44 



THE FROG 



SPERMATOGENESIS 



OOGENESIS 



Primordial Germ Cells 

 (.undifferentiated) 



Period of Division 

 ( mitosis ) 



Growth Period 

 ( synapsis and tetrad formation) 



1st Meiotic Division 

 ( disjunction of split 

 homologous chromosomes ) 



2nd Meiotic 

 Division 

 ( separation of 

 half -chromosomes ) 



Mature 

 Germ Cells 

 (gametes) 



Spermatozoa 



Ovum 



Fig. 29. — Gametogenesis in animals; diagrammatic. Homologous chromo- 

 somes are lettered alike; A and B are autosomes, X and Y are sex chromo- 

 somes. The chromosomes shown in black represent the paternal contribution, 

 while the un.shadctl ones are from the mother. During the growth period 

 food is stored in the cytosome of the primary oocyte; this yolk remains in 

 the ovum and is not distributed to the pohir bodies. 



