61-70 6 4 8 2 8 2 22 8 73.3 (1-10) 71-80 6 4 8 2 7 3 21 9 70.0 (11-20)

The experiments of this table were made by F.D. Bosworth.

One trial in which the subject failed to return to the water within thirty minutes.

In these experiments there is a gradual increase in the number of correct choices (_i.e._, choice of the 'open' pa.s.sage) from 50 per cent. for the first ten trials to 90 per cent. for the last ten (trials 51-60). The test of permanency, made after two weeks, shows that the habit persisted.

Although the observations just recorded indicate the ability of the crawfish to learn a simple habit, it seems desirable to test the matter more carefully under somewhat different conditions. For in the experiments described the animals were allowed to go through the box day after day without any change in the floor over which they pa.s.sed, and as it was noted that they frequently applied their antennae to the bottom of the box as they moved along, it is possible that they were merely following a path marked by an odor or by moistness due to the previous trips. To discover whether this was really the case experiments were made in which the box was thoroughly washed out after each trip.

The nature of the test in the experiments now to be recorded is the same as the preceding, but a new box was used. Fig. 2 is the floor plan and side view of this apparatus. It was 44.5 cm. long, 23.5 cm.

wide and 20 cm. deep. The part.i.tion at the exit was 8.5 cm. in length.

Instead of placing this apparatus in the aquarium, as was done in the previous experiments, a tray containing sand and water was used to receive the animals as they escaped from the box. The angle of inclination was also changed to 7. For the triangular s.p.a.ce in which the animals were started in the preceding tests a rectangular box was subst.i.tuted, and from this an opening 8 cm. wide by 5 cm. deep gave access to the main compartment of the box.

[Ill.u.s.tration: FIG. 2. Floor Plan and Side View of Labyrinth Number 2.

_E_, entrance chamber from which animal was started; _C_, cloth covering _E_; _M_, mirror; _T_, tray containing sand and water; _G_, gla.s.s plate; _P_, part.i.tion; _R_, right exit pa.s.sage; _L_, left exit pa.s.sage. Scale 1/8.]

A large healthy crawfish was selected and subjected to tests in this apparatus in series of ten experiments given in quick succession. One series a day was given. After each test the floor was washed; as a result the experiments were separated from one another by a three-minute interval, and each series occupied from thirty minutes to an hour. Table II. gives in groups of five these series of ten observations each. The groups, indicated by Roman numerals, run from I. to IX., there being, therefore, 450 experiments in all. Groups I.

and II., or the first 100 experiments, were made without having either of the exit pa.s.sages closed, in order to see whether the animal would develop a habit of going out by one side or the other. It did very quickly, as a matter of fact, get into the habit of using the left pa.s.sage (L.). The last sixty experiments (Groups I. and II.) show not a single case of escape by the right pa.s.sage. The left pa.s.sage was now closed. Group III. gives the result. The time column (_i.e._, the third column of the table) gives for each series of observations the average time in seconds occupied by the animal in escaping from the box. It is to be noted that the closing of the Left pa.s.sage caused an increase in the time from 30.9 seconds for the last series of the second group to 90 seconds for the first series of the third group. In this there is unmistakable evidence of the influence of the change in conditions. The animal after a very few experiences under the new conditions began going to the Right in most cases; and after 250 experiences it had ceased to make mistakes. Group VII. indicates only one mistake in fifty choices.

TABLE II.

HABIT FORMATION AND THE MODIFICATION OF HABITS IN THE CRAWFISH.

Results in Series of Ten. Avs. in Groups of 50.

Series L. R. Time. L. R. L. R. Time.

Group I. 1 9 1 45 Per Cent.

2 3 7 69 3 9 1 20 4 4 6 72 5 10 31 -- -- 35 15 70 30 47.4

II. 1 10 29 2 10 30 3 10 30 4 10 28.8 5 10 30.9 -- ---- 50 100 30 .... ....

III. 1 4 6 90 2 2 2 8 89.2 1 3 1 9 36.7 1 4 2 8 51 2 5 1 9 43 2 -- -- -- 10 40 7 20 80 62 .... ....

IV. 1 3 7 124 1 2 2 8 44 5 3 2 8 37 4 4 10 34 5 2 8 1 -- -- -- 9 41 11 18 82 60 .... ....

V. 1 10 44 2 2 10 35 4 3 3 7 76 3 4 2 8 50 7 5 1 9 50 4 -- -- -- 6 44 20 12 88 51 .... ....

VI. 1 2 8 45 2 2 10 41 5 3 1 9 41.8 7 4 10 32.7 7 5 10 8 -- -- -- 3 47 29 6 94 40 .... ....

VII. 1 1 9 39 4 2 10 38 7 3 10 30.7 3 4 10 42 6 5 10 48 4 -- -- -- 1 49 24 2 98 39.5

R. L.

.... ....

VIII. 1 8 2 147 1 2 9 1 26 3 8 2 49 2 4 9 1 38 2 5 9 1 41 -- -- -- 43 7 5 86 14 60.2 .... ....

IX. 1 1 9 41 2 2 8 39 1 3 10 29 4 1 9 47 5 1 9 32 1 10 90 38 -- -- -- 5 45 2

The dotted lines at the beginning of groups indicate the closed pa.s.sage.

