744 PROTOZOOLOGY 



P. multimicronucleatum Powers and Mitchell (Figs. 19; 20; 28; 29; 

 316, c). The largest species, 200-330/x long; three to seven contractile 

 vacuoles; four or more vesicular micronuclei; a single macronucleus; 

 in fresh water. Cytology and physiology (Muller, 1932) ; division and 

 conjugation (Stanghoner, 1932; Koster, 1933); relation to Oiko- 

 monas and bacteria in culture (Hardin, 1944). 



P. bursaria (Ehrenberg) (Figs. 84; 88; 316, d). Foot-shaped, some- 

 what compressed; about 100-1 50^ by 50-60/z; green with zoochlo- 

 rellae as symbionts; a compact micronucleus; a macronucleus; two 

 contractile vacuoles; in fresh water. Relation between Chlorella and 

 host (Parker, 1926; Pringsheim, 1928); micronuclear variation 

 (Woodruff, 1931); bacteria-free culture (Loefer, 1936); removal of 

 symbionts (Jennings, 1938; Wichterman, 1948); conjugation (p. 189). 



P. putrinum Claparede and Lacbmann (Fig. 316, e). Similar to P. 

 bursaria, but a single contractile vacuole and an elongated macronu- 

 cleus; no zoochlorellae; 80-150m long; in fresh water. 



P. calkinsi Woodruff (Fig. 316, /). Foot-shaped; posterior end 

 broadly rounded; 100-150/t by 50/x; 2 vesicular micronuclei; 2 con- 

 tractile vacuoles; in fresh, brackish and salt water. Ecology, mor- 

 phology, mating types (Wichterman, 1951). 



P. trichium Stokes (Fig. 316, g). Oblong; somewhat compressed; 

 50-105 (80-90) /i long; a compact micronucleus; two contractile 

 vacuoles deeply situated, each with a convoluted outlet; in fresh 

 water. Structure and division (Wenrich, 1926); conjugation (p. 190) 

 (Diller, 1948, 1949). 



P. polijcaryum Woodruff and Spencer (Fig. 316, h). Form similar 

 to P. bursaria; 70-1 10/* long; 2 contractile vacuoles; 3-8 vesicular 

 micronuclei; in fresh water. 



P. woodruffi, Wenrich (Fig. 316, i). Similar to P. polycaryum; 150- 

 210jtx long; 2 contractile vacuoles; 3-4 vesicular micronuclei; brackish 

 water (Wenrich, 1928). 



Although Paramecium occurs widely in various freshwater bodies 

 throughout the world and has been studied extensively by numerous 

 investigators by mass or pedigree culture method, there are only a 

 few observations concerning the process of encystment. Blitschli con- 

 sidered that Paramecium was one of the Protozoa in which encyst- 

 ment did not occur. Stages in encystment were however observed in 

 P. bursaria (by Prowazek) and in P. putrinum (by Lindner). In re- 

 cent years, four observers reported their findings on the encystment 

 of Paramecium. Curtis and Guthrie (1927) give figures in their text- 

 book of zoology, showing the process (in P. caudatuml) (Fig. 317, a-c), 

 while Cleveland (1927) injected Paramecium culture into the rectum 



