CHAPTER XXIV 

 THE ALLIES OF THE PERCH : PISCES 



Halcyon prophecies come to pass 

 In the haunts of bream and bass. 



MAURICE THOMPSON. 



Definition of Pisces (L&t. piscia, a fish). The perch is a mem- 

 ber of the class Pis'ces. Fishes are cold-blooded vertebrates, 

 adapted to life in the water. In the lower forms the notochord 

 persists as a continuous rod; in the higher fishes it is replaced 

 by the vertebra. The body is covered with a skin, in which 

 are numerous mucus-glands. Scales are usually present, set 

 in pouches in the skin. In the great majority of forms gills are 

 the only organs of respiration. Locomotion is usually effected 

 by means of fins. With very few exceptions, fishes lay eggs 

 from which the young are hatched ; that is, they are oviparous. 



There is a remarkable uniformity of type in the class when 

 the number of species (about fifteen thousand) and the length 

 of time they have been in existence is considered. Professor 

 Dean, of Columbia University, says : " The evolution of fishes 

 has been confined to a noteworthy degree within rigid and 

 unshifting bounds ; their living medium, with its mechan- 

 ical effects upon fish forms and structures, has for ages been 

 almost constant in its conditions ; its changes of temperature 

 and currents have rarely been more than of local impor- 

 tance, and have influenced but little the survival of genera 

 and species widely distributed ; its changes, moreover, in the 

 normal supply of food organisms cannot be looked upon as 

 noteworthy." 



We shall consider three of the four groups into which the 

 fishes are usually divided. 



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