THE URIXOGENITAL SYSTEM 



399 



this multiplication and the consequence is a great increase in 

 thickness. At the same time the sexual cords cease to grow, 

 and become converted into tubes with a wide lumen, and low 

 epithelium; and the stroma increases notably in amount. The 

 inner surface of the germinal epithelium, or ovigerous layer of 

 the ovary, then begins to form low irregular projections into the 

 stroma, or the latter begins to penetrate the ovigerous layer at 

 irregular distances so as to produce elevations. This condition 

 is well illustrated in Fig. 229. 



FIG. 229. Cross-section of the ovary of a young embryo of Numenius 

 arcuatus. (After Hoffmann.) 



bl. v., Blood-vessel, germ. Ep., Germinal epithelium, r., Mesonephric 

 canals (rete ovarii). s. c., Sexual cord. 



In the course of development the ovigerous layer continually 

 increases in thickness, and the projections into the stroma form 

 veritable cords of ovigerous tissue, which correspond to the 

 cords of Pfliiger in the mammalian ovary. The cords carry 

 the primitive ova with them. The surface of the ovary also 

 begins to become lobulated by the extension of the stroma tra- 

 beculae. Successive stages in the growth and differentiation of 

 the primitive ova occur from the surface towards the inner ends 

 of the ovigerous strands. Fig. 230 represents a section through 

 the ovary of a fledgling of Numenius acuatus three or four days 



