254 



FRESH-WATER BIOLOGY 



89 (94) Body flexible; one or two flagella 90 



90(93) Flagella two '.,... 9 1 



91 (92) Secondary flagellum very small, directed backward. . Astasia Stein. 



Representative species. 



FIG. 403. 



92 (91) 



Astasia trichophora. 

 (After Conn.) 



X 410. 



. . Astasia trichophora Ehrenberg 1830. 



Body elongate, usually wider posteriorly. 

 Primary flagellum very thick at the base and 

 long. Nucleus central; contractile vacuole an- 

 teriorly located. Length, when extended, 30 to 

 60 ft. Common among diatoms and algae. 



Secondary flagellum about half as long as the primary; both flagella 



directed forward Distigma Ehrenberg. 



Representative species Distigma proteus Ehrenberg 1830. 



Body very plastic; when contracted, distended in one 

 or two regions. Endoplasm with dark-colored corpuscles. 

 Nucleus central; contractile vacuole in the anterior region. 

 Length, when extended, 95 /* Pond water. 



FIG. 404. Distigma proteus. co, contractile vacuole; n, nucleus; 

 X 330. (After Stein.) 



Distigma proteus. 

 ph, pharynx. 



93 (90) Flagellum single; body elongate, tapering posteriorly. A long tubu- 



lar pharynx Atractonema Stein. 



Representative species Atractonema tortuosa Stokes 1885. 



Body flexible but persistent in shape, colorless, 

 enclosing oblong dark-bordered corpuscles. Fla- 

 gellum about half as long as the body. Movements 

 rotary on the long axis. Length 50 to 80 M- In 

 vegetable infusions. 



FIG. 405. Atractonema torluosa. X 625. (After Stokes.) 



94 (89) Body not flexible 95 



95 (98) With longitudinal or spiral ridges 96 



96 (97) Elongate or crescentic, with four longitudinal ridges; flagella, two, 



unequal Sphenomonas Stein. 



Representative species. . . Sphenomonas quadrangular is Stein 1878. 



Body subfusiform, with the ridges fawning a quadrate outline in cross sec- 

 tion. Long flagellum stout, four times the length of the shorter one. A 

 large amylaceous corpuscle usually enclosed in the endoplasm. Length 40 M. 

 Fresh water. 



FIG. 406. Sphenomonas quadrangular is. X 400. (After Butschli.) 



97 (96) Nearly ellipsoidal, with many spiral ridges. . Tropidoscyphus Stein. 



98 (95) Without ridges 99 



