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antero-lateral flagella; Costia necatrix (Leclerq) is also 3-flagellate; causes destructive epidemics in fish-hatcheries. Family 8.—. Body pyriform, the pointed end posterior; flagella 4 anterior.

Tetramitus (Perty) (T. calycinus of Kent, Fig. 2, 11, 14), is the “calycine monad” of Dallinger and Drysdale; Trichomonas, Donné, possesses a longitudinal undulating membrane, and is an innocuous human parasite; it is possibly related to Haemoflagellates on one hand and to Trichonymphidae on the other.

Family 9.—. Mouth-spots two, or one, with a distinct construction; flagella symmetrically arranged; nucleus bilobed or geminate. Hexamitus (Duj.) (Fig. 2, 5), saprophytic and parasitic; Trepomonas (Duj.), freshwater; Megastoma (Grassi) ( = Lamblia of Blanchard), with constricted mouth-spot and blepharoplast (kineto-nucleus) parasitic in the small intestine of Mammals, including Man.

Family 10.—. Flagella numerous, sometimes accompanied by one or more undulating membranes; cytoplasm highly differentiated; contractile vacuole absent; all parasitic in insects (all except Lophomonas in Termites—the so-called White Ants.)

Lophomonas (St.) (Fig. 2, 9); parasitic in the cockroach; Dinenympha (Leidy), Pyrsonympha (Leidy); Trichenympha (Leidy) (Fig. 3, 1).

Family 11.—. Flagella short, numerous, ciliform. uniformly distributed over the flat oval body; nuclei small, numerous, uniform.

Only genus, Opalina (Purkinje and Valentin) (Fig. 3, 2-6), in bladder and cloaca of the frog (usually regarded as an aberrant ciliate, but E.R. Lankester expressed doubts as to its position in the 9th edition of this encyclopaedia).

Order 2.—CHRYSOMONADACEAE. Contractile vacuole simple (in fresh-water forms) or absent; plastids yellow or brown always present; reserves fat.

Family 1.—. Body naked, often amoeboid in active state, or sometimes with a cup-like theca, a gelatinous investment, a firm cuticle, or silicified shell; reserves fat or leucosin (starch in Zooxanthella); eye-spot present. Chromulina (Cienk.) often forms a golden scum on tanks; Chrysamoeba (Klebs); Hydrurus (Agardh), theca of colony