332 Journal of Comparative Neurology and Psychology. 



those on the right. When the light was held on the blind side the insect showed 

 no inclination to turn away from it. The movements of the insect were slow, 

 but, after about twenty minutes, it suddenly began to turn vigorously to the light 

 and became much more active, following the lamp around with eagerness and 

 rapidity. In several trials in which it was placed three feet away from the lamp 

 it went towards it in nearly a straight line, correcting its deviations from a straight 

 course, whether to the right or the left, by the appropriate turn. It soon became 

 quite excited and several times attempted to fly. It would follow the light when 

 it was in front and to the right side by turning directly to the right. If, when 

 the light was reached, it was changed to some other part of the table the insect 

 would turn around and make for it in nearly a straight line. After moving about 

 in this way for some time it settled down so as to rest its body against the top of 

 the table. The light was then placed near the specimen, but it paid no attention 

 to it until it was moved opposite the left eye, when it began to move slowly away 

 from it by crawling sideways. The whole character of the insect's behavior now 

 became suddenly changed. It became sluggish and stealthy in its actions instead 

 of vigorous and excited. It would respond to the light by moving sidewise 

 instead of straight ahead, and only when the light was placed in a certain posi. 

 tion. After moving the light around the specimen its negative reaction became 

 more decided and then suddenly changed to positive. It would follow the light 

 around either to the right or to the left, but if the light were held too far to the 

 right side it would not turn directly towards it. The specimen had several other 

 fits of reacting negatively when its conduct was essentially as described above. 

 It was caused to become positive each time by keeping the light near the left eye. 

 Its negative reaction would in each case grow more vigorous and then suddenly 

 give way to the positive response. The appearance of the positive response 

 seemed to indicate the attainment of a certain degree of excitement. 



The differences between the negative and positive responses 

 of the specimens experimented with are very striking. The 

 peculiarites of the negative reaction are probably due to the fact 

 that only when the light shines directly into the left eye is the 

 stimulus strong enough to produce action. When out of the 

 direct glare of the light the insect is content, and it gets away 

 by the most direct method. In the positive reaction the insect 

 is attempting to get more of the stimulus ; it is in a state of 

 increased phototonus, and each movement that brings it nearer 

 the light tends to increase its activity. 



/^. Phototaxis as Modified by Experience and Habit. 

 That Ranatra is able to modify its reaction to light as the result 

 of experience was shown by several experiments. The attempt 

 was made to determine if Ranatras which perform circus move- 

 ments when one eye is blackened over would in time come to 



