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0.058

AN ANAIYSIS OF THE LEARNING PROCESS IN THE SNAIL,
by
Elizabeth I. Thompsons


A DISSERTATION
submitted in partial fulfillment
of the requirements for the
degree of
DOCTOR OF PHILOSOPHY
in
THE UNIVERSITY OF MICHIGAN,

1916.

ii •
TABLE OF CONTENTS e
Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
I • Modifiability studied by a method analogous to the
Pawlow salivary reflex method – learning
thorough conditioned stimuli . . . . . . . . . . . . . . . . . . . . 3
1. Outline of Problem • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 * Material and methods in general • . . . . . . . . . . . . . . . . . 6
3. Response to the food stimulus • . . . . . . . . . . . . . * * * * * * 8

A. The response a reflexe - - - - - - - - - - - - - - - - - - - - - - 8
Be The number and duration of reactions
in normal food stimulus response . . . . . . . . . . . 12
4. Response to the conditioned food stimulus,
stmultaneous food and pressure stimuli . . . . . . . . .17
As Special apparatus and methods . . . . . . . . . . . . . . .18
B. Experiments which show lack of response
of untrained snails to pressure alone . . . . . . 21.
C - Training experiments to determine res-
ponse to the conditioned food stimulus
first food pressure series. . . . . . . . . . . . . . . . . 21.
De Experiments with pressure alone on train-
ed snails; association • , . . . . . . . . . . . . . . . . . . , 36
Be Experiments to determine the effect of
training on the food pressure response
- second food pressure series • . . . . . . . . . . . . a 40

5. Summary Of Observations. . . . . . . . . . . . . . . . . . . . . . . .48

6. Discussion of modifiability through the method
of Simultaneous stimuli . . . . . . . . . . . . . . . . . . . . . . . 64
II • Modifiability studied by the labyrinth method. . . . . . . 60
1. Introduction.....................................60
2* Apparatus and material. . . . . . . . . . . . . . . . . . . . . . . . . . , 63
3. Experiments on preference . . . . . . . . . . . . . . . . . . . . . . . . 67
A. Experiments to test right-left preference . . .67
B. Experiments to test preference for an

ascending or descending path. . . . . . . . . . . . . . .73
4 * Experiments on learning the U shaped labyrinth:
choice of right and left paths: punishment
filure to get air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
iii
5. Experiments with Y shaped labyrinth: roughness
of as a warning signal: electric shock punish-
ment • - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -106
6 * Experiments with Y shaped labyrinth: mechanical
signal as warning signal: electric shock punish-
ment • - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 136
7. Summary of Observations • . . . . . . . . . . . . . . . . . . . . . . . . . .161.
8 * Discussion of learning by the labyrinth methode . . eló5
III • Conclusions • , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171
IV. Literature cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172

iv.
Fig.
Fig.
- Fige
Fig.
Fig.
Fig.
Fig.
Fig.
le
2.
3.
4 •
5.
6.
7.
8,
9.
LIST OF ILLUSTRATIONS •
showing the apparatus which required the
simultaneous application to the Snail of food
and pressure, and pressure alone . . . . . . . . . . . . . . . . .19
Curve showing distribution of reactions per 50
trials with the food-pressure stimulses for each
of two Snails (4, 5). . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Showing the U shaped labyrinth used in the
right-left discrimination tests • , . . . . . . . . . . . . . . . e6?
Showing the apparatus used to control light
conditions, the Y shaped labyrinth, and the
rheostat; used to control the electric current
employed in administering the shock. . . . . . . . . . . . . .65
Showing the distribution of error for snail
No. 1 in a series of 282 right-left discrimina-
tion tests, extending over a period of 48 days. ... elC3

Showing the distribution of error for snail No.
2 in a series of 307 right-left discrimination
tests, extending over a period of 54 days . . . . . . . . 104
Showing the distribution of error for snail Noe
3 in a series of 299 right-left discrimination
tests, extending over a period of 54 days. . . . . . . .105
Showing the distribution of error in the rough-
shock-Smooth tests for snail No. 9 in a total
of 215 trials extending over a period of
38 days • - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -130
Showing distribution of error in the rough-
shock-Sfflooth tests for Snail No. 10 - - - - - - - - - - - - - -131.

10. Showing the distribution of error in the rough-

Fig.11.
Fig.12.
shock-Smooth tests for snail No. 11 in a
total of 178 trials extending over a period
of 25 days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
Showing the distribution of error in the rough-
shock-smooth tests for snail No. 27 in a total
of 57 trials extending over a period of 12 days . .133
Showing the distribution of error for snail No.
19 in a series of 141 tests, extending over a
period of 19 days, in which a mechanical
stimulus was used in connection with the electric
shock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * * * * * -134
Fig. 13.
Fig. 14 •
Fig. 15.
Fig. 16.
Fig. 17.
Showing the distribution of error for snail No.
21 in a series of 174 tests, extending over a
period of 27 days, in which a mechanical
stimulus was used in connection with the
electric shock. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 155
Showing the distribution of error for snail
No. 22 in a series of 184 tests, extending over
a period of 27 days, in which a mechanical stim—
ulus was used in connection with the electrič
shocke - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -156
Showing the distribution of error for snail No.
9 in a series of 147 tests, extending over a
period of 21 days, in which a mechanical
stimulus was used in connection with the
electric shock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157

Showing the distribution of error for snail No.
10 in a series of 173 tests, extending over a
period of 23 days, in which a mechanical
Stimulus was used in connection with the
electric shock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Showing the distribution of error for snail No.
13 in a series of 121 trials, extending over
a period of 17 days, in which a mechanical
Stimulus was used in connection with the
electric shock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159



AM AMALYSIS OF THE TEARNING PROCESS IN THE
SMAIL, PHYSA GyPINA SAY.
INTRODUCTION,
The experiments included in this paper were begun with
the purpose of determining the ability of snails to discrim-
inate between sensory stimuli • To this end a method was
adopted analogous to the salivary reflex method of Pawlow.
Its use showed, among other things, a form of modifiability
of behavior that could be interpreted only as learning- the
capacity to form associations • The original plan to use this
capacity as a basis for studies in discrimination was then
changed. The discrimination experiment s were deferred and
the work was continued in order to determine if the snail,
which can form associations, can also solve a simple labyrinth.
The paper thus falls into two parts - Part one deals with
modifiability as disclosed by the method of conditioned
stimuli - with the power to form simple associations • Part
two takes up the further question of the ability of the snail
to solve a labyrinth and discusses the relation of this to the
formation of simple associations • It is the purpose of the
writer to return to the study of discrimination •
To Professor Jacob Reighard, who suggested the original
problem and under who se direction the work was done, the writer

is indebted for constant as sistance, to Professor John F.
Shepard she is indebted for criticism and suggestions for
the use of the labyrinth method, to Professor George Re
LaRue, aid in designing of the apparatus and to Horace B.

A
Baker and Harold Cummins for the identification of the Snails.

I, MODIFIABILITY AS DISCLOSED BY A METHOD
ANALOGOUS TO THE PAWLOW SALIVARY REFLEX METHOD,
le Outline of the Problems The snail, Physa gyrina
Say, like many other species, has the habit of crawling
suspended from the surface film of the water. Its shell is
then below and the ventral surfaces of the muscular foot and
the head are exposed to view from above. The mouth may then
often be seem to open and close many times in succession.
Dawson (1911) found that when the region within a millimeter
or two of the mouth was touched with a bit of food or a cle an
glass rod, a chewing motion of the mouth parts began which
"would continue for perhaps an hour or so, even if the animal
were placed in fresh clean water." She found that the same
stimuli applied to other parts of the animal produced no move-
ments of the mouth parts. Familiarity with the mouth movements
of this snail suggested that it might be a reflex of the same
definite character as the salivary reflex made use of by
Pawlow and his pupils in their studies of association and
discrimination in the dog.
Pawlow (1904) opened the duct of the parotid gland of
a dog to the outside by means of a fistula. He then measured
the secretion and determined its quality (viscosity), when
induced, first by the odor or sight of food unaccompanied by
other experimental stimuli. Pawlow called this food stimulus
an "unconditioned" stimulus. He then measured the secretion



induced by food stimulation in the presence of an auxiliary

(or secondary) stimulus such as sound or color. This he called
a "conditioned" stimulus. After using the conditioned stimulus
for a time, he omitted the primary stimulus (food) and found
that the secretion was induced by the auxiliary stimulus, the
tone or color, alone . He believed that he had shown conclusive-
ly that the animal had formed an association between the two
stimuli since at first it had not reacted to the secondary
stimulus, but after this stimulus had been used for a time in
connection with the primary or food stimulus it had reacted
to the secondary stimulus alone - Then by changing slightly
the tone, color or other secondary stimulus used, he determined
Whether the animal reacted to this altered stimulus and to what
extent • A change in the reaction was taken as evidence that
the animal discriminated between the original and the altered
stimulus. Thus power to discriminate between stimuli was tested.
Pawlow and his followers believed that the method could
be used on only a limited number of mammals. "Its obvious
limitation appears in the number of organisms with which it
may be employed. Evidently it cannot be used for the study
of animals which lack salivary glands, and even among those
animals which do possess the se glands there are many which
surely would not lend themselves satisfactorily to the method.
It seems the refore as if Pawlow's method were especially import-
ant in animal psychology as a means to the intensive study of
the mental life of a limited number of mammals." (Yerkes and
Morgulis, 1909). The oretically, however, this method is

applicable to any organism that responds to a stimulation by
a specific, measurable reflex of muscles or glands. Such
reflexes occur in many of the lower forms; among them is the
mouth movement of Physa.
It was decided then to determine:
(1). The character of the response following a
single application of a food stimulus to the mouth parts of
the snail. Such a response consists of one or more reactions.
A single complete movement - one reaction - may be compared
to the secretion of a drop of saliva in the Pawlow experi-
ments. A determination of the number of reactions per response
was deemed comparable to Pawlow 's measurement s of the salivary -
secretion induced by food alone or resulting from an "uncondition-
ed" stimulus •
(2). Following this the application of two stimuli
together, that is, food to the mouth parts and pressure at a
fixed distance from the mouth, would, it was believed, correspond
to Pawlow's "conditioned" stimulus • The number of reactions
constituting each response would correspond to his measurements
of saliva under such cond it ions •
(3). It was then planned to apply the associated or
auxiliary stimulus alone in the absence of food, in order to
determine from the presence or absence of reactions resulting,
whether or not an association had been formed between the two
stimuli.
2. MATERIAL AND METHODs.
The snails used in the exp eriments were collected in
an oxbow pond that had been completely cut off from a small
Greek • Several hundred were brought into the laboratory and
placed in large glass aquaria containing water plants such as
slodea and spirogyra. An effort was made to have the environ-
ment in the se aquaria as nearly like the natural habit at as
possible • Besides the water plants upon which snails usually
feed, fresh lettuce was placed in the aquaria • They at e this
in comparatively large quantities, and seemed to prefer it to
other plant food.
When the tank containing recently captured snails was
jarred or disturbed in any way, they would instantly expel
the air from the lung, retract into their shells, and drop
from the surface film, upon which they were crawlins, to the
bottom of the tank. Many of them frequently remained motion-
less on the bottom for an hour or more before they again sought
the surface and refilled their lungs. It became necessary
therefore, to "tame" the snails which were to be used in
the experiments, to so) accustom them to handling that they
would remain extended and retain the air in the lung while
they were being worked upon.
About twenty specimens of approximately the same size
were selected for the tests. These were placed in two bacteria
dishes. In each aish was about a liter of water with water


plants and as much lettuce as the snails would eat . The snails
were taken in the hand at intervals and moved about under water.
Each was held in the hand beneath the water until it emerged
from the shell and suspended itself from the surface film.
They gradually became accustomed to this handling to such an
extent that they could be moved from dish to dish, at the will
of the operator without retracting or expelling the air from
the lung ,
The se "tamed" snails were then divided into two groups.
Each individual was numbered by means of white water-proof
paint applied to the shell after it had been thoroughly area.
These groups were worked on alternate days. Each group was
starved for a period of wenty-four hours before tº ests were
made • The snails belonging to the group were thus believed
to be in approximately the same state of hunger at the time
of experimentation. After a group had been worked on it was
allowed to feed for twenty-four hours and was again starved,
before it was used, In this way an attempt was made to obtain
physiological uniformity among the snails directly under observ-
ation. The physical conditions were also kept as uniform as
possible • The whole series of daily exp eriments was carried
on at approximately the same hour • Each snail in turn was
placed in a clean dish of fresh, filtered tap water. - The
water was of the same depth and at the same (room) temper-
ature as that in which the snails had been living. The light-
ing was at all times uniform with that in which the animals


had been living. Each individual was put through a series
of ten tests per day with one exception (check series Table I)
and a separate record made of each.
3. THE RESPONSE TO THE FOOD STIMULUS.
In order to utilize the snails it was necessary to know:
(1) Whether the mouth reactions occur only as the result
of external stimulation, and
(2) Their consistency as to the number of reactions and
the duration of the response following a single stimulus.
Should they occur regularly as the result of external stimula-
tion and only then they must be regarded as "involuntary"
responses or reflexes, available for the purpose of the
experiments. Upon the constancy and duration of the response." ends
its value for quantitative uses.
As The response to the food stimulus a reflex:
It was found by observation that the mouth movements of Physa.
were induced not only by food and mechanical st imulation of
the mouth region, but that they sometimes occurred when no
such stimuli could be detected. Such apparently voluntary
movements might be due to the stimuli from microscopic particles
in the water. A check series of experiment s was deemed necess-
ary in order to determine whether or not the mouth reactions
might normally occur without external stimulation and if so
under what conditions and with what frequency . In the se tests
each snail, under the controlled conditions just ment ioned, was
in turn held in the hand of the operator until it suspended it-
self from the surface film. It was then permitted to move
about, and was touched only when necessary to keep it from


crawling down the sides of the dish. At such times it was
pushed gent ly toward the center of the tank with a sterile
glass rod • Each animal was thus kept crawling on the surface
film for an average period of forty-five minutes under constant
observation and a record was made of each mouth reaction. It
was found to be impossible to keep the snail absolutely free
from all chance stimulation of the mouth. It has been shown
that the animal uses the same method of locomotion in crawling
on the surface film that it does in moving over any substratum,
that is, it crawls along a mucous path which it secretes as
it moves and which remains behind it resting on the surface
of the water. (Parker, 1912); (Dawson, 1911). The mucus thus
left on the surface may reach the mouth of the snail as it
moved about . In several instances this mucus was observed
to touch the mouth parts and such contact was followed by
reactions. These are noted in the following table • Stimulation
of this sort is the probable cause of all other reactions that





occur in the test series.

10
T. A B L & I.

Showing the number of reactions of the mouth of six individuals of
Physa gyrina says kept under observation in filtered tap water for 32%
hours, when not stimulated by the application of food to the mouth region.
The snails had been without food for 24 hours preceding the tests • They
were divided into two groups of three each and tested on alternating days.
No. of Noe of Period of No e Of mouth Noe of mouth No e Of egg
snail, days observation reactions, reactions masses deposit-
tested in minutes no visible Fºotº ed in 24 hours
- each day e stimulus • stimulations preceding testse
60
45
60
60
60
60
18
19 60
45
60
60
60
60
60
45
60
60
60
20
21 30
60
60
60
60
60
22 30
60
60
60
60
60
23 30
60
60
60
60
60
Total time of observation, 32.75 hrs •
Total number of reactions, 38,
Total number of reactions, no visible cause 17 44.73%
Total number of reactions, mucous stimulation 21 55.26%
Average number of reactions per hour le16
Average number of reactions, no visible cause, per hr s 51
O
:i
11
This table shows that when six snails were kept
under observation for nearly thirty-three hours (about five
and a half hours each) in filtered tap water only 38 mouth
reactions were observed, an average of 1.16 per hour. If we
allow for each reaction 1.25 second s the duration of the 38
reactions is 47.50 seconds. of the 38 reactions 21 or 55.2%
were observed to be due to mucus stimulation and the remainder
were probably due to the same cause - Owing to the fact that
the mucus is colorless, and, as it occurs on the surface of
the water - transparent, it is exceedingly difficult to deter-
mine its presence at all times. Any attempt to bring it into
view by the addition of color such as powdered carmine would
only serve to make it more effective as a stimulus. The re-
actions which did occur can then be accounted for . The
mouth reactions of Physa may, then, be regarded as a true re-
flex, an "unlearned response" (Watson, 1914), which occurs
normally as the result of external stimulation of the mouth
or the tissues immediately surrounding it. For experimental
purposes we may say that the reaction occurs only as the re-
sult of external stimulation. If now, the snail were placed
in water freed from microscopic particles by filtration and
the mouth reactions were practically always induced by bring-
ins food directly into contact with the mouth, the reactions
must be regarded as reflexes, that is, involuntary - Such
a series of reactions then might be interpreted as an "uncon-
ditioned reflex" (Pawlow, 1904). The number of the reactions




and the duration of the series prove an available substitute
12
for the measurements of saliva in inquiries into the be-
havior of a group of animals widely separated from mammals.
B. Number and Duration of Reaction in the Normal Food
Stimulus Response.
The snails which were used in all of the remaining
tests had been fed upon lettuce while in the laboratory; for
this reason lettuce was used as a food stimulus in all the
experiments. A small piece taken from a fresh leaf was
applied to the normally inactive mouth of the snail by means
of forceps and immediately withdrawn. This stimulus served
to start movements of the mouth parts, and an exact record
of the number of reactions thus induced was kept for each in-
dividual. During work a record was also made of the length
of time that the reactions persisted that is, the duration

of the response.

Tº a b 1 e II.

Showing the number of reactions of the mouth of two individuals of
Physa gyrina Say, resulting from a single application of food to the mouth.
The tests were made in filtered tap water on alternating days. The snails had
been starved for 24 hours preceding the tests,
No e Of Noe of Serial No. for No e Of No. of Duration
snail. days Moe of *food trial reactions of response
tested, Trial, stimulus" for per in sece
º- seriesa ãays responses
4. 1. l 1. l l l
2 2 2 O O
3 3. 3. 1 1.
4. 4. 4. 6 10
5- 10 5-10 5-10 - 0.
Totals 10 8 12
Ave per
response 2 e66 1.5
2 11 11 l l l
12 12 2 6 10
13 13 3 38 50
14 14 4. * x O
15 15 5 l l
16 16 tº 6 1. l
17 17 7 3. 5
18 18 8 l l
19-20 19-20 9-10 O O
Totals 10 51 69
Ave per
response 7,28 1.35
3. - 21 21 l O O
22 22 2 1. l
23 23 3 l 1
24 24 4. 1. l
25 25 5 l l
26 26 6 1 1.
27 27 7 2 3
28 28 8 O O
29 29 9 l l
30 30 10 0. O
Totals 10 8 9
Ave per
response lel4 1.12
4. 31 31 l 3 4.
32 32 2 2 2
33 33 3. l l
34 3 4. l l
35 35 5 l l
36 36 6 2 2
37 37 7 l l
38 38 8 2 2
39- 40 39-40 9-10 O O






14




No. of No. of Serial No e for No. of No e Of Duration
snail, days no, of * food. trial reactions of response
tested trial. stimulus" for per in
series • ‘lays responsºle seconds •
24- Totals 10 . 13 14
Ave per -
response 1.62 1.07
5, 41 4l l ll 15
42 42 2 6 8
43 43 3. O O
44 44 4. 3. 3.
45 45 5 l l
46 46 6 O O
- 47- 50 47–50 7-10 * x O
Totals 10 21 27
Ave per
response 5,25 le28

*Gases in which lack of response was due to known mechanical disturbance
indicated by x•


Total number of trials, 50
Total number of stimuli followed by response, 29
Per cent, of stimuli followed by response, 58%
Total mumber of reactions, 101
Average number of reactions per trial, 2a02
Average mumber of reactions in only those trials
in which response occurred, 3.e48
Total time of reactions, 2.18 mine
Average time of reaction, le?9 secs

Average number of reactions per minutes 46.5l.


