1. Both the horse and mare begin to use sexual intercourse at two years old. Such early cases, however, are rare, and their offspring small and weak; and generally they commence at three years old, and they continue to produce better colts till they are twenty years old. The period of gestation is eleven months; parturition takes place in the twelfth. The male does not impregnate the female in any particular number of days; but at times in one, two, or three, sometimes in more. The ass mounts and impregnates more quickly than the horse; and the act of intercourse is not laborious in horses as it is in oxen. Next to the human subject, the horse in both sexes is the most lascivious of all animals. The sexual intercourse of the younger horses takes place before the usual age according to the goodness and abundance of their food. The horse generally produces but one colt, or sometimes two at the outside. The hemionus has also been known to produce two, but this is considered extraordinary. The horse begins sexual intercourse at thirty months old, so that it can produce proper colts when it has done changing its teeth. Some have been known, they say, to impregnate mares while changing their teeth, unless they were naturally barren. 2. The horse has forty teeth. It sheds its four first teeth at thirty months old, two above and two below. A year afterwards, it sheds four more in the same manner, two above and two below. And again, at the end of the next year, it sheds four more in the same manner. When it is four years and a half old, it sheds no more; and individuals have been known to shed them all at first, and others that have shed them all in the last year. These circumstances are rare, so that it usually happens that the horse is most fit for sexual intercourse at four years and a half old. The older horses are more full of semen, both the males and the females, than younger ones. Horses will copulate both with their dams and with their offspring; and it is thought to be a sign that the herd is complete, when they copulate with their offspring. The Scythians ride upon their pregnant mares when the embryo begins to turn in the uterus, and say that it renders parturition more easy. All other quadrupeds lie down in the act of parturition; wherefore their young are always produced lying on their side; but when the mare feels that the time for parturition is approaching, she stands upright to part with her colt.