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 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.

CHAPTER XV. WHETHER THE INFANT IN THE MOTHER'S WOMB BE AN ANIMAL.

Plato says, that the embryo is an animal; for, being contained in the
mother's womb, motion and aliment are imparted to it. The Stoics say
that it is not an animal, but to be accounted part of the mother's
belly; like as we see the fruit of trees is esteemed part of the trees,
until it be full ripe; then it falls and ceaseth to belong to the
tree; thus it is with the embryo. Empedocles, that the embryo is not an
animal, yet whilst it remains in the belly it breathes. The first breath
that it draws as an animal is when the infant is newly born; then
the child having its moisture separated, the extraneous air making an
entrance into the empty places, a respiration is caused in the infant by
the empty vessels receiving of it. Diogenes, that infants are nurtured
in the matrix inanimate, yet they have a natural heat; but presently,
when the infant is cast into the open air, its heat brings air into
the lungs, and so it becomes an animal. Herophilus acknowledgeth that a
natural, but not an animal motion, and that the nerves are the cause of
that motion; that then they become animals, when being first born they
suck in something of the air.

CHAPTER XVI. HOW EMBRYOS ARE NOURISHED, OR HOW THE INFANT IN THE BELLY
RECEIVES ITS ALIMENT.

Democritus and Epicurus say, that the embryos in the womb receive their
aliment by the mouth, for we perceive, as soon as ever the infant is
born, it applies its mouth to the breast; in the wombs of women