OF THE PROTOZOA. DYSTEEIA. 391 



widely diiferent fi'om one greatly depressed, covered with a dorsal plate, and 

 whose organs of locomotion are short flexible setae scattered over the soft 

 ventral surface. 



" But I am by no means sure that it should be placed among the Infusoria 

 at all. Mr. Huxley observes that ' the absence, in an animal which takes 

 soHd nutriment, of an alimentary canal with distinct walls, united with the 

 presence of a contractile vesicle, with the power of transverse fission, and 

 with ciHa as locomotive organs, is a combination of characters found only in 

 the Infusoria. 



^' Now the presence of a contractile vesicle, and of locomotive cilia, are 

 quite as characteristic of the Eotifera as of the Infusoria. The absence of 

 an ahmentary canal is, I think, not proved : it seemed to me that the animal 

 possessed a defined digestive cavity, though very ample. In Sacculus — an 

 indubitable Rotiferon, which carries its large eggs in the manner of a Bra- 

 chionus — the alimentary canal, without apparent distinction of stomach and 

 intestine, is so large that it occupies fully five-sixths of the whole volume of 

 the lorica ; and though it is invariably found filled with a green Alga, on 

 which the animal feeds, the walls of the digestive cavity are not better defined 

 than in Dysteria. There remains, then, only the fact of increase by trans- 

 verse fission. This, I confess, is a strong point, if well estabhshed. But it 

 does not seem certain, fi'om Mr. Huxley's words, whether he witnessed the 

 progress of constriction from an early stage until two perfect animals were 

 formed out of one, or only saw an individual so strongly constricted that the 

 result seemed legitimately inferable. If the latter was the case, is it not just 

 possible that it was an example, not of spontaneous fission, but of malforma- 

 tion, instances of which are frequent among the highest animals ? It is highly 

 worthy of note that the nucleus, so characteristic of the Infusoria, was not 

 found, even under carefid search with acetic acid. 



" The presence, position, and movements of the foot, hinged as it is upon 

 a tubercle, and the form of the principal organs of manducation, seem to me 

 to determine the place of Dysteria within the class Rotifera ; while, at the 

 same time, the lack of internal motion, the apparent want of distinct muscle- 

 bands, the great extent of the vibratory ciha, and the absence of a rotatory 

 arrangement, show that it occupies one of the vanishing points of the class." 



Mr. Gosse next proceeds to examine to which group of Rotatoria it ap- 

 proaches most nearly, and concludes, as above intimated, that it ought to 

 have a place in the family Monoceyxadece, represented by the genera Mono- 

 cerca and Mastigocerca, although, at the same time, a very aberrant genus. 

 He adds " that it has also remote relations with the Salpinadce, and especially 

 with the Coluridce (through Monura) ; and that it is an annectant form be- 

 tween the Eotifera and the Infusoria {i. e. the Ciliata), with a preponderance 

 of the characters of the former class." 



