310 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



which encloses a clear nuclear substance in which 

 there is a limited amount of chromatin, and the nu- 

 cleus, therefore, does not stain heavily. The nucleo- 

 lus, on the other hand, is very prominent and is 

 called the germinal spot. Not infrequently two 

 nucleoli may be found. There is some doubt whether 

 a cell membrane to the ovum is present before fer- 



Primordial sexual cell. 



Spermatogonia . 

 \ 



Spermatocyte I. order. 



Spermatocytes II. order. 



Spermatids. 



Zone of proliferation. 

 (The generations are 

 much larger.) 



Zone of growth. 



Zone of maturation. 



Fig. 226. Schematic diagram of spermatogenesis as it occurs in 

 ascaris (after Boveri). (" Ergebn. d. Anat. u. Entw., " Bd. I.) 



tilization. After fertilization such a membrane 

 appears and is called the mtelline membrane. As a 

 rule each Graafian follicle contains one ovum ; in rare 

 cases follicles are found with two and even with three 

 ova. 



When a Graafian follicle ruptures and an ovum is 



