It is precisely this restriction to what is absolutely necessary that is the surest sign, here and elsewhere, that the character in question has been brought about by natural selection. And if this is the only possible, and at the same time quite sufficient explanation of the remarkably well-defined colour deliminations in all Lepidoptera, there can be no reason why we should try to drag in any other factor to explain the case of _Tropidoderus_, the less so as here again selection alone can account for the green of the exposed surfaces; and furthermore, the modification, common in other Phasmidæ, of the most anterior green stripe of the posterior wing into a firm cover protecting the soft abdomen, also points to natural selection; the cover-wings proper have here become too short, and so the edge of the posterior wing has been modified into a hard rib, which protects the soft body of the insect (Fig. 11, _H. horn_). No differences in illumination, and no _direct_ effect of any external influence whatever could have brought that about. How much more I might adduce in this connexion! The manifold diversity of colour and form adaptation is so great among insects, to which protection from their enemies is so necessary, and especially among butterflies, that I should never come to an end if I were to try to give even an approximate idea of it. Let us, therefore, turn now from such cases to a higher--the highest--grade of adaptation, that in which there is not only a mimicry of special and complex coloration, but in which the whole animal has become like some external object, and is thereby secured from discovery. We must first consider the case of our lappet moth (_Gastropacha quercifolia_), which in its copper-red colour and in the remarkable shape and dentated edges of its wings, and finally in the quite extraordinary clucking-hen-like attitude of the wings when at rest, greatly resembles some dry oak-leaves lying one above the other.