ORGANS OP LOCOMOTION. 



127 



tiguous fluid, as they thus propel the body onwards. 

 In some species, as the Paramecium aurelia and 

 others, these cilia are 

 regularly arranged, so 

 as to encircle the body; 

 but in most, they only 

 encircle the mouth, or 

 are ranged in its 



PARAMECIUM AURELIA. 



vicinity. Besides act- 

 ing as organs of loco- 

 motion, they are agents in the acquisition of food; 

 they produce by their incessant vibration a current 

 in the water converging to the mouth, and hurry- 

 ing along with it either 

 smaller animalcules or 

 minute portions of vege- 

 table matter, on which 

 they feed, and which, but 

 for this singular provision, 

 they could not otherwise 

 obtain. 



The mouth of the 

 polygastric animalcules is 

 generally found to be a 

 simple dilatable and con- 

 tractile orifice ; but in some species, it appears 

 under the form of a small projecting beak, or rather 

 tube, composed of numerous teeth of an elongated 

 shape, and calculated both Tor the prehension of 

 food, and for bruising it previously to its being 



CILIA OF THE YORTICELLA. 



