440 THE P&OTOZOA 



ORDER III. : HYPOTRICHA. Ciliata typically of creeping habit ; the body 

 flattened, with dorsal and ventral surfaces, the ciliation highly modified 

 and specialized, usually with cirri on the ventral surface. 



Principal families: (1) Peritromidce, with cilia on the ventral surface ; 

 example : Peritromus. (2) Oxytrichidce, with cirri ; examples : Oxytricha, Uro- 

 styla, StylonycMa. (3) Euplotidce ; example : Euplotes (Fig. 182). 



ORDER IV. : PERITRICHA. Typically of sedentary habit, the locomotor 

 cilia reduced to a single ring or absent temporarily or permanently ; the 

 adoral spiral runs down into a deep depression, the vestibule, into which 

 open the anus and contractile vacuoles, and at the base of which is the mouth, 

 leading into the oesophagus. 



Suborder 1 : Scaiotricha.The adoral zone describes a left-handed spiral. 



Two families: (1) Spirochonidce : Spirochcna, ectozoic on the gill-plates 

 of Gammarus pulex, has a non- contractile body which bears at the upper 

 extremity a spirally-folded membranous funnel, on the inner side of which 

 is a zone of cilia. Allied genera are Kentrochona and Kentrochonopsis, both 

 ectozoic on the gill-plates of Nebalia. (2) Licnophoridce ; example : Licnophora, 

 ectozoic on various marine animals (one species entozoic in the respiratory 

 trees of Holothurians) ; attachment by a sucker-like disc. 



Suborder 2 : Dexiotriclia.The adoral zone describes a right-handed spiral. 



Family : Vorticellidce, with three subfamilies : (a) Urceolarince, unstalked, 

 attached temporarily by a sucker or disc, surrounded by a persistent zone 

 of locomotor cilia; examples: Trichpdina, Cydochceta. (6) Lagenophryince ; 

 example : Lagenophrys. (c) Vorticdlince, with numerous genera : Vorticdla, 

 Carchesium, Zoothamnium, etc., with contractile stalks ; Epistylis, Opercu- 

 laria, Campandla (Fig. 183), Ophrydium, etc., with non-contractile stalks ; 

 Cothurnia, Vaginicola, with sheaths ; Scyphidia, free-swimming. 



The entozoic Ciliata exhibit two different methods of. nutrition : first, the 

 holozoic method, in which the animals ingest solid food- particles, like the 

 free-living species, and possess in consequence a distinct mouth and contain 

 food- vacuoles in their interior ; secondly, the osmotic method, seen in the 

 astomatous forms, which absorb fluid nutriment by diffusion from their host, 

 and in which a mouth is rudimentary or absent and food-vacuoles are not 

 found. The Ciliata of the astomatous type represent the truly parasitic 

 forms, a familiar example of which is the genus Opalina, with species parasitic 

 in the common frog and other vertebrates. Common entozoic genera of the 

 holozoic type are Balantidium and Nyctotherus, found in the digestive tracts 

 of various animals ; such forms are perhaps for the most part scavengers ; 

 according to Comes (A.P.K., xv., p. 54), Balantidium nourishes itself exclu- 

 sively on red blood-corpuscles, which are set free in the intestine from wounds 

 caused by other parasites, especially Trematodes. Species which inhabit 

 the human intestine are Balantidium coli, B. minutum, and Nyctotherus fdba. 



On the other hand, ciliates may crop up in cultures of human fasces, which, 

 like the amoebae and flagellates found there, are not to be regarded as in- 

 habitants of the human intestine, but as free-living forms which have passed 

 through the digestive tract in an encysted condition without being destroyed, 

 and germinate when set free from the gut. An example is Chilodon dentatus 

 (undnatus], described by Guiart from human fseces ; possibly also the ciliates 

 described by Martini (850) in a case of dysentery. 1 



The free-living Ciliata exhibit, as a rule, great uniformity of character 

 in the active state, occurring constantly in one specific form which only 

 varies slightly in size under natural conditions ; they are, in fact, as nearly 

 as possible monomorphic. Some of the parasitic forms exhibit, how- 

 ever, a well-marked recurring cycle of forms in relation to the special 

 necessities of their mode of life, as is described below (p. 450). In some 

 free-living forms also different forms occur in the same species. The small 

 free-swimming conjugants (gametes, so called) of the sedentary Vorticellids 

 have been noted above (p. 172). In Leucophrys patula, a free-swimming 

 species, large and small individuals occur; but, according to Prowazek (861), 



