302 GENEEAL HISTOKY OF THE rNTUSORIA. 



(XXX. 1, 2). The opening of this vestibule or ante-room to the entrance of 

 the digestive tube, i. e. the mouth, should not be confoimded with the latter, 

 as often has been done. A funnel-like hollovi^ having the true oral aperture 

 at its bottom, is met with in Paramecium, and may have the same appellation 

 extended to it. Among the processes about the mouth facilitating the inglu- 

 tition of food, we have just alluded to the wreaths, rows, and tufts of cilia, 

 mostly large and strong like bristles, and to special developments of the sur- 

 face of the body. Several species possess a tuft of cilia almost indistinguish- 

 able from a plaited membrane ; for instance, Colpoda Ciwullus (XXIX. 37) 

 and Chilodon CucuUulus have what Ehrenberg called a tongue, but which, as 

 we have seen. Stein has resolved into a thick pencil of ciliary bristles. A 

 similar structure prevails in PUuronema and Alyscum (Duj.), in Cyclidium 

 and Aphthonia (Perty). In Glaucoma (XXVIII. 4) and Cyclidium marga- 

 ritaceum, " the margins of the buccal orifice appear," says Lachmann {op. cit. 

 p. 216), "to be produced into two valves which are in constant motion." A 

 special curved or spirally-turned row of cilia directs a cuiTent into the mouth 

 in Stentor, Spirostomum, Bursaria, Chcetospira (XXIX. 5, 6), Oxytrichiim, 

 Euptlotes, and Aspidiscina, and a nearly straight row in Chilodon and Colpoda. 

 In Coleps, Traclielius, Enchelys, and TracJielocerca, the mouth opens imme- 

 diately upon the suiface without any conducting ciKary channel, and is sur- 

 rounded by a simple circle of cilia. The mouth is protrusible in Prorodon and 

 Nassula (XXVIII. 8, Qb), and not distinguished by any special external array 

 of cilia. In the true Vorticellina and in the Ophrydina, as above mentioned, 

 the complex ciliary apparatus dii-ects the cm-rent into a cavity, the vestibu- 

 lum common to both the mouth and anus ; and lastly, in Paramecium the 

 cilia are uniform at all parts, and the coiu-se of food to the mouth provided 

 for by a wide and deep tapering channel. In size the mouth varies both in 

 different genera and in relation to the dimensions of the animals ; but in all it 

 is more or less extensile, so that foreign particles or other animalcules are 

 engulfed "within it even when their diameter equals that of the body itself. 



The oral aperture opens below into a rudimentary digestive tube (XXVII. 

 1, 10, 11 ; XXIX. 4 ; XXX. 1, 11, 29), fonned by an involution of the ex- 

 ternal integument. It is commonly a fimnel-shaped space, which, for the 

 sake of a name, may be called the pharpix or digestive tube ; within this, 

 and especially near its entrance, a few vibratile cilia are mostly seen, serving 

 by their action to accelerate the onward transmission of the particles of food. 

 The walls of this cavity are formed by a special very extensile membrane, 

 which, as supporting the internal cilia, may be called a ^basement mem- 

 brane.' The pharynx extends (as a gently tapering, mostly cui'ved, tube) 

 obliquely inwards towards the centre of the general cavity of the body, where 

 it abruptly ends. Its length is subject to considerable variation in different 

 genera. In Paramecium and allied genera, and in Oxytrichina, it is short and 

 of greater relative width ; in Chilodon, Nassula, Prorodon, and others it is 

 continued, from the posterior extremity of the so-called cylinder of teeth, far 

 into the interior. It is also of very considerable length in the Vorticellhia 

 generally, as illustrated by Epistylis and Opercularia (XXX. 1). 



" In Ehrenberg's families," Lachmann teUs us {op. cit. p. 217), ^' Oxy tri- 

 china, Euplotes, and Aspidiscina (as also in Stentor, Bursaria, and Spirosto- 

 mum), we meet with an internally ciliated oesophagus, and a ciuwed line 

 open towards the right, composed of strong ciha leading to the mouth." This 

 oesophagus alwaj^s forms " an open tube, and is often collapsed at fts inner 

 extremity, and thus forms a transition to the oesophagus of the following 

 groups. 



*' Many Infusoria," he continues, " have a completely collapsed oesophagus, 



