390 ENTOMOLOGICAL NEWS [Nov., '13 



Calaveras County, California, elevation 2,300 feet. A series 

 of four specimens collected by Mr. G. R. Pilate, at El Centro, 

 Imperial County, California, is to be referred to Series 1 

 and 2 of the present paper. 



The material just discussed does not in any way elucidate 

 the relation between Olla abdominalis and Olla plagiata Casey. 



The above interesting series has caused considerable specu- 

 lation as to the factors which act to bring about this variation 

 in pigmentation. The normal tendency in Olla abdominalis is 

 toward albinism. 



I desire to mention the conclusions or theoretical sugges- 

 tions of W. L. Tower, who made his studies on Lepti- 

 notarsa 10-lineata. His experiments extended over a period 

 of eleven years, and his results have been published by the 

 Carnegie Institution at Washington. 



Tower believes that color production in insects is depend- 

 ent on the action of a group of closely related enzymes, of 

 which chitase, the agent which produces hardening of chitin. 

 is the most important. He demonstrates by a series of well- 

 planned experiments that colors are directly modified by the 

 action of external agencies, namely: temperature, humidity, 

 food, altitude and light. Food chiefly affects the subhypo- 

 dermal colors of the larvae, and does not enter much into ac- 

 count, the most important agents affecting the adult coloration 

 being temperature and humidity. A slight increase or a slight 

 decrease of temperature or humidity was found to stimulate 

 the action of the color-producing enzymes, giving a tendency 

 to melanism; but a large increase or large decrease of tem- 

 perature or humidity was found to inhibit the action of the 

 enzymes, producing a strong tendency to albinism. 



There seems to be no logical reason why we should not 

 reason from analogy. Let it be granted that there is such 

 an enzyme as chitase or its analogues present during the 

 earlier stages in the ontogenesis of insects and that tempera- 

 ture and humidity can produce the optimum state for the 

 activity of such enzymes, just as they do for other ferments, 

 notably those for the conversion of proteids into peptones. 



