302 H. M. KINGERY 



pithelium, the cells adjacent to it extend up around and down 

 under it, enclosing it while it is still in the epithelium. Thus, 

 when the oocyte is left behind, or under the epithelium in the 

 tunica albuginea, it is surrounded by a primary follicle made up 

 of a few flattened cells. 



6. In the mouse the primitive germ cells have a course of 

 development different from that of the definitive oocytes. The 

 former, of the first or embryonic proliferation, undergo synizesis; 

 then they pass through the stages pachytene, diplotene, dictyate or 

 dictye (of von Winiwarter) and are then overtaken by degen- 

 eration, which may be atrophy or a degenerative fragmentation. 



The cells formed from the germinal epithelium after birth, 

 the definitive oocytes, have a different history; their chromatin 

 is in the form of an irregular network, clumps of chromatin at 

 the intersections, with from two to five nucleoli in the meshes. 

 With the growth of the oocyte, the chromatin becomes attenu- 

 ated and stains more faintly until there is the appearance of 

 irregular granules of chromatin connected by very slender chroma- 

 tin strands and the remnants of the linin reticulum, and one 

 large faintly s.taining nucleolus with frequently one or two others 

 more deeply stained. This condition persists until the egg is in a 

 mature Graafian follicle, ready for maturation. 



7. The evidence from a study of the mouse ovary, while not, 

 perhaps, conclusive on this point, tends to show that the 'pri- 

 mordial germ cells' ('Ureier') probably degenerate, playing no 

 part in the development of the definitive ova. 



Oocytes originating from cells of the germinal epithelium by a 

 process of differentiation, the 'primitive germ cells,' develop .to 

 a certain point and then degenerate. None of these cells take 

 part in the formation of the definitive ova. 



8. The definitive germ cells develop by a process of differentia- 

 tion from cells of the germinal epithelium. Stages can be ob- 

 served, transitional between mesothelial cells on the one hand 

 and primary oocytes in Graafian follicles on the other. This 

 differentiation takes place after birth and before sexual maturity, 

 constituting a 'new formation' of germ cells. 



