26 THE MODE OF EATING. 



selves at home, and feed readily. It is interesting to 

 watch the husiness-like way in which they proceed. 

 I have just been looking carefully at a Top doing his 

 work, watching the modus operandi '^iXh a pocket-lens. 

 At very regular intervals, the proboscis, a tube with 

 thick fleshy walls, is rapidly turned inside out to a 

 certain extent, until a surface is brought into con- 

 tact with the glass having a silky lustre ; this is the 

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

 tubular proboscis enfolds its walls again, the tongue 

 disappearing, and every filament of conferva being 

 carried up into the interior from the little area which 

 had been swept. The next instant, the foot mean- 

 while 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 again the whole is withdrawn ; and this proceeds with 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 swathe after swathe 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 structm'e of the 

 tongue, which I am about to notice, leaves a series of 

 successive cmwes all along the course which the Mol- 

 lusk has followed, very closely like those which mark 

 the individual swathes cut by the mower in his course 

 through the field. 



The tongue, by which this operation is performed, 



