REACTIONS OF ARTHROPODS TO LIGHTS 473 



Simocephalus showed a movement toward the violet. Yerkes' 

 ('99, p. 182) conchisions are 'SSimooephalus prefers the orange 

 and yellow of a gas spectrum. This response to the spectrum 

 is a photopathic reaction, and is not, so far as is known, chromo- 

 pathic." 



Hess ('10) has made some recent investigations on the reactions 

 of invertebrates to spectral light. A large part of this work 

 was devoted to experiments upon insects and small crustaceans. 

 Hess placed larvae of Porthesia chrysorrhoea at the bottom of a 

 parallel-walled glass vessel. In the dark the larvae remained 

 on the bottom but when the vessel was illuminated from the 

 side by the spectrum, the animals immediately started to crawl 

 upwards in the yellow and green, the most luminous region of 

 the spectrum. In the blue and red the less illuminated areas the 

 larvae remained below. WTien only two colors, the red and blue 

 of either spectral or screened light, were used, the larvae were 

 most responsive to the blue. This agrees with Loeb's results 

 secured by tests on various animals with these two colors. Hess, 

 however, does not agree with Loeb in believing that the more 

 refrangible raj^s are the most effective of all the spectrum, since, 

 he has shown that the larvae are more responsive to the green 

 and yellow regions of the spectrum than to the blue end. Hess 

 found that Hyponomeuta variabilis, Dasychira fascelina, Lasio- 

 campa potatoria and Phragmatobia fuliginosa responded to the 

 spectrum and to the colors in a way similar to that of the Porthesia 

 larvae. Among other arthropods, he tested the effect of colored 

 light on the movements of the eye in Daphnia and the aggrega- 

 tion in the spectrum of the crustacean Cypridopsis, the larvae 

 of Culex pipiens, Musca and Chironomus plumosus, the adult 

 insects Cocciuella septempunctata, Culex pipiens, bees, house 

 flies and ichneumon flies and the marine crustaceans, Podopsis 

 slabberi and Atylus swammerdamii. In all of these forms Hess 

 found the yellow-green region of the spectrum most effective in 

 stimulating the animals. The animals which were positive in 

 white hght aggregated in the yellow and green; those which are 

 negative, in the violet and red. As to the vision in the inverte- 

 brates Hess maintains "dass bei alien bislier untersuchten Wirbel- 



