In the human species, the seed of the male enters into the matrix, the cavity of which is considerable; and when it meets with a sufficient quantity of female semen, a mixture of the organic particles succeed, and the formation of the foetus ensues: the whole, perhaps, is done instantaneously, especially if the liquors are both in an active and flourishing state. The place where the foetus is formed, is the cavity of the matrix, because the seed of the male can enter there more easily than into the trunks; and as this viscera has but one small orifice, which is always shut, excepting when the ardour of love causes it to open, the materials of generation remain there with safety, and scarcely ever reissue but by rare and unfrequent circumstances: but as the liquor of the male sprinkles the vagina, before it penetrates the matrix, by the activity of the organic molecules which compose it, it may go farther into the trunks, and, perhaps, into the ovarium. As the liquor of the female has already its perfection in the glandular bodies of the testicles, from which it flows and moistens the trunks and other parts before it descends into the matrix, and as it may issue out of the vacuities left around the neck of the matrix, it is not impossible, that the mixture of the two liquors may be made in all these different places. It is, therefore, probable that foetuses are often formed in the vagina, but which fall out as soon as they are formed, because there is nothing to retain them. It may also sometimes happen, that foetuses are formed in the trunks; but this case is very rare, and cannot happen but when the seminal liquor of the male enters the matrix in great plenty.