OF THE ROTATORIA. 4/7 



another circumstance, a water-vascular system is indistinct in Steplianoceros, 

 and would be overlooked, as Leydig remarks, did not the knowledge of its 

 form and of its existence in other Kotatoria direct in the search for it ; and, on 

 the other hand, such a structure has not been sought after in Boiverhanlcia. 



These and other considerations, which might easily be added to, lessen the 

 differential characters, and, together with the many undoubted points of re- 

 semblance between Boiverhanlcia and Steplianoceros, incline us to the very 

 prevalent opinion that there is a real affinity between Rotifera and Bryozoa, 

 although we would not go so far as some naturalists and place the genus 

 Steplianoceros among the latter. 



Huxley entertains an adverse opinion, and believes that " there is a funda- 

 mental error in approximating the Polyzoa and the Rotifera at all, that the 

 resemblance between Steijhanoceros and a Polyzoon is very superficial, and 

 that the relations between the Polyzoa and the Rotifera are at the best mere 

 analogies." 



The resemblances between the Rotatoria and the Ciliated Protozoa are 

 merely superficial. Vaginicola is enclosed in a transparent sheath, like a 

 Floscularia or a Tuhicolaria ; the urceolated indi\iduals of Ophrydium are 

 grouped into gelatinous balls, like those of ConocMlus ; the ciliary wreath 

 about the head of Vorticella, Stentor, and Vaginicola makes an approxima- 

 tion to that of Rotatoria ; and the contractile muscular pedicle of Vorticella 

 and Zoofhamnium recalls, in some respects, the retractile pedicles of the fixed 

 Rotatoria. 



A connecting link is, however, supplied between the Ciliated Protozoa and 

 the Rotatoria by most genera of the family Ichthydina, which Ehrenbei'g 

 indeed numbered among the latter class. This great microscopist had but an 

 imperfect acquaintance with their organization ; and at the present time our 

 knowledge of it is far from complete. The genera referred to are IchtJiydiimi 

 and Cha^tonotus ; and perhaps Mr. Gosse's genus Saccidus should be united 

 with them. The genus Glenopliora of Ehrenberg is not recognized by most 

 naturalists. 



They differ from Rotatoria in having no transverse joints or folds to the 

 body, no water- vascular system, no appreciable muscles or nerves, whilst 

 the ciliary wreath is on the model of Ciliated Protozoa, and the alimentary 

 canal after the type of that of Nematoda and of Anguillula. The vibratile 

 ciha extend also over the abdominal surface of Ichthydium, and over both 

 the ventral and dorsal of Clioitonotus, Lastly, according to M. Schultze they 

 are hermaphrodite, and have pin-shaped spermatozoa. These peculiarities of 

 organization have induced observers generallj- to exclude these genera from 

 Rotatoria. Dujardin has found a place for them along mth Coleps ; and a 

 doubtful subgeniLS he named Planariola, as a subclass of Ciliated Protozoa, 

 unlike the rest of this class in being symmetrical. 



Another link between Rotifera and the Ciliata is to be found in the peculiar 

 genus Dysteria, which Prof. Huxley referred to the Euplota, and Mr. Gosse 

 to the Monocercadeoi among the Rotatoria (see p. 387). 



CLAssiTicATiojiT. — Siuce no observers, prior to Ehrenberg, duly recognized 

 the Rotatoria as a class distinct from the Protozoa, we may at once commence 

 with an analysis of the classification he has proposed. 



^ This was based on the apparent structure of the rotary organ, of which he 

 distinguished two types : 1. in which the circlet of cilia is complete — Mono- 

 troclia ; 2. in which it is diWded into two or more segments — Sorotrocha. 

 Each typical form was subdivided ; the first into Holotroclia, in which the 

 ciliated ring is entire, and Schizotrocha, in which the wreath is notched. The 

 iiccond {SorotroeJia)mio PoJyfrocha, with a compound wreath of several lobes 



