MIMICRY 51 



infrequent, although a considerable number might be 

 collected. On the other hand, some resemblance 

 between the colour of an animal and its surroundings 

 is to be traced in the majority of the members of 

 many groups. Familiar examples are afforded by the 

 white colour of animals which live in snow, the tawny 

 grey colour of most desert species, the green of grass- 

 frequenting animals, and so on. It is perhaps not quite 

 certain that in some of these cases the peculiar colour 

 is not evoked by the direct action of some cause which 

 affects different species in the same way ; but such a 

 cause awaits discovery, and in the meantime natural 

 selection has certainly a strong claim to be regarded 

 as the proper explanation. 



A more strict use of the term mimicry, however, is 

 to restrict it to cases where one species apes the colour 

 pattern or other external character proper to another 

 species which inhabits the same region ; and the idea 

 of mimicry has been put forward as especially appro- 

 priate in cases where the mimicked species is common, 

 and can be thought to possess some special means of 

 protection. Several supposed examples of this phe- 

 nomenon have been described in the case of different 

 genera of tropical butterflies, but the best of them 

 seem to be open to criticism, since there is nothing 

 to prove that colour patterns of the same type may 

 not have arisen from the same causes in quite different 

 groups. In cases where the environment to which the 

 different forms were exposed was similar as would be 

 the case in a single locality such a process of parallel 

 evolution might be thought to be all the more likely. 



42 



