130 Embryonic Development of Ovary and Testis of Mammals 



B. Ovary. — The tissues to be considered in this organ are as follows : 



1. Cords of Pfliiger and peritoneum. 



2. Medullary cords. 



3. Eete tubules. 



4. Interstitial cells and stroma. 



1. Cords of Pfiuger, and Pei'itoneum. — The cords of Pfliiger, were seen 

 to arise in the 2.5 cm. pig embryo as columns of cells growing into the 

 stroma from the peritoneum. During later stages, they lengthen by 

 centrifugal growth, cell multiplication taking place largely at their points 

 of attachment to the peritoneum. One can find all stages in the develop- 

 ment of the oogonia (see Plate VI, Fig. 22) from the stage when they 

 are indistinguishable from the other cells of the peritoneum from which 

 they originate, to that in which more mature forms of oocytes are found 

 in the deeper-lying portions of the cords of Pfliiger. There is a gradual 

 transition in these cells; the degree of maturity corresponding with the 

 distance from the surface of the ovary. In the rabbit, certain small 

 nuclei of cells without cell boundaries divide by amitosis (Plate VI, Fig. 

 22). These cells of the cords of Pfliiger correspond to the germinative 

 cells of the seminiferous tubules. In the ovary, they are destined to 

 form the granulosa cells, although it might well remain an open question 

 whether some of these amitotically dividing cells do not also transform 

 into sex cells. 



In certain of the later stages of the pig (13 and 15 cm. embryos), 

 tubular cords of Pfliiger make their appearance (Text Fig. 3). They 

 extend from the peritoneum for some distance into the medullary sub- 

 stance. By the development of the cells forming these peritoneal tubules 

 they become transformed into solid cords containing primitive sex cells 

 and other elements similar to the peritoneal cells of which these invagi- 

 nations were originally composed. The latter are destined, in part at 

 least, to form the granulosa. In the manner above described, these hol- 

 low tubules become transformed into solid cords of Pfliiger, in every 

 way homologous with the cords laid down at an earlier period of develop- 

 ment. In still later stages, the cords of Pfliiger are found to have 

 widened, branched, and anastomosed to such an extent as to form an 

 almost unbroken cortical zone, through which plates of connective tissue 

 extend in a radial direction, marking out the original limits of the 

 cords. Their inner ends are broken up to form nests of cells which be- 

 come surrounded by layers of the invading stroma. In this manner are 

 formed the follicles with their connective tissue theca, the oocyte and 

 granulosa cells being derived from the cords of Pfliiger. 



Kolliker, 98, Mihalkovics, 85, Eouget, 79, Biihler, 94, hold the view 



