OOGENESIS IN THE WHITE MOUSE 287 



ported such a view. The last course, degeneration, seems to 

 be the most probable fate of these cells. 



There are not many examples in the literature of a new forma- 

 tion of epg-cells after birth. Van Beneden ('80) described in 

 the adult bat a formation of egg-cells from the germinal epithelium. 

 From his description and figures, the process resembles the 

 formation of oocytes in the mouse before sexual maturity; but, 

 as he did not connect this process with that in the embryo, it is 

 difficult to say whether it is strictly comparable with the con- 

 dition in the mouse. 



Lane-Claypon ('05), in a study of the ovary of the rabbit, 

 concludes that from the germinal epithelium are formed defini- 

 tive ova, foUicle cells, and interstitial cells. These interstitial 

 cells, from their origin, are potential egg-cells, and, under the 

 proper stimulus, are capable of developing into ova. In this 

 case, the proper stimulus is provided in some way by pregnancy, 

 and a number of these cells become differentiated into oocytes. 

 Apparently these conclusions have not been confirmed by other 

 authors, and hence lose something of their force. 



Von Winiwarter and Sainmont ('08) state that in the cat, at 

 about the age of three and one-half or four months, a renewal 

 of the activity of the germinal epithelium provides a new supply 

 of germ cells w^hich develop into the definitive ova, when all 

 the egg-cells of the first and second proliferations have degener- 

 ated. In a note appearing about the same time ('08^), they 

 state that these definitive ova come either entirely from this 

 third proUferation, or partly from it and partly from undifferenti- 

 ated cells left over from the second.^ 



^ "Es tauchen nun jetzt in den Epithelhaufen unci Striingen dcr Corticalis 

 Kleine Gruppen von Zellen auf, deren Kerne im Staubformigen oder deutobrochen 

 Stadium sind. Diese Fonnen waren schon seit langer Zeit nicht mehr vorhan- 

 den, und da sie den ersten Stuf en des Wachstunis des Oocj^ten cntsprechen, ist es 

 augenscheinlich, dass sie mit einer Neubildung von Eiern zusammenhangen. . . 

 Wir glauben bewiesen -zu haben, dass in Saugetierovarium nicht nur samtliche 

 MarkstrJiuge, sondern auch alio Eier und Follikel der primitiven Corticalis dem 

 Untergang anheimfallen. Die definitiven Eier entstammen entweder von undif- 

 ferenzierten Zellen der zweiten Proliferation (Pfliigersche Schlauche) oder von 

 Zellen der dritten Wucherung oder invaginations 6pithelials. Es ist uns nicht 

 moglich, wenigstens morphologisch, die Elemente der einen und anderen zu 

 unterscheiden." (v. Winiwarter and Sainniont, '08 a, p. 616.) 



