POLYMASTIGINA 297 



furrows; posterior end bluntly narrowed or lobed; no apparent 

 cytostome; 4 flagella; a contractile vacuole anterior; fresh water. 



C. triciliatum C. (Fig. 135, d). Spherical, ovoid or heart-shaped; 

 27-60iu long; flagella as long as the body; pond water. Rhodes (1919) 

 made a comprehensive cytological study of the organism. 



Genus Costia Leclerque. Ovoid in front view; pyriform in profile; 

 toward right side, a funnel-like depression, at the posterior end of 

 which are located cytostome (?) and 2 long and 2 short flagella; con- 

 tractile vacuole in posterior half; longitudinal division; encystment; 

 ectoparasitic in various freshwater fishes. 



P \f' % % 



% '^- "0 • 



2 7 8 9 10 



Fig. 136. Enteromonas hominis, X1150. 1, 2 (da Fonseca); 3-6, living 

 trophozoites; 7, 8, stained trophozoites; 9, 10, stained young and mature 

 cysts (Wen3^on and O'Connor). 



C. necatrix (Henneguy) (,Fig. 135, e-j). 10-20^1 by 5-10/x; compact 

 nucleus central; a contractile vacuole; cyst uninucleate, spherical, 

 7-IOm in diameter; when present in large numbers, the epidermis of 

 fish appears to be covered by a whitish coat. 



C. pyriformis Davis. A similar form; but smaller in size; 9-14^11 by 

 b-Sfx. Davis (1943) observed the organism on trout [Salmo irideus 

 and Salvelinus fontinalis) . 



Genus Enteromonas da Fonseca (Tricercomonas Wenyon and 

 O'Connor). Spherical or pyriform, though plastic; 3 anterior flagella; 

 the fourth flagellum runs along the flattened body surface and ex- 

 tends a little freely at the posterior tip of body; nucleus anterior; 

 no cytostome; cyst ovoid and with 4 nuclei when mature; parasitic 

 in mammals. Da Fonseca (1915) originally observed only 3 flagella 

 and no cysts; 4 flagella and encysted forms were noticed in Tri- 

 cercomonas by Wenyon and O'Connor (1917); in da Fonseca's ori- 

 ginal preparations, Dobell (1935) observed 4 flagella as well as cysts 



