inches in length, which is embedded in the jaw; but sometimes, though
rarely, both are equally developed on the two sides. In the female both
are always rudimentary. The male cachalot has a larger head than that
of the female, and it no doubt aids him in his aquatic battles. Lastly,
the adult male ornithorhynchus is provided with a remarkable apparatus,
namely a spur on the foreleg, closely resembling the poison-fang of a
venomous snake; but according to Harting, the secretion from the gland
is not poisonous; and on the leg of the female there is a hollow,
apparently for the reception of the spur. (7. Owen on the cachalot and
Ornithorhynchus, ibid. vol. iii. pp. 638, 641. Harting is quoted by Dr.
Zouteveen in the Dutch translation of this work, vol. ii. p. 292.)
When the males are provided with weapons which in the females are
absent, there can be hardly a doubt that these serve for fighting with
other males; and that they were acquired through sexual selection, and
were transmitted to the male sex alone. It is not probable, at least in
most cases, that the females have been prevented from acquiring such
weapons, on account of their being useless, superfluous, or in some way
injurious. On the contrary, as they are often used by the males for
various purposes, more especially as a defence against their enemies,
it is a surprising fact that they are so poorly developed, or quite
absent, in the females of so many animals. With female deer the
development during each recurrent season of great branching horns, and
with female elephants the development of immense tusks, would be a
great waste of vital power, supposing that they were of no use to the
females. Consequently, they would have tended to be eliminated in the
female through natural selection; that is, if the successive variations
were limited in their transmission to the female sex, for otherwise the
weapons of the males would have been injuriously affected, and this
would have been a greater evil. On the whole, and from the
consideration of the following facts, it seems probable that when the
various weapons differ in the two sexes, this has generally depended on
the kind of transmission which has prevailed.
As the reindeer is the one species in the whole family of Deer, in
which the female is furnished with horns, though they are somewhat
smaller, thinner, and less branched than in the male, it might
naturally be thought that, at least in this case, they must be of some
special service to her. The female retains her horns from the time when
they are fully developed, namely, in September, throughout the winter
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