398 THE DEVELOPMENT OF THE CHICK 



During this period the sexual cords become converted into 

 the semeniferous tubules, rete, and vasa efferentia; and the 

 sexual tubules of the Wolffian body into the epididymis. About 

 the end of the third week the sexual cords obtain a lumen, owing 

 to rearrangement of the cells; at the same time a basement mem- 

 brane appears over the outer ends of the cells, and the semenif- 

 erous tubules are definitely established (Fig. 228). In these • 

 one can easily recognize the descendants of the primitive ovai/ 

 which may now be called spermatogonia, and the epithelial or 

 supporting cells. The irregularly anastomosing sexual cords in 

 the region of the hilus become the rete cords, which acquire a 

 lumen shortly after hatching. The rete cords are united to the 

 neighboring renal corpuscles by the original strands and these 

 form the vasa efferentia. 



As regards the formation of the epididymis : the renal corpuscles 

 of the Wolffian tubules concerned diminish in size, the glom- 

 erulus disappears and the cells of the capsule become cylindrical. 

 These changes progress from the lateral side of the Wolffian 

 body towards the testis; that is to say, the more lateral corpuscles 

 are first affected. A rudiment of the non-sexual part of the 

 Wolffian body persists in the mesorchium of the male, between 

 testis and kidney. It is known as the paradidymis. 



Development of the Ovary. (There is no complete account of 

 the development of the ovary in the chick; the following account 

 is based on Hoffmann's description of Grallatores and Natatores.) 



The right ovary may attain a considerable size; but sooner 

 or later it degenerates and is never functional; moreover, its 

 growth does not follow a normal course of differentiation. The 

 description applies, therefore, only to the left ovary. 



In the indifferent gonad, primitive ova leave the germinal 

 epithelium and enter the stroma and sexual cords at corresponding 

 stages of development whether the organ is to become ovary or 

 testis. Such, however, in the case of the ovary, are destined to 

 degenerate, along with the sexual cords. The definitive ova 

 are derived from primitive ova that have remained within the 

 germinal epithelium. 



The characteristic feature of the development of the ovary 

 is, then, a cessation of migration of primitive ova from the 

 germinal epithelium after a certain stage and a multiplication 

 in situ. The epithelial cells of the germinal epithelium share in 



