276 FUNCTIONS AND INSTINCTS. 



sea water itself, either from animalcules or other 

 marine substances requiring only absorption, but 

 the Gastropods that we are next to notice live 

 upon more solid food, and such as cannot be 

 digested without a more powerful action upon it. 

 Of this description are the dippers 1 which are 

 furnished with a singular organ or gizzard that 

 proves their predaceous or carnivorous habits ; 

 the remaining genera are herbivorous, but as 

 they exhibit no very interesting traits I shall 

 proceed to the next Order. 



The Trachelipods, constituting Lamarck's third 

 Order of Molluscans, may be divided into those 

 that are herbivorous, and those that are car- 

 nivorous, the first having no respiratory siphon, 

 with which the others are furnished. 



The herbivorous Trachelipods may be sub- 

 divided into terrestrial and aquatic, and the 

 latter into those that inhabit fresh water or salt. 

 It is not known that any of the predaceous ones 

 are terrestrial. The terrestrial ones not only 

 devour the leaves and stems of plants, but some 

 also attack their roots, one species, defended by 

 an operculum or mouth-cover, devours those of 

 the violet. 2 Others of this tribe are found on 

 trees, under moss, or feeding on the lichens ; 

 the shells of some of these are what are called 

 turrited 3 or long and slender, with spiral whirls, 



1 Bull a. 2 Cyclostoma elegans. 3 Clausilia. 



