1330 



THE UKO-GENITAL SYSTEM. 



In anamniate vertebrates, fishes, and amphibia, the mesonephros persists as the 

 secretory organ of the adult. 



Allantois 



Uro-genital^ 

 part of cloaca*""-..^ 



Rectum 



Wolffian duct 



Bladder 



-Rectal part 

 of cloaca t. 



Neural tube 



Notochord 



FIG. 1039. TAIL END OF HUMAN EMBRYO BEFOKE 



THK TlMB AT WHICH THE WOLFFIAN DUCTS 



REACH THE CLOACA. (Drawn from a model con- 

 structed by Prof. F. Keibel. ) 



Post anal gut 



Notochord 



FIG. 1040. TAIL END OF HUMAN EMBRYO. The 

 Wolffian ducts open into the anterior part 

 of the cloaca. (Drawn from a model con- 

 structed by Prof. F. Keibel. ) 



Pronephros. From what is known regarding the development of lower animals, it seems 

 certain that the Wolffian duct originally served as the duct of the still earlier secretory organ- 



Body of vertebra 

 Spinal ganglion 



Spinal medulla 



wrw'. r <4 



Arch of vertebra v ,,, 



Ilium (cartilage) 



V 



Wolffian duct ^ 





Miillerian'duct 



} Intestine 

 Genital gland 

 Mesonephros 



FIG. 1041. TRANSVERSE SECTION THROUGH THE LOWER PART OF THE TRUNK OF A HUMAN EMBRYO OF 

 ABOUT 7 WEEKS. (Specimen in the possession of Prof. J. Symington. ) 



the Pronephros. In man the pronephros arises nearer to the head end of the embryo than 

 the later formed mesonephros, and its tubules can only with difficulty be distinguished 



