PHOTOTAXIS 55 



blackened eye. The same experiment was tried on several 

 postively phototactic insects with the same results. In the 

 small sand flea Orchestia agilis which is sometimes positive 

 and sometimes negative in its reactions to light blackening 

 over one eye causes circus movements toward the normal 

 side when it is positive and hi the reverse direction when 

 it is negative. Since throwing this form into water changes 

 its phototaxis from positive to negative it can be made to 

 go around in a circle in either direction according to the 

 medium in which it is placed. Similar circus movements 

 after one eye was blackened over have been observed by 

 Parker in Vanessa, by Hadley in the lobster, and by Rddl 

 in various kinds of arthropods. 



Not all phototactic insects, however, perform circus 

 movements when blinded on one side. If the honey bee, 

 for instance, which is strongly positive, is treated in this 

 way it usually follows the light almost as directly as when in 

 a normal condition. In the water scorpion Ranatra I have 

 found that while in some specimens there is a strong tendency 

 to perform circus movements toward the normal side, 

 others go toward the light in a direct line. In some instances 

 specimens which at first performed circus movements came 

 after a number of trials gradually to straighten their path 

 toward the light until finally they followed it in a straight 

 line. Back swimmers, Notonecta, which at first performed 

 circus movements and approached the light only after much 

 wasted effort, were found to straighten their course and 

 follow the light as well as if they had use of both eyes. These 

 facts indicate that phototaxis may fall to a certain extent 

 under the pleasure-pain type of behavior which will be con- 

 sidered in a later chapter. Light in some animals is followed 

 much as an object of interest is pursued by a higher animal. 

 If a creature learns to go to the light an element of satisfac- 



