52 MANUAL OF ZOOLOGY SECT. 



A mouth is absent in many parasitic forms, and nourish- 

 ment is obtained by the absorption of the digested food of 

 the animal in which the Infusorial) is parasitic. In the 

 Tentaculifera, in which a mouth is also absent, nourish- 

 ment is drawn in by means of the tentacles in the manner 

 already described. In the rest there is a mouth and gullet, 

 usually situated, as in Paramcecium, at the end of a buccal 

 groove, or peristome. 



In Vorticella and its allies (Fig. 19, p, and Fig. 22) the 

 body is in the shape of a wine-glass, the stem of which is 

 represented by a slender stalk (j/.), while the rim is the 

 equivalent of the peristome (per.) : in the area which the 

 peristome encloses is an elevated disc of protoplasm, be- 

 tween which and the peristome on one side is the open- 

 ing of the mouth (mth.) : the only cilia run in a spiral band 

 round the peristome, round the edge of the disc, and 

 down into the gullet (gull.). An anal spot is present in 

 Vorticella and many other forms ; in a few there is, instead, 

 a distinct anal aperture (Fig. 19, 2, a.). 



A chitinoid skeleton (Fig. 21) occurs in a few forms; 

 usually it is bell-shaped, sometimes it is perforated by a 

 number of apertures (i) so that it resembles in appearance 

 the skeleton of some of the Radiolaria. A chitinoid lid or 

 operculum (2, 3, op.) may be fixed to the edge of the 

 peristome, and when the animal is retracted into its case, 

 accurately closes the mouth of the latter. 



Colonies occur in many of the Infusoria. Some allies of 

 Vorticella (Fig. 19, p) develop highly complex colonies, the 

 slender stalk branching again and again, and each terminal 

 branch ending in a zooid. A remarkable colonial form 

 is Dendrosoma (Fig. 20, p), one of the Tentaculifera : it 

 has a creeping stem from which branches spring upwards, 

 each terminating in a zooid with suctorial tentacles ; and 



