276 GASTEEOPODA. 



their mantle is a fleshy disk scarcely separated from 

 the rest of the skin, and only occupies the forepart 

 of the back, where it covers the pulmonary cavity. 

 It often encloses in its thickness a small flat shelly 

 plate. These animals are herbivorous ; they feed 

 principally upon young plants, fruits, mushrooms, 

 &c., and are most voracious towards evening. 

 During the heat of the day they remain concealed 

 under stones, or beneath some heap of half-decayed 

 leaves, or even in the earth, and they seldom come 

 out except in the morning and evening when the air 

 is humid; they are especially abundant after rain. 

 During the cold season they bury themselves in the 

 ground and remain torpid. 



The Snails {Helix) have a complete and apparent 

 shell. Their structure differs very little from that of 

 the Slugs, and their habits are nearly the same. In 

 summer they are very voracious and destructive, but 



Fig. 212.— garden snail. 



in autumn they eat little. On the a]3proach of 

 winter they retu^e into some hole and draw them- 

 selves into their shell, shutting up the aperture with 

 a kind of door secreted by the edge of the mantle. 

 The species of Snails are very numerous ; they are 

 found in all parts of the world. 



The Aquatic Air-breathing Gasteropods have but two 



