REPRODUCTIVE ORGANS IN THE FEMALE. 309 



of spermatozoa, only one of which penetrates the 

 substance of the ovum. 



The substance of the ovum is known as the mtellus. 

 It is a soft semifluid substance composed of cyto- 

 plasm in which is deposited a liberal supply of food 

 material called deutoplasm. The nucleus of the 



Primordial egg-cell. 



Germinal zone. 



Zone of mitotic division. 

 (The number of gen- 

 erations is much larger 

 than here represented.) 



Zone of growth. 



Zone of maturation. 



Oocyte I. order. 

 Oocyte 11. order. ^^A V I. P.B. 



\ f\ 



\ 



Matured ovum. 



^r 



II. P.B. 



Fig. 225. Scheme of the development and maturation of an ascaris 

 ovum (after Boveri): P. B., Polar bodies. (From "Ergebn. d. Anat. u. 

 Entw.," Bd.-I.) 



ovum is called the germinal 'vesicle, which is placed 

 to one side of the cell. The nucleus is unusually 

 large, about 0.05 mm. in diameter, and has all the 

 characteristics of an ordinary cell nucleus. This 

 was first described by Purkinje in the ovum of birds 

 in 1835. There is a well-defined nuclear membrane 



