FISHES. 11 



or ventral fins; the vertical fins possessed by many, 

 which rise up on the back, are termed the dorsal, and are 

 often armed with sharp points : those on the lower sur- 

 face of the body, corresponding to the dorsal, are desig- 

 nated as the anal fins ; and the one which terminates the 

 tail, the caudal. Most of them have a sac in the inte- 

 rior of their bodies, by which they can render themselves 

 specifically lighter or heavier than the water ; this sac, 

 called the air vessel or swimming-bladder, can be com- 

 pressed or dilated at the pleasure of the fish, as it rises 

 to the surface of the water, or sinks to its depths. In 

 some this bladder is wanting ; such either keep near the 

 bottom, and can only rise slowly, by the aid of their fins. 

 It sometimes occurs in the torrid zone that fish remain 

 too long on the surface of the water ; when this is the 

 case, the sun's rays, falling fiercely, so operate on the 

 air contained in the swimming bladder that it can not be 

 compressed, and the poor creatures must remain where 

 they are until the cool of the evening, before they can 

 sink to the bottom. 



The figure of the head varies in different species ; the 

 senses of seeing and hearing are acute; some possess 

 that of smell in a high degree, as they are attracted by 

 strongly odorous bodies at a considerable distance. The 

 sense of taste, on the other hand, is not well developed, 

 as the tongue is often osseous, and furnished with teeth. 

 Their whole bodies are covered with scales, or a parch- 

 ment-like skin ; therefore the sense of touch is not very 

 acute; there may be some, having fleshy projections 

 from their mouths, that form an exception; these are 

 called the beard, and serve as feelers for groping about 

 in the mud after worms, etc. Their teeth are of a 

 peculiar form, exhibiting no difference as cutting, canine, 



