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 consequently tending to vary
in the same manner. We often see a tendency to analogous variability in
the plumage of our domestic breeds belonging to distinct species. Thus
top-knots have appeared in several species. In an extinct variety of
the turkey, the top-knot consisted of bare quills surmounted with
plumes of down, so that they somewhat resembled 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. (72. See my
work on The Variation of Animals and Plants under Domestication, vol.
i. pp. 289, 293.)
In regard to colour, hardly anything need here be said, for every one
knows how splendid are the tints of many birds, and how harmoniously
they are combined. The colours are often metallic and iridescent.
Circular spots are sometimes surrounded by one or more differently
shaded zones, and are thus converted into ocelli. Nor need much be said
on the wonderful difference between the sexes of many birds. The common
peacock offers a striking instance. Female birds of paradise are
obscurely coloured and destitute of all ornaments, whilst the males are
probably the most highly decorated of all birds, and in so many
different ways that they must be seen to be appreciated. The elongated
and golden-orange plumes which spring from beneath the wings of the
Paradisea apoda, when vertically erected and made to vibrate, are
described as forming a sort of halo, in the centre of which the head
looks like a little emerald sun with its rays formed by the two
plumes. (73. Quoted from M. de Lafresnaye in Annals and Mag. of
Natural History, vol. xiii. 1854, p. 157: see also Mr. Wallace s much
fuller account in vol. xx. 1857, p. 412, and in his Malay
Archipelago. ) In another most beautiful species the head is bald, and
of a rich cobalt blue, crossed by several lines of black velvety
feathers. (74. Wallace, The Malay Archipelago, vol. ii. 1869, p.
405.)
[Fig. 48. Lophornis ornatus, male and female (from Brehm).
Fig. 49. Spathura underwoodi, male and female (from Brehm).]
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