Sex is determined after conception has taken place. At an early stage of the embryo certain cells are set apart. These, later, form the sex glands. Modern research claims to have discovered the secret of absolutely determining sex in the human embryo, but even if these claims are valid they have not as yet met with any general application.
Some twelve days after conception, the female ovule or egg, which has been impregnated by the male spermatazoön, escapes from the ovary where it was impregnated, and entering a tube (Fallopian) gradually descends by means of it into the cavity of the womb or uterus. Here the little germ begins to mature in order to develop into an exact counterpart of its parents. In the human being the womb has only a single cavity, and usually develops but a single embryo.
Sometimes two ovules are matured at the same time. If fecundated, two embryos instead of one will develop, producing twins. Triplets and quadruplets,[14] the results of the maturing of three or four ovules at the same time, occur more rarely. As many as five children have been born alive at a single birth, but have seldom lived for more than a few minutes.
The development of the ovule in the womb is known as gestation or pregnancy. The process is one of continued cell division and growth, and while it goes on the ovule sticks to the inner wall of the womb. There it is soon enveloped by a mucous membrane, which grows around it and incloses it.
The Primitive Trace, a delicate straight line appearing on the surface of the g
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