MOLLUSC A: THEIR TONGUES 65 



tion in food or manner of feeding. With the Trochus, the 

 proboscis, a tube with thick, fleshy walls, is rapidly turned 

 inside out to a certain extent, until a surface is brought 

 into contact with the glass, having a silky lustre: this is 

 the tongue ; it is moved with a short sweep, and the tubu- 

 lar proboscis infolds its walls again; the tongue disappear- 

 ing, and every filament of conferva being carried up into 

 the interior from the little area which had been swept. 

 The next instant, the foot meanwhile having made a small 

 advance, the proboscis unfolds again, the tongue makes 

 another sweep, and again the whole is withdrawn; and 

 this proceeds with great regularity. I can compare the 

 action to nothing so well as to the manner in which the 

 tongue of an ox licks up the grass of the field, or to 

 the action of a mower cutting down swath after swath 

 as he marches along. The latter comparison is more strik- 

 ing, for the marks of progress which each operator leaves 

 behind him. Though the confervoid plants are swept off 

 by the tongue of the Mollusk, it is not done so cleanly 

 but that a mark is left where they grew; and the peculiar 

 form and structure of the tongue, which I have above 

 noticed, leave a series of successive curves all along the 

 course which the Mollusk has followed, very like those 

 which mark the individual swaths cut by the mower in 

 his course through the field. 



The Periwinkle's table-manners differ slightly from 

 those of his relations. When he eats, he separates two 

 little fleshy lips, and the glistening 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 



