202 THE VITAL FUNCTIONS. 



ingly stomachs, which, however they may vary 

 in their form, are alike simply membranous in 

 their structure, and act by means of the solvent 

 power of their secretions. Among Reptiles, only 

 a few exceptions occur to this rule. The com- 

 mon Sea-Turtle which is brought to our tables, 

 is one of these ; for it is found to feed exclu- 

 sively on vegetable diet, and chiefly on the sea- 

 weed called zostira mavitima; but though very 

 muscular, it has not the cuticular lining which 

 forms an essential character of a gizzard. Some 

 Tortoises, also, which eat grass, make an ap- 

 proach to the same structure. 



In Fishes, indeed, although the membranous 

 structure of the stomach invariably accompanies 

 the habit of preying upon other fish, yet there is 

 one species of animal food, namely, shell-fish, 

 which requires to be broken down by powerful 

 means before it can be digested. In many fish, 

 which consume food of this kind, its trituration 

 is effected by the mouth, which is, for this pur- 

 pose, as I have already noticed in the Wolf-fish, 

 armed with strong grinding teeth. But in 

 others, an apparatus similar to that of birds is 

 employed ; the ofiice of mastication being trans- 

 ferred to the stomach. Thus the Mullet has a 

 stomach endowed with a degree of muscular 

 power, adapting it, like the gizzard of birds, to 

 the double office of mastication and digestion ; 

 and the stomach of the Gillaroo trout, a fish 



