2 54 FRESH-WATER BIOLOGY 



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



90 (93) Flagella two 91 



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



Representative species \ stasia trichophora Ehrenberg 1830. 



/yTj^^~^^—~r^~y-^.r~—.^ Body elongate, usually wider posteriorly. 



t>>Pi^;^^^^£^s^^ Primary flagellum very thick at the base and 



^i^^^^=^=^^^^^ long. Nucleus central; contractile vacuole an- 



FiG. 403. Astasia trichophora. X 410. teriorly located. Length, when extended, 30 to 



(Alter Conn.) 60 m Common among diatoms and algae. 



92 (91) 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. 



^^_^__^^<^^^^^::^^^j^-^ Nucleus central ; contractile vacuole in the anterior region. 



^^^;ssss=*ss^^*^^^^^^^v_^^ Length, when e.xtended, 95 /x. Pond water. 



* "^ Fig. 404. Distigma proteus. cv, contractile vacuole; n, nucleus; 



ph, pharynx. X 33° (After Stein.) 



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



lar pharynx Atractonema Stein. 



Representative species Atractoiuma tortuosa Stokes 1885. 



Body flexible but persistent in shape, colorless, 



enclosing oblong dark-bordered corpuscles. Fla- 



^,.^^^55.^^^^ ^<''o'^^3~-^2-^ gellum about half as long as the body. Movements 



<i^^^^-'-^^^^>>___^.,('^^ rotary on the long axis. Length 50 to 80 n. In 



^""^^^^^S^ vegetable infusions. 



Fig. 405. Atractonema tortuosa. 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 fopming 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 quadrangularis. X 400. (After Biitschli.) 



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



98 (95) Without ridges 99 



