CLASS OF FISHES. 379 



tongue ; and as the nasal fossae consist of cavities which are 

 traversed neither by air nor water mixed with air, the power 

 of smell cannot be acute. The organ of hearing is enclosed 

 within the cavity of the cranium, and is composed of a ves- 

 tibule and three semicircular canals, which sounds can only 

 reach by vibrations of the common integuments and bones of 

 the cranium. The eyes, it is true, are large, but not very 

 moveable, the iris is not contractile, and the lens is spherical ; 

 they have neither eyelids nor lachrymal apparatus. In some 

 flat fishes as the sole, plaice, turbot both eyes are placed on 

 one side of the head, and this want of symmetry extends to 

 other parts of the body. 



485. Fishes are very voracious : a very few only live 

 chiefly on vegetables ; and they are indiscriminate as to their 

 food. Some species have no teeth ; but in most there exist 

 several rows, as in the shark (Fig. 390) ; we find them, 

 indeed, attached to several bones with which they unite, for 



Fig. 387. Dorsal fin of Fig. 388. Kemora ; Sucking Fish, 



the Remora. 



they have no roots ; they are shed at regular intervals and 

 replaced by new teeth, and being generally all of one kind 

 they receive their names from the bones which carry them, 

 as palatine, vomerine, maxillary, &c. But in different species 

 they vary very much in form, being sometimes so fine and 

 thickly set as to resemble the pile of velvet, in others they 

 are strong robust hooks, rounded tubercles, or sharp cutting 

 plates. 



486. Some, as the lamprey, live by suction, nevertheless 

 they also have teeth. There is no salivary apparatus, and the 

 gullet is short, the liver large and soft, and the pancreas is 

 replaced by the pancreatic caeca surrounding the pylorus; 

 finally, the position of the extremity of the gut varies much ; 

 the kidneys are extremely large, extending on both sides of 

 the vertebral column, and nearly throughout its whole length. 



