WHEEL-BEABEBS. 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 commonly 

 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 resi- 

 dence the much -cleft leaves of the Water Crowfoot (Ra- 

 muiculus 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 

 widening at the mouth, is affixed by the lower extremity 



