MORPHOGENESIS OF THE MAMMALIAN OVARY 373 



folliculi that can, under certain unknown conditions, induce 

 maturation. 



In the period of sexual maturity the development of the 

 Graafian follicles is quite variable and the morphology of the 

 ovar}^ fluctuates correspondingly. Figure 15 shows a typical sec- 

 tion of the zones of the adult ovary, the zona parench;yanatosa 

 consisting of cortex and zone of Graafian ^follicles (epithelio- 

 stromal zone), and the zona vascularis. 



GENERAL CONCLUSIONS 



The results of this study of 60 series of cat ovaries may be 

 summed up briefly at this point. From the stage with which the 

 stud}' began, when the ovarian character of the organ is clearly es- 

 tablished (75 mm. fetus) to sexual maturity, the ovary increases 

 in diameter approximately five times. The growth zone appears 

 to be mostly peripheral, in and beneath the mesothelial covering 

 epithelium that is the source of the ova and folHcle cells. The 

 greatest activity appears in the primitive cortex beneath the sur- 

 face epithelium rather than in the latter, and growth continues 

 here well into the postpartum period, as von Winiwarter and 

 Saiimiont have shown. Up to approximately the third week 

 postpartum the surface epitheUum and the underlying cell cords 

 of mesothelial origin form a common mass, the latter being con- 

 nected with the former. Subsequently (third week) they are 

 separated by the appearance of a tunica albuginea. 



At the margins of the ovary bordering the hilum the growth 

 activity continues much longer (up to approximately three to 

 four months) and along this bordering zone the surface epithelium 

 retains its connection with the underlying egg and follicle cell 

 groups. 



The deeper masses of cells of mesothelial origin are the older 

 and differentiation follows a centrifugal course save at the mar- 

 gin where younger stages in the oogenesis are to be encountered 

 long after they have disappeared from t"he remainder of the ovary. 

 In this growth the stroma plays an important part. The growth 

 of the ovary may be said therefore to be mainly peripheral and 

 marginal, and the differentiation centrifugal and marginal. . 