At the beginning of Group VIII. the Right instead of the Left pa.s.sage was closed in order to test the ability of the animal to change its newly formed habit. As a result of this change in the conditions the animal almost immediately began going to the Left. What is most significant, however, is the fact that in the first trial after the change it was completely confused and spent over fifteen minutes wandering about, and trying to escape by the old way (Fig. 4 represents the path taken). At the end of the preceding group the time of a trip was about 48 seconds, while for the first ten trips of Group VIII. the time increased to 147 seconds. This remarkable increase is due almost entirely to the great length of time of the first trip, in which the animal thoroughly explored the whole of the box and made persistent efforts to get out by the Right pa.s.sage as it had been accustomed to do. It is at the same time noteworthy that the average time for the second series of Group VIII. is only 26 seconds.

For Group IX. the conditions were again reversed, this time the Left pa.s.sage being closed. Here the first trial was one of long and careful exploration, but thereafter no more mistakes were made in the first series, and in the group of fifty tests there were only five wrong choices.

The fifth column, R. L. and L. R., of Table II. contains cases in which the subject started toward one side and then changed its course before reaching the part.i.tion. In Group III., for instance, when the Left pa.s.sage was closed, the subject started toward the Left seven times, but in each case changed to the Right before reaching the part.i.tion. This is the best evidence of the importance of vision that these experiments furnish.

The first experiments on habit formation proved conclusively that the crawfish is able to learn. The observations which have just been described prove that the labyrinth habit is not merely the following of a path by the senses of smell, taste or touch, but that other sensory data, in the absence of those mentioned, direct the animals.

So far as these experiments go there appear to be at least four sensory factors of importance in the formation of a simple labyrinth habit: the chemical sense, touch, vision and the muscle sense. That the chemical sense and touch are valuable guiding senses is evident from even superficial observation, and of the importance of vision and the muscle sense we are certain from the experimental evidence at hand.

[Ill.u.s.tration: FIG. 3. Path taken by crawfish while being trained to avoid the left pa.s.sage. Marks along the gla.s.s plate and part.i.tion indicate contact by the antennae and chelae.]

Of the significance of the sensations due to the 'direction of turning' in these habits the best evidence that is furnished by this work is that of the following observations. In case of the tests of Table II. the subject was, after 100 preliminary tests, trained by 250 experiences to escape by the Right-hand pa.s.sage. Now, in Groups III.

to VII., the subject's usual manner of getting out of the closed pa.s.sage, when by a wrong choice it happened to get into it, was to draw back on the curled abdomen, after the antennae and chelae had touched the gla.s.s plate, and then move the chelae slowly along the Right wall of the part.i.tion until it came to the upper end; it would then walk around the part.i.tion and out by the open pa.s.sage. Fig. 3 represents such a course. In Group VIII. the Right pa.s.sage was closed, instead of the Left as previously. The first time the animal tried to get out of the box after this change in the conditions it walked directly into the Right pa.s.sage. Finding this closed it at once turned to the Right, _as it had been accustomed to do when it came in contact with the gla.s.s plate_, and moved along the side of the box just as it did in trying to get around the end of the part.i.tion. The path taken by the crawfish in this experiment is represented in Fig. 4. It is very complex, for the animal wandered about more than fifteen minutes before escaping.

The experiment just described to show the importance of the tendency to turn in a certain direction was the first one of the first series after the change in conditions. When given its second chance in this series the subject escaped directly by the Left pa.s.sage in 33 seconds, and for the three following trips the time was respectively 25, 25 and 30 seconds.

Upon the experimental evidence presented we base the conclusion that crawfish are able to profit by experience in much the same way that insects do, but far more slowly.

[Ill.u.s.tration: FIG. 4. Path taken by crawfish which had been trained to avoid the Left pa.s.sage, when the Right pa.s.sage was closed. Showing turning to the right as in Fig. 3.]

It was thought that a study of the way in which crawfish right themselves when placed upon their backs on a smooth surface might furnish further evidence concerning the ability of the animals to profit by experience.

Dearborn[3] from some observations of his concludes that there is no one method by which an individual usually rights itself, and, furthermore, that the animals cannot be trained to any one method. His experiments, like Bethe's, are too few to warrant any conclusions as to the possibility of habit formation.

[3] Dearborn, G.V.N.: 'Notes on the Individual Psychophysiology of the Crayfish,' _Amer. Jour. Physiol._, Vol. 3, 1900, pp.

404-433.

For the following experiments the subject was placed on its back on a smooth surface in the air and permitted to turn over in any way it could. Our purpose was to determine (1) whether there was any marked tendency to turn in a certain way, (2) whether if such was not the case a tendency could be developed by changing the conditions, and (3) how alteration in the conditions of the test would affect the turning.

A great many records were taken, but we shall give in detail only a representative series. In Table III., 557 tests made upon four subjects have been arranged in four groups for convenience of comparison of the conditions at different periods of the training process. Each of these groups, if perfect, would contain 40 tests for each of the four subjects, but as a result of accidents II., III., and IV. are incomplete.

TABLE III.

RE-TURNING OF CRAWFISH.

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

I. 2 22.5 77.5 14.6 40 3 42.5 57.5 2.6 40 4 52.8 47.2 4.3 38 16 44.5 55.5 22.5 45 -- ---- ---- ---- --- 40.6 59.4 10.8 163

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

II 2 28 72 50 43 3 32 68 6.2 50 4 -- 100 6.8 40 16 31.3 68.7 39.3 42 -- ---- ---- ---- --- 22.8 77.2 25.6 175

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

III 2 2.5 97.5 46.5 40 -- -- -- -- -- 4 20 80 5.5 40 16 41 59 15 49 -- ---- ---- ---- --- 21.2 78.8 22 129

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

IV. 2 2 98 41 50 -- -- -- -- -- 4 32.5 67.5 7.3 40 -- ---- ---- ---- --- 17 83 24 90