, Professor Klunzinger 
 has, certainly with reason, publicly embraced the view long ago 
 put forward by me, that both fishes are but one species. From 
 the influence of different habitats, the one living in lakes, the 
 other in the rapid waters of mountain brooks, they have become 
 so different that the}^ have been taken for distinct species, 
 notwithstandino- that it has ever been of the neatest difficulty 
 to discover any really definite distinction between them. 
 
 In a similarly slight degree does the salmon-trout Salmo 
 trutta differ from the lake and brook trout, so that we must 
 regard, with Klunzinger, this also as a " biological species." 
 
 The comparison of the American fauna with the European 
 shows a large number of curious parallel forms, i.e. several of 
 our species of animals have representatives in Xorth America 
 which are very similar to them, but which have so many 
 peculiar characters that they are described as distinct species, 
 or at least form distinct varieties. Thus the reindeer : Cervus 
 tarandus and C. caribou, Aud. and Bachm. ; Canis lupus, of 
 which orientalis as our, occidentalis as the American wolf 
 are distinguished ; Ursus arctos our brown bear, and Ursus 
 americanus and ferox in North America ; Cervus elaphus, 
 our stag, and C. canadensis, the Wapiti stag ; Bison europffius 
 and B. americanus, etc. 
 
 These relations of forms can only be explained on the 
 ground that the faunae of America and Europe were once 
 united by the connection of the two continents, and that they 
 have gradually formed two distinct groups from the difference 
 of the environment. It is also certain, as I have before men- 
 
IV THE A USTRALIAN FA UNA 
 
 107 
 
 tioned, that the American fauna, especially in regard to 
 markings, has remained at an earlier stage of evolution ; 
 thus the differentiation has been partly accomplished l.v 
 genepistasis. 
 
 Species representing one another in this way (vicarious 
 species) exist also, as is well known, in abundance in the 
 faunse of various parts of the world ; only both the separation 
 and the relationship are not as a rule so clearly expressed as 
 they are between the European and American forms. 
 
 The most striking example, how^ever, of the importance of 
 climate, character of the soil, and isolation in the mouldinf^ 
 
 o 
 
 of the organic world, is supplied by the very peculiar fauna 
 and flora of Australia. Australia affords us an enclosed area 
 of evolution in nature on a large scale than which no better 
 could be wished. Marsupial animals represent there the 
 most diverse groups of our mammals in a series of parallel 
 forms. There are marsupials which are proxies for our 
 Eodents, others for our Paiminants, and so forth, and these 
 have a dentition similar to that of the Eodents and Euminants 
 respectively ; nay more, the representatives of the Euminants 
 have a multiple stomach. 
 
 Darw^inism of course says this similarity has arisen 
 through selection based on the same requirements : since in 
 Australia no other animals except marsupials have developed 
 out of the lower forms, therefore the marsupials have adapted 
 themselves to the diverse possibilities of the country. In 
 other countries, however, the evolution of mammals proceeded 
 in various directions from the original marsupials, and so 
 arose the diversity of the mammalian kingdom. But, without 
 doubt, the direct influence of the uniformity of the Australian 
 area ought to be held responsible for the uniformity of the 
 animals and plants belonging to it, and the fact that the mar- 
 supials have assumed in their organisation similar relationships 
 to those of the other mammalian groups outside Australia is 
 
108 ACQUIRED CHARACTERS sec. 
 
 undoubtedly to be attributed partly • to the immediate 
 influence of the external world — for the becrinninos of the 
 
 o o 
 
 various organs appeared originally within and without 
 Australia independently, and have evolved themselves into 
 completely analogous structures. 
 
 Besides, we cannot say that other higher forms of life 
 could not have arisen in Australia, for new plants and animals 
 transported thither from other parts of the world get the 
 upper hand of the Australian forms and crowd them out. 
 
 One of my assistants, Dr. Vosseler, has made an observation 
 which, if the result is really due to the causes to which he 
 ascribes it, forms a noteworthy contribution to the view advo- 
 cated by me as to the causes of the transformation of forms. 
 
 Dr. Vosseler had at the beginning of the year 1886 (6th Feb., 
 that is now one and a quarter years ago) a number of fully 
 developed young Salamanders (Salamandra maculata) taken 
 from the oviduct of the mother. These he put into a spacious 
 aquarium for subsequent use, where he left some which 
 he completely forgot, and which therefore were not fed. After 
 the little creatures had remained thus over a year without 
 being properly fed (for the aquarium contained only Algae and 
 a few Infusoria) they were again found. In the whole of this 
 time they had only grown from three centunetres to five centi- 
 metres, and had not undergone any metamorphosis. They had 
 not quitted the water, although it was possible for them to do 
 so, and up till the present day they still remain in the water ; 
 they have retained the large gills, the long tail, and in 
 general all the characters of the larva?, and they lead an active 
 existence as aquatic animals. Investigation showed that 
 these creatures, which usually feed on worms, all kinds of larvie, 
 etc., had nourished themselves with Alsjae to2:ether with In- 
 fusoria. They had thus become almost complete vegetarians. 
 
 In other cases. Amphibians, which under natural conditions 
 lose their gills and change into exclusively air-breathing 
 
IV NUTRITION AND PIIYLETIC GROWTH 
 
 109 
 
 terrestrial animals, have been compelled to retain their ^A\\% 
 and remain aquatic by being prevented from leaving the water, 
 or at least from breathing much air directly, as for instance 
 when the vessel in which they were contained was covered 
 by a cloth. The success of such experiments shows Ijy 
 itself the important part which the direct influence of external 
 conditions plays in the modification of organisms. 
 
 The fact, if proved, that insufficient nourishment can cause 
 an organism to remain at a low stage of its normal develop- 
 ment, i.e. can retard its phyletic growth, just as bad nourisli- 
 rnent hinders the individual growth, would go very far to 
 justify the explanation of the evolution of forms as growth. 
 
 Indeed, nature affords instances which make it a priori 
 probable that inadequate nutrition may have this effect. 
 It is well known that the cockchafer takes three years to 
 develop in the south of Germany, four years in the 
 north. In South Germany every third year is a cockchafer 
 year, in the north every fourth. But it happens in South 
 Germany, after a long inclement winter, that in one region or 
 another even there the development is retarded by a year ; 
 and accordingly in localities which are adjacent but sheltered 
 in different degrees the cockchafer years are not tlie same. 
 In exceptionally warm summers even in the north the 
 cockchafers appear a year earlier ; these are the beetles which 
 fly in August and September. 
 
 The last period of its life beneath the earth the larva passes 
 in the chrysalis state. The change into the chrysalis takes 
 place usually in the early summer of the year which precedes 
 the appearance of the beetle. The variations of temperature 
 accelerate or retard the chrysalis stage. As the variation of 
 temperature, however, shortens or prolongs the feeding-time of 
 the larva, it may be assumed that the change of tlie voracious 
 larva into the chrysalis stage is conditioned partly by 
 nutrition. 
 
110 ACQUIRED CHARACTERS sec. 
 
 Now, the larval stage of the cockchafer certainly repeats 
 a stage in the ancestral evolution. And this example shows 
 that the ancestral evolution must have been retarded under 
 unfavourable conditions of temperature or nutrition — in other 
 words, that the evolution of the type was, like the individual 
 growth itself, conditioned by warmth and nutrition. 
 
 Moreover, it seems self-evident that a corresponding effect 
 must be ascribed to warmth alone, as is shown bv the influ- 
 ence of temperature on the period of development, in the most 
 various species, not only of larvae, but also of chrysalids, which 
 take no nourishment. I shall shortly have to speak at 
 greater length on the importance of warmth in the modification 
 of species. Previously I have to point out some facts which 
 show still further the influence of nutrition in the process. 
 
 Every boy knows that the butterfly called the "brown bear," 
 Euprepia caja, can be reared in various varieties, according to 
 the different nourishment wdiich is supplied to the caterpillar. 
 Here again the varieties which arise through change of 
 food are not fortuitous but perfectly definite. For the differ- 
 ences of the markings which numerous such varieties in my 
 collection exhibit are not irregular, but reveal, as in other 
 cases, quite definite directions of modification. 
 
 Other butterflies are also known on whose colourincr and 
 
 o 
 
 markings the food of the caterpillars has great influence. I 
 have special grounds for the conviction that many new species 
 have arisen through the caterpillars having been at one time 
 or another forced to accommodate themselves to a chancre of 
 food. In evidence of this is the fact that numerous very 
 slightly differing species of Vanessa, e.g. V. polychloros, xautho 
 nielas, 1. album, and urticic, lay their eggs on different plants. 
 It is natural to infer that in such cases the difference in 
 the quality of the food has been the cause of the origin of 
 different characters. 
 
 I have to consider now a special example, which I have 
 
IV COL UR - VA RIA TION IN THE CA T 
 
 111 
 
 carefully followed out, of the effect of a general change in the 
 external conditions, and particularly in the nourishment, on 
 the modification of organisms, another proof of the inheritance 
 of acquired characters. 
 
 Our domestic cat is certainly derived from the fawn- 
 coloured cat (Felis maniculata). The two cannot he distin- 
 guished, as I have proved in the journal HumMdt, 1886, 
 either by the skeleton or by any other really decisive criterion. 
 Still the fawn-coloured cat, apart from her yellow-gray colour, 
 seems to be somewhat more slenderly built and also to have 
 somewhat shorter and smoother hair than our domestic cat 
 usually has. The latter, moreover, in consequence of the 
 protection which it enjoys in the house, has gradually varied 
 much in colour and marking, while the wild (although amon^ 
 the Niam-Mam, according to Schweinfarth, it is half tamed 
 and replaces the domestic cat) fawn-coloured cat in Africa is 
 adapted to the colour of the desert, and has retained the 
 original transverse stripes, which so often occur even in the 
 domestic cat on a gray ground. This transverse striping and 
 gray colour is also evident in the wild cat, wliich, in my 
 opinion, is likewise to be regarded, not as a proper species, 
 but as a variety of the Felis maniculata domestica, which is 
 developing into a species. Special breeding, selection, has 
 evidently not been much applied to the markings of the cat 
 in Egypt^ where it has been domesticated from the most 
 ancient times. The pleasure of reproduction has been freely 
 permitted there to all cats ; scarcely any cats were killed, for 
 the cat was sacred. Thus we have in the variety of marking 
 in the house cat, not something produced by selection, but 
 somethincj which has arisen from the effect of external environ- 
 ment, firstly from the absence of selection, and ultimately from 
 some direct causes of modification. 
 
 I have pointed out that this variation also is not alto- 
 gether irregular, but exhibits certain fundamental lines. 
 
112 ACQUIRED CHARACTERS sec. 
 
 In still higher degree is this true, as I have shown, for our 
 domestic dogs. " The apparently innumerable varieties in the 
 markings of these animals — spots, dots, and streaks — are by no 
 means fortuitous, irregular, but can be traced back to a per- 
 fectly definite fundamental plan." ^ 
 
 Tliis fundamental plan of marking in the domestic dog and 
 the domestic cat of course approximates to the original mark- 
 ing, from which it is derived by the strengtliening and coal- 
 escence of parts, but as a whole it is something new. There 
 is evident in it (at least in the dog) a new definite direction 
 of evolution, which can only be due to causes connected witli 
 the domesticated condition. It is true that human selection 
 in the breeding of dogs must be directed to a certain 
 symmetry, even in markings. Dogs which have less of this 
 symmetry are less propagated, but in valuable races of dogs, 
 e.g. pointers, even this degree of selection is out of the ques- 
 tion ; and as the regularity of which I now speak, and which 
 I have demonstrated by figures in Humholdt, has hitlierto 
 been noticed by no one, and was unknown, therefore it could 
 not be an object to the breeder. I may remark in addition 
 that according to my observation the apparently irregular 
 spots in our cattle can be referred to a perfectly definite law. 
 For the dog and the cat, however, the remarkable fact comes 
 to notice, that the new plan in the markings has a certain 
 agreement in both, in both arose independently, through modi- 
 fication of the same parts of the original transverse striping 
 common to both. This striping can still be recognised as a 
 token of the original blood relationship between the dog and 
 the cat. 
 
 I have traced in detail this modification of the marking in 
 its beginnings in the street dogs of Constantinople, and hav^e 
 already published some remarks on it in the journals already 
 named. These dogs are evidently the immediate descendants 
 
 ^ Cf. Iluinboldt, and ZoologischerAnzeiger, loc. cit. 
 
IV THE DOGS OF CONSTANTINOPLE 
 
 113 
 
 of jackals. They were originallyjackal.swhich,undertlieprotL'c- 
 tion of the noble Mohammedan custom not to harm animals 
 but to cherish them and feed them, established themselves 
 in the neighbourhood of men in villages and towns, althou^rh 
 men did not domesticate them or assume ownership in them. 
 They are thus in perfect liberty. These dogs supply tlie best 
 proof of the truth of what I have before said, viz. that the 
 cessation of natural selection through the struggle for existence 
 in a natural state, and the positive influence of the environ- 
 ment of civilised life, are the causes which have produced the 
 new characters in these dogs. In place of the old jackal 
 colour, the yellow of the desert, and the traces of definite in- 
 herited markings upon this general colour, appear the begin- 
 nings of another colouring and of a new marking of spots, 
 the latter following the law which, with the help of the 
 explanation given by me in Hmiibolclt, can always be recog- 
 nised more or less distinctly in our domestic dog. Each dog 
 is on the occurrence of these changes apparently quite 
 different from every other, but in reality the dark spots are 
 constantly on definite portions of the skin, the light or white 
 spots on the intermediate portions. No man, no kind of 
 selection, has contributed to this result : for the dogs' sense of 
 beauty cannot be adduced in favour of sexual selection (in 
 which, in dogs, the sense of beauty scarcely plays a 
 part) in this modification : because the new characters, 
 making their appearance for the first time in spite of tlie long 
 continued inheritance of the old, are always irregular in com- 
 parison with these, and often have a positively ugly irregular- 
 ity. The ears of these Constantinople street-dogs occasionally 
 begin to show signs of drooping at the tips, a change which is 
 so complete in many of our races of dogs, e.g. in pointers, that 
 they have lost much in the sense of hearing by domestication. 
 This change is obviously due to the absence of the need to 
 use their ears, and to the cessation of selection in relation to 
 
 I 
 
114 ACQUIRED CHARACTERS sec. 
 
 hearing — an acute perception of sound is no longer so necessary 
 as in the natural state. But the reason why these dogs begin 
 to erect the tail and carry it upriglit, wliile the ancestral 
 jackal, like the wolf, carries it lianging down, is not so easy 
 to discover, although the fact could scarcely be explained as 
 a case of adaptation.-^ As a rule, the Constantinople dogs re- 
 tain not merely the exact shape of the jackal, the pointed 
 head, the narrow body, etc., but also the brownish yellow 
 ground colour, although they are spotted with black, or black 
 and wdiite. Occasionally, however, the black or white 
 becomes preponderant — dogs imiforndy black have come 
 under my notice, especially on the Asiatic side of the 
 Bosphorus, in Scutari. 
 
 In a journey through Eoumelia and Bulgaria over the 
 Balkans — from Constantinople to Adrianople, Philippopolis, 
 Sophia, and thence to Lom-Palanka on the Danube — 1 was 
 able to trace, I may say step by step, a transformation of the 
 brown, somewhat spotted jackal-dog into an ordinary domes- 
 tic dog, which is at first like the Pomeranian breed, with a 
 sliort compressed body and tail rolled up, and which, in con- 
 sequence of better nourishment, is large and strong, and more 
 uniformly coloured, most often white. The farther one passes 
 into Christian re<^ions — that is, the more the dog becomes a 
 house animal, the more does he show this transformation, of 
 which a great part is undoubtedly due to better nourishment — 
 in other words, to directly acquired and inherited characters. 
 
 I have to remark further that through these observations, 
 and through the study of ancient monuments, particularly of 
 those of the tombs in Athens, where the departed are con- 
 stantly represented with their favourite dogs, I have reached 
 the conviction that the Pomeranian is a breed directly derived 
 from the jackal, and must be considered one of the most 
 ancient breeds. All the dogs on those Greek monuments are 
 
 ^ See a subsequent passage. 
 
IV DOMESTIC DOGS 
 
 11 
 
 r 
 
 0> 
 
 Pomeranians. A breed equally ancient is the Eskimo do 
 which probably comes directly from the wolf. Both breeds 
 have retained the pointed, erect ears of their ancestors. 
 
 Apart from all this there is, it must be allowed, scarcely 
 an animal which affords a more perfect example of pammixis 
 than the street dog of the East— c.^. in Constantinople— and 
 the house cat. In the former pammixis, whicli in Dur dogs 
 is troublesome, is unchecked. The animals carry on their 
 family life on road and path in sight of every one. The 
 mother drops her pups in the most crowded streets of the 
 city, and lies suckling and warming them in the middle of 
 the path, without avoiding man, who, if he be a ]\Iohanimedan, 
 disturbs her not, but habitually steps aside and leaves her in 
 peace. 
 
 In spite of this pammixis in these dogs definite new mark- 
 ings, formed according to a law and identical with those of 
 our domestic dogs, have appeared, obviously in consequence 
 of new conditions of life. 
 
 Why a definite shape of body has not been impressed on 
 domestic dogs I will not decide. Eeasons are not far to seek. 
 In any case, a continual struggle still occurs between the old 
 shape and tlie new. The external conditions in the regions in 
 which the dog has been domesticated are very various. He has 
 been modified in verv different deejrees in these different 
 regions. Crosses between the separate stages of modification 
 are always taking place, and man constantly by selection 
 seizes upon the result of these unions. In the Eastern dog 
 also this strui^ole between old and new still occurs, but man 
 does not interfere in it; in the Eastern dog, therefore, tlie 
 new characters are least obscured in their beginnings : througli 
 this dog I was first led to tlie discovery of the law whicli the 
 markings follow. 
 
 Dogs thus show, in my opinion, that new characters are 
 due to external conditions and an internal direction of 
 
116 ACQUIRED CHARACTERS sec. 
 
 evolution, aud can be acquired and inherited in spite of all 
 panimixis. 
 
 Experiments ox the Influence of Temperature 
 
 ON Lepidoptera 
 
 The direct influence of warmth on the modification of 
 animals is further shown by the experiments of Dorfmeister 
 and "Weismann on butterflies.^ 
 
 Since the fourth decade of this century it has been known 
 that the two butterflies Vanessa Levana and Vanessa Prorsa, 
 formerly considered as different species, are really one and 
 the same. And, indeed, in these two forms of the same 
 butterfly we have two generations developed at different 
 seasons of the year. V. Levana is the winter form, V. 
 Prorsa the summer form. The chrysalis of Levana remains 
 dormant during the winter, the butterfly emerges in the 
 spring, breeds immediately, and its progeny go through their 
 whole development in tlie summer; from their chrysa- 
 lids emerge the V. Prorsa, whose progeny then pass the 
 winter as chrysalids, and in the spring produce the Levana. 
 These two forms of butterflies are differently coloured and 
 marked, and it is in complete agreement with many other 
 examples of the effect of warmth on the formation of pigment 
 in the integument, that the summer form (exposed to warmth), 
 Prorsa, is much more deeply coloured than the winter form 
 (exposed to cold), Levana. The former is deep black, the 
 latter brown-yellow in its ground colour. The characters of 
 the two also afford a very strong proof of the correctness of 
 my theory of the importance of correlation in the formation 
 
 1 G. Dorfmeister, " On the Effect of Different Degrees of Warmth applied 
 during the Period of Development on the Colouring and Markings of Butterflies," 
 Mitt, des naturwiss. Vereins fur Steiermark, 1864 ; and A. Weismann, 
 Studien zur Descendenztheorie, I. Udier den Saison-DimorjMsmus der Schmet- 
 terlinge, 1875. 
 
IV VANESSA PRORSA AND VANESSA LEV AN A 117 
 
 of new species; for tlie transition from one form to the 
 other is sudden and immediate, inasmuch as not one but 
 several new characters separate the one from the other. 
 
 The original form is obviously the Levana, which approxi- 
 mates in colour and markings to related species of Vanessa, 
 especially to Vanessa polychloros and c. album. The sunmier 
 form, Prorsa, shows nothing of this marking ; it has on the 
 two black wings a transverse row of light spots, and on the 
 anterior wing in addition to this row some white dots ; its 
 whole marking aiopears to connect it very closely with the 
 genus Limenitis. 
 
 If in the whole habitat of Vanessa Prorsa such climatic 
 changes were to take place that the form produced by cold 
 were no longer developed, then the Prorsa would alone remain 
 as a new species, which would be classed according to its mark- 
 ing rather among the species of Limenitis than among the 
 species of Vanessa above named, or would in any case take 
 a position completely separate from the latter. 
 
 Weismann has himself attempted to prove that their colour- 
 ing is not protective to butterflies during their flight, " because 
 the colour of the background against which they are seen is 
 continually changing, and because] their fluttering movement 
 would betray them to their enemies in spite of the most com- 
 plete adaptation to the background." He declared, on the 
 basis of his own observations, that butterflies are most liable 
 to be seized by their enemies when at rest with their wings 
 folded together, and especially at night ; in the latter case, 
 mostly by spiders. For this reason butterflies so often have 
 colourings and markings on the underside of their wings 
 which mimic the surface on which they settle. 
 
 In fact, who has not, in the attempt to catch buttertiies, 
 met with the experience that the insect suddenly vanished 
 from his sidit ? It had settled somewhere, and even with 
 the keenest sidit could no more be found. Even the common 
 
118 ACQUIRED CHARACTERS sec. 
 
 thistle butterfly (Vanessa cardui) shows something of the 
 kind, although not so completely as other species. As soon 
 as it has settled on the ground, as it does in play, with wings 
 folded together, it can only be discerned if it has been seen to 
 settle, or if, as it generally does, it flaps its wings. 
 
 It may be held, indeed, that butterflies are protected from 
 the beaks of birds which pursue them in flight by the size of 
 their wings, since a bird is more likely to bite a piece of 
 the wing than to grasp the body. 
 
 If I mistake not, another naturalist has already expressed 
 this view somewhere. Some years ago I came across a 
 peculiar proof of its correctness. On a hot summer's day I 
 was on the high plateau of the Swabian Alp ; far and wide 
 no water was visible, but at one spot in the field-path there 
 ran over it the outflow of a little spring, forming a shallow, 
 clear pool in the track. Here sat hundreds of butterflies, 
 all whites and blues, closely crowded together, drinking 
 thirstily. On my approach a number of birds (stone-chats) 
 flew from the spot, and when I came up I found a number of 
 maimed butterflies lying fluttering on the ground ; pieces had 
 been bitten from the winces of most of them — indeed the 
 wings were often torn to pieces before the birds succeeded 
 in crettino: the bodies of the butterflies, althouQ-h these were 
 sitting fjuietly on the ground. And only because they were 
 sitting on the ground had the birds been able to get their 
 bodies. 
 
 Thus the colour and marking of the upper side of the 
 butterfly's wing cannot be regarded as an adaptation, as a 
 protection against enemies. But there remains another 
 adaptation, that due to sexual selection : the colours and the 
 markings may be a sexual attraction. I am of opinion that 
 this is generally the case. Details of colour and marking, 
 however, as their sudden development shows, and as numerous 
 facts besides liave convinced me, are due to physiological causes. 
 
IV VANESSA PRORSA AND VANESSA LEV AN A 
 
 119 
 
 Such causes were assumed by AVeismann for the origin of 
 season-dimorphism, i.e. the formation of winter and sunmier 
 forms of animals.^ He tried accordingly, by raising the 
 temperature in winter, to rear Prorsa directly from tlie 
 offspring of Prorsa, and conversely, by lowering the tempera- 
 ture in summer, to rear Levana directly from the brood of Levana. 
 Similar experiments had already previously been made by 
 the Styrian entomologist Georg Dorfmeister. It seems, how- 
 ever, that such experiments have been even more widelv 
 made, for an acquaintance told me tliat as a boy he had 
 practised the same thing with his companions successfully at 
 his home in Darmstadt, and indeed on Vanessa Levana and 
 Prorsa. Weismann put chrysalids of Vanessa Prorsa, which 
 he had reared from the caterpillars of butterflies whicli 
 emerged in April, into an ice-box with a temperature of 10°- 
 12°. C. This temperature, however, was not low enough 
 to produce Levana again ; but the experiment succeeded so 
 far " that instead of the Prorsa form to be expected under 
 ordinary conditions most of the butterflies emerged as the so- 
 called Porima, i.e. as an intermediate form between Prorsa and 
 Levana, occasionally observed in nature, which possesses more 
 or less of the markinos of Prorsa, but still mingled with much 
 of the yellow of Levana." 
 
 As already remarked, the Levana, not the Prorsa, is the 
 original form. Weismann's figures of this single case again 
 seem to give support to my view that the males, as a rule, are 
 a stage in advance in evolution, and that therefore their 
 characters indicate those of the variety or species which 
 follows next in evolution. The male in the Levana figured 
 by Weismann in Fig. 1 has the greatest likeness to the 
 female Porima which passes through its male (Fig. 3) into the 
 
 ^ I would suggest instead of the Avord season -dimorphism, first used by 
 Wallace, which is in every respect monstrous, the word hora-dimorphism, or the 
 shorter expression season-variation. 
 
120 ACQUIRED CHARACTERS sec. 
 
 female of I'rorsa (Fig. 6). But as there are many more 
 intermediate forms than those figured by AVeismann, this 
 explanation requires furtlier confirmation. Afterwards Prorsa 
 chrysalids were placed by AVeismann in a temperature of 
 0°-l°.25 C. in the ice-chamber : out of twenty butterflies, fifteen 
 now changed into Porima, and amomj^ these were three which 
 w^ere almost indistin<^uishable from Levana. Five remained 
 unaffected by the cold and emerged as the summer form l*rorsa. 
 
 Dorfmeister had never applied such low^ temperatures, and 
 had only succeeded in obtaining Porima. 
 
 The converse experiment of Weismann to rear Prorsa from 
 Prorsa by raising the temperature succeeded, among forty 
 chrysalids which were kept in a forcing-house at 15°- 31° 
 C, only with four, of which three were Prorsa and one Porima ; 
 all the rest produced Levana in the next spring. 
 
 The majority of the species of our white butterflies 
 (Pierid?e) show very strikingly a winter and a summer form. 
 In the winter form of Pieris Napi the roots of the wings are 
 much powdered on the upper side. In this case Weismann, 
 by keeping the chrysalids of the progeny of the winter form 
 three months in the ice- cellar and allowing them to emerge 
 in the hothouse, obtained perfect winter forms. But there is 
 a variety of P. napi wiiich lives in the Swiss Alps, in the Jura, 
 and in the polar regions, and wiiich can be described as a 
 very dark form of the winter variety of Napi : P. Bryonire. 
 The male of Bryonire is almost exactly similar to the ordinary 
 winter form of ISTapi, from wiiich the female differs by the 
 gray -bro war powdering of the entire upper surface. In the 
 polar regions BryonioB is the only form of Napi ; in the Alps 
 (excepting some isolated regions) it is mixed with the or- 
 dinary Xapi. I agree witli AVeismann that Bryonife 
 must be the ancestral form of Napi, basing my opinion on 
 the fact that, as "VVeismann's figures show, a series exists 
 from the female of the former as starting-point through 
 
IV PIERIS NAPI AND PIERIS BRYONI^E 121 
 
 its male to tlie female of the ordinary winter form of Xapi, 
 through the male of the latter to the female, and so to the 
 male, of the summer form. Here also the males always show 
 the beginning of the new characters which distinguish tlie 
 next variety, which is one degree higher. The common Xapi 
 must therefore, according to this interpretation, he regarded 
 as a variety which has arisen from Bryoniie through tlie 
 influence of a warmer climate, as the commencement of a 
 new, wdth us the only, species. 
 
 AVeismann placed the chrysalids of Bryonire in a hot- 
 house at 15°- 30° C, but only BryoniaB emerged; he failed 
 to convert Bryoniae into ISTapi, as he had conversely, by the 
 application of cold, changed the summer form of Napi into the 
 winter form. 
 
 Thus in Levana, as in Xapi, the progeny of the cold form 
 are converted by cold again into the cold form, but only ex- 
 ceptionally the progeny of the warm form into the warm 
 form. In other words, the application of cold had an effect, 
 the application of warmth generally none. 
 
 But in summer two generations of Prorsa occur. The first 
 takes flight in July, the second in August. The latter sup- 
 plies the chrysalids which form the Levana after the winter, 
 and which Weismann could only exceptionally, through 
 warmth, chano^e as^ain into Prorsa. Weismann concludes 
 from this that different reactions follow the same stimulus, 
 and that this difference can only lie in the physical nature of 
 the generation operated on, not outside it. According to him, 
 cold and warmth are not the direct causes of the origin of the 
 Levana and Prorsa forms, but only the indirect. The change 
 of the progeny of the cold form back again into the cold form 
 throucjh cold he refers to reversion to the ancestral form. 
 
 The origin of Prorsa is explained as having occurred 
 gradually through the gradual rise of the warmth of the 
 climate, i.e. of the summer. As the Levana is the ancestral 
 
122 ACQUIRED CHARACTERS sec. 
 
 form of I'rorsa it cannot revert to I'rorsa, and therefore the 
 hitter is not produced artificially. Weisniann further argues 
 that the different Trorsa ijenerations must liave different 
 physical constitutions, because the later of the two cannot be 
 converted by warmth into I'rorsa. 
 
 In answer to this, it is to be remarked tliat it was this 
 second generation of Prorsa which in one case on the applica- 
 tion of warmth again produced some I'rorsa ("Weismann's 
 experiment, 10 A). And thus the hypothesis of reversion 
 breaks down and that of the direct influence of warmth is 
 proved. 
 
 Dorfmeister, however, has, as will be discussed in the fol- 
 lowing, by the application of warmth produced Prorsa out 
 of Prorsa. 
 
 If warmth had less influence than cold there might be an 
 explanation for it. AVeismann goes on the assumption that 
 artificially applied warmth affords the same stimulus as the 
 natural. I am of opinion that this is not to be expected. At 
 least in artificial experiments the effect of the light of 
 summer is w^anting. Further, the duration of the period of 
 development in them has always been longer than in the case 
 of the warm forms under natural conditions. Besides, the 
 natural rise and fall of temperature, and in general the 
 naturally effective degrees of warmth as well as the effect of 
 radiant heat, cannot be imitated. So that the stimulus of 
 artificial warmth is not the same as that of natural. In the 
 case of cold the conditions are much simpler. 
 
 In actual fact, however, Dorfmeister's experiments show 
 that artificial warmth has the same effect as natural. 
 
 Taking all in all, from the facts already detailed, in my 
 opinion, the simple conclusion follows, that it is obviously 
 the action of warmth which in the natural state originally 
 produced one form of butterfly out of another, and that adap- 
 tation had nothing to do with the matter. 
 
I V THER SEASON- VA RIE TIES 
 
 123 
 
 There are still other butterflies known which liave a 
 summer and a winter form which were formerly believed to 
 be distinct species, cjj. the two blue forms, very different in 
 marking and in size, Lyca^na Polysperchon and L. Amyntas, 
 as shown by P. C. Zeller^ by rearing experiments; furtlier, 
 the white forms belonging to the Mediterranean shores, An- 
 thocharis Belia and A. Ausonia, as shown by Dr. Staudinger.- 
 
 Weismann speaks of five such species. But there are 
 more whose winter and summer forms were formerly described, 
 not as species, but as varieties. Weismann mentions twelve. 
 Among these are several of our commonest white butter- 
 flies, and also the commonest of our blue species, Lycaena 
 Alexis, in which the differences between winter and summer 
 form are very small. I may add that the sail -butterfly 
 (Papilio Podalirius) forms a southern darker variety, P. Feist- 
 hamelii Dup. (South Europe, North Africa, West Asia), and 
 that this produces in Algiers a second peculiarly marked 
 generation, the P. Letteri, Const. 
 
 The American butterfly Papilio Ajax wherever it occurs 
 appears in three varieties, viz. var. Telamonides, Walshii, 
 and Marcellus. The American entomologist Edwards has 
 shown by breeding experiments that all three belong to one 
 cycle of development, and that Telamonides and Walshii 
 emerge only in spring, while Marcellus occurs only in summer, 
 and in three successive generations. Marcellus is therefore 
 the form produced by summer, that is, by warmth. Tela- 
 monides and Walshii, according to Weismann, are to be 
 regarded as the ancestral forms. Of these Telamonides is 
 considered to be due to "imperfect reversion," like Porima. 
 Walshii as the original form of the species. Edwards records 
 that out of fifty pupse of the second summer generation of 
 
 ^ Stett. entomolog. Zeitsch. 1849. 
 
 - Ibid. 1862 : " The Species of the Lepidopterous geuus luo, with Keniarks on 
 Local Varieties." 
 
124 ACQUIRED CHARACTERS sec. 
 
 Marcellus forty-five produced Marcellus imagines after four- 
 teen days, and five did not cliange until April of the next 
 year, and then into Telanionides ; of the pupie of each of the 
 three summer generations only a portion produced butterflies 
 after a short period (fourteen days) ; another much smaller 
 portion did not change till the following spring, and then into 
 the winter form. Weismann concludes from this that " here 
 there is no doubt that, not external conditions of various kinds, 
 but purely internal causes determine the retention of the 
 long-inherited direction of development, for all the larv?e and 
 pupie of the many different broods w^ere exposed simul- 
 taneously to the same external influences." 
 
 This statement, in my opinion, is probably to be thus 
 altered : The external conditions cause, as a rule, the repro- 
 duction of tlie parent form, but on some individuals the 
 summer warmth has not sufflcient influence ; they do not 
 develop before the wdnter, and the winter cold, i.e. the absence 
 of warmth and light, then determine the emergence of the 
 cold form. It is a question, therefore, obviously of the dif- 
 ferent sensitiveness of the individuals in regard to external 
 influences, a difference which is equally striking in the meta- 
 morphosis of the Axolotl, in wdiich also some individuals are 
 more prone than others to change into Amblystoma. 
 
 In the highest degree noteworthy for my views, however, 
 is the fact already pointed out, that as in the Axolotl, so in 
 these butterflies, there are not a large number of transitional 
 forms in the metamorphosis side by side, but that in every 
 case when transitional forms do occur they form distinctly 
 separate stages. Only when the ancestral and the new form 
 live side by side and interbreed, as with Bryonia3 and Napi 
 in the Alps and tlie Jura, do the varieties show intermediate 
 forms. In Lapland, on the contrary, BryoniaB is constant. 
 The intermediate form Porima is a great rarity in nature as 
 in experimental breeding. 
 
IV INTERPRETATION OF THE FACTS 
 
 12; 
 
 Weismann, regarding tlie reappearance of the cold variety 
 as a reversion, not recognising the direct influence of cold, but 
 rather postulating internal causes, attempts to discover otlier 
 causes which might likewise determine this reversion. And 
 he believes he can point out warmtli and mechanical move- 
 naent as such additional causes. 
 
 In the summer of 1869 great heat prevailed at the time of 
 the development of the second summer generation of Levana- 
 Prorsa. From a batch of this generation an unusually lar^^e 
 proportion of Porima were developed (out of sixty to seventy, 
 eight to ten.) 
 
 As Porima is half way to the cold variety, the fact is to 
 me very incomprehensible, and I should suppose that other 
 causes than the extra warmth determined the formation of 
 Porima, for to assume this as the cause would be to com- 
 pletely contradict all the facts previously detailed. 
 
 In another case, a number of Pieris Napi, although they 
 had been reared in a heated room, all emerged in the following 
 spring as the winter form. But the pupae had made in the 
 summer a seven hours' railway journey ; and so the shaking 
 on the railway is taken as the cause of the reversion in this case. 
 
 Unable as I am to grant that causes so completely opposite 
 as warmth and cold have the same effect in the modification 
 of forms, I am equally unable to agree that such difterent 
 causes as warmth and mechanical shaking produce the same 
 result. Since w^armth has obviously, under natural conditions, 
 determined the transformation into new forms in the cases 
 previously discussed, I shall hold for the present that only 
 cold has the power of causing a reversion to the original form. 
 That effect of warmth, under natural conditions, which con- 
 sists in the formation of new varieties which are so distinct 
 that they have been in many cases long regarded as species, 
 has been evidently a direct effect. And it would need, as I 
 before pointed out, only a slight change in the external con- 
 
126 ACQUIRED CHARACTERS sec. 
 
 ditions, or a change in the sexual products arising by 
 correlation, to produce from such varieties absolutely separate 
 species, or to exterminate one of them. 
 
 It is in complete accord with this hypothesis, and witli my 
 whole view of the origin of species, that the variety Bryoniae 
 is in the far north a constant sharply defined species. There 
 are other sucli cases of great interest. Anthocharis Bella 
 and Ausonia were first recognised as the summer and winter 
 form of the same species by Staudinger. They live on the 
 shores of the ^Mediterranean, extending to the middle of France. 
 In the mountains of the Yalais in the neighbourhood of the 
 Simplon Pass the winter form is alone produced. A second 
 generation is not developed in the short summer, but all the 
 pup?e remain througliout the winter. Here also, as in Bryoni?e, 
 my claims as to the effect of external conditions are com- 
 pletely fulfilled, whether Ausonia and Bryoniae, as Weismann, 
 supposes, are or are not survivals from the ice-age in the 
 localities in question. 
 
 Polyommatus Phlseas L., the blue butterfly so common 
 with us, which ranges from Lapland to Sicily, has in Lapland 
 only one generation in the year, in Germany two. But only 
 in South Europe do these two generations differ from one 
 another, in Germany they are still similar. 
 
 Another blue form, Lyc?ena Agestis, has a twofold season 
 variation : " The butterfly occurs in three forms : A and B 
 alternate in Germany as winter and summer form, B and C 
 are the winter and summer form in Italy. Thus the form B 
 occurs in both climates, Init appears in Germany as the 
 summer in Italy as the winter form. The German winter 
 form A is completely wanting in Italy, w^hile the Italian 
 summer form (var. Allous) does not occur in Germany." 
 Here we have plainly a little chain of modifications obviously 
 produced by climatic conditions, in which adaptation plays no 
 part, and for wliich only the views on the causes of modifica- 
 
IV WEISMANN'S EXPLANATION 
 
 12; 
 
 tion whicli I maintain give a satisfactory explanation. :\Iy 
 works on the affinities of butterflies will bring to lifrht 
 numbers of such species evidently produced by climatic 
 influences, which are obviously connected but distinct from 
 one another. Here I have intentionally discussed tlie ex- 
 amples brought forward by Weismann, firstly, in order to 
 use his results for my argument as those of an impartial 
 witness ; and secondly, in order to introduce the agreements 
 and the differences between my explanations and his. To 
 these examples of the effect of climate on the formation of 
 butterflies, may be added that of Pararge Egeria, which in 
 South Europe appears in the variety Meione. Meione, how- 
 ever, is connected with Egeria by an intermediate form of 
 the Ligurian coast, which does not produce a summer and 
 winter generation. 
 
 In a separate chapter on " The Nature of the Causes of 
 Change " Weismann lays stress on the case of Polyommatus 
 Phl?eas as show^inii; that climate, and not the duration of 
 development, determines the formation of climatic varieties. 
 But, he proceeds, the nature of the change essentially depends 
 on the organism itself, not on the warmth to whicli it is 
 exposed. It is not the quantity of the black pigment pro- 
 duced which distino'uishes the summer from the winter form, 
 but the mode of its distribution on the wings. Under the 
 influence of warmth arise quite different markings : starting 
 from the markings already present, quite new ones are 
 developed, or, "as I may express it in other words, the 
 direction of evolution of the species is quite altered. The 
 complicated chemico-physical processes in the metabolism of 
 the dormant pupae are gradually altered until they result in 
 a new marking and colouring of the butterfly. That in these 
 processes the constitution of the species plays the chief i^arl, 
 and not the external agent warmth ; that the latter rather per- 
 forms the function of the spark which, as Darwin appropriately 
 
128 ACQUIRED CHARACTERS sec. 
 
 expresses it, sets fire to the explosive substance, while the 
 nature and extent of the explosion caused depend on the 
 quality of the explosive material — this is proved by many 
 other facts. Were it not so, increased warmth would 
 necessarily in all butterflies change a given colour always in 
 the same way, always into the same otlier colour. Tliis is not 
 the case; for while Polyommatus I'liLneas becomes black in the 
 south, Vanessa Urticiie, wliicli is likewise red, becomes blacker 
 in the north ; and many other examples well known to 
 entomologists can be adduced as evidence. On the other 
 hand, we find conversely that species of similar physical con- 
 stitution, that is to say, species nearly related, under the same 
 climatic conditions change in an analogous way." Of this 
 our white butterflies are mentioned as examples. "But 
 nothing can more strikingly prove that here everything 
 depends on pliysical constitution than the fact that in some 
 species the male individuals change differently to the female." 
 The females of Bryonite have undergone through climate a 
 crreater chanf^e than the males,^ the converse is the case in 
 Phlieas. 
 
 " The external influences were exactly the same, but the 
 reaction of the organism was different. ... I bring this 
 specially forward because, in my opinion, Darwin ascribes 
 too great an influence to his sexual selection when he refers 
 to that alone the formation of secondary sexual differences. 
 The case of Bryoniie teaches us that the latter can appear 
 from purely internal causes, and, until experiment has sup- 
 plied some fixed point as to the extent of the influence of 
 sexual selection, the view is justifiable that the sexual dimor- 
 
 ^ In answer to this I must point out tliat the warmth variety, P. Xaj^i, is the 
 newer, Bryonise the ancestral form. On my view of male preponderance the 
 female Bryonise must be the farthest removed from Napi, and the male Napi the 
 farthest evolved. So it is true that the female of Bryonise and the male of Napi 
 are at the greatest distance, but it is the latter, not the former, which has been 
 most changed by climate. 
 
 1 
 
IV EARLIER AND LATER VIEWS OF WEISMANN 129 
 
 phism of butterflies has its causes in great part in the diller- 
 ences in physical constitution of tlie sexes. It is quite 
 another matter in the case of those sexual characters whicli, 
 like the voice of male grasshoppers, have an undoubted im- 
 portance in the relations of the sexes. These can certainlv 
 with greater probability be derived from sexual selection." 
 
 Eegretting as I do that my views are so mucli in opposi- 
 tion to those of Weismann, it is some consolation to me tliai 
 this opposition essentially applies only to his new views, not 
 to his old, which latter in very important points agree witli 
 mine. From the quotation just given this is sufficiently 
 evident, and I myself could not find better cases in support 
 of my views than those there brought forward ; nor could 1 
 more distinctly oppose the excessive estimation of sexual 
 selection than Weismann formerly did when criticising 
 Darwin. And yet Darwin attributed to that process an 
 importance but very slight in comparison to the omnipotence 
 with which Weismann to-day endows it, notwithstanding 
 that the experiments desired by Weismann in the above 
 passage are yet to be made. The great agreement between 
 many propositions of Weismann's earlier theories and my 
 view strikes me now most forcibly as I read his treatise 
 again for the purpose of this discussion of the question 
 of the effect of climate on the modification of forms. In the 
 sixth section of this treatise, under the heading of general 
 conclusions, Weismann even makes the statement that differ- 
 ences of specific value can arise entirely through the influence 
 of external conditions of life. He believes that species- 
 formation, at least in Lepidoptera, has taken place to a large 
 extent in this way, and among them more than other animals, 
 because the conspicuous colours and markings of the wings 
 and body are without biological importance, that is, are of no 
 use for the preservation of the individual, and therefore of the 
 species, and thus they cannot have come under the operation 
 
 K 
 
130 ACQUIRED CHARACTERS sec. 
 
 of natural selection. He says that it is on tliese grounds that 
 Darwin sought to derive the markings of butterflies, not from 
 ordinary, but from sexual selection ; but that sexual selection 
 in the origin of the colours of butterflies can be dispensed with. 
 He then raises the question whether species of Lepidoptera, 
 in so far as they arise through changes of climate, only alter- 
 nate between two forms — a cold-form and a warmth-form — or 
 whether each new chanije of climate does not rather, if it be 
 pronounced enough to cause a modification, give rise to a new 
 form. In the previous pages I have contended against the 
 view wliicli AVeismann now liolds on this important question, 
 that tlie alternation of external influences must hinder the 
 modification of species, forgetting that Weismann himself has 
 formerly upheld my view at least in respect of the changes of 
 climate. He says : " I believe that the old forms are never pro- 
 duced again by alternation of climate, but always still newer 
 ones ; that therefore a periodically repeated change of climate 
 is by itself sufficient in tlie course of a long period of time to 
 produce a series of successive new species. . . . The climate, 
 when it has acted in the same manner on several genera- 
 tions one after another, will f^raduallv brines about an altera- 
 tion in the physical constitution of the species whicli 
 will make itself visible by an alteration in colour and 
 marking. Now, when this newly-acquired physical constitu- 
 tion of the species, which we will suppose has been firmly 
 established by inheritance through a long series of generations, 
 is subjected again to a permanent change of climate, this 
 latter, even if it be exactly the same as at tlie time of the 
 first form of the species, cannot possibly bring back that first 
 form. The nature of the external influence is the same, it is 
 true, but the constitution of tlie species is by no means the 
 same. Just as a white butterfly, as was shown previously, 
 exhibits quite other alterations than a blue or one of the 
 Satyridai under the influence of the same change of 
 
IV DORFMEISTER'S EXPERIMENTS 
 
 131 
 
 climate, so must the modification which is produced i'roni 
 the transformed species of our example after the return of 
 the first climate be different — though perhaps in a less 
 degree — from the original form of the species. In otlier 
 words, if in succeeding geological periods only two different 
 climates alternated on the earth, yet from every species of 
 butterfly subjected to this alternation would be derived an 
 endless series of different species. In reality the variety of 
 climates must have been much greater, and climatic changes 
 for a given species have taken place, not only throuyli 
 periodical variations of the ecliptic which may be assumed 
 to occur, but through geological transformations, and also 
 through migrations of the species itself. Thus from tliis 
 sincjle cause — variation of climate — a continual chan^'c of 
 species must have taken place. When we reflect that species 
 extinct elsewhere must have survived locally, and add to 
 these those local forms which owe their oricjin to amixis/ we 
 cease to be astonished at the enormous number of species of 
 Lepidoptera which w^e find on the earth at the present day." 
 
 It is unnecessary for me specially to point out how dis- 
 tinctly the above passage, which so exactl}^ agrees with my 
 own views, implies the recognition of the inheritance of 
 acquired characters. 
 
 Dorfmeister has, he tells us, ever since 1845 made experi- 
 ments on the effect of temperature on the colour and marking 
 of butterflies. He explains first of all that through many 
 years' experience in rearing caterpillars he has been convinced 
 that the production of varieties of butterflies depends mucli 
 more on climatic conditions, in which temperature is a chief 
 factor, than on either food or hybridisation. Dorfmeister learns 
 from his experiments that temperature exercises the greatest 
 influence on the colour and marking of butterflies when it 
 
 1 Cessation of interbreeding. Pammixis^indiscrinuiiate interbreeding. 
 
132 ACQUIRED CHARACTERS sec, 
 
 acts Upon them during the change into the pupa, or shortly 
 afterwards. In many a rise of temperature produces a lighter, 
 more brilliant ground-colour, a fall a darker or less brilliant ; 
 for examjile, in Vanessa lo, UtriciTe, etc. In Euprepia Caja 
 the red-yellow ground colour of tlie posterior wings is changed 
 by a rise of temperature into vermilion-red ; by a fall, into 
 ochre-yellow. 
 
 Dorfmeister considered the A^anessa Prorsa, on account ot 
 the slighter definition of its marking, to be the lower form. 
 The marking of Levana is much more complex, and much 
 more finely delineated. But as the simple Prorsa is in fact 
 the higher form, it affords a perfect example of the proposi- 
 tion sustained by me in opposition to Nageli, that simplifi- 
 cation of characters can appear in new forms. 
 
 The chief result of Dorfmeister's experiments is just this, 
 that he has obtained Prorsa, with its simple colours and 
 marking, by means of warmth from Prorsa, and in fact from 
 the summer generation of Prorsa which takes flight in August. 
 Thus in his hands the experiment, which in Weismann's with 
 few exceptions failed, repeatedly and abundantly succeeded. 
 On the other hand, he was unable to rear the cold form from 
 the cold form. 
 
 Dorfmeister draws no particular inferences from his results. 
 He refers finally to the necessity of completing his experi- 
 ments, and emphasises his inability to decide whether the 
 modifications obtained be the direct consequences of the rise 
 of temperature, or only indirect, depending on the shortening 
 of the period of develoi)ment caused by the increased tem- 
 perature. 
 
 But it seems to me to follow decisively from the cases 
 recorded by him that the greater the warmth he applied, 
 and consequently the quicker the development, the darker 
 the colour and the simpler the marking of the Prorsa forms 
 he obtained, and therefore the farther removed they were from 
 
IV ARTIFICIALL Y PROD UCED FORMS 
 
 133 
 
 the Levana. In the case in which he got the darkest and 
 the simplest Prorsa lie applied a still higher temperature tlian 
 Weismann, although only for a short time : the caterpilLars, as 
 soon as they had hung themselves up to change into the 
 pupa stage, "were exposed in the morning on a part of the stove 
 to a maximum temperature of 32°. 5 C. and towards midday 
 had become pupa?;" they afterwards developed in the room. 
 
 Since the pupa, which under natural conditions produces 
 Prorsa, has a dormant period of only a few days, while that 
 which produces Levana has one of six months, Dorfmeister, by 
 increase of temperature and the consequent abbreviation of 
 the period of development, has simply imitated the effects of 
 summer. 
 
 But the fact which appears to me of the utmost importance 
 is that Dorfmeister, from different temperatures and different 
 periods of development, has obtained a wliole series of 
 stages of modification between Levana and Prorsa, wdiile sucli 
 intermediate stages under natural conditions very rarely 
 occur. He himself remarks that during more than forty years' 
 collecting he met with only one specimen of such an inter- 
 mediate stage in the wild state, in places where Levana and 
 Prorsa were quite common. The rarity of the intermediate 
 forms (called Porima) is evidently the reason that Levana and 
 Prorsa have been considered distinct species. Under natural 
 conditions, therefore, there is obviously as a rule only one 
 average of summer temperature which produces the ordinary 
 Prorsa. But Dorfmeister has by the application of tempera- 
 tures beneath this average in a few experiments artificially 
 produced a whole series of such transition stages. These 
 stages can be divided into two groups — (1) those which must 
 be described as transition forms between Levana and Prorsa ; 
 (2) those which are different stages of Prorsa. Tlius, wliile 
 the latter were produced by the highest temperature and 
 the shortest period of development, the former were reared 
 
134 ACQUIRED CHARACTERS sec. 
 
 after the action of moderate warmth from the same second 
 generation of Prorsa. Dorfmeister kept caterpillars in process 
 of changing into pupa3, or the pupie themselves, twenty-two 
 days at a temperature of 12°.5 C, and then let them develop 
 in the room. A portion of these pupa3, which belonged to the 
 second Prorsa generation, emerged the same autumn, another 
 portion, like Levana, in the following spring. The former 
 were intermediate between Prorsa and Levana (Porima) in two 
 stages, the latter were Levana partly approximating to Porima. 
 
 The Prorsa obtained acjree with forms which also occur in 
 natural conditions. I find them all in my collection. AVhether 
 this is true for the various Levana or Porima forms I cannot 
 say. The possibility that artificial varieties are produced 
 which do not occur under natural conditions is meanwhile 
 not excluded. 
 
 If I interpret Dorfmeister's experiments rightly, it is 
 possible to satisfy the greatest demand that can be made as 
 to the influence of external conditions on the modification of 
 organisms ; it is possible to call forth, thermometer in hand, 
 definite varieties which are possibly absolutely new, not occur- 
 rinij under natural conditions. 
 
 T cannot sufficiently emphasise the fact that the warmth and 
 cold forms of Prorsa and Levana, differing as they do, not by 
 one, but by several new characters, together afford the most 
 conspicuous example of the correlative, " kaleidoscopic " origin 
 of new forms. 
 
 This fact leads at once to a question closely connected 
 with it, namely, whether such discontinuous modifications 
 depending on external influences are not only apparently dis- 
 continuous, whether they are not stages in the course of a 
 modification of the species which once proceeded gradually, 
 so that they are merely reversions to forms formerly dominant. 
 I am quite of opinion that this explanation applies in many 
 cases, and equally so that in others it does not — that rather in 
 
IV CHANGES IN GENERAL COLORATION 
 
 135 
 
 these other cases we have the formation of new characters bv 
 the influence of external conditions. This is proved by the 
 conversion of Levana into Prorsa, and that of Bryoniie into 
 Napi. In both cases the cold-form is the original, the warmtli- 
 form the new. Warmth has evidently in Levana - Prorsa 
 gradually produced a darker, more simply marked form, 
 which in its extreme stages hitherto occurs but rarelv. Arti- 
 ficial warmth can easily produce this extreme stage. Ptetarded 
 development depending on cold can also produce the cold-form 
 — nothing indicates any necessity to explain the origin of 
 either form by reversion. 
 
 Further PcEmarks on the Causes which Change the 
 General Colouring of Animals 
 
 I must here make some further remarks on another ques- 
 tion, namely, that of the effect of external agents, particularly 
 of light and warmth, on the total coloration. 
 
 Dorfmeister would of course say that in Lepidoptera also 
 warmth produces more vivid, more brilliant colours, while dull 
 shades predominate under the influence of cold. This agrees 
 perfectly with my assumptions, and does not contradict the 
 facts brought forward by Weismann, provided that we consider 
 the part that light plays in certain cases [c.g, in high regions, 
 Pieris Bryonise), and when we further reflect that lighter 
 general coloration can be obtained by distribution of the 
 dark pigment without any necessary diminution thereof. 
 
 But the case also occurs in which the colours under the 
 influence of warmth and light undoubtedly become lighter. 
 Thus by rearing the caterpillar of Xanthia Cerago in a higher 
 temperature up to the pupa stage, Dorfmeister obtained tlu' 
 variety flavescens Esp., which occurs also in natural con- 
 ditions, and which is lighter coloured than the principal form. 
 Exceptional cases of this kind, in which warmth actually 
 
136 ACQUIRED CHARACTERS sec. 
 
 calls forth ligliter coloration, can only be explained by a 
 peculiarity in the composition of the pigment. 
 
 More frequently light causes paleness. Indeed, in animals 
 after death, light causes bleaching of the same colours which, 
 united with warmth, it helped to produce during life. The 
 care with which collections of insects have to be shielded from 
 the light is sufficient proof of this ; during the life of the 
 animiils the brilliant and dark colour was called forth by 
 active metabolism under the influence of warmth and light, 
 after death this colouring matter undergoes changes in the 
 lidit which cause it to bleach. 
 
 O 
 
 But there are also colours which are bleached by the effect 
 of light during life. In birds this bleaching appears to 
 play a great part in the change of colours. It is clear also that 
 in life both processes may compete together, and I have entered 
 upon these questions once more in order to show with what 
 caution they must be handled, and how little can be inferred 
 from single examples. 
 
 Exactly the same antagonism exists, as has been previously 
 mentioned, in the influences of moisture and other agencies. 
 I may be allowed to make here some additional remarks on 
 this subject also. 
 
 If moisture generally produced darkness of colour, all 
 aquatic animals would be necessarily dark-coloured, which is 
 notoriously not the case. Proteus anguineus, which lives in 
 the caves of the Karst mountains about Adelsberg, is like other 
 cave animals perfectly colourless. That the absence of colour 
 is in this case due to the absence of light is shown by the fact 
 that when the animal is kept in the light it becomes dark. 
 And this fact alone proves the correctness of my view con- 
 cerning the direct action of light, and shows that pammixis is 
 not required in order to explain the colourlessness of cave- 
 dwelling animals. 
 
 The view that the darker colour of Arion empiricorum on 
 
IV LEYDIG ON THE EFFECT OF MOISTURE 137 
 
 the sea coast may be caused by the greater moisture of the 
 atmosphere, notwithstanding the lowness of level, is supported 
 by a remark of Leydig's ^ on Helix nemoralis. Ley dig says : — 
 " The influence of light and warmth is very distinctly 
 evident in the colouring of Helix nemoralis in this region. The 
 fine citron yellow exhibited by the shell of this snail at 
 Mainz and in the sunny vineyards of the Main valley is 
 wanting on the banks of the lower Khine. ... On the other 
 liand, it is interesting to notice liow in the neighbourhood of 
 Bonn and lower down the Ehine the red of this snail deepens 
 into chocolate brown, and thus forms the beautiful variety 
 above mentioned, which must attract the attention of every 
 collector. It is perhaps too much to say that the moisture of 
 the plain of the lower Ehine determines this change of colour, 
 but we must keep in view the possibility that the moisture 
 coming up the valley from the sea, which certainly here at 
 Bonn has a distinct effect on the vegetation, has something to 
 do with the matter. . . . And just as in a former publica- 
 tion I attributed to similar causes the formation of black 
 varieties of our native reptiles, such as Yipera berus var. 
 prester, Lacerta vivipara var. nigra, the black variety of 
 Anguis fragilis, so I would maintain that there is a connec- 
 tion between the orvrnw of the black varieties of Lacerta 
 muralis which have meanwhile been made known by 
 Eimer . . . and be it noted all of them occurring on the 
 small islands of the Mediterranean, and the action of the 
 moist sea air."- Leydig goes on to mention that in the 
 Entomologische Zcitimg of Stettin, in 1877, a collector of 
 insects stated concerning the Lepidoptera at Bilbao that they 
 
 ^ F. Leydig, Ueber Verhreitung der Thieve im RhongeUrge und Mainthal mit 
 Hinhlick auf Eifel und Rheinthal in Verhandlungen des naturhistorischen Vereiris 
 der preussischen Rheinlande und Westfalens, 1881, p. 156 et seq. 
 
 2 Cf. the subsequent section on the relation of adaptation to the origin of 
 varieties among lizards. As long ago as 1874 {Lacerta vmralis ccerulea) I con- 
 sidered moisture as having some effect in i^roducing darkness of colour in these 
 animals. 
 
138 ACQUIRED CHARACTERS sec. 
 
 show a distinct tendenc}' towards the darkening and blacken- 
 ing of the shades of colonr, as in tlie north and on the Alps, 
 and he also stated tliat the proximity of the sea — the moisture 
 of the air therefore — seemed to cause this variation. Another 
 lepidopterologist reports {Ihid. 18T9) that a moist clayey soil 
 seems in many species to produce a darker colouring. 
 
 I have noticed in my own studies of Lepidoptera that 
 many species of the small islands of the Indian Arcliipelago, 
 in comparison with their nearest allies of the Asiatic, and also 
 of the European and American continents, are distinguished by 
 remarkably dusky colours. The species of Papilio, Heimocrates, 
 Xonius, and others, witli the Australian Leosthenes, in fact 
 form a well-marked dull-coloured group contrasting with the 
 yellow Podalirius and its allies of the continent. The 
 Antiphates forms of the Archipelago are also distinguished by 
 their dark marking. 
 
 On the other hand, the PapilionidDe of tropical Africa have 
 strikingly dull, dark shades of colour in comparison with their 
 allies from regions where there is less heat, or less moist heat. 
 
 If we take a general survey of our field- and meadow- 
 iiowers in spring and summer we see that in spring, on the 
 whole, the colours white and yellow predominate, while red and 
 blue only appear later in the year. And, indeed, red precedes 
 blue. This is in accordance with the physiological changes 
 of the pigment, which show themselves more or less visibly 
 in many red or blue flowers during their development, and 
 also in some decree in the change of colour which occurs in 
 foliage leaves in autunui. 
 
 What I wish to point out here is that a quite similar substi- 
 tution of one predominating colour for another occurs also, on 
 the whole, in butterflies with increasing warmth of climate. 
 Taking the Papilionidae again as an example, we find those 
 of Europe, North Asia, and jSTorth America generally light 
 yellow, or almost white ; while in Africa, and to a great extent 
 
IV DECREASE OF SIZE IN INSULAR FORMS 139 
 
 in India, and South America, in closely related forms, instead 
 of light yellow, dark yellow, and greenish blue, then red and 
 blue and finally black appear. 
 
 Influences of Locality on the Variation of Animals, and 
 
 THEREBY ON THE FORMATION OF SpECIES 
 
 Finally, on islands there are evidently some local external 
 influences of unknown nature, but probably likewise connected 
 Avith climate and nutrition, which control the evolution of 
 species, e.g. in butterflies, especially affecting their size. 
 
 I need only remind students of the Lepidoptera of the 
 Papilio-species of Java on one hand and of Celebes on the 
 other. The original identity of the species on the two islands is 
 obvious. But those of Celebes are now considerably larger 
 than their blood-relations in Java, and exhibit atthe same time 
 slight differences of colour and marking more or less pro- 
 nounced when compared with the latter. To almost every 
 Java species there corresponds a larger, stronger species in 
 Celebes. This I have proved not merely from the material 
 already available in collections, but from numerous specimens 
 kindly collected for me by Herr Seubert, forest-overseer in 
 Java, and by Herr Bauer, merchant, in Celebes. 
 
 The larger, more luxuriant island possesses, therefore, in this 
 case, the larger butterflies. Similarly the species of PapilionidiB 
 which occur in the Antilles are smaller than those of the 
 neighbouring mainland, although otherwise but slightly 
 different from them. 
 
 The butterflies of Sardinia also are in general smaller and 
 also more darkly coloured than those of the mainland. The 
 same holds for the common fox in the Isle of INIan.^ It is well 
 known that Sardinia possesses numerous peculiar varieties, or 
 species of animals generally. Papilio Hospiton, which occurs 
 
 1 A, R. Wallace, Beitrage zur naturlichen ZuchtwaM, German edition, by A. 
 B. Mayer, 1870. 
 
140 ACQUIRED CHARACTERS sec. 
 
 there and in Corsica, is notliiiig else than a smaller swallow- 
 tail with much darker win its and without tails. 
 
 In all these cases and in numberless otliers, in addition 
 to, and together with the difference in size, other peculiar 
 characters are present, so that new species are established. 
 
 Wallace mentions in a chapter in his Contrihntio')is to 
 Natural Selection entitled, " Variation specially influenced by 
 Locality," other such cases, and among them also the striking 
 instance of Java and Celebes to which I have referred. He 
 remarks that almost the only case previously known of the 
 direct influence of locality is recorded by Darwin in the Origin 
 of Species, namely, that herbaceous groups of plants show a 
 tendency on islands to become arborescent, while in the animal 
 w^orld no such facts are known. Then he continues : "In 
 considering the nearly allied species, local forms, and varieties 
 which occur in the Indian and Malayan regions, I find that 
 larger or smaller districts or even single islands impress a 
 special character on the majority of their Papilionidoe. Thus 
 (1) the species of the Indian region (Java, Sumatra, and 
 Borneo) are almost invariably smaller than the allied species 
 which inhabit Celebes and the Moluccas ; (2) tlie species of 
 Xew Guinea and Australia are likewise, although to a less 
 degree, smaller than the nearest species or varieties of the 
 ^Moluccas ; (3) in the Moluccas the species of Amboina are 
 the largest ; (4) the species of Celebes equal or even surpass 
 those of Amboina in size ; (5) the species and varieties of 
 Celebes possess a striking peculiarity in the form of the 
 anterior wings, wliich is different from that in the allied 
 species and varieties of all the surrounding islands ; (6) tailed 
 species of India or of the Indian region become tailless as 
 they extend eastwards through the Archipelago ; (7) in 
 Amboina and Ceram the females of several species are darker 
 coloured, wdiile in the neighbouring islands they are more 
 brilliant." 
 
IV WALLACE'S OBSERVATIONS 141 
 
 Specially striking are the peculiarities mentioned by 
 Wallace in the form of the anterior wings in the species of 
 Papilio of Celebes ; the anterior wings are in general more 
 elongated and sickle-shaped, the front margin is more strongly 
 curved than in the species of other districts, and usually makes 
 a sudden bend, an anejle, near the base of the w^ino-. 
 
 As tins peculiar form of the wing in Celebes occurs not 
 only in species of Papilio but also in Pieridse and species of 
 other families, Wallace believes its origin is due to an advan- 
 tage in the struggle for existence ; he supposes that these 
 large butterflies must, in consequence of the sickle-like shape 
 of the anterior wing and its curved front edge, be able to turn 
 suddenly in flight with greater ease, and in this way bafHe 
 their pursuers. He thinks this the more probable because 
 the only Papilio in Celebes which does not possess this 
 peculiarity in the wings, P. Polyphontes of the Polydorus 
 group, appears to be protected in other ways. 
 
 This is certainly possible, although considerations already 
 noticed, showing that large wings actually protect butterflies 
 from capture during flight, are opposed to it, and although 
 Wallace is unable to name the pursuers which are baffled. 
 Por the very reason that the same peculiarity occurs in differ- 
 ent but allied families, it should rather, however, be regarded 
 as the consequence of a direction of evolution, a phyletic 
 growth determined by peculiar conditions of climate or 
 nutrition, and similarly with the disappearance of tails 
 towards the East. The differences in size also of butterflies 
 on islands probably have their causes in differences in the 
 abundance of nutritive resources. 
 
 With reoard to the tails, to Wallace's observations I am 
 able to add that it is the higher species of the genus Papilio 
 in which they disappear, so that we have to deal with their 
 disappearance from the genus. 
 
 Moreover, the peculiarities of the colouring of butterflies 
 
142 ACQUIRED CHARACTERS sec. 
 
 in particular islands, such as those Wallace mentions, and 
 many others known to me, are certainly not to be considered 
 as due to selection, but in part at least are to be recognised as 
 stages of evolution in a definite direction, which I shall not 
 discuss here in detail. Thus Wallace himself, joint-discoverer 
 with Darwin of the principle of utility, says : " But this 
 hypothetical explanation of the form and veining of the wings 
 in the Celebes butterflies does not apply to other cases of 
 local moditication. Why the species of the western islands 
 are smaller than those in the islands lying farther to the east, 
 why those of Amboina surpass those of Dschilolo and New 
 Guinea in size, why the tailed species of India begin to lose 
 these appendages in the islands, and on the shores of the 
 Paciflc no longer show a trace of them, and why in three 
 different cases the females of the Amboinese species are less 
 gaily coloured than the corresponding females of the sur- 
 rounding islands — these are questions we cannot yet attempt 
 to answer." 
 
 Tliese are, therefore, characters whose utility in any case 
 cannot be proved, in which the determining influence of selec- 
 tion cannot be recognised — are certainly acquired and inherited 
 characters. 
 
 I can increase the number of these examples by many 
 others taken from this same group — the butterflies ; cases in 
 which the variations determining the origin of species are so 
 small, so obviously in constant progress towards definite 
 directions of evolution, that their explanation by selection is 
 in fact absolutely excluded. 
 
 Importance of the Stimulation of the Nervous System in 
 
 RELATION TO ADAPTATION AND THE ORIGIN OF SpECIES 
 
 The reader will perhaps wonder that I did not assign a special 
 role from the beginning to the action of the nervous system 
 
IV INFLUENCE OF NERVES ON COLOUR 143 
 
 among the causes of the moelification of colours in animals, 
 since the influence of its action in this respect is well known. 
 But it is clear that this is in most cases only an indirect 
 influence determined by other causes, especially light and 
 warmth, so far as it aflects the question of the permanent 
 modlflcation of animal forms. 
 
 The nerves may influence the colouring of the skin in two 
 ways : either by changing the supply of blood, and the de- 
 position of pigment depending upon it — that is, indirectly, or 
 directly by changing the shape of the pigment -cells. The 
 first action depends more upon temperature, the second more 
 upon light. Warmth increases the flow of blood to the skin, 
 cold diminishes it — the former by dilating, the latter by con- 
 tracting the blood-vessels; both, however, must act directly by 
 expanding and contracting the pigment-cells, like illumination. 
 
 Finally, electric stimulation, or division of nerves, acts 
 upon the colour of the skin. After removal of the cerebellum 
 in a frog the skin becomes strikingly variegated. As excite- 
 ment produces temporary paleness or redness in the human 
 skin, and as irritable, malicious persons are always distin- 
 guished by a pale yellowish complexion, in consequence of 
 constant excitement of the nervous system, so the colours of 
 animals vary with excitement, sometimes to a striking 
 degree. I may mention the familiar case of the chameleon, 
 which when angry and after death turns yellow. The tree- 
 frog also alters in colour in captivity, apparently through 
 nervous excitement, as is usually said from discontent. 
 
 But in the latter case the direct influence of the colour of 
 the surroundings must evidently also be taken into account, 
 for the tree-frog, like many other animals, assimilates its 
 colour to that of its temporary environment.^ 
 
 It is well known that many other animals likewise change 
 
 ^ This process is usually described by the inappropriate expression : sympa- 
 thetic colouring. I would substitute for this : stimulation-colouring. 
 
144 ACQUIRED CHARACTERS sec. 
 
 •their colours in accordance with their surroundings, and 
 thereby become less conspicuous. Besides the chameleon, I 
 will only mention the Sepias among the Cephalopods. This 
 is a much more delicate action of light than that which merely 
 changes tlie colour from light to dark, as occurs in so many 
 cases — a sudden action instead of the gradual etlect by which, 
 for instance, darkness of tint is produced after some time in 
 man ; and physiologically different, for in the former case it 
 is a question of change in the shape of the pigment - cells 
 under the influence of the nervous system, in the latter of 
 deposition of pigment. 
 
 Such sudden alteration of colour under the influence of 
 liglit is strikingly shown in certain fishes, e.g. trout, grayling, 
 minnows. In tliese tlie colour of individuals kept in the dark 
 becomes lighter on sudden exposure to light in consequence 
 of contraction of the pigment-cells. 
 
 We attach too exclusive an importance to " adaptation " — 
 as I attempted to point out by examples previously given- — 
 when we think to explain by selection every similarity 
 between the colourins: of an animal and that of the sjround on 
 wliicli it lives. For, as we have seen, animals may become 
 similar in colour to their surroundings, actually adapted in 
 colour, quite by chance ; for instance, in consequence of the 
 direct, necessary action of light, i.e. of the surrounding colours, 
 and therefore without selection. ]\Iany really wonderful 
 cases of adaptation, apparently due to selection, probably 
 come under this category. 
 
 It is also to be noticed that even rapid changes of colour 
 may also be due to a chemical action of light, and not invari- 
 ably to nervous influences. It lias been observed, for example, 
 that the pupie of butterflies during their development take on 
 the colours of their surroundings. Pupa; have assumed the 
 red colour of a cloth enveloping them, a colour to which they 
 could scarcely be exposed under natural conditions, and to 
 
IV CHEMICAL ACTION OF LIGHT 145 
 
 which in any case they could not have been adapted by selec- 
 tion without special conditions of life which ought to be 
 explicitly pointed out. Yet, notwithstanding this, the pheno- 
 menon has been assumed without further question to be due 
 to adaptation by selection. 
 
 This interpretation I would meet with the following"'" 
 proposition : The substance composing the envelope of the 
 pupa possesses as a fact the property of being changed by 
 light like a photographic plate, and the relation of this pro- 
 perty to the outer world may be useful, but it does not neces- 
 sarily owe its origin to selection. 
 
 That this substance is so constituted as to exhibit in action 
 a process of colour- photography, the goal of so much human 
 longing and striving, leads to another consideration. 
 
 Since the discovery of visual red in the retina of the eye, 
 a substance which quickly bleaches under the action of light 
 after death, and which is situated in the very cells of the 
 retina on which light falls, we are brought near to the con- 
 ception that sight, especially the perception of colours by the 
 eye of the higher animals and of man is likewise a chemical 
 process, a kind of photography. 
 
 A short step farther in the specialisation of nervous stimu- 
 lation or nervous conductivity might well render comprehen- 
 sible the wonderful fact above referred to, that the colours of 
 the environment of an animal may be reflected in the colours 
 of its skin. For it is self-evident that the path of action of 
 the coloured light is principally through the eyes. Experiments 
 prove this : after the eyes have been removed, the action of 
 the colour of the environment on the colour of the skin ceases. 
 
 Thus, in many cases, chemical action and stimulation of 
 the optic nerves may be closely connected in the process by 
 which the colours of animals are affected by light. 
 
 Whether simple chemical action of the light upon the 
 skin, or such action taking place indirectly through the eyes, 
 
 L 
 
146 ACQUIRED CHARACTERS sec. 
 
 or simple general stimulation of the nerves, determines the 
 change of colour, or whether, lastly, the gradual action of 
 selection simultaneously plays a part in the matter, it will of 
 course be often difficult to decide for any given case. 
 
 The following really astonishing case of " adaptation " of 
 the colouring of an animal to the ground on which it lives 
 forces upon me the idea that selection does not play a part 
 in it, but that it is due to the direct external action of the 
 colour-stimulus ; the effect, however, probably not showing it- 
 self at once, but appearing more gradually than in many cases. 
 
