ion, the bearing of
which has been almost entirely overlooked by writers on both sides of
this question. One of the most general external characters of the
terrestrial mammalia is the hairy covering of the body, which, whenever
the skin is flexible, soft, and sensitive, forms a natural protection
against the severities of climate, and particularly against rain. That
this is its most important function, is well shown by the manner in
which the hairs are disposed so as to carry off the water, by being
invariably directed downwards from the most elevated parts of the body.
Thus, on the under surface the hair is always less plentiful, and, in
many cases, the belly is almost bare. The hair lies downwards, on the
limbs of all walking mammals, from the shoulder to the toes, but in the
orang-utan it is directed from the shoulder to the elbow, and again from
the wrist to the elbow, in a reverse direction. This corresponds to the
habits of the animal, which, when resting, holds its long arms upwards
over its head, or clasping a branch above it, so that the rain would
flow down both the arm and fore-arm to the long hair which meets at the
elbow. In accordance with this principle, the hair is always longer or
more dense along the spine or middle of the back from the nape to the
tail, often rising into a crest of hair or bristles on the ridge of the
back. This character prevails through the entire series of the mammalia,
from the marsupials to the quadrumana, and by this long persistence it
must have acquired such a powerful hereditary tendency, that we should
expect it to reappear continually even after it had been abolished by
ages of the most rigid selection; and we may feel sure that it never
could have been completely abolished under the law of natural selection,
unless it had become so positively injurious as to lead to the almost
invariable extinction of individuals possessing it.

_The constant absence of Hair from certain parts of Man's Body a
remarkable Phenomenon._

In man the hairy covering of the body has almost totally disappeared,
and, what is very remarkable, it has disappeared more completely from
the back than from any other part of the body. Bearded and beardless
races alike have the back smooth, and even when a considerable quantity
of hair appears on the limbs and breast, the back, and especially the
spinal region, is absolutely free, thus completely reversing the
characteristics of all other mammalia. The Ai