Chap. XI. Butterflies and MotJu. 3 1 1 



the males are beautiful to an extraordinary degree, the females 

 almost inyariably exhibit some degree of beauty. From the 

 many 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 con- 

 clude that the causes have generally been the same which have 

 determined the brilliant colouring of the males alone of some 

 species, and of both sexes of other species. 



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 " 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 bril- 

 liantly-coloiired 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 of the action of the surrounding 

 conditions. 



With animals of all kinds, whenever colour has been modified 

 for some sijeeial purpose, this has been, as far as we can judge, 

 either for direct or indirect protection, or as an attraction between 

 the sexes. With many -species of butterflies the upper surfaces 

 of the wings are obscure; and this in all probability leads 

 to their escaping observation and danger. But butterflies 

 would be particularly liable to be attacked by their enemies 

 when at rest ; and most kinds whilst resting raise their wings 

 vertically over their backs, so that the lower surface alone is 

 exposed to view. Hence it is this side which is often coloured 

 so as to imitate the objects on which these insects commonly 

 rest. Dr. Eossler, I believe, first noticed the similarity of the 

 closed wings of certain Vanessse and other butterflies to the 

 bark of trees. Many analogous and striking facts could be 

 given. The most interesting one is that recorded by Mr. 

 Wallace ' of a common Indian and Siimatran butterfly (Kallima), 

 which disappears like magic when it settles on a bush ; for it 

 hides its head and antennte between its closed wings, which, 

 in form, colour and veining, cannot be distinguished from a 

 withered leaf with its footstalk. In some other cases the lower 



» 'The Naturalist on the Ama- 1867, p. 10. A woodcut of the 



tons' vol. i. 186:i, p. 19. Kallima is given by Mr. Wallace in 



' See the interesting article in 'iHardwicke's Science Gossip,' Sept 



ih- ' Westminster Review,' July 1807, p. 196. 