TABLE II (continued)
No. of No. of Serial Noe for No e Of No. Of Duration
Snails days noe of "food trial reactions of response
tested, trial stimulus" for per in
seriesa day. £889918&a Bººs
5 1. l 1 l 24 30
2- 4 2-4 2-4 O O
5-10 5-10 5-10 * x O
Totals 10 24 30
AV e. per º
response 24 le25
2 ll 11 l 5 10
12 12 2 l l
13 13. 3 * x O
14 14 4. O O
15 15 5 l l
16 16 6 1. l
17 17 7 2 3
18 18 8 l 1.
19 - 20 19-20 9–10 * x O
Totals, 10 11 17
Ave per
response, 1.83 1.54
3. 21 21 l l l
22. 22 2 l l
23 23 3. 1. 1.
24 24 4. 2 3.
25 25 5 2 3
26 26 6 l l
27-30 27-30 7-10 *::: O
Totals 10 8 10
AV, per le33 1s25
response
4. 31 31 l 3 3.
32 32 2 4. 5
33 33 3. 4. 5
34 34 4. 2 2
35 35 5 l l
36 36 6 l l
37 3? 7 l l
38 38 8 1 1.
39 39 9 4. 4.
40 40 10 1 l
Totals 10 22 24
AVs per
response 2e2 leO9
*
TABLE II (continued)
No. of No. of Serial Moe for No. of No. Of Duration
Snails days No. Of *food trial reactions of re-
tested. trial stimulus" for per sponse
series • to-days _responses in sece
5 5 41 4l 1 19 22
42 42 2 20 22
43 43 3. 5 6
44 44 4. 10 12
45 45 5 4. 8
46 46 6 6 5
47 4? 7 1 l
48 48 8 O O
49 49 9 3. 4.
50 50 10 6 8
Totals 10 º 88
AVs 8,22 1.18

*Gases in which lack of response was due to known mechanical disturbance
indicated by x•

Total number of trials, 50
Total mumber of stimuli followed by response, - 32
Per cent • of stimuli followed by response, 64%
Total number of reactions, 139
Average number of reactions per trial, 2.78
Average number of reactions in only those trials in which
response occurred, 4s 35
Total time of reactions, 2.81 mine
Average time per reaction, - la?l sece
Average mumber of reactions per minute, 45.9

Summary snails 4 and 5,

Total number of stimuli (trials) 100
Total number of stimuli followed by response 61
Per cent s of stimuli followed by response, 61%

Table II shows that when a food stimulus is applied
to the mouth region of Physa gyrina Say, response occurs in
61% of 100 trials with two snails. The individual records
show that the number of reactions making up the response
varies from 1 to 38. The first 30 trials of the series of
50 trials for snail 4 shows 67 reactions, while the following
20 trials give 34 reactions with an average of 2.83 reactions
per response. In the case of snail 5 the corresponding
numbers are 43 and 96 reactions with an average per response
of 3. 3 and 5.05. This indicates in the case of snail 5 a.
tendency to recover during the second part of the series
from the inhibiting effect of the manipulation (adaptation).
In snail 4 the recovery may be delayed beyond the limits of
the series. The series is in both cases too short to afford
anything more than a suggestion as to the occurence of adap-
tation. The absence of reaction in certain trials, the
wide variation in their number in those trials in which they
occur and in the differences between individual snails is
brought out in the summary (p.48) and is discussed later.
The average number of reactions per response furnishes a
means of comparison of the results here obtained with those
recorded in the part of this paper which deals with the si-
multaneous use of two stimuli.
4 • . RESPONSE TO THE CONDITIONED FOOD STIMULUS:
SIMULTANEOUS APPLICATION OF FOOD AND PRESSURE.
There is then determined the number of reactions of
the mouth parts induced by a single definite stimulation and


constituting a single response, the duration of the response
18
and of the single reaction. The stimulus according to
Pawlow's terminology would be "unconditioned" or primary.
An attempt was next made to use a "conditioned" or double
stimulus by the simultaneous application of pressure and
food.
A. Special Apparatus and Methods. This required the
construction of a Special apparatus which would ſhake possible
the application of a uniform pressure at a fixed distance
from the food stimulus when the latter was applied to the
mouth of the Snail. Out of the several appliances tried,

the one here pictured (fig. 1) gave the best results.


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20
(A) was a wire nail which served as a handle. A
small strip of sheet metal (B) 5mm in width, and bent in the
form of a square cornered U, was soldered to its end. B
contained two smooth edged holes, one directly above the
other and both as large as would permit the free movement
through them of smooth steel rod (C) which was made from a
No. 5 sewing needle. C was kept from dropping through the
holes, by a fine wire (D) which was passed through the eye
of the needle. To the lower end of the rod C was soldered
a U shaped piece made of no. 30 platinum wire. One limb
of the U (E) 16mm in length ended in a small hook. The
other limb (F) -18mm in length, ended in a three-pronged, dull
pointed platinum fork 3mm wide and turned at right angles to
the base of the U shaped piece. (A) was held in the hand
of the operator and the fork on the lower end of F was al-
lowed to rest; on the exposed ventral surface of the snail
at the same time that food (a small piece of lettuce rolled
between the fingers to form an inverted cone) suspended from
the hook at the lower end of E was applied to the mouth of
the snail. The free movement of the lower part of the ap-
paratus permitted by the smooth edged holes in B, made it
possible for the operator to manipulate the apparatus in such
a way that it remained practically stationary upon the sur-
face of the snail during the period of stimulation in spite



of the constant motion of the animal.

21
B. Experiments which show lack of response of un-
trained snails to pressure alone.
Before using the apparatus in experiments with the
conditioned stimulus, a series of twenty trials was made on
each of six snails in order to learn whether the application
to the foot of the pressure fork alone induced response.
The snails were starved for twenty-four hours previous to
the experiments and each was tested in filtered tap water.
The above described apparatus without food was applied t;o
the upturned ventral surface of the foot. It was placed
upon the animal in such a way that the food hook was just
above the mouth. Pressure was thus applied to the same
part of the foot that would receive it if the double stimuli,
food and pressure, were being applied together, In the total
of 120 trials 4 responses occurred (3.33%) and these were
probably due to mucous stimulation. Pressure alone, as
applied with the apparatus used is followed by response in
SO small a percentage of the trials that its occurrence




does not vitiate the experiments which follow .
C. Experiments to determine response to the con-
ditioned food stimulus: first food and pressure series.
By means of the food-pressure apparatus, food and
uniform pressure were next applied simultaneously in a long
series of trials. Both stimuli were immediately withdrawn
and the number of reactions of the mouth counted and recorded
as before . Table III shows the record obtained in this
attempt to form an association between two dissimilar stimuli
applied simultaneously.
T. A B L R III.


Showing the mumber of reactions of the mouth of two individuals of
Physa gyrina Say, resulting from the simultaneous application of two dissimilar
stimuli, food and pressure. The tests were made in filtered tap water on alter-
nating days. The snails had been starved for 24 hours preceding the tests •
Noa of Moe of Serial No e for No e of No e of Duration
Snails days No e of *food & trial reactions of response
tested, trial. pressure" for per in
stimulus days responses SëC e
series •
4. 6 51-60 1-10 1-10 O O
7 61-70 11-20 1-10 O O
8 71-80 21-30 1-10 O ()
9 81-9) 31-40 1–10 O O
10 91-100 41-50 1-10 O O
11 100-110 51-60 1-10 Q O
Totals 60 O O
12 111 61 l 4. 5
112 62 2 l l
113 63. 3. 2 2
114-120 64-70 4-10 O O
Totals 10 7 8
Ave per
response 2e33 lslå.
13 121-130 71-80 1-10 O O
14 131 81 l O O
132 82 2 1. l
133 83 3 8 10
134-140 84-90 4-10 O O
Totals 10 9 11
Ave per
response, 4.5 le22
15 14l 91 l l l
142 92. 2 l 1
143 93 3 O O
144 94 4. 2 2
145–150 95-100 5-10 O O
Totals, 10 4. 4.
AV, per
response, le:33 1s0
16 151-166 101-110 1-10 0. O
17 161 111 l 16. 18
162 112 2 6 8
163 113 3. O O
164 114 4. l l
165 115 5 l l
166 116 6 O O
167 117 7 l l
168 118 8 l l
169 119 9 2 2
170 120 10 O O
Ave per
response, 4.0 1.14

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24

TABLE III (cont.)
No. of No. of Serial Moe for No. of Noe of Duration
Snail days No. of *food & trial reactions of response
tested a trial a pressure" for per in
stimulus days responses $3& e
series a
4- 22 211 161 1. l l
212 l62 2 O O
213 163 3 l l
214 164 4. l l
215 165 5 l l
216 166 6 l l
217-220 167-170 7–10 O O
Totals 10 5 5
AV, per
response 1s0 1.0
23 221 171 l 10 15.
222 172 2 12 16.
223 173 3. 2 2
224 174 4. l l
225 175 5 l l
226 176 6 4. 5
227 177 7 l l
228 178 8 9 12
229 179 9 3 4.
230 18O 10 1 1.
Totals 10 44 56
Ave per
response 4.4 le27
24 231-240 181-190 1-10 O O
25 241 191 l 4. 5
242 192 2 l l
243 193 3 4. 5
244 194 4. 1. l
245 195 5 l l
246 196 6 4. 5
24? 197 7 1. l
248-250 198-200 8-10 O 0.
Ave per
response 2e28 le18
* 26 251 201 l 2 2
252 2O2 2 3. 4.
253 203 3. 6 8
254 204 4. l l
255 205 5 l l
256 2O6 6 2 2
257 2O7 7 2 2
258 208 8 3 4.
259 209 9 2 2
260 210 10 2 2
Totals, 10 24 28
Av. per
response


2
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4.
1.16
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25
Table III (Conte).

Moe of Noe of Serial Moe for Moe of No e Of. Duration
Snail, days Moe of *food & trial reactions of response
tested, trial, pressure" for per in
stimulus days responses $6&e
_ _ series º
24- 27 261 211 1 3 4.
262 212 2 4. 5
263 213 3. 5 6
264 214 4. O O
265 215 5 l 1.
266-270 216-220 6-10 O O
Totals 10 13 16
Ave per
response, 3.25 le23
28 271 221 l 4. 5
2?2 222 2 l l
273 223 3 2 2
274 224 4. 1. 1.
275 225 5 l 1.
276 226 6 4. 5
277 227 7 l l
278 228 8 1 l
279 229 9 2 2
280 230 10 l l
Totals 10 18 20
Ave per
response, 1.8 lell
29 281 231 1 l l
282 332 2 1 1
283 233 3. l l
284 234 4. l 1.
285 235 5 l l
286-290 236-240 6-10 O O
Totals 10 5 5
Ave per
responses leO 1-0
30. 291 24l l 10 12
292 242 2 l 1
293 243 3. 1 l
294 244 4. 1 : 1
295 245 5 l l
296. 246 6 l 1.
297-300 247-250 7-10 0 O
Totals 10 15 17
Ave per
responses 2.5 le13
26
TABLE III (conte
-
Nos of No. of Serial No. for No. of No. of Duration.
Snail, days No e of "food & trial reactions of response
tested, trial. pressure" for per in
stimulus day. response e $863 e
series a
4– -
31 301 251 l 4. 5
3O2 252 2 5 6
303 253. 3. 5 6
Totals, 3. lá 17
Average per
responses 4.66 le21
*Gases in which lack of response was due to known mechanical disturbance
indicated by x•
Total number of trials, 253
Total number of stimuli followed by response 99
Per cente of stimuli followed by response, 35%
Total number of reactions, 393;
Average mumber of reactions per trial, 1.55
Average number of reactions in only those trials in which
response occurreds 3.e.96
Total time of reactions, 7.58 mine
Average time per reaction, 1.15 sec.
Average number of reactions per minutes 5.1 s64


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28

TABLE III. (cont
No. of No. of Serial
Snaile days No. of
tested, trial.
TE
Totals
AV, per
response
20 191
192
193
194
195
196
197
198
199-200
Totals,
AV, per
response,
2l 201-210
22 211-220
Totals,
23 221
222
223
224
225-230
Totals,
Ave per
response,
24 231
232
233
234
235
236-240
Totals,
AVs per
response,
25 241
242
243
244
245-250
Totals,
Ave per
response,
No e for Noe of No. Of Duration
*food & trial reactions of
pressure" for per response
stimulus day, response. in sece
—series, -
10 74 85
9.25 le14
141 l l l
142 2 1. l
143 3. 2 2
144 4. 2 2
145 5 6 8
146 6 7 8
147 7 3. 4.
148 8 l l
149-150 9-10 O O
10 23 27
2.87 le13.
151-160 1-10 O O
161-170 10 O O
20 O O
171 1. 4. 5
172 2 5 6
173 3. 3. 4.
174 4. 1 l
175-180 5-10 O O
10 13 16
3.25 1.25
181 l 1 l
182 2 O Q
183 3. O O
184 4. l 1.
185 5 1. l
186-190 6-10 O O
10 3. 3.
1.0 1.0
191 l 10 12
192 2 1. l
193 3 l l
194 4. 1. l
195-200 5-10 O O
10 13 15
3.25 1.15







29
TABLE III (cont.)

No. of No. of Serial No. for No. of No. Of Duration
Snails days No. of "food & trial reactions of
tested. trials pressure" for per response
stimulus day. responses in sece
series •
5 Ł
26 251 201 l 3. 4.
252 202 2 2 2
253 203 3 5 6
254 204 4. 1 l
255 205 5 l l
256 206 6 l l
257 207 7 l l
258 208 8 l 1
259 209 9 l 1.
260 210 10 1 l
Totals 10 17 19
Ave per
responses 1.7 lell
27 261-270 211-220 1-10 O O
28 271-280 221-230 1-10 O O
Totals, 20 O O
29 281 231 1. l 1.
282 232 2 2 2
283 233 3. 1 l
284. 234 4. l 1.
285-290 235-240 5-10 O O
Totals, 10 5 5
Ave per
response, le25 leO
30 291 24l l 5 6
292 242 2 1. l
293 243 3. 4. 5
294 244 4. 4. 5
295 245 5 4. 5
296 246 6 5 6
297 247 7 l l
298 248 8 3 4.
299 249 9 l l
300 250 10 O O
Totals 10 28 34
Ave per
response 3ell 1.21




TABLE III (cont.)
Total number of trials,
Total number of stimuli followed by responses
Per cent 2 of stimuli followed by response,
Total mumber of reactions,
Average number of reactions per trials
Average number of reactions in only those trials in
which response occurred,
Total time of reactions,
Average time per reactions
Average number of reactions per minute,
Summary snails 4 and 5.
Total mumber of stimuli (trials)
Total mumber of stimuli followed by response
Per cent * of stimuli followed by responses
250
62
24%
225
0.9
3.62
4e53 mine
lell sec.
51.92
503
161
32%
TABLE III A


The table shows for snail 4, the distribution of re-
sponses of each ten trials of the first 250 trials shown in
Table III. The numerators of the fractions in column 2 are
the number of reactions for the ten trials, the denominators
are the number of responses. The values in Column 4 are
obtained by dividing the numbers in column 3 by the numera-
tors in column 2.

Trials No. No. Reactions Total duration Average duration
per response. in Seconds of of the reactions
the responses of in Column 2.
the ten trials
of Column 1.
1- 60 0
61 - 70 7/3=2.33 8 l. 14
71 - 80 O O O
81- 90 9/2=4.5 ll 1.22
91-100 4/3=1.33 4. 1.0
101-110 O O O
111-120 28/7-4.0 32 1. 14
121-130 14/7 =2.0 15 1. O'7
131-140 72/5 =14.4 81 l. 12
141-150 71/6=ll.8 82 l. 15
151-160 34/6-5.66 39 l. 14
161-170 5/5-l 5 1.00
171-180 44/10=4.4 56 1. 27
181-190 O O O
191–200 16/7 =2.28 19 1.18
201-210 24/10=2.4 28 1. 16
211-220 13/4=3.25 16 1.23
221-230 18/10=1.8 2O l, ll
231-240 5/5=l 5 1... O
241-250 15/6 =2.5 17 1.13
251-253 14/3-4.66 17 1.21




TABLE III B.
Trials Total No. Av. No. of Total No. Av. no. of
of reactions reactions of reactions reactions
Snail 4 per response Snail 5. per response.
l- 50 O 0. O 0.
51-100 20 0.4 14 0.21
101-150 185 3. 7 132 2. 64
151-200 99 2. O 29 O. 58
201-250 75 l. 5 50 l.0



From Table III it appears that when two stimuli were
applied simultaneously, food to the mouth and pressure to
the foot, there was at first an inhibitory effect upon the
reflex. This is shown in the first 60 to 80 trials in which
no reaction followed the application of the double stimulus.
A slight inhibition continued throughout this series of tests
as indicated by the average number of reactions per response,
that for snail 4 being 3.96, and for snail 5, 3.62 as com—
pared with averages of 3.48, and 4.35 for the same snails
(Table II) in the tests in which the "unconditioned" stimulus,
food, was used. For the food-pressure response the aver-
ages in the numkſerical order of the six snails 3.96, 3.62,
l. 96, 4.1, l. 58, 3.78, or a mean for all Six snails of 3.18.
The corresponding values for the normal food response are
3.48, 4.35, 6.5, 6.5, 3, 4, 10.93, with a mean value of 5.86
for the six snails. Along with the reduction in the number
of reactions there is in the food-pressure response an accel-
eration of the individual reaction as compared with that of
normal food response . At the same time the average dura-
tion of the reactions in the food-pressure response is less
than that of the normal food response. Expressed in number
of reactions per minute the values are 51.84, 51.92, 65.45,
5l. 72, 56.7, 50. 84 with a mean of 54. 74. The corresponding
values for the normal food responsº.6.51, 45.9, 46.15, 46.51,
44.44, 48.00, with a mean of 46.25. Under food-pressure
stimulation the reactions thus occur at the rate of 8.49
more per minute than under the normal food stimulus.



The distribution of the reactions over the series of
250 trials is shown for snails 4 and 5, in Tables III A and
III B and is represented by the graph figure 2. From these
it appears that the number of reactions increases from 0 in
the early trials to from 20 to 60 in trials 50 to 100 and
reaches a maxium in trials 100 to 150. It becomes less in
the subsequent trials although there is some recovery in
trials 200 to 250 in the case of snail 5. Table III A also
shows the great fluctuation in the number of reactions per
response . While fluctuating, the numbers nevertheless show
a general tendency of increasing to a maximum in the neigh-
borhood of trial 150 and then diminishing toward trial 250.
Table III A shows two other facts worthy of note. Of the
no-response trials, two sets (71–80 and 101-110) fall within
t; he first; 101 trials while but one (181-190) occurs in the
final 140 trials of the series. In other words the no-
response trials make up 18% of the first 110 trials and but
7% of the final 140 trials. They are lacking in the region
of maximum response. The further general fact to be noted
is the relative uniformity in the average duration of the
reactions of separate responses. The method of timing the
response duration by means of the stop watch is necessarily
inaccurate, especially with values which, as in this case,
are frequently in the neighborhood of a second. If a more
accurate method were available greater uniformity might be
expected. With the method employed it is noteworthy that
the agreement is so close.
The food-pressure series thus shows the following
characteristics; (1) an absence of reaction at its beginning,


36 3
(2) a rise to a maximum number of reactions per response ;
(3) a subsequent decline in the number of reactions per re-
sponse; (4) a less average number of reactions per response
as compared with the normal food series; (5) an accelera-
tion in the number of reactions per minute; (6) a fairly
constant reaction duration. This is doubtless characteris–

tic of all Series.
D. Experiments with pressure alone on trained snails:
association:
The third part of the problem called for the applica-
tion of the secondary stimulus alone. Any mouth reactions
which might follow (beyond those attributed to chance stimu-
lation of the mouth), would, according to the Pawlow theory,
be evidence that an association had been formed between the
essential or primary or "unconditioned" stimulus and the
secondary – or in this case, between food and pressure.
The series of tests was carried on in exactly the same man-
ner as the experiments just described. The same apparatus
was used but no food was placed upon the food hook. Since
the food hook was shorter than the pressure fork (fig. 1) it
did not touch the mouth, which therefore received neither
food nor mechanical stimulation. The pressure fork was ap-
plied to the usual place on the ventral surface of the Snail.

The following table (IV) shows the results obtained.


37

Table IV.
Showing the number of reactions of the mouth of two
individuals of Physa gyrina Say, resulting from the application
of pressure alone as a stimulus, after an attempt had been made
to establish an association between the two stimuli, food and
pressure (Table III). The tests were made in filtered tap
water on alternating days. The snails had been starved for
24 hours preceding the tests. -
No. of No. of Serial No. No , for No. of No. of Duration
Snail days of trial "pressure" trial reactions of
tested stimulus for day per response response
series S & C S =
4 31. 304 l 4 * 3 4.
305 2 5 1. 1.
306 3 6 1. l
3O7 4. 7 l 1.
3O8 5 8 l 1.
309 6 9 1. 1.
310 7 10 O O
Totals 7 8 9
Av. per response 1. l. 33 l. 12
32 311 8 l l 1.
312 9 2 1. l
3.13–320 10-17 3-10 O O
Totals 10 2 2
Av. per response 1.0 1.0
33 321-330 18-27 1-10 O O
34 331-340 28-37 1-10 O O
* For trials 1-3 on the 31st day see Table III (31st. day).
Total number of trials (last 20 trials omitted) 17
Total number of stimuli followed by response 8
Per cent of stimuli followed by response 47%
Total number of reactions 10
Average number of reactions per trial 0. 58
Average number of reactions in only those trials in which
response occurred 1. 25
Total time of react; ions - ll Sec.
Average time per reaction l. 1 Sec.
Average number of reactions per minute (estimated) 54.54


TABLE IV (continued)

No. of No. of Serial No. for No. of No. of Duration of
Snail days No. of "pressure" trial reactions response in
tested trial stimulus for day per Sé G =
Series response
5 31 3Ol l l 11 14
- 3O2 2 2 l 1
303 3 3 l l
304 4. 4. 12 14
305 5 5 l 1.
306 6 6 5 6
307 7 7 3 4.
308-310 8-10 8-10 O O
Totals 10 34 4l
Av. per response 4.85 1. 22
32 3.11 ll l l 1.
312 - 12 2 l l
3.13-320 13-20 3-10 O O
Totals 10 2 2
Av. per response 1.0 l.0
33 321-330 21-30 l-10 O O
34 331-340 31-40 1-10 O O
Total number of trials (last 20 omitted) 20
Total number of stimuli followed by response 9
Per cent of stimuli followed by response 45%
Total number of reactions - 36
Average number of reactions per trial 1.8
Average number of reactions in only those trials in
which response occurred 4.
Total time of reactions - 43 Sec.
Average time per reaction - 1 - 19 Sec.
Average number of reactions per minute (estimated) 50.42
Summary snails 4 and 5
Total number of stimuli (trials) 37
Total number of stimuli followed by response 17



Per cent of stimuli followed by response 45.9%
39
Table IV shows that when the secondary stimulus, pres–
sure, alone was applied to the mouth of Physa, the mouth reacted
in 17 out of 37 trials With two individuals, or in 45.9% of the
trials. No mucous stimulation was observed. The average
number of reactions per response was for snail 4, 1.25 and for
snail 5, 4.0 (Table IV). Snails Nos. 6, 7, 8, 14 were given
a similar series of tests which are not here tabulated in detail
but are summarized in Table W. C. These showed the following
average number of reactions per response 4.92, 6.09, 8.0, 3.8.
The mean for the six snails is 4.67. The mean for the normali
food series is for six snails 5.86. For the food-pressure
Series it is 3.18. The average duration of reactions for the
pressure response of trained snails is less than for the normal
food response. The average rate per minute is 53.9, 7.65
reactions per minute in excess of that of the normal food re-
Sponse .
These trials followed 48 hours after the completion of
the training in the food-pressure series. In the case of
snail 4, response followed the first nine trials. The last;
two of these are separated by an interval of 48 hours from the
first Seven. The effect of training thus persisted for 96
hours. Similar results were obtained from Snails, 5, 6, 7,
8 and 14.
Immediately following the mouth response to pressure
of trained snail No. 4 (Table IV) seven successive applications
of pressure gave no response. Similar results were obtained




with the other five snails.
Snails which before training gave no response to pres–
Sure, gave, following training, a response consisting of a series
of mouth reactions. This response is given on the first trial
and continues to be given in trials extending over a period of
96 hour S. It then suddenly ceases. There is no response of
the mouth to subsequent stimulation of the foot by pressure.
E. Experiments to determine the effect of training on
food-pressure response: Second food-pressure series.
It was believed that another series of tests on the
same snails, reintroducing the same "conditioned" stimulus,
would be of interest in showing the ease or difficulty in re-
establishing the reflex. As noted in Table IV, the snails
were tested on two experimental days after pressure alone had
failed to be effective as a stimulus . Allowing for the alter-




nation of experimental days, made necessary by the twenty-four
hours of starving previous to experimentation, the second series
of tests using food and pressure as a stimulus, was started
approximately 120 hours after the disappearance of reaction
upon the application of pressure as a stimulus. Fifty tests
were given and the results appear in Tables V and VI D.

