MARINE AND FRESHWATER FISHES 



BRITISH ISLANDS. 



CLASS PISCES.— FISHES. 



The class of fishes embraces an extensive series of 

 vertebrated or backboned animal forms exhibiting the 

 utmost diversity in size, form, habits, and organisation. The 

 more highly organised fish types so closely approach 

 structurally certain members of the class Amphibia — in- 

 cluding the Frogs, Newts, and Salamanders — as to be with 

 difficulty distinguished from the representatives of that 

 section, while the lowest known type (Amphioxus), No. 232, 

 is so deficient in all those characters by which ordinary fish 

 are recognised, and is in other respects so structurally 

 modified, as to form a connecting link with the lower or 

 invertebrate animal series. Defined in its most general 

 and comprehensive sense the class of fishes may be 

 described as a group of vertebrate animals of essentially 

 aquatic habits. The limbs, when present, take the form of 

 two pairs of ventrally developed appendages, which, while 

 homologous with the fore and hind limbs of the higher 

 vertebrata, are not divided in a similar manner by articula- 

 tions into the distinct regions of arm, forearm, and hand, or 



B 



