REACTIONS OF ARTHROPODS TO LIGHTS 511 



If it is assumed that the reactions of Periplaneta are brought 

 about by chemical changes produced by hght on the photore- 

 ceptors of the organism, it is conceivable that there exist within 

 the organs photo-chemical substances, not unhke triphenjdfulgid, 

 which have reversible reactions. In blue or violet triphenylfulgid 

 changes from orange-yellow to a dark brown compound; in the 

 red and yellow rays this reaction is reversed. Though no such 

 substances are known to exist in the body of the cocki'oach, 

 it is nevertheless an interesting suggestion and when our knowl- 

 edge of the chemistry of the reactions of animals to light is better 

 known, it is possible that explanations of such complicated reac- 

 tions as those of Periplaneta, as well as those of other organisms, 

 may be easily explained. 



6. SUMMARY 



1. The larvae of Calliphora and Zeuzera and the adults of 

 Calliphora, Drosophila, and Feltia are responsive to each of the 

 four colors of the spectrum used in these investigations. 



2. The colors in the order of their efficiency in stimulating 

 the larvae of CaUiphora are beginning with the most effective: 

 green, blue, yellow, red. 



3. The order of the effectiveness of the colors in stimulating 

 the larvae of Zeuzera and the adults of Calliphora, Drosophila, 

 and Feltia is the order of the natural sequence of the colors in 

 the spectrum: blue, green, yellow, red. 



4. The relative stimulating efficiency of the rays of any part 

 of the spectrum is independent of intensity, and is not the same 

 for all animals nor for different ages of the same animals. 



5. The more refractive rays of the spectrum are not always 

 the most effective in stimulating an organism. 



6. Periplaneta americana is responsive to blue, green and 

 yellow, but is indifferent to red. It is positive to blue and nega- 

 tive to both green and yellow. Green and yellow are practically 

 equal in their stimulating efficiency, as far as the reactions of 

 Periplaneta are concerned. 



