'74 



ROTIfERA. 



true explanation of the once mysterious phenomenon is as fol- 

 lows : Examined under high powers, the cilia have the appear- 

 ance of moving in waves, in the production of which from a dozen 

 to twenty cilia are concerned, the highest point of each wave 

 being formed by a cilium extended to its full length, while the 

 lowest point between every two waves is occupied by one folded 

 down upon itself, the intervening space being filled by others in 

 every intermediate degree of extension. As the continuance of 

 each cilium in any one of these positions is of the shortest possible 



FIG. 176. SKELETON u HEEL-BEARER. 



duration, and each takes up in regular succession the action of 

 the adjoining one, that cilium which, by being completely folded 

 up, formed the lowest point between any two waves, in its turn, 

 by its complete extension forms the highest point of the next 

 wave, and thus, while the cilia are alternately bending and un- 

 bending themselves, the waves appear to travel onward, while the 

 cilia never change their position. 



The ciliary apparatus is evidently under the control of the 

 animal. The whole fringe of cilia may be instantly set in motion, 

 and as instantly stopped, or their action regulated to any degree 

 of rapidity. 



A very slight examination of these minute creatures with the 

 microscope will show that the ciliary movement answers a double 

 purpose. If the little Rotifer attaches itself to some fixed object 

 by means of its forcipated tail, as represented in the figure (Fig. 



