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On The Generation Of Animals   


and the matter (or body) which contains the life being included
within it.

The class of snails is the only class of such creatures that has
been seen uniting, but it has never yet been sufficiently observed
whether their generation is the result of the union or not.

It may be asked, if we wish to follow the right line of
investigation, what it is in such animals the formation of which
corresponds to the material principle. For in the females this is a
residual secretion of the animal, potentially such as that from
which it came, by imparting motion to which the principle derived from
the male perfects the animal. But here what must be said to correspond
to this, and whence comes or what is the moving principle which
corresponds to the male? We must understand that even in animals which
generate it is from the incoming nourishment that the heat in the
animal makes the residue, the beginning of the conception, by
secretion and concoction. The like is the case also in plants,
except that in these (and also in some animals) there is no
further need of the male principle, because they have it mingled
with the female principle within themselves, whereas the residual
secretion in most animals does need it. The nourishment again of
some is earth and water, of others the more complicated combinations
of these, so that what the heat in animals produces from their
nutriment, this does the heat of the warm season in the environment
put together and combine by concoction out of the sea-water on the
earth. And the portion of the psychical principle which is either
included along with it or separated off in the air makes an embryo and
puts motion into it. Now in plants which are spontaneously generated
the method of formation is uniform; they arise from a part of
something, and while some of it is the starting-point of the plant,
some is the first nourishment of the young shoots.... Other animals
are produced in the form of a scolex, not only those bloodless animals
which are not generated from parents but even some sanguinea, as a
kind of mullet and some other river fishes and also the eel kind.
For all of these, though they have but little blood by nature, are
nevertheless sanguinea, and have a heart with blood in it as the
origin of the parts; and the so-called 'entrails of earth', in which
comes into being the body of the eel, have the nature of a scolex.

Hence one might suppose, in connexion with the origin of men and
quadrupeds, that, if ever they were really 'earth-born' as some say,
they came into being in one of two ways; that either it was by the
formation of a scolex at first or else it was out of eggs. For
either they must have had in themselves the nutriment for growth (and
such a conception is a scolex) or they must have got it from
elsewhere, and that either from the mother or from part of the
conception. If then the former is impossible (I mean that nourishment
should flow to them from the earth as it does in animals from the
mother), then they must have got it from some part of the conception,
and such generation we say is from an egg.

It is plain then that, if there really was any such beginning of the
generation of all animals, it is reasonable to suppose to have been
one of these two, scolex or egg. But it is less reasonable to
suppose that it was from eggs, for we do not see such generation
occurring with any animal, but we do see the other both in the
sanguinea above mentioned and in the bloodless animals. Such are
some of the insects and such are the testacea which we are discussing;
for they do not develop out of a part of something (as do animals
from eggs), and they grow like a scolex. For the scolex grows towards
the upper part and the first principle, since in the lower part is the
nourishment for the upper. And this resembles the development of
animals from eggs, except that these latter consume the whole egg,

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