MORPHOGENESIS OF THE MAMMALIAN OVARY 365 



disassociation or breaking up of the egg cords in which the growth 

 of the stroma has been largely instrumental. This leads to the 

 isolation of the ova or groups of ova, and from these have come 

 the ova which occur in the medullary follicles that begin their 

 development in the third week after birth. In illustration of 

 this interpretation there are submitted as text figures 1 to 6, 

 six photographs of sections taken entirely at random and there- 

 fore not of illustrative value otherwise. In these the centrifugal 

 oogenetic wave is indicated by the synizesis stage apparent in all 

 save the first and last in which the ova are in the pre- and post- 

 synizetic stages, respectively. From a comparison of these it 

 will become apparent, I believe — if the growth of the ovary be 

 kept in mind — that the large ova in the deeper portion which in 

 the last two figures are in developing medullary follicles are derived 

 from the progressive breaking up of the inner portions of the so- 

 called egg-cords. 



The third difference of interpretation of the medullary follicles 

 concerns the meaning of the peculiarities of their foi-m. The view 

 of von Winiwarter and Saimnont, that the great ii-regularity and 

 peculiar form of the follicles encountered in the ovary of the cat 

 at this stage is due to the destructive activity of the ovarian stroma 

 by penetrating and enucleating the follicle, has been noted above. 

 The striking peculiarity of the follicles developing during this 

 period was observed by myself before I had become aware of the 

 work of von Winiwarter and Sainmont and they had been inter- 

 preted in quite the reverse direction, namely, as progressive rather 

 than regressive pictures. Further examination and considera- 

 ation has but confirmed me in the interpretation. The medul- 

 lary follicles began their progressive development early in the third 

 week after birth, although a close limitation of the time of their 

 appearance cannot be given. The numerous ova in the ovary 

 within the zone of the primitive cortex possess well-marked fol- 

 licular epithelium. Some of them are definitely within so-called 

 medullary cords of elongated form, others within moie irregular 

 masses. A number lie free in the stroma, surrounded only by a 

 single layer of folhcle cells which may vary from flattened to col- 

 umnar in shape. Such ova are particularly found in the peripheral 



THE AMERICAN JOURNAL OF ANATOMT, VOI,. 15, NO. 3 



