=The Origin of the New Germ-Cells.--=On account of the unusual importance from the standpoint of inheritance, which attaches to the germ-cells, a final word must be said about their origin in the embryo. While the evidence is conflicting in some cases, in others it has been well established that the germ-cells are set apart very early from the cells which are to differentiate into the ordinary body tissues. Fig. 7_A_, p. 38, shows a section through the eight-celled stage of _Miastor_, a fly, in which a single large, primordial germ-cell (_p. g. c._) has already been set apart at one end of the developing embryo. The nuclei of the rest of the embryo still lie in a continuous protoplasmic mass which has not yet divided up into separate cells. The densely stained nuclei at the opposite end of the section are the remnants of nurse-cells which originally nourished the egg. Fig. 7_B_, p. 38, is a longitudinal section through a later stage in the development of _Miastor_; the primitive germ-cells (oög) are plainly visible. Still other striking examples might be cited. Even in vertebrates the germ-cells may often be detected at a very early period. =Significance of the Early Setting Apart of the Germ-Cells.--=It is of great importance for the reader to grasp the significance of this early setting apart of the germ-cells because so much in our future discussion hinges on this fact. The truth of the statement made in a previous chapter that the body of an individual and the reproductive substance in that body are not identical now becomes obvious. For in such cases as those just cited one sees the germinal substance which is to carry on the race set aside at an early period in a given individual; it takes no part in the formation of that individual's body, but remains a slumbering mass of potentialities which must bide its time to awaken into expression in a subsequent generation. Thus an egg does not develop into a body which in turn makes new germ-cells, but body and germ-cells are established at the same time, the body harboring and nourishing the germ-cells, but not generating them (Fig. 2, p. 13). The same must be true also in many cases where the earliest history of the germ-cells can not be visibly followed, because in any event, in all higher animals, they appear long before the embryo is mature and must therefore be descendants of the original egg-cell and not of the functioning tissues of the mature individual. This need not necessarily mean that the germ-cells have remained wholly unmodified or that they continue uninfluenced by the conditions which prevail in the body, especially in the nutritive blood and lymph stream, although as a matter of fact most biologists are extremely skeptical as to the probability that influences from the body beyond such general indefinite effects as might result from under-nutrition or from poisons carried in the blood, modify the intrinsic nature of the germinal substances to any measurable extent.