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.

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.

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.)

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'.

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;

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.

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.

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.

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.

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.

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.

in other words, it has a
crop, and at the same time its oesophagus is wide and spacious in
front of the stomach, and the crop is at some distance, relatively
to its size, from the oesophagus at that part.

Further, in most birds, the gut is thin, and simple when loosened
out. The gut-appendages or caeca in birds, as has been observed, are
few in number, and are not situated high up, as in fishes, but low
down towards the extremity of the gut. Birds, then, have caeca-not
all, but the greater part of them, such as the barn-door cock, the
partridge, the duck, the night-raven, (the localus,) the ascalaphus,
the goose, the swan, the great bustard, and the owl. Some of the
little birds also have these appendages; but the caeca in their case
are exceedingly minute, as in the sparrow.

The quail also has

the oesophagus widened out at the lower extremity, and in the
aegocephalus and the owl the organ is slightly broader at the bottom
than at the top. The duck, the goose, the gull, the catarrhactes,
and the great bustard have the oesophagus wide and roomy from one
end to the other, and the same applies to a great many other birds. In
some birds there is a portion of the stomach that resembles a crop, as
in the kestrel. In the case of small birds like the swallow and the
sparrow neither the oesophagus nor the crop is wide, but the stomach
is long. Some few have neither a crop nor a dilated oesophagus, but
the latter is exceedingly long, as in long necked birds, such as the
porphyrio, and, by the way, in the case of all these birds the
excrement is unusually moist. The quail is exceptional in regard to
these organs, as compared with other birds;

In regard to their

internal parts birds differ from other animals
and from one another. Some birds, for instance, have a crop in front
of the stomach, as the barn-door cock, the cushat, the pigeon, and the
partridge; and the crop consists of a large hollow skin, into which
the food first enters and where it lies ingested. Just where the
crop leaves the oesophagus it is somewhat narrow; by and by it
broadens out, but where it communicates with the stomach it narrows
down again. The stomach (or gizzard) in most birds is fleshy and hard,
and inside is a strong skin which comes away from the fleshy part.
Other birds have no crop, but instead of it an oesophagus wide and
roomy, either all the way or in the part leading to the stomach, as
with the daw, the raven, and the carrion-crow.

An exceptional property in fishes and in birds for the most
part is the being furnished with gut-appendages or caeca. Birds have
them low down and few in number. Fishes have them high up about the
stomach, and sometimes numerous, as in the goby, the galeos, the
perch, the scorpaena, the citharus, the red mullet, and the sparus;
the cestreus or grey mullet has several of them on one side of the
belly, and on the other side only one. Some fish possess these
appendages but only in small numbers, as the hepatus and the
glaucus; and, by the way, they are few also in the dorado. These
fishes differ also from one another within the same species, for in
the dorado one individual has many and another few. Some fishes are
entirely without the part, as the majority of the selachians. As for
all the rest, some of them have a few and some a great many. And in
all cases where the gut-appendages are found in fish, they are found
close up to the stomach.

Some affirm that the same phenomenon is observable with
serpents as with swallow chicks; in other words, they say that if
you prick out a serpent's eyes they will grow again. And further,
the tails of saurians and of serpents, if they be cut off, will grow
again.

With fishes the properties of the gut and stomach are similar;
that is, they have a stomach single and simple, but variable in
shape according to species. For in some cases the stomach is
gut-shaped, as with the scarus, or parrot-fish; which fish, by the
way, appears to be the only fish that chews the cud. And the whole
length of the gut is simple, and if it have a reduplication or kink it
loosens out again into a simple form.

The stomach

of the serpent is like a more spacious gut,
resembling the stomach of the dog; then comes the gut, long, narrow,
and single to the end. The heart is situated close to the pharynx,
small and kidney-shaped; and for this reason the organ might in some
cases appear not to have the pointed end turned towards the breast.
Then comes the lung, single, and articulated with a membranous
passage, very long, and quite detached from the heart. The liver is
long and simple; the spleen is short and round: as is the case in both
respects with the saurians. Its gall resembles that of the fish; the
water-snakes have it beside the liver, and the other snakes have it
usually beside the gut. These creatures are all saw-toothed. Their
ribs are as numerous as the days of the month; in other words, they
are thirty in number.