386 BIOLOGY OF THE PROTOZOA 



Family 5. Paramecidse, Biitschli.— Up to the present including 

 only the genus Paramecium of which the common forms P. caudatvm 

 and P. aurelia are elongate and cigar-shape with a si)irally-wound 

 peristome and a gullet in which a single undulating membrane lies. 

 P. piitrinum is shorter, more plump, and lacks the spirallv' wound 

 peristome. P. bursaria is flattened somewhat kidney-shape, has 

 one micronucleus, and is usuall\' well supplied with symbiotic 

 Zoochlorella. P. calkinsi is similar to bursaria but has two micro- 

 nuclei and lacks the symbionts. Star-shape contractile vacuoles and 

 canals present in all. 



Famih/ (». Isotrichidae, Biitschli— These are parasitic ciliates with 

 thickened periplast and with a general and dense covering of cilia. 

 They live, probably as commensals, in the fore-stomach of rumin- 

 ants. 



(See Schuberg, 1888, or Eberlein, 1895 for genera.) 



Ordek II. HETEROTRICHIDA, Stein. 



In this and the following Orders of ciliates the peristome bears 

 on its left margin, a row of differentiated aggregates of cilia termed 

 membranelles the row being known as the adoral zone. In this 

 Order the adoral zone is woimd to the left and the body is covered 

 with a coating of fine cilia which, however, as in Holotrichida, may 

 be variously reduced. The varying forms of the body are due, in 

 the main, to modifications of the frontal field which may be at 

 right angles to the long axis of the body (Stentoridai' and Bursarida:') 

 or parallel with it. These differences form the main basis of divi- 

 sion into families as follows: 



Famih/ ]. Plagiotomidse, Clap, and Lach., Biitschli. In this 

 family the peristome and frontal field is characteristically narrow 

 and elongate with the adoral zone rinming from the anterior end to 

 the mouth near the center of the body. Typical Genera: 



1. Conchyphihiriiis, body laterally compressed; anterior rounded. 



2. Blepharisma (Fig. 174, p. 891), color usually pink; peristome 

 straight; pointed at end. 



3. Helicostoma, peristome oblique with spiral gullet. 



4. Metojms (Fig. 171, B), body distinctly twisted; not contractile. 



5. Nyctotherns (Fig. 171, C), parasitic; form oval to bean-shape. 

 (3. P/fl f//o<o;/?a, parasitic(?); anterior pointed, posterior truncate, 



7. Porpostotna, body not twisted nor compressed; two crescentic 

 oval lips. 



8. Spirostomiim (Fig. 30, p. 70), body A'ery long, band-form and 

 highly contractile. 



Family 2. Stentoridse, Stein. — In this family the frontal field is at 

 right angles to the long axis of the body, or in Climacthstomum at a 

 marked angle with such axis. In some genera the frontal field is 



