do not present themselves to the eye as a whole, but partially concealed
among other leaves. Even those butterflies which, like the species of
Kallima and Anaea, represent the whole of a leaf with stalk, ribs, apex,
and the whole breadth, are not actual copies which would satisfy a
botanist; there is often much wanting. In Kallima the lateral ribs of the
leaf are never all included in the markings; there are only two or three on
the left side and at most four or five on the right, and in many
individuals these are rather obscure, while in others they are
comparatively distinct. This furnishes us with fresh evidence in favour of
their origin through processes of selection, for a botanically perfect
picture could not arise in this way; there could only be a fixing of such
details as heightened the deceptive resemblance.

Our postulate of origin through selection also enables us to understand why
the leaf-imitation is on the lower surface of the wing in the diurnal
Lepidoptera, and on the upper surface in the nocturnal forms, corresponding
to the attitude of the wings in the resting position of the two groups.

The strongest of all proofs of the theory, however, is afforded by cases of
true "mimicry," those adaptations discovered by Bates in 1861, consisting
in the imitation of one species by another, which becomes more and more
like its model. The model is always a species that enjoys some special
protection from enemies, whether because it is unpleasant to taste, or
because it is in some way dangerous.

It is chiefly among insects and especially among butterflies that we find
the greatest number of such cases. Several of these have been minutely
studied, and every detail has been investigated, so that it is difficult to
understand how there can still be disbelief in regard to them. If the many
and exact observations which have been carefully collected and critically