294 



THE ELASMOBRANCH FISHES 



part and the only way that the number of segments can be determined is by 

 the number of collecting tubules leaving the kidney. In the rays the kidneys 

 may be divided into numerous asymmetrical lobules, which show little tend- 

 ency toward orderly arrangement ; or the kidneys of the two sides may be en- 

 tirely dissimilar. This is seen sometimes in Baja clavata where the left kidney, 



Fig. 254. Urogenital system of male. A. Sqnatina. B. L'aja. (From Borcea. ) 



C.C., central canal of testis; ct., collecting tube; led., kidney; m.v., median vesicle; nph., 

 nephrostome; sc, sperm sac; s.d., segmental duct; s.v., vesicula seminalis; t., testis; «., 

 ureter; ug., urogenital sinus; v.d., vas deferens; v.e., vas efferens. 



probably because of pressure from the digestive organs, becomes divided into 

 widely separated parts. 



DUCTS OF KIDNEY 



In a type like Sqimiina (see male, fig. 254a) the collecting tubules {ct.) which 

 drain the anterior part of the kidney empty directly into the Wolffian duct, 

 and those of the posterior part join a ureter (?<.). This is essentially the con- 

 dition in Heptanchus, except that in Heptanchus the ureter is of immense 

 size. In Scyllium (see p. 189, fig. 177a) the Wolffian duct is terminated by an 

 enlarged portion, the urinary vesicle (u.v.), and the collecting tubules in the 

 posterior part of the kidney are dispersed at their termini, several of them 

 joining to form a diminutive ureter only at the place where they empty into 

 the urinary sinus. A modification of this plan is met with in the rays in 



