THE URINOGENITAL SYSTEM 397 



endothelium. The stroma of the primitive testis remains scanty 

 up to the eleventh day. It then increases rapidly between the 

 sexual cords and also forms a layer between germinal epithelium 

 and seminiferous tubules, which becomes the all)uginea. Inter- 

 stitial cells appear in the stroma of the testis about the thirteenth 

 day and increase so rapidly as to form an immense amount by the 

 twentieth day (Swift). 



As the testis increases in size it projects more from the sur- 

 face of the Wolffian body, and folds arise above and below it 

 as well as in front and behind, that progressively narrow the 

 surface of apposition, which in this way becomes gradually 

 reduced to form the hilum of the testis, through which the rete 

 cords pass to the neighboring renal corpuscles (cf. Figs. 221 and 

 222). 



As the testis is attached to the anterior portion of the Wolffian 

 body, the latter may be divided in two portions, an anterior 

 sexual and a posterior non-sexual portion. In the latter part of 

 the period of incubation the non-sexual portion undergoes ab- 

 sorption while the anterior portion becomes converted into the 

 epididymis. 



The irregularly anastomosing rete cords in the region of the 

 hilum are united to the neighboring renal corpuscles by the original 

 strands and these form the vasa efferentia. In order to complete 

 the urinogenital union it is necessary that the rete cords unite 

 with the seminiferous tubules. The exact manner in which this 

 takes place has not been worked out for the chick; but there is 

 no doubt that this union does take place so that the seminiferous 

 tubules connect by way of the rete with the mesonephric tubules 

 and thus with the Wolffian duct. 



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. 



The development of the ovary in the chick has been studied 

 m recent years by Firket and by Swift. 



The right ovary never undergoes much development after 



