The Dissection of the Fish 



33 



sosteus) the valve is reduced to a rudiment of three or four con- 

 volutions near the end of the intestine. In the sharks and 

 skates the intestine opens into a cloaca, which contains also 

 the urogenital openings. In all fishes the latter lie behind the 

 orifice of the intestine. In the bony fishes and the. ganoids 

 there is no cloaca. 



Length of the Intestine. — In all fishes, as in the higher ver- 

 tebrates, the length of the alimentary canal is coordinated with 

 the food of the fish. In those which feed upon plants the intes- 



FiG. 20. — Stone-roller, Campostomu anomalum (Rafinesque). Family Cyprinidw. 

 Showing nuptial tubercles and intestines coiled about the air-bladder. 



tine is very long and much convoluted, while in those which 

 feed on other fishes it is always relatively short. In the 

 stone -roller, a fresh-water minnow {Campostoma) found in the 

 Mississippi Valley, the excessively long intestines filled with 

 vegetable matter are wound spool-fashion about the large air- 

 bladder. In all other fishes the air-bladder lies on the dorsal 

 side of the intestinal canal. 



