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On The Generation Of Animals   

whereas in the scolex, when the upper part has grown by taking up into
itself part of the substance in the lower part, the lower part is then
differentiated out of the rest. The reason is that in later life
also the nourishment is absorbed by all animals in the part below
the hypozoma.

That the scolex grows in this way is plain in the case of bees and
the like, for at first the lower part is large in them and the upper
is smaller. The details of growth in the testacea are similar. This is
plain in the whorls of the turbinata, for always as the animal grows
the whorls become larger towards the front and what is called the head
of the creature.

We have now pretty well described the manner of the development of
these and the other spontaneously generated animals. That all the
testacea are formed spontaneously is clear from such facts as these.
They come into being on the side of boats when the frothy mud
putrefies. In many places where previously nothing of the kind
existed, the so-called limnostrea, a kind of oyster, have come into
being when the spot turned muddy through want of water; thus when a
naval armament cast anchor at Rhodes a number of clay vessels were
thrown out into the sea, and after some time, when mud had collected
round them, oysters used to be found in them. Here is another proof
that such animals do not emit any generative substance from
themselves; when certain Chians carried some live oysters over from
Pyrrha in Lesbos and placed them in narrow straits of the sea where
tides clash, they became no more numerous as time passed, but
increased greatly in size. The so-called eggs contribute to generation
but are only a condition, like fat in the sanguinea, and therefore the
oysters are savoury at these periods. A proof that this substance is
not really eggs is the fact that such 'eggs' are always found in
some testacea, as in pinnae, whelks, and purple-fish; only they are
sometimes larger and sometimes smaller; in others as pectens, mussels,
and the so-called limnostrea, they are not always present but only
in the spring; as the season advances they dwindle and at last
disappear altogether; the reason being that the spring is favourable
to their being in good condition. In others again, as the ascidians,
nothing of the sort is visible. (The details concerning these last,
and the places in which they come into being, must be learnt from
the Enquiry.)

Book IV


WE have thus spoken of the generation of animals both generally
and separately in all the different classes. But, since male and
female are distinct in the most perfect of them, and since we say that
the sexes are first principles of all living things whether animals or
plants, only in some of them the sexes are separated and in others
not, therefore we must speak first of the origin of the sexes in the
latter. For while the animal is still imperfect in its kind the
distinction is already made between male and female.

It is disputed, however, whether the embryo is male or female, as
the case may be, even before the distinction is plain to our senses,
and further whether it is thus differentiated within the mother or
even earlier. It is said by some, as by Anaxagoras and other of the
physicists, that this antithesis exists from the beginning in the
germs or seeds; for the germ, they say, comes from the male while
the female only provides the place in which it is to be developed, and
the male is from the right, the female from the left testis, and so
also that the male embryo is in the right of the uterus, the female in
the left. Others, as Empedocles, say that the differentiation takes

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