We saw that, in the full-grown ovarian egg, the germinal vesicle rises to the surface and there becomes transformed into the first polar spindle. Now this shows, in its equatorial plane, double the number of chromosomes normal to the species. This duplication comes about, not directly before the nuclear division, but much earlier in the young mother-egg-cell; it is only the change in the time of the splitting of the chromosomes that is unusual. The first maturation division takes place nevertheless in accordance with the usual plan of nuclear division; it is, as I have called it, an 'equation division,' that is, both daughter-nuclei again receive the same number of chromosomes as the young mother-egg-cell had to start with, namely, the normal number of the species. Thus, if the young mother-egg-cell had four chromosomes (Fig. 76, _A_), this number would double to eight at an early stage (_B_), but the first maturing division would give each daughter-nucleus four (_C_ and _D_). In the second maturation division the case is different, for here no splitting and duplicating of the number of chromosomes takes place, but the existing number, by being distributed between the two daughter-nuclei, is reduced to half in each (_E_ and _F_). For this reason I have called it a 'reducing division.' In our example, therefore, the ovum, as well as the second polar body, would contain only two chromosomes (Fig. 76, _F_). [Illustration: FIG. 76. Diagram of the maturation divisions of the ovum. _A_, primitive germ-cell. _B_, mother-egg-cell, which has grown and has doubled the number of its chromosomes. _C_, first maturation division. _D_, immediately thereafter; _Rk1_, the first directive cell or polar body. _E_, the second maturation spindle has been formed; the first polar body has divided into two (2 and 3); the four chromosomes remaining in the ovum lie in the second directive spindle. _F_, immediately after the second maturation division; 1, the mature ovum; 2, 3, and 4, the three polar cells, each of these four cells containing two chromosomes.] I cannot enter into the details of the process here, for we are dealing with essentials and not with isolated and, so to speak, chance details, but I must emphasize the fact that the same process of reduction of the number of chromosomes takes place in this or an analogous manner in all animal ova, and can be demonstrated also in most of the chief groups of plants. Whether it be, as many have maintained, that the reduction is not always first effected by the 'maturation divisions,' but in some cases takes place earlier in the primitive egg-cell[12], so much is certain, that the nuclei which come together for 'fertilization' only contain half the normal number of chromosomes, and this is true not only of the ovum but also of the sperm-nucleus. [12] See the discussion of this point in chapter xxii.