220 AN INTRODUCTION TO ZOOLOGY. 



possessing gills instead of lungs. The Gasteropoda 

 have a head, usually possessing paired tentacles : they 



crawl along the ground by means of their foot, and they 

 have, as a rule, both otocysts and eyes. They have a 

 tongue which is armed with teeth, and serves them 



Fig. 71.— The Sea-Ear, ffaiiotis tubei-culota ; 1, Empty shell : 2, LivinE animal 

 era .\-liiig on its broad toot. 



to grate away their food. This tongue is called the 

 tongue-ribbon, or odontophore (tooth- carrier), and 

 its pattern varies so much in the dififerenfc groups of 

 the class, that it has been sometimes made a basis 