41
Tº A B I. E. We

Showing the number of reactions of the mouth of two individuals of
Physa gyrina Say, Resulting from the simultaneous application of food and
pressure after the complete disappearance (Table IV) of the effect of the
association established between these two stimuli (Table III) • The tests
were made in filtered tap water, on alternating days. The snails had been
starved for 24 hours preceding the tests •
Moe of Moe of Serial Mos No. for No e Of Moe of Duration
snails days Of *food & trial reactions Of
tested. trials pressure" for per response
stimulus, days responses in sece
£nd series.
4. 35 341 l l 11 13.
342 2 2 10 12
343 3. 3. 2 3.
344-350 4-10 4-10 O O
Totals, 10 23 28
Ave per
response, 7,66 1.21
36 351 11 l 3. 5
352 12. 2 3. 5
353 13; 3. 7 10
354 14 4. 6 8
355 15 5 3 5
356 16 6 2 3
357 17 7 1. 1
358 18 8 2 3.
359 19 9 2 3.
360 20 10 2 3
Totals, 10 31 46
Ave per
response, -- 3.1 1.e48
37 361 2]. l 8 11
362 22 2 6 8
363 23 3. 3. 5
364 24 4. 8 10
365 25 5 2 4.
366 26 6 5 8
367 27 7 6 9
368 28 8 7 10
369 29. 9 5 7
370 3 O 10 3 5
Totals, 10 53 77
Ave per
responses 5,3 le45


TABLE. W. (Cont.)
Moe of Moe of serial No. No a for No e Of Moe of Duration
snails days of "food & trial reactions of
tested, trial. pressure" for per response
stimulus, daye responses in sece
2nd series.
4– 38 371 31 l 29 35
372 32 2 9 12
373 3.5 3 9 12
374, 34 4. 4. 6
375 35 5 4. 6
376 36 6 3. 5
377 37 7 6 9
378 38 8 4. 6
379 39 9 3. 5
380 40 10 9 11
Totals, 10 80 105
Ave per
response, 8 1.31
39 381 41 l 3 5
382 42 2 3. , 5
383 43 3. 2 3.
384 44 4. 2 3
385 45 5 3 5
386 46 6 2 3.
387 47 7 3 5
388 48 8 2 3
389 49 9 3 5
390 50 10 1 l
Totals, 10 24 38
Ave per
response, 2.4 1.16
Total number of trials, 50
Total number of stimuli followed by response, 43
Per cents of stimuli followed by response, 86%
Total number of reactions, 211
Average number of reactions per trial, - 4s.22
Average number of reactions in only those trials in
which response occurred, 4.9
Total time of reactions, 4.9 mine
Average time per reaction, la:39 sece

Average number of reactions per minute, 43.16.
TABLE. We (continued).
No. of Noe of Serial No, Noe for Moe of Noe of Duration
snails days of ºfood & trial reactions of re-
testede trials pressure" for per sponse
stimulus, daye response, in sece
- Bui series •
5 35 341 l l 9 11
342 2 2 8 10
343 3. 3. 1 1.
344 4. 4. 2 3
345 5 5 l 1
346-350 6-10 6-10 O O
Totals, 10 21 26
Ave per response, 4.2 1.23
36. 351 11 l l l
352 12 2 5 7
353 13 3. 5 9
354 14 4. 13 16
355 15 5 2 3
356 16 6 3. 5
357 17 7 2 3.
358 18 8 6 8
359- 360 19–20 9-1) O O
Totals, - 10 37 52
Ave per -
responses 4s62 1.e4
37 361 21 1 5 7
362 22 2 4. 6
363 23 3. 4. 6
364 24 4. 2 4.
365 25 5 9 14
366 26 6 15 20
367 27 7 10 13
368 . 28 8 8 11
369 29 9 5 7
370 30 10 2 3
Totals, 10 64 91
Ave per
responses - 6.4 1,48

TABLE We (cont inued)
No.2 of Moe of Serial Noe for No. of No. of Duration
snail. days Moe of "food & trial reactions of response
- tested, trial pressure" for per in
stimulus, days responsee $6C e
2nd series •
38 371 31 l 5 11
372 32 2 5 11
373 33 3 3 6
374 34 4. 4. 8
375 35 5 4 8
376 36 6 1 l
377 37 7 2 5
378 38 8 2 5
379 39 9 3. 6
380 40 10 6 12
Totals 10 35 73.
Ave per
response, 3 e5 2,08
Total mumber of trials, 40
Total number of stimuli followed by response, 33
Per cent of stimuli followed by response, 82.5%
Total number of reactions, 15?
Average number of reactions per trial, 3,92
Average mumber of reactions in only those trials in
which response occurred, 4,75
Total time of reactions, 4s 33 mine
Average time per reaction, 1s54 sec,
Average number of reactions per minute, 38,96.
Summary snails 4 and 5. -
Total number of stimuli (trials) 90
Total number of stimuli followed by response, 76
Per cent of stimuli followed by response, 84.4%

45
Table V shows that movements of the mouth occurred in
76 out of 90 trials, with two individuals, or in 84.4% of the
trials. The first series of tests in which the "conditioned."
stimulus was used showed reaction occurring in #61 out of 100
trials or 61%, when food alone was used as a stimulus (Table
II). These differences show the wearing away of the inhibi-
tion caused by the secondary stimulus (Table III) and by the
experimental manipulation. The mean number of reactions per
response for Snails 4 and 5...e., 0.91 less than for the normal
food response and l.01 more than in the food-pressure series





With untrained snails. The inhibition of the response to food
by the pressure stimulus has nearly disappeared.

T A B 1, E WIe

showing a summary of the number of reactions of the mouth of four
individuals of Physa gyrina Say, resulting from (A) food stimulus alone,
cf. Table II; (B) food and pressure used simultaneously, cfe Table III;
(G) pressure alone, cf. , Table IV; (D) food and pressure used simultaneously,
2nd, series, cf. Table W. The tests were made in filtered tap water on
alternating days, The snails has been starved for 24 hours preceding the
tests,
Snail Snail Snail Snail
A. Stimulus Food. 6 7 8 14
Total number of trials, 42 50 60 60
Total mumber of stimuli followed by
response 2 8 38 4? 32
Per cent, of stimuli followed by
reaction, 19% 76% 78.3% 53.3%
Total number of reactions, 52 24? 143 350
Average number of reactions per trial 1.23 5.14 2.38 5.83
Average mumber of reactions in only
those trials in which response
occurred, 6.5 6.5 3,4 10.93
Total time of reactions (minutes) 1,13. 5,33 3,23 7.35
Average time per reaction (seconds) 1s5 le29 1,39 le25
Average number of reactions per mine 46 elä 46.51 44,44 48.
Be Stimulus Food and Pressure.
Total number of trials, 250 250 253 250
Total number of stimuli followed by
responses 33 82. 53 47
Per cente of stimuli followed by
reaction, 13.2% 32.8% 20.9% 18.8%
Total number of reactions, 65 337 84 182
Average number of reactions per trial, 0.26 1.34 0.03 0.72
Average number of reactions in only
those trials in which response
occurred, le.96 4.1 1.58 3,87
Total time of reactions (minutes) le? 6,56 1.5 3.6
Average time per reaction (seconds) lel le16 1.07 1.18
Average number of reactions per mine 65.445 5le'?? 56 e? 50,84
Ce Stimulus Pressure.
Total number of trials, 30 20 17 20
Total mumber of stimuli followed by
response, 13 11 3. 5
Per cents of stimuli followed by
reaction, 43.3% 55% 17.5% 25%
Total number of reactions, 64, 67 24 19
Average number of reactions per trial, 2.13 3.35 le4l 0.95
Average number of reactions in only
those trials in which response
occurred, 4,92 6,09 8s 3.8
Total time of reactions (minutes) 1.28 le35 0.5 0.38
Average time per reaction (seconds) 142 le? 1.25 1.21
Average mumber of reactions per mine 64 alé 64,16 48, 49.54
47
TABLE WI. (conte)

D. Stimulus Food and Pressure (2nd series).
Total mumber of trials,
Total number of stimuli followed by
responses
Per cente of stimuli followed by
reactions
Total mumber of reactions,
Average number of reactions per trial,
Average number of reactions in only
those trials in which response
occurreds
Total time of reactions (minutes)
Average time per reaction (seconds)
Average number of reactions per mine
Snail
6
50
16.
32%
123
2,46
7.68
2,51
le21
49.54
Snail
50
72%
173
3.e46
4,8
3,78
ls31.
45.8
Snail
50
88%
158
3al6
3,59
3,28
le24
48 e38
Snail
14
25

120
2-4

4.8
2a53
le?6
47,61





48
5. Summary of Observations.
1. All observations and experiments were made on the Physa
gyrina Say while suspended from the surface film in a dish of
filtered tap-water. In this position the lower surfaces of
the foot and head are exposed and the movements of the mouth
are visible .
2. When food (lettuce) or an inert substance (glass rod) is
quickly applied to such a snail on or near the mouth and im-
mediately withdrawn there results a response which consists of
one or more opening and closing movements of the mouth. A
Single opening and closing of the mouth is referred to as a
reaction. A response consists of one or many reactions in
succession and takes place after the Withdrawal of the stimula- -
ting substance.
3. Before the snails were used they were "tamed" by handling
until they no longer visibly reacted to the mechanical distur- -
bances incidental to the experiments.
4. All experiments were conducted under approximately uniform
physical conditions, that is in filtered tap water at room tem-
perature and with constant light intensity.
5. In all tests except those of the preliminary series each
snail was used at intervals of forty-eight hours. It was al-
lowed to feed freely during the first half of this period but
was given no food during the second half of the period. By
thus controlling the food an attempt was made to have all snails
in the same physiological state at the time of using them.
6. As a means of detecting variations in physiological state


a record was kept of the egg masses deposited by each snail,
but no relation was found between the egg-laying activity and
49
any results of the experiments.
7. Each snail was distinguished by a number painted on the
shell and a separate record was kept for each.
8. After a preliminary series of experiments involving six
snails (nos. 18–23), six other snails were used in the remain-
ing experiments. For two of these (4, 5) complete records are
presented in Tables II, III, IV, v, p ºr the remaining
*****44ff.
four (6, 7, 8, 14) a summary of results is given in Table VI, p46.
9. Reactions of the mouth do not occur in the absence of ex-
ternal stimulation (preliminary test series). six snails
(nos. 18–23, Table I, p. 44) were kept under observation for a
total period of 32.75 hours (an average of 5.47 hours each),
without stimulation. During this time but eight responses -
occurred with a total of 38 reactions. Three of the responses
were seen to follow contact of the mouth of the snail with parts
of the mucous track left by the animal in its normal movements
on the surface film. The remaining five responses probably
followed similar contact with this nearly invisible mucus. For
experimental purposes the mouth response may be said to occur
only as the result of the external stimulation. It is "in-
voluntary." The error introduced into later experiments as
a result of unobserved mucous stimulation is not enough to
vitiate the experiments.

10. The normal food-response. When food was applied to the
mouth and at once withdrawn response followed in 61% of the
tests (average for snails 4 and 5). The average response
consisted of 3.93 reactions . The average time of reaction was
1.25 sec. or 46.2 reactions per minute, Table II, p. 13.
ll. The average number of reactions constituting the normal
food-response varied with the individual snail as follows:
No. 4, 3.48; No. 5, 4.35: Nos. 6 and 7, 6.5; No. 8, 3.4; No. 14,
10.93. The mean for all six snails is 5.86.
12. The average duration of a single reaction in the normal
food-response is much more nearly the same in different in-
dividuals than is the number of reactions constituting a re-
Sp011Se . This average in seconds for the six snails in the
order of paragraph ll is, 1.29, 1.21, 1.3, l. 29, 1.39, 1.25.
The values are obtained by dividing the duration of the re-
sponse in seconds (as obtained with a stop watch) by the number
of its component reactions . At the above rate the number of
reactions per minute for the six snails would be 46.51, 45.9,
46 - 15, 46.51, 44.44, 48.0, or 8 mean of 46.25 reactions per
minute. -
13. An apparatus (food-pressure apparatus, Fig. 1, p. 17) was
devised for the simultaneous application of two unlike stimuli,
food to the mouth and pressure to the foot, at a fixed distance
from the mouth.
14. Pressure response of untrained snails. By means of the
food-pressure apparatus pressure was applied to the foot at a
fixed distance from the mouth. No stimulus Was applied to any
other part of the animal . in one hundred twenty applications
of pressure to two Snails (60 each) but four responses were ob-
tained. Response thus occurred to 3.3% of the applications
of pressure . The responses were probably due to chance stimu-
lation by inucus. Response to pressure on the foot with the
apparatus used, occurs in so small a percent of cases that it

does not affect the experiments Summarized below.
15. Food-pressure response . When food was applied to t; he
mouth and pressure to the foot at the same instant no response
followed in the first 60 to 80 trials, in two series of 250
trials each (snails 4, 5). Response followed in the remaining
trials (170-190) of each series. With six snails and 376 re-
ponses the average number of reactions per response was 3.42
as compared with 5.86 with the same snails when the food stimu-
lus alone was used (Tables III, VI, B. p.22,4%), The Snails
are referred to as "trained." -
16. Pressure response of trained snails. Forty-eight hours
after the completion of their training, pressure alone was ap-
piled to the foot of the six trained snails (paragraph 15).
In the case of Snail no. 4 response followed the first nine
Strials. The last two of these were separated by an interval
of 48 hours from the first Seven. The effect of training thus
persisted for 96 hours. Similar results were obtained from
snails 5, 6, 7, 8, 14 (Tables IV, VI, C, p.37f;46).
17. Cessation of pressure response in trained snails. Im-
mediately following the ninth response to pressure of trained
snail no. 4 ſparagraph 16) seven successive applications of
pressure gave no response ; 48 hours later ten applications gave
no response ; 96 hours after the last response ten applications
failed to give any response. Similar results were obtained
with the other five snails. Cessation of response to preSSlire
after training is sudden and final (Tables IV, VI, C, p.37;49.
18. 120 hours after the last response to pressure of snail no. 4



(paragraph 16) a series of 50 trials was run on this snail by
the simultaneous application of food and pressure. Response
52
followed the first three trials and occurred in 86% of the sub-
sequent trials (cf. paragraph lä), with an average of 4.9
reactions. Similar results were obtained with snail no. 5.
The average number of reactions per response was 4.84 for the
two snails, 0.91 less than for the normal food response (para-
graph 10) and 1.01 more than in the first food-pressure series
(paragraph 15). The interference of the pressure stimulus
with the response to food has nearly disappeared. (Tables IV,
WI, B, pp.37 and 46). -
19. The average number of reactions in the food-pressure re-
sponse is less than the number in the normal food response.
The numbers for the six snails in their numerical order is
3.96, 3.62, 1.96 (Table III), 4.1, l. 58 and 3.87 (Table WI, B,
p. 46). The average for the six snails is 3.18. Application
of pressure to the foot at the same time with food to the mouth
shortens the response.
20. The average duration of the reaction is less in the food-
pressure responses than in the normal food response. The num-
ber per minute for the six snails in numerical order is 51.84,
51.92, 65.45, 51. 72, 56.7, 50.84 Tables III, WI, B, pp. 2% and
46). This is a mean distribution of 54 - 74, or 8.49 reactions
per minute in excess of the normal food response. (paragraph 12).
21. In the food-pressure series, the average number of reactions
per ten trials rises to a maximum in the neighborhood of the
150th response in a series of 250 trials and then declines to-
ward the end of the series – Table IIIA and graph, figure 2.
22. The average number of reactions per response resulting from





the application of pressure alone to the foot of trained snails
(paragraph 16) is greater than the average number resulting
from the application of either food or food-pressure stimulation
The numbers for the six snails in their numerical order is l 25,
4.0, 4.92, 6.09, 8.0, 3.8, or a mean of 4.67 reactions per re-
Sponse . These averages differ more than those of either food
or food-pressure responses (Tables II, III and WI, A and B).
23. The average duration of the reactions resulting from the
pressure stimulus alone on the foot of the trained snails is
less than that of the normal food response. This is shown by
the average number of reactions per minute for the six snails,
53.9, which is 7.65 more than with the normal food response
(Tables IV and VI, C). The reaction duration is notably con-

stant.



6 º DI SCUSSION -
A. Method. The experimental method used in this
research will be called the method of training by the use of

simultaneous stimuli. The term may be applied to any pro-
cedure in which two unlike stimuli are applied together, to
the one of which the animal has previously responded by a
definite reflex, but to the other of which it has failed to
respond by the same reflex. The purpose is to establish
response to the second stimulus alone . The stimuli may be
referred to as primary and secondary and the primary stimulus
may be called "conditioned" when used with the secondary (Paw-
low's terms). The term, as thus defined, includes the sali-
vary reflex method of Pawlow.
Comparison of the method with the salivary reflex
method. The Pawlow method has been described (p.3 ff ). It:
requires that the responses to the primary stimulus be a re-
flex, a so-called involuntary response, and that it be measur-
able . In order to meet the first requirement the response
must , (a) occur only in response to external stimulation, (b)
"always" occur in response to external stimulation; that is,
it should occur with sufficient regularity to be available
for experimental uses.
That the mouth response of Physa occurs only in re-
sponse to stimulation of the mouth region has been shown. In
six animals carefully guarded from such stimulation for a to-
tal period of nearly thirty-three hours (about five and half
hours to each animal) the response occurred but eight times.


Three of these responses were due to observed accidental
55
stimulation and the rest were doubtless due to the same cause.
On the other hand, as the tables show, stimulation of the
mouth region induces the response in a sufficient percentage
of trials to make it available for experimental purposes.
The response is therefore a reflex available for these purposes.
The response of Physa to stimulation of the mouth re-
gion unaccompanied by other stimulation will be referred to as
the normal food response. It consists of one or more opening
and closing movements of the mouth. Each complete opening
and closing movement is spoken of as a reaction. The response
is measurable in terms of the number of its reactions as well
as in duration. An inspection of the tables shows very great
fluctuation in the numerical value of the response.
B. Probable causes of fluctuation in response are not
difficult, to find . They arise in part from the accidents of
manipulation and are in part due to the physiological state
of the snails. It is not an easy matter to apply a stimulus
to the mouth of a snail in motion and àelicately suspended from
the surface film. The difficulty is increased when two stimu-
li must be accurately placed at the same time. If the pres-
sure is applied with the pressure fork strictly vertical, it is
only that of the weight of the movable part of the apparatus
and should be constant . Slight deviation from the vertical is
inevitable and must result in occasional variation in pressure
and in the manner in which the food reaches the mouth. These
accidents should shorten response. That unskilled manipulation
sometimes inhibits response entirely is clear from those cases



marked X in the tables. It is fair to assume that they partial-
56.
ly inhibit other responses. They depend in part on the phys-
iological state of the operator. Added to these personal
factors the tendency to produce irregularity in response are
vibrations of an unstable building due to slamming of doors,
passing of street cars and movements of people. Other accidents
prolong response . Probably at times portions of food are re-
tained in the mouth of the snail and the response may be pro-
longed. At times accidental stimulation from unobserved mu-
cus secreted by the snail, is added to that of the food on the
hook and response is prolonged.
That the physiological state of the animal is in part
responsible for fluctuations in response is indicated by the
no-response shown in tables II, and III. Some of these were
known to be due to mechanical disturbance and are marked x in
the tables. Others were probably due to disturbance. Others
again may be attributed to the physiological state of fatigue,
although it is believed that the method of testing the snails
alternately practically eliminated this element. It is note-
Worthy that a large percentage of the no-response trials occurs
at the end of the day's series. This may be attributed to
fatigue or adaptation - in either case a changed physiological
state .
With a more delicate apparatus, and particularly the
elimination of external disturbances such as the vibrations
caused by sudden jars beyond the limits of the experimental
room, responses of more constant value might be obtained. It
is quite possible that responses obtained by more refined aeth-
ods would equal those of the salivary reflex method in con-



stancy. - /
57
Throughout each of the tables it is to be noted that
the duration of the individual reaction is reasonably uni-
form. It fluctuates mainly between 1.0 and 1.25 Seconds.
The fluctuations may be attributed to the method of timing
with a stop watch. Were a better method available for the
purpose, much greater uniformity in the reaction duration
would doubtless appear. The uniformity actually found is
striking and indicates that the use of the single reaction
as a unit for measuring the response is justified. The unit;
is probably as accurate as the drop of saliva.
That the method described in this paper would yield
results if used in the study of discrimination in the snails
the Writer does not doubt, . It seems to offer for this pur-
pose whatever advantage the Pawlow method affords although
possibly in a less degree. It is also available in working
out many of the details of the association process in a sta-
tistical way.
The data presented in this paper show that the beha-
vior of the snail is modified by two processes, adaptation
and learning.
Adaptation appears throughout the experiments and needs
no extended discussion. It is enough to cite the following
instances. Others will doubtless appear from a study of the
tables.
(a ). The snails became "tame." When first brought
into the laboratory they expel the air from the lung and drop
from the surface film when in the least disturbed. AFTER A





