292 THE INHABITANTS OF THE SEA. 



In these genera, which have been arranged by Cuvier in a 

 separate order (Tubulibranchiata), the foot is naturally reduced 

 to the state of an adhesive organ, its chief functions consisting 

 in opening and closing the lid. 



The sea-snails are either predaceous or herbivorous ; among 

 the pectinibranchiates, those with circular mouths to the shell 

 are vegetable feeders, while such as have an aperture ending in 

 a canal are animal feeders. Considerable modifications of 

 internal structure indicate this difference of food; and the 

 external organs, particularly about the mouth, exhibit a corre- 

 sponding variety of form. In those which feed on vegetables 

 the mouth is generally a slit furnished with more or less perfect 

 lips, armed with a simple cutting apparatus, which is often 

 powerful enough to divide or dismember comparatively hard 1 

 substances. 



In most animal feeders the mouth presents the appear- 

 ance of a proboscis that can be protruded or shortened at 

 the will of the animal, and which, grasping the food, conveys 

 it to a spine-armed tongue, by the aid of which it is pro- 

 pelled into the gullet without mastication or any preparatory 

 change. 



In the Whelk and its shell-boring allies, the alternate pro- 

 trusion and retraction of the proboscis, which is here of a much 

 more complicated structure, causes the sharp tongue to act as a 

 rasp or auger, capable of drilling holes into the hardest shells. 

 It is this circumstance which renders the whelk so formidable 

 an enemy to mussel and oyster banks. During the erection of 

 Bell-rock lighthouse, an attempt was made to piant a colony of 

 mussels on the wave-beaten cliff, as they were likely to be of 

 great use to the workmen, and especially to the light keepers, 

 the' future inhabitants of the rock ; but the mussels were soon 

 observed to open and die in great numbers. "For some time,'' 

 says Mr. Stevenson in' his interesting narrative, " this was 

 ascribed to the effects of the violent surge of the sea, but the 

 Buccinum lapillus having greatly increased, it was ascertained 

 that it had proved a successful enemy to the mussel. The 

 buccinum was observed to perforate a small hole in the shell, 

 and thus to suck out the finer parts of the body of the mussel ;„ 

 the valves of course opened, and the remainder of the shell-fish 

 was washed away by the sea. The perforated hole is generally 



