134 GENERAL BIOLOGY 



the opening of the shell when the animal withdraws into 

 it. Is there such a plate, or operculum, in the form you are 

 studying? 



The lines that run parallel to the mouth of the shell are 

 lines of growth. Are these uniformly spaced? Can you 

 explain any variations? The whorls or turns of the shell 

 run around a central axis, the columella. Observe the 

 columella and the spirals of the shell in a broken shell. 

 Describe the relations of the columella to the other parts 

 of the shell. 



Make a drawing of the snail from the side, showing the 

 foot, head, shell. 



