WHEEL-BEARERS. 251 



The last specimen of this class of tiny favourites that I 

 shall show you is one of more than ordinary beauty. It 

 is the Two-lipped Tube-wheel of the Hornwort (Limnias 

 ceratophylli). Hitherto we have seen such examples as 

 have the power of freely swimming from place to place at 

 pleasure ; but there is a considerable group, of which this 

 is a member, which are permanently stationary, being 

 fixed for life to the leaves or stems of the vegetation that 

 grows under water. The stiff and spinous whorls of the 

 Hornwort (Ceratophyllum demersum), that grows com- 

 monly in sluggish streams and pasture-pools, is a favourite 

 resort of the species, but it is not confined to any one 

 plant. Here, for instance, it has chosen as the site of 

 its residence the much-cleft leaves of the Water Crow- 

 foot (Ranunculus aquatilis) ; those leaves, I mean, 

 which, growing wholly under the water, are divided into 

 a multitude of slender finger-like filaments, so different 

 from those which float on the surface, and which are 

 merely notched. 



You can readily find the Tube-wheels by the aid of a 

 pocket lens, and even with the naked eye when you have 

 seen one or two. By holding up this phial, in which a 

 little plant of the Crowfoot is growing, and searching, with 

 the lens, the window being in front of you, the filaments, 

 one by one, you will readily perceive, here and there, 

 little shining objects standing up or projecting in various 

 directions from the surface of the leaves. The colony is 

 rather numerous in this case, and we shall have no diffi- 

 culty in selecting our specimens. 



On this filament, which I have seized with the tips of 

 a pair of pliers, I can see at least half-a-dozen of the 

 little parasites. This, then, I will nip off from the 

 plant, and put it with its tiny population into the live- 

 box. Here it is ready for examination. 



Several of the animals are in the field of view ; but we 

 will look at one at a time. A long narrow tube, slightly 



