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On The Generation Of Animals   

female generative organs. The passage of the solid food also has
been closed before now in sheep and some other animals; there was a
cow in Perinthus which passed fine matter, as if it were sifted,
through the bladder, and when the anus was cut open it quickly
closed up again nor could they succeed in keeping it open.

We have now spoken of the production of few and many young, and of
the outgrowth of superfluous parts or of their deficiency, and also of


Superfoetation does not occur at all in some animals but does in
others; of the former some are able to bring the later formed embryo
to birth, while others can only do so sometimes. The reason why it
does not occur in some is that they produce only one young one, for it
is not found in solid-hoofed animals and those larger than these, as
owing to their size the secretion of the female is all used up for the
one embryo. For all these have large bodies, and when an animal is
large its foetus is large in proportion, e.g. the foetus of the
elephant is as big as a calf. But superfoetation occurs in those which
produce many young because the production of more than one at a
birth is itself a sort of superfoetation, one being added to
another. Of these all that are large, as man, bring to birth the later
embryo, if the second impregnation takes place soon after the first,
for such an event has been observed before now. The reason is that
given above, for even in a single act of intercourse the semen
discharged is more than enough for one embryo, and this being
divided causes more than one child to be born, the one of which is
later than the other. But when the embryo has already grown to some
size and it so happens that copulation occurs again, superfoetation
sometimes takes place, but rarely, since the uterus generally closes
in women during the period of gestation. If this ever happens (for
this also has occurred) the mother cannot bring the second embryo
to perfection, but it is cast out in a state like what are called
abortions. For just as, in those animals that bear only one, all the
secretion of the female is converted to the first formed embryo
because of its size, so it is here also; the only difference is that
in the former case this happens at once, in the latter when the foetus
has attained to some size, for then they are in the same state as
those that bear only one. In like manner, since man naturally would
produce many young, and since the size of the uterus and the
quantity of the female secretion are both greater than is necessary
for one embryo, only not so much so as to bring to birth a second,
therefore women and mares are the only animals which admit the male
during gestation, the former for the reason stated, and mares both
because of the barrenness of their nature and because their uterus
is of superfluous size, too large for one but too small to allow a
second embryo to be brought to perfection by superfoetation. And the
mare is naturally inclined to sexual intercourse because she is in the
same case as the barren among women; these latter are barren because
they have no monthly discharge (which corresponds to the act of
intercourse in males) and mares have exceedingly little. And in all
the vivipara the barren females are so inclined, because they resemble
the males when the semen has collected in the testes but is not
being got rid of. For the discharge of the catamenia is in females a
sort of emission of semen, they being unconcocted semen as has been
said before. Hence it is that those women also who are incontinent
in regard to such intercourse cease from their passion for it when
they have borne many children, for, the seminal secretion being then
drained off, they no longer desire this intercourse. And among birds
the hens are less disposed that way than the cocks, because the uterus
of the hen-bird is up near the hypozoma; but with the cock-birds it is
the other way, for their testes are drawn up within them, so that,

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