The physicians maintain, that sterility in women may arise from the womb; for if it be after any ways thus affected, there will be barrenness,—if it be more condensed, or more spongy, or more hardened, or more callous, or more carneous; or it may be from low spirits, or from an atrophy or vicious distemper of body; or, lastly, it may arise from a twisted or distorted configuration. Diocles holds that the sterility in men ariseth from some of these causes,—either that they cannot at all ejaculate any sperm, or if they do, it is less than nature doth require, or else there is no generative faculty in the sperm, or the genital members are flagging; or from the obliquity of the yard. The Stoics attribute the cause of sterility to the contrariant qualities and dispositions of those who lie with one another; but if it chance that these persons are separated, and there happen a conjunction of those who are of a suitable temperament, then there is a commixture according to nature, and by this means an infant is formed. CHAPTER XIV. HOW IF COMES TO PASS THAT MULES ARE BARREN. Alcmaeon says, that the barrenness of the male mules ariseth from the thinness of the genital sperm, that is, the seed is too chill; the female mules are barren, for their womb does not open its mouth (as he expresses it). Empedocles, the matrix of the mule is so small, so depressed, so narrow, so invertedly growing to the belly, that the sperm cannot be regularly cast into it, and if it could, there would be no capacity to receive it. Diocles concurs in this opinion with him; for, saith he, in our anatomical dissection of mules we have seen that their matrices are of such configurations; and it is possible that there may be the same reason why some women are barren. CHAPTER XV. WHETHER THE INFANT IN THE MOTHER’S WOMB BE AN ANIMAL.