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 in 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 Radl 
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 satisfae- 
