II.] INTRODUCTION. ' XXxi 



consists of Infusoria and other animalcules, which are 

 conveyed to their mouths, by an action analogous to 

 that of suction, through the inhalant tube or the outer 

 folds of their mantle. The Buccinum or whelk tribe prey 

 upon other moUusks (especially bivalves) by drilling 

 holes in their shells with their proboscis, which is armed 

 with a formidable apparatus of teeth. The whelks are 

 also very troublesome to fishermen, being often found 

 sucking and sticking to the bait when the lines are taken 

 up. Numbers of them may be caught in lobster-pots 

 baited with fish or meat, if laid down on a sandy instead 

 of a rocky ground. Most of the littoral univalves feed 

 on sea-weed. The common Limpet forms by means of 

 its foot a shallow excavation in the rock. When the 

 tide returns it goes out to its pasture, browsing like an 

 herbivorous quadruped ; and it returns to its hole when 

 the tide retires. The track left by its grazing on the 

 submarine vegetation which clothes the adjoining rock 

 is very perceptible and is sometimes tortuous or maze- 

 like. Land and freshwater snails, as well as slugs, are 

 for the most part herbivorous, as gardeners know to 

 their cost in the former case; but some of them also 

 devour animal matter, and a few are cannibals. The 

 food of the Testacella consists almost exclusively of 

 living earthworms ; and a full account of its carnivorous 

 and voracious propensities will be found in this volume. 

 Snails have been taken with insects in their mouths, 

 which they were swallowing by degrees ; and, accord- 

 ing to M. Bonnafoux, the Helix aspersa has been known 

 to perforate birds^ eggs in deserted nests, in order 

 to feed on their contents. The number of curved si- 

 liceous teeth which arm the tongues or lingual plates 

 of snails is prodigious (amounting in some species to 

 many thousands), being arranged in several rows. Some 



