The Descent of Man

Again, 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 from end to end;
and these in the tail of the Paradisea apoda attain
a length of thirty-four inches (71. Wallace,
in 'Annals and Magazine of Natural History,'
vol. xx. 1857, p. 416, and in his 'Malay Archipelago,'
vol. ii. 1869, p. 390.): in P. Papuana (Fig.
47) they are much shorter and thin. 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 have been admired
by the female. The fact of the feathers in widely
distinct groups having been modified in an
analogous manner no doubt depends primarily
on all the feathers having nearly the same
structure and manner of development, and