Having once originated, the sexual type of reproduction possessed a definite survival value which assured its continuation. Sex makes possible a crossing of strains, which evidently possesses some great advantage, since the few simple forms which have no such division of reproductive functions have undergone no great development and all the higher, more complicated animals are sexual. This crossing of strains may make possible greater variety, it may help in crossing out or weakening variations which are too far from the average, or both. Schäfer[4] thinks that an exchange of nuclear substance probably gives a sort of chemical rejuvenation and very likely stimulates division. At any rate, the groups in which the reproductive process became thus partitioned between two kinds of individuals, male and female, not only survived, but they underwent an amazing development compared with those which remained sexless. There came a time in the evolution of the groups possessing sexual reproduction, when increasing specialization necessitated the division into reproductive and non-reproductive cells. When a simple cell reproduces by dividing into two similar parts, each developing into a new individual like the parent, this parent no longer exists as a cell, but the material which composed it still exists in the new ones. The old cell did not "die"--no body was left behind. Since this nuclear substance exists in the new cells, and since these generations go on indefinitely, the cells are in a sense "immortal" or deathless. In a one-celled individual, there is no distinction between germinal and bodily functions. In the more complicated organisms, however, there are innumerable kinds of cells, a few (the germ cells) specialized for reproduction, the others forming the body which eats, moves, sees, feels, and in the case of man, _thinks_. But the germ-cells or germplasm continue to be immortal or deathless in the same sense as in the simplest organisms. The body, in a historical sense, grew up around the germ-cells, taking over functions a little at a time, until in the higher animals nutrition and other activities and a large part even of the reproductive process itself is carried on by body-cells. When we think of a man or woman, we think of an individual only one of whose innumerable activities--reproduction--is carried on by germ-cells, and this one only at the very beginning of the life of a new individual. Human societies, needless to remark, are not organized by germplasms, but by brains and hands--composed of body cells. If these brains and hands--if human bodies--did not wear out or become destroyed, we should not need to trouble ourselves so much about the germplasm, whose sole function in human society is to replace them.