78 MANUAL OF NATUKAL HISTOKY. 



FISHES. 



Among the countless myriads of living creatures 

 which inhabit the boundless domain of waters on 

 our globe, none are more extensively diffused, or are 

 more generally known to mankind than the finny 

 tribes which we are now about to consider. They 

 are found alike in salt and in fresh water ; in the 

 former, whether it be the vast ocean, or the more 

 restricted sea, gulf, or inlet; and in the latter they 

 equally pervade lake, river, streamlet, or pond. None 

 of their fellow inhabitants of the deep present greater 

 diversity in size, form, or general configuration, and 

 none more abound in points interesting to the human 

 race. As fully two-thirds of the earth's surface are 

 occupied by water, it may be easily supposed that 

 fishes form considerably the largest division of the 

 vertebrate sub-kingdom. In the zoological scale 

 they stand lowest in the list of vertebrate animals ; 

 that is to say, that although perfect in their own 

 day and generation, they never attain to such an 

 advanced state of general development as those 

 classes which precede them. Their structure is 

 admirably adapted for residence in the medium by 

 which they are surrounded, as their bodies are nearly 

 of the same specific gravity as the element which 

 they inhabit, while their shape being that which 

 offers the least amount of resistance, is no less beau- 

 tifully calculated for favouring their powers of mo- 

 tion. 



Being excluded from direct contact with atmos- 



