MOLLUSCOUS ANIMALS. 155 



to the bodies of most of their inhabitants by mus- 

 cles, and by these they are able to open or shut 

 them at pleasure. 



Pearls, which are so ornamental as articles of 

 dress, are procured from a bivalve shell-fish : they 

 are found growing in shells in many parts of the 

 world, and are common in some of our own rivers. 

 The principal fishing-ground for them, however, is 

 on the shores of the island of Ceylon, where vast 

 numbers of shells are brought up by divers from 

 great depths in the sea. Mother-of-pearl is the 

 inner lining of shells, freed from the rough outside 

 crust. 



Molluscous animals live on the land and in the 

 water. Those which dwell on land breathe by a 

 contrivance somewhat like our lungs ; and those 

 which inhabit the water have gills like fish. 



The mode by which these creatures keep them- 

 selves in a state of rest is highly curious. This is 

 done, in many of them, by means of a sucker, 

 which is a soft, muscular body, like what is called 

 the foot, or the belly of snail. It is quite as- 

 tonishing how fast many of them stick by this 

 means ; but whenever we are on a rocky sea-shore 

 we may easily learn by endeavouring to gather 

 limpets. Others hold themselves by a kind of 

 glue, or cement, which adheres to any thing which 

 it touches ; and many shells are actually fastened 

 to rocks by a stony matter, so that the animals 

 which inhabit them never move from one -spot. 



The motions of this part of the animal kingdom 



