CHAPTER IV. 

 THE MOLLUSCA OR MOLLUSKS. 



SECTION I. 



THE MOLLUSCA CONSIDERED AS A BRANCH. 



THE Mollnsca have a soft body which is enveloped by a 

 muscular skin called a mantle, and in most cases protected 

 by a shell ; and they are not .jointed nor radiated in their 

 internal structure. 



The name Mollusca is derived from the Latin mollis, 

 soft. 



The shells are the parts of these animals which we 

 oftenest see; for when the animal is dead the soft parts 



FIG. 524. 



A living Mollusk expanded. 



soon disappear, and only the shell remains. Curious and 

 wonderful as the shells are, they often give only the 

 FIG. 525. faintest idea of the appearance of 



the animals when alive. 



The shell is a part of the animal, 

 and not a mere house which it enters 

 and leaves at pleasure ; although the 

 so-called animal readily expands 



Mollusk dead-or contracted. much beond the ]imitg Q f thig 



