Chapter I.

1. We have treated of the other internal parts of animals, their number, their nature and varieties. It now remains for us to speak of the organs of generation. In females these are always internal; but there is much difference in males, for some sanguineous animals have no testicles at all, in others they are internal; and in some animals with internal testicles, they are placed near the kidneys, in others near the abdomen; in other animals they are external. The penis of these last is sometimes united to the abdomen, in others it is loose as well as the testicles; but in promingent and retromingent animals it is suspended from the abdomen in a different manner. Neither fish nor any other animal with gills, nor the whole class of serpents, have testicles; neither has any apodal animal which is not internally viviparous.

2. Birds have testicles, but they are internal and near the loins, and so have oviparous quadrupeds, as the lizard, tortoise, and crocodile, and among viviparous animals, the hedgehog. In some viviparous animals they are situated internally upon the abdomen, as the dolphin among apodal creatures, and the elephant among quadrupeds. In other animals the testicles are external. It has been previously observed, that the manner and position of their junction with the abdomen is various, for in some they are joined on and do not hang down, as in swine, in others they hang down as in man.

3. It has also been observed that neither fishes nor serpents have testicles, but they have two passages hanging down on each side of the spine from the diaphragm, and these unite in one passage above the anus, by above, we mean nearer the spinal column. At the season of coition these passages are full of semen, which exudes on pressure; the differences among these may be seen by dissection, and in another place they will each be considered more particularly.

4. All oviparous animals, whether bipeds or quadrupeds, have their testicles placed in the loins below the diaphragm, some of a white colour, others ochreous, but in all surrounded with small veins; from each of these a passage is produced, which afterwards become united in one, and, as in fish, open near the anus. This is the penis, which is inconspicuous in small animals; but in the larger, as the goose and such like, it becomes more conspicuous immediately after coition.

5. And these passages, both in fish and other animals, are joined to the loins below the stomach and between the entrails and the great vein, from which passages proceed to each of the kidneys; and, as in fish, the semen may be seen entering them at the period of coition, when these passages become very conspicuous, but when this season is passed the passages again become invisible. So also the testicles of birds are either small or entirely invisible when not excited, but when urged by desire they become very large; this is so remarkable in pigeons and partridges, that some persons have supposed that they had no testicles during winter.

6. In some of those animals in which the testicles are placed forwards, they are internal and upon the abdomen, as in the dolphin; in others they are externally conspicuous upon the extremity of the abdomen. These animals are similar in other respects, but differ in this, for in some the testicles are uncovered, and others that have external testes they are placed in a scrotum.

7. This is the nature of the testicles of all viviparous animals with feet: from the aorta, passages like veins proceed to the head of each testicle, and two others from the kidneys, these last are full of blood, but those from the aorta contain no blood. From the head of each testicle to the testicle itself, there proceeds a thicker and more muscular passage, which is in each testicle reflected back to the head of the testicle, and from this point they again unite upon the penis towards the fore-part of it.

8. And both these passages which are reflected back upon themselves, and those which are seated upon the testicles, are covered with the same membrane as the testes themselves, so that unless this membrane is taken away, they all appear to be one passage. These last passages, which are seated upon the testicle, contain sanguineous fluid, but less than those above from the aorta; but in the reflected passages of the duct which is upon the penis, the fluid is white. A passage also leads from the bladder, and is united to the upper part of this duct, which is enclosed in the part called the penis as in a husk. The accompanying diagram will illustrate the position of these parts.

9. The origin of the passage from the trachea, a; the head of the testes and the descending passages, b b; the passages which proceed from these, and are seated upon the testicle, c c; the reflexed passages which contain the white fluid, d d; the penis, e; the bladder f; the testicles, g g. But when the testicles are cut out or otherwise destroyed, the upper passages are retracted; in young animals castration is performed by bruising the testicles, in older animals by excision. And it has happened that a bull has begotten young if admitted to the female immediately after castration. This is the nature of the testicles of animals.

10. The uterus of the females that possess this organ is not of the same nature, nor alike in all, but they differ from each other both in viviparous and oviparous animals. The uterus is double in all those animals in which it is situated near the external organ of generation, one part lying on the right side, the other on the left, but the origin is one, and there is but one os uteri, which is like a very fleshy tube, and in most animals, especially those of a large size, it is cartilaginous. One part of this organ is called the uterus and delphys (whence the word adelphi, brothers), and the vagina and os uteri are called metra.

11. In all viviparous animals, whether bipeds or quadrupeds, the uterus is placed below the diaphragm, as in the human female, the bitch, sow, mare, and cow, and it is the same in all horned animals. At the extremity of the uterus most animals have a convoluted part called the horns; these are not distinct in all oviparous animals; but in some birds they are placed near the diaphragm, and in some fishes below, as in the viviparous bipeds and quadrupeds. But they are thin, membranaceous, and long, so that in very small fish each part of the roe appears as one ovum, as if the fish which are said to have a crumbling roe had but two ova, for it is not one ovum but many, and therefore it may be resolved into many.

12. In the uterus of birds the vagina is below, fleshy and tough, but the part near the diaphragm membranaceous and very thin, so that the eggs appear to be outside the uterus. In large birds the membrane is more conspicuous, and if inflated through the vagina, it swells and enlarges at places; in small birds these parts are not conspicuous. The uterus of oviparous quadrupeds, as the tortoise, lizard, frog, and such like, is of the same nature, for the vagina below is one and fleshy, but the division and the ova are higher up and near the diaphragm.

13. In those apodal creatures which are outwardly viviparous and inwardly oviparous, as the sharks and selachea—[The selachea are apodal, furnished with gills, and viviparous]—the uterus is divided, and as in birds, it commences below and extends towards the diaphragm. The ova are situated between the division, and above near the diaphragm; and the animal is produced from the ovum after this has descended into the open space.

14. The difference between the uteri of these fish and others may be studied more accurately in drawings of dissections. Serpents also differ much both among themselves and from other animals, for all serpents except the viper are oviparous; this one is viviparous, though at first internally oviparous, wherefore, in many respects, its uterus resembles that of the cartilaginous fishes. The uterus of the serpent is long, like the body, and descends downwards, beginning from one duct and continuing on either side of the spine as far as the diaphragm, as if each were a passage, in which the ova are placed in order; these ova are not extruded singly, but connected together like a chain.

15. In all animals that are either internally or externally viviparous, the uterus is situated above the abdomen; in all oviparous creatures it is placed below, near the loins. Those that are externally viviparous, but internally oviparous, partake of both characters, for the lower part in which the ova are situated is near the loins, the other part whence the ova are extruded above the intestines. And there is also this difference in the uteri of animals: those which have horns and not teeth in both jaws have cotyledons in the pregnant uterus, and some of those also with teeth in both jaws, as the hare, the mouse, and the bat. But other viviparous animals with teeth in both jaws, and with feet, have a smooth uterus. The embryo is not united to the cotyledon, but to the womb. This is the manner of the internal and external heterogeneous parts of animals.