14 GENERAL niSTOEV OF 



appearance, it is said to be filiform, or thread-like; but, when it 

 tapers toward the extremity, like an eye-lash, or cilium, it is called 

 flafjelliform. This organ is used by the animalcule both for locomotive 

 and purveying pxu'poscs. When the creature is in rapid motion 

 through the water, this instrument is seen to act as an oar or paddle, 

 in facilitating a progressive movement, whilst, at the same time, a 

 current is created in the direction of its mouth, providing for the 

 prehension of food. This member is not easily seen, inasmuch as 

 considerable skill in the use of the microscope is requu'cd to show it, 

 nor will even that, in all cases, suffice. The emplojoncnt of finely- 

 divided indigo or carmine, and the use of stops or diaphrag-ms imder 

 the object in the microscope, afford the surest proof of its existence. 

 When, by these means, its action has been detected, allow the water 

 to evaporate, and you may notice a streak or mark, as it diics, left 

 upon the glass, thus giving conclusive evidence of the presence of 

 this organ. Sometimes the mouth is furnished with two of these 

 proboscidcs, or cilia, nearly of eq^ual length with_^the bodj', as in the 

 genus Chhrogonmm. 



When these cilia are disposed in clusters, as with some of the 

 larger polygastric animalcules, their structure may be more correctly 

 ascertained. In the family Oxytrichina (see Engraving), the different 

 modifications of these filiform organs constitute excellent character- 

 istics of the genera. 



Cilia may be described as hairs seated apparently upon a bulb. 

 They perform a rapid vibratory motion, the point of each describing 

 a comparatively large circle, whilst the base merely turns round upon 

 its articulating surface, or part of the bulb to which it is affixed. 

 Ehrenberg is of opinion that there are two kinds of cilia, viz. Cilia 

 continua, in which the bulb is a continuation, or merely enlarged 

 termination of each cilium ; and Cilia a/rticulata, in which there is a 

 joint or articulation of the cilium to the bulb. Examples of the 

 former may be observed in the Stylonycliia mytiliis ; and of the latter 

 in the Paramecium aurelia {fig. 330). Cilia in tlieii' arrangement are 

 either separate and independent, or combined, forming in the latter 

 case the rotary organ of the Rotatoria. In the first or simple form 

 which exists in Polygastrica, the ciHa are usually set round the mouth, 



