FISHES. 381 



a class of animal? distinct from all others, and exclusively destined by 

 their conformation to live, move, and perform the acts which are 

 essential to its nature in the atery element. 1 his is their place in 

 the creation ; here are they to reside from their origin ; here they are 

 to remain until the destruction of the present order of things ; nor is 

 it by empty metaphysical speculations, or by very superficial approxi- 

 mations, that we are to estimate their class as a development, a per- 

 fect state, an ennobling, as it were, of that of the mollusca, or as a rude 

 first draught, or the foetal condition of vertebrated classes. 



There is no doubt that the mollusca breathe as fishes do, by gills ; 

 have, in common with the latter, as with every other class of ver- 

 tebrated animals, a nervous system, a circulation, an intestinal canal, 

 and a liver ; and no one is better acquainted with this than myself, 

 who was the first to make known their anatomy, and their zoological 

 relations. 



As animal life has received only a definite number of organs, it 

 must follow, as a matter of necessity, that some at least of these 

 organs should be common to many classes. But where else is there any 

 other resemblance ? Is the frame-work of these animals, is their entire 

 system of locomotion to be compared to the others in the smallest of 

 their parts ? And how could the organs even which are now common to 

 the mollusca and fishes be brought into the relations and connexions 

 which they have in the latter and in other vertebrated animals? By what 

 process of transition could nature have brought us from the one to the 

 other ? It is very easy, I am aware, by entirely forgetting all their 

 differences, to get up a definition which would comprehend only what 

 they have in common ; but this definition would always remain a 

 mere abstraction of the mind, a definition purely nominal, a vain com- 

 bination of words which could never be represented by any common 

 system, however divested of details we should try to conceive it 

 to be. 



The same method is adopted to bring everything together, as may be 

 wished for, ultimately, as any two beings, however remote from each 

 other they might be, would always resemble each other in some point, 

 were it only by their existence. 



The heart even in the mollusca, which have only one, is placed in a 

 direction contrary to that of fishes, and is attached to the junction 

 of the branchial veins and arteries. In many of them the limbs are in 

 the head ; in others the organs of generation are on the side ; fre- 

 quently those of respiration are above those of digestion, or disappear 

 completely over every portion of the dorsal surface. In a word, they 

 have branchiae ; so have the fishes, but there is the whole of the 

 affinity between them. 



Hence it is observed, that as often as people wish to sally forth with 

 these formulae, which are purely verbal or metaphysical, they neces- 

 sarily wander into comparisons which have not the least possible title 

 to be admitted. 



For one of these gentlemen the shells of bivalves represent the 

 opercula of fishes : for another the shield of the cuttle fish is a true 

 fibrous bone : a third will have it that the scales of the sturgeon, or the 

 spines of the diodons, would ultimately become an external skeleton. 

 Some others are disposed to seek analogies for them in the Crustacea ; 



