THE COLORATION OF ANIMALS 



87 



has already been shown in the form and colour. Indeed, even the 

 sharp division of the wing surface into a darker inner and a lighter 

 outer portion, which occurs in many species of Ancea, gives a very 

 vivid impression of a leaf crossed by a midrib. 



It is not without a purpose that I have lingered so long over the 

 leaf-butterflies. I wished to make it clear that we have by no means 

 to do with a few exceptional cases, but with a great number, in all of 

 which resemblance to a leaf has been aimed at, although it has been 

 attained in varying degrees, and by very diverse ways. Whoever 

 surveys this wealth of fact must certainly receive the impression, 

 that, wherever it was advantageous to the existence of the species, 

 the evolution of such a deceptive resemblance has also been possible. 

 In any case one cannot but be convinced that it is not a case of 

 chance resemblance, as some na- 

 turalists have recently tried to 

 maintain. 



But I have not yet quite 

 finished my outline-survey of the 

 facts, for I must not omit to men- 

 tion that, in the evergreen tropical 

 forests, there are also large noc- 

 turnal Lepidoptera, which mimic 

 leaves, sometimes green ones, some- 

 times brown, dead ones. 



Fig. 1 6 gives a good picture, 

 reduced to two-thirds, of such a 

 species, Phyllodes ornata, from 

 Assam. The posterior wings are conspicuously coloured in deep black 

 and yellow ; in the resting position they are covered by the anterior 

 wings, and these are red-brown with black markings which precisely 

 and clearly mimic the ribs of a leaf. The midrib begins near the tip 

 of the anterior wing, but breaks off half-way across the wing at two 

 silvery white spots, similar to those in many of the diurnal forms, which 

 also mimic decaying leaves. Three pairs of side veins go off backwards 

 and forwards with remarkable regularity from the midrib, almost at the 

 same angle, and parallel to one another, and three more are indicated 

 by vague shading. Then the midrib begins again in the internal half 

 of the wing, though only represented by a broad shading. The whole 

 suggests two torn, rotten leaves, one partly covering the other ; and 

 the deception will certainly be perfect when the moth rests on the 

 ground or among decaying leaves. 



That all these extremely favourable j^i'otective colorations find 



G 3 



Fig. i6. Phyllodes ornata, from Assam. 

 Upper surface with leaf-like marking only 

 on the anterior wing, which is the only 

 part visible when at rest ; "5 nat. size. 



