UNIVALVES. 



GASTERoroDA IS a namo given by somo naturalists 

 to a very extensive group of molluscous animals ; 

 the term is derived from two Greek words, signi- 

 fying stomacli 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, tliQ 

 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 bo 

 adduced of gasferopods ; and one may tell by their 

 Blimy tracks, shining like silver in the morning 

 sunshine, that during the night, which is their 

 principal feeding-time, they manage to get over a 

 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 if; by doing this 



