PROTECTIVE RESEMBLANCE 141 



to the red admiral butterfly (Pyrameis atalanta), which has 

 a dark and a glittering variety of the chrysalis, but no 

 green form, he writes : " I have shown that this species 

 is also susceptible, and that either variety of pupa is pro- 

 duced by the appropriate environment. Rut this chrysalis 

 is very commonly found attached to the food-plant, and 

 when this is the case it hangs suspended in a tent formed 

 of leaves carefully spun together by the caterpillar, so that 

 it is concealed from view. The larva also often has the 

 habit of partially biting through the leaf-stalk or stem, so 

 that the leaves of its retreat hang down and wither. The 

 dead brown leaves thus afford a far more harmonious back- 

 ground for the dark pupa, if by any chance it becomes 

 exposed to view." 



So far as is known, no adult insect, in its own lifetime, 

 is able to adapt its colours to a particular environment ; 

 nor is this surprising when we remember that, in the 

 perfect state, the integuments usually become hard and 

 lifeless. Nevertheless, through the agency of natural 

 selection, different races of the same species undoubtedly 

 acquire a coloration appropriate to the localities which 

 they frequent. Thus Professor Poulton " observed that 

 a very abundant grasshopper was invariably reddish-brown, 

 like the earth, upon the island of Heligoland, but that 

 the same species was always sand-coloured or green on 

 the flat, sandy Dune, separated by three-quarters of a 

 mile of sea." It is also noteworthy that the colouring 

 of many insects, especially Lepidoptera, tends to become 

 darker as the range of the species recedes from tropical or 

 sub-tropical regions. This is probably due to the greater 

 sombreness of vegetation — especially the prevalence of 

 dark tree trunks and undergrowth — in northern countries. 

 Moreover, there is reason for thinking that the smoke of 

 our great manufacturing areas, by blackening the tree 



