600 



PROTOZOOLOGY 



P. calkinsi Woodruff (Fig. 283, /). Foot-shaped; posterior end 

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

 tractile vacuoles; rotation of body clockwise when viewed from pos- 

 terior end; in fresh and brackish water 



P. trichium Stokes (Fig. 283, g). Oblong; somewhat compressed; 

 60-120/i long; micro nucleus compact; 2 contractile vacuoles deeply 

 situated, each with a convoluted outlet; in fresh water. 



P. polycaryum Woodruff and Spencer (Fig. 283, h). Form similar 

 to P. hursaria; 70-1 10m long; 2 contractile vacuoles; 3-8 vesicular 

 micronuclei; in fresh water. 



Fig. 284. a-c, encystment in a species of Paramecium (Curtis and 

 Guthrie); d-f, encystment of P. caudatum, X380 (Michelson). 



P. woodruffi, Wenrich (Fig. 283, ^). Similar to P. polycaryum; 150- 

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

 water. 



Although Paramecium occurs widely in various freshwater bodies 

 throughovit 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. Biitschli con- 

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

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

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

 cent years, four observers recorded their findings on the encystment 

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

 book of zoology, showing the process (in P. caudatum?) (Fig. 284, a-c), 



