102 THE INVERTEBRATA 



Suborder VESTIBULATA (HYMENOSTOMATA) 



Holotricha with a mouth and a gullet (vestibule) which is permanently 

 open and usually possesses an undulating membrane ; and with mega- 

 and micronuclei. 



Colpoda (Fig. 86 E). Kidney-shaped ; with large vestibule on con- 

 cave side ; but no undulating membrane ; and no peristome. Fission, 

 binary or repeated, takes place in a cyst. Common in infusions, fresh- 

 water and marine. 



Colpidium. As Colpoda ; but with undulating membrane. Common 

 in infusions, freshwater and marine. 



Paramecium (Fig. i6). Slipper- or pear-shaped according to 

 species; with undulating membrane^; and peristome. Common in 

 infusions, freshwater and marine. 



Order HETEROTRICHA 

 Ciliata which possess a gullet, permanently open and provided with 

 undulating membrane; an adoral wreath, curving clockwise; and 

 most often on the rest of the body a uniform covering of cilia ; and 

 whose body is not depressed. 



Suborder POLYTRICHA 



Heterotricha which retain the uniform ciliation of the general surface 

 of the body. 



Balantidium (Fig. 87 A). Egg-shaped; the peristome a deep 

 groove at the anterior end. Parasitic in the rectum of frogs, the in- 

 testine of man (where it is occasionally harmful), etc. 



Nyctotherus (Fig. 87 B). Kidney-shaped; with permanent anus. 

 Parasitic in the rectum of frogs, the intestine of man, etc. 



Spirostomum (Fig. 88 B). Rod-shaped; with the peristome as a 

 long groove; meganucleus beaded; several micronuclei. In fresh 

 waters and marine. 



Stentor (Fig. 88 C). Long and funnel-shaped ; attached by the base, 

 but often frees itself to swim ; meganucleus beaded ; several micro- 

 nuclei. The animal is very highly contractile. In fresh waters. 



Suborder OLIGOTRICHA 



Heterotricha of shortened form ; with the body cilia reduced to a few 

 rows or absent. 



This suborder contains two tribes of very different habits, the 



pelagic Tintinnina, and the Entodiniomorpha, forms of bizarre shape 



parasitic in the alimentary canal of mammals, chiefly in the stomach 



of ruminants. Both suborders have an anterior peristome with very 



^ It is said that Paramecium has four parallel undulating membranes. 



