518 THE DESCENT OE MAN. 



close relation within the same genus between a well -pro- 

 nounced difference in color between the sexes and the 

 nature of the nest constructed. Thus the male house- 

 sparrow {Passer domesticus) differs much from the female, 

 the male tree-sparrow {P. montanus) hardly at all, and yet 

 both build well-concealed nests. The two sexes of the 

 common fly-catcher {Muscicapa gr-isola) can hardly be 

 distinguished, while the sexes of the pied fly - catcher 

 (M. litctuosa) differ considerably, and both species build 

 in holes or conceal their nests. The female blackbird 

 {Turdus merula) differs much, the female ring-ouzel {T. 

 torquatus) dift'ers less, and the female common thrush 

 {T. musicus) hardly at all from their respective males; yet 

 all build open nests. On the other hand, the not very 

 distantly allied water-ouzel (Ciriclus aquaticus) builds a 

 domed nest, and the sexes differ about as much as in the 

 ring-ouzel. The black and red gvou^Q (Tetrao tetrix 2iiidi 

 T. scoticus) build open nests in equally well-concealed 

 spots, but in the one species the sexes differ greatly, and 

 in the other very little. 



Notwithstanding the foregoing objections, I cannot 

 doubt, after reading Mr. Wallace's excellent essay, that 

 looking to the birds of the world a large majority of the 

 species in which the females are conspicuously colored (and 

 in this case the males with rare exceptions are equally 

 conspicuous) build concealed nests for the sake of protec- 

 tion. Mr. Wallace enumerates* a long series of groups in 

 which this rule holds good; but it will suffice here to give 

 as instances the more familiar groups of kingfishers, tou- 

 cans, trogons, puff'-birds (Capitonidse), plantain - eaters 

 (Musophagae), woodpeckers and parrots. Mr. Wallace 

 believes that in these groups, as the males gradually ac- 

 quired through sexual selection their brilliant colors, these 

 were transferred to the females and were not eliminated by 

 natural selection owing to the protection which the already 

 enjoyed from their manner of nidification. According to 

 this view, their present manner of nestling was acquired 

 before their present colors. But it seems to me much 

 more probable that in most cases, as the females were 

 gradually rendered more and more brilliant from partaking 

 of the colors of the male, they were gradually led to change 



* "Journal of Travel," edited by A. Murray, vol. i, p. 78. 



