The Descent of Man

length. In another closely-allied genus of nightjars,
the shafts of the elongated wing-feathers
are naked, except at the extremity, where there
is a disc. (68. Sclater, in the 'Ibis,' vol. vi. 1864, p.
114; Livingstone, 'Expedition to the Zambesi,'
1865, p. 66.) Again, in another genus of nightjars,
the tail-feathers are even still more prodigiously
developed. In general the feathers of
the tail are more often elongated than those of
the wings, as any great elongation of the latter
impedes flight. We thus see that in closelyallied
birds ornaments of the same kind have
been gained by the males through the development
of widely different feathers.
It is a curious fact that the feathers of species
belonging to very distinct groups have been
modified in almost exactly the same peculiar
manner. Thus the wing-feathers in one of the
above-mentioned night-jars are bare along the
shaft, and terminate in a disc; or are, as they are
sometimes called, spoon or racket-shaped. Feat-