10 



THE EGGS OF MAMMALS 



due to the plane of cell division (Figure 2). In the third 

 stage the daughter cells extend two cell layers below the 

 epithelium. And by the fourth stage, occurring during 

 dioestrus, several hundred young ova surrounded by a few 

 folUcle cells are found just beneath the epithelium (Figure 3). 



vm~' 



Fig. 2. A late anaphase in the germinal epithelium of the mouse. 

 The plane of division is nearly parallel to the surface of the ovary. 

 (From the American Journal of Anatomy.) 



According to Allen the tunica albuginea forms ^'from con- 

 nective tissue ingrowth during the absence of ovogenetic 

 proliferation of the germinal epithelium." Allen notes a 

 relatively intact tunica in animals that have had a long 

 period of dioestrus and also a complete or an almost complete 

 absence of young follicles. 



Cowperthwaite (1925) has criticized Allen's data On the 

 grounds that he gives no demonstration of the presence of 

 meiosis in these presumable new ova. Typical meiotic 

 phenomena in adult ovaries have, in fact, rarely been ob- 

 served. De Winiwarter (1920) noted oocyte formation in 

 the region of the hilum in ovaries of cats shortly after puberty 

 but no such process in the remaining tissue, and Gerard 



