74 SEXUAL SELECTION : BIRDS. Part IL 



The barbs of the feathers in various widely-distinct 

 birds are filamentous or plumose, as with some Herons, 

 Ibises, Birds of Paradise and Gallinaceae. In other 

 cases the barbs disappear, leaving the shafts bare ; and 

 these in the tail of the Paradisea ajooda attain a length 

 of thirty-four inches.^^ Smaller feathers when thus 

 denuded appear like bristles, as on the breast of the 

 turkey-cock. As any fleeting fashion in dress comes 

 to be admired by man, so with birds a change of 

 almost any kind in the structure or colouring of the 

 feathers in the male appears to liave been admired by 

 the female. The fact of the feathers in widely dis- 

 tinct groups, having been modified in an analogous 

 manner, no doubt depends primarily on all the feathers 

 having nearly the same structure and manner of deve- 

 lopment, and consequently tending to vary in the same 

 manner. We often see a tendency to analogous varia- 

 bility in the plumage of our domestic breeds belonging 

 to distinct species. Thus top-knots have appeared in 

 several species. In an extinct variety of tlie turkey, 

 the top-knot consisted of bare quills surmounted with 

 plumes of down, so that they resembled, to a certain 

 extent, the racket-shaped feathers above described. In 

 certain breeds of the pigeon and fowl the feathers are 

 plumose, with some tendency in the shafts to be naked. 

 In the Sebastopol goose the scapular feathers are greatly 

 elongated, curled, or even spirally twisted, with the 

 margins plumose.®^ 



In regard to colour hardly anything need here be 

 said ; for every one knows how s]3lendid are the tints 



66 Wallace, in 'Annals and Mag. of Nat. Hist.' vol. xx. 1857, p. 416 

 and in liis ' Malay Archipelago,' vol. ii. 1869, p. o*J0. 



6' See my ^vork on 'The Variation of Animals and Plants under 

 Domestication,' vol. i. p. 289, 293. 



