DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS. 115 



DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS. 



The urinary and generative organs originate in connection with the intermediate 

 cell-mass, a portion of mesoblast which is seen in sections of the early embryo lying 



Fig. 136. PART OP A TRANSVERSE SECTION OP A CHICK EMBRYO OF 2 DATS, 6 HOURS. (Kolliker.) 2 f 



uw, protovertebra ; mp, lateral mesoblast ; dfp, splanchnopleuric mesoblast ; Tip, somatopleuric 

 mesoblast ; p, pleuro-peritoneal cleft (ccelom) ; wg, Wolffian duct ; wk, part of intermediate cell-mass 

 from which Wolffian body will become developed. 



between the paraxial mesoblast and the pleuro-peritoneal cleft, and abutting against 

 the external epiblast (fig. 39, p. 37). 



Fig. 137. SECTION THROUGH AN EXTERNAL GLOMERULUS 



OF THE PRONEPHROS FROM A CHICK OF ABOUT 4 DAYS' 



INCUBATION. (Balfour. ) 



gl, glomerulus ; gc, peritoneal epithelium ; Wd, Wolffian 

 duct ; ao, aorta ; iiie, mesentery. 



-4^( Ssrj^eai 



"KBHoSs 



i , ^* > TI i .'^.fl.'jjr.'^ "..> 



^?pX'0 V 



&*tffe5.fc 



Some of the cells of this intermediate cell-mass 

 become differentiated into a longitudinally run- 

 ning cord, which subsequently acquires a lumen, 

 and is then known as the Wolffian duct (from its 

 discoverer, Caspar Friedrich Wolff) (fig. 136, wg). 

 Posteriorly the duct opens into the cloaca. The 

 anterior part of the duct becomes connected with 



imaginations of the peritoneal epithelium, between which vascular glomemli project 

 freely into the peritoneal cavity (fig. 137). These glomeruli constitute the head 

 kidney, fore-kidney or pronephros. 1 Along its inner side, somewhat further back- 



1 Hertwig. According to Balfour and Sedgwick, these glomeruli form the anterior part of the 

 Wolffian body, and the head kidney is represented by the MUllerian invaginations referred to later on 

 (seep. 122 and fig. 145). 



I 2 



