The Dissection of the Fish 29 
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 
Fic, 18.—Jaws of a Parrot- trong incisors may indicate the choice 
fish, Sparisoma aurofrenatum m 
(Val). Cuba. of snails and crabs as food. Two or 
more of these different types may be 
found in the same fish. 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- 
