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On The Generation Of Animals   

earth, to get nourishment, until it is perfected to the point of being
now an animal potentially locomotive. So Nature has first designed the
two blood-vessels from the heart, and from these smaller vessels
branch off to the uterus. These are what is called the umbilicus,
for this is a blood-vessel, consisting of one or more vessels in
different animals. Round these is a skin-like integument, because
the weakness of the vessels needs protection and shelter. The
vessels join on to the uterus like the roots of plants, and through
them the embryo receives its nourishment. This is why the animal
remains in the uterus, not, as Democritus says, that the parts of
the embryo may be moulded in conformity with those of the mother. This
is plain in the ovipara, for they have their parts differentiated in
the egg after separation from the matrix.

Here a difficulty may be raised. If the blood is the nourishment,
and if the heart, which first comes into being, already contains
blood, and the nourishment comes from outside, whence did the first
nourishment enter? Perhaps it is not true that all of it comes from
outside just as in the seeds of plants there is something of this
nature, the substance which at first appears milky, so also in the
material of the animal embryo the superfluous matter of which it is
formed is its nourishment from the first.

The embryo, then, grows by means of the umbilicus in the same way as
a plant by its roots, or as animals themselves when separated from the
nutriment within the mother, of which we must speak later at the
time appropriate for discussing them. But the parts are not
differentiated, as some suppose, because like is naturally carried
to like. Besides many other difficulties involved in this theory, it
results from it that the homogeneous parts ought to come into being
each one separate from the rest, as bones and sinews by themselves,
and flesh by itself, if one should accept this cause. The real cause
why each of them comes into being is that the secretion of the
female is potentially such as the animal is naturally, and all the
parts are potentially present in it, but none actually. It is also
because when the active and the passive come in contact with each
other in that way in which the one is active and the other passive (I
mean in the right manner, in the right place, and at the right time),
straightway the one acts and the other is acted upon. The female,
then, provides matter, the male the principle of motion. And as the
products of art are made by means of the tools of the artist, or to
put it more truly by means of their movement, and this is the activity
of the art, and the art is the form of what is made in something else,
so is it with the power of the nutritive soul. As later on in the case
of mature animals and plants this soul causes growth from the
nutriment, using heat and cold as its tools (for in these is the
movement of the soul), and each thing comes into being in
accordance with a certain formula, so also from the beginning does
it form the product of nature. For the material by which this latter
grows is the same as that from which it is constituted at first;
consequently also the power which acts upon it is identical with
that which originally generated it; if then this acting power is the
nutritive soul, this is also the generative soul, and this is the
nature of every organism, existing in all animals and plants. [But
the other parts of the soul exist in some animals, not in others.] In
plants, then, the female is not separated from the male, but in
those animals in which it is separated the male needs the female


And yet the question may be raised why it is that, if indeed the
female possesses the same soul and if it is the secretion of the
female which is the material of the embryo, she needs the male besides

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