CAUSE OF CUTICULA COLORS. 137 



abandoned this view and concluded that the colors arise as the result of the 

 action of a katalytic agent or enzyme upon the primary cuticula, which pro- 

 duces a hardening of the cuticula and the development of cuticula colors. 

 This view is supported by microscopic and experimental evidence and by the 

 isolation of enzymes that are able to produce colors. Later, Dewitz has 

 obtained similar results in the study of the brown cuticula colors of lepidopter- 

 ous pupae. Recently, however, Enteman, discussing the color of Polistes, 

 holds that the pigment is elaborated from the protoplasm of the hypodermal 

 cells and passes through the pore canals to the outer surface, where it gathers 

 in large drops which spread over the surface and fuse. This view, I believe, 

 is not supported by any adequate evidence. 1 



In a former paper I have shown that neither light, oxidation, drying, nor 

 kindred external agencies are factors which bring about the development of 

 these colors, but that their cause is located within the animal itself. Here 

 also it was shown that enzymes are active in the production of color changes. 

 Since the publication of that paper I have experimented further upon species 

 of this genus with the following results : 



EXPERIMENTS POINTING TO THE EXISTENCE OF ENZYME ACTION. 



In 1895 I found that pupae of decemlineata kept at temperatures of 43 to 

 45 C. showed a most peculiar phenomenon. In pupae that were dead and 

 had begun to undergo postmortem changes, the cuticula colors of the head, 

 pronotum, and legs were observed to continue changing, often until the dark 

 areas were normally developed. Since then I have often observed this in 

 high-temperature experiments. Sometimes the color pattern developed is 

 abnormal, but the colors are always normal in every way. I have found that 

 other species undecimlineata, multitceniata, rubicunda, dilccta, violescens, 

 and signaticollis also behave in the same manner ; so that it appears that the 

 phenomenon is a general one in the genus. 



In low temperatures, o to 5 C, which produce a great mortality, 

 no color has been observed to develop. In these experiments both of the 

 extreme temperature conditions produce an equal degree of mortality, but in 

 one, color develops after death, and in the other it does not. Similar results 

 have been observed in experiments with extreme conditions of moisture. 



That this color development is due to causes within the animal and proper 

 to it and not to outside factors, such as bacteria, temperature, or moisture, has 

 been shown by the experiments which follow. 



It is known that chloroform vapor stops the growth of bacteria and the 

 ordinary activities of animals, but that katalytic agents are not affected by 

 its presence. In a former paper I have given some experiments along this 

 line, and I shall now add a new series upon the beetles of this genus. Pupae 



1 A recent study of color development in tropical species of Polistes shows that there 

 is no foundation for the belief expressed by Enteman. 



