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On The Generation Of Animals   

are sometimes female and sometimes male instead. For the female is, as
it were, a mutilated male, and the catamenia are semen, only not pure;
for there is only one thing they have not in them, the principle of
soul. For this reason, whenever a wind-egg is produced by any
animal, the egg so forming has in it the parts of both sexes
potentially, but has not the principle in question, so that it does
not develop into a living creature, for this is introduced by the
semen of the male. When such a principle has ben imparted to the
secretion of the female it becomes an embryo.

Liquid but corporeal substances become surrounded by some kind of
covering on heating, like the solid scum which forms on boiled foods
when cooling. All bodies are held together by the glutinous; this
quality, as the embryo develops and increases in size, is acquired
by the sinewy substance, which holds together the parts of animals,
being actual sinew in some and its analogue in others. To the same
class belong also skin, blood-vessels, membranes, and the like, for
these differ in being more or less glutinous and generally in excess
and deficiency.


In those animals whose nature is comparatively imperfect, when a
perfect embryo (which, however, is not yet a perfect animal) has
been formed, it is cast out from the mother, for reasons previously
stated. An embryo is then complete when it is either male or female,
in the case of those animals who possess this distinction, for some
(i.e. all those which are not themselves produced from a male or
female parent nor from a union of the two) produce an offspring which
is neither male nor female. Of the generation of these we shall
speak later.

The perfect animals, those internally viviparous, keep the
developing embryo within themselves and in close connexion until
they give birth to a complete animal and bring it to light.

A third class is externally viviparous but first internally
oviparous; they develop the egg into a perfect condition, and then
in some cases the egg is set free as with creatures externally
oviparous, and the animal is produced from the egg within the mother's
body; in other cases, when the nutriment from the egg is consumed,
development is completed by connection with the uterus, and
therefore the egg is not set free from the uterus. This character
marks the cartilaginous fish, of which we must speak later by

Here we must make our first start from the first class; these are
the perfect or viviparous animals, and of these the first is man.
Now the secretion of the semen takes place in all of them just as does
that of any other residual matter. For each is conveyed to its
proper place without any force from the breath or compulsion of any
other cause, as some assert, saying that the generative parts
attract the semen like cupping-glasses, aided by the force of the
breath, as if it were possible for either this secretion or the
residue of the solid and liquid nutriment to go anywhere else than
they do without the exertion of such a force. Their reason is that the
discharge of both is attended by holding the breath, but this is a
common feature of all cases when it is necessary to move anything,
because strength arises through holding the breath. Why, even
without this force the secretions or excretions are discharged in
sleep if the parts concerned are full of them and are relaxed. One
might as well say that it is by the breath that the seeds of plants
are always segregated to the places where they are wont to bear fruit.
No, the real cause, as has been stated already, is that there are

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