Chap. XL] BUTTERFLIES AND MOTHS. 370 



in those groups in which the sexes present any difference 

 of color, the females usually resemble the males to a cer- 

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

 traordinarv decree, the females almost invariably exhibit 

 some degree of beauty. From the numerous cases of gra- 

 dation 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, whatever they may be, which have 

 determined the brilliant coloring 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 colors to the 

 great heat and moisture of these zones ; but Mr. Bates 4 

 has shown, 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-colored males and 

 plain-colored 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 beau- 

 tifully-arranged colors are the purposeless result of the 

 nature of the tissues, and 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 protection or as an attraction be- 

 tween the sexes. With many species of butterflies the 

 upper surfaces of the wings are obscurely colored, and 

 this in all probability leads to their escaping observation 

 and danger. But butterflies when at rest would be par- 

 ticularly liable to be attacked by their enemies ; and al- 



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



