AN INTRODUCTION TO THE METAZOA 



83 



Oogenesis. — The origin of the female germ cell or egg is 

 called oogenesis (Fig. 48). Stages are passed through by the 

 germ cells corresponding almost exactly to those described under 

 spermatogenesis (Fig. 47). Before the growth period the germ- 

 cells which will produce eggs are known as oogonia (Fig. 46, A ; 



p.b.i- 



mi* 



IJ 





Fig. 4g. — Diagrams illustrating the maturation, fertilization, and cleavage 

 of an egg. The primordial germ-cell is represented as possessing four chro- 

 mosomes. 



