Now that we have stated the magnitudes, the properties, and the
relative differences of the other internal organs, it remains for us
to treat of the organs that contribute to generation. These organs
in the female are in all cases internal; in the male they present
numerous diversities.

    In the blooded animals some males are altogether devoid of
testicles, and some have the organ but situated internally; and of
those males that have the organ internally situated, some have it
close to the loin in the neighbourhood of the kidney and others
close to the belly. Other males have the organ situated externally. In
the case of these last, the penis is in some cases attached to the
belly, whilst in others it is loosely suspended, as is the case also
with the testicles; and, in the cases where the penis is attached to
the belly, the attachment varies accordingly as the animal is
emprosthuretic or opisthuretic.

    No fish is furnished with testicles, nor any other creature
that has gills, nor any serpent whatever: nor, in short, any animal
devoid of feet, save such only as are viviparous within themselves.
Birds are furnished with testicles, but these are internally situated,
close to the loin. The case is similar with oviparous quadrupeds, such
as the lizard, the tortoise and the crocodile; and among the
viviparous animals this peculiarity is found in the hedgehog. Others
among those creatures that have the organ internally situated have
it close to the belly, as is the case with the dolphin amongst animals
devoid of feet, and with the elephant among viviparous quadrupeds.
In other cases these organs are externally conspicuous.

    We have already alluded to the diversities observed in the
attachment of these organs to the belly and the adjacent region; in
other words, we have stated that in some cases the testicles are
tightly fastened back, as in the pig and its allies, and that in
others they are freely suspended, as in man.

    Fishes, then, are devoid of testicles, as has been stated, and
serpents also. They are furnished, however, with two ducts connected
with the midriff and running on to either side of the backbone,
coalescing into a single duct above the outlet of the residuum, and by
"above" the outlet I mean the region near to the spine. These ducts in
the rutting season get filled with the genital fluid, and, if the
ducts be squeezed, the sperm oozes out white in colour. As to the
differences observed in male fishes of diverse species, the reader
should consult my treatise on Anatomy, and the subject will be
hereafter more fully discussed when we describe the specific character
in each case.

    The males of oviparous animals, whether biped or quadruped, are
in all cases furnished with testicles close to the loin underneath the
midriff. With some animals the organ is whitish, in others somewhat of
a sallow hue; in all cases it is entirely enveloped with minute and
delicate veins. From each of the two testicles extends a duct, and, as
in the case of fishes, the two ducts coalesce into one above the
outlet of the residuum. This constitutes the penis, which organ in the
case of small ovipara is inconspicuous; but in the case of the
larger ovipara, as in the goose and the like, the organ becomes
quite visible just after copulation.

    The ducts in the case of fishes and in biped and quadruped
ovipara are attached to the loin under the stomach and the gut, in
betwixt them and the great vein, from which ducts or blood-vessels
extend, one to each of the two testicles. And just as with fishes
the male sperm is found in the seminal ducts, and the ducts become
plainly visible at the rutting season and in some instances become
invisible after the season is passed, so also is it with the testicles
of birds; before the breeding season the organ is small in some
birds and quite invisible in others, but during the season the organ
in all cases is greatly enlarged. This phenomenon is remarkably
illustrated in the ring-dove and the partridge, so much so that some
people are actually of opinion that these birds are devoid of the
organ in the winter-time.

    Of male animals that have their testicles placed frontwards, some
have them inside, close to the belly, as the dolphin; some have them
outside, exposed to view, close to the lower extremity of the belly.
These animals resemble one another thus far in respect to this
organ; but they differ from one another in this fact, that some of
them have their testicles situated separately by themselves, while
others, which have the organ situated externally, have them
enveloped in what is termed the scrotum.

    Again, in all viviparous animals furnished with feet the
following properties are observed in the testicles themselves. From
the aorta there extend vein-like ducts to the head of each of the
testicles, and another two from the kidneys; these two from the
kidneys are supplied with blood, while the two from the aorta are
devoid of it. From the head of the testicle alongside of the
testicle itself is a duct, thicker and more sinewy than the other just
alluded to-a duct that bends back again at the end of the testicle
to its head; and from the head of each of the two testicles the two
ducts extend until they coalesce in front at the penis. The duct
that bends back again and that which is in contact with the testicle
are enveloped in one and the same membrane, so that, until you draw
aside the membrane, they present all the appearance of being a
single undifferentiated duct. Further, the duct in contact with the
testicle has its moist content qualified by blood, but to a
comparatively less extent than in the case of the ducts higher up
which are connected with the aorta; in the ducts that bend back
towards the tube of the penis, the liquid is white-coloured. There
also runs a duct from the bladder, opening into the upper part of
the canal, around which lies, sheathwise, what is called the "penis".

