MORPHOGENESIS OF THE MAMMALIAN OVARY 355 



face mesothelium, being apparently more abundant in the earlier 

 stages in which the- egg cords are relatively more broadly con- 

 nected with it. It but shares with the underlying egg cords a 

 common growth activity and in no sense can it be regarded as the 

 sole direct center of proliferation from which the latter are formed. 

 Indeed, at birth the mitoses are more abundant in the outer por- 

 tions of the egg cords than in the surface epithelium with which 

 they are connected. The synizesis figure of the germ cells forms 

 a convenient landmark which serves to mark the centrifugal 

 march of differentiation within the egg cords. Mitoses continue 

 to occur within the peripheral portion of the egg cords until about 

 two weeks after birth. 



von Winiwarter and Sainmont have described the divisions of 

 the oogonia as practically ceasing at the time of birth, marked 

 multiplication appearing again in the twenty-first-day ovary and 

 becoming permanently arrested soon thereafter. I have seen no 

 evidence of such a periodicity in the oogonial divisions in the 

 material employed by me, which, it must be confessed, was not 

 as abundant as that studied by these authors. The advance of 

 the 'wave of synizesis' appeared a fairly steady centrifugal pro- 

 gression. In the thirty-three-day ovary the superficially located 

 germ cells of the cords were in the synizesis stage, all the more 

 deeply placed cells being postsynizetic. In all subsequent stages 

 the ova were definite oocytes and in the seven-weeks' ovary the 

 definitive cortex with its primary or resisting follicles was differ- 

 entiating out of the primitive cortex. 



In its development the ovary of the cat, as far as concerns 

 the growth and differentiation of the cells that — according to the 

 writer's interpretation — are to become the definitive ova of the 

 period of sexual maturity, conforms to the plan described by Felix 

 for the human o\'ary, the egg cords being less distinct in the human 

 ovary and the neogenic zone described by Felix less developed 

 as a distinct zone in the cat. The distinctness of the neogenic 

 zone destined to furnish the ova of the mature period would appear 

 to be likewise evident earlier than in the cat. The stroma by 

 its growth evidently plays an important part in the breaking up 

 of the egg cords and the formation of the primary follicles of the 



