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 oogonia 

 enlarge to become primary oocytes (Fig. 48, b). In each primary 



Spermatogenesis 



V3X 



I\ 



Multiplication Period 



Croh/th period 



Pairing of Chromosor, 

 / \ } Reducing division 



Obgcnesis 



J 



A 



FIG. 49. Diagram showing the parallel between maturation of the sperm- 

 cell and maturation of the ovum. (From Guyer.) 



oocyte 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. 



