side have learned to know (after one trial, or, perhaps, even before it by inherited instinct) that red or yellow bands and belts in caterpillars are the outward and visible sign of uneatableness. The second group or set of caterpillars is edible and tasty: it, therefore, governs itself accordingly, and has recourse to the exactly opposite tactics. Caterpillars of this class are smooth and naked: they never have the brilliant "warning colours" of the nasty-tasted kinds: and they show a marked absence of the beautiful metallic sheen, the strange melting iridescent hues and spots which add beauty to the charms of so many among the uneatable species. Such fat and smooth-skinned edible caterpillars are, of course, very tempting juicy morsels to birds and other insect-eating animals. Their motions, like those of all grubs, are slow; and if they lived exposed on their food-plants, after the fashion of the protected hairy and bitter kinds, they would all he eaten up before they had time to turn into moths or butterflies. Here, therefore, natural selection has produced the contrary result from that which it produces among protected kinds. Caterpillars of this edible type which showed themselves too openly and imprudently have got picked off by birds, like sentries and pickets who make themselves too conspicuous to the enemy's sharpshooters. Only the most prudent, modest, and retiring grubs have survived to become moths or butterflies, and so be the parents of future generations, to whom they hand on their own peculiarities. In this way the edible caterpillars have acquired at last a fixed hereditary instinct of lurking under leaves, or in dark spots, and never showing themselves openly. The larvæ of the butterfly group as a whole thus fall into two great classes (as far as regards habits alone, I mean): the _protected_, which are either hairy or nasty, and which flaunt themselves openly; and the _unprotected_, which lurk and skulk, endeavouring to escape notice as sedulously as their rivals the protected endeavour to attract it.