2. The manner of their disappearance also is unaccountable; for in a few days they all vanish, although beforehand they could not be exterminated by smoking and digging them out, nor by hunting them and turning swine among them to root up their runs. Foxes also hunt them out, and wild weasels[213] are very ready to destroy them; but they cannot prevail over their numbers and the rapidity of their increase, nor indeed can anything prevail over them but rain, and when this comes they disappear very soon. [213] Perhaps ferret, Mustela varo, or weasel. 3. In a certain part of Persia the female fœtus of the mice are found to be pregnant in the uterus of their parent. Some people say and affirm that if they lick salt they become pregnant without copulation. The Egyptian mice have hair nearly resembling that of the hedgehog. There are other kinds which go upon two feet, for their fore feet are small and their hind feet large.[214] They are very numerous. There are also many other kinds of mice. [214] Serboa, Dipus gerbillus, or D. jaculus. BOOK THE SEVENTH. CHAPTER I. 1. The circumstances attending on the growth of man, from his conception in the womb even to old age, derived from his peculiar nature, are after this manner. We have already treated of the distinctions of the male and female and their parts. The male begins to have semen at about the age of fourteen complete. At the same time hair begins to appear on the pubes. As Alcmæon of Crotona says that flowers blossom before they bear seed, about the same period the voice begins to become more harsh and irregular. It is neither quite harsh, nor deep, nor all alike, but it resembles a discordant and harsh instrument. This is called τραγίζειν, to have a voice like a goat. 2. This is more conspicuous in those who attempt the gratification of sexual desires; for those who are vehement in these desires rapidly pass into a man's voice. In those that refrain themselves the contrary occurs. In those who, like some singers, endeavour to avoid this change, the voice will continue for a long while, and never undergo any great change. The breasts also and pudendum not only increase in size, but their general appearance is changed. At this period of life, if a person is urged to the emission of semen, the discharge is accompanied with pain as well as pleasure.