EXCRETORY ORGANS. 699 



original openings into the body cavity, and others are without 

 them. They are divided into two groups, an anterior forming 

 the mesonephros or Wolffian body, which pours its secretion 

 into the Wolffian duct ; and a posterior group forming a gland 

 which is probably equivalent to the kidney proper of amniotic 

 Craniata, and is connected with the ureter. 



In the male the following parts are present (fig. 393): 



(1) The Miillerian duct (in.d\ consisting of a small rudi- 

 ment attached to the liver, representing the foremost end of the 

 oviduct of the female. 



(2) The mesonephric duct (w.d} which precisely corresponds 

 to the mesonephric duct of the female, but, in addition to 

 serving as the duct of the Wolffian body, also acts as a vas 

 deferens (vd). In the adult male its foremost part has a very 

 tortuous course. 



(3) The ureter (d), which has the same fundamental con- 

 stitution as in the female. 



(4) The segmental tubes (s.t). The posterior tubes have 

 the same arrangement in both sexes, but in the male modifica- 

 tions take place in connection with the anterior tubes to fit them 

 to act as transporters of the semen. 



Connected with the anterior tubes there are present (i) the 

 vasa efferentia (VE], united on the one hand with (2) the 

 central canal in the base of the testis (nf), and on the other with 

 the longitudinal canal of the Wolffian body (lc\ From the 

 latter are seen passing off the successive tubuli of the anterior 

 segments of the Wolffian body, in connection with which Mal- 

 pighian bodies are typically present, though not represented in 

 my diagram. 



Apart from the absence of the pronephros the points which 

 deserve notice in the Elasmobranch excretory system are (i) 

 The splitting of the segmental duct into Wolffian (mesonephric) 

 and Mtillerian ducts. (2) The connection of the former with 

 the mesonephros, and of the latter with the abdominal opening 

 of the segmental duct which represents the pronephros of other 

 types. (3) The fact that the Miillerian duct serves as oviduct, 

 and the Wolffian duct as vas deferens. (4) The differentiation 

 of a posterior section of the mesonephros into a special gland 

 foreshadowing the metanephros of the Amniota. 



