186 PRIMITIVE TYPES OF INTELLIGENCE 
not allow the meat to be pulled away from the forceps until 
the crayfish struggled awhile to secure it; at the same time I 
moved my hand about so as to accustom the animal to my 
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 seized. With careful manage- 
ment the latter instinct may be made to predominate over 
the former and gradually the fear of one’s movements be- 
comes much reduced. ‘The crayfish finally came to associate 
the approach of my hand with being fed, and would rear upand 
hold out its larger chele 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 in the aquarium, and a 
piece of fish put behind it. The number of crabs entering 
