36 ROTATORIA OE WHEEL- ANIMALCULES. 



the other hand, when near death, their velocity 

 diminishes, and ample opportunity is afforded for ob- 

 serving that the movements consist of a rapid bend- 

 ing inwards and outwards, over the edge of the cup. 

 This is best seen in a side view. The action is repeated 

 by each cilium in succession, with such rapidity and 

 regularity that, when viewed from above, the fringe 

 looks like the rim of a wheel in rapid revolution. 

 A similar appearance, produced by the same cause, 

 in another class of animalcula, of much more com- 

 plex structure than the Vorticellse, has procured for 

 it the name of Rotifera, or wheel -bearers. The 

 result of this combined movement of the cilia is, 

 that a constant stream of water is drawn in towards 

 the centre of the cup, and thrown off over the sides, 

 when, having reached a short distance beyond the 

 edge, it circles rapidly in a small vortex, curling 

 downwards over the lips. These currents are ren- 

 dered evident by floating particles in the water. The 

 possession of these vibratile cilia is not peculiar to 

 this class of animals ; indeed, there is good reason to 

 believe that there is scarcely a living creature, from 

 the lowest animalcule, or plant germ, up to man 

 himself, that is not provided with them in some part 

 or other. In many of these Infusoria the cilia con- 

 stitute the organs of locomotion ; while in the higher 

 forms they serve various other purposes, but chiefly 

 that of directing the flow of the various internal 

 fluids through their proper channels. But the pecu- 



