ICHTHYOLOGY. 551 



Generally they are placed opposite to each other on the two 

 sides of the head, so as to look sidewise, but in species that ha- 

 bitually live in deep water, they are placed on the top of the 

 head, and look upward. In one genus of Sharks, called, on this 

 account Hammer-heads, the head is enormously widened, so as 

 to present two long lateral processes, at the extremities of which 

 the eyes are placed; the shape of the head, much resembling 

 that of the hammer used in caulking ships, (see Hammer-headed 

 Shark on the Chart.) We must not omit here to notice the fact 

 that a species of blind fish, Amblyopsis, (Gr. amblus, dim. opsis, 

 vision,) spelceus, (Gr. spelaion, a cave.) has been found in the 

 Mammoth Cave in Kentucky. The Saw-fishes have the snout 

 prolonged into a straight bony blade, along the edges of which 

 are set pointed teeth directed outward. 



Some of the species are endowed with a property quite pecu- 

 liar to this class of Vertebrates. This is the power of giving 

 electric shocks, at will, to other creatures, possessed by the Tor- 

 pedo, (Plate XIV. fig. 13 ;) and the Gymnotus, or electric 

 eel. The electric organs consist of numerous six sided cells 

 containing a number of delicate membranous plates, sepa- 

 rated from each other by a transparent jelly-like fluid. In 

 the Torpedo, the plates are placed vertically, and form two masses 

 one on each side of the head ; in the Gymnotus, they are hori- 

 zontal and form four sub-organs, one pair on each side of the 

 body. 



The organs of voice are, in fish, entirely wanting. The Cat- 

 fish, Pimelodus, is, however, said to make a peculiar sound by 

 the vibration of its cirri, or barbels, (Plate XIV. fig. 8.) The 

 WEAK FISH, Otolithus regalis, makes a peculiar and seemingly 

 abdominal grunting when caught, as does also the BLACK DRUM, 

 Pogonias chromis. 



The food of fishes is, for the most part, animal. Some browse 

 the sea- weeds that wave around the rocks of the coast, and oth- 

 ers nibble the soft parts of fresh water vegetation ; but the great 

 majority are carnivorous. The soft- bodied animals of the sea, 

 such as the Actinia, the Medusa, the Annelida, and the naked 

 Mollusca, afford food to multitudes ; others are furnished with 

 strong teeth to grind down the newly formed parts of coral, and 

 devour the living polyps ; and a large number feed greedily on 

 Star-fishes, Crustacea, and the Shelled Mollusca. In fresh wa- 

 ter, worms, leeches, and the larvae of insects satisfy the appe- 

 tite of many. Besides these sources of supply, Fishes every- 

 where feed upon Fishes, the larger upon the smaller. Their 

 voracity is extremely great, no limit to their appetite appearing 



