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On The Generation Of Animals   

a whole not to have one colour only, the kind being easily moved in
both directions so that the colours both change more into one
another and are more varied. The opposite holds with the uniformly
coloured; they do not change except by an affection of the colour, and
that rarely; but still they do so change, for before now white
individuals have been observed among partridges, ravens, sparrows, and
bears. This happens when the course of development is perverted, for
what is small is easily spoilt and easily moved, and what is
developing is small, the beginning of all such things being on a small

Change is especially found in those animals of which by nature the
individual is whole-coloured but the kind many-coloured. This is owing
to the water which they drink, for hot waters make the hair white,
cold makes it dark, an effect found also in plants. The reason is that
the hot have more air than water in them, and the air shining
through causes whiteness, as also in froth. As, then, skins which
are white by reason of some affection differ from those white by
nature, so also in the hair the whiteness due to disease or age
differs from that due to nature in that the cause is different; the
latter are whitened by the natural heat, the former by the external
heat. Whiteness is caused in all things by the vaporous air imprisoned
in them. Hence also in all animals not uniformly coloured all the part
under the belly is whiter. For practically all white animals are
both hotter and better flavoured for the same reason; the concoction
of their nutriment makes them well-flavoured, and heat causes the
concoction. The same cause holds for those animals which are
uniformly-coloured, but either dark or white; heat and cold are the
causes of the nature of the skin and hair, each of the parts having
its own special heat.

The tongue also varies in colour in the simply coloured as
compared with the vari-coloured animals, and again in the simply
coloured which differ from one another, as white and dark. The
reason is that assigned before, that the skins of the vari-coloured
are vari-coloured, and the skins of the white-haired and dark-haired
are white and dark in each case. Now we must conceive of the tongue as
one of the external parts, not taking into account the fact that it is
covered by the mouth but looking on it as we do on the hand or foot;
thus since the skin of the vari-coloured animals is not uniformly
coloured, this is the cause of the skin on the tongue being also

Some birds and some wild quadrupeds change their colour according to
the seasons of the year. The reason is that, as men change according
to their age, so the same thing happens to them according to the
season; for this makes a greater difference to them than the change of

The more omnivorous animals are more vari-coloured to speak
generally, and this is what might be expected; thus bees are more
uniformly coloured than hornets and wasps. For if the food is
responsible for the change we should expect varied food to increase
the variety in the movements which cause the development and so in the
residual matter of the food, from which come into being hairs and
feathers and skins.

So much for colours and hairs.


As to the voice, it is deep in some animals, high in others, in
others again well-pitched and in due proportion between both extremes.
Again, in some it is loud, in others small, and it differs in

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