MOLLUSCA, THE SHELL-FISH 99 



Gasteropoda (stomach-footed animals), is sup- 

 posed to be descriptive of the way in which a 

 snail crawls. Half getting out of its shell, so to 

 speak, it does its best to lay its body to the 

 ground, and its so-called "foot" is an extensive 

 muscular expansion underlying its body, not just 

 a muscular organ thrust out of the shell, as in 

 some other groups. The shell, the mode of crawl- 

 ing, and the " horns," tipped with eye-specks, and 

 directed, intelligently and inquisitively, towards 

 things of interest these make up, for most peo- 

 ple, the idea of Snail. But the most distinctive 

 feature of the class is a less obvious feature, 

 namely, the structure of the tongue. We may 

 see, on any damp day or dewy evening, the snail 

 working away with its tongue at some tender 

 leaf. Its tongue is practically a file with which 

 it files away the substance of the leaf, the result- 

 ing green mash being thus made ready in minute 

 quantities for the snail to swallow. Thus are 

 made the too familiar holes which disfigure the 

 leaves of plants in our garden. When seen under, 

 the microscope, the file-like structure of the 

 tongue is visible; indeed, in large tongues, it 

 may, to some extent, be made out with the naked 

 eye. Across the tongue, which is a flat ribbon- 

 like structure, there runs a pattern of small teeth, 

 bilaterally symmetrical, and this pattern is re- 

 peated over and over again throughout the whole 

 length of the tongue. It might be thought that 

 snails' tongues, being so much alike in their mode 

 of use, would not need to be very various in pat- 

 tern : but far from this, they vary in appearance 

 as much as the shell. Not only is there a differ- 

 ent pattern for every different order of the class, 

 but a different pattern for every genus ; nay, 



