how it arises 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, because the 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 ejaculated 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.