57 n ELASMOBRAXCIIII. 



(2) The mesonephric ducts {w.d), the other product of the seg- 

 mental ducts of the kidneys. They end in front by becoming con- 

 tinuous with the tubukis of the anterior persisting segment of the 

 mesonephros on each side, and unite behind to open by a common 

 papilla into the cloaca. The mesonephric duct receives the secretion 

 of the anterior tubuli of the primitive mesonephros. 



(3) The ureter which carries off the secretion of the kidney 

 proper or metanephros. It is represented in my diagram in its most 

 rare and differentiated condition as a single duct connected with the 

 posterior segmental tubes. 



(4) The segmental tubes (s.t) some of wiiich retain their 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. 398) : 



(1) The MuUerian duct (m.d), consisting of a small rudiment 

 attached to the liver, representing the foremost end of tiie 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 constitution 

 as in the female. 



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

 same arrangement in both sexes, but in the male modifications 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 (1) the vasa 

 efferentia ( VE), united on the one hand with (2) the central canal in 

 the base of the testis (nt), and on the other with the longitudinal 

 canal of the Wolffian body (fc). From the latter are seen passing off 

 the successive tubuli of the anterior segments of the Wolffian bodv, 

 in connection with which Malpighian bodies are typically present, 

 thovigh not represented in my diagram. 



Apart from the absence of the pronephros the point=? which deserve 

 notice in the Elasmobranch excretory system are (1) The splitting of 

 the segmental duct into Wolffian (mesonephric) and MuUerian 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 tlie 

 MuUerian duct serves as oviduct, and the Wolffian duct as vas 

 deferens. (4) The differentiation of a posterior section of the meso- 

 nephros into a special gland foreshadowing the metanephros of the 

 Anmiota. 



