GENETIC FACTORS IN THE ORIGIN OF DIVERSITY 381 



The spermatogonia, originally few in number, multiply by the ordinary 

 process of cell division, mitosis. For sake of simplicity in the diagram only 

 one of these mitoses is indicated, and this is done without including all the 



SPERMATOGONIA 

 (many mitoses) 



PRIMARY SPERMATOCYTE 



(shown at metaphase) 



SECONDARY 

 SPERMATOCYTES 



(shown at metaphase) 



SPERMATIDS 



SPERMS 



FIG. 17.2. Meiosis (spermatogenesis) in the male. 



Stages in the process (see Fig. 5.2, p. 83). Eventually each resulting 

 spermatogonium becomes a primary spermatocyte. By this time each 

 chromosome has duplicated itself. The two resulting duplicate chromo- 

 somes (chromatids) are for the time being held together by the centromere 



