36 LESSON VI. 



others, on the contrary, by their very lightness 

 are enabled to float on the surface of the water, 

 and offering no resistance, are gently carried 

 along by its waves ; some anchor themselves 

 securely by a byssus to rocks, and thus bid defi- 

 ance 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 contrivances for their preservation. 

 But in spite of these, a breach is sometimes 

 made in their shell ; but this they have the 

 power of repairing, by exuding a calcareous 

 matter, similar to that with which they at first 

 constructed the shell. 



LESSON VII. 



Teacher. To-day you shall tell me all that 

 you remember respecting shells, and I will put 

 it together in a more regular manner. 



SHELLS. 



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 in glands in its body. 

 The colouring matter exudes from the pores 

 of the mantle, penetrates the shell before it is 

 hardened, and the colours being arranged in 



