[From Aristotle, Generation of Animals, with an English translation by A.L. Peck, Cambridge, MA: Harvard University Press, 1953.]
 

ARISTOTLE

GENERATION OF ANIMALS
 

1.2.

As far as animals are concerned, we must describe their generation just as we find the theme requires for each several kind as we go along, linking our account on to what has already been said. As we mentioned, we may safely set down as the chief principles of generation the male and the female; the male as possessing the principle of movement and of generation, the female as possessing that of matter. One is most likely to be convinced of this by considering how the semen is formed and whence it comes; for although the things that are formed in the course of Nature no doubt take their rise out of semen, we must not fail to notice how the semen itself is formed from the male and the female, since it is because this part is secreted from the male and the female, and because its secretion takes place in them and out of them, that the male and the female are the principles of generation. By a "male" animal we mean one which generates in another, by "female" one which generates in itself. This is why in cosmology too they speak of the nature of the Earth as something female and call it "mother," while they give to the heaven and the sun and anything else of that kind the title of "generator," and "father."

Now male and female differ in respect of their logos, in that the power or faculty possessed by the one differs from that possessed by the other; but they differ also to bodily sense, in respect of certain physical parts. They differ in their logos, because the male is that which has the power to generate in another (as was stated above), while the female is that which can generate in itself, i.e., it is that out of which the generated offspring, which is present in the generator, comes into being. Very well, then: they are distinguished in respect of their faculty, and this entails a certain function. Now for the exercise of every function instruments are needed, and the instruments for physical faculties are the parts of the body. Hence it is necessary that, for the purpose of copulation and procreation, certain parts should exist, parts that are different from each other, in respect of which the male will differ from the female; for although male and female are indeed used as epithets of the whole of the animal, it is not male or female in respect of the whole of itself, but only in respect of a particular faculty and a particular part - just as it is "seeing" and "walking" in respect of certain parts - and this part is one which is evident to the senses. Now in the female this special part is what is called the uterus, and in the male the regions about the testes and the penis, so far as all the blooded animals are concerned: some of them have actual testes, some testicular passages. There are also differences between male and female in those of the bloodless creatures which have this opposition of the sexes. In the blooded animals the parts which serve for copulation differ in their shapes. We must note, however, that when a small principle changes, usually many of the things which depend upon it undergo an accompanying change. This is clear with castrated animals, where, although the generative part alone is destroyed, almost the whole form of the animal thereupon changes so much that it appears to be female or very nearly so, which suggests that it is not merely in respect of some casual part or some casual faculty that an animal is male or female. It is clear, then, that "the male" and "the female" are a principle. At any rate, when animals undergo a change in respect of that wherein they are male and female, many other things about them undergo an accompanying change, which suggests that a principle undergoes some alteration.
 
 

2.7.

It is, of course, a general problem why any particular male or female is sterile: there are men and women who are sterile, and there are instances in the several kinds of animals, e.g., horses and sheep. But with the mules we have a whole race which is sterile. Leaving this exception for the moment: elsewhere the causes of sterility are numerous. (a) Men and women alike are sterile from birth if they are imperfect in the regions employed for copulation; as a result, the men do not grow a beard but remain as eunuchs, while the women do not reach puberty; (b) others become sterile as they advance in age, sometimes (i) because they have put on too much flesh: in men who are too well fed and in women who are too fat the seminal residue is used up for the benefit of the bodily system, so that no semen is formed in the men and no menstrual discharge in the women; sometimes (it) because of disease; the semen which the men emit is fluid and cold, and the discharges of the women are poor and full of morbid residues. But in very many cases, in both sexes, this drawback is due to imperfections in the parts and regions employed for intercourse. Some of these imperfections are curable, some are not; those, however, who have become deformed during the original constitution of the embryo, have a special tendency to remain infertile throughout; thus, masculine-looking women are produced in whom the menstrual discharges do not occur, and effeminate men whose semen is thin and cold. On this account the water-test is quite a fair one for infertility in the male semen, because the thin, cold semen quickly diffuses itself on the surface, whereas the fertile semen sinks to the bottom; for though it is true that a substance which has been concocted is hot, yet that which has been set and compacted and possesses thickness has certainly undergone concoction. Women are tested (a) by, means of pessaries: the test is whether the scent of the pessary penetrates upwards from below to the breath which is exhaled from the mouth; (b) by means of colours rubbed on to the eyes, the test being whether they colour the saliva. If the required result is not forthcoming, it is proved that the passages of the body through which the residue is secreted have got obstructed and have closed up, for of all the regions in the head the eyes are the most seminal, as is proved by the fact that this is the only region which unmistakably changes its appearance during sexual intercourse, and those who overfrequently indulge in it have noticeably sunken eyes. The reason is that the nature of the semen is similar to that of the brain; its matter is watery whereas its heat is a mere supplementary acquisition. Also the seminal discharges come from the diaphragm, because the first principle of the natural organism is there, so that the movements initiated in the genital organs penetrate to the chest, and the scents from the chest become perceptible through the breathing.