r BINARY ORGANS. 



303 



division of the mesonephros into an anterior and a posterior section 

 may be observed (comp. Figs. 237, pd, and 238, m.d, w.d, s.t}. In 



FIG. 237. DIAGRAM OF THE PRIMITIVE CONDITION OF THE KIDNEY IN AN 



ELASMOBRANCH EMBRYO. (After Balfour.) 



pd, segmental duct : it opens at o into the body-cavity, and its other extremity com- 

 municates with the cloaca ; x, line along which the division appears which 

 separates the segmental duct into Leydig's (Wolffian) duct above, and the 

 Miillerian duct below ; s.t, segmental tubes : they open at one end in the body- 

 cavity, and at the other into the segmental duct. 



,*. 



FIG. 238A. DIAGRAM OF THE ARRANGEMENT OF THE URINOGENIFAL ORGANS IN 

 AN ADULT FEMALE ELASMOBRANCH. (After Balfour.) 



m.d, Miillerian duct ; w.d, Leydig's (Wolffian) duct ; d, ureter ; s.t, segmental 

 tubes : five of them are represented with openings into the body-cavity : the 

 posterior segmental tubes form the mesonephros ; or, ovary. 



PIG. 236s. DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS IN 

 AN ADULT MALE ELASMOBRANCH. (After Balfour.) 



m.d, rudiments of Miillerian duct : w.d, Leydig's (Wolffian) duct, marked vd in 

 front, and serving as vas deferens ; s.t, segmental tubes: two of them are 

 represented with openings into the body-cavity ; d, ureter ; t, testis : nt, canal 

 at the base of the testis ; VE, vasa efferentia ; Ic, longitudinal canal of the 

 Wolffian body. 



the male, the former comes into connection with the genital gland 

 (Fig. 238B, VE, nt, t}, and its tubules open directly into the 



