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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2925 times)
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« Reply #135 on: February 09, 2009, 03:13:02 pm »

* See remarks to this effect, on the "Feeling of Beauty among
Animals," by Mr. J. Shaw, in the Athenaeum, Nov. 24, 1866, p. 681.
  *(2) See Dr. Murie's account with coloured figures in Proceedings,
Zoological Society, 1872, p. 730.
  *(3) Mr. Monteiro, Ibis, vol. iv., 1862, p. 339.
  *(4) Land and Water, 1868, p. 217.

  The head, again, often supports fleshy appendages, filaments, and
solid protuberances. These, if not common to both sexes, are always
confined to the males. The solid protuberances have been described
in detail by Dr. W. Marshall,* who shews that they are formed either
of cancellated bone coated with skin, or of dermal and other
tissues. With mammals true horns are always supported on the frontal
bones, but with birds various bones have been modified for this
purpose; and in species of the same group the protuberances may have
cores of bone, or be quite destitute of them, with intermediate
gradations connecting these two extremes. Hence, as Dr. Marshall
justly remarks, variations of the most different kinds have served for
the development through sexual selection of these ornamental
appendages. Elongated feathers or plumes spring from almost every part
of the body. The feathers on the throat and breast are sometimes
developed into beautiful ruffs and collars. The tail-feathers are
frequently increased in length; as we see in the tail-coverts of the
peacock, and in the tail itself of the Argus pheasant. With the
peacock even the bones of the tail have been modified to support the
heavy tail-coverts.*(2) The body of the Argus is not larger than
that of a fowl; yet the length from the end of the beak to the
extremity of the tail is no less than five feet three inches,*(3)
and that of the beautifully ocellated secondary wing-feathers nearly
three feet. In a small African night-jar (Cosmetornis vexillarius) one
of the primary wing-feathers, during the breeding-season, attains a
length of twenty-six inches, whilst the bird itself is only ten inches
in length. In another closely-allied genus of night-jars, the shafts
of the elongated wing-feathers are naked, except at the extremity,
where there is a disc.*(4) Again, in another genus of night-jars,
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 closely-allied birds ornaments of the same kind
have been gained by the males through the development of widely
different feathers.

  * "Uber die Schadelhocker," Niederland. Archiv. fur Zoologie, B. i.,
Heft 2, 1872.
  *(2) Dr. W. Marshall, "Uber den Vogelschwanz," ibid., B. i., Heft 2,
  *(3) Jardine's Naturalist Library: Birds, vol. xiv., p. 166.
  *(4) Sclater, in the Ibis, vol. vi., 1864, p. 114; Livingstone,
Expedition to the Zambesi, 1865, p. 66.

  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. Feathers of this kind occur in the tail of a motmot
(Eumomota superciliaris), of a king-fisher, finch, humming-bird,
parrot, several Indian drongos (Dicrurus and Edolius, in one of
which the disc stands vertically), and in the tail of certain birds of
paradise. In these latter birds, similar feathers, beautifully
ocellated, ornament the head, as is likewise the case with some
gallinaceous birds. In an Indian bustard (Sypheotides auritus) the
feathers forming the ear-tufts, which are about four inches in length,
also terminate in discs.* It is a most singular fact that the motmots,
as Mr. Salvin has clearly shown,*(2) give to their tail feathers the
racket-shape by biting off the barbs, and, further, that this
continued mutilation has produced a certain amount of inherited

  * Jerdon, Birds of India, vol. iii., p. 620.
  *(2) Proceedings, Zoological Society, 1873, p. 429.

  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:* in P.
Papuana (see fig. 47) they are much shorter and thin. Smaller feathers
when thus denuded appear like bristles, as on the breast of the
turkey-****. 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 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.*(2)

  * Wallace, in Annals and Magazine of Natural History, vol. xx.,
1857, p. 416, and in his Malay Archipelago, vol. ii., 1869, p. 390.
  *(2) See my work on The Variation of Animals and Plants under
Domestication, vol. i., pp. 289, 293.
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