142 HABITS OP GASTEROPODA: 



of ancient armour, which, connected with a tough mar- 

 ginal band, form a complete shield to the animal. 



These several orders of Gasteropoda are as various in 

 their habits as in their organization. A large number 

 feed on marine plants, but many are carnivorous, prey- 

 ing on other Mollusca, as well as on any animal sub- 

 stance offered to them. Among spiral shells, those with 

 circular mouths to the shell, like the old genus Turbo, 

 are vegetable feeders; while such as have an aperture 

 ending in a canal, like Buccinum, and Murex, are 

 animal-feeders. Very important modifications of inter- 

 nal structure indicate this difference of food, and the 

 external organs, particularly about the mouth, exhibit a 

 corresponding variety of form. In those which feed on 

 vegetables the mouth is generally a slit, furnished with 

 more or less perfect lips, armed with a simple cutting 

 apparatus, which is often a powerful instrument, en- 

 abling the animal to eat its way through comparatively 

 hard substances. But the animal feeders are provided 

 with a much more complex organ, which serves the 

 double purpose of an arm to secure the prey, and a 

 channel to convey it to the stomach. The proboscis of 

 the Whelk, or JBuccinum, is an organ of this character 

 of a highly curious structure ; and, armed with it, the 

 creature can pierce through the hardest shells in search 

 of food. This proboscis can either be protruded to a 

 considerable length, and used as an arm movable in 

 every direction, or it may be wholly drawn in, contract- 

 ing on itself, like the horns of a snail, till it disappear 

 within the body of the animal. Its movements depend 

 on the action of a very complex system of muscles. It 



