PECULIAR CHARACTERS OF FI8HES. 11 



they really formed a circular group by themselves. 

 Again, it i§ notorious that some of the eels of the 

 genera Murcena, Ophisurus, &c. have so completely 

 the aspect of the water serpents, that it is only upon 

 the naturalist examining them, that their different 

 classes are detected. * Upon the whole, therefore, we 

 must admit that every thing yet known regarding the 

 classes in question strengthens this belief, and adds 

 another instance to what we have seen among birds, 

 that the " primary divisions of every group are three 

 actually, but five apparently." 



CHAP, II. 



ON FISHES IN GENERAL, 



(10.) Fishes constitute by far the most numerous class 

 of vertebrated animals, whether we regard the number of 

 individuals, or the variety of their forms. When we 

 consider that more than two thirds of the globe is 

 covered by water, — that element peculiarly appropriated 

 for their habitation, — we shall not be surprised at this 

 superiority of numbers. On the contrary, we may 

 fairly suppose that not more than one half of the 

 species really existing have yet been made known. 



(11.) The peculiarities in the inward form of fishes, 

 by which they are distinguished from all other animals, 

 need not be enlarged upon ; yet, as many of them, like 

 the eels, assume the form of serpents, and others re- 

 semble the young of the amphibian frogs, it is neces- 

 sary to characterise them as aquatic vertebrated animals, 

 breathing by means of internal gills, and undergoing 



* The museum of the Zoological Society contains many striking illus- 

 trations of this fact. 



