THE OVARIAN OVU^.r. 



^77 



as arisino^ simnltaneotisly, although doubtless the germs may be lielcl 

 to have had previous existence as parts of the germinal epithelium 

 covering the primordial structure of the ovary. By the middle of 

 foetal life, or at the end of the fifth month, the follicle, which is at 

 first only a space for the germ in the ovarian stroma, has received 

 a simple lining of scattered cells, which afterwards in their more 

 developed form constitute the tunica granulosa, and the germinal 

 vesicle is by the same time surrounded by a small quantity of clear 

 protoplasm, or com.mencing yolk, which separates the vesicle from the 

 granular cells. Still later the zona pellucida appears as a clear mem- 

 branous covering of the yolk protoplasm. By the sixth or seventh 

 month of fcetal life an immense number of such small ova closely em- 

 braced by the enclosing Graafian follicles have appeared, so that the 

 ovary appears to be almost entirely occupied by them ; and as they 

 may be counted in prepared specimens of sections, it is easy to estimate 

 their number in tJie entire ovary. The result of such estimates gives 



Fisr. 338 



338. — Ova in different stages of puogeess 



Highly iiagnified. 



A, pvimordial ovum from human fcetus of eiglit months ; B, early follicle of raLbit 

 witli ovum enclosed; C, the same of the pigeon ; D, another of the same more advanced 

 the secondary yolk commencing ; E, ovum of the rabbit from a follicle of i of an inch 

 in diameter ; a, epithelium of the discus proligenis ; h, zona pellucida, showing radiateil 

 linearj structure, perhaps too strongly marked ; c, germinal vesicle ; d, germinal macula r 

 c, yolk substance with tine granules and small oil globules. 



an amount of not less than .30,000 or 40,000 for each ovary of the 

 human foetus before birth. The formation of new ova and Graafian 

 follicles probably still continues for some time, but at a much slower 

 rate than during foetal life. 



