254 PISCES. 



urinary bladder that is rarely absent, and is always situated posterior 

 to the intestinal canal ; a position by which, according to our pres- 

 ent knowledge, Fishes may be distinguished from all other Verte- 

 brata. The urinary bladder, or when this is wanting, as in Urano- 

 scopus scaber, the urogenital aperture, opens behind the anus. The 

 ureters open into different parts of the bladder, and the form of the 

 latter varies exceedingly, being either cylindrical or fusiform, and 

 frequently, as in many species of Gadus, prolonged into caeca or 

 cornua. 



In the Rays and Sharks the kidneys are proportionately much 

 shorter than in other Fishes ; they are frequently more or less lobu- 

 lated, and resemble the kidneys of the Chelonia ; the urinary bladder 

 is either absent, or present, as in the Rays, where it is two-horned. 

 The Cyclostomi have no bladder, and in Petromyzon the external 

 rounded edge of the kidneys projects freely into the ventral cavity, 

 and the organs themselves are prolonged in front into a dense spongy 

 mass of adipose cells. In Lepidosiren annectens, the kidneys, long 

 and narrow, are completely separate, and the urinary bladder opens 

 into the posterior region of the cloaca. Some detached glandular 

 bodies have been found in the posterior part of the ventral cavity in 

 the vicinity of the abdominal pore in Amphioxus, and been stated to 

 be renal organs. 



As regards the more minute structure of the urinary organs, their 

 substance is generally loose and spongy in the Osseous Fishes, but 

 firmer in the Plagiostomi. The urinary canals are for the most part 

 long and very tortuous, but not ramified ; in the Cyclostomi, at least 

 in Petromyzon, they form short, straight, caecal tubes. The Mal- 

 pighian bodies, or renal glomerules, are not absent, though they are 

 of small size in Fishes, and, as would appear from injections that have 

 been made of them, imperfectly formed. 



Certain bodies have been recently discovered to occur pretty gene- 

 rally in Fishes, and been regarded as Renal Capsules. They are 

 particularly distinct in the Plagiostomi, as the Rays, but even in these 

 large Fishes they are very small, and, as in Raia oxyrhynchus, are 

 seen as small bean-shaped bodies, similar to the kidneys, but of a 

 paler color. The renal capsules of either side are connected by 

 vessels with the apex of the kidneys. In the Bony Fishes, which 

 were previously denied to possess these organs, a pair of small red- 

 dish-white corpuscules, mostly placed behind the kidneys against 

 the vertebral column, have been recently found, e. g. in Cyprinus, 



