The non-independent cells which remain united in communities or states, and thus constitute the body of higher organisms, are propagated in the same manner as are independent single-celled organisms, for example, Amœba (Fig. 2). Just as in that case, the cell with which most animals and plants commence their individual existence, namely, the egg, multiplies itself by simple division. When an animal, for instance a mammal (Fig. 3, 4), develops out of an egg, this process of development always begins by the simple egg-cell (Fig. 3) forming an accumulation of cells (Fig. 4) by continued self-division. The outer covering, or cell membrane, of the globular egg remains undivided. First, the cell-kernel of the egg (the so-called germinal vesicle) divides itself into two kernels, then follows the cell-substance (the yolk of the egg) (Fig. 4 _A_). In like manner, the two cells, by continued self-division, separate into four (Fig. 4 _B_), these into eight (Fig. 4 _C_), into sixteen, thirty-two, etc., and finally there is produced a globular mass of very numerous little cells (Fig. 4 _D_). These now, by further increase and heterogeneous development (division of labour), gradually build up the compound many-celled organism. Every one of us, at the commencement of our individual development, has undergone the very same process as that represented in Fig. 4. The egg of a mammal—represented in Fig. 3, and its development in Fig. 4—might as well be that of a man, as of an ape, dog, horse, or any other placental mammal. [Illustration: FIG. 4.—First commencement of the development of a mammal’s egg, the so-called “cleavage of the egg” (propagation of the egg-cell by repeated self-division). _A._ The egg, by the formation of the first furrow, falls into two cells. _B._ These separate by division into four cells. _C._ The latter have divided into eight cells. _D._ By repeated division a globular accumulation of numerous cells has arisen.] Now, when one examines this simplest form of propagation, this self-division, it surely cannot be considered wonderful that the products of the division of the original organism should possess the same qualities as the parental individual. For they are parts or halves of the parental organism, and the matter or substance in both halves is the same, and as both the young individuals have received an equal amount and the same quality of matter from the parent individual, one can but consider it natural that the vital phenomena, the physiological qualities should be the same in both children. In fact, in regard to their form and substance, as well as to their vital phenomena, the two produced cells can in no respect be distinguished from one another, or from the mother cell. They have _inherited_ from her the same nature.