PISCES. 77 



external portion of these organs consists usually of 

 a varying number of slender rays, on which a thin 

 membrane is stretched. A fin formed in the same 

 manner, called the dorsal, generally runs down the 

 back, and another, the anal, is near the vent. The 

 covering of fishes seems most to resemble that of 

 the Serpents, but differs widely from it. It consists 

 of scales, often delicately sculptured and beautifully 

 transparent, usually overlapping each other at the 

 edge. 



The following eloquent passage from Cuvier's 

 Ichthyology, sums up in a few words the most im- 

 portant peculiarities of this Class of animals : "Being 

 aquatic, that is to say, living in a liquid which is 

 heavier, and offers greater resistance than air, their 

 power of motion has been necessarily disposed and 

 calculated for progression as well as for elevation, 

 which is also accomplished by them with ease. Hence 

 arises that form of body which offers least resistance, 

 (the chief seat of muscular force residing in the tail,) 

 the shortness and expansibility of their limbs, the 

 membranes which support them, the smooth or scaly 

 covering, and the total absence of hairs or feathers. 

 Breathing only through the medium of water, their 

 blood is necessarily cold, and their vitality, the 

 energy of their senses and movements, are conse- 

 quently less than in Mammalia and Birds. Their 

 brain, therefore, or rather a composition similar to 

 it, is proportionally much smaller, and the external 

 organs of their senses are not of a nature to admit 

 of powerful impressions. Fishes, in fact, are, of all 



