8o Studies in Animal Behavior 



Several years ago it seemed to me very desir- 

 able to study tropisms with the view of testing the 

 possible presence of any more highly developed 

 functions than are postulated by the reflex theory. 

 For some reason this particular quest, which involves 

 one of the most important theoretical considerations 

 connected with the tropism theory, had been almost 

 completely neglected. I have already alluded to 

 some of the initial experiments which consisted in 

 blacking over one of the eyes in several phototac- 

 tic species of arthropods and then observing their 

 reactions to light under various conditions of ex- 

 posure. It was found that in several positively pho- 

 totactic species blinding one eye tended to make the 

 animal perform circus movements toward the nor- 

 mal side. In several negative species similarly 

 blinded, circus movements were performed in the 

 reverse direction. This is what the reflex theory 

 of tropisms would lead us to expect. That the re- 

 lations discovered are fairly general is evinced by 

 the discovery by other investigators as well as by 

 myself of a number of other forms which react in 

 a similar manner. Great individual variation was 

 found in the degree to which the tendency to per- 

 form circus movements was manifested, some forms 

 after being blinded on one side continuing to go 

 toward or away from the light in a nearly straight 

 line. The fact observed by myself in Ranatra and 

 Notonecta and subsequently found by Miss Brun- 

 din in Orchestia, that individuals which at first per- 



