2. Order Cryptomonadina. Biflagellate, autotrophic, entirely free-living flagellates of fresh water and sea. Chromatophores chiefly brown, characteristic flattened form of cell, unicellular, uninucleate. Reproduction by simple fission. Fertilization proc esses unknown. Important types : Cltilomonas (colourless).
3. Order Chloromonadina. One or two flagella autotrophic; chromatophores with bright green colouring matter, the nature of which is not yet exactly known. One-celled, un:nucleate.
4. Order Euglenoidina. Most have one, a few two, flagellae ; usu ally autotrophic with a peculiar cystostome; (fig. 16) ; some of the autotrophic forms as well as the heterotrophic kinds can also eat solid food. Chromatophore green. In stagnant ponds and cesspools. The structure and division of the nucleus is character istic. Unicellular and uninucleate. Reproduction by simple fis sion; fertilization only known in certain heterotrophic forms such as Scytornonas. Important types : Euglena, Phacus, Traclielo monas, Peranema (heterotrophic).
5. Order Dinoflagellata. Usually with two flagella, lying in a special and characteristic way in two body furrows, one disposed longitudinally and the other spirally around the body (fig. 17). Both the structure and method of division of the nucleus are also characteristic. Most dinoflagellates are autotrophic ; but there are also some that eat living organisms, heterotrophic, and many parasitic forms which flourish in marine animals; these do not possess a flagellum. The autotrophic dinoflagellates are most generally provided with a plated cellulose armour. They live for the most part as plankton organisms in the sea. Usually unicellular—a few of the parasitic forms are multicellular and uninucleate. Reproduction by simple fission or multiple division (swarm-spore formation) fertilization processes unknown. Important types : Ceratium, Gymnodinium (naked) Blastodinium (parasitic) ()Minium (parasitic).
The organism responsible for phosphorescence is Noctiluca miliaris (fig. 18) a rather large swollen bladdery uniflagellate protozoan, faintly red-coloured, heterotrophic, eating living organ isms, which produces an intense light at night but only under the stimulus of a physical or chemical shock. The relationship of this form with other dinoflagellates is shown by the organization of its swarm cells.
6. Order Phytomonadina (V olvocineae). A group containing entirely free-living autotrophous biflagellate species with cup shaped green chromatophores ; a very few species are destitute of chromatophores and feed themselves in the way described above. The lower phytomonadines are unicellular, the higher, multicellu lar. Uninucleate. Reproduction by simple fission, or, in the mul ticellular forms, by rapidly succeeding divisions (fig. 2). Fertili
zation: in the lower forms (Chlamydomonas) hologamous and morphologically isogamous; in the higher forms (Volvox), ooga mous. The zygote has a resting period and following this, in the unicellular forms four individuals slip out, and in the multicellu lar forms, a colony. The reduction division takes place shortly before the germination of the zygote. Important types :— Chlamydomonas (fig. I), Polytoma (heterotrophous) Gonium, Eudorina (fig. 2), Pleodorina, Volvox (fig. 19). See also ALGAE.
7. Order Protomonadina (an artificial group). Heterotrophous organisms with one or two flagella. To this group belong the most important of the parasitic flagellates, the trypanosomes which are put with other forms in the family Herpetomonadinae. The pos session of a so-called blepharoplast is characteristic of the trypan osomes and various closely related forms. This organoid is a little ball of protoplasm lying directly under the basal granule of the flagellum ; it resembles the nucleus in several characteristic properties and divides by simple fission (fig. 7). Earlier it was often regarded as a second nucleus, and was even given the name "kinetonucleus," but this view cannot be supported. The trypano somes have only one flagellum ; this is developed in the blood parasites as a characteristic undulating membrane (fig. 7). The equally parasitic Trypanoplasmae have also a second free flagel lum; the free-living Bodonidae have two free flagella. The trypanosomes are blood parasites of the mammals, birds, amphib ians and fishes ; they swim in the blood plasma and are for the most part carried from one host to another by blood-sucking insects, or (in the case of fishes and frogs) by leeches. The related Leishmaniae are cell-parasites which only pass through the body fluids and are normally not equipped with flagella (fig. 2o). Other relatives of the trypanosomes, the Leptomonadae, live in the intestines of insects that do not suck blood and are sup posed to be the ancestral forms of the trypanosomes. Some trypanosomes are harmless, great numbers on the other hand are pathogenic; e.g., Trypanosoma gambiense, the cause of African sleeping sickness of man ; Trypanosoma rhodesiense, cause of another kind of sleeping sickness; Schizotrypanum cruzi cause of schizotrypanosis of man in Brazil ; Leishmania donovani (fig. 2o) cause of the kala-azar disease of man; Leishmania tropica, cause of Oriental sore; Trypanosoma brucei (fig. 7) cause of the Nagana pest of hoofed animals in Africa; Trypanosoma evansi, cause of the surra pest of hoofed animals in India; Trypanosoma equiperdum, cause of the stallion plague (dourine) of horses.