5. The following are the ages at which animals acquire the power of reproduction. The sheep and goat arrive at puberty within a year after they are born, and especially the goat, and the males as well as the females, but the offspring of these males and of the others is different. For the males are better the second year than when they become older. In hogs, the male and female unite at eight months old, and the female produces her young when she is a year old, for this agrees with the period of gestation. The male reaches puberty at eight months old, but his offspring are useless till he is a year old. But these periods, as we have said, are not always the same, for swine will sometimes copulate when they are four months old, so as to have young and nurse them at six months old, and boars sometimes reach puberty at ten months old, and continue good to three years old. 6. The bitch reaches puberty within a year after birth, and so does the dog, and sometimes this takes place at the end of eight months, but more frequently in the male than in the female. The period of gestation is sixty days, or one or two, or perhaps three days more, but never less than sixty days, or if they produce young in a less time, it never comes to perfection. The bitch is ready for sexual intercourse again in six months, but never sooner. The horse reaches puberty in both sexes at two years old, and is capable of reproduction, but its offspring at that age are small and weakly. For the most part, sexual intercourse begins at three years of age, and the colts continue to improve from that period till they are twenty years old. The male is useful till he is thirty years old, so that he can beget during almost the whole of his life, for the horse generally lives five-and-thirty years, and the mare more than forty, and a horse has been known to live seventy-five years. 7. The ass reaches puberty in both sexes at the age of thirty months; they rarely, however, produce young till they are three years, or three years and six months old. But it has been known to be pregnant and bring up its young within the year. The cow also has been known to produce young and rear it within the year after birth, which grew to the ordinary size, and no more.[163] [163] This probably means "to such a size as might be expected from the early age of the parent." 8. These are the periods of puberty in these animals. The seventieth year in man, and the fiftieth in woman, is the latest period of reproduction, and this happens rarely, for only a few have had children at this time of life. Sixty-five is generally the boundary in one sex, and forty-five in the other. The sheep produces young till it is eight years old, and, if well treated, until it is eleven, though the act of copulation is continued in both sexes during the whole period of life.