THE GRASSHOPPER AND THE SNAIL S3 



the snail " walk " by means of this " foot"? The body 

 is covered by the mantle, an edge of which may be seen 

 just at the margin of the shell. The soft, flexible body 

 and firmer muscular foot can both be withdrawn into the 

 protecting shell. 



Find on the head a pair of extensible tentacles, the 

 feelers, with the eyes (dark spots) at their bases. Most 

 other snails and slugs have two pairs of tentacles or 

 horns, the eyes being on the tip of the second pair. 

 Find also the mouth, and examine with a lens the pecul- 

 iar ribbon-like radula or tongue, which is covered with 

 fine curved teeth. The radula is drawn back and forth 

 across the food, and by it small particles of the leaf are 

 rasped off. Leaves which have been fed on will show 

 the rasped or scraped places. 



Find also, usually just at the surface of the water, 

 when the snail has come up to breathe, a small hole on 

 the right side of the body; this is the breathing pore, 

 and air entering here passes into a small sac-like space, a 

 simple kind of lung. 



Examine a shell and note the following parts: the 

 aperture at the large end, the apex or pointed end, 

 the lip or outer edge of the aperture, the lines of growth 

 parallel with the lip, the suture or spiral groove on the 

 outside, the spire comprising all the whorls or turns, 

 and the columella or inner axis of the spire. Do the 

 whorls of all the shells turn the same way.? What is 

 the use of the shell .-' 



Make a drawing of the right-hand side of a snail and 

 its shell representing the animal fully extended; name 

 all the parts of the snail and shell. 



If pond snails cannot be found, garden snails or slugs 

 may be studied. The slug is a snail-like animal without 

 a shell. 



