198 ENTOMOLOGY 



from the absence of pigment, if they live in regions of con- 

 tinual darkness, but have more or less pigmentation in propor- 

 tion respectively to the greater or less amount of sunlight to 

 which they have access. 



Curiously enough, light often hastens the destruction of 

 pigment in insects that are no longer alive, for which reason 

 it is necessary to keep cabinet specimens in the dark as much 

 as possible. Life is evidently essential for the sustension or 

 renewal of the pigments. 



A chrysalis not infrequently matches its surroundings in 

 color. This phenomenon has been investigated by Poulton, 

 who has proved that the color of the chrysalis is determined 

 largely by the prevalent color of the surroundings during the 

 last few days of larval life. Larvae of Pieris rapes, raised 

 upon the same food plant (all other conditions being made as 

 nearly equal as possible) produced dark pupae if kept in dark- 

 ness for a few days just before pupation; yellow light arrested 

 the formation of the dark pigment and gave green pupae ; while 

 light colors in general gave light-colored pupae. This color re- 

 semblance is commonly assumed to be of protective value, and 

 perhaps it is. Nevertheless, it is a direct effect of light, and 

 does not need to be explained by natural selection, even though 

 it cannot be denied that natural selection may have helped in 

 its production. 



Poulton extended his studies to the adaptive coloration of 

 caterpillars and has published the results of an extensive 

 series of experiments which prove that the colors of certain 

 caterpillars also are directly produced by the same colors in 

 the surrounding light. Gastropacha quercifolia, which always 

 rests by day on the older wood of its food plant, was given 

 black twigs, reddish brown sticks, lichens, etc., to rest upon, 

 and though all the larvae were from the same cluster of eggs, 

 and had been fed in the same way, each larva gradually- 

 assumed the color or colors of its resting place, resulting in 

 exquisite examples of protective resemblance, the most re- 

 markable of which were those in which the larvae assumed the 



