366 THE DESCENT OF MAN. 



she has simply retained to a large extent her primordial 

 colors. 



Finally, as we have seen, various considerations lead to the 

 conclusion that with the greater number of brilliantly col- 

 ored Lepidoptera it is the male which has been chiefly 

 modified through sexual selection; the amount of difference 

 between the sexes mostly depending on the form of inherit- 

 ance which has prevailed. Inheritance is governed by so 

 many unknown laws or conditions that it seems to us to act 

 in a capricious manner;* and we can thus, to a certain ex- 

 tent, understand how it is that with closely allied species 

 the sexes either differ to an astonishing degree, or are iden- 

 tical in color. As all the successive steps in the process of 

 variation are necessarily transmitted through the female, a 

 greater or less number of such steps might readily become 

 developed in her; and thus we can understand the frequent 

 gradations from an extreme difference to none at all between 

 the sexes of allied species. These cases of gradation, it 

 may be added, are much too common to favor the supposi- 

 tion that we here see females actually 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. 



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

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

 light on many obscure problems. It had previously been 

 observed that certain butterflies in South America belong- 

 ing to quite distinct families resembled the Heliconidae so 

 closely in every stripe and shade of color that they could 

 not be distinguished save by an experienced entomologist. 

 As the Heliconidae are colored in their usual manner, while 

 the others depart from the usual coloring of the groups to 

 which they belong, it is clear that the latter are the imi- 

 tators, and the Heliconidae the imitated. Mr. Bates further 

 observed that the imitating species are comparatively rare, 

 while the imitated abound, and that the two sets live min- 

 gled together. From the fact of the Heliconidae being 



* " The Variation of Animals and Plants under Domestication," vol. 

 ii, chap, xii, p. 17. 

 f " Transact. Linn. Soc.," vol. xxiii, 1862, p. 495. 