 The grasshopper with red hinder-wings banded with black, 
 which is so common with us (in Germany) in summer, 
 Acridium germanicum (CEdipoda germanica), when it occurs 
 on the reddish-brown Triassic clay of Tubingen, resembles 
 this ground so closely with its wings folded, that it cannot 
 be distinguished from it. A little above the clay on the hills 
 of this neighbourhood there occurs a whitish sandstone, 
 sometimes only for the breadth of a path or in somewhat 
 larger surfaces, frequently surrounded by the former. On 
 these small patches of lighter ground I find regularly only 
 grasshoppers with quite light upper wings, so that they can 
 scarcely be distinguished from the soil. And I have else- 
 where observed the same remarkable adaptation. One of my 
 friends, who is not usually accustomed to pay special attention 
 to such animals, told me that he had been much surprised to 
 notice that on the two banks of a brook on which the soil was 
 of different colours, the grasshoppers were in each case exactly 
 like the ground in colour. Without doubt these were Acri- 
 dium germanicum or Acridium ccerulescens — the latter species 
 appears to show the same adaptation. 
 
 Experiments must decide whether this is a case of stimula- 
 tion-colouriu!^. That such stimulation-colouring occurs in the 
 tree-frog I have mentioned above, and it evidently occurs 
 also in other Amphibia. 
 
IV CAUSES OF COLOUR- ADAPTATION 147 
 
 Years ago I was much struck to find in a pine-wood in 
 the Tauber valley (at Bronnbach near Wertheini) that the 
 numerous toads living there, without exception, had the 
 yellowish red colour of the pine-needles covering the ground. 
 The common frog also, Eana temporaria, changes colour accord- 
 ing to the colour of the ground, not rapidly, but gradually. 
 
 It seems to me, we may safely assume that such stimu- 
 lation-colouring has been in many cases the ultimate cause, 
 the origin of the formation of a permanent and hereditary 
 adapted colouring : for when any species or variety of an 
 animal has lived throughout a long time on a particular 
 ground, of which the colour has been constant, and has by 
 nerve-stimulation taken on this colour from the beginning, 
 this colour may at last fix itself in the animal unchangeably. 
 
 In this way a colour -adaptation, in a high degree un- 
 changeable, may be produced without any selection, without 
 the struggle for existence ; and probably many colour- 
 adaptations of animals of restricted habitat are to be ex- 
 plained in this way. 
 
 Among such cases, probably, belongs a remarkable colour- 
 adaptation in frogs observed by Wiedersheim : the common 
 frog in the Engadine has always the speckled colour of the 
 granite on wdiich it lives. 
 
 It goes without saying, that selection may favour such 
 direct adaptation, and this has probably been the case with the 
 wonderful degree of adaptation to the surroundings shown by 
 the colour of wall -lizards, as I have proved by extensive 
 researches, — colour-adaptations which, moreover, have doubt- 
 less been determined by the most various causes.^ 
 
 My chief assistant. Dr. Fickert, has at my suggestion made 
 the following experiment in order to test the action of 
 
 1 Cf. the section on the bearing of adaptation upon the origin of varieties in 
 lizards. 
 
148 ACQUIRED CHARACTERS sec. 
 
 differently coloured surroundings on the common frog (Eana 
 temporaria) : Three frogs approximately similar in colour 
 were j^laced in three glass vessels, of wliich the first stood 
 on a black, the second on a green, and the third on a white 
 surface, being surrounded up to a height of some five centimetres 
 with the same colour. After about an hour and a lialf, the frog 
 a on the black surface was the darkest, h on tlie white the 
 liglitest, while the frog c surrounded by green was inter- 
 mediate in colour between the two. Hereupon the frog a was 
 transferred to the glass on the white, frog h into the one on the 
 black surface. After three-quarters of an hour they were again 
 examined, and a was the lightest, h the darkest. Then c and h 
 were interchanged, and in a quarter of an hour c was the 
 darkest, while h was intermediate in colour between c and a. 
 "When, finally, h and a were interchanged, a change of colouring 
 appeared immediately ; h became light again, and a took the 
 intermediate tint between h and c. The change of colour seemed 
 to be due to the fact that when the colour became lighter, the 
 pigment distributed over the skin was collected in particular 
 places in small dark spots, and when it became darker, it was 
 spread out more uniformly over the whole surface of the body. 
 
 When I repeated the same experiment with the same 
 frogs on the following day I only observed a slight change of 
 colour, although this was still noticeable. But one frog and 
 a toad (Bufo vulgaris), which I had left during the following 
 night in a quite dark vessel, had both become blackish brown 
 in the morning. After I had placed them in the light on a 
 light surface the frog immediately began to get lighter in 
 colour, and continued to change gradually, so that after half 
 an hour it was biownisli yellow. In the toad the change of 
 colour occurred much more slowly : only after some time 
 could I see that it was distinctly lighter, and it was a wdiole 
 hour before it became light brown. 
 
 Three other frocrs chanc^ed colour in the course of about an 
 
IV GABRIEL KOCH'S EXPERIMENTS 149 
 
 liovir, as in Dr. Fickert's experiment — only the one surrounded 
 with green was ahnost as light as that on the white surface, 
 and the one entirely excluded from light, although it became 
 distinctly darker in that time, even after four hours could only 
 be called brown, not dark. 
 
 We have thus the remarkable fact that the change of 
 colour in frogs begins at once, but only slowly reaches its full 
 extent, and that it also takes place slowly in toads, which 
 entirely agrees with my interpretation of the change in 
 favour of adaptation without selection. 
 
 Paeticular Facts which prove the Influence of Nutri- 
 tion AND other external CONDITIONS ON THE VARIATION 
 
 AND Formation of Species in Lepidoptera 
 
 After I had in vain applied to various experts for trust- 
 worthy personal observations upon the effect of the nutrition 
 of the caterpillars on the variation of Lepidoptera, and had 
 concluded the preceding pages, a book was brought to my 
 notice entitled The Indo- Australian Leioidoptera, etc., tvitJi a 
 Discussion of the Origin of Colour's in Fupcc, by Gabriel Koch 
 (second edition, Berlin, 1873). This work contains some facts 
 of much importance for my arguments, and its author, on the 
 basis of these facts, expresses some views on the origin of 
 varieties which completely harmonise with mine. 
 
 Koch states that his attempts to influence the colours of 
 Lepidoptera by the feeding of the caterpillars date from the 
 year 1832, when he succeeded in producing in Chelonia Hebe 
 either fiery or dull red on the under wings, and in bringing 
 out more strongly either the black marking or the white 
 ground alternatively by feeding with different j)l^i^ts.^ 
 Other successful experiments were made on Chelonia Caja, 
 and Nemeophila plantaginis.^ 
 
 1 PuLlished in a paper on Die Raujpen icncl Schmetterlinge der Wetterau. 
 - Vicl. G. Koch : Die Schmetterlinge des svxhvestlichen DeutscMands. 
 
150 ACQUIRED CHARACTERS sec. 
 
 Kocli employs the facts he brings forward to support a 
 theory set up by him concerning tlie origin of the colours, 
 which physiologically is somewhat audacious. According to 
 this theory, a yellowisli slime overlies the imago's wings before 
 its emergence. This slime consists of granules, which after- 
 wards form the pigment particles of the imago. The cater- 
 pillars obtain the substance of this slime from the plants they 
 feed on in the form of vegetable salts, acids, and tannin. Koch 
 was, I believe, originally a simple artisan of Frankfurt (a tin- 
 man), and we cannot be severe upon him for explaining the 
 production of colour as a simple laying on of pigment. On 
 the other hand, it is highly gratifying to see facts employed 
 by such a man scientifically, that is, so as to afford general 
 conclusions, so that it must be said of him, that with simple 
 unskilled judgment he hits the nail on the head. 
 
 Koch guards himself against the charge of not recognising 
 the action of light on the formation of colours : he says this 
 action is shown by the fact that diurnal Lepidoptera all have 
 more vivid colours than the nocturnal. Warmth and light, 
 however, according to him, do not act differently. 
 
 Koch's results are as follows : — 
 
 A change in marking is easily produced by a change in the 
 plants fed upon (the "bear" and other species). 
 
 Nocturnal species which live exclusively on conifers have 
 dull colours, usually gray, as for example our pine hawk- 
 moth (Sphinx pinastri), or the pine -spinner (Gastropacha 
 pini), and several foreign species. This is so invariably true 
 that Koch was able to conclude from the colours of certain 
 species from Sydney and Baltimore that the caterpillars lived 
 upon coniferous plants, and when he suggested that they should 
 be sought on such plants his conclusion was found to be correct. 
 
 It is known, Koch says, that when the caterpillars of our 
 German " bears " (Chelonia s. Euprepia caja) are fed from 
 their hatching to their metamorphosis with leaves of Lactuca 
 
IV INFLUENCE OF FOOD ON COLOUR Vol 
 
 sativa or Atropa belladonna, not one of the imagines pro- 
 duced resembles the original form; when the insects have 
 been fed on lettuce the white ciTound- colour of the win^s 
 predominates ; when fed on deadly nightshade the brown 
 markings of the upper wings often coalesce and the wdiite 
 vanishes ; in like manner the blue markings on the lower 
 wings fuse together and displace the orange-3^ellow ground 
 colour. To which I may add, that according to Koch's w^ork, 
 The Lepidoptera of South- West Germany, feeding with bella- 
 donna and poppies produces dark-coloured imagines. Koch 
 made experiments wdth similar results on Chelonia plantaginis 
 and Gastropacha pini. Finally, he refers to experiments with 
 similar results on species of Militaea and Argynnis, as already 
 known. 
 
 "Must not," concludes Koch, "similar processes occur 
 equally, and even on a larger scale, in the natural life of the 
 countless forms of the class in question ? When a great 
 number of individuals perish through an occasional scarcity 
 of their proper food-plant, must not nevertheless considerable 
 numbers survive by contenting themselves with other allied 
 food materials, and so give rise to varieties wdiose origin we 
 do not dream of, and which therefore we are led to regard as 
 new species ?" 
 
 Further, he brings forward instances to show that cold 
 or w^armth, moisture or dryness of climate, change the size 
 and colouring of Lepidoptera. 
 
 Thus the chess-board butterfly (Arge Galathea) in middle 
 Germany is quite different in appearance from its dark varieties 
 (Procida and Leucomelas) which occur in the Tyrol and the 
 southern parts of Europe ; the speedwell butterfly (Melit^a 
 Artemis) in middle Germany is always smaller and duller 
 coloured than its highly coloured varieties (Desfontainesi and 
 Beckeri) in Spain. Our buckthorn butterfly (Gonopteryx 
 rhamni) acquires in Southern Italy and Portugal a large 
 
152 ACQUIRED CHARACTERS sec. 
 
 orange-coloured spot on its anterior ^vings (var. Cleopatra). 
 Further, not rarely a long period of dry or moist weather 
 exercises a considerable influence on the size of the following- 
 generation. Immediately after a continuously dry summer 
 Ijutterflies are always smaller than after a moderately moist 
 season. The second generation of Argynnis Selene, which 
 takes flight in the height of summer, is always smaller than 
 the first generation, wliicli is produced in spring, and so on. — 
 " If, then, such important facts are observed in many species of 
 our small continent, why should not similar effects be possible 
 in extra- European species, whicli are spread over so large a 
 territory where they are influenced by the most varied climates, 
 differently composed soils, and to some extent quite different 
 food plants ? In a hemisphere where the conditions of tem- 
 perature are so varied, why should not the tropical sun, under 
 which varieties are generally acknowledged to occur, be also 
 the chief cause of variation ? Thus the origin of the immense 
 Lepidoptera of the East Indies is to be ascribed to the moisture 
 and heat of the climate {e.g. the Ornithoptera) ; and, on the 
 other hand, the small size of the Australian forms is to be 
 attributed to the dryness of the Australian climate. 
 
 " If Lepidoptera pass during the rainy season in their 
 normal habitat into another region where the rainy season 
 has not begun and where great heat and a dry atmosphere 
 prevail, or if they pass from the monsoon region, which is 
 neither deficient in water nor in rain, into the ever-dry and 
 waterless continent of Australia, diminution of size in the 
 very next generation is sure to take place. But as the climate 
 in Australia is permanently dry, the diminution which occurs 
 remains permanent in all subsequent generations in their 
 new habitat, and the deteriorated condition of the species is 
 established for ever." 
 
 Thus permanent local varieties are produced. There are 
 therefore numerous Lepidoptera which in moist climates are 
 
IV KOCH'S CONCLUSIONS 153 
 
 larger, in Australia smaller. But there are also very large 
 native species in Australia {e.g. the giant hawk-moths Brachy- 
 giossa triangularis and B. Australasise, etc.) Instances of 
 species which become smaller in Australia are Chserocampa 
 celerio, Sphinx convolvuli, Euchelia pulchra, and many others. 
 
 Koch further discusses the importance of the season of the 
 year in which Lepidoptera appear, and mentions, after re- 
 ferring to Vanessa Levana, and Prorsa, that the second 
 generation of Argynnis Selene, which takes flight in the 
 height of summer, also has finer and blacker spots and 
 markings than the one which comes out in spring. 
 
 Thus Koch also reaches the conclusion that the origin of 
 permanent varieties is to be ascribed to external infl.uences, 
 and the most important result gained by his work is that 
 he makes it probable that many forms at present considered 
 as species are only similar permanent varieties. It is a re- 
 markable proof of the hold which the idea of the permanence 
 of species has upon systematists, that Koch never once refers 
 to the question whether species might not arise or have 
 arisen in this way, although he supplies instances thereof. 
 
 In the preceding I believe I have proved beyond a doubt 
 that external influences — climate, light, warmth, moisture, 
 and differences of food — modify organisms directly, even 
 without the aid of selection, and that inasmuch as the modi- 
 fications so caused are inherited, they will give rise and must 
 have given rise to new species. I presuppose, however, that 
 the inheritance of characters acquired through the action of 
 external influences is an indisputable fact. 
 
 Characteks acquired by Use 
 
 It is a self-evident physiological fact that practice or 
 use strengthens and improves the organs of the body, while 
 disuse causes them to deteriorate. 
 
154 ACQUIRED CHARACTERS sec. 
 
 The causes of this effect of practice lie firstly in the in- 
 creased supply of blood which it produces, and secondly in 
 the more delicate adjustment of nervous and muscular action. 
 
 That characters acquired through use or disuse are in- 
 herited, and must therefore aid in the formation of new species, 
 can, I believe, be proved more easily than any other of the 
 propositions I am maintaining. If I were to bring together 
 all the facts which could be used as evidence on this point, 1 
 should never come to the end of them, for I should have to 
 refer to all the facts of comparative anatomy and physiology. 
 But I intend to show in particular that use and disuse by 
 themselves must lead to the formation of new permanent 
 characters, without the aid of selection, for even this I hold 
 to be a physiological necessity. 
 
 Lamarck long ago explained the degeneration of the eyes 
 in animals living in darkness by disuse. 
 
 But how are eyes evolved ? 
 
 The pigment-spots which at the present day are the only 
 representatives of these organs in many animals show evi- 
 dently the first stage of their evolution. 
 
 The stimulus of liglit acting upon spots of the outer skin 
 specially suited for seeing, i.e. for " feeling at a distance," has 
 produced a deposition of pigment in these spots, because they, 
 originally endowed only with the sense of touch, have con- 
 stantly been directed towards the light in order to receive 
 the more delicate stimulus of the ether waves. PiGrment 
 cannot have been the primitive organ of sight, nor can it at 
 present, in any instance, be itself such an organ. But pigment 
 is so far absolutely necessary for sight that it serves to separate 
 the rays of light falling on the nerve-endings. Pigment is 
 deposited around primitive tactile cells, and separates each 
 one from its neighbours, or it is deposited in some of the 
 touch -cells, leaving one free here and there. The touch-cells 
 
 
IV ORIGIN OF VISUAL ORGANS 155 
 
 which remam ■unpigmented become sight -rods. I have 
 described such superficial pigment-spots representing eyes in 
 their simplest form, in Medusae, e.g. in Aurelia aurita.-^ By 
 their means, in my opinion, the simplest kind of sight is 
 effected in this way, that of the rays coming from any object, 
 one passes through each such sight-rod and is separated from 
 neighbouring rays, and so the lights and shades of the object 
 are communicated to the nervous system in a number of 
 separate points, so that a representation of the object is 
 obtained in the nervous system by a flat image composed of 
 points. The lighter and darker points of the object are each 
 represented in the nervous system, as when an object is seen 
 throuc^h a number of minute holes in a card. This kind of 
 sight by points can only be effected by these lowly developed 
 eyes in such low forms as the Medusae, not, as most zoologists, 
 following Johannes MilUer, assume, by the highly developed 
 complex eyes of insects, in which images must certainly be 
 formed. The origin of eyes capable of this kind of sight 
 depends then on the deposition of pigment around touch-cells 
 for the purpose of separating the different light-rays received 
 from one another. We have already seen what an importance 
 light has in the production of pigment. Without the stimulus 
 of light, the pigment so essential to the formation of an eye 
 could not be produced ; without the continuation of the 
 stimulus, that is, without constant use, the eye cannot con- 
 tinue to exist at all ; but by constant use it is improved and 
 perfected. The same stimulus which it is the function of 
 the eye to receive, namely, light, created and still maintains 
 the essential and fundamental element of the organ. 
 
 Exactly the same statement holds also for the other 
 sensitive cells, for the cells of smell, taste, and hearing, as 
 for those of touch and for sight-rods. They have all been 
 ultimately evolved from indifferent epidermic cells, and the 
 
 1 Th. Eimer, Die Medusen. 
 
156 ACQUIRED CHARACTERS sec. 
 
 specific external stimuli, so closely allied to the stimulus of 
 touch to which they respond, must have gradually produced 
 their specific nature. Only by use, by constant exercise, can 
 they be specifically maintained, and by use, at the same time, 
 they are improved. 
 
 In tliese considerations, the truth of which is undeniable, 
 lies the best proof of the great importance of use, the great 
 importance of acquired and inherited characters, in the modi- 
 fication of orcjans. 
 
 Thus every organism owes its peculiar structure essentially 
 to the use of its parts ; nay more, owes its continued existence 
 exclusively to this exercise and the unceasing action of external 
 stimuli. Without any exercise all our organs would degener- 
 ate ; we should perish as surely as if we were dead, if only for a 
 moment external stimuli ceased their action upon us. Life 
 is truly nothing else than the expression of the interaction 
 between the organism and the stimuli of the external world, 
 and natural oradual death is due to the fact that the oro'anism 
 becomes incapable of receiving stimuli. 
 
 Thus the statement that the eyes of animals living in 
 darkness are atrophied through disuse may be more exactly 
 rendered into this, that the cessation of the stimulus of light 
 causes the pigment to fade, and must therefore cause deteriora- 
 tion of the eyes. 
 
 For the rest, in the preceding it was my intention only to 
 point out that stimulation from without, i.e. use, according 
 to my view, even without selection, must necessarily form 
 organs, strengthen, and perfect them, and I did not think of 
 denying the fact of the influence of selection, c/j. in the 
 formation of eyes. 
 
 Among the examples which Lamarck brings forward in 
 support of the modification of organs by use, and which are, 
 it is true, in most cases, partially to be referred to selection, 
 is one to which I have to devote further consideration. He 
 
IV INTESTINES OF DRUNKARDS 157 
 
 says : " M. Tenon states in a communication to the Science 
 Section, that in investigating the intestinal tube in several 
 men who during a great part of their lives had been inveterate 
 drunkards, he found it always extraordinarily shortened in 
 comparison with the same organ in all men who had not 
 been addicted to the habit. 
 
 "It is known that great drinkers, or those who have 
 given way to drunkenness, take very little solid nourish- 
 ment, that they scarcely eat at all, and that the liquids which 
 they take in excess and constantly suffice to nourish them. 
 
 " As liquid nourishment, especially spirituous liquors, do 
 not remain long in the stomach and intestines, the stomach 
 and the rest of the intestinal canal in drunkards are no 
 longer accustomed to be distended, just as in persons who 
 lead a sedentary life, who constantly occupy themselves with 
 intellectual work, and who are accustomed to take very little 
 food. Gradually and in course of time their stomach is con- 
 tracted and their intestine shortened. 
 
 " It is not a question here of narrowing and shortening 
 caused by a wrinkling of the parts, which would allow of the 
 usual extension as soon as the intestines, instead of being 
 continually empty, were again filled, but it is a question of a 
 real narrowing and shortening, so that these organs would 
 burst before they were distended to the usual extent. 
 
 " Let a comparison be made between two men of the 
 same age, of whom one is devoted to study and habits of 
 mental work, which weaken his digestion, and has conse- 
 quently become accustomed to eat very little, while the other 
 takes plenty of exercise daily, goes out often, and eats well, 
 and it will be found that the stomach of the first scarcely has 
 any capacity, and that a very small quantity of food fills it, 
 while that of the second has not only maintained its 
 capacity, but even increased it. 
 
 " Here then is an organ which is considerably changed in 
 
158 ACQUIRED CHARACTERS sec. 
 
 its dimensions and its capabilities during the individual life 
 simply in consequence of a change of habit." 
 
 By this example the zoologist will be immediately reminded 
 of the fact that many of our domestic animals have a 
 larger intestine than the wild species from which they are 
 derived. Other morphological differences between the wolf 
 and the dog having been sought in vain, one zoologist has 
 recently attempted to make this difference in the length of 
 the intestine serve as such. But it is clear that this is only 
 a difference due to physiological conditions ; it is evidently 
 caused by the difference in the food of the domestic and the 
 wild animal. The wolf feeds upon flesh, the dog has to 
 accustom himself to vegetable food also. The domestic cat, 
 also evidently from the same causes, has a longer intestine 
 than the wild cat. It is a universal fact that, amon^^ wild 
 animals, the carnivorous have a much shorter intestine than 
 the herbivorous. In the development of the frog the two 
 types succeed one another, clearly in relation to the food. 
 The tadpole, which feeds principally on Algse, to some extent 
 on Infusoria, has an intestine of surprising length ; the adult 
 frog, feeding only on small animals, has a very short intestine. 
 It is very natural that a shorter gut suffices for the nutritious 
 food of the flesh-feeders, while the less nutritious vegetable 
 food, in order that the necessary nutriment may be got from 
 it, must be taken in larger quantities and digested for a 
 longer time. Therefore a longer intestine is useful to the 
 vegetable-feeder. 
 
 But in what way has the gut been lengthened in the 
 domestic animals which live partially on vegetable food ? 
 
 That this has been brought about by selection cannot 
 certainly be supposed, for although the longer intestine is an 
 advantage to the nutrition of the dog and cat, yet the differ- 
 ence in this respect between the tame and the wild animal is 
 not so great that the life of the animals in a domesticated 
 
IV RIGHT-HANDEDNESS 159 
 
 condition could depend on it. There can, in my opinion, be 
 no doubt that the elongation in fact depends on mechanical 
 causes — that as the intestine in a drunkard is shortened during 
 his life, so it has been mechanically lengthened in the 
 vegetable-feeding animal by the greater quantity of food 
 taken ; and the new character has been inherited, so that now 
 it is looked upon by one zoologist as a specific distinction. 
 
 It is a very remarkable fact that nearly all men use the right 
 arm much more than the left. Since all races of men, even 
 the most remote and most uncivilised, have this habit, we 
 cannot suppose that it has simply been acquired by practice, 
 and thus become hereditary. It is more probable that there 
 is something in the structure of the body, e.g. in the direction 
 and force of the course of the nutrient liquids, which gives 
 the right side of the body its superiority, if the mere position 
 of the heart towards the left is not the determining cause, on 
 account of the greater disturbance which that organ would 
 suffer if the left arm were chiefly used. Cases of left- 
 handedness rather favour than contradict such a supposition, 
 for in these cases parents and teachers have taken trouble 
 enough to train children to the usual habit, but in vain. 
 
 It is to be supposed that this reverse habit is due to 
 congenital reversion of nutritive relations, such as that pro- 
 duced in the simplest way in complete reversion of the situs 
 viscerum. I do not know if it has been ascertained how far 
 left-handed people, e.g. left-handed swordsmen among students, 
 exhibit this inversion. It would be a praiseworthy task to 
 investigate whether some recognisable anatomical conditions 
 do not underlie their peculiarity of habit. 
 
 Notwithstandincj this view of the connection between 
 organic conditions and the priority of the right arm, I believe 
 that the skill and strength of the latter, especially of the right 
 hand, are partly to be attributed to use. Martins, the editor 
 
160 ACQUIRED CHARACTERS sec. 
 
 of Lamarck's Philosophic Zoologiquc, explains tliem exclusively 
 in this way. He maintains that in consequence of greater 
 exercise the right arm is thicker and heavier, and all its 
 parts, bones, muscles, nerves, vessels are stronger than those 
 of the opposite side. And he adds,^ that the Dutch naturalist 
 L. Harting has proved that the differences are already present 
 in the new-born child which has not yet made use of its 
 limbs, and that this gives rise, independently of example and 
 instruction, to the innate tendency to employ the right arm 
 in preference to the other. 
 
 The skill of the right hand as compared with the left, in 
 fact, depends upon a number of congenital conditions, which 
 can only be explained by the inheritance of acquired peculi- 
 arities of muscular action, that is, ultimately, of the muscu- 
 lature and nerve supply. 
 
 In this conclusion I am confirmed by another observation. 
 I noticed that the Arabs in Egypt in a great number of 
 actions make skilful use of the toes instead of the finGfers. 
 This is particularly striking in the turners, who in turning 
 wood use the foot as well as the hand with much skill ; and 
 the same power was exhibited in the operations of weaving 
 by the Dinka negroes recently travelling with Nubians in 
 Germany. In the Egyptians the great toe plays an important 
 part. Beggars sometimes pick up pieces of money by grasp- 
 ing them between the great and the second toes instead of 
 grasping them with the hand. And the rapidity with which 
 this is usually done gives an idea of the dexterity possessed 
 by the toes. The skill, however, with which even young boys 
 use their toes in similar ways again leads us to infer some 
 congenital organic peculiarities. 
 
 Moreover, it cannot be douljted that the deficiency in the 
 development of our toes and their want of dexterity are to be 
 ascribed to degeneration, and as both must be hereditary, our 
 
 ^ Op. cit. Biogrcqohischs Einleitung, p. 35. 
 
IV EVOLUTION OF SNAKES 161 
 
 toes afford an example of hereditary characters acquired 
 through disuse, of which I shall treat in the following chapter 
 under the title " Degenerated Organs," and, conversely, this 
 deterioration itself shows that strength and skill are really 
 inherited. This degeneration or deterioration must, however, 
 among us, as we wear boots, be somewhat greater than in the 
 barefooted Arabs, and therefore the latter must be from their 
 birth more fitted to use their toes than we. At the same 
 time it is known that our babies still make grasping move- 
 ments with their toes. 
 
 Lamarck explains the origin of the elongated body in 
 snakes by the exertions they make in order to force them- 
 selves through narrow holes. It is evident from the preced- 
 ing that I should not hesitate in certain cases to allow that 
 such efforts on the part of an animal to elongate any organ 
 for a definite purpose might result in a hereditary modifica- 
 tion. But Lamarck's views on the effects of use have been 
 so much neglected, for the very reason that here, as in other 
 cases, the examples brought forward by him are not con- 
 vincinCT. It seems to me inconceivable that the elousrated 
 body of a snake could have been produced in such a 
 way. 
 
 But the origin of the elongated bodies of creeping 
 vertebrates is really a great enigma. 
 
 Not only snakes, but the Blindworm (Anguis fragilis) and 
 other animals have acquired, along with the degeneration of 
 the limbs and the development of a creeping habit, a worm- 
 like form of body. If this could be considered as due to con- 
 stantly repeated stretching out, as a rope or an india-rubber 
 tube can be at last made longer by continual stretching, 
 Lamarck's explanation could not be so flatly rejected. But 
 in all these cases the elongation is connected with an increase 
 in the number of vertebrae — in some a very great increase. 
 
 M 
 
162 ACQUIRED CHARACTERS sec. 
 
 Pure Darwinism is contented to explain this elongation 
 of body as adaptation produced by selection. 
 
 It is true that it permits of more rapid motion, and there- 
 fore gives an advantage in the struggle for existence to the 
 animals wliich have acquired it. But Darwinism leaves us 
 entirely without an answ^er to the question, Why, in what 
 way, has the number of the vertebne been increased ? 
 
 Evidently the elongation of body is connected with the 
 disappearance of the limbs. Snakes, like the blindworms, 
 are descended beyond a doubt from lizard-like animals. But 
 the long tail of the lizards shows that they themselves are 
 descended from animals whose body was elongated, worm- 
 like, composed of many similar segments (metameres), had 
 many vertebra3. Their tail vertebras are the more rudimentary 
 the more posterior they are in position. Thus it may well 
 be inferred, conversely, that the vertebral column as a whole 
 has been shortened in lizards in proportion to the degree of 
 development of the limbs — as also in other vertebrates, unless 
 the tail has acquired a particular function, as e.g. in the 
 kangaroo and the apes, etc. When the limbs began again to 
 disappear, and the body again to move in a writhing, creeping 
 manner, the original condition might again gradually return, 
 if the shortening arose through disuse and degeneration, 
 favoured by selection. Now selection contrariwise favours the 
 elongation of the body, its reversion to the earlier condition ; 
 which, however, results directly from the fact that the original 
 energy of growth attains again its unrestrained freedom, or 
 may even proceed beyond the original limits. 
 
 The elongation of body in creeping vertebrates seems so 
 extraordinary as to demand an explanation of its ultimate 
 causes. But I can come to no other conclusion than that 
 physiological grow^th unhindered or even i'avoured by actual 
 conditions must play the chief part in the matter, wdiile 
 exercise (habit) and selection have only an auxiliary effect. 
 
IV EVOLUTION OF SNAKES 163 
 
 Use will be only so far essential that it determines the dis- 
 tribution of liquids through the whole body, so that its 
 growth up to a certain limit is rendered possible ; while in 
 the lizard, for example, the tail is at a disadvantage. 
 
 Snakes have in some cases as many as 300 dorsal 
 vertebrae, Saurians 15 to 100. The length of the neck of 
 the Giraffe depends only on the elongation of the individual 
 neck vertebrse, in birds partly on this and partly on an 
 increased number of vertebrae. The Swan has 23 neck 
 vertebrae, the other Lamellirostres and the Storks up to 17, 
 the singing birds 10 to 14, the running birds (Cursores) 15 to 
 18, the Cormorant (Carbo) 18, Podiceps 19. 
 
 Since, therefore, very long necks are differently formed, 
 even among allied forms, and since, on the other hand, short 
 necks often have the same structure as long, effort cannot for 
 this reason alone have determined the development of the 
 former, and mere selection may likewise be rejected. The 
 principal determining cause must rather have been a definite 
 law of growth, which again must have been influenced by 
 peculiar conditions in the life of the ancestors of each 
 group. 
 
 Further, the view I have suggested, that the atrophy of the 
 limbs physiologically, i.e. correlatively, contributes towards 
 producing the reversion of the body to its original condition, 
 that it may cause the recurrence of the original course of 
 growth, is supported by the consideration that the develop- 
 ment and maintenance of the limbs must withdraw a quantity 
 of material from the rest of the body, and that this material 
 is restored to the latter when the limbs degenerate. Since at 
 the same time the previously rudimentary tail begins again 
 to be used, several processes tend to the development of the 
 snake-form. 
 
 I have to mention here still another case brought forward 
 
164 ACQUIRED CHARACTERS sec. 
 
 by Lamarck as evidence of the effect of use in the formation 
 of new characters, in order to employ it in my own argument. 
 
 Lamarck says of the Euminantia, in reference to the 
 origin of their horns : " In their ebullitions of wrath, which 
 principally occur in the males, their emotions by their 
 intensity direct the fluids more strongly to this part of the 
 head (the forehead), and therefore there takes place in the 
 one case a secretion of horny substance, in the other a 
 formation of bone -tissue mixed with horn -tissue, by which 
 solid processes are formed ; hence the horns of the ox tribe 
 and stacf tribe." 
 
 Shortly before this he mentions that the ruminants fight 
 together by pushing with the forehead, but it does not occur 
 to him to seek in this fact the stimulus which causes the 
 formation of horns. In my opinion the first beginnings of 
 the formation of frontal processes in the Cavicornia, and of 
 the antlers in the Cervidse, are to be attributed to this 
 stimulus. By the inheritance of a simple swelling on each 
 side of the frontal bone, by the continued inheritance and 
 increase of this swelling in consequence of constantly re- 
 peated stimulation, the frontal processes were produced in 
 Cavicornia, and also the antlers among the Cervid^e. The 
 latter, having a special form in each species, and regularly 
 advancing in development and perfection each year up to a 
 certain limit, afford one of the best examples in support of 
 my conception of organic growth in the animal kingdom. 
 For although selection plays some part in this development, 
 it cannot possibly have had in view from the first the form 
 peculiar to each species, and have brought it into existence 
 unaided by other causes. That the ultimate cause of the 
 development lies rather in regular processes of growth is 
 shown by a fact concerning the antler of the roe-deer, which 
 is of particular importance in relation to my whole view. 
 
 The antler of the roe-deer is known to be distinguished, 
 
IV FUNCTIONAL ADAPTATION 165 
 
 when it has peeled, by elevations on its surface, which are 
 called "pearls." The antler very often has an extremely 
 long pearl on the internal side of the main stem. In one of six- 
 points it is between the lowest branch and the base. This 
 structure is obviously the commencement of a new branch in 
 process of evolution, for it is occasionally as much as an inch 
 long, and then has all the appearance of a new branch, 
 and " may be counted as such in venery." ^ 
 
 In this we have therefore an instance of the oris^in of a 
 new part of an organ by simple growth. 
 
 Only in this gradual way, by the inheritance of acquired 
 modifications sometimes together with degeneration, number- 
 less organs in the animal body can have been evolved. Con- 
 sider the limbs of Ungulata and other animals : the foot of 
 the horse, of the ostrich, the hind-foot of the kangaroo, in 
 their partly degenerate, partly specialised structure, depend 
 only upon inherited acquirements due to adaptation to the 
 same physiological demand, i.e. diminution of the number of 
 the toes, and increase in strength of the one or few remaining for 
 the sake of greater firmness and more rapid progress on hard 
 ground — in contrast, for example, with the five-toed foot of the 
 elephant, which is adapted to prevent any sinking into the soil. 
 
 The treatment of comparative anatomy, especially of 
 osteology, from this physiological point of view, which at 
 present, to my regret, has almost entirely fallen into disuse, 
 has its own special attractions, and affords at every point 
 support to my views. In this respect so-called analogous 
 organs are of the utmost importance — organs which, although 
 occurring in very different animals not immediately allied by 
 descent, have a very similar form, because they serve the 
 same purpose ; thus, for instance, the similarity in the forma- 
 tion of the limbs in the cases just mentioned, the development 
 
 ^ Cf. J. H. Blasius, Naturgeschichte der Sdugethiere DeutscMands, 1857, s. 464. 
 
166 ACQUIRED CHARACTERS sec. 
 
 of a sternal keel for the attachment of the pectoral muscles 
 in flying and burrowing animals, in birds, bats, moles, etc. 
 
 It is frequently possible in such cases to form definite 
 conclusions as to the future form of organs which at pres- 
 ent are seen in process of modification. Thus my friend 
 Wiedersheim in a very interesting paper ^ has recently drawn 
 attention to some facts in human anatomy wliich indicate 
 the future modification of tlie human body, assuming that 
 existing causes continue to act. In man certain muscles are 
 now increasing, namely, the adductors of the thumb and the 
 musculi glutei, in the face the mimetic musculature is on 
 the increase, the pelvic girdle is increasing, the ilia are becom- 
 ing wider apart — and all this in addition to the degeneration 
 of orcjans throudi disuse, which in a still hiorher def:free 
 indicates the future structure of man. 
 
 It is clear that the progressive development of the in- 
 telligence has likewise gradually effected the increase in the 
 size of the cranium in proportion to the facial part of the 
 skull in man, by means of the increased size of the brain, so 
 that the brain case now forms the principal part of the skull. 
 But it appears that in the most highly developed races of 
 man, provision is made for the farther increase of the brain- 
 case : as Gratiolet has pointed out, in these races the union 
 of the cranial sutures proceeds from behind forwards, so 
 that a greater development of the frontal lobes, on which 
 intelligence depends, is rendered possible ; or rather, the 
 vigorous growth of the frontal lobes has conversely given rise 
 to this arrani^ement. In the lower races of man the union of 
 
 o 
 
 the sutures proceeds from before backwards, as in the apes.- 
 
 I forbear here to enter more minutely into the importance 
 of the inheritance at particular ages of life of characters 
 
 ^ R. Wiedersheim, Der Ban des Menschen als Ze^igniss fur seine Vergangenheit, 
 Freiburg i.B. 1887. - Cf. Wiedeusheim, op. cit. 
 
IV HOMOCHRONOUS INHERITANCE 16/ 
 
 wliicli certainly often depend upon acquirement, and which 
 must contribute to the modification of the organic world, 
 namely, the facts of the inheritance of characters of the 
 parents by the children in such manner that they appear in 
 the latter at the same age in which they occur in the former. 
 This kind of inheritance has been called homochronous ; it is 
 obviously a necessary consequence of the law of correlation. 
 Thus the characters which accompany sexual maturity can 
 only appear w'hen the sexual organs have reached maturity. 
 But many characters belong here which have been acquired 
 by use and habit, as the fact, to be discussed subsequently, 
 and already mentioned by Darwin, that the peculiarities of 
 handwriting when inherited by a son from his father only 
 appear at a ripe age. 
 
 On account of the contrast in which it stands with this 
 homochronous inheritance, I must here mention an ob- 
 servation which at the same time illustrates the influence 
 of the condition of the organism as a whole, at the time of 
 generation, upon the germ. 
 
 I observed that children of very old parents, especially of 
 old fathers (male preponderance) have in their early years — 
 as children — features of a remarkably old appearance. 
 
 I have repeatedly tested the correctness of this observation 
 by appeal to impartial witnesses, and am able to state it with 
 certainty. 
 
 A senile expression of face may certainly be called a 
 character acquired through use. 
 
 In the following I will adduce a few additional instances 
 of the inheritance of characters acquired by exercise, some 
 due to habits of life, some to training, and some instances of 
 mental characters, although I shall subsequently have to de- 
 vote special consideration to the latter, above all, to instinct. 
 
 Is it not due essentially to better nourishment, to 
 
168 ACQUIRED CHARACTERS sec. 
 
 the conditions of domesticated life in general, that our hens 
 lay eggs and our cows give milk almost all the year round ? 
 How else are we to explain that our hens, ducks, and even 
 geese have almost completely lost the power of flight ? not to 
 mention the modifications of structure, some of considerable 
 importance, e.g. in the skeleton, which almost all our 
 domesticated animals exhibit, when compared with the wild 
 forms from which they are descended, and which cannot in 
 any way benefit them. 
 
 Weismann points out as evidence against the inheritance 
 of acquired characters, that articulate speech and the art of 
 piano-playing are not inherited, but only the predispositions 
 thereto. But each of these is obviously not an acquired 
 " character " of the organism, but only an artistic skill, which 
 has been learned. But the necessary tones of voice which 
 constitute a gradually acquired character — indeed voice itself, 
 and the acquired faculty of forming certain tones melodiously 
 in a definite succession — are inherited. 
 
 In no less a degree faculties acquired through education, 
 through training, by various domesticated animals, e.g. by our 
 breeds of dogs, are transmitted by heredity — no one w^ould 
 doubt this who had ever observed the behaviour of a young 
 untrained pointer in presence of game which he has never 
 before seen, and compared it wdth the behaviour of a mongrel 
 of the same age. 
 
 Here is an instance. Some years ago I was surprised to 
 see a pointer in my possession which had never before seen a 
 partridge, had never been taught to point at them, point at a 
 covey of partridges perfectly correctly, standing motionless 
 with head outstretched, fore -paw lifted up, and tail stiffly 
 erected. Exactly the same thing happened a few days ago 
 with a pointer now five months old which was sent to me by 
 one of my cousins who is chief forester in the Taunus, who 
 assured me that this dog had never yet had a partridge in 
 
IV INHERITED FACULTIES IN DOGS 169 
 
 front of his nose. There are thorough -bred pointers which 
 require no training at all, but which have completely 
 inherited the habits to which their ancestors were educated, 
 so that only a slight restraint till they have become perfectly 
 obedient is necessary to make them equal to the most 
 perfectly trained dogs. How different it would be with a 
 monojrel or a Pomeranian or a drover's doij. 
 
 Once I took home from the Black Forest a dosj about two 
 weeks old and brought him up. He grew up into what is 
 called a Wildhodenhund, which in shape and size is between 
 a badger-hound and a pointer — nearer the former than the 
 latter — and which is used to drive game towards the sports- 
 man by barking. My dog began as soon as he grew 
 up, although he was never taken out shooting, to drive 
 game on his own account in the neighbourhood of my house, 
 which is in the country, and in spite of all punishment 
 extended his operations farther and farther every day. At 
 last he ran away in the morning, and onlv returned covered 
 with perspiration and tired out in the evening. I had to give 
 him away, but on account of his inveterate habit he was of 
 no use anywhere, and he finally came to an end on the dis- 
 secting table of a university laboratory. 
 
 And even as I write this I can hear the barking of a 
 neighbour's dog, which was sold to him when young as a 
 badger-hound. But it is half a Wildhodenhund, and has the 
 habit of running about madly through gardens and yards in 
 the neighbourhood for some hours in the day, barking cease- 
 lessly, with his head down and his nose towards the ground 
 as though searching for game. In accordance with his 
 descent he still retains in part the peculiarities of the Wild- 
 hodenhund, and, without making further use of them, shows 
 them by running about in the attitude characteristic of those 
 dogs and barking in the same way, not knowing why, but 
 impelled by the mechanism of the brain-cells which he has 
 
170 ACQUIRED CHARACTERS sec. 
 
 inherited from his ancestors, and which were acquired by 
 them. He acts like a wound-up watch, by " instinct." 
 
 From the point of view of evohition it is in vain to seek 
 for any other explanation of instinct than that which regards 
 it as inherited habit. Automatic actions, i.e. those which 
 we perform involuntarily without being conscious of them, 
 although they were originally consciously performed and con- 
 sciously learned, enable us better to understand this inherit- 
 ance of habit by our own experience. We act automatically 
 in consequence of habit. If such habit is inherited, we speak 
 of instinctive actions, of instinct. A good example of the 
 origin of instinct is afforded by the above described behaviour 
 of my young pointers. These cases show that not only in 
 bodily but in mental life one generation is connected with 
 another. Such inheritance of acquired mental characters is, 
 in my view, of great importance in the social life of animals 
 and the explanation thereof.^ That all the ingenuity of 
 animals, so far as it is not due directly to the exercise of 
 intelligence and reason, i.e. of reflection at the time, can only 
 be explained by such inheritance, is self-evident. 
 
 Without this inheritance of faculties developed by practice, 
 neither instinct nor any higher mental evolution could be 
 explained. jSTot only in their bodily characters, in their lia- 
 bility to particular diseases, in their bodily movements, but in 
 their whole intellectual life, the nations and races of mankind, 
 which must have descended from common ancestors, show 
 quite peculiar characteristics, e.g. the Jews, which must have 
 once been acquired by their forefathers. Among these char- 
 acters those which are to be ascribed to imitation from genera- 
 tion to generation can easily be distinguished, but only for a 
 short time, for imitation also is inherited, and becomes a 
 permanent acquisition. 
 
 It is also an example of the inheritance of acquired char- 
 
 ^ Cf. my lecture, XJeher den Begnff des thierischen Individuum. 
 
IV INHERITANCE OF HANDWRITING 171 
 
 acters due to habit that the handwriting of the son often 
 shows the same characteristics as that of the father, althouoli 
 there has been no imitation. I can instance myself in 
 confirmation of this. As I left home at a very early age I 
 had very little opportunity for imitation, and, morever, the 
 similarity of my w^riting to my father's was not developed till 
 later years, and, as I am able to affirm, entirely independently. 
 The causes of this inheritance in any case lie essentially in 
 the inheritance of peculiarities of the fingers, of their muscu- 
 lature, and in their consequently inherited peculiarities of 
 position and motion, apart from the fact that certain pecu- 
 liarities of mental character are expressed in the handwriting. 
 But the expression of disposition in an acquired faculty is 
 also inherited. 
 
 Without wishing to help to prove that character is indi- 
 cated by handwriting to the ridiculous degree assumed by 
 journals in need of circulation wdiich trade upon human 
 vanity, I w^ould yet declare my agreement with the often- 
 expressed opinion, that in general a vigorous large hand- 
 writing shows vigour and frankness, a small prim hand shows 
 a reserved, subtle nature, fond of minute expedients and 
 indirect ways. 
 
 I must return here once more to the question already 
 touched upon, why most dogs carry their tails erect, while 
 wolves and jackals, from which they are descended, do not. 
 Only the dogs which are nearest to the original forms, as the 
 jackal-dogs of the East and our sheep-dogs, which are not far 
 removed from the wolf, carry their tail depressed like the 
 wolf and jackal. The erection of the tail by the domestic 
 dog is obviously an acquired and inherited character, and one 
 in which selection is out of the question. It is difficult to 
 discern the causes of this alteration. It seems to me, how- 
 ever, allowable to suppose that it has a psychical basis. It is 
 known that the dog lets its tail droop when in fear of punish- 
 
172 ACQUIRED CHARACTERS sec. 
 
 ment, and generally when in a mentally depressed condition, 
 or even draws it in tightly between his legs, while during 
 the feelings of security, pride, or conquest he elevates it. 
 ^lust not, then, the feeling of security, which the dog as a 
 domesticated animal almost always possesses to a much 
 greater degree than his wikl ancestors, have gradually pro- 
 duced tlie habit of constantly carrying the tail erect ? I 
 know not of course how wolves and jackals carry the tail when 
 specially well pleased — they may possibly then elevate it 
 somewhat. Of the fox, however, apparently in contradiction 
 to my interpretation, it is known that he raises his standard 
 in flight ; but this may be an expression of the consciousness 
 the animal has of mental power, or it may be merely a conse- 
 quence of a high degree of excitement, in which condition 
 dogs too, e.g. when fighting, or in the case of the pointer when 
 pointing, raise their tails. 
 
 I will add here another hypothesis similar to that of the 
 orio'in of horns. It seems to me that the combs and wattles of 
 
 o 
 
 our domestic fowls are to be ascribed to similar causes. The 
 originals of these fowls in India (Gallus bankiva) have these 
 appendages only slightly developed. It is known to every 
 keeper of fowls how much they fight, especially in confined 
 enclosures, pecking at each other's heads and combs, not to 
 mention the similar habit of the cock in treading. In a 
 free condition, the hens probably contrive to evade these 
 attacks, and it seems to me allowable to ascribe the extreme 
 development of the comb in our domestic fowls, although 
 artificial selection has doubtless to be considered, to the 
 constant external stimulus referred to, to find in this stimu- 
 lus the causes of the greater development. The ultimate 
 causes of tlie commencement of tlie development may of 
 course in fowls, as witli tlie horns of ruminants, lie in purely 
 physiological internal phenomena of growth. 
 
IV WEISMANN ON VARIABILITY 173 
 
 Inheritance of Injuries and Diseases 
 
 Weismann expresses himself concerning acquired characters 
 as follows •} " Acquired characters are universally understood 
 to be those which arise in consequence of the action of 
 external forces upon the organism, in contrast to those which 
 proceed from the constitution of the germ." To which it 
 might be objected, according to my views, that the germ also 
 may acquire characters and transmit them by inheritance, and 
 that it is, moreover, always affected by the condition of the body. 
 How far Weismann admits this will be discussed in the sequel. 
 Characters acquired during individual life Weismann describes 
 as transient, because, according to his view, they cannot be 
 transmitted by inheritance, " for it is obviously a consequence 
 of the theory of the continuity of the germ -plasm, that 
 characters can only be inherited when their rudiments are con- 
 tained in the germ-plasm, but that modifications which occur 
 in the developed body in consequence of external influences 
 must be limited to the organism in which they arise. The 
 latter must therefore be the case with mutilations, and with 
 the effects of exercise, or of the disuse of any part of the body. 
 
 " If then this is true, there is not only an end of all 
 Lamarckism, i.e. of the view which derives the modification of 
 species from the direct influence of the conditions of life, 
 especially from the increased or diminished use of particular 
 parts, but it becomes necessary to discover a new basis for 
 one factor of selection, namely, variability. For variability 
 has hitherto been attributed to the variable influences which 
 act upon the organism without intermission. But if all the 
 influences which might make bodies individually different 
 have only a transient and not an inheritable effect, the 
 individual variations which form the material for selection to 
 work upon cannot arise in this way." 
 
 ^ Biolog. Centralblatt, loc. cit. 
 
174 ACQUIRED CHARACTERS sec. 
 
 This exposition is in direct contradiction to my views. 
 
 But farther on AVeismanii makes some concession. He 
 says, " But althougli I hold it improbable that individual 
 variability can depend on a direct action of external influences 
 upon the germ-cells and their contained germ-plasm, because 
 — as follows from sundry facts — the molecular structure 
 of the germ-plasm must be very difficult to change, yet it is 
 by no means to be implied that this structure may not 
 possibly be altered by influences of the same kind continuing 
 for a very long time. Thus it seems to me the possibility is 
 not to be rejected, that influences continued for a long time, 
 that is, for generations, such as temperature, kind of nourish- 
 ment, etc., which may affect the germ- cells as well as any 
 other part of the organism, may produce a change in the 
 constitution of the germ -plasm. But such influences would 
 not then produce individual variations, but would necessarily 
 modify in the same way all the individuals of a species living 
 in a certain district. It is possible, though it cannot be 
 proved, that many climatic varieties have arisen in this 
 manner. Possibly other phenomena of variation must be 
 referred to a variation in the structure of the germ -plasm 
 produced directly by external influences. At present we 
 cannot decide upon this ; but this much may be maintained, 
 that influences which are mostly of variable nature, tending 
 now in one direction, now in another, can hardly produce a 
 change in the structure of the germ -plasm, and this is the 
 reason why the causes of inheritable individual differences 
 must be sought elsewhere than in these varying influences." 
 
 ..." No one has doubted," he says further, in reply to 
 objections made by Yirchow, " that there are a number of 
 congenital deformities, birtli- marks, and other individual 
 peculiarities, which are inherited. But these are not acquired 
 characters in the above sense. True, they must once have 
 appeared for the first time, but we cannot say exactly from 
 
IV WEISMANN ON ACQUIRED CHARACTERS 175 
 
 what causes ; we only know that at least a great proportion 
 of them proceed from the germ itself, and must therefore be 
 due to alteration of the germinal substance. 
 
 " If Virchow could show that any single one of tliese 
 hereditary deformities had its origin in the action of some 
 external cause upon the already formed body (soma) of the 
 individual, and not upon the germ-cell, then the inheritance 
 of acquired characters would be proved. But this no one has 
 yet succeeded in proving, often as it has been maintained." 
 The inheritance of artificially produced diseases, accord- 
 ing to AYeismann, is no proof. " Unless I am much 
 mistaken," he says, " the transmission of acquired epilepsy to 
 the following generation, the occurrence of which is not to be 
 denied, is not due to inheritance, but to infection of the izerm, 
 to the transference of living disease-producing organisms." 
 
 As Weismann himself in another place makes use of the 
 expression that his view is a matter of conviction, that no 
 proof of it can be brought forward, all that can be done is to 
 bring against it, as we have done, the facts that contradict it. 
 In particular, that view seems to me to have no prospect of 
 being accepted so long as there is no peculiar pathology of 
 the germ -plasm, and so long as the assumption that the 
 physiology of the germ-cells is so exceptional in comparison 
 with that of the other cells of the body, as Weismann's theory 
 requires, is unsupported by any basis of proof. 
 
 Of course it is true that the consideration on account of 
 which he proposed his theory seems to be in Weismann's 
 favour, namely, that this theory would explain the portrait- 
 like inheritance of characters, and reversion. But it is a 
 question whether such an explanation is not possible on other 
 grounds. " We are well aware," he remarks in one of his 
 latest writings,^ " that all bodily and mental peculiarities may 
 
 ^ TJeher den Ruckschritt der Natur, Berichte der Qialurforscherulen Gesellschaft 
 zu Freiburg i. B. Bd. ii. Heft i. 1886. 
 
176 ACQUIRED CHARACTERS sec. 
 
 be transmitted from the parents to the children . . . but the 
 ancestors possessed all these peculiarities by virtue of the 
 properties of their germs." 
 
 What agencies, then, must be asked, in reply, have first 
 introduced new peculiarities into the ancestral series ? By 
 what means have quite new characters arisen at all in organic 
 beinfjs ? Sexual combination could not oricrinate them : it 
 could only work from tlie beginning with what already 
 existed, was already present. 
 
 If I understand Weismann aright, the variability inherited 
 by the germ-plasm from unicellular ancestors is supposed to 
 have created these innovations. But such an assumption, 
 it seems to me, is purely hypothetical. It stands entirely 
 without proof, and finds its support only in the explanation 
 of portrait -like inheritance and reversion which is hypo- 
 thetically possible by its aid. 
 
 In opposition to this assumption I believe I can appeal to facts 
 even with regard to the inheritance of injuries and diseases. 
 
 That injuries, when continued for an extremely long time, 
 may be inherited is proved to my mind by atrophied 
 (rudimentary) organs. The degeneration of these organs 
 depends incontestably on disuse : in consequence of disuse the 
 blood -supply is diminished, in consequence of the decrease 
 of nutrition degeneration takes place. If we consider tlie 
 course of gradual degeneration, e.g. of the tail as it must have 
 taken place in the higher mammals, to have proceeded in 
 this purely physiological manner from the tip towards the 
 root, the process is much the same as if the tip of the tail 
 had been in many successive generations amputated, and the 
 shortening had been inherited, and then the shorter tail thus 
 acquired had been farther sliortened artificially, and so on. 
 In any case in the degeneration of the tail an acquired 
 character has been inherited by the offspring, a character 
 
IV INHERITED INJURIES Yll 
 
 which in the causes of its origin is closely similar to a 
 perpetually repeated mutilation. Great periods of time, 
 however, have been necessary in this case for the accomplish- 
 ment of the final result. 
 
 I add here some cases of inherited injuries which seem to 
 me to be authentic. A. Decandolle describes one such case 
 with the assurance that it is perfectly true.^ In the year 
 1797 a girl twenty-one years old was thrown from a carriage, 
 and in consequence had a scar about five centimetres wide over 
 the left ear and temple, which remained without hair. Married 
 in 1799, she bore a son in 1800, in whom the hair was absent 
 from the same area, and remained so. The son of this man, 
 born in 1836, had no such defect, but it was present in his 
 grandson born in 1866, and in 1884 in this last individual, 
 when he was eighteen years old, the peculiarity was disap- 
 pearing. 
 
 Dr. Meissen, of Falkenberg, records in the number of 
 Humholdt for June 1887 the following case of inheritance of 
 an injury in his own family : " When I was seven or eight 
 years old I had the chicken-pox, and I recollect with com- 
 plete distinctness that I scratched one of the pustules on 
 the right temple, in consequence of which I had a small 
 white scar at this spot. Exactly the same scar, which I 
 had of course ceased to think of, on exactly the same spot, 
 was present on my little son, now fifteen months old, when 
 he came into the world. The resemblance is so perfect that 
 it surprises everyone who sees the little mark." 
 
 My assistant, Dr. Vosseler, relates that his mother in her 
 eighteenth year injured the ring-finger of her right hand by 
 squeezing it between the door -latch and the door, so that it 
 
 ^ Alphonse Decandolle, Histoire des sciences et des savants depuis deux siecles, 
 
 jprecedee et suivie d'autres etudes sur des sujets scientifiques, en particulier sur 
 
 Vheredite et la selection, Geneve, Bale, H. Georg, 1885. Cf. also on the whole 
 
 question : Lucas, Traite 'philosophique et physiologique de Vheredite, etc., Paris, 
 
 1847 ; and E. Roth, Die Thatsachen derVererhung, Berlin, 1885. 
 
178 ACQUIRED CHARACTERS ^ sec. 
 
 was bent towards the radial side between the last and the 
 middle joint, and remained the rest of her life rigid in this 
 position. Dr. Vosseler, who was born two years later, has 
 had the same crookedness of the same finger from his birth, 
 and a brother of his also. The peculiarity was more marked 
 in his youth than it is now. 
 
 The following was related to me by my colleague Professor 
 Dr. V. Siixinger : His father-in-law had a pair of long-tailed 
 pointers, which had once produced a litter of long-tailed pups. 
 1 n order to obtain short-tailed pups, he had the tails of both 
 shortened. The bitch from that time produced repeatedly short- 
 tailed pups only. As tlie most careful attention was paid to 
 the parents, no error can be suspected in this case, wdiich, 
 moreover, appears to excite no surprise among dog-breeders. 
 
 Brown - Sequard,^ as is well known, has shown that 
 epilepsy is inherited by the offspring of guinea-pigs, in which 
 it has been produced by division of the sciatic nerve, or of a 
 portion of the spinal cord. In like manner, a peculiar altera- 
 tion of the shape of the ear, or a partial closing of the eyelids, 
 is inherited by the offspring of animals in which these 
 changes were caused by dividing the sympathetic. Thirdly, 
 exophthalmia was inherited by guinea-pigs in whose parents 
 this protrusion of the eyes had occurred after an injury to 
 the spinal cord, as also ekchymosis and dry gangrene, as well 
 as other trophic disturbances in the ear, due in the parents 
 to an injury to the corpus Tcstiforme. Fifthly, loss of certain 
 phalanges or of whole toes of the hind feet, which had 
 occurred in the parents in consequence of division of the 
 sciatic nerve. Sixthly, diseased condition of the sciatic 
 nerve in the offspring of guinea-pigs in which this nerve was 
 divided, and the occurrence of the phenomena which Brown- 
 Sequard had described as characteristic of the increase and 
 decrease of epilepsy. Further, Brown-Sequard possessed forty 
 
 ^ Compt. rend. torn. xciv. p. 697, Paris, 1882. 
 
IV CASE OF SHORTENED FINGERS 179 
 
 guinea-pigs in which one or both eyes showed more or less 
 morbid change, and which were descended from three indi- 
 viduals in which one eye had become diseased in conse- 
 quence of transverse section of the corpus restiforme. Lastly, 
 twenty guinea-pigs exhibited muscular atrophy on the upper 
 and lower sides of the thigh, in whose parents such atrophy 
 had been caused by section of the sciatic nerve. Mention 
 of Brown- Sequard's observation of the inheritance of the 
 loss of phalanges of the hind foot in guinea-pigs caused 
 by injury to the sciatic nerve, gives me an opportunity to 
 describe an extremely remarkable case of the inheritance of 
 congenital shortening or deformity of the fingers which I 
 observed in a young man studying in Tubingen this summer. 
 
 Mr. was a law student twenty years of age, and 
 
 meeting him by chance, I was much struck by the fact that 
 the second and third fingers on both his hands were much 
 shorter than usual, although his bodily structure was in other 
 respects perfectly normal. He kindly placed himself at my 
 disposal for the purpose of more exact examination. 
 
 The result of this examination and the peculiarities of 
 inheritance in this case are so remarkable, that it would be 
 difficult to find another case comparable with it. With 
 regard to the inheritance, I will mention first that, according 
 
 to the statement of Mr. , his mother and the youngest of 
 
 his three brothers, who is fourteen years of age, have exactly 
 the same defect, while the eldest, twenty-one years, and the 
 third, sixteen years old, are without it. In the brother and 
 the mother the shortening is not so great as in himself. It 
 does not occur in other relatives. As to its causes nothing is 
 known to him. 
 
 Exact investiqation shows that in both hands the fourth 
 finger is much the longest, on the right the middle finger, on 
 the left the index finger is the shortest, so that leaving out 
 the thumb the following is the order of the fingers in size : — 
 
180 ACQUIRED CHARACTERS sec. 
 
 In the right hand : 4, 5, 2, 3. 
 
 ,j l6It ,, 4rj O, O, ^» 
 
 In myself the order is : 
 
 right „ 3,2,4,5. 
 left „ 3, 4, 2, 5. 
 In the latter case the fourth is scarcely longer than the 
 second, in the former the second very little longer than the 
 fourth. 
 
 The order of size is usually 3, 4, 2, 5. 
 
 Exact measurement gives for the fingers of Mr. : 
 
 Right Hand. Left Hand, 
 
 2d finger 'Z'S cm. 7*2 cm. 
 
 3d „ 7*4 cm. 8*8 cm. 
 
 4th „ 10-4 cm. 10-4 cm. 
 
 5th „ 8-7 cm. 8-9 cm. 
 
 measuring always from the terminal knob of the metacarpal 
 to the tip of the finger. The shortness of the second and 
 third fingers in both hands is caused by a strongly marked 
 shortening of the middle-finger joint. This joint is : — 
 
 Right Hand. Left Hand. 
 
 In the 2d fine^er 1*2 cm. 1*0 cm. 
 
 „ 3d „ I'G cm. 1'5 cm. long. 
 
 The joint is therefore only half to one- third the usual length. 
 
 The first joint of the third finger of the right hand is also 
 shortened : it is only 3*5 cm. long; that of the same finger of 
 the left hand is 5 cm. 
 
 The measurements of these joints is somewhat too great 
 in proportion to the length given for the whole fingers, 
 because tliey are taken from knuckle to knuckle with the 
 fini:jer bent. 
 
 Externally the shortened fingers give no impression of 
 deformity, with the exception of the index finger of the left 
 
IV CASE OF SHORTENED FINGERS 181 
 
 hand, the first joint of which is particularly slender, and 
 which altogether is somewhat weak. 
 
 As the shortening of the fingers is very similar on both 
 hands, it can scarcely be supposed that it has been derived 
 
 from some injury incurred by an ancestor of Mr. durino- 
 
 life. If the idea of self-mutilation were to suggest itself, it 
 would be at once disposed of by the fact that the general 
 shortening is due to the shortness of the middle finger-joint. 
 
 But comparison with Brown-Sequard's experiment suggests 
 the reflection, whether the ultimate causes of the shorteninc^ 
 or atrophy are not to be sought in some disease, or some 
 injury of the spinal cord in an ancestor. 
 
 Another possibility is that the germ of some ancestor was 
 in some way affected or injured, and such derangements of 
 the germ are certainly very often the causes of congenital 
 defects. In this case, since the shortening of the fingers 
 occurs on both sides, the injury must have affected some of 
 the embryonic cells which take part in the formation of the 
 trophic centres or centres of innervation of the fingers in 
 question. 
 
 On the other hand, how can the first origin of this merely 
 local structural defect be explained by sexual combination ? 
 I confess I am unable to conceive such an explanation, 
 especially as it is not merely a question of a character formed 
 by the greater development of ancestral characters, but cer- 
 tainly to some extent of a pathological atrophy. 
 
 It is known that numerous other instances of the inherit- 
 ance of injuries have been recorded, e.g. inheritance of the 
 artificially shortened tail of a bull, of artificially produced horn- 
 lessness in cattle, many cases of inheritance in man of curva- 
 ture in a finger caused by injury, inheritance of the absence of 
 one eye which had been lost by the father during life by disease, 
 etc. The opponents of the inheritance of acquired characters 
 flatly assert that these statements are unauthenticated stories, 
 
182 ACQUIRED CHARACTERS sec. 
 
 anecdotes of no value as evidence. They attempt to deprive 
 the experiments of Brown -Sequard, confirmed by others 
 (Westphal and Obersteiner), on the inheritance of artificial 
 epilepsy in guinea-pigs, of importance, by explaining^ "that 
 this transmission of acquired epilepsy to the following genera- 
 tion, the occurrence of which is not to be denied, depends 
 not on heredity, but on inoculation of the germ, on the trans- 
 ference of living disease-producing organisms." 
 
 Since, however, this hereditary epilepsy was produced l)y 
 partial or complete section of the spinal cord, or by division 
 of the nervus iscliiadicus, when epileptic attacks could only 
 be produced some weeks after the operation by pinching the 
 skin on the lateral parts of the head and neck (epileptogenous 
 zone) ; since Westphal, who expressly states that he entered 
 upon these experiments with distrust, was able to produce 
 inheritable epilepsy by blows with a hammer on the head of 
 the animals — that assumption seems to be entirely unfounded. 
 But Ziegler, although he will not contest the possibility that 
 a transmissible disease due to infection may have followed 
 the operation, prefers to try to diminish the force and im- 
 portance of the experiments of Brown -Sequard, Westphal, 
 and Obersteiner, by asking if the guinea-pigs on which the 
 operations were made may not have been already predisposed 
 to disease ; if the appearance of epilepsy may not have been 
 due to general decrepitude, rather than to the inheritance of 
 a disease experimentally produced.^ 
 
 If epilepsy can actually be produced by blows upon the 
 head, and then inherited, as Westphal states (it showed itself, 
 according to that author, in the tw^o young ones of a guinea-pig 
 
 1 Wei.smann, Biolog. Centralblatt, 15th Marcli 1886 ; Westphal, Berlin. 
 Klin. Wochenschrift, 1871 ; Obersteiner, Med. Jahrbucher, 1875. 
 
 ^ E. Ziegler: Konnen ericorbene pathologische Eigenschaften vererbt tcerden, 
 und loie entstehen erbliche Krankheiten und Missbildungen ? Jena, G. Fischer, 
 1886. Published separately, from the Beitrdgen zicr pathol. Anatomie u. Physio- 
 logie of Ziegler and Nauwerck, Bd. i. 
 
IV INHERITABLE ARTIFICIAL EPILEPSY 183 
 
 made epileptic in this way), then the possibility of infection 
 is excluded. The only question is whether in this experiment 
 the animal was not already pregnant when the experiment 
 was made. If it was, then the evidence is not conclusive. 
 Apart from this, it is evident at first sight that there is more 
 justification for Ziegler's objection than for the other. But 
 why should all the guinea-pigs operated upon in Berlin, 
 Vienna, and Paris have been decrepit, and why should 
 guinea-pigs be generally decrepit? The fact that they are 
 domesticated is no evidence for this assumption, for they are 
 all domesticated, they exist only in captivity, their wild 
 ancestors are not even known ; for thousands of years they 
 have been reared only under man's protection, for they were 
 kept by the ancient Peruvians and Chilians, and they seem 
 to thrive very well under this protection, as is proved especi- 
 ally by their almost incredibly rapid multiplication. Still 
 Ziegler may be justified in demanding that the experiments 
 should be repeated. 
 
 With regard to the other experiments of Brown- Sequard 
 and Deutschmann ^ concerning acquired and inherited affec- 
 tions of the eye, Ziegler holds that these are to be explained 
 as cases of infection and inflammation, and that therefore 
 they afford no evidence of inheritance. 
 
 Some of Brown-Sequard's experiments, nevertheless, as the 
 inheritance of an atrophy of the foot in the guinea-pig after 
 section of a nerve, seem to me to afford unassailable evidence, 
 unless indeed any one would assume that here too the cause 
 lay in an infection conveyed to the germ. But with such 
 purely arbitrary assumptions anything could be proved. 
 
 I repeat that a single certain case of the inheritance of 
 acquired characters upsets the whole theory of inheritance 
 being exclusively limited to the germinal cells ; and it seems 
 
 ^ Deutschmann, Ueher Vererhung von erivorhenen Augen - affektionen bei 
 Kaninchen (Zehender's Klin. Moncdshldtter, 1880). 
 
184 ACQUIRED CHARACTERS sec. 
 
 to me that in the preceding instances enough of the inherit- 
 ance of injuries has been given to prove this inheritance — 
 putting aside my previous attempt to argue in favour of the 
 same conchision from the natural evokition of atrophied 
 organs. The latter argument seems to me sufficient by itself 
 to settle in the affirmative the question wliether acquired 
 characters and injuries are inherited. 
 
 Moreover, it is self-evident that the injuries of a body are 
 not all hereditary to the same degree, and furtlier, that in- 
 juries are inherited in different degrees in different animals. 
 
 The idea naturally suggests itself that injuries affecting 
 parts far removed from the centre of circulation — parts less 
 richly supplied with blood — are most likely to be inherited. 
 
 The question of the inheritance of injuries is further closely 
 connected with that of the reproduction of parts removed 
 from the body : the lower the grade of organisation, the less 
 the degree to which division of labour is carried, the more 
 easily will such losses be repaired, the less probably will 
 injuries be inherited. Therefore it is to be supposed that 
 such inheritance will occur much oftener in the higher 
 animals than in the lower, scarcely at all in plants. 
 
 We have now to enter upon the inheritance of diseases of 
 spontaneous origin. The negative standpoint in this question 
 has been advocated by my friend Ziegier in the paper above 
 cited, and in a lecture " On the Inheritance of acquired 
 pathological Characters and the Origin of inheritable Diseases 
 and Malformations." ^ He concludes that the former as well 
 as the latter arise always from changes in the germ. 
 
 Zieder holds that so long as it was assumed that fertilisa- 
 tion was a process in which a distribution and solution oi' 
 the spermatic substance in the ovum took place, the trans- 
 
 ^ Separate edition, from the Verhandlungen des Kongresses fur innere Medicin 
 in Wiesbaden, 1886. 
 
 » 
 
IV ZIEGLER ON INHERITANCE 185 
 
 mission of acquired characters was conceivable ; and Darwin, 
 by his " pangenesis," and Haeckel, by his theory that repro- 
 duction and heredity depend on the transference of a definite 
 form of motion (motion of the plastidula) from the parental 
 organs to the organic molecules of the generative cells, offered 
 an explanation of the phenomenon of the inheritance of ac- 
 quired characters considered by both as proved. But Ziegier 
 says that since newer researches have shown that fertilisation 
 is a purely morphological process, the inheritance of acquired 
 characters is excluded. This view is further supported by 
 tlie argument that the sexual cells are not elements which 
 could be derived from any cells of the organism whatever. 
 The nuclei of an organ of the fully-developed organism could 
 only possess by inheritance the property of producing, with 
 the aid of the cell-protoplasm, tissue of a single kind. The 
 structure of the sexual cells, on the other hand, must be 
 so constituted, that from the offspring of two nuclei which 
 coalesce, all the cells of the individual body, including new 
 sexual cells, can arise. 
 
 I have already expressed my opinion upon the view which 
 regards reproduction as a purely morphological process. I 
 should hold it no less justifiable to regard life in general as a 
 morphological process, for reproduction is a part of the life of 
 the organic world. 
 
 That the sexual cells give rise to not only one, but to the 
 several kinds of tissue-cells, is their most peculiar (specific) 
 function in multicellular animals ; but if multicellular animals 
 have been derived from unicellular, this distinction cannot be 
 a fundamental one, and must have been evolved in course of 
 time — as an acquired and inherited property. Since the 
 cause of the evolution of this distinction can only depend on 
 the advantage of division of labour, following upon the ad- 
 vantage previously gained by colonial life, and division of 
 labour consists in physiological relations between the cells of 
 
186 ACQUIRED CHARACTERS sec. 
 
 the organism and the outer world, the distinction must be 
 essentially due to external influences — to which is likewise 
 due the beginning of all histological evolution (differentiation) 
 in the body, to which I shall again refer. 
 
 Ziegler believes that the causes of the origin of germ 
 variations which lead to inheritable deformities and diseases 
 may be of three kinds — (1) Union of sexual nuclei which 
 are not adapted for copulation ; (2) disturbance of the copu- 
 latory process itself ; (3) injurious influences which affect the 
 sexual nuclei or the fertilised ovum at a time when separation 
 of the sexual cells from the body cells has not yet occurred. 
 " If the embryo is injuriously affected at a later period, either 
 a malformation or constitutional anomaly arises, which is not 
 inherited, or only the sexual cells are injured, in which case 
 the body -cells develop normally, and a disturbance shows 
 itself only in the development of the next generation." 
 
 The union of sexual nuclei not adapted for copulation is, 
 according to Ziegler, the most frequent and most important 
 cause of hereditary local malformations as well as of heredi- 
 tary morbid tendencies, or of a defect in any system of the 
 whole organism. " When in a family whose members show 
 no special talents a genius suddenly appears, the natural 
 explanation is, that sexual nuclei unusually well-fitted for 
 union have united in copulation, and that in consequence 
 the nervous system has reached an unusually perfect organ- 
 isation." In like manner arise tendencies to mental disease, 
 etc. If the nuclei are altogether unadapted to one another, 
 sterility results, as in the sexual nuclei of distinct species. 
 
 Thus what Ziegler is here discussing is the self-evident 
 effect of crossing, the importance of which I fully acknowledge, 
 and on which I have already expressed similar views ; but it 
 still requires to be explained in what way the sexual cells 
 originally acquired the peculiarity of being adapted to the 
 production of a genius. 
 
