The Problem of Orientation 81 



formed circus movements later come to go toward 

 the light in a nearly straight course, indicates a ca- 

 pacity for regulation in behavior if not a primitive 

 form of learning, and suggests the possibility that 

 the normal tropisms of these forms are not wholly a 

 matter of direct reflex action. Were these animals 

 pure reflex mechanisms we should expect their cir- 

 cus movements to continue. But judging from their 

 behavior, these animals follow light more or less 

 after the manner in which higher animals pursue 

 their prey or any other object of interest. Possibly 

 the same may be true of the fiddler crabs which move 

 sidewise toward the light instead of orienting them- 

 selves in the usual manner with their longitudinal 

 axis parallel to the rays. Loeb is inclined to the 

 conclusion that "in the fiddler crabs in the first place 

 there is an entirely different connection between the 

 retina and the locomotor muscles from that in other 

 crustaceans, and that, secondly, there is a special 

 peculiarity in regard to the function of the two re- 

 tinas whereby they do not act like symmetrical sur- 

 face elements." In the light of the facts mentioned 

 above it is, I believe, doubtful if we need to assume 

 any far-reaching modifications of nervous structure 

 to account for the peculiar orientation of these 

 crabs. This conclusion is supported, I think, by the 

 experiments of Miss Brundin on Orchestia traskiana 

 in which the amphipods which have a narrow com- 

 pressed body were compelled to travel on one side 

 by being confined between two horizontal glass 



