. The cell in development and inheritance. Cells. 234 REDUCTION OF THE CHROMOSOMES 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. The attempts to find such an explanation have led to some of the most interesting researches of modern cytology ; and though only partially successful, they have raised many new questions which promise to give in the end a deeper insight into some of the fundamental questions of cell-morphology. For this reason they deserve careful considerati
. The cell in development and inheritance. Cells. 234 REDUCTION OF THE CHROMOSOMES 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. The attempts to find such an explanation have led to some of the most interesting researches of modern cytology ; and though only partially successful, they have raised many new questions which promise to give in the end a deeper insight into some of the fundamental questions of cell-morphology. For this reason they deserve careful consideration, despite the fact that taken as a whole the subject still remains an unsolved riddle in the face of which we can only return again and again to Boveri's remark that whatever be its theoretical interpretation the numencaT reduction of the chromosomes is itself not a theory but a Fig. 114. — Formation of the polar bodies before entrance of the spermatozoon, as seen in the living ovarian egg of the sea-urchin, Toxopneustes (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 (yp. b. I, 2) ; e. the egg-nucleus. I-n this animal the first polar body fails to divide. For its division see Fig. 89. 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 maturation conforms to the same type in both sexes, which show as close a paral- lel in this regard as in the later history of the germ-nuclei. Stated in the most general terms, this parallel is as follows : ^ In both sexes the final reduction in the number of chromosomes is effected in the course of the last two cell-divisions, or maturation-divisions, by which the definit
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