52 Lessons in Zoology. 



If the children are old enongh, they may now be led to see that 

 while the left Bide of the mantle of the oyster can work steadily at 

 shell-building, the right side la constantly interrupted in ita work by 

 the opening and closing of the valves, and that this aooonnts for 

 the small size of the right valve. 



Tell me in what ways the soft parts of the oyster are 

 like those of the clam. 



They have each a mantle and two pairs of g^ls. They 

 have a mouth and two pairs of palpi. They have a heart. 



Tell me some things that are unlike in the soft parts. 



The oyster's mantle is open, and the clam's is closed. 

 The oyster has one muscle, and the clam has two. The 

 oyster's heart is close to the muscle, and the clam's is 

 under the beak. I dnn't pee why the oyster hasn't any 

 foot nor any siphon ? 



Fig. 2. 



Where does the clam live ? 



He buries himself in the mud. He digs down into the 

 mud with his foot 



What use has he for his siphon ? 



He reaches up to the water with it. 



Where does the oyster live ?. 



He fastens himself to a rock. I see ; he doesn't need 

 a foot because he doesn't dig in the mud, and he doesn't 

 need a siphon because his whole shell is in the water. 



Oysters naturally live on rocks or hard substances (Fig. 2) , 

 and after the young ones swim about for a while, they die if 

 they cannot find something hard to grow on, but they fatten 



