5. If any are born before the seventh month, they never live. Those of seven months are the first that are developed, but these are usually weakly, wherefore, also, they wrap them in wool. Many of these infants have the passages, as the ears and nostrils, imperforate. As they grow, however, they assume a proper form, and many of them survive. In Egypt, and some other places, where the women suffer little pain in parturition, and where they bear many children with ease, those even at the end of eight months are capable of living, even although they should be monstrous; but in such places children born in the eighth month may survive and be brought up. In Greece, however, few of them survive, and most of them perish; and people suspect that if any of them survive, the exact period of conception must have been mistaken by the mother. 6. Women suffer most in the fourth and eighth month, and if the fœtus dies in the fourth or eighth month, they usually die also; so that not only children born in the eighth month often perish, but their mothers also perish with them. In the same way, the period of conception probably is mistaken by those who have been pregnant more than eleven months; for in these cases the beginning of the conception escapes the notice of females, for frequently after the uterus has been distended with flatulence, women have copulated and conceived, and supposed that the former condition in which they observed the usual symptoms, was the commencement of gestation. CHAPTER V. 1. The human subject also differs from other animals, as to the number of the perfect offspring produced at a birth. For the human subject differs both from animals which produce but one, and those which produce many; for, generally speaking, and, in most cases, women have but one child at a time, though cases of twins occur frequently, and in many places, as in Egypt, three or four at a birth have been known in some particular places, as I have observed before. Five at a birth are the most that have been produced. This has been observed to take place in many cases, but in one case only have twenty been produced at four births, for five were born each time, and many of them were reared. In other animals, if the twins are male and female, there is no more difficulty in rearing and preserving them, than if they were both of the same sex. In the human subject there are few cases of twins surviving, when one was male and the other female.