1 CHTHYOLOGY. 



same purpose as lungs in other animals ; without the inter- 

 vention of an auricle and ventricle. The blood after being' 

 pushed forward by the heart into the ramification of the 

 gills, is received by a large number of small veins which 

 unite and form a descending aorta, as in the Mammalia 

 tribe. 



The general form of a fish may be not improperly 

 compared to that of a Ship, the tail being regarded as the 

 rudder, and the side fins as the oars, provided for impulse 

 through the watery medium in which they dwell. For the 

 purpose of raising or depressing their bodies in the Sea, 

 they are provided with a curious air bladder, which by 

 muscular compression can be made to condense the air 

 contained therein, and by this means becoming themselves : 

 specifically lighter or heavier than the medium in which 

 they move, they can easily rise or descend at pleasure. 



Fishes are also endued with the sense of hearing, which 

 has been made evident by several curious experiments ; and 

 the organ which is adapted for this purpose is situated 

 immediately behind the eyes. 



Their scales form a convenient kind of moveable 

 armour, which is thoroughly covered with a glutinous 

 substance for the purpose of gliding more easily through 

 the waves. 



They have also the power of smelling in a very exquisite 

 degree, as is evidenced by their peculiar manner of taking 

 or rejecting the bait. 



Their eyes are placed variously, being most generally 

 on the sides of the head, but on the flatter kinds of fish 

 always at the top or summit, being in this manner more 

 essential to their preservation. 



