508 ALFRED O. GROSS 



which the Calhphora larvae are more affected by the green rays 

 and answer any possible objection that the results shown in the 

 records were caused by slight differences in the apparatus, inten- 

 sities, et cetera, employed for the larvae and for the adults. 

 This experiment proves that the relative stimulating efficiency 

 of the rays of different colors is not the same for all animals 

 nor for different ages of the same animal, and that the more 

 refractive rays are not always the most effective. 



Mast ('11) in developing the same idea, cites as evidence the 

 following investigations among others: Wilson ('91), who found 

 hydra to be more responsive to blue than to violet; his own work 

 ('00) on amoeba, an animal which is also affected most by the 

 blue; the work of Bert ('68), Lubbock ('81 a, '83) and Yerkes 

 ('99, '00) on Daphnia, a crustacean, which aggregated in the 

 yellow-green region of the spectrum; and the investigations of 

 Engelmann ('82), who discovered that Bacterium photometricum 

 collected in the infra red of the spectrum. These investigations 

 do not prove that hydra and amoeba are affected most by the 

 blue rays, the Daphnia most by the yellow-green and Bacterium 

 photometricum most by the infra red independent of the inten- 

 sity factor. They do show, however, that the animals tested 

 respond differently in degree to the various rays of the spectrum, 

 since presumably the spectrum used was similar in each case. 

 If the results of these investigations are reliable, then, in the 

 same spectrum amoeba and hydra are affected most by the blue, 

 Daphnia most by the green-yellow and Bacterium photometricum 

 most by the infra red. This work, therefore, in spite of the fact 

 that intensity was ignored, supports the view that the stimulating 

 efficiency of the rays of different wave lengths is not the same 

 for all animals. 



The reactions of Calliphora larvae to colored lights are similar 

 to those exhibited by these larvae to white light, as demonstrated 

 by Herms ('11). The larvae, when opposing balanced colors of 

 the same wave length are used, crawl, after orientation, in a 

 direction approximately perpendicular to the direction of the 

 rays, as I have shown in the observations presented in this paper. 

 If lights of the same intensity but of different wave lengths 



