At one end of the ovary, generally that nearest to the oviduct, there is a mass of protoplasm, containing nuclei which actively divide; this is the germarium (Fig. 15, A, B, C). As a result of proliferation in the germarium, nucleated masses are thrown off into the cavity of the ovary; each such mass contains four nuclei, and its protoplasm soon becomes divided into four portions, one round each nucleus, so that four cells are produced. In the simpler ovaries, such as that of _Leptodora_ (Fig. 15, A), these sets of four cells are arranged in a linear series within the tube of ovarian epithelium; in other cases, as in _Daphnia_, the arrangement is more irregular. In the normal development of parthenogenetic eggs, one cell out of each set of four becomes an ovum, the other three feeding it with yolk and then dying. Weismann[32] has shown that the ovum is always formed from the third cell of each set, counting from the germarial end, so that in the ovary of _Leptodora_ drawn in Fig. 15, A, the ova will be formed from the cells marked E_{1}, E_{2}, E_{3}. At certain times, one or two sets of germinal cells fail to produce ova; the epithelial wall of the ovary thickens round these cells, so that they become incompletely separated from the rest in a so-called “nutrient chamber” (Fig. 15, B, _N.C_). Germ-cells enclosed in a nutrient chamber degenerate and are ultimately devoured by the ovarian epithelium. The significance of these nutrient chambers is unknown. [Illustration: FIG. 15.—=A=, Ovary of a parthenogenetic _Leptodora hyalina_; =B=, base of another ovary of the same species, showing a so-called “nutrient chamber”; =C=, ovary of a female _Daphnia_, showing the formation of a winter-egg. _E_, _E_{1}–E_{3}_, Parthenogenetic egg; _Ep_, ovarian epithelium; _G_, germarium; _N.C_, nutrient chamber; _O.D_, oviduct; _W_, winter-egg; 1, 2, 4, the other three cells of the same group; II, III, two other groups of germ-cells. ]