268 ZOOLOGY 



nautilus and pearly nautilus, the latter made famous by our poet Holmes, 

 also belong to this group. 



Octopus. 



Habitat of the MoUusks. — Mollusks are found in almost all 

 parts of the earth and sea. They are more abundant in temperate 

 localities than elsewhere, but are found in tropical and arctic 

 countries. They are found in all depths of water, but by far the 

 greatest number of species live in shallow water near the shore. 

 The cephalopods live near the surface of the ocean, where they 

 prey upon small fish. The food supply evidently determines to a 

 large extent where the animal shall live. Some mollusks are 

 scavengers, others feed on living plants. 



We have found in the forms of Mollusc a studied that almost all 

 mollusks live in the water. There is one great group which forms, 

 a general exception to this, certain of the snails and slugs called 

 pulmonates. But even these animals are found in damp localities, 

 and at the approach of drought they become inactive, remaining 

 within the shell. The European snail {Helix pomatia), imported 

 to this country as a table delicacy, exists for months by plugging 

 up the aperture to the shell with a mass of slimy material which 

 later hardens, thus protecting the soft body within. 



Economic Importance. — In general the mollusks are of much 

 economic importance. The bivalves especially form an important 



