LAND SNAILS. 31 



20. If a land-snail is taken out of its shell (and this can 

 be done if boiling water be first poured upon it, and then 

 with a pin the animal can be readily picked out), it will pre- 

 sent this appearance (Fig. 25) : 



Fig. 25, — Land Snail removed peom its Shell, —m. Mantle. 



The portion contained within the shell presents the 

 same general appearance as the shell itself. A free border, 

 or collar, is seen which corresponds to the aperture of the 

 shell. This border is called the mantle, and is a character- 

 istic feature of all the snails thus far studied. It is the edge 

 of the mantle which deposits the successive layers of the 

 shell, and increases its size. In the slug, there is only the 

 limy scale ; this is buried in the mantle, which is plainly seen 

 covering a portion of the back, like a shield (Fig. 22, a). 



CHAPTEE IV. 



SEA SNAILS. 



21. Classes that live near the sea-coast may now study 

 the marine, or salt-water snails. These may be collected 

 alive at low tide, upon rocks, or under the sea-weed. By 



