400 STRUCTURE OF VERTEBRATES. 



DIAGRAM XXIV. 



Urinogenital System. 



Fig. I (after Hatschek) shows diagrammatically the primitive segmental 

 ducts (s. d.) and their associated nephridia, Ns. nephrostoma, M. Mal- 

 pighian tubule. The dotted lines indicate segments of the body. 



Fig. 2 (after Balfour) shows for one side the primitive condition of the 

 kidney in an Elasmobranch embryo : — s. d. the segmental duct, becoming 

 split into MuUerian duct {M. d.) and WolfBan duct [W. d.), i. the seg- 

 mental tubes or nephridia. 



Fig. 3 (after Balfour) shows for one side the nature of the urinogenital 

 organs in a female Elasmobranch : — ov. the ovary, M. d. the Miillerian 

 duct or oviduct, t. the anterior mesonephros or Wolffian body, W. d. 

 the Wolffian duct, k. the kidney formed from posterior nephridia, u. the 

 ureter, cl. the cloaca. 



Fig 4 (after Balfour) shows for one side the nature of the urinogenital 

 organs in a male Elasmobranch : — t. the testis, v. e. the vasa efferentia, 

 t, the anterior mesonephros or epididymis, le. a longitudinal vessel 

 receiving the vasa efferentia, W. d. the Wolffian duct or vas deferens, 

 k. the kidney formed from posterior nephridia, u. the ureter, d. the 

 cloaca, M. d. an anterior rudiment of the Miillerian duct. 



