THE SNAIL. 57 



2. The "horns" are the feelers, or tentacles; touch 

 them ; what would seem to be their use ? 



3. The dark spots at the bases of the tentacles are the 

 eyes; are they borne on a stalk in any common 

 snails ? 



4. Watch the snail crawling on the glass ; near the front 

 of the foot the mouth may be seen ; observe its open- 

 ing and shutting as the snail gathers food from the 

 surface of the glass. Do snails clean the glass or 

 foul it ? 



Most snails have a ribbon-like tongue, fastened at 

 each end, and covered with teeth; as this tongue is 

 applied to an object, and drawn rapidly back and 

 forth, it acts like a rasp ; in this way some marine 

 snails bore holes through the shells of other mollusks 

 and feed on them. 



5. Many snails have gills; others breathe by a simple 

 lung. Watch the snails, to see if any of them come 

 to the surface to get air ; how is this done ? 



THE SNAIL-SHELL. 



1. The pointed end is the apex. 



2. The opening at the large end is the aperture. 



3. The outer edge of the aperture is the lip. 



4. The lines parallel to the lip are the lines of growth. 



5. The spiral groove on the outside is the suture. 



G. The turns of the shell between the groove are the 

 whorls. 



7. The whorls, taken together, make the spire. 



8. The lid closing the aperture is the operculum; is this 

 present in all the snails you find ? 



