60 MAN [Chap. VIII 



Letter 429 from you. But, as I am sure from your greater knowledge 

 of Ornithology and Entomology that you will write a much 

 better discussion than I could, your paper will be of great 

 use to me. Nevertheless I must discuss the subject fully 

 in my Essay on Man. When we met at the Zoological 

 Society, and I asked you about the sexual differences in 

 kingfishers, I had this subject in view ; as I had when I 

 suggested to Bates the difficulty about gaudy caterpillars, 

 which you have so admirably (as I believe it will prove) 

 explained. 1 I have got one capital case (genus forgotten) of 

 a [Australian] bird in which the female has long tail-plumes, 

 and which consequently builds a different nest from all her 

 allies. 2 With respect to certain female birds being more 

 brightly coloured than the males, and the latter incubating, 

 I have gone a little into the subject, and cannot say that 

 1 am fully satisfied. I remember mentioning to you the 

 case of RhyncJioca, but its nesting seems unknown. In some 

 other cases the difference in brightness seemed to me hardly 

 sufficiently accounted for by the principle of protection. 

 At the Falkland Islands there is a carrion hawk in which 

 the female (as I ascertained by dissection) is the brightest 

 coloured, and I doubt whether protection will here apply ; 

 but I wrote several months ago to the Falklands to make 

 enquiries. The conclusion to which I have been leaning 

 is that in some of these abnormal cases the colour happened 

 to vary in the female alone, and was transmitted to females 

 alone, and that her variations have been selected through 

 the admiration of the male. 



It is a very interesting subject, but I shall not be able 

 to go on with it for the next five or six months, as I am 

 fully employed in correcting dull proof-sheets. When I 

 return to the work I shall find it much better done by you 

 than I could have succeeded in doing. 



1 See a letter of Feb. 26th, 1867, to Mr. Wallace, Life and Letters III., 

 p. 94. 



2 Menura superba: see Descent of Man (1901), p. 687. Rkynchcea, 

 mentioned a line or two lower down, is discussed in the Descent, 

 p. 727. The female is more brightly coloured than the male, and has 

 a convoluted trachea, elsewhere a masculine character. There seems 

 some reason to suppose that " the male undertakes the duty of 

 incubation." 



