IN A SNAILERY. 21 



sented by sandstone and volcanic rocks.* Hot springs are 

 very likely to be inhabited by mollusks, even when the tem- 

 perature exceeds 100 Fahr., and the waters are very strong- 

 ly impregnated with mineral salts. 



Snails are mainly vegetarians, and all their mouth-parts 

 and digestive organs are fitted for this diet. Just beneath 

 the lower tentacles is the mouth, having on the upper lip a 

 crescent-shaped jaw of horny texture, with a knife-like, or 

 sometimes saw-like, cutting-edge. The lower lip has noth- 

 ing of this kind, but in precisely the. same attitude as our 

 tongue is arranged a lingual membrane, long, narrow and 

 cartilaginous, which may be brought up against the cutting- 

 edge of the upper jaw. This " tongue " is studded with 

 rows of infinitesimal silicioas "teeth," 11,000 of which are 

 possessed by our common white-lipped helix, although its 

 ribbon is not a quarter of an inch long. All these sharp 

 denticles point backward, so that the tongue acts not only 

 as a rasp, but takes a firm hold upon the food. On hold- 

 ing the more transparent snails up to the light it is easy to 

 see how they eat, and you can hear a nipping noise as the 

 semicircular piece is bitten out of the leaf. Their voracity 



* See Dr. Hayden's Report of the United States Geological Survey, 1874; 

 and the Popular Science Monthly, July, 1875. 



