336 C. T. HUDSON. 



provisional places assigned to them ; owing either to their un- 

 usual forms, or to their not having been sufficiently studied. 



The great majority of the Rotifers carry on their heads lines 

 or clusters of moving cilia, by means of which they swim and 

 conduct food into their mouths. Ehrenberg's first division 

 into groups is in accordance with the supposed forms of these 

 ciliated curves and clusters ; and each group is again divided 

 into Rotifers that have, and into those that have not, a lorica 

 or case. 



Lastly, these groups are sub-divided into genera mainly in 

 accordance with the presence or absence of eyes, with their 

 number and with their situation ; while in the larger groups 

 the form of the trochal disc and foot, and the number of teeth 

 in the jaws, are also made use of to help in separating the 

 genera. 



The result is that the Eotifera are divided into four groups, 

 according to the following plan : 



Class— ROTATORIA. 

 * A simple continuous ciliary wreath . . Monotrocha. 

 ** A compound or divided ciliary wreath . Sorotrocha. 



* Monotrocha. 

 (a.) An unbroken-edged ciliary wreath . . . Holotrocha. 

 (6.) A scalloped ciliary wreath Schizotrocha. 



** Sorotrocha. 

 («.), A many-parted ciliary wreath .... Polytrocha. 

 (6.) A two-parted ciliary wreath Zygotrocha. 



and as each of these groups is sub-divided into a loricated and 

 an il-loricated family, we have finally an arrangement by 

 which all known Rotifers are made to take their places in one 

 or other of the eight families of the following neat and sym- 

 metrical system : 



STT^i^4.^^„i „ C il-loricated . . Icthydina. 



Holotrocha . -s i ■ i. j rm ■ i- 



(. loncatea . , Chicistina. 



Schizotrocha 4 "-I-Th^- • Mcgalotr„cl,«a. 



(. loricated . . ±loscularia. 



/-T)«i„+«„„i.„ C il-loricated . . Hydatinsea. 



f Polytrocha. .| lo^i^ated. . Euchlanidota. 



Sorotrocha • j r iMoricated . . Philodinjea. 



CZygotrocha .| j^ricated. . Brachion^a. 



