expanded makes quite a grand appearance. (63. Mr. Monteiro, Ibis,
vol. iv. 1862, p. 339.) Even the iris of the eye is sometimes more
brightly-coloured in the male than in the female; and this is
frequently the case with the beak, for instance, in our common
blackbird. In Buceros corrugatus, the whole beak and immense casque are
coloured more conspicuously in the male than in the female; and the
oblique grooves upon the sides of the lower mandible are peculiar to
the male sex. (64. 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 (65. Ueber die Schadelhocker, etc., Niederland.
Archiv. fur Zoologie, B. I. Heft 2, 1872.), 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. (66. Dr.
W. Marshall, Uber den Vogelschwanz, ibid. B. I. Heft 2, 1872.) 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 (67. Jardine s Naturalist Library: Birds, vol.
xiv. p. 166.), 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. (68. Sclater, in the Ibis,
vol. vi. 1864, p. 114; Livingstone, Expedition to the Zambesi, 1865,
408