TIME they no longer drop from the surface film under any mod–
erate stimulation. To secure the expulsion of air from the
lungs it is then neccessary to use mechanical means.
(b) The snails recover from inhibition of the mouth
response due to manipulation. This appears in Table III.
Here inhibition is more marked in the first 60–80 trials;
after that the snails recover and the number of reactions per
response increases as the trials proceed until it reaches a
maximum toward the middle of the series.
(c) A waning of response occurs in the series of trials
shown in Table III. Following a maximum number of reactions
per response toward the middle of the series, the number grad-
ually diminishes to the end of the series tries. The snails
are becoming adapted to the stimulus (anticipatory?) which is
not followed by its wonted reward. The same thing occurs in
the pressure response of trained snails shown in Table IV.
Here response is entirely lacking toward the end of the series.
(d) The absence of the response in the final trials
on many days series appears in Table III. This may be due to
fatigue, but is more likely the result of adaptation.
Other cases of adaptation in the snail appear in the
paper sh Dawson (1911) and in the work of Nagel (1894). -
Learning, modifiability by association. snails ºntº
gave no mouth response to pressure on the foot, were so modi-
fied by the simultaneous application of pressure to the foot
and food to the mouth, that they then gave the mouth response
to pressure on the foot . The effect of training with the
simultaneous stimuli persisted for ninety-six hours after the
cessation of training . Objectively this persistence of the
training effect stimulates memory. Its psychological im-


59
plication is not discussed here.
The training process was accompanied by a shortening
of the average duration of the individual reactions, in other
Words in an increase in their rate, as compared with the rate
obtaining when the food Stimulus alone was used. This ac-
celeration is no doubt due to the unwonted stimulus applied
to the foot and may be taken as evidence (if any is needed)
that this stimulus was effective. The training process was
accompanied by a reduction in the average number of reactions
per response and this again may be attributed to the unworted
foot-stimulus and may be accepted as evidence of its effec-
tiveness.
Notable in the training series of trials is the in-
crease in the number (average) of reactions per response after
the initial inhibition. The average number of reactions per
ten trials rises to a maximum in the neighborhood of the 150th
trial and then declines. It is probable that the training
has produced its maximum effect in the neighborhood of the
150th trial. This could only be learned by testing the ef-
fect of training in a number of Snails trained for various per-
iods. Such a series of tests would probably show that snails
whose training was interrupted when it had produced its maxi-
mum effect, would show responses extending over a longer per-
iod and with a greater average number of reactions. At any
rate the relation of the length of the training period to the
strength and persistence of its effect could thus be statis-
tically investigated.
60
II - MODIFIABILITY STUDIED BY THE LABYRINTH METHOD.

l: Introduction. The evidence of learning in the snail,
Physa gyrina Say, obtained by the use of the method of simulº-
taneous stimuli suggested the query whether the snail could solve
a simple labyrinth. Failure to solve the labyrinth would be
evidence that this requires a capacity beyond that of forming
simple associations. The labyrinth method has been used ex-
tensively in nearly all groups of vertebrates, less extensive-
ly among invertebrates. Notable among the work on the latter
group is the work of Yerkes (1902) on the crayfish Carcinus
ranulatus, Yerkes and Huggins (1903) on habit formation in
the crayfish Gambarus affinis, Fielde (1901) and Shepard (1916)
on ants, and Yerkes (1912) on earthworms,
Just as the natural habits of rats in running about in
narrow horizontal passages suggested to Small (1899) a series
of such passages for experimental work, so the structure and
habits of Physe suggested an upright or vertical path. Physa.
breathes air and does not remain under water indefinitely when
the so called lung is full of air. When a new supply of oxygen
is required it commonly seeks the surface of the water, al-
though bubbles below the surface are some times "tapped" for air
by the snail (Dawson 1911). In order to gain the surface it
ordinarily crawls up the stems of water plants growing in its
natural habitat. It seems then as though the tests might be
placed on a purely natural basis by mechanically depriving the
snail of air and placing it at the base of an upright path
61

leading to the surface of the water. The animal's need for
air furnishes the motive necessary to action. This need also
suggested a natural punishment and reward for a correct or
incorrect choice of paths, that is, the attainment of air at
the end of the path or failure to get it.

02
7 7.5
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/2/zce o vas.
2,-/o/z7 azzz7 o že Z/2v27 zzzce55 Zo Z7e5z///27ce
o//Že vvo/a/ - A5,- 5/2oyzzy27 oz//zzz Za zoerezo
výž a coo/7 zo Ze zázez- C- /7o/vzo/7Ž / Azz/ro/ //
4 /e7a74 75e vá/c/, azzo/orez žhe ze /2ázoŽ o //7e ožov
o že /zz/ .


63
2- Apparatus and Material. The labyrinth used had the
form of a rectuangular U on an upright stem. (Fig. 3) One
arm of the U reached the surface of the water while the other
was so much shorter that the snail could not reach the surface
from its tip. Warious materials were tried eit in the con-
struction of the apparatus, such as cardboard coated with
paraffine to protect it from the water, metal, mica, and
celluloid. The latter was finally selected because the surface
of this material is like that of glass upon which snails crawl
readily and also because it could be easily cut and manipul—
ated should it be decided to alter the form of the path, Trans-
parent celluloid 2 1/2 cm. in thickness was used in constructing
the path (fig. 3). The upright arms A and B were 8 1/2 mm.
by 4.9 cm., the base of the U – C was 8.5 mm. by 4.25 cm.
This rested on an upright stem D 8.5 mm by 3.6 cm, the base
which was cemented into a block of lead E, 2.1 cm by l.6 cm
by 6 mm. The celluoid part of the apparatus was carefully
Squared to the lead base before the cement was allowed to
harden. Since Physa in crawling up anything but a broad sur-
face has a tendency to crawl in spiral direction, as may be
readily demonstrated by allowing it to crawl up a glass rod
placed upright in the aquarium, it was necessary to keep the
animal confined to one side of the apparatus, in order to
test out its right or left preference. In an attempt to
accomplish this, the celluloid path was backed with galvanized,
1/2 inch meshed wire netting, so cut that the entire path was
bordered by a "picket fence" of wire, the pickets extending




outward in the same plane as the path rather than at right

64 º
angles to it. By cutting out every other "picket" the re-
maining wires were just far enough apart to make it mechan-
ically impossible for the snail to pull its shell between
them. This decide proved an effective but not an absolute
barrier, in as much as the animal occasionally managed to
crawl over the end of a "picket." The number of crossings
became so reduced by its use, that this source of error was
practically eliminated. The wire was cemented to the path
by means of celluloid dissolved in acetone. The wires them-
Selves and the lead base were also coated with this material,
So that all parts of the completed apparatus with which the
Snail would come in contact were either made of celluloid
or coated with it. This apparatus when in use was placed
in the exact center of the experimental tank, thus bringing
it directly under the centered light, so that the rays fall-
ing on each branch of the path A and B (fig. 3) were of
equal intensity and thus the possibility of phototropism dir-
ecting the course of the snail was avoided a Tap Water at room
temperature was used in the experimental tank. This tem-
perature varied within the limits of a degree or two but it
will appear later in the records of the experiments that the
Variations in temperature were the cause of no irregular-

ities in the results,

65
Ž4.
Ž% 5/ou/22 Zºe 9227&s 2.322/72%/72%
co/o/// cozz/ozs, eaze.”zezz/zz/, /s/.22e2/22–
/2/2/2/3 Z/52.7//z /ø/a/~ eyoe”/zzeº, cº////eos/2/2/sea /z
co/o/22 7%e e/ec// cºre/7/2/2//oyed///722/zz/º/zz
7%e 3/oz A.

66
In order to conduct the experiments under controlled
lighting conditions and thus avoid any possible phototropic
influence it was deemed advisable to create special condi-
tions governing the light and keep them uniform throughout
the experiments (Fig. 4). An experimental tank consisting
of a battery jar 6 inches high and 4 inches in diameter
was painted black on the outside and a level floor was
obtained by means of a false bottom made of weighted paraf-
fine • The center of the bottom was marked in the paraffinee
This tank, during experimentation, was placed in the center
of a "house" constructed from gray beaver-board fastened
together with strips of gummed paper and painted dead black
on the inside • The walls were 26 cm, by 38 cm, with a strip
19 cm, by 5 cm. cut from the lower edge on three sides for
ventilation. *or this purpose also small holes uniformly
spaced were punched 2 cm, from the upper edge of the four
sides. The fourth wall, the one next the operator, had a
horizontal slit 2 cm. wide cut in it at 10 cms from the tope
The part of this wall below the slit was made removable • With
the lower part of the fourth wall removed the operator could
prepare experiment S without taking the tank from the "house."
When the movable part of the fourth wall was replaced there
remained a slit 2 cm. in width, through which observations
could be made. The top of the "house" was ground glass
above which at a distance of 4 cm. was an 8 candle power
electric light. This was centered over the "house" and
held in a stationary position by means of a wooden frame •

67
two thicknesses of ordinary medium weight white paper were
placed on top of the ground glass to further weaken and
diffuse the light. The room in which the apparatus was
located was darkened during experimentation. This appara-
tus was used without change throughout the experiments,
The labyrinth itself was varied to conform with the require-
ments of each set of experiments. All snails used were
tamed, individually numbered and kept under the same condi-
tions as in the experiments with simultaneous Stimuli •
3. Experiments on preference • Two different kinds
of preference tests were carried out , The first, was to
find whether a tendency to turn to the right or left exist-
ed. The assymetry of the animal suggested the possibility.
The second part of the test was to find any possible pre-
ference for an ascending or descending pathe
A • Experiment to test right or left preference. In
the first series an unpainted glass dish of beaker type,
containing tap water at room temperature was placed in the
center of the experimental "house" and the ventilating
spaces at the bottom of the walls of the "house" were block-
ed to exclude light. The air was forced from the lung of
the snail by pressing its body gently back into its shells
It was then placed against the side of the dish at the four
points of the compas in turn. It was allowed in each case
to crawl up the side of the dish for air. The path was
sketched and its right or left divergence from a perpendicular






noted. The snails were handled with forceps and always
placed on the horizontal bottom of the dish at right angles
to the surface to be traveled. The mucous trail left Orl
the sides of the dish was broken up after each trial by
brusing the traveled surface with a clean camel's hair
brush. Three snails Nos. 15, 16 and 17 were used and four tests
given each on two consecutive days. The record follows:
TABLE WII.
Showing the deviation from a perpendicular shown by
three individuals of Physa &# Say, in following an
unconfined path up the side of a cylindrical glass dish
in search of aire
Trial Snail Snail Snail
number 15 16 17
First day l Left; Right Right
2 Right Theft; Right
3 Left Right Right
4. Left Left: Right
Second day l Theft; Left Right
2 Ileft Left Ileft;
3 Right Right Right
4 Right Left Right
TOTAL - 5I, 3R 51, 3R LI, 7R
Total number of trials 24
Total number of deviations to the right 13 approximately 54%
Total number of deviations to the left li approximately 45%
This experiment was based upon the normal behavior of
the snail in its search for air, its path from the bottom of
the dish to the surface was not limited in any way • Besides
the record just given, three points of general interest
were observed:





69
le. At no time during these experiments did the
snail appear to make any effort to obtain air except
at the surface of the water. In as much as the depth
of the water in the experimental tank was greater than
that in the home aquarium, the observations conflict
with those of Dawson (1911) which refer, however, to
young snailss
2. The touching of the tentacles to the surface
of the dish, at intervals, on either side of the path
of the snail appeared in no case to alter the direct-
ion of the path,
3. There appeared to be no effort on the part of
the snails under observation in these experiments, to
re-distribute its weight by shifting the shell from
side to side. Such shifting of the shell might exert
a pull upon the body of the animal, strong enough to
turn it; in one direction more than anothere
In the second series of preference tests the U-shaped
labyrinth was used. Both of the upright arms reached the
Surface of the water so that, a choice of either did not
result in punishments
Six snails were used. They were divided into two
groups of three each and tested on alternate days. This
division was made because six snails could not be worked
each day during the time at the disposal of the operators
and it was deemed advisable to have records from more than
three snails. Each snail in each group of three was given
- --


70
ten trials per day. Enough fresh tap water at room
temperature was placed in the experimental tank to reach
the top of the arms of the U apparatus resting in the center
of the dish. The Snail was taken from the bacteria dish in
which it was kept at room temperature, and held in the hand
while the body was gently pressed back into the shell by
means of a dull metal seeker. In this way the snail was
compelled to expell air from its lunge. The animalſº, now
negatively geotropic, was placed on the base of the U -
E (Fig. 3) by means of long forceps. The apex of the shell
rested on base E while the opening of the shell touched the
stem D. Thus when the snail came out of its shell, which
it usually did almost immediately, it at once started to
crawl up the stem D to the surface. At the top of D it
turned either to the right or left on the cross bar C and
then moved up either arm A or B to the surface of the water
where it was permitted to obtain air. It was then lifted
off with the hand, as gently as possible and returned to its
individual dish where it was allowed to feed undisturbed While
the other two snails of the group were tested in a similar
way. After each test the celluloid apparatus was removed
to a separate dish of water and thoroughly cleaned with a
stiff brush in order to remove the mucous trial left by the
tested snail and thus make it impossible for the next snail
to follow the traile
A complete record was made for each test given to each
individual snail. Yerkes (1912) method, modified to suit the
experiments, was adopted in making the records • Outlines of


71
the labyrinth were drawn on separate slips of paper and
the course chosen by each snail traced on one of these,
The time required for the trip was taken with a stop-watch.
The additional data of date, time of day, and temperature
were added to the slip, and a record was also made of the
eggs, if any, which had been deposited within twentyefour
hours previous to the tests. It was thought that a later
analysis of the records might show some relation between the
physiological condition of the animal caused by egg laying,
and the results of the experiments.
The following table shows the results obtained from a
series of forty tests on each of six snails:



72
Tº A B L E VIIIa
Showing the right and left preference of six individuals of Physa
gyrina Say, which had been deprived of air and placed at the base of a
vertical U shaped path resting on an upright stems. Both arms of the U
reached the surface. The horizontal of the U necessitated a choice of
paths (figs 2) • The snails had been starved for 24 hours preceding the
tests. The apparatus was thoroughly cleaned between tests •
Nos of No. of No. Of Moe of Noe of
snail. days trials left right
testede per days choices a Choices a Bºss
15 l 10 8 2 O
16 - 10 7 3 0
17 - 10 7 3. O
** 24 2 10 2 8 O
25 10 1. 9 l
26 10 2 8 l
15 3 10 5 5 O
16 10 5 5 l
17 10 8 2 l
24 4. 10 3. 7 O
25 10 5 5 O
26 IO 4. 6 O
15 5 10 6 4. O
16 10 1 9 O
17 10 5 5 O
24 6 10 3 7 l
25 - 10 2 8 1
26 10 3. 7 l
15 7 10 8 2 O
16 10 6 4. O
17 10 9 l l
24 8 10 2 8 O
25 10 8 2 O
26 10 6 4. l
Total mumber of trials 240
Total number of left turns 116 approximately 48%
Total number of right turns 124 approximately 52%


73
* Experiments to test preference for an ascending or
descending path. If the cross bar of the U should not be
horizontal, the snail after ascending the stem would have
a choice of a descending path on one side and an ascending
path on the other. In a set of preference tests an attempt
was made to determine whether the animal showed preference
for either of these paths. In order to tilt the labyrinth
at various angles the experimental tank was placed on a
small board 8 1/2 in. by 10 in. by 1/4 in. made of three
layers to insure an unwarped surfaced. One end of the
board was pierced by two screw eyes set one inch from the
edge. By turning these screws the board, together with
the apparatus resting upon it, could be readily adjusted
to any angle. The angle used in each experiment was measured
with a Sterret spirit level. The slant of the right and
left sides of the path was frequently and irregularly
reversed in order to avoid any possible right and left
habit formation during experimentations
These tests were like those just described, in the
tilting of the appartus. The records were made in the
same way. The tabulated results followe

TABLE IX,
Showing the tendency of six individuals of Physa gyrina Bay, to
follow an ascending or a descending path when the apparatus was tilted at
angles varying between 57* and 7° 47' from the horizontal. The U shaped
apparatus (fig. 2) was used, both arms of the U reaching the surface. It
was cleaned between tests. The snails had been starved for 24 hours pre-
ceding the tests. - -
Moe of No. Of No. Of No. Of No e Of Deviation trans-
snail. days trials "up" *down” verse bar from
ºtested per choices • choices e a horizontale
ãº-
15 l 10 7 3. 09 57?
2 10 9 l
3 10 6 4
4. 10 4. 6
5 10 6 4.
Totals 50 32 18
6 10 5 5 O° 23°
7 10 3. 7 19 54°
8 10 7 3. 3° 49'?
9 10 5 5 5° 44?
10 10 8 2 7° 40?
Totals 50 28 22
16 l 10 7 3. Oo 57?
2 10 7 3
3 10 3. 7
4. 10 4. 6
5 10 5 5
Totals - 50 26. 24
º 6 10 7 3 O° 23'ſ
7 10 2 8 19 54°
8 10 4. 6 3° 49'?
9 10 5 5 5° 44?
10 10 6 4. 79 40?
Totals, 50 24 26
17s 1 10 7 3. o° 57°
2 10 7 3.
3. 10 5 5
4. 10 9 1.
- 5 10 3 7
Totals, 50 31 19
66 10 7 3 O° 23'ſ
7 10 6 4. 1° 54?
8 10 5 5 3° 49'?
9 10 6 4. 5° 44?
10 10 6 4. 70 40"
Totals 50 30 20


TABLE IX (continued) 75
Noe of No. Of No. of No e of No. of Deviation of
snail. days trials "up" *down” horizontal
testede per day. choices choices r. i.es les
24 1 10 6 O”57
2 10 6 4.
3 10 3. 7
4. 10 9 l
5 10 5 5
Totals 50 29 21
6 10 7 3 09 23?
7 10 6 4. 1° 54°
8 10 5 5 3° 49?
9 10 6 4. 5° 44?
10 10 10 O 70 40t
Totals - 50 34 16
25 l 10 5 5 Oo 57°
2 10 5 5
3 10 5 5
4. 10 5 5
5 10 6 4.
Totals 50 26 24
6 10 6 4. 09 25°
7 10 4. 6 1° 54?
8 10 4. 6 3° 49'?
9 10 7 3. 5° 44?
10 10 8 2 7° 40?
Totals 50 29 21
26 l 10 3. 7 Oo 57°
3. 10 8 2
4. 10 5 5
5 10 6 4.
Totals 50 28 22
6 10 4. 6 0° 23?
7 10 4. 6 19 54°
8 10 6 4. 3° 49'?
9 10 6 4. 5° 44?
10 10 5 5 7° 40?
Totals 50 25 25
Total mumber of trials 600
Total mamber of trials in which ascending path was chosen 34° 57%
Total number of trials in which descending path was chosenzā8 43%


TABLE IX A.
Summary of Table IX, showing an arrangement of the
choices of the six snails tested according to the angle made
by the cross bar of the U with a horizontal.
Snail Angle of inclination to horizontal of cross bar of U-
No. shaped labyrinth, degrees.
0 - 1 1 - 2 3 - 4 5-- s 7 – 8
up down up down up down up down up down
15 32 18 3 7 7 3 5 5 8 2
Totals # #
16 26 24 2 8 4 6 5 5 6 4
Totals # #
17 31 19 6 4. 5 5 6 4. 6 4.
Totals z: #
24, 29 21 6 4 5 5 6 4 10 O
7 – 3
Totals 36 24
25 26 24 4 6 4. 6 7 3 8 2
Totals # #
26 28 22 4 6 6 4 6 4. 5 5
Totals # #
* : # *, *, *, *, *, *, * *


77
Table IX shows that when six individuals were given a
choice of an ascending or a descending path, both of which
ended at the surface, and when the angle of deviation from
a horizontal at the point of selection was not greater than
7°40', the ascending path was chosen in 342 trials out of
600 or in 57% of the trials. An arrangement of the choices
according to the angle made by the cross bar with the horizon-
tal is shown in Table IX A. This shows a strong tendency to
follow the upward path only at the angle 7-8 degrees. In
further experiments the cross bar of the U was kept horizon-
tal. •
-
4. Experiments_on_learning the U-shaped labyrinth; Choice
gf right and left path; punishment failure to get aire In as ::=
much as the snails showed a slight tendency to turn toward the
right in the preference tests, the right arm of the U-shaped
path was now shortened by cutting 2 cm. from the upper ende A
choice of this arm would lead to punishment (failure to get
air) and would be a wrong choice • When a wrong choice was
made the snail had to retrace its path to the point of choice
where it usually continued its course along the horizontal
bar and up the long arm to the surface of the water • This
was the only modification made in the apparatus for the learn-
ing experiments. The methods of handling the animals and the
apparatus were the same as in the preceding tests • Three
snails were used in these experiments. They were at first
tested every other day but it soon seemed advisable to test
them every day. The three snails were worked in turn and as

78
many trips given each as was possible in the time at the
disposal of the experimenter. The number of trips per day
varied considerably because it was found that sometimes
individual snails refused to start up the labyrinth. At
such times they were frequently allowed to remain at the base
of the stem for a considerable length of time in the hope
that the tests might be continued in regular order. Some-
times, however, work on the individual snail so affected,
had to be discontinued for the day. When a snail lost its
hold on the labyrinth and dropped to the bottom of the tank
during its test, it was immediately started up again and this
Second trip was given the same serial number as the previous
One with a Small letter after it; e The same method of record-
ing the observations was used as that described for the pre-
ference tests. A record was also made of the "latent" period,
that is, the time between the placing of the animal at the
base of the stem and the actual start on the upward path,
Although noted in the tabulations this record appears to have
no bearing on the results of the experiments, since fluctua-
tions were probably due in part to the fact that the snail
Still retained a small amount of air in its lung, delaying
Slightly its need of a fresh supply, In constructing curves
based upon these records the percentage of errors or wrong
choices for each snail per day was used. An analysis of
the records appéared to show no relation between the latent
periods, oviposition, the time required for the trip and the
number of errors,


