66 LESSON X. 



put to you upon all that I have detailed. What 

 kind of animal inhabits the cone 1 



Child. It is one that breathes by means of 

 gills ; has a pair of tentacula bearing eyes ; and 

 its mouth is a long proboscis. 



Teacher. There is one part of the animal 

 which you have not noticed. 



Child. It has an operculum attached to its 

 foot, with which it closes the aperture of its 

 shell. 



Teacher. What is remarkable in the habits of 

 these mollusca ? 



Child. They are supposed to absorb the 

 matter of which the interior convolutions of their 

 shells are composed. 



Teacher. What then is the appearance of the 

 shells when cut in halves 1 



Child. The interior parts of the whorls are 

 thin, while the outer parts of the shell are com- 

 paratively thick and strong. 



Teacher. What advantage is the animal sup- 

 posed to derive from the different degrees of 

 thickness in the external and internal convolu- 

 tions? 



Child. The thinness of the interior diminishes 

 the weight, while the thickness of the exterior 

 preserves its strength. 



- Teacher. What is there remarkable in the 

 external appearance of these shells 1 



Child. They are remarkable for the regu- 

 larity of their form, the brightness of their 

 colours, and the variety and beauty of their mark- 

 ings. 



