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On The Generation Of Animals   

trodden by another cock, the whole brood of chicks turn out like the
second cock. Hence some of those who are anxious to rear fine birds
act thus; they change the cocks for the first and second treading, not
as if they thought that the semen is mingled with the egg or exists in
it, or that it comes from all parts of the cock; for if it did it
would have come from both cocks, so that the chick would have all
its parts doubled. But it is by its force that the semen of the male
gives a certain quality to the material and the nutriment in the
female, for the second semen added to the first can produce this
effect by heat and concoction, as the egg acquires nutriment so long
as it is growing.

The same conclusion is to be drawn from the generation of
oviparous fishes. When the female has laid her eggs, the male spinkles
the milt over them, and those eggs are fertilized which it reaches,
but not the others; this shows that the male does not contribute
anything to the quantity but only to the quality of the embryo.

From what has been said it is plain that the semen does not come
from the whole of the body of the male in those animals which emit it,
and that the contribution of the female to the generative product is
not the same as that of the male, but the male contributes the
principle of movement and the female the material. This is why the
female does not produce offspring by herself, for she needs a
principle, i.e. something to begin the movement in the embryo and to
define the form it is to assume. Yet in some animals, as birds, the
nature of the female unassisted can generate to a certain extent,
for they do form something, only it is incomplete; I mean the
so-called wind-eggs.


For the same reason the development of the embryo takes place in the
female; neither the male himself nor the female emits semen into the
male, but the female receives within herself the share contributed
by both, because in the female is the material from which is made
the resulting product. Not only must the mass of material exist
there from which the embryo is formed in the first instance, but
further material must constantly be added that it may increase in
size. Therefore the birth must take place in the female. For the
carpenter must keep in close connexion with his timber and the
potter with his clay, and generally all workmanship and the ultimate
movement imparted to matter must be connected with the material
concerned, as, for instance, architecture is in the buildings it

From these considerations we may also gather how it is that the male
contributes to generation. The male does not emit semen at all in some
animals, and where he does this is no part of the resulting embryo;
just so no material part comes from the carpenter to the material,
i.e. the wood in which he works, nor does any part of the
carpenter's art exist within what he makes, but the shape and the form
are imparted from him to the material by means of the motion he sets
up. It is his hands that move his tools, his tools that move the
material; it is his knowledge of his art, and his soul, in which is
the form, that moves his hands or any other part of him with a
motion of some definite kind, a motion varying with the varying nature
of the object made. In like manner, in the male of those animals which
emit semen Nature uses the semen as a tool and as possessing motion in
actuality, just as tools are used in the products of any art, for in
them lies in a certain sense the motion of the art. Such, then, is the
way in which these males contribute to generation. But when the male
does not emit semen, but the female inserts some part of herself
into the male, this is parallel to a case in which a man should

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