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This eBook from the Gutenberg Project consists of approximately 678 pages of information about Harvard Psychological Studies, Volume 1.
for the statements made by Bethe.  At least a hundred trials should have been made.  The same objection holds in case of the second experiment.  In all probability Bethe’s statements were made in the light of long and close observation of the life habits of Carcinus; we do not wish, therefore, to deny the value of his observations, but before accepting his conclusions it is our purpose to make a more thorough test of the ability of crustaceans to learn.

[Illustration:  FIG. 1.  Ground Plan of Labyrinth. T, triangular compartment from which animal was started; P, partition at exit; G, glass plate closing one exit passage.  Scale 1/6.]

For determining whether the crawfish is able to learn a simple form of the labyrinth method was employed.  A wooden box (Fig. 1) 35 cm. long, 24 cm. wide and 15 cm. deep, with one end open, and at the other end a triangular compartment which communicated with the main portion of the box by an opening 5 cm. wide, served as an experiment box.  At the open end of this box a partition (P) 6 cm. long divided the opening into two passages of equal width.  Either of these passages could be closed with a glass plate (G), and the subject thus forced to escape from the box by the choice of a certain passage.  This box, during the experiments, was placed in the aquarium in which the animals lived.  In order to facilitate the movement of the crawfish toward the water, the open end was placed on a level with the water in the aquarium, and the other end was raised so that the box made an angle of 6 deg. with the horizontal.

Experiments were made under uniform conditions, as follows.  A subject was taken from the aquarium and placed in a dry jar for about five minutes, in order to increase the desire to return to the water; it was then put into the triangular space of the experiment box and allowed to find its way to the aquarium.  Only one choice of direction was necessary in this, namely, at the opening where one of the passages was closed.  That the animal should not be disturbed during the experiment the observer stood motionless immediately behind the box.

Before the glass plate was introduced a preliminary series of tests was made to see whether the animals had any tendency to go to one side on account of inequality of illumination, of the action of gravity, or any other stimulus which might not be apparent to the experimenter.  Three subjects were used, with the results tabulated.

Exit by Exit by
Right Passage Left Passage. 
No. 1 6 4
No. 2 7 3
No. 3 3 7
16 14

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