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 1 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. 



