THE BIOLOGICAL BACKGROUND OF GENETICS 



203 



THE MATURING OF GAMETES 



The primordial germ cells, previously described as having been set 

 apart from the soma at a relatively early period of development and 

 located in germ glands (ovaries and testes), pass through a period of 

 comparative inactivity until sexual maturity arrives. At the dawn 



» 



Fig. 45. — Diagram of the germ track in Ascaris. E; egg; Pi, P 2 , Pi, stem 

 (germinal) cells; P A , primordial germ cell. Circles represent somatic cells, while the 

 four black dots outside of the circles represent the masses of chromatin that are 

 eliminated. (From Boveri, igio.) 



of sexual maturity the germ cells wake up and enter upon a period of 

 great activity, during which mature gametes are produced. The his- 

 tory of the production of gametes differs somewhat in the two sexes. 

 That of the male, called spermatogenesis, is a little simpler than that 

 of the female, called oogenesis, and will be described first. 



Spermatogenesis. — The first sign of renewed activity of the male 

 germ cells is evidenced by a succession of rapid cell divisions, the 



