156 . FISHES. 



the urogenital ducts. The Dipnoi possess a cloaca. In 

 Ceratodus the ureters open into it by a common openiug, 

 separate from the genital opening ; and no closed uiiaary 

 bladder has been developed. Zepidosiren has a small "urinary 

 bladder ; the ureters do not communicate directly with it, but 

 terminate separately on small papillee in the dorsal conipart^ 

 ment of the cloaca. The other Ganoids lack a cloaca, and the 

 urogenital opening is behind the vent as in Teleosteans. In 

 all the genital and urinary ducts coalesce towards their end. 

 The Sturgeons have no urinary bladder, whilst it is present 

 in Amia, the ureters opening separately into it. 



The kidneys of Teleosteans are situated likewise w;ithout 

 the peritoneal cavity, immediately below some part of the 

 vertebral column, 9,nd vary exceedingly with regard to form 

 and extent. Sometimes they reach from the skull to between 

 the muscles of the tail, sometimes they are limited to the 

 foremost part of the a;bdominal cavity (in advance of the 

 diaphragm), but generally their extent corresponds to that of 

 the abdominal portion of the vertebral column. Frequently 

 they are irregular on their dorsal surface, filling every avail- 

 able recess, flat, attenuated on the sides,' more or less coales- 

 cent towards the middle; in other fishes they are more 

 compact bodies. The ureters terminate, either separate or 

 united, in a urinary bladder, varying in shape, which opens 

 by a short urethra behind the vent. The urinary opening 

 may be separate or- confluent with thatoS the genital ducts, 

 . and is frequently placed on a more or less prominent papdla 

 (papilla urogenitalis). If separate, the- urinary opening is 

 behind the genital ; and if a papiUa is developed, its extre- 

 mity is perforated "by the urethra, the genital opening being 

 situated nearer the base. A few Teleosteans show an arrange- 

 ment similar to that of Chondropterygians and Dipnoi, the 

 urogenital openings being in the posterior wall of the rectum 

 (SymhranchidcB, Pediculati, and some Eleetognathi). 



