240 DARWIXIS^Sr chap. 



families or orders. One creature seems dissiuised 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 knoA\'Ti that such resemblances do occur, as, for 

 example, the clear-Avinged moths of the families SesiidtB and 

 TEgeriidse, many of which resemble bees, wasps, ichneumons, 

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

 semblance ; and the parasitic flies (Yolucella) 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 Avas looked upon as one of the inexplicable 

 curiosities of nature, till j\Ir. Bates studied the iDheuomenon 

 among the butterflies of the Amazon, and, on his retiu'n home, 

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

 these. Everywhere in that fertile region for the entomologist 

 the brilliantly coloured Heliconidaj abound, with all the char- 

 acteristics Avhich I have already referred to when describing 

 them as illustrative of "warning coloration." But along 

 A\ath them other butterflies were occasionally ca23tured, Avhich, 

 though often mistaken for them, on account of their close 

 reseml)lance 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 Leptalis and Euterpe, each of which closely imitates 

 some one species of Heliconida?, inhabiting the same region and 

 frequenting the same localities. It must be remembered that 

 the two families are altogether distinct in sti'ucture. The 

 Iarva3 of the Heliconidae are tubercled or spined, the pupai 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 ^Yith. 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 "wnll 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 crpially like a Camberwell beauty — so like in both 



' See Transactions of the Unnean Society, \o\. xxiii. pp. 495-566, coloured 

 plates. 