IV ZIEGLER'S VIEW ANALYSED 187 
 
 With regard to disturbances of the process of copulation 
 itself, it appears, says Ziegier, that, e.g. the simultaneous fer- 
 tilisation of an ovum by two spermatozoa results in a double 
 monster. 
 
 As instances of injurious conditions affecting the sexual 
 nucleus or the fertilised ^g^g, it is pointed out that substances 
 taken up from without — poisons, for example — are brought by 
 the blood to the sexual cells, and others produced in the 
 body are conveyed to the sexual organs. Thus " it seems as 
 if alcohol, for example, might have an injurious effect upon 
 the sexual cells, not merely by destroying the health of the 
 parents, but also directly. 
 
 " If the organism is reduced by suffering or weakened by 
 age, it is probable that some deterioration of the sexual cells 
 may be the consequence, so that their copulation produces 
 badly-developed offspring." 
 
 Here one is reminded of my instance of the inheritance of 
 the signs of old age. I will not go further into the compari- 
 son of the two cases, the special case just mentioned and the 
 general case stated by Ziegier. But the latter by itself 
 seems to me to grant by implication the inheritance of 
 acquired characters, the influence of the condition of the 
 whole body at a given time upon the properties of the 
 germ-cells, — to grant that a reduced condition of body, i.e. 
 a character acquired during life, is inherited by the offspring. 
 
 If, moreover, alcohol can act upon the germ through the 
 blood, and any morbid change in any part of the body can 
 act in like manner, and if such influence can be inherited, 
 then the dependence of the condition of the germ upon that 
 of the whole body, and the possibility of the inheritance of 
 acquired characters, is again fully recognised, and the only 
 difference between our two opposing views is one of words. 
 The assumed importance of double fertilisation in the origin 
 of double monstrosities seems to me to indicate plainly 
 
188 ACQUIRED CHARACTERS sec. 
 
 enough the importance of the effect of external influences 
 upon the germ (and upon the offspring). ^ Indeed, according 
 to the explanation I have given of the ultimate causes of 
 sexual combination, fertilisation in general is to be regarded 
 as an instance of external action upon the germ-plasm, al- 
 thougli I maintain the original equivalence of the male and 
 female portion of the germ. The view that fertilisation must 
 be regarded as an instance of external action is expressed 
 also by Virchow in his paper on " Descent and Pathology," 
 and he adds : " In a more rigorous sense it can be described as 
 an acquired modification of the egg-cell." He points out 
 further, that in general very much of what is regarded as 
 internal cause {causa interna), is really external influence 
 {causa externcc). " As a rule, a multicellular organism, w^hen 
 variation takes place, is not altered in all its parts ; usually 
 only a portion of the cells is the seat of change. Upon this 
 portion, or to express it more accurately, on each of the cells 
 affected, the remaining unaffected cells can exert an external 
 influence, and conversely the cells originally unaffected can be 
 influenced by those wdiich are affected as by external agents. 
 The conception of a causa externa applies therefore not merely 
 to those influences which affect the organism from without, 
 but also to those which arise from other cells or inner parts 
 and affect the individual cells either on the surface or in the 
 internal parts of the body. Only those causes which really 
 arise from the mechanism of the cells themselves are true 
 internal causes." Thus, then, correlation also is, in accord- 
 ance with my views, regarded as a phenomenon which has its 
 causes in external influences. Further : *' When an infectious 
 substance is generated in one part of the organism and acts 
 upon another part, it is in relation to the latter just as truly 
 
 ^ Cf. on this subject the papers of G. Born : Beitrdge zur Bastardirung 
 zwischen den einheimischen Anurenarten, Archiv. f. Physiologie, Bd. xxxii. p. 
 477 ; and E. Pfliiger u. Smith : Untersuchungen iiber Bastardirung der anureii 
 Batrachier u. die Prinzipien der Zeugung, Tbid. p, 558, 559. 
 
IV VIRCHOW'S SUPPORT 189 
 
 a causa externa as if it was generated outside the organism 
 and introduced from without into it." 
 
 I myself, as might be expected from my general views, 
 have never used the expression internal causes except in the 
 sense of the action of the given constitution of the body, 
 itself partly due to external influences, upon the direction 
 of evolution. 
 
 The supporters of the doctrine of the continuity of the 
 germ-plasm, since they deny the inheritance of characters 
 acquired by the body during life, and admit on the other 
 hand the heredity of those due to influences acting directly 
 on the germ-cells, set up a completely artificial distinction 
 between the nature and the j^roperties of the germ-cells 
 before and after segmentation. Such distinction is not only 
 altogether hypothetical, but completely contradicts that uni- 
 formity which proves the morphological and physiological 
 unity of the living world. 
 
 I have already attempted to demonstrate on other grounds 
 the inconsistency of the supposition of the non-inheritance 
 of acquired characters with that of the unity of the living 
 world. It can also be shown by another consideration that 
 the conception of a fundamental difference between the pro- 
 perties of the germ-cells and of the larva, or of the adult 
 body, must be false, namely, the consideration just indicated, 
 that the £^erm-cells contain in themselves the material and 
 the properties for the formation of the germ-layers and of all 
 the various cell materials of the adult body ; and that the 
 variety of the latter can only have its ultimate causes in 
 external conditions — must therefore be acquired. 
 
 I will not here discuss further the inheritance of acquired 
 morbid conditions, leaving the defence of my views in this 
 point to those special authorities who are on my side, some of 
 whom, like Virchow, have already expressed their support. In 
 particular, with regard to evidence, I may refer to the paper 
 
190 ACQUIRED CHARACTERS sec. 
 
 of Eoth already mentioned, a paper in other respects note- 
 worthy, which contains numerous instances in favour of 
 pathological inheritance, and in which the question of heredity 
 in general is profoundly discussed. 
 
 I would here add a few words on the inheritance of but 
 one kind of diseases, namely, mental diseases. That mental 
 diseases are inherited to a considerable degree no one wdll 
 deny. 
 
 But it is quite beyond doubt that among such hereditary 
 mental diseases are some which can only have arisen from 
 external influences on the nervous system, not through direct 
 modification of the germ. 
 
 The restless chase of life especially which is so character- 
 istic of our time leads in certain classes of the population 
 to an over- excitement of the nervous system which often 
 expresses itself in actual mental disease, and which — the over- 
 excitement as well as the actual disease — is certainly inherited. 
 Wliere disease commences cannot be determined, for by the 
 nature of the case it is impossible to define the boundary 
 between the two. Every over -excitement of the nervous 
 system is morbid, even when it is confined within the limits 
 of the socially permissible. The brain -workers especially, 
 whose life is often a struggle with their nerves, know the 
 truth of tliis, at least those wdio accept the conclusions of 
 physiological inquiry. 
 
 But the question may be asked, Whether the cultured classes 
 generally of the present day, using the term in a wide sense, 
 are to be regarded as perfectly normal with respect to their 
 nervous system ? The same question may be asked of their 
 children, even before the latter have begun to expose them- 
 selves to the abnormal conditions which have injuriously 
 affected their parents and ancestors. Our peasants and their 
 children, on the other hand, enjoy traditionally sound nerves. 
 
 As among single classes, so also among different nations 
 
IV MENTAL DISEASES 191 
 
 very different conditions in this respect are to be observed 
 — conditions which form the most important peculiarities, 
 constitute a part of their character. Many nations which 
 have become exhausted by their own civilisation, or are 
 becoming exhausted, prove this clearly enough, and there are 
 examples obvious enough and even belonging to most recent 
 times which I need not particularise. Such nations are some- 
 times conscious that they need to be reinvigorated by the 
 introduction of healthy blood from another race. Crossing is 
 here the only possible remedy remaining. But the disease 
 can only be explained by the aid of the action of external 
 influences upon the nervous system. 
 
 It is actually inconceivable that the system of organs, 
 which not only is the instrument of the relations of the body 
 to the outer world, but which of necessity owes its origin 
 and its evolution to these relations, should not be capable of 
 undergoing hereditary morbid changes in consequence of such 
 relations when they are injurious. 
 
 It is intelligible that the direct action of external conditions, 
 or certain states of the nervous system which are ultimately 
 ascribable to injurious external influences, lead to "fixed 
 ideas," to the tendency to self-accusation, to melancholy and 
 suicide, and that these aberrations may be hereditary seems 
 certain. But the origin of these aberrations cannot be com- 
 prehended unless they are acquired through relations to the 
 outer world. It is therefore inconceivable that in germ-cells, 
 whose ancestors were never exposed to corresponding in- 
 fluences, the conditions for the origin of these aberrations 
 should suddenly occur. For mental diseases have their seat 
 in the brain, and the earliest ancestors of man must have 
 acquired the brain itself through relations to the outer world 
 — and only these relations could produce those diseases in it. 
 It is therefore certainly intelligible (even if it be not admitted 
 that melancholia, for example, is a disease depending on 
 
192 ACQUIRED CHARACTERS sec. 
 
 definite changes in the brain, and to a certain degree definite 
 and capable of hereditary transmission) that a morbid state 
 of the brain wliich may have melancholia as a result (if 
 external conditions occur which excite its outbreak) is 
 acquired and transmitted by a human being provided with 
 nerves and brain. 
 
 It is also intelligible that such a condition may be acquired 
 through union with another sexual cell, provided that one or 
 both of the uniting sexual cells possess the acquired and 
 inherited tendency thereto. 
 
 It is, however, perfectly inconceivable, if the living world 
 be regarded as a continuous whole, that such a condition 
 should ever have come about without acquirement and 
 inheritance. 
 
 Mental capacity is an acquirement, and mental diseases 
 are diseases of relation. 
 
 As for the rest, it is certain that not only mere general 
 morbid conditions of the nervous system are inherited, but 
 also definite tendencies to mental disease, and likewise 
 definite mental abilities. The terms by which we express 
 both are of less importance, for, by the nature of the case, 
 these are only too often more or less artificial and elastic 
 (conventional). 
 
 It is obvious that the mechanism of the human brain 
 has become by acquirement so delicate that a high degree 
 of division of labour has taken place in it, wliich can only 
 depend on the fact that definite groups of brain-cells each 
 exercise and can only exercise definite functions. These 
 groups form " centres " which have assumed not the simplest 
 of such functions, elementary functions, but those of more 
 compound character, often indeed those which respond to the 
 demands of recently-developed civilisation. 
 
 I appeal, therefore, not to the numerous physiological 
 experiments which, by the aid of the results of i)athological 
 
IV CEREBRAL LOCALISATION 193 
 
 anatomy, have long ago made known the localisation of 
 elementary functions in the brain as a fact beyond dispute, 
 but, for instance, to the fact that the faculty of speech, 
 which was obviously acquired through the relations of men 
 to one another, according to pathological evidence has its 
 seat in a definite part of the human brain, in the left temporal 
 lobe. Loss of the power of speech, aphasia, may temporarily 
 occur as a consequence of excessive mental exertion. I have 
 myself experienced this fact, and know that in this condition 
 the power to speak is lost, but not the ability to produce 
 sound. One is only unable to find and to utter words ; one 
 is perfectly conscious of this and is astonished that it is so, 
 and makes vain endeavours to overcome it. 
 
 I consider as a similar condition of less degree another 
 which I have often observed in myself during great mental 
 fatigue, and which friends have told me they also have 
 experienced, namely, that in writing one repeatedly omits 
 letters from a word, or puts wrong letters instead of the 
 right. 
 
 It is universally known that in great mental fatigue one 
 often " forgets " the commonest names, and I have already 
 made the observation on myself that this especially occurs when, 
 as for example in systematic natural history, one has worked 
 at names too much ; the part of the brain which is concerned 
 with such matters is then exhausted and fatigued. 
 
 The following highly peculiar case which seems to me to 
 prove the fact that very complicated faculties, the acquirements 
 of civilisation, are connected with definite parts of the brain, I 
 was able to observe accurately within the last few months : — 
 
 A young man who was a connection of mine, and who 
 was a student here in Tubingen, began to require an unusual 
 amount of sleep. As the consequence of this was that he 
 usually did not get up till near mid -day, it was at first 
 attributed to causes which seemed very natural — to irregular 
 
 o 
 
194 ACQUIRED CHARACTERS sec. 
 
 habits of life. This suspicion became apparently a certainty 
 when the student, notwithstanding the remonstrances, re- 
 quests, and threats of his troubled parents, never wrote 
 a letter home, not even for money. Arguments on my 
 part succeeded in obtaining promises from him, but these 
 were never fulfilled. In the meanwhile, discreet inquiries 
 elucidated the fact that the student in other respects led a 
 thoroughly regular life ; that he generally went home before 
 midnight, and went to bed; and in particular, that he exercised 
 in all his other affairs a painstaking orderliness, as being the 
 son of a merchant he had always been accustomed to do. His 
 landlady stated that latterly, as always previously, when he 
 went away for a day he gave up his key to her in a sealed 
 packet. 
 
 On account of these facts I became convinced that the 
 young man must be suffering from a local inflammation of 
 the brain, or that a local inflammation of the cerebral mem- 
 brane must be causing pressure on a certain portion of his 
 brain, and that therefore a part of this organ which influenced 
 the activity of the will towards the particular direction of 
 letter- wTiting, and towards this alone, was for the time func- 
 tionless ; for the mental abilities of the subject and his 
 power of will were, and are still, in other respects normal, 
 apart from the effects of the great amount of sleep he required. 
 His general force of will is, however, only moderately de- 
 veloped. I was confirmed in this conviction by the fact that 
 at times symptoms appeared in him which might well be 
 ascribed to temporary increase of a chronic local inflamma- 
 tion of the cerebral membrane, symptoms some of w^liich had 
 a similarity to those of cramp of the neck, of meningitis 
 cerebrospinalis, although no fever ever appeared. After 
 constant medical treatment the student now, after some 
 months, is apparently well and healthy, only he cannot be 
 induced to write a letter. 
 
IV VIEWS OF VON KRAFFT-EBING 195 
 
 I brought forward this case because I followed it carefully 
 with great interest. Insanity doctors doubtless know numerous 
 others of a similar character. 
 
 It is, moreover, a fact generally known, that just such defi- 
 ciencies in the power of will in respect of various but definite 
 actions, in other words, of claims of human life, have helped 
 to determine the character of individuals and their descend- 
 ants, the character of whole families and peoples — that such 
 deficiencies are hereditary. 
 
 And because these deficiencies, because also the nerve- 
 cells of the brain in which they have their seat, owe their 
 origin to relations to the outer world, therefore they must 
 have been acquired. 
 
 The following, as an irrefragable proof of the inheritance 
 of mental diseases as diseases acquired through relations 
 to the outer world, I give in the words of an authority in 
 psychiatry, Dr. von Krafft-Ebing. 
 
 It is a 'priori a probable supposition that the doctrine of 
 inherited sin, which still finds place in the Christian religion, 
 especially in the Catholic Church, is derived from a knowledge 
 of the facts of heredity, just as the Mosaic and Moham- 
 medan prohibition of the eating of swine-flesh j^robably has 
 its ultimate cause in the experience of possible injurious 
 effects of that food, although trichinae as the cause of disease, 
 leaving tapeworms out of the question, could not have been 
 known. 
 
 But this view of the origin of " sin " is strongly supported 
 by the following record of facts concerning heredity as one of 
 the causes of insanity. Dr. von Krafft-Ebing says in the 
 section on this subject in his Textbook of Psychiatry : ^ — 
 
 1 E. V. Kraift-Ebing, Lehrhuch der Psychiatrie, 1879, Bd. i. p. 153, seq. 
 Cf. Prichard, Treatise of Insanity, p. 157 ; Lucas, Traite jihilosophiqxie et lihysio- 
 logiqxLe de Vheredite, Paris, 1847 ; Morel, Traite des Degenerescences, etc. Paris, 
 
196 ACQUIRED CHARACTERS sec. 
 
 " By far the most important cause of insanity is the 
 transmission of psychopathological tendencies, especially of 
 cerebral infirmities, by means of procreation. 
 
 " The fact of the heredity of psycliical defects and diseases 
 was known even to Hippocrates. It is only the special action 
 within the limits of this province of a general biological law 
 which plays a stupendous part in the organic ^vorld, on which 
 indeed the whole progress of the human race depends. 
 
 " After tuberculosis there is scarcely a class of diseases in 
 which heredity works so powerfully as in psychical diseases, 
 but on the percentage of cases in which its effects are evident 
 authorities differ. The percentage of cases determined by 
 heredity given by statisticians (Legrand du Saulle, o'p. cit. 
 p. 4), varies from 4-90 per cent. It is obvious that a constant 
 factor cannot produce effects in such a variable manner. The 
 cause of the difference can only lie in the different method 
 by which the statistical analysis was produced. Much 
 depends on tlie question, from what classes of people the 
 material of the statistics was derived. In aristocratic circles, 
 in communities secluded from intermixture with surrounding: 
 peoples, in exclusive religious societies (Jews, sectarians, 
 Quakers), where close interbreeding is practised, the percentage 
 of hereditary cases is greater than in a floating population. 
 But the point of view of the different statisticians has also been 
 different. Many investigators have only recognised heredity 
 when insanity could be proved in the parents (direct similar 
 inheritance). But the definition of heredity cannot be so 
 narrowly limited. Three essential facts are here to be con- 
 sidered. 
 
 1857 ; Idem, Archiv. gener. September, 1859 ; Hohnbaum, AUgein. Zeitschr. f. 
 Psych. 5, p. 540 ; Morel, Traite des Maladies mentales, pp. 114, 258; Ibid., 
 De Vheredite viorbide progressive, Archiv. gener. 1867 ; Voisin, Gaz. des. H6pit. 
 1858, 16; Moreau, V Union medic. 1852, 48; Jung, Allg. Zeitschr. f. Pschy. 
 21-23, Ann. Med. Psych. November 1874 ; Legrand du Saulle, Die erhliche 
 Geistesstorung, German by Stark, 1874 ; Ribot, Die ErUichkeit, German by 
 Hotzen, 1876 ; Hagen, Statist. Untersuch. Erl. 1876, 
 
IV VARIATIONS OF INHERITED INSANITY 197 
 
 " (d) Atavism. — The bodily and mental organisation and 
 character can be transmitted from the first to the third 
 generation, without any necessity that the second and inter- 
 mediate one should exhibit the peculiarities of the first 
 — thus the condition of the life and health of the grand- 
 parents are of interest for us. 
 
 " {h) Only in rare cases is the actual disease transmitted 
 in procreation (congenital insanity, hereditary syphilis), as a 
 rule only the disposition thereto. Actual disease only occurs 
 when accessory injurious influences produce an effect based 
 upon that disposition. ... 
 
 " We must, therefore, consider also the state of health of the 
 relatives (uncles, cousins, aunts), and, since here also the law 
 of atavism holds good, the possible diseases of great-uncles 
 and great-aunts. 
 
 " (c) Only exceptionally does the same disease develop in 
 ascendant as in descendant in consequence of the transmis- 
 sion of morbid dispositions. On the contrary, there exists 
 a remarkable variability in the forms of disease which may 
 almost claim the value of a law (the law of polymorphism or 
 transmutation). 
 
 " The transmutations are innumerable. The most varied 
 neuroses and psychoses occur side by side in families with a 
 hereditary taint, and one after another throughout genera- 
 tions, and teach us that from a biological, etiological stand- 
 point they are only branches from one and the same 
 pathological stem. 
 
 " The fact of the variability of the morbid conditions due to 
 heredity necessitates a careful examination of the question. 
 With what conditions and symptoms of morbid nervous 
 organisation hereditary transmission, direct or modified, is 
 connected ? 
 
 " (a) In this respect there is no uncertainty about those 
 cases in which psychoses present themselves in both the 
 
198 ACQUIRED CHARACTERS sec. 
 
 ascendant and the descendant (liomogeneous inheritance). 
 In many of these cases the psychosis has even in both 
 generations the same form, and its outbreak depends 
 on the same accessory causes, e.g. parturition (uniform 
 inheritance). 
 
 " (yg) The recurrence of suicide ^ throughout successive 
 generations is an equivalent phenomenon belonging to the 
 same class, i.e. the tendency to suicide, which is almost 
 always a symptom of melancholia or of a neuropsychopathic 
 constitution which is unable to endure arduous condi- 
 tions of life. Particularly convincing are those cases of 
 suicide in which ascendant and descendant destroy them- 
 selves under almost the same conditions of life and at 
 a similar age. Genealogical tables actually exist which 
 show that whole unhappy families have died out through 
 suicide." 
 
 " (ry) Equally certain are the hereditary effects of constitu- 
 tional neuropathies, though they may only consist in a 
 habitual migraine or in a hysteria or epilepsy.^ 
 
 " The hereditary morbid factor may make itself felt in the 
 descendants in a mere neuropathic constitution, in the pro- 
 duction of neuroses, but also of psychoses, even to idiocy, as 
 the worst form of hereditary degeneration. 
 
 " (8) The hereditary influence of pathological character in 
 tending to insanity is firmly established. 
 
 " Visionaries, perverse, eccentric characters, oddities, or 
 hypochondriacs have not only extremely often ascendants 
 
 ^ Tigges, Vierteljo.hrschr. f. Psychiatne, 1868, No. 3,4, p. 334. 
 
 - Morel, Traite des mal. ment. p. 404 ; Ribot, p. 147; Lucas, ii. p. 780 ; 
 Ann. Med. Psych. May 1844, p. 389. 
 
 3 Trousseau, Med. Klin. German by Culmann, 1867, p. 88 ; Moreau [o]). 
 cit.) found among 364 epileptics 62 epil., 17 hyster., 37 apoplect., 38 insane rela- 
 tives, 195 times convulsions, consumption, scrofula, eclampsia, asthma, dipso- 
 mania, etc., among the parents or relatives ; Martin, Ann. Med. Psych. Novem- 
 ber 1878, shows that the children of epileptics die in large numbers in convul- 
 sions. 
 
IV CRIME AND INSANITY 199 
 
 and collateral relatives who are diseased in mind or nerves^ 
 but also neuropathic, insane, even idiotic offspring. 
 
 " These problematic beings, who mostly from their child- 
 hood feel, think, and act differently from other people, are 
 also themselves in constant danger of becoming insane, and 
 are often candidates for a degenerate form of true insanity 
 — namely, primary madness, to which also their offspring are 
 more particularly liable. 
 
 " (e) That criminal and vicious habits of life ^ stand in 
 hereditary relation to insanity is proved by the frequency 
 with which insanity and other neurotic degenerations occur 
 in habitual criminals themselves and in their blood-relations, 
 their ascendants and descendants. The contrast nevertheless 
 remains between crime as a moral and insanity as an organic 
 degeneration. The point of contact of the two lies simply in 
 the fact that insanity may show itself under the clinical form 
 of moral depravity (see moral insanity), and is frequently 
 falsely taken for the latter. The passion for drink must also 
 be included in the series of factors having a hereditary in- 
 fluence. In this case homogeneous inheritance seldom occurs, 
 usually heterogeneous ; the parents who have degenerated in 
 consequence of excesses in alcohol give life to children who 
 come into the world idiotic or hydrocephalous or with neuro- 
 pathic convulsive constitutions, who soon perish of convul- 
 sions, while among those who survive, epilepsy, hysteria, 
 mental diseases, and, in fact, the worst forms of psychical 
 degeneration, develop from the morbid constitution of the 
 nerve centres. 
 
 "Thus Marce records the case of a drunkard who had 
 
 1 Roller, Allg. Zeitschr. f. Psych, i. p. 616 ; Heinrich, ibid. 5, p. 538 ; 
 Solbrig, Verhrechen und Wahnsinn, 1867 ; Legrand du Saulle, Ann. d'Hyg. 
 October 1868 ; Despine, Etude sur les FacuUes Intellect, et Morales, Paris, 1868 ; 
 Laycock, Journal of Mental Science, October 1868 ; Brierre, Les Fous CHminels 
 de V Angleterre, German by Stark, 1870 ; Thomson, Journ. of Mental Science, 
 October 1870. 
 
200 ACQUIRED CHARACTERS sec. 
 
 sixteen children. Fifteen died young ; the only survivor was 
 epileptic. According to Darwin, the families of drunkards 
 become extinct in the fourth generation. According to 
 ^larce, the decjeneration is as follows : — 
 
 " I. Generation : Moral depravity, excessive indulgence in 
 
 alcohol. 
 
 11. ,, Drink mania, maniacal attacks, general 
 
 paralysis. 
 
 III. „ Hypochondria, melancholia, taedium vitae, 
 
 impulse to suicide. 
 
 IV. „ Imbecility, idiocy, extinction of the family.^ 
 
 *' It is a wonderful fact, which is nevertheless established by 
 cases brought forward by Flemming, Euer, and Demeaux, 
 that even children of parents usually temperate, when their 
 generation has chanced to occur during an exceptional time 
 of intoxication, have in a high degree a tendency to mental 
 derangement and nervous diseases. This evil influence may 
 even show itself from birth as congenital weakness of intellect 
 or idiocy. 
 
 " Griesinger draws attention to the fact that genius ^ some- 
 times occurs alongside of hereditary idiocy. Moreau even 
 went so far as to explain genius as a neurosis. That men of 
 genius not seldom (Schopenhauer's grandmother and uncle 
 were imbecile) have insane, psychically defective relations, 
 and produce children who are weak-minded or even idiotic, is 
 certain. It seems as if a higher internal orcfanisation of the 
 nervous elements common to both, in one case, under the 
 
 ^ Cf. the valuable work of Taguet, TJeher die erhlichen Folgen des A Ikoholismus, 
 Ann. Med. Psych. July 1877 ; Morel, Traite des Degeneresc. p. 116 ; Jung, Allg. 
 Zeitschr.f. Psych. 21, pp. 535, 626 ; Biir, Alkoholismus 1878, p. 360. 
 
 ^ Cf. Hagen, Ueber Verioandtschaft des Genie mit dem Irresein, Allg. Zeitschr. 
 f. Psych. 33, Hefts 5, 6 ; Maudsley, translated by Bohra, p. 309 ; Moreau, 
 Psychologie Morhide, 1859. 
 
IV ORIGINAL CA USES OF INSANITY 201 
 
 influence of peculiarly favourable conditions, reaches a higher 
 development ; in another, under unfavourable conditions, 
 leads to psychical degeneration. 
 
 " Whether consanguinity in marriage^ is to be regarded as a 
 factor in hereditary degeneration must for the present remain 
 undecided. The experiments of breeders of animals, who, it 
 is true, breed only from perfect individuals, as well as the 
 pedigree of the Ptolemies, go to disprove it. It is possible 
 that it remains for a long time without effect, so long as the 
 pairing individuals continue free from degenerative tendencies. 
 If this is not the case, rapid degeneration soon occurs — 
 albinism, deaf muteness, idiocy, sterility. 
 
 "Lastly, there can be no doubt that everything which debili- 
 tates the nervous system and the generative powers of the 
 parents, be it immaturity or too advanced old age, previous 
 debilitating diseases (typhus, syphilis), mercurial treatment, 
 alcoholic or sexual excesses, overwork, etc., may give rise to 
 neuropathic constitutions, and thereby indirectly to every 
 possible nervous disease in the descendants. 
 
 " The importance of heredity in our province becomes 
 particularly clear when the fate of families afflicted 
 with psychical disease is followed through several genera- 
 tions." 
 
 "A genealogical table, compiled from my own observations, 
 will exhibit this : — 
 
 1 Darwin, EJien Blutsverwandter, German by v. d. Velde, 1876 ; Devay, Du 
 Danger des Mariages consanguins, Paris, 1857 ; Baiidin, Ann. d'Hyg., second 
 ser. xviii. p. 52 ; Mitchel, ibid. 1865 ; Allg. Zeitschr. f. Psych. 1850, p. 359. 
 According to Beauregard {Ann. d'Hyg. 1862, p. 226), from 17 marriages between 
 relations 95 children were born, of whom 24 were idiots, 1 deaf, 1 a dwarf, 37 
 entirely normal. 
 
 2 Cf. the interesting tables of Bird, Allg. Zeitschr. f. Psych. 7, p. 227 ; Tagnet, 
 Ann. Med. Psych. July 1877; Doutrebente, ibid. September, November 1869, 
 {Schmidt's Jahrb. 145, p. 3). 
 
202 
 
 ACQUIRED CHARACTERS 
 
 SEC. 
 
 
 First 
 
 Second 
 
 Third 
 
 Fourth 
 
 Fifth 
 
 Generation. 
 
 Generation. 
 
 Generation. 
 
 Generation. 
 
 Generation. 
 
 I 
 
 
 1. Daughter, 
 
 1. Daughter, 
 
 
 
 
 mentally dis- 
 
 history un- 
 
 ? 
 
 
 
 eased. 
 
 known. 
 
 2. Daughter, 
 mentally dis- 
 eased. 
 
 3. Son, maniac. 
 
 None. 
 None. 
 
 
 
 2. Daughter, 
 
 7 healthy chil- 
 
 1 
 
 
 
 healthy. 
 
 dren. 
 
 
 
 
 3. Daughter, 
 
 1. Son, ment- 
 
 
 Father ment- 
 
 
 mentally dis- 
 
 ally diseased, 
 
 None. 
 
 ally diseased. 
 
 
 eased. 
 
 suicide. 
 
 
 A daughter, the 
 
 
 2. Daughter im- 
 becile. 
 
 3. Daughter, 
 
 None. 
 
 
 only child, be- 
 
 
 
 
 came ment- 
 ally diseased. 
 
 
 periodically 
 mad. 
 
 None. 
 
 Mother normal. 
 
 
 
 
 
 
 
 4. Daughter, 
 
 2 Sons, history 
 
 1 
 
 
 
 healthy. 
 
 unknown. 
 
 c 
 
 
 
 5. Son, ment- 
 
 None. 
 
 
 
 
 ally diseased. 
 
 
 
 
 6. Son, ment- 
 
 1. Son, heal- 
 
 ? 
 
 
 
 ally diseased. 
 
 thy. 
 
 
 
 
 2. Son, insane. 
 
 None. 
 
 
 
 
 3. Daughter, 
 
 Daughter 
 
 
 
 
 healthy. 
 
 insane. 
 
 
 
 7. Son, heal- 
 
 3 healthy chil- 
 
 <i 
 
 
 
 thy. 
 
 dren. 
 
 
 
 
 8. Son, heal- 
 
 5 healthy chil- 
 
 ? 
 
 
 
 thy. 
 
 dren. 
 
 
 " Of these thirty-seven individuals, therefore, descended 
 from ancestors mentally diseased, thirteen are insane and 
 twenty-four normal, but the history of some is wanting, and 
 others are still very young. 
 
 " A review of all the facts mentioned teaches us that in- 
 sanity, regarded broadly, is a phenomenon of degeneration 
 whose determining conditions are to be sought in congenital 
 morbid dispositions transmitted to the germ in consequence 
 of hereditary pathological states of the brain in the as- 
 cendants, or in injuries of the cerebral organisation of the 
 individual incurred in the course of life. 
 
IV THE FATE OF AFFECTED FAMILIES 203 
 
 "The morbid disposition produced by either of these factors, 
 whether infirmity or actual disease, shows, according to the 
 biological law of heredity, a strong tendency to be transmitted 
 in some form or other to the descendants. 
 
 " Thus the words of the Holy Scripture, ' I will visit upon 
 you the sins of your fathers unto the third and fourth genera- 
 tion,' have a profound significance, and the manner of life, the 
 lot in life, and the selection of the ascendants in great 
 measure determines the fate in life of coming generations. 
 The conventional German expression wolilgeboren acquires 
 from our point of view a sense full of importance. 
 
 "The kind of transformation which takes place in the course 
 of hereditary transmission, the special form of the nervous or 
 psychical infirmity, depends on individual and external, often 
 accidental conditions. In this question science has not yet 
 attained to the formulation of laws. 
 
 " It can only be said generally, that when two affected 
 individuals unite for reproduction, or when unfavourable 
 interfering conditions (drunkenness, debilitating influences, 
 etc.), are added to the unfavourable constitution of the gener- 
 ating individual, the morbid affection of the descendants 
 becomes continually more serious, and in the continued trans- 
 mission of psychopathic degenerative tendencies a progressive 
 aberration proceeds till the extreme forms are reached. 
 Psychoses are in such conditions developed from neuropathies, 
 at first still quite benignant and conforming to the type 
 of psychoneuroses, afterwards continually more degenerate 
 (cyclical, periodic, moral, impulsive insanity), till finally 
 idiocy occurs. Then nature extinguishes the pathological 
 family, which loses the physiological capacity for reproduc- 
 tion. Conversely, however, regeneration is possible up to a 
 certain stage through crossing with healthy blood from an 
 untainted, unaffected family, or through the effect of favour- 
 able conditions of life. The forms of disease then become 
 
204 ACQUIRED CHARACTERS sec. iv 
 
 continually milder, and if the crossing is continued the 
 degenerative tendency may entirely disappear. 
 
 "The interesting question, answered by Morel in the affirma- 
 tive, Whether hereditary insanity exists as a clinical form, 
 must remain an open one.^ 
 
 "According to my experience, hereditarily degenerative 
 insanity is only a particular case of degenerative insanity 
 in general. 
 
 " With regard to the above question, stress must be laid 
 upon the difference between mere hereditary predispositions 
 (latent tendencies) and hereditary disease, i.e. where the factor 
 of heredity acts with a determining and injurious effect on 
 the mental and bodily development and constitution of the 
 individual. 
 
 " Insanity in cases of mere hereditary predisposition differs 
 from cases which are not hereditary in no way except by its 
 appearance at an earlier age, and in consequence of trivial 
 accessory causes, its more sudden outbreak and more rapid 
 recovery, as well as its more favourable prognosis. 
 
 " In the stages of transition to hereditarily degenerative 
 insanity the forms become more serious and more organic, 
 and certain symptoms of degeneration (stupor, impulsive acts, 
 periodicity) become noticeable." 
 
 I have repeated the observations of Von Krafft-Ebing 
 word for word, because they so often actually give verbal 
 expression to my own views, and because, as the reader will 
 find for himself, they supply in their details examples sup- 
 porting my views than which none better could be imagined. 
 
 It might almost be supposed that I had based my remarks 
 on these instances. But I only read Von Krafft-Ebing's work 
 after my section on the inheritance of diseases was already 
 Avritten. 
 
 ^ Cf. Emminghaus, Allg. Psychopath, p. 322. 
 
SECTION V 
 
 DISUSE OF ORGANS — DEGENERATION — PAMMIXIS 
 
 In the paper previously mentioned, " Retrogression in Nature," 
 Weismann replies with greater detail and precision than on 
 previous occasions to the objections which may be made — as 
 they have been made by me — to his theory on account of the 
 facts of the degeneration of organs in consequence of disuse. 
 
 Starting from the proposition that "the adaptation of 
 living beings in all their parts depends on the process of 
 natural selection," he infers that this adaptation must be 
 maintained by the same means by which it was produced, 
 and that it must again disappear as soon as this means, 
 natural selection, fails to act. 
 
 In other words, he says : Through natural selection alone 
 forms have come to be what they are. By the continuation 
 of natural selection only are they maintained in their present 
 state. If selection ceases, they of necessity retrograde. But 
 selection with respect to a particular organ obviously ceases 
 as soon as that organ is no longer necessary (" the reverse 
 side of natural selection ") — its cessation therefore produces 
 the degeneration of organs. 
 
 It is, according to my view, self-evident that the cessation 
 of natural selection ^ can as little cause the retrogression of 
 
 ^ Weismann employs the expression NaturzuchUing (natural breeding) only in 
 the sense of Auslese (selection), herein following Darwinism in general. This use 
 
206 DEGENERATION sec. 
 
 an organ as natural selection can cause it to develop. Selec- 
 tion is, I must ever repeat, no physiological factor "which 
 could directly produce anything new, or whose cessation 
 could annul anything existing. Organs are produced by 
 external stimuli, or by use acting upon the material given in 
 a given case, with the aid of general and of sexual selection. 
 Weismann, while he refuses to recognise what I assume to 
 be the principal influences as having any important effect, 
 while he puts forward natural selection or its cessation as 
 active accents, brini]js forward another factor to aid in the 
 carrying out of the modification due to these agents, namely, 
 sexual intermixture. According to him, the degeneration of 
 the powers of organs and the organs themselves is not due to 
 the diminution and cessation of its activity, with the aid of 
 the cessation of natural selection and of sexual intermixture, 
 but is due to the latter two causes only. He says those parts 
 wliich are no longer useful are no furtlier subject to selection 
 — the individuals multiply sexually, therefore, ecjually whether 
 those parts are developed or not. All individuals unite 
 without reference to the character in question, and therefore, 
 through pammixis, through general intermixture, the char- 
 acter must vanish. 
 
 Weismann's explanation of degeneration is certainly 
 correct, so far as the proposition from which it is derived 
 is correct — the proposition that all adaptation of forms 
 depends on natural selection ; and, I must add, so far as all 
 that exists in the forms of organic nature depends on 
 adaptation. 
 
 I have, however, strenuously opposed these propositions, 
 
 of the term natural breeding may easily lead to the error of treating selection 
 as an active force. It would be better always to use the term selection where 
 the survival of the fittest in the struggle for existence is meant, since natural 
 breeding, according to the view advocated by me, can occur without any 
 selection. Directly acting external stimuli and the use or disuse of organs effect 
 modifications of living forms, and this may be properly described as natural 
 breeding. 
 
WE IS MANN'S EXPLANATION 207 
 
 and thus, to my mind at least, the general validity of Weis- 
 mann's conclusion falls to the ground. 
 
 That this conclusion — putting aside the fact that it does 
 not regard the ultimate causes of the degenerations — is fully 
 justified with respect to a large number of characters is, 
 for every one who accepts the principle of utility, a fact 
 long established and indisputable. Its justice is proved most 
 clearly and most simply, for instance, by the disappearance of 
 the adapted colouring of the wild ancestors in our domestic- 
 ated animals — e.g. rabbits — in consequence of domestication. 
 
 But the conclusion does not hold good for any indifferent 
 characters, including those which depend on correlation, nor 
 for those which are accidentally useful and which have arisen 
 from and are maintained by external influences. 
 
 That indifferent structures may undergo degeneration 
 appears from physiological considerations indisputable. In 
 his short paper, "The Origin of New Species through the 
 Decay and Disappearance of Old Characteristics," Oscar 
 Schmidt has, as I have already remarked, pointed out a case 
 in sponges which, in my view, bears upon this subject. It 
 concerns the genus Caminus. 0. Schmidt had previously 
 said that the fine Caminus Vulcani of the Adriatic Sea 
 probably belonged to the Tetractinellidse, notwithstanding the 
 absence in it of the four-rayed siliceous spicules characteristic 
 of that order. Subsequently he obtained a Caminus (C. 
 osculosus, Grube) which contained in no small numbers such 
 spicules in process of degeneration. 
 
 In the specimen which Grube had before him, however, 
 these spicules, as could be still shown, were very rare, and 
 in some preparations entirely wanting. On re-investigating 
 Caminus Yulcani, 0. Schmidt found in this sponge also 
 scattered remains of such degenerate four-rayed spicules, but 
 none in Caminus apiarium. " And thus," says 0. Schmidt, 
 ^' in Caminus proof is afforded that by the disappearance of an 
 
208 DEGENERATION sec. 
 
 important, formerly diagnostic, ordinal character a new form 
 of generic value has been produced." 
 
 The causes of the disappearance of the four-rayed spicules 
 in 0. Schmidt's opinion remain in obscurity. But he also 
 holds that their presence or absence in Caminus does not 
 depend on selection, since other spicules, uniaxial and stellate, 
 are present, and because the genus in no respect gives the 
 impression of degeneration, ratlier seems " to stand at the 
 acme of life." Schmidt classes these spicules among those 
 characters which, as he justly says, are somewhat indefinitely 
 called " morphological," that is, immaterial, indifferent. 
 
 Indeed, in Caminus the uniaxial spicules are beginning 
 here and there to degenerate, but independently of the 
 degeneration of the quadriaxial. 
 
 It may of course be objected that the quadriaxial spicules in 
 Caminus were once useful, and that they are now disappearing 
 in consequence of the cessation of selection, because other use- 
 ful characters have appeared in this genus of sponges wliich 
 make the presence of the quadriaxial spicules unnecessary. 
 But proof of this is wanting. 
 
 And the extreme variation of the skeletal parts of sponges 
 in one and the same species indicates in the clearest way 
 that the form of these parts is a character whose variation, 
 at all events within very wide limits, remains entirely un- 
 affected by selection. 
 
 Oscar Schmidt points out further that numerous other 
 cases in sponges have been described by Haeckel and himself, 
 in which the organisms are beginning to change into new 
 species by the disappearance of certain forms of their skeletal 
 structures. And I am able to add that in the markings of 
 animals — e.g. butterflies — characters everywhere degenerate 
 whose present or former use cannot be discerned, which we 
 must resjard as non-essential. 
 
 Weismann supposes that even in those cases in which 
 
DEGENERATION OF EYES 209 
 
 adaptation is not . demonstrated it is really present. But 
 such an assumption belongs to the domain of faith. 
 
 "We ought on the contrary to say : We know that definite 
 stimuli must produce an effect on or in the organism — that 
 they must give rise to definite changes of form, definite 
 characters, whether these be useful to the organism or not. 
 
 When we maintain this we take our stand, not on mere 
 assumptions, but on physiological facts. Normal physiology 
 and pathology in like measure speak for us with the weight 
 of all their fundamental truths. 
 
 Thus there is certainly a physiological basis for the belief 
 that the above -described variations of the sponge -skeleton 
 are simply to be ascribed to changes of external, i.e, of 
 nutritive conditions, of the material composition of the body. 
 
 From this point of view I will permit myself to discuss 
 the several instances which Weismann gives in his latest 
 paper in support of his explanation of the degeneration of 
 disused organs. 
 
 Weismann attributes the degeneration of the eyes in 
 subterranean animals to the cessation of natural selection. 
 Without any doubt, this cause is of very great importance. 
 But with equal certainty physiological considerations lead to 
 the conviction that continual absence of the stimulus of light 
 by itself, without anything else, must gradually injure and 
 finally destroy the capability of the eye to serve as the organ 
 of sight. First of all, the profuse circulation of blood in the eye 
 would be diminished, and thereby the nutrition of the whole 
 be affected ; the muscles, the accommodation apparatus, would 
 become unfit for use ; the retina would be altered. At the 
 same time, the pigment of the eye, which is always connected 
 with the action of light, would disappear, and thus already 
 the eye as such would be rendered almost useless, brought 
 morphologically nearly to the stage of an organ merely 
 susceptible to light, from which it was evolved. 
 
 p 
 
210 DEGENERA TION sec. 
 
 It is a physiological demand that constant, regular, not 
 excessive use of any organ is absolutely necessary to its 
 maintenance. Indeed, the stimulus to which it responds is 
 undoubtedly the influence to which an organ owes its origin 
 and its o^radual evolution. 
 
 Let us dwell somewhat further on the eve. 
 
 Weismann says : '' Short sight, it is true, can be acquired, 
 but then it is not inherited, as I at least believe myself 
 bound distinctly to suppose. In my opinion, we owe the 
 extensive prevalence of shortsightedness, not merely to the 
 excessive straining of the eyes and to the continual observa- 
 tion of near objects, but to pammixis, the cessation of natural 
 selection in this direction ; for we are as much subject to 
 the effects of these causes as all other organisms. As it is 
 pretty nearly indifferent in the present state of society — 
 especially since spectacles were invented — whether the in- 
 dividual sees somewhat farther or a somewhat less distance, 
 the organ of sight has come under the action of pammixis." 
 
 That Weismann's conclusion is possibly partially true also 
 in this instance we readily admit. But proof is wanting 
 of the principal assertion, that short sight is not simply 
 hereditary. The question would have to be tested accurately 
 by the oculists with respect to Weismann's statements, to 
 be treated statistically. He himself does not speak very 
 decidedly on the point. 
 
 He says further, moreover, in connection with this same 
 subject, that the deterioration of bodily advantages in us, in 
 comparison with our forefathers, is to be considered in rela- 
 tion to the high development of our intellect. But this 
 intellect can surely only have been gradually acquired and 
 transmitted by our forefathers. It depends upon experience, 
 which certainly cannot be produced by variability of the 
 germ-plasm. I shall have occasion subsequently to consider 
 this question at greater length. 
 
DEGENERATION OF STAMENS 211 
 
 With regard to the eye Weismann himself admits that its 
 action might be affected by want of exercise, " inasmuch as 
 the chemical changes which take place in the retina when 
 vision takes place must cease when the eye is no longer 
 exposed to light." " But," he says, " how could the stamen of 
 a flower be affected by the alternative, whether the pollen 
 which it bears reaches the stigma of another flower or not. 
 And yet we know that hermaphrodite flowers have in some 
 cases reverted to the original separation of the sexes, by the 
 atrophy of the stamens in one flower, of the pistil in the 
 others. Whether this particular case is to be explained by 
 the cessation of selection — whether active natural selection 
 does not play a part in it — is another question. But let us 
 follow it further. After the anthers in the evolution of the 
 species have atrophied and entirely disappeared, their stalks 
 persist, not rarely possessing considerable length and thick- 
 ness. Gradually, but very gradually, these also degenerate, 
 and we find them in many species still of considerable length, 
 in others already quite short, in others again completely 
 absent, and only occasionally appearing in a particular flower 
 as a reminiscence of their former general presence. The 
 filament of the anther is no longer used, but how could it be 
 thereby directly affected and caused to atrophy ? Its struct- 
 ure has remained the same, the sap circulates in it as before, 
 and flows into it as much as into the neighbouring petals 
 or the pistil. From our standpoint the matter is easily 
 explained, for the mere filament of the stamen is perfectly 
 immaterial to the continued existence of the species of plant 
 in question ; natural selection therefore withdraws its hand 
 from the organ, and it gradually atrophies." 
 
 Here also, in my view, it must be claimed that the 
 absence of external stimuli contributes to produce the effect 
 — on the one hand, the absence of the stimulation of the 
 female organs of the hermaphrodite by the process of fertilisa- 
 
212 DEGENERA TION sec. 
 
 tion, on the other, the cessation of the stimulation caused by 
 the action of insects in gathering the pollen. 
 
 ^Moreover, correlation plays a particularly important part 
 in the sexual organs, at least in the animal kingdom, and it 
 is well known how prone stamens are to degenerate in plants 
 generally. 
 
 Weismann lays particular stress on the fact that wingless- 
 ness as a character of the asexual workers amomx ants is 
 inherited from the winged sexual individuals. " It is there- 
 fore impossible that the degeneration of the wings, possibly 
 caused by disuse in the individual animal, should be trans- 
 mitted to a succeeding generation." 
 
 The immediately obvious reply to this is mentioned by 
 Weismann himself, when he says : " It might perhaps be 
 maintained that the loss of the wings occurred previously to 
 that of the power of reproduction, but such a supposition 
 must on verv definite Gjrounds, which I must here omit to 
 particularise, be rejected." But what if the degeneration of 
 the wings and of the sexual organs proceeded simultaneously — 
 correlatively ? This appears to me probable, on account of 
 the important correlative connections of the sexual organs. I 
 shall subsequently have to speak further, in reference to bees, 
 of the power of correlation, which shows itself especially 
 in the modification of the sexual organs. What is there 
 said will apply to the case of ants, wdiich is not completely 
 disposed of here. 
 
 The absence of hair in the larger marine mammals is 
 attributed to the cessation of natural selection : " The hairy 
 covering is no longer necessary in the water — the layer of fat 
 supplies its place." Here again I cannot banish the idea 
 that physiological causes are also concerned in this alteration. 
 It is certainly striking that no animal which develops and 
 always lives in the open water possesses a horny epidermis, 
 and hairs are horny structures of the epidermis. Whales, to 
 
HERMIT-CRABS 213 
 
 take these as an example, of course develop in the body of 
 the mother, and the embryos possess an inherited light 
 covering of hair, which is no longer present in the adults. 
 That the action of water is unfavourable to the cornification 
 of the epidermis necessary for the formation of hair — be it 
 even merely in the succession of the hairs during the later 
 independent life — and that the hair, therefore, and also be- 
 cause it could be dispensed with and was not an advantage 
 to the motion of the animal, has been gradually lost, is not 
 surprising. Cornification depends essentially on the loss of 
 water. Only exceptionally, for particular purposes, is horn 
 developed here and there in exclusively aquatic animals 
 {e.g. the horny teeth of the lampreys, whalebone of whales). 
 
 On the other hand, we find cuticular structures — hard 
 secretions formed by the epidermis — widely distributed in 
 aquatic animals, and forming their egg-cases. Such cuticular 
 structures often form a case for the body of the animal, into 
 which it can withdraw itself. This secretion consists of 
 other material than the cornified epidermis of the verte- 
 brates. 
 
 The parts of the body which are included in such cuticular 
 sheaths often degenerate. Similarly, the hinder part of the 
 body of the hermit crab, which is inserted into a whelk shell, 
 degenerates, and the hard cuticle of the crab which is 
 protected by the shell has become soft and tender. Weis- 
 mann ascribes this alteration entirely to the absence of 
 natural selection. He says : " The use of the shell depends 
 sim^Dly on its entirely passive presence. Whether the animal 
 is by it protected against thrusts or bites, or whether it is 
 threatened by no such dangers, is quite indifferent to the 
 shell itself and its proper development ; it loses and gains 
 nothing thereby, and least of all does its perfection depend 
 on its being as often as possible battered with thrusts and 
 bites. It cannot possibly be caused to atrophy by the fact 
 
214 DEGENERATION sec. 
 
 that in the whelk shell it is out of the reach of such blows. 
 When, therefore, the cuticular armour atrophies exactly in 
 proportion as the body is covered by the protecting mollusc- 
 shell, this can only be explained by the consideration that 
 on the parts of the body covered by the whelk shell the 
 armour is superfluous and of no consequence; and that 
 natural selection, therefore, could no longer be concerned in 
 its maintenance." 
 
 In this instance I can only make the objection which I feel 
 obliged to make in all the rest : By selection alone nothing 
 whatever can be produced, and the cessation of selection is 
 not the only cause of the disappearance of anything which 
 has been evolved. 
 
 It is scarcely necessary to mention what hinders the 
 perfect development of the cuticular armour (by which is 
 meant that of the posterior end of the hermit crab ensconced 
 in its protecting gasteropod shell). The armour, according to 
 ni}^ view, was produced in consec|Uence of external stimuli 
 acting continually on the epidermis of the animal : the 
 cuticular structure was excreted as the effect of these stimuli. 
 The stimuli were the first cause of the commencement of its 
 formation. It served the animal as a protection. Selection 
 thereupon picked out those animals which were most* 
 efficiently armoured. After the crabs had concealed them- 
 selves in gasteropod shells, the external stimuli could no 
 longer act upon their skin, and at the same time the selection 
 ceased, and so ensued the degeneration of the hard cuticle. 
 
 By the co-operation of the degeneration caused by disuse, 
 and not by parnmixis alone, as Weismann insists, according to 
 my view, all cases are explamed in which the mouth parts 
 have atrophied or even the intestine degenerated in animals 
 which have altogether ceased to feed. The latter applies to 
 the males of the Eotifera, the former to many nocturnal 
 Lepidoptera, and to the Ephemera. Such animals either have 
 
DEGENERATION OF FUNCTIONS 215 
 
 a large store of nourishment in the body, or they live like 
 the Ephemera only a short time. 
 
 Simple considerations of a general kind are sufficient to 
 show that the mere cessation of selection — sexual union with- 
 out selection — pammixis — cannot possibly be the exclusive 
 or even the principal cause of degeneration. It is a fact that 
 most organs reach com^pUU degeneration very slowly. But 
 their functional powers they lose very soon, and this can only 
 depend on the fact that they liegin to degenerate very soon 
 after they cease to be used, and to degenerate in the most 
 essential parts, in the co-ordination of these parts which is the 
 condition of the performance of the function. That the mere 
 morphological framework remains so long, and for such a 
 long time constantly reappears, is due to the persistence with 
 which characters acquired by the ancestors are repeated in 
 the descendants, — the morphological being inherited long 
 after the functional has been abandoned. The latter vanishes 
 lirst, and with it the essential existence of the organ. When 
 it has completely vanished, the organ can scarcely ever again 
 be recalled to the same activity — if the same function becomes 
 again necessary to the organism, it must hel^D to develop a 
 new organ. But I do not intend to exhaust this question 
 here, and will only point out that the loss of the function 
 means the loss of the most essential part of the organ, for 
 the form without contents is dead, worthless. Thus for us 
 degeneration is a certain result as soon as the function 
 has completely departed ; a revival of it is impossible. The 
 atrophy of the organ must then inevitably follow, step by 
 step ; however distant may be its completion, its occurrence 
 is certain. 
 
 If the degeneration of functions, e.g. of instincts, took 
 place merely in consequence of the cessation of selection, 
 of pammixis, this degeneration, especially that of mental 
 characters, would proceed infinitely more slowly than it 
 
216 DEGENERATION sec. 
 
 actually does. For it would require sexual union of all the 
 individuals of a species repeated through many generations, 
 while selection remained inactive. Pammixis, all-mingling, 
 can only mean that all attain to sexual intercourse irrespective 
 of selection ; not only the individuals which in this or that 
 direction are best fitted for the maintenance and improvement 
 of the species, unite sexually, but in these directions there is 
 no longer any best or better — in these directions no further 
 selection is made : thus all individuals, whether well or ill 
 provided in these particular respects, succeed in reproducing 
 themselves, and so the characters in question are gradually 
 lost. "What length of time, I repeat, would be required for 
 functions to degenerate, if they could only degenerate in this 
 way, and how rapidly they do actually degenerate. Scarcely 
 a few thousand years were required for the most powerful, 
 most dominant nations to deteriorate, to degenerate mentally, 
 and even bodily, to the very limits of capacity for existence. 
 Two generations are sufficient in a community for the citizens 
 who, from wealthy benefices and foundations, have become 
 accustomed to an idle life, to degenerate, not by pammixis, 
 but because they no longer exert their powers. In rapid 
 alternation, after a small number of generations, the capacity 
 and powers of the burgess families rise and fall ; dignified 
 or jjarasitic life continued through a few generations leads to 
 completely unhealthy mental decay. 
 
 Not cessation of selection is here the principal influence, 
 but primarily the neglect of mental and bodily exercise, 
 whose effects rapidly and powerfully transmit themselves. 
 
 But I think I need not go further into the evidence that 
 the degeneration of organs is a process which is to be ex- 
 plained as the inheritance of acquired characters, es]3ecially 
 when what has been previously said on tlie subject and the 
 countless facts which comparative anatomy and physiology 
 contribute to this evidence are borne in mind. And the great 
 
PAMMIXIS 217 
 
 importance which must be ascribed to degeneration in the 
 formation of species is shown by the most elementary know- 
 ledge of animal forms. 
 
 Pammixis 
 
 Pammixis, it is self-evident, only affects the question of 
 the modification of species in cases of forms which are 
 confined and isolated within a comparatively narrow territory, 
 if by pammixis is meant the cessation of selection and the 
 consequent levelling sexual intercourse of all forms without 
 distinction — that is, in English, in-and-in-breeding. In small 
 political districts, especially in those which are in mountain- 
 ous regions, such as are found among Germans, especially in 
 Switzerland, the effect of in-breeding must with respect to 
 human beings be particularly evident, as far as the produc- 
 tion of similarity of characters is concerned. But even here 
 the result which first appears is obviously only that one or 
 another character which has arisen from the action of some 
 external conditions on a few individuals becomes prevalent. 
 Thus in the Canton of Aj^penzell I noticed an extremely 
 remarkable variety of man among the male population. This 
 variety is distinguished by perfectly curly, luxuriant, reddish- 
 brown hair on the large skull. Selection, either general or 
 sexual, cannot by any means be assumed here. Eather the 
 origin of the peculiarity is due either directly to the general 
 action of external conditions, or a few ancestors have acquired 
 it as a result of such conditions, or have introduced it, and 
 impressed it on the whole population. But it follows from 
 my previous arguments that such general distribution, unless 
 favoured by external conditions, is very very gradual. 
 
 Nageli found that when he planted numerous species of 
 Hieracium from different regions all together in the botanic 
 garden, new species with peculiar characters were produced 
 
218 DEGENERATION ] sec. 
 
 by their crossing. This instance of tlie " formation of new 
 species by crossing " shows that new forms may actually arise 
 by sexual mixture, and it is well known that crossing, infusion 
 of new blood, generally conduces to the vigour of the race. 
 But in unrestricted nature crossing cannot evidently have 
 such an important influence in the modification of forms. I 
 mean, that if the importance of crossing were so great, then 
 the differences between the members of a nation in different 
 districts would necessarily be much greater than it actually 
 is. For it is known that mixture amonoj much the i^reater 
 part of a nation (the population of a country) takes place only 
 within quite narrow limits. In mountainous regions inter- 
 breeding is, as I have said, naturally much closer than in 
 the level country. In the former, in secluded valleys, it is 
 true, strikingly peculiar types occur, since in them remnants 
 of an older period maintain themselves with very little inter- 
 mixture ; I will mention only the dark small (in many respects 
 also degenerate) men in the valleys of the Baden Black Forest, 
 who are probably remnants of the Celts who retired to those 
 corners before the German invasion and there remained. But 
 even in level regions, considering the obstacles to intercourse 
 interposed by rivers, etc., distinct types of people would be 
 produced by the natural limitation of intercourse to a greater 
 extent than is actually the case. The natural conditions of 
 intercourse are such that thousands of such varieties would 
 have been formed in a relatively small area, each with a 
 central point where the peculiar character was most pro- 
 nounced. But simple calculation shows that perfect mingling, 
 even within a small area, requires a very long time. In order 
 that 500 people of each sex should each pair once together, 
 250,000 unions are necessary. What movements of popula- 
 tion, not to mention time, would be required before fifty or 
 sixty millions of Germans were mingled together ? But 
 since, as a matter of fact, mingling occurs only within each 
 
THE JEWS 219 
 
 group, if mingling alone determined the evolution of forms, as 
 many varieties would necessarily arise as there were groups 
 within which mingling took place. But this is by no means 
 the case. I have already discussed the long-continued per- 
 sistence of the contrast between dark and fair individuals, and 
 another similar case may be here adduced. In the open hill- 
 country of Old Wlirttemberg a brachycephalic (Sarmatic or 
 Turanian?^) race of men, most distinctly characterised by small 
 size, black straight hair, scanty growth of beard, prominent 
 cheek-bones, low forehead, and strikingly slit-like eyes, has 
 persisted among the well -developed Germans. They are 
 possibly survivors of Hunnish intruders. One who has an 
 eye for such things can always recognise these people among 
 the other strata of the population which are of comparatively 
 mixed race. 
 
 The figures indicated above acquire a much greater im- 
 portance when it is remembered that if my assumptions are 
 true, in many cases several unions are required to produce 
 actual blending. For we reckon thirty years to a generation. 
 We should expect to see the greatest effects of mutual blend- 
 ing among the Jews, who do not number more than 600,000 
 heads in the German Empire. They are still but little injured 
 by close breeding ! But they seem to me, on the whole, 
 through the influence of our climatic and other conditions, to 
 show some approximation to the rest of the population, even 
 in their external appearance, in their bodily structure. In 
 fact, there are many German Jews who in personal appearance 
 look like Germans. 
 
 It will perhaps be objected that with regard to the import- 
 ance of sexual blending I consider only comparatively short 
 periods of time, while for the physiological modification of 
 forms I claim extremely long periods. I make this claim by 
 
 1 Cf. H. V. Holder, ZusammensteUimg der in Wiirttemherg vorkommenden Scha- 
 dxlformen und deren Maasse, Stuttgart, 1876. 
 
220 DEGENERATION sec. v 
 
 no means for all cases. But I must insist that since the action 
 of sexual mixing assumed by Weismann presupposes differ- 
 ences among the mingling individuals, the periods of time 
 necessary for that action presuppose the time required for the 
 evolution of these differences. 
 
 It is thus clear, that modification by sexual mixture 
 requires not only the time which is necessary for the accom- 
 plishment of the mixture, but in addition, the time the external 
 conditions have needed in order to produce the differences 
 which such action starts from. 
 
 I by no means deny that sexual mixture has any influence 
 at all in the production of new forms ; but I believe that it 
 cannot possibly be the only determining cause, and therefore 
 I contend against it in detail. If it were all-powerful, great 
 differences in the production of species would exist among the 
 various gi^oups of the animal kingdom, for those animals 
 which possess but slight powers of locomotion would neces- 
 sarily produce more species than the others, because among 
 them sexual mixture is more limited. Moreover, some 
 animals are more stationary than others, even when they 
 possess similar powers of locomotion. What I previously 
 said of the individuals of a nation must apply still more to 
 the innumerable animals which are confined to the narrowest 
 limits of habitat, and which keep to such limits more than is 
 usually supposed. Since in these cases, e.g. in reptiles,^ slight 
 local barriers set limits to migration for a long time, if the 
 view of the all-powerful effect of sexual mixture were correct, 
 thousands of species and varieties would have arisen where 
 only one exists. 
 
 Sexual mixture is, in fine, only one of the agencies which 
 may promote the formation of species. 
 
 ^ Cf. my paper on the " Variation of the AVall-Lizard," p. 261 et seq. 
 
SECTION VI 
 
 MENTAL FACULTIES AS ACQUIRED AND INHERITED CHARACTERS 
 
 Those who refuse to admit the inheritance of acquired 
 characters must also deny that mental faculties have been 
 produced and perfected by experience and the inheritance of 
 this experience. 
 
 And yet the mental faculties can only have arisen in con- 
 sequence of the mutual relationship between organisms and 
 the external world. 
 
 The Function of the Brain 
 
 The brain, which is the organ of spontaneous action, is 
 nothing else than an apparatus for the storing up of faculties 
 and experiences, which have been either acquired and trans- 
 mitted by the ancestors or acquired during the individual life 
 of its present possessor. 
 
 I say experiences intentionally, and will endeavour to 
 justify the expression. 
 
 It is the function of the brain that, having the experiences 
 of every time at its disposal, it shall enable the body to make 
 use of any external demands upon it — stimuli — according to its 
 requirements, not to respond to them directly in merely reflex 
 action. This is rendered possible by the accumulation of 
 experience, and by the acquired and hereditary faculty of the 
 brain to bring experiences into their proper relations, to use 
 
222 MENTAL FACULTIES sec. 
 
 them in relation to and in conjunction with new external 
 influences at a given moment for the best advantaQ;e of the 
 whole organism. 
 
 Reflex Action 
 
 The starting-point of the evolution of all mental faculties 
 must be sought in reflex action. The lower animals are in the 
 scale of mental evolution, so much the more do they respond 
 to the outer world by reflex action — the lowest perhaps act 
 only in this way : every stimulus which reaches the animal 
 calls forth directly and at once a movement or an action. The 
 more highly a central nervous system, a brain, is developed, 
 so much the more is the sphere of reflex action restricted, so 
 much the more can experiences and faculties be accumulated 
 and transmitted, so much the less will the animal react 
 directly to each stimulus, so much the more will it draw 
 conclusions from that experience — act with reflection. 
 
 Thus the more highly the brain is developed, so much the 
 more firmly stands the organism when confronted with the 
 manifold claims of the outer world ; and conversely, the more 
 manifold the claims to which its conditions of life expose it, 
 the more perfect must be the faculties of its brain. 
 
 When our brain is not healthy, or when our general state 
 of health is imperfect — if we are merely, for instance, suffering 
 from a disordered stomach — the brain no longer works pro2:)erly, 
 the regular relation between the experiences stored up in it 
 ceases, reflex action again results from stimulation Avliich 
 would otherwise not call forth a direct response. The person 
 is irritable, and behaves unsuitably — after the manner of 
 unreasoning animals — he acts involuntarily.-^ 
 
 ^ It follows from the above that no fundamental distinction exists between 
 voluntary and involuntary action. In this sense I expressed myself as early as 
 1873 :— 
 
 " By 'will' I understand the release, as the effect of some stimulus, of a portion of 
 the powers which are accumulated in the brain cells, existing in a condition of tension, 
 
VI INTELLIGENCE AND REASON TIZ 
 
 Intelligence, Eeason, Habit (Automatic Actions), 
 
 Instinct 
 
 I conceive the distinction between intelligence and reason 
 in the following way : Intelligent actions are those which 
 only have in view the momentary and immediate personal 
 interests; reasonable action is that which also considers in 
 relation to its experience and faculties the general interests 
 — fellow-men — and the future, knowing that by so doing 
 personal interests are doubly protected — or which depends on 
 general conclusions. These definitions by no means imply 
 that there are no animals which act according to reason. 
 Indeed, it can be proved by examples, to those who reflect 
 without prejudice, that animals reason; and that in animals 
 actions founded on reason become automatic and are inherited 
 I have already pointed out in my Freiburg address. 
 
 I describe as automatic actions those which, originally 
 performed consciously and voluntarily, in consequence of 
 frequent practice, come to be performed unconsciously and 
 involuntarily. Herein I differ from those who use the term 
 automatic as synonymous with reflex. Instead of the expres- 
 sion automatic actions, that of habitual actions may be used. 
 
 and connected with the material of those cells. The powers are partially inherited, 
 partially acquired or modified by adaptation. This adaptation is effected either 
 hy external stimuli, in an empirical way by means of the senses, or by internal 
 stimuli proceeding from the condition of the brain, or body, itself at the moment. 
 Since the condition of tension is altered by stimuli, cumulative effects of stimuli 
 increase the tension to its limits, and a final stimulus is at last capable of effecting 
 the release. Will is thiis the result of a number of factors, which are partly 
 hereditary and material, partly directly or indirectly derived from the outer world. 
 Involuntary and voluntary action do not differ essentially, but only in so far that 
 the latter presui:>poses an accumulation, a storing-up of impressions in a common 
 organ (the brain), and the possibility of an interaction of these. The will can 
 therefore never be free. The erroneous idea of its freedom depends in each 
 particular case on the neglect of factors of which it is always the slave. 
 
 " By consciousness I understand the sensation of the condition, as affected by the 
 outer world, of the brain at a given moment " {Zoolog. Studien auf Capri, i. Bero'i 
 ovatus, ein Beitrag zur Anatomie der Fd2)2)enquallen, Leipzig, Engelmann, 1873). 
 
224 MENTAL FACULTIES sec. 
 
 This effect of habit greatly facilitates our daily life, for it 
 includes a number of actions which we perform from morning 
 till night as it were involuntarily, although we have once 
 had to take pains to learn them, from the actions we perform 
 on rising in the morning to those of going to bed. Thus the 
 brain is left at liberty to work in other directions, to acquire 
 new faculties. 
 
 Such acquired automatic actions can be inherited. Instinct 
 is inherited faculty, especially is inherited habit. Or to state 
 it more accurately, instinct is the power of habitually acting 
 without reflection so as to attain a given object — in such a 
 way as intelligence or even reason might dictate — in response 
 to internal stimuli depending on the condition of the body, 
 and to external, or without the latter. 
 
 !N'o other scientific explanation of instinct seems to me 
 possible. 
 
 I divide instincts into perfect and imperfect. The former 
 are those w^hich are inherited in such a complete manner 
 that thev need no further stimulation, no kind of ouidance, 
 no practice. These are inherited automatisms. They include, 
 for instance, the collection of honey by bees and other insects, 
 the formation of the cocoon by caterpillars, numerous "building 
 instincts," the impulse in young water-birds to seek the water 
 and their power of swimming immediately, the love of parents 
 for their children, brooding instincts, and so on. 
 
 Imperfect instincts require to be called into action by an 
 external stimulus, or to be developed by guidance and prac- 
 tice. In these there is merely an inherited capacity for 
 automatic action. To this class beloncj the buildino: of suit- 
 able nests by birds, and for the most part the instincts of 
 game -dogs. Here also belong many other faculties called 
 forth by very short experience (compare the following). 
 
 Imperfect instinct passes, without any limit which can be 
 distinctly defined, into faculty acquired during life. 
 
VI THE ORGANIC WORLD AS A WHOLE 225 
 
 The view I have given of the nature of mental faculties 
 and of their origin, and particularly this view of the nature 
 of instinct, will appear the more probable the more the reader 
 assimilates and understands the consequences of the idea that 
 the organic w^orld is a connected whole, and that in particular 
 the most nearly related forms are clearly to be regarded as 
 differentiated by division of labour, as organs of a larger 
 organisation. " Thus the individual," as I concluded in my 
 address on this subject, " On the Notion of the Individual in 
 the Animal Kingdom," " as the German term for individual 
 justly implies (einzelwesen), is a constituent portion, not 
 merely of its own species, but also of the totality of the 
 animal world. It follows from this conception that the 
 animal world, in connection with the rest of the universe, is 
 a harmonious whole formed of correlated parts, in which no 
 part deserves an absolute superiority over another. If the 
 animal world be considered as such a whole, we reach the 
 idea of our profound philosopher Oken, and regard the 
 individuals as the organs of a co-ordinated whole." 
 
 It is certain that rigidly logical reasoning must necessarily 
 admit the conception that individuals are organs, and species 
 and genera, by virtue of their definite structure adapted to defin- 
 ite ends, are organs of a higher order, of the whole living world. 
 
 Thus — leaving aside anything more comprehensive — in any 
 case, immediately related forms are connected together as 
 members of a whole, within which they have, if we count 
 millions of years as minutes, only " recently " differentiated 
 themselves. We may, leaving aside species and genera, 
 grasp the idea firmly merely with regard to the members of a 
 widely branching family — and this we are surely entitled to 
 do. When we do so, the supposition that mental characters 
 are inherited with the bodily, with the brain cells also the 
 acquired impressions which have produced and developed 
 their infinitely sensitive and complex structure, cannot a 
 
 Q 
 
226 MENTAL FACULTIES sec. 
 
 priori have anything startling about it. That tlie supposition 
 is actually true we possess evidence in abundance, not only 
 in the facts of instinct, but in the whole mental evolution of 
 animals and of mankind. 
 
 If the acquirement and inheritance of mental characters, 
 which can only rest upon a corporeal basis, were not possible, 
 neither man nor civilisation would exist. 
 
 The examples which Weismann adduces in support of the 
 opposite view with regard to instinct seem to indicate, as is 
 of course only consistent on his part, that he completely 
 renounces the explanation of instinct as inherited faculties 
 and habits. This would imply that he believes in the possi- 
 bility of the evolution of all the mental faculties of animals 
 without the aid of inherited experience ; in other words, of 
 the improvement of the nervous system by inherited acquire- 
 ments. 
 
 Weismann appeals to cases " in which degenerations may 
 affect only a single instinct, while the animal remains com- 
 pletely unaffected thereby in its general form and general 
 functions." 
 
 He mentions that the instinct of flight possessed by the 
 wild ancestors of our domesticated animals has in the latter 
 more or less completely disappeared. But he says the case 
 of guinea-pigs shows how slowly this instinct disappears 
 under domestication ; ever since the discovery of America, 
 that is, for about four hundred years, have they been 
 dependent on man, and they still start at every loud noise 
 and try to flee. I have always referred to guinea-pigs as 
 an instance of animals whose wild originals are entirely 
 unknown, as unknown as those of the gold-fish, and which, 
 like the latter, have probably been maintained from time 
 immemorial and still exist only under the j)rotection of man. 
 If this be so, the peculiarity referred to by Weismann is still 
 more in his favour. I know well this characteristic of guinea- 
 
VI THE INSTINCT OF FLIGHT 227 
 
 pigs. Is it really the instinct of flight which has persisted 
 from a period so remote ? It is a fact that tlie little creatures 
 are in other respects very confiding, and willingly permit 
 children to play with them, without betraying fear of man. 
 This peculiarity might therefore possibly be also explained 
 either as due to continued experience with regard to danger, 
 or to specially developed reflex action deeply rooted in their 
 nervous system. The former supposition is made more prob- 
 able by the fact that guinea-pigs are very quarrelsome among 
 themselves, are apt to fight viciously with one another, and 
 also to devour their young. 
 
 On the other hand, the rapidity with which animals can 
 become tame and fearless, as soon as they are relieved of fears 
 for their safety, is proved to my mind by the following facts. 
 When I was staying in the Dutch island of Eottum, in West 
 Frieslancl, the water-rail (Eallus aquaticus), which is usually 
 so shy, ran about close to me in the ditches so fearlessly that 
 I could almost have caught it with my hands. This island 
 is let by the Dutch government to an egg-bailiff, whose duty 
 consists in collecting birds' eggs, and therefore no bird is 
 allowed to be hunted there ; it is especially forbidden to 
 shoot at them. On the roof of the bailiff's house, to which a 
 ladder leads for the sake of the outlook towards the Dutch 
 continent and our island of Borkum, a starling perched him- 
 self every morning close by me and twittered joyously and 
 carelessly to the world around as though he did not see me. 
 In the Delta of the ISTile, and elsewhere in Egypt, I found in 
 winter the same migratory birds, which when with us are so 
 shy, extremely tame, because, on account of the Mohammedans' 
 kindness to animals, they are not pursued by them — only by 
 Europeans, especially by murderous Englishmen belonging 
 to uncultivated, but unfortunately, out of England, the pre- 
 vailing classes. In my garden every sparrow and every crow 
 knows me from afar because I persecute these birds. Once, 
 
228 MENTAL FACULTIES sec. 
 
 in the presence of a friend, I shot down a crow from the roof 
 of my house, while the pigeons and starlings on the same 
 roof, to the great astonishment of my friend, to w^hom I had 
 predicted it, remained perfectly quiet. They had learned by 
 frequent experience at what my gun was aimed, and knew 
 that it did not threaten them. 
 
