198 COLOR PHOTOGRAPHY. 



brighter colors came about in the light. 1 It is worth noting that dark 

 surroundings in a bright light brought out somewhat lighter dark 

 forms than complete darkness. 2 I will return to this point. 



How far the above described characteristics of a color-receptive body 

 must be assumed for the coloring matter of the skin of caterpillars, in 

 explanation of their color adaptation, dependson the extent of this adap- 

 tation. This question is connected with the other, whether the caterpil- 

 lars are restricted in their adaptation to colors which they might meet 

 with in nature, or if they can take on also others. Poulton 3 has in gen- 

 eral observed only the first case. But he has showed that it is not pe- 

 culiar situations but the light which exerts the influence; for not only 

 were green leaves and brown twigs effective, but also green and brown 

 strips of paper. White strips of paper and different colored glass 

 windows were similarly active. 4 



If, however, caterpillars are able to take on other colors than those 

 of their natural surroundings, these could not be looked upon as pro- 

 tection colors. An explanation of this kind was rejected by Poulton in 

 the cases of Pieris brassicce and Pieris rapce, which changed into pupae 

 in a glass cylinder two-thirds covered with orange-colored paper. This 

 color destroyed the dark coloring matter more than any other except 

 white and gave rise to bright yellowish-green pupae. 



A pronounced deviation from natural colors is mentioned by Bed 

 darcl, who says : 5 "Mr. Morris succeeded in producing white, red, sal- 

 mon, black, and blue pupae of Danais chrysippus ; they are only green 

 or pink in nature." It must therefore be assumed that the coloring 

 matter of these caterpillars possesses in a high degree the character- 

 istics of a color-receptive substance, as already defined. 



From these examples it follows that the biological explanation of 

 protection coloring is not satisfactory; but it in no way follows that 

 natural selection was not in play in the production of the color-receptive 

 pigments of the caterpillars. For it is easily possible that if these are 

 capable of reproducing the natural colors of the surroundings, they also 

 with the same chemical constitution have the capacity of reproducing 

 other colors. 



The assumption that this constitution possesses, in some measure, the 

 characteristics of a color-receptive substance is confirmed by another 

 experiment of Poulton. Since the caterpillar's skin could readily 

 assume the color of leaf-green, the light of this color must be particu- 

 larly active in decomposing the dark pigment that is secreted in the 

 skin in the absence of light. Poulton investigated, in the case of Pieris 



'See, for example, Poulton, Phil. Trans., 178 : page 430,1887; and Trans. Eut. Soc, 

 pages 328, 353, 1892. 



2 Poulton. Trans. Ent. Soc., pages 329, 385. 1892. 



'Poulton. Trans. Ent. Soc, page 470. 1892. 



-"Poulton. Trans. Ent. Soc. See for example tables, pages 461, 466. 1892. 



5 Frank E. Beddard. Animal Coloration. London: Swan, Sonnenscliein & Co., 

 page 137. 1895. 



'Morris. Journ. Bombay Nat. Hist. Soc, 1890, according to Beddard. 



