These, of course, survived while their companions were devoured.

Those among their descendants that were still more like Heliconidae again survived, and at length the imitation would become tolerably perfect.

Thereafter, as the protected group diverged into distinct species of many different colours, the imitative group would occasionally be able to follow it with similar variations,--a process that is going on now, for Mr.Bates informs us that in each fresh district he visited he found closely allied representative species or varieties of Heliconidae, and along with them species of Leptalis (Pieridae), which had varied in the same way so as still to be exact imitations.

But this process of imitation would be subject to check by the increasing acuteness of birds and other animals which, whenever the eatable Leptalis became numerous, would surely find them out, and would then probably attack both these and their friends the Heliconidae in order to devour the former and reject the latter.

The Pieridae would, however, usually be less numerous, because their larvae are often protectively coloured and therefore edible, while the larvae of the Heliconidae are adorned with warning colours, spines, or tubercles, and are uneatable.