the most diverse ways, sometimes by
mere variations in the form of the insect and in its colour, sometimes
by an elaborate marking, like that which occurs in the Indian
leaf-butterflies, Kallima inachis. In the single butterfly-genus Anaea,
in the woods of South America, there are about a hundred species which
are all gaily coloured on the upper surface, and on the reverse side
exhibit the most delicate imitation of the colouring and pattern of a
leaf, generally without any indication of the leaf-ribs, but extremely
deceptive nevertheless. Anyone who has seen only one such butterfly
may doubt whether many of the insignificant details of the marking can
really be of advantage to the insect. Such details are for instance the
apparent holes and splits in the apparently dry or half-rotten leaf,
which are usually due to the fact that the scales are absent on a
circular or oval patch so that the colourless wing-membrane lies bare,
and one can look through the spot as through a window. Whether the
bird which is seeking or pursuing the butterflies takes these holes for
dewdrops, or for the work of a devouring insect, does not affect
the question; the mirror-like spot undoubtedly increases the general
deceptiveness, for the same thing occurs in many leaf-butterflies,
though not in all, and in some cases it is replaced in quite a peculiar
manner. In one species of Anaea (A. divina), the resting butterfly looks
exactly like a leaf out of the outer edge of which a large semicircular
piece has been eaten, possibly by a caterpillar; but if we look more
closely it is obvious that there is no part of the wing absent, and that
the semicircular piece is of a clear, pale yellow colour, while the rest
of the wing is of a strongly contrasted dark brown.

But the deceptive resemblance may be caused in quite a different manner.
I have often speculated as to what advantage the brilliant white C
could give to the otherwise dusky-coloured "Comma butterfly" (Grapta C.
album). Poulton's recent observations ("Proc. Ent. Soc"., London, May 6,
1903.) have shown that this represents the imitation of a crack such as
is often seen in dry leaves, and is very conspicuous because the light
shines through it.

The utility obviously lies in presenting to the bird the very familiar
picture of a broken leaf with a clear shining slit, and we may conclude,
from the imitation of such small details, that the birds are very sharp
observers and that the smallest d