300 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
Maturation of the egg-cell—As regards the behavior of the 
chromosomes the maturation of the ovum parallels that of the sperm- 
cell. There are not so many primordial germ-cells formed and only 
one out of four of the ultimate cells becomes a functional egg. As in 
maturation of the sperm-cell there is a growth period in which oégonia 
enlarge to become primary odcytes (Fig. 48, 6). In each primary 
Spermatogenesis Oogenesis 
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Fic. 49.—Diagram showing the parallel between maturation of the sperm- 
cell and maturation of the ovum. (From Guyer.) 
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odcyte as in the primary spermatocyte the chromosomes pair and two 
rapidly succeeding divisions follow in one of which the typical numeri- 
cal reduction in the chromosomes occurs. A peculiarity in the 
maturation of the ovum is that there is a very unequal division in 
the cytoplasm in cell-division so that three of the resulting cells 
usually termed polar bodies are very. small and appear like minute 
buds on the side of the fourth or egg-cell proper. 
