3. If the union takes place frequently, and sufficient time is not allowed to intervene, the female soon becomes barren. For which reason those who attend to this business do not permit them to have continual intercourse, but interpose a proper interval. The mare will not admit the he ass, nor the she ass the horse, unless the he ass has been suckled by a mare. They are careful, therefore, to admit only those asses which they call hippothelæ, _i.e._ asses which have been suckled by a mare. These copulate by force in the pastures, like horses. CHAPTER XXIV. 1. The oreus (mule) mounts and copulates after shedding the first teeth, and when seven years old is able to engender; and the ginnus is produced when he mounts upon a mare. After this he no longer continues to copulate. The female oreus also has been impregnated, but the fœtus has never been known to come to maturity. The hemioni (female mules) of Syria, near Phœnicia, admit the male and procreate. The kind, however, though similar, is not the same. Those which are called ginni are produced from a mare, when the fœtus has received some injury in the uterus, like dwarfs among men and metachœra among swine; and the ginnus, like the dwarf, has a large genital organ. 2. The hemionus has a long life; for they have been known to live for eighty years, as in Athens, when they built the temple, this individual, though failing with age, helped in drawing, and went beside them, and encouraged the yoke mules to their work, so that an edict was made, commanding the corn-dealers not to drive it away from the vessels filled with corn. The female mule (oreus) grows old sooner than the male. Some persons say that she is purified when making water, but the male ages more rapidly from smelling the urine. 3. This is the manner of the reproduction of these animals. Those who are employed in bringing up these animals recognize the young from the old in this way. If the skin, when drawn back from the cheek, soon recovers its shape, the animal is young; if the skin continues wrinkled for a long while, the creature is aged. CHAPTER XXV. 1. The camel is pregnant ten months, and always produces a single young one, for this is its nature. They separate the young camel from the herd at a year old. The camel will live more than fifty years. The season of parturition is in the spring, and the female continues to give milk until she conceives again. Their flesh and milk are exceedingly sweet. The milk is drunk mixed with two or three times its quantity of water.