Page:EB1911 - Volume 23.djvu/262

Rh the south it is practically extinct; but ten were reported from a reserve in Zululand in 1902. A detached colony exists, however, near Lado, on the Upper Nile. No specimen of this species has ever been brought alive to Europe. Mr F. C. Selous gives the following description of its habits:—

“The square-mouthed rhinoceros is a huge, ungainly looking beast, with a disproportionately large head, a large male standing 6 ft. 6 in. at the shoulder. Like elephants and buffaloes they lie asleep during the heat of the day, and feed during the night and in the cool hours of early morning and evening. Their sight is very bad; but they are quick of hearing, and their scent is very keen; they are, too, often accompanied by rhinoceros birds, which, by running about their heads, flapping their wings, and screeching at the same time, frequently give them notice of the approach of danger. When disturbed they go off at a swift trot, which soon leaves all pursuit from a man on foot far behind; but if chased by a horseman they break into a gallop, which they can keep up for some distance. However, although they run very swiftly, when their size and heavy build is considered, they are no match for an average good horse. They are, as a rule, very easy to shoot on horseback, as, if one gallops a little in front of and on one side of them, they will hold their course, and come sailing past, offering a magnificent broadside shot, while under similar circumstances a prehensile-lipped rhinoceros will usually swerve away in such a manner as only to present his hind-quarters for a shot. When either walking or running, the square-mouthed rhinoceros holds its head very low, its nose nearly touching the ground. When a small calf accompanies its mother, it always runs in front and she appears to guide it by holding the point of her horn upon the little animal's rump; and it is perfectly wonderful to note how in all sudden changes of pace, from a trot to a gallop, or vice versa, the same position is always exactly maintained. During the autumn and winter months (i.e. from March to August) the square-mouthed rhinoceros is usually very fat ; and its meat is then most excellent, being something like beef, but yet having a peculiar flavour of its own. The part in greatest favour among hunters is the hump, which, if cut off whole and roasted just as it is in the skin, in a hole dug in the ground, would, I think, be difficult to match either for juiciness or flavour.”
 * (W. H. F.; R. L.*)

 RHINTHON (c. 323–285 ), Greek dramatist, son of a potter. He was probably a native of Syracuse and afterwards settled at Tarentum. He invented the hilarotiagoedia, a burlesque of tragic subjects. Such travesties were also called phlyaces, (“fooleries”) and their writers phlyacographi. He was the author of thirty-eight plays, of which only a few titles (Amphitryon, Heracles, Orestes) and lines have been preserved, chiefly by the grammarians, as illustrating dialectic Tarentine forms. The metre is iambic, in which the greatest licence is allowed. The Amphitruo of Plautus, although probably imitated from a different writer (Archippus of the Middle Comedy), may be taken as a specimen of the manner in which such subjects were treated. There is no doubt that the hilarotragoedia exercised considerable 'influence on Latin comedy, the Rhinthonica (i.e. fabula) being mentioned by various authorities amongst other kinds of drama known to the Romans. Scenes from these travesties are probably represented in certain vase paintings from Lower Italy, for which see H. Heydemann, “Die Phlyakendarstellungen auf bemalten Vasen,” in Jahrbuch des archäologischen Instituts, i. (1886).

Fragments in monograph by E. Völker (Leipzig, 1887); See also E. Sommerbrodt, De Phlyacographia Graecorum (Breslau, 1875); W. Christ, Geschichte der griechischen Litteratur (1898).  RHIZOPODA, the name given by Dujardin (pro parte, 1838) to a group of Sarcodine Protozoa. They are distinguished by their pseudopods, simple or branched, passing by wide bases into the general surface, never fine radial nor fusing into complex networks; skeleton absent or a simple shell (“test,” “theca”), never (?) a calcareous shell, nor represented by a siliceous network, nor spicules. Reproduction by binary fission; by division or abstriction of buds after the body has become multi-nucleate; or by the resolution of the body into numerous uninucleate zoospores (amœbulæ or flagellulæ) which may conjugate as gametes; plasmodium formation unknown; encystment (in “resting cysts” or “hypnocysts”) common. Without a knowledge of the history it is impossible to distinguish a naked Lobose from the Amoebula (pseudopodiospore) of a Myxomycete or Proteomyxan. As to the name, Dujardin included the thecate Lobosa, the Filosa, and the Reticularia or

(q.v.). The latter had already received the name Foraminifera (for their shells) from d'Orbigny; and as it is impossible to separate naked from thecate Lobosa we have merged his Amoebina (Amibiens) in the larger group. The Filosa were removed by Lang from the Reticularia; in habit and test they are inseparable from the Lobosa; and though their cytoplasm approximates to that of Reticularia, their ectosarc is much less granular, though not free from granules as stated by Lang.

