THE MODE OF EATING. 



33 



useful inhabitants of a marine tank ; they make 

 themselves at home, and feed readily. It is inter- 

 esting to watch the business-like way in which 

 they proceed. At very regular intervals, the pro- 

 boscis, 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 then the tubular proboscis infolds 

 its walls again, the tongue disappearing, and every 

 filament of conferva being carried up into the inte- 

 rior 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 is withdrawn ; and this proceeds with great regu- 

 larity. 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 

 striking for the marks of progress which each ope- 

 rator leaves behind him. Though the confervoid 

 plants are swept ofi" by the tongue of the MoUusk, 

 it is not done so cleanly but that a mark is left 

 where they grew ; and from its peculiar form and 

 structure, the tongue leaves a series of successive 

 curves all along the course which the MoUusk has 

 followed, very closely like those which mark the 

 individual swathes cut by the mower in his course 

 through the field. 



The unsightly appearance thus left must be got 

 rid of by mechanical means. A stick with a bit 

 of rag tied around its end, or, what is better still, 

 a brush made on purpose, like a nail-brush with a 

 D 



