316 Illinois State Laboratory of Natural History. 



1. Subclass Ciliata. Cilia persistent through life; food 

 taken through a mouth, except in some parasitic forms. 



1. Order Gymnostomata. Mouth usually closed when 

 not in use, without undulating membrane or well- 

 developed ciliary structures ; food taken by swal- 

 lowing ; throat, if present, without ciliary structures, 

 usually surrounded by a wall of more or less indu- 

 rated parallel longitudinal rods. Three families. 



2. Order Trichostomata. Mouth or throat rarely closed, 

 provided with well- developed undulating membrane 

 or ciliary structures, food usually drawn in or 

 engulfed. 



1. Suborder Aspirotricha. Body invested with fine 

 and comparatively uniform cilia, no anterior 

 spiral adoral wreath. 



2. Suborder Spirotricha. A spiral to nearly circular 

 adoral ciliary fringe bordering a differentiated 

 peristome-field and ending at the mouth ; cilia of 

 fringe often broad or lamellate. 



1. Section Heterotriclia. Entire surface usually 

 rather uniformly ciliated, the adoral series larger 

 than the rest, and more or less spirally arranged. 

 Four families. 



2. Section Oluiotricha. Body more or less globular 

 or obconic ; peristome-field wholly on the anterior 

 end, adoral wreath nearly or entirely a closed cir- 

 cle ; ciliation well developed to wanting ; in some 

 instances loricated. Four families. 



3. Section Hypotrielia. Body usually flattened; 

 i ventral cilia modified into setae or styles, back 



usually with rows of stiff bristles ; peristome- 

 field about in the plane of the ventral surface, 

 adoral wreath bordering its left and anterior 

 sides, and sometimes a part of its right side. 

 Four families. 



4. Section Perltrielia. Solitary or united in social 

 colonies ; cilia confined to the adoral wreath encir- 

 cling the expanded terminal peristome-field ; a 



