1865.] 205 



The subject of divergence in secondary sexual characters in the sexes 

 of species is of the highest interest; the phenomena are extremely va- 

 ried and complicated and I know, have almost puzzled our great master 

 himself, Mr. Darwin. Mr. Wallace and myself read with great care 

 the excellent account given by Mr. Walsh in the Proceedings of the 

 Entomological Society of Philadelphia (Vol. I, p. 349), of the variety 

 Glaucus of Papilio Tarn us $ . Mr. Wallace is about to publish a 

 philosophical memoir in the Linnsean Transactions, on the Papiliones 

 of the Malay Archipelago, and will quote this article on Papilio Glau- 

 cus. It is one of the most interesting and difficult cases of sexual vari- 

 ation. Our Argynnis Paphia var. Valesiana, seems to form a parallel 

 case, but none of our European Entomologists have worked out the 

 geographical distribution as your Mr. Walsh has instructively done. 

 My views on this subject are at present somewhat hazy, but such as 

 they are I give you tbem as follows. 



I aaree with Mr. Darwin that the formation of a sexual distinction 

 in colors, form, ornament, &c. can be explained only on the principle 

 that he has applied to the origin of species. First, slight varieties arise 

 peculiar to one sex ; if these slight peculiarities give their possessors 

 any advantage in their life-career over their none-varying fraternity, 

 they survive dangers to which these latter are exposed and so leave 

 progeny when the others do not ; and this progeny by the laws of in- 

 heritance tends in successive generations to become more and more 

 true to the parental varietal type. Now the kinds of advantage pos- 

 sessed by sexual varieties, I believe, are resolvable into two. The first 

 (the only one mentioned by Darwin) is when the males possess orna- 

 mental plumage or gift of song or strength of tusk and spur — as in 

 Mammals and birds, which give the owners a superiority in competing 

 for the favors of the female or in fighting with other males. The process 

 of evolution of a striking male divergence, is the same as that which I 

 have mentioned above ; namely, slight varieties arise, and the most 

 advantageous ones survive and propagate their kind, whilst the others 

 die childless and so on until the complete male beauty remains as a 

 fixed form. The other kind of advantage, which has occurred to me 

 as existing in nature, is that of the possession of some peculiar color or 

 form or habit by one sex to enable it to escape dangers peculiar to itself 

 owing to its haunts being somewhat different from those of the opposite 

 sex. I believe the consideration of this will account for the strongly 

 marked female divergencies which are so common in Butterflies. T 

 doubt much whether a female variety is ever purely climatal, i. e. due 