T A B L E X.
Showing the choice of choices made by three individuals of Physa, in
attempting to reach the surface of the water for airs. A U shaped labyrinth
was used. The right arm was so short that the snail could not obtain air by
following it (punishment), while air might be obtained at the top of the left
arm (reward). The apparatus was cleaned between trials. The snails had been
starved for 24 hours preceding the tests.
*Indicates that an egg mass was deposited by the snail during the 24
hours immediately preceding the tests on the day markede
No. of No. of No. Of Moe of No. of No e of Iatent. Duration
snail. days trial trial correct incorrect period of trip
tested for for or left or right seconds Séº e
series day. choices choices • -
1 *1 l l l O 90 181
2 2 1. O 58 98
3. 3. O l 69 340
4. 4. 1. O 27 132
5 5 l O 72 124
6 6 l O 45 92
Totals 6 5 1. 361 96?
83% 16% Av. 60.16 Av.161.16
*2 7 1. l O 14 82
8 2 l O 62 148
9 3. 0. l 149 265
10 4. l Q 89 117
11 5 1 O 92 128
12 6 O l 135 222
13 7 1. O 90 12.5
14 8 l O 43 109
Totals 8 6 2 674 1196
75% 25% Av. 84.25 Av 149.5
*3 15 l l O 49 82.
16. 2 l Q 70 94
17 3. l O , 145 74
18 4. 1. 0. 329 83
19 5 1. O 195 75
20 6 l O 135 109
21 7 0. l 409 220
Totals 7 6 l 1332 737
85% 14% Av. 190.28 Av. 105-28
*4. 22 l 1 O 185 154
23 2 O l 169 132
24 2a 1. O 64 90
25 2b l O 28 88
26 3 l O 183; 171
27 4. 1 Q 38 95
28 5 1. O 50 77
Totals, 7 6 1. 717 80?
85% 14% Av. 102.42 Av 115.28

80
ABLE * (contal
No. of No. of No. of No. of No. of No. of Latent Dºration
snail, days trial trial correct incorrect period. of trip
tested for for of left or right secs. sec.
series • day — choices — choices
1 5 29 1. 1. O 174 132
- 30 2 1. O 40 150
31 3. 1. O 95 78
32 4. 1. O 83 193
33 5 O l 73 171
34 5a l O 72 100
Totals, 6 5 1 537 824
83% 16% Av 89.5 Av. 137.33
*6 35 l 1. O 185 103
36 2 l 0. 210 87
37 3. 1. O 69 112
38 4. O l 49 212.
39 4a 0 1 43 163
40 4b O 1. 19 82
41 4c 1. 0 40 92
42 5 O l 45 269
Totals, 8 4. 4. 660 1120
50% 50% Av 82.5 Av. 140
7 43 l l O 27 108
44 2 O l 70 344
45 3. l Q 93. 1.59
46 4. l 0. 198 191
4? 5 1. O 112 107
48 6 O l 30 169
49 6a O 1 31 233
50 6b 1 O 52 95
Totals, 8 5 3. 613 1406
62% 37% Av. 76.62 Av. 175.75
8 51 1 1. O 52 114
52. 2 l O 94 103
53 3 l O 34 113
54 4. l 0 69 112
55 5 l O 54 136
56 6 Q 1. 88 262
57 7 O l 51 363
Totals, 7 5 2 442 1203
71% 28% Av.63.14 Av. 171.85
*9 58 1 l Q 131 118
59 2 l Q 35 99
6) 3. l Q 64 94
61 4. 1. Q 80 87
62 5 l O 53 97
Totals, 5 5 O 363 495
100% Ave 72.6 Åve 99


TABLE * (cont).
No. of Moe of Not of No. of Nos of Nos of 18tent. Duration.
Snails days trial trial correct incorrect period of trip
tested for for or left or right secs secs.
mº-T- series's ãay choices — choices -
l 10 63 1. 1. O 83 145
64 2 Q l 152 496
65 3. O 1. 48 314
66 4 1 O 100 184
67 5 l Q 79 112
Totals, 5 3. 2 462 1251
60% 40% Av. 92.4 av. 250.2
*11 68 l l O 97 191
69 2 1 O 57 94.
70 3. 1 0. 152 96.
71 4. O 1 154 351
72 5 O l 47 493
º 6 0 1 74 263
74 6a 1 O 53 115
Totals, 7 4. 3. 634 1603
57% 42% Av. 90.57 Av. 229
*12 75 1 O 1. 13? 417
76 2 O 1. 84 463
77 3 O 1 50 325
78 4. 0. l 108 264
79 5 l O 40 93
80 6 O 1. 33 319
81 7 l O 76 122
Totals, 7 2 5 528 2003
28% 71% Av. 75.42 Av. 286.14
13 82 1. 1 O 188 133
83. 2 O 1. 49 265
84 3. 0 l 320 431
85 4. 0 l 180 662
86. 5 l O 120 167
87 6 O 1. 128 3.18
88 7 O 1. 4? 279
Totals, 7. 2 5 1032 2255
- 28% 71% Av.147.42 Ave 322-14
*14 89 l l Q 42 148
90 2 O l 14? 250
91 3. O l 44 322.
92. 3a 0. 1 114 24?
93 {ºb O 1 15 196
94 3c Q 1. 155 192
95 3d 0 l 187 258
96. 3e O l 59 414
97 4. Q 1 88 256
98 5 O 1. 62 325
99 6 O 1. 66 345
Totals 11 1. 10 979 2953
º 9% 90% Ave.89 Av. 268.45

TABLE X (contal
No. of Moe of Moe of No. of No. of No. of Patent. Duration
snails days trial trial correct incorrect period of trip
tested for for or left or right $663 e $3C e
series day choices choices,
1. *15 100 l O 1. 73 1058
101 2 O l 50 37;
102 3. O l 55 454
103 3a 1. O 62 129
Totals 4. 1 3. 238 2014
25% 75% Av 59.5 Av. 503.5
16 104 l l O 31 155
105 2 1. O 107 107
106 3. l O 176 133
107 4. l O 128 154
108 5 1 O 88 13ſ.
109 6 O l 64 266
110 7 0 - l 110 188
111 7a l O 14 108
Totals, 8 6 2 718 1248
75% 25% Av.89.75 Av. 156
*17 112 l l O 71 134
113 2 O 1 89 770
114 3 1 Q 53 160
115 4. O l 75 294
116 5 O 1. 78 571
117 6 l O 77 156
118 7 l O 43 182
Totals, 7 4. 3. 486. 2267
57% 42% Ave 69,42 Ave 323s 85
18 119 l l O 52 149
120 2 l 0 75 138
121 3. 1 Q 65 165
122 4. O l 50 729
123 5 O l 101 307
Totals, 5 3. 2 343 1488
60% 40% Av. 68-6 Av. 297.6
19 124 l O l 37 528
125 2 O 1. 206 263
126 3. O l 88 261
12? 4. O 1. 73 1039
138 5 l O 95. 162
Totals, 5 l 4. 499 2253
20% 80% Av. 99.8 Av. 450.6
20 129 1 Q 1 45 622
139 la l O 38 129
131 2 1 O 3? 197
132 3. Q 1 81 348
133 4. 1. 0. 85 172.
134 5 l O 135 14?
Totals, 6 4. 2 421 1615
66% 33% Ave 70,16 Av. 269,16

TABíº R. (conte)
No. of No. of No. of No. of No. of No. of Patent. Duration
snail, days trial trial correct incorrect period of trip
tested for for or left or right 86 Ce sèC e
series a day. choices choices,
1. *21 135 l 1 O , 97 245
136 2 O 1. 57 354
137 2a 1. O 33 199
138 3. l O 151 177
139 4. 1 O 97 201
140 5 0 1. 82. 855
Totals 6 4. 2 517 2031
66% 33% Av.86.16, Av.338.5
*22 141 1 1 O 74 204
142 2 1. O 140 138
143 3. 1. O 76 186
144 4. 1. O 71 133
145 5 O 1 76 594
146 5a 1. O 36 103
Totals, 6 5 1. 473 1358
83% 16% Ave 78.83 Av. 226.33
23 14? l l O 67 199
148 2 O 1 194 349
149 3. 1. O 94. 222
150 4. l O 55 177
151 5 1. 0 109 119
152 6 l O 86. 154.
153 7 O l 89 728
154 7a. 1. O 37 144
Totals, 8 6 2 731 2092
75% 25% Ave 91.37 Ave 261.5
24 155 1 O l 75 1316
156 2 O 1. 268 492
157 3 O 1. 287 401
158 3a O 1. 40 584
159 3b 1 O 94 155
160 4. O 1. 13.1 623
Totals, 6 1. 5 895 3571
16% 83% Av,149,16Ave 595-16
25 161 l O 1. 45 13:13
162 2 O 1. 71 730
163 3. O 1. 51. 274
164 4. O 1. 42 313.
165 5 O 1 64 338
Totals, 5 O 5 273 2968
- 100% Ave 54 e6 Ave 593-6
26 166 1 O l 52 1712.
- 167 2 1. Q 95. 175
168 3. O 1. 74 549
169 3a O 1. 42 645
170 3b 1. O 42 163
Totals, 5 2 3 305 3244
40% 60% Av-61 Av,648.8

84 ||
TABLE Xe (cont.)
No. of Moe of Noe of No. of Moe of No. of Patient Duration
snail, days trial trial correct incorrect period of trip
tested for for or left or right $6 Ce 88C e
series • day. choices choices a
*27 171 1. l O 118 164
172 2 () 1 162 473
173 3 O 1. 12? 824
174 3a O l 168 462.
175 4 O 1 90 720
Totals, 5 l 4. 665 2645
20% 80% Av.133 Ave 528.6
28 176. l O 1. 86 821
177 2 O l 69. 718
178 3. O 1. 121 489
179 4. O l 38. 805
180 5 O 1 60 3.11
Totals, 5 O 5 374, 3.144
100% Ave 74.8 Ave 628.8
29 181 l 0 1. 52 1774
182 2 l O 58 215
183 3 O 1. 61 915
184 4. O l 70 344
4. 1. 3. 24l 3248
Totals, 25% 75% Ave 60.25 Ave.812
30 185 1 O l 50 2364
186 2 O l 180 750
187 3. O l 216 1325
Totals, 3. O 3 446 4439
100% Avel48,66Ave1479,66
31 188 l l O 126 276.
189 2 1 00 37 203
190 3 1 Q 48 118
191 4. O l 44 641
192 5 O 1. 71 466
Totals, 5 3. 2 326 1704
60% 40% Avs 65.2 Ave 340,8
32 193 1 O 1. 75 354
194 2 O 1. 105 1200
195 3. l O 101 1835
196 4 1 O 70 206
197 5 l O 48 139
Totals, 5 3. 2 399 2082
60% 40% Av. 79.8 Ave 416.4



85
TABLE X (contal
No. of No. of
snails
No. of
days trial trial
tested. for for
series • ãays.
T1 *33 198 1.
199
200
201
202
No e of
51.
f
Totals,
34 203
204
205
206
207
Totals,
35 208
209
210
211
i
Totals,
*36 212
213
214
215
216
i
Totals,
37 217
218
219
22
221
;
Totals,
222
223
224
225
226
*38
;
Nos of
correct;
or 1eft;
choicess
i
*i
|
7
%
4.
:
i20%
40%
No e Of £atent. Duration
incorrect period of trip
or right Sece sed,
choices • -
1. 89 595.
l 65 124 ||
l 76 797 ||
1. 56 1380 ||
l 120 760
5 406, 3656
100% Ave 81.2 Av. 731.2
1. 41 1740
1 33 910
1. 74 559
O 75 123
l 32 912
4. 255 4244
80% Av.5l Ave 848.8
O 10 197
1. 182. 648.
O 72. 172
O 123 164
1. 387 1181
25% Ave 96.75 Av. 295.25
O 48 120
O 53. 143
l 48 1271
1. 108 394
1 99 630
3. 361 2558
60% Av. 72.2 Avt 511.6
1. 64 283
1 60 3.18
1. 75 910
O 42 218
l 54 355
4. 295 2084
80% Ave 59 Av. 416.8
1. 21 526
Q 26 18?
O 49 133
l 43 58?
1. 72 330
3. 211 1763
60% Ave 42e2 Ave 352.6


BLE X cont
No. of Nos of Nos of Nos of No. of No. of Latent. Duration
snail. days trial trial correct incorrect period of trip
testeds for for or left or right 86 G e 86 G e
1. series a days choices a choices a
39 227 l 1 O 28 170
228 2 O 1. 98 462
229 3. O l 45 42?
230 3a 1 O 23 114
231 4. 1. O 4? 131
Totals 5 3. 2 24l 1304
60% 40% Ave 48.2 Av. 260.8
40 23? l l O 103 109
233 2 O l 128 652
234 3. O 1. 5 414
235 3a O l 25 338
236 4. l O 80 151
Totals, 5 2 3. 394 1664
40% 60% Avs?8.8 Ave 332-8
4l 237 1. l O 125 121.
238 2 l 0. 61 12?
239 3 * O l 58 254
240 4 0 l 164 482
241 5 O 1. 81 388
Totals, 5 ^2. 3. 489 1372
40% 60% Ave 97.8 Ave 274.4
42 242 1. 1. O 95 154
243 2 O l 60 265
244 3 O 1. 66 275
245 4. O 1. 66 555
246 5 1. 0 130 139
Totals, 5 2 3. 417 1388
40% 60% Av. 83.4 Ave 277.4
*43 24? 1. 1. O 65 197
248 2 : 1. O 33 122
249 3 1 O 3? 135
250 4 O 1 90 730
251 5 0 1. 73 625
Totals, 5 3. 2 298 1809
60% 40% Av. 59.6 Av. 36.1.8 |
||
44 252 1 1 O 64 123
253 2 l O 59 93.
254 3 l Q 39 119
255 4. O 1 63 364
256 5 O 1 70 311
257 6 1 O 58 141
258 7 O l 36 218
259 8 O 1. 48 250
Totals, 8 4. 4. 43? 1619 º
50% 50% Av. 54.68 Ave 202,37

TABLE Xs (cont.)
No. of No. Of
snail. days
tested.
1 45
Totals,
*46
Totals,
47
Totals,
48
Totals,
No. of
trial
for
series •
260
261
262
263
264
265
266
267
268
269
270
271
272.
273
274
275
276
277
278
279
280
281
282
No e of
trial
for
—days—
i
i
No e of
correct;
or left
choices
O
l
O
6l13
l%%%
No. of Latent. Duration
incorrect period of trip
or right $60 e $90 e
—choicess
1. 210 681
O 86. 108
1. 113 532
2 409 1321
66% Ave 136.33 Ave 440,33
1. 43 745
O 90 105
1. 20 182
1. 23. 740
I 75 1784.
l 50 1386
l 112 477
l 23 438
7 436 585?
87% Ave 54 e5 Ave 732-12
O 69 130
1. 58 1379
1. 35, 492.
l 99 734
1. 126 358
1. 79 358
5 466 3873,
83% Ave 77-6 Ave 645.5
O 20 300.
l 55 510
1. 103 1785
O 77 285
O 143 521
O 67 466
2 465 3867
33%
Ave 77.5 Ave 644.5


5 u_m in a r Y- 88
Smail Day No e of Correct Incorrect Latent Duration
l trials or left or right period of trip
Choices choices. Seº e 86&e
*1 6 5 l 361 96?
*2 8 6 2 874 1196.
*3 7 6 l 1332 737
*4 7 6 l 717 80?
5 6 5 l 537 824
*6 8 4. 4 660 1120
7 8 5 3. 613 1406
8 7 5 2 442 1203
*9 5 5 O 363 495
10 5 3. 2 462 1251
*11 7 4. 3. 634 1603
*12 ºr. 2 5 528 2003
13 7 2 5 1032 2255
*14 11 l 10 979 2953
*15 4. 1. 3 238 2014
16 8 6 2 718 1248
*17 7 4 3. 486 226?
18 5 3. 2 343 1488
19 5 1 4. 499 2253
20 6 4. 2 421 1615
*21 6 4. 2 517 2031
22 6 5 l 473 13:58
23 8 6 2 731 2092
24 6 l 5 895 3571
25 5 O 5 273. 2968
26 5 2. 3 305 3244
*27 5 1 4. 665 2643
28 5 O 5 374 3.144
29 4. l 3. 24l 3248
30 3. O 3. 446 4439
31 5 3. 2 326 1704
32 5 3. 2 399 2082.
*33 5 O 5 406 3656
34 5 1. 4 255 4244
35 4. 3. l 387 1181
*36 5 2 3. 361 2558
37 5 l 4. 295 2084
*38 5 2 3 211 1763
39 5 3. 2 24l 1304
40 5 2 3 394 1664
41 5 2 3. 489 1372
42 5 2 3. 417 1388
*43- 5 3. 2 298 1809
44 8 4. 4. 43? 1619
45 3 l 2 409 1321
*46 8 l 7 436 585?
47 6 1 5 466 3873,
48 6 4. 2 465 3867
Total number of trials, - 282
Total number of correct or left choices, 136 Approximately 48%
Total number of incorrect or right. " 146 Approximately 52%
Total latent (sec.) 23651
| Total duration of trials (secs) 101789
Average latent time (sec.) 83.86
Average duration of trials (sec.) 360s 95

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90
TABLE * (contal
Smail. Dºy Moe of No. for Correct Incorrect Latent. Duration
trials day. or left or right period of trip
- choices choicess $80 e 88Cs
2 7 37 l Q 1. 20 469
38 2 1 O 45 94.
39 3. O l 50 490
40 3a O l 25 511 -
41 4. 1. O 44 111
42 5 l O 37 92.
Totals, 6 3. 5 221 176?
50% 50% Av.56.83, Av. 294.5
8 43 l O 1. 50 787
44 2 O l 45 594
45 3. O l 35 355
46 4. l O 24 87
47 5 l Q 68 126
48 6 l O 354 124
Totals, 6 3. 3. 574 2073,
50% 50% Av. 95.83 Av. 345.5
*9 49 l O l 54 1012
50 2 O l 42 589
51 3 l O 81 123
52 4. O l 52 596,
53 5 1 Q 230 71
Totals, 5 2 3 459 2391
40% 60% Ave 91.8 Ave 478,2
10 54 l O l 60 488
55 2 O 1. 34 520
56 2a Q l 18 210
57 3 O 1. 53 560
58 4. l O 101 111
59 5 O 1 41 722
Totals, 6 l 5 307 2609
- 16% 83% Av.51,16 Ave 434.85
*11 60 l 0 l 57 195
61 la l O 18 130
62 2 l O 44 93
63 3. O 1 95 303
64 4. 1 O 68 123
65 5 O l 59 208
66 6 0 l 44 391
67 68. O 1 37 106
68 6b O l 33 396
Totals, 9 3 6 455 1945
33% 66% Av. 50.55 Ave 216-11

91
TABLE X (contal
Smail Day Moe of Nos for Correct Incorrect ſatent. Duration
trial. day or left or right period of trip
- choices choices • 36C e 36Ce
2 *12 69 l O 1 33 886
70 2 O l 57 586
71 3 O 1. 98 639
72 4. 1. O 35 103
73 5 l O 95 71
74 6 O 1 30 188
75 6a l O 26 89
76 7 l 0 6? 93
Totals, 8 4. 4. 441 2655
50% 50% Av. 55.12, Av.531.87
13 77 l 1 O 75 111
78 2 O l 45 322
79 3. O 1 96. 868
80 4. O l 56 496
81 5 l 0 164 90
82 6 l O 218 73
83. 7 l O 117 116
Totals, 7 4. 3 771 2086
57% 42% Av. 110.14 Ave?98
14 84 l O l 99 479
85 2 l O 35 103 -
86 3 O 1. 47 218 --
87 4. 1. O 41 156
88 5 O 1 42 178
89 5a l O 31 72
90 6 1 O 60 148
Totals, 7 4. 3. 355 1354
57% 42% Avs50.71 Av.193s 42
*15 91 l 1 O 71 182
92 2 l O 111 118
93 3 O l 37 3.19
Totals, 3 2 l 219 619
66% 33% Av. 73 Av. 206.33
16 94 l l O 37 164
95 2 l O 65 125
96 3 O l 145 295
97 4. O l 47 326
98 5 O 1 89 228
99 6 l O 405 111
100 7 O 1 227 888
101 7a O 1 38 191
102 7b 1 O 3.11 l62
Totals, 9 4. 5 1364 2490
44% 55% Av.151.55 Av.276.66

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TABIs A (contal

Sºails. Day. No. of No. for correct Incorrect Latent; Duration
trial. day, or left or right period of trip
choices choices • $80 e $63 Ge
2. 37 204 l O l 46 58
205 la O l 52 3136
206 2 O 1 15? 1102
207 3 O l 29 710
208 4. O l 44 820
Totals 5 O 5 328 5826
100% Av. 68.6 Av. 1165.2
*38 209 l O l 40 414
210 la l O 50 119
211 2 O l 62 811
212 3. O l 60 357
213 4. O 1 43 478
Totals, 5 l 4. 255 21.79
20% 80% Ave 51 Ave 435.8
39 214 1. O 1 22:5 823
215 2 0. 1 43 2571
216 3. 1 O 32 139
217 4 O l 55 723
218 5 O l 4? 2143
Totals, 5 1. 4 400 6399
20% 80% Ave 80 Ave 1279.8
*40 219 1. O l 372 1689
220 2 0 l 40 371
221 3. O l 36 1170
222 4. O l 53 1005
223 5 O l 50 420
Totals, 5 0 5 551 4655
100% Av.110.2 Av. 931
41 224 l O 1 65 468
225 2 O l 342 762
226 3 l O 92. 224
227 4. l O 161 111
228 5 O 1 69 767
Totals, 5 2 3 739 2332
40% 60% Avel45,8 Ave 466,4
42 229 l O l 70 570
230 2 l O 77 124
231 3 1 O 41 148
232 4. 1 O 183 12.5
233 5 0 1 155 691
Totals, - 5 3. 2 526 1658
- 60% 40% Avalø5.2 Ave 331.6
43 234 l l O 108 19?
235 2 O 1 49 357
236 3. 1 O 278 156
237 4. l O 90 145
238 5 l 0 68 152

