OF THE TORTICELLIJTA. 589 



they are Vortkellce or Carchesia with a rigid hollow pedicle, without an 

 internal contractile band. The situation of the mouth and anal opening is 

 easily demonstrated by the employment of coloured food. In E. pJicatilis, says 

 Ehi'enberg, the whole coiu-se of the ahmentary canal can be seen. A con- 

 tractile sac and a short band-like nucleus are observable in many ; the latter, 

 however, is spherical in E. nutans. Longitudinal self-division and gemmation 

 frequently seen. The Epistylides are among the largest of the Yorticellina, 

 and are exclusively found in pure water, on aquatic plants or animals. 



Stein's researches throw additional light on the structure of EpistyliSj 

 which, he says, resembles generally that of Vorticella. The body has usually 

 an ovoid or almost spindle-shaped figm^e, truncate in front, where a slightly 

 everted ciHated peristom, of a sphincter- or lip-like character surrounds it, and 

 gives to the whole being somewhat of a bell-shape. AVithin the peristom is a 

 ciliary disc capable of being protnided or retracted at the pleasiu-e of the 

 animal, and having on one side the oral apertui-e. This disc is the '* rotary 

 organ " in Stein's description, and in EpistyJis its pedicle or stem is always 

 short and thick. ^Tien retracted, the sphincter-Kke peristom closes over the 

 rotary organ like a lid, and then the whole animal acquires a pear-shaped or 

 globiilar fig-ure. ^\Tien the contraction has proceeded to its utmost, the 

 peristom appears like a wedge-shaped or cylindrical process surmounting the 

 body. The mouth opens into a slightly coiled, tapering tube, which ends 

 abruptly towards the centre of the body ; near its tennination is a contractile 

 vesicle, and not far from the last an elongated band-like or reniform nucleus. 

 EpistyJis multiplies in precisely the same manner as Vorticella, by fission 

 and gemmation. Stein believes he has traced a cycle of changes through 

 which it passes, between the encysted condition on the one hand, and the 

 development of a ciliated TnchocUna-]ike embryo from an Acinetiform phase 

 of existence on the other. His observations tend to show that the embryonic 

 being developed from the Acineta of Epistylis anastatica is similar to Tnclwdina 

 G-randinella (Ehr.), and probably identical with it. In E. nutans he satisfied 

 himself of the occurrence of similar transformations, but felt less assm^ed of 

 their occurrence in E. grandis, E. herherifomnis, E. Barha, and E. p)licatilis. 



The stem or pedicle is inflexible. No canal, as represented by Ehrenberg, is 

 usually discoverable ; but sometimes the stem is finely striated longitudinally, 

 and in older specimens has at valuing distances transvei-se lines or false joints. 

 Dujardin proposed to amalgamate the two genera Epistylis and Opercularia, 

 since he could distinguish no generic differences between them. In this pro- 

 posal, however, he was wi^ong, for, as Stein shows, there are sufficient di- 

 stinctive peculiarities to warrant their generic independence. (See description 

 of Opeeculaeia.) The animals seated on its branches, by their mode of 

 articulation, enjoy considerable latitude of motion, and are also able in some 

 degree to shorten themselves by the annular segments of theii' base. 



The stem is secreted by the animalcules it supports. When fission has taken 

 place, two beings are for a time seen seated at the extremity of the same 

 pedicle ; but soon each begins to produce from its attached base a new pedicle 

 for itself, and thus the original stem becomes branched, and this in a fiu'cate 

 or dichotomous manner. 



All the members of the same little tree (polypidom) are of nearly equal 

 size. In the case of E. nutans, the largest noticed were l-20th of a line in 

 length ; whilst in other polypidoms, whose stems and branches were propor- 

 tionately thinner, examples were met with of very minute size (XXYII. 22, 

 23). In the smallest, no anterior cilia and no contained globules were 

 visible ; in larger ones, though only l-loOth of a line in length (XXYII. 23), 

 such were found. These latter fonns constitute Epistylis Botrytis (Ehr.). 



