DIGESTION IN FISHES. 203 



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 invertebrated classes we occa- 

 sionally meet with instances of structures ex- 

 ceedingly analogous to a gizzard, 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, 

 which is often provided, not only with a me- 

 chanism analogous to a gizzard, but also with 

 rows of gastric teeth. 



Chapter VIII. 

 Chylification. 



The formation of Chyle, or the fluid w^hich is 

 the immediate and exclusive source of nutriment 

 to the system, takes place in the intestinal tube, 

 into which the chyme prepared by the stomach 

 is received, and where farther chemical changes 

 are effected in its composition. The mode in 

 which the conversion of chyme into chyle is 

 accomplished, and indeed the exact nature of the 

 changes themselves, being, as yet, very imper- 



