38 



INBREEDING AND OUTBREEDING 



are similar in all essential features, as may be seen in Fig. 

 9, the elimination of three out of four of the oocytes taking 



SPERMATOSESBSIS 



I 



Spermatc- 

 gonia 



'7)Kv>> I Multiplication 

 yv) f period 



OBGENESIS 



I 



, Primary . 

 Spermatocyte 



Secondary 

 spermalo- 

 cytes 



Spevm- 

 atios 



Sperm- (c\ 

 atozoa 



\} 



Growth period 



Pairing of Chromosomes 



Reducing division 



Ob'gonia 



Primary oocyte 



Secondary oocyte 



(ovum and f irst 



polar body) 



Mature ovum 



and polar bodies 



Mature ovum 



of 



ali zed 

 ovum with 



full 7:umber of 



chromosomes 



restored 



Fia. 9. Diagram of gametogenesis showing the parallel between maturation of the sperm 

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



place in order that their store of nutritive materials may 

 go to make one large egg. 



Fertilization consists in the fusion of one egg with one 

 sperm, thus bringing back the double number of chromo- 



