136 THE WEALTH OF THE SEA 



fishes have inferior mouths, that is, mouths below 

 the head, as in the sturgeons, sharks, and skates. 

 Others have mouths opening upward, as in the goose- 

 fish already mentioned. The most common form of 

 mouth is of moderate size, and is terminal and 

 directed slightly upward. 



Interesting, in fact, grotesque developments of 

 the jaws take place in some fishes. In the half -beaks, 

 for example, the lower jaw is developed as a tooth- 

 less, sword-shaped appendage, reaching far beyond 

 the mouth and frequently being longer than the rest 

 of the head. In the saw-fishes the upper jaw is 

 greatly extended. Furthermore the sword-shaped 

 projection is provided on each edge with a row of 

 large teeth giving it the appearance of a double- 

 edged saw. In the gars, both jaws are excessively 

 elongated, and each is provided with long slender 

 teeth. The purpose of the unusually developed jaws, 

 in at least some of the species, is difficult to explain. 

 In some they serve as weapons of defense, in others 

 of offense, and in still others of offense and defense. 



Many fish, as already stated, gulp their food and 

 therefore do not need teeth to masticate it. Nearly 

 all fishes, nevertheless, have some sort of teeth, vary- 

 ing greatly in size and shape among the species. 

 Frequently the teeth serve only to grasp and to hold 

 the prey until it can be swallowed. Such teeth gen- 

 erally are sharply pointed and directed inward and 

 backward, as in the weakfishes. Sharks often have 

 teeth directed inward and backward, with broad 

 bases surmounted by triangular cusps with finely 

 and sharply notched cutting edges. Teeth of this 