TABLE * (contal 96
Smails Day No. of Mo, for Correct Incorrect Laterit. Duration
trial. day. or left or right period of trip
choices choices, 880 e 89Cs.
TE
Totals, 43 5 4. l 593; 100? -
80% 20% Av. 118.6 Av. 201.4
*44 239 l O l 43 282.
240 2 O l 142 440
241 3 Q l 210 3.18
242 4. Q l 105 1175
243 5 O 1. 31 296
Totals, 5 O 5 531 2511
100% Avloé.2 Ave 502.2
45 244 1 l O 260 178
245 2 0 l 211 969
246 3. 1. O 51 138
247 4. 1. O 71 168
248 5 O l 55 535
249 6 1 O 75 298
250 7 O l 64 1551
251 7a. O 1. 57 756
Totals, 8 4. 4. 844 45.93
50% 50% Av. 105.5 A.V. 574 el?
46 252 l O l 80 798
253 2 O l 37 1078
254 3 O l 41 1486
Totals, 3 O 3. 158 3362
100% Av. 52.66 Av. 1120.66
4? 255 1. O l 105 1116
256 la 1 O 60 210
257 2 l O 83. 195
258 3. O 1. 75 848
259 4. 1 O 142 216.
260 5 l O 99 249
261 6 O l 107 604
Totals, 7 4. 3 671 3438
57% 42% Ave 95.85 Ave 491.14.
48 262 1 O l 148 1591
263 2 O l 104 1994
264 3. l 0 191 124
265 4. O l 40 846
266 4a O l 1006 856
267 5 ... O l 162 728
Totals, 6 1 5 1651 5838
16% 83% Av.269,16 Av. 873-16


| 97
TABLE Ka (conts)
Snails Day Moe of No. for Correct Incorrect Latent. Duration
trial day or left or right period of trip
choice. choices BeCa 88C a
2 49 268 l O l 294 585.
269 2 O l 42 255
270 3. O l 68 478
271 4. O l 40 790
272 5 l Q 198 278
273 6 O l 82. 628
Totals, 6 l 5 724 301.4
16% 83% Av. 120.66 Av.502,33
*50 274 l O l 135 158
275 la O 1 26 843
276 2 O l 33 327
277 3. l O 142 173
278 4. O l 37 412
279 5 O l 80 650
280 5a O l 54 1972
281 6 1 O 38 198
282 7 O 1. 75 448
283, 8 O l 75 570
Totals, 10 2 8 693. 5751
20% 80% Av. 69.3 Avså75.1
51 284 l O l 2? 985
285 la 1 O 28 116
286 2 O 1 58 220
287 3 O l 110 635
288 4. O 1 72 1496
Totals, 5 l 4. 295 34.52
20% 80% Ave 59 Av. 690.4
52 289 l O l 75 1562
290 la O l 49 793
291 2 O l 117 1128
292 3. O l 51 558
293 3a l Q 50 121
294 4. 0 l 154 755
295 4a l O 50 154
Totals, 7 2 5 546 5051
28% 7.1% Ave 78 Ave 721 a 57
!
53 296 1 0 l 175 1992
29? 2 O 1. 210 5.99
298 5 0 l 310 608
239 3a O l 446 400
300 4. O 1 93 490
301 43. O 1. 285 680
Totals, 6 O 6 1519 4769
100% Ave 253,16 Av •794.83




98
T A B I. E. K. (cont
Snails Day, Noe of Noe for Correct Incorrect ſatent Duration
trial. day. or left or right period of Trip
choice choices $80 e $83.8
2 54 302 1 O 1 168 92.2
303 la l O 66 144
304 2 O l 119 386
305 3. O l 13? 991
306 4. 0 l 405 306
30? 5 O l 93 455
Totals, 6 l 5 988 3204
16% 83% Av.164.66 Av. 534

99
TABLE ** [Contal 5 m. m. In a r ya |
Snail Day No. of Correct Incorrect Latent Duration - |
2 trials or left or right Period of trip
choices a choices, - sect 800 e
1. 5 4. l 136 769 -
*2 8 8 O 365 739 |
*3 7 3. 4. 263 2002 |
*4 5 3. 2 221 1074
5 6 2 4. 238 1292
*6 5 5 O 437 556
7, 6 3 3 221 1767
8 6 3 3. 574 2073,
*9 5 2 3. 459 2391 -
10 6 l 5 307 2609 -
*11 9 3 6 455 1945
*12 8 4. 4. 441 2655 |
*13 7 4. 3. 771 2086
14 7 4. 3 355 1354
*15 3 2 1. 219 619 |
16 9 4. 5 1364 2490
17 7 4. 3. 915 2084
*18 7 2 5 615 3071
19 5 4. l 904 1288
20 5 2 3. 646 2324
21 5 3. 2 899 2.946
*22 7 l 6 547 34.66
23 7 6 l 1312 1597
24 4. 0 4. 1401 5406
25 5 2 3 1166 2289
26 4. 2 2 622 4765
*27 5 1 4. 534 2204
28 5 O 5 1206 305?
29 4. l 3. 92.8 2007
*30 3 O 3 643 38.91
31 4. 2. 2 333 56.11
32 5 l 4. 653 3408
33 5 O 5 1185. 5050
*34 5 1 4. 375 2792.
*35 4. l 3. 394 304?
36 5 2 3. 1722 2438
37 5 O 5 328 58.26 º
*38 5 l 4. 255 21.79
39 5 l 4. 400 6399
*40 5 O 5 551 4655
41 5 2 3. 729 2332
42 5 3 2. 526 1658
45 5 4. l 593 100?
*44 5 O 5 531 24ll
45 8 4. 4. 844 4593,
46 3. O 3 158 3362
4? 7 4. 3. 671 3498
48 6 l 5 1651 5239
49 6 1 5 724 3014
*50 10 2 8 693. 5751

100
TABLE * (contal
Day Noe of Correct Incorrect Latent
trials or left or right period
choices choices Bege
51 5 1. 4. 295.
52 7 2 5 54?
53 6 O 6 1519
54 6 l 5 988
Total number of trials,
Total number of correct or left choices
Total mumber of incorrect or right choices
Total latent time (sec.) 35829
Ave latent time (sec.)
Total duration of trips (sec.) 157562
513,23
Av. duration of trips (sec.)
Duration
of trip
36C e
34.52
5051
4769
3204
Approximately 38%
Approximately 62%

101
5 tº m in a £ V. Table X (cont.)
Snail Day Noe of Correct Incorrect. Laternt Duration |
trials or left or right period of trip
choices choices. S60 e $8& e
T3 ºl 2 1 l 80 507
*2 … 7 4. 3 332 1931 ||
3. 6 5 l 401 1255
*4 5 O 5 510 1552
5 6 1 5 260 2882 |
6 7 2 5 915 1513 -
7 5 2 3. 559 3637 |
8 6 I 5 170 3807
9 5 4 l 344 798
10 5 2 3 266 2521
*11 6 3 3. 347 1664
*12 7 4. 3. 25? 3227
13 7 2 5 752 3389
14 7 3 4. 755 3676,
*15 3 l 2 135 2503
16 7 3 4. 1607 1859
17 7 3 4. 948 2545 |
*18 5 1 4. 510 1753 |
19 5 2 3 751. 2681
20 5 2 3. 840 4931
21 4. 2 2 305 1570
22 4. 1. 3. 363 3?41
*23 8 6 2 694 2083
24 4. 3. 1. 303 787
*25 7 2 5 948 2774
26 5 2 3. 652 904
* 27 5 2 3. 7.59 2054
28 5 2 3. 42? 1378
*29 5 1 4 1314. 2240
30 5 1 4. 381 2420
31 4. 3 l 546 1768
32 5 l 4. 890 3665
*33 5 l 4. 281 1682.
34 5 2 3. 479 3857
35 4. O 4. 322 2762
36 5 3. 2 546 1229
37 5 Q 5 472 2805
*38 5 2 3. 445 1443
*39 5 4. 1. 197 602
40 5 l 4. 140 1515
*41 5 4. l 280 1025
42 5 1 4. 482. 1203
43 5 l 4. 763 1921
44 5 1. 4. 409 1852
45 8 2 6 873 2646
46 3 l 2 779 2281
47 7 6 l 635. 801
48 5 3. 2 333 969
49 6 1 5 429 1644
*50 10 3. 7 787 3.245
*%



102
3 u. In m_a_r. Ye TABLE X (conts).
Snail Day Nos of Çorrect; Incorrect
trials or left; or right
choices choices,
Laterſ; Duration
period of trip
3. 51 8 O 8
52 7 3. 4.
53 6 O 6.
*54 6 2 4.
Total number of trials
Total number of correct or left choices,
Total number of incorrect or right choices,
Total latent time (sec.)
39C a 88C e
1.188 324?
605 3121
811 2971
847 1494
299
113 Approximately 38%
186 Approximately 62%
304.24
Av. latent time (sec.) 101,75
Total duration of trips (sec.) 118330
Av. duration of trips (sec.) 395,71
T A B L E X A.
Summary or left-right discrimination tests.
Snail 1. 2 3.
Total number of trials,.. 282 307 299
Per cent. of incorrect choices, 52 62 62
Av. latent time (sec.) 83.86 116.6 101.75
Ave duration of trips (sec.) 360.65 513,23 395.71
-



|-|-----------|-±
_|-------|------
103
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* Cu tº £ € ¥ ON "X & O.Ä. MAE N ^ ' OO （ESSE Æ TE-1-1 naxa

106
Table X shows that in a total of 888 trials on three
individuals of Physa, in a series of tests offering a choice
of right and left paths, with a reward for the correct choice
(left), the incorrect path (right) was followed in 58.8% of
the trials. The graphs (figs. 5, 6, 7, p.ſ.º.) show very great
irregularity in the time distribution of the right and wrong
choices. There are days when the record is perfect, other
days when all choices are wrong. Between these is even in-
termediate condition. But with all their fluctuations the
curves rise toward the end. The number of wrong choices in-
creases as the series lengthens. A slight excess of incor-
rect choices is to be expected on account of the tendency to
turn to the right shown in the right-left preference tests.
That this excess should increase toward the end of the series
is unexpected. The significance of this is discussed in
another place . These records show no indication of learning.
5- Experiments with the Y-shaped labyrinth: rough-
ness of path as a warning sign: electric shock punishment.
It seemed either that the problem itself was too difficult
or that the reward and punishment were not great enough to
force its solution. In its natural habitat; the Snail often
depends on plant stems as a means of reaching the surface of
the water when a fresh supply of oxygen is needed. The stems
must frequently be too short . The problem is then familiar
to the snail and should be easy . To make the problem still
easier it was decided to modify the labyrinth as follows:
1. A Y-shaped labyrinth was used so that the snail could make
a choice immediately upon reaching the top of the stem of the

107
Y. The Y was made of glass tubing. 2. The snail was not
confined to one side of it. Owing to the spiral course fol-
lowed by the ascending animal, there was no right and left
choice. 3. One side of the Y was made rough and the other
left smooth. The choice was between rough and smooth. The
training series has shown that the snail feels the delicate
pressure on the foot of the three pronged pressure fork of
food-pressure apparatus (fig. 1). It should therefore feel
the difference between a rough and smooth path. 4. For the
failure-to-get-air punishment with the U-shaped labyrinth
there was substituted the electric shock. Reward was the
getting of air.
Glass tubing, 5mm in diameter, in the form of a Y was
used. One arm of the Y, 4.5 cm. in length, reached the sur-
face of the water. The other arm, 3.5 cm. in length, was
short enough so that the animals could not reach the surface
The stem of the Y was 3cm long. Two (No. 23) silk insulated
copper wires were passed through the stem to the upper end
of the short arm, where they connected with two fine platinum
wire (No. 26) rings passing around the end of the short arm
close enough together so that an electric current could be
passed between them, when proper connections were made • The
upper ends of both arms were then closed with sealing wax to
keep out the water. A hollow base, 4-cm by 2Gm by 1.5cm of
lead was made, in order to permit an outlet for the wires •
These passed from the lower end of the stem of the Y into a
rubber tube which carried them, protected from the water,
through the metal base, along the floor of the experimental


108
tank and upward to the outside. Outside of the experimental
"house" the wires passed through a switch, within easy reach
of the operator, and were then connected with a graphite rheo-
stat and the regular 220 volt lighting system. By careful
experimentation it was found that a current of 0.3 voltage
caused them to draw backward into the shell to such an extent
that they lost their hold on the glass tubing and dropped to
the bottom of the tank. The short arm of the Y from the -
point of divergence to within a millimeter or so of the plat-
inum wires was roughened by means of a band of block tin 2mm
in width and lmm thick passing around it in a spiral. The
metal was then insulated with a coat of liquid celluloid and
further roughened by a coat of coarse cutting sand imbedded
in the celluloid before it haraenea. These precautions ap-
peared desirable because it seemed possible that enough mucus
might be secreted by the snail in crawling over sand alone, |
to fill in the spaces between the grains and thus make a -
smooth surface upon which to travel. This hardly seemed pos-
sible over the ridges of metal used, inasmuch as they were
far enough separated so that the snail had to sink down into
the space between, in passing over them. If the Snail turned
toward the short arm at the top of the stem it immediately
came in contact with the rough ridges and a little later with
the bare electric wires at which point the punishment was ad-
ministered by closing the circuit. No attempt was made to
keep the snail on one side of the apparatus. It sometimes
crawled in an irregular spiral but frequently kept on one side •
The whole apparatus was made shorter than the celluloid laby-
rinth previously used, in order to shorten the time used in


109
each test and thus make a greater number of tests possible in
a given time. The methods of manipulation and cleaning the
apparatus were the same as in the previous tests, and in order
to avoid any possible tendency of the snail to follow the same
path in consecutive trips, the labyrinth was frequently turned
so that; the short arm was as often toward the left as the
right. The "map" method before described was adopted in mak-
ing the records. Four snails were used and a total of 664
trials given. The curves were based upon the percentages of
errors for each snail per day.

-
º º º -
- º
-
-
--

110
Table Xl.
Showing the number of correct and incorrect turns made by three
individuals of Physa, in their attempts to reach the surface of the water
on the Y apparatus. Error was punished by an electric shock of 0.3 volt-
age • The Warning stimulus was roughness. The apparatus was cleaned
between trials. The snails were starved for 24 hours preceding tests.
*Indicates that an egg mass had been deposited by the snail during the 24
hours immediately precéding the tests of the day marked.
No. of No. of No. of No. of No. of No. of latent Duration of
snail days trial trial correct incorrect period trips sec.
tested for for day choices choices sec.
series
9 l l 1 - l O 132 66
2 2 O 1. 245 120
3 3 O l 285 223
Totals - 3 1 2 662 389
33% 66% Av. 220.66 Av. 129.66
2 4. l O 1 90 18O
3 5 l 1 O 121 133
6 2 l O 186 149
7 3 1 O 130 69
Totals 3 3 O 43? 351
1% 0 Av 145.66, Av. 117.
4. 8 1 1 O 210 111
9 2 O l 102 214
10 2a. O l 195 80
11 2b O Ik 151 99
12 3 O 1. 103 376
Totals 5 l 4. 761 880
º 20% 80% Av. 152.2 Av. 176.
5 13 l O l 76 87
14 la l O 110 63
15 2 O 1. 76 364
16 3 O l 298 152
17 3a. O l k55 368
Totals 5 l 4 715 1034
20% 80% av. 143 Av. 206.8
6 18 1 O l 146 205
19 la l O 39 74
20 2 O 1 78 477
21 3 O 1. 44 416
Totals l 3 30, 1142
25% 75% A, 76.75 Av 285.5


111
TABLE XI. (contal
No. of No. of No. Of No. Of No. Of No. of Latent Duration
snail. days trial trial correct incorrect period of trip
tested for for choices choices • §e Ce 36C e
series day
9
22 l l O 184 76
23 2 O l 96. 151
24 2a O l 49 135
25 2b l O 235 83.
26 3 O l 90 87
27 38. l O 583. 98
28 4. O 1. 281 76
Totals 7 3. 4 1518 706
42% 57% Av.216.85. Avl()0.85
29 1 l O 92. 83.
30 2 O l 90 164
31 3. O l 87 59
32 3a O l 43 64
33 3b l O 90 55
34 4. l O 448 82.
Totals 6 3 3. 850 50?
50% 50% Av. 141.66Av. 84.5
9 35 1 l O 192. 72.
36. 2 l O 104 107
37 3 l O 105 142
38 4. O l 722 178
39. 5 O 1 136 88
40 5a 0. l 189 6?
41 5h l O 130 145
Totals 7 4. 3 1578 799
57% 42% Av. 225.42 Avil4.14
10 42 l l Q 125 51
43 2 l O 59. 75
Totals 2 2 O 184 126
100% Av. 92 Av, 63
11 44 1 O 1 102 502
45 2 O l 34 596,
46 2a 0 1. 56 605
4? 3 0 l 56 214.
48 3a O l 24 472
Totals 5 O 5 272 2389
100% Ave 54,4 Av. 477.8


112
TABLE XI (cont.)
Snail Day No. of No. for Correct Incorrect Latent Duration
trial day choices choices period of trip
$6 Ce 36C e
9 12 49 l l 0 64 54
50 2 1 O 84 72
51 3 0 l 48 436
52 4 0 l 85 166
53 4a O 1. 21 95
54 4b l O 42 106
55 5 O l 80 64
56 5a O 1. 196 206
Totals, 8 3. 5 620 11.99
37% 62% Av. 77.5 Av. 149.87
13 57 1 l O 48 75.
58 2 1. O 29. 280
59 3. 1. O 39. 73
Totals 3 3. O 116 428
100% Avs 38.66 Ave 142 s.66
14 60 1 O 1. 135 115
61 la 1. 0 30 59
62 2 O 1 112 459.
63 2a. O l 32 177
Totals 4. 1 3. 309 810
25% 75% Av,77.25 Av.202.5
15 64 l 1. O 50 71
65 2 O l 12.9 60
66 2a O 1 122 67
67 2b l O 54 60
68 3. l O 81 206
Totals 5 3. 2 436 464
60% 40% Av. 87.2 Av. 92.8
16 69 l 1. O 43 85
70 2 O l 10 43.
71 2a O l 93. 88
72. 2h O 1. 34 66
73 26 1. O 46 69
74 3. l O 58 129
Totals 6 3 3. 284 480
50% 50% Av. 47.33 Av. 80
17 75 1. l O 50 95.
76. 2 l O 57 163
77 3. 1 O 70 198
78 4. 0 l 94 107
79 4a 0 l 4? 60
Totals 5 3. 2 3.18 623
60% 40% Av. 63.6 Av. 124.6
113
TABLE XI (contal
Snail Day No. of No. for Gorrect Incorrect Latent. Duration
trial. day. choices choices period of trip
36C e 88C, e.
T 9 - -
18 80 l O l 61 584
81 la l O 21 5?
82 2 O 1. 55 156
83 3. l O 26 98
84 4. O l 65 69
85 4a l O 53 66
86. 5 O 1 47 186
Totals 7 3. 4. 328 1216
42% 57% Av. 46.85 Av. 173.71
19 87 l O 1 40 423
88 2 l O 79 82
89 3. O l 34 472
90 3a O 1. 28 215
91 3h l O 41 166
Totals 5 2 3. 222 1358
40% 60% Av. 44.4 Av. 271.6
20 92 l 1. O 10 60
93. 2 Q 1. 62 121
94 2a O 1 12. 222
95 2h l O 23. 22.8
Totals 4. 2 2 107 631
50% 50% Av. 26.75 Av. 157.75
21 96 l O l 50 23?
97 la l O 42 66
98 2 l O 86. 79
99 3. 1. O 41 86
100 4. O l 74. 212
Totals, 5 3. 2 293 680
60% 40% Ave 58.6 Ave 136
22 101 1 O l 27 228
102 2 1. O 66 120
103 3. O l 123 121
104 3a l O 171 77
105 4. 1. Q 50 63
106 5 1. O 129 67
Totals 6 4. 2 566 676
66% 33% Av. 94.33 Av. 112.66

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90T $36 T O eT go:
093 G9 T O T #02 12 6
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118
TABLE XI (cont.)
5 tº m in a r yi
Snail Day No. of Correct; Incorrect Laterſt Duration
9 trials choices Choices period of trip -
Søø e $6G e
l 3 l 2 662 389
2 l O l 90 180
3. 3. 3. O 4&f 35.1
4. 5 l 4. 761 880
*5 5 l 4 715 1034
*6 4. l 3 307 1142
7 7 3 4. 1518 706.
8 6 35 3. 850 507
9 7 4. 3. 1578 799
10 2 2 O 184 126
11 5 O 5 272 2389
12 8 3 5 620 11.99
13 3 3. O 116 428
14 4. l 3. 309 810
15 5 3. 2 436 464
16 6 3. 3. 284 480
17 5 3. 2 3.18 623
18 7 3 4. 328 1216 |
19 5 2 3. 222 1358
20 4. 2 2 107 631
21 5 3 2 293 680
22 6 4. 2 566 676.
23 7 4. 35 1105 1157
24 5 2 3. 896 748
25 10 6 4. 1045 1646
26 7 5 2 476. 899 -
27 8 3 5 493 1648
28 7 2 5 4.17 1302
29 4. 1 3 212 1085
30 7 4. 3. 465 1648
31 7 2 5 549 2627
32 10 5 5 668 2728
33 8 4 4. 381 24.24
34 6 2 4. 196 795.
35 6 2 4. 288 1152.
36 5 1. 4. 412. 899
37 7 1 6 301 1644
38 5 2 3 249 674
Total number of trials, 215
Total number of correct trials, 95 Approximately 44%
Total mumber of incorrect trials, 120 tº 56%
Total latent time (sec.) 19126
Ave latent time (sec.) 88.95
Total duration of trips (sec.) 59.270 -
Av. duration of trips (sec.) 275.9



