1. In many birds the male alternates with the female in the duty of incubation, as we observed in speaking of pigeons, and takes her place while she is obliged to procure food for herself. In geese the female alone sits upon the eggs, and having once begun, she never leaves them during the whole process of incubation. The nests of all water birds are situated in marshy and grassy places, by which means they can keep quiet and still have food within their reach, so that they do not starve all the while. The females alone, among the crows, sit on the eggs, which they never leave; but the males bring them food and feed them. 2. The females of the pigeons begin to sit at twilight, and remain on the nest the whole night, till dawn; and the male the rest of the time. Partridges make two nests of eggs, upon one of which the male sits, on the other the female; and each of them hatches and brings up its own: and the male has sexual intercourse with its young as soon as they are hatched. CHAPTER IX. 1. The peacock lives about twenty-five years, and produces young generally at three years old; by which time also they have obtained their variegated plumage: and it hatches in thirty days, or rather more. It only produces young once a-year, laying twelve eggs, or not quite so many. It lays its eggs at intervals of two or three days, and not regularly. At first they lay only eight. The pea-fowl also lays barren eggs: they copulate in the spring, and lay their eggs immediately afterwards. 2. This bird sheds its feathers when the leaves of the trees begin to fall, and begins to acquire them again with the first budding in the spring. Those who rear these birds place the eggs for incubation beneath domestic fowls; because the peacock flies at, and torments the hen when she is sitting; for which reason some of the wild birds make their escape from the males before they begin to lay and sit. They place only two eggs under domestic fowls, for these are all that they can hatch and bring out; and they take care to put food before them, that they may not get up and desert their incubation. 3. Birds at the season of sexual intercourse have large testicles. In the more lascivious they are always more evident, as the domestic cock and the partridge. In those that are not always lascivious, they are less. This is the manner of the gestation and reproduction of birds. CHAPTER X.