28 STRUCTURE OF THE MOUTH. 



of liis victim. The general structure is common to 

 all tlie Gasteropod Mollusca, but tlie varieties in 

 tlie mode and pattern of tlie dentation are almost 

 infinite. 



The little Top, for example, has the teeth set in 

 eleven longitudinal rows, along the central part of the 

 ribbon ; while the edges, which are turned over on each 

 side, are formed into oblique combs ; — altogether a 

 very elaborate affair. But even this is exceeded by 

 the tongue of the Livid Top {T. zizi'pliinus) ^ a larger 

 and handsomer species, not rare among the lower 

 rocks. (/&e Flate II.) Here the teeth are long 

 overarching glassy plates, finely pointed, and minutely 

 saw-toothed along their edges, while the lateral combs 

 are composed of curved teeth, gradually diminishing 

 in thickness. 



Perhaps eveiy variety is accompanied by some vari- 

 ation in food or mode of feeding. The Periwinkle, I 

 see, has a manner of his own, which differs slightly 

 from that of the Trochus. When he eats, he separates 

 two little fleshy lips, and the glistering glass-like 

 tongue is seen, or rather the rounded extremity of a 

 bend of it, rapidly running round like an endless band 

 in some piece of machinery ; only that the tooth- 

 points, as they run by, remind one rather of a watch- 

 wheel. For an instant this appears, then the lips 

 close again, and presently re-open> and the tongue 

 again performs its rasping. It is wonderful to see ; — 

 perhaps not more wonderful than any other of God's 

 great works, never more gi'cat than when minutely 

 great ; — but the action and the instrument, the perfect 

 way in which it works, and the effectiveness w4th 



