83 



into the blood while these are going on, serves 

 all the purposes of a supply of alimentary mat- 

 ters from without. 



Let us proceed, next, to the vertebral animals. 

 In many fishes the gullet is enormously wide ; 

 and in some it is furnished, like the tongue, and 

 some other parts of the mouth, with regular 

 teeth. In the myxine there are numerous open- 

 ings from the gullet into the respiratory bags, 

 which lie on each side of it ; and, in the greater 

 number of fishes, this canal opens into the air- 

 bladder, a long narrow sac running down the 

 body, close to the spine, and serving the purpose 

 chiefly of enabling the animal to rise in the wa- 

 ter, which it effects by inflating, at will, this sac 

 with air. In some fishes, as in the sea-devil, the 

 stomach is divided by a transverse constriction 

 into two portions ; but these divisions are still 

 more remarkable in the shark, in which the right 

 portion of the stomach is almost entirely distinct 

 from the left, and assumes nearly the form of an 

 intestine. In most fishes, the stomach is of that 

 kind called membranous ; but in a few, as the 

 trout and mullet, it is of a fleshy, and almost 

 cartilaginous consistence, like the gizzards of 

 fowls, and so hard as to break the shells of those 

 animals on which these fishes subsist. The in- 

 testinal canal of fishes is distinguished principally 

 by the spiral or serpentine direction of the nu- 

 merous plaits into which the internal membrane 

 of it is folded ; and which are believed, by de- 

 taining the alimentary matters in their passage 



