THE URINOGENITAL 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. 
Fic. 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.¢., 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- 
becule. 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 
