342 Journal of Comparative Neurology and Psychology. 



ently in one respect, since in going towards the light the anter- 

 ior side is turned so as to face the brightest part of the field of 

 vision while the posterior surface of the eye is kept facing the 

 darkest part. The impulses from the two sides of the eyes do 

 not antagonize each other. The experiments of blackening 

 over the anterior sides of the eyes show that the sides looking 

 away from the light, as well as those looking towards it, play a 

 part in orientation, although they must respond, so far as seek- 

 ing intensity of stimulus is concerned, in opposite ways. 



The method of trial and error plays, I think, only a sub- 

 ordinate role in the phototaxis of Ranatra, although in some 

 situations it undoubtedly comes into play. There is a certain 

 amount of random movement in the behavior of this form, but 

 deviations from the direct path to the light are usually corrected 

 by an appropriate turn, and not by making a lot of trial move- 

 ments and following up the successful ones. Ranatras often 

 show periods of hesitation between two directions of turning. 

 Specimens that perform circus movements when one eye is 

 blackened over usually manifest a decided hesitancy when they 

 have turned so that the normal eye looks approximately away 

 from the light. They often stop in their course, turn this way 

 and that, often many times, and occasionally settle down to rest, 

 as if in despair over the situation. Sometimes they turn directly 

 towards the blind side and go to the light ; at other times they 

 reach the light only after performing a complete circus move- 

 ment to the left. When past the critical point their movements 

 usually take place with little hesitation. 



Specimens with only the posterior half of one eye exposed 

 often turn slightly this way and that during the first part of their 

 course, as if attempting to get their bearing. If they deviate 

 either to the one side or the other they frequently stop, as if 

 they perceived something to be wrong, turn back and forth sev- 

 eral times, and then proceed nearly straight towards the light. 

 In nearly all specimens thus treated one can detect a tendency 

 to veer over towards the normal side, but there are equally ob- 

 vious efforts to check deviations that are made from the direct 

 path. There is an uneasiness which appears much like impa- 



