78 THE EVOLUTION THEORY - 



are yellowish instead of green. Brunner says of this: 'The phe- 

 nomenon gives the impression that the more brilliant colour is 

 a character due to daylight. If several sheets of white paper of 

 unequal dimensions be placed one above the other, . . . and exposed 

 to the sun, after a short time silhouettes of the smaller sheets will 

 appear on the larger ones, either in a lighter or in a darker colour. 

 Probably this "fading" of the covered parts in the Phasmid also 

 belongs to this " category of photographs." ' This seems convincing, 

 but analogous phenomena in other insects prevent our regarding the 

 pretty comparison with the photograph as a sufficient explanation. 

 If it were a question of a diurnal butterfly, such an assumption would 

 have to be rejected on this ground alone, that the wing colouring is 

 developed in the pupa, and appears perfect and unalterable as soon 

 as the perfect insect emerges. But in the pupa the position of the 

 wings is exactly the reverse of that seen in the resting attitude of 

 a butterfly, that is, the protectively coloured under side of the wing 

 is not turned towards the light but away from it. Moreover, in the 

 pupa the anterior wings cover the posterior ones completely, no 

 matter what the wing position may be later in the perfect insect. 

 Furthermore, the thick and often darkly coloured sheath of the pupa 

 prevents the light having any effect, and not a few species pass their 

 pupal stage in such dark places— for instance, under stones, as in the 

 case of many ' Blues ' — that the light can hardly reach them. And if 

 the light did exercise an influence, how could it produce such diverse 

 coloration as the protective colours of diurnal butterflies, on the one 

 side dark, even to blackness, on the other side, yellow, reddish, and 

 even white and pure green ; and how should the same rays of light 

 call forth complicated colour patterns on one and the same surface, 

 for instance, the white, sprinkled with green, of the Aurora butterfly 

 (A nthocharis cardaminis) ? Finally, we have only to remember that 

 numerous nocturnal Lepidoptera pass through their pupa stage under- 

 groimd, although they exhibit brilliant as well as protective colours 

 in the most appropriate distribution, to reject once for all the 

 hypothesis that the influence of light plays any decisive r61e in deter- 

 mining the distribution of the colours on the wings of Lepidoptera. 



But it is otherwise with Tropidoderus. In this case the wings 

 grow gradually during the slow growth of the animal, which takes 

 place in full light, and the wings of the young insect probably lie one 

 above the other, in exactly the same position, and cover the same 

 places as in the full-grown form ; we might, therefore, from the facts 

 of the case, admit the possibility that the yellow of the covered 

 portions is due to the exclusion of light. 



