DIGESTION IN BIRDS. 179 



nivoroiis animals ; and have accordingly 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 secre- 

 tions. Among Reptiles, only a few exceptions oc- 

 cur to this rule. The common Sea-Turtle which is 

 brought to our tables, is one of these ; for it is 

 found to feed exclusively on vegetable diet, and 

 chiefly on the sea-weed called Zostira maritima ; 

 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 approach 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 office of mastication being transferred 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 masti- 

 cation and digestion ; and the stomach of the Gil- 

 laroo trout, a fish peculiar to Ireland, exhibits 

 nearly the same structure as that of the turtle. 

 The common Trout, also, occasionally lives upon 

 shell-fish, and swallows stones to assist in breaking 

 the shells. 



