36o 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



mass or into the tail. In many the anterior portion differs from the rest and is 

 called a head kidney, although it is not a pronephros. It is rather a peculiar 

 tissue, rich in lymph cells, developed from the walls of the cardinal veins. The 

 nephridial ducts (WoliTian) are usually imbedded in the substance of the meso- 

 nephros (fig. 380, d), but sometimes they run on the ventral surface of the orgaa 



Fig. 380. — Urinary organs of teleosts, after Haller. A, pronephros and ducts of 

 young Salmo fario; B, excretory organs of adult perch, Perca fiuviatilis; C, of carp, Cy- 

 Prinus carpio; a, aorta; cv, caudal vein; d, urinary duct; m, mn, mesonephros; pcd, pes, 

 right and left postcardinaJ veins; p, pti, pronephros; r, rectum; «, urinary bladder; w, 

 wd. Wolffian duct. 



The ducts of the two sides unite behind and from this union and in some cases 

 from the wall of the cloaca, a urinary bladder is formed. The external urinary 

 opening is behind the anus, sometimes united with the genital opening. 



The ovaries may be flattened, plaited lobes, bound to the peritoneal wall by 

 mesovaria. From this condition, which occurs in many salmonids, many modifi- 

 cations may be traced. Thus in the same family (fig. 381) there is frequently 



