Chap. XI. BUTTERFLIES AND MOTHS. 391 



male having transferred his colours to the female, 

 or to the male having retained, or perhaps reco- 

 vered, the primordial colours of the genus to which the 

 species belongs. It also deserves notice that in those 

 groups in which the sexes present any difference of 

 colour, the females usually resemble the males to a cer- 

 tain extent, so that when the males are beautiful to an 

 extraordinary degree, the females almost invariably ex- 

 hibit some degree of beauty. From the numerous cases 

 of gradation in the amount of difference between the 

 sexes, and from the prevalence of the same general type 

 of coloration throughout the whole of the same group, 

 we may conclude that the causes, whatever they may 

 be, which have determined the brilliant colouring of the 

 males alone of some species, and of both sexes in a more 

 or less equal degree of other species, have generally 

 been the same. 



As so many gorgeous butterflies inhabit the tropics, it 

 has often been supposed that they owe their colours to 

 the great heat and moisture of these zones ; but Mr. 

 Bates 4 has shewn by the comparison of various closely- 

 allied groups of insects from the temperate and tropical 

 regions, that this view cannot be maintained; and the 

 evidence becomes conclusive when brilliantly-coloured 

 males and plain-coloured females of the same species 

 inhabit the same district, feed on the same food, and 

 follow exactly the same habits of life. Even when 

 the sexes resemble each other, we can hardly believe 

 that their brilliant and beautifully-arranged colours are 

 the purposeless result of the nature of the tissues, and 

 the action of the surrounding conditions. 



With animals of all kinds, whenever colour has been 

 modified for some special purpose, this has been, as far 



4 ' The Naturalist on the Amazons,' vol. i. 1863, p. 19. 



