The Oyster. 51 



clam. Near the beak on the convex side of the shell are 

 the two pairs of palpi, and between them the mouth 

 (Fig.l.m). 



Lesson II. 



This leeson, which is mainly a review, may be given with the aid 

 of the sheila, according to the following ontline : 



Tell me some things about the oyster shell. 



It has two valves. One valve is large and convex, the 

 other is smaller and flat. The large valve was fastened 

 to a rock. The shell is broad at one end and pointed at 

 the other. The pointed end is called the beak. The 

 outside of the shell is very rough, and the lines of growth 

 show very plainly. There is a hinge not far from the 

 beak, and a brown ligament. 



What can you tell about the inside of the shell ? 



The inside of the shell is nearly smooth. It is white 

 or yellowish. Near the middle is a large dark place 

 made by the muscle. There is a pallial line near the 

 edge. 



The shape of the gills and the palpi may also sametimes be seen 

 on the inside of the shell. 



In what ways are the oyster shell and the clam shell 

 alike ? 



Each has two valves. They have each a hinge and a 

 ligament. Each has a beak. They have a pallial line. 

 Each has a brown skin and lines rf growth on the out- 

 side. They are made of layers of lime and flesh. 



In what ways are they unlike ? 



The clam shell is smoother than the oyster shell. The 

 oyster shell has the beak at one end, the clam shell has it 

 on top. The clam shell has both valves of the same size, 

 but the oyster has one large valve and one small one. 



