HOLOTRICHA 601 



while Cleveland (1927) injected Paramecium culture into the rectum 

 of frogs and observed that the ciliate encysted within a thin mem- 

 brane. Michelson (1928) found that if P. caudatum is kept in Knop- 

 agar medium, the organism becomes ellipsoidal under certain condi- 

 tions, later spherical to oval, losing all organellae except the nuclei, 

 and develops a thick membrane; the fully formed cyst is elongated 

 and angular, and resembles a sand particle (Fig. 284,/). Michelson 

 considers its resemblance to a sand grain as the chief cause of the cyst 

 having been overlooked by workers. In all these cases, it may how- 

 ever be added that excystment has not been established. 



Genus Physalophrya Kahl. Without peristome; but cytostome lo- 

 cated near the anterior half of body, resembles much that of Para- 

 mecium; although there is no membrane, a ciliary row occurs in the 

 left dorsal wall of cytopharynx; in fresh water. Taxonomic status is 

 not clear; but because of its general resemblance to Paramecium, the 

 genus with only one species is mentioned here. 



P. spumosa (Penard) (Fig. 282, g). Oval to cylindrical; highly 

 plastic; cytoplasm reticulated; numerous contractile vacuoles; 150- 

 320/i long; in fresh water. 



Family 9 Colpodidae Poche 



Genus Colpoda Mliller. Reniform; flattened; right border semi- 

 circular; posterior half of left border often convex; oral funnel in the 

 middle of flattened ventral side, but toward left border where de- 

 pression occurs, which leads into peristome cavity and gives rise 

 dorsally to a diagonal groove; left edge of cytostome bears a cross- 

 striped ciliated area, but no protruding membrane as in Bryophrya 

 (p. 602) ; macro nucleus spherical or oval, central; contractile vacuole 

 terminal; in fresh water. Many species. 



C. cucullus M. (Fig. 285, a, h). About 80m (50-120m) long; anterior 

 keel with 8^10 indentations; macronucleus with a stellate endosome; 

 trichocysts rod-form; food vacuoles dark; in fresh waiter with decay- 

 ing plants and infusion. 



C. inflata (Stokes) (Fig. 285, c). 40-80^ long; anterior keel with 6-8 

 indentations; in fresh water in vegetation. 



C. calif ornica Kahl (Fig. 285, d). About 30^ long; highly flat- 

 tened; cytostome small; pro trichocysts very granular; cilia delicate, 

 long, in a few rows; macronucleus M-ith a stellate endosome; in moss; 

 California. 



C. steini Maupas. 30-50m long; 5-6 preoral ridges; in fresh water. 

 Reynolds (1936) found that it adopts itself to various organs of the 

 land slug, Agriolimax agrestis. 



