THE ORIGIN OF THE DEFINITIVE OVA 7 



number of these cells is by mitosis only, and no new cells 

 are recruited from somatic tissue. This view is set forth at 

 some length by Hegner (1914, also Vanneman, 1917). It 

 leads naturally to the conclusion long maintained as a 

 biological truism that by the end of embryonic life or shortly 

 thereafter the complete quota of future eggs is attained 

 (c/. Waldeyer, 1870 and 1906; Felix, 1912 and Pearl and 

 Schoppe, 1921). The calculations of Aschner (1914) indi- 

 cating the presence of some 400,000 ova in the human ovary 

 at birth furnishes an apparent statistical substantiation. 

 Furthermore, meiotic phenomena are observable in these 

 primordial germ cells during embryonic and prepubertal 

 life (Cowperthwaite, 1925) but not thereafter, and the as- 

 sumption is made that typical meiosis is necessary for the 

 formation of definitive ova. 



This conception of a large early store of future ova is 

 scarcely controverted by a second group of investigators 

 who admit the primordial germ cells as precursors of the 

 future ova, but who claim that additional egg cells are 

 supplied by proliferations from the germinal epithelium. 

 Brambell (1927) in a careful study of the developing gonads 

 of the mouse finds that the primordial germ cells persist 

 throughout embryonic life and undergo maturation stages, 

 but declares that additional cells from the germinal epi- 

 thelium must be responsible for the large increase of cortical 

 cells found in the gonad before the formation of the tunica 

 albuginea in ten and twelve day embryos. 



Perhaps the largest group of observers consists of those 

 who also consider post-pubertal production of new egg cells 

 non-existent or negUgible but who find that the primordial 

 germ cells degenerate and are replaced by secondary pro- 

 liferations during embryonic or prepubertal life. Thus 

 Rubaschkin (1908, 1910, 1912) decided that the large dif- 

 ferentially staining primordial germ cells with their prom- 

 inent attraction spheres degenerate in the early guinea pig 

 embryo and are replaced by two successive proliferations 

 from the germinal epithelium. De Winiwarter and Sainmont 



