184 PRIMITIVE TYPES OF INTELLIGENCE 
dark hole if there is any within reach, and with its whole 
energies bent upon getting away from the large creature 
into whose hands it is taken, what wonder if the devil fish, 
if it would otherwise be remembered, should be temporarily 
forgotten. 
The second experiment likewise is one which involves the 
conquest of a strong instinctive proclivity and it includes 
also too small a number of trials to be in any way con- 
vincing. 
The later experiments of Yerkes on Carcinus were more 
fortunate in yielding positive results. The crabs were placed 
in a box one end of which led to an aquarium. The end 
nearest the aquarium was divided so as to afford a right and 
a wrong path to the water. With successive trials the crab 
came to learn, although with extreme slowness, to choose 
the right path. Other simple labyrinths were employed 
and the crab in each case succeeded, after a sufficient number 
of trials, in learning the way to the water. The work of 
Cowles on Ocypoda yielded confirmatory results, although 
the idiosyncrasies of the animal caused the results to be 
somewhat less clearly defined. 
Experiments similar to those on Carcinus were performed 
by Yerkes and Huggins on the crayfish. A simple labyrinth 
was constructed consisting of a box having asmall compart- 
ment at one end, and an opening at the other leading to an 
aquarium. From the open end a median partition extended 
back a short distance, and one of the passages so formed 
was closed with a glass plate. The crayfish liberated from 
the small compartment was provided with a choice of two 
paths only one of which would lead it to the water; and the 
endeavor was made to ascertain if the crayfish, after anumber 
of trials, would unerringly choose the right path. The 
crayfish used were put through a number of preliminary ex- 
