, 

 66 STRUCTURE OF FISHES. 



is distributed to the different parts of the body, whence it is 

 again returned to the heart by the veins. 



The whole structure of fishes is as clearly designed to attain 

 the end of motion irt the water, as the structure of birds is in- 

 tended for motion in the air. They are destitute of limbs, and 

 their motions are effected by means of their fins and tail, 

 which act upon the water like oars, either propelling the ani- 

 mal forward, or moving it upward, downward, or to either side. 



Fishes are covered with a thick, strong skin, and most of 

 them with scales, which are arranged one over another in an 

 imbricated form, like slate or shingles on the roof of a house. 

 Their bodies are also invested with a covering of thin slime, 

 or mucus, which defends them from the immediate contact 

 of the water. Their forms vary exceedingly, and are much 

 more numerous than those of the animals heretofore described. 

 They vary also in size. Some are armed with strong, sharp 

 spines ; some with a sword or saw ; and most of them with 

 teeth. The latter, however, are not intended for the purpose 

 of chewing, but merely for that of seizing and retaining prey, 

 which is swallowed whole. A few are possessed of a very 

 remarkable species of defence, which consists in the power of 

 inflicting upon whatever living creature comes in contact 

 with them, a powerful electrical shock. These shocks are 

 so powerful, that, in South America, horses driven into the 

 pools which fishes of this kind inhabit, have been stunned, 

 and sometimes even killed. 



Fishes have but a small brain. They have the senses of 

 seeing, hearing, smelling, and tasting. That of touch they 

 probably possess but imperfectly, as they have no organ which 

 seems intended for its exercise, except the snout and mouth, 

 and in some species, a sort of feelers, growing around the 

 mouth. Their skeleton is constructed of bones, generally 

 softer and less earthy than those of other animals, and indeed 

 in some they are entirely cartilaginous. Their stomach and 

 intestines are formed upon the same general plan with those 

 of other vertebral animals, and digestion is carried on in the 

 same general way. They feed principally upon other fishes, 

 upon worms, and shell-fish. They are long-lived, attain to 

 their full growth slowly, and exhibit but few signs of intelli- 

 gence or remarkable instinct. 



Their constant residence in the water prevents that accu- 

 rate knowledge of their character and habits of life, which 

 would afford materials for a more copious detail. They are 

 divided into orders and genera, according to certain differ- 



