| Exit by Right Passage | Exit by Left Passage. | |
|---|---|---|
| No. 1 | 6 | 4 |
| No. 2 | 7 | 3 |
| No. 3 | 3 | 7 |
| 16 | 14 |
Since there were more cases of exit by the right-hand passage, it was closed with the glass plate, and a series of experiments made to determine whether the crawfish would learn to avoid the blocked passage and escape to the aquarium by the most direct path. Between March 13 and April 14 each of the three animals was given sixty trials, an average of two a day. In Table I. the results of these trials are arranged in groups of ten, according to the choice of passages at the exit. Whenever an animal moved beyond the level of the partition (P) on the side of the closed passage the trial was counted in favor of the closed passage, even though the animal turned back before touching the glass plate and escaped by the open passage.
TABLE I.
HABIT FORMATION IN THE CRAWFISH.¹
| Experiments. | No. 1 | No. 2 | No. 3 | Totals | Per cent | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Open | Closed | Open | Closed | Open | Closed | Open | Closed | Open | ||
| 1-10 | 8 | 2 | 5 | 5 | 2 | 8 | 15 | 15 | 50.0 | |
| 11-20 | 4 | 6 | 8 | 2 | 6 | 4 | 18 | 12 | 60.0 | |
| 21-30 | 6 | 3² | 8 | 2 | 8 | 2 | 22 | 7 | 75.8 | |
| 31-40 | 9 | 1 | 8 | 2 | 8 | 2 | 25 | 5 | 83.3 | |
| 41-50 | 8 | 2 | 8 | 2 | 7 | 3 | 23 | 7 | 76.6 | |
| 51-60 | 10 | 0 | 8 | 2 | 9 | 1 | 27 | 3 | 90.0 | |
| TEST OF PERMANENCY OF HABIT AFTER 14 DAYS' REST. | ||||||||||
| 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) | ||||||||||
¹The experiments of this table were made by F.D. Bosworth.
²One 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' passage) 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 passed, 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 partition 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 space in which the animals were started in the preceding tests a rectangular box was substituted, and from this an opening 8 cm. wide by 5 cm. deep gave access to the main compartment of the box.