forming branching tubes, simulating a yellow Conferva in mountain torrents; Dinobryon (Ehrb.) (Fig. 1, 8, 15); Stylochrysalis (St.); Uroglena (Ehrb.); Syncrypta (Ehrb.), and Synura (Ehrb.) (Fig. 1, 5) form floating spherical colonies; Zooxanthella (Brandt), symbiotic as “yellow cells” in Radiolaria Foraminifera, Millepora, and many Actinozoa.
Family 2.—Coccolithophoridae. Body invested in a spherical test strengthened by calcareous elements, tangential circular plates, “coccoliths,” “discoliths,” “cyatholiths,” or radiating rods “rhabdoliths.” These are often found in Foraminiferal ooze and its fossil condition, chalk; when coherent as in the complete test, they are known as “coccospheres” and “rhabdospheres.” Coccolithophora (Lohmann), Rhabdosphaera (Haeckel).
Order 3.—CRYPTOMONADACEAE. Contractile vacuole (in freshwater forms) simple; plastids green, more rarely red, brown or absent; reserves starch; holophytic or saprophytic. Cryptomonas (Ehrb.); Paramoeba (Greeff) has yellow plastids and shows two cycles, in the one amoeboid, finally encysting to produce a brood of flagellulae; in the other flagellate, and multiplying by longitudinal fission (it differs from Mastigamoeba in possessing no flagellum in the amoeboid state, though it takes in food amoeba-fashion); Chilomonas (Ehrb.).
Order 4.—CHLOROMONADACEAE. Contractile vacuoles 1-3, a complex of variable arrangement; pellicle delicate; plastids discoid chlorophyll-bodies; reserves oil; eye-spot absent even in active state; holophytic or saprophytic, though with an anterior blind tubular depression simulating a pharynx. Coelomonas (St.), Vacuolaria (Cienk.).
Order 5.—EUGLENACEAE. Vacuole large, a reservoir for one or more accessory vacuoles, contractile and opening to the surface by a canal (“pharynx”) in which are planted one or two strong flagella; pellicle strong often striated; nucleus large, chromatophores green, complex or absent; reserves paramylum granules of definite shape, and oil; nutrition variable; body stiff or “metabolic,” never amoeboid. Among the true Flagellates these are the largest, few being below 40 μ and several attaining 130 μ in length of cell-body (excluding flagellum). Encysted condition common; the green forms sometimes multiply in this state and simulate unicellular Algae.
Family 1.—Euglenidae. Radial (monaxial) forms; nutrition saprophytic or holophytic, mostly one flagellate. (1) Chromatophore large; eye-spot conspicuous. Euglena (Ehrb.) (Fig. 1, 13, 17), with flexible cuticle and metabolic movements (this is probably Priestley’s “green matter” through which he obtained oxygen gas)—a very common genus; Colacium (Ehbg.), in its resting state epizoic on Copepoda, which it colours green; Eutreptia (Perty), biflagellate; Ascoglena (St.); Trachelomonas (Ehrb.), with a hard brown cuticle; Phacus (Nitszche), with a firm rigid pellicle, often symmetrically flattened; Cryptoglena (Ehbg.). (2) Chromatophores absent. Astasia (Duj.), body metabolic; Menoidium (Perty), body not metabolic, somewhat inflected and crescentic; Sphenomonas (Stein), with a short accessory trailing flagellum in front peeled; Distigma (Ehbg.) (Fig. 1, 27, 28), very metabolic, with two unequal flagella and two dark pigment spots.
Family 2.—Peranemidae. Bilaterally symmetrical, often creeping, pharynx highly developed, with a firm rod-like skeleton, sometimes protrusible; nutrition saprophytic and holozoic. Peranema (Ehbg.) and Urceolus (Mereschowsky), uni-flagellate creeping, very metabolic. Petalomonas (St.), uni-flagellate flattened with a deep ventral groove, not metabolic; Heteronema (Duj.) and Tropidoscyphus (St.), with a small accessory anterior trailing flagellum; Anisonema (Duj.) and Entosiphon (St.), with the trailing flagellum as long as the tractellum or even much longer.
Order 6.—VOLVOCACEAE. Contractile vacuole simple anterior; cell always enclosed in a cellulose wall (sometimes gelatinous) perforated by the two (more rarely four, five) diverging anterior flagella; reserves starch; chlorophyll almost always present, except in Polytoma, sometimes masked by a red pigment; nutrition usually holophytic, rarely saprophytic, never holozoic. Brood-division in active state common, radial.
Family 1.—Chlamydomonadidae. Cell-wall firm not gelatinous, rarely forming colonies. Fore-end of the body with two or four (seldom five) flagella. Almost always green in consequence of the presence of a very large single chromatophore. Generally a delicate shell-like envelope of membranous consistence. 1 to 2 simple contractile vacuoles at the base of the flagella. Usually one eye-speck. Division of the protoplasm within the envelope may produce four, eight or more new individuals. This may occur in the swimming or in a resting stage. Also by more continuous fission microgametes of various sizes are formed. Conjugation is frequent.
