ADDITIONAL ANIMAL STUDIES 185 



food, they are important economically on account of the pearly 

 matter that is found on the inside of their shells. This ■ is used in 

 making buttons and other articles. In fact, there is a considerable 

 industry in this line 

 along the Missis- 

 sippi River. i&^&^S^ ^feeler 



Oysters are rni- 

 portant as an arti- 

 cle of food. The 

 oyster &hermen re- 

 ceive annually from "•"=i»^''}'^a5^»sS)B»=*' " mouth 

 twenty to thirty mil- ^^^ ^33 _ ^^^ ^^^^_ 

 lions of dollars from 



these mollusks collected from the oyster beds along the Atlantic Coast. 

 A certain kind of mollusk, known as the pearl oyster, secretes within 

 its shell the pearls of commerce. These are formed of a material 

 similar to that found on the inner layerS of the fresh water mussel. 



E. Reptiles 



140. The turtle. — The body of a turtle may be divided into four 

 regions; namely, head, neck, trunk, and tail. The larger part of a 

 turtle, the trunk, is covered by a shell, and to this shell the bony 

 skeleton is firmly united. The two pairs of legs, however, are freely 

 movable, but can be drawn within the shell for protection. The 

 toes of the feet are armed with sharp, curved nails, and the legs are 

 covered with scales. The legs are used for walking and also for 

 swimming. In some turtles the legs become broad and flat and 

 are of but little use except for swimming. 



The head, neck, and tail can also be drawn into the shell. Scales 

 cover the neck and part of the head. The jaws of the turtle, often 

 called the beak, possess no teeth. The eyes, protected by the eye- 

 lids, the nostrils, and the ear openings, are readily seen. 



Turtles reproduce by means of eggs, which are comparatively 

 large. Turtle eggs are often used for food. These animals breathe 

 throughout their entire Ufe by means of lungs. 



