CHAPTER XI. 



THE SNAIL (Helix Aspersa). 



AN EXPERIMENTAL STUDY FOR PUPILS. 



As a preliminary to the experimental study of the snail, 

 the pupils should note its general structure, discovering 

 the position of the mouth, eyes (at tip of long horns), 

 breathing opening (under the shell at the right side). 

 The yellowish region surrounding the opening of the shell 

 is the thickened margin of the "mantle" which is con- 

 cealed beneath it. This region is usually termed the collar. 

 The flat muscular region on which the snail creeps is 

 known as the " foot." Snails and slugs which crawl on 

 the under side of their bodies are known as Gasteropoda. 

 (Gaster = belly ; pous ~ foot). The GTasteropoda form a 

 sub-division of the soft-bodied animals termed MOLLUSCA. 



Place the living snail upon a slate or sheet of paper or, 

 best of all, a piece of glass. 



Observe first its mode of locomotion an apparent 

 gliding motion upon a flat sole extending the whole length 

 of the animal. Calculate its rate of motion in inches per 

 minute. With the snail upon a piece of glass, when it 

 commences to move observe the mechanism from the lower 

 surface. Describe what you see. Compare this mode of 

 movement with that of an earthworm. Remark on the 

 presence or absence of variations in length of the body 

 in motion. Cause the animal to retreat into its shell and 

 leave it until it emerges. Repeat this experiment several 



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