242 YERKES. 



stimulation stood in the way of the establishment of new modes 

 of response. 



Bethe should not have expected a few experiences to modify 

 or inhibit such fundamentally important reactions as those to 

 light and to food. Almost any reaction can be modified if time 

 enough be devoted to that end, but it is as unlikely that a crab 

 would learn to avoid the dark or to inhibit its food -taking reac- 

 tion after a half dozen harmful experiences in a certain situation 

 as it is that the grasshopper would learn to inhibit its jumping 

 by a few experiences in a glass box. For the modification of 

 such reactions hundreds, not tens, of experiences are necessary. 



In view of the obvious unfairness of Bethe's tests of Carcinns 

 I have made a further study of the ability of the American spe- 

 cies of Carcinns, C. granulatus, which is similar to the Euro- 

 pean form, C. imcnas. My effort has been to determine whether 



Floor Plan of Experiment Box. Scale one eighth. 



the animals can learn (i) a simple labyrinth path to their food, 

 and (2) to avoid the unpleasant experience of being captured in 

 a hand-net and taken from the aquarium. 



The crabs were kept in an aquarium about 60 cm. long, 38 

 cm. wide and 35 cm. deep, over which an experimenting box 40 

 cm. x 20 x 12 was placed so that its exit passage just touched 

 the surface of the water. The accompanying cut which is the 

 floor plan of the box, shows, in addition to the entrance passage 

 , in which the crab was placed by the operator at the beginning 

 of each experiment, two alleys which were closed by glass plates 

 G, G. Experiments were made to discover whether the green crab 

 would learn to avoid these blind alleys in its efforts to get back 

 to the water of the aquarium, and if so how quickly it would 

 learn. 



