DOUBLE CONCEPTION.
If two germs be evolved simultaneously, each may be impregnated by spermatozoa, and a twin pregnancy be the result. This is by no means a rare occurrence. It is very unusual, however, to have one birth followed by another after an interval of three or four months, and each babe present the evidences of full maturity. Perhaps such occurrences may be accounted for on the supposition that the same interval of time elapses between the impregnation of the two germs as there is difference observed in their birth; that after the act of insemination, sperm was carried to each ovary; that one had matured a germ ready for fecundation, then impregnation and conception immediately followed, and the decidua of the uterus hermetically sealed both Fallopian tubes, and thus securely retained the sperm within the other Fallopian canal. The stimulus of the sperm so pent up causes that ovary to mature a germ, although it may do so slowly, and after two or three months it is perfected, fertilized, and a second conception occurs within the uterus. If each embryo observe a regular period of growth and each be born at maturity, there must be an interval of two or three months between their births. But it is far more common for the parturition of the first, displaying signs of full maturity, to coincide with the birth of a second which is immature and which cannot sustain respiratory life. The birth of the latter is brought about prematurely, by the action of the uterus in expelling the matured child.