The workmanship of Nature is admirable also in the seal, for
though a viviparous quadruped it has no ears but only passages for
hearing. This is because its life is passed in the water; now the
ear is a part added to the passages to preserve the movement of the
air at a distance; therefore an ear is no use to it but would even
bring about the contrary result by receiving a mass of water into
itself.
We have thus spoken of sight, hearing, and smell.
3
As for hair, men differ in this themselves at different ages, and
also from all other kinds of animals that have hair. These are
almost all which are internally viviparous, for even when the covering
of such animals is spiny it must be considered as a kind of hair, as
in the land hedgehog and any other such animal among the vivipara.
Hairs differ in respect of hardness and softness, length and
shortness, straightness and curliness, quantity and scantiness, and in
addition to these qualities, in their colours, whiteness and blackness
and the intermediate shades. They differ also in some of these
respects according to age, as they are young or growing old. This is
especially plain in man; the hair gets coarser as time goes on, and
some go bald on the front of the head; children indeed do not go bald,
nor do women, but men do so by the time their age is advancing.
Human beings also go grey on the head as they grow old, but this is
not visible in practically any other animal, though more so in the
horse than others.
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