INTRODUCTION. 59 



which liave been placed in our systems above them. 

 In form they are perhaps the most varied beings in 

 creation, and the most fertile fancy could scarcely 

 depict a shape or appearance to which a resem- 

 blance would not be found. They are of " hideous 

 and loathsome bulk," or of the most graceful forms, 

 and gorgeous and resplendent colours ; but still 

 among all these we may trace the characteristic 

 shape of a fish, in the head being placed at once 

 upon the shoulders without any length of neck, 

 followed by the body, and finished by the tail ; 

 and the parts will be all adapted to the different 

 modes of gaining sustenance, whether it is to be 

 procured by stealth and deceit, or by strength 

 and swiftness. 



Living in a different element from that which 

 maintains most of the mammalia and birds, we find 

 the external covering of fishes to consist of plates, 

 or scales, supplying the place of hair or feathers. 

 The skin of fishes completely surrounds the body, 

 clasping close to the muscles, and serving as an 

 outward skeleton, as the bones do for a protection 

 to the inward parts. The scales are composed of 

 two substances, the one allied to that of horn, the 

 other to that which forms the enamel of teeth. 

 They are placed in little mucous cavities of the 

 corion, or true skin ; they are generally formed 

 of delicate plates or leaves, secreted by the skin, 