119
TABLE XI (contal
snail Dºw No. of no. for correct incorrect latent. Duration
10 trial. day choices choices period. of trip
- $63& © - 58&s
l 1. l + 0 94 78
2 2 O l 571 50
3. 2a O l 555 1.59
4. 3. O l 141 91
5 3a O l 76 84
6 3b O l 56 137
totals, 6 l 5 1493. 599
- 16% 83% Av. 248.83 Av. 99.83
2 7 1 l O 301 88
8 2 O l 533 215
9 3. 1. O 273. 92
totals, 3 2 l 1107 395.
66% 33% Av. 369 Av. 131.66
3 10 l 1. O 75 85.
11 2 O 1 106 74
12 2a l O 422 110
13 3. O 1. 289 89
14 3a O l 493. 11?
15 3b 1 O 156 100
Totals, 6 3. 3. 1541 575
50% 50% Av.256.83 Av. 95.83.
4. 16 l l O 93 130
5 17 l 1. 0 64 76.
18 2 O 1. 107 209
19 2a O 1 73 748
Totals, 3 1 2 244 1033
33% 66% Av. 81.33 Av. 344,33
6 20 l l O 117 82
21 2 O l 1735 85
22 2a O l 140 31?
Totals, 3 1 2 430 484
33% 66% Av.145.33 Av. 161.33
7 23. l O l 129 77
• 24 la O 1. 22 65
25 1b l O 12. 83
26 2 1 0 194. 88
27 3 l O 520 64
28 4. O l 71 80
Totals, 6 3 3. 948 457
50% 50% Av. 158 Av. 76 •16

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TABLE XI. (cont.) |
Duration |
Snails Day No. of Moe for Gorrect Incorrect Latent of trip
10 trial day choices choices péfiod 89&e
_ 36&e |
- 31 200 T 44 76 |
201 36 76
202 40 106
203 56 98
204 72. 61
;
248 417
Ava 49-6 Av. 83,4
5
Totals
32 205
206
2O7
208
209
210
98 130
66 92
56 125
70 225
35 168
60 94
i
24.
76
Totals 6 385 834
Ave 64,16 Avel39
33 211 l 71 130
212 la 36 595.
213 lb. 28 309 |
214 lc 90 185
|
Totals 4. 225 1219 -
Ave 56°25 Ave:304.75
|
- -







126
Summary
Snail Day No. of Correct; Incorrect; Latent. Duration of
10 trials choices choices period trip
Sec Seº e
l 6 1 5 1493 599
2 3 2 l 1107 395
3 6 5 3 1541 575
4. 1. 1. O 93 130
5 3 1. 2 244 1033
6 3 1. 2 430 484
7 6 3 3 948 457
8 5 l 4. 1390 568
9 2 1 1. 711 173
10 5 2 3 1339 1010
11 5 3 2 863 827
12 9 3 6 2659 1081
15 10 3 7 931 1391
14– ... 6 l 5 514 2030
15 6 2 4. 1265 818
16 8 4. 4. 481 1014
17 11 3 8 833 2029
18 9 5 4. 1539 745
19 5 1. 4. 431 396
20 14 4. 10 11.95 2509
21 9 1. 8 760 1833
£22 7 3 4. 1041 1727
23 5 1. 4. 297 658
24 3 2 1. 206 322
25 11 2 9 1280 1250
26 6 3 3 359 1197
27 15 5 10 1019 1546
28 5 4. 1 397 413
29 8 2 6 876 1008
30 7 1. 6 339 756
31 5 2 3 248 4.17
32 6 3 3 385 834
33 4. l 3 225 1219
Total number of trials 214
Total number of correct trials 75 Approximately 35%
Total number of incorrect trials 139 Approximately 65%
Total latent time (sec.) 27439
Ave latent time (sec.) 128 e21
Total duration of trips (sec.) 3.1444
Av. duration of trips (sec.) 146.93

127
Summary
Snail Day Moe of
11 trials
l 4.
2 6
3 5
4. 9
5 7
6 5
7 8
8 7
9 5
10 3
11 9
12 6
13 9
14 6
15 5
16 8
17 7
18 10
19 7
20 9
21 7
22 7
23 7
24 8
25 14
Total number of trials
Correct;
choices
TABLE XI (continued) •
Total number of correct trials
Total number of incorrect trials
Total latent time (sec.)
Ave latent time (sec.?
Total duration of trips
Total duration of trips
|
$60 e
$6&e
|
Incorrect
choices
Laterit;
period
Seºe
223
2265
674
1536
1716
684
1229
965
810
409
1044
819
1237
859
542
1124
1344
842
790
463
528
358
587
931
1578
178
75 Approximately 42%
103 Approximately 58%
23557
132e34
21273
119e 5
Duration of trip
S6 Ge .
563
1136
319
904
863
1146
2852
717
4.38
262
872
503
785
530
681
890
730
1060
698
640
460
749
800
853
1821
128
TABLE XI (continued)
Summary
Snail Day No. of correct Incorrect Latent Duration of trip
27 trials choices choices period Sece
$90 e
1 4. 2 2 57.7 552
2 3 1. 2 61? - 823
3 5 1. 4. 797 2965
4. 6 1. 5 1908 1339
5 5 1. 4. 1294 2267
6 4. O 4. 752 - 2940
7 4. 2 2 944 1574
8 7 O 7. 1119 2379
9 5 4. l 1915 729
10 6 2 4. 849 1352
11 5 3 2 735 1131
12 3 l 2 865 1304
Total number of trials 57
Total number of correct trials 18 Approximately 32%
Total number of incorrect trials 39 Approximately 68%
Total latent time (sec.) - 12372 -
Aver, "latent time (sec.) 217 s 22
Total duration of trips (sec. 7 19355
Aver, duration of trips (sec.) 339e 56

129
TABLE XI Ae
Summary of rough-shock smooth tests.
Snail 9
215
Total number of trials
% of incorrect choices 56
Av. latent time (sec.) 88s. 95
Av. duration of trips (sec.) 275.9
10
214
65
128.21
146,93
11
1.78
58
132e34
119e 5
27
57
68
217 e22
339,56


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135
Table XI shows the trials of four snails on the rough-
shock smooth Y shaped labyrinth. These cover periods of 38,
35,25, and 12 days and involve 215, 214, 178 and 57 trials
or a total of 664 trials. Of these 401 or 60.3% give wrong
choices. The curves show great irregularity especially in
the first third of their courses • Nearly all the days on
which the choices were either all right or all wrong fall
in this part of the curves. After this the curves fluttuate
less from the fifty per cent - level, but rise slightly as they
proceed. In this series the Snails climb a labyrinth of
cylindrical glass and are free to move on any side of it;
there is no question of right or left. The choice is made
between rough and smooth. No rough-Smooth preference tests
were made, but there is evident in this series a tendency to
prefer the rough side and that in spite of the punishment
which the choice brings. Not only is a preference shown for
the rough side, buths shown by the upward tendency of the
curves this preference increases with the lengthening of the
series. This may be taken as additional evidence that rough-
ness was an effective stimulus. The further significance of

these facts is considered in the discussione
136
- 6- Experiments with Y shaped labyrinth: mechanical
stimulation as warning signal. The results treated in
Table XI and in the group of figures 8, 9, 10, ll, show no
indication of learning. It is believed that the large per-
centage of error might have been lowered in a greater number
of tests, but this would probably not account for the type of
curve obtained. It was then suggested by Dr. John º'. Shepard
that while the snails were unable to solve the labyrinth they
might nevertheless be able to form a simple association under
the conditions of the labyrinth experiments. They might show
on the labyrinth a capacity equal to that developed under
tests with simultaneous stimuli. A series of tests was there-
fore carried out, using the Y apparatus with the electric
shock punishment but modified as follows: 1: In place of
roughness on the shock side a mechanical warning stimulus was
used which could be observed to effect the snail. 2: The
wrong arm of the labyrinth was shortened so that the shock
followed immediately on the warning stimulus. The time rela-
tion of the two stimuli was similar to that in Yerkes (1912)
experiments with earth worms and approached that of the method
of simultaneous stimuli • The Y apparatus just described
was used in a slightly modified form. All traces of the sand
and metal were removed. The long arm of the Y was shortened
to 3 cm, in order to bring the reward nearer the point of
divergence of the paths, while the short arm was reduced to
1.5 cm. in length in order to bring the punishment nearer to
the point of the path which necessi tated choice of the part



137
of the snails. The snail was placed at the base of the path
in the usual way. If at the top of the stem, the 'short arm
was chosen, as soon as the turn was made, the tentacles and
head were stroked with a hair. This was fastened to the
end of a small stick so that it could be handled by the
operator. This tactile stimulus was immediately followed by
the usual electric shock. The fact that the tentacles were
withdrawn and the animal recoiled slightly when touched with
the hair, showed conclusively that the tactile stimulus was
effective. While Gheck tests showed that the irritation was
not severe enough to make this stimulus serve as a punish-
ment. Six snails were used and the usual method of record-
ing and curve plotting was followed e
- 138
TABLE XII.
Showing the number of correct, incorrect , and correct by
association trials in a series of tests in which an electric
shock was used as punishmant in connection with a mechanical
warning stimulus. The Y apparatus was used with the arms shortened
to 3cm and l. 5cm. In case of error in choice the snail was stroked
across the dorsal head region with a hair and then given a shock -
of 0.3 voltage, The apparatus was cleaned between tests. Four snails
were used and they had been starved 24 hours preceding the tests.
No. of No. of No. of No. of No. of No. of No. Of Duration
snail days trial tria i correct Choices errors of
tested for tor choices correct - trip, sec.
- series day by
º associa-
tion
9. l l l O O l 134
2 2 l O O 70
3 3 O O l 98
4 3a O O l lić
5 4. O O l 171
6 5 O O l 27].
7 6 O O l 135
8 7 l O O 66
9 8 O O 1. 175
Totals 9. 2 O 7 1236
22% 77% Av. 137.33
2 LO l O O l 140
ll 2 O l O 147
12 3 l O O 103
13 4. O l O 21C
14 5 O l O 33].
15 6 l O O 135
Totals 6 2 3 l 965
33% 50% 16% Av. 160.83
3 16 l l O O 70
17 2 l O O 128
18 3 O O l 274
19 3a O l O 39].
2O 4 O O l 440
21 5 O O l 1428
22 5a O O l 234
º 23 6 l O O 124
Totals 8 3 1 4 3O89
37% 12% 50% Av. 386. 12
4 24 l O l O 181
25 2 l O O 70
26 3 O l O 211
27 4. l O O 95
28 5 l O O 92
39 6 l O O 94
3O 7 l O O 124

139
No. of No. of No. of No. of No. of No. of No. of Duration
snail days trial trial correct choices errors of
tested for for choices correct trip, sec.
series day by
- associa-
3 tion
Totals - 7 5 3. O 867
71% 28% Av. 123.85
5 3.1 l O O l 196
32 2 O O l 33.I.
33 3 O O l 432
34 4 l O O 85
35 5 O O l 585
36 6 l O O 99
37 7 O l O 403
Totals 7 2 l 4. 3.131
28% 14% 57% Av. 304.42
6 38 l O l O 163
39 2 l O O 92
40 3 l O O GO
4l 4. l O O 69
42 5 O O l 490
43 6 l O O 92
44 7 l O O 227
45 8 l O O 77
Totals 8 6. l l 1270
75% 12% 12% Av. 158.75
7 46 l O O l 165
47 2 O O 1. 173
48 3 l 0. O 63
49 4. l O O 69
50 5 l O O 82
51 6 O O l 910
53 7 l O O 95
53 8 O l O 372
Totals 8 4 l 3 1929
50% 12% 37% Av. 241. 12
8 54 l l O O 70
55 2 O O l 2O5
56 3 l º O O 47
57 4. O O l 273
58 4a l O O 53
59 5 l O O 52
6O 6 O l O 514
6l. 7 O l O 261
62 8 l O O 92
Totals 9 5. 2 2 1566
55% 22% 33% Av. 174


140
No. of No. of No. of No. of No. of No. of No. of Duration
snail days trial trial correct choices errors Of
test ed for for choices correct trip, sec.
séries day by
- associa-
3– tion
|
9 63 l O O l 14.6
64 la l O O 57
65 2 O O 1. 230
66 2a l O O 53
67 3 O O l 391
68 4 O O l 321
69 4a O O l 453
70 4b O O l 379
Totals 8 2 O 6 1939
25% 75% Av. 241.12
10 71 l O O l 179
72 2 O l O 270
73 3 O O l l2O
74 3a O l O l39
75 4. O l O 256
76 5 O l O 341
77 6 O l O 559
Totals 7 O 5 2. 1864.
7.1% 28% Av. 266.28
il 78 l 1 O O 449
79 2 l O O 40
8O 3 O O l 5.15
81 4 O O l 460
82 5 l O O 61
83 6 O O l 151
84 6a O O l 912
Totals 7 3 O 4. 2 L88
42% 57% 312.5
12 85 l l O O 63
86 2 l O O 56
37 3 l O O C32
38 4 l O O 72
89 5 O 1 O 197
90 6 l O O 53
Totals - 6 5 l O 492
83% 16% Av. 83


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142
No. of No. of No. of No. of No. of No. of No. of Durat, ion
snail days trial trial correct choices errors of
test ed for for choices correct trip, sec.
series day by
associa-
9 tion
18 124 l l O O 90
125 2 l O O 50
l26 3 O l O 328
127 4 l O O Il O
128 5 l O O 8O
129 6 l O O 76
130 7 l O O 560
Totals 7 6 l O 1294
85% 14% Av. 184.85
19 131 l O l O 86
l32 2 O l O 89
133 3 l O O ll.0.
134 4. l O O 96
135 5 1 O O 196
136 6 l O O 126
Totals 6 4. 2 O 703
66% 33% Av. 117. 16
2O 137 l O O l 425
138 la O l O 585
139 2 l O O 1.65
- 140 3 l O O 51
14l 4. O l O 3O8
Totals 5 2 2 l lA34
40% 40% 20% Av. 286.8
2l 143 l l O O 79
lá3 2 l O O 60
144 3 O l O 754
lA5 4 l O O 74
146 5 () O l 546
147 5a l O O 63
Totals 6 4 l 1 1575
66% 16% 16% Av. 362.5
- 143
Summary
|Snail Day No. of Correct Correct by Incorrect Duration
9 trials choices association choices in sec.
l 9 2 O 7 1236
2 6 2 3 l 965 -
3 8 3. l 4. 3O89
4 7 5 2 O 867
5 7 2 l 4. 2131
6 8 6 l l 127C
7 8 4. l 3 1929
8 9 5 2 2 1566
9 8 2 O 6 1929
10 7 O 5 2 1864
ll 7. 3 O 4 21.88
12 6 5 l O 492
13 6 4. l l 765
14 6 3 2 l 1200
15 7 4. 3 O 689
16 6 3 3 O 88.1
17 8 6 2 O 1431
18 7 6. l O 1394
19 6 4. 2 O 703
2O 5 2 2 l 1434
21 6 4. l l 1575
Total number of trials 147
Total number correct by chance 75 Approximately 51%
Total number correct by association 34 Approximately 33%
Total number incorrect 38 Approximately 26%
Total duration in seconds 2.94.98 -
W. duration in seconds - 200. 66


-
- 144
No. of No. of No. of No. of No. of No. of No. of Duration º
snail days trial trial correct choices errors of
tested for for choices correct trip, sec.
series day by
associa-
19 tion
l l l O O l 137
3 2 O O l 195
3 2a O O l 67
4 2b O O l 109
5 2c O O l LO3
6 3 l O O 76
7 4. O O l 556
8 4a O O l 219
9 4b l O O 55
Totals 9 2 O 7 1517
22% 71% Av. 168.55
2 10 l l O O 46
ll. 2 l O O 35
12 3 l O O 47
13 4 O l O 257
14 5 l O O 58
15 6 l O O 75
16 7 O l O 184
17 8 l O O 58
Totals 8 6 2 O 756
75% 25% Av. 94.5
3 18 l l O O 54
19 2 O O l 29'?
2O 3a O l O 233
31 3 l O O 64
22 4 O 1. O 195
33 5 O l O 133
24 6 l O O 77
25 7 l O O 8O
Totals 8 4 3 l 1133
50% 37% 12% Av. 141.62
4 26 l O l O 46
27 2 O l O 289
28 3 O l O 2OO
29 4. O O l 236
3O 5 l O O 37
3]. 6 O O l 4.1.1
Totals 6 l 3 2 1299
16% 50% 33% Av. 216.5

145.
No. of No. of No. of No. of No. of No. of No. of Duration
snail days trial trial correct choices errors of
test ed for for choices correct trip, sec.
series day by
- associa-
19 tion
5 32 l l O O 72
33 3 O O l 90
34 2a l O O 36
35 3 O l () 145
36 4. O O l 237
37 4a 1. O O 57
Totals 6 3 l 2 637
50% 16% 33% Av. 106. 16
6 38 l l O O 60
39 2 l O O 65
40 3 l Q O 56
4l 4. O l O 156
42 5 l O O 246
Totals 5 4. l O 583
80% 20% Av. 116.6
7 43 l O O l 765
44 la O O l 122
45 lb O l O 315
46 2 l O O 70
47 3 l O O 87
48 4. O l O 270
Totals 6 2 3 2 1629
33% 33% 33% Av. 371.5
8 49 l l O O 45
50 2 l O O 76
5l. 3 l O O 74
53 4. l O O ll2
53 5 O l O 426
Totals 5 4. l O 733
80% 20% Av. 146.6
9 54 l l O O 1Ol
55 2 l O O 81
56 3 l O O 58
57 4 O O l 7OO
58 4a l O O 59
59 5 l O O 83
60 6 O l O 323
Totals 7 5 l l 1405
7.1% 14% 14% Av. 200.71

146.
No. of No. Of No. of No. of No. of No. of No. of Duration
snail days trial trial correct choices errors of
test ed for for choices correct trip, seq.
- series day by
associa-
19 tion
10 61 | () 1. O 264
62 2 O l O 141
63 3 l O O 58
64 4 O l O 92
65 5 l O O 52
63 6 O O l 354
67 6a O O l 370
68 7 l O O 82
Totals 8 3 3 2 1413
37% 37% 25% Av. , 176.63
ll. 69 l l O O 7].
70 2 O O l 382
71 2a l O O 3O
72 3 l O O 105
73 4 l O O 152
- 74 5 O l O 358
75 6 l O O 103
Totals 7 5 l l 1331
71% 14% 14% Av. 175.85
12 76 l l O O 65
77 2 l O O 72
78 3 l O O 65
79 4. l Q O 58
8O 5 l O O 68
81 6 O O l 306
82 6a l O O 12O
Totals 7 6 O l 754
85% 14% Av. 107.71
13 83 l l O O 204
84 2 l O O 42
85 3 l O O 48
86 4 O l O 150
3? 5. 0 O l 312
88 5a l O O 83
89 6 O O l 429
90 6a O O l 303
Totals 8 4. l 3 1572
50% 12% 37% Av. 196.5

147.
No. of No. of No. of No. of No. of No. of No. of Durat iOn
snail days trial trial correct choices errors of
test ed for for choices correct trip, sec •
series day - by
associaa.
19 tion
14 91 l l O O 33
92 2 l O O 54
93 3 O l O 197
94 4 O O l 74
95 4a O l O 225
96 5 l O O 64
97 6 l O O 87
98 7 O l O 95
Totals 8 4 3 l 829
50% 37% 12% Av. 103.63
15 99 l l O O 44
LOO 2 O l O 195
101 3 O O l 155
103 3a l © O 62
LO3 4. l O O 69
104 5 O l O 664
Totals 6 3 2 l 118O
50% 33% 16% Av. 196.66
i 6 105 l l O O 75
lò6 2 l O O 5l.
107 3 l O O 67
108 4. l O O 42
109 5 O l O 485
ll.0 6 l O O 68
Totals 6 5 l O 788
83% 16% Av. 131.33
17 lll l O l O 2O6
113 2 l O O 62
ll3 3 l O O l63
ll.4 4 l O O 78
l15 5 l O O 76
lló 6 O l O 390
Totals 6 4 2 O 975
66% 33% Av. 163.5
18 117 l O l O 163
118 2 l O O 5l
119 3 l O O 64
120 4. l O O 73
131 5 l O O 247
123 6 O l O 297
Totals 6 4 2 O 895
66% 33% Av. 149. 16

148.
No. of
No. of No. of Duration
No. of No. of No. of No.
snail days trial trial correct choices errors of
test ed for for choices correct trip, sec,
series day by -
associa-
19 t; ion
19 123 l l O O 87
l24 2 l O O 50
135 3 O l O 3O2
126 4 O l O 510
13? 5 O O l 88
128 5a O O l 1Ol
Totals 6 2 2 2 1138
33% 33% 33% Av. 189.66
2O 129 l l O O 86
130 2 O O l 148
131 2a l O O 72
l32 3 O l O 363
133 4 l O O 58
134 5 l O O 93
Totals 6 4. l l 82O
66% 16% 16% Av. 1136.66
21 135 l l O O 58
136 2 O O l 210
137 2a O l O 564
138 3 l O O 49
139 4 l O O 56
l40 5 O O l 439
141 5a O l O 86
Totals 7 3 2 2 lăl2
42% 28% 28% Av. 216


Day No. of Correct Correct by
trials choices association
Summary
Snail
19
I
2
3
4
5
6
7
8
9
IO
ll
12
13
l4
15
l6
17
18
19
2O
21
Total number
Total number
|Total number
|Total number
Total
º
of trials
correct by chance
correct by association
incorrect
| - duration of trips in seconds
": duration of trips in seconds
Incorrect;
choices
14l
78
34
29
22799
161.69
Duration
in sec.
1517
756
ll.33
1399
63?
583
1629
733
lA05
l413
l231
754
1572
829
118O
788
975
895
1138
82O
1512
Approximately 55%
Approximately 34%
Approximately 31%
l49.



