Bell, Reactions of Crayfish. 323 



ment to take food readily. An interesting case of " learning," i.e., 

 modification of reaction, developed in this connection. The 

 animals were regularly given their meat from a pin, bent slightly 

 at the end to prevent the meat slipping off until it was given a little 

 pull, and attached to a string. When the animals were first put 

 into the aquarium they could not be got to notice this arrangement, 

 but in a few weeks several of them learned to reach up for it 

 quite vigorously. 



After the animals have become accustomed to their surround- 

 ings, when a bit of meat is thrown into the aquarium in which they 

 are lying quietly two or three minutes usually elapse before there 

 is any movement. Then they begin to exhibit a vague general 

 restlessness which increases until finally they start to move about. 

 These movements seldom have any great definiteness, and it is 

 only in the rarest cases that an animal is observed to move di- 

 rectly toward the meat. Usually the movements seem vague and 

 undetermined, but the restlessness increases and frequently the 

 vague movements gradually lead the animal nearer to the source 

 of the stimulus. If the meat be suspended about five centimeters 

 above the bottom of the aquarium the animal frequently passes 

 directly under it without seeming to notice it. Often, however, 

 the animal will return and pass back and forth under the meat, 

 seeming to be vaguely attracted to the spot but not able to locate 

 the source of the stimulus exactly. In case the antenna touches 

 the meat the animal grasps at it at once w4th the chela, usually 

 very accurately. In a few cases as the animal was passing to and 

 fro under the me?.t it seemed to reach upward somewhat with 

 the chelae and if by chance one of these touched the morsel it was 

 very quickly and accurately seized. This was especially observed 

 of animals that had been kept in the aquarium for some time and 

 fed in this manner. Moving the bit of meat slightly seemed to 

 increase the tendency to reach upward, but did not materially 

 increase the accuracy of these movements. Only when the meat 

 was touched was there an accurate response. 



From these observations we must conclude that sight plays 

 little or no part in procuring food, and at best only serves to direct 

 the animal's actions in a general way toward a moving object. 

 The reaction to chemical stimulation is more important, and is 

 seen in a general restlessness resulting in rather indefinite move- 

 ments, w^hich, nevertheless, usually bring the animal nearer the 



