CHAPTEE VIII. 



THE ORGANS OF NUTRITION AND DIGESTION. 



Fishes are either exclusively carnivorous or herbivorous, 

 but not a few feed on vegetable substances as well as animal, 

 or on mud containing alimentary substance in a living or 

 decomposing state. Generally they are very voracious, espe- 

 cially the carnivorous kinds, and the rule of " eat or be eaten " 

 applies to them with unusual force. They are almost con- 

 stantly engaged in the pursuit and capture of their prey, the 

 degree of their power in these respects depending on the 

 dimensions of the mouth and gullet and the strength of the 

 teeth and jaws. If the teeth are sharp and hooked, they are 

 capable of securing the most slender and agile animals ; if 

 this kind of teeth is combined with a wide gullet and disten- 

 sible stomach, they are able to overpower and swallow other 

 fish larger than themselves ; if the teeth are broad, strong 

 molars, they are able to crush the hardest aliments ; if they 

 are feeble, they are only serviceable in procuring some small 

 or inert and unresisting prey. Teeth may be wanting alto- 

 gether. Whatever the prey, in the majority of cases it is 

 swallowed whole ; but some of the most voracious fishes, like 

 some Sharks and Characinidce, are provided with cutting 

 teeth, which enable them to tear their prey to pieces if too 

 large to be swallowed whole. Auxiliary organs for the pur- 

 pose of overpowering their prey, which afterwards is seized 

 or torn by the teeth, like the claws of some carnivorous 

 mammals and birds, are not found in this class ; but in a 



