52 LESSON VIII. 



Teacher. Yes, and you must distinguish 

 these two lips. What is their position ? 



Child. One is on the outside of the mouth. 



Teacher. That is called the outer lip ; and 

 where is the other. 



Child. Upon the body whorl. 



Teacher. To what part of the shell is it near ? 



Child. It is near to the columella. 



Teacher. Yes, and it is thence called the 

 columellar lip. In what respect do these lips 

 resemble ours ? 



Child. They are the borders of the mouth. 



Teacher. Right. But how do they differ 

 from our lips ? 



Child. They are not moveable. 



Teacher. Do you suppose this is any disad- 

 vantage to the animal. 



Child. Certainly, for he cannot close his mouth, 

 and so exclude the water or keep out enemies. 



Teacher. True, but those species which 

 would suffer from such an exposure, are pro- 

 vided with a kind of lid which fits into the mouth 

 and closes the entrance to the shell, when the 

 animal retires within it. This lid is called the 

 operculum, a Latin word, signifying a covering. 

 The shells which are furnished with this appen- 

 dage are said to be operculated. Did you ever 

 observe any thing at all like it in the snails ? 



Child. The entrance to the shell is guarded 

 by a thin covering during the winter. 



Teacher. The animals belonging to land 

 shells, as for instance snails, protect themselves 

 from the inclemency of winter, by forming a tern 