TABLE XII (continued)
Summary
Snail Day No. of Correct Correct by Incorrect Duration
| 10 trials choices association choices in see.
l 7 3 O 4 786
2 5 5 O O 581
3 ll. 7 O 4 3359
4 1O 4. O 6 992
5 7 3 O 4. 773
6 6 3 O 3 21.18
7 8 5 O 3 803
8 5 3 O 2 26?
9 9 4. 2 3 1200
1C 1C) 2 l 7 2735
ll 7. 4. l 2 829
12 7 5 l l 986
13 6 2 l 3. 1826
l4 9 4. l 4. 1367
15 9 4. 2 3 787
l6 8 4. O 4. 1011
17 7 5 l l 415
18 l'O 2 O 8 1821
39 7 5 2 O 629
2O 6 2 4. O 1274
21 6 l 4. l 1010
22 7 3 l 3 1093
23 6 4 l l 1957
| Total number of trials 173
Total number correct by chance 84 Approximately 48%
| Total number correct by association 22 Approximately 13%
| Total number incorrect 67 Approximately 39%
Total duration of trips in seconds 276.18
Av. rātāration of trips in seconds 139. 64


15l.
TABLE XIII (continued).
Summary
Snail Day No. of Correct Correct by
13 trials association
l 5 O O
2 5 3 O
3 1O 6 O
4. 5 3 O
5 6 3 O
6 5 4 O
7 lC) 5 l
8 5 4 O
9 10 5 l
10 7 2 l
ll 7 3 l
12 8 4. O
13 8 6 O
l4 9 5 2
15 8 3 4.
16 6 3 2
17 7 3 2
Total number of trials
| Total number correct by chance
Total number correct by association
Total number incorrect -
Total rate (sec)
Av. rate (sec.)
Incorrect
l2]
62
14
45
341.71
199.76
Rate
36 C.
1651
2402
1829
1OOO
1155
388
23.90
616
2640
2654
1220
1471
686
1909
620
454
1086
Approximately 51%
Approximately 12%
Approximately 37%

TABLE XII (continued) 152.
Summary
Snail Day No. of Correct Correct by Incorrect Rate
21 trials association - 8&C e
l 6 5 O l 821
2 8 6 O 2 1311
3 8 3 O 5 1850
4. 7 2 l 4. 1576
5 6 2 O 4 1471
6 8 2 3. 4. 2263
7 7 5 O 2 934
8 8 6 l l 890
9 8 8 O O €692
l O 5 l O 4 1596
ll. 4. 3 O l 673
12 5 3 2 O 987
13 6 3 2 l 589
14 5 5 O O 533
15 6 3 3. l 730
16 7 6 O l 71.2
l? 7 4 O 3 830
18 7 6 O l 1173
19 6 3 l 2 2262
2O 6 4. O 2 1059
21 5 4. l O 664
22 6 4 l l 893
23 8 4 O 4 2O8O
24 6 2 2 2 1708
25 5 2 2 l 1364
26 8 4. l 3. 1294
27 6 3 2 l 1233
Total number of trials 174 -
Total number correct by chance 103 Approximately 59%
Total number correct by association 2O Approximately #3%
| Total number incorrect - 5l Approximately 39%
| Total rate (sec.) 3.21.78
Av. rate (sec.) 184. 93

TABLE XII (continued). 153.
Summary
Snail Day No. of Correct Correct by Incorrect Rate
22 trials association . 88C a
l 6 l O 5 1283
2 8 2 l 5 l403
3 7 4. O 3 994
4. 6 3 l 2 998
5 8 l O 7 1778
6 8 5 l 2 1334
7 8 3 l 4. 1866
8 12 l l 10 23.48
9 7 2 l 4 1657
10 5 O O 5 1031
11 5 4. O I 856
12 6 4. O 2 1583
13 7 4 O 3 158
14 5 2 O 3 776
15 9 3 2 4. 1257
l6 7 4 O 3 1048
17 9 4 l 4 1738
18 6 5 O l 1010
19 7 4. l 2 1040
2O 7 2 O 5 2546
21 5 2 l 2 2384
22 5 l 4 O 1217
23 7 3 2 2 1850
24 6 3 2 l 1219
25 6 4 l 1 690
26 6 4 l l 599
27 6 4. l l 79
| Total number of trials 174
Total number correct by chance 79 Approximately 45%
Total number correct by association 22 Approximately 13%
Total number incorrect 73 Approximately 42%
Total rate (sec.) 3.6865
Av. rate (sec.) 211.86
TABLE XII As
Summary of tests in which a mechanical stimulus was used
in Connection with electric shocke
Snail 9 19 10 13 21 22
Total number of trials 147 141 173 121 174 174
% of choices correct by
Chance 51 55 48 62 59 45
% of choices correct by -
* association 23 24 13. 14 12 13.
% of incorrect choices 26 21 39 45 29 42
Ave duration of trips in
second, 200,66 161,69 139,64. 199.76 184-93 211.86

155.
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l60.
Table XII shows that in a total of 930 trials on
six individuals of Physa, 51.2% were correct by chance; that
is, the correct path was chosen without contact with the warm-
ing stimulus. In 15.6% of the trials the correct path was
chosen after contact with the warning stimulus, but without
punishment, showing that a weak association had been formed
between the two stimuli. In 32.5% of the trials, the warm-
ing stimulus was disregarded and punishment received. This
shows that the behavior of the snails tested was modified
during the experiments in as much as they apparently learned
to recognize the warning stimulus and turned back before
receiving the electric shock. The snails profited by experience -
The slightly downward tendency of the jagged curves based on
these records tries. i2.'s, is, 15, 16, 17pºsſ) ShoWS an
erratic decrease in error, weak association and limited
associative memory •
- -
- --- - --


161.
7. SUMMARY OF OBSERVATIONS,
1. All observations and experiments were made on the
snail Physa gyrina Say while in tap water at room temperature
and under uniform light ing conditions.
2. When the air is pressed from the lung of Physa and
it is placed in the water at the base of a U-shaped labyrinth
supported on an upright stem, it crawls up the stem and along
the arms of the U to the surface of the water. Fig. 3, p.6%
3. Experiments to test right or left preference : first
Series •
In a series of 24 trials in which three individuals of Physa
were deprived of air and placed on the bottom near the wall of
a glass dish filled with water, and allowed to crawl unhindered
to the surface of the water, the path chosen deviated from a
perpendicular toward the right in 54.1% of the trials and toward
the left in 45.8% of the trials. This showed that the natural
path chosen by the three snails tested, in traveling over a
flat unrestricted substratum to the surface of the water for
air, in a comparatively small number of trials, deviated some-
what to the right. Table VII, p. 68
4. Experiments to test right and left preference.”
second series •
When the U apparatus (paragraph lº) is bordered by a "picket
fence" of wires, the snail is forced to travel on one side •
When it reaches the top of the stem it must turn toward either
the right or left end of the horizontal bar of the u to reach
the surface of the water. Fig. 3, p.6%
5. In a series of 240 trials in which the two arms of


162.
the U were identical and both reached the surface of the water,
the three snails tested followed the right arm in 51.6% of the
trials and the left arm in 48.3%, showing a slight right prefer-
ence for the snails tested. Table VIII, p. 7%
assessº” to test preference for an ascending or
In order to determine the lack or presence of a preference for
an ascending or a descending path, the U shaped labyrinth was
so tilted that the bar of the U deviated from a horizontal at
angles varying from 57" to 7° 40'. In 600 trials the three
snails tested chose the descending arm in 43% of the trials and
the ascending arm in 57%, showing a slight preference for an
ascending path. Table IX, p. 74
7. In subsequent experiments in which the U. labyrinth
was used the horizontal bar was kept level.
8. In the experiments to test learning, complete records
are presented for two individuals in each series of tests and
summaries of results are given for additional snails tested-
9. Experiments on learning the U-shaped labyrinth a
In a series of 888 tests on three individuals of Physa, using
the U-shaped labyrinth with the right arm shortened so that a
snail could not reach the surface of the water from its upper
end, thus making failure to obtain air serve as a punishment
incident to the choice of this arm, 58.8% of the turns were
toward the right, that is, incorrect, and 41.8% toward the
left or correct. There is then shown no evidence of ability
in the snail to distinguish right or left in connection with
failure to obtain air (punishment) and the attainment of air
(reward). Table X, p. 77



10. The curves based on these trials show irregularity
at the beginning and an upward tendency toward the latter end,
indicating an increase in the tendency to turn toward the right
as the trials proceed. Figs. 5-7, p. 123-125
11. Experiments with Y-shaped labyrinth: roughness of
the path as a warning stimulus: electric shock as punishment.
In a series of 664 tests a Y-shaped path of glass tubing, un-
limited by wires, was used. One arm of the Y gave access to
the surface of the water and the other was shortened and
supplied with wires over which a 0.3 volt electric current could
be sent. The space between the point of divergence of the two
arms and the wires was roughened. The four snails tested chose
the short arm or punishment in 60.3% of the trials. This series
of tests then shows no indication of learning. Table XI, p. //o
12. The curves based on these trials show less irregular-
ity than those in the preceding tests (paragraph 10) but the
same upward tendency toward the latter end, indicating an increas-
ing frequency of rough-shock choices as the trials proceed.
Figs. 8-11, p. 150-133.
13. Experiments with Y-shaped labyrinth: mechanical stimu-
lation as warning signal. In a series of 930 tests the Y appar-
atus was used but instead of roughness in connection with the
electric shock, the snail was stroked on the tentacles and dorsal
head region with a hair, preceding the shock if a wrong choice
were made. Check tests showed that the irritation caused by the
warning stimulus was not sufficient to cause it to serve as a

l64.
punishment. The six snails tested chose the short arm and
punishment in 32.5% of the trials, the long arm, by chance in
51.2% and the long arm through association in 15.6%. Modification
of behavior through the formation of an association between the
two stimuli, one serving as punishment, the other as a warning
signal, is thus shown • Table XII, p. 157.
14. The curves based on these trials show irregularity
throughout but a downward tendency toward the latter end indicat-
ing the formation of a weak association between the two stimuli
used. rise. H3-17, p. 155-157.
15. The last series of experiments (paragraph 13) shows
results comparable to those obtained in the first part of the
present work which indicated an association formed between two
dissimilar stimuli, food and pressure, in a series of tests
based on the Pawlow salivary methode
-º-
---

l65.
8. Discussion.
The foregoing attempt to learn whether the man san
solve a simple vertical U- or Y-shaped labyrinth fallº into three
Series.
1. In the first of these there was used a U-shaped
labyrinth supported on a stem and bordered by a paling of wires
so that the snail could crawl up but one side of it. At the
top of the stem ºw had a choice of a right or left path. If
the right path were chosen it led to the right vertical bar of
the U from the top of which the snail could not reach the surface
of the water. If the left path were chosen it led to the vertical
bar of the U, longer than the right, from the top of which the
snail could fill its lung with air. The upward course of the
snail is in search of air. Choice of the right path resulted
in failure to get air which was assumed to act as punishment.
Such a choice was regarded as incorrect. Choice of the left;
path led to the attainment of air, which was regarded as reward
and such choice was registered as correct.
Preliminary tests showed that the snails have a slight
preference for the right path, preference possibly related to
the assymetry of the animal. It was to be expected that this
right preference would appear at the beginning of the series of
learning tests, but that it would be soon corrected by the result
of the learning process. If the snails actually learned and a
curve were plotted showing their percentage of errors from eadh
successive day's experience, this curve would start somewhere


166.
above the 50% level on account of the right preference, which
would result in an excess of incorrect choices. If the snail
did not learn and were in no way affected by its experiences
with the labyrinth the curve of errors might be expected to
follow the fifty per cent, level while fluctuating above and
below it.
An inspection of the graphs for this series shows that
they follow neither one of the courses predicted. They are
quite irregular, but show with the progress of time, a distinct
rise above the fifty per cent. level. The snails not only do
not learn, but their percent age of errors increases as the series
of trials lengthens. Nothing has been detected in the physical
environment to direct the snail toward either side. Tt is in a
symmetrical environment as to structure of labyrinth, surround-
ing tank and house, lighting and temperature • The cause of the
increasing tendency to turn toward the right must then be sought
in the animal itself. We may say that with the progress of the
trials the animal's preference for a turn toward the right increases.
If we assume that the disturbances incident to the experimental -
handling of the animal increase its natural tendency to turn to
the right we have an "explanation" of the upward course of our
curve showing the distribution of errors over the series of trials.
This increasing tendency to turn toward the right might
inhibit learning. While the curves do not show that the animals
learn, they cannot be accepted as final evidence that the animals
might not learn unier other conditions. Had punishment been pro-


l67.
vided on the left side of the labyrinth and reward on the right
side, then the right preference, increasing with the series,
would have resulted in an error-distribution curve dropping
toward the zero level. Such a Gurve, showing a decrease in
the percentage of errors as it proceeded, might have been taken
as final evidence of learning, had not the right-left preference
tests been performed,
2. In the second series of labyrinth tests the U-shaped
labyrinth was discarded and in its place was used a Y-shaped
labyrinth of cylindrical glass tubing. Owing to the snails
tendency to crawl in a spiral such a labyrinth offers no choices
of right or left; the snail is free to move in any direction in
order to reach its top. One arm of this labyrinth was made
rough While the other remained smooth. Thus roughness Served
as a means of discrimination between the two. At the upper end
of the rough arm the snail received an electric shock. The rough-
ness served as a warning signal of the approaching shock, no
rough-smooth preference tests were made •
The curves again show much irregularity, but not so much
as those with the U-shaped labyrinth. There are again days on
which all choices are correct and other days on which all are
incorrect. Nearly all of these days, however, fall in the first
third of the curves, with the result that this part is much more
irregular than that which follows. After their first thirds the
curves remain nearer the fifty per cent, level, but on the whole
tend to lie above it. In other words, the percentage of error
|


l68,
again increases as the series lengthens. As it was suggested
that in the case of the U-shaped labyrinth the increase in error
percentage was due to an increase in right preference, so it
may be suggested that it is here due to increase in roughness-
preference. Experiments are needed to test the existence of
roughness preference. -
If the punishment had been placed on the smooth arm of
the labyrinth and there had been no learning, the curve would
nevertheless have descended toward the O level on account of
the roughness preference. The result would have been an appar-
ent decrease in error percentage with the progress of the curve,
an apparent evidence of learning, really however an increase of
roughness preference.
3. The third series of labyrinth tests was planned, to
test the capacity of the snail to form associations on the
labyrinth that it had failed to solve. The Y shaped labyrinth
was used, but all traces of roughness were removed. The short
arm was shortened still more making the interval between the
warning stimulus and the punishment less than in the preceding
tests. The warning stimulus adopted was the irritation caused
by stroking the dorsal head region and tentacles of the snail
with a hair. That this stimulus was an irritation was evidenced
by the fact that its use caused the snail to withdraw its tent;-
acles, and at times to ſpartially retract its head toward the
edge of its shell. Check tests, however, showed that the irrit:-
ation was not severe enough in itself to act as punishment • The
labyrinth as before offered no choice of right or left -

169.
The curves of error percent age show much irregularity
but a slight downward tendency. In 15.8% of the to tal of 930
trials, the snails changed their course from the wrong to the
right path after contact with the warning stimus but before
the shock (punishment) was received. Since the warning stimulus
was known to irritate the animal, there could have been no prefer-
ence for the wrong side of the labyrinth to offset the associative
effect of the shock (punishment). The 15% of correct-by-associa-
tion trials, then, represents the strength of the association
formed between the warning stimulus and the punishment, no part
of which could have been masked through preference for the signal
stimulus used. This series of tests then shows the formation
of a weak association between two stimuli, one used as a warn-
ing of the punishment to follow if the course be not changed.
Physa then, profits by experience, but cannot be said to solve
a labyrinth. The work with the modified apparatus is merely
confirmatory of that by the method of simultaneous stimuli.
It shows no greater capacity on the part of the snail than was
made evident by that methods
Observational work on mollusks has been reported, but
little experimental work has been done on this group of animals,
none along the lines of the present work. Kollman (1877)
attributed consciousness to Octopus vulgaris, basing his con-
clusions, however, on observation rather than experiment . In
his analysis of this report, Schneider (1909) explains the
behavior observed as reflexive, not conscious, and hence



l'70.
typical of any of the lower animals. Pieron (1909) concludes
that the octopus is capable of learning, and although Kafka (1914)
- reports this work he does not analyze it. Modifiability of
behavior then may be attributed to members of the Cephalopod
group. Perion experimented on the waning of the effect of
stimuli inducing reflexive action in Limmea stagnalis and
Littorina, which he terms memory. Associative memory, as observ-
ed in the present work was believed to be an added proof of
learning, but no attempt was made to determing its exact dur-


ation nor the way in which it developed. The work of Pieron

is here of interest only in that it deals with so-called memory
in closely related forms •



171 .
Tſſ - Conclusions •
1 * The present work on the snail Physa gyrina Say,
gives much evidence of capacity for adaptation- the getting-
used-te-the-stimulus. This is quite apart from evidence fo
fatigue which appears in some places.
2. In addition to adaptation its behavior is modifi-
able by experience in another way. As the result of prolonged
training with two simultaneous stimuli it is found to have
acquired response to one of these stimuli to which it did
not before respond. It has formed an association between
the two stimuli •
3. This definite acquired response is retained for
four days beyond the completion of the training (memory).
4. When put through a long series of tests with the
simplest form of labyrinth, under controlled conditions it:
shows no capacity to solve the labyrinthe
5. On a similar labyrinth it gives evidence of the
capacity to form associations •
6. The capacity to form associations does not then
suffice for the solution of the 'simplest labyrinth, that is,
"selective" ability is apparently lacking-
172,
1.
2.
3.
5.
6.
7,
8.
9.
10.
ll.
12.
13.
14 •
15.
16.
IV. Literature cited.
Dawson, J., 1911. The biology of Physa. Behavior Monogr. I, 4.
Fielde, A. M., 1901. A study of an ant. Proc. Philadelphia
Acad. Nat s Sci., vol. 53, p. 425.
- - - - - 1901. Further study of an ant. Ibid., vol. 53, p. 521.
Jennings, H. S., 1906 • Behavior of the lower organisms.
New York,
Kollmann, 1877 - Aus dem Leben der Cephalopoden. Wierteljahrsschr
Wiss Pilo S. Bd. I. -
Kafka, G - , 1914 • Einführung in die Tierpsychologie. Leipzig.
Morgulis, S., 1914 • Pawlow's theory of the function of the
central nervous system and a digest of some of the more
recent contributions to this subject from Pawlow's
laboratory • Jours of An. Behave vol. 4, No. 5, p. 362.
------ 1914. The auditory reactions of the dog studies by
the Pawlow methode Ibid., vol. 4, No. 2, p. 142.
Nagel, W. A., 1894 - Beobachtungen uber den Lichtsinn augen-
loser Muscheln. Biol. Cent . , Bd. 14, S. 385.
Nicolai, G. F., 1907. Die physiologische Methodik zur Erfor-
Schung der Tierpsyche - Joure fe Psyche us Neur., Bd .10,
S. l. .
------- 1908. Das Lernen der Tiere (auf Grund von Versuchen
mit Pawlowscher Spiechelfistel). Cent. f. Physiol. , Bd.
22, S - 362.
Oberli, L. A., 1909. Reflexes conditionnels du cote de l'oeil
chez le chien. Arche, de Sci • Biol • t < p <
Parker, G. H., 1912. The mechanism of locomotion in gastro-
pods. Jour of Morph., vole 22, p * 155-
Pawlow, I. P., 1904. Sur la secretion psychique des glandes
salivaires. Arch. interm e de Physiol. , t e I, p *
------ 1906. The scientific investigation of the psychical
faculties or processes in the higher animals. (Huxley
Lecture for 1906).
Brit: , Med. Jour • , vol. • pe 871 (Pub. in part ).
Lancet, vol. , p. 911. (Pub. in full).
Science, N. S., vol. 24, p. 613. (Pub. in part).
Pieron, H., 1909. Sens de l'Orientation et memoire topo-
graphique de la limnee. Compt rend - Acad. Sci • Paris,
14

l'73,
17. -----1909. , La loi d'evonouissement des traces mnemoniques
en fonction du temps chez la limnee. Ibid., 149.
18. ----- 1911 - Les curbes d'envonouissement des traces mnemon-
iques • Ibid., 152, p. 1115.
19. -----1911. Sur la determination de la periode d'establisse-
º dans les acquisitions mnemoniques. Ibid., 152, p.
20. Schneider, K. C. , 1909. Worlesungen über Tierpsychologie.
Leipzig.
21. Shepard, J. F., (1916?) (Unpublished, referred to by per-
mission).
22. Small, W. S. . , 1899. An experimental study of the mental
processes of the rat, I. Am. Jours of Psyche, vol. 11, p. 80
23. Spaulding, E. G., 1904 • An establishment of association in
hermit crabs, Eupagurus longicarpus • Jour, of Comp -
Neur • and Psyche, vol. 14, Q e 49.
24. Washburn, M. F., 1908. The animal mind • New Yorks
25. Watson, J. B., 1914. Behavior. An introduction to
comparative psychology. New York.
26. Yerkes, R. M., 1902. Habit formation in the green crab,
Garcinus granulatus • Biole Bull - , Vol. 3, p. 241 -
27. -------1912. The intelligence of the earthworm. Jour. of
Ana Behave vol. 2.
28. Yerkes, R. M., and Huggins, G. E. , 1903, Habit formation
in the crawfish, Cāmbarūs affinis. Harvard Psych.
Studies, vol. i., p. 565 •
29. Yerkes, R. M., and Morgulis, S., 1909. The method of
Pawion in animal psychology • Psych a Bull . . vol. 6,
No. 8, Iº e 257 e - -


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