364 HANDBOOK OF PROTOZOOLOGY 



nucleus. Two contractile vacuoles on the aboral surface. The 

 posterior end is more rounded than P. caudatum. 



Paramecium miiltimicronucleatiim Powers and Mitchell (Fig. 

 156, c). Body as a rule is slightly larger than P. caudatum. With 

 three to seven contractile vacuoles. Four or more vesicular 

 micronuclei and a single macronucleus. 



Paramecium hursaria (Ehrenberg) (Fig. 156, d). Foot- 

 shaped, somewhat compressed. Body about 100 to 200 microns 

 long by 50 to 60 microns broad. Containing Zoochlorellae as 

 symbionts. A single compact micronucleus; two contractile 

 vacuoles. 



Paramecium putrinum Claparede and Lachmann (Fig. 

 156, e). Similar to P. hursaria, but a single contractile vacuole 

 and an elongated macronucleus. No Zoochlorellae. Body about 

 80 to 150 microns long. 



Paramecium calkinsi Woodruff (Fig. 156,/). Foot-shaped; 

 posterior end broadly rounded. Body 100 to 130 microns long 

 by 50 microns broad. With two vesicular micronuclei. Two 

 contractile vacuoles. The rotation of the body is clockwise, 

 viewed from the posterior end. Fresh or brackish water. 



Paramecium trichium Stokes (Fig. 156, g). Body oblong; 

 somewhat compressed; about 70 to 100 microns long. A single 

 compact micronucleus. Two contractile vacuoles deeply situa- 

 ted, each with a convoluted outlet. 



Paramecium polycaryum Woodruff and Spencer (Fig. 156, h). 

 Body form similar to P. hursaria. Length 70 to 110 microns. 

 Two contractile vacuoles. Vesicular micronuclei three to eight 

 in number. 



Paramecium woodruffi. Wenrich (Fig. 156, i). Similar to P. 

 polycaryum. Length 150 to 210 microns. Two contractile 

 vacuoles. Three or four micronuclei, vesicular. Brackish water. 



Although Paramecium occurs widely in various fresh-water 

 bodies and has been studied extensively by numerous investi- 

 gators by mass or pedigree culture method, there are only a few 

 observations concerning the process of encystment. Biitschli 

 considered that Paramecium was one of the Protozoa in which 

 encystment did not occur. But stages of encystment have been 

 observed in 1899 in P. hursaria (by Prowazek) and in P. 

 putrinum (by Lindner) , In recent years, three observers recorded 



