246 NATURE'S TEACHINGS. 



teeth overlap each other, so that some care in manipulation is 

 required before their form can be made out. 



Along the centre of the tooth-ribbon run successive rows of 

 email, lancet-shaped teeth, six in a row, so that altogether there 

 are eight teeth in each row. 



The power of this weapon is astonishing. Some of my 

 readers may be aware that Whelks are carnivorous beings, and 

 that they swarm upon any dead animal which may be found in 

 the sea. Indeed, when we hear of the mutilations which take 

 place on dead corpses after a shipwreck, and which are generally 

 attributed to fishes, we may make up our minds that the real 

 delinquents are the Whelks, together with various Crustacea, 

 and that the principal instrument in effecting such mutilation 

 is the tooth-ribbon which has just been described. 



The Whelks feed largely upon other molluscs, in spite of 

 their shells. A periwinkle has a peculiarly hard shell, and yet 

 Mr. Rymer Jones saw a Dog-whelk (Purpura la,pillus) eat a 

 periwinkle in a single afternoon, first boring a hole through its 

 shell with the tooth-ribbon, and then, by means of the same 

 weapon, licking it, so to speak, out of its shell. 



The Periwinkle itself has a similar tooth- ribbon, and so have 

 the Limpet and the pretty Top-shell. These creatures are 

 vegetarians, but they are furnished with similarly armed 

 tongues, and use them in the same way. Nothing is easier 

 than to see these tooth-ribbons in .use. When sea- water is 

 kept in glass vessels, a green flocculence is sure to collect upon 

 the glass and to render it opaque. 



If, however, a few Periwinkles and Top-shells are placed in 

 the tank, they immediately set to work at this confer void growth, 

 and by means of the tooth-ribbon sweep off the green sub- 

 stance, leaving the glass nearly clean. This movement can be 

 seen with the naked eye, but with the assistance of a pocket 

 lens the "action of the tooth-ribbon is beautifully shown as it 

 issues from its socket, makes its sweeping curve, with the tiny 

 teeth glittering like specks of glass, and then is withdrawn 

 ready for another sweep. 



Should sea-water and living Periwinkles not be easily 

 obtained, the same phenomenon may be observed in fresh 

 water, and with the common Pond-snail, which may be caught 

 by thousands in any stream and in most ponds- 



