CILIATA 



73 



III. Hypotricha. In these (Fig. 29, C) which usually resemble 

 Paramecium in their general form, the cilia have disappeared except on 

 the oral surface and here they have become restricted to localized tufts 

 and fused together. At the edge of the peristome they form ciliary 

 plates like those of Stentor but in addition to these there are a number 

 of stout pointed structures — each formed of a group of fused cilia — on 

 the tips of which the creature runs about as on so many legs. The 

 movements of the Hypotricha as they run hither and thither on some 

 solid surface in an apparently purposeful manner form perhaps their 



Examples of Ciliata. A, Stentor; B, Vorticella : C, Stylonychia. an, Anus ; c.v, contractile 

 vacuole ; N, macronucleus ; n, micronucleus ; ps, pseudopodia ; t.v, tributary vacuole. 



most Striking characteristic. Two common members of the group are 

 Stylonychia (Fig. 29, C) with its dumb-bell-shaped macronucleus and 

 two micronuclei and Kerona which may often be observed running up 

 and down on the surface of Hydra (see p. 87). 



IV. Peritricha. Here the ciliary coating is still more reduced — 

 there being only a spiral of ciliary plates round the edge of the peristome 

 with sometimes a circle of small cilia in addition. A well-known example 

 is Vorticella (Fig. 29, B) — the Bell animalcule — which may often be found 

 attached to freshwater plants. The general shape is that of a bell — the 

 handle prolonged into a slender stalk by which the creature is attached 



