REACTIONS OF ARTHROPODS TO LIGHTS 497 



preliminary tests with single colored lights. However, when the 

 larvae were tested with red, they seemed to orient less accurately 

 than when stimulated by any one of the other colors, a result 

 indicating that the less refrangible rays are least effective. 



In the experiments with balanced pairs of monochromatic 

 lights the larvae were started in the middle of the slate or sheet 

 of paper and in the center of the field of light. They were placed 

 with their axes at right angles to the rays of light. This posi- 

 tion gave the anterior end of the animal, which, presumably, 

 is the only part sensitive to light, equal opportunity to stimula- 

 tion by the lights of equal intensities coming from opposite 

 sources. 



When the larvae were exposed to paired lights of the same 

 colors, they oriented, not with their axes perpendicular to the 

 Hght rays, as was the case with the blow-fly larvae, but toward 

 one light or the other approximately parallel to the direction of 

 the rays (figs. 36 and 37). When paired hghts of different colors 

 were used the larvae turned toward the light containing the 

 more refrangible rays (figs. 38-43). 



In addition to the method used in the experiments just de- 

 scribed, the larvae were started at one edge of the slate and 

 allowed to orient definitely to the rays of one light before turn- 

 ing on the opposing light. Figures 44 and 45 are records of the 

 paths taken by a larva when thus tested with the green-yellow 

 pair of lights. In the records reproduced in figure 44, the larva 

 was started at A and was allowed to crawl towards the A^ellow 

 light to the position at B, when the green light from the oppo- 

 site was turned on. When thus exposed to the influence of 

 two lights the larva did not, in this case, reverse its course imme- 

 diately but continued to before orienting to the green. The 

 distance crawled by the larvae after the green light was turned 

 on varied considerably in the several tests with the same and 

 different larvae. In some cases the response was immediate and 

 in a very few tests the larvae crawled off the sheet of paper 

 towards the yellow light without exhibiting the least e\'idence 

 of the effect of the green. The visual organs, the larval eyes 

 or ommata, on the anterior end of the larvae are not in a favor- 



