UNIVALVES. 
GaASTEROPODA is a name given by some naturalists 
to a very extensive group of molluscous animals; 
the term is derived from two Greek words, signi- 
fying stomach and foot;—it has reference to the 
kind of fleshy foot which generally occupies the 
whole under side of the body, and by the con- 
traction and extension of the muscles of which, the 
creature is enabled to glide, with a slow but steady 
motion, from place to place. The Slug and the 
Snail are the commonest examples which can be 
adduced of gasteropods ; and one may tell by their 
slimy tracks, shining like silver in the morning 
sunshine, that during the night, which is their 
principal feeding-time, they manage to get over @ 
considerable extent of ground, although “a snail’s 
gallop” is a proverbial expression for slow motion ; 
but it is astonishing how much work of any kind 
may be done if one “‘keeps at it”; by doing this 
