Sensory Discrimination: Vision 153 



pears here. Hess (306), of course, holds that all crus- 

 taceans are totally color-blind, arguing from his results on 

 the relative stimulating effect upon them of different T 

 spectral colors. Minkiewicz (494, 495), on the other 

 hand, believes he has evidence of color discrimination in 

 certain crabs. The hermit crabs, for instance, are natu- 

 rally attracted to Ught, but when subjected to colored lights 

 they do not seek them in the order of their intensity. 

 Green is the most attractive color, violet next; then the 

 order is "blue, yellow, red, and black. " He finds it possible 

 with crabs, as with worms (see page 147), to reverse the 

 response to white light without reversing the response to 

 color (493). Minkiewicz's most remarkable observations 

 were made on certain crabs (Maia) which have the instinct 

 possessed by many crab species of attaching to their shells 

 foreign objects, bits of seaweed and the like, serving the 

 purpose of making them less conspicuous in their ordinary 

 environment. When these crabs are kept for some time in 

 an aquarium lined with a certain color, their subsequent 

 behavior is modified in two ways, (i) On being given bits 

 of paper some of which are colored like the aquarium, while 

 others are of a different color, the crabs select for deco- 

 rative purposes the bits that match their surroundings. 

 (2) When placed in another aquarium offering a choice 

 between two compartments, one with walls matching 

 those of the tank they have left, the other with differently 

 colored walls, the crabs choose the former. Two American 

 investigators have performed experiments similar to these. 

 Pearse (567) fails to get any evidence that when crayfishes, 

 spider crabs, crab spiders and caddis fly larvae are kept 

 in colored boxes they develop any tendency to choose later 

 an environment of the same color. On the other hand, 

 Stevens (693) , working with a Pacific coast crab which has 



