ORIGIN OF DEFINITIVE SEX-CELLS 467 



Except as regards the origin of the oogonia, I agree with 

 d'Hollander in his findings. 



Sainmont ('05) in his investigations on oogenesis in the cat 

 described the cords of second prohferation as composed of oogonia, 

 which were derived from primordial germ-cells. However, he 

 retracted this opinion in 1909 in an article on spermatogenesis 

 and oogenesis in the cat, in which he collaborated with von 

 Winiwarter. 



Since 1904, the date of d'Hollander's article, all investigators 

 with the exception of Riibaschkin and his pupils have adopted 

 the opinions of d'Hollander as regards the origin of the oogonia 

 in the chick. 



The ovary of the 11-day-old embryo resembles closely that of 

 that 10-day embryo. 



The cell buds have now attained a size which warrants their 

 being called cords of the second proliferation. In the cortical 

 cords the oogonia still show signs of activity, although it is not 

 so marked as in the two preceding stages. The oogonium it- 

 self resembles closely the same element as described in the 9-day 

 ovary. In between the oogonia are a few much smaller cells, 

 which show occasional mitotic figures, and which are derived 

 from the cells of the germinal epithelium. These are the deep 

 indifferent cells of d'Hollander, the elements from which the 

 follicular epithelium is derived in later stages. 



The next ovary studied was from a chick embryo of 14 days' 

 development. 



The cortical cords are much more massive — in some as many as 

 30 oogonia may be counted in a single section of one (fig. 8). 

 The cords now extend down into the medulla for some distance, 

 although they are still separated from it, as well as from each 

 other, by a thick layer of connective tissue (fig. 8). In places 

 the cortical cords are separated from the epithelium by a layer 

 of this connective tissue, which in this position, under the ger- 

 minal epithelium, may now be called the true albuginea (fig. 8). 

 The germinal epithelium now consists of a single layer of cubical 

 to columnar cells. 



