Page:Darwinism by Alfred Wallace 1889.djvu/262

 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 Sesiidæ and Ægeriidæ, many of which resemble bees, wasps, ichneumons, or saw-flies, and have received names expressive of the resemblance; and the parasitic flies (Volucella) which closely resemble bees, on whose larvæ the larvæ 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. The facts are, briefly, these. Everywhere in that fertile region for the entomologist the brilliantly coloured Heliconidæ abound, with all the characteristics 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 Pieridæ. Mr. Bates notices fifteen distinct species of Pieridæ, belonging to the genera Leptalis and Enterpe, each of which closely imitates some one species of Heliconidæ, 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 Heliconidæ are tubercled or spined, the pupae suspended head downwards, and the imago has imperfect forelegs in the male; while the larvæ of the Pieridæ are smooth, the pupæ 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 Continent was equally like a Camberwell beauty—so like in both