All vegetation is reducible then to three kinds; the first is, when the growth proceeds from the superior extremity, as in herbs, plants, trees, and the antlers of stags; the second, when it is made from the inferior extremity, as in horns, claws, nails, hair, scales, tusks, teeth, feathers, and other exterior parts of animal bodies; the third when the growth advances from both extremities at the same time, as in bones, cartilages, muscles, tendons, and other internal parts of animals. Of all three the proximate cause is the superabundance of organic nourishment, and the only effect, the assimilation of that nourishment, to the mould wherein it has been received. Thus the animal grows more or less quickly in proportion to the quantity of such nourishment, and when the growth is nearly completed, it then seeks to employ itself in the propagation of new organized beings in the manner as we have before stated. The difference between animals, which, like the stag, have fixed seasons, and those which can engender at all times, proceeds likewise from the manner of their feeding. Man and domestic animals, which every day receive an equal quantity of sustenance, and frequently to an excess, may engender at all seasons. The stag, and most wild animals on the contrary, who suffer much from want in the winter, have no superabundance, nor are in a state to engender till they have recruited themselves during the summer; and it is then the rutting season commences, and during which he exhausts himself so much that he remains the whole winter in a state of langour. His flesh and blood are then so impoverished that worms breed under his skin, which still adds to his misery, and which do not perish till the spring, when he recovers new life from the active nourishment he is abundantly furnished with by the fresh production of the earth.