URINOGENITAL ORGANS 



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cells which enclose the ovum project, as the discus proligerus, into 

 the cavity of the follicle. When ripe, the ovum, surrounded by a 

 vitelline membrane, comes to the surface of the ovary and breaks 

 through into the abdominal cavity ; l it then passes into the 

 coelomic aperture of the oviduct. 



Spermatozoa. In the male, as in the case of the female, primi- 

 tive germinal cells can be at first distinguished in the development 



PS KB 



FIG. 340. SECTION THROUGH A PORTION OF THE OVARY OF A MAMMAL, 

 SHOWING THE MODE OF DEVELOPMENT OF THE GRAAFIAN FOLLICLES. 



D, discus proligerus ; El, ripe ovum, with its germinal vesicle (K) and germinal 

 spot; KE, germinal epithelium, ingrowths from which extend into the 

 stroma of the ovary to form the ovarian tubes ( PS) : the stroma is pene- 

 trated by vessels (g, y) ; Lf, liquor folliculi ; Mp, zona pellucida, showing 

 radiated structure ; <S", cavity between the follicular epithelium (tunica 

 granulosa, My) and the primitive ova ; Tf, theca folliculi ; U, U, primitive 

 ova. 



of the generative elements. These give rise to a series of seminal 

 tubules (Fig. 363), containing larger and smaller cells; the former 

 undergo division to form the active and relative minute sperms 

 or spermatozoa. The nucleus gives rise to the so-called " head " of 

 the sperm, while the surrounding protoplasm becomes differ- 

 entiated to form the motile " tail," the ' neck " arising from the 

 centrosome of the cell (p. 3). 



1 In Mammals a certain amount of blood is poured out through the broken 

 ends of the vessels in the stroma of the ovary into the cavity of the follicle 

 vacated by the ovum ; around it a cellular investment is formed from the follicle- 

 cells, and further modifications take place, resulting in a body of yellow colour, 

 known as the corpus luteitm, the function of which may possibly be that of 

 a "gland with internal secretion" (cf. under Pancreas, Adrenals, &c). 



G G 2 



