210 



PROTOZOA. 



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

 tapers toward the other end, by which the animal may attach 

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

 wise immediately under the cuticle produce energetic move- 

 ments. Stentor polymorphus * when attached builds a gelatinous 

 case. S. cceruleus.* Balantidium coli (fig. 149) appears in the 

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

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

 tum and Nyctotherus faba. 



Order III. Peritricha. 



In the Peritricha there is always a broad peristome area with 

 the cytostome; the opposite end has a corresponding pedal disc 

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



FIG. 150. Carchesium polypinum. (After Biitschli.) Left, a single animal; right, three 

 stages of division, cv, contractile vacuole; n, macronucleus: n', micronucleus; 

 JVv, food vacuoles: os, cytopharynx; per, peristome; vs, reservoir of contractile 

 vacuole; *, undulating membrane ; vst, vestibule; wk, ring on which 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, tliQ peristome lips folding 

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

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

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

 angle (fig. 150, n f ). 



The best known representatives are the VORTICELLID^E (figs. 147, 150), 

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



