206 TROPICAL NATUEE, AND OTHER ESSAYS. 



Mr. Darwin, which first shook my belief in sexual/' 

 or more properly female^' selection. The long series 

 of gradations, by which the beautifully shaded ocelli 

 on the secondary wing-feathers of this bird, have been 

 produced, are clearly traced out ; the result being a set 

 of markings, so exquisitely shaded as to represent 

 ''balls lying loose within sockets'' — purely artificial 

 objects of which these birds could have no possible 

 experience. That this result should have been attained 

 through thousands and tens of thousands of female 

 birds all preferring those males whose markings varied 

 slightly in this one direction, this uniformity of choice 

 continuing through thousands and tens of thousands of 

 generations, is to me absolutely incredible. And when, 

 further, we remember that those which did not so vary, 

 would also, according to all the evidence, find mates and 

 leave ofi*spring, the actual result seems quite impossible 

 of attainment by such means. 



Without pretending to solve completely so difiicult a 

 problem as that of the origin and uses of the variously 

 coloured plumes and ornaments so often possessed by 

 male birds, I would point out a few facts which seem 

 to afi'ord a clue. And first, the most highly-coloured 

 and most richly- varied markings occur on those parts 

 of the plumage which have undergone the greatest 

 modification, or have acquired the most abnormal de- 

 velopment. In the peacock, the tail- coverts are enor- 

 mously developed, and the eyes " are situated on the 

 greatly dilated ends. In the birds-of-paradise, breast, 

 or neck, or head, or tail-feathers, are greatly developed 

 and highly coloured. The hackles of the cock, and the 

 scaly breasts of humming-birds are similar developments ; 