Genera.—Chlorangium (Stein), lacking green chlorophyll; Chlorogonium (Ehr.) (Fig. 1, 6, 7); Polytoma (Ehr.) (Fig. 2, 8); Chlamydomonas (Ehr.) (Fig. 1, 1, 2, 3); Haematococcus (Agardh) ( = Chlamydococcus, A. Braun, Stein); Protococcus (Conn, Huxley and Martin); Chlamydomonas (Cienkowski), causes red snow and “bloody rain”; Carteria (Diesing), quadri-flagellate; Spondytomorum (Ehrb.), forming floating colonies; Coccomonas (St.); Phacotus (Perty); Zoochlorella (Brandt), is the name given to undetermined Chlamydomonads found multiplying in the resting state within and in symbiotic relation to other Protozoa, to the freshwater sponge, Ephydatia, Hydra viridis, and to the Turbellarian, Convoluta viridis (in which last species the active form has been recognized as a Carteria).
Family 2.—Volvocidae. Cell-wall gelatinous; always associated in colonies; cells, as in Family 1. The number of individuals united to form a colony varies very much, as does the shape of the colony. Reproduction by the continuous division of all or of only certain individuals of the colony, resulting in the production of a daughter colony (from each such individual). In some, probably in all, at certain times copulation of the individuals of distinct sexual colonies takes place, without or with a differentiation of the colonies and of the copulating cells as male and female. The result of the copulation is a resting zygospore (also called zygote or oospermo or fertilized egg), which after a time develops itself into one or more new colonies.
Genera.—Gonium (O. F. Müller) (Fig. 1, 14); Stephanosphaera (Cohn); Pandorina (Bory de Vine); Eudorina (Ehr.); Volvox (Ehr.) (Fig. 1, 18, 20).
The sexual reproduction of the colonies of the Volvocaceae is one of the most important phenomena presented by the Protozoa. In some families of Flagellata full-grown individuals become amoeboid, fuse, encyst, and then break up into flagellate spores which develop simply to the parental form (Fig. 1, 23 to 26). In the Chlamydomonadidae a single adult individual by division produces small individuals, so-called “microgametes.” These conjugate with one another or with similar microgametes formed by other adults (as in Chlorogonium, Fig. 1, 7); or more rarely in certain genera a microgamete conjugates with an ordinary individual megagamete. The result in either case is a “zygote,” a cell formed by fusion of two which divides in the usual way to produce new individuals. The microgamete in this case is the male element and equivalent to a spermatozoon; the megagamete is the female and equivalent to an egg-cell. The zygote is a “fertilized egg,” or oosperm. In some colony-building forms we find that only certain cells produce by division microgametes; and, regarding the colony as a multicellular individual, we may consider these cells as testis-cells and their microgametes as spermatozoa.
Cystoflagellata (Rhynchoflagellata of E. R. Lankester) and Dinoflagellata are scarcely more than subdivisions of Flagellata; but, following O. Bütschli, we describe them separately; the three groups being united into his Mastigophora.
Further Remarks on the Flagellates.—Besides the work of special Protozoologists, such as F. Cienkowski, O. Bütschli, F. v. Stein, F. Schaudinn, W. Saville Kent, &c., the Flagellates have been a favourite study with botanists, especially algologists: we may cite N. Pringsheim, F. Cohn, W. C. Williamson, W. Zopf, P. A. Dangeard, G. Klebs, G. Senn, F. Schütt; the reason for this is obvious. They present a wide range of structure, from the simple amoeboid genera to the highly differentiated cells of Euglenaceae, and the complex colonies of Proterospongia and Volvox. By some they are regarded as the parent-group of the whole of the Protozoa—a position which may perhaps better be assigned to the Proteomyxa; but they seem undoubtedly ancestral to Dinoflagellates and to Cystoflagellates, as well as to Sporozoa, and presumably to Infusoria. Moreover, the only distinction between the Chlamydomonadidae and the true green Algae or Chlorophyceae is that when the former divide in the resting condition, or are held together by gelatinization of the older cell-walls (Palmella state), they round off and separate, while the latter divide by a “party wall” so as to give rise either to a cylindrical filament when the partitions are parallel and the axis of growth constant (Conferva type), or to a plate of tissue when the directions alternate in a plane. The same holds good for the Chrysomonadaceae and Cryptomonadaceae, so that these little groups are included in all text-books of botany. Again among Fungi, the zoospores of the Zoosporous Phycomycetes (Chytrydiaceae, Peronosporaceae, Saprolegniaceae) have the characters of the Bodonidae. Thus in two directions the Flagellates lead up to undoubted Plants. Probably also the Chlamydomonads have an ancestral relation to the Conjugatae in the widest sense, and the Chrysomonadaceae to the Diatomaceae; both groups of obscure affinity, since even the reproductive bodies have no special organs of locomotion. For these reasons the Volvocaceae, Chloromonadaceae, Chrysomonadaceae and Cryptomonadaceae have been united as Phytoflagellates; and the Euglenaceae might well be added to these. It is easy to understand the relation of the saprophytic and the holophytic Flagellates to true plants. The capacity to absorb nutritive matter in solution (as contrasted with the ingestion of solid matter) renders the encysted condition compatible with active growth, and what in holozoic forms is a true hypnocyst, a state in which all functions are put to sleep, is here only a rest from active locomotion, nutrition being only limited by the supply of nutritive matter from without, and—in the
