THE ELASMOBRANCII FISHES 289 



ureter ends blindly. In its median segment it increases somewhat in diameter 

 and then taiHM-s gradually to its posterior part where as a nsnal thing it joins 

 the Wolffian duet. The collecting tul)nles which enter the ureter are arranged 

 with regularity thronghont the greater part of its course, but the anterior two 

 or three join as a common duct and enter a kind of pocket in the median side 

 of the ureter (see fig. 252) . In the short connnon segment formed by the union 

 of ureter and Wolffian duct, near the cloaca, considerable variation prevails. 

 In one immature female the left combined Wolffian duct and ureter entered 

 slightly posterior to the right and in another these relations were reversed. 

 In figure 252 it will be observed that the Wolffian duct and the ureter enter 

 the urinary sinus ( u.s.) separately and that in this specimen a singular condi- 

 tion obtains in which there are two urinary sinuses, one on the right, the other 

 on the left side. 



The urinary sinus terminates in a urinary papilla (two papillae in fig. 252) 

 which is perforated at its end. Nitrogenous waste matter collected from the 

 kidney is ejected through this into the cloaca (cl.) and thence to the exterior. 



It would appear from general proportions that the posterior part of the 

 kidney is by far the more effective part of the organ in the removal of nitrog- 

 enous waste matter. If this is so the greater part of the waste passes through 

 the ureter. 



The urinary organs in the male have much the same appearance in general 

 as those in the female. In the male, however, some of the tissue and ducts have 

 undergone great change correlated with the fact that in the adult they entered 

 secondarily into the service of the genital system. 



The kidney of an immature male of 75 cm. in length is shown in figure 251b. 

 It is 18.8 cm. long and has 12 segments in the anterior part and 14 in the poste- 

 rior. In general it extends farther forward and is somewhat better developed 

 anteriorly than is that of the female. But this is due, as we shall see presently, 

 to its relation to the genital organs. 



The collecting tubules (ct., fig. 251a) entering the Wolffian duct are ex- 

 ceedingly small and could be made out with care in the most anterior part of 

 the kidney. Posterior to this region they are distinctly arranged segmentally, 

 each tubule leaving the segment at about its middle part. At the proximal end 

 of the kidney there are certain other tubules {v.e., fig. 251b) which are a part 

 of another system which will be described presently. 



The Wolffian duct, in the ui)per part of its course, is thrown into numerous 

 coils like those of the adult female, but here they are more pronounced and 

 continue to the beginning of the enlarged part of the kidney. From this place 

 posteriorly the tube increases in diameter and passes ventral to the enlarged 

 ureter as it does in the female. 



The ureter (u., fig. 251b) is much like that of the female and receives prac- 

 tically the same number of collecting tubules. After it unites with the vas def- 

 erens (modified Wolffian duct) the two empty into the urogenital sinus (ug.). 



