270 H. M. KINGERY 



or twenty-five days after birth (figs. 11,12). As they degenerate, 

 they are gradually replaced by the definitive ova whose follicles 

 have by this time begun to enlarge. 



In the course of the degeneration of the primitive oocytes 

 (those of embryonic origin) the space they occupied in the center 

 of the ovary becomes filled with stroma and blood vessels which, 

 in their growth, form the definitive medulla (figs. 11 to 13). 

 This is well formed by about twenty-eight days after birth. 

 What may now be termed the definitive cortex is filled with 

 follicles containing oocytes of postnatal formation (definitive 

 germ cells) and follicles of embryonic origin (primitive germ 

 cells) which project into it from the medulla. Thus, the de- 

 finitive medulla of the adult ovary includes the embryonic 

 medulla and a large part if not all of the embryonic cortex. 

 The definitive cortex is exclusively of post-partum formation. 



The origin of the rete ovarii is still an open question. Von 

 Winiwarter and Sainmont ('08) describe the rete of the cat as 

 arising from the organ of Mihalkowics which forms a net-like 

 structure of solid cords of cells which later acquire lumina. 

 This net-work of tubules retains its connection with the urini- 

 ferous tubules (epoophoron) and forms a new connection with 

 the inner ends of the medullary cords. The organ of Mihalkowics 

 is described as arising from the capsules, of the glomeruli in the 

 cephalic part of the mesonephros. 



Felix ('12) states for man that, in the degeneration of the 

 mesonephros the glomeruli, corpuscles, and secretory parts of 

 the uriniferous tubules are the first to go, and the collecting 

 tubules persist. The 'rete blastema,' a product of the epithelial 

 nucleus which itself has arisen from the germinal epithelium, 

 forms a net-work of cords. These cords, which are solid at 

 first, but acquire lumina about birth, form the rete ovarii. 

 They connect up with the collecting tubules of the mesonephros. 



Kingsbury ('13) suggests that, in the cat, the rete may arise 

 partly from the mesothelium at the cephalic end of the ovary 

 and partly from ingrowths from the mesonephros. 



In the mouse the mesonephros has a relatively slight develop- 

 ment and degeneration sets in early. I did not make a special 



