480 GENERAL HISTOKY OF THE INFUSORIA. 



mitted, yet several writers, such as Siebold, Perty, and Gosse, have been con- 

 tent to employ it in the absence of a better. Indeed, before a correct natural 

 classification of the Rotatoria can be made, the organization of each inde- 

 pendent form must be investigated, and the signification and relative import- 

 ance of its parts determined. 



Various temporary arrangements have been suggested. Ehrenberg himself 

 indicated a division of the class according to the form and disposition of the 

 ahmentary canal, and another according to the structure of the dental appa- 

 ratus. Both these are unsatisfactory and artificial ; and even theii' author 

 was compelled to admit that genera and species were thereby associated in 

 alliances quite diff'erent from those they occuj^ied in his accepted system. 



Dujardin considers that, " in the present state of science, we do not possess 

 the elements of a definite classification ; " and therefore proposes, as a merely 

 provisional scheme, four grand divisions of the Rotatoria, including the Tardi- 

 grada: viz., 1. those which live fixed by their posterior extremity; 2. those which 

 have but one mode of locomotion, and are always swimmers ; 3. those which 

 enjoy two modes of progression — by crawling, after the manner of leeches, and 

 by swimming ; 4. those which creep by moveable imcini on their lower sm-- 

 face, and are destitute of cilia. It is the Tardigrada which constitute this 

 fourth division ; and they so far differ from Rotatoria, particularly in the ab- 

 sence of a ciliary apparatus and the presence of rudimentary feet, that their 

 alliance with the latter is generally objected to ; even Dujardin himself views 

 it as of doubtful propriety. 



The classification of Dujardin, omitting the Tardigrada, is as follows : — 



FamiHes. 



, ^. , „ f Flosculariens. 



1. Fixed forms | Melicertiens. 



r Brachioniens. 



2. Having one mode of locomotion, viz. by swimming -j Furculariens. 



[ Albertiens. 



3. Having two modes of locomotion : 1. by swimming ; | jjqtiferes. 



2. by crawhng J 



For the further division into genera we must refer to Dujardin's work. 

 The system, as Leydig remarks of it, is founded on a correct principle, and 

 recommends itself by its simplicity. The groups of individuals it brings 

 together generally consort by natural affinities ; still some are exceptional and 

 aberrant, and occur as disjecta membra. 



Leydig makes the attempt to form a di\ision, primarily according to the form 

 of the body, and secondarily, to the nature and the presence or the absence 

 of the foot-process. There are three primarj^ fonns : — 1. in which the figure 

 is club-shaped or cylindrical ; 2. in which it is saccular ; 3. in which it is 

 compressed. The accompanying plan represents in full the system in ques- 

 tion. The Ichtliydhia are omitted. 



LEYDIG'S CLASSIFICATION. 



A. Figure club-shaped or cylindrical. 



I. With a long, transversely wrinMed, attached foot. 



In tliis section are comprised the families (Ecistina, Megalotrochcpa, and 

 FloscuIaricBa of Ehrenberg, excepting the genera Pfygura, Glenoi)hora, 

 Cyphonautes, and Microcodon. The last belongs to another section ; 

 and the other tlu'ee are incomplete forms. 

 II. With a long, jointed, telescopic, and retractile foot. 



Is represented by the family Fhilodincea (Ehr.). 

 III. With a long, jointed, not retractile foot. 



Includes' the genera Scaridiian and Dinocharis (Ehr.). 

 IV. With a short foot and long foot-processes. 



Includes the genera Moriocerca, Furciilaria, and Microcodon (Ehr.). and the 



