76 



OUTLINES OF NATURAL HISTORY. 



CHAPTER XIX. 



CLASS PISCES. 



The class Pisces (Latin, piscis, a fish) includes tlie familiar 

 animals which are projierly known as fishes. As the type 

 of this vast and universally distributed group, we may 

 take the common Perch {Perca fluviatiiis) of the rivers 

 and lakes of Britain and Northern Europe. 



The general shape of the body in the Perch (fig. ^2) is 

 somewhat spindle-shaped, tapering towards both ex- 

 tremities, and thus adapting the animal for rapid and 

 easy movement in a watery medium. From the tip of 



d 



■ - c 



Fig- 33.— The common Perch {Perca fluviatiiis). Gill-cover, wth the gill- 

 slit behind it ; p One of the pectoral fins, the left ; v The left ventral tin ; 

 d The first dorsal fin ; d' The second dorsal fin ; c The caudal fin or tail ; 

 a The anal fin ; I Lateral line. 



the nose for about a quarter of its whole length the thick- 

 ness rapidly increases, and then it more slowly diminishes 

 towards the tail for the remaining three-quarters of its 

 length. The body is also considerably compressed or 

 flattened from side to side, and its height is much greater 

 than its width. 



