48 LESSON IX. 



Child. Have we now mentioned all the parts ? 



Teacher. No, you must examine your shells 

 more attentively. 



Child. The edges of the mouth. 



Teacher. By what name are the edges or bor- 

 ders of our mouths called ? 



Child. Lips. Is the same term applied to 

 the edges of the mouth of shells ? 



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 which part of the shell is it near ? 



Child. It is near to the columella. 



Teacher. It is therefore 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. I should think it is, for he cannot 

 close his mouth, and exclude the water or keep 

 out enemies. 



Teacher. True, but those species which would 

 suffer from such an exposure, are provided with a 

 kind of lid which fits into the mouth and closes 

 the entrance to the shell, when the animal retires 



