[Illustration: FIG. 15. _Cærois chorinæus_, from the lower Amazon, in its resting attitude. _V_, anterior wing. _H_, posterior wing. _mr_, midrib of the apparent leaf. _sr_, lateral veins. _st_, hint of a leaf-stalk.] Quite different from the leaf-marking either of _Cœnophlebia_ or _Kallima_ is that of one of the Satyrides of the lower Amazon valley, _Cærois chorinæus_ (Fig. 15). If one spreads this butterfly out in the usual way it does not look in the least like a leaf, and one only sees a number of curiously placed disconnected stripes on the under surface of the wing. But if the wings be folded together to correspond with the sitting position of the butterfly, there appears the figure of a leaf, of which, however, only half is present, and whose midrib (_mr_) runs obliquely forward from the inner angle of the posterior wing. Here, again, it is not difficult to guess that this straight stripe has arisen, by displacement and straightening, from a curved line inherited from some remote ancestor, and it is these precise changes which are the work of the adaptive processes of natural selection. The same applies to the lateral ribs (_sr_), which are here four in number. But even the division of the wing surface by a single dark line, such as that which crosses the middle of the posterior wing of _Hebomoja_ (Fig. 9), an Indian butterfly, heightens not inconsiderably the resemblance of the resting butterfly to a leaf, a resemblance which has already been shown in the form and colour. Indeed, even the sharp division of the wing surface into a darker inner and a lighter outer portion, which occurs in many species of _Anæa_, gives a very vivid impression of a leaf crossed by a midrib. It is not without a purpose that I have lingered so long over the leaf-butterflies. I wished to make it clear that we have by no means to do with a few exceptional cases, but with a great number, in all of which resemblance to a leaf has been aimed at, although it has been attained in varying degrees, and by very diverse ways. Whoever surveys this wealth of fact must certainly receive the impression, that, wherever it was advantageous to the existence of the species, the evolution of such a deceptive resemblance has also been possible. In any case one cannot but be convinced that it is not a case of chance resemblance, as some naturalists have recently tried to maintain. But I have not yet quite finished my outline-survey of the facts, for I must not omit to mention that, in the evergreen tropical forests, there are also large nocturnal Lepidoptera, which mimic leaves, sometimes green ones, sometimes brown, dead ones. [Illustration: FIG. 16. _Phyllodes ornata_, from Assam. Upper surface with leaf-like marking only on the anterior wing, which is the only part visible when at rest; ⅔ nat. size.]