Tusks and horns are manifestly of high importance to their possessors,
for their development consumes much organised matter. A single tusk of
the Asiatic elephant one of the extinct woolly species and of the
African elephant, have been known to weigh respectively 150, 160, and
180 pounds; and even greater weights have been given by some authors.
(33. Emerson Tennent, Ceylon, 1859, vol. ii. p. 275; Owen, British
Fossil Mammals, 1846, p. 245.) With deer, in which the horns are
periodically renewed, the drain on the constitution must be greater;
the horns, for instance, of the moose weigh from fifty to sixty pounds,
and those of the extinct Irish elk from sixty to seventy pounds the
skull of the latter weighing on an average only five pounds and a
quarter. Although the horns are not periodically renewed in sheep, yet
their development, in the opinion of many agriculturists, entails a
sensible loss to the breeder. Stags, moreover, in escaping from beasts
of prey are loaded with an additional weight for the race, and are
greatly retarded in passing through a woody country. The moose, for
instance, with horns extending five and a half feet from tip to tip,
although so skilful in their use that he will not touch or break a twig
when walking quietly, cannot act so dexterously whilst rushing away
from a pack of wolves. During his progress he holds his nose up, so as
to lay the horns horizontally back; and in this attitude cannot see the
ground distinctly. (34. Richardson, Fauna Bor. Americana, on the
moose, Alces palmata, pp. 236, 237; on the expanse of the horns, Land
and Water, 1869, p. 143. See also Owen, British Fossil Mammals, on
the Irish elk, pp. 447, 455.) The tips of the horns of the great Irish
elk were actually eight feet apart! Whilst the horns are covered with
velvet, which lasts with red-deer for about twelve weeks, they are
extremely sensitive to a blow; so that in Germany the stags at this
time somewhat change their habits, and avoiding dense forests, frequent
young woods and low thickets. (35. Forest Creatures, by C. Boner,
1861, p. 60.) These facts remind us that male birds have acquired
ornamental plumes at the cost of retarded flight, and other ornaments
at the cost of some loss of power in their battles with rival males.
With mammals, when, as is often the case, the sexes differ in size, the
males are almost always larger and stronger. I am informed by Mr. Gould
that this holds good in a marked manner with the marsupials of
Australia, the males of which appear to continue growing until an
unusually late age. But the most extraordinary case is that of one of
the seals (Callorhinus ursinus), a full-grown female weighing less than
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