352 



THE GENITOURINARY ORGANS. 



formed, not by a longitudinal splitting of the chromosomes, but by 

 a transverse division. 



In the process of development of the ova, three periods are 

 therefore distinguishable. The first, or period of proliferation, rep- 

 resents a stage of repeated mitotic division in the oogonia, during 

 which the latter become gradually reduced in size. In the second, 

 or period of growth, the oogonia increase in size and are then ready 

 for the third, or period of maturation. In the latter, by means of 

 a modified double mitotic division, uninterrupted by any resting 

 stage, the matured ovum and the polar bodies are formed. These 

 several periods are represented in figure 283. 



The manner in which the fully developed Graafian follicle 



Primordial egg-cell. 



Oogonia 



Oocyte I. order. 



Oocyte II. order. 



Matured ovum. 



Germinal zone. 



Zone of mitotic division. 



(The number of genera- 

 tions is much larger than 

 here represented.) 



of growth. 



I. P. B. / Zone of maturation. 



\ A I 



II. P.B. 



Fig. 283. Scheme of the development and maturation of an ascaris ovum (after Boveri) : 

 P. B., Polar bodies. (From " Ergebn. d. Anat. u. Entw.," Bd. I.) 



bursts and its 'ovum is freed is still a subject of controversy ; the 

 following may be said regarding it : By a softening of the cells 

 forming the pedicle of the discus proligerus, the latter, together 

 with the ovum, are separated from the remaining granulosa, and lie 

 free in the liquor folliculi. At the point where the follicle comes in 

 contact with the tunica albuginea of the ovary, the latter, with the 

 theca folliculi, becomes thin, and in this region, known as the 

 stigma, the blood-vessels are obliterated and the entire tissue grad- 

 ually atrophies ; thus a point of least resistance is formed which gives 

 way at the slightest increase in pressure within the follicle, or in its 

 neighborhood. 



