2. The reproductive function in men usually continues active till they are sixty years old; if they pass beyond this period, till they are seventy; and some men have had children at seventy years old. It frequently happens that, when marriages are unfruitful, both men and women become pregnant, if the marriage is dissolved and they marry again. The same thing takes place respecting the birth of male and female children. For sometimes only children of one sex are produced by a marriage; and if this is dissolved, and the parents marry again, children of the other sex are produced. These things also vary with the age of the parents; for some when young have female children, and when older males, though the contrary sometimes takes place. 3. The same is the case with the whole of the reproductive function. For some persons have no children when they are young, but have them afterwards; others have children at first, but none afterwards; and there are some women who conceive with difficulty, but when they have conceived bear children; others conceive easily, but the fœtus never comes to maturity. There are also both men and women who only produce children of one sex, as the story goes of Hercules, who had but one daughter in seventy-two children. Those who have been barren, and either after great care, or from any other cause, at last conceive, more frequently bear a daughter than a son. It often happens also that men who have engendered become impotent, and subsequently return to their former condition. 4. Maimed parents produce maimed children; and so also lame and blind parents produce lame and blind children; and, on the whole, children are often born with anything contrary to nature, or any mark which their parents may have, such as tumours and wounds. Such marks have often been handed down for three generations; as if a person had a mark on their arm which was not seen in the son, but the grandson exhibited a dark confused spot on the same place. The circumstances, however, are rare; and sound children are generally produced from lame parents; nor is there any complete certainty in these matters; and children resemble their parents or their grandparents, and sometimes they resemble neither. This is handed down for many generations; as in Sicily, a woman cohabited with an Ethiopian, her daughter was not black, but her daughter's child was so.