NERVOUS SYSTEM OF FISHES. 61 



case of a land animal ; and a flying fish is ob- 

 liged to descend to respire, in like manner as a 

 swimming quadruped, or disguised mammiferous 

 animal, as we may term a whale, is under the 

 necessity of ascending for the same purpose. 



The head of fishes exercises but a slight move- 

 ment independent of the rest of the body, but the 

 jaws, opercular bones, branchial arches, and other 

 parts, are very free in their motions. The muscles, 

 like those of other vertebrated animals, are com- 

 posed of fleshy fibres more or less coloured, and 

 of tendonous fibres of a white or silvery aspect. 

 With the exception, however, of certain spinal 

 muscles, which are sometimes of a deep red, the 

 flesh of fishes is much paler than that of quadrupeds, 

 and still more so than that of birds. In several 

 species it is even entirely white. 



SECTION VI. 



The Nervous System, and Senses of Fishes. 



As fishes respire through the intervention of 

 water alone, that is, as they can scarcely avail 

 themselves, in rendering their blood arterial, of 

 anything more than the small portion of oxygen 

 contained in the air which is suspended in the 

 water, their blood is necessarily cold, and the 

 general energy and activity of their senses are by 

 no means so great as those of quadrupeds and birds. 





