ADAPTATION FOR PROTECTION FROM ENEMIES 87 



Suggested drawings. 



a. Dorsal margin of the clam. 



b. Side view of the clam. 



c. The clam with one valve removed or lifted back. 



d. The clam with one valve and one mantle lobe removed. 



e. The edge of a broken shell. 

 /. Diagram of cross sections. 



2. THE SNAIL— A TYPE OF MOLLUSCA 



To show Another Type of Exoskeleton 

 Materials. 



Specimens of pond snails, edible snails, and " slugs, " and 

 other land snails, and a collection of shells of various 

 types. 



Definitions. 



Gasteropoda, the name of the class to which the snail 

 belongs. 



Spire, the coiled portion of the snail shell. 



Aperture, the opening of the shell. 



Lip, the edge of the shell forming the margin of the 

 aperture. 



Whorl, a single coil of the spire. 



Suture, the depression between the whorls. 



Foot, the flat disk-like structure on which a snail creeps. 



Breathing pore, an opening in the mantle used in res- 

 piration. 



Lingual ribbon, the rasp or file like tongue of the snail. 



Observations. 



1. Why is a snail called a univalve ? 



2. Identify the head and mouth of the snail. Watch 

 the snail feeding and examine the mouth of the snail with 



