PRIM!TI\T S OF K 



not allow the meat to be pulled away from the I .ntil 



the crayfish struggled awhile to secure it : at the same time I 

 moved my hand about so as to accustom the animal to 

 movements. There is a struggle between the instinct to 

 flee from a large moving object and the instinct to secure a 

 savory morsel which has been seiied. With careful mar. 

 ment the latter instinct may be made to predominate o 

 the former and gradually the fear of one's movements be- 

 comes much reduced. The crayfish finally came to associ a te 

 the approach of my hand with being fed, and would rear up and 

 hold oat its larger chelae much as in the ordinary posture for 

 defense, . . . One individual would greet me as I entered 

 my room in the morning by raising up its chelipeds and 

 coming toward me, and it would follow me about as I went 

 from one side of its enclosure to the other. When fed, 

 however, it would manifest no further interest in my move- 

 ments^ 



The ability of hermit-crabs to form associations has been 

 proven by the experiments of Spaulding on Pagurus longi- 

 carpus. Several specimens of this active species were placed in 

 an aquarium supplied with running water. A dark screen was 

 made so that it could be placed in the middle of the aquarium 

 leaving only a narrow slit on either side through which the 

 crabs could pass from one compartment to the other. As 

 the hermits are positively phototactic they tend to keep 

 in the lighter half of the aquarium, and to make the lighting 

 of the two parts as different as possible one side of the aquar- 

 ium was covered with heavy dark paper. When the screen 

 was put in the aquarium, and all the crabs placed behind it, 

 they quickly made for the openings at the sides of the parti- 

 tion and went out into the light. Every day the screen 

 was inserted for a given interval hi the aquarium, and a 

 piece of fish put behind it. The number of crabs entering 



