WHEEL-BEARING ANIMALCULES. 1 79 



minating the body, to some stationary object, (as, 

 for example, an aquatic plant,) the animalcule sets 

 its cilia in action, and thereby produces a rapid 

 current in the contiguous water, converging to the 

 creature's mouth, and hurrying thither such minute 

 particles, either of an animal or vegetable nature, 

 as are drawn into the mimic Charybdis. It appears 

 that the cilia of these animalcules, whatever their 

 own structure may be, are governed by a muscular 

 apparatus, which is very conspicuous, and which 

 retracts them, when not in use, within a kind of 

 sheath, where they are safely lodged till their action 

 is required. 



The rotifer a may be described as shell-covered 

 animalcules, their body being enclosed in a mode- 

 rately firm or horny investment, but of extreme 

 delicacy and very transparent, so that the internal 

 viscera may be perceived through it. The upper, 

 or free margin of this shell, is often indented, or 

 ornamented with regular projections, and is con- 

 tinued by means of a fine membrane to the bases of 

 certain elevations around the mouth, termed lobes, 

 from which arise the cilia already described. This 

 membranous continuation of the shell does not con- 

 fine the ciliary apparatus, but permits it to be 

 retracted at pleasure within the shell. 



These creatures present great variations of form 

 and colour ; but all have at the posterior extremity 

 of the body a pair of forceps or pincers, instruments 

 of prehension, by which they attach themselves at 



