SHELLS. 31 



termed testaceous ; the case of insects is a phos- 

 phate of lime, and is called crustaceans. The 

 carbonate of lime, of which the shells are formed, 

 is secreted in the glands of the mantle, and oozing 

 out, takes the form of the animal, and gradually 

 hardens. When the mollusk is small, the shell 

 is proportionally so ; but as the animal increases, 

 it adds to the dimensions of its abode by addi- 

 tions at the opening, and to its thickness by layers 

 from within. The colour and marking with 

 which the shells are diversified, are produced in 

 the pores of the mantle, and are there arranged 

 in the same pattern as that which appears on the 

 shell, Shells are either terrestrial, fluviatile, or, 

 marine. 



LESSON VI. 



Teacher. Tell me what you know of the sit- 

 uations in which shells are placed : and the 

 dangers to which they are exposed. 



Child. They are in the sea and must be car- 

 ried about by the waves an d often dashed against 

 rocks. 



Teacher. Yes ; they are exposed to the dash- 

 ing of the waves and often borne by the violence 

 of storms against rocks or carried with impe- 

 tuosity down rapid rivers ; you can easily imagine 



