308 THE DESCENT OP MAN. 



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 conclude that the causes have generally been the 

 same which have determined the brilliant coloring 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 colors to the great heat 

 and moisture of these zones; but Mr. Bates" has shown by the 

 comparison of various closely-allied groups of insects from the 

 temperate and tropical regions, that this view cannot be main- 

 tained; and the evidence becomes conclusive when brilliantly- 

 colored males and plain-colored females of the same species 

 inhabit the same district, feed on the same food, and follow ex- 

 actly the same habits of life. Even when the sexes resemble 

 each other, we can hardly believe that their brilliant and beau- 

 tifully-arranged colors are the purposeless result of the nature of 

 the tissues and of the action of the surrounding conditions. 



With animals of all kinds, whenever color has been modified 

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

 either for direct or indirect protection, or as an attraction be- 

 tween the sexes. With many species of butterflies the upper sur- 

 faces 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 exjjosed to 

 view. Hence it is this side which is often colored so as to imitate 

 the objects on which these insects commonly rest. Dr. Rossler, 

 I believe, first noticed the similarity of the closed wings of cer- 

 tain 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 

 Sumatran butterfly (Kallima), which disappears like magic when 

 it settles on a bush ; for it hides its head and antennaa between its 

 closed wings, which, in form, color and veining, cannot be dis- 

 tinguished from a withered leaf with its footstalk. In some other 

 cases the lower surfaces of the wings are brilliantly colored, and 

 yet are protective; thus in Thecla rubi the wings when closed 

 are of an emerald green, and resemble the young leaves of the 

 bramble, on which in spring this butterfly may often be seen 

 seated. It is also remarkable that in very many species in which 



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



' See the interesting article in the 'Westminster Review," July 1867, 

 p. 10. A woodcut of the Kallima Is given by Mr. Wallace in 'Hard- 

 wi«ke's Science Gossip,' Sept. 1867, p. 196. 