 I mention these instances in the conviction that Weis- 
 mann himself knows many such, and that he has argued from 
 but one peculiar case, which, in my o2:)inion, is possibly not 
 quite correctly interpreted, and, at any rate, is not by itself con- 
 clusive. When Weismann ascribes the disappearance of the 
 instinct of fear to the cessation of natural selection, I must 
 insist that my examples are entirely opposed to such a view. 
 They rather confirm the well-known fact that timidity even 
 in wild animals can be dispelled in a comparatively short time 
 by the results of experience, and that even deep-seated, 
 inherited timidity — the instinct of fear, if it must be called 
 so — can vanish in consequence of experience. They show 
 further, that this instinct of fear, because it can be dispelled 
 by experience, must be founded upon inherited, acquired 
 experience. 
 
 At the conclusion of his discussion of the instinct of fear 
 "Weismann says : " Among guinea-pigs, as among the various 
 kinds of pheasants which are bred in the poultry-yard, the 
 youngest animals are the wildest. The instinct of flight is 
 therefore here still inherited almost without any diminution, 
 and each individual has to be tamed anew. The tameness of 
 the adult animal is here still an ' acquired ' tameness, i.e. a 
 character acquired during the individual life ; it has not yet 
 affected the germinal cells : or rather, it is not yet the result 
 of such modification of the germinal cells as must gradually 
 take place in consequence of general crossing, but it arises 
 in exactly the same way as in a wild animal captured when 
 young, a fox, wolf, finch, or rat, all of which can be tamed to 
 
 i 
 
yi INSTINCT AND EXPERIENCE 229 
 
 a certain degree, i.e. can accustom themselves to the absence 
 of enemies." 
 
 These sentences would agree perfectly with my own views, 
 so far as they admit that acquired characters are taken up by 
 the germ-plasm ; but the words " such as must gradually take 
 place in consequence of general crossing " bring into promi- 
 nence the complete contradiction between our respective 
 doctrines — by which I do not mean to say that I do not also 
 allow some importance to pammixis in the degeneration of 
 mental characters. However, in order to estimate the degree 
 of inherited fear, e.g. in pheasants in presence of man, we 
 must rear them ourselves, and not leave them to be reared by 
 the hens ; chickens reared by the mother-hen are shy from the 
 first, those reared by man are tame directly after hatching 
 (cf. the following). 
 
 According to my ideas, the evolution of instinct is as much 
 due to the impress of experience as the taming of the indi- 
 vidual animal ; the loss of fear in the latter in consequence of 
 experience gives the foundation for the development of in- 
 stinct — when it is inherited we call it instinct. And the 
 same holds true for the degeneration of instinct. I am unable 
 in this case any more than in morphological relations to 
 separate completely the individual and its descendants. 
 
 To Weismann's explanation of the degeneration of the 
 food-seeking instinct, which he also discusses, I feel obliged 
 to make not only the same objections as I have made to his 
 explanation of the loss of the instinct of flight, but others in 
 addition. 
 
 Weismann attempts to trace also to the cessation of natural 
 selection, to pammixis, the fact that various animals have 
 forgotten how to seek food, even in some cases how to feed ; 
 young birds (nestlings) are fed passively, and similarly certain 
 species of ants, and certain individuals in ant communities. 
 The red ant (Polyergus rufescens), as is well known, steals the 
 
230 MENTAL FACULTIES sec. 
 
 pupae of the gray ant (Formica fusca), and rears them up that 
 they may feed its larvae and itself ; for it has itself entirely 
 lost the capability of seeking food. Such degeneration of the 
 instinct in question and of others extends to the workers, that 
 is, to animals which produce no offspring. " The disappearance 
 of such instincts cannot therefore possibly have arisen from the 
 fact that the individual animal became accustomed no longer 
 to seek its food for itself, and that this habit was transmitted 
 in any degree whatever to its offspring." 
 
 The latter argument appears very cogent. It must, how- 
 ever, be pointed out that the fertile ants also are passively 
 fed, and queen-bees too ; and that, therefore, an inheritance 
 of the degeneration of the instinct of food-seeking may very 
 well have occurred. But even if this were not the case, the 
 occurrence of inherited degeneration might, according to my 
 views, very well be explained in another way ; but for this I 
 must refer to the case of the inheritance of the characters of 
 the equally sexless worker-bees, which I shall discuss subse- 
 quently. 
 
 In my opinion, at all events, the absence of natural selec- 
 tion is neither necessary nor sufficient to explain the dis- 
 appearance of the food- seeking instinct. Under ordinary 
 circumstances, if an animal takes no nourishment, it starves, 
 and pammixis is at an end. In the cases hitherto mentioned, 
 the seeking of food has been replaced by the passive reception 
 of food. There is nothing to prevent the assumption that the 
 loss of the instinct of seeking food has been acquired by the 
 individual as a result of the passive reception of food from 
 the parents or other individuals, and been transmitted by 
 inheritance. The Axolotls which I have kept in confinement 
 for many years have forgotten how to seek food by their own 
 action, because they are regularly fed with meat from the 
 hand of the attendant. If this condition were to continue 
 through generations, the absence of this spontaneous action 
 
VI INSTINCT AND INTELLIGENCE 231 
 
 would necessarily become liereclitary, simply because, as a 
 result of this indifference, a whole series of the animal's 
 faculties must suffer decay — partly as a direct consequence 
 of the disuse of organs, partly in consequence of the cessation 
 of natural selection. But since the latter must be always 
 of less importance in confinement, the action of the former 
 cause, as further considerations will show, would chiefly 
 determine the degeneration. Finally, the Axolotls, simply 
 through disuse of their organs, would, like the workers of 
 Polyergus rufescens, reach a condition in which they would 
 be incapable of taking food in any other way than by being 
 fed with the hand. 
 
 Particular Instances of Intelligence and PiEason in 
 
 Animals 
 
 I cannot by any means recognise as instinct all that in the 
 preceding has been so described, especially what was referred 
 to as the instinct of fear, or what was mentioned by me 
 in discussing the nature of instinct. When starlings and 
 pigeons remained undisturbed on the roof from which I brought 
 down a crow with my gun, when certain birds recognise me 
 in the garden as a friend, others as a foe, that is not instinct, 
 but intelligence ; for in comparatively short time the creatures 
 drew from the facts certain conclusions respecting me, and 
 l)ehaved accordingly. Among all the facts I have men- 
 tioned, that which shows most clearly the exercise of in- 
 telligence is, that the same migratory birds which in Europe 
 in consequence of their experience are most shy of man, in 
 Africa, whither they go in winter, and where they are not 
 pursued, are quite tame. It is certain that on the northern 
 coasts also birds, ducks for instance, which are in many places 
 protected there for the sake of their eggs, as in Eottum, 
 distinguish between friendly and hostile shores. The eider- 
 
232 MENTAL FACULTIES sec. 
 
 duck, for example, ^vhich, in places Avhere it is protected, has 
 voluntarily domesticated itself, and every year comes from a 
 distance to take up its abode with man, doubtless avoids 
 other places which are dangerous to it. 
 
 Those who seriously believe that mental powers are to 
 be explained by the accidental variations of the germ-plasm, 
 as those must who deny the heredity of acquired characters, 
 will of course estimate the mental powers of animals accord- 
 ing to the requirements of their belief, and may also describe 
 all those powers without distinction under any indifferent 
 name whatever. Instinct is such an indifferent name, when 
 the idea of instinct is not connected with the inheritance of 
 acquired characters. But all explanation, all comprehension 
 of the gradual modification and perfection, and of the nature 
 of mental faculties in general, is then excluded. 
 
 I recognise the instinct of fear, i.e. fear acquired through 
 the experience of ancestors, and inherited. But the cases I 
 have already described show how easily this "instinct" in many 
 animals can be dispelled by experience, and give place to the 
 knowledge that they can have confidence in man. And, on 
 the other hand, my own observation shows how quickly their 
 confidence is converted into distrust by experience. Count- 
 less other facts prove that fear and confidence, trust and 
 distrust, in animals alternate in different cases according to 
 the circumstances. 
 
 Some years ago a male chaffinch in my garden had become 
 so tame with me that he flew after me eveiy where in order to 
 take the hemp seed and meal-worms which I offered him. 
 Wherever I went or stood in the garden the finch appeared 
 from the bushes, perched on the nearest branch or on the 
 ground in front of me, and with his powerful chirp — " Pink, 
 pink " — demanded his food. But if he had not noticed me, I 
 had only to whistle in imitation of his chirp and he appeared. 
 At last he used to come after me even into the house and 
 
VI OBSERVATIONS ON BIRDS 233 
 
 follow me from room to room asking to be fed. Yet, in spite 
 of his trustfulness, I could not induce him to feed out of my 
 hand. It was evident that he constantly endeavoured to 
 overcome the remnant of timidity which still survived in him, 
 but he could not yet succeed. Still I strove to attain this end, 
 and the visible progress made permitted the hope that I should 
 shortly succeed, when an unfortunate accident suddenly altered 
 the condition of affairs and put an abrupt end to his confidence. 
 One day a sparrow on a tree in front of my window was 
 piping indefatigably his monotonous shrill chirp, which pierces 
 the ear the more irritatingly the more energetically it is uttered 
 and the greater its well-known deficiency of cadence. As the 
 fellow had repeatedly disturbed me at my work in this way, 
 I resolved on his destruction, and, creeping within range, I 
 fired at him with a small chamber-gun loaded with small 
 shot. At the shot my beloved finch flew suddenly from the 
 tree where he had been perched unnoticed by me. The shot 
 must have passed around him. My sorrow for the accident 
 was deep, for what was to be expected occurred — the finch 
 afterwards carefully avoided me, and notwithstanding all 
 enticements, I could only with difficulty induce him again to 
 take from the ground at a great distance from me food which 
 I had scattered. But after a short time he disappeared 
 entirely from my garden with the family which he had 
 established. 
 
 This happened two years ago. At that time, when I sat 
 at a certain table in my garden, a red-tail often came with 
 the finch, and like him picked up, though always with great 
 caution, the meal-worms which I threw to him or laid on the 
 table. After my misfortune over the finch, I took no further 
 notice of the red-tail. A few days ago I sat again at the 
 same table, and when I happened to throw away a match, the 
 red-tail flew down, thinking I had thrown him a meal-worm 
 as I used to do. And even when he found his mistake he 
 
234 MENTAL FACULTIES sec. 
 
 remained close to me, liying from twig to twig, expecting I 
 should throw him something for the young ones which he had 
 to feed, and which were crying for food among the bushes. 
 
 Still further removed from instinct are the following 
 instances of mental operations in birds. 
 
 The cunning of sparrows and their prudence with regard 
 to danger is well known. One snowy winter recently, when 
 the sparrows around the house were very hungry, I made an 
 attempt to catch a number under a large sieve, the edge of 
 which was supported on one side by a piece of wood, which 
 was connected with a long string : the string was covered up 
 in the snow, and passed through an opening in the door into 
 the house, where my little son watched, ready to pull the 
 string as soon as some sparrows went under the sieve. Corn 
 was strewed about under the sieve and around it as bait. 
 The sparrows gathered in dozens round the sieve, and picked 
 up the corn up to its very edge to the last grain, then flew 
 round and screamed at the sieve in hunger and rage, but not 
 one was enticed under it. 
 
 Such facts are sufficiently familiar, yet the intelligence of 
 animals astonishes any one when he sees it himself for the 
 first time. 
 
 Eecently a friend showed me how one can feed the tomtits 
 in winter abundantly without having to fear that the 
 impudent sparrows will steal the food. He has on his 
 verandah boxes nailed to the wall and posts, in which he puts 
 the food. The tits take the food out of these, but the 
 sparrows are afraid the boxes might be dangerous to them, 
 might contain something intended to destroy them, or that 
 they might be caught in them, and therefore they leave the 
 food untouched. As they know well that at other times they 
 are pursued by the owner of the house and the tits not, the 
 fact that the tits suffer no harm by taking the food in the 
 boxes is not enough to remove their distrust. This high 
 
VI INTELLIGENCE OF SPARROWS 235 
 
 degree of prudence is evidence not for an instinctive fear in 
 them, having its origin in variation of the germ-plasm, but of 
 a high degree of capacity to reflect and draw conclusions — of 
 a high degree of intelligence. 
 
 But the following observation on the mental capacities 
 of sparrows surprised me most ; it is a still more striking 
 example of the memory of birds than the case of the red -tail 
 previously described. 
 
 Every year I require a large number of birds for the 
 zootomical studies of my students. As I am naturally 
 averse to sacrificing useful birds, I turned my attention first 
 of all to the sparrow, as the commonest among those of our 
 birds which do far more harm than good, although our laws 
 — I might say in an almost incredible way — still protect 
 them. One day I read in an agricultural paper the advertise- 
 ment of a trap with which twelve or more sparrows could be 
 caught at a time. That was what I wanted. I sent for one 
 of these traps. It consists of a wire -basket of cylindrical 
 shape, about 18 in. high, and the same in diameter, the upper 
 end forming a funnel-shaped tube projecting inwards towards 
 the bottom of the basket. It is constructed, therefore, after 
 the fashion of the glass ink-pots which may be upset without 
 spilling the ink, and like certain mouse- and rat-traps or fish- 
 traps. When the animals have passed through the funnel 
 into the trap, on the bottom of which bait is strewn, they 
 cannot find the way out again. 
 
 The result of the use of my trap was surprising : almost 
 immediately quite a dozen sparrows were caught in it. 
 These were brought away as carefully as possible, so that 
 none were taken out in sight of their companions. The trap 
 was again set, and this time nine sparrows were caught 
 equally quickly. I was very pleased with the invention, 
 for it seemed likely to put an end for the future to all my 
 difficulties. But it was to be otherwise. I noticed already 
 
236 MENTAL FACULTIES sec. 
 
 that all the sparrows caught were young birds, hatched the 
 same spring, and therefore of little experience. Not a single 
 old sparrow had entered the trap. And when I set it for the 
 third time, not one sparrow went into it — it stood for week 
 after week ; the yard was full of sparrows, but I caught no 
 more. 
 
 However, I looked forward confidently to the next year — 
 then, I thought, young sparrows will get caught again ; and 
 about two dozen would have been enough material for my 
 purpose. But I had reckoned without the — intelligence of the 
 sparrows. When I got out the trap again next year, and had 
 it set, not a sparrow went into it. But a curious spectacle was 
 observed : apparently several sparrows had the desire and the 
 intention to go into the trap, and these were obviously the 
 young inexperienced birds which had been hatched since the 
 trap was last set ; but others, of course the older birds who 
 had learnt the danger of the wire-basket from the loss of their 
 families, kept them back by constant earnest warnings, for 
 the males, as soon as one of the yellow beaks approached the 
 cage, uttered their warning cry most loudly, the cry wdiich 
 they always make when danger is present, and which consists 
 in a lonfT shrill rattlin^ " r-r-r-r-r." 
 
 But the most singular fact is this : It is now nine years 
 since I set the trap for the first time. Since then I have 
 repeated the attempt almost every year, and each time with 
 the same result — not one sparrow more has ever entered the 
 trap, not even last winter, when, in consequence of the deep 
 long-lying snow, the birds were in great want. The know- 
 ledge or the tradition of the danger attached to the wire- 
 basket has been maintained, even although I once omitted to 
 set it for two years. 
 
 Every lover of living nature, and particularly every sports- 
 man, knows the cunning of crows. They allow the harmless 
 pedestrian to approach quite near to them, but from the 
 
VI CUNNING OF CROWS 237 
 
 sportsman with his gun they flee far away. I have repeatedly 
 shown to friends the following example of their intelligence. 
 My garden slopes up the side of a steep hill, covered witli 
 vines. Crows are fond of settling on the vine-props, resting 
 without motion, and apparently careless and heedless of their 
 surroundings. Formerly, when the trees of the garden were 
 lower, they could look down on a table which stood there. 
 On the table I placed my gun, and beside it a stick. As 
 soon as I took up the gun, the crows flew away at once ; if I 
 took up the stick, they remained quiet where they were. They 
 noticed everything which went on, recognised the gun, and 
 rightly judged it was dangerous to them, even from the con- 
 siderable distance at which they were perched. 
 
 The more one observes the higher animals in their natural 
 free state, the more one is filled with wonder at their intelli- 
 gence. Intelligence alone, and not instinct, will explain the 
 fact that the cattle-heron (Ardea russata) in Egypt, when flee- 
 ing before the sportsman, shelters itself under the oxen and 
 buffaloes, because it knows that it is there protected from his 
 gun. For it is not to be suj)posed that this has become an 
 automatic, a hereditary habit, simply because, as I have said, 
 it is only slaughter-loving foreigners who occasionally shoot 
 birds in that country. 
 
 A curious instance of fear in an animal came under my 
 notice during my stay at Eottum. The egg -keeper had a 
 young dog of large size, a kind of sheep-dog in breed. As no 
 one on the island troubled himself about this animal, he 
 attached himself to me uninvited for want of companionship, 
 and followed me everywhere. One day I went down to the 
 shore to bathe. I had chosen a place beneath a high sand- 
 hill, where the sea deepened gradually, so that I could go out a 
 long way without getting beyond my depth. The dog had 
 followed me, and he sat down on the sand-hill and watched me 
 undress. With growing curiosity he followed each of my move- 
 
238 MENTAL FACULTIES sec. 
 
 ments as I took off one garment after another. At first this 
 curiosity was an agreeable one : something like the pleasure of 
 having a certain degree of comprehension of what was going on 
 was expressed in the repeated nodding of his head, in the droll 
 oblique turning of one side of it to the object of his attention 
 with an upward look, which is a well-known attitude in young- 
 dogs. But when I proceeded further in my operations, and 
 was about to take off my shirt, I saw signs of agitation and fear 
 appear in the dog ; once or twice he suddenly drooped his 
 ears, hitherto erect, and turned his head as if to run away, then 
 took courage to remain longer. These signs of anxiety gave 
 place to the greatest terror when I had thrown off my shirt ; 
 the dog looked at me for a moment in horror, but when I went 
 into the water and more and more of me was covered, so that 
 perhaps I seemed to him to grow smaller, or to vanish, the 
 prodigy was too much for him, he suddenly laid his ears back, 
 drew his tail between his legs, and ran as fast as he could run 
 inland from the place. When shortly after I appeared again 
 in my clothes near the house, the dog looked at me from afar 
 with the greatest distrust, and afterwards took care to keep out 
 of my way. The whole occurrence gave me the impression 
 that the dog was terrified at the appearance, to him previously 
 unknown, of an almost unclothed and afterwards naked man, 
 and that he did not give way to panic from the first, before I 
 went into the water, because he had not yet drawn the 
 conclusion that he had to do with a spectre. 
 
 This case proves how cautiously the idea of instinctive fear 
 must be used, at least in the sense of fear of definite objects. 
 The dog was afraid of something which he had never yet seen, 
 because it appeared to him incomprehensible, mysterious, 
 ghostly. Such a condition in an animal still further deserves 
 notice, because the possibility of forming supersensuous con- 
 ceptions is intimately connected with it, and because it may 
 accordingly be suspected that animals are endowed with this 
 
VI SUPERSTITION IN ANIMALS 239 
 
 power also. Fear of things incomprehensible is indeed the 
 cause of such conceptions among men, and among many 
 savage peoples is still at the present day clearly the cause of 
 their belief in a higher being. It is stated ^ that dogs do not 
 bark at naked men, which is probably to be attributed to fear 
 of the unknown, Kke their fear of thunder. Also tamers of 
 wild animals are said to go naked into the cages in order to 
 train the animals. H. Spencer considers that even fetichism 
 exists in dogs ; that, judging from certain circumstances, they 
 believe inanimate objects to be alive.^ 
 
 G. J. Eomanes ^ has made some interesting experiments, 
 similar to mine, on dogs. I will quote the most important of 
 them here. Eomanes relates : — 
 
 " My dog was in the habit, like many others of his kind, 
 of playing with bones, by tossing them in the air, so as to 
 throw them a little distance from him, and so making them 
 appear to be alive, whereby he procured himself the imaginary 
 pleasure of killing them. One day I offered him for this 
 purpose a bone to which I had fastened a long thin thread. 
 After he had tossed it a little while in the air, I took the oppor- 
 tunity, when it had fallen a little distance from him, to draw it 
 slowly away by means of the long invisible thread. The dog's 
 whole behaviour immediately changed. The bone which he had 
 before only treated as if he believed it alive, now became really 
 alive in his eyes, and his astonishment was boundless. He 
 approached the bone at first with great caution . . . ; but as 
 the gradual movement did not cease, and he became quite cer- 
 tain that the motion could not be set down to that which 
 he himself had communicated, his astonishment changed into 
 
 ^ Cf. e.g. Adolf v. Conring, Marokko, das Land und die Leute, Berlin, 1S80. 
 Mansur, when he steals at night into the tent to Fatme, who is sleeping beside 
 her husband, goes " completely naked, because he knows that no dog barks at a 
 naked man." 
 
 2 Herbert Spencer, Principles of Sociology. 
 
 2 G. J. Eomanes, Mental Evolution in Animals. 
 
240 MENTAL FACULTIES sec. 
 
 terror, and lie ran away to hide himself under some piece of 
 furniture and look upon the incomprehensible spectacle of a 
 bone which had come to life, from a distance. . . . 
 
 " One day I took him into a carpeted room, where I blew 
 a soap bubble, and then made it glide along the floor by means 
 of a current of air. He at once showed the greatest interest 
 in the bubble, but seemed unable to decide whether the thinf^ 
 was alive or not. At first he was very cautious, and followed 
 the bubble only at a certain distance ; but when I encouraged 
 him, he went nearer with his ears pointed and his tail 
 depressed, evidently with great distrust, and retired immedi- 
 ately it began to move again. After some time, during which 
 I had always kept at least one bubble on the carpet, he 
 became more courageous, and the scientific spirit getting the 
 upper hand over his sense of the mysterious, he became at 
 last bold enough to go cautiously up to a soap-bubble and 
 touch it with his paw. The bubble of course burst at once, 
 and I never saw surprise so strongly expressed. When the 
 burst bubble was replaced by another, I encouraged him to 
 approach it for a long time in vain ; at last, however, he went 
 up to it again and cautiously stretched out his paw as before, 
 of course with the same result. After this second attempt, 
 nothing could induce him to make another, and when I 
 continued to urge him he ran out of the room, to which no 
 coaximj could brino- him back." 
 
 Another mental quality which is to be considered, not as 
 instinct, but as mental faculty of a higher kind, is curiosity, 
 which, even among animals in wdiich other mental powers are 
 but slightly evolved, obviously plays a great part. When I 
 was sketching at Eottum with my sketch-book in front of me, 
 the cows which were grazing around came nearer and nearer, 
 formed a circle round me, and stood motionless, stretchincr out 
 their necks and staring at my paper to see w^hat was going 
 on. They came so near to me as to be a nuisance, and I had 
 
VI THE APOLLO SAUROKTONOS 241 
 
 to drive them away with a stick. But they always repeated 
 their attempts to discover the secret. 
 
 In my memoir on Lacerta muralis coerulea, I described 
 how the boys of the island of Capri take advantage of the 
 curiosity of the lizards to catch them with ease, althouoh 
 otherwise their capture is so difficult. They take a long stiff 
 withered stalk of grass and make a noose on its thinner end. 
 Then they lie down at full length, and hold the grass-stalk in 
 front of them with outstretched arm opposite the crevice in 
 which a lizard has just hidden itself. The creature's curiosity 
 is so excited that it comes nearer and nearer to the noose in 
 order to examine it, and the boy is able to pass it over the 
 lizard's head and catch it. In order to further stimulate the 
 lizard's curiosity, the boys by spitting on the noose make a 
 shiny bladder over it. 
 
 In a later publication I attempted to explain the famous 
 statue of the Apollo Sauroktonos by means of this method of 
 catching lizards, the practice of which is widely spread in 
 other parts of Italy also. This statue, as is well known, 
 represents a youth not much beyond boyhood, who, in a watch- 
 ful attitude, leaninsj with his left arm ao^ainst the trunk of 
 a tree, and holding in his right hand a portion of a thin 
 staff, follows with his eyes a lizard crawling up the tree- 
 trunk. Archaeologists suppose that the boy is intending 
 to transfix the lizard with an arrow, of wliich the stick 
 represents a portion. But the lizard is crawling towards 
 the boy. This fact and the whole attitude of the figure, as 
 well as the way in which he holds the stick in his fingers, 
 seem to me to indicate in the clearest way that in the Saurok- 
 tonos we have a boy who is snaring a lizard with a noose of 
 grass. For that attitude is in every detail one of quiet wait- 
 ing, almost of negligence, and the boy holds the piece of stick 
 in his hands lightly and playfully, not firmly and securely as 
 
 1 Variiren der Mauereidechse, Section " Sauroktonos." 
 
 K 
 
242 
 
 MENTAL FACULTIES 
 
 SEC 
 
 one holds an arrow when abont to kill something with it. 
 
 Lastly, the expression of the face is peaceful, indicative ratlier 
 
 of play than serious effort. 
 
 As I said, the meaning of the statue is only comprehensible 
 
 on this explanation, and with it tlie work appears in all its life- 
 like truth and harmony.' 
 A copy of the Saurok- 
 tonos, which was dug out 
 ill the year 1777 on the 
 Palatine, exists in the 
 Vatican ; another smaller 
 in bronze, found at S. Bal- 
 bina, is in the Villa Al])ani 
 in Eome ; among others, 
 one in Paris. The two 
 first I know from my own 
 observation. In the most 
 known and most beauti- 
 ful, that in the Vatican^ 
 the two arms from the 
 shoulders are restorations; 
 in that of the Villa Albani 
 the rioht hand is said to 
 ^'^- 1- have been restored or 
 
 repaired ; also in the Paris specimen the right forearm with 
 
 the hand is said to be new, as well as the fingers of the left, 
 
 ' Some archaeologists have, it is true, expressed a, view more similar to mine, 
 namely, that the boy is intending to tickle the lizard with his stick. The view 
 that he wislies to kill it with his aiTOw is derived, so far as T know, from the state- 
 ment of Plinius {Hist. Nat. xxxiv. 70) : " Fecit (ex acre Praxiteles, to whom he 
 ascribes the statue) puberem Apollinem subrepenti lacertfe cominus sagitta insi- 
 diantem (pu-m sauroctonou vocant." According to this author, Apollo wishes to 
 foretell the future from the convulsions of the dying lizard. An epigram of Mar- 
 tial referring to our statue says : — 
 
 *' Sauroctonus Corinthius {i.e. of Corinthian bronze). 
 
 Ad te reptanti, puer insidiose, lacertje 
 
 Parce, cupit digitis ilia j)erire tuis." 
 
VI LOCAL KNOWLEDGE IN ANhVALS 243 
 
 But in all the way the arm and hand are lield, as well as 
 the attitude of the whole body, point to the light handliiv of 
 a grass-stalk. 
 
 I know not whether the method of catchiug lizards in a 
 noose was also practised in Greece, or is so now. The close 
 relations between Italy and Greece, even if this were not the 
 case, would have sufficed to supply Praxiteles with the sub- 
 ject of his statue. 
 
 Such practices can often be traced back to very ancient 
 times, and are inherited and maintained in subsequent ages 
 with very great persistence. A fresco in the Etruscan 
 Museum in the Vatican affords me another example of 
 this. It represents a boy holding a string attached to the 
 legs of a bird and allowing the bird to flutter, an act which 
 is still at the present day one of the commonest of the 
 cruelties to which animals are daily subjected in Italy. 
 This amusement therefore has been practised by thoughtless 
 children, at least since the time of the Etruscan people, a 
 time reachinii; back into the darkness of an unknown 
 antiquity. 
 
 To these reflections, made in my essay upon the variation 
 of the wall-lizard, I would add, in reference to the subject 
 here under consideration, that by the remark that such prac- 
 tices are inherited by posterity, I meant not inherited as an 
 instinct, but handed down. But any one who is acquainted 
 with the facts of Italian cruelty towards animals will agree 
 with me that the contempt and mercilessness with whicli 
 animals are treated there, in the land which contains the 
 seat of the head of Catholic Christendom, does in fact almost 
 convey the impression of an hereditary habit, as also does the 
 compassion towards animals among the Mohammedans, which 
 afibrds such a striking contrast. 
 
 In the essay alluded to I have also insisted that lizards 
 are very stationary, i.e. that every lizard confines its move- 
 
244 MENTAL FACULTIES sec. 
 
 nieiits to a detiiiite restricted area, and that it has the most 
 exact kno\vled<?e of its retreats within that area, and under- 
 stands how to reach them quickly and hide in them when it 
 is pursued. But if it is driven from its home it runs about 
 helplessly and aindessly, and can be captured with ease. 
 This fact led me in that paper to describe an observation 
 on a similar certainty, acquired during life, in tlie knowledge 
 of its surroundings, even in a shore - crab : "Animals also 
 which are credited with mental powers still more feeble than 
 those of the lizard seem to have a similar knowledge of 
 locality, and to find their way to their accustomed retreats 
 with as much certainty. I witnessed years ago in Capri a 
 comical proof of this in a shore-crab (Carcinus m?enas). In 
 a large pool hollowed out in the rocks, shut off all round 
 from the sea, and only reached by the waves in rough weather, 
 stood a fisherman trying to catch a crab of that kind ; he pur- 
 sued it with his two hands joined together so as to form a 
 scoop in which to lift it out. The crab swam in a straight 
 line towards the opposite side of the pool, which was some 
 metres away. Softly and cautiously the fisherman followed 
 it, evidently pleased to see the crab going towards the rock, 
 between which and his hands he expected to catch it. But 
 just as his hands were about to seize the creature, it slipped 
 beneath them into a hole in the rock, and the discomfiture of 
 the fisherman was received with laughter by tlie numerous 
 bystanders who had watched his attempts with keen interest. 
 It must be inferred that the crab had swam across the whole 
 pool in certain knowledge of the position of its hole ; and the 
 jeers bestowed on the fisherman showed that the spectators 
 attributed this conscious intention to the animal beforehand, 
 and regarded the fisherman as the victim." 
 
 I know well enough that many of the examples I give 
 here of actions in animals only to be explained by direct 
 
VI NEWLY-HATCHED CHICKS 
 
 245 
 
 experience, that is, by intelligence and not by instinct, are 
 far surpassed by others which are known ; but I have pre- 
 ferred, as everywhere else in this book, to use new. examples 
 which have come under my own observation. 
 
 Experiments and Observations on Instinct in 
 
 NEWLY-HATCHED ChICKENS 
 
 Last year I had some chickens hatched in an incubating 
 apparatus. They had never seen a mother, and were never 
 taught to seek food. I placed some millet seed in front of 
 them in a vessel ; they took no notice of it. Then I took 
 some of the seed in my hand and let it fall on the hard 
 wooden floor so that the grains rebounded. The chickens 
 then at once pecked at it, and in a short time fed without 
 assistance. But tlie thing that surprised me most was this : 
 a fly flew close by the eyes of a chicken which had only left 
 the egg-shell about half an hour before, and the little creature 
 pecked at it as if it had been long accustomed to catch flies. 
 Similar cases have indeed been frequently observed. 
 
 It may be objected that this was nothing but simple reflex 
 action — and of course it is reflex action. But the wonderful 
 fact is that this action was so perfectly adapted to the external 
 requirements ; the chick snapped at the fly in order to catch 
 it ; it made with accuracy all the movements suited to this 
 purpose. If it had caught the fly, it would have bitten it up 
 and eaten it as it ate the millet. It had evidently brought 
 into the world, in its brain, a mechanism which included an 
 inherited mental image of the flight of a fly, an inheritance of 
 the effect of the stimulation which flies have exerted upon its 
 ancestors during their life for ages past. A proof of this is 
 that the same chicken responded quite differently to otlier 
 similar stimuli acting on its eyes, e.g. to a rapid movement 
 of the fingers. In short, the chicken's behaviour towards the 
 
246 MEN7\4L FACULTIES sec. 
 
 fly was a consequence of innate instinct, like that of itself 
 and brethren towards the millet seed. 
 
 In the. present year I have again made similar experiments 
 on chickens, and with more care. I took two chicks away 
 from the hen into my own care immediately after they w'ere 
 hatched, and wrote down exactly their behaviour under the 
 experiments I made on them. I will distinguish the tw'o 
 in the folio win f^ according- to their colour as the brown and 
 the wdiite. There is no need to insist that when I bei^an to 
 study them they knew^ nothing of the world, that they had no 
 previous experiences whatever, hut I am compelled to point 
 out the impossibility of doubt with regard to this on account 
 of the high degree in which thev exhibited the faculties 
 acquired l.>y their ancestors. I w^as extremely surprised by 
 their actions, and confess I should have considered them 
 incredible if I had not observed them mvself. Thev are 
 alone sufficient to demonstrate the inheritance of acquired 
 characters as an incontrovertible fact, and to show what a 
 tremendous importance belongs to this inheritance, especi- 
 ally wdiere mental acquirements are concerned, and wdiat 
 importance belongs to instinct in the life of animals. 
 
 I proceed now to the description of my observations, only 
 remarking that the wdiite chicken was from the first some- 
 what behind the brown in the exercise of its faculties. 
 
 After they ^vere hatched, I kept the little creatures warm 
 during the night in a basket wdth some w^adding near the 
 stove, and on the second day of their life I placed them on 
 a Ijoard, on wdiich millet and crushed buckwheat had been 
 ])laced. 
 
 To my very great surprise the brown one pecked at once 
 at the millet grains, without having its attention in any way 
 directed to them ; and indeed at the first attempt it touched 
 a grain with as much certainty as if it had pecked at millet 
 for ever so long. But it did not succeed in taking up the 
 
VI OBSERVATIONS ON CHICKS -ji; 
 
 grain in its beak. A second attempt immediately afterwards 
 likewise failed, but at the third, which succeeded without a 
 pause, the grain w^as grasped and swallowed, and now the 
 little creature went on feeding as though it had done so for 
 years ! The three first pecks at the millet were made in 
 rapid succession, evidently and incontestably with the inten- 
 tion of eating the grain. There must therefore be for the 
 chicken in the form and general appearance of the grain a 
 stimulus which awakes innate conceptions, and causes them 
 to be employed. It was probably not chance that the 
 chicken pecked first at the millet and not at the crushed 
 buckwheat; the natural roitndness and brightness of the 
 millet grains may be supposed to have been the cause. Soon 
 afterwards the chick pecked at the buckwheat and ate some, 
 but like its sister it always preferred the millet. Therefore 
 the question, however hazardous it may seem at first sight, 
 forces itself upon us, whether the chicken did not have an 
 innate idea that millet w^as a more suitable food for it than 
 buckwheat ? The question becomes, however, perfectly natural 
 when I state that the chicken, when I put sand before it 
 shortly afterwards instead of food, pecked at it no more than 
 at the board on which it stood. Unfortunately I omitted at 
 the beginnimx to set before the chicks sand and other kinds 
 of food besides those mentioned, at the same time. 
 
 The white chick also pecked at the millet grains, but 
 missed them repeatedly. 
 
 Thus after the brown chick had eaten abundantly, and the 
 white had made only unsuccessful attempts to do so, I ptit 
 them both back into their basket. 
 
 Three hours afterwards I placed them again on the board, 
 having placed upon it, besides the food, a large drop of water. 
 
 The brown chick immediately began to feed again ; at first 
 it took no notice of the drop of w^ater, but wdien the latter 
 was made to tremble by shaking the board, it immediately 
 
248 MENTAL FACULTIES sec. 
 
 drank from it with perfect success in the well-known fashion 
 of adult fowls. 
 
 Now for the first time it dropped its excrement. A little 
 later passing by this it pecked at it, but spat away wiiat it 
 took up with disgust. Considering its previous behaviour 
 one might wonder that the chick had not an innate aversion 
 to its excrement. But it must be remarked that the first 
 excrement has not the same nature as the subsequent, but is 
 surrounded with a gelatinous covering, and consists chiefly of 
 the remains of the embrvonic nutriment. 
 
 Both chicks were at once attracted by a fly which crawled 
 on the board, and pecked at it repeatedly, without being 
 able to catch it. It is very curious that after their first 
 attempt at catching flies failed, both afterwards took no notice 
 of them. Indeed they acted upon every first experience in a 
 really wonderful way. 
 
 The white chick now also ate millet. 
 
 I laid before them boiled ^g^, finely minced. They pecked 
 at it at once and swallowed it, both yolk and albumen in 
 equal quantities, although one at first preferred the yolk. 
 
 I offered them some earth-worms of moderate size. When 
 those be^an to crawl the chicks looked at them with all the 
 signs of fear, and withdrew from them.-^ On the other hand, 
 they began to peck determinedly at one another's toes. They 
 pecked immediately at some chopped salad put before them, 
 then at first left it, but afterwards pecked at it again and ate 
 of it. 
 
 On the third day the white one went by chance near a 
 drop of water again placed on the board, and drank from it 
 at once, without having watched how the brown one drank 
 
 ^ I may remark here that even the old fowls in my enclosed fowl-run are always 
 uneasy at first when earth-worms are throAvn to them ; they show unmistakable 
 signs of shrinking and even of fear, and it is often some time before any of them 
 overcome their repugnance and devour the worms, while others never touch them 
 at all. 
 
VI OBSERVATIONS ON CHICKS 249 
 
 before. Afterwards both drank regularly from such drops 
 of water. 
 
 They looked at a bee with curiosity, and at flies also, but 
 pecked at neither. 
 
 The white one fluttered its wings for the first time, as young 
 fowls are accustomed to do, in the manner which indicates a 
 feeling of contentment, and later it scratched repeatedly on 
 the wooden surface in just the same way as the old hens when 
 they scratch in sand or manure in search of small animals 
 or other food. To see them scratching on the smooth board, 
 from which there was nothing to scratch out, was exceedingly 
 comical ; and as the action was afterwards repeated without 
 any result in the same way and under the same conditions, 
 it afforded a perfect example of strongly inherited habit. 
 Clean white sand was untouched by either chick. 
 
 In the forenoon of the fourth day water was for the first 
 time put before the chicks in an earthenware saucer, while 
 previously it had only been placed on the wooden tray in 
 large drops. Spite of the unfamiliarity of the vessel, the brown 
 one drank at once when it chanced to cro near the vessel. 
 
 In the afternoon the chicks were placed for the first time 
 in the open air on the gravel in the garden, in the sun. They 
 looked about with surprise, stretching their necks, and appeared 
 afraid. They would not take their ordinary food which lay 
 before them on the wooden tray, but very soon began to peck 
 at the gravel, and to seek food. One pecked at the side of a 
 box, each began to take up a small stone in the beak again 
 and again as if to swallow it, until it was lost, when the chick 
 began on another. It seemed that they now required small 
 stones and sand in the gizzard, and wished to swallow them. 
 They also tried the most various objects with their beaks, 
 such as bits of wood, etc., throwing away what was useless. 
 Thus after a few moments of surprise they felt themselves as 
 it were in surroundings long familiar to them, in their natural 
 
250 MENTAL FACULTIES skc 
 
 environment, all parts of which they knew how to use. They 
 tried to escape from my control in every direction, and in all 
 respects behaved as if guided Ijy old experience of their own. 
 
 A wood-louse which ran by was pecked at, but afterwards 
 avoided. Flies no longer attracted attention. The brown 
 chick, after it had at last eaten its fill of the food before it, 
 went evidentlv with intention to the drinkin<j- vessel it had 
 used in tlie morning, and the wliite one followed the example. 
 Both fluttered their wings repeatedly in the fulness of their 
 comfort and contentment. 
 
 Fifth and sixth day. They peck — on the board in a room 
 — vigorously at small pieces of egg-shells which have been 
 put before them, and eagerly tr}^ to swallow them. Sand, 
 which was put on the board as w^ell as their food, they leave 
 untouched. Chopped chives they try, but do not eat, but 
 finely minced meat put before them they eat at once with 
 enjoyment. 
 
 Thus they knew from the first how to choose the food 
 that suited them either without trial or after a single trial. 
 They acted at once on every experience, even against their 
 own interest, for they have now become perfectly indifferent 
 to small insects, even ants, after their first attempts to catch 
 them failed. 
 
 The white chick scratches repeatedly with a sort of dancing 
 motion on the smooth wood, the brown has not yet performed 
 this action. The latter made the movement first on the eighth 
 day. 
 
 Both chickens from the first showed alarm at unexpected 
 noises, such as a loud cough. On the seventh or eighth day 
 when I made such a noise while they were before me on 
 the table, and they had just run away from me in fear, I 
 imitated the voice of a hen callin<? to her fellows. At this 
 both chicks turned suddenly round and ran, as though old 
 memories w^ere weakened in them, straight towards me as 
 
VI OBSERVATIONS ON CHICKS 251 
 
 though to seek protection. But as I could not supply the 
 place of the soft warm wings of the mother-hen, they suddenly 
 stood still, and when I afterwards began to imitate the voice 
 of the hen again, they took no notice. The cry " Cluck, cluck," 
 with which the hen calls her chickens, although I uttered it 
 as naturally as possible, had no effect. But the behaviour I 
 have described as caused by the imitation of the hen's chat- 
 tering was so striking that it cannot possibly be ascribed to 
 chance, especially as both chickens exhibited it at the same 
 time ; and it ought not to excite surprise, that when the 
 benefit instinctively expected was not received the behaviour 
 was not repeated, considering the decision with which the 
 young chickens act at once upon every experience. Still such 
 experiments ought to be repeated on other chickens. It is 
 also a reasonable question, whether the sitting hen may not 
 chatter sometimes on her nest, and whether the chicks may 
 not thus, even in the egg, hear something of the fowl's 
 language. Experiments therefore should also be made with 
 chicks hatched by an artificial incubator. 
 
 Moreover, the little creatures were from the first not afraid 
 of me, but they did not willingly allow me to take hold of 
 them, and the less so as time went on, because they found 
 by experience that I sometimes thereby deprived them of 
 liberty and put them back into their basket. As it had been 
 stated by Herr Spalding that chickens were thrown into the 
 greatest terror by a hawk, although they had never seen one 
 before, I made the experiment of trying to terrify them with 
 a sparrow-hawk stuffed with the wings extended. They took 
 not the least notice of the object, which of course does not 
 exclude the possibility of their behaving differently in presence 
 of the livimr bird. 
 
 Up to the eighth day, in consequence of the abundance of 
 food given to them, they had lived together without jealousy 
 or strife. On this day I again gave them some earth-worms. 
 
252 MENTAL FACULTIES sec. 
 
 After I had repeatedly thrown these in front of them the 
 brown chick began to worry one. Immediately the white 
 one came to seize it away from him. And so the chicks 
 pursued one another and quarrelled over every worm which 
 one of them had seized. 
 
 On the twelfth day I took my two charges to the hen by 
 whom they had been hatched, and wlio was in a dove-cot w^ith 
 her other chicks. My chicks immediately retreated from the 
 old hen, in evident terror, into a corner, while she looked on 
 them with a hostile eye. In fact, the hen only waited till I 
 had apparently gone away, and then fell upon her unknown 
 children with savage pecks. I had to take them away from their 
 mother. The two orphans soon ran about in the yard alone, 
 searching for food, showing no inclination to go through the 
 wide railing to the old hens in the fowl-run. They learned 
 to look after themselves, but kept always near the house, 
 never going far from it. One day the wdiite one disappeared, 
 having probably fallen a victim to a cat. The brown one, 
 left alone, used to come regularly to us at meals, which 
 we took in the garden, to pick up the crumbs which were 
 thrown to him. He would have nothing to do with his 
 fellows in the fowl-run, or wath the old hen which was confined 
 there with his brothers and sisters and clucking after them, 
 and at night he repaired to some unknown hiding-place. 
 This behaviour of his towards his own race in comparison 
 with his behaviour towards mankind is extremely remarkable, 
 because it was the consequence of experience which therefore, 
 as with respect to the catching of flies, had conquered and 
 displaced inborn instinct. For the bird is now — it is just 
 eight weeks old — so tame, that when it wants food it suffers 
 itself to be taken up and stroked, while its brothers and 
 sisters who were brought up by the hen are extremely shy. 
 It takes food preferably from the hand, and usually perches 
 for this purpose on the back of the garden-seat between us or 
 
VI OBSERVATIONS ON CHICKS 253 
 
 on our shoulders. But from glittering substances like spoons 
 and forks he will not take anything. He also runs after us 
 in the garden, but between meal-times he will be his own 
 master, and avoids the hand which tries to catch him. Many 
 times when we took a meal in the house and not in the "-aiden, I 
 have seen him running about round the empty table at dinner- 
 time obviously expecting us : his stomach is his clock. Very 
 comical is his behaviour when he is satisfied. He sits then 
 with his crop full on the back of the garden-seat among us, 
 ruffles his feathers, and shuts his eyes, so that my children 
 when they saw this for the first time thought he was froin'>' 
 to die. But he is only struggling with sleep ; he now and 
 then cleans his feathers and skin, then puts his head in the 
 usual fashion under his left wing, and begins his mid-day 
 nap. 
 
 Meantime he has given up his indifference to small 
 animals, and especially towards flies; at these he snaps 
 everywhere, and catches them with great skill. He has 
 never gone outside my yard and garden, although the open 
 fence offers no hindrance to his doing so. 
 
 He appears, after eight weeks of life, like a "self-made 
 man," as a " character " who knows his objects, although he 
 has scarcely reached half the size of an adult fowl. But 
 what he is, and what he can do, he is and can through 
 the employment of the abundant powers which he has 
 inherited from his ancestors, and which were acquired by 
 these. 
 
 How is it, on the other hand, conceivable that the vari- 
 ability of the germ-plasm, inherited from unicellular organ- 
 isms, in combination with continued sexual mixture, could 
 lead to such innate faculties as our chicken has shown ? 
 
 I must confess that the assumption of a variability in the 
 germ-plasm inherited from unicellular ancestors, and con- 
 tinually increased, wdth the effects ascribed to it by its advo- 
 
254 MENTAL FACULTIES six. 
 
 cates, seems to me, in face of these facts, to make no less a 
 (lemainl on tlie luiderstandiiig than miracles. 
 
 The difference hetween the chickens I studied this year 
 and those last year in tlieir first behaviour with regard to 
 food is possibly due to the I'act that food was first set 
 before the former some time after hatching, so that they 
 pecked at tlie millet as soon as they saw it from hunger, 
 while the latter being fed immediately after they were 
 hatched, had to be attracted by the falling of the grains. 
 Only a repetition of the experiments can decide this question. 
 But the fact that the young birds, without ever having seen 
 seed or water before, began to eat and drink, is sufficient 
 alone to excite wonder at so high a degree of inheritance of 
 acquired powers. It is true that this fact is very general, for 
 we must not forget that the young of countless other animals 
 take food at once in the same way, for example, every newly- 
 hatched caterpillar; but closer relations of course between 
 the caterpillar and its food-plant exist and are inherited than 
 in the case of chickens. 
 
 Experiments carried out by !Mr. Douglas Spalding^ on 
 newly-hatched chicks have afforded results similar to mine. 
 
 That writer placed a cap over the heads of chickens 
 which he took out of the egg before their eyes had been 
 capable of sight. When after one to three days he withdrew 
 the cap, the chicks seemed almost withoiit exception stunned 
 by the light, and remained for some minutes motionless. 
 
 ^ Douglas Spalding, Macmillan a Magazine, 1873. Cf. also W. Preyer : iJie 
 Seek des Kindes, Leijizig, 1882, \\ 82. The chickens preferred the yolk of egg 
 to the albumen from the first. The observation communicated to Romanes by 
 Allen Thomson, according to which chickens hatched on to a carpet did not 
 scratch as long as they were kept on it, but began at once to do so when some 
 gravel was strewn over it, is explained by the latter as due to the absence in the 
 one case, the action in the other, of the accustomed stimulus, the experience of 
 which is inlit-riteil ('Romanes, Mental Ki:obdton !n Animals, p. 174). 
 
VI AJR. SPALDING'S OBSERVATIONS 'Ih 
 
 00 
 
 " When one of my little pupils was twelve days ukl, while 
 it was running about near me, it uttered the peculiar cry with 
 which fowls denote the approach of danger. I looked up, 
 and saw a hawk which was circling at a great height above 
 us. Equally striking was the effect of the voice of the hawk 
 heard for the first time. A young turkey which I took 
 possession of when he began to chirp in the still unbroken 
 egg-shell was, on the morning of the tenth day of his life, just 
 engaged in taking his breakfast out of my hand when a 
 young hawk in his box close by us uttered a clear ' cheep, 
 cheep ' ; the poor turkey shot like an arrow to the other side 
 of the room, and stood there motionless and paralysed with 
 terror till the hawk gave out a second cry, when he ran out 
 of the open door to the farthest end of the lane, and there 
 remained for ten minutes crouched in a corner. Several 
 times more in the course of the day he heard that disturbing 
 sound, and each time with the same symptoms of fear. 
 
 " Frequently I sa\v hens lift their wings when they were 
 only a few hours old, that is, as soon as they could hold their 
 lieads upright, even wdien they were prevented from using 
 their eyes. The art of scratching for food, which one might 
 think must above everything else be acquired by imitation 
 (for a hen with her chickens spends half her time in scratch- 
 ing before them) forms nevertheless an undoubted instance of 
 instinct. Without any opportunity for imitation, chickens 
 which were kept entirely isolated began to scratch at the age 
 of tw^o to six weeks. As a rule the character of the ground 
 invited them to this ; I have often seen first attempts at it, 
 which looked like a kind of nervous dance, on a smooth 
 table. 
 
 " As an example of unacquired skill, I can mention that 
 when I put four one-day-old ducks into the open air for the 
 first time, one of them immediately snapped at a fly and 
 €auoht it in its flicfht. But still more interesting in iny 
 
256 MENTAL FACULTIES sec. 
 
 opinion is the deliberate artfulness with which the turkey 
 already mentioned, not yet a day and a half old, hunted flies. 
 He aimed carefully with his beak at flies and other small 
 insects witliout actually pecking at tliem, and while he did 
 this his head trembled like a hand which one tries to hold 
 motionless by an effort. I observed and recorded this when 
 I did not yet understand the meaning of it ; for not till 
 afterwards did I discover that it is an invariable habit of the 
 turkey when he sees a fly sitting on any object to creep 
 slowly and with cautious steps to the unsuspicious insect, 
 and to stretch out liis head very carefully and surely to the 
 distance of about an incli from his prey, which he then 
 seizes with a sudden stroke." 
 
 The Instinct of the Cuckoo in Laying her Eggs in other 
 
 Birds' Nests 
 
 This instinct has been much discussed on account of its 
 peculiarity, especially since Darwin gave an explanation for 
 it. Darwin says in tlie Origin of Species: "It is supposed 
 by some naturalists that the more immediate cause of the 
 instinct of the cuckoo is that she lays her eggs not daily, but 
 at intervals of two or three days, so that if she were to make 
 her own nest and sit on her own eggs, those first laid would 
 have to be left for some time unincubated, or there would be 
 eggs and young birds of different ages in the same nest. 
 This explanation is not sufficient, for the American cuckoo 
 makes her own nest, lays her eggs in it, and has eggs and 
 young successively hatched, all at the same time. She also 
 lays her eggs occasionally in other birds' nests." Darwin, as 
 is known, then supposes that the ancient progenitor of our 
 European cuckoo had the habits of the American cuckoo, 
 and that she occasionally laid an egg in another bird's 
 nest. " If the old bird profited by this occasional habit 
 
VI INSTINCT OF THE CUCKOO 257 
 
 tlirough being enabled to migrate earlier, or through any 
 other cause; or if the young were made more vigorous by 
 advantage being taken of the mistaken instinct of another 
 species than when reared by their own mother, encum- 
 bered as she could hardly fail to be by having eggs and 
 young of different ages at the same time ; then the old 
 birds or the fostered young would gain an advantage. 
 And analogy would lead us to believe that the young thus 
 reared would be apt to follow by inheritance the occasional 
 and aberrant habit of their mother, and in their turn 
 would be apt to lay their eggs in other birds' nests, and 
 thus be more successful in rearing their young. By a 
 continued process of this nature I believe that the strange 
 instinct of our cuckoo has been developed. It has also 
 recently been ascertained on sufficient evidence, by Adolf 
 Muller, that the cuckoo occasionally lays her eggs on the 
 bare ground, sits on them, and feeds her young. This rare 
 event is probably a case of reversion to the long lost 
 aboriginal instinct of nidification." 
 
 Thus here again is conspicuous the importance ascribed to 
 chance, on which Darwin bases his whole theory; and for this 
 very reason I devote particular consideration to the instinct 
 of the cuckoo. It seems to me a priori impossible that 
 instincts can be explained by mere accidents, and it seems to 
 me especially impossible that the young bird derived from 
 an ^^g which was accidentally laid in the nest of another 
 species should " by inheritance " be more likely " to follow 
 the occasional and aberrant habit of its mother" — of the 
 mother which it had never seen. If there is any greater 
 inclination in the young bird, it can only be, in my opinion, 
 the inclination acquired from the experience which it passed 
 through in the nest of its foster-parents during its own 
 youth ; ^ through the impressions it received of its foster- 
 
 1 Cf. Walter, Brehm's Thierleben, second edition, vol. iv. p. 217. 
 
 S 
 
258 MENTAL FACULTIES sec. 
 
 parents and of the nature of their nest. And it is in fact all 
 the more probable that such experience is the principal factor 
 in the case in question, and that it has at last become 
 instinctive by inheritance, because we know that the 
 experience of youth also in ourselves, and in the animals 
 of which we know anything on this point, is retained 
 with extraordinary tenacity. Thus, for example, a single 
 punishment is as a rule sufficient to make a young pointer 
 indifferent to hares. Accordingly, the young cuckoo is 
 iniluenced, not by the inheritance of the occasional habit of 
 its mother, but by the experiences of its education, and by the 
 deficiencies of its education. The cuckoo can never learn to 
 build nests, and must completely lose the nidificating instinct. 
 But, apart from these considerations, it is a question if the 
 occasional laying of eggs in other birds' nests was really the 
 ultimate cause of the cuckoo's instinct. I deny this, and 
 believe tliat the original progenitors of our cuckoo when they 
 began to lay their eggs in other nests acted by reflection and 
 with design. We have no certain knowledge that the cuckoo 
 does not at tlie present day lay its eggs in other birds' nests 
 after conscious reflection. We do not know, therefore, how far 
 this action is due to intelligence. That it is not a perfect 
 instinct is shown by the fact above mentioned, that our 
 cuckoo at times sits on her own eggs and feeds her young; 
 and it is especially noteworthy that it builds no nest for the 
 purpose. 
 
 This is of course disputed. Brehm ascribes the statement 
 to a confusion of the cuckoo with the goat-sucker, but Darwin 
 himself regards it as satisfactorily proved. But if the fact is 
 considered unproved, the other fact that the American cuckoo 
 sometimes incubates its own eggs, sometimes lays them in 
 other birds' nests, and a priori the assumption tliat the 
 instinct of our cuckoo has been gradually developed, imply 
 that there was a time when it still occasionally incubated 
 
VI HABITS OF THE CUCKOO 259 
 
 its own eggs, as conversely the American cuckoo now only 
 
 occasionally lays its eggs in other nests. Who can prove 
 
 that reflection did not underlie this difference of action, 
 
 determining it according to the different conditions ? For the 
 
 cuckoo certainly shows reflection in its choice of nests in 
 
 which to lay its eggs, and in many other actions. Ihit 
 
 whether our cuckoo acts at the present day from pure instinct 
 
 or still by reflection — even assuming the first — it is, I believe, 
 
 necessary, in order to explain the instinct, to start from the 
 
 supposition that it has arisen by the inheritance of habit 
 
 originally intelligent. The conditions of life of the bird enable 
 
 us to understand easily enough the ultimate causes of the habit. 
 
 The cuckoo lives the life of a vagabond. It wanders about 
 
 restlessly ; in the first place, it remains with us only a few 
 
 months, from April to August; secondly, even in the region 
 
 where it settles here it has no permanent station, it wanders 
 
 now in one direction now in another. This restlessness is 
 
 caused by its insatiable appetite and sexual desires. It is 
 
 ever seeking food and mates. Its food consists principally of 
 
 caterpillars, especially those which, like Gastropacha pini, 
 
 occur only here and there in great abundance. The cuckoo 
 
 must therefore move about in order to satisfy its need of food. 
 
 When it has found a swarm of caterpillars it revels in excess, 
 
 and its sexual requirements are increased. It enjoys on 
 
 account of its loose life the worst of reputations ; the bonds 
 
 of marriage are unknown to it, especially to the lady-cuckoo. 
 
 Brehm says of it, with regard to this : " Any one who doubts 
 
 the intense lustfulness of the cuckoo needs only to visit its 
 
 sleeping-places repeatedly. To-day are heard the voice of the 
 
 female, the soft wooing of the male ; to-morrow only the cry 
 
 of the latter ; the former is then blessing a neighbour or a 
 
 distant mate." ^ Farther on : " Although he meets with no 
 
 reluctance, desire seems to drive him out of his senses. He 
 
 ^ Brelira, Illustr. Thierleben, second edition, vol. iv. p. 215. 
 
260 MENTAL FACULTIES sec. 
 
 is literally mad as long as the pairing time continues, he 
 screams unceasingly, so violently that his voice breaks down, 
 constantly scours his neighbourhood, and sees in every other 
 his rival in love, the most hateful of all adversaries." ^ But 
 the female is the greater rover ; the male remains within a 
 more limited range. The former ''roves throughout the 
 whole summer, that is, as long as its egg-laying period lasts, 
 irregularly through the ranges of various males, attaches 
 herself to none, but abandons herself to all who please her, 
 Avaits not to be sought, but starts of her own accord to seek 
 adventures, and after her desire is satisfied pays no further 
 attention to the mate who has just shown her favour. A 
 female which I watched near Berlin, which was recognisable 
 througli having had a tail feather shot away, visited, so far as I 
 could discover, the stations of no less than five males, but 
 probably extended her excursions still farther. Every other 
 female doubtless behaves in the same wav, as other observa- 
 tions prove almost to certainty." " I have often," remarks 
 Walter, " seen a male in company with a female when she 
 extended her excursions to a more distant region, e.g. across a 
 large lake, suddenly desert her and fly back, at first in a wide 
 circle, and then in a straight line to his own district. If the 
 female had already laid an ^^^^ in the latter she returned 
 thither, although not till another day. Only in case she 
 could not find another nest in the neif^hbourhood of the one 
 
 o 
 
 first used, she remained longer away, and was not seen again 
 for days." " On the other hand, other females now pass con- 
 stantly through the same district, and thus every male, if not 
 by every, at all events by some female, has his desires 
 satisfied. Tliese dissolute and vacjabond habits in the female 
 give, in my opinion, the most simple and most satisfactory 
 explanation of certain facts connected with the deposition of 
 the eggs, which have hitherto been mysterious." " These 
 
 ^ Ibid. p. 213. ^ Brehni, second edition, vol. iv. pp. 211, 212. 
 
VI CAUSES OF THE CUCKOO'S HABITS 261 
 
 habits in the female are doubly remarkable because the 
 males are at least twice as numerous as the females. Brehm 
 supposes that the females wander about principally to find 
 nests in which to lay their eggs. It seems to me that 
 it is rather to be explained by their insatiable sexual 
 desires. 
 
 The female lays her eggs, not like other birds in rapid 
 succession, but at considerable intervals. Most authorities 
 say the interval is from six to eight days. In observed cases 
 a female produced at least two eggs in a week, in others the 
 second was not laid till six days after. There appears, there- 
 fore, to be great variation in this respect. And this agrees 
 with my view of the cause of the peculiarity of the species 
 which is related to the long duration of the egg-producing 
 period. It was probably ultimately determined by the irregular 
 habits of life, the irregular, but on the whole extraordinarily 
 abundant consumption of food, and the varying demands of 
 sexual excitement. Thus our domestic hens have been 
 brought by continued high feeding to lay eggs throughout 
 the greatest part of the year, and to receive the male through- 
 out the whole of this time. The latter condition must tend 
 to increase the number of eggs laid. In man and many 
 domesticated animals even winter has no effect in diminishing 
 generative activity, as it has in most of our wild animals. It 
 is even possible, although not proved, tliat the cuckoo con- 
 tinues to lay eggs during the whole of its period of reproduc- 
 tion — during about two months — and so lays as many as 
 twenty to twenty-four eggs (Brehm). 
 
 That the production of eggs is extended in the cuckoo 
 over so long a period is not therefore the only and ultimate 
 cause of its instinct. But because, in consequence of its mode 
 of feeding and the sexual demands therewith connected, it 
 forms no regular family ties, but is compelled to lead a 
 vagabond life, therefore it does not lay its eggs in rapid sue- 
 
262 iMEXTAL FACULTIES SEC. 
 
 cession like other birds, and cannot incubate like these. Its 
 ancestors, therefore, not accidentally, but from reflection, laid 
 their eggs in other birds' nests, and tliis habit has now 
 perhaps become instinctive, but is also doubtless maintained 
 by the eftects of experience, in that the young cuckoos know 
 the cliaracteristics of their foster-parents' nest, but have never 
 learnt to build a nest, and have inherited no instinct of 
 nidification from their parents. 
 
 There are vagabonds in human society, in the lowest as well 
 as the highest, who lead in all respects a cuckoo's life — our 
 knowledge of these enables us better to understand the 
 instinct of the cuckoo. Such people trouble themselves no 
 more than the cuckoo about their offspring, but let others 
 look after them, and even leave them at other people's doors, 
 or at the door of the foundling hospital. 
 
 But it is extremely remarkable that the cuckoo has still so 
 far retained the instinct of providing for its offspring in spite 
 of its pleasure-seeking life, that it secures the maintenance 
 of the species although the instinct of incubation has been 
 entirely lost. Compare with this again the habits of our 
 domestic fowls. In them the incubating instinct is obviously 
 gradually being lost ; it occurs only in a few individual 
 hens. ^lost hens are indifferent to the fate of the eggs they 
 lay, or even, like the domestic duck, simply let them drop 
 anywhere. Domestic ducks, like domestic hens, have for- 
 gotten how to build a nest, like the cuckoo. But the original 
 form of the domestic duck (Anas boschas) makes a nest in 
 which she lays eiglit to sixteen eggs. The original of the 
 domestic fowl (Gallus bankiva) in India also lays in a nest, 
 only roughly prepared it is true, eight to twelve eggs, and, like 
 the wild duck, lays them in rapid succession, so that they 
 are hatched all toj^^ether. 
 
 The difference in the persistence of the parental instinct 
 in domestic fowls and ducks on one hand, and in the cuckoo 
 
vr ORIGIN OF INCUBATION 263 
 
 on the other, I can only explain to myself by the fact that 
 the eggs are taken away from the former, so that many of 
 them have completely lost the habit of providing in any way 
 for the maintenance of the species — lost it in consequence of 
 experience acquired during life, and inherited ; while every 
 cuckoo must remain in a certain relation to her offspring. 
 On the other hand, the cuckoo knows by inherited as well as 
 by continually renewed memory that she has been reared by 
 her foster-parents, whom she must recognise. She must 
 come, therefore, to the reasonable conclusion that her offspring 
 will be reared by birds like her foster-parents. It is to be 
 remarked that there are in fact only a very limited number 
 of birds to which the cuckoo entrusts its eggs. Our European 
 cuckoo confines its attentions principally to the reed- warblers, 
 the water- wagtails, the hedge-sparrows, and the pipits. 
 
 It will of course be asked w^hy does the cuckoo take care 
 to provide for her eggs ? For she cannot know that she was 
 produced from an egg. But this objection applies also to the 
 care of all other birds for their eggs. Every bird must, from 
 the first time it hatches its eggs, draw the conclusion that 
 young will also be produced from the eggs which it lays 
 afterwards, and this experience must have been inherited as 
 instinct. Besides this, it is allowable to assume that physio- 
 logical causes are present which give rise to the habit of 
 incubation. At the period of reproduction an abundant fiow 
 of blood towards the sexual organs takes place, especially to 
 the oviducts and ovaries, which in birds whose eggs are 
 provided with a large yolk require abundant nutrition at 
 this period. The blood thus required, after the eggs are laid, 
 causes an increased sensation of warmth in the skin, whicli 
 the bird perhaps, as other naturalists have supposed, origin- 
 ally tried to alleviate by sitting on the cooler eggs. This may 
 have been the first inducement to sitting, which afterwards 
 gradually became instinctive. 
 
264 MENTAL FACULTIES sec. 
 
 Moreover, it is undecided how far all birds, even before 
 they begin to incubate themselves, obtain a knowledge of 
 their origin from eggs by observing others incubating. 
 
 The cuckoo has no longer the impulse to incubate because 
 in her, in consequence of the slower rate at which her eggs 
 are produced, different physiological conditions occur than in 
 other birds, and this is true likewise of domestic hens and 
 ducks. The time must come, although it cannot be predicted, 
 when the latter will cease to incubate altogether, if the 
 present conditions continue. That the incubating instinct 
 in birds must have developed gradually follows from the 
 fact of their derivation from reptiles. It will be replied to 
 this, that the Pythonidse lie upon their eggs ; but I am 
 inclined to suppose that this is really a case of the protection 
 of the eggs by their parents, wdiich is observed in so many 
 other animals, — at the same time I by no means reject the 
 supposition that this protecting habit may have been among 
 the conditions from which the habit of incubation took its rise 
 in birds. When the gradual evolution of the high temperature 
 of the blood, either connected or not with the desire to cool 
 the skin, is added, the rest follows naturally. 
 
 The instinct of taking care of offspring is one of the most 
 rooted, one of the most perfect of all which occur in animals, 
 and it is surprising enough that it can be lost even under the 
 influence of domestication, as in our hens and ducks. That . 
 the instinct has not entirely disappeared in the cuckoo I 
 have attributed partly to the possibility of the persistence of 
 a certain degree of relation between the old cuckoos and 
 their young, without, how^ever, laying much weight upon this 
 reason. I felt, however, obliged to refer to that possibility, 
 because the love of parents for their children and their care 
 for them obviously depends ultimately on the advantages of 
 society, or on the advantages which the members of a family 
 afford one another, and particularly which the children afford 
 
VI HABITS OF MOLOTHRUS 265 
 
 to the parents in old age. To be alone in the world is in 
 itself painful. Accordingly the instinct of caring for off- 
 spring is a social instinct, and it belongs, according to my 
 practical view of " reason," to the class of reasoning instincts, 
 since it connects the care for the future of the species with 
 the care for the family. At the lower stages of its evolution 
 the egoistical side of this instinct will still be strongly pro- 
 minent, but as the relations are continually refined, and with 
 the mental evolution of the organism become more manifold 
 and more spiritual, the most ideal conduct results from it. 
 
 Darwin mentions that some species of Molothrus, a genus of 
 American birds, allied to our starlings, have habits like these of 
 the cuckoo. He believes that among the species of this genus a 
 series can be arranged which shows the evolution of the instinct. 
 According to Mr. Hudson, Molothrus badius sometimes 
 builds a nest of her own, sometimes lays her eggs in another 
 bird's after she has thrown out the nestlings of the latter, 
 sometimes builds a nest for herself on the top of the one appro- 
 priated. She usually sits on her own eggs and rears her own 
 young ; but probably she occasionally leaves them to be reared 
 by other birds, for young of this species have been observed 
 clamouring to old birds of another species for food. Another 
 species, Molothrus bonariensis, according to Darwin, has the 
 parasitic instinct much more highly developed. As far as is 
 known, this bird invariably lays its eggs in the nests of others ; 
 but it is remarkable that several together sometimes commence 
 to build an irregular untidy nest of their own in singularly 
 ill -adapted situations, as on the leaves of a large thistle. 
 They never, however, so far as Mr. Hudson ascertained, com- 
 pleted a nest for themselves. They often lay so many eggs 
 — from fifteen to twenty — in the same foster-nest, that few 
 or none can possibly be hatched. They have, moreover, the 
 extraordinary habit of pecking holes in the eggs, whether of 
 
266 MENTAL FACULTIES sec. 
 
 their own species or of their foster-parents which they find 
 in the appropriated nests. They drop also many eggs on the 
 bare ground, wliicli are thus wasted. But I should think 
 that tlie habits of this species perhaps indicate rather a de- 
 generation of the parasitic instinct than a higlier development 
 of it in comparison with tlie preceding species. The bird 
 seems beginning to make less careful provision for its eggs. 
 A third species, the Isl. pecoris, behaves exactly like our 
 cuckoo. Now, it is an important fact in relation to my view 
 of the evolution of the cuckoo's instinct that the M. pecoris 
 also is polygamous, and this seems also true of j\I. badius. 
 Mr. Hudson says, according to Darwin, they live sometimes 
 quite promiscuously together, sometimes they pair. 
 
 PiEASONixG Instincts 
 
 The Bee as an Example of the Im.'portance of acquired and 
 inherited Characters in the Modification of Forms 
 
 I here adduce first a case which in many respects supports 
 ray views in the most striking way, especially with regard to 
 the inheritance of mental cliaracters, and with regard to the 
 great part which is played by correlation in the alteration 
 of the sexual organs. 
 
 We know that in bees the asexual condition of the w^orkers 
 is the result of insufficient nourishment in the larval state, 
 for within the first eight days of their life the larvie which 
 are destined to become workers can by better feeding — by 
 the feeding which the queen -larVcC receive — be reared into 
 sexually-perfect queens, capable of reproduction. 
 
 This is, be it said in passing, one of the most beautiful, 
 incontrovertible instances of the direct influence of external 
 conditions on the development of structure. 
 
 Here also the workers possess a whole series of peculiar 
 characters of the body which are obviously correlated with 
 
VI QUEEN BEES AND WORKERS 26; 
 
 the repression of the sexual organs, for when the worker 
 larvae royally fed develop into queens, they develop all the 
 characters of the queen. 
 
 But the most interesting point is that the worker bees, 
 whose duty it is to feed the larvae, only in case of necessity, 
 only when no young queens exist, rear queens from worker 
 larvae. This almost compels the conclusion that they con- 
 sciously, under ordinary conditions, rear only workers, au 
 abundance of which is so necessary to the community. But 
 even if they do this instinctively, how do they attain to their 
 wisdom with regard to rearing queens and to many other 
 matters ? It can, it seems, be no more inherited from their 
 parents, queen and drone, than the winglessness of worker 
 ants from the winged parents — indeed, much less, for the 
 wisdom of the worker bees is in many respects much greater 
 than that of the parents. These mental faculties of the 
 worker bee exist in germ in the worker larvae, and if these 
 do not receive the royal food those faculties develop ; yet 
 when the larvae are fed with the food of larval queens, the 
 peculiar mental characters of the queen, not those of the 
 w^orker, are developed together with the sexual organs and 
 other bodily characters. And all this is brought to pass by a 
 little more nourishment ! 
 
 But all this can only be explained with the aid of the 
 inheritance of acquired characters, by a very large measure of 
 this inheritance, and by correlation. Not in the least, on the 
 other hand, by the continuity and variability of the germ- 
 plasm, and by sexual mixture or pammixis. 
 
 The larvae of bees must have inherited in their brains 
 the possibility of a number of faculties which have been 
 acquired by their ancestors. I say possibility intentionally, 
 and not rudiments, in order to prevent misunderstand- 
 ing. For w^e have here to deal not with rudiments, 
 which would have to be developed into complete facul- 
 
268 MENTAL FACULTIES sec. 
 
 ties by exercise ; we have to deal rather with two sets 
 of connected characters which develop into perfection without 
 any need of further practice, according as the larva receives 
 the extra food or not. These two groups of characters unite 
 together to form a whole, just as from a number of pieces of 
 glass in a kaleidoscope two synnnetrical pictures appear, 
 according to the way it is shaken. In consequence of the 
 better nourishment, a different development of the brain takes 
 place 'pariimssu with the development of the other characters, 
 so that a perfectly definite set of mental characters becomes 
 simultaneously predominant. 
 
 As I have said in my Freiburg address, w^e must regard 
 the different forms of bees, queen, drones, workers, as discon- 
 tinuous organs of one whole, which have been evolved from 
 a sinG[le indifferent ancestral form. And this differentiation 
 can only be the result, not merely of external demands, but 
 also of direct external influences — especially of experiences. 
 
