broken piece, or the half or two-thirds of a leaf, but then the leaves
themselves frequently 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 more
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 discussed for instance by Poulton[47] were
thoroughly studied the arguments which are still frequently urged
against mimicry would be found untenable; we can hardly hope to find
more convincing proof of the actuality of the processes of selection
than these cases put into our hands. The preliminary postulates of the
theory of mimicry have been disputed, for instance, that diurnal
butterflies are persecuted and eaten by birds, but observations
specially directed towar