    All these descriptive particulars may be regarded by the light of
the accompanying diagram; wherein the letter A marks the
starting-point of the ducts that extend from the aorta; the letters KK
mark the heads of the testicles and the ducts descending thereunto;
the ducts extending from these along the testicles are marked MM; the
ducts turning back, in which is the white fluid, are marked BB; the
penis D; the bladder E; and the testicles XX.

    (By the way, when the testicles are cut off or removed, the ducts
draw upwards by contraction. Moreover, when male animals are young,
their owner sometimes destroys the organ in them by attrition;
sometimes they castrate them at a later period. And I may here add,
that a bull has been known to serve a cow immediately after
castration, and actually to impregnate her.)

    So much then for the properties of testicles in male animals.

    In female animals furnished with a womb, the womb is not in all
cases the same in form or endowed with the same properties, but both
in the vivipara and the ovipara great diversities present
themselves. In all creatures that have the womb close to the genitals,
the womb is two-horned, and one horn lies to the right-hand side and
the other to the left; its commencement, however, is single, and so is
the orifice, resembling in the case of the most numerous and largest
animals a tube composed of much flesh and gristle. Of these parts
one is termed the hystera or delphys, whence is derived the word
adelphos, and the other part, the tube or orifice, is termed metra. In
all biped or quadruped vivipara the womb is in all cases below the
midriff, as in man, the dog, the pig, the horse, and the ox; the
same is the case also in all horned animals. At the extremity of the
so-called ceratia, or horns, the wombs of most animals have a twist or
convolution.

    In the case of those ovipara that lay eggs externally, the wombs
are not in all cases similarly situated. Thus the wombs of birds are
close to the midriff, and the wombs of fishes down below, just like
the wombs of biped and quadruped vivipara, only that, in the case of
the fish, the wombs are delicately formed, membranous, and
elongated; so much so that in extremely small fish, each of the two
bifurcated parts looks like a single egg, and those fishes whose egg
is described as crumbling would appear to have inside them a pair of
eggs, whereas in reality each of the two sides consists not of one but
of many eggs, and this accounts for their breaking up into so many
particles.

    The womb of birds has the lower and tubular portion fleshy and
firm, and the part close to the midriff membranous and exceedingly
thin and fine: so thin and fine that the eggs might seem to be outside
the womb altogether. In the larger birds the membrane is more
distinctly visible, and, if inflated through the tube, lifts and
swells out; in the smaller birds all these parts are more indistinct.

    The properties of the womb are similar in oviparous quadrupeds, as
the tortoise, the lizard, the frog and the like; for the tube below is
single and fleshy, and the cleft portion with the eggs is at the top
close to the midriff. With animals devoid of feet that are
internally oviparous and viviparous externally, as is the case with
the dogfish and the other so-called Selachians (and by this title we
designate such creatures destitute of feet and furnished with gills as
are viviparous), with these animals the womb is bifurcate, and
beginning down below it extends as far as the midriff, as in the
case of birds. There is also a narrow part between the two horns
running up as far as the midriff, and the eggs are engendered here and
above at the origin of the midriff; afterwards they pass into the
wider space and turn from eggs into young animals. However, the
differences in respect to the wombs of these fishes as compared with
others of their own species or with fishes in general, would be more
satisfactorily studied in their various forms in specimens under
dissection.

    The members of the serpent genus also present divergencies either
when compared with the above-mentioned creatures or with one
another. Serpents as a rule are oviparous, the viper being the only
viviparous member of the genus. The viper is, previously to external
parturition, oviparous internally; and owing to this perculiarity
the properties of the womb in the viper are similar to those of the
womb in the selachians. The womb of the serpent is long, in keeping
with the body, and starting below from a single duct extends
continuously on both sides of the spine, so as to give the
impression of thus being a separate duct on each side of the spine,
until it reaches the midriff, where the eggs are engendered in a
row; and these eggs are laid not one by one, but all strung
together. (And all animals that are viviparous both internally and
externally have the womb situated above the stomach, and all the
ovipara underneath, near to the loin. Animals that are viviparous
externally and internally oviparous present an intermediate
arrangement; for the underneath portion of the womb, in which the eggs
are, is placed near to the loin, but the part about the orifice is
above the gut.)

    Further, there is the following diversity observable in wombs as
compared with one another: namely that the females of horned
nonambidental animals are furnished with cotyledons in the womb when
they are pregnant, and such is the case, among ambidentals, with the
hare, the mouse, and the bat; whereas all other animals that are
ambidental, viviparous, and furnished with feet, have the womb quite
smooth, and in their case the attachment of the embryo is to the
womb itself and not to any cotyledon inside it.

    The parts, then, in animals that are not homogeneous with
themselves and uniform in their texture, both parts external and parts
internal, have the properties above assigned to them.