3. There is evidence of their having reached the age of puberty, for as in the human subject the mammæ begin to enlarge and become cartilaginous; it is, however, difficult to detect this without practice, for the enlargement is not very great. This takes place in the female, nothing of the kind occurs in the male. The males generally begin to lift up their leg to make water when they are six months old. Some do not do so till they are eight months old, and others before they are six months old, for, to speak plainly, they do this as soon as they reach puberty; all the females sit down to make water; some, however, even of these lift up their leg for this purpose. The female never produces more than twelve puppies, generally five or six, and sometimes only one; those of Lacedæmon generally have eight; both sexes continue to enjoy sexual intercourse as long as they live. 4. It is a peculiarity of the Lacedemonian dog, that it is more ready for sexual intercourse after hard work than when idle; the male of this kind lives ten years, the female for twelve, most other dogs live fourteen or fifteen years, some even twenty, for which reason some persons think that Homer is right when he makes the dog of Ulysses to have died at the age of twenty. On account of the hard work which the Lacedemonian dogs have to endure the female lives longer than the male; in other races this is not so plainly observed, but the male is usually longer lived than the female. The dog does not shed any teeth except those called the canine teeth, these are shed by both sexes at four months old. Because they shed these only, a question is raised, for some persons altogether deny that they shed only two teeth, for it is difficult to meet with these, and others, when they see that they shed these, think that they must shed all their teeth. People judge of the age of a dog by its teeth, for in young dogs they are white and sharp, in old ones they are black and blunted. CHAPTER XXI. 1. The cow is impregnated with a single act of coition, and the bull mounts upon her with such violence that she bends beneath his weight. If he fails to impregnate her after twenty days, she is again admitted to the bull. Old bulls will not mount the same cow several times in the same day unless there is some intermission, but young bulls, incited by the strength of their desires, will force the same cow several times, and will mount upon many in succession. The bull is one of the least lascivious of animals. The conqueror copulates with the female, but if he become impotent from frequent sexual intercourse, the inferior will attack him, and often prevail.