DH. X.] NATURAL SELECTION, 27 



insects by tLeir disgusting taste, that tliey are exactly 

 imitated by at least three genera of diurnal moths. In other 

 parts of the world similar phenomena have been noticed. 

 The relationship of the leptalis to the heliconia is repeated 

 in India, in the Philippine Islands, in the Malay archipelago, 

 and in various parts of Africa ; the protected insect being, 

 in all these cases, very much less numerous than the insect 

 whose colours it mimics. In similar -wise, bees and wasps 

 are often imitated by beetles, by flies and even by moths. 

 '^ For further details I must refer to Mr. Wallace's essay, 

 which is a singularly beautiful specimen of inductive reason- 

 ing, The facts already cited are quite enough to sustain the 

 general conclusion that the colours of animals are in the main 

 determined by the exigencies of the struggle for existence. 

 Where it is for the advantage of an animal to be concealed, 

 as in the great majority of cases, its colour, whether brilliant 

 or sombre, is such as to protect it. But where the animal is 

 otherwise adequately protected — either by its peculiar habits, 

 by a sting, a disgusting odour or taste, or a hard carapace — 

 and where it is not needful for it to be hidden from the prey 

 upon which it feeds, then there is usually no reference to 

 protection in the colour of the animal. In some of these 

 cases, however, a very conspicuous colouring becomes pro- 

 tective — as in the case of the jet-black toad which Mr. 

 Darwin saw in La Plata, which emitted a poisonous secretion, 

 ind which, when crawling over the sandy plain, could not 

 -ail to be recognized b}"- every passing creature as an object 

 to be avoided. 



In many cases the gorgeous tints of the otherwise protected 

 male animal are due to what is called " sexual selection," — 

 to the continual selection of the more beautiful males by the 

 females. To this cause is due the magnificent plumage of 

 the male bird of paradise ; and Mr. Darwin would similarly 

 explain the brilliant colours of many male butterflies. In 

 hia work on the "Descent of Man " may be found an account 



