74 GASTEROPODA. 
CLASS III. GASTEROPODA. 
(Crawling Mollusks.) 
lr we examine the manner in which the common 
Garden Snail crawls, and especially if we look at 
it through a pane of glass as it glides up on the 
outside of the window, we shall see that the whole 
of the under-part of the body forms a wide fleshy 
disk, which is applied to the surface upon which 
the animal moves. Carefully watching this, we 
perceive that there are minute muscular move- 
ments constantly taking place over the whole disk, 
by means of which the animal advances with an 
uniform gliding progression. This disk, and its 
peculiar action, afford the most important character 
by which this Class of animals is distinguished, 
and hence they have been named Gasteropoda, 
which signifies belly-footed. 
The upper surface of the body is covered with 
a fleshy cloak, the edges of which usually project 
in a greater or less degree, overlapping the foot- 
disk and other organs. This is called the mantle. 
There is a distinct head, more or less conspicu- 
ous, according as it more or less projects from 
beneath the edge of the mantle; it is furnished 
with tentacles, varying in number from two to six, 
arranged in pairs on each side. ‘These are pro- 
bably delicate organs of touch, and perhaps they 
may be connected with other senses also. The 
majority of species are furnished with eyes, com- 
