CHAPTER XVIII 

 THE FISHES 



In treating of fishes we shall describe first a typical fish 

 such as a perch, sunfish, trout or bass, some one of which 

 is easily obtainable in almost every locality. One notable 

 feature of the organization of the fish is the adaptation of 

 the form of its body for gliding through the water with the 

 least amount of resistance. The posterior part of the 

 body tapers into a thin, vertical tail fin which is expanded 

 to give it a broad purchase against the water and it is 

 strengthened by a number of long, flexible rays. The tail 



Pel 



FIG. 128. A typical fish. A, anal fin; c, caudal or tail fin; D, dorsal fin; 

 N, nostril; Op, operculum; Pec, pectoral fin; Pel, pelvic* fin. 



is the principal organ of locomotion in the fish and the 

 bulk of the muscle of the body is used in effecting the to 

 and fro movement of this organ, which results in propelling 

 the animal forward. As in most vertebrates a typical 

 fish has four paired limbs represented by the anterior, or 

 pectoral, and the posterior, or pelvic, fins. These, like the 

 tail fins, are thin, flattened organs strengthened by means 

 of rays. While the lateral or paired fins may aid in swim- 

 ming forward, their main uses are to keep the body in a 



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