MANUAL OF NATUEAL HISTORY. 341 



food which is conveyed to their stomachs by 'the in- 

 cessant vibratile action of their ciliated wheels. The 

 Wheel- Animalcules propagate their species by means 

 of eggs, or ova. which are invested with a thin 



OO ' ' 



transparent shell, through which the embryo Rotifer 

 may be plainly discerned. 



III. CLASS. ROTIFERS (Rotifera). 



Mouth in general armed with jaws, and furnished 

 with rotatory cilia ; intestinal canal ending by two 

 distinct orifices; formed for swimming. Repro- 

 duce by eggs. 



I. OBDER. MONOTROCHIANS (Monotroch^). 



A single continuous ciliated wheel. 



1. FAMILY. Fish-Rotifers (Ichthydiidse). Margins 



of the rotatory organ entire ; skin soft or 

 naked. 



2. FAMILY. Social-Rotifers ((Ecistidse). Margins 



of wheels entire ; skin hard or loricated. 



3. FAMILY. Large-wheeled Rotifers (Megalotrochi- 



dse). Margins of the rotatory organ incised 

 or flexuous ; not enclosed in a shell. 

 4 FAMILY. Bristle-Rotifers (Flosculariidse). Lori- 

 cated ; rotatory organ with sinuous, lobed, or 

 multifid margins. 



II. ORDER. SOROTROCHIANS (Sorotrocha). 



A compound or divided ciliated wheel. 

 1. FAMILY. Pellucid-Rotifers (Hydatinidss), Body 

 without a shell ; rotatory organ many-parted. 



