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On The Generation Of Animals   

of hot air in it because of the internal heat; afterwards, when the
heat has evaporated and the air has cooled, it turns liquid and
dark; for the water, and any small quantity of earthy matter there may
be, remain in semen as it dries, as they do in phlegm.

Semen, then, is a compound of spirit (pneuma) and water, and the
former is hot air (aerh); hence semen is liquid in its nature
because it is made of water. What Ctesias the Cnidian has asserted
of the semen of elephants is manifestly untrue; he says that it
hardens so much in drying that it becomes like amber. But this does
not happen, though it is true that one semen must be more earthy
than another, and especially so with animals that have much earthy
matter in them because of the bulk of their bodies. And it is thick
and white because it is mixed with spirit, for it is also an
invariable rule that it is white, and Herodotus does not report the
truth when he says that the semen of the Aethiopians is black, as if
everything must needs be black in those who have a black skin, and
that too when he saw their teeth were white. The reason of the
whiteness of semen is that it is a foam, and foam is white, especially
that which is composed of the smallest parts, small in the sense
that each bubble is invisible, which is what happens when water and
oil are mixed and shaken together, as said before. (Even the ancients
seem to have noticed that semen is of the nature of foam; at least
it was from this they named the goddess who presides over union.)

This then is the explanation of the problem proposed, and it is
plain too that this is why semen does not freeze; for air will not


The next question to raise and to answer is this. If, in the case of
those animals which emit semen into the female, that which enters
makes no part of the resulting embryo, where is the material part of
it diverted if (as we have seen) it acts by means of the power
residing in it? It is not only necessary to decide whether what is
forming in the female receives anything material, or not, from that
which has entered her, but also concerning the soul in virtue of which
an animal is so called (and this is in virtue of the sensitive part
of the soul)- does this exist originally in the semen and in the
unfertilized embryo or not, and if it does whence does it come? For
nobody would put down the unfertilized embryo as soulless or in
every sense bereft of life (since both the semen and the embryo of an
animal have every bit as much life as a plant), and it is
productive up to a certain point. That then they possess the nutritive
soul is plain (and plain is it from the discussions elsewhere about
soul why this soul must be acquired first). As they develop they also
acquire the sensitive soul in virtue of which an animal is an
animal. For e.g. an animal does not become at the same time an
animal and a man or a horse or any other particular animal. For the
end is developed last, and the peculiar character of the species is
the end of the generation in each individual. Hence arises a
question of the greatest difficulty, which we must strive to solve
to the best of our ability and as far as possible. When and how and
whence is a share in reason acquired by those animals that participate
in this principle? It is plain that the semen and the unfertilized
embryo, while still separate from each other, must be assumed to
have the nutritive soul potentially, but not actually, except that
(like those unfertilized embryos that are separated from the mother)

it absorbs nourishment and performs the function of the nutritive
soul. For at first all such embryos seem to live the life of a
plant. And it is clear that we must be guided by this in speaking of
the sensitive and the rational soul. For all three kinds of soul,

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