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On The Generation Of Animals   

reflected part of the duct in man and similar animals.


Serpents copulate twining round one another, and, as said above,
have neither testes nor penis, the latter because they have no legs,
the former because of their length, but they have ducts like for on
account of their extreme length the seminal fluid would take too
long in its passage and be cooled if it were further delayed by
testes. (This happens also if the penis is large; such men are less
fertile than when it is smaller because the semen, if cold, is not
generative, and that which is carried too far is cooled.) So much for
the reason why some animals have testes and others not. Serpents
intertwine because of their inaptitude to cast themselves alongside of
one another. For they are too long to unite closely with so small a
part and have no organs of attachment, so they make use of the
suppleness of their bodies, intertwining. Wherefore also they seem
to be slower in copulation than fish, not only on account of the
length of the ducts but also of this elaborate arrangement in uniting.


It is not easy to state the facts about the uterus in female
animals, for there are many points of difference. The vivipara are not
alike in this part; women and all the vivipara with feet have the
uterus low down by the pudendum, but the cartilaginous viviparous fish
have it higher up near the hypozoma. In the ovipara, again, it is
low in fish (as in women and the viviparous quadrupeds), high in
birds and all oviparous quadrupeds. Yet even these differences are
on a principle. To begin with the ovipara, they differ in the manner
of laying their eggs, for some produce them imperfect, as fishes whose
eggs increase and are finally developed outside of them. The reason is
that they produce many young, and this is their function as it is with
plants. If then they perfected the egg in themselves they must needs
be few in number, but as it is, they have so many that each uterus
seems to be an egg, at any rate in the small fishes. For these are the
most productive, just as with the other animals and plants whose
nature is analogous to theirs, for the increase of size turns with
them to seed.

But the eggs of birds and the quadrupedal ovipara are perfect when
produced. In order that these may be preserved they must have a hard
covering (for their envelope is soft so long as they are increasing
in size), and the shell is made by heat squeezing out the moisture
for the earthy material; consequently the place must be hot in which
this is to happen. But the part about the hypozoma is hot, as is shown
by that being the part which concocts the food. If then the eggs
must be within the uterus, then the uterus must be near the hypozoma
in those creatures which produce their eggs in a perfect form.
Similarly it must be low down in those which produce them imperfect,
for it is profitable that it should be so. And it is more natural
for the uterus to be low down than high up, when Nature has no other
business in hand to hinder it; for its end is low down, and where is
the end, there is the function, and the uterus itself is naturally
where the function is.


We find differences in the vivipara also as compared with one
another. Some produce their young alive, not only externally, but also
internally, as men, horses, dogs, and all those which have hair, and
among aquatic animals, dolphins, whales, and such cetacea.


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