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 saprophytic in the colourless forms, holophytic in the coloured; but these divergent methods are exhibited by different species of the same genus, or even by individuals of one and the same species under different conditions. Binary fission has been widely observed, both in the active condition or after loss of the flagella: it differs from that of true Flagellates in not being longitudinal, but transverse or oblique (fig, 2, 2). Repeated fission (brood-formation) within a cyst has also been observed, as in Pyrocystis and Ceratium; and possibly the chains of Ceratium and other (fig. 2, 5 and 6) genera are due to the non-separation of the brood-cells. Conjugation of adults has been observed in several species, the most complete account being that of Zederbauer on Ceratium hirundinella (marine): either mate puts forth a tube which meets and opens into that of the other (as in some species of Chlamydomonas and Desmids); the two cell-bodies fuse in this tube, and encyst to form a resting zygospore. The Dinoflagellates are relatively large for Mastigophora, many attaining 50 (″) in length. The majority are marine; but some genera (Ceratium, Peridinium) include fresh-water species. Many are highly phosphorescent and some by their abundance colour the water of the sea or pool which they dwell in. Like so many coloured Protista, they frequently possess a pigmented “eye-spot” in which may be sunk a spheroidal refractive body (“lens”).

The affinities of the Dinoflagellata are certainly with those Cryptomonadine Flagellates which possess two unequal flagella; the zoospores or young of the Cystoflagellates are practically colourless Dinoflagellates.

1. Gymnodiniaceae: body naked, or with a simple cellulose or gelatinous envelope; both grooves present. Pyrocystis (Murray), often encysted, spherical or crescentic, becoming free within cyst wall, and escaping whole or after brood-divisions as a form like Gymnodinium; Gymnodinium (Stein); Hemidinium (Stein); Pouchetia (Schütt) (fig. 2, 7) with complex eye-spot; to this group we may refer Polykrikos (Bütschli) (fig. 2, 9), with its metameric transverse grooves and flagella.

2. Prorocentraceae (Schütt) ( = the Adinida of Bergh); body surrounded by a firm shell of two valves without a girdle band; transverse groove absