58 Studies in Animal Behavior 



ageats, and especially the fact that the witless crea- 

 tures continue to go toward the light even when 

 they are brought thereby into a region where the 

 heat proves fatal to them, seem to bear out the 

 conclusion that the phototaxis of these animals is 

 in the nature of an involuntary or "forced" response. 

 This view is strengthened by the results of certain 

 experiments on individuals which were blinded on 

 one side. These experiments were undertaken with 

 the view of ascertaining something of the mechanism 

 of orientation. The amphipods do not become ori- 

 ented by bending the body toward the light, but by 

 the unequal activity of the appendages on the two 

 sides of the body. In forms with positive photo- 

 taxis it was found that blackening over one eye 

 caused the amphipod to perform circus movements 

 toward the normal side. In negatively phototactic 

 species it was found that the same treatment caused 

 circus movements in the reverse direction. It is 

 probable therefore that impulses received by the 

 eyes cross in the central nervous system and become 

 carried to the appendages on the opposite side of 

 the body, causing them to act with greater vigor, 

 thus bringing the animal into a position of orienta- 

 tion. This supposition led to the experiment of 

 cutting the brain lengthwise through the center in 

 several species of arthropods and it was found that, 

 although sensitiveness to light could be shown to 

 remain, all power of orientation to light was en- 

 tirely destroyed. 



