832 THE ANIMAL KINGDOM. 



size, but there may be a band of larger adoral cilia. The Heterotricha have 

 an investment of fine cilia covering the body, but a band, straight or 

 curved, of membranellae borders a naked peristome. Its posterior end, or 

 left-hand end, enters the mouth with a spiral twist if the band is curved. In 

 shape, extent, and position the peristome varies a good deal. It is much 

 depressed in the Tintinnodea, and in some of them a row of fine paroral 

 cilia lie to the inner side of the membranellae. Some species of Stentor 

 possess fine setae, apparently pro- and re-tractile, mingled with the cilia 

 of the body. The Hypotricha have the dorsal aspect either naked or beset 

 with fine setae, of which one or more are posterior in position, long, and 

 occasionally compound. Cilia are confined to the flattened ventral aspect : 

 in the two families Oxytrichidae and Euplotidae they take the form of 

 cirri, either claw-like at their apex (tmcini] or straight (styli), which are 

 grouped in a definite manner 1 . The same two families and the genus 

 Peritromus possess a peristome in the shape of an arcuate groove on the 

 left-hand anterior edge of the body. The cilia in connection with it are 

 disposed in special lines or bands ; one band is always present, an adoral 

 fringe of membranellae; a second, known nspraeoral, is very generally found 

 near the dorsal edge. Two others, the endoral and paroral^ are not so 

 common. A vibratile membrane. may take the place of the praeoral band. 

 In the Peritricha the body is non-ciliate except in the Urceolarine genus 

 Trichodinopsis ; the cilia are confined to one or more encircling bands, 

 or to a spiral band as in Vorticellina, Vaginicolina, and Ophrydina, which 

 consists of membranellae (Biitschli). The right hand end of the spiral 

 enters the mouth, and it is situate on a terminal retractile disc, which is 

 protected in the retracted condition by the closing over of a raised wall or 

 peristome, also by a thickened operculum attached below the peristome on 

 one side (Pyxicola, Pachytrochd), or a moveable operculum within the lorica 

 (Thuricola) 2 ' Noteworthy peculiarities are the following : the perioral 

 contractile collar of the Peritrichan, Torquatella typica ; the girdle of 

 springing setae in Halteria \ the tentacles, long, scattered, retractile, of 

 Actinobolus radians, four, short, knobbed, perioral, of Mesodinium pulex, 

 which, though Acinetarian in aspect, are not suctorial 3 . 



1 The groups in question are : (i) frontal, anterior and on the animal's right ; (2) -ventral, 

 sometimes replaced by rows of cilia ; (3) anal s. transverse ; (4) marginal, a fringing row of short 

 cilia, either continuous, or interrupted posteriorly. The caudal is really a group of dorsal setae 

 according to Maupas ; see A. Z. Expt. (2), i. p. 535 et seqq, and Saville Kent's Infusoria, fig. J, 

 p. 760. 



2 For the limitations of the term Peritricha, see Geza Entz, Mitth. Zool. Stat. Naples, v. p. 407 ; 

 Id. Z. W. Z. xxxviii. p. 183 et seqq. ; Biitschli, M. J. xi. p. 553. The terms ' right' and 'left hand' 

 applied to the adoral band of cilia mean the animal's right or left, the mouth being considered as 

 ventral in position. For the paroral cilia of Tintinnodea, see Entz, op. cit. supra, Naples, pp. 

 395-6 ; for the peristome of the Hypotrichans, Saville Kent's Infusoria, fig. 2, pp. 760-1, and Biol. 

 Centralblatt. iii. p. 236. 



3 Actinobolus, Entz, Z. W. Z. xxxviii. p. 167; Mesodinium^ Id. op. cit. supra, Naples, p. 308. 



