STRUCTURE AND INSTINCT. 347 



the purposes for which it has been designed, we 

 are entitled to reckon that of supplying many of 

 the wants of the human race. 



Another family of fishes, of which many of the 

 various species are familiar to our readers, is that 

 of the Pleuronectidce, so called from the remark- 

 able circumstance of their swimming on one side. 

 These are what are popularly known as flat fish, 

 and comprehend eighteen or twenty kinds, inclu- 

 ding among them the plaice, the flounder, and its 

 varieties, the halibut, the turbot, and several 

 kinds of sole. The characters peculiar to this 

 race of fishes are so distinct as to render it one of 

 the most marked and insulated of all the families 

 into which the finny tribes have been subdivided. 

 There is a singular want of symmetry in some 

 parts of the figure of the flat fish. The head 

 appears as if forcibly twisted to one side, in con- 

 sequence of which the mouth appears distorted. 

 The body is compressed, and almost surrounded 

 by the dorsal and anal fins as with a fringe. The 

 habitation of these fishes is the bottom of the sea, 

 and they are not furnished with the air-bladder so 

 frequently forming part of the structure of those 

 fishes which frequent the higher parts of the 

 water. Reference has already been made to the 

 very remarkable resemblance which fishes present 

 in their hues to that of the ground they frequent. 

 In no instance is this more striking than in the 

 tribe of fishes to which we now refer. While the 

 side next the ground is white, the upper side, 

 which is exposed to the light is of some dark 



