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 Sesiidse and 
PEgeriid®, 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 hies 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 Leptalis 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 tuberclcd 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 Camberwell beauty—so like in both 
1 See Transactions of the Linnean Society, vol. xxiii. pp. 495-566, coloured 
plates. 
