210 



PROTOZOA. 



the spiral, forms the broader end of the body, which gradually 

 tapers toward the other end, by wliich the un.iniii] may attach 

 itself by small plasma tlireads. Muscle fibres which run length- 

 wise immediately under the cuticle produce energetic move- 

 ments. Stentor 2)olymorp]iiis* ^y\\eu attaclied builds a gelatinous 

 case. S. cmruleus* Balantidium coli (fig. 1-49) appears in the 

 large intestine of men ill with diarrlicea; it also occurs in swine 

 without causing sickness. Other parasites of man are B. minu- 

 tuin and Nyctotherus faba. 



Order III. Peritricha. 

 In the Peritricha tliere is always a broad peristome area with 

 the cytostome; the ojiposite end has a corresjoonding pedal disc 

 or is narrowed like a goblet and ends in a stalk (fig. 150). Onlv 

 iwi. 



ust. 



Fig. loO.^CarclLeshimpolypiiium. (After BUtschli.) Left, a single animal: riaht, three 

 stages of division, cv, contraetile A'acuole; u, macronucleus; »', micronucleus: 

 J\'u, food vacuoles; os, cytophars'nx; per, peristome; vs, reservoir of contractile 

 vacuole; um, undulating membrane ; I'sf, vestibtile; ii:k\ ring on trliich a posterior 

 circle of cilia may develop. 



the adoral ciliated spiral is constant. It arises from the swollen 

 margin of the peristomial area, and continues on the ' operculum," 

 a ciliated disc which projects free from the peristomial area, but 

 in contraction is drawn close against it, the peristome lips folding 

 over all. Besides, there may be a temporary or permanent circle 

 of cilia near the hiiuler end. The nucleus is usually sausage- 

 shaped, much bent, and with the small micronucleus in its hinder 

 angle (fig. IfvO, «/). 



The best known ropresentativcs are the Vorticellid.s (figs. 147, 150), 

 attached by a long stalk which is usually hollow and contains a slightly 



