THE SNAIL. 151 



times without unduly annoying the animal. Meanwhile 

 observe an orderly series of movements, and record what 

 they are. 



Make any other observations on its movements that 

 occur to you. 



Discover how the animal is breathing. Note the open- 

 ing and closing of the pulmonary aperture (under the shell 

 on the right side). Leave the snail to itself and observe 

 whether this opening and closing occurs at regular inter- 

 vals, whether frequently or seldom. Study next some 

 snails feeding on lettuce leaves. Write down what you 



Fig. 54. The edible Snail (Helix pomatia). 



An unsymmetrical type, p.ap, pulmonary aperture ; /, foot ; g.ap, genital 

 aperture ; m, mouth ; s.h, short horns ; e, eye. 



see and hear. (The teacher will explain the presence of 

 a toothed ribbon in the mouth on which the food is 

 rasped.) 



Special senses : Sight. Examine the organs of vision. 

 Note their situation and how they are protected. What 

 happens when the animal retracts its * horns " ? Deter- 

 mine by experiment the range of vision. This may be 

 done by carefully approaching the eyes with a pencil or 

 fine brush. Note how near it is possible to come before 

 the eyes are retracted. Test the response to moving and 

 stationary objects. 



