MOLLUSKS. 



203 



MOLLUSKS, OR SOFT-BODIED ANIMALS. 



The term MoUusk comes from a word which means. 

 soft, and these animals have a soft body with no 

 backbone nor internal skeleton ; nor is the body di- 

 vided into rings or joints, as in the Arthropods and 

 Worms. Most of them have a hard covering called a 

 shell, and are often called slicllfish ; but they are in 

 no way related to Fishes. The shells are the parts 

 which we oftenest see ; for when the animal is dead, 

 the soft parts soon disappear, and only the shell 

 remains. Curious and wonderful as the shells are, 

 they often give only the faintest idea of the appear- 

 ance of the animals when alive. See the differences 



Fig. 354. — Helix. Alive. 



between Figures 354 and 355, where the first repre- 

 sents the shell alive and the animal expanded, the 

 second the shell as when dead, 

 or when the animal is concealed 

 in the shell. It is important to 

 know that the shell is a part of 

 the animal and not a mere house 

 which it enters and leaves at 

 pleasure ; although it readily ex- Fig. 355.— Helix. Dead. 

 pands much beyond the limits of the shell, and with- 



