308 GEORGE W. BARTELMEZ 



(1) The first growth period, the final stages of which are pre- 

 sented by the youngest oocytes in the adult ovary — the primordial 

 follicles. The primordial follicle has a bilateral structure which 

 can be traced through the ovarian history and which is marked 

 primarily by the fact that the polar axis intersects the long axis 

 nearer to one end. 



(2) The] second growth period, during which" the bilateral sym- 

 metry of the oocyte is impressed upon the connective tissue fol- 

 licle which in turn plays a part in the preservation of the sym- 

 metry of the oocyte as a whole during the subsequent growth. 

 The germinal vesicle comes to lie nearly but not quite at the center 

 of the oocyte, its eccentricity marking the polar axis which is 

 constant throughout oogenesis. Two ooplasmic zones are differ- 

 entiated: central and peripheral protoplasm. 



(3) During the period of differentiation the germinal vesicle 

 migrates peripherally, its path determining the position of the 

 latebra, which as a result of the corresponding position of the 

 germinal vesicle in the preceeding stages, is nearer one end of 

 the ooplasmic long axis. The Anlage of the blastodisc appears 

 about the germinal vesicle. The oocyte becomes free to rotate 

 within its follicle, probably as a result of the formation of the 

 zona radiata. 



(4) The final growth period is initiated by the stimulus of 

 mating and in the course of it the great mass of yolk is laid down 

 in such form that the eccentricity of the latebra is preserved. 



Data have been obtained on the character of the process of 

 ovulation and the orientation of the egg in the oviduct. The 

 position of the latebra nearer one end of the long axis determines 

 which end of the egg shall pass down the oviduct first and the 

 activity of the infundibulum and other factors orient the follicle 

 so that its long axis coincides with the oviducal axis. 



The blastodisc is formed symmetrically about the germinal 

 vesicle and the segmental disc and periblastic zones can be dis- 

 tinguished by the end of the period of differentiation. The embry- 

 onic axis first appears unmistakably in the formation of the 

 periblast in the mature ovarian egg. During the final stages of the 

 second maturation, at the time when fertilization has normally 



