or THE VORTICELLIXA. 581 



tional form between the radiated type of Vorticellina and the bilateral one of 

 Oxytrichina and Eiiplotina. Lastly, Lachmann states that Trichodina and 

 Urocentrum are not YorticeUina, and makes Stentor the representative of a 

 new family, which he calls Stentorinse. In this proposed new family he 

 includes besides Stentor, a new genus (Chcetospira), Spirostomum, and a 

 fourth genus which he has merely referred to without naming or de- 

 scribing it. In the above plans of classification there is this in common, 

 that the genera Stentor, Trichodina, and Urocentrtim are excluded from 

 among the Vorticellina, an exclusion warranted by their difference of organ- 

 ization and general characters. At the same time we are of opinion that 

 the association of the Ophrydina "uith the YorticeUina is not correct in a 

 systematic point of \iew, the existence of external sheaths being a weU- 

 marked and sufficiently distinctive character, although the homology in organ- 

 ization is otherwise, in every essential point, very close and striking. Pro- 

 bably Trichodina and Urocentrum should constitute an allied family or a 

 sub-family of YorticeUina ; Stentor the type of a second family ; whilst the 

 remainder of Ehrenberg's group, viz. Vorticella, Carchesium, Epistylis, Ojper- 

 cularia, and Zoothamnimn, might be caUed the true YorticeUina. The new 

 genus Spirockona, again, stands apart by so many pecuUarities that it cannot 

 be included within either of the groups proposed, and must be regarded as 

 the (at present) soUtary type of a new family, having the internal organization 

 of YorticeUina, but destitute of their peculiar ciUated head. In framing his 

 generic and specific distinctions, Elu-enberg made use of characters of no real 

 value, — such, for instance, as the occurrence of simUar and dissimilar bodies 

 (zooids) on branching stems otherwise alike, the height of the stem, the thick- 

 ness of its branches, and the dimensions of the attached animalcules. 



The family Urceolarina (Duj.) is thus characterized: — "Animals variable 

 in form, changing from a trumpet- or a hemispherical to a globular form ; 

 cihated throughout, with a fringe of much stronger cilia along the upper and 

 anterior margin of the body, continued as a spiral coU into the oral cavity, 

 which is on the same border. They present the ordinary swimming move- 

 ment, and can for a short time arrest their progress by fixing themselves by 

 their posterior extremity to external objects." "This famUy," observes 

 Dujardin, " connects the YorticeUina with the Bursarina, and includes the 

 genera Stentor, Urceolaria {Trichodina, Ehr.), Ophrydium, and Urocentrum.^' 

 The last-named genus is treated as very doubtful. As already seen, Perty 

 adopts this family Urceolarina, but modifies it by rejecting Ophrydium, and 

 adding Spirostomum. 



Genus STEOTOR (XXYIII. 16, 17 ; XXIX. 8).— Animal without pedicle, 

 free, or attached by the posterior extremity of the body, which is conical, 

 although it admits of very considerable modifications of form ; it is entirely 

 covered with ciUa ; a wreath of larger ones surmounts the head. Ehrenberg 

 considered the longitudinal striae along the body, and the circular ones at the 

 anterior part, muscular fibres. The anterior cUiary wreath is coiled in a 

 spiral manner about the head ; in some species a row of longer ciUa extends 

 from the mouth, in a fringe-Uke mamier, to the middle of the body. The 

 Stentors increase by self- division, which is either longitudinal or obhque. 

 The nucleus is band-like, monUiform, or round. The contractUe vesicle is 

 large, round, and placed on a level with the ciUary T^Tcath, close to the 

 oesophagus ; it gives off, above, an annular branch, which surrounds the head 

 of the animalcule just beneath the fringe of cUia, and below, a straight 

 branch extending to the posterior extremity of the animalcule (XXIX. 7). 

 The anus may often be perceived for a considerable time both before and 

 after the discharge of matters. It is situated on the back, close beneath the 



