240 DARWINISM chap. 



families or orders. One creature seems disguised in order to 

 be made like another; hence the terms "mimic" and mimicry, 

 which imply no voluntary action on the part of the imitator. 

 It has long been known that such resemblances do occur, as, for 

 example, the clear-winged moths of the families Sesiidae and 

 ^Egeriidae, many of which resemble bees, wasps, ichneumons, 

 or saw-flies, and have received names expressive of the re- 

 semblance ; and the parasitic flies (Volucella) which closely 

 resemble bees, on whose larvae the larvae of the flies feed. 



The great bulk of such cases remained, however, unnoticed, 

 and the subject was looked upon as one of the inexplicable 

 curiosities of nature, till Mr. Bates studied the phenomenon 

 among the butterflies of the Amazon, and, on his return home, 

 gave the first rational explanation of it. 1 The facts are, briefly, 

 these. Everywhere in that fertile region for the entomologist 

 the brilliantly coloured Heliconidae abound, with all the char- 

 acteristics which I have already referred to when describing 

 them as illustrative of "warning coloration." But along 

 with them other butterflies were occasionally captured, which, 

 though often mistaken for them, on account of their close 

 resemblance in form, colour, and mode of flight, were found 

 on examination to belong to a very distinct family, the Pieridae. 

 Mr. Bates notices fifteen distinct species of Pieridae, belonging 

 to the genera Lep talis and Euterpe, each of which closely imitates 

 some one species of Heliconidae, inhabiting the same region and 

 frequenting the same localities. It must be remembered that 

 the two families are altogether distinct in structure. The 

 larvae of the Heliconidae are tubercled or spined, the pupae sus- 

 pended head downwards, and the imago has imperfect fore- 

 legs in the male ; while the larvae of the Pieridae are smooth, 

 the pupae are suspended with a brace to keep the head erect, 

 and the forefeet are fully developed in both sexes. These 

 differences are as large and as important as those between pigs 

 and sheep, or between swallows and sparrows ; while English 

 entomologists will best understand the case by supposing that 

 a species of Pieris in this country was coloured and shaped 

 like a small tortoise-shell, while another species on the Con- 

 tinent was equally like a Camber well beauty — so like in both 



1 See Transactions of the Linnean Society, vol. xxiii. pp. 495-566, coloured 

 plates. 



