178 ENTOMOLOGY 



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 super- 

 fluous, as an explanation of this kind of protective coloration. 



Professor W. M. Wheeler has suggested that "such phenomena as 

 the permanent protective coloration of insects may be regarded as the 

 stereotyped, highly specialized end-stage of a more ancient ability 

 actively to change color in response to color changes in the environment, 

 an ability still possessed by some primitive insects like the grasshoppers 

 and mantids, though much more pronounced in cephalopod mollusks, 

 fishes, amphibia and lizards." 



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 Cyaniris pseudargiolus 

 are simply a direct effect of cold upon the wintering chrysalides. 

 Similarly the spring brood (variety marcia) of Phyciodes tharos owes its 

 distinctive coloration to cold, as Edwards has proved experimentally. 

 Lepidoptera have been the subject of very many temperature experi- 

 ments, some of which will be mentioned presently in the consideration 

 of seasonal coloration. 



Speaking generally, warmth (except in melanism} tends to induce a 

 brightening and cold a darkening of coloration, the darkening 

 being due to an increased amount of black or brown pigment. Temper- 

 ature, whether high or low, seldom if ever produces new pigments, 

 but simply alters the amount and distribution of pigments that are 

 present already. 



Effects of Moisture. Very little is known as to the effects of mois- 

 ture upon coloration. The dark colors of insular or coastal insects as 

 contrasted with inland forms, and the predominance of dull or suffused 

 species in mountainous regions of high humidity, have led observers 

 occasionally to ascribe melanism and suffusion to humidity. In these 



