580 SYSTEMATIC HISTORY OF THE INFUSORIA. 



higUy sensitive pedicle can be protnided. The portion of the ciliary spii-al 

 outside the vestibuliim is not of equal length in aU Yorticellina : in many, 

 e. g. Vorticella, Carcliesimn, ZoGthamniiim, Scyphidia, Trichodina, some species 

 of Epistylis, (fee, it describes scarcely more than one circuit round the disc, 

 whilst in Opercidaria articulata and Epistylis Jiavicans it runs round the disc 

 three times ; in other species intermediate lengths occur. The ciliary wreath, 

 moreover, consists of a double row of cilia : those of the outer one are usually 

 somewhat shorter than those of the inner, and though inserted upon the 

 margin nearly in the same line as the others, yet they are set at a different 

 angle, and apparently far more strongly bent outwards. In the vestibulum 

 and oesophagus the cilia appear to stand in a single row. The peristom usually 

 bears no cilia. There is no sufficient proof of the existence of muscles of the 

 same type as those of the higher classes of animals. The contractile vesicle 

 is single and circular ; the nucleus sometimes oval, but often elongated and 

 band-hke. Besides fission and gemmation, tine propagation by lining germs 

 or embryos, developed in the coui^se of more or less complete transformations, 

 affords an additional means of perpetuating and extending the several species. 

 The genera are distributed as follows : — 



{Body covered with ciHa Stentor. 

 Body smooth, cilia anterior Trichodina. 



Tail present Urocentriim. 



f Stalk flexible, f ^^P^^ VorticeUa. 



Form of stalked J deflection spkal \ -o i j n i, • 

 bodies similar \ ^ ^ Branched Carchesium. 



Body stalked-often ^ \^^^^^ m^e^hXe EpistyHs. 



branched like a tree ' ^ -^ "^ 



Bodies of aif- J ^^^^ ^^^^^^^ Opercularia. 



ferent form ... | g^^^j. jSexible, deflection spiral... Zoothamnium. 



Of the several genera named and distinguished by Ehrenberg, two only 

 are accepted by Dujardin, yiz. Epistylis, with a rigid pedicle, and VorticeUa, 

 with a contractile stalk, simple or branched. He places Carchesium with the 

 latter, maintaining that a generic character is not to be found in the simple 

 or branched condition of the stalk alone, when the bodies are similar. More- 

 over, he failed to meet with animalcules having the characters assigned to the 

 genera Opercularia and Zoothamnium. by Ehrenberg. A tliird genus, imder 

 the name of Scyphidia, is established by him for the sessile species ; whilst 

 a fourth, Vaginicola, comprises all those species invested with a membranous 

 sheath, and corresponds, in its constituent species, to the family Ophrydina 

 (Ehr.) after the exclusion of Ophrydium. 



Perty makes a different distribution of the Yorticellina to that proposed 

 by Ehrenberg. Like Dujardin, he rejects the genera Stentor and Urocentnm, 

 and transfers them to a family Urceolarina. On the other hand, he adds 

 Scyphidia of Dujardin to the true Yorticellina, and makes no mention of 

 Carchesium. Lachmann is another writer who rejects Urocentrum from the 

 Yorticellina. Stein points out various defects in Ehrenberg's grouping of 

 Yorticellina ; and whilst he would, on the one hand, detach from it Stentor, 

 Trichodina, and Urocentmun, he would, on the other, associate with it the 

 several sheathed genera which form the family Ophrydina, viz. Ophrydium, 

 Vaginicola, Tintinnus, and Cothurnia. Apart fi'om these changes in the distri- 

 bution of admitted genera, he adds two new ones, Lagenophrys and Spirocliona, 

 remarking of the former, that, in its free condition, it constitutes a transi- 



