ATTEMPT TO RE-CLASSIFY THE ROTIFEES. 353 



each other J and show that the form of the trophi is a good 

 characteristic for separating the families. But a difference in 

 the shape and disposition of the trochal disc and its ciliary 

 wreaths generally accompanies a difference in the manducatory 

 organs; and the two together will, I think, serve as good 

 guides to a re-classification of the Rotifers into families. This 

 I have attempted in the annexed scheme, but of course there 

 are genera which do not fall readily into this arrangement ; 

 such aberrant forms as Trochospheera, Acyclus, and Dic- 

 tyophora, it would be difficult to place in any classification. 



The parasitic Rotifers (as might have been expected) contain 

 some very strange creatures, such as Drilophaga and 

 Seisou; and would I think be better put in a class by them- 

 selves. Such difficulties however must attend every attempt 

 to marshal Nature's endless varieties into well-marked bat- 

 talions. Nature knows no hard lines of separation, and the 

 best of classifications can be only that which contains the 

 fewest faults. 



Perfectly satisfactory classification is the product of imper- 

 fect knowledge; when the commoner and better separated 

 forms are alone known to us, and when the rarer intermediate 

 forms (which are the despair of the classifier and the delight of 

 the naturalist) are as yet undiscovered.^ 



Class — ROTIFERA. 



Order I. — Rhizota. 



Fixed forms ; foot attached, transversely wrinkled, non- 

 retractile, truncate. 



Fam. 1. Flosculariadee (figs. 10, 11). 



Mouth central ; ciliary wreath a single half-circle above the 

 mouth ; trophi uncinate. 



* Some years ago it was thought that the Rotifers miglit possibly be divided 

 into two groups ; the one monoecious, the other dioecious. But later re- 

 searches have rendered this improbable. For, of the twelve families into 



