SNAIL. 



HELIX POMATIA. 



FOR this study the French snail is suggested, but the 

 common pond snails, Physa, Planorbis, Limnsea can be 

 used. 



1. The Living Animal. How does the snail move? What 

 is the shape of the foot? What is the relation of the foot 

 to the rest of the body? What is its relation to the shell? 

 The anterior part of the foot is called the propodium, the 

 posterior portion the metapodium, and between these two 

 is the mesopodium. Are these regions sharply marked off? 



2. Head. At the anterior end note the position and form 

 of the mouth. Tentacles are present in this region. How 

 many? Size and form? Touch one with a needle. What 

 happens? On the tentacles are small, pigmented, glisten- 

 ing spots, the eyes. Note their position and number. 



Locate the anal opening on the right side of the head. In 

 the air-breathing snails the respiratory opening is near the 

 anal opening. 



3. Shell. Is there a division into valves? How many 

 turns does the shell make? Do the shells vary in size? 

 Do the coils turn to the right, or to the left? Is the coiling 

 loose or close, flat or conical? The apex of the shell is the 

 oldest part, the opening of the shell is the newest part of the 

 shell. In some species one side of the mouth of the shell 

 is drawn out into a spout-like process. For what purpose 

 is this? In some snails there is an oval plate which closes 



