Sexually reproducing animals and plants pass their cells and genetic information to subsequent generations through a type of cells called "germ cells" (Fig. 5-6). The fate of these germ cells is different from that of the somatic cells that form various structures of the body; the germ cells are passed on to the next generation. The separate fates of the germ cells and somatic cells begin with cleavage after fertilization. In organisms such as fruit flies and frogs, those fates are determined by special substances stored in the egg-cell cytoplasm, called "germplasm." By this mechanism, only the cells that pass on germplasm become germ cells, and all the other cells become somatic cells. A similar mechanism is known to exist in us mammals.