66 S. J. HOLMES 



exposed to the varying influence of lights and shadows from a 

 multitude of objects. 



In other experiments insects were held above an easy-running 

 horizontal disk or turn-table which they could rotate with their 

 feet. Light was made to fall upon the insect from one side. 

 If the insect attepted to turn toward the light the movements 

 of its feet would rotate the disk in the reverse direction. Butter- 

 flies proved to be very convenient forms to work with since by 

 grasping them with their wings held together above the back 

 they could be easily held above the disk so that their feet could 

 move it in either direction. Under these conditions several 

 species "of butterflies were found to rotate the disk quite con- 

 stantly away from the illuminated side in their efforts to turn 

 toward the light. They would also promptly change the di- 

 rection of rotation when the light was carried from one side of the 

 insect to the other. Some species of Diptera gave results quite 

 parallel to those obtained with the butterflies. 



As was pointed out, the slight movements of one's hand, 

 although these were minimized by the use of a hand rest, and 

 the movements of the head of the insect due to its own activities 

 in rotating the disk, would produce some fluctuation in the 

 amount of stimulation received by the eye, but these changes 

 were necessarily small. The general outcome of both sets of 

 experiments was therefore favorable to the view that the con- 

 tinuous stimulating influence of light is a potent factor in effect- 

 ing orientation. 



In a paper on the reactions of Euvanessa antiopa to light Mr. 

 W. L. Dolley (2) has questioned the conclusion just expressed, 

 and has described some experiments whose results in his opinion 

 justify a different interpretation. Dolley's work was done 

 under the supervision of Prof. S. O. Mast whose views regarding 

 the so-called "continuous action theory' ' he apparently shares. 

 The apparatus that Dolley employed, consisting of an easy- 

 running horizontal disk above which the insect could be held, 

 was in principle the same as ours. The wings of the butterfly, 

 however were held in a clamp, thus getting rid of one source of 

 movement. In other respects the body and especially the head 



