CHAPTER II
THE TRANSITION FROM CELL TO HUMAN BEING
In the functional processes alluded to in the preceding chapter, the male germ-cell and the female germ-cell unite in a practically equal division of substance. We say “practically” because the maternal and the paternal influences are not equally divided in the offspring. One or the other usually predominates. But, as a general rule, it may be said that in the development of the embryonal life the process of cell division proceeds in such a way that every germ of the child's future organism represents approximately one-half maternal and one-half paternal substance and energy.
In this process lies the true secret of heredity. The inherited energies retain their full measure of power, and all their original quality in the growing and dividing chromosomes (the chromosome is one of the segments into which the chromoplasmic filaments of a cell-nucleus break up just before indirect division). On the other hand, the egg-substance of the female germ-cell, which is assimilated by the chromosomes, and which is turned into their substance by the process of organic chemistry, loses its specific plastic vital energy completely. It is in the same way that food eaten by the adult has absolutely no effect on his qualitative organic structure. We may eat ever so many beef-steaks without acquiring any of the characteristics of an ox. And the germ-cell may devour any amount of egg-protoplasma without losing its original paternal energy. As a rule a child inherits as many qualities from its mother as from its father.
DETERMINATION OF SEX
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.
EARLY DEVELOPMENT
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.
TWINS
Sometimes two ovules are matured at the same time. If fecundated, two embryos instead of one will develop, producing twins. Triplets and quadruplets, 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.