6 



POPULAR CONCHOLOGY. 



have recourse to various methods to enable theui to swim ; 

 some only float, borne as the winds and waves direct ; a 

 few can glide along the surface of the water, the body 

 and shell hanging down below, the foot alone retaining 

 them in this position ; others, by squirting out suddenly a 

 stream of water, which they have taken into their shells, 

 send themselves forward in an opposite direction; and 

 others swim, by using their foot as a fin, and moving it 

 from one side to the other. In those Mollusca which affix 

 themselves permanently to a submarine object, the method 

 of attachment varies considerably ; some, for instance, are 

 fixed by the shell, some by a continuation of the foot 

 either in a mass, or divided into separate fibres, some by a 

 tube, and others by a number of threads, which they spin 

 and fix to different parts of the rock or other substance 

 on which they dwell ; some excavate holes in soft rocks, 

 and others in timber. In the locomotive Mollusca the 

 foot is often serviceably employed for the purpose of bur- 

 rowing in the sand and mud, to enable them to conceal 

 themselves underneath, being used very effectively as a 

 scoop, and thus enabling the animal to hide itself in a 

 short time, and to emerge when all danger is over. The 

 land Mollusca live mostly in moist places and woods, and 

 glide about by the aid of the muscular foot. 



With regard to the food on which Mollusca live, there 

 is as much variety as exists among animals of a more 

 complicated organisation : some are carnivorous, others 

 herbiverous, and the substances on which they feed, 

 whether animal or vegetable, are consumed by them in 

 various states, some preferring the living, whilst others 

 prefer the dead or putrescent form. To meet these dif- 

 ferent forms of nutrition, various and diversified organs 

 are required : and it will be found that in these animals, 

 as well as in the other ranks of creation, the appropriate 



