THE SNAIL. 



143 



Make a table of differences between the snail and 

 the clam. 



Clam. 



Snail. 



Shell. 

 Body. 

 Foot 

 Gills . 

 Eyes . 

 Head 



From your table of differences, make a logical 

 definition of a Lamellibranch. 



Clam 



Table of Resemblances. 

 soft body ; no skeleton 



„ ., < usually enclosed in a calcareous shell 

 Snail ) . 



{ body covered with a mantle which secretes the shell 



From your table of resemblances, make a definition 

 of a mollusk. 



Additional Facts About the Snail. 



The foot of the snail, instead of being narrow 

 and plough-like, as in the clam, is flat, and adapted 

 for crawling over a smooth, hard surface. The 

 mouth opens in the foot, rather forward of the 

 center. There is an organ called the tongue, or 

 lingual ribbon, or odontophore, which moves 

 across the aperture of the mouth when the mouth 

 is open. 



Most of our land and fresh-water snails eat vege- 

 table food, either algae or decaying vegetation. This 

 may be associated with the fact that the aperture is 

 entire, having no notch, or prolongation. Many sea 

 snails are carnivorous. The aperture of such a snail 