The majority of Rhizopoda are fresh-water forms, some occurring in the film of water on mosses, among Sphagnum, or about the bases of grass-haulms; many, however, are exclusively marine. The aquatic forms generally may lurk among Confervae or higher weeds, or lie in the bottom of decomposing or excrementitious matter in still or slow-flowing waters. Of these some may become temporarily pelagic, floating up by the formation of gas vacuoles (containing probably CO2) in the cytoplasm. It is easy to verify this by placing Arcella (fig. 1, 7) in a drop of water on a glass cover and inverting this over a glass ring; the Arcella sink to the free convex surface of the drop and escape from this most unnatural position by secreting gas-vacuoles; when they float up to contact with the glass cover, so as to touch it by the convex back of the shell, they put forth long pseudopodia which attach themselves to the glass and by their contraction turn the animal over, so that it can crawl over (i.e. under) the glass. Amoeba (Entamoeba) histolytica, Schaudinn, is the cause of tropical dysentery and hepatic abscess in man. Pelomyxa (fig. 1, 5-6) is remarkable for containing symbiotic bacteria. Zooxanthellae (symbiotic green cells—Algae or Flagellates) occur in several species; and Paulinella contains two sausage-shaped blue-green bodies, “chromatophores,” which are probably symbiotic Cyanophyceae. The shell, even when not a simple membrane, has always a continuous inner membrane of a complex nitrogenous substance containing sulphur, allied to keratin and termed pseudochitin. The outer layer when present is composed of little hollow prisms (Arcella, fig. 1, 7), sand, or inorganic matter first swallowed by the animal (Difflugia, Pseudodifflugia), sometimes partially digested (Lecquereuxia), or else of plates secreted as “reserve plates” within the cytoplasm of the animal Cyphoderia (fig. 6, B), Quadrula, Nebelia, Euglypha (figs. 4, 6, A), &c. In Quadrula irregularis alone are the plates said to be calcareous; elsewhere they are always siliceous and simply refractive, so that the silica is probably hydrated (opal). The cement is possibly of silicified pseudochitin. This material is often permeated by a ferric oxide or hydrate, even when it is not coloured rusty brown. Shell formation of the membranous test is by simple surface-excretion; under budding we describe its accomplishment in the aggregated shells.

The “pylome,” or aperture for the protrusion of the protoplasm, is usually single. There are two pylomes at opposite poles in several Filosa (Ditrema), hence united by some authors into a distinct family (fig. 7, 1, 5, 11), and in the gelatinous theca of Trichosphaerium (fig. 5) are numerous permanent pylomic pores. The nucleus is variable in form and character. In Amoeba binucleata two nuclei are always present; and some genera are permanently plurinucleate (Pelomyxa, Arcella, fig. 1, 7). It often gives forth fragments into the cytoplasm, the “chromidia” of R. Hertwig, which, as in (q.v.), may play an important part in reproductive processes. The contractile vacuole (there are two in Arcella, fig. 1, 7) in actively progressing Rhizopods always discharges at the hinder end. Absent or sluggish in marine forms, it is of constant occurrence lin all fresh-water Rhizopods except Pelomyxa.

The pseudopods vary greatly in type. In Amoeba princeps (fig. 1, 4) they are mere promontory-like extensions of the body; in A. radiosa (fig. 1, 1-3) and Trichosphaerium (fig. 5) they are distinct slender processes, tapering, and either blunt or finely pointed at the apex; in Pelomyxa (fig. 1, 5, 6) as in A. (Lithamoeba) discus (fig. 2) they are “eruptive,” hemispherical, formed apparently by the rupture of the ectoplasm, and the outpouring of the endoplasm which at once differentiates a clear outer layer as a new ectoplasm; in Amoeba limax during