_Protozoa moving (and feeding in holozoic forms) by long flagella: pseudopodia when developed usually transitory: nucleus single or if multiple not biform: reproduction occurring in the active state and usually by longitudinal fission, sometimes alternating with brood-formation in the cyst or more rarely in the active state: form usually definite: a firm pellicle or distinct cell-wall often present._ The Flagellates thus defined correspond to Bütschli's group of the Mastigophora. The lowest and simplest forms, often loosely called "Monads," are only distinguishable from Sarcodina (especially Proteomyxa) and Sporozoa by the above characters: their artificial nature is obvious when we remember that many of the Sarcodina have a flagellate stage, and that the sperms of bisexual Sporozoa are flagellate (as are indeed those of all Metazoa except Nematodes and most Crustacea). Even as thus limited the group is of enormous extent, and passes into the Chytridieae and Phycomycetes Zoosporeae on the one hand, and by its holophytic colonial members into the Algae, on the other.[115] CLASSIFICATION. A. Fission usually longitudinal (transverse only in a cyst), or if multiple, radial and complete: pellicle absent, thin, or if armour-like, with not more than two valves. I. Food taken in at any part of the body by pseudopodia 1. PANTOSTOMATA _Multicilia_ Cienk.; _Mastigamoeba_ F. E. Sch. (Fig. 37, 4). {110}II. Food taken in at a definite point or points, or by absorption, or nutrition holophytic. 1. No reticulate siliceous shell. Diameter under 500 µ (1/50"). * Contractile vacuole simple (one or more). (α) Colourless: reserves usually fat: holozoic, saprophytic or parasitic 2. PROTOMASTIGACEAE (β) Plastids yellow or brown: reserves fat or proteid: nutrition variable: body naked, often amoeboid in active state (_C. nudae_), or with a test, sometimes containing calcareous discs ("coccoliths," "rhabdoliths") of peculiar form (_C. loricatae_) 3. CHRYSOMONADACEAE _Chromulina_ Cienk.; _Chrysamoeba_ Klebs; _Hydrurus_ Ag. _Dinobryon_ Ehrb. (Fig. 37, 11); _Syncrypta_ Ehrb. (Fig. 37, 12); _Zooxanthella_ Brandt; _Pontosphaera_ Lohm.; _Coccolithophora_ Lohm.; _Rhabdosphaera_ Haeck. (γ) Green, (more rarely yellow or brown) or colourless: reserves starch: fission longitudinal 4. CRYPTOMONADACEAE _Cryptomonas_ Ehrb. (Fig. 37, 9); _Paramoeba_ Greeff. (δ) Green (rarely colourless): fission multiple, radial 5. VOLVOCACEAE ** System of contractile vacuoles complex, with accessory formative vacuoles or reservoir, or both. (ε) Pellicle delicate or absent: pseudopodia often emitted: excretory pore distinct from flagellar pit: reserves fat 6. CHLOROMONADACEAE