SHELLS. 53 



looking at it, the front being opposite to 

 him. 



Teacher. Give me the derivation and appli- 

 cation of the word spire. 



Mention the different kinds of spires, with the 

 derivation of the terms which you use. 



Whence is the term suture derived ? 



How do the sutures vary ? 



What different projections occur on the sur- 

 faces of shells ? 



From what is the term varices derived ? 



How are the cavities of the shells often 

 closed ? 



Tell me the derivation of the word operculum. 



What different kinds of opercula are there ? 



What are the shells called which have a beak ? 



What is the mouth said to be when it has no 

 beak ? * 



* These model lessons have been drawn out with great 

 minuteness in order to exhibit two principles, very important 

 to be applied in this kind of instruction. 1st. That the object 

 itself should be presented to the children ; that their powers of 

 observation may be stimulated and directed by appropriate 

 questions ; and thus a considerable portion of their knowledge 

 be acquired by themselves, instead of all being simply 

 communicated by the Teacher. 2nd. That whatever supple- 

 mentary information is given should be reproduced by the 

 class before the conclusion of the lesson. 



