Leaf-like Butterflies 53 
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 semi- 
circular piece is of a clear, pale yellow colour, while the rest of the 
wing is of a strongly contrasted dark brown (Fig. C). 
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! 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 deviation from the 
usual arrests their attention and incites them to closer investigation. 
It is obvious that such detailed—we might almost say such subtle— 
deceptive resemblances could only have come about in the course of 
long ages through the acquirement from time to time of something 
new which heightened the already existing resemblance. 
In face of facts like these there can be no question of chance, 
and no one has succeeded so far in finding any other explanation to 
replace that by selection. For the rest, the apparent leaves are by 
no means perfect copies of a leaf; many of them only represent the 
torn or 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 
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 under- 
stand 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. 
1 Proc. Ent. Soc., London, May 6, 1903. 