 Only thus can we explain to ourselves the fact that the 
 peculiarities of the workers, notwithstanding that they do not 
 reproduce, are inherited — they are inherited not indeed 
 through the workers themselves, but from the ancestors. The 
 sexual union of drone and queen produces a germ which 
 possesses all the characters which the original bee must have 
 possessed at the time when as yet no separation into queen 
 and drones and workers had occurred. 
 
 From the fertilised egg can proceed a worker, or with 
 better nourishment, a queen, also a drone, but the latter not 
 directly but still indirectly; the C[ueen "buds," she lays eggs, 
 and if these are not fertilised, drones are produced from them. 
 We have, however, compared fertilisation with conjugation, 
 and represented it as a kind of nutrition : if, then, the egg of 
 the queen is from the first better nourished by the spermato- 
 zoon, it gives rise to a female or a worker larva. 
 
 The two sexes of plants and animals, according to the pre- 
 
VI EVOLUTION OF BEES 269 
 
 ceding considerations, appear in all cases as separate organs 
 of an original form in which both were united, a view which 
 is supported by other well-known facts. Accordingly, there 
 is reason to maintain that the separation of the sexes depends 
 partly on conditions of nourishment, and their peculiar 
 characters (especially in mental attributes), partly on correla- 
 tion. To this question I shall return, and then at the same 
 time attempt to explain parthenogenesis by considerations 
 closely connected with those I have just suggested. 
 
 The case under examination thus appears to me to have 
 a peculiar importance in the treatment of wider questions, 
 and therefore I will shortly summarise the results of my 
 reflections upon it. 
 
 1. The facts that queen bees can be reared from worker 
 larvse by better nourishment, and that the former have bodily 
 and mental characters quite different from those of the latter, 
 show clearly, 
 
 'a. the influence of nutrition on the modification of 
 
 forms, 
 h. the importance of correlation in the same process — 
 the importance of kaleidoscopic transformation. 
 
 2. This remarkable process, in particular the fact that the 
 mental characters of the two kinds of bees, workers and 
 queens, are so completely different, and in each case so 
 distinctly form a complete whole, can only be explained on 
 the assumption that both sets of characters were originally 
 united in one form, and that their separation has resulted in 
 consequence of the necessity of division of labour, througli 
 kaleidoscopic transformation, so that the two complementary 
 forms appear as organs of that original form. 
 
 3. But the orimnal form included the drones also. It is 
 
 o 
 
 in consequence of richer nourishment of the ^gg that even 
 w^orker larvae are produced : on nourishment by the sper- 
 matozoon, that is, on fertilisation. If this nourishment is not 
 
270 MENTAL FACULTIES sec. 
 
 supplied, drones are produced. Thus drones, workers, and 
 queens are to some extent to be regarded as organs of an 
 original creature wliicli united the characters of all three. 
 
 4. The effect of conditions of nutrition on the mental 
 characters appears to me above all remarkable, considering 
 the exclusive individuality which those characters present in 
 the different kinds of bees, especially as they can only have 
 been developed as a result of experience. Of course I do not 
 maintain that the separation of the mental characters into 
 three groups, as it exists now in its present perfection and 
 exclusiveness, arose suddenly, any more than that the peculi- 
 arities of bodily structure in the three forms of bees so arose : 
 correlation must have played a part at the very beginning of 
 the differentiation. But these three forms of bees have each 
 gradually advanced towards higher perfection in consequence 
 of the action of external conditions (or of experience) and of 
 selection, and the sudden transformation which now occurs, 
 e.g. of a worker larva into a queen through better nourish- 
 ment, forms an abbreviated repetition of the evolution which 
 formerly proceeded gradually. 
 
 Moreover, I assume that for some time only males and 
 females existed in the bee community, and no workers. 
 
 The conditions existing among the humble-bees enable us 
 to understand the evolution of the forms of bees according to 
 my view. 
 
 " In spring, when the all-vivifying sun has warmed the 
 ground to a certain depth, a female liumble-bee creeps forth 
 from a hole dug by herself in the ground, usually in a position 
 exposed to the sun, or from a rotten tree-trunk, or from a 
 clump of moss, or from some other retreat in which she has 
 passed her winter sleep." Thus Professor Eduard Hoffer com- 
 mences his description of the liumble-bees of Styria,^ and he 
 
 ^ E. Hoffer, Die Iluvimeln Steiennark's, Lehensgeschichte und Beschreibung 
 derselben. Graz, 1882. 
 
VI LIFE-HISTORY OF HUMBLE-BEES 271 
 
 goes on to describe the foundation of the humble-bee family as 
 follows : At first the female humble-bee flies from flower to 
 flower sipping honey, then she seeks a place in which to 
 build her nest. When she has found a place, any suitable 
 hole, she carries into it moss, grass, leaves, hairs of animals, 
 and fine needles of the fir or pine, and builds a nest closed on 
 all sides, and provided with only a single opening directed 
 towards the rising sun, and usually concealed. Then she 
 collects honey and pollen, makes a cell of wax, fills it witli 
 pollen soaked with honey, and lays a pair of eggs in it. 
 From these larvas soon emerge, which grow rapidly, and 
 therefore require much food. The mother now toils ener- 
 getically day and night for the welfare of her children, by 
 day chiefly collecting, and feeding the larvse, by night biting 
 up and arranging the materials of the nest, coating it with a 
 wax-like material, and warming her young. She allows her- 
 self little rest, except when the weather is bad. At last, in 
 the beginning of May, or in some forms several weeks later, 
 the first young humble-bees creep forth. These are workers, 
 much smaller than the mother or queen — are in fact stunted 
 queens. They fly forth at once to collect honey and pollen, 
 which they bring into the nest. As long as there are but few 
 of these workers the mother continues to fly out also to the 
 fields and collect industriously, but afterwards she goes out 
 less ; she now remains much at home, laying eggs and tend- 
 ing them. At last she ceases entirely from going out, her 
 wings, as a rule, becoming useless. Some of the workers tend 
 their younger sisters, who are still in the cells, and feed 
 them, work at the construction of the nest, keej) it clean, and 
 lick and warm the young bees when they creep forth. The 
 workers raise a great humming if the nest is disturbed, and 
 defend it by stinging the invader. Thus the queen lives with 
 her handmaids several weeks, about three months, continually 
 adding to their number. As a rule, about July young of a 
 
272 MENTAL FACULTIES sec. 
 
 much larger size emerge, likewise resembling tlie queen, the 
 so-called " small females " or large workers, i.e. females whose 
 reproductive organs are developed, but who generally produce 
 only drone-eggs, though under certain circumstances they can 
 lay eggs which liatch into females or workers. These large 
 workers and the small workers and the old female, all three 
 kinds, now lay drone-eggs in large numbers, from wdiicli males 
 are hatched. Not till the end of summer does the mother 
 again lay queen -eggs. There exist now therefore in the 
 family — (1) the old queen, Avho is frequently incapable of 
 flight and destitute of hairs ; (2) numerous young queens ; (3) 
 the ordinary or small workers ; (4) the large w^orkers or small 
 females ; (5) the drones or males. All the workers throughout 
 the summer Hy forth to collect about a quarter of an hour 
 before sunrise, awakened by a peculiar humming, the voice of 
 the trumpeter. The males also go to the fields, but only 
 from ten in the morning to four in the afternoon, and only 
 for themselves. They do no w^ork in the nest — although 
 Hotter saw them occasionally assist, but only when the roof 
 w^as taken away from a nest. On fine sunny days in July, 
 August, September, and the first half of October, the young 
 queens fly from the nest, settle on flower stems, broad leaves, 
 fences or walls in the sun, and are there sought by the drones 
 of their own or other nests, wooed, and then fertilised during 
 flight. When the young queens are all thus in a condition 
 wiiich enables them to found new colonies in the following' 
 year, the whole family gradually disperses. The accepted 
 males soon die, the rest fly about a great deal, return no more 
 to their home even at night, but usually remain out on 
 flowers, and gradually perish (a melancholy example of un- 
 successful existence). 
 
 If one takes off the mossy covering from a nest at its most 
 flourishing period he usually comes upon a wall of wax, and 
 when he removes this he sees, not the regular honeycomb of 
 
VI COMPARISON OF HUMBLE-BEES WITH HIVE-BEES 273 
 
 bees and wasps, but a somewhat irregular mass, consisting of 
 larger and smaller pupa -cells, shaped like a hazel-nut, and 
 usually of a fine whitish -yellow colour, darker clumps of 
 larva-cells, and smaller clumps of eggs of the size of a lentil- 
 seed, or a pea, or even as large as a bean. Some of the 
 thimble -like pupa -cells from which the bees have already 
 emerged seem to have been converted by a coating of wax 
 into receptacles for honey and pollen ; but one also sees a 
 large number of proper honey-cells which are made of wax, 
 and of which, on a very favourable day, ten or more are 
 constructed. 
 
 In the humble-bee family there are but two sexes, male 
 and female, for the small and large workers are only 
 females with sexual organs imperfectly developed in con- 
 sequence of imperfect nourishment, especially of being 
 insufficiently supplied with honey during their larval 
 life. 
 
 The moral of these facts is the followinoj : The humble- 
 bee queen is not yet so exclusively a breeding mother as 
 the bee queen. The latter is the mother, or reproductive 
 individual, of the bee community, and nothing else ; she is the 
 female reproductive organ of the social organism ; she collects 
 not, she builds not, she does not even feed herself, but is 
 fed by the workers : the humble-bee queen undertakes all 
 these duties at the commencement of her public career. The 
 same applies to the drones : the humble-bee drones feed 
 themselves, and, although only exceptionally, take part in 
 work ; the bee drones on the contrary are fed by others, like 
 the bee queen, and do no work. The humble-bee drones 
 have almost lost all independence with regard to all other 
 functions than the sexual, like the bee drones, but they have 
 not travelled so far in this direction as the latter. The same 
 also applies to the workers. The bee workers no longer lay 
 any eggs. True, quite recently cases have been recorded in 
 
 T 
 
274 MENTAL FACULTIES sec. 
 
 our bee journals by bee-keepers in which workers copulated 
 with drones. These cases have excited a degree of incredulity 
 and of sensation for whicli there is no justification. For since 
 the workers are merely imperfect females, it can cause no 
 surprise if their sexual organs are in occasional instances 
 more completely developed — perhaps througli the larvae 
 being accidentally better nourished — or even if they show 
 the instinct of copulation. It is, moreover, known that 
 workers in hives that have no queen sometimes lay eggs, and 
 that from these drones are hatched. These exceptional cases 
 among worker bees afford a perfect transition to the conditions 
 wliicli normally occur among humble-bees. In these the 
 workers still regularly lay drone -eggs, indeed, the earliest 
 brood of workers, the small workers, can lay drone-eggs only, 
 while the large workers or small females are said to be able, 
 as remarked above, under certain circumstances to lay female- 
 eggs. Thus tlie workers of the humble-bees are not yet, 
 like those of the hive -bees, exclusively workers. But the 
 influence of nutrition is here directly before our eyes. The 
 first brood of workers, laid at a time when the queen has to 
 do everything herself or with the aid of few workers, can of 
 course not be so well fed as the second brood, produced when 
 the whole of the first brood render assistance. This better 
 nourished brood, according to Hoffer, have developed sexual 
 organs : their more highly nourished condition shows itself 
 also in their greater size, and they sometimes lay eggs from 
 wliich females are hatched, which must therefore be fer- 
 tilised. Lastly follow the young queens, whose larvae, 
 with the assistance of both broods of workers, can be 
 fed best of all, and the eggs of which have likewise 
 received by fertilisation an important addition of nutritive 
 material. 
 
 The present conditions among bees must have had a 
 similar origin, but in them the complete evolution of the 
 
VI SOCIAL ORGANISATION OF BEES 275 
 
 community has taken place, while the humble-bees, and 
 similarly the social wasps, only reach the status of a large 
 family. The bees sacrifice the welfare of the individual with 
 relentless determination to the advantage of the state, in that 
 they kill their drones when they have become useless, while 
 these among the humble-bees perish gradually. The humble- 
 bee queen dies in her second year ; but the bee queen in her 
 second year, when she has reared offspring, is compelled in 
 the interest of the state to leave the hive and found for her- 
 self a new state. But this state -organisation has, for the 
 mother of the whole and for the workers, the advantage that 
 their life is secured for a longer time, for the workers among 
 the humble-bees do not survive the winter, while those of 
 the bees do. 
 
 In these respects we have in wasps conditions similar to 
 those of the humble-bees. 
 
 The foundation of this essential difference between humble- 
 bees, or wasps, and the economy of the bees, obviously consists 
 in the fact that the reasoning instinct, i.e. the forethought 
 for the future — in this case primarily for food — is far greater 
 in hive -bees than in humble-bees and wasps, which provide 
 no winter store, and whose females have to pass the winter 
 in seclusion. 
 
 The state -organisation of bees and ants has often been 
 praised as the ideal of social and political arrangements. 
 But it must be remembered that in these animal communities 
 the individual is unconditionally responsible to the state for 
 all its activity, as the state's servant, and if it does not fulfil 
 this responsibility, or if it has served its purpose, it is 
 expelled or destroyed. The queen -bee does not begin to 
 provide for the reproduction of the hive until there are a 
 sufficient number of workers to secure adequate maintenance 
 for two hives, and the female humble-bee or wasp likewise 
 begins her family by providing workers. This is according 
 
276 MENTAL FACULTIES sec. 
 
 to reason; while the causes of the social problems in mankind 
 depend in great part on unreasoning conduct with respect to 
 the establishment of families, and for the rest on the burden 
 of idlers in the state. 
 
 In the preceding the origin of the sexually imperfect 
 workers in the communities of humble-bees and bees — and 
 the same will hold for the social wasps and ants — has been 
 ascribed to deficiency of nourishment. The question now 
 arises : Is this development accidental, or can we recognise 
 in its beginnings the evidence of reflection in the animals 
 which form the family or state ? Obviously the latter 
 alternative must decisively be affirmed. The animals, when 
 they founded families or states, must have seen the advantage 
 of several members living together, the fruitfulness of co- 
 operation. The bees, for instance, must also have seen that 
 the Gjathering of stores for the winter was useful to them. 
 In the explanation of this forethought chance is perhaps not 
 to be excluded : it may be that in exceptionally favourable 
 summers the animals gathered unusually abundant stores, so 
 that at least a part of them, instead of perishing in autumn, 
 survived the winter w^ith the queen, and these were able then 
 in the following spring to go to work again at once. Selection 
 cannot here have had much influence, since the workers do 
 not reproduce. In order to make these favourable conditions 
 constant, insight and reflection on the part of the animals, 
 and inheritance of these faculties, were necessary. Whereby 
 it is to be borne in mind that the queen-bee originally collected 
 and built alono- with the rest, and that she must have trans- 
 mitted to her offspring the experience thus acquired. It 
 might be objected to this, and pure Darwinism will make the 
 objection, that the instinct of laying in a store might have 
 arisen merely because the queens, wlio happened to be the 
 most industrious collectors, survived those wdiich were less 
 industrious, and so at length a race arose wdiich laid in a 
 
VI ORIGIN OF THE STORING INSTINCT Tn 
 
 winter store quite meclianically without knowing wherefore. 
 But if this were so, it would be impossible to understand 
 why the instinct of storing in the queen has in reality not 
 been improved, but has been lost. And this view is also 
 improbable on account of the high mental endowments — not 
 of an instinctive character — which are displayed by the 
 hymenoptera. 
 
 The origin of the storing instinct might again be exj^lained 
 by the supposition that the winter, or in warmer regions the 
 time unfavourable to collecting, has been gradually prolonged, 
 and that only those communities of bees survived which 
 were the most industrious. But the same objections as were 
 made against the previous view apply to this, and in addition 
 various others into which I will not here enter. 
 
 It seems to me, indeed, necessary to assume that a gradual 
 prolongation of the period of the year unfavourable to collect- 
 ing must have contributed to the development of the bee 
 community in its present condition, and especially to the 
 accumulation of larger stores ; but it is equally necessary to 
 suppose that reflection and foresight in the bees worked 
 hand in hand with this cause, and have been increased by 
 experience.'^ A proof that bees even now collect their stores 
 in full consciousness that these are a necessity for them is 
 afforded by the fact, known to every bee-master, that the 
 bees, especially the Italian, angrily pursue the person who 
 has taken away their honey. Even several days after the 
 removal of the honey individual bees pursue any one in the 
 neighbourhood of the hive and endeavour to sting him. 
 According to statements which seem to me perfectly reliable, 
 bee-keepers who allowed their bees no peace and continually 
 took from them the last drop of their honey have been 
 
 ^ In Australia, where tlie bees find supplies almost all the year round, the 
 instinct of collecting a store for future use is said in fact to disappear in a com- 
 paratively short time, so that it is necessary constantly to renew it by the im- 
 portation of foreign queens. 
 
278 MENTAL FACULTIES sec. 
 
 suddenly attacked by them, apparently with a common 
 purpose, and been very severely injured by them. 
 
 As reason in general cannot have arisen suddenly from 
 particular causes, or in particular cases, but must rather have 
 been gradually evolved under the influence of external 
 conditions, so in bees the evolvition of the existing reasoning 
 instinct of collecting must have taken place quite gradually, 
 and must have arisen at first from simple intelligent actions 
 adapted to immediate needs. I do not intend to pursue this 
 question in further detail, but will only point out, that the 
 production of sexually imperfect workers in itself is a highly 
 remarkable instance of conscious consideration by the in- 
 dividual of the advantage of the community. For the only 
 possible explanation of the origin of the workers is that the 
 orioinal bee or humble-bee could not feed all her larvse suffi- 
 ciently, and that she obtained an advantage in her house- 
 keeping by the workers thus produced. The insect must 
 have recognised this advantage, and afterwards, accordingly, 
 reared similar workers intentionally by insufficient feeding. 
 Another explanation which might be given is, that certain 
 individuals began to sacrifice themselves to the requirements 
 of the community by neglecting to feed themselves to such 
 an extent that their sexual organs no longer attained their 
 full development. 
 
 Further Eemarks on Eeasoning Instincts and 
 Intelligent Instincts in Animals 
 
 It is self-evident that all cases in which animals display 
 forethought for the winter by storing provisions, or providing 
 themselves with winter quarters in which to protect them- 
 selves, must be described as cases of reasoning instinct, as 
 also the cases in which individual animals provide nourish- 
 ment for the use of their offspring at a later time. 
 
 One of the most remarkable instincts of this kind is 
 
 "• I 
 
VI INSTINCT OF MASON-WASPS 279 
 
 that of the mason -wasp (Odynerus parietum), and allied 
 predatory wasps. The mason -wasp makes a hole about 
 10 cm. deep in a bank of clay, moistens and softens the clay 
 she has removed with saliva, and probably also with water, 
 and builds w^ith it a tube leading from the mouth of the hole 
 and prolonging it. The tube at first stands out at right 
 angles to the bank, then bends downwards. Probably this 
 arrangement is chosen in order that the water may run off 
 more easily, just as the cells of the paper- wasp (Polistes 
 gallica), which are made of chewed wood, are turned down- 
 wards, so that the rain may be kept out as much as possible, 
 while the bees, contrariwise, build their cells upright, so that 
 the honey may remain in them. But the wasp casts out 
 some granules of clay from the mouth of the tube. Taschen- 
 berg ^ supposes that this is the material with which she after- 
 w^ards closes the tube. When the nest is ready, the wasp 
 brings into it larvae of beetles and other insects, which she 
 has paralysed by stinging them in the ganglia which govern 
 muscular action. This is one of the most marvellous in- 
 stincts that exist : since the wasp operates on various larvse 
 with nervous systems of various forms, she must effect the 
 paralysis in various ways, and even apart from this, she 
 makes a physiological experiment which is far in advance of 
 the knowledge of man. The wasp thus carries one motionless 
 but livino' larva after another into her tube until it is full, 
 and she rolls up the larvse and packs them so skilfully that 
 they take up as little room as possible. Finally, she lays her 
 egg in the store of living food, and closes the opening with clay. 
 Then she begins a new tube, and so lays one ^gg after another. 
 What a wonderful contrivance ! What calculation on the 
 part of the animal must have been necessary to discover it I 
 The larvae of the wasp require animal food. Dead food 
 enclosed in the cell w^ould soon putrefy, living active animals 
 
 ^ Brehm's Thierleben, second edition, vol. ix. p. 240. 
 
280 MENTAL FACULTIES sec. 
 
 would disturb the egg, and accordingly the wasp paralyses 
 grubs and packs them like sacks of meal one after another in 
 the cell. How did she arrive at this habit ? At the begin- 
 ning she probably killed larvre by stinging them anywhere, 
 and then placed them in the cell. The bad results of this 
 showed themselves ; the larva3 putrefied before they could 
 serve as food for the larval wasps. In the meantime the 
 mother-wasp discovered that those larvae which she had stung 
 in particular parts of the body were motionless but still alive, 
 and then she concluded that larvae stung in this particular 
 way could be kept for a longer time unchanged as living 
 motionless food. It may be suggested that the wasp only 
 paralysed the larvae in order to carry them more easily ; but 
 even if this were the case, she must, since she now invariably acts 
 in this way, have drawn a conclusion by deductive reasoning. 
 
 In this case it is absolutely impossible that the animal 
 has arrived at its habit otherwise than by reflection upon the 
 facts of experience. 
 
 An accurate observer, Lichtenstein, states, with regard to 
 the laying and incubation of the ostrich, that during the 
 breeding- time one cock and three or four hens live together, 
 and he continues : " All the hens lay their eggs in the same 
 nest, which consists of nothing more than a round depression 
 in the somewhat loose clayey soil, of such a size that one hen 
 can cover it. Eound the hole the birds scratch up the soil, 
 so as to make a kind of wall, against which the outermost 
 eggs are supported. Each ^gg in the nest stands on end, so 
 that the largest number possible can be packed in it. As 
 soon as there are ten to twelve eggs in the nest the birds 
 begin to incubate, and this they do in turns, the hens reliev- 
 ing one another by day, the cock alone sitting at night, in 
 order that he may repel the attacks of the jackal and the wild 
 cat, who greedily watch for an opportunity to steal the eggs. 
 In the meantime the hens still continue to lay eggs, not only 
 
VI HABITS OF THE OSTRICH 281 
 
 until the nest is full, which is the case when it contains 
 thirty eggs, but even afterwards. These last -laid eggs lie 
 irregularly round about the nest, and seem to be intended by 
 nature to satisfy the rapacity of the enemies above mentioned, 
 to whom she prefers to surrender these fresh eggs than those 
 already incubated. But these eggs have also a more im- 
 portant use, namely, to serve as the first food for the young 
 ostriches, which when they are hatched are as big as an 
 ordinary fowl, and whose tender stomachs are not at first able 
 to digest the hard food of the adults. The old ones them- 
 selves break these eggs for them one after another, and in a 
 short time with this nutritious food bring them on so far that 
 they are able to seek their own food." The same observation 
 has also been made by others, and Brehm doubts it on in- 
 sufficient grounds.-^ That there are cases of young animals 
 fed by the parents' eggs is proved by the black Alpine sala- 
 mander (Salamandra atra). This animal brings forth living 
 young without gills and with completely developed lungs, in 
 complete contrast to all other tailed Amphibia, the young of 
 which are born with gills, and this is well known to be due 
 to the fact that the conditions of life of the Alpine sala- 
 mander do not allow it to deposit its eggs in the water. The 
 young, therefore, imder the stress of the external conditions, 
 develop, until the lungs are completely formed, in the oviducts 
 of the mother. In these oviducts a remarkable struggle for 
 existence takes place, so that only one larva develops in each, 
 and this nourishes itself at the expense of the other eggs in 
 the oviduct until it reaches its maturity. I mention this 
 because Brehm regards it as something entirely novel that 
 birds should be fed on their parents' eggs. Such a method 
 of nutrition occurs only in this single instance among 
 Amphibia. 
 
 Thus in the Alpine salamander most of the eggs which 
 
 ^ Loc. cit. vol. vi. pp. 198, 199. 
 
282 MENTAL FACULTIES sec. 
 
 would otherwise develop are devoured by two more favoured 
 larvfe. 
 
 But the case of the ostrich could only be employed as an 
 example of a reasoning instinct if it could be assumed that 
 the hens have come to co-operate in incubating a large 
 number of eggs with the intention of providing the first food 
 for their young. As the conditions of the case are not known 
 more minutely it is not possible to form an opinion upon it ; 
 but in any case it is intelligent instinct, or intelligent action, 
 when the ostriches make use of these eggs to feed their young ; 
 and I chose this example to bring into view the distinction 
 between the two kinds of mental action, as well as on account 
 of its interest, because it is little known, and because ostriches 
 are proverbially described as stupid animals. 
 
 But what was it that taught the beaver to dam back 
 the flowing water by a regular weir built of tree trunks, 
 sticks, and branches, in order that some of the burrows 
 which lead to the face of the river-bank from the building 
 which it so skilfully constructs might be always under 
 water ? 
 
 What taught the ants to carry on regular agricultural 
 operations, to collect the seeds of certain grasses, let them 
 germinate, then to bite off the germ — to malt, in fact, and to 
 dry the seeds, and keep them for future requirements ? What 
 taught them to keep slaves, and make these feed them, until 
 more than one species have forgotten how to feed themselves 
 by their ow^n exertions ? 
 
 I will not enter upon a minute consideration of the 
 wonderful facts presented to us by the social life of the 
 Hymenoptera, and especially by the ants. These facts, which 
 so strikingly illustrate instincts of reason, were long doubted, 
 but have been completely established, particularly by Forel, 
 who has fully confirmed the observations of Huber, and 
 largely added to them, in his excellent work. I need not 
 
VI AN A CT OF SELF-IMMOLA TION B V ANTS 283 
 
 mention Huber's observations on bees, many of which every 
 observant keeper of bees can personally confirm.^ 
 
 Fore! comes to the conclusion, from his own observations 
 on ants, that they are capable of sacrificing themselves for 
 the general good, the highest ideal of conduct to wliich we 
 can require man himself to attain ; and if such conduct has 
 in animals become instinctive, the fact must cause us to 
 marvel the more at their mental and social life, and human 
 society must confess that it has scarcely advanced so far. 
 
 The Countess ISTostiz, wdio died in Meran a few years 
 ago, accompanied her first husband, the entomologist Heifer, 
 in the journey to Asia described in the book Heifers Rcisen, 
 wdiich she edited from his diaries. This extremely talented 
 woman, seldom at fault in the observation of nature, assured 
 me that she witnessed the following incident with her ow^n 
 eyes: A train of ants in active migration arrived at the 
 bank of a brook which they wished to cross. The vanguard 
 examined at one or two places the part of the bank whence, 
 as the result showed, the crossing w^as to be made ; then a 
 number of the ants, holding fast to some stalks of grass on 
 the bank, went into the water ; others mounted on those and 
 held on to them, and others held on to these, and so on ; 
 so these ants drowned themselves and formed a bridge over 
 which the body of the army then passed over to the other 
 bank. It can only be concluded that these ants first care- 
 fully examined the breadth of the brook and the other con- 
 ditions, and thereupon determined to choose this method of 
 crossing. This may seem a rash conclusion, but only because 
 people in general, and many naturalists, immensely under- 
 estimate the mental faculties of animals, and therefore the 
 majority are always inclined to receive as fables the state- 
 
 1 Forel, Les Fourmis de la Sxdsse, Bale, Geneve, Lyon, 1874 ; P. Huber, 
 Recherches sur les Mceurs des Fourmis indigents, Paris, 1810 ; F. Huber, 
 Nouvelles Observations sur les Abeilles, second edition, Paris, Geneve, 1814. 
 Cf. also the works of Lubbock. 
 
284 MENTAL FACULTIES sec. 
 
 ments of those who have minutely studied the life of any 
 class of animals. It is indeed the custom to set down the 
 most wonderful mental powers in animals without distinction 
 as instinct, because men think tliey can thereby reduce the 
 importance of these faculties, and conceive them as some- 
 thing mechanical implanted in the animal's nature from the 
 beginning. Men have an idea they must at any price 
 preserve their fancied exceptional position in the animal 
 world, even though it be at the cost of their delight in nature, 
 and of their own intellectual progress. Moreover, those 
 among them who suppose they serve the Creator by their 
 belief, do not perceive that the case is just the opposite, since 
 they reduce his power instead of magnifying it. But apart 
 from this, such a view altogether excludes every explanation 
 of instinct and of the mental faculties of animals. 
 
 On the other hand, when we explain instinct as inherited 
 experience, its phenomena appear as the result of continued 
 practice due to this experience. On this view, intelligence 
 and reason, it is true, become mechanical, but in a way which 
 does not diminish the importance of instinct, but which, on 
 the contrary, brings into stronger light the acuteness of the 
 original powers of reflection in animals, and their conscious 
 direction to a definite object. Instincts of intelligence and 
 of reason are in all cases a highly important factor in the 
 evolution of mental faculties. By the establishment of 
 these, and, in a less degree, of automatic actions, as already 
 pointed out, powers are set free which can be applied to 
 further mental effort ; they evidently constitute a means for 
 the progressive development of the mental life. 
 
 As in the evolution of the individual body an abbrevia- 
 tion takes place in course of time which affords time, 
 material, and energy for further modification, so is it in 
 mental evolution : instinct is evolved by a suitable abbrevia- 
 tion, simplification of the process of thought. 
 
VI SELF-CONTROL IN A DOG 285 
 
 It follows from my view of instinct, as I shall show more 
 fully hereafter, that we cannot always draw a dividino- line 
 
 between the voluntary exertion of intelligence or reason 
 
 between action depending on immediate reflection — and 
 instinct. Those who take the lowest possible estimate of 
 the mental life of animals will not admit the former at all, 
 although both intelligence and reason are necessary ante- 
 cedents of the latter. Some of the cases already mentioned 
 show the difficulty of distinguishing between intelligence 
 and reason on the one hand and instinct on the other, as well 
 as the self-evident difficulty of distinguishing intelligence 
 from reason. The ants who by the sacrifice of their own 
 lives built a bridge across the stream for the benefit of the 
 community possessed certainly reasoning instincts ; but this 
 particular case of self-sacrifice must have been due to the 
 direct voluntary exercise of reason, because it must have 
 been an exceptional case. Here, therefore, the application 
 of the general reasoning instinct depended on conclusions 
 drawn by reflections made at the moment. 
 
 Whether ants, when they carry their pupae, according to 
 the temperature, towards the centre or the surface of their 
 nest, act on instinct or reflection, and whether they or the 
 bees act by the former or the latter in numerous other such 
 instances, we cannot from the nature of tlie case decide. 
 But countless facts prove that here as in the case above con- 
 sidered, instinct and reflection supplement and alternate with 
 one another, or else that reflection operates principally or 
 exclusively. 
 
 A theological friend of mine who studies attentively tlie 
 mental powers of his dog, an animal of no particular breed, 
 resembling a jackal in size and form, tells me the following 
 story about him : The dog, who is extremely active, pug- 
 nacious, and courageous, was persecuted for weeks by a 
 butcher's dog of about the same size, apparently from envy 
 
286 MENTAL FACULTIES sec. 
 
 because " Ami " at the daily visit to the butcher's shop 
 received a scrap of sausage. The butcher's dog after every 
 visit followed him down the street barkiug and yelping, and 
 running close at his side. " Ami " was quite a match for his 
 adversary, as the result of several fights showed, but it \vas 
 evident that the strife at last became distasteful to him, and 
 besides he saw that his master disapproved of it. He no 
 longer allowed himself to be irritated, and then he gave up 
 his visit to the butcher's shop. The provocation was, however, 
 continued when the peaceful " Ami," accompanying his 
 master in his usual walk, w^ent past the butcher's shop. 
 From the street in which this shop stands two side streets 
 diverge some distance on one side of the shop, joining the 
 main street again farther on. One day " Ami " left his 
 master at the place where these streets diverge, ran through 
 one of them, and awaited him at the place where they unite 
 again. Afterwards he regularly made the same detour, 
 choosing sometimes one sometimes the other of the side 
 streets. He thus avoids meeting the brawler, not from fear, 
 as his own character proves, for he has never shown any fear 
 of his enemy, but because he washes to avoid strife. 
 
 Dr. Fickert tells me he has observed two quite similar 
 cases in another dog. 
 
 If men behaved as "Ami" did — which would be an excep- 
 tional occurrence — we should say they behaved reasonably. 
 It seems in fact that the dog drew the general conclusion 
 that constant strife is useless, and it is better to avoid it ; but 
 of course it cannot be decided whether it was so, or whether he 
 simply concluded that his opponent might at last handle him 
 severely. But whether the behaviour of the dog be called 
 reasonable or intelligent, it cannot be called instinctive. 
 
 Dr. Fickert tells me also the following story about a dog 
 which he possessed : This dog found by, experience that 
 when he tried to swim across the rapid stream of the Neckar 
 
 * I 
 
VI INSTANCES OF INTELLIGENCE IN ANTS 287 
 
 he was carried down by tlie current, and therefore could not 
 reach a particular place on the opposite bank which was 
 suitable for landing. He therefore used to go along the 
 shore some distance up the river before he jumped into the 
 water, and so swimming straight forwards, and being carried 
 down by the stream at the same time, he crossed in a slant- 
 ing direction to the landing-place. This was intelligent 
 reflection, not instinct. 
 
 Professor Leuckart observed a highly remarkable example 
 of intelligence in ants. The insects were crawling up the 
 trunk of a tree in order to reach some aphides. Leuckart 
 painted a ring of tar half-way up the trunk to see what the 
 insects would do. They could not go either up or down 
 across the sticky obstacle. For a time they ran up and 
 down restlessly, but at last those who were below the ring 
 descended to the ground. After a time they came back 
 each with a grain of earth between her jaws ; one after the 
 other placed her morsel of earth on the tar, so that gradually 
 a bridge was formed across it, over which the insects passed 
 in safety. That they should have recourse to an expedient 
 so remarkable was not instinct but intelligence ; but if they 
 intended to rescue the ants on the upper side of the ring, then 
 they acted by reason. However, it is known that ants in 
 such cases know how to help themselves by dropping from 
 the branches to the ground. 
 
 Father Gredler of Bozen records the following observation, 
 made in his monastery : ^ " One of my colleagues had for some 
 months placed food on his window-sill for the benefit of a com- 
 munity of ants (Formica aliena, Foerst.), which held regular 
 processions from the garden to the window of his room. When 
 I described to him the experiments made long ago by Gleditsch, 
 and recently by more modern students of ants, the amusing 
 idea occurred to him to fasten an empty ink-bottle by a thread 
 
 ^ Zoologischer Garten, vol. xv. p. 434. 
 
288 MENTAL FACULTIES sec. 
 
 to the cross-bar of the window. In this vessel the ants' food, 
 some crushed sugar, was placed, and in order that the ants 
 might be aware of the new position of the food provided for 
 them a nuniber of individuals were placed in it. The busy 
 little creatures took up their crumbs of sugar, soon found their 
 way up the only means of communication, the suspending 
 thread, along the cross-bar and down the window-frame, and 
 reached their companions on the window-sill, to continue from 
 there their usual journey down the high w^all to the nest in the 
 garden. It was not long before a regular traffic over the new 
 road from the window-sill to the store of sugar was organised, 
 and so a few days went by without offering anything novel. 
 But one morning the traffic ceased at its old terminus, and the 
 ants again obtained their groceries from a nearer source — 
 namely, from the window-sill. Not a single individual made 
 the journey thence to the vessel of sugar. Yet this had not 
 been emptied. By no means ; but a dozen individuals were 
 working vigorously and unweariedly in the vessel above, 
 simply carrying the grains of sugar to its edge and throwing 
 them down to their comrades on the sill below." 
 
 P. Huber made the following observation : He watched 
 an ant building a covered way out of earth : first it erected a 
 vertical wall on one side, then it raised a second vertical wall 
 parallel to the first, in order to support a roof on the two, and 
 so form the gallery. It had begun to extend the roof out 
 horizontally from the upper edge of the second wall ; appar- 
 ently it was intended to rest upon the first wall on the other 
 side, but this had been carried too high. Then a second ant 
 came by, looked at the defective structure, examined it, drove 
 the unskilful builder away, pulled down the walls, and built 
 the whole anew. 
 
 P. Huber also records the followiuG^ observation in humble- 
 bees, which build their combs horizontally one over tlie other : 
 
 ^ P. Huber, Recherches, p. 47. 
 
VI EVIDENCE OF INTELLIGENCE IN HONEYCOMB 289 
 
 A very irregular piece of comb placed on a very smootli table 
 vibrated so much and so continually that the humble-bees 
 could not work on it. In order to prevent the vibration, two 
 or three of them held the comb fast, by setting their fore feet on 
 the table and the hind feet on the comb. By relieving one 
 another they continued this for three days, until the necessary 
 supporting columns of wax were finished.-^ Darwin, according 
 to Eomanes,^ ji-^stly remarks in his posthumous manuscript, 
 that such a case could scarcely have ever occurred in nature. 
 Self - evidently the animals must have acted entirely from 
 reflection upon the particular circumstances ; they acted like 
 the ants in the two last-mentioned cases, not instinctively, but 
 intelligently. 
 
 The construction of the honeycomb by bees seems to be the 
 work of pure instinct. But it is proved by experiments made 
 by Huber that the insects vary the structure of the comb in 
 accordance with external circumstances, and these likewise are 
 experiments which have no counterpart in nature, so that the 
 bees here again must have based their arrangements on the 
 results of intelligent reflection. It is clear that the building of 
 the comb requires very considerable instinctive dexterity, that 
 it must with regard to its essential character be reckoned among 
 constructive instincts ; but reflection seems not to have been 
 completely eliminated from it, it seems to be by no means 
 a perfectly unmixed instinct. The view that the cells, as Herr 
 Mullenhoff^ has recently attempted to prove, arise quite 
 mechanically through the mutual pressure of the bodies of the 
 bees at work, whereby they must necessarily become hexagonal, 
 is certainly unfounded. Any one who has once examined the 
 edge of an unfinished comb will admit this. Towards the edge 
 of such a comb the cells gradually diminish in height. The 
 
 1 p. Huber Fils, Observations sur x^lusieurs genres de bourdons, honMnatrices 
 deLinne, Transact. Linn Soc. vol. vi. pp. 214-299, London, 1801. 
 ^ Romanes, lac. cit. p. 225. 
 3 Pfliiger's Archivfur die gesammte Physiologie, vol. xxxii, pp. 589-618. 
 
 U 
 
290 MENTAL FACULTIES sec. 
 
 external wall of some of the outermost cells last commenced 
 is still wanting. The floor of the cells here is as thin as else- 
 where. Evidently the bees build up this wall in its proper 
 shape, and do not produce it by pressure. Similarly the con- 
 struction of the half-cells which the bees begin a comb with, 
 those which attach the comb to its surface of suspension, is 
 inexplicable on this view. For these half-cells resemble cells 
 divided longitudinally, which alternate with entire cells. It is 
 self-evident that only by this means can a foundation be made 
 from which to proceed with the construction of six-sided cells 
 according to the regular plan. Does the construction of this 
 commencement of the comb, which consists of cells different 
 from those of the rest of the comb, depend upon instinct? In 
 such cases it has been usual to talk of variations, of various 
 directions of instinct, and E. v. Hartmann has assumed this 
 explanation for the present case.-^ It is indeed obvious that in 
 this way instincts in various directions may arise in response 
 to definite and persistent external requirements. But how 
 can we explain by such definitely-directed instincts the fact 
 that the bees, when in the course of a comb of worker-cells they 
 wish to build the much wider drone-cells, make each succeed- 
 ing row of cells somewhat wider till they have finally attained 
 to the size of the drone-cells ? The art of the performance 
 depends of course in this case upon instinct, but such a 
 gradual change, which has to be arranged according to the 
 external conditions, seems to me distinctly to imply reflection 
 also, like so many other facts in the mental life of bees which 
 are usually lightly described as instinct. 
 
 That bees really exercise even a high degree of reflection in 
 building their combs is shown most completely by the follow- 
 ing observations and experiments of F. Huber : Once the bees 
 
 ^ Eduard v. Hartmann, I)as Unhevmsste vom Standpunkt der Physiologie und 
 Descendenztheorie, second edition, Berlin, 1877, p. 189. Hartmann calls such 
 instincts poljTiiorphous, but he also admits the importance of reflection in appar- 
 ently instinctive action, op. cit. p. 200. 
 
VI CONSTRUCTIVE SKILL OF THE SPIDER 291 
 
 had made on a wooden surface the beginnings of two combs, 
 one to the right, the other to the left, in such a way that the 
 latter should support an anterior, the former a posterior comb, 
 and the two when finished should be separated by the usual 
 distance between two combs in a hive. But the bees found that 
 they had not allowed sufficient distance. What did they do 
 in order to avoid losing the work already done ? They joined 
 the beginnings of the two combs into one. The curvature 
 necessarily produced was in the continuation of the comb 
 completely levelled, so that the lower part of the comb 
 became as regular as one properly commenced. 
 
 In another case the bees had commenced a comb on the 
 lower edge of a glass plate. As the work proceeded it was 
 evident that the comb would become too heavy for the narrow 
 surface of attachment. The bees therefore built the comb at 
 first regularly upwards on both sides of the glass, attaching it 
 to the latter by the surface ; but farther up they contented 
 themselves with merely carrying a layer of wax over both 
 sides of the glass plate until they reached the wood in which 
 . the plate was fastened, and there obtained a secure hold for 
 their structure. 
 
 The skill of the garden -spider in building her web no 
 doubt depends on instinct, but only with regard to the main 
 process : here also reflection is exercised on many points. In 
 the mere choice of the place where the net is to be spread, 
 the spider needs to take many things into consideration : 
 direction of wind, sunlight, abundance of insects, and, above 
 all, the assurance that the web will be safe from disturbance 
 in the place selected, require a host of intelligent conclusions 
 — the question of security from disturbance alone requires a 
 number. And yet how correctly the spiders usually judge in 
 this very respect. And when the locality for the net is 
 chosen, the spider has to decide the points at which the frame 
 of the net to which the spokes are fastened shall be attached, 
 
292 
 
 MENTAL FACULTIES 
 
 SEC. 
 
 and so on. In each sinfile case acfain the threads which 
 connect the spokes to the frame must be adapted to the con- 
 ditions of the latter ; and lastly, it is known that the spider 
 . not only in this regular work, but still more in repairing her 
 web, in doing which she fulfils the highest requirements of 
 mechanical adaptation, gives undoubted evidence of compli- 
 cated reflection. 
 
 Of course those who attribute to animals neither intellic^ence 
 nor reason, but only instinct, will call that which I describe 
 as evidence of reflection, variation of instinct, or endeavour to 
 bring it within the conception of definitely directed instincts. 
 
 But these facts only become comprehensible by the explan- 
 ation of instinct as inherited experience, i.e. as intelligent 
 and reasonable actions which have become automatic. I 
 fully admit that in the construction of a net or a honeycomb 
 various directions of instinct may have been developed, but 
 other actions of animals have not yet become purely instinc- 
 tive, and others again are exercised quite freely and spon- 
 taneously. But even spontaneous action in animals is often 
 only slightly removed from instinctive, as is shown by the 
 facts I have described concerning the chick, facts which 
 prove that these animals have become by inheritance capable 
 of making use of experience immediately in a surprising way. 
 Such an animal as this chick is extremely clever. I can 
 now add to the account already given, that when I had 
 fed it a single time, instead of on the table on which it was 
 usually fed, in. front of the door of my study, to which a 
 brido^e of considerable length leads from the garden, it came 
 regularly to this bridge expecting food. I am certain that 
 much which gives us the impression of pure instinct depends 
 on such a rapid employment of experience by animals. 
 
 The mental activities of many animals are obviously very 
 limited in extent, but we must always remember that we 
 know in general much too little in detail of this mental life, 
 
VI ABSENCE OF INSTINCT IN MAN 293 
 
 and that from the nature of the case we are only able to 
 recognise its manifestations to a very limited degree, that 
 therefore our low estimate of these mental powers is based on 
 very little information. This limited extent of the mental 
 activities is compensated by definite instincts, whose operations 
 fulfil the essential requirements of the animal, and which are 
 so conspicuous as to attract our attention, while the rest of the 
 animal's actions due to mental faculties escape notice. But if 
 the explanation of instinct which I have given is recognised 
 as correct, even animals which act chiefly from instinct must 
 be described as " clever." 
 
 The more manifold the demands upon an organism from 
 the outer world, in particular, the more they are subjected to 
 change of circumstances, so much the less can fixed instincts 
 be developed, so much the more will the brain have to be 
 developed, and to be capable of immediate and free response 
 to these external demands. Accordingly, in man there is but 
 little instinct, while voluntary action is very highly developed ; 
 but this is also connected with the fact that his body is 
 imperfectly adapted in many respects to external requirements. 
 Our senses, for example, as they exist are only sufficient 
 because their low degree of acuteness is compensated by the 
 high development of the brain, — this alone, for instance, has 
 enabled man to live under climatic conditions which, like 
 those of even our temperate zone, would not supply his 
 primary wants without special appliances. 
 
 The slow and long development of the mental and bodily 
 powers of man is connected with this higher stage of mental 
 evolution which he has reached. Since man, in consequeoce 
 of the great complexity and the great variability of the 
 conditions under which he lives, cannot inherit experience, 
 therefore he must acquire his experience during his life, and 
 thus he attains independence at a relatively late period of 
 life. In this respect the anthropomorphous apes are nearest 
 
294 
 
 MENTAL FACULTIES 
 
 SEC. 
 
 to man, and among different human races it is obvious that 
 the rate of development is nearly inversely proportional to 
 their standard of culture, and clearly both are under the 
 influence of climate. The preceding considerations explain 
 how certain constitutional predispositions in a single direc- 
 tion, such as musical talent, arithmetical talent, etc., can 
 appear at so early an age (phenomenal children), and are so 
 frequently hereditary. Such faculties approach most closely 
 in character to the instincts of animals ; they are due to the 
 inheritance of the results of practice, although occasionally 
 such talents may arise from favourable sexual mixture, from 
 crossing. Just as in animals, men with such special faculties 
 are by no means necessarily possessed of great general mental 
 power ; on the contrary, other mental faculties often diminish 
 to a corresponding degree, simply because only the special 
 powers can be employed or applied in the struggle for exist- 
 ence. Thus in many cases it is not the nations which stand 
 highest in culture in which musical talent, for instance, has 
 become quite general. I mention only the gipsies, Magyars, 
 and Tschechs. The latter nation has, besides the services 
 rendered by its wandering musical companies, done another 
 crreat service to mankind, it has contributed the invention 
 of the dance known as the polka.^ For the Tschechs are also 
 born dancers. The resemblance to instinct in such inherited 
 talents, in the musical talent of such nations, shows itself 
 especially in the fact that it is not a case of the higher 
 music, of faculty for lofty composition, but merely of the 
 inheritance of the faculty of performing the ordinary music. 
 
 Eeflex Action and Instinct 
 
 It is customary to connect the idea of instinct with nervous 
 
 ^ It was invented by a peasant girl, who danced the step for her own pleasure. 
 Cf. R. Andree, Tschechische Gdnge, 1872, p. 272, asserted on the authority of A. 
 Waldau. 
 
VI VOLITION IN THE SPINAL CORD 295 
 
 action, and I have done so too, but with a significance not 
 hitherto usual, since I have expressly included in instinct 
 reasoning action inherited through habit. The extent of the 
 idea of instinct is also usually limited within the range of 
 the action of the nervous system by the exclusion of reflex 
 action from it. Only actions or inclinations, i.e, faculties for 
 action, are called instincts which take place as if they were 
 due to reflection without actually being so. 
 
 But there are evidently two kinds of reflex action : one 
 purely involuntary, in the development of which conscious 
 experience, a brain, has had no influence in its earliest phyletic 
 origin. To this kind belongs, for instance, the peristaltic 
 movement of the intestine under the stimulus of food taken 
 into it. Also the rhythmical motion of the heart. To it also 
 belong numerous motions of the parts of lower organisms or 
 of the whole of such organisms excited directly by stimula- 
 tion. In another group of reflex actions, those which were 
 originally voluntary, it is evident that they were once, at an 
 earlier period, under the control of the brain, of experience ; 
 they are really automatic, in all their characters are now 
 removed from all relation to the action of the brain, in such a 
 way that such relation must be deduced from special reflec- 
 tion. Here belong some of those reflexes which take place 
 involuntarily, but which can even now be performed by 
 the will, e.g. the execution of purposeful co-ordinated motions 
 by particular groups of muscles on stimulation of the 
 appropriate nerves. The mechanism at work in this case 
 can only have arisen in consequence of practice originally 
 influenced by the brain, that is, in consequence of experience. 
 
 The reader will be here at once reminded of the well- 
 known experiment with acetic acid upon frogs, which is 
 usually quoted as evidence of the very great importance of 
 reflex action ; when acetic acid is, placed upon the skin of a 
 decapitated frog on one side, the nearest limb of that side 
 
296 MENTAL FACULTIES sec. 
 
 makes the appropriate motions to wipe away the acid. If this 
 limb be cut off, the frog tries to remove the acid with the 
 limb of the other side. I cannot admit this to be reflex 
 action ; it is evidently voluntary action set up by nerve- 
 cells of the spinal cord which possess the power of volition.-^ 
 In Annelids and Arthropods voluntary action is much 
 more clearly exhibited by the posterior part of the ventral 
 nerve -cord, which corresponds to the spinal cord of verte- 
 brates ; and other lower vertebrates, e.g. tortoises, likewise 
 exhibit indications of voluntary action in the decapitated 
 condition. 
 
 On the other hand, the contraction ot the fingers, which 
 follows upon stimulation of the nerves of the arm, and which 
 is generally subject to the will, is an instance of reflex action 
 which was originally dependent on the brain. Possibly the 
 involuntary winking of the eyelids is also a member of this 
 class, of reflexes which are fundamentally automatic, but not 
 the respiratory movements, although these can to a certain 
 extent be influenced by the will. A reflex action of tliis 
 second class is not necessarily adapted to an end, it may even 
 be very inappropriate ; in any case, it can only by accident 
 imply intelligent or reasonable motives. But the actions 
 which I call automatic are always purposeful, intelligent, or 
 reasonable. 
 
 I have still a lively recollection of the circumstances in 
 which I was first in danger from a shell in the war of 1870-71. 
 AVe were at the beginning of the campaign before Strassburg 
 in one of the small forts on the riqht bank of the Rhine at 
 Kehl, and I was standing with some comrades in a spacious 
 room in the fort at a table, occupied at the moment in follow- 
 ing on a map according to the latest information the advance 
 of our troops upon Paris, when a shell came through the 
 
 ^ Compare also Goltz, Beitrdge zur Lehre von den Funktionen der Nervencentra, 
 Berlin, 1869. 
 
VI AUTOMATIC BEHAVIOUR OF SOLDIERS 297 
 
 barred window and burst over our heads. I remember 
 perfectly that immediately upon the explosion, which filled 
 the room with gunpowder smoke and the dust of the plaster 
 of the shattered walls and ceiling, I threw my body and arms 
 about in rapid motions, at which I afterwards laughed heartily 
 myself, for these motions were as purposeless as possible — 
 instead of contracting my body within a smaller space, I 
 greatly increased its surface by these reflex motions. Very 
 quickly, however, I learnt in future on similar occasions to 
 act appropriately. Later on, while we lay before the fortress 
 on the left bank of the Ehine on the island of Sporen, when 
 a shell from the Strassburo; citadel fell in our neisfhbourhood, 
 I no longer beat about with my arms, but crouched together 
 into the smallest space without further reflection — by force 
 of habit, automatically. If I had acted thus appropriately 
 on the occasion of the first shell, as by habitual action 
 inherited from my forefathers, I should have acted from 
 instinct. When on a subsequent occasion, it was in the fight 
 at Chateauneuf, a chassepot ball flew so close past my ear that 
 the pressure of the air produced the impression that the ball 
 had struck me, I actually clapped my hand to my ear, evidently 
 in consequence of the inherited habit of grasping any part of 
 the body suddenly threatened, so as to protect it — that is, I 
 acted by instinct. 
 
 Moreover, it is well known that in war men soon become 
 so accustomed to shot and shell that they expose themselves 
 with more and more indifference, almost with heedlessness, 
 while the automatic motions of self-protection become rarer 
 and are only exhibited in the most dangerous circumstances. 
 When the first large projectile, a shrapnel-shell, from Strass- 
 burg burst over the open space in front of the church of the 
 village of Kehl, and scattered its balls around, I was much 
 astonished to see our colonel continue his walk across the 
 place with folded arms, without looking round, although 
 
298 MENTAL FACULTIES sec. 
 
 somewhat later, after some practice and experience, such be- 
 haviour seemed to me perfectly natural. 
 
 Our soldiers did not even consider it worth while to rise 
 from their beds when a shell came through a loophole into the 
 narrow corridor where they slept, and there burst with a 
 frightful crash, after the bombardment of our little fortifica- 
 tion already mentioned had been continued for several nights. 
 But when, after the surrender of Strassburg, it altogether 
 ceased, we slept badly at first on account of the unaccustomed 
 silence, like a miller whose mill has stopped. 
 
 These examples show in the clearest way that re- 
 flex and automatic action cannot be sharply separated ; 
 how easily the latter is acquired by us during life ; and 
 further, that it passes directly into instinct, as my view 
 supposes. 
 
 But since it is impossible, as will be shown more particu- 
 larly, to establish a point in the animal scale beyond which 
 a brain can be demonstrated, for voluntary action certainly 
 takes place even where no defined brain is present, and since 
 in lower animals it is very difficult to distinguish voluntary 
 from involuntary action, and nervous action from the results 
 of ordinary physico-chemical reaction, therefore it is difficult 
 to say whether this or that action in the lower animals is to 
 be referred to such reaction, or to reflex action, or to habit, or 
 to instinct. 
 
 Thus, according to the preceding considerations, automatic 
 action may be described as habitual voluntary action, instinct 
 as inherited habitual voluntary action, or the capacity for 
 such action. 
 
 According to the preceding, instinct cannot be distinguished 
 from some kinds of reflex action, from the reflex action which 
 was originally voluntary, by its mode of origin ; and the 
 reflex action originally voluntary, again, cannot be definitely 
 separated from pure reflex action. Thus there is some temp- 
 
VI E. V. HARTMANN ON INSTINCT 299 
 
 tation to describe reflex action also as instinct, and to speak 
 of a reflex instinct, and an instinct of intelligence and of 
 reason. In fact, this course lias been adopted by E. v. Hart- 
 mann in the criticism ^ which he published, at first anony- 
 mously, of his own Philosophy of the Unconscious. In the 
 chapter on the " Instincts of the subordinate central organs of 
 the nervous system," he says : " When an isolated and washed 
 frog's heart goes on beating for hours, the cause of this can 
 only be sought in the predisposition of the cardiac ganglia to 
 rhythmical action, which excites the muscular fibres of the 
 heart to contractions in the same rhythm. Such a predisposi- 
 tion in the ganglia, of which the typical active manifestations 
 have as much of the character of spontaneity as the instinct- 
 ive expression of will in any animal can ever have, must be 
 called instinct as undoubtedly as its functions must be called 
 will, since the unconscious purposefulness of its results is not 
 to be called in question. . . . 
 
 " What is true of the movements of the heart of course holds 
 good for the movements of the stomach and intestines, and for 
 the tone of the viscera, the blood-vessels, and muscles in rela- 
 tion to the sympathetic nervous system, as well as for the 
 respiratory movements in relation to the medulla oblongata ; 
 it likewise holds in relation to the cerebellum for those spon- 
 taneous movements and actions which birds and mammals 
 execute after the extirpation of the cerebral hemispheres. . . . 
 Here we arrive at once at the chapter of reflex movements, 
 and, in fact, instinct and reflex action cannot be separated, for 
 in instinct also some external motive of action must always 
 be present, and the action follows upon this motive necessar- 
 ily, therefore, in a reflex manner." And farther on : " As we 
 have seen that all forms of bodily dexterity are acquired, in- 
 herited, and when inherited improved by practice, so we must 
 
 1 Das Unheiousste vom StandpunU der Physiologie und Descendenztheorie, 
 Berlin, second edition, 1877, p. 206, et seq. 
 
300 MENTAL FACULTIES sec. 
 
 assume the same to be true of all those faculties which, 
 whether they have their seat in the cerebrum or in the lower 
 nerve centres, have in an eminent degree a reflex character, and 
 therefore are described in the narrower sense as reflex move- 
 ments." 
 
 In fact, it seems to be an unavoidable and self-evident 
 consequence of my view also that all reflex action is a property 
 acquired by practice, that it is inherited dexterity produced by 
 exercise. But if reflex action is included under the term 
 instinct, one must logically go so far, as E. v. Hartmann 
 does, as to speak of an instinct of the lower nerve centres, e.g. 
 of the sympathetic ganglion cells which govern the movements 
 of the heart and the intestine. Thus V. Hartmann explains 
 " the purposefulness of the reflex instincts of the lower nerve 
 centres" partly as the "outflow or as a ca;put mortimm of 
 former conscious purposeful action of the cerebrum" — as 
 though all purposeful action must have been originally influ- 
 enced by the latter. Xay, further, he goes so far as to main- 
 tain "the essential similarity and continuity of transition 
 between instinct and natural recuperative power," and to 
 express the opinion that it is impossible to establish a different 
 principle of explanation for the two phenomena. " Accord- 
 ingly, the w^ay in which the type of the whole worm is 
 contained in the ganglion of the worm -ring in process of 
 regeneration is to be described as a molecular ganglionic 
 predisposition established by inheritance." Further, "We 
 can consequently have no scruples in supposing the existence 
 in the ^anf]jlia which cjovern the vecretative sexual functions 
 of predispositions for the regulation of the development of 
 eggs and spermatozoa — the most important and most delicate 
 products in the whole of organic life — predispositions of the 
 same nature as those for the regeneration of lost parts of the 
 body, or for the construction of the comb of the bees, of the 
 web of the spider, or the shell of the Nautilus." 
 
VI IMPULSE AND INSTINCT 301 
 
 Therewith Y. Hartmann evidently partly returns to the 
 mysticism of the Philosophy of the Unconscious, which he is 
 endeavouring in his self-criticism to refute. On the other 
 hand, he comes to consequences according to which all 
 development, all growth, would have to be described as 
 instinct. 
 
 This example shows that we must limit the idea of instinct, 
 and I believe that this is best done in the way I have 
 adopted, namely, by applying the term only to those inherited 
 habits which are so adapted to a purpose that they appear to 
 be due to intelligence or reason. 
 
 V. Hartmann's error of attributing will to the ganglia of 
 the sympathetic nerve system is evidently due to a complete 
 misunderstanding of the functions of the nervous system. 
 Such ganglia are nothing more than the collecting foci of the 
 nerve paths, and at the same time apparatus for the reinforce- 
 ment of the stimuli (accumulators).-^ That their action also 
 depends on acquired and inherited properties, after the preced- 
 ing arguments, does not require to be insisted upon ; but it 
 has never even been under the influence of the will, still less 
 are they capable of originating spontaneous voluntary action. 
 
 In accordance with his view, as above sketched out, V. 
 Hartmann defines instinct as "purposeful action without 
 consciousness of the purpose." 
 
 Impulse and Instinct 
 
 Although we may rightly talk of the instinct of seeking 
 food in higher animals, it is impossible among the lower to 
 establish a limit above which the taking of food is influenced 
 by a choice due to nervous action. In the same way such a 
 limit cannot be established for the commencement of the 
 sexual instinct ; indeed, in my opinion, the commencement of 
 sexual activity depends ultimately on processes of nutrition. 
 
 ^ Cf. the next section. 
 
302 MENTAL FACULTIES sec. 
 
 Since all nervous action must have been gradually evolved 
 through relations of the organism to the outer world, the diffi- 
 culties referred to lie in the nature of the case, and can there- 
 fore only be considered as in favour of the justice of the view 
 I advocate. But these difficulties constantly make themselves 
 felt to an uncomfortable degree in the attempt to distinguish 
 between impulse and instinct. Ought we really to describe 
 the sexual impulse as an instinct ? Certainly it has as much 
 right to be so called as the migratory impulse, which appears 
 in spring and autumn, even in birds which have been reared 
 and kept all their lives in cages. The migratory impulse is 
 evidently excited by hereditary changes in the circulation 
 which occur at those times, by local blood pressure, which 
 again influences the nervous system, while the latter, on its 
 side, is excited by this change in the condition of the body to 
 the inherited automatic production of a number of acts which 
 are connected with this change. In principle the same is true 
 of the sexual impulse. 
 
 And yet impulse is not instinct, as has often been hastily 
 assumed. Impulse is merely the urgent desire to get rid 
 of an unsatisfactory condition of the body, to remove an 
 unpleasant feeling. Instinct finds the appropriate means of 
 effecting this : thus e.g. not the sexual impulse, but the pur- 
 poseful "endeavour to satisfy the impulse, is an instinct. But 
 the two things, the impulse, and the endeavour to satisfy it, 
 cannot be separated : thus, to use the case of the migratory 
 impulse again, the physiological condition of the body 
 which produces it, and the expression of the impulse itself, 
 cannot be separated. Similarly, hunger and thirst are so far 
 instincts that they cannot be separated from the instinct of 
 seeking food. Physiology describes both as general feelings : 
 they show themselves as needs felt by the nervous system, 
 caused by an internal condition of the body acting as a 
 stimulus — needs which must so far be called instinctive, that 
 
VI IMPULSE AND INSTINCT 303 
 
 tliey include so much of inherited experience as enables them 
 to find directly the means for their own satisfaction. 
 
 Thus we get back to the difficulty of finding the limit of 
 instinct towards the lower end of the animal scale. The 
 need of nourishment, in other words, the faculty of assimilation, 
 is a fundamental property of protoplasm ; upon it depends, in 
 animals provided with nerves, the feeling of the need of taking 
 nourishment, and through inherited experience the instinctive 
 practice of satisfying the need. The question has often been 
 argued, whether a new-born child seizes the mother's nipple 
 itself or must be directed to it. Without doubt the former is 
 the case : the child feels the need of nourishment, it expresses 
 it at once by means of acquired and inherited faculties by 
 crying, by means of the same faculties it makes sucking 
 motions with its mouth, as we also do in the adult condition 
 quite unconsciously, when we have a great desire for food 
 and drink and think of them — motions which in many self- 
 indulgent epicures have produced a quite characteristic form 
 of mouth, with soft prominent lips, seen, e.g., in so many clerical 
 gentlemen who find the world pleasant. These movements are 
 the same which the tongue makes in tasting, they consist prin- 
 cipally in the pressing of the tongue against the hard palate. 
 The child feels with its lips the warm soft breast of the 
 mother, and then at once seizes the nipple and sucks, in 
 accordance with its acquired and inherited faculties. Every 
 one who has watched new-born animals when sucking, knows 
 these facts, and knows that the mothers do not need to guide 
 their young to suck. 
 
 But although the necessity of nutrition is a fundamental 
 property of the protoplasm, the question arises, at what point 
 does the inception of food cease to be a mere physico-chemical 
 act and begin to depend on nervous action ? Where does the 
 feeling of bungler commence ? This feeling must be at once 
 connected with the impulse to satisfy it, although at first 
 
304 MENTAL FACULTIES sec. 
 
 inherited experience cannot have taught how to satisfy it. 
 Not until the inherited experience of proper method 
 has been acquired does instinct exist — but here again the 
 impulse itself, and the endeavour to satisfy it in accordance 
 with inherited experience are difficult to separate. 
 
 I have considered instinct as a faculty which can be called 
 into exercise by external or internal stimuli. These internal 
 stimuli consist in the temporary condition of the body, and 
 show themselves as impulses. The sexual impulse appears 
 first at a definite period of life, as hunger at a definite time 
 of day, and with them the instinct of satisfying them. If the 
 sexual organs are removed, both impulse and instinct cease. 
 Hunger we cannot remove. 
 
 Concluding Eemaeks on Instinct 
 
 My experiments on chickens show that the exercise of 
 instincts is determined by definite inherited mental images 
 of things, e.g. of the kind of food. But I consider it especially 
 necessary again expressly to point out that it is also in a high 
 degree the general acquired faculty of learning what actions 
 are suitable, of making use of the slightest experience, which 
 enables the animals so quickly to make themselves at home 
 in the world, and not always, however it might appear so at 
 first sight, perfect instinct, i.e. the inborn complete capacity 
 for performing certain actions. 
 
 The faculty of rapid learning implies in the particular 
 cases of its application a small remnant of independent 
 reflection, which beautifully shows how instinct arises. When 
 this reflection disappears in a particular case, we have pure 
 instinct. If we do not regard its importance, we believe we 
 have nothing but instinct before us. This explains how 
 diflicult it often is to decide how much in a particular action 
 is to be ascribed to instinct. 
 
VI DARWIN ON INSTINCT 305 
 
 The advantage of the faculty of learning rapidly lies in 
 the abbreviation of the process, whereby time is saved. 
 
 In instinct this abbreviation is still more complete, has 
 reached its highest stage — now the organism works intelli- 
 gently and according to reason in the directions concerned with 
 the same certainty and accuracy as the reflex mechanism 
 from which intelligence and reason have been evolved, but 
 which was only sufficient to meet the most common and 
 most general demands of the outer world. 
 
 Darwin gives no special explanation of instinct, he only 
 states his agreement with Peter Huber in the belief that with 
 instinct is mingled a small amount of judgment or intelli- 
 gence, even in animals which stand at a very low level in the 
 scale of nature.i He says it is easy to show that quite dis- 
 tinct mental faculties are usually included under this name. 
 In his posthumous essay on instinct, published by Eomanes 
 in his book on mental evolution in animals, Darwin still only 
 gives examples of the faculty, and as in his previous works 
 his object is exclusively to explain its evolution as a weapon 
 in the struggle for existence by the principle of utility. Thus 
 his posthumous manuscript concludes with the words : - "It 
 may not perhaps be quite logical, but in any case it is in my 
 view much more satisfactory, that I do not need to regard the 
 young cuckoo who casts its foster-brethren from the nest, 
 the slave-makinq; ants, the larvae of the Ichneimionida3 which 
 consume the living body of their victims, the cat playing 
 with the mouse, the fish-otter and cormorant with living fishes, 
 as instances of instincts which have been specially bestowed 
 on each animal by the Creator, but that I can consider them 
 as partial expressions of one general law which leads to the 
 progress of all organic beings — the law : Defend yourselves, 
 vary, let the strong live, the weak die." 
 
 Eomanes describes instinct as reflex action with which is 
 
 1 Origin of Species, sixth edition, p. 287. - Oji. cit. p. 437. 
 
 X 
 
306 MENTAL FACULTIES sec. 
 
 mingled an element of consciousness.^ This definition of the 
 term implies of course that he gives the name of instinct to 
 much which in my opinion is not instinct. For further 
 details I refer the reader to the book itself. 
 
 Irritability and Sensation — Will 
 
 In the preceding I have assumed that a brain is necessary 
 for the exercise of voluntary action, but it will be seen from 
 the following discussion, that I do not demand as the appar- 
 atus of voluntary action in multicellular animals a brain 
 morphologically recognisable as an organ, since in the lower 
 multicellular forms and in their larvre the ectodermic 
 or ectoblastic cells obviously are the instruments of voluntary 
 action. Of course beyond a certain stage of evolution certain 
 definite cells have more and more assumed the function of 
 central government. Where the seat of voluntary action is 
 to be sought in unicelullar forms, is a question which I shall 
 consider in the next section. Suffice it to say at present, that 
 it seems to me necessary even in these to assume a definite 
 organ in the cell as nerve-centre, which stores up the impressions 
 of the rest of the cell and makes use of them as if by will 
 — that the whole cell-plasm together cannot be brain. And 
 in like manner there must be paths in the cell which conduct 
 the external stimuli to the central organ. These paths are 
 probably protoplasmic threads, and on grounds to be subse- 
 quently set forth I believe I may claim the nucleus as the 
 central organ. For such nervous substance not yet morpho- 
 logically recognisable the term neuroplasm or nerve-plasma 
 may be used. But if voluntary action is to be assumed in 
 organisms wliich possess not even a nucleus, as in Monera, 
 
 ^ Op. cit. p. 169. Cf., on the other hand, Wuudt, Grundzilge der Psychojyhr/sik; 
 Leipzig, 1874, p. 809, et seq. ; this author advocates a view of in.stinct.^which in 
 essentials agrees with mine. 
 
 I 
 
VI THE WILLS OF A TOMS 307 
 
 tlren a certain mass of the plasma might be imagined as the 
 organ of will, since it is certain that the nucleus develops 
 from the ordinary plasma, appears as a "precipitate" therein. 
 However, we shall shortly see that much which appears to be 
 voluntary action in such low organisms is certainly nothing 
 of the kind. 
 
 E. V. Hartmann, Haeckel, and others, speak of the will of 
 atoms : in order to surmount the difficulty of the limitation, 
 in other words, of the origin of the voluntary action, they 
 attribute will to all protoplasm and all matter. This 
 assumption implies another, namely, that atoms are endowed 
 with sensation, that sensation and capacity for stimulation 
 cannot be separated (Zollner). In this way the question of 
 the first appearance of sensation is also got rid of. All organisms 
 possess sensation, plants included, and in the unicellular the 
 protoplasm is endowed with both sensation and will.^ Nfiy, 
 even the atoms of inorganic bodies have sensation. " On 
 what, " says Haeckel,^ " finally rests the generally accepted 
 chemical doctrine of the relations of affinity of bodies, unless 
 on the unconscious assumption that the atoms which attract 
 or repel one another are animated with definite inclinations, 
 and that they, following these sensations or impulses, possess 
 also the will and the power to move towards one another and 
 from one another ? ... If the ' will ' of man and the higher 
 animals seems free in contrast with the ' fixed ' will of the 
 atoms, this is a deception caused by the contrast between the 
 extremely complex voluntary motions of the former and the 
 extremely simple voluntary motions of the latter. The atoms 
 will the same thing everywhere and at all times, because 
 their inclination towards the atom of every other element is 
 . . . unchangeable and defined. . . . On the other liand, the 
 
 1 Botanists, in fact, always speak of the sensation of plants, make no distinction 
 between irritability and sensation. 
 
 2 E. Haeckel, Bie Perigenesis cler Plastidule oder die WellenzeuguiKj dcr 
 Lebenstheilchen, Berlin, 1876. 
 
308 MENTAL FACULTIES sec. 
 
 inclination and voluntary motion of the higher organisms 
 seems free and independent, because in the ceaseless circula- 
 tion of matter in them the atoms are constantly changing 
 their relative positions and manner of combination, and hence 
 the final resultant of the innumerable voluntary motions of 
 the constituent atoms is highly composite and ceaselessly 
 varying. 
 
 " AMiile we thus from the mechanical standpoint of monism 
 conceive all matter as animate, every material atom as pro- 
 vided with a constant and eternal atomic soul, we fear not to 
 bring upon ourselves the charge of materialism. For our mon- 
 istic standpoint is as far removed from one-sided materialism 
 as from empty spiritualism. In this view only can we find a 
 reconciliation of the crude atomic, and the empty dynamic 
 theories of the universe, which have hitherto so violently 
 contended against one another, and both of which in their* 
 one-sidedness are dualistic. As the mass of the atom is 
 indestructible and unchangeable, so the atomic soul insepar- 
 ably connected therewith is eternal and imperishable. 
 Transitory and mortal are only the countless and ever- 
 changing combinations of the atoms, the infinitely manifold 
 modalities in which the atoms unite to form molecules, the 
 molecules to form crystals and plastids, the plastids to form 
 organisms. Tliis monistic conception of atoms is alone in 
 harmony with the great laws of the ' Conservation of Energy ' 
 and the ' Indestructibility of Matter ' which the natural 
 philosophy of the present day rightly regards as its irremov- 
 able foundations." 
 
 I would only ask what is materialism if this view of 
 Haeckel's is not — on what grounds does he assert that it is 
 not ? To say that the atoms are " animated " is merely to give 
 his doctrine an attractive appearance in the eyes of the 
 opponents of materialism. 
 
 Although I am very much at one w^ith Haeckel in giving 
 
VI ABSENCE OF SENS A TION IN PLANTS 309 
 
 a mechanical conception of the idea of will, as follows from 
 the explanation of will given on p. 223, I must strenuously 
 protest against his application of the word. I connect the idea 
 of will exclusively with nervous substance, or with the 
 nerve-plasma which represents it : will is not a property of 
 protoplasm, still less of matter in general, but a property of 
 nervous tissue, in most cases of definite nerve -cells — 
 the will is an acquired and inherited property. The nerve- 
 cells of the brain alone are capable of storing up external 
 influences, i.e. the action of stimuli, as experience, in such a 
 way as is required for voluntary action in the sense of the 
 " release of forces existing in a state of tension." The will 
 depends upon movement, as does the whole of mental life, 
 and life in general. Irritability and sensation likewise 
 depend upon motion, but sensation also is a property of 
 nervous substance, or of the nerve-plasma, is not possessed 
 by plants any more than by inorganic bodies ; but the latter 
 are also destitute of irritability, which, however, is a property 
 of protoplasm. Inorganic bodies possess only the property of 
 combining together according to regular laws in consequence 
 of attraction and repulsion. Irritability is a fundamental 
 property of protoplasm; capacity for sensation, on the contrary, 
 is a property acquired by it. 
 
 Haeckel's conception depends upon a quite arbitrary use 
 of the terms. It arises simply from the desire to find unity 
 in nature, even in the province of mental phenomena ; for it 
 appears indeed at first sight dualism to suppose that one 
 class of organisms is endowed with sensation and will, 
 another not. But this demand for unity has no justification 
 — it forgets the fact of the modification of the properties of 
 organic nature by the action of external stimuli, it con- 
 founds acquired powers with the fundamental properties of 
 matter. 
 
 It is absolutely unnecessary and in contradiction to 
 
310 MENTAL FACULTIES sec. 
 
 important facts, to assume, as the botanists do, that irritability 
 and sensation are equivalent (identical) ; the very fact that 
 in animals a special nervous system, nerve-fibres and nerve- 
 cells, have arisen, wliich are absent in plants, proves of itself 
 that the motions which constitute the recej^tion and conduc- 
 tion of stimuli in animals must be quite different to those in 
 plants, for the stimuli are, as we shall see, the causes of the 
 origin of the nervous system. Xervous substance is something 
 peculiar to animals. It is true there are animals which possess 
 the power of voluntary action, and therefore sensation — the 
 latter is a necessary antecedent of the former — which yet 
 possess no morphologically demonstrable nerves, c/j. the lowest 
 multicellular and the unicellular forms. But here, as was 
 previously argued, portions of the protoplasm must act, with 
 regard to the stimuli they receive or conduct, as nervous 
 substance — only these parts are not yet externally recognis- 
 able as nervous paths. For the single reason, then, that the 
 substance which reacts to stimuli in animals, which in any 
 case in the higher animals is the instrument of sensation and 
 voluntary action, is quite peculiar to animals, it is allowable 
 to infer that the two latter faculties belong^ to animals onlv. 
 AVe might thus in a certain sense recur to the old aphorism 
 of Linn?eus : " Lapides crescunt, plantar crescunt et vivunt, 
 animalia crescunt, vivunt et sentiunt." 
 
 In fact, the division of the organic world, according to the 
 evidence of the capacity for receiving " nerve-stimuli " and 
 acting upon them, is still that which should be first estab- 
 lished. The Linmean proposition, interpreted as meaning that 
 all animals, in contrast to plants, are capable of sensation 
 and the exercise of will, would therefore certainly be more 
 justified than the doctrine of the will and sensation of atoms. 
 But I attribute to animals merely the special faculty of 
 reacting to nerve stimuli. This does not imply that they all 
 are capable of sensation and will. It is an evident fact, and 
 
VI MOVEMENTS CAUSED BY STIMULI 311 
 
 one that corresponds \Yith the whole evohition of the nervous 
 system, that multicellular animals act more and more by 
 reflex action the lower their position. Voluntary action 
 must in its origin be traced back to reflex action. It is a 
 question, indeed, whether the movements of the lower multi- 
 cellular animals, like the sponges, are not exclusively reflex.^ 
 The same holds for the unicellular, in which paths in the 
 protoplasm must supply the place of nerves. 
 
 But it matters not whether we explain the power of 
 sensation as a property of all animals as distinguished from 
 plants, or as a property which first appears in the animal 
 kingdom — it is even on the first supposition not a funda- 
 mental property of protoplasm, but something which has 
 been gradually acquired. 
 
 '^But how is it to be explained? If we regard all the 
 effects of stimulation as motion, we are naturally led to 
 explain sensation as a special quality of this motion, a 
 quality indeed which' resides in certain nuclei, in the higher 
 animals in the nuclei of the ganglionic cells, an " excitation " 
 the manifestation of which constitutes consciousness, the 
 general sensation of the whole organism. 
 
 The fundamental property of protoplasm is (I repeat it), 
 not sensation and voluntary action, but irritability (response 
 to stimulation). From that property are evolved by acquisi- 
 tion and inheritance the irritability of nerves in animals, and 
 the power of sensation and will. 
 
 I leave it, therefore, undecided whether the latter faculties 
 belong to all animals. But in any case, a number of the 
 phenomena of movement in lower organisms, like those of 
 spermatozoa, which seem to be voluntary, are, according to 
 my investigations, nothing but the result of definitely-directed 
 
 1 Although the actions of the free -swimming larvfe of these animals might be 
 properly ascribed to volition, yet the whole activity of the adult sponge might be 
 reflex, as a consequence of degeneration of the nervous faculties, which occurs 
 often to such an extraordinary extent in other animals. 
 
312 MENTAL FACULTIES sec. 
 
 movements of the protoplasm, whicli are themselves the result 
 of the reaction, which has become regular, of the protoplasm 
 to stimuli. Such, for instance, are obviously the movements 
 of the cilia of ciliated cells, so far as these are not affected by 
 nerves. The forward movement of the spermatozoa of the 
 toad and of the salamander is caused by rhythmical streamings 
 of the protoplasm succeeding one another like waves, and I 
 have shown that this rhythmical motion occasionally passes 
 into the amceboid,-^ so that we have some OTound forrerardiuo- 
 the latter also as involuntary, although it appears to be 
 voluntary. In fact, I cannot accommodate myself to the idea 
 that the amoeboid cells which wander about like amoebae in 
 our blood-vessels and throughout our bodies are independent 
 beings endowed with sensation and will. 
 
 Botanists have made more investigations than zoologists 
 into the stimuli which cause locomotion in the lower 
 organisms, or w^hich accelerate or give a definite direction to 
 their movements, movements which at first sight appear to 
 be altogether voluntary. I will quote here an instance of 
 the first case ; another of no less importance is aftbrded by 
 the experiments of Pfeffer, discussed on p. 334. 
 
 The movement of Myxomycetes is influenced by-: — 
 1. Moisture (Hydrotropism) : In their young stages they 
 wander from the parts of the substratum {i.e. of the deposit 
 on which they are creeping), which are gradually drying up, 
 towards those which continue moist longer ; " it is even 
 possible, by bringing moist bodies into the proximity of any 
 ramifications, to cause the production of pseudopodia, which 
 elevate themselves from the substratum, and soon come into 
 
 ^ Th. Eimer, Unters. ilber d. Bau u. d. Beioegunci der Samenfdden, o^j. cit. 
 Accordingly the ultimate cause of the motion of the spermatozoa of the Mam- 
 malia also must lie in amoeboid movements in constant directions. With regard 
 to ciliated cells compare the following. 
 
 - E. Stahl, Zur Biolorjie der Myxomyceten, Botan. Zeitung, 1884, No. 10-12. 
 Abstract in Sitzv.nrjsbericht der Jenaischen Gesellschaft fur Medizin und Naivft- 
 wissensch. 1883, Sitzung vom 16th November. 
 
VI MOVEMENTS OF MYXOMYCETES 313 
 
 contact with the moist object, so as to enable the whole mass 
 of the Plasmodium to migrate on to it." On the entrance of 
 the Plasmodia into the fructifying condition, positive hydro- 
 tropism gives place to negative ; the myxomycete quits the 
 moist substratum and creeps upwards on to the surface of dry 
 objects. 
 
 2. Unequal distribution of warmth in the substratum, and 
 
 3. Unequal supplies of oxygen also cause locomotion in 
 the Myxomycete. 
 
 4. Chemical substances soluble in water have a similar 
 action. Contact of the plasmodia on one side with solutions 
 of common salt, saltpetre, carbonate of potash, cause them to 
 withdraw from the dangerous spot, while infusion of tan, or 
 a dilute solution of sugar, produces a flow of the protoplasm 
 and ultimately translocation of the whole plasmodial mass 
 towards the source of nourishment. Some solutions have an 
 attractive or repulsive effect according to their degree of 
 concentration. 
 
 5. Finally, they withdraw from light (negative lielio- 
 tropism). 
 
 With regard to the acceleration or definite direction of 
 movement produced entirely by stimuli, compare the follow- 
 
 ing :- 
 
 " The knowledge of the remarkably delicate reaction of the 
 Plasmodia under external influences enables us to compre- 
 hend how these tender structures, destitute of every kind of 
 external protection, are able to carry on their existence. 
 The Plasmodia which are not yet ripe for reproduction are 
 kept in the moist substratum by positive hydrotropism, 
 which is assisted by negative heliotropism. 
 
 " But within the darkness and moisture of the substratum 
 the Plasmodia by no means remain in one place, because the 
 differences in the chemical composition of the substratum 
 cause continual migrations. The plasmodia have the faculty 
 
314 MENTAL FACULTIES sec. vi 
 
 in a wonderful way of avoiding harmful substances and, 
 traversing their substratum in all directions, of taking up the 
 materials they require. 
 
 " When the internal changes have proceeded so far that 
 the Plasmodia approach the fructifying condition, they are 
 brought by the negative hydrotropism which now sets in 
 from the moist parts of the ground in the forest or wood to 
 the surface, where they creep up various upright objects, 
 often only forming rigid reproductive capsules at some height 
 from the ground. 
 
 '' When in autumn the substratum becomes gradually 
 colder, a change which takes place from the surface down- 
 wards, the Plasmodia migrate into deeper regions still having 
 a higlier temperature. When the cooling proceeds very 
 gradually, which especially happens in large tan-heaps, the 
 Plasmodia may in their migration reach somewhat consider- 
 able depths, where they then change into sclerotia. To find 
 the sclerotia of /Ethalium in winter it is therefore not 
 seldom necessary to search through the mass of tan to a 
 depth of several feet. When the temperature again begins 
 to rise, the sclerotia again germinate, and movement in the 
 opposite direction takes place from the deeper and cooler 
 parts to the upper portions already warmed." 
 
 In the locomotion of the Myxomycetes, then, we see 
 extremely interesting cases of movements due to stimulation. 
 Heliotropism, geotropism, hydrotropism, trophotropism, in 
 general, are stimulus-movements, and ultimately all growth 
 depends on stimulus-movement. It is the most primitive kind 
 of protoplasmic movement. Stimuli in fixed directions and 
 constantly repeated produced, but only secondarily, fixed 
 paths of conduction, and responses of a quite definite kind 
 (reflexes). Thus arose nerves and finally apparatus for 
 storing up stimuli, arose sensation and will — as acquired 
 and inherited faculties. 
 
SECTION VII 
 
 ORGANIC GROWTH : THE MORPHOLOGICAL AND PHYSIOLOGICAL 
 EVOLUTION OF THE LIVING WORLD AS THE RESULT OF 
 FUNCTION 
 
 In Section IV., under the heading " Characters acquired by 
 Use," I have abeady indicated in a general way the influence 
 of use in the modification of organic forms. I have now to 
 show in detail that all organisation, and above all, the first 
 development of organs, and further, all higher physiological 
 evolution depends on use, is to be traced to the inheritance 
 of acquired characters. 
 
 The Origin of Organisation in Unicellular Animals 
 — The Fundamental Biological Law 
 
 Whoever assumes that complexity of organisation has 
 arisen in consequence of the gradual evolution of the living 
 world must also assume that all living beings, both plants 
 and animals, have been derived from the simplest beginnings, 
 from unorganised particles of protoplasm ; in other words, 
 from organisms which were destitute of organs. 
 
 The term organism was first employed by Aristotle, and 
 was based upon the fact that each part of a living being is 
 an instrument, opyavov, for the whole. In his time organisms 
 
316 ORGANIC GROWTH sec. 
 
 without organs were yet unknown ; they were first discovered 
 by the aid of the microscope. They are represented by the 
 simple minute morsels of protoplasm to which Haeckel has 
 given the name of ^lonera {fjLovi)pri<; simple). These are cells 
 possessing neither nucleus nor investing membrane, which 
 nevertheless lead an independent existence, and of some of 
 which the whole life cycle is known. In these beings organs 
 only appear at the moment they are needed, and at any part 
 of the body, they are not developed beforehand, and have no 
 definite shape. These organs are processes of the protoplasm 
 of variable form, "false feet," or j^seudopodia, by means of 
 which the body crawls about or takes in food. AYhen the 
 cell returns to a condition of rest the pseudopodia flow back 
 again, are withdrawn and disappear, while the body assumes 
 a spherical shape. The conception of an organ as a part of 
 the body constructed for a definite function is therefore not 
 applicable to these pseudopodia, it applies only to the per- 
 manent instruments of the more complex beings which alone 
 are in the full sense of the word orfranisms. 
 
 In the creatures next above these in the animal scale, in 
 the Amoebae, a permanent organ first appears, namely, the 
 cell-nucleus. Besides this there are also present the so-called 
 contractile vacuoles, which, however, in some cases appear 
 now in one place, now in another, and then again disappear, 
 and whose claim to be considered permanent organs is there- 
 fore doubtful. Locomotion and the inception of food are 
 still effected by pseudopodia. In the next stage in the series 
 of unicellular animals a membrane appears as a permanent 
 organ, while cilia take the place of the pseudopodia, to w^hich 
 are necessarily added a mouth for taking in food, and in 
 many cases an anus. The body is still in most cases capable 
 of changing its form, and owes this power sometimes to the 
 differentiation and modification of the outermost layer of 
 protoplasm lying immediately beneath the membrane, this 
 
vii EVOLUTION OF PROTOZOA 317 
 
 layer becoming striated or fibrillar. The fibrils are always 
 arranged in the direction which enables them most easily to 
 produce the usual contraction of the body, viz. perpendicu- 
 larly to the plane of this contraction. In the stalk of the 
 bell animalculae (Vorticellidse) the fibre to which the con- 
 traction of the stalk is due, according to the researches of 
 Kiihne, has exactly the same physiological properties as the 
 muscular substance of multicellular animals.-^ 
 
 Thus these ciliated Infusoria are cells with a very delicate 
 organisation, which must have been gradually developed in 
 the course of ancestral evolution, and this certainly cannot 
 have taken place as a result of the variation of their germ- 
 cells, for the simple reason that they do not possess any. It 
 must have taken place in consequence of acquirements due 
 to use, and in consequence of the inheritance of such acquire- 
 ments. 
 
 It is most clearly shown in the appearance of a specially 
 differentiated layer of contractile substance beneath the 
 surface of the body, and in the appearance in the stalk of the 
 Vorticellidae of muscle substance equivalent to that of the 
 higher animals, that activity or function calls forth organic 
 or physiological differentiation. 
 
 This important proposition, which I might call the ele- 
 mentary fundamental law of all biological science, implies 
 the most complete opposition to the denial of the inheritance 
 of acquired characters, afi&rms the opposite. 
 
 Protoplas7n has the froipcrty of hdng altered and trans- 
 formed hy the action of external stimuli. 
 
 Anions external stimaili are to be understood both those 
 acting directly and those which act indirectly by aftecting 
 the functions of the organism. 
 
 1 " The stalk of the Vorticellidas behaves exactly like frog's muscle : even when 
 isolated from the rest of the animal it can be made to contract, and even be 
 tetanised, by the stimulus of variations of an electric current," etc. Cf. W. Kiihne, 
 Myologische Untersuchungen, Leipzig, 1860, p. 216 or 213. 
 
318 ORGANIC GROWTH sec. 
 
 The evidence for this fundamental law lies in the followino: 
 facts : (1) that numerous animals, although they possess no 
 organs structurally adapted thereto, regularly perform actions 
 which pre-suppose corresponding powers in the protoplasm, 
 or even imply that the evolution of such organs has already 
 begun ; (2) that various organs at first serve for many pur- 
 poses, and that division of labour, i.e, the increase in the 
 number of organs and their specific differentiation appears 
 only by degrees in the series of organisms ; (3) that the 
 larvae of even the most highly organised animals only 
 possess powers corresponding to those described under 1 and 
 2, — that, therefore, in this matter also the biogenetic law 
 completely holds good. 
 
 The two first of the above propositions are sufficiently 
 proved by unicellular animals alone when their activities are 
 compared with those of the multicellular. 
 
 The second proposition is further supported by the general 
 description of the evolution of organisation given above ; the 
 evidence required for the third can only be afforded by 
 multicellular animals. 
 
 The striated layer in the Infusoria already mentioned is 
 also evidence of the truth of the first proposition. The 
 ciliated Infusoria which possess that layer exhibit the 
 commencement of the evolution of a muscular layer, which 
 commencement can only be ascribed to the constantly repeated 
 contraction in a given direction of that part of the body. 
 And in the stalk of the Vorticellid?e, by the continuance of 
 the same activity, a muscular fibre has arisen, which behaves 
 physiologically in just the same way as the muscles of multi- 
 cellular animals. 
 
 The actions of the ciliated Infusoria in relation to the 
 outer world are such that will must certainly be ascribed to 
 them. This is proved by the simple observation of the 
 character of their movements, apart from all else. Their 
 
VII WILL IN INFUSORIA 319 
 
 movements are entirely spontaneous, and the variety of 
 these is due to their power of moving all or different sets of 
 cilia more slowly or more quickly, or keeping them at rest. 
 The hypotrichous Infusoria/ e.g. Euplotes Charon, at one 
 moment shoot through the water with their cilia in rapid 
 motion, at another run about on the bottom on ah ''03 or other 
 objects, using their cilia as legs, and moving like Isopods. 
 The behaviour of such Infusoria towards one another, accord- 
 ing to some observers (Engelmann), looks as if they were 
 running after one another in play. 
 
 Yet in these Infusoria, endowed with mental faculties, "we 
 can discover no nerves and no brain. It seems to me prob- 
 able, from comparison with the relations of the cells of multi- 
 cellular animals, that their nuclei, while at the same time 
 connected with reproduction, or one of them, also acts as the 
 central organ of the nervous system. This idea is supported 
 by the fact recently demonstrated, that when an Infusorian is 
 cut into two only one part grows again to a complete animal, 
 namely the part which contains the nucleus, or at least a 
 piece of it.^ The same holds good for snails in regard to the 
 brain. If from a garden-slug (Limax agrestis) the head with 
 the brain is cut off, it no longer grows again into a complete 
 animal, as it does after mutilations in which the brain has 
 not been removed.^ A. Gruber, on the contrary, believes that 
 
 ^ Those provided with cilia on the under surface only. 
 
 2 A. Gruber, Bdt. zur. Kenntn. d. Physiol, tc. Biolorjie der Protozoen. 
 Berichte d. ncdurf. Ges. zu Freiburg i.B. 1886 ; M. Nussbaum, Sitzungsber. d. 
 niederrhein. Ges. f. Nat. u. Heilkunde in Bonn, 1884, p. 259, seq. Fr. Schmitz 
 and J. V. Hanstein found the same was true of the division of plant-cells. In 
 this connection, in my opinion, the general importance of the nucleus as the organ 
 of life comes into consideration. Cf. the following. 
 
 '^ The reproduction of the head of snails was shown to occur by Spallanzani 
 as early as the year 1764. The Rev. Schaefl'er was astonished to observe that 
 the snails in his garden whose heads he had cut off with the shears in order to 
 destroy them again became perfect (Schseffer, Versuche mit Schnecken, 1768-70). 
 According to Tarenne {Cochlioperie, recueil d' eo:periences siir les Helices terrestres, 
 1808), the brain and the buccal nerve mass also grow again. But it seems certain 
 that the retention of the cesophageal nerve-ring is indispensable to the contiuua- 
 
320 ORGANIC GROWTH sec. 
 
 at least in the higher protozoa, in the ciliata, the seat of 
 nervous activity is to be sought principally in the outer layer 
 of protoplasm, and that the will resides in every protoplasmic 
 element, that nervous action is not limited to definite paths. 
 He supports his view by the fact that the movements in the 
 two parts of an Infusorian in process of division exactly 
 correspond so long as they are connected by a strand of 
 protoplasm, however thin (Stentor). The same thing is 
 observed also after incomplete artificial division. This proves, 
 he says, ''that the nervous power of the cell is diffused." 
 In the figure given in illustration a Stentor is represented 
 diagramatically as divided transversely, that is, so that the 
 nucleus also is transversely divided. Whether pieces with- 
 out nucleus act voluntarily is not stated. But it would be 
 necessary to determine this. My experiments in dividing 
 Meduste, to be shortly discussed, afford a perfectly analo- 
 gous case, and yet localised cerebral ganglia are certainly 
 present there. If, as I shall endeavour to show, nuclei 
 actually form central nervous organs in multicellular animals, 
 it is evidently highly probable that they do so also in 
 the unicellular. In the cases referred to of multicellular 
 animals in which a circumscribed brain is not yet present, 
 the exertion of will is only to be conceived as proceeding 
 from circumscribed central points (nuclei) which are in 
 connection with one another, and to which the impressions 
 received by the rest of the cell are conveyed. Since all 
 tlie action of will depends on the emplo3'ment of impres- 
 sions which must be conveyed to the organ of will along 
 separate protoplasmic conducting paths, therefore the organ 
 of will can scarcely be the whole protoplasm of the body, 
 but rather the very presence of a will implies in itself 
 
 tion of life in snails. Duges and jNIoquin Tandou obtained this result (cf. Milne- 
 Edwards, Le<^ons sur la Physiologie et VAnatoviie Connmree, Tome viii. p. 304), 
 and recently J. Carriere has confirmed it {Studie/i iiber die Regenerationserschein- 
 ungen der Wirbellosen, I. Regeneration bei PubnoruUen, Wiirzburg, 1880. 
 
VII CONDUCTION OF STIMULI IN PROTOZOA 321 
 
 division of labour in the province of nervous life, and it 
 is impossible to see why the nucleus should not be con- 
 sidered as central nervous organ in unicellular forms, if 
 it can be shown that it plays this part in the multi- 
 cellular. 
 
 However, the question can only be decided in the future. 
 Possibly special fibrils for the conduction of nerve stimuli 
 will yet be demonstrated by more exact researches directed 
 to this point,^ and will at the same time lead us to the 
 central organ. In any case, nerves like those of the multi- 
 cellular forms are not present, and yet the animals evidently 
 receive stimuli by means of the cilia which are connected 
 with the protoplasm, which stimuli must be conducted along 
 definite paths to the central organ. These paths can be 
 nothing but strands of protoplasm ; probably they are formed, 
 
 ^ Cf. Engelmann, Zar Anatomie iind Physiologie der Flimmerzellen, PjlUr/ers 
 Archiv, Bd. xxii. 1880, p. 505. This investigator believes he has seeu such 
 fibrils in Stylonychia passing into cilia which vibrate at diflerent rates. I may 
 also remark that I have repeatedly found the ciliated cells of the surface of the 
 mantle and gills in Anodon to be most distinctly connected with nerves which 
 obviously fulfil the same purpose. After treatment with bichromate of potash 
 the cells can easily be isolated still in connection with the nerves, I have 
 hitherto failed to see a connection between the nerves and the fine protoplasmic 
 threads Avhich I was able in these cells to trace downwards below the nucleus, 
 and which are continued above into the cilia, but such a connection is very prob- 
 able (cf. Eimer : Weitere Nachrichten uber den Bau des Zellkerns, nebst Bemer- 
 kungen iiber Wimperejnthelien, Archiv fur mikroskop. Anatomie, Bd. xiv. 1877). 
 I consider these threads as nervous paths, as nerve-plasma, and the knowledge of 
 these was the basis of my view that in the Infusoria also the protoplasmic threads 
 form nervous paths. From the analogy of the relations of the fibrils from the 
 cilia in the ectoderm-cells of MedusEe which I have described (cf. Die Medusen, 
 Taf. iv. ), it may be assumed that these threads in Infusoria also pass into the 
 nucleus. On the other hand, that such threads pass into nerve-fibrils, I have 
 shown in the ectoderm-cells of Carmarina hastata (Cf. Medusen, Taf. xii. fig. 
 8, 19 ; Taf. xi. etc.) These cells appear distinctly striated longitudinally ; their 
 protoplasm is clearly transformed into nerve-plasma, and the fibrils representing 
 the latter, diverging from one another below, are continued directly into the 
 nerve-fibrils of the ring-nerve (" brush cells "). The fact that each of these ecto- 
 derm-cells is thus in connection with numerous nerve-fibrils, would seem to show 
 that they still act as central nerve-cells, although ganglionic nodules have already 
 been developed beneath the epithelium (cf. below : the first development of the 
 central nervous system, especially Hydra). 
 
 Y 
 
322 ORGANIC GROWTH sec. 
 
 as already remarked, by fibrils of protoplasm having the 
 ordinary appearance. 
 
 We shall see that even in the lower multicellular animals 
 the conduction of nerve stimuli takes place without the 
 presence of actual nerves. I have only touched upon the 
 much less definitely understood relations in the ciliated In- 
 fusoria in order to indicate that there is a parallelism between 
 these and the important facts to be shortly discussed, and to 
 lead up to the latter. 
 
 In the preceding I have principally referred to muscles and 
 nerves as evidence in support of my propositions, and shall 
 follow the same course hereafter, because these organs of so- 
 called animal life are specially suited to bring into view the 
 effect of the relations of the organism to the outer world. 
 
 The essential distinction between the formation of organs 
 in the unicellular and multicellular forms is that in the 
 former the organs appear as parts of the cell, which is itself 
 the animal, while in the latter each organ is formed of 
 numerous cells. For instance, in the unicellular Yorticella a 
 part of the cell forms a muscle-fibre, in the multicellular 
 many cells form a muscle, which is physiologically equivalent 
 to that muscle-fibre. Morphologically, therefore, the two can 
 be no more compared than any other organs in the two 
 divisions of animals. But that they, like other organs in the 
 two groups, are physiologically equivalent, that in each 
 case, from a quite different starting - point, an appar- 
 atus acting in a similar way in relation to the outer 
 world has been produced, this alone warrants the conclu- 
 sion that it was this very relation to the outer world 
 w^hich modified the protoplasm in both cases into an 
 equivalent though not homologous structure, that the in- 
 heritance of acquired characters is here exemplified. 
 
VII EVOLUTION OF ORGANISATION 323 
 
 The Evolution of Organisation in Multicellular 
 
 Animals 
 
 Tlu Evolution of the Germinal Layers as Primitive Organs 
 
 Multicellular animals must have arisen from colonies, 
 formed in consequence of the advantage of association, of uni- 
 cellular forms still at a low grade of development, of protozoa 
 which had yet developed no kind of permanent organs except, 
 perhaps, the nucleus. The way in which these colonies were 
 formed was, probably, that the new protozoa produced by 
 division did not separate, but remained connected ,until the 
 colony had a sufficient number of members. But a solid 
 sphere (Morula) could not have been the most suitable 
 arrangement of those members, although they may at first 
 have assumed that arrangement, as some do still ; the best 
 arrangement must have been that which enabled all the 
 members to exercise their powers for the benefit of the whole 
 and the parts, and as these powers were the same in each, 
 this condition could only be fulfilled when all the cells were 
 equally exposed • at the surface, so that they formed a single 
 layer constituting the wall of a spherical vesicle containing a 
 central cavity. Thus all the individuals were in the besf 
 position to obtain equal information as to the conditions ot 
 the outer world, and for common defence, as in our square of 
 infantry bristling with bayonets. There are also living forms 
 still showing this arrangement of the " blastula," e.g. the co- 
 lonial Volvocid?e, consisting of unicellular flagellate Algae, 
 each of which directs its flagellum outwards, as the soldier his 
 bayonet. Before long, to effect locomotion in a definite direc- 
 tion, certain more powerful cells must have gained a supe- 
 riority over the rest and assumed the leadership, so that now the 
 several cells co-ordinated the movements of their processes, 
 
324 ORGANIC GROWTH sec. 
 
 and these became synchronous on all sides, and thereby the 
 locomotion of the whole forwards or backwards took place. 
 
 Those cells which were situated at the pole of the blas- 
 tula must have specially developed their power of food-incep- 
 tion, because they had most opportunities of exercising it : 
 they came first and most frequently into contact with food. 
 As several neighbouring cells thus devoted themselves more 
 and more exclusively to food-inception, the first step was 
 taken, functionally, in the evolution of the first common 
 organ, of the digestive endoderm, and also in the formation of 
 an invagination of one pole of the blastula, which gave rise 
 to a second common organ, the primitive gut. Every increase 
 in the def]rree of this invagination was an advantaf]re to the 
 nutrition of the whole, for more food could be taken up in it. 
 In this respect, therefore, selection may have been actively at 
 work. Thus arose the gastrula, an organism of the form of 
 an egg-cup, with a wall of two layers of cells lying one over 
 the other, of which the inner is derived from the invagination 
 of an original single layer. 
 
 With this invagination we get at once two chief or primi- 
 tive organs of the multicellular animals, the ectoderm and 
 endoderm. While the latter serves only for the reception of 
 food, the former has functions of three kinds : — 
 
 (1) The protection of the body on the outside, as its cover- 
 ing ; (2) to act as the organ of relation, instead of a nervous 
 system, to place the body in communication with the outer 
 world ; (3) locomotion. 
 
 With regard to the latter, it is to be observed that it was 
 probably s, definitely-directed activity, namely, locomotion in 
 a definite direction, which led to the development of per- 
 manent flagella on the cells in place of the irregular, variable 
 pseudopodia. And this modification must have taken place 
 before the completion of the endoderm, for the latter itself 
 still bears flagellate cells, while at the same time it can also 
 
VII ORIGIN OF PRIMITIVE ORGANS 325 
 
 send forth pseudopodia to take up food ; but its flagella are 
 retractile, as all flagella, being derived from pseudopodia, 
 must have been originally, and as in many other cases they 
 are still, e.g. in the Flagellata. 
 
 Again, it must have been in consequence of function (use) 
 that the endoderm cells gradually came to differ from those of 
 the ectoderm in size and internal structure, and when the 
 gastrula developed into a fixed sessile animal, disuse caused 
 the disappearance of the flagella. 
 
 As there are now living forms which retain the morula 
 and blastula form, so there are others which exhibit the 
 gastrula form, although the gastrula has undergone various 
 modifications. Hydra is such an animal. 
 
 In Hydra it is also evident how a third primitive organ ot 
 animals arose, namely, the mesoderm. 
 
 In Hydra and many allied forms the ectoderm cells con- 
 sist of two parts, an external, which receives stimuli, and an 
 internal, which is muscular (neuro- muscular cells). This 
 differentiation also cannot possibly have arisen except as a 
 result of function, of activity. In other animals the separate 
 layer of supporting and muscular cells forming the mesoderm 
 arose by growth and multiplication towards the interior, by 
 the separation of special cells from the ectoderm and endoderm. 
 
 It must be described as a special peculiarity belonging to 
 the organisation of a j)ortion of the mesoderm cells, that there 
 " crystallises " in them calcareous or siliceous or horny matter, 
 the first especially in perfectly definite, and often extremely 
 complex, shapes. 
 
 The formation of the supporting skeleton of these lower 
 animals, therefore, has probably not been determined by use 
 or function, but rather by definite laws of development, and 
 selection; but this applies, not so much to the origin of 
 definitely shaped calcareous or siliceous spicula, as to the 
 solidity of the skeleton in general. 
 
326 ORGANIC GROWTH sec. 
 
 Origin of Muscles 
 
 A striking proof of the importance of activity, function, in 
 the evolution of the organism is afforded by the mesoderm in 
 the muscles of that layer. 
 
 In unicellular forms and the larv?e of the multicellular 
 free and rapid movement in the water is effected by flagella. 
 ^Muscles evidently first arise in consequence of ever-repeated 
 changes of form, of the bending, extension, and contraction of 
 the body, by which it is diminished in order to avoid danger, 
 or enlarged in order to seize food, or moved in various ways 
 in fi^ditino- and in locomotion. 
 
 It is well known to histologists how difficult it sometimes 
 is to distini][uish smooth muscle-cells from certain connective- 
 tissue-cells. Both arise in the mesoderm, from the same 
 fundamental layer. I showed in a particular case years ago 
 that, in fact, connective-tissue and muscle pass directly one 
 into the other, the latter developing first in those directions 
 of the body in which contraction takes place, while in the 
 rest only connective tissue arises. This is the case among 
 the Ctenophora in Beroe ovatus, where the gelatinous tissue 
 of the body is traversed by connective-tissue-fibres and very 
 simple muscle-fibres, which pass into one another so gradually 
 that a boundary between the two cannot, in spite of all 
 endeavour, be determined. The muscle-fibres consist of long 
 tubes of contractile substance, which in the fresh condition 
 seem homogeneous, but can be separated into longitudinal 
 fibrils by reagents, and which contain unorganised protoplasm 
 containing nuclei at intervals. These fibres are surrounded 
 by a sarcolemma. " The typical connective-tissue-fibres are 
 cylindrical, strongly refracting, delicate threads running a 
 straight or contorted course, and are usually enlarged to a 
 spindle-shape at places by nuclei, which, however, lie at 
 very long intervals from each other. In the coarser fibres a 
 
vri MUSCLE AND CONNECTIVE-TISSUE 327 
 
 clear streak can be seen in the centre, which in many cases 
 appears as a canal, so that then the whole fibre forms a tube." 
 Between the typical connective-tissue- and muscle-fibres there 
 occur " forms perfectly intermediate, and there is no means 
 of defining a distinction between the fibres which contain tlie 
 smallest proportion of contractile substance and those which 
 contain none at all, for even staining with carmine supplies 
 no criterion when only a small quantity of this substance is 
 present. The first unmistakable trace of contractile substance 
 appears in the fibres as a doubly refracting layer on the inner 
 wall of the central cavity, surrounding the axis of the fibre as 
 a delicate envelope. 
 
 "The connective -tissue -fibres traverse the gelatinous 
 substance of the animal from within outwards, as well as 
 from above downwards ; very often, however, in a direction 
 at ris^ht ancjles to that of the muscle-fibres. 
 
 "... In the lower Medusse, and also in the Acraspedota, 
 the gelatinous supporting tissue of the body is not yet 
 traversed by muscle-fibres, but only by connective-tissue- 
 fibres. It seems here not to be itself contractile, or only by 
 the aid of the musculature lying upon it. In the Ctenophora 
 the gelatinous tissue is abundantly traversed by muscle-fibres 
 passing from wall to wall, and it can therefore be contracted 
 in itself. 
 
 " Here, from the cell layer which produced both connective- 
 tissue- and muscle-fibres, the latter have developed in those 
 directions in which the body made the greatest efforts to 
 contract. In those directions in which such effort was made 
 not at all, or only slightly, the evolution went no farther than 
 the formation of connective -tissue -fibres, or at most there 
 arose muscle-fibres which contain but a small proportioif of 
 contractile substance. 
 
 " In a direction at right angles to that in which, at a given 
 part of the body, contraction exclusively occurs, the con- 
 
328 ORGANIC GROWTH sec. 
 
 tractile substance will be least developed, and hence we shall 
 find the most typical connective-tissue-fibres at right angles 
 to the muscle-fibres." ^ 
 
 AVhen I speak of an eftbrt to contract, I do not of course 
 intend to support Lamarck's view, especially not in the sense 
 that anything can be produced by the " will." 
 
 Contractility is one of the fundamental properties of proto- 
 plasm, and by excessive exercise of this property, according 
 to my explanation, the characteristic muscular substance is 
 produced from the protoplasm. That effort is exerted in this 
 process is self-evident, but this produces an effect not directly, 
 but only indirectly. 
 
 Only thus can be explained the fact that musculature is 
 everywhere most developed in those parts of animals in which 
 its presence is most necessary to their requirements, e.g. in 
 ]\Iedus?e, which move by the contraction of the bell, on the 
 under side of the bell ; in worms, whose locomotion is due 
 to contortions and creeping and twisting, in the "dermo- 
 niuscular tube " ; in snails, in the foot ; in bivalves, in the 
 adductor muscles, etc. 
 
 How could selection, or even sexual mixture produce 
 muscles at particular parts of the body where previously 
 none were present? Selection and mixture can only deal 
 with what is in existence. 
 
 But the muscles of multicellular animals afford in yet 
 another direction evidence in support of my view of the 
 modification of organisation by functional activity. 
 
 Origin of Striation m Muscles 
 
 The text - books of histology still continue to divide 
 TQUScles into the smooth and the transversely striated. On 
 
 1 Vid. Beroe ovatics, 1873, op. cit. p. 30, seq. Similar results have been 
 obtained by my friend Flemming with regard to the connective-tissue- and muscle- 
 cells in the urinary bladder of Salamandra maculata. He says : " There are per- 
 
VII ORIGIN OF STRIATION 329 
 
 the whole the former means the muscle-cells, the latter the 
 muscle -fibres. But from the comparative standpoint this 
 division is quite unjustifiable, for there are transversely 
 striated muscle -cells as well as striated muscle -fibres, and 
 there are also unstriated, smooth muscle-fibres (Ctenophora). 
 Moreover, every one who has carefully pursued comparative 
 studies of muscles will aoree with me that the transverse 
 striation arises gradually, so that transitions occur between 
 striated and unstriated musculature. Thus the distinction 
 between muscle-cells and muscle-fibres can only be admitted 
 as in accordance with fact, if it is understood that the former 
 are uninucleate, the latter multinucleate, since there are 
 simple uninucleate muscle-cells which are so elongated that 
 they might equally well be called fibres in the ordinary sense 
 of the word. 
 
 On the other hand, recently histologists speak more 
 than formerly of the " muscle-prisms " {mushelhdstclien) as 
 the fundamental element of the striated muscle-fibre. But 
 the fibril is rather to be considered as the fundamental 
 element, and comparative observation leads necessarily to 
 the conclusion that the subdivision of this fibril into single 
 successive rods, which seems to exist in the most highly 
 developed condition of striation (the fact is still not abso- 
 lutely decided), can only be something acquired at a late 
 stage of evolution, and that at earlier phylogenetic stages it 
 does not occur at all. 
 
 Thus I have already in my work on the Medusce 
 advanced the proposition, and endeavoured to prove it, that 
 the striation of muscle is produced through its own activity, 
 is therefore an acquired and inherited character. 
 
 The evidence for this lies in the following : (1) Striated 
 
 manent intermediate stages of form between uninucleate muscle-cells and counec- 
 tive-tissue-cells, and therefore no sharp distinction between the two." — Zeitschr. 
 f. wiss. Zoologie, Bd. xxx. Supplement, 1878, p. 473. 
 
330 ORGAXIC GROWTH sec. 
 
 muscle only occurs, but also always occurs, where very active 
 muscular contractions take place. Thus the visceral mus- 
 culature of Vertebrata is everywhere composed of smooth 
 muscles, with the exception of the heart, which is composed 
 of striated muscle-cells — the former, therefore, occur at everv 
 part of the viscera where movement is slow, the latter alone 
 Avhere it is extremely active. A no less significant fact is 
 the foUowinij : leavino; aside the smooth muscle-cells which 
 occur in the mesoderm of sponges, the neuromuscular cells 
 form the commencement of the development of the nmscula- 
 ture in the zoophytes. But in spite of their primitive 
 character the muscular elements of these cells, in cases in 
 which they produce vigorous and rapid motion, are trans- 
 versely striated, while in other cases they are smooth. They 
 are smooth in Hydra, but striated on the lower surface of the 
 bell in the Medusae, which, in order to effect locomotion, 
 respiration, and to obtain food, is in constant motion. 
 
 The inactive Mollusca have generally smooth muscle- 
 cells — striated muscle occurs only in one position, namely, 
 in the adductors of those Lamellibranchs which can swim 
 swiftly in the water by the rapid flapping of their valves, as 
 butterflies fly by the flapping of their wings, e.g. Pecten. But 
 in relation to this question the adductors of Anodon are still 
 more worthy of attention : in these I find the first traces 
 of striation, but it is not yet a permanent morphological 
 character ; it appears only temporarily and only at separate 
 parts of the fibre, merely as the outward sign of activity. 
 
 It is usually stated that the Arthropods have striated 
 muscle-fibres only. It is true that in these actively-moving 
 animals the striation is especially well marked, and it is in 
 them that the subdivision of the fibril into " prisms " has 
 been described, this supposed constitution having been 
 afterwards attributed to all muscle -fibres as thou^fh the 
 " prisms " were the elementary parts of the fibrils everywhere. 
 
VII EVOLUTION OF SENSE-CELLS 331 
 
 Even the intestinal musculature of the Arthropods is trans- 
 versely striated ; and the intestine obviously in Crustacea as 
 well as in Insecta has in a pre-eminent degree a respiratory 
 function, and on account of this, as well as in many cases in 
 consequence of the ceaseless action of the digestive machinery, 
 it is in constant movement. 
 
 But if we examine the muscles of the thorax of flies in 
 the beginning of spring when they have just been revived 
 by the warmth, and have not yet flown, we find tliat the 
 fibrils are almost all smooth without any striation, an 
 observation which has been for years regularly repeated in 
 my histological demonstrations. This spring in these classes 
 we made the experiment of repeatedly shaking up the flies 
 so as to make them move and fly, and thought, even after 
 this slight motion of the wings, we could notice that a much 
 greater number of the fibrils were striated than before. 
 When we examined the thoracic muscles of flies this summer 
 we found all the fibrils most perfectly striated. 
 
 Evolution of the various Sense-Cells from a Co^lmon 
 
 Cell Layer 
 
 The history of the nervous system proves if possible still 
 more conclusively than the origin and development of muscle 
 how completely the origin and elaboration of organs are 
 governed by external stimuli and by exercise. 
 
 It is actually required by my theory that the nervous 
 system should, as it in fact does, proceed from the epiblast. 
 For the nervous system consists of the organs of relation, that 
 is, the organs by which the body is placed in relation to the 
 environment, by the reception of stimuli and the excitement 
 of a response to them. If, as we must assume, not only 
 according^ to the bioG^enetic law, on account of all the facts 
 of embryogeny, but also on account of the structure of the 
 
332 ORGANIC GROWTH sec. 
 
 lower multicellular animals now living, all multicellular 
 animals have been derived from forms whose only organs 
 were two or three germ layers, then the external germ layer, 
 the ectoderm, must naturally have originally been the 
 medium of those relations to the external world. And in 
 these multicellular forms which still consist only of these 
 " j)i'iniitive organs " the ectoderm must be still the medium 
 of relation. This most external of the three layers of cells 
 of the larva or of the body came, and comes, first into con- 
 tact with the outer world. All external stimuli acted first 
 upon it. By the repeated incidence of the stimuli this layer 
 must have become more and more fitted for their reception, 
 and subsequently for dealing with them, must have had 
 these capacities exercised and strengthened. Only thus can 
 it be explained that the nervous system, that brain and 
 ganglia wherever they can be distinguished, arise from the 
 epiblast. 
 
 Again, the most important parts of the nervous system, 
 the brain and higher sense organs, the organs of sight and 
 hearing, and also of taste and smell, are always situated in 
 those parts of the body wdiich come most into contact with 
 the outer world, which are so placed as to be oftenest affected 
 by stimuli — in worms, molluscs, arthropods, and vertebrates 
 at the anterior end, in Medusae on the edge of the bell and 
 so on. 
 
 The sense organs are not only derived from the epiblast, 
 but usually remain situated in the ectoderm. The sensory 
 cells moreover are developed from ordinary ectoderm or 
 epiblast cells. 
 
 At first only simple epiblast or epidermis-cells were present 
 everywhere ; from these touch-cells were developed. All the 
 higher sense- cells have been developed from touch- cells — 
 this is irrefutably proved by comparative anatomy. 
 
 The origin of the various sense-organs from the epidermis- 
 
vn SEiVSE- CELLS OF A URELLA 
 
 333 
 
 cells is, as I have shown, seen in a wonderfully beautiful 
 way in the sense-organs of the toponeurous Medusae, e.g. 
 of Aurelia aurita.^ Here at particular spots in the margin 
 of the bell, on the so-called marginal bodies and in their 
 neighbourhood, lie in close proximity, visual, auditory, and 
 probably olfactory organs, as well as tactile organs, formed 
 by groups of epidermic-cells specifically modified. A pave- 
 ment epithelium covers the greater part of the surface of the 
 bell. The cells of this epithelium at the edge of the marginal 
 bodies change first into flagellate cylindrical cells, which also 
 line certain depressions of the surface near the marginal 
 bodies, and here probably are subservient to smell or taste, 
 but also, like the ordinary flat epithelium, are doubtless 
 tactile. Such flagellate cells are modified here and there 
 into a kind of visual rod, and, the cells surrounding these 
 acquiring pigment, the eye of the jelly-fish is formed. Close 
 to these eyes on the clavate extremity of the marginal body 
 the epithelium again becomes flat, and a vesicle containing 
 crystals being developed beneath it, forms the auditory 
 epithelium. 
 
 The history of the sensory-cells, their origin from one 
 and the same primitive form, even if nothing else did, woidd 
 indicate that all sensory stimuli may be but different 
 qualities of one and the same stimulus, difterent forms of 
 motion of external media — even the stimuli of taste and 
 smell. 
 
 The coarsest of these stimuli is that of touch. To this 
 the epidermis-cells were in any case susceptible from the 
 beginning, and the protoplasm of even the lowest protozoan 
 is also affected by it. Whether or how far this is also true 
 of the other stimuli is not yet established. The remarkable 
 
 1 Cf. Die Medusen, and my address to the Congress of Naturalists at Munich 
 in 1877: "On Artificial Divisibility and the Nervous System of the Medusa-," 
 published in the Proceedings of the Congress, also i^riuted Avitli additions in the 
 Arch./, mik. Anat. Bd. xv. 1877. 
 
334 ORGANIC GROWTH sec. 
 
 facts brought to light by Pfeffer open a far-stretching vista 
 of possibilities witli regard to the effect of stimuli on the 
 lower oriranisms. l*fefter has shown that chemical stimuli 
 affect certain vegetable spermatozoa; that, for instance, they 
 are attracted in water by malic acid, and that they collect 
 in fine tubes filled Avith that substance, as though impelled 
 by a secret force, so that they can be captured in such tubes.^ 
 I have already referred to a similar remarkable sensibility to 
 stimuli on the part of protoplasm, at p. 312. 
 
 It seems therefore certain that the sensitiveness of 
 protoplasm to mechanical stimuli, like that of contact, and 
 to chemical stimuli, is one of its fundamental properties. 
 Since the other stimuli, termed sense stimuli, are merely 
 more delicate kinds of one or other of these, the question 
 arises whether protoplasm is from the first sensitive to these, 
 although only in a very slight degree, or whether it has only 
 become sensitive to them by practice under the coarser 
 stimuli — has been educated to perceive them. With regard 
 
 ^ \V. Pfetfer, Lokomotorische liichtungsheivegungen durch chemische Heize, 
 Berichte der deutschen botanischen Gesellschaft, Bd. i. 1883, p. 524: "Malic 
 acid is the specific stimulus wliicli attracts the autherozooids of ferns into the 
 open archegonia. In like manner, wlien this substance is unequally distributed 
 in water the autherozooids of Selaginella move towards the spots where it is most 
 concentrated. In a similar sense cane-sugar is the specific stimulus of the authero- 
 zooids of the leaf-moss. . . . Not one particular, but every nutritious substance 
 is, when unequally distributed in solution, a stimulus to motile bacteria, which 
 move towards the richer or better nourishment. I have also found that an extract 
 of meat is able to attract the swarm - sjiores of Saprolegnia and Trepomonas 
 agilis, one of the Flagellata. All these are cases of chemical stimulation, by 
 which the motile organism is excited to travel by its ordinary means of loco- 
 motion towards the more concentrated medium, that is, in the opposite direction 
 to difl'u.sion." 
 
 Pfeffer attracted the autherozooids of ferns witli malic acid into capillary 
 tubes, and with exceedingly small quantities of the substance : the eflfect was 
 marked even with a solution of '0001 per cent. 
 
 We have here, then, a chemical stimulus which ensurea-fertilisation — the 
 malic acid conducts the autherozooids of ferns. Other autherozooids are influenced 
 by other such stimuli, e.g. those of mosses by cane-sugar. For further details 
 see W. Pfeffer, Lokomotorlsche liichtungsbeioegu/ngeii durch chemische Reize in 
 Untersuch. aits dem. But. Inst, zu Tubingen, Bd. i. 1881-85, p. 363. 
 
VII ACTION OF SENSORY STIMULI 335 
 
 to which question we may refer to the fact that the stimulus 
 of light affects very primitive organisms, and that bacteria 
 travel towards the water that contains most oxygen. We can 
 also assert definitely that in many of the lower multicellular 
 animals simple epidermic, or at any rate tactile-cells, must be 
 capable of perceiving various kinds of stimuli, since touch and 
 taste-cells and touch and olfactory- cells pass into one another 
 by gradual transition, and since touch-cells become in some 
 cases visual-cells, in others auditory ; while, on the other 
 hand, the so-called end-organs, which usually serve as organs 
 of taste, have in some cases become eyes, as Grenacher ^ has 
 shown in the Arthropoda. The evolution of organs of touch, 
 or of touch and taste into eyes is also beautifully shown in 
 leeches. It is obviously in the lower animals, whose senses 
 are not acute, more difficult to determine whether or how far 
 they perceive gustatory or olfactory stimuli, and still more, 
 whether they distinguish either from touch. But after 
 numerous researches and observations of my own, so much 
 seems to me certain, that originally one and the same cell 
 perceives different sensory stimuli, as, for instance, many 
 animals which have no eyes, such as insect larvie and worms, 
 are evidently affected by light through their epidermic cells, 
 and indeed it seems to act upon them as a painful tactile 
 stimulus. Probably all so-called sensory stimuli act upon 
 protoplasm originally in the form of tactile stimuli, hence 
 the fact that all sensory- cells first appear morphologically as 
 tactile-cells. Sensitiveness to diverse kinds of stimuli must 
 therefore have been gradually evolved in different ectoderm- 
 cells as a division of labour. 
 
 Animals thus probably originally perceived light and 
 sound, and, to judge from anatomical relations, smell and 
 taste also, not as such, but as tactile sensation, and many 
 still so perceive them, by means of one and the same kind of 
 
 1 Grenacher, Unters. iiber das Sehorgan der Arthropoden, Gottingen, 1879. 
 
336 ORGAXIC GROWTH sec. 
 
 cell. At a later stage the functions of the cells diverge, while 
 the cells themselves develop specific forms. Evidently touch, 
 smell, and taste continue longest to be perceived by the same 
 cells, and for this reason we look in vain in many of the 
 lower multicellular animals for separate organs for these 
 sensations. 
 
 The sensory stimuli, as various stages of one and the same 
 stimulus of motion, have, according to my view, been the 
 ultimate cause of the origin of various specific sense organs, 
 a view I previously expressed with special reference to eyes. 
 
 This evolution of the characters of sense-cells could not 
 possibly have been produced by sexual mixture and selection, 
 — by variation of the germ-cells — altliough I do not deny to 
 the first two processes a share in the accomplishment of the 
 result. Not variations of the germ-cells which occurred by 
 chance in a definite direction, but a definite capacity of 
 modification in the protoplasm of the ectoderm — the property 
 of the latter of becoming altered in a definite way under 
 particular stimuli — has determined the modification. 
 
 The best evidence of the truth of this, and at the same 
 time of the effect of use, lies in the fact that the higher sense 
 organs have always developed on the parts of the body best 
 adapted for the reception of the respective stimuli, and in 
 different animals on different parts, while the larvae had 
 originally an ectoderm all of one kind, as the lower multi- 
 cellular animals have in their adult condition. 
 
 A proof, moreover, that the organism under the action of 
 external influences can only undergo particular definite modifi- 
 cations, that it can only yield to external demands by modifi- 
 cation in a definite and limited degree, lies, as I have already 
 urged, in the"Medusa3,"^ in the fact that the higher sense-organs 
 
 ^ p. 220, seq. I refer here to my description of the auditory organ of the 
 Medusa Carmarina as compared with the ordinary structure of the auditory organ 
 of the cycloueurous Meduste and many worms. Cf. my previously cited address 
 to the Naturalists' Congress at Munich, 1877 ; also Die Medusen, p. 222. 
 
VII INDEPENDENT ORIGIN OF SENSE ORGANS 337 
 
 (auditory and visual) often have a quite similar structure in 
 animals by no means closely related, and this in cases where 
 they must have arisen independently, because the common 
 ancestors of both, and even the ancestral forms of both 
 derived from the latter, were entirely w^ithout such organs. 
 
 Certain Medusae and worms, for example, have perfectly 
 similar auditory organs, although these cannot have been 
 derived one from the other — indeed the auditory organs 
 of many Medusae and worms are more closely similar to one 
 another than to those of other Medusae or other worms. 
 Consider the eyes of vertebrates and cuttle-fishes. In the 
 latter is repeated the whole plan of structure of the retina of 
 the former, only in the reverse order : in the vertebrate eye the 
 expansion of the optic nerve lies on the inside of the retina : 
 in the invertebrate on the outside. In the slug Onchidium, 
 however, as Semper has shown, we find the same relations as 
 in the vertebrate. All these three kinds of eyes must then 
 have arisen independently, and yet they are constructed of 
 the same parts. 
 
 " This fact," I insisted further, " is of quite peculiar im- 
 portance. It shows in the clearest w^ay . . . that in conse- 
 quence of the relations of organisms to particular infiuences 
 of the external world perfectly similar forms may arise, even 
 without any immediate blood-relationship between them, not, 
 on my view, because the material provided in the animal 
 organism had little capacity for evolution, but because with 
 this material organs can only be constructed within narrow 
 limits of variation to fulfil in the best possible degree a 
 perfectly definite and constant requirement from without." 
 
 I said further that the anatomy of the sense organs offers 
 specially numerous examples of this in two directions ; tliat 
 notwithstanding the absence of all direct relationsliip of 
 descent (1) resemblance, or exact similarity of form, has 
 arisen ; (2) that similar forms, but in different combination, 
 
338 ORGANIC GROWTH sec. 
 
 have been produced. Further, " the more definite, the more 
 powerful and continuous, and the less modified by other 
 influences the actions of the external world on given 
 organised materials, the more similar will be the structural 
 forms which they produce, even when the blood-relationship 
 of these materials is by no means close. 
 
 " Such an action is present in those definite unchangeable 
 physical influences which determine the origin of the sense- 
 organs in a given formative material, in consequence of the 
 necessary requirements of adaptation. The power of adapta- 
 tion, in comparison with that of heredity, here comes into 
 extraordinary prominence. The influences of the former are 
 very powerful. Even where the manifold slighter relations of 
 life between individuals come into play reciprocally, these 
 relations after repeated action Imve a great effect in changing 
 forms, and w^hen long continued are important agents in modi- 
 fication. But the influences wdiich primarily govern every 
 organism in consequence of the necessities of its existence, 
 the physical influences of the media in which it lives, con- 
 stitute forces which, tliough simple, are counteracted by no 
 opposing factors, which are ever powerfully acting in the same 
 way, and to which, from the given material, only a limited 
 variety of structural modifications can be adapted. And there- 
 fore, in spite of the endless variety in detail, in particulars, a 
 certain uniformity of organisation in the gross must exist : 
 thus the same plans of structure may appear repeatedly 
 where there is no close blood -relationship to account for 
 them. Since the continuous influence of elementary physical 
 forces necessarily exhibits itself most in the organisation of 
 the sense organs, a comparative anatomy of these organs, 
 founded essentially upon heredity, can only be established 
 usually within the smaller divisions of the animal kingdom, 
 and among all others their similarities of form are the least 
 trustworthy guides to phylogenetic relations." 
 
VII EVOLUTION OF THE NERVOUS SYSTEM 339 
 
 These arguments are directed against the prevailing 
 fashion in comparative anatomy of referring all similarities 
 of form dogmatically to blood-relationship, and of leaving the 
 direct and indirect influences of the external world out of 
 consideration. The view here urged that the nervous system 
 and sense organs have been formed in the multicellular 
 animals from the original body covering, from the epiblast, 
 because the epidermis has naturally from the first been the 
 medium of relation to the outer world, because it received 
 impressions and required to be rendered capable of giving 
 the impulse to reaction against those impressions, to defence 
 and attack, this view will be opposed by no embryologist or 
 physiologist. But perhaps the most important support for 
 this view will be afforded by tracing the first appearance of 
 a morphologically distinguishable nervous system in the 
 animal series, as I have traced it in the Ctenophora and 
 Medusae. 
 
 The Origin of the Central Nervous System 
 
 Embryology has long since taught us that not only in the 
 Vertebrata, but also in the Arthropoda, Mollusca, and 
 Vermes, the central nervous system is developed from epiblast- 
 cells, which separate from the superficial layer whence they 
 are derived and pass to a deeper position, and has also shown 
 that such animals develop from similar embryos which 
 consist of germinal layers, and which are evidently genetically 
 related tooether. It has also long^ been known that lower 
 forms of the Metazoa exist, which remain throughout life 
 essentially in the morphological condition of these embryos, 
 and which although no separate nervous system can be recog- 
 nised in them, clearly manifest the power of sensation and 
 even of volition. Thus the question necessarily arose wliether 
 these powers in such forms do not reside in the ectoderm. 
 
 Accordingly, N. Kleinenberg has explained tlie cylindrical 
 
340 ORGANIC GROWTH sec. 
 
 epidermis-cells which give off internally a transversely-placed 
 fibrillar process, so that a fibrous layer is formed between the 
 ectoderm and endoderm, as neuromuscular-cells,^ that is, as 
 epidermis-cells whose outer part is capable of receiving nerve 
 stimuli, while the internal process is of muscular nature, and 
 transforms directly the stimuli received by the former into 
 motion. 
 
 The Hydra is simply a gastrula-sac consisting of two 
 layers, these neuromuscular-cells (the ectoderm) and digestive 
 cells (the endoderm), and provided wath prehensile arms. 
 When a direct reaction ensues upon stimuli falling on the 
 ectoderm - cells, the movements of the animal are reflex 
 actions, and it unconsciously performs movements on stimu- 
 lation, just as the Mimosa folds its leaves when they are 
 touched. 
 
 The question how the Hydra can exercise volition as it 
 certainly does, without a separate central nervous system is 
 not discussed by Kleinenberg. Yet, when we observe the 
 motions and general behaviour of many free - swimming 
 ciliated larvae, the conviction is forced upon us that although 
 they consist only of epiblast and hypoblast, they pursue 
 definite purposes, that their actions are in some degree 
 directed by a will. It must therefore be assumed, whether 
 nervous cells are somewhere present in Hydra or not, that 
 ectoderm cells in the lower Metazoa are the seat of volition. 
 But a morphologically recognisable nervous system consisting 
 of separate nerve-cells and nerve-fibres must, according to 
 these considerations, in its most primitive form lie immediately 
 beneath the epidermis, connected on the one hand with the 
 latter, on the other with muscles. Moreover, it probably 
 extended at first as a layer all over the body. 
 
 These predictions were completely fulfilled by my 
 researches upon Beroii ovatus.^ The further conclusion was 
 
 ^ Kleinenberg, Hydra, 1872. - Cf. Beroe ovatus, loc. cit. 1873. 
 
VII NER VO US S YS TEM OF MED USAi 341 
 
 also verified, that the formation of a definitely circumscribed 
 brain will take place by the gradual concentration of nerve- 
 cells at one or several points of the body which are most 
 exposed to contact with the external world, and on which 
 therefore the sense organs develop. These conclusions were 
 verified both by the anatomical and the physiological 
 investigation.-^ 
 
 The central nervous system of Beroe ovatus consists of 
 nerve-cells w^hich lie beneath the delicate epidermis of thin flat 
 epithelial-cells, which are distributed over the whole surface 
 of the body, but are accumulated in larger numbers at tlie 
 closed end of the sac-shaped body in the neighbourhood of 
 the sense organ there situated. At this spot the nerve-cells 
 form externally a sense - ganglion, and beneath that the 
 rudiment of a definite brain formed of aggregated nerve-cells. 
 But the nerve-cells scattered over the whole surface are con- 
 nected by delicate nerve-fibrils on one side with the epidermis- 
 cells, on the other with the muscle-fibres which traverse the 
 gelatinous tissue (neuromuscular fibres). 
 
 The nervous system of the great Scyphomedusae, the 
 toponeurous Medusae, is, according to my anatomical re- 
 searches, first published in 1877, but suggested in 1873 by 
 my section experiments, similarly constructed ; but the 
 accumulations of nerve-cells wdiich represent brains are here 
 found chiefly on the edge of the bell, again in the neighbour- 
 hood of the sense-organs. Brains connected by a ring-nerve 
 are formed in the same position in the cycloneurous Medusa?, 
 and their cells and fibres are demonstrably formed of ectoderm 
 
 ^ Cf. Th. Eimer, Versuche uber k'dnstliche Theilbarkeit von Beroe ovatus, 
 angestellt zum Zweck der Controle seiner Morphologischen Befunde iiber das 
 Nervensystem dieses Thieres, Arch.f. mik. Anat. Bd. xvii. 1879. 
 
 - Sitzungsberichte der physikalisch-medicinischen Gesellschaft zu Wurzburg fur 
 
 das Gesellschaftsjahr 1873-74, Part ii., erste Sitzung am 13 Dez. 1873 ; .iiul 
 
 Ueher kiinstliche Theilbarkeit Ton Aurelia aurita und Cyanea capiUata in 
 
 2ohysiologische Individuen, etc., Verh. der 2^hys.-med. Ges. zu Wurzb. N.F. Bd. v. 
 
 1874. 
 
342 ORGANIC GROWTH sec. 
 
 cells, whicli are connected with the ectoderm, but which have 
 come to lie beneath it. 
 
 Thus we have in the IMedusae a laminar central nervous 
 system extending over the body, whose cells are commencing 
 to concentrate at spots particularly suitable for communication 
 with the external world, and there to form definite brains. 
 In tlie higher Metazoa, in Vermes, Mollusca, Arthropoda, 
 and Vertebrata, these brains, or ganglia, are completely 
 formed, but their embryonic condition still indicates the 
 epiblast as their original place of origin. 
 
 But in the former case the first appearance of a morpho- 
 logically recognisable nerve-system in the animal series, its 
 formation from the ectoderm, can only be explained as tlie 
 effect of the constant action of external influences upon the 
 organism, and by the inheritance of this effect — by the 
 inlieritance of acquired characters with the aid of selection. 
 
 Accidental variabiHty of the germ-plasm as a determining 
 cause seems here also completely excluded. 
 
 A more detailed account of the researches above mentioned 
 on the nervous system of the Meduspe, and especially of 
 my experiments upon the subject, is contained in the address, 
 " On the Idea of the Individual in the Animal Kingdom," 
 which forms the Appendix to this work ; for a full discussion 
 I must refer to my original papers. 
 
 Only one point further I must draw attention to : the 
 nerve-cells in the Ctenophora and Scyphomedusae are so far 
 from being morphologically differentiated and recognisable, 
 that I have been accused of mistakinsj connective-tissue-cells 
 for nerve-cells. It is, however, obviously, on my view of the 
 matter, necessary that nerve-cells should at the commence- 
 ment of their evolution be similar to other cells. It is a 
 known fact that even in higher animals the nerve-cells in the 
 embryonic condition cannot be distinguished from other 
 embryonic cells. Only function could impress upon nervous. 
 
VH VICARIOUS NERVE-CENTRES 343 
 
 as on other cells, a definite morphological character. Thus I 
 sought at first in vain for nerve- cells or brains in the 
 Scyphomedusse and could only discover the spots at which 
 the latter exist by the section-experiments above mentioned. 
 Such experiments afterwards completely confirmed my 
 description of the nervous system of Beroe. In both cases, 
 in Beroe as in the Scyphomedusae, the presence of a number 
 of nerve-cells, or of brains, could be recognised by the fact 
 that the parts in question, when separated from the rest of 
 the animal, alone, or at least in a pre-eminent degree, exhibited 
 life (movement). 
 
 In Beroe I had found anatomically a gradual decrease in 
 the abundance of the nerve-cells from the closed end towards 
 the aperture. In power of movement the parts of the animal 
 when divided transversely exactly corresponded to this result. 
 The separated polar portion moved immediately after its 
 separation, in all respects like an entire uninjured animal. 
 The nearer to the aperture they were taken, the more the parts 
 were affected by separation, the longer time elapsed before they 
 showed traces of movement, the less were they capable of life. 
 
 Vicarious Nerve-Centres. 
 
 In the course of my section -experiments I observed a 
 remarkable fact which at present stands alone, and which has 
 an important bearing on my whole argument. 
 
 The Medusa Aurelia aurita, when I had removed from it 
 all the primary nerve-centres, became completely motionless. 
 But after the animal thus mutilated had lain several days in 
 clean sea-water, it gradually commenced to exhibit movements 
 again : one day, movements at first trembling and irregular 
 appeared in the umbrella. These movements evidently 
 started from a definite spot which might be at any part 
 of the umbrella, and extended thence over the whole, 
 just as in the uninjured animal they proceed from 
 
344 ORGANIC GROWTH sec. 
 
 the nerve-centres on the margin. Gradually the movements 
 of the animal became regular, they succeeded one another in 
 a definite rhythm, as in the entire animal, and the animal 
 thenceforth behaved completely like an uninjured specimen. 
 Thus a new nerve-centre had been formed in place of the old 
 from the nerve-cells scattered over the body-surface, and had 
 taken upon itself the movement and direction of the animal. 
 [ have repeated this experiment many times with the same 
 result, and have observed mutilated animals living in this way 
 more than eight days. 
 
 The movements of Medusae are, as I have shown, involun- 
 tary, but they can be retarded or hastened, diminished or in- 
 tensified voluntarily. As involuntary movements they are 
 respiratory, as voluntary they are the means of locomotion. 
 
 The only possible explanation of the reappearance of the 
 movements is that the need of respiration in the still living 
 but motionless animal first produces convulsive contractions, 
 which gradually become rhythmical. But how it happens 
 that they become rhythmical, and that this rhythm may be 
 controlled by some portion of the nerve-cells scattered over the 
 body, and how these cells are able to influence the movements 
 by volition remains a mystery, unless we assume that all the 
 nerve-cells of the Medusa still possess, as an inherited and 
 originally acquired character, the faculty of directing motion, 
 even after the function of direction has been assigned to the 
 nerve-centres of the margin of the umbrella. In order to 
 explain the facts, it must be further assumed that some of the 
 nerve-cells of the surface have retained this faculty in a higher 
 degree than others, or that they happen to be more vigorous at 
 a given moment, and are therefore able to exert their inlierited 
 faculty more powerfully than the rest. It would thus only 
 require external stimulation to bring this faculty into action : 
 Medusae which were left after the operation in unchanged 
 water deficient in oxygen, did not recover their power of motion. 
 
 I 
 
VII AN EXPERIMENT ON AUKELIA 345 
 
 I must here refer to a particular experiment which bears 
 upon this subject.^ It must be explained that in Aurelia 
 aurita, on which the experiment was made, there is an anus 
 between every two marginal bodies. 
 
 On 29th August, at 12 noon, of two specimens of Aurelia 
 18 cm. in diameter, I cut away from one the marginal 
 bodies, from the other the parts around the anal openings. 
 The first remained after the operation entirely motionless, 
 the second contracted as usual. In the former, twitcliings 
 occurred only when I pricked it with a needle — slight 
 imperfect contractions. 
 
 Second day. 30th August, 11 A.M. The animal (0) 
 deprived of its marginal bodies lies flat, extended, and motion- 
 less, the remaining parts of the margin somewhat turned 
 upwards. Even when pricked with a needle it reacts extremely 
 feebly. The other specimen (M) still contracts actively. The 
 separated pieces of contract vigorously, as they did yester- 
 day immediately after their removal ; the separated portions 
 of M have, on the contrary, lost their fresh appearance, they 
 are no longer elastic, but flabby and thin — they seem to be 
 dead, for not even the tentacles on them react to stimulation. 
 
 Third day. 31st August. M contracts most vigorously (in 
 the same water) at least ten times per minute, but generally 
 much oftener. On still not a single contraction is to be 
 perceived. 
 
 Fourth day. 1st September, 12 noon. M contracts (in the 
 same water) vigorously. makes at intervals of 2 J, IJ, 1^ 
 minutes slight contractions, but only with two particular 
 anal lappets out of the eight, and these two contract 
 simultaneously. When the animal is pricked in the centre 
 with a needle, the same two lappets which exhibit spon- 
 taneous movements contract strongly, and some of the others 
 
 1 It is described as Experiment D at p. 81, et seq., of the Mcdnncv. Cf. tig. f) 
 below. Tlie dotted lines in the figure terminate on the margin at the anal apertures. 
 
346 
 
 ORGANIC GROWTH 
 
 SEC, 
 
 contract feebly, while yesterday no spontaneous movement, 
 and scarcely any reaction to stimulation were observed in 
 this specimen. The Medusa, therefore, has recovered itself 
 in certain parts only ; in these parts vicarious centres of con- 
 traction must have been established, the action of which does 
 not extend beyond their boundaries. Tlie specimen still lies 
 flat and extended, while M when contracting assumes com- 
 pletely the bell-like shape. Three-quarters of an hour after 
 the addition of clean water, contracts at intervals of 2, 1^, 
 \\ minutes the same two anal lappets as before. ^I contracts 
 very actively. Both behave almost in the same way as in the 
 old water. 
 
 Fifth day. 2d September. M contracts actively in the old 
 water ; lies still and begins to decompose, only the two anal 
 lappets wliich yesterday contracted spontaneously are still 
 entire. The other anal lappets have dissolved away, except 
 two, pieces of which are still left. 
 
 Sixth day. 3d September, 8.30 a.m. Only some of the 
 separated pieces of which contain marginal bodies are left 
 alive, all the rest is in process of dissolution. Putrefaction in 
 the vessel, wiiich has also caused the death of M. 
 
 Seventh day. 4th September. The fragments containing 
 marginal bodies alive yesterday are still alive, but are reduced 
 to narrow ("75 cm. broad) strips, and each is merely a mar- 
 ginal body with a morsel of the umbrella margin connected 
 with it. 
 
 Eighth day. 5th September. One fragment of the margin 
 with its marginal body still alive and contracting, although 
 the water is completely putrid from the decomposing Medusa 
 left in it all ninht. 
 
 In this case, therefore, two new nerve-centres came 
 into action in two portions of a Medusa while the rest was 
 dying, and these centres, when the living portion of the body 
 was stimulated, produced contraction in the anal lappets con- 
 
VII RESULTS OF SECTION IN BEROE 347 
 
 trolled by them, just as do the " brains " of the intermediate 
 parts in the uninjured animal. 
 
 It is also remarkable that when the Scyphomedusee die gradu- 
 ally the brains with the parts surrounding them remain alive 
 longest — Aurelia thus gradually perishes, until at length only 
 eight small fragments containing the nerve-centres are left,^ 
 and in like manner Beroe dies towards the aboral pole which 
 contains the greatest number of nerve- cells. But when I cut out 
 one of the eight antimeres of an Aurelia, containing a marginal 
 body in the middle of its lower edge, its death proceeded 
 in the manner explained by the accompanying figure.^ It 
 began in the middle and proceeded upwards and 
 downwards, until only the lowest portion con- 
 taining the marginal body remained. And this 
 piece went on diminishing towards the marginal 
 body. 
 
 The results of section in Beroe still more strongly 
 support my hypothesis of the development of vicar- 
 ious nerve-centres. 
 
 The locomotion of the Ctenophora is effected by 
 the strokes of the small paddles formed by the con- 
 crescence of cilia, again a motion which can take 
 place both involuntarily and voluntarily. 
 
 Separated portions of this animal all behave after ^^'^^ -• 
 some time exactly like the whole : no difference in the move- 
 ments can be recognised — voluntary motion of the paddles 
 is evident even in the fragments. 
 
 Thus certain nerve-cells here also must assume the function 
 of direction. But this occurs the more quickly, as follows 
 from the facts already described, the greater the number of 
 such cells present in the fragment — only the polar fragment 
 
 ^ Die Medusen, p. 80, et seq. 
 
 2 From Die Medusen, fig. 10, where p. 61, et seq., contain further details of the 
 process of dying. The stalked knob represents the marginal body. 
 
348 ORGANIC GROWTH sec. 
 
 moves immediately after its separation iu the same way as 
 the uninjured animal. 
 
 The preceding results lead to tlie inference that a definitely 
 circumscribed nervous system is not absolutely necessary for the 
 exercise of volition. Co-ordinated movement mi^ht also occur 
 if the nerve-cells were uniformly scattered over the whole 
 surface of the body, without a permanent centre. This was 
 tlie original condition, and in a still earlier stage the seat of 
 volition was in the ectoderm cells. The latter is even now 
 the case in some two-layered, free-swimming larvae which 
 exhibit voluntary action, and the presence of special nerve- 
 cells is not indispensable to the activity of e.(j. the Hydra. 
 Quite recently attempts have been made to demonstrate the 
 existence of such cells in Hydra, but it seems to me the 
 evidence is at present insufficient. The fact that each frag- 
 ment of a Hydra, however it is cut up, behaves like an entire 
 animal, and that it grows into an entire animal, that this is 
 true even of a fragment of one of its tentacles, indicates that 
 morphologically expressed centralisation can scarcely exist in 
 this animal. 
 
 That a single will can exist even with a number of brains, 
 is also beautifully shown by the Medusa. I have shown how 
 the eight brains of Aurelia produce single movements : the 
 impulse proceeds always from one of the brains, and passes 
 immediately to the others — sometimes one, sometimes another 
 originating the impulse — but this does not exclude the 
 possibility of all eight acting at the same time, indeed, 
 this is probably necessary for the production of certain 
 movements. 
 
 Now, whether in a given animal there are eight such 
 central points of nervous activity or thousands — as many as 
 there are nerve-cells or ectoderm-cells on the body surface — 
 makes no difference. If we assume that Hydra has no special 
 nerve-cells, then the impulse which produces action may start 
 
VII THE NUCLEUS AS A NERVE-CENTRE 349 
 
 now from one, now from another ectoderm-cell, or group of 
 such cells, and spread from thence — by simple contact since 
 no nerves exist — to the neighbouring cells, and so communicate 
 itself to all the muscular processes. 
 
 Brains, or a brain, as the case may be, could only arise in 
 consequence of the fact that certain ectoderm-cells, or groups 
 of such, came more frequently into contact with the outer 
 world, and accumulated experience, or that were from their 
 favourable position adapted to form the middle point for the 
 activities of a larger number of neighbouring cells — cerebral 
 ganglia could only be developed in consequence of the 
 inheritance of acquired characters. 
 
 The Cell-IS^ucleus as a Central Nervous Organ. 
 
 But if the individual cells of the ectoderm are capable, as 
 the view I am advocating supposes, of giving rise to volun- 
 tary action, we must seek in them some apparatus which serves 
 as a central nervous organ ; and this apparatus can only be the 
 nucleus. 
 
 Thus I am brought back to a question previously sug- 
 gested, Whether the nucleus of the unicellular organism is 
 not also to be regarded as its central nervous organ ? 
 
 For the larval Blastula is certainly, like the Yolvox colony, 
 only an aggregation of unicellular beings. And an affirma- 
 tive answer to the above question is supported by numerous 
 facts which I have already brought forward in my papers on 
 Beroe and on the Medusae. In these I have described the 
 nucleus in general as the central organ of the cell, as its organ 
 of life, in the sense that it originates and governs the pro- 
 cesses of life in the cell, while in the animal cell I have con- 
 sidered the nucleus as the central nervous organ. 
 
 I was first led to this view by considering the great 
 importance of nuclei in every nervous system. The nucleus 
 
350 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 and not the cell-plasma is the essential part of a nerve-cell : 
 the latter serves only for conduction. Hence the extra- 
 ordinarv niac^nitude of the nuclei in the Q,anf;jlion-cells of all 
 animals which possess a somewliat highly developed nervous 
 system.^ 
 
 Secondly, this supposition is strongly supported by the 
 peculiarities of the nuclei in the nerve-fibres of the lower 
 multicellular animals. In these fibres, as I liave shown for 
 instance in Beroii, the nuclei, surrounded with very little pro- 
 toplasm, are placed at intervals in such a way that a nervous 
 fibril passing through the nucleolus connects one nucleus to 
 another. Thus these primitive nerves look like chains of 
 nuclei connected by conducting fibrils, and resemble a series 
 of telegraph stations connected together for the purpose of 
 renewing or strengthening the current at the beginning of 
 each stage. Obviously the ganglionic swellings along the 
 nerves in higher animals, e.g. the spinal ganglia, form a simi- 
 lar apparatus, but with the added function of crossing the 
 conducting fibres.^ 
 
 Thirdly, I find that also in the sensory-cells of Medusae 
 nerve-fibrils pass through the nucleolus, and are continued, 
 as already mentioned, into the cilia, or terminate in the nuclei 
 of the epidermic-cells.^ The same thing occurs in the sensory- 
 cells of higher animals. 
 
 Fourthly, nerves frequently terminate in the nuclei of 
 cells which are not sensory, and this mode of termination 
 will, I believe, be found in future to be very common. It 
 occurs, for instance, in the epidermis, in muscle-cells, etc., 
 and in all probability, as before mentioned, in ciliated cells. 
 
 ^ Even in the nen'e-cells of Medusae (Carmarina hastata) the cell-plasm 
 obviously consists of conducting fibrils {Medusen, Taf. viii. figs. 8, 10) ; and 
 the same thing is easy to observe in the nerve-cells of the cerebral ganglia of 
 Helix pomatia. 
 
 - Cf. Beroe, Taf. viii. fig. 72; Medusen, Taf. xi. fig. 9. 
 
 ^ Medusen, Taf. iv. figs. 1, 7, 21; Taf. xiii. fig. 9, etc. 
 
VII INTRA- CELLULAR NERVE-FIBRILS 351 
 
 In the latter the cilia are connected at their bases with fine 
 fibrils, which probably pass through the nucleus and form the 
 continuation of nerve-fibrils. 
 
 Lastly, it is evident that the nerve-fibrils start from the 
 nucleoli of the nerve-cells, for they pass in a radiate manner 
 from the nucleolus and form a fibrillar network in the 
 nucleus. On the other hand, the same histological relations 
 are seen in nuclei in which nerve -fibres terminate, most 
 clearly in Medusse, but also in the higher animals. I con- 
 sider the so-called " Elmer's ring of granules," which is also 
 most clearly to be seen in many nerve-cells, to indicate the 
 points where the fibrils radiating from the nucleolus bend 
 round to join the complicated network of the nucleus.^ 
 
 This fibrillar network in the nucleus — and this is the par- 
 ticular bearing of the preceding upon our subject — must, 
 like the fibrils in the cell which are connected with it, be of 
 nervous nature, and this is undoubtedly the condition of 
 things in the ganglion-cells of the higher animals : it can be 
 seen, for instance, in the cerebral ganglia of the Helix 
 pomatia. Even in Medusie (in the marginal bodies) definite 
 fibres of extraordinary delicacy serving exclusively as nerves 
 liave arisen ^ — the " dotted substance " in the brain of hii^her 
 animals is the indication of a fibrillar network connectino- 
 the cells, and the structure of this is so delicate that it will 
 probably never be possible to follow out the course of the 
 fibrils. But these nerve-fibrils must have been derived from 
 simple strands of ordinary protoplasm, and such they are still 
 in cells which are not specifically nervous. 
 
 From such protoplasmic strands true nervous substance 
 with infinitely delicate and regular connections must have 
 been formed by the constant passage of nervous impulses and 
 
 1 Cf. Die Medusen, Taf. viii. fig. 6, 7 ; Taf. ix. figs. lOn ; Taf. xi. fig. 10 ; 
 Be7'oe, Taf. viii. bes. fig. 82 ; and Weitere Nachrichten iiber den Bait, des Zell- 
 kernes, etc., loc. cit. Taf. vii. 
 
 - Cf. Die Medusen, Taf. iv. figs. 2, 6, 13, 1 i, etc. 
 
352 ORGANIC GROWTH sec. 
 
 by the inheritance of the properties so acquired. Similarly, 
 only by modification of the original ordinary protoplasm, in 
 consequence of the constant exercise of nervous action, can 
 conducting nerve-fibres and nerve-cells have arisen. Spon- 
 taneous variations of the germ-plasm cannot possibly have 
 produced a system of organs so wonderfully delicate, both 
 morphologically and physiologically, exclusively as a means 
 of relation between the organism and the external w^orld. 
 This must have arisen through external influences and 
 exercise. 
 
 The fibrillar network above described occurs also in the 
 germinal vesicle of the egg-cell, even with the radial arrange- 
 ment round the germinal spot. That which may afterwards 
 become the path of nervous impulse is originally the path of 
 nourishment, and the radiation of the strands to and from a 
 central point is the most effective for the latter purpose. In 
 the streaming of the protoplasm of vegetable-cells, e.g. in the 
 hairs of Tradescantia, we see the commencement of this 
 typical arrangement of protoplasmic threads. The protoplasm 
 flows as though driven by a secret force — as also in the Fora- 
 minifera — towards the central point and then again from it : 
 the central point being the nucleus which originates and 
 governs the vital processes in the cell. Such paths, at first 
 fluid, became fixed, and finally, where they had to convey 
 nervous stimuli, became nervous fibrils. 
 
 The same fibrillar network in the nuclei of the germinal 
 cells, in the germinal vesicle, is considered by Weismann, on 
 the other hand, as the idioplasm, i.e. the firm substance which 
 conveys the characters of the species from generation to 
 cjeneration. 
 
 I have already in the Medasm laid weight on the fact 
 that only in the ova of animals are the nuclei so extraordin- 
 arily large as in the ganglion-cells, and have attempted to 
 explain '' the prominent part played by the nucleus in ova, 
 
^'" ORIGIN OF NER VE- FIB RES 
 
 353 
 
 and also in spermatozoa," the "great importance possessed 
 by these elements as the instruments of an enormous develop- 
 ment," by the suggestion that the nuclei originate tliis 
 development, " a supposition which is considerably supported 
 by the most recent observations" (1878). 
 
 Originally even the multicellular animals had no special 
 paths of nervous conduction. Possibly in the ectoderm-cells 
 of Hydra a network of ordinary protoplasmic threads still 
 constitutes the communication between cell and cell, nucleus 
 and nucleus. 
 
 , Oeigin of ISTerve-Fibres and their Vicarious Action. 
 
 But a more distinct morphological effect of the exercise of 
 nervous action is seen in ectoderm-cells, in which the course 
 of nervous impulses is through the cells lengthwise to the 
 nerves or muscles connected with them. For instance, in the 
 ectoderm-cells over the nerve-ring of Medusae, which are con- 
 tinued into nerve-fibrils, and also in the sensory portion of 
 neuro-muscular cells, the cell-plasm is, as I have already 
 mentioned, longitudinally striated in consequence of its 
 transformation into extremely fine fibrill?e. In the former 
 instance these fibrillse pass directly into nerve-fibrils ; in the 
 latter, they pass into the muscular portion of the cell, after 
 having in both cases come into connection witli the 
 nucleus. These relations are quite similar to those described 
 in ciliated cells — that is, the fibrillse are nerve-strands which 
 have been produced by functional activity from the proto- 
 plasm of ordinary epithelial-cells.^ 
 
 It follows from the preceding that the nerves of Zoophytes 
 originally consisted of chains of cells derived from the ecto- 
 derm. This is also the most probable origin of the nerves of 
 the higher animals. In the gelatinous tissue of Scyphomedusa?, 
 in Aurelia aurita for example, we find that the amoeboid cells 
 
 1 Cf. Die Medusen, Taf. xii. figs. 8, 12 ; Taf. xi. fig. 6, and others. 
 
 2 A 
 
354 ORGANIC GROWTH sec. 
 
 of that tissue, connected by definite but extremely primitive 
 nerve-fibres, form chains passing through the tissue from one 
 surface to the other. I believe that we have here a survival 
 of the most primitive nervous communications in multicellular 
 animals. The course of nervous impulses, originally variable, 
 has probably become fixed in consequence of their continual 
 passage in the same direction ; and from the same cause, to 
 judge from the relations above described of neuro-ectodermic- 
 cells, has been developed the axis-cylinder, composed of fine 
 fibrils, of the nerves of higher animals. 
 
 The nerves of the cycloneurous Medusse, which are also 
 chains of nerve-cells, are, on the other hand, developed in such 
 a way that they remain dividing ectoderm-cells connected 
 from the first by nerve-fibrils, which are processes from them- 
 selves. Thus arise the ganglion-cells interpolated in these 
 animals in the course of nerve-fibres. 
 
 AVlien making experiments on the section of Medusae, I 
 made an observation on the vicarious action of nerve-fibres, 
 which finds its proper place here. I was trying at the time 
 to ascertain whether in the Scyphomedusie (toponeurous 
 Medusae) a nerve (ring-nerve) is present at or near the 
 margin of the umbrella. With this object I made a cut in an 
 Aurelia aurita, with scissors, through the margin for a distance 
 of 1 cm. between every two marginal bodies, in order to see 
 whether the interdependence of the movements of the eight 
 portions of the umbrella on one another, in other words, 
 whether the co-ordination of the motion excited by the 
 activity of the several ganglia, would continue or not. As the 
 co-ordination was completely maintained, I next, in another 
 Aurelia, cut out the whole central portion, leaving a 
 continuous marginal ring about 1-| cm. broad, and contain- 
 ing all the eight marginal bodies.^ This ring began, after 
 a pause such as always occurred after similar operations 
 
 ^ The following figure is also taken from the Medusce, p. 31. 
 
VII 
 
 EXPERIMENT ON A U RE LI A 
 
 355 
 
 in consequence of the shock, to contract rhythmically like an 
 entire specimen, while the central portion sank to the bottom 
 as if dead. Then I made cuts through the outer edge of the 
 ring inwards for 1 cm. between every two nerve-centres, so 
 that the portions which each contained one of the latter were 
 only connected by eight bridges, \ cm. wide, at the inner edge 
 of the ring. The co-ordination of the movement of the several 
 parts continued still as before. It continued also when I pro- 
 longed half of the cuts till only a thin connecting strand was 
 left. I also prolonged the other four cuts, and then made 
 alongside each of these another cut in the opposite direction 
 from the internal edge of the 
 ring nearly to the natural 
 margin. Thus three of the 
 portions were connected 
 together and with their 
 neighbours only by a flat 
 piece of tissue a few mm. 
 broad, and only directly 
 connected in the direction 
 of one of the diagonals of 
 these flat pieces. Now, 
 the CO - ordination of the 
 contractions of the several portions became uncertain 
 the more uncertain the smaller the connecting bridges 
 of tissue. Thus it is proved that tlie several nerve-centres 
 are connected, not by a ring -nerve, but by the delicate 
 nerve -fibrils which pass in various directions through the 
 gelatinous tissue, that is, by nerves which in this case again 
 have by no means the morphological character of ordinary 
 nerves, but which have the appearance of connective-tissue- 
 fibres, and which are not yet united into bundles, into proper 
 nerve- cords. 
 
 I repeatedly observed that the co-ordination of the move- 
 
 FiG. 3. 
 
356 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 «.^. 
 
 h 
 
 J\j 
 
 ments of the several portions, after having been destroyed by 
 the cuts, after a time was re-established. Communication 
 must therefore have been effected by nerves which previously 
 did not perform this function ; some nerve-fibrils must have 
 taken up the function of others, have acted vicariously in 
 place of tliese.^ 
 
 Experiments on Beroe gave me similar results.- I have 
 
 already briefly stated that in this 
 animal also when parts are separ- 
 ated a new centre of action 
 appears in them. I now return 
 to this subject, and give a short 
 account of my experiments. 
 ~ Experiment A. — I cut five Beroes 
 into three parts transversely so as to 
 form from each three parts of equal 
 B height, of which the upper, A, con- 
 tained the aboral pole, with the 
 largest aggregation of ganglion-cells ; 
 the lower, C, contained the mouth ; 
 while the third, B, was the middle 
 Q portion of the body. 
 
 After the division, the movement 
 of the swimming-plates ceased com- 
 pletely in all the pieces, but re- 
 commenced after a short time in 
 all those pieces which contained 
 Shortly afterwards, movement began 
 again in those portions distinguished as B and C, but in these 
 ceased again after a time, while in the A pieces it continued. 
 
 ■i: 
 'i 
 
 '/a 
 
 Fio. 4. 
 
 an aboral sense-organ. 
 
 When I examined the pieces again after four hours, I 
 
 ^ Cf. Die Medusen, p. 31. Romanes's results also proved the same vicarious 
 action of nerve-tibres in Medusae, Phil. Trans, vols, clxvi., clxvii. 
 " Archiv. f. mikr. Anat. Bd. xvii. 
 
VII EXPERIMENTS ON BEROE 357 
 
 found active movement going on in almost all the pieces ; in 
 A, however, the plates were most active, and some of the B 
 and C pieces showed no motion. 
 
 Then I cut off small fragments from these various portions 
 of the animals. The swimming -plates of these fragments 
 were immediately after the operation in all cases motionless, 
 but after two hours I found active movement soinir on in 
 them also. 
 
 On the second day the plates were still in active motion in 
 all the pieces, the small fragments included, excepting a few 
 of the latter. On the third day all showed active movement. 
 
 On the piece forming the middle portion of one Beroe was 
 exhibited the peculiar phenomenon, that the plates of one row 
 vibrated in the opposite direction to that of the others, and 
 the movement in this row was no less active than elsewhere, 
 and, as in the others, proceeded in waves in rapid succession. 
 Everywhere else the movement in the separate pieces pro- 
 ceeded in the same direction in which the plates vibrated in 
 the entire animal : the waves passed from the aboral pole 
 towards the mouth. 
 
 This reversion of direction in the swimming -plates of a 
 single row of one piece of an animal while the rest vibrated 
 normally forms a very remarkable instance of independent 
 nervous action in a separate piece of an animal, an instance 
 of reversal of function. Moreover, I observed repeatedly on 
 the separated tube-shaped middle portion of a Beroe that the 
 movement in one and the same series of plates could proceed 
 now in one direction, now in the other. 
 
 Many repetitions of such experiments gave the same 
 results : the movement of the swimming-plates always ceased 
 after the division for a moment or for some minutes, some- 
 times even for some hours, but in all cases recommenced, 
 reappearing always earliest in the pieces which contained the 
 sense-organ, and later in the others. Usually also in the 
 
358 ORGANIC GROWTH sec. 
 
 former the motion after its reappearance attained sooner than 
 in the others to the rapidity which it had in the entire 
 animal — in fact, in many of the pieces without sense-organ, or 
 in fragments of these, the motion remained permanently 
 slower, as well as more irregular, than it was in the entire 
 animal. Most of the pieces, however, recovered completely, and 
 halves of Beroe containing no sense-organ usually soon swam 
 about exactly like an entire animal, and also in the same direc- 
 tion as the latter, the mouth forwards, they reacted to stimuli 
 exactly as entire animals, and seemed to be not at all inferior 
 to these in psychical capabilities. Such a piece had also the 
 power, like an entire animal, of stopping at pleasure the 
 motion of any one of the rows of plates. As in the entire 
 animal, the movement in the pieces as a rule commenced at 
 the edge nearest the sensory-pole, and proceeded towards the 
 mouth. But in rare cases I saw the movement commence 
 somewhere in the course of the row of plates. 
 
 The difference between the results of experiments on Beroe 
 and those on Medusae shows that in the latter the localisation 
 of nervous action has proceeded further than in the former, a 
 conclusion with which my histological observations are in 
 perfect harmony. In Beroe the total body-surface is in a 
 still higher degree to be regarded as the brain, the accumu- 
 lation of ganglion-cells in the sensory-pole in Beroe is more 
 gradual and less distinctly defined than in the marginal bodies 
 of Medusae. In the latter I was able to stop all movement by 
 pricking with a needle any one of the eight nerve-centres, in 
 Beroe this is not possible. In Beroe separated portions soon 
 begin to move again, in Aurelia aurita it was first necessary that 
 a vicarious nerve-centre should be formed from cells which had 
 either lost or almost lost the function of central nerve-cells. 
 Hence motion reappeared in Aurelia rarely, and always in a 
 manner which exhibited most clearly the clumsiness of the 
 action of the apparatus at first. In Beroe, on the contrary, 
 
VII EXPERIMENTS ON BEROE 359 
 
 the independent activity of the pieces followed very quickly 
 and from the first with greater certainty. Beroii shows 
 therefore, with respect to the nervous system, a much more 
 embryonic condition than the Medusa investigated. 
 
 Experiment B. — I cut through one of tlie rows of plates of 
 a Beroe and the subjacent tissue, with a pair of scissors, at a 
 point about 2 cm. below the aboral pole, at the level of ./; in 
 Fig. 4. The movement of the plates ceased for a moment in 
 the whole animal. Then the movement recommenced first 
 in the uninjured rows of plates, next in the upper portion of 
 the divided row, a, and lastly in the lower portion of the same, 
 t. After it was re-established everywhere, it appeared that the 
 motion in the two portions of the row operated upon, above 
 and below the cut, went on independently. Both in a and h 
 it was rapid, in h it could even attain greater rapidity than 
 in a. In both portions the direction of the motion was 
 towards the mouth, and the movement consisted in the same 
 rapid succession of waves as in the uninjured animal. The 
 fact that the waves in the two sections were independent was 
 established not only by mere observation, but more certainly 
 by the following experiment : wdien I lightly touched the 
 upper portion with a needle the movement ceased in it for a 
 moment, while in h it went on as before — and similarly the 
 movement could be stopped in the low^er portion wdiile it 
 continued in the upper. Immediately after the operation, the 
 waves in a proceeded from the aboral pole to the incision, 
 while in I waves quite independent of these in a began at the 
 incision and passed towards the mouth ; but eight hours after- 
 wards it appeared to the eye as if the connection between a 
 and h was re-established, as if continuous Avaves beginning at 
 the aboral pole were propagated through a across the incision 
 to h and then to the mouth. It was found, however, when I 
 was touched with a needle that the movement in this portion 
 was interrupted, but not in a. Thus a certain degree of 
 
360 ORGANIC GROWTH sec. 
 
 independence in the activity of the two portions still existed. 
 On the other hand, if I touched a in the same wav, the 
 movement was no longer interrupted in this portion only, but 
 in botli a and h. It follows that the connection was almost 
 completely re-established. Three hours before it had still been 
 possible to interrupt the movement in a alone by a touch. 
 
 Towards evening I divided the other seven rows of 
 swimming-plates as well, by making a shallow circular cut 
 round the whole body, from the cut already made. The 
 movement of the plates thereupon ceased all over the animal, 
 but recommenced very soon on the row previously operated 
 on, and after some time on the oral segments of all the rows, 
 last of all on the oral portions of the rows — but in these it 
 was irregular and not very vigorous. 
 
 On the following day at 10 A.M. I found all the plates of 
 the animal operated on in active motion. But a complete 
 connection between the oral and aboral portions of the 
 rows was not everywhere established. In four of the rows 
 the waves seemed to be continued from one portion into the 
 other, they were propagated apparently continuously across 
 the cut ; but in the other four they evidently originated in 
 each portion independently, only occasionally they had in two 
 of these the appearance of continuity — however, in the latter 
 it was still possible to interrupt the movement in the lower 
 portions while it continued in the upper, but the converse 
 was not possible. 
 
 Experiment B I have made with different variations on 
 numerous other Beroes, and with results essentially the same: 
 gradual recovery of the movement and of its continuity in the 
 several rows always took place, until the movement went on 
 in the animal after the operation in the same way as before. 
 
 But the following phenomenon also was repeatedly ob- 
 served : when a circular cut was made in a Beroe in the 
 manner above described some centimetres below the aboral 
 
VII EXPERIMENTS ON BE ROE 361 
 
 pole, and after the movements had again become regular and 
 vigorous in both the oral and aboral portions of the rows, but 
 before their connection in the two portions was completely 
 restored, the animal was completely divided into two parts 
 by deepening the cut already made, then the movement in 
 the two parts immediately after the complete separation went 
 on exactly as it had before the separation. In such a case 
 the larger tube-shaped oral portion of the animal swam away 
 exactly as if it were an entire uninjured animal, just as a 
 branch of an oleander tree, which has been made to send 
 forth roots while still attached to the stem by being sur- 
 rounded at a particular spot with earth contained in a pot, 
 goes on growing independently when it is separated from the 
 mother-plant by a cut below the roots. 
 
 Thus, while the movements of the swimming -plates is 
 stopj)ed for a time by dividing a Beroe into two parts or 
 into several, and usually also by merely making a superficial 
 cut in the animal, yet when the separation is preceded by the 
 preliminary operation above described, it may be completed 
 without producing any effect on the divided portions. This 
 proves that the two portions acted quite independently before 
 the complete separation, and that the reappearance of the 
 continuity of the movement of the plates must be the con- 
 sequence of a subsequent concrescence, or must be caused by 
 the establishment of new nervous paths which take the place 
 of the old. 
 
 Facts are also known which prove the vicarious action of 
 nerve-fibres in Vertebrata, for example, in the results which 
 follow from alternate section of the two halves of the spinal 
 cord. 
 
 The facts above brought forward not only show liow 
 rapidly during individual life parts of the organism can be- 
 come adapted to special functions ; they enable us also to 
 
362 ORGANIC GROWTH sec. 
 
 understand how in course of time such functions have 
 become localised, and have modified the structure of the parts 
 devoted to them more and more, as each generation inherited 
 the alteration produced in its predecessor. 
 
 I will now add some further arguments concerning this ques- 
 tion, derived from a subject to wliich I have already referred. 
 
 The Acquisition and Inheritance of Peculiarities of 
 Voice and Speech, and the Speech of Animals 
 
 I have already opposed Weismann's argument against the 
 inheritance of acquired characters, which depends on the 
 assertion that neither the faculty of speaking nor of reading 
 is inherited. 
 
 In one of his latest wTitings ^ he says : " When we ade- 
 quately realise how energetically and how uninterruptedly 
 we practise speaking throughout our whole lives, w^hether Ave 
 are speaking aloud, or thinking silently to ourselves, and 
 when we consider that in spite of this continual practice 
 which has been performed by all human brains and vocal 
 organs for centuries, the faculty of speech has not in the least 
 degree become established as a hereditary character, we shall 
 be inclined ever afterwards strongly to doubt that any 
 acquired characters in the true sense of the word can ever be 
 inherited." 
 
 I have already remarked that we ought not to expect the 
 faculty of speech, or of reading, to be inherited, because these 
 are very complex accomplishments, not simple faculties of 
 the organism, which alone we bring with us into the world 
 at birth. 
 
 Apart from the fact that the development of human speech 
 dates from a period geologically recent, we cannot argue about 
 its heredity from the length of time which has passed since 
 
 ^ TJeber den Rilckschritt in der Natur (Retrogression in Nature). 
 
VII INHERITED PRONUNCIATION 363 
 
 its origin, because it has not been constantly the same from 
 its beginning. Thus our living languages are only about 
 two thousand years old, and even in this time have been 
 modified. It is surely enough, as I before insisted, that we 
 have acquired and inherited the faculty of perceiving tones, 
 and producing sounds of various pitch. The rest depends on 
 conventions and practice of comparatively short duration. 
 
 It is certainly impossible to contest that the faculty of 
 producing particular vocal sounds has evidently become 
 hereditary in the members of different nations. While I was 
 writing the preceding during a sojourn on the island of 
 Spiekeroog, an Italian organ-grinder came before the window 
 of my room and ground out his shrill tunes. I asked him 
 where he was going to-day. To " Orik," said he. I knew no 
 such town. At last I found from his residence-permit that 
 he meant the town of Aurich on the mainland. I en- 
 deavoured in vain to make him pronounce the name cor- 
 rectly. " Orik " he continued to repeat ; it was perfectly im- 
 possible for him to pronounce the "au" and " ch." It may 
 be objected, that in this case it was simply want of practice ; 
 that if the Italian practised for some years he would certainly 
 at last be able to pronounce the word " Aurich " quite cor- 
 rectly, and the children of Italian parents would certainly 
 have no difficulty if they were brought up in Germany. 
 Granted, but not unconditionally. A trace of the tendency 
 to speak in the Italian manner would probably remain even 
 in the latter case.^ How is it to be explained that the Jews, 
 wherever they are found in Germany or elsewhere, pronounce 
 
 ^ In consequence of the efforts of the German Scholastic Association young 
 people of German race, Cimbrians and Goths, but speaking only the Italian lan- 
 guage, are frequently brought from South TjtoI to Germany in order that they 
 may learn German. It has been noticed in such people that "the structure of 
 their vocal organs being of the Germanic type, they learn High German with 
 peculiar facility." Cf. Filnfter Jahreshericht des Frankfurter Vereins zur Unier- 
 stiitzung deutscher Schulen im Amlande, 1887. An accurate investigation of 
 such cases would be of great value. 
 
364 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 certain sounds of the German or other native lanouaoe in a 
 peculiar manner, even when they are scattered in small 
 numbers among a population of German or other nationality, 
 unless we attribute it to peculiarities of the larynx, of its 
 muscles and nerves, that is, of the powers of movement in 
 the organ ? The native pronunciation must as undoubtedly 
 depend on the congenital structure of the larynx as, con- 
 versely, an artificially acquired pronunciation must in time 
 have an influence on that structure. We can most easily 
 form a judgment in this matter when we consider the dialects 
 of our native language, because here we are able to appre- 
 ciate the slightest variations. What variety we find in the 
 pronunciation of the German " ch," from the harsh throat- 
 sound of the Alemannic people in Switzerland and Upper 
 Baden to its complete conversion into " sch " which frequently 
 occurs among people of Prankish race ! I have special per- 
 sonal grounds for the conclusion that the faculty of producing 
 the Alemannic throat-sound is inherited, that it depends on 
 peculiarities of the larynx. But as we know almost every 
 village has its dialectic characteristics, and these evidently 
 depend in many cases on peculiarities of voice. The strangest 
 and ugliest peculiarities of voice and speech that can be found 
 among Germans are those of the inhabitants of the rural 
 part of the town of Tubingen : in their speech the shrillest 
 falsetto alternates with the harshest bass in all possible 
 transitions, which it is impossible for an ordinary German to 
 imitate. It seems as though the vocal muscles of these people 
 had been by the most laborious practice so distorted as to 
 pronounce the simplest sounds of speech in a perverted and 
 barbarous way. Any one who doubts that this is due to 
 peculiar anatomical and physiological relations of the vocal 
 organs — although the variations may be too minute to be 
 demonstrated — must believe it possible to produce with a 
 fiddle the tones of a brass instrument out of tune. And there 
 
VII INHERITED PRONUNCIATION 365 
 
 can also be no doubt that this pronunciation, which occurs 
 only among a limited population, and moreover only in one 
 part of a single town, has been inherited. It seems to me 
 that such a peculiar pronunciation could only have been 
 developed in one of two ways : either some man possessed it 
 accidentally in consequence of laryngeal peculiarities, and 
 transmitted it to his descendants ; or some influential per- 
 sonages introduced it by a deliberate perversion of pronuncia- 
 tion, and others imitated them, and thereby the larynx 
 gradually acquired peculiar characters, which in course of 
 time were more strongly developed and inherited. These are 
 probably the two ways in which dialects in general and ulti- 
 mately languages have arisen.-^ 
 
 My conclusions concerning this subject are strongly sup- 
 ported by the facts presented by the voice and speech of 
 
 ^ It is certain that the accurate investigation of the order in which sounds 
 appear in children, of the development of the powers of pronunciation and of 
 forming words, such as Professor Preyer carried out on his own children (cf. Die 
 Seele der Kinder), might throw a great deal of light on this subject if it were 
 applied to the most various nations. We might by its means discover the primi- 
 tive sounds which formed the basis of subsequent evolution. It has struck me 
 that many children use the sound " eng " at a very early age to express any feel- 
 ing or the desire for anything. In the latter case it is often very vigorously 
 uttered, the head, arms, and hands being at the same time stretched out in 
 sudden jerks towards the desired object. Idiots sometimes have recourse to the 
 same sound all their lives. I have a remembrance dating from my early youth 
 of such a man in a village, who was for this reason nick-named " Eng-eng." Pos- 
 sibly there is a profound connection between these phenomena and the fact that 
 the anthropomorphous apes of Africa have the same or similar names in their 
 native habitat. The gorilla is called "engena" or "ingjina," the chimpanzee 
 " engesego " or " ingjisego." On the speech of children compare also K. Vierordt, 
 Deutsche Revue, Bd. iii. p. 29. Herodotus (ii. 2) relates that the Egyptian king 
 Psammetich (670-616) endeavoured to discover which was the most ancient of all 
 nations and languages in the following way : He gave two new-born children to 
 one of his shepherds to be brought up without hearing any sound of human 
 speech. They were to lie in an isolated hut, and the shepherd was to take she- 
 goats to them at proper intervals that they might suck milk. After two years 
 the children came to the shepherd with outstretched hands and cried " Bekos " 
 (evidently an imitation of the bleating of the goats). As that was the Phrygian 
 word for bread the Egyptians concluded that the Phrygians were older than they. 
 A similar experiment was made by the Emperor Frederick II, but the children 
 under trial died too soon ( Vide Kaumer, Geschichte der Hohenstau/en). 
 
366 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 birds. That the peculiarly-constructed larynx of a singing- 
 bird must owe its peculiarities and capabilities entirely to 
 acquirement and inheritance, scarcely any one can doubt. In 
 these animals the faculty of singing is actually hereditary: it 
 is a fact that song-birds kept in captivity, even when they 
 have had no opportunity of imitating old birds, begin to sing, 
 and learn, though but imperfectly, to sing like their ancestors. 
 We may therefore expect that speech in animals, when it is 
 very simple, when it consists of only a limited number of 
 sounds and sound-combinations, will be inherited more com- 
 pletely than in ourselves. Hitherto so little attention has 
 been paid to these matters that even at the present day some 
 zoologists and zoological text- books still regard not only 
 reason but articulate speech also as exclusive possessions of 
 the human race. What knowledge have we of the speech of 
 animals to justify us in maintaining such a general distinc- 
 tion ? It is certain that the language of many birds possesses 
 a copious vocabulary, and among these are some of compara- 
 tively little intelligence, for instance, our domestic fowls. These 
 creatures converse with one another with their hoarse voices 
 often for hours together, as do also, among others, the 
 swallows by their twitterings. Although these conversations 
 are to us unintelligible, it is not extremely difficult gradually 
 to learn something of the language of fowls and other birds, 
 to understand their expressions of surprise and alarm, of 
 pleasure, invitation, and warning. After much careful study 
 it seems to me that such modes of expression are universal 
 among fowls, and that they are hereditary, for one finds them 
 used in the same way by individuals from the most various 
 districts, and even when chickens are taken from the fowl- 
 house when quite young they develop the same language. 
 In this case it is the same as in that of instinct : the simpler 
 the language, the fewer the definite requirements which the 
 powers of vocal expression have to satisfy, so much the more 
 
VII LANGUAGE OF BIRDS 367 
 
 completely are they inherited — so much the less variable is 
 the mechanism of the vocal organs which is developed. 
 
 Nevertheless, the languages of animals have their dialects, 
 possibly even that of the same species differs in different 
 regions. Any one who has passed sleepless nights in Naples 
 in the oppressive heat of August, will have discovered that 
 the crowing of the cocks there is different from that of ours 
 at home : they shriek in the most unmelodious fashion with 
 a force which goes to one's marrow. Possibly the creatures 
 have developed their great power of voice in order to make 
 themselves heard above the noise of the streets, and the 
 peculiarity has been gradually confirmed by heredity in 
 course of time. 
 
 In our gardens the blackbirds give warning to all other 
 birds when a cat makes its appearance. As soon as one of 
 these beasts of prey shows itself they follow it from branch 
 to branch, uttering the cry "dag, dag, dag," in rapid suc- 
 cession, the greater their alarm the quicker the tempo. Then 
 the smaller birds come and join them with a confusion of 
 anxious cries. At evening, when twilight comes on, the 
 blackbirds utter the same cry for a time, but then it is not a 
 warning cry, and the other birds do not so interpret it. At 
 this time the blackbirds fly about as though quarrelling, 
 scolding, and pursuing one another before they go to sleep. 
 The meaning of this behaviour I have not been able to dis- 
 cover. When the blackbirds first see anything which makes 
 them anxious — as when they first catch sight of a cat — they 
 utter once only, flying from one place to another, a short 
 succession of sounds which, as far as I remember, is something 
 like " diridiridiridirollo." Now, I have noticed that the black- 
 birds of different districts, for instance those of the mountains 
 at certain places where I listened to them, in comparison 
 with those of Tubingen, present in these cries very con- 
 siderable, even surprising differences. Local variation of the 
 
368 ORGANIC GROWTH sec. 
 
 note is also known to occur in the chaffinch (Fringilla 
 ccelebs) and in the nightingale (Luscinia Philomela). 
 
 I have made the latter remarks chiefly \yith the object of 
 recommending the study of a subject, which although it 
 ought to supply science with some remarkable facts, has 
 hitherto received very little attention from zoologists. 
 
 G. Jager ^ says with reference to this subject, " By means 
 of looks, gestures, and sounds animals speak a very plain 
 language, and it requires only a somewhat persevering 
 attention to learn this language. . . . Tliis sound and 
 gesture - language reveals to us completely the feelings of 
 animals, and their desires sufficiently disclose to us their 
 intellectual powers. The sound - language which most 
 mammals and birds, and some reptiles, fishes, and insects 
 possess, consists of cries expressing feelings, like the utter- 
 ances of a child in its earliest years ; these cries are more or 
 less prolonged tones, i.e. vowels, or noises, i.e. consonants, 
 which are uttered once or several times in succession, while 
 human words are combinations of tones and noises arranged 
 according to definite laws, articulate. The interjections of 
 our word-language are the most closely related to the cries of 
 sensation of animals, for the former are in fact nothing but 
 cries of sensation scattered among our vocabulary of words. 
 The cries of animals, however, have not merely the value of 
 interjections, they are something more. Thus the animal 
 can express several sensations by modification of its 
 voice, by modulation of its tones. Thereby animals are 
 able to communicate their sensations and condition even 
 during the night when they cannot see each other's 
 gestures." 
 
 On the language of monkeys I find some remarks by J. von 
 Fischer,^ who quotes the above passage from Jiiger. He says 
 
 ^ Zoologischer Garten, Bd. iii. p. 268, 1861. 
 ^ Zoologischer Garten, Bd. xxiv. p. 294, et seq. 1883. 
 
 I 
 
VII LANGUAGE OF MONKEYS 369 
 
 concerning Macacus eiythrtens, s. Ehesus, as follows : " In 
 fact, one learns to nnderstand the language of animals in a 
 very short time. I understood the sound-language of each of 
 my monkeys, and knew exactly thereby the state of its feelings 
 at any particular time. As the requirements of the life of 
 animals are much simpler and less variable than ours, so is 
 their sound-language much more limited. But the homely 
 peasant speaks a language much poorer in words than that 
 of the cultivated member of town society. The vocal 
 expressions of the Ehesus were very simple, and consisted of 
 vowels, so that they most resembled the interjections of 
 human speech, although they had not exclusively the signifi- 
 cance of the latter. The utterance at different times varied 
 much in pitch, in force, and in quality, according to the 
 feelings of the animal, so that the monkeys were well provided 
 with means of expressing the temporary condition of their 
 emotions." 
 
 The Ehesus expressed his feelings partly by voice and 
 partly by facial expression. When he desired a thing, he 
 cried " oh," or " o-oh," in the latter case the second syllable 
 beino' hioiier than the first. At the same time he laid his 
 ears close to his head, drew back his brows, and pointed his 
 lips. Joy and pleasure he expressed by a grunting or 
 guro'liiiQ; throat -sound, which sounded like a hoarse "iili." 
 At the same time he laid back his ears for a short time, drew 
 back all the skin of his head for a moment with a jerk, his 
 eyebrows being thus also drawn back, and stretched out his 
 mouth with the lips narrowed. In extreme pleasurable 
 excitement, when he laughed, he disclosed his teeth as far 
 back as the middle of the molar series, and uttered a slight 
 tittering sound like " kikiki," and so on. 
 
 Valuable results w^ould certainly be obtained if students of 
 language would take up this subject, and would endeavour to 
 investigate what I think ought to be recognised as the speech of 
 
 o 
 
 2 B 
 
370 ORGANIC GROWTH sec. 
 
 animals. One of them, Schleicher/ remarks : " Speech, that 
 is, the expression of thoughts by words, is the only character 
 exclusively peculiar to man "; in support of which conclusion 
 he appeals to Huxley's well-known essay " Man's Place in 
 Nature," in which that investigator comes to the conclusion 
 that speech alone separates man from the anthropoid apes 
 most nearly related to him. 
 
 But even though these anthropoid apes have really no 
 power of speech, it does not follow that the faculty is not 
 possessed by other animals. 
 
 Let us learn of those who study language what speech 
 consists in. 
 
 Schleicher says on this point : " Sound-gestures, in some 
 cases highly -developed sound-gestures, for the direct ex- 
 pression of its feelings and desires, the animal possesses, and 
 by means of these, as by means of other gestures, animals are 
 able to communicate their feelings to one another. Accord- 
 ingly it is usual to talk of the speech of animals. But the 
 faculty of directly expressing thought by means of sound is 
 possessed by no animal, and this alone is the meaning of 
 speech. How fully this is in fact recognised in our ordinary 
 consciousness is shown by the consideration that an ape 
 endowed with speech, or even an animal utterly different 
 from man externally, if it possessed the power of speech, 
 would be regarded by us as a man." 
 
 The zoologist and the anatomist, be it remarked by the 
 way, would leave the attitude of mind described in the last 
 sentence to the philologist, and likewise the subsequently- 
 expressed conclusion that microcephalous idiots are not to be 
 regarded as really human, because in these speech, and even 
 the capacity for it, is wanting. 
 
 But apart from this, if the definition which Schleicher 
 
 ^ A. Sclileiclier, Vehcr die Bedeutung der Sprache fur die Naturgeschichte 
 des Menschen, Weimar, 1865. 
 
VII EVOLUTION OF ARTICULATE SPEECH 371 
 
 gives of speech is correct, then animals speak ; for, as is shown 
 by the instances I have given, and as the simple observation 
 of nature teaches, many of them indisputably possess " the 
 faculty of directly exchanging their thoughts by means of 
 sound." 
 
 I go even farther, and maintain that even what is called 
 " articulate " speech does not constitute a distinction between 
 man and the lower animals. And in this the remarks of 
 Schleicher himself aftbrd me assistance. For in the same 
 short paper he says : " Scientific investigation proves clearly 
 that speech is something which has been quite gradually 
 developed, something which once did not exist. The com- 
 parative anatomy of languages discloses that the more highly 
 organised languages have been evolved quite gradually from 
 simpler languages, probably in the course of very long periods 
 of time : at least the science of language finds nothing to 
 contradict the conclusion that the simplest modes of express- 
 ing thought by sound, the languages of simplest structure, 
 have gradually been derived from sound-gestures and imita- 
 tions of sounds such as animals employ. . . . But if speech 
 alone makes the man, then our primitive ancestors were not 
 at the beginning what we now call men, for they only 
 became men with the development of sj^eech. But the 
 development of speech is for us equivalent to the evolution 
 of the brain and the vocal organs. Thus the results of the 
 science of language lead necessarily to the conclusion that 
 man has been gradually evolved from lower forms, a con- 
 clusion at which the natural science of the present day is 
 known to have arrived from other premises. For this reason 
 alone the investigation of speech is of great scientific import- 
 ance, especially in relation to the evolution of man. . . . 
 Those lauCTuages wdiich have hitherto been analysed into 
 their simplest elements, and those wdiich have remained at 
 the simplest stage of evolution, show that the oldest forms of 
 
372 ORGANIC GROWTH sec. 
 
 all languages were essentially the same. The oldest sounds of 
 which languages consist are those which express perceptions 
 and ideas. Expressions of relation (distinction of parts of 
 speech, declension, conjugation), are at this stage wanting; 
 all this is a later development, to which many languages 
 have not attained, and which the others exhibit in different 
 degrees of perfection. Thus, to indicate one example in 
 Chinese at the present day, there is no distinction in sound 
 between the parts of speech ; true verbs, as distinguished 
 from nouns, among all the languages I have studied, I have 
 found only in the Indogermanic. Morphologically, but only 
 morphologically, according to our results, all languages are 
 originally essentially similar ; but on the other hand, even 
 these primitive languages must have been different in sounds, 
 as well as in the ideas and perceptions which were reflected 
 in the sounds, and must have further differed in their capa- 
 city for evolution. For it is positively impossible to derive 
 all languages from one and the same primitive form." 
 
 In his earlier and more widely-known work, in which he 
 explains the origin of language on Darwinian principles,^ 
 Schleicher gives an example in support of these views. He 
 says there : " The oldest form of the words which now in 
 German appear as That, getlian, thun, Thdter, was at the 
 time when the original Indogermanic language arose, dim, 
 for this syllable dha ... is found to be the common root of 
 all these words. At a somewhat later stage of development, 
 in order to express definite relations, the roots which then 
 performed the part of words were pronounced twice and 
 another word, another root was added on to them ; but each of 
 these elements was still independent. For instance, in order 
 to indicate the first person of the present tense, the speaker 
 said dha dha ma, from which, at a subsequent period in the 
 
 ^ A. Schleicher, Die Darwin' sche Tkeoi'ieunddie Sjjrachvjissenscha/t, Weimar, 
 1863. 
 
VII REDUPLICATION OF SOUNDS 373 
 
 history of the language, by fusion of the elements together, 
 and by virtue of the tendency to alteration in the roots, was 
 produced dhaclhdmi (in Sanskrit dddhd7ni, Old Bactrian 
 dadhdmi, Greek rlOrjfjLc, Old High German torn, Uiom for 
 titomi, modern High German, time)." 
 
 I think the above completely justifies me in speaking of 
 tlie sounds uttered by blackbirds as their language. " Dag, 
 dag, dag," is as good a sound as " dim, dha, dha," not distin- 
 guished from the latter as an " imitative sound " or a " sound- 
 gesture." We may conclude that it means in general, " Take 
 care ! Danger ! " but with a special tone and in a certain suc- 
 cession it probably means distinctly " Cats ! " — uttered in 
 another way, perhaps " Owl ! " or " Crow ! " and in any case the 
 variation of the same "word" which the blackbirds utter 
 every evening has a meaning quite different, for then the 
 other birds take no notice of the cry. 
 
 Thus, just as in the lower stages of human speech, the 
 development, the complexity of language in birds evidently 
 just proceeds from the repetition of sounds. By different 
 modes of repetition and by differences of tone in addition a 
 variety of things can be expressed. But in the language of 
 blackbirds, as in the higher stage of evolution of human lan- 
 guage, the further step has been taken of adding another 
 sound at the end of a repetition, in the cry, " diridiridirirollo." 
 Thus all the elements necessary to the development of the 
 most perfect language are present. The drum-language of the 
 negroes of the Cameroons shows how much can be said 
 merely by variations in the repetition and in the loudness of 
 a single tone, which is less than an uttered sound. Thus 
 flexibility of speech is not always so complete a criterion of 
 mental capacity as we are accustomed to assume without 
 further reflection. The want of flexible speech is wanting in 
 the anthropomorphous apes, not because their brains are too 
 lowly organised, but because their laryngeal mechanisms are 
 
374 ORGANIC GROWTH sec. 
 
 not sufficiently delicate. It is true of co\irse that the develop- 
 ment of speech causes modifications in the brain and nervous 
 system, but primarily only such modifications as relate directly 
 to speech, and only at a later time those which are connected 
 with tlie higher mental development made possible by speech. 
 If not only is our higlily-evolved language derived from a 
 simple sound-language, but there are at the present day 
 tribes who have never advanced beyond the latter stage, then 
 no fundamental distinction exists between the language 
 formed by the voices of animals and human speech. It 
 depends, as I have said, merely on the structure of the larynx 
 that the animals most nearly related to man have no well- 
 developed vocal language. Such animals contrive to make 
 themselves understood in other ways ; the apes convey a great 
 deal of meaning by facial expression, while insects, e.rj. the 
 Hymenoptera, especially the ants, have evidently a highly- 
 evolved means of communication in the tactile language of 
 their antennae. 
 
 But if the development of speech depends on the structure 
 of the larynx, w^e ought to be able to point out evident ana- 
 tomical differences in this organ even among different races of 
 men. This objection I have often heard expressed by 
 eminent philologists, with the addition, " But nothing of 
 the kind has ever been found ; " Avhence it was then concluded 
 that the structure of the larynx has nothing to do with the 
 origin of dialects or with the evolution of language. It is 
 quite true that nothing of the kind has been found ; but to 
 anatomists and physiologists such a discovery is not neces- 
 sary to enable them to ascribe the modifications of language 
 essentially to anatomical causes, in other w^ords, to the 
 acquisition and inheritance of anatomical and physiological 
 peculiarities depending on habitual use. Schleicher takes 
 exactly the same view of this question as myself, and in 
 quoting his words I am brought back to a subject already 
 
VII ACQUISITION OF FOREIGN LANGUAGES 375 
 
 discussed, the learning of foreign languages, my view on 
 which is further developed by Schleicher. On the latter sub- 
 ject he says : ^ "If language really depends on particular 
 adjustments in the brain and vocal organs, how is a man able 
 to acquire any other or even several other languages besides 
 his own ? To which I might . . . answer that a man can 
 learn to walk on all fours, or even on the hands alone, and 
 yet no one will doubt that our natural mode of progression 
 is determined by our bodily structure, and is the expression 
 of that structure. But let us examine into the objection 
 more minutely. The first question to be asked is. Whether a 
 foreign language is ever perfectly acquired and appropriated ? 
 I doubt this, and at most will only admit it to be possible 
 when a man exchanges his native language for another in 
 early childhood." In that case, however, the person in ques- 
 tion would be a different person, for his brain and vocal 
 organs would develop in another direction. It is furtlier to 
 be considered, in talking of the acquisition of European lan- 
 guages, that all the Indogermanic languages belong to the 
 same family, and, regarded broadly, are species of the same 
 lanouao'e. " But show me the man who thinks and speaks 
 with perfectly equal facility in German and Chinese, or in 
 the New Zealand and Cherokese tongue, or in Arabian and 
 Hottentot, or in any other two languages differing in tlieir 
 fundamental constitution. I do not believe such a man 
 exists, any more than I believe that any individual will ever 
 be able to walk with equal agility and comfort on all fours 
 and on his two feet. It is often even impossible to us to pro- 
 nounce sounds peculiar to foreign languages, or even to distin- 
 guish these with our ears correctly and exactly." He con- 
 cludes, therefore, that a given vocal organ, like every otlier 
 kind of organ, has a definite function, which is, and remains, 
 always natural to it. 
 
 1 TJeler die Bedeutung der Sjirache, etc. 
 
376 ORGANIC GROWTH sec. 
 
 The postulate from which Schleicher derives these con- 
 clusions is the belief : " That the activity, the function of an 
 organ is, so to speak, only one of the qualities of the organ 
 itself, although it is not always possible to the scalpel and 
 the microscope of the investigator to exhibit the material 
 causes of that quality." As with gait, so it is with speech. 
 Speech is the symptom, perceived by the ear, of a complex of 
 material relations in the structure of the brain and vocal 
 organs, with their nerves, bones, muscles, etc. Lorenz 
 Drefenbach had already expressed the same ideas : " The 
 material basis of language and its varieties has not yet been 
 anatomically demonstrated, but to my knowledge a compara- 
 tive investigation of the vocal organs of people speaking 
 different languages has never yet been undertaken. It is 
 possible, even probable, that such an investigation would lead 
 to no satisfactory results ; nevertheless, this would by no 
 means be enough to destroy the conviction of the existence of 
 material conditions of language in the structure of the body. 
 For who would deny the existence of such conditions, although 
 they are still concealed from direct perception, and possibly 
 can never be made the object of direct observation ? " The 
 results of infinitesimal quantities and relations are, he con- 
 tinues, in some cases wonderfully striking ; as, for example, in 
 the phenomena of the spectrum, of colour and smell in 
 plants, and so on. As light is to the sun, so is sound to 
 speech ; as in the former the character of the light is evidence 
 of a material condition, so in the latter the character of the 
 sound. 
 
 With these arguments of the philologist I fully agree, and 
 here repeat the proposition which forms the subject of the whole 
 of the present section, and emijraces that of the preceding : 
 That functional activity — exercise — universally precedes and 
 determines the higher evolution of organs. The larynx of our 
 ancestors was at first quite incapable of j^roducing language 
 
VII DIRECT AND INDIRECT STIMULATION 377 
 
 — as it was exercised in the production of various kinds of 
 sounds, it produced them more and more perfectly, and 
 its capabilities were gradually improved. These capabilities 
 therefore are acquired, they were transmitted from one gene- 
 ration to another ; but as they were developed ever greater 
 changes must have taken place in the powers of contraction 
 of the muscles and the efficiency of the nerves of the organ, 
 and above all in the vocal chords. These chancres, on account 
 of the great delicacy of the mechanism, were able to produce 
 great effects, although they are not anatomically demonstrable 
 — any more than the special structure of the fingers which 
 helps to determine a peculiar handwriting can be exhibited 
 by dissection. Accidental variations of the vocal chords 
 under the action of selection may have promoted the progress 
 of the evolution. 
 
 Concluding Eemarks. 
 
 In the second section I gave reasons for the conclusion 
 that the external stimuli which act directly upon the pro- 
 toplasm are the primary causes of the manifold variety among 
 organic forms. On the other hand, as I there explained, I 
 regard the influences of use, of functional activity, which have 
 been discussed in the last and preceding sections, as the 
 indirect or secondary causes of growth and of the modifica- 
 tion of structure. As the direct influence of stimulation, 
 which I have previously named "impression," promotes 
 growth, so also does exercise, which modifies the protoplasm 
 and, by producing an increased inflow of the nutritive fluids, 
 adds to its bulk. 
 
 But in many cases the effects of direct and indirect stimu- 
 lation cannot be separated. When a stimulus acts constantly 
 in a certain way upon the protoplasm, the latter is exercised 
 in a corresponding manner, and is thereby modified. In fact, 
 when we speak of use as the cause of growth or of the modi- 
 
378 ORGANIC GROWTH sec. vii 
 
 fication of structure, we mean spontaneous use, the active 
 motion of the organism ; and the influence of exercise in 
 causing growth is therefore principally observed in animals. 
 But when subsequently we consider for a short time the 
 causes of modification in the vegetable kingdom, we shall see 
 clearly how impossible it often is to separate the direct effects 
 of external stimuli from those of exercise, how the two 
 frequently coincide. And from a physical point of view this 
 requires no explanation. 
 
 It is, however, a necessary consequence of my conception 
 of frrowth that I should re^jard the effects of indirect stimula- 
 tion of the living- substance also as orowth. 
 
SECTION VIII 
 
 the idea of oeganic growth — the law of organic 
 
 form — recrescence 
 
 The Idea of Organic Growth 
 
 We have to distinguish from one another («) individual 
 (personal) growth, (h) the growth of the race (the species) or 
 phyletic growth. The latter is, however, merely the sum of 
 the modifications due to growth which the individuals of a 
 line of descent have undergone in course of time, by which 
 modifications, together with the separation between it and its 
 allies, the species is constituted. Usually personal (individual) 
 organic growth means the regular changes which take place 
 in a given organism under external influences (food, warmth, 
 light, gravity, etc.), and which are connected with an increase 
 in size ; for we assume that this growth depends on the 
 multiplication of the particles of the body, and accordingly 
 the assimilation of nutritive material enters largely into our 
 idea of the process. 
 
 On the other hand, by organic growth I mean every 
 physiological change of structure which is naturally produced 
 in a given organism by external influences or by constitutional 
 causes, which is not morbid and not accidental, and which is 
 permanent, or only temporary because it j^recedes a further 
 stage of modification. 
 
380 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 Growth, therefore, does not necessarily produce visible 
 alterations — the changes which precede an increase in size 
 are growth, and so are alterations in the position of particles 
 (molecules) which produce no increase in size ; such a change 
 of position may only cause an alteration in the form of the 
 body, but it may even produce a diminution in size. 
 
 Growth is by no means necessarily the result of the 
 assimilation of food : the action of any external stimuli is 
 capable of causing changes in the position of the particles 
 of the body, and thereby of causing growth in my sense of 
 the term. The idea includes every inheritable alteration 
 either of material or form in the organism, or (as underlying 
 these) every alteration of the interaction of forces in the 
 organism ; and therefore the result produced by stimuli 
 influencing the protoplasm indirectly is growth. Therefore, 
 also, even diminution in size and degeneration is grow^th. 
 Thus plants and animals grow to a smaller size in the north 
 and on mountains than in the south and in valleys, and the 
 exclusive influence of one condition, abundance of food, leads 
 to the degenerate processes of growth which parasitic forms 
 exhibit in organs related to other conditions. 
 
 Thus two things are necessary to produce growth (1) the 
 given composition of the organism ; (2) the action of stimuli 
 (food being considered as a stimulus). It was in reference to 
 the former that I described in previous works some of the 
 causes of the modification of forms as " internal " or " consti- 
 tutional causes." 
 
 Since living Ijeings differ from one another in the composi- 
 tion of their bodies, so stimuli act differently upon them, 
 produce in some changes different from those they produce in 
 others : they grow in different w^ays. 
 
 The constitution of the body, which has so important an 
 influence in determining the course of growth in an organism, 
 is to a very great extent the result of the inheritance of 
 
VIII INDIVIDUAL GROWTH 381 
 
 characters from ancestors ; to a small extent it is due to 
 acquirement, i.e, modification, during individual life, or is the 
 consequence of the mingling of the characters of the parents. 
 This latter small element in the constitution of the body is 
 the cause of individual variation; but it is of the greatest 
 importance, because on it depends essentially the continuous 
 modification of forms. 
 
 If the individual growth of the organism is, as according to 
 the preceding we may briefly express it, in the last result 
 nothing but the effect of external stimuli (including food) upon 
 the tissues, and if we assume that there Avas a primitive 
 organism from which all succeeding living beings have been 
 derived, then the variety of growth which took place in the 
 latter must of necessity have been originally due to the 
 variety of the external influences (stimuli) under various con- 
 ditions. Sexual mixture was not at the beginning in 
 operation. But the peculiarities thus acquired were inherited 
 by the organism in its whole and in its parts, and selection 
 increased them. The greater the number of modifications 
 thus by continued inheritance acquired by a succession of 
 organisms, the greater will be the peculiarity of constitution 
 produced. 
 
 Thus the individual growth of every plant and every 
 animal is a brief and rapid repetition, under the continued 
 influence of similar stimulation, of the series of eftects pro- 
 duced by external stimuli in the course of vast periods of time 
 on the tissues of its ancestors. 
 
 The character of the individual growth of every living 
 being therefore depends essentially on phyletic growth, the 
 individual growth includes phyletic growth in itself For 
 even the peculiarities of constitution of different individuals 
 which are due to inheritance are really a consequence of 
 phyletic growth. 
 
 Since the individual o-rowth of every living being is thus a 
 
382 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 stage of phyletic growth, since the hitter, wherever we con- 
 template it, represents a sum of individual growths, both 
 are traced hack to one and the same process — fundamentally 
 they cannot be separated. 
 
 Phyletic growth, or the evolution of the organic world ever 
 into higher and more complex forms, or at least into forms of 
 dilferent structure, is, as I have said, merely the sum of the 
 processes of growth of the ancestors — together with the 
 result of external influences on the forms during their develop- 
 ment and their existence. This additional modification which 
 the individuals as such undergo is — together with the influence 
 of crossing — the very cause of the constantly progressing 
 evolution. All that the members of a series of individuals 
 directly connected by descent acquire constitutes together 
 the material for the formation of new species. 
 
 Individual growth was described above as a process which 
 according to constant laws forms permanent conditions, or con- 
 ditions which when they are transient constitute stages in the 
 further development in the same direction. The same was 
 previously asserted of phyletic growth ; it forms permanent 
 stages which serve as the basis for further development, and 
 which thus render progression (or retrogression) possible. 
 
 The variety of the external conditions, i.e. of the external 
 stimuli (including food) and of the constitution, together with 
 crossing, necessarily led to variety of growth, to variety of 
 structure, necessarily led to the formation of a variety of 
 species, provided that separation of the continuous chain of 
 forms into separate links took place. 
 
 Thus we can appropriately speak of the organic growth of 
 species. 
 
 The reader should compare the previous propositions with 
 the arguments of Section 11.^ I liave there made special 
 use of the biocjenetic law as evidence that the world of 
 
 1 Pp. 21, 25, 51, etc. 
 
VIII CROSSING AND SELECTION 383 
 
 organisms has grown in course of time out of cells. I 
 described the individual development as an abbreviation of 
 phylogenetic growth. 
 
 Growth, in the sense of continual modification under the 
 influence of stimuli is a fundamental property of protoplasm. 
 
 Since the manifold variety of the forms of the organic 
 ^vorld is due to growth, it is seen to be a necessary consequence 
 of that fundamental property. 
 
 As I have already insisted in a previous passage,^ repro- 
 duction also is a fundamental property of protoplasm, because 
 it is indeed nothing else than continued growth ; and, I have 
 to add, since it essentially consists in the transmission of the 
 properties of one protoplasmic unit (person) to another, it is 
 on this fundamental property of protoplasm that the im- 
 mortality of life depends. 
 
 Crossing and Selection as Indirect Causes of Growth 
 
 Besides growth as the result of the action of stimuli, w^e 
 have to consider in relation to the production of the hetero- 
 o'eneity of the organic world, and as indirect causes thereof, 
 crossing (sexual mixture) and selection. Of these two cross- 
 ing alone is capable of creating anything new, of contributing 
 by its own action to the growth of the organic w^orld. This 
 possibility is due to the fact that by the mingling of two 
 forms a third new form may be produced. But this does not 
 occur to so great a degree nor so commonly as is frequently 
 assumed. ^Nevertheless the influence of crossing in the 
 modification of forms is an important one. Natural selection 
 can, as I have repeatedly remarked, create nothing new. It 
 only so far contributes to the growth of the organic world that 
 it selects the forms which are most fitted for life, and pre- 
 serves them for the future action of new stimuli and of 
 
 1 p. 24. 
 
384 ORGANIC GROWTH sec. 
 
 crossing. Its influence is highly important, but it produces 
 its results principally by the aid of crossing : by sexual 
 mixture various directions of growth already determined may 
 be united and strengthened or modified in the most various 
 ways. Whatever in the result of mixture is useful, has a 
 greater claim to exist and is capable of giving rise to new, 
 altered directions of growth. Thus the powder of selection lies 
 chiefly in the promotion and diversification of organic growth. 
 It is like crossing, only an indirect cause of the evolution of 
 living beings. As was previously pointed out, sexual 
 differentiation, the necessary antecedent of crossing, has itself 
 only been developed in course of time — is itself the result of 
 peculiarities of growth in two different directions, and these 
 peculiarities of growth are again primarily conditioned by 
 peculiar external 'influences (nourishment), and preserved by 
 selection. 
 
 The Law of Oeganic Form : Its Application to the 
 Form and Structure of Plants 
 
 In accordance with the preceding, we may formulate a law 
 of the form of living beings in the following terms : The 
 external form of every individual, every variety, species, 
 genus, family, etc., is the resultant of a number of processes 
 of growth wdiich have taken place in its ancestors, together 
 with the effect of external conditions which have acted upon 
 it during its individual development and life, and of spon- 
 taneous internal modifications. 
 
 In other words : The external form of every organism is 
 the result of the action of external influences on all its 
 ancestors, together with the effect of such influences and of 
 spjontaneous internal modifications during its individual 
 Hfe. 
 
 The influence of selection is included in this definition. 
 
VIII BOTANICAL EVIDENCE 385 
 
 Moreover, by " form " I mean here essentially the form which 
 grows from the germ by natural necessity as the result of 
 regular growth. But with the words " during its individual 
 life " reference is made also to the alterations of form which 
 organisms undergo during life and which may be inherited. 
 These inheritable modifications produce at first little or 
 scarcely any visible external alteration ; they are internal, 
 dynamic. Nevertheless, as I have stated, external features 
 due to age, and even mutilations, as well as diseases which 
 affect form, may be inherited. 
 
 By the expression " spontaneous internal modifications " I 
 mean the alterations produced by constitutional causes, among 
 them some senile changes, which help to determine form. 
 
 Vegetable physiology supplies the most palpable evidence 
 that the forms of organisms are determined by the influence 
 of external forces on protoplasm, by acquired and inherited 
 properties. 
 
 Is it not the influence of light which determines the 
 direction of growth in plants ? Do not light and air produce 
 the direction, expansion, and position of leaves on which 
 nutrition depends ? Is it not the force of gravity wliieh 
 determines the form of roots and causes them to grow towards 
 the centre of the earth ? Has not nutrition the most profound 
 influence on the form of all parts of plants ? Is not the 
 influence of temperature equally important ? 
 
 To which the reply will be made : that if all external 
 stimuli were removed all these effects would disappear, that 
 they themselves are not inherited, but only the predispositions 
 towards them. I have already remarked previously that every 
 " predisposition " presupposes a molecular modification. AVith 
 the predispositions are inherited the modifications wliicli 
 alone render possible definite directions of growth under the 
 influence of external stimuli. It is certainly true that if all 
 
 2 c 
 
386 ORGANIC GROWTH sec. 
 
 stimuli are removed all organic form disappears. If only 
 the necessary warmth is wanting, tliere is an end of it. Life 
 itself, and with it all the forms in which it resides, are only 
 the effects of stimuli, and therefore the above objection is 
 entirely delusive. Indeed, the definition of species, genera, etc., 
 is rendered possible only by the characters produced by 
 external influences. Take away the latter, and with them 
 the characters conditioned by them, and we have no species, 
 genera, etc., no "kinships" left. It follows from this con- 
 sideration that, as already maintained, the question of the 
 formation of species is by no means so profoundly affected as 
 systematists, and, curiously enough, physiological botanists 
 suppose, by the fact that plants — as, for instance, species of 
 cereals — revert to an original form when the external condi- 
 tions which determine their peculiarities cease to act. 
 
 We employ colours as distinguishing characters. Chloro- 
 phyll is a most important factor in the life of plants, and yet 
 in tlie absence of light the green colour disappears — it is not 
 inherited, but the materials which are its basis are inherited, 
 and these materials have been acquired. If we removed from 
 plants during their development the stimuli which act upon 
 them, without causing their death, so that we obtained 
 abnormal forms, these would still retain by inheritance 
 certain established properties which would cause them, when 
 the action of the stimuli was renewed, to develop only in the 
 definite directions which were natural to them. 
 
 In all organisms definite tendencies of growth are inherited, 
 which alone constitute the specific qualities of the various 
 species. 
 
 The stimulus of gravity having acted upon plants during 
 endless ages, so that roots were developed in a downward 
 direction, the parts wdiich became roots by this particular 
 kind of growth have necessarily developed a tissue of a 
 special character, a tissue wdiose cells tend to grow towards 
 
VIII BOTANICAL EVIDENCE 387 
 
 the centre of the earth, and in. that direction only. Tlie 
 roots also developed in consequence of their peculiar growth 
 special morphological characters, a cell -structure which is 
 more or less different from that of other parts of plants. All 
 such speciality of structure has certainly arisen simply as a 
 result of the inheritance of acquired characters, and it consti- 
 tutes the type, the "kind" of the plant. Similarly tlie 
 tendrils of climbing plants — structures which owe their 
 origin to the action of external stimuli, to the inheritance 
 of acquired characters — are essential to the definition 
 of their species ; and equally so are the position and 
 colours of the leaves, etc., which are due to the action of 
 light and air. In all such cases special morphological and 
 physiological characters have arisen in consequence of tlie 
 continuous action of stimuli, and the functional activity in 
 definite directions thereby set up in the cells of plants — 
 direct stimulation and functional action cannot here for the 
 most part be separated. In many such cases the direct 
 effects of stimuli and function, and the inheritance of these 
 effects, are so obvious, that it seems to me we must recognise 
 them unless we refuse to recognise cause and effect altogether. 
 
 Must not the water which a desert-plant stores up within 
 itself, in order to keep itself alive in spite of drouglit, have 
 had an indirect and direct influence on its whole internal 
 constitution? And when a seaside -plant like Salicornia 
 herbacea takes so much salt from the sea-water that it has a 
 salt taste, must not this salt have had an influence on its 
 whole cell-structure — an influence which enters into its whole 
 specific character and which is inherited ? Who would sub- 
 stitute for such obvious action of the simplest causes the 
 accidental variation of the germ-plasm and selection ? 
 
 I will not here present the anatomical evidence of my 
 view, since every text-book of botany will supply it. I will 
 only adduce some especially remarkable and cogent fiicts. 
 
388 ORGANIC GROWTH sr.r-. 
 
 The parenchyma of the leaves of plants which grow in the 
 light differs completely in cell-structure from that of those 
 which <:?Tow in the shade : the cells in the two cases are of 
 quite difterent shape, — in the latter long and prismatic, in 
 tlie former short, and so on.-^ 
 
 The so-called compass-plants place their leaves in sun- 
 shine so that their edges are directed to the north and south, 
 whereby the leaf is least exposed to the sun. This peculiarity 
 was first observed in the North American Silphium laciniatum, 
 but is found equally developed, according to E. Stahl, in a 
 native species of lettuce, Lactuca scariola.^ The vertical 
 leaves turn their largest surface to the rising sun. In pro- 
 portion as the sun rises higher, the angle at which its rays 
 strike the leaves becomes smaller, until finally at mid-day all 
 the leaves when regarded in the direction of the sun's rays 
 present only their edges to the eye. In the afternoon the 
 incident angle of the sun's rays upon the leaves again 
 gradually increases, so that towards evening the light again 
 strikes them at right angles. Silphium laciniatum belongs 
 like Lactuca to the Compositae. But the leaves of many 
 Papilionaceae, e/j. of the beans, in strong sunshine place 
 themselves edgewise : by the twisting of the articular pro- 
 tuberance the leaves are brought into the position which 
 presents the smallest surface to the sun. By this means 
 excessive heating and illumination are avoided. 
 
 Plants show this property especially in dry regions, and 
 it is probably much more widely distributed than it has yet 
 been observed to be. However, some other plants are known 
 in which it occurs in a less degree. 
 
 This, therefore, is a case in whicli the action of stimulation 
 is useful, as it is for instance in the carnivorous plants, in 
 
 ^ Cf. E. Stahl, Ueher den Einjtuss des sonnigen oder schcUtigen Standorts 
 OAif die Av.shildv/iig der Lauhhldtter, Jenaische Zeitschr. Bd. xvi. 1883. 
 
 ^ E. Stall!, Ueher sogenannte Comiyasspjlanzen, Jenaische Zeitschr. Bd. xv. 
 1881. 
 
viiT RECRESCENCE 389 
 
 which extraordinarily minute quantities of material often 
 cause the reaction. Sensitiveness of this kind in relation t(j 
 certain stimuli is inherited. There can, however, be no doubt 
 that light and air have had an influence in the manner supposed 
 by me also on the permanent inherited position of leaves. 
 
 Indeed, I believe that leaves in general owe their origin 
 partly to the action of light and air. That adaptation has 
 had some influence in their production, both generally and in 
 particular in the evolution of their more minute structure, is 
 to me self-evident, but that, e.g. the variety of form of the 
 leaves of our native trees is essentially due to adaptation, is a 
 belief for which I can find no basis. I consider the differ- 
 ences rather to be for the most part the simple results of 
 growth as affected by direct external stimuli, principally by 
 nourishment, a conclusion supported by the changes which 
 occur when the nutrition is altered. Of course the forms are 
 partly determined by the veins of the leaves, which are the 
 channels for the passage to and fro of the nutritive material, 
 and which have the additional function of keeping the leaves 
 expanded. But it is not possible to say that just this ur 
 that distribution of the veins is a necessary requirement of 
 adaptation — this also is an obvious consequence of definite 
 directions of growth. 
 
 The Eecrescence of Lost Parts as an Example of 
 
 Organic Groavth 
 
 The discussion of the influence of definite directions of 
 growth on the form of organisms leads me to the subject of 
 recrescence, which it seems to me can only be explained by 
 the aid of my theory of organic growth. 
 
 Eecrescence is, in fact, nothing but an effect of the same 
 causes which condition growth in definite directions. Among 
 cases of recrescence two kinds can be distinguished (1) 
 
390 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 those in which obvious external stimuli directly excite the new 
 process of growth ; (2) those in which no such excitation occurs. 
 Among the tirst group is the growth into new plants of parts 
 of a plant when cut off and brought under favourable external 
 conditions — such as cuttings which send forth roots when 
 they are set in the earth, and grafts. Grafting can with 
 certain limitations be performed on the bodies of animals, 
 including man. I allude to the transference of pieces of 
 another person's skin to the human head, or to other parts of 
 the body-surface (transplantation).-^ 
 
 A similar phenomenon, although it does not fall under the 
 definition of the term grafting, is the readhesion of noses, ears, 
 and even finger-joints which liave been cut off, when they are 
 immediately brought into contact with the exposed surface — 
 a process of growth which like grafting is so far connected 
 with recrescence that to effect the readhesion new parts must 
 be formed — therefore the last remnant of recrescence in 
 man.^ 
 
 Vochting has shown that the action of gravity alone is suffi- 
 cient to produce roots on cuttings from plants, and that it is 
 not even necessary to set them in the earth : if twigs of willow 
 beariuGj buds of similar age alongj their whole length are laid 
 in a chamber wliich is kept dark and saturated with moisture 
 (or in moist earth) roots appear on the under side only. Still 
 more striking is the effect of an external stimulus in Lepis- 
 mium radicans, a plant belonging to the Cactus tribe, on the 
 production of roots, for these are produced on any part of the 
 sprouts of this plant from which the light is excluded.^ 
 
 ^ Recently Thiersch has even transplanted pieces of the skin of a negro on to a 
 white man, and conversely ; in the first case the pieces soon became white, in 
 the latter black. 
 
