OOGENESIS IN THE WHITE MOUSE 293 



gether with their folUcle cells — which are apparently left over 

 from the first prohferation (v, footnote 3, p. 281) — will make up 

 the definitive cortex. Von Winiwarter and Sainmont do not 

 say so in so many words, but, since they repeat (cf. p. 281 to 283) 

 the assumption made by the senior author in 1900, that cells of a 

 new formation must pass through the nuclear transformations 

 seen in the germ cells of embryonic origin, the inference is that 

 these cells of this post partum proliferation do possess such a 

 nuclear history. The promised later chapter, dealing with this 

 particularly, will doubtless clear up a number of the questions 

 arising from their preliminary account. 



In the mouse the period during which egg-cells are formed from 

 the germinal epitheUum is prolonged, from birth or shortlj^ 

 after, nearly to sexual maturity, instead of being limited to a 

 small part of that time. The process is much more marked 

 during the first half of this period, and becomes gradually slower 

 until it stops shortly before sexual maturity. Correlated with 

 this prolonging of the period during which germ cells are formed 

 from the germinal epithelium is the entire absence of anything 

 resembling 'cords' or tubular down-growths in the ovary after 

 birth. As has been described above (p. 268 and 269), the germ 

 cells arise singly and make their way individually out of the germi- 

 nal epithelium into and through the tunica albuginea. It might 

 be considered that the 'tubular' or 'cord -like' down-growths, such 

 as those found in the cat, are here, shallowed out and retarded, 

 reduced to single cells. It is entirely probable that this prolong- 

 ing of the period, during which definitive oocytes arise from the 

 germinal epithelium, and the 'down-growth' of individual cells, 

 instead of groups of cells, are to be correlated with the small size 

 of the ovary in the mouse. There is not enough room in the 

 organ to contain all the definitive ova, as well as the degenerating 

 primitive oocytes, and, as a result, the process of formation of 

 the former is retarded and prolonged over a long period, and the 

 germ cells arise singly instead of in groups. These definitive 

 egg-cells are added outside the earlier formed primitive oocytes, 

 and room for their growth is provided for b}^ the degeneration 



JOURNAL OF MORPHOLOGY, VOL. 30, NO. 1 



