724 journal of Comparative Neurology and Psychology. 



Nevertheless, there is no orientation exhibited by virtue of this' 

 reaction. This was made evident by painting one side of the animal 

 with the lamp-black mixture, leaving the head exposed. A worm 

 thus treated turned away from the light, bending the body indiffer- 

 ently towards the right or the left, as in a normal specimen. Obvi- 

 ously, if the worm were oriented by unilateral stimulation of the 

 general body surface, it would turn in the direction of the covered 

 side, the light affecting the exposed portion causing greater movement 

 on that side and hence the bending away from it. 



Orientation takes place by means of the light receptors, entirely. 

 These organs of both sides of the body were covered and the larva 

 thrown into the sunlight with its anterior end directed towards the 

 light. The animal was entirely indifferent, moving directly towards 

 the light as well as away from it. The ocelli are therefore the only 

 organs of orientation to light in the larva. 



Unilateral stimulation was then examined. The pigment spots 

 of one side (the right) were covered with the mixture and the worm 

 placed in the light as before. Orientation occurred, whereby the 

 larva turned away from the light and continued in a more or less 

 straight path as far as it was permitted to go. One individual in 

 forty exhibited circling. This larva had the ocelli on the right side 

 blackened and when placed in the illuminated area, it began to move 

 in circles with the covered side within. However, after a few circles, 

 the animal ceased circling and moved in a straight path away from 

 the light. A check was made to this experiment, to obviate any 

 chance of some of the ocelli being left exposed, by the use of a hot 

 needle to sear the chitin of that side of the head. When this was 

 done on both sides of the head, no response to light was given, and it 

 is fair to assume that when applied to one side, it is equally efficient. 



The fact that the ocelli on one side of the head were able to orient 

 the animal, was seen in another set of experiments. An individual 

 was selected to fit the rubber tube and the ocelli on the right side of 

 the head were covered with the lampblack mixture. The anterior 

 end of the animal was directed towards the light. Diffuse light was 

 used. As the animal emerged from the tube, the number of times 

 it turned to the right and the number of times to the left were 



