3 



The Dissection of the Fish 



the canines are in front. In some families the last tooth in 

 either jaw may be a "posterior canine," serving to hold small 

 animals in place while the anterior teeth crush them. Canine 

 teeth are often depressible, having a hinge at base. 



Teeth very slender and brush-like are called setiform. Teeth 

 with blunt tips are molar. These are usually enlarged and fitted 



for crushing shells. Flat teeth set in 

 mosaic, as in many rays and in the 

 pharyngeals of parrot-fishes, are said 

 to be paved or tessellated. Knife-like 

 teeth, occasionally with serrated edges, 

 are found in many sharks. Many 

 fishes have incisor-like teeth, some 

 flattened and truncate like human 

 teeth, as in the sheepshead, sometimes 

 with serrated edges. Often these teeth 

 are movable, implanted only in the 

 skin of the lips. In other cases they 

 are set fast in the jaw. Most species 

 with movable teeth or teeth with ser- 

 rated edges are herbivorous, while 

 strong incisors may indicate the choice 

 of snails and crabs as food. Two or 

 more of these different types may be 

 The knife -like teeth of the sharks are 

 progressively shed, new ones being constantly formed on the 

 inner margins of the jaw, so that the teeth are marching to be 

 lost over the edge of the jaw as soon as each has fulfilled its 

 function. In general the more distinctly a species is a fish- 

 eater, the sharper are the teeth. Usually fishes show little dis- 

 crimination in their choice of food ; often they devour the young 

 of their own species as readily as any other. The digestive 

 process is rapid, and most fishes rapidly 'increase in size in the 

 process of development. When food ceases to be abundant the 

 fishes grow more slowly. For this reason the same species will 

 grow to a larger size in large streams than in small ones, in lakes 

 than in brooks. In most cases there is no absolute limit to 

 growth, the species growing as long as it lives. But while some 

 species endure many years, others are certainly very short- 



FIG. 18. Jaws of a Parrot- 

 fish, Sparisoma aurofrenatum 

 (Val.). Cuba. 



found in the same fish. 



