14 LESSON IL 



their peculiar habits. Did you ever observe 

 when you have been on the sea-coast, numerous 

 shells clustered together on the rocks and stones ? 



Child. Yes, barnacles ; are they the animals 

 which never move from the spot to which they 

 are attached ? 



Teacher. Yes, the barnacles and many other 

 mollusks live and die on the spot where their 

 existence first commenced. 



Child. How are they fixed to the spot ? 



Teacher. Some of them, as the barnacles, 

 are cemented to the rocks by the same sub- 

 stance of which their shells are formed ; others 

 have a less permanent mode of adhesion, and 

 fasten themselves by means of a viscid liquid 

 which they discharge from glands in their bodies ; 

 some produce silky filaments, one extremity of 

 which remains in connexion with themselves, 

 while the other is fixed to marine substances, 

 and thus anchoring themselves, they float secure 

 in the ocean. The bundle of filaments which 

 the animal draws from his body for this purpose 

 is called a byssus.* Do you know any other 

 shells that are with difficulty removed from the 

 rocks ? 



Child. Yes, the limpet. 



Teacher. The manner in which this mollusk 



* The children should see and examine for themselves these 

 contrivances. A pinna with its byssus, and barnacles on a 

 stone are easily procured. The web of the spider would give 

 them a good idea of the work of the pinna, being produced in 

 a very similar manner. 



