Chap. XI.] BUTTERFLIES AND MOTHS. 397 



ditions, that they seem to us to be most capricious in their 

 action ; 23 and we can so far understand how it is that with 

 closely-allied species the sexes of some differ to an aston- 

 ishing: decree, while the sexes of others are identical in 

 color. As the successive steps in the process of variation 

 are necessarily all transmitted through the female, a 

 greater or less number of such steps might readily become 

 developed in her ; and thus we can understand the fre- 

 quent gradations from an extreme difference to no differ- 

 ence at all between the sexes of the species within the 

 same group. These cases of gradation are much too com- 

 mon to favor the supposition that we here see females ac- 

 tually undergoing the process of transition and losing 

 their brightness for the sake of protection ; for we have 

 every reason to conclude that at any one time the greater 

 number of species are in a fixed condition. With respect 

 to the differences between the females of the species in 

 the same genus or family, we can perceive that they de- 

 pend, at least in part, on the females partaking of the col- 

 ors of their respective males. This is well illustrated in 

 those groups in which the males are ornamented to an ex- 

 traordinary degree ; for the females in these groups gener- 

 ally partake to a certain extent of the splendor of their 

 male partners. Lastly, we continually find, as already 

 remarked, that the females of almost all the species in the 

 same genus, or even family, resemble each other much 

 more closely in color than do the males ; and this indi- 

 cates that the males have undergone a greater amount of 

 modification than the females. 



Mimicry. — This principle was first made clear in an ad- 

 mirable paper by Mr. Bates, 24 who thus threw a flood of 



53 ' The Variation of Animals and Plants under Domestication,' vol. ii 

 chap. xii. p. 17. 



84 ' Transact. Linn. Soc' vol. sxiii. 1862, p. 495. 



