296 THE ELASMOBRANCH FISHES 



orly by a conical urinary papilla. Its complexity in the rays results, from the 

 anterior extension of the horns of the sinus, which take the shape of the 

 arms of a tuning fork, the narrower urinary sinus being the base (Trygon). 



An incision through the papilla (Squalus, fig. 253a) gives a view of the 

 inner walls of the urinary sinus. Emptying into it on each side of the female 

 is the Wolffian duct (w.d.), and as evaginations of its walls are certain wdde 

 pockets (sc.) comparable to the sperm sacs of the male. 



The relation of the ureter to the Wolffian duct (vas deferens) in the male is 

 markedly different from that of the female. Only the ureter wall be described 

 at this place since a description of the WoMan duct will be given in a study 

 of the genital system. The ureter in the male is confined to the posterior part 

 of the kidney where it receives collecting tubules from ten to fourteen seg- 

 ments. These may enter regularly' as short tubules along its course {Squalus 

 and Squatina) or they may join it in two groups, one at its anterior end and 

 the other near its entrance to the urinary sinus {Scyllium, Raja) . In Scyllium 

 the ureter of the male is an enlarged sinus, as in Heptanchus. 



FINER ANATOMY OF KIDNEY 



In a section through the Elasmobranch kidney multitudes of structures are 

 met which are the effective organs for the removal of nitrogenous waste; these 

 are the renal corpuscles. A renal corpuscle, in simple terms (fig. 255a), is like 

 a hollow rubber ball (Bowman's capsule) , one side of which has been pushed in 

 to form a double wall and the opposite side pulled out over a small area into 

 a long neck (renal tubule, r.f.). Into the cavity of this invagination a blood 

 vessel enters, coiling up as the glomerulus (gl.) or knot of vessels. Nitrog- 

 enous waste matter collected by the blood is brought by the glomerulus into 

 the capsule through the w^alls of which it passes into the renal tubule. The 

 renal tubule (r.t.) carries it into the collecting tuble (c.f.) which joins the 

 Wolffian duct (w.d.) (or the ureter). Thus it passes through the urinary 

 papilla and out at the cloaca. 



NEPHROSTOME AND SEGMENTAL DUCT 



In order to understand the origin of a Bowman's capsule a second series of 

 correlated structures may first be considered. Each one of these when com- 

 plete, consists of a nephrostome {nph.) or funnel (fig. 258) opening from the 

 body cavity, a terminal part, the median vesicle {m.v.), and between the two a 

 segmental duct {s.d., fig. 258b). 



The nephrostome may best be studied in the Elasmobranchs h\ treating 

 them first with Flemming's fluid. To get the best results the digestive tract 

 should be removed from a fresh specimen and a little of the fluid allowed to 

 remain for a short time in the dorsal part of the body cavity. Under such a 

 procedure the nephrostomes are colored as dark patches of the dorsal peri- 

 toneal lining of the body cavity near the middle line and on the mesentery. 

 These are the funnels which may be relatively large as in Squatina {nph., 



