THE MICROSCOPE IN ZOOLOGY. 163 



A. Intestinal tube absent. 



Body variable, without cilia. 



Carapace absent, . _ '. . " , . , . ASTASI^A. 



Carapace present, . . ... DINOBRYINA. 

 Cilia or seta3 present. 



Carapace absent, ... . :-. CYCLIDINA. 



Carapace present, . > ' . . . PERIDIN^A. 



B. Intestinal tube present. 



Orifice single. 



Carapace absent, . # .. ;" . . VORTICELLINA. 

 Carapace present, . . .; . . . OPHRYDINA. 

 Two opposite orifices. 



Carapace absent, .... . . ENCHELIA. 



Carapace present, . . ., . . COLEPINA. 

 Orifices differently placed. 

 Carapace none. 



No tail, but a proboscis, .> . TRACHELINA. 

 Tail present, mouth anterior, . OPHRYOCERCINA. 

 Carapace present, . . ./... ASPIDISCINA. 

 Orifices ventral. 



Carapace absent. 



Motion by cilia, .... COLPODEA. 



Motion by organs, .... OXYTRICHINA. 



Carapace present, . . . . . EUPLOTA. 



IV. ROTATORIA OR WHEEL ANIMALCULES. These are 

 microscopic, aquatic, transparent animals, of a higher 

 organization than the Infusoria, and belonging in all 

 probability to the class Vermes. Their chief interest to 

 the microscopist is derived from the possession of a more 

 or less lobed, retractile disk, covered with cilia, which, 

 when in motion, resemble revolving wheels. They have 

 also a complicated dental apparatus, and generally a dis- 

 tinct alimentary canal, and are reproduced by ova. Some 

 are more or less covered by a carapace, and in most there 

 is a retractile tail-like foot, sometimes terminated by a 

 suctorial disk or a pair of claw-like processes. The ner- 

 vous and vascular systems are not well known, although 

 traces of them are seen. The young of some possess an 

 eye which often disappears in the adult. They are re- 



