INFUSORIA. 



765 



INFUSORIA. 



WE now come to the Infusoria, creatures which are all of very minute dimensions, 

 and respecting which there is great uncertainty prevailing. As with the preceding 

 class, no definite system has yet been invented by which they can be arranged ; and 

 in many cases physiologists are undecided whether the tiny beings are veritable species, 

 or whether they are but the larval forms of higher beings ; while, in some cases, it can- 

 not be precisely ascertained whether they belong to the animal or vegetable kingdom. 



Without, therefore, occupying our space with disquisitions which would require a 

 volume for their full elucidation, we will proceed at once to some of the more remark- 

 able forms among these curious beings. 



Vorticefla citrina. 



Stentor polymorphic. 



Two species of Infusoria are given in the accompanying illustration, both of which 

 may be found in soft water that has been allowed to remain in the open air, and in 

 which any vegetable matter has been permitted to decay. As may be seen, by reference 

 to the illustration, both these creatures are affixed by footstalks to some object on which 

 they make their residence, and both agree in having a bell-like mouth, edged with a 

 fringe of cilia. 



These organs are set upon the edge of the mouth, and their object is indirectly to 

 draw food into the system by creating certain currents in the surrounding water. When 

 the cilia are exposed to a good microscope, they appear to be formed like the cogs of a 

 little wheel, which is rotating with great rapidity ; and it is not until a close examina- 

 tion detects the real cause of this appearance that its illusory nature is discovered. As 

 in the case of the cilia attached to the higher animals, of which a notice has already 

 been given, each fibril bends in regular succession, so as to produce the effect of waves 

 upon the eye. 



When the Infusoria are free, the continual movement of the cilia causes them to move 

 with greater or lesser swiftness through the water, each fibril acting as a minute paddle, 

 and having a distinct feathering movement like that of an oar handled by a skilful rower. 

 It is a most curious sight to observe the admirable manner in which they make their 

 strokes, the flattened sides striking the water so as to give the greatest force to the blow, 