 ^ For other examples see 0. Weber, Die Gewehserkranhiingea im Allgemevnen 
 und ihre Ruckvnrkung o.vf den Gesavimtorganismus. I. Bd. i. Abschnitt of V. 
 Pitha and Billroth, Handhnch der allg. und spec. Chinirgie, 1865. ' 
 
 •' H. Vochting, Sitzungsh. d. niederrhein. Gesellsch. f. Noiur-u. Heilkunde 
 in Bonn, Sitz. v. 3 Jan. 1876. — On the divisibility of plants and the influence 
 
VIII NATS PROBOSCIDEA 391 
 
 Cases belonging to the second of the above-defined groups 
 are much the more important for my argument, for in tliem 
 the recrescence is evidently entirely the result of the definitely 
 directed powers acquired by the ancestors and transmitted by 
 them to their descendants. 
 
 The processes which underlie recrescence are no others than 
 those which condition asexual multiplication. Indeed, in 
 lower animals, where recrescence leads to tlie production 
 of entire animals, the two phenomena coincide in every 
 respect. Whether we cut a small annelid, a water-worm 
 (Nais proboscidea), into two parts, with the result that each 
 part grows into a new perfect individual, or whether the worm 
 divides itself spontaneously and grows into two new animals, 
 in both cases we have exactly the same process. 
 
 In the recrescence of the water- worm we have an example 
 of the second kind of recrescence ; there is no external 
 stimulus which directly prompts it. Of the relation of 
 nutrition to the process I say nothing — the possible objec- 
 tions to be made on this ground are obvious of themselves, as 
 also the considerations by which they can be extenuated or 
 overcome. The parts of the worm, without any special 
 external stimulation during the process, grow in a definite 
 direction in a perfectly constant manner again into an entire 
 animal— that is for me the principal fact. New eyes and a 
 new tentacle are produced on the anterior segment, and a new 
 nerve-ring and cerebral ganglia within it. From this anterior 
 segment, by its repeated division, the longitudinal growth of 
 the new animal takes place, that is, from before backwards, 
 just as in natural division. This recrescence evidently repeats 
 the process which originally led to the formation of the worm 
 with its eyes and proboscis, when it was evolved from a uniseg- 
 
 of internal and external forces on the formation of their organs, see Pfliiger's 
 Archiv f. Physiol. Bd. xv. (Extract from Ueher Organhildung im Pjlanzenrexch, 
 I. Bonn, 1878.) 
 
392 ORGANIC GROWTH sec. 
 
 mental organism, as we have otouucIs for assumino- it once 
 was.^ 
 
 The same process repeats itself in tlie individual develop- 
 ment of the worm — in all these cases we have definitely 
 directed processes of growth, which can only be the result of 
 inheritance. 
 
 The remarkable fact that in an animal thus divided organs, 
 and sometimes very complex organs, develop in the proper 
 positions, without any aid from the direct action of external 
 stimuli, requires to be illustrated by further examples before 
 I enter more minutely into its explanation. 
 
 Everyone knows that when the tail of a lizard is cut off 
 another grows in its place — even Pliny dilates upon the fact. 
 Aristotle mentions its occurrence in salamanders and snakes. 
 But the recrescence of such a complex highly-evolved organ 
 as the eye of vertebrates is much more remarkable. Blumen- 
 bach recorded the occurrence of this recrescence as early as 
 the last century, first in newts,^ and afterwards in Batrachia^ 
 (according to Merkel it had previously been recorded by 
 Briihl). But this recrescence only takes place when some 
 remnants of the various layers of the eye are left in connec- 
 tion with the uninjured optic nerve.^ In Batrachia, according 
 to Blumenbach, the lower jaw is also reproduced. The legs 
 of newts, when renewed, grow again in the same way as when 
 they develop in the larva3.^ The spinal cord is also repro- 
 duced in Amphibia and reptiles, as, for instance, in tadpoles, 
 in newts, in Pleurodeles Waltlii — in the latter animal very 
 completely in five months. The spinal ganglia likewise are 
 renewed, apparently growing out from the spinal cord.^ That 
 
 1 Cf. p. 62. 
 
 - Blumenbach, Specimen physiologiae comparatae, 1787, p. 31. 
 
 •^ Idem, Kleinere Schriften zur vergleichenden, Physiologie, 1800, p. 31. 
 
 ■* J. Ch. Eggers, Von cler Wiedererzeugung, Wiirzburg, 1821. 
 
 ^ Gotte, Ueher Entwicklung und Regeneration des Gliedmassenskelets der 
 Molche, Leipzig, 1879. 
 
 ^ P. Fraisse, Die Regeneration von Geweben u. Organen hei den Wirbelthieren, 
 
VIII CAUSE OF RECRESCENCE 393 
 
 the legs and claws of Crustacea, the tentacles of snails, and 
 even the heads of the latter, if the brain is not destroyed, 
 are reproduced is well known, and has already been partly 
 discussed. Equally well known is the recrescence of the 
 arms of star-fishes. The leajs of insects also sfrow acrain. I 
 have only brought together here a few out of the large number 
 of instances of recrescence. 
 
 How then does it come about that such organs, many of 
 them exceedingly complex, grow again from the body at tlie 
 places where they were originally present, without the direct 
 action of stimuli ? 
 
 The old explanation was that it was due to the "formative 
 tendency," and this was deemed sufficient. We may still use 
 the same term, provided that we get rid of the meaning 
 which the earlier school attached to it, namely that of a 
 spontaneous impulse more or less independent of matter. If 
 we guard against this, if there be any need to do so, and 
 employ the term in the sense of the action of definitely 
 directed forces contained in the material of the organism, 
 then there is nothing to be said against it. We apply the 
 word " shoots " in an entirely passive sense to parts of plants. 
 And in the same sense recrescence consists in the production 
 of shoots, of normally- constructed parts which are, as it were, 
 shot out from the organism by natural necessity. Thus we 
 may use the word tendency or impulse in an active sense, 
 though with certain limitations, in speaking of recrescence. 
 But we conceive the formative tendency not as an independ- 
 ent force by the action of which everything is explained, but 
 as a force of which we have to discover the causes. 
 
 My view is that the recrescence of lost parts of tlie 
 organism must be ascribed to heredity, that the latter is tlie 
 
 hesonders AmphiUen und Reptilien, Cassel and Berlin, 1885. In reptiles 
 (lizards and geckos) the recrescence of the spinal cord takes place only 
 
 imperfectly. 
 
394 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 mechanical cause of the restoration of the mutilated organism 
 as a whole to its previous form. 
 
 Ever-repeated inheritance not only causes every organism 
 to repeat in its individual development the directions of 
 growth by which its form is determined, but, even after that 
 development is completed, causes those directions of growth 
 to manifest themselves in the restoration of lost parts. For 
 recrescence not only depends on exactly the same causes as 
 ontogeny, it is to be regarded as a continuation of the latter. 
 By the ever- repeated inheritance of the characters of an 
 organism, and therewith of its organic unity, it has come 
 about that heredity not only reconstitutes this unity by 
 development, but also endeavours to reconstitute it after 
 injury. 
 
 In order to understand this we must previously grasp 
 the fact that all the several particles of which the 
 organism is composed, that all the cells, all their molecules, 
 stand to one another in perfect correlation, so that each is 
 influenced bv the fate of the others, and that also in each 
 such particle there is something of the tendency to form a 
 wdiole — to unite together with the other particles to form a 
 whole, just as inorganic particles crystallise into a whole from 
 the mother liquid. The formation of crystals is in fact 
 scarcely less mysterious than the development of organic 
 forms — the latter also, to return to a previous comparison, is 
 a kind of crystallisation. Thus I also come back to the con- 
 ception of correlation, which is nothing else than the 
 expression, the consequence of the relations of all particles of 
 the organism with one another. 
 
 I liave explained correlation also as organic crystallisation, 
 and recrescence is in fact an instance of correlation. 
 
 My conception of the nature of the process of recrescence 
 becomes more intelligible when the attention is fixed, not on 
 the morphological parts of the body, but on the forces which 
 
VIII RECRESCENCE FROM MINUTE FRAGMENTS 395 
 
 govern them, when the organism is conceived as the 
 expression of a sum of forces which mutually supplement 
 one another, which govern the particles and restore their 
 equilibrium when it is destroyed — restore equilibrium in the 
 sense of reconstituting the previously existing whole. 
 
 That a tendency to develop into the whole by growth is 
 impressed upon the several particles of the organism by 
 heredity is best shown by the fact that many multicellular 
 plants and animals can be subdivided almost into their con- 
 stituent cells with the result that each portion grows again 
 into an entire organism. Since Trembley's time it has been 
 known that the smallest parts into which our common Hydra 
 is divided become new entire individuals. The question, 
 however, arises whether such fragments must not consist 
 of at least two connected cells, an ectoderm -cell and an 
 endoderm-cell, if recrescence is to ensue ^ — because the ecto- 
 derm and the endoderm even in these lower animals respec- 
 tively have special characters established by heredity. In 
 any case, recrescence from a single cell must be possible in 
 those lower organisms which consist of simple colonies. It 
 takes place in this way even in higher plants. A very 
 remarkable instance of this is recorded by Vochting : - '-'A 
 piece from the middle of the surface of a vigorous thallus of 
 Lunularia vulgaris w^as cut up with a sharp knife on a 
 smooth plate of cork until the fragments were so small as to 
 form a coarse-grained pulp. The largest fragments were 
 about half a cubic millimetre in size, while the smallest were 
 considerably smaller. This pulp was spread out on moist 
 sand and protected as much as possible from external dis- 
 turbing agents. After some time young sprouts showed 
 
 ^ According to Tli. W. Engelmann this is in fact the case. Cf. Zool. Anz. I. 
 
 p. 77, 1878. . , 
 
 - H. Vochting, Ueher die Regeneration cler MarchoMien, Pnngsheim s 
 Jahrbucher fur wissensch. Botanik, Bd. txvi. heft 3, pp. 15, 16, Berlin, 
 
 1885. 
 
396 ORGANIC GROWTH sec. 
 
 themselves, at first one or two, but afterwards an ever- 
 increasing number, and at last quite a forest of young fronds 
 were growing from the pulpy mass. Examination showed 
 that by far the greater number of the particles had remained 
 fresh and been able to produce adventitious sprouts. 
 
 " This experiment clearly shows how remarkably the 
 thallus of this plant is able to endure external violence, what 
 energy of life resides in even the smallest aggregate of its 
 cells. This is almost sufficient proof that the unit}^ 
 of the organism is contained potentially in each single 
 vegetative cell ; indeed, it ought not to be impossible under 
 suitable conditions to prove the truth of this proposition by 
 direct experiment." 
 
 By experiments on the subdivision of willows, Vochting 
 obtained further results, which led him to the following con- 
 clusions : " In whatever direction we divide the organism (the 
 willow), and to whatever degree w^e continue this subdivision, 
 in every fragment the whole organism lies as it were con- 
 cealed, provided that the fragment contains cambium-cells. 
 If the subdivision could be actually carried so far as to 
 isolate an uninjured cambium-cell, this cell w^ould doubtless 
 be able to reproduce the whole organism." 
 
 Such facts can only be explained in this way : That to 
 each cell of an organism possessing such a power of re- 
 crescence, as to a germ- cell, the properties which the whole 
 organism inherited have been transmitted also by heredity ; 
 and that, further, every such cell, like a germ cell, by inherit- 
 ing the tendencies of growth and the general formative 
 powers of the ancestors, has acquired the capacity of growing 
 ai^ain into a whole organism. 
 
 The higher such an organism stands in the scale, so much 
 the more formative capacity must it have inherited — the 
 willow more than the Lunularia, — and in a series of species 
 directly descended from the same ancestors in a straight line, 
 
VIII RECRESCENCE IN DIFFERENT DEGREES 397 
 
 the more highly-organised species must always contain in 
 itself the sum of the most essential of the tendencies of 
 growth of the lower, and must be capable of exhibiting those 
 tendencies. 
 
 Thus, as it seems to me, as by individual development, so 
 also by recrescence, complete proof of the truth of my theory 
 of the organic growth of the living world is supplied. 
 
 I must make my argument complete by entering further 
 into details. 
 
 The reason why the power of recrescence is greater in 
 simple organisms than in more complex, why in general it is 
 greater in proportion as the grade of organisation is lower is 
 obvious : for, as was stated above, the power of recrescence 
 depends upon the retention by the cells of the organism of the 
 properties of the germ-cell, or mother-cell. The lower we 
 descend in the scale of multicellular animals and plants, the 
 more these approximate to colonies of unicellular beings — the 
 more is each of the component cells similar or equivalent to 
 every other, similar or equivalent to the germ or mother-cell. 
 Therefore recrescence in a simple cell-colony such as consti- 
 tutes any of the lowest multicellular plants or animals is not 
 surprising — it almost explains itself that every cell of such a 
 colony can grow again into the whole. Every cell in such 
 colonies possesses every capacity required for independent 
 life. The higher the grade of the organism, that is, the 
 greater the degree to which division of labour, the differentia- 
 tion of the formative tendency into various directions, has 
 been carried, so much the less is this the case, so much the 
 more do its cells depend on other cells, its parts on other 
 parts, finally on central organs, without whose aid they can- 
 not live and multiply, and therefore cannot produce re- 
 crescence. Again, the power of recrescence is greater in 
 youth than in age. It is greatest indeed in the embryonic or 
 foetal condition, as is shown, for instance, by the development 
 
398 ORGANIC GROWTH sec. 
 
 of incomplete rudiments of fingers after fcetal self-amputation 
 in man.^ 
 
 The reason of this is that the cells have still in the young 
 state — the younger, the more — the same general character as 
 in lower organisms; further, that the protoplasm has not 
 been completely used up in forming definite structures, 
 and is in every respect less exhausted, more capable of 
 life and growth than in the adult condition. The more 
 minute explanation of the differences will be given in what 
 follows. 
 
 In organisms also which have no fixed external form, as, 
 for instance, many sponges, the recrescence of the whole out 
 of any part is not very surprising, and yet it is only a step 
 from this to the recrescence of the definite recfular forms of 
 such multicellular animals as the Hydra. How^ever, the 
 differentiation of the cell -layers even in sponges makes 
 the explanation of the process less self-evident. The 
 greater the differentiation of function and the constancy 
 and complexity of structure the more difficult it becomes to 
 understand recrescence. For from the formation of the f^erm- 
 layers onwards the functions of the cells of multicellular 
 animals increasingly diverge : the cells of the various layers 
 soon begin, if I may so express it, to meet with different 
 experiences, they must acquire different capabilities. They 
 must therefore gradually be restricted to the power of forming 
 only organs or parts of organs which proceed from the germ- 
 layer to which they belong. 
 
 It is obvious, however, that in considering the question our 
 inquiries cannot stop at the germ-layers, the simple or primi- 
 tive organs which retain their original character in zoophytes 
 throughout life : they must be extended to every portion of a 
 germ-layer which is destined with others to form some part of 
 the body, and therefore to every complex organ, and in plants 
 
 ^ Cf. Spiegelberg, Lehrhuch der Geburtshiilfe, Lahr, 1878, p. 356. 
 
VIII LIMITA TIONS OF RECRESCENCE 399 
 
 to every group of cells which is to form a part of the organism. 
 The question is in every case, To what degree the formative 
 possibilities of the cells in question have become unchangeable 
 and definitely restricted, to what degree they are still of a 
 general kind. That at the lower stages of development 
 these possibilities are still general we have already seen. We 
 know that in plants even of a high grade of organisation roots 
 may grow from the most various parts if these are brought 
 under suitable conditions. Indeed, according to Vochting's 
 experiments, any fragment of a willow may, as we have seen, 
 grow into a perfect tree,^ provided only that the fragment 
 contains a certain formative tissue, namely, cambium. These 
 facts might suggest the question whether a special cell-tissue 
 is not present also in the adult animal from which all parts 
 can be produced, a kind of animal cambium, a general forma- 
 tive tissue which retains general formative powers through- 
 out life. The blood will first occur to us as most likely to 
 fulfil these conditions, and especially the white blood-cells, 
 which take so prominent a part in constructive and destruc- 
 tive processes, — but we have no evidence that these can 
 produce any but mesodermic tissues, no evidence that 
 endodermic or ectodermic tissues can be produced in higher 
 animals from other than their own primitive layers. In fact, 
 it follows from the nature of heredity that they cannot. To 
 
 1 I have already pointed out how impossible it is to reconcile such facts as 
 -this with the theory of the continuity of the germ-plasm. From the fragment of 
 willow is formed a willow tree with its reproductive organs, that is with germ- 
 plasm, and thus the latter is contained in the fragment— in Lunularia is contained 
 in any particle whatever. Van Bambeke {Poarquoi nous ressemhlons d no.s 
 parents ? Bruxelles, 1885) also draws attention to the same conclusion, pointing 
 out that from a piece of a Begonia leaf a whole plant with its flowers may pro- 
 ceed. But his assertion (p. 46), that Weismann assumes the presence of germ- 
 plasm in somatic-cells is evidently due to a misunderstanding. Weismann only 
 supposes that small quantities of germ-plasm are present in the somatic-cells of 
 hydroid polyps, " afterwards passing through an endless succession of cells till 
 they reach those remotest individuals of the colony in which the sexual products 
 are formed," etc. {Continuitdt, p. 61). But here the germ-plasm only excep- 
 tionally occurs in somatic-cells, and migrates from them to others. 
 
400 
 
 ORGANIC GROWTH 
 
 SEC. 
 
 explain the recrescence of complex tissues and organs in the 
 higher animals, it is necessary to assume, not merely that the 
 parts have a general relationsliip to one another, a general 
 inherited formative tendency, but that they have at the same 
 time a special formative tendency directed towards the 
 structure of tlie part to which they belong. This special 
 relationship shows itself in the fact that these parts are 
 specially correlated with one another which are derived from 
 the same germ-layer, epidermis, hair and horns, for instance, 
 in Mammalia. 
 
 Tlie higher the ^rade of oroianisation in the animal kino- 
 dom, the greater the division of labour, the more complex the 
 organs, so much the less are all cells in a condition to repro- 
 duce different parts or the whole body, so much the more are 
 their powers restricted to the redevelopment of particular parts. 
 
 Thus it is evident that the cells of certain reoions of the 
 body of the higher organisms are endowed by heredit}^ with 
 particular tendencies of growth : they have a tendency by 
 union with one another to constitute, to complete, particular 
 parts. This is an instance of the establishment by functional 
 action and heredity of definitely directed forces. 
 
 This is shown to me in the simplest way by another ex- 
 periment of Yochting's : he hung up a twig of willow in a posi- 
 tion the reverse of the natural, in a vessel where it was 
 exposed to moisture and the other conditions favourable to 
 growth. This twig produced roots not only at the lower end, 
 where their development was favoured by gravity, but also 
 and in superior numbers at the upper end — evidently there in 
 consequence of the established hereditary tendencies of growth. 
 
 Subsequently Herr Vochting drew my attention to some 
 remarks of his which well express the significance of the 
 examples I have previously given of definite growth- 
 tendencies due to acquirement and inheritance, although for 
 his part he puts forward the view I maintain as only 
 
VIII EFFECTS OF LIGHT AND GRA VITY 401 
 
 hypothetical. He speaks of the explanation of the gradual 
 increase in height of plants on the earth, and says : " If we 
 start from the conception that the geotropic and lieliotropic 
 organs were first produced under the influence of gravity and 
 light, it follows according to the views now current upon the 
 evolution of organisms, that wherever other conditions were 
 also favourable, more and more lofty forms must have been 
 produced, till at last the existing giants of the vegetable king- 
 dom were developed." And in a previous passage : " After 
 I had demonstrated the influence of gravity and light on the 
 development of roots and sprouts, the idea naturally offered 
 itself that the fundamental contrast between the two was to 
 be regarded as a gradually accumulated effect of these two 
 forces, especially of gravity. In fact, it would appear very 
 strange if these forces, notwithstanding their constant in- 
 fluence, had produced no hereditary properties. Wlien we 
 reflect that the pace to which a mare is trained is inherited 
 by the filly, we are logically compelled to look for the heredi- 
 tary result of those forces in the organisms on which they 
 have acted in the same way for inconceivable periods of time. 
 If such a result were not present it would be in the highest 
 degree surprising." ^ 
 
 Vochting thus meets the arguments by which Sachs 
 opposes his view, that the results of his experiments on the 
 recrescence of plants are to be regarded as phenomena of 
 heredity. Sachs looks upon these phenomena as the result 
 of the influence of gravity on the young growing organs. 
 The opposing action of light and gravity does not, he says, 
 depend on heredity, but the contrast represents only a " pre- 
 disposition," which is implanted in the organs of every 
 individual by light and gravity during its development.- 
 
 1 Cf. H. Vochting, Ueher Spitze und Basis an den P/lanzenorganrii, 
 
 Botan. Zeitung, pp. 596-97. 
 
 2 J. Sachs, Stof und Form der Pflanzenorgane, Arheiten des bot. Inst, zu 
 
 WiiTzburg, Bd. ii. p. 469, et seq. 
 
 2 D 
 
402 ORGANIC GROWTH sec. 
 
 But this is to dispute heredity altogether, it is niaintained 
 that the variety of plant -forms is due to external stimuli 
 only, which act upon plants during their development. 
 "Whither does such a view lead? To the denial of the very 
 nature of embryonic development, which incontestably de- 
 pends principally on heredity. It leads to the assumption 
 that all germs are equivalent, and that the fact that from a 
 cherry-stone a cherry-tree, from a pea a pea-plant arises, is 
 due only to the difference of external stimuli. 
 
 In a work ^ in which he defends himself against Sachs's 
 attacks, Vochting uses language which even more distinctly 
 than the previous quotations shov/s the agreement between 
 his views and mine, an agreement which I value the more 
 because it was only after the preceding pages had been 
 written that I became accurately acquainted with the con- 
 tents of the work referred to. Amongst otlier things he 
 says that every organ, of whatever kind it may be, contains 
 internal determining conditions, and these in the cases re- 
 corded by him primarily determined at what points roots 
 should arise in a fragment of willow. Such internal condi- 
 tions " primarily determine the position of new formations. 
 The effects of the action of the external stimuli are thus 
 modified by internal factors." 
 
 These " internal conditions " are the same as those whic]i 
 I have called constitutional causes.^ 
 
 Like Sachs, Pfluger also denies heredity ^ — and inasmuch 
 
 ^ Ueher Organhildunfj im Pflanzenreich, ii. p. 192, Bouu, 18S4. 
 
 ^ Saclis has since (J. Sachs, Stoff unci Form der Pflanzenorgane, ii., Arh. d. 
 hotan. Inst, zu WUrzburg, Bd. ii, p. 689), not only assumed that there are such in- 
 ternal causes, but even declared that he never denied their existence. It may be 
 remarked that Sachs {Natunoissenschaftliche Rundschau 1886, No. 5) also main- 
 tained that he had put forward the theory of the continuity of the germ-plasm 
 before Weismann (Sachs, PJianzenjihysiologie 1882, ch. xliii.) But as Weismann 
 replied (Zu/r Annahme eiaer Continuitdt des Keimj^lasmas. Ber. d. naturf. (Jes. zu 
 Freiburg i. B. 1886), Sachs only referred to the fact that from the germ-sub- 
 stance of one generation that of the following is derived. 
 
 ^ Pfl tiger, Ueber den Einfluss der ScMoerkraft auf die Theilung der Zellen 
 
Yiii EFFECT OF GRAVITY ON DEVELOPMENT 403 
 
 as lie repudiated the inheritance of acquired characters he 
 must be allowed the credit of preparing the way for the 
 theories of Weismann and Nageli. His view depends on his 
 discovery that gravity has an influence on the development 
 of the embryo even in animals, since the rudiment of the 
 young frog appears, not as usual in the dark, but iu the light 
 pole of the egg when the latter is kept uppermost. I'flliger 
 proceeds therefore from the argument, that if heredity existed 
 the dark hemisphere of the frog's egg would have retained by 
 inheritance alone the function of forming the principal part 
 of the embryo. But this interpretation of the facts cannot 
 well be sustained, because as Pflliger himself admits, the 
 whole segmentation certainly proceeds from the nucleus, and 
 the artificial inversion of the egg possibly causes a simple 
 change of position of the nucleus, and thereby of the seat of 
 its influence on the surrounding protoplasm. It is possible 
 that the protoplasm follows the nucleus in its change of posi- 
 tion. The movement of the nucleus may be due to its having 
 a lower specific gravity than the rest of the ^gg. Experi- 
 ments on the action of gravity would therefore be much 
 better evidence for Pfluger's contention if gravity produced 
 the same effect after segmentation was completed.^ 
 
 In connection with his results concerning the influence of 
 gravity on development, Pfluger discusses recrescence, seeking 
 
 und auf die EntiuicUung des Embryo, Arch. f. die gesammte Physiolofjie, Bd. 
 
 xxxii. 1883. 
 
 1 According to Raiiber and Roux (Rauber, Schioerkraftversuche mi Forellen- 
 eiern, Sitz.-Ber. Nat-Ges. Leipzig, Feb. 1884; Roux, Ueher die Entwukl- 
 ung der Froscheier hei Aufhehung der richtenden Wirkung der Schwere, 
 Breslauer Aerztl. Zeitimg, 22 Miirz 1884), under the influence of a centrifugal 
 force the embryo is formed in the direction of that force, a result which 
 harmonises with the explanation I have given above. Cf. also Bom ( Ueber den 
 Einfiuss der Schivere auf das Froschei, Arch. f. mikrosk. AmiL Bd. xxiv. 
 1885), who formerly maintained the explanation given above, but aftorwanls, it 
 seems to me on insufficient grounds, abandoned it. 0. Hertwig also ( U'tkheti 
 Einfiuss iibt die Schwerkraft auf die Theilung der Zellen, Jen. Zeitsch. /. 
 Naturw. Bd. xviii.), after experiments on Echiuoderm ova denies any profound 
 importance to Pfluger's results. 
 
404 ORGANIC GROWTH sec. 
 
 to use this phenomenon also as an argument against heredity. 
 Since a part of the body taken from the whole grows again 
 from the remainder — is formed anew — it is evident that it 
 is formed again notwithstanding the absence of all hereditary 
 connection between the lost part and its substitute. At the 
 same time he endeavours to give an explanation of recrescence 
 in the following fashion : ^ '' When just what was lost is 
 replaced, it is clear that the newly-produced member does not 
 arise from a pre-existing germ of the member. The sectional 
 surface of the stump of the arm draws nutritive material to- 
 wards itself, and organises the molecules of that material into 
 an arm. The organising force is, however, a molecular force, 
 which cannot extend its influence from the living substance 
 of the stump to a distance, but acts only by attracting tlie 
 nutritive molecules which come within the sphere of activity 
 of the molecules of the stump, driving them into definite 
 positions, and so gradually produces a new living layer over 
 the exposed surface. The organisation of this new layer evid- 
 ently depends on the law of the organisation, i.e. of the 
 molecular arrangement and the chemical condition of the sur- 
 face over which the new layer is formed. The condition of 
 this layer is, in a word, the mathematically necessary con- 
 sequence of the condition of the older generating layer. But 
 since in the embryonic development this latter layer was also 
 in existence before that now reproduced arose, so this must 
 then have arisen in exactly the same way as it now arises for 
 the second time. Thus layer is formed upon layer, the 
 younger always the cliild of the older, until the organ is again 
 entire. The process of recrescence therefore consists in this, 
 that the exposed surface of the stump of the arm acts, as it is 
 always acting, on the molecules of the layer next to it, direct- 
 ing, arranging, organising them, so that every nutritive par- 
 ticle which comes within the region of that surface at once 
 
 ^ Op. cit. pp. 65, QQ. 
 
VIII PFLtJGER ON RECRESCENCE 405 
 
 obeys the laws prescribed by it. . . . Since therefore the 
 most superficial layer of living molecules in the mutilated 
 stump, an almost imponderable minute quantity of substance, 
 produces the whole limb with mathematical necessity, very 
 much as a snowflake forms an avalanche, and since this is 
 true of all members, therefore it is not difficult to conceive 
 that the whole head and trunk can be produced from a very 
 much smaller surface, a kind of ellipsoid, if adequate nutritive 
 material is supplied to this surface." Farther on it is par- 
 ticularly insisted that the regenerating action takes pLace 
 always in a definite direction. If a nerve -trunk is cut 
 through, the surface of the portion still connected with the 
 nerve-centres exhibits an enormous regenerating activity, 
 while the other surface, together with the peripheral nerve, 
 perishes, although otherwise it is under the same conditions 
 as the former surface. The organising surfaces of a body 
 show therefore a polarisation, in that the one of their sides 
 does not exhibit the same properties as the other. The direc- 
 tion of the polarisation of the regenerating surfaces is the 
 cause of the direction of growth, and for this reason a part of 
 an animal cannot in general by growth regenerate the whole 
 animal. The peculiarity mentioned by Pfliiger of the recres- 
 cence of nerves seems to me to demand a different and obvious 
 explanation. It is easy to understand why only the central 
 portion of the divided nerve remains alive and exhibits the 
 power of recrescence, while the peripheral dies, for only the 
 former remains under the necessary influence of all the vital 
 conditions of the whole body, is still active as a nerve ; the 
 other has given up its activity as a nerve, and must therefore 
 
 as such perish. 
 
 Pfltiger thus supposes that just as in the embryonic 
 development of an organ its growth at a given moment takes 
 place always from the already formed " polarised " terminal 
 surface, so also in recrescence. That, he says further, in o 
 
406 ORGANIC GROWTH sec. 
 
 dog when the gall-duct or a long piece of nerve is cut out it 
 is regenerated is intelligible, because the piece removed is 
 the result of the direct and indirect organising action of the 
 surface exposed by the section, and is continually (in the 
 restorative processes of metabolism) being reformed by that 
 action. 
 
 In reply to this it may be remarked that a part serving a 
 particular purpose may be regenerated sometimes in the in- 
 terior of the body in consequence of simple mechanical con- 
 ditions and simple stimulation — possibly, for instance, a duct 
 conveying a liquid, the contents of which took the same 
 course after it was severed as before. But the idea that after 
 the removal of any part the polarisation of the proximal 
 exposed surface is the cause of its recrescence seems to me 
 sufficiently disproved by the fact that parts of animals can 
 grow again into entire animals. This fact can only be 
 explained on the assumption that all parts of the body, in 
 consequence of an acquired definite growth-tendency, have a 
 share of a definite formative power in the way I have main- 
 tained, although the higher the grade of the animals the more 
 heredity has produced a certain degree of peculiarity in the 
 formative powers of the several parts. All the facts of 
 recrescence, it seems to me, are incontestably in favour of, not 
 against, the heredity of acquired characters. Moreover, 
 Pfliiger himself, at the conclusion of his arguments, has a 
 sentence which at least in a certain sense acknowledc^es the 
 influence of the entire organism in recrescence. " If," he says, 
 " in certain regions of the body, by poisons or injuries, the 
 groups of molecules are disturbed out of their normal arrange- 
 ment and thrown into disorder, then almost the whole body, 
 all of it that remains normal, exerts a constant organising 
 influence until from layer to layer the normal arrangement of 
 the particles is re-established ; each layer imposes a definite 
 law on the one succeeding it and works without intermission 
 
VIII PHYSIOLOGICAL RECRESCENCE 407 
 
 until it gradually again impresses its own stamp upon its 
 neioflibour." 
 
 To my thinking, on the contrary, the recrescence of lost 
 parts falls under the same laws of acquirement and inherit- 
 ance as ordinary growth : it is nothing else but growth pro- 
 ceeding with increased vigour under peculiar conditions. 
 
 How natural a process it is, and how justified we are in 
 asserting its subjection to the ordinary laws of growth, and 
 how dependent it is upon the contemporary condition of the 
 whole body, is excellently shown by the recrescence of the 
 horns of the Cervidae, and by the periodic renewals of hair 
 and feathers. These are instances, not of pathological, but 
 purely physiological recrescence, and examples of recrescence 
 in general than which none better can be conceived. In the 
 Cervidae, with the exception of the reindeer, the horns are 
 developed only in the males, and after castration they cease 
 to be developed in them. They develop according to per- 
 fectly definite laws every time they are renewed, becoming 
 more complicated every year : they grow. But this growtli, 
 their normal recrescence, no longer goes on when the testes 
 are removed ; the horns degenerate and diminish with the 
 cessation of sexual activity. 
 
 This example at the same time clearly exhibits the rela- 
 tion of recrescence to correlation, on which I have already 
 insisted. 
 
 Eecrescence is only the increased action under special con- 
 ditions of a process which constantly goes on in our bodies as 
 lono- as we live. Like recrescence, the constant renewal of 
 the parts of the body, even of the highest animals, through- 
 out life depends upon acquired and inherited growth-tendency, 
 on acquired and inherited formative power. This renewal is 
 essentially nothing but a gradual process of recrescence. To 
 explain it, it is necessary to assume what I have assumed 
 for the recrescence of lost parts, and what all growth resulting 
 
408 
 
 ORGANIC GROWTH 
 
 SEC. VIII 
 
 in a definite form presupposes, namely, that by the inheritance 
 of acquired characters there is established in every developing 
 and every adult organism a relation of the particles to one 
 another, which finds its expression in their striving to form 
 themselves into the whole, and to maintain or re-establish the 
 co-ordinated whole ; and further, that the higher the degree to 
 which division of labour is developed, so much the more are 
 special growth-tendencies developed in the several parts. 
 
 Another consideration which I must emphasise on account 
 of its importance to the above view and to my whole theory 
 of the organic growth of the living world is this : that the 
 renewal of the cells of the body which goes on constantly 
 throughout life, that is, the division of the cells, depends on 
 the same processes which accompany the division of the 
 original egg-cell, and which take place during the whole of 
 development. This continued multiplication or recrescence 
 of cells in the adult body thus appears as in some sense an 
 after-effect of fertilisation, as a continuation of the process of 
 growth which constitutes the development of the organism. 
 Thus the whole metamorphosis of organisms, their whole 
 life, depends upon the acquisition and inheritance of 
 properties, and on the growth thereby determined. If the 
 capacity for this ceases the organism dies. 
 
CONCLUSION 
 
 I CONCLUDE the first part of this book with the Address 
 following, not only because it contains some of the most 
 important of the views here expounded, but especially because 
 it expresses the fundamental conception from w^hich all my 
 views arise — the doctrine of the unity of organic nature. 
 
 My view of the causes of the origin of species is nothing 
 but the logical application of that conception to the explana- 
 tion of the manifold variety of the living world. It miglit be 
 replied that this conception equally influences the minds of all 
 who endeavour to explain the origin of species by the gradual 
 modification of organisms. It is true that no evolutionist at 
 the present day contests the fact that varieties, species, genera, 
 families, etc., more or less plainly pass by transitions into one 
 another, and that these are in the last result artificial concep- 
 tions. Indeed, it is the most confident disciples of the doctrine 
 of evolution, of Darwinism, who most loudly complain, not 
 merely of the manufacture of species, but particularly tliat 
 systematists regard varieties, not as a kind of transition from 
 species to species, but as a comparatively unimportant devia- 
 tion from the established type of the species. Nevertheless, 
 in the more recent attempts to explain evolution, tliis principle 
 of the unity of organic nature has been more or less dis- 
 regarded. These attempts show that transmutationists make 
 no less distinction between variety and species tlian the 
 systematists. For the former recognise that certain influences 
 
410 CONCLUSION 
 
 of tlie external world are the causes of the origin of varieties, 
 but deny that the same causes have led to the evolution of 
 species. They also abandon that principle when they main- 
 tain that the modification of unicellular forms is governed by 
 other laws than those which regulate that of the mul- 
 ticellular. 
 
 And it is certainly astonishing that this really self-evident 
 truth has never yet been followed to its conclusions, namely, 
 that if the same fundamental laws hold throughout the 
 organic world, and if species are only a collection of 
 individuals, and genera a collection of species, families 
 only a collection of genera, and so on, groups which have dif- 
 ferentiated themselves from a number of originally similar 
 individuals, that then the same laws must hold for the 
 development of these groups as for that of the individual, 
 that the causes which modify an individual within the 
 boundaries of a species must be the same as those which 
 modify it beyond these boundaries. Finally, that therefore 
 also the special laws of growth which influence and modify 
 an individual during its life, must be essentially those which 
 underlie the manifold variety of the whole world of organic 
 forms. 
 
 Any one who thus completely renders allegiance to the 
 supremacy of the principle of the unity of the organic world, 
 who rejects everything which contradicts this principle, can- 
 not help admitting that in truth, as I assert, the ultimate 
 origin of the various kinships in the animal and vegetable 
 Idngdom is to be traced to individual differences, and that the 
 differences between the former, like the latter, must be 
 essentially determined by external conditions, by the modi- 
 fications of organic growth. 
 
 Only in this way also is it possible to explain in a natural 
 way, as I have attempted to do, the origin and unity of all 
 forms of mental action. 
 
APPENDIX 
 
i 
 
ON THE IDEA 
 
 OF THE 
 
 INDIVIDUAL IN THE ANIMAL KINGDO.AI. 
 
 An Address delivered at the 56th Congress of Germccn Naturalists and 
 Physicians at Freiburg, i.B., on the 21st September 1883, 
 
 BY 
 
 Peof. De. G. H. THEODOR EIMER of Tubingen. 
 
 From the stenographic report published in the daily proceedings of tlie 
 
 CoDgress. 
 
 Man loves to isolate himself from Nature. 
 
 He is reluctant to confess his kinship with beiugs wliich 
 he thinks beneath him. 
 
 He alone will be lord, alone ^yise ; he the crown of 
 creation. 
 
 But who gives him the right to assume this pre-eminence ? 
 
 How small is his power 1 
 
 Man the mighty — is powerless against the iiitinitesimal 
 organisms which seek to enter his blood and destroy liini. 
 
 A wave kills him, while the ocean is teeming with life 
 that mocks his sovereignty. 
 
414 . APPENDIX 
 
 Does not the consciousness of our weakness, of our imper- 
 fection, steal upon us when we see the bird of prey circling in 
 the air ? He is scarcely visible to our dim eyes ; yet sees the 
 smallest creature on the earth which he has chosen for his 
 prey. 
 
 Does he think more humbly of himself, this king in his 
 own realm, than the lord of creation beneath him ? 
 
 Yet no less has every animal perfect right to feel himself 
 lord in his own kingdom ; for each is perfectly adapted in its 
 own way — if it were not, were it not lord in its own fashion, 
 it would not exist. 
 
 "When we look at the smallest Infusorian under the micro- 
 scope we see that it feels itself supreme in the drop of water 
 which is its universe — actively and confidently it feels about, 
 moves like an arrow hither and thither, unconscious in whose 
 hand it is, and that in a few minutes the drop of moisture on 
 which its life depends will have disappeared. 
 
 And if any one replies that man, though not in every 
 detail, yet on the whole is lord of the earth, let him consider that 
 this lord, so full of pride one moment, in the next becomes 
 conscious of his weakness, and humbles himself before a 
 liigher power. 
 
 For this self-subjection, which resigns our fate into higher 
 hands and implores their aid in time of need, is first prompted 
 by our helplessness under the blows of life, under the resist- 
 less powers of the outer world, under the might of death. 
 
 Thus man, the lord of creation, the contemptuous despiser 
 of the Nature surrounding him and its creatures, bows him- 
 self in humility before this Nature, degrading himself to idol- 
 worship, placing in the hand of a feeble fellow-creature the 
 sceptre of infallible wisdom and power. 
 
 How can we find a way out of this state of contradiction, 
 how discover the limits of the claims which man can with 
 dignity make upon the external world, and thereby lay the 
 
APPENDIX 415 
 
 foundation for a more harmonious development of his mental 
 life? 
 
 I believe by the universal recognition of the actual rela- 
 tions towards one another of organic beings in nature. 
 
 In the choice of my method of treating this question 1 
 have been guided by the desire of showing by special investi- 
 gation how mistaken are those who are never tired of main- 
 taining that the doctrines of Natural Science, especially the 
 newest, are in antagonism to morality, and to idealism in 
 general. 
 
 I will point out how rather the contrary is the case, how 
 these very doctrines, rightly understood, coincide with the 
 laws which make the noblest claims on life. 
 
 And how could it be otherwise since these laws liave 
 sprung from the original demands of Nature herself 
 
 To carry out my purpose I intend to attack the apparent 
 independence of the animal organism which is implied in the 
 word individual, i.e. indivisible, to dispute the claim of the 
 organism to separate isolated existence, and will endeavour to 
 prove that the conception of such an indivisible entity is 
 unable to withstand a more exact investigation. 
 
 I shall endeavour to prove this (1) by a consideration of 
 the question of the isolated unity of individuals themselves ; 
 and (2) by the consideration of the direct connection of the 
 individuals, even of different species, with one another, as 
 shown by new evidence. 
 
 I 
 
 Amono- the differences which have been stated to dis- 
 tinguish animals from plants, it has been insisted that one of 
 the most prominent is that the animal is a complete distinctly- 
 defined unity from which no part can be separated witliout 
 injury to the whole, and without the probable destruction of 
 the separated part, while plants on the contrary are tolerant 
 
416 APPENDIX 
 
 of the most varied injuries, and can be artificially divided, 
 multiplied by division. This conception is connected with 
 and is indispensable to the other conception, that the animal 
 as distinguished from the plant possesses an indivisible soul. 
 
 In consequence of this conception, the greatest astonish- 
 ment was excited when in the middle of the last century 
 Trembley showed that a small insignificant but genuine 
 animal, the Hydra or fresh-water polyp, which lives in our 
 waters, could be cut up into quite small pieces in the most 
 various directions, with the result that each piece grew into a 
 new perfect individual. These experiments attracted the great- 
 est notice, not only from naturalists, but also from philosophers 
 and theologists, on account of their bearing on the question 
 of the indivisibility of the soul. 
 
 The philosopher Bonnet and others repeated the experi- 
 ments of Trembley, and extended them to other animals, f 
 especially to a small worm which likewise lives in our fresh 
 waters, the Nais proboscidea, an animal which resembles the 
 earth-worm in form and is allied to it. It was found that 
 when this worm is cut transversely into several portions each 
 part goes on living after the division. But it was also found 
 that this worm multiplies by dividing itself in exactly the 
 same way as it can be divided artificially. 
 
 But it must be pointed out that the conditions are different 
 in the two cases. The whole Hydra can be cut up in all 
 directions ; but in the worm there are a number of segments 
 in linear series which are to a certain degree independent — 
 the rings of the body, — and subdivision cannot go beyond the 
 separation of these without endangering the life of the parts. 
 
 But the physiological treatment of zoology has in recent 
 times been extraordinarily neglected, in my opinion, to the 
 great injury of the science; and such physiological experiments 
 were not for a long time continued. It struck me as very 
 desirable to try experiments of a similar kind, for it seemed 
 
APPENDIX 417 
 
 to me that by operating on animals intermediate in organisa- 
 tion between the Hydra and the worm it might be possible 
 to discover traces of the commencement of the nervous system 
 in the animal kingdom. 
 
 For in the worm we have — and this is the reason why we 
 can divide it with the result mentioned into its component 
 parts (segments) — a nervous system whicli is repeated in 
 every segment — a nerve-cord which runs along the ventral 
 side of the animal, and in every segment enlarges into a 
 ganglion, and each of these ganglia can in some sort be 
 reo-arded as a brain of the animal. It is the same with the 
 other organs — each is repeated in every segment of the worm, 
 so that the animal is to be regarded as a composite of several 
 parts, each of which is a whole complete in itself. But this 
 worm was developed from a simple unsegmented larva. 
 
 For my first experiments I took various kinds of jelly- 
 fishes. I will here only mention those which I made on the 
 large kinds. Many of you know these creatures, at least 
 those who live at the sea-side or visit watering-places. Some 
 kinds of them are at times a great annoyance to bathers, for 
 when they come in contact with the skin they cause great 
 irritation by means of small glands they possess which send 
 out minute stings charged with an acid. Such a jelly-fish may 
 be compared to an umbrella if we suppose that the latter 
 is made of a watery gelatinous substance, and that instead 
 of the wires which form the ribs of the umbrella there are 
 canals running in the jelly which meet in a common chamlier 
 at the apex of the umbrella, the stomach of the animal, and 
 open to the exterior through the stick of the umbrella by an 
 aperture at its lower end, the mouth. Eound the margin of 
 this umbrella, at regular distances, there exist several small 
 bodies, which have long been conjecturally regarded as sense- 
 organs, the so-called marginal bodies, each one at the end of a 
 
 canal. 
 
 2 E 
 
418 
 
 APPENDIX 
 
 When I divided one of these animals into two halves by 
 an incision passing through the summit, each half went on 
 swimming independently. It must be borne in mind that 
 the locomotion of the large jelly-fishes is produced by 
 dilation and contraction of the umbrella. Then I cut the 
 animal into four, then into eight parts ; I could cut it into as 
 many parts as there were marginal bodies — and each separate 
 piece endeavoured to go on moving independently. 
 
 When I took one of these pieces — a radius of the whole 
 creature — and cut off pieces from this radius, each piece when 
 
 Fig. 5. 
 
 Fig. 6. 
 
 separated was dead and motionless if it did not contain the 
 small body on the margin, the so-called marginal sense-organ. 
 But the smallest piece containing this organ continued to 
 move, pulsated rhythmically in a perfectly constant manner, 
 somewhat as the heart of a frog when dissected out from the 
 body. A prick with a needle in a particular part of the 
 marginal organ, and the motion in this small portion also 
 ceased. In this organ then was the starting-point of the 
 motion, here was the nerve-centre. 
 
 When I cut out the central portion of the umbrella so 
 that only the margin was left, the latter went on moving quite 
 
APPENDIX 419 
 
 cheerfully in the water like an independent and uninjured 
 animal, but the central piece seemed dead. AVhen from an 
 entire specimen I cut out all the marginal organs except one, 
 the animal went on moving as if it were perfectly uninjured ; 
 but if I cut away all the marginal bodies, the animal seemed 
 dead, no longer moved. 
 
 If one carefully observes how the uninjured animal moves 
 in the water, he will notice that the motion starts always 
 from one of the marginal bodies and spreads in various direc- 
 tions as if it were propagated through telegraph wires, liut 
 at one moment the motion besjins at this orizan, the next at 
 another, the next again at another. 
 
 Where then are we to look for the individual in such an 
 animal ? It is not an indivisible whole, but a divisible, and 
 divisible into so many parts. But neither can we describe 
 the smallest part of the whole which is capable of life as an 
 individual, for such a part cannot continue its independent 
 life indefinitely, it perishes after a time. 
 
 If we compare these phenomena with those which I have 
 described in the case of the worm we see a difference. In 
 the latter case we also obtain by section a part capable of 
 independent life, but it only remains an individual for a 
 moment ; immediately afterwards it begins to develop again 
 into an entire worm, which does not happen in the jelly-fish. 
 
 But to proceed further. When I made a jelly-fish motion- 
 less and then kept it in conditions favourable to life in pure 
 sea-water, then after a time, at some spot or other on the 
 summit, twitchings appeared ; these movements extended to 
 wider and wider areas, became more rapid and vigorous, and 
 after a time a regular pulsation was re-established in the 
 mutilated animal — it continued to live. Thus a new centre of 
 life has arisen at some point in the animal, anil this new 
 centre now accomplishes the movements of the whole — a most 
 marvellous phenomenon, which, however, is explained by the 
 
420 APPEXDIX 
 
 peculiar relations of the nervous system. These on further 
 inquiry were revealed to me by the minute microscopical 
 investigation of these animals. 
 
 This nervous system, in fact, represents the beginning of 
 all nervous systems. It consists, besides nerve- fibres, of 
 nerve-cells, which are scattered over the surface of the animal, 
 and at various points are aggregated so as to form the 
 beginnings of central organs, a number of separate brains. 
 But so slight is the difterentiation of the peripheral from the 
 central nervous system, that, under certain necessary conditions, 
 a rudimentary brain of this kind can to some extent develop 
 itself from the scattered nerve-cells in any other position, 
 that is, some other group of nerve-cells can begin to act as a 
 brain. 
 
 Subsequent microscopical researches made by others have 
 confirmed my observations and extended them to other 
 zoophytes. 
 
 Time will not allow me to describe the experiments and 
 researches which I have made on the ribbed Medusce 
 (Ctenophora) — experiments which would of course aftbrd a 
 deeper insight into phenomena of this kind ; I will therefore 
 pass on to another consideration which may throw some light 
 on the question of the definition of the individual in the 
 animal world. 
 
 There are animals which are usually not very appropriately 
 described as colonies. The corals are of this class ; they all 
 arise originally from single beings, each from a simple larva, 
 which begins to divide itself, and ultimately comes to form a 
 colony of numerous individuals, as it is usually expressed. 
 But a coral colony is by no means a co-ordinated whole ; it 
 can be divided up in every direction into these single creatures 
 (polyps), and each will grow into a new colony, a new animal- 
 tree. 
 
 It is much the same with star-fishes and sponges. These 
 
APPENDIX 421 
 
 also are composed of single parts, eacli of wliicli can, when 
 separated from the whole, under certain conditions, grow into 
 a new animal — in sponges this takes place in any fragment 
 separated from the whole and tlirown again into the water. 
 We have thns in all these cases, in the adult animal, not 
 something simple, and this is what I want to emphasize, 
 but an aggregate of similar members. 
 
 Such an aggregation occurs also in animals where it is not 
 usually suspected — for instance, in insects and their alHes, in 
 the group of Arthropoda generally. A fly or a bee is not 
 an originally simple whole, but it is clearly evident I'rom its 
 developmental history that it was evolved from a worm-like 
 creature, i.e. one which consisted of a linear series of similar 
 parts. We recognise this condition still to some extent in the 
 caterpillar, and also in the maggot or simihar larva of other 
 forms. Thus the bee has been evolved from a series of secj- 
 ments originally equivalent. But a unity has been developed 
 in this animal in consequence of the division of labour which 
 has taken place among the segments. The various organs are 
 no longer distributed equally among the several segments of 
 the body, but collected together, united in difterent regions. 
 This applies also to the nervous system, although closer 
 observation shows that here there is not yet the unity whicli 
 might be expected. For the several nerve-centres which are 
 present in the body of an insect have more or less different 
 functions : stimulation of one group of nerve-centres alfects 
 the sexual organs, of another the locomotive organs, and so on. 
 I only say therefore that in the body of an insect we have 
 a composite structure which has arisen from a number of 
 equivalent segments ; in consequence of division of labour 
 these segments have been united into a single body, differen- 
 tiated into several groups composed of dilferent organs and 
 lying one behind another. 
 
 The same is the case in our own bodies. P2ven tlie 
 
422 APPENDIX 
 
 mammals, including man, are not simple individuals ; 
 our bodies are transversely segmented. In the course 
 of evolution, it is true, amalgamation or concentration has 
 proceeded to a very higli degree, at least in the highest 
 animals ; but in the lower forms of the vertebrata this is 
 scarcely carried further than is the case in the Arthropoda, 
 especially in insects. The central points towards ^vhich the 
 segments have been united appear plainly when we attempt 
 to divide these animals also in different directions. Insects 
 can be divided with the result that the separate parts, e/j. 
 the posterior part of a stag-beetle, retain for a long time 
 an independent life — a very long time if they are pro- 
 tected from desiccation. The same holds also for verte- 
 brates ; for w^e can cut off the head of a frog and the 
 remaining part of the nervous system retains its functional 
 activity. It seems to me certain, notw^ithstanding the con- 
 trary view which still prevails, that voluntary action in this 
 animal proceeds also from parts of the spinal cord ; for after 
 the head has been cut off the creature evidently acts quite 
 consciously. A tortoise, it is also known, can survive de- 
 capitation for a long time, and apparently likewise responds 
 voluntarily to external stimuli. The higher we ascend in the 
 animal scale, the less do we find separated parts capable of 
 surviving, and the more does that possibility of recrescence 
 disappear which still exists in the lower vertebrates, in which, 
 for instance, legs or tails are reproduced when lost. In our- 
 selves, traces of this power of recrescence still remain in the 
 formation of scars, and in the reattachment of certain parts 
 which are restored to their place immediately after they have 
 been separated from the body. 
 
 Our subject can also be illustrated by facts of the reverse 
 kind. As in the cases mentioned, a differentiation and union of 
 equivalent parts produced a compact and co-ordinated whole 
 — individuals, as it were, being specialised into organs — so in 
 
APPENDIX 423 
 
 other animals organs become externally separated from the 
 body, so that locomotive organs, digestive organs, sexual 
 organs, remain connected with the body only by a peduncle. 
 
 This occurs in Zoophytes, for instance in the Siphonophora, 
 in lower forms of animals generally. It also liappens that 
 organs of this kind separate from the whole and swim about 
 independently; that sexual organs, for example, leave the 
 common body, and, provided with visual and auditory organs, 
 move freely in the water ; and that from the mingling of the 
 sexual elements of these isolated sexual organs new animals 
 arise. It even happens that in the course of evolution such 
 sexual organs come to be the principal form of the species, 
 while the original stock gradually dwindles away — ^just as 
 (and the comparison might be pursued far) if the separate 
 blossoms of a tree, male and female, separated and moved 
 about freely, and gradually in the course of evolution came to 
 exist as independent species, while the original tree gradually, 
 as such, disappeared. 
 
 The Medusas afford instances of both these kinds of 
 phenomena. 
 
 Again I will illustrate the subject by a brief reference to 
 another class of facts, namely, those of the social life of some 
 animals. In a bee-hive there are, as is familiarly known, 
 different kinds of individuals: there are the queen, the 
 drones, and the workers. In a community of animals allied 
 to these, the ants, and also in Termites, we have still another 
 class of specialised members, called, because they serve for 
 the protection of the social body, soldiers. These ditlerent 
 classes all work together for the goodof the whole community 
 in the wonderful manner known to all of us. 
 
 How can we account to ourselves for the origin of these 
 different forms ? Only by this explanation : that they have 
 all been derived from a single primitive form, the organs of 
 
424 APPENDIX 
 
 which have been atrophied or specialised, as the case may 
 be, in one direction or another ; that in this way the classes 
 have been differentiated, and at the same time alterations of 
 the organs of nutrition and of mental life have been pro- 
 duced. AVe can, in fact, describe the different members of 
 the bee-community as organs of the state, and a wide outlook 
 is opened for us when we devote even a brief consideration 
 to the mental life of this animal society in relation to the 
 question of the existence of real individuals in organic nature. 
 
 We know that mere " intelligence " alone is ascribed to 
 animals as distinguished from man ; it is not admitted that 
 they are also possessed of ''reason," and it is remarkable that 
 this distinction is upheld to the present day even by 
 zoologists. But it is my belief that no perfectly definite 
 distinction between intelligence and reason is possible. We 
 distinguish, to put it briefly, intelligence from reason essentially 
 only by this, that the latter takes account not only of the imme- 
 diate requirements of the single creature, but considers also 
 indirectly, deductively, everything which affects that creature ; 
 that reason does not merely live from hand to mouth, looking 
 only to immediate needs, but considers future needs depend- 
 ing on the time and also the society in which the individual 
 lives. Eeason will therefore always take account of the 
 future and of the community in which the individual lives, 
 because it must reflect that the good or ill of the community 
 is the good or ill of the individual. 
 
 Now, when we regard the mental life of a bee community 
 from this point of view, we necessarily find that it shows 
 reason in a liii^h de^Tee. The animals act throughout 
 according to the requirements of a w^ell-organised state in 
 various directions. They act in complete accordance with the 
 common interest of all the single members of tlie state, and 
 with the requirements of the future. It is true that it seems 
 to the observer as if this action was in many cases median- 
 
APPENDIX 425 
 
 ical, as if the auimals' conduct was in particular instances not 
 the direct result of mental reasoning, but as if they performed 
 reasonable actions mechanically. But in other instances we 
 are compelled to admit that, after fully considering the parti- 
 cular circumstances, they do what is best for the future and 
 for the common weal. 
 
 If we suppose, for example, that the collection of honey 
 has become mechanical, that the bees no longer reason con- 
 sciously in performing this labour, yet we must assume that 
 originally they began to collect honey from reflection and 
 reasoning ; for otherwise they would never have come to do 
 it mechanically. AYe can also say, on the other hand, that 
 by inheritance actions originally due to reason have gradually 
 become mechanical, automatic, instinctive, so that the animals 
 continue to practise them mechanically as the inheritance of 
 ao-es. It mio-ht be thoudit that to regard the social life of 
 the bees in this way as merely mechanical degrades it in our 
 estimation. But such a judgment would be mistaken. Since 
 these actions are performed automatically, the animals are 
 left free to exert themselves in other ways : they have time, 
 opportunity, and energy to apply their mental activity in 
 other directions ; and we can even see in the development of 
 such a state of things the ideal condition of the state, since 
 the individual performs his part for the good of the whole 
 more and more mechanically, and as a matter of course, and 
 is no longer compelled to consider on each occasion wlu'ther 
 he must do it, and how. 
 
 Kegarding the phenomena in this way, we see a marvellous 
 unity resulting from the combination and co-operation of the 
 mental activities of separate units, since these now work for 
 the good of the community in a perfectly constant manner, 
 like the parts of a machine. 
 
 Let us consider yet another side of the question. I said 
 
426 APPENDIX 
 
 previously that even the development of male and female 
 forms among the members of the bee community was a case 
 of division of labour. This proposition may be extended to 
 the rest of the organic world, and it may be said that 
 wherever a male and female sex exists there is no real perfect 
 individual. The two parts absolutely belong to one another, 
 and ouly form a whole together, not each for itself. 
 
 But still further. The whole nuiltitude of higher animals 
 are all composed of cells. Only the lowest animals are uni- 
 cellular — in this sense also all higher forms are compound 
 aggregates. AVe might accordingly, in seeking a basis for the 
 idea of the individual, describe the lowest forms which are 
 not sexually separate as individuals, as indivisible wholes. 
 But even this view on more minute investigation proves 
 false, for the multiplication of every such individual and its 
 orig;in from another are found to be the results of the same 
 process as the multiplication even of the highest forms : of 
 the separation of parts from the whole, of a division or 
 budding, as the case may be. 
 
 Yet another point of view. In the process of metabolism 
 there is a constant assimilation of nourishment and excretion 
 of effete material taking place in the body, and therefore a 
 constant change of the constituents of the body. No organ- 
 ism continues the same, and even if we were able to speak of 
 an isolated organic being, we could only do so by speaking of 
 the shortest given moment in the existence of an animal, for 
 at every moment its substance is changing. 
 
 We can, of course, artificially establish individuals in the 
 most various ways ; we can say that by an individual w^e 
 understand this or that, if we define our conception in each 
 case in a particular way. But, as I have shown, in the last 
 result we come to the conclusion that the contemplation 
 of single organisms makes it impossible for us to give a 
 perfectly logical definition of " individual," for the simple 
 
APPENDIX 427 
 
 reason that siicli an indivisible organic unit does not exist : 
 it does not exist because all single forms are directly or in- 
 directly connected with one another. 
 
 Herewith I come to the consideration of the second part 
 
 of my subject. 
 
 II 
 
 The doctrine of evolution, we all know, assumes tliat the 
 whole of nature forms a great whole — in particular, that tlie 
 animal kingdom is a connected wdiole. It is very remarkable 
 that the knowledge of the grounds on which this doctrine 
 rests has not become so widely extended among us in 
 Germany as might have been expected. I believe the reason 
 of this lies in the circumstance that German research has 
 almost entirely confined itself to the investigation of anatomy 
 and embryology ; while Darwin, who infused a new life into 
 the doctrine of the evolution of species, took account chiefly 
 of the external forms of animals and plants, and particularly 
 of their biolof^ical relations. It is for the fjreater numbei- 
 of men absolutely impossible to follow the researches into 
 details on which the doctrine of evolution among us, in the 
 German way of treating it, is supported. The study of 
 systematic zoology and botany, which principally depends on 
 the investigation of external form, has even been expressly 
 and publicly tabooed by the principal representatives of 
 Darwinism, and it has been declared scientifically unallow- 
 able to occupy one's self with such things at all. I have long 
 been of a different opinion, and believed it would be profit- 
 able to fix the attention keenly for once on a living creature 
 commonly accessible, to consider the external relations of 
 some single animal or some single plant, and in this way to 
 seek material for the discussion of the connection of forms 
 with one another. And, in fact, I obtained in this way some 
 very remarkable results. 
 
 Hitherto the sionificance of the markings, the spots and 
 
428 APPEN-DIX 
 
 stripes, which occur on the skins of animals has been under- 
 vahied in a quite extraordinary way. It has been the 
 custom to consider all this as of no importance, and no one 
 has thought of looking in any way for the laws which govern 
 these phenomena and the connection between them. But by 
 attentive examination I found that these characters followed 
 most wonderfully definite laws, that there is no point in the 
 marking of any animal which has not a quite special and 
 definite typical importance, and that among all the markings 
 which occur on the surface of tlie animal-body a high degree 
 of connection is to be recognised. Thus there are different 
 types of marking which pass by gradual modifications one 
 into another, so that, when the extreme forms of such mark- 
 ings are connected by the intermediate forms, those which 
 are apparently most different can be brought into a coiniected 
 relationship. 
 
 For example, if we place together all the Lepidoptera 
 which belong to one group, the butterflies, we shall find 
 that there are surprising connections between one species 
 and another, between this and a third, and so on ; connec- 
 tions which point to the perfectly gradual modification of 
 the species according to the plan of arborescent ramification, 
 and to the fact that the cause of this depends on the varia- 
 tion of the species, in other words of the individual, in 
 perfectly definite directions. The species varies here and 
 there, but only in a few perfectly definite details, and 
 usually in one direction only. There appears on the wing, 
 for instance, first a new minute streak as a darkening in a 
 perfectly definite position ; on a second specimen of the same 
 species it is larger and shows whither the evolution will lead. 
 In the most nearly allied species it forms a constant con- 
 spicuous diagnostic character, in the next it is still more 
 altered in the direction indicated, perhaps accompanied by 
 another new variation appearing for the first time. So we 
 
 I 
 
APPENDIX 429 
 
 pass from species to species ; the last compared witli the 
 first shows scarcely any resemblance, but the intermediate 
 forms connect them completely. Thus we pass from Tapilio 
 Podalirius to P. machaon, thence to tlie species of Vanessa, 
 of Hipparchia, of Apatura, and so on, and finally we recognise 
 the indirect connection of all the species. 
 
 But the matter may be made much clearer by another 
 example. I am able to demonstrate that dogs and cats are 
 indirectly related. The evolution of the carnivora proceeds 
 from the civet cat. The markings of this form lead to those 
 of the cats, of the hyenas, and of the dogs, and if you look at 
 any dog which approximates to the original form of the 
 Canidte, that is, which has the jackal or wolf form, you can 
 discern in very faint dark marks on its skin the stripes of the 
 hyena, and certain corresponding markings of the domestic 
 cat. Even the most conspicuous variations of the markings 
 of the dog which have gradually been produced, the spots 
 of the most varied kinds which are apparently irregularly 
 scattered over the body, can be traced back to these original 
 lines. Again we have always original darker areas which 
 extend over a larger area, then vary in different ways, divide 
 into separate portions, coalesce, and so on, and thus produce 
 markings between which it is apparently impossible to trace 
 any connection. I notice, for instance, that the markings of 
 hunting and sporting dogs can be traced to a simple plan : 
 you find in most cases a spot on the hindquarters, two on 
 the back, one spot on the neck, and again another on the 
 
 head. 
 
 These examples must sufiice for the present occasion. I 
 have next to point out that the males always are the first to 
 assume new characters. To this law I have given the name 
 of " male preponderance." The males then are always at a 
 more advanced stage of evolution than the females. Ihit 
 there is at the same time a difference depending ^m\ age, for 
 
430 
 
 APPENDIX 
 
 the older males assume new characters first and transmit 
 them to the whole species. Of this also very instructive 
 examples might be given ; but I will not enter upon these, 
 but will only mention that the females usually exhi1)it the 
 markings of the young males, that they therefore — if the 
 ladies will permit me so to express it — stand at a lower stage 
 than the males. On the other hand, the young always 
 exhibit the original markings — therefore in any race the 
 young in respect of marking stand at the level of a long past 
 generation. It is known, for instance, that in many deer 
 certain markings on the side of the body occur only in the 
 young, in others in the adult females also, and only in rare 
 cases in the adult males. The whole modification of the 
 marking proceeds from a longitudinal striping into a spotted 
 condition, and finally into transverse striping, till the mark- 
 ing disappears altogether. If we take the roe-deer or the red- 
 deer as an example, we have in the young a longitudinal 
 striping, which is, however, already resolved into spots, or 
 very soon is so resolved. In the old roe-deer this kind of 
 markinij: is no longer seen, in the female red-deer it lasts 
 longer. Cervus axis, on the other hand, still stands at the 
 lowest stage of evolution, for even the adult male retains the 
 longitudinal striping. Dama vulgaris, the fallow-deer, is in 
 an intermediate condition, for it shows the fully-developed 
 longitudinal striping only in the young and the females ; but 
 even here it is but feebly defined. Similarly we find that in 
 our wild cat the marking in the young animal is at first still 
 more or less of a longitudinal striping, afterwards resolves itself 
 into spots, then becomes a transverse striping, until in the 
 old animal, and especially in the old males, the marking has 
 almost disappeared. AVe have here a good illustration of the 
 so-called biogenetic law, the law that the development of 
 any animal repeats the stages which were successively 
 reached by its ancestors. 
 
APPENDIX 431 
 
 But there is another point to notice. We find that the 
 evolution of marking proceeds also in a definite direction in 
 this respect ; that as a rule modification extends from behind 
 forwards, so that when the male assumes a new stage of 
 marking it appears first at the posterior end of the body. 
 Thus we may see in birds of prey that tlie tail lirst shows 
 the transverse striping, while in the middle of the body we 
 have spots, and on the anterior part, the head and neck, there 
 are still longitudinal stripes. When we place a wliole series 
 of allied species alongside one another we can see which is 
 the most advanced in evolution, and we may possibly detect 
 in this species the traces of a new marking on the most 
 posterior part of the body of the male. In the course of 
 generations the new marking advances forwards, then still a 
 new one begins behind and passes forwards, and at last a 
 trace of the first is only to be found remaining on the most 
 anterior part of the body of any descendant, and o;ily in a female 
 (postero-anterior evolution). A similar progress of modification 
 clearly takes place in many animals in the direction from the 
 lower to the upper side of the body (infero-superior evolution). 
 
 In this way we can recognise that a definite evolution 
 passes over the individual forms in a definite succession of 
 stages by a natural necessity. 
 
 This conclusion is in a certain sense opposed to Darwin's, 
 since it recognises a perfectly definite direction in the evolu- 
 tion and continuous modification of organisms, which even 
 down to the smallest detail is prescribed by the material 
 composition (constitution) of the body. According to this 
 conclusion, the real Darwinian principle, that of selection 
 depending on utility, is only effective within the limits whicli 
 are prescribed by the material composition of the body, that 
 is, by the fixed directions of evolution. 
 
 Accordingly there is nothing fortuitous, but everything in 
 evolution to the smallest detail is governed by laws. 
 
432 APPENDIX 
 
 Chance only selects to a certain degree. 
 
 This view thus removes an objection which has so often 
 been raised against the Darwinian attempt to explain the 
 evolution of the organic world, namely, the predominance of 
 chance, while on the otlier hand it does not undervalue the 
 importance of Darwinism. It sees the essential factor in the 
 origin of species in the progress towards, or the temporary 
 continuance in, definite stages of evolution (genepistatic 
 evolution). 
 
 And so we can imagine all forms which externally show 
 their connection with one another — apart from the fact that 
 they are also connected by their internal organisation, only in 
 a manner wliich is not so clear to every one, — ^ve can imagine 
 the whole series of all the individuals of one line of descent 
 at a given moment united together into a whole, if we con- 
 ceive that the whole course of evolution which has taken 
 place in organic nature in the course of endless periods is 
 condensed into this moment. Then we should again have 
 a whole, the original larva from which the manifold variety 
 of organic nature has evolved itself. But as things now 
 exist in nature we have in species only separate fragments of 
 the whole, which have separated themselves more and more 
 from the original — fragments, moreover, which are regarded at 
 a particular stage in a continuous evolution the end of which 
 cannot be seen. For if Ave accurately examine into the 
 meaning of the propositions which I have established, we 
 shall find that it follows from them that in a wdiole complete 
 evolutionary series the succeeding must always be the more 
 highly evolved, the preceding always the more lowly evolved 
 — as it were, the larva of the succeeding. 
 
 And when we take the whole series, we find that the most 
 highly evolved must pass through in its life, though in a 
 brief and condensed fashion, the evolution of the w^hole series; 
 the changes, to extend more generally the special case, passing 
 
APPENDIX 433 
 
 for the most part in the direction from behind forwards over 
 the whole body. We recognise therefore the most intimate 
 relations one with another among all the single individuals. 
 Thus the preceding is always as it were the larval form of 
 the next following ; and thus of him who considers himself 
 the culmination of all things it can only Ije said that in 
 all probability he likewise will be nothing more tlian 
 the larva of a succeeding form which will be evolved 
 from him. 
 
 When we thus place ourselves among other organic beings, 
 and disdain to arrogate to ourselves an exceptional position in 
 comparison with them, it is self-evident that we must of 
 necessity apply to ourselves the laws which here reveal 
 themselves. 
 
 Thus for the future the idea of a whole in organic nature 
 completely disappears, whether we attempt to regard as such 
 a whole single beings or groups of beings, let the latter be 
 described as species, orders, or classes. 
 
 Thus the single being, as the German term for individual 
 {einzehuesen) rightly implies, is but a fragment, not merely 
 of its own species, but also of the totality of the animal 
 
 kingdom. 
 
 In the light of tb^s conception, the latter in connection 
 with the rest of nature is seen as a harmonious whole con- 
 sisting of many members, in which no part has any right to 
 an absolute pre-eminence over another. 
 
 When we consider the animal world as such a whole, we 
 reach the conception of our great philosopher Oken, who 
 regarded individuals as the organs of the wdiole. 
 
 °The manifold variety of individuals then appears as tlie 
 result of division of labour as much as the formation of organs 
 
 within the individual. 
 
 This conception implies at the same time the recognition 
 of a life which is at least relatively eternal, immortal, a life 
 
 2 F 
 
434 APPENDIX 
 
 in which the Q-ood continues to live through the effort of the 
 individual, through the improvement of the offspring. 
 
 This conception disdains the idea of doing good for the 
 sake of reward ; it desires to do it for its own sake, for the 
 benefit of all. Good, however, is not sometliing prescribed 
 from without ; we call only that tlie good which is serviceable 
 to the common wellbeing, and because it has become service- 
 able to the common wellbeing. 
 
 Only so far as is not inconsistent wdth the good of all will 
 the individual put forth his might in the struggle for 
 existence. 
 
 He must ever keep this in view if he wdll avoid injuring 
 liimself. 
 
 For even the utility principle does not demand brute 
 strength throughout, but leaves room for universal love, the 
 action of which, as reason tells the individual, will always 
 reflect back upon himself. 
 
 Thus our conception leads not only to the comjDlete recog- 
 nition of the rights of our neighbour, but also to the most 
 complete subordination in family and state. 
 
 It is the most uncompromising opponent of that confused 
 idea of freedom so injurious to the common good which 
 claims unlimited independence for the individual. 
 
 It takes in some sense the social life of the bees for its 
 model, in which the work of the individual for the com- 
 munity has become automatic action. 
 
 And that in our civilised life we act to some extent in this 
 way may be proved by the fact that we have come in ordin- 
 ary morals to regard the good as something absolute, univer- 
 sally admitted, to make the conscience responsible for its 
 violation, and to strive towards the ideal. 
 
 If the thinkinf!; man whose mental vision sees the infinite 
 multitude of worlds, or if the student of nature is questioned 
 concerning our position and significance in the universe 
 
APPENDIX 435 
 
 beyond the limits of that nature wliicli is accessible to him, 
 he will point to the Infusorian wliose horizon is limitccl to 
 the drop of water which contains it. 
 
 Our duty is work ; our right is free investigation ; our 
 satisfaction the establishment of a grain of trutli for ilic 
 benefit of mankind ; our hope — knowledge. 
 
 THE EKD 
 
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