THE HABITS AND LIFE HISTORY OF A POND SNAIL 41 



ment. Some will be seen swimming along the surface of 

 the water. In what position are they? Note the move- 

 ments of swimming. Note that the portion of the body 

 outside of the shell is triangular in shape. The greater part 

 of this is the foot. Note in a swimming specimen the 

 mouth, which is a small aperture that opens and shuts 

 rythmically. It is on the under side of the head. Note 

 that the triangular foot ends squarely just behind the head. 

 Watch one come to the top and turn on its back. As it does 

 so, note the round opening just inside of the shell. This 

 is the respiratory opening and it leads to the lung. The 

 snails come to the surface at intervals to take in air through 

 this opening. Touch an individual with a pencil. Does it 

 drop to the bottom ? As it does so what does it give off ? 

 The lung is used as a hydrostatic apparatus as well as for 

 breathing. When the snail wishes to descend for safety, it 

 gives out from the lung one or more bubbles of air; this 

 causes the body to become heavier. 



Make a drawing of the snail, as it is swimming on the sur- 

 face of the water, to show its foot and head with the mouth. 



How many tentacles has this snail ? Where are the eyes ? 

 How many are there ? 



Make a drawing of the shell from above. 



B. LIFE HISTORY OF THE SNAIL. If these snails were 

 brought into the house in February or March, the eggs 

 may soon be found on the sides of the jar, or on leaves, 

 sticks, etc. They will appear as transparent, gelatinous 

 masses, about the shape and size of half of a pea or 

 bean. Note the number of eggs in each mass. Mount a 

 few of them on a slide, and examine with a J objective. 

 What is the shape of a single egg ? Note the transparent 

 capsule ; like a shell, about each one. If they are nearly 



