THE GERM-CELLS 



41 



{b) Spermatogenesis. 



The observation of the reducing division in the ovum 

 suggested to biologists to look for a similar process in the 

 male germ-cell. This process was actually found to occur, 



A B 



Fig. 30. — Spermatogenesis and Maturation of the Ovl'M com- 

 pared. (After Hertwig, Weismann, and Delage.) 



A, Spermatogenesis. — a-^, the primitive sperm-cell ; ag, the mother 

 sperm-cell ; ^3, two sperm-cells ; a^^, four sperm-cells. 



5, Maturation of Ovum. — b-^, the primitive ovum ; 60, the mother 

 egg-cell ; b^, ovum and first polar body [pb-^ ; b^, ovum with 

 second polar body {pb^, and division of first polar body into 

 two. 



but it is here slightly different from the ovum ; for while 

 the ovum rids itself of half its chromosomes during its 

 maturation, the halving of the chromosomes in the sperm- 



6 



