PKOTEOMYXA.] PROTOZOA 839 Dujardin, Histoire naturdle des Infusoires, 1841 ; Pdtchard, In fusoria, 1857. Tlie general questions relating to protoplasm and to the consti tution of the Protozoon body as a single cell are dealt with in the following more recent treatises: Max Schultze, Ucber den Organ- is mus der Polythalamicn, 1854, and Ucber das Protoplasma der RhizopodcnundPflanzcnzellen, 1863; and Engelman-n, article "Pro- toplasma" in Hermann s Handworterbuch der Physiologic, 1880. Special works of recent date in which the whole or large groups of Protozoa are dealt with in a systematic manner with illustra tions of the chief known forms are the following : Butschli, " Pro tozoa, " in Bronn s Classen und Ordnungcn dcs ThierreicJis, a comprehensive and richly illustrated treatise now in course of publication, forming the most exhaustive account of the subject matter of the present article which lias been attempted (the writer desires to express his obligation to this work, from the plates of whi .-h a large proportion of the woodcut figures here introduced have been selected); AV. S. Kent, Manual of the Infusoria, 1882 an exhaustive treatise including figures and descriptions of all species of Flagellata, Dinonagellata, Ciliata, and Acinetaria ; Stein, lier Orgunismus der Infusionsthiere, 1867-1882; Haeckel, Die liudiolarien, 1862; Archer, " Kesume of recent contributions to oui knowledge of freshwater Rhizopoda," Quart. Jour, of Micro - s um cal Science, 1876-77; Zopf, " Pilzthiere " (Mycetozoa), in Eiicyklopadie der Naturwissenschaften, Breslau, 1884. We shall now proceed to consider the classes and orders of Protozoa in detail. PllOTOZOA. Characters. Organisms consisting of a single cell or of a group of cells not differentiated into two or more tissues ; incapable of assimilating nitrogen in its diffusible compounds (ammonia or nitrates) or carbon in the form of carbonates, except in special instances which there is reason to regard as directly derived from allied forms not possessing this capacity. The food of the Protozoa is in consequence as a rule taken in the form of particles into the protoplasm either by a specialized mouth or by any part of the naked cell-substance, there to be digested and rendered diffusible. GKADE A. GYMXOMYXA, Lankester, 1878 (64). Ckaractcrs. Protozoa in which the cell-protoplasm is entirely or partially exposed to the surrounding medium, during the active vegetative phase of the life-history, as a naked undifferentiated slime or viscous fluid, which throws itself into processes or " pseudopodia " of various form either rapidly changing or relatively constant. Food can be taken into the protoplasm in the form of solid particles at any point of its surface or at any point of a large exposed area. The distinction into so-called "exoplasm" and " eiidoplasm " recognized by some authors, is not founded on a permanent differentiation of substance corresponding to the cortical and medullary substance of Corticata, but is merely due to the centripetal aggregation of granules lying in a uniform undiffer entiated protoplasm. The cell-individual exhibits itself under four phases of growth and development (1) as a swarm-spore (monadiform young or flagellula) ; (2) as an amoeba form ; (3) as constituent of a plasraodium or cell-fusion or conjugation ; (4) as a cyst, which may be a flagellulavSchwarme)-producing cyst, an amiebula-producingcyst, a covered-spore(chlamydospore) -producing cyt (sporocyst sens, stric., Zopf), or a simple resting cyst which docs not exhibit any fission of its contents (hypnocyst). Any one of these phases may be greatly predominant and specialized whilst the others are relatively unimportant and rapidly passed through. CLASS I. PROTEOMYXA, Lankester. C/uiractcrs. Gymnomyxa which exhibit in the amceba phase various forms of pseudopodia often changing in the same individual, and do not produce elaborate spore cysts; hence they are not re ferable to any one of the subsequent six classes. Mostly minute forms, with small inconspicuous nucleus (absent in some ?). A division into orders and families is not desirable, the group being confessedly an assemblage of negatively characterized or insufficiently known forms. Genera. Vampyrella, Cienkowski (15); Vampyrellidium, Zopf (13) ; Spirophora, Zopf ( = Amoeba radiusa, Perty) ; Haplococcus, Zopf ; Leptophrys, Hertwig and Lesser (16) ; Endyomena, Zopf ; Eiimullu, Sorokin (17) ; Myxastrum, Haeckel (1) ; Entcnmyxa, Cienkowski (18) ; Colpodella, Cienkowski (19) ; Pseudospora, Cien kowski (20) ; Protomonas, Cienkowski (15) ; Diplopliysalis, Zopf (13) ; Gymnococcus, Zopf ; Aphelidium, Zopf ; Pseudosporidium, Zopf ; Protomyxa, Haeckel (1) ; Plasmodiophora, Worouin (21) ; Tctramyxa, Gobel (22) ; Gloidium, Sorokin (23) ; Gymnophrys, Cienkowski (24) ; Mijxodictyum, Haeckel (1) ; Bodcria, Wright (25) ; Biomyxa, Leidy (92) ; Protogcnes, Haeckel (1) ; Protamceba, Haeckel (1); Nuclearia, Cienkowski (26); Monobia, Aim. Schneider (27) ; Archerina, Lankester (14). The forms here brought together include several genera (the first nineteen) referred by Zopf to the Mycetozoa, some again (Vampyrella, Myxastrum, Nuclearia, Monobia) which are by Butschli associated with the Heliozoa, others (Protamceba, Gloidium) referred by the same authority to the Lobosa (Amteba-a) and others (Colpodella, Protomonas) which might be grouped with the lower Flagellata. By grouping them in the manner here adopted we are enabled to characterize those higher groups more satisfactory and to give a just expression to our present Want of that knowledge; of the life-history both of these forms and of the higher Gymnomyxa which when it is obtained may enable us to disperse this hetero geneous class of Proteomyxa. The group has the same function in relation to the other classes of Gymnomyxa which the group Verities has been made to discharge in relation to the better defined phyla of the Metazoa ; it is a lumber-room in which obscure, lowly- developed, and insufficiently known forms may be kept until they can be otherwise dealt with. It is true that, thanks to the researches of Continental botanists (especially Cienkowski and Zopf), we know the life-history of several of these organisms; but we are none the less unable to con nect them by tangible characteristics with other Gymnomyxa. Nearly all of the above-named genera are parasitic 1 rather than " voracious," that is to say, they feed on the organized products of larger organisms both plants and animals (Haplococcus is parasitic in the muscles of the pig), into whose tissues they penetrate, and do not, except in a few cases (Protomyxa, Vampyrella), engulph whole organisms, such as Diatoms, &c. , in their protoplasm. Many live upon and among the putrefying debris of other organisms (e.g., rotting vegetable stems and leaves, excrements of animals), and like the Mycetozoa exert a digestive action upon the substances with which they come in contact comparable to the putrefying aud fermentative activity of the Schizomycttes (Bacteria). Fig. II. illustrates four chief genera of Proteomyxa. Protomyxa aurantiaca was described by Haeckel (1), who found it on shells of Spirula on the coast of the Canary Islands, in the form of orange yellow flakes consisting of branching and reticular protoplasm nourishing itself by the ingestion of Diatoms and Peridinia. This condition is not a simple amoeba phase but a "pliismodium" formed by the union of several young amcebffi. The plasmodium under certain conditions draws itself together into a spherical form and secretes a clear membranous cyst around itself, and then breaks up into some hundreds of Hagellula: or swarm- spores (Fig. II. 2). The diameter of the cyst is - 12 to "2 millimetre. The flagellulae subsequently escape (Fig. II. 3) and swim by the vibratile movement of one end which is drawn out in the form of a coarse flagellum. The swarm -spore now passes into the ama-ba phase (Fig. II. 4). Several of the small amcebte creeping on the surface of the spirula-shell then unite with one another and form a plasmodium which continues to nourish itself by "voracious" inception of Diatoms and other small organisms. The plasmodia may attain a diameter of one millimetre and be visible by the naked eye. A nucleus was not observed by Haeckel in the spores nor in the amoeba phase, nor scattered nuclei in the plasmodium, but it is not improbable that they exist and escaped detection in the living con dition, in consequence of their not being searched for by methods of staining, &c. , which have since come into use. A contractile vacuole does not exist. Vampyrella s2)irogyriK, Cienkowski (Fig. II. 5, 6, 7), is one of several species assigned to the genus Vampyrella, all of which feed upon the living cells of plants. The nucleus previously stated to be absent has been detected by Zopf (13). There is no con tractile vacuole. The amceba phase has an actinophryd character (i.e., exhibits fine radiating pscudopodia resembling those of the sun-animalcule, Actinophrys, one of the Heliozoa). This species feeds exclusively upon the "contents of the cells of Spirogyra, effect ing an entrance through the cell-wall (Fig. II. 5), sucking out the contents, and then creeping on to the next cell. In some species of Vampyrella as many as four amoeba-individuals have been observed to fuse to form a small plasmodium. Cysts are formed which enclose in this species a single amoeba-individual. The cyst often acquires a second or third inner cyst membrane by the shrinking of the protoplasmic body after the first encystment and the subsequent formation of a new membrane. The encysted pro toplasm sometimes merely divides into four parts each of which creeps out of the cyst as an Actinophrys-like amoeba (Fig. II. 7) ; in other instances it "forms a dense spore, the product of which is not known. Protogenes primordialis is the name given by Haeckel to a very simple form with radiating filamentous pseudopodia which he observed in sea-water. It appears to be the same organism as that described and figured by Max Schultze as Amaba porrecta. Schultze s figure is copied in Fig. II. 12. No nucleus and no con tractile vacuole is observed in this form. It feeds voraciously on smaller organisms. Its life-history has not been followed over even a few steps. Hence we must for the present doubt altogether as to its true affinities. Possibly it is only a detached portion of the
protoplasm of a larger nucleate Gymuomyxon. The same kind of