FISHES 261 



aquatic animal, insomuch that in the old authors, and even in some of 

 the writers of modern times, we frequently find this name given to 

 Whales, to Molluscous animals, and those of the Crustacea ; a sort of 

 confusion which it is the easier to explain when we consider that the 

 class of fishes is one of those which are most strictly limited by in- 

 variable characters. 



Nothing can be more clear and exact than the definition of Fishes, 

 in general acceptation, at present, namely, that they are vertebrated 

 animals with red blood, breathing by branchiae, and through the 

 medium of water. 



This definition arises from observation ; it is the result of analysis, 

 or what is called in physical science an empyrical formula. But its 

 propriety may also be demonstrated by the synthetic method, for if it 

 be exactly comprehended, it will enable us to understand the nature 

 of that division of beings to which the definition applies. 



Vertebrated animals must, of necessity, be those which have an 

 internal skeleton, a brain, and spinal marrow enveloped in the ver- 

 tebral column (a), the muscles exterior to the bones, only four extremi- 

 ties, and the organs of the four primary senses in the head, &c. 



Agnatic animals, that is to say, living in a liquid medium of greater 

 specific gravity, and more resisting, than air ; they must have their 

 moving power exactly adjusted to accomplish progression : but 

 elevation can be easily effected by them ; hence we find them with 

 bodies capable only of the smallest force of resistance, the principal 

 muscular power being in the tail; hence, also, the contraction of 

 their limbs, the expansibility of the latter, and of the membranes, by 

 which they are supported ; and hence, finally, are the integuments 

 smooth and scaly, and altogether destitute of feathers and hairs. 



Performing the process of respiration simply through the medium 

 of water, in other words, only availing themselves of the small pro- 

 portion of oxygen which is contained in the air mixed with the water, 

 for the purpose of giving an arterial character to their blood, it follows 

 that this blood must remain cold, and that, consequently, the vitality 

 of the fishes, and the energy of their senses and of their motions must be 

 inferior to those of the mammalia and the birds. And, in point of fact, 

 their brain, though similar in its structure, is much smaller than it is 

 in the former classes, and their external organs of sense are not ofi 

 nature to enable them to feel any very powerful sensations. The 

 fishes, therefore, form that division of the vertebrated animals which 

 possess the least appreciable signs of sensibility. Excluded from the 

 use of elastic air, they are consigned to eternal dumbness, at least 

 this is very nearly the case, and all those feelings which vocal sounds 

 are calculated to excite, are to them for ever strangers. Their eyes 

 have no faculty of motion, their faces are long and fixed, their limbs 

 are incapable of flexion, and always moving in one single mass, afford 

 no opportunity for the play of their physiognomy, and no power for 

 the expression of their emotions; their ear enclosed on ('very side in 



ft^ (a) To guard against any misunderstanding with respect to the assertion 

 that the brain is in the vertebral column, we must mention that the skull is regarded 

 as only a vertebra extensively developed. — Eng. Ed. 



