COLOR AND COLORATION 163 



in proportion 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 es- 

 sential for the sustention 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 rapce, 

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

 equal as possible) produced dark pupae if kept in darkness 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 resemblance 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 produc- 

 tion. 



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. Gastro pacha 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 variegated 

 coloration of lichens. Only the younger larvae, however, proved to be 

 susceptible to the colors of the environment; unlike those of Amphidasis 

 betularia, in which the older larvae also were sensitive to the surrounding 

 light. Here again, natural selection is unnecessary, even if not superfluous, 

 as an explanation of this kind of protective coloration. 



Effects of Temperature. The amount of a pigment in the wing of a 

 butterfly depends in great measure upon the surrounding temperature 

 during the pupal stage, when the pigments are forming. Black or brown 

 spots have been enlarged artificially by subjecting chrysalides to cold; 

 hence it is probable that the characteristically large black spots on the 

 under side of the wings of the spring brood of our Cytiniris pscudargiolus 



