52 MANUAL OF ZOOLOGY sect. 



at intervals so as to look like a string of beads, or branched. 

 In nearly all cases one or more micronuclei are present. 

 In Vorticella and others there is a single contractile vacuole 

 which opens, as in Euglena, through the intermediation of 

 a reservoir into the gullet. In other Infusoria there may 

 be one, two, or many contractile vacuoles. In some instances 

 the protoplasm is hollowed out by numerous non-contractile 

 vacuoles. Trichocysts mainly occur in the forms with a uni- 

 form coating of cilia ; more complicated bodies of similar 

 character termed nematocysts (<?, c) occur in some cases. 



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 infusorian is parasitic. In the Tentacu- 

 lifera, in which a mouth is also absent, nourishment 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, g, and Fig. 22) the 

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

 represented by a slender stalk (sf), 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 opening 

 of the mouth (mth) : the only cilia present run in a spiral 

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

 do'.vt: 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 (/) so that it resembles in appearance 

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

 operculum (2, J, op) may be fixed to the edge of the peri- 



