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 

 1 



Odgenesis 



Multiplication Period 



Growth Period 



f 



V 



/ \ 



*&&*$ (^)) P<""9 t Chromosomes U^^}Pr mO r y Hcyti 



/ \ j Reducing division I |\ 



Secondar 

 iptrmac 

 fyltj 



Full number of 

 fe'slorey" 



Oflcfary odcytt 

 fi?ru/n and first 

 * polar 6oay) 



I vRHaturtn 



'ana pour 



Mature ovum 



ovum 



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. 



