DIGESTION IN PISHES. 147 



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 purpose, 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 em- 

 ployed; the office of mastication being transferred to the 

 stomach. Thus, the Mullet has a stomach endowed witli 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 peculiar to Ireland, 

 exhibits, though in a less degree, the same structure. The 

 common trout, also, occasionally lives upon shell-fish, and 

 swallows stones to assist in breaking the shells. | 



Among the invertcbrated classes we occasionally meet 

 with instances of structures exceedingly analogous to a giz- 

 zard, and probably performing the same functions. Such 

 is the organ found in the Sepia; the earth-worm has both a 

 crop and a gizzard; and insects offer numerous instances, 

 presently to be noticed, of great complexity in the structure 

 of the stomach, wdiich is often provided, not only with a 

 mechanism analagous to a gizzard, but also with rows of 

 gastric teeth. 



