THE MICROSCOPE IN ZOOLOGY. 163 



A. Intestinal tube absent. 



Body variable, without cilia. 



Carapace absent, ..... ASTASI.EA. 



Carapace present, DINOBRYINA. 



Cilia or setae present. 



Carapace absent, ..... CYCLIDINA. 



Carapace present, ..... PERIDIN^A. 



B. Intestinal tube present. 



Orifice single. 



Carapace absent, ..... YORTICELLINA. 



Carapace present, OPHRYDINA. 



Two opposite orifices. 



Carapace absent, ..... ENCHELIA. 

 Carapace present, ..... COLKPINA. 

 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 leos 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- 



