ON BRISTOL ROTIFERS. 157 



the difference that Ehrenberg draws between the loricated and 

 illoricated sub-division of each groap, it looks very neat and 

 symmetrical on paper, but this symmetry can only be obtained by 

 applying the term lorica to such widely diverse structures as the 

 hardened integument of Brachionus, the pelleted case of Melicerta^ 

 and the fluffy investment of Lacinularia. 



Lcydig and Dujardin have both studied the Rotifers, and have 

 both tried their hands at classifying them. Leydig has added 

 greatly to our knowledge of their structure, but his classification 

 is even looser than Ehrenberg's. Dujardin, on the other hand, 

 has not been a very successful observer, but he has suggested a 

 classification which is much superior to Ehrenberg's, and will, I 

 think, be the basis of that which will ultimately be adopted. 

 Cope has followed on the same line as Leydig, and has improved 

 on his predecessor, as was to be expected from his wide and 

 accurate knowledge of the subject ; and the result, with some 

 slight modifications, is as follows : — 



The Rotifers may be divided into two great groups : 

 I. The fixed forms. 



II. The swimmers. 

 And the latter group may be sub-divided into 



A. Those that swim only. 



B. Those that swim, and also creep like a leech. 

 Group I. contains all the tube-making Rotifers, and naturally 



falls into two families, viz. — 



(i.) Floscularia3a 

 and (ii.) Melicertadaea, 

 in which (i.) contains those tube-makers whose mouth is symmetri- 

 cally situated with respect to their trochal discs, and (ii.) those 

 in which it is asymmetrically situated. 

 Sub-division A. contains the families 



(iii.) Brachionaea, 



(iv.) Hydatinsea, 

 (iii.) being those free-swimmers which have a lorica, and (iv.) 



