^98 NATURAL SCIENCE. November. 



any advantage to the insect. Natural selection in this case must follow 

 the same course as human selection, which first put Darwin on the 

 track of it. A breeder does not create varieties of pigeons, or fowls, 

 or dogs : the utmost he can do is to seize upon any natural tendency 

 to vary in a certain way, and perpetuate and accumulate it. Fowls 

 often have a small crest — that is, the feathers on the top of the head 

 are elongated ; by breeding from these for many generations, and 

 carefully selecting the most pronounced examples, the breeder produces 

 the magnificent crest of the houdan. He cannot do the same thing 

 with pigeons, because they have no tendency to vary in that way ; 

 but they often have the feathers on the back of the head twisted 

 upwards, and this has been made a normal feature in several distinct 

 breeds. 



What then initiates the likeness which natural selection 

 perfects into mimicry ? Of course many causes may combine, of 

 which some may be merely accidental, or may result from the con- 

 ditions of the creature's Hfe. The first element of likeness in an insect 

 which mimics a green leaf is greenness, and this may be merely the 

 result of its feeding on leaves and absorbing the colouring matter from 

 them. A very large proportion of the larvae of moths and butterflies 

 are green from no other cause. The direct action of light may be 

 another agency. Again, in view of the enormous number and variety 

 of forms that have come upon the stage since the first appearance of 

 life on our planet, we must allow that the doctrine of chances alone is 

 sufficient to account for a great many superficial, or even close, resem- 

 blances. The perfectly ludicrous likeness of the pupae of butterflies 

 of the genus Spalgis to the face of a baboon, or ape, can be explained 

 in no other way. In that instance the likeness, being of no advantage 

 to the insect itself, could not come under the operation of natural 

 selection, but in other cases it may have been otherwise. When, 

 however, one considers some of the more striking instances of mimicry, 

 together with the manner in which they are associated with certain 

 peculiarities of habit necessary to render them effective, all these 

 explanations together fail to satisfy the mind : one is forced to the 

 conviction that there must be some special influence at work con- 

 forming the pattern to its copy. 



Take, for example, the leaf-butterfly, KaJlima, one of the most 

 familiar and certainly one of the most extraordinary cases of mimicry 

 known to us. This butterfly is brilliantly coloured on the upper 

 surface, being chiefly blue in one species, and purple and yellow in 

 another ; but the under surface is an almost absolutely perfect repre- 

 sentation of a dead leaf. The colour is some shade of brown, not 

 •exactly the same in any two specimens ; a dark, diagonal line traces the 

 midrib, a network of finer lines represents the venation, and there are 

 even stains and mouldy patches, and sometimes small transparencies 

 which look like holes in the leaf. Even the shape of the wings is 

 modified to carry out the deception, and the ends of the posterior pair 



