(_a_) Flagella long: nucleus single: parasitic in insects TRICHONYMPHIDAE _Dinenympha_ Leidy; _Joenia_ Grassi; _Pyrsonympha_ Leidy; _Trichonympha_ Leidy; _Lophomonas_ St.; _Maupasia_ Schew. (_b_) Flagella short, ciliiform, uniformly distributed: nuclei very numerous, all similar: parasitic in Amphibia OPALINIDAE _Opalina_ Purkinje and Valentin (Fig. 41). VOLVOCACEAE A. Cells usually isolated, separating after fission or brood-formation. Usually green (sometimes red), more rarely colourless saprophytes CHLAMYDOMONADIDAE _Chlamydomonas_ Ehrb.; _Phacotus_ Perty; _Polytoma_ Ehrb.; _Sphaerella_ Sommerf. (Fig. 43); _Zoochlorella_. B. Cells multiplying in the active state by radial divisions in the same plane and usually incurving to form a spherical colony, united in a gelatinous investment, sometimes traversed by plasmic threads VOLVOCIDAE _Gonium_ O.F.M.; _Eudorina_ Ehrb.; _Pandorina_ Bory (Fig. 45); _Stephanosphaera_ Cohn; _Volvox_ L. (Fig. 44). {112}[Illustration: FIG. 37.—Various forms of Flagellata. 2, 6-8, 10, 13, 14, Protomastigaceae; 11, 12, Chrysomonadaceae; 9, Cryptomonadaceae; 1, 3, Euglenaceae; 4, Pantostomata: note branched stalk in 13; branched tubular theca in 14; distinct thecae in 11; stalk and theca in 10. In 2, flagellate (_a_) and amoeboid (_b_) phases are shown; in 5, flagellate (_a_) and Heliozoan (_b_) phases[116]; in 8 are shown two stages in the ingestion of a food particle (_f_); _chr_, plastoids; _c.vac_, contractile vacuole; _f_, food particle; _g_, gullet; _l_, theca; _nu_, nucleus; _p_, protoplasm; _per_, peristome; _v.i_, vacuole of ingestion. (From Parker and Haswell, mostly from Bütschli's _Protozoa_.)] {113}The modes of nutrition are threefold: the simplest forms live in liquids containing decaying organic matter which they absorb through their surface ("saprophytic"): others take in food either _Amoeba_ fashion, or into a vacuole formed for the purpose, or into a definite mouth ("holozoic"): others again have coloured plastids, green or brown or yellow ("holophytic"), having the plant's faculty of manufacturing their own food-supply. But we meet with species that show chromatophores at one time and lack them at another; or, again, the same individual (_Euglena_) may pass from holozoic life to saprophytic (_Paramoeba_, some Dinoflagellates) as conditions alter.