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On The Generation Of Animals   

isolated faculty. Clearly, then, the distinction of sex is a first
principle; at any rate, when that which distinguishes male and
female suffers change, many other changes accompany it, as would be
the case if a first principle is changed.


The sanguinea are not all alike as regards testes and uterus. Taking
the former first, we find that some of them have not testes at all, as
the classes of fish and of serpents, but only two spermatic ducts.
Others have testes indeed, but internally by the loin in the region of
the kidneys, and from each of these a duct, as in the case of those
animals which have no testes at all, these ducts unite also as with
those animals; this applies (among animals breathing air and having a
lung) to all birds and oviparous quadrupeds. For all these have their
testes internal near the loin, and two ducts from these in the same
way as serpents; I mean the lizards and tortoises and all the scaly
reptiles. But all the vivipara have their testes in front; some of
them inside at the end of the abdomen, as the dolphin, not with
ducts but with a penis projecting externally from them; others
outside, either pendent as in man or towards the fundament as in
swine. They have been discriminated more accurately in the Enquiries
about Animals.

The uterus is always double, just as the testes are always two in
the male. It is situated either near the pudendum (as in women, and
all those animals which bring forth alive not only externally but also
internally, and all fish that lay eggs externally) or up towards
the hypozoma (as in all birds and in viviparous fishes). The
uterus is also double in the crustacea and the cephalopoda, for the
membranes which include their so-called eggs are of the nature of a
uterus. It is particularly hard to distinguish in the case of the
poulps, so that it seems to be single, but the reason of this is
that the bulk of the body is everywhere similar.

It is double also in the larger insects; in the smaller the question
is uncertain owing to the small size of the body.

Such is the description of the aforesaid parts of animals.


With regard to the difference of the spermatic organs in males, if
we are to investigate the causes of their existence, we must first
grasp the final cause of the testes. Now if Nature makes everything
either because it is necessary or because it is better so, this part
also must be for one of these two reasons. But that it is not
necessary for generation is plain; else had it been possessed by all
creatures that generate, but as it is neither serpents have testes nor
have fish; for they have been seen uniting and with their ducts full
of milt. It remains then that it must be because it is somehow
better so. Now it is true that the business of most animals is, you
may say, nothing else than to produce young, as the business of a
plant is to produce seed and fruit. But still as, in the case of
nutriment, animals with straight intestines are more violent in
their desire for food, so those which have not testes but only
ducts, or which have them indeed but internally, are all quicker in
accomplishing copulation. But those which are to be more temperate
in the one case have not straight intestines, and in the other have
their ducts twisted to prevent their desire being too violent and
hasty. It is for this that the testes are contrived; for they make the
movement of the spermatic secretion steadier, preserving the folding
back of the passages in the vivipara, as horses and the like, and in
man. (For details see the Enquiries about Animals.) For the testes

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