36 LESSON VII. 



no resistance, are gently carried along by its 

 waves; some anchor themselves securely by a 

 byssus to rocks, and thus bid defiance to danger ; 

 others, by adding to the weight of their bark, can 

 descend and seek a shelter in the bed of the 

 ocean. There are many other beautiful contri- 

 vances for their preservation. But in spite of 

 these, a breach will sometimes be made in their 

 shell ; this however they have the power of re- 

 pairing, by exuding a calcareous matter, similar 

 to that with which they at first constructed the 

 shell, and so filling up the hole. 



LESSON VII. 



Teacher. To-day you shall tell me all that 

 you remember respecting shells, and I will put it 

 together in a regular manner. 



Shells are the coverings or habitations of a 

 species of mollusca. They are formed by the 

 animal itself of carbonate of lime and gelatine : 

 these substances are secreted by glands in its body. 

 The colouring matter exudes from the pores of 

 the mantle, penetrates the shell before it is har- 

 dened, and the colours being arranged in order 



