BEHAVIOR IN LOWER METAZOA 257 



This habit formation took place in the same manner when the floor 

 of the pen was carefully washed out after each trial, showing that the 

 animals were not merely following a path marked by an odor from the 

 previous passage along it. It was evident that the customary direction 

 of turning played a large part in the behavior. When the left passage 

 was closed, the crayfish that had erred into this passage escaped by turn- 

 ing to the right, as indicated by its path in Fig. 141. When after the 

 establishment of this habit, the right passage was closed (Fig. 140), 

 the animal tried persistently to escape from this passage by turning to 

 the right, as it had previously done. 



Spaulding (1904) studied the modifiability of behavior in the food 

 reactions of the hermit crab. These animals tend to remain in the hghted 

 parts of the aquarium. They were fed by placing a small, dark screen 

 with a fish beneath it in a certain part of the aquarium. The diffusion 

 of juices from the fish set the 

 crabs to moving about ac- 

 tively, and in the course of 

 time some passed beneath 

 the screen. Here the food 

 was found. At first it took 

 the crabs a long time to find 



it under these conditions. Fig. 141. — Path followed by crayfish while being 



/~> i-L f; i J 1 tin trained to avoid the left passage. On erring into this 



wn tne nrst uay Oniy mree passage^ it escapes by passing to the right, thus forming 



out of thirty succeeded in the habit of turning to the right. After Yerkes and 



fifteen minutes. But by the ^"^^'"'• 



third day, twenty of the thirty had passed beneath the screen fifteen 

 minutes after it was introduced. At the end of the eighth day, twenty- 

 eight out of the twenty-nine present had passed beneath the screen 

 inside of five minutes. The crabs had become so modified that they 

 went quickly beneath the screen as soon as it was introduced. 



Now the experiments were varied by placing in the aquarium the 

 screen alone, without the food. Most of the animals passed beneath 

 it as before. Thus, on the thirteenth day of the experiments, twenty- 

 five specimens out of twenty-seven present had passed under the screen 

 within five minutes. After they had entered they were fed, in order that 

 the association between the screen and food might not be destroyed. 



Phenomena of this character are usually spoken of as learning, or 

 as the formation of habits or associations. The facts may be expressed 

 in a purely objective way as follows : When subjected to the stimulus 

 of the screen and the food, the animals reacted to the food by gathering 

 about it — incidentally of course gathering under the screen. After 

 many repetitions of such stimulation, the animals had become changed 



