30 ' CLASSIFICATION CV FISHES. 



timeS;, as in Gymnotus and ChimcEra, extending nearly 

 the whole length of the fish. This is very observable 

 in the sub-family Silurin<^, which also represents the 

 Apodes ; and we again trace a similar development of 

 the anal fin among the BlennidcB and the genera Cepola, 

 Ophidium, &c. 



(33.) The CAUDAL fin alone remains to be noticed. 

 It is^ to us^ a most unaccountable circumstance, that 

 every naturalist who has hitherto wi'itten upon Ichthyo- 

 logy, should have followed each other in paying so little 

 regard to the fins in general, but more especially to this^ 

 which (with the tail itself) is as important to the 

 motion of a fish as the rudder is to a ship, or as is the 

 tail of a swallow in directing its flight. That such is 

 the true office of the tail and its fin, among fishes, is 

 too obvious to require being enforced by argument ; and 

 yet, while the importance of this member is so fully 

 acknowledged in quadrupeds and birds, that it often 

 furnishes the only decisive generic character^ it has 

 hardly ever been considered in this fight in ichthyology ; 

 and not only whole groups of species, but even of sula- 

 genera, have of late years been described, where the 

 tail is hardly ever mentioned, or_, if so, only inci- 

 dentally. Our own impressions on this subject, after a 

 long and laborious investigation, induce us to consider 

 that, in a natural arrangement of this class, the form 

 of the caudal fin is just as important in fishes as that 

 of the tail in birds ; and that it is, consequently, one of 

 the best characters for the determination of natural 

 groups or types that can possibly be found. We 

 view it, in fact, as much more determinate than those 

 slight modifications of the teeth, upon which so many 

 of the modern sub-2:enera have been founded, to the 

 infinite perplexity of all but the professed anatomist; 

 and, what is worse, to the cutting up and frittering 

 away, as we conceive, of natural alHances. subordinate, 

 in different degrees, to each other. The experienced 

 ichthyologist, well acquainted with the variation of this 

 member, will not fail to observe that the swiftest 



