=Duration of Pregnancy.=--The consideration of this subject is of importance in its relation to the legitimacy of a child. The natural period of human gestation is usually stated at forty weeks, ten lunar or nine calendar months, or 280 days. In Prussia, the period is extended to 302 days, and in the Code Napoleon to 300; in Scotland, ten months is held as the limit. The duration of human gestation is subject to considerable variation; in some females it is always protracted; in others, always premature. Several modes of calculation are adopted by women: 1. Ascertained date of impregnation from one coïtus. 2. Supposed sensations of female at time of conception. 3. Suppression of the catamenia. This is open to the objection, that causes other than that of impregnation may arrest them. The catamenia may be stopped by cold or other causes for two or three months, and then, before their return, pregnancy may occur, thus upsetting all calculations. The usual mode of calculation is from two weeks after the last menstruation, and the period so fixed is corrected by the time at which quickening occurs. 4. Period of quickening. (_a_) Quickening supposed when pregnancy is absent. (_b_) Pregnancy without quickening. (_c_) Variations in the time of its occurrence. Whichever may be the mode of calculation adopted, it may be stated that, as a rule, the period of human gestation is from 275 to 280 days, and that cases of alleged pregnancy beyond 300 days must be received with considerable caution. The pregnancy of the Countess of Gloucester was held, in the reign of Edward II., to be legitimate, although her husband had been dead one year and seven months at the date of the application. =Premature Births.=--The question may be asked, At what period of gestation may a child be born viable--that is, capable of living and attaining to maturity? Seven months, or 210 days, is considered as the limit; but cases have been recorded of children born at six months being reared. The Roman law admitted the legitimacy of seven-months’ children. (For the Signs of Immaturity, see “Table of the Development of the Embryo,” pp. 35, 36.) =Superfœtation.=--The term is used to imply the conception of a second embryo in a woman already pregnant, and the birth of two children at one time, differing considerably in their maturity, or of two births, a considerable period of time elapsing between each. The possibility of this occurrence has been doubted.