REACTIONS OF ARTHROPODS TO LIGHTS 507 



I do not mean to say that either Daphnia or many of the other 

 arthropods or the other animals investigated by Hess are not 

 more responsive to yellow-green rays than to those of shorter 

 . wave length, but I do maintain that in none of these experiments 

 have the investigators proven that the yellow-green rays are 

 more potent than the blue rays, when the factor of intensity is 

 eliminated. 



The results of the present investigations have shown con- 

 clusively that when lights of equal intensity are used, the adults 

 of Calliphora, Drosophila and Feltia and the larvae of Zeuzera 

 are more responsive to blue than to green or yellow. 



The reactions of the animals named in the preceding paragraph 

 agree with the statements of Loeb ('05) and of Davenport ('97) 

 that the more refrangible rays of the spectrum are more effective 

 stimuli than the less refrangible rays. But the hypotheses of 

 Loeb and of Davenport are not in accord with the results of the 

 experiments upon the Calliphora larvae, which are most respon- 

 sive to the green rays of the spectrum. Loeb's hypothesis was 

 based on the results of experiments which involved the use of 

 only two colors, namel}^, blue and red. In his experiments upon 

 larvae and other animals he did not compare the efficiency of 

 the blue end of the spectrum with the green and yellow rays. 

 Loeb therefore did not have sufficient evidence, as has been 

 pointed out by other authors, on which to base such a general 

 conclusion. 



In order to have an unobjectionable basis for comparing the 

 results of the experiments upon Calliphora larvae with those on 

 adult insects under the blue-green combination of Ughts, the 

 adult Calliphora and also adult Drosophila were each tested 

 w^ith the same lights and adjustments that were used in taking a 

 series of records similar to those shown in figures 15 and 18 and 

 inmiediateh^ after the observations on the larvae. Out of 37 

 adult Calliphora used in five tests, 24 went to the blue and only 

 13 to the green; likewise in a second check experiment out of 

 42 Drosophila 33 went to the blue and only 9 to the green. These 

 tests demonstrate that the adult flies are more responsive to the 

 blue under conditions of illumination identical with those in 



