66 Introduction to Animal Morphology. 



CHAPTER X. 



INFUSORIA. 



Class 8. I^Y-USOBSK [Wrisbcrg). — Minute (^^iro" - 1^/') 

 ciliated bodies, probably simple plastides, or, at most, 

 cytocormi, with a firm chitinous cuticle, an ectosarc 

 and an endosarc, a contractile vesicle and a nucleus. 

 A separate tubular fold of cuticle may form a sheath 

 distinct from the outer body wall (Vaginicola), or the 

 hinder end may be extended into a pedicle or an 

 anchor apparatus (Trichodina). The cilia may cover 

 the whole surface, and be all of the same kind 

 (holotricha), or some may be long or specialized into 

 styli, setae, uncini (heterotricha). They maybe on the 

 under surface alone (hypotricha), or only on a peri- 

 stome around the mouth (peritricha). Sometimes an 

 undulating membrane takes the place of cilia (Undu- 

 lina Pleuronema). The integument in Paramsecium, 

 Nassula, Bursaria, &c., includes sharply contoured 

 trichocysts like those of Turbellaria, considered as 

 touch-organs by SfciUy or as poison-organs by Leuckart. 

 Beneath the cuticle in Stentor, Prorodon, &c., is a 

 contractile, striped material, possibly a simple form of 

 muscle. In Spirostomum these striae are spiral, and 

 the body contracts in their direction. The contractile 

 stalk of Vorticella has also a highly-refracting 

 muscular axis [Kilhne ; its muscularity is denied by 

 Mccznikow, as it is structureless, myophanic). The 

 outer layer of this stem is cuticle, and it straightens 

 the stalk by its elasticity. There is usually a mouth, 

 which may only be seen during feeding (Amphileptus^ 

 he), or it may have a ciliated pharynx (Paramaecium), 



