398 



THE DEVELOPMENT OF THE CHICK 



the indifferent stage; it is destined to retrogress, and finally it 

 disappears. 



In the indifferent gonad the sexual cords are formed in the 

 same way whether the organ is to become ovary or testis; but, 

 whereas in the case of the testis these cords are destined to form 

 the functional seminiferous tubules, in the case of the ovary they 

 form only the cords of the medulla. The cortex of the ovary 

 which includes the functional follicles develops from a second 



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., rete ovarii, 

 s. c, Sexual cord. 



proliferation of the germinal epithelium. The sexual cords cease 

 to grow, and become converted into tubes with a wide lumen, 

 and low epithelium; shortly after hatching they entirely dis- 

 appear. 



The characteristic feature of the development of the ovary is 

 a second period of intensive growth of the germinal epithelium 

 accompanied by a rapid increase of the primordial germ-cells 

 contained in it. This goes on very rapidly during the eighth to 

 the eleventh days of incubation. The inner surface of the ger- 

 minal epithelium, or ovigerous layer of the ovary, begins to form 



