128 ANIMAL • BIOLOGY 



96. Adaptations for food gcjtting. — Laboratory study. 



1. Open the jaws of a fresh or of a preserved fish. (Fish of 



large size, e.g. cod, should be used if possible, the 



jaws being held wide open with pieces of wood.) 



Look for teeth on the jaws and the roof of the 



mouth. 

 a. State the location of the teeth and give some idea of 



their number. 

 6. Rub the fingers gently back and forth over the teeth. 



Do they point backward or forward ? How do you 

 know? 



Describe any other characteristics of the teeth. 



c. Of what use would the teeth be in catching other 



fish for food ? 



d. Why would the shape of the teeth make them of no 



use in grinding food ? 



2. Drop some fish food into a jar containing living goldfish.* 



Describe all the movements that you see the fish 

 make while feeding. 



97. Food and food getting among fishes. — -Unlike plants, 

 fishes cannot make their food from materials found in the 

 water, air, and soil, but must secure it ready-made from 

 plants or other animals. The goldfish, for example, de- 

 pends largely on vegetable food, while the cod ^ and the 

 perch for the most part feed upon other animals smaller than 

 themselves. Since these fishes must catch and hold their 

 prey, their jaws are provided with many sharp teeth that 

 point backward, and so prevent the escape of any active 



• If none of the fish eat readily, this experiment should be deferred. 



^ "The cod is omnivorous, and feeds upon various kinds of ani- 

 mals, including crustaceans, molluscs, and small fishes, and even 

 browses upon Irish moss and other aquatic vegetation. AH sorts 

 of things have been found in cods' stomachs, such as scissors, oil 

 cans, finger rings, rocks, potato parings, corn cobs, rubber doUs, 

 pieces of clothing, the heel of a boot, as well as other hew and rare 

 specimens of mollusks and Crustacea." — Jordan and Evermann, 

 "American Pood and Game Fishes." 



