. The cell in development and inheritance. Cells; Cells. 174 REDUCTION OF THE CHROMOSOMES assumed an actual degeneration or casting out of half the chromo- somes during the growth of the germ-cells — a simple and easily intelligible process. The whole weight of the evidence now goes to show, however, that this view cannot be sustained, and that rediLctioti is effected by a rearrangement and redistribution of the nuclear sub- stance without loss of any of its essential constituents. It is true that a large amount of chromatin is lost during the growth of the ^SS-"^ It is nevertheless certa
. The cell in development and inheritance. Cells; Cells. 174 REDUCTION OF THE CHROMOSOMES assumed an actual degeneration or casting out of half the chromo- somes during the growth of the germ-cells — a simple and easily intelligible process. The whole weight of the evidence now goes to show, however, that this view cannot be sustained, and that rediLctioti is effected by a rearrangement and redistribution of the nuclear sub- stance without loss of any of its essential constituents. It is true that a large amount of chromatin is lost during the growth of the ^SS-"^ It is nevertheless certain that this loss is not directly con- nected with the process of reduction; for, as Hertwig and others have shown, no such loss occurs during spermatogenesis, and even in the oogenesis the evidence is clear that an explanation must be sought in another direction. We have advanced a certain distance towards such an explanation and, indeed, apparently have found it. Fig. 86. — Formation of the polar bodies before entrance of the spermatozoon, as seen in the living ovarian egg of the sea-urchin Toxcpneustes (x 365). A. Preliminary change of form in the germinal vesicle. B. The first polar body formed, the second forming. C. The ripe egg, ready for fertilization, after formation of the two polar bodies (p. b., I, 2) ; e, the egg-nucleus. In this animal the second polar body fails to divide. For division of the second polar body see Fig. 64. in a few specific cases. Yet when the subject is regarded as a whole, the admission must be made that the time has not yet come for an understanding of the phenomena, and the subject must there- fore be treated in the main from an historical point of view. A. General Outline The general phenomena of maturation fall under two heads ; viz. oogenesis, which includes the formation and maturation of the ovum, and spermatogenesis, comprising the corresponding phenomena in case of the spermatozoon. Recent research has shown that matura- tion confo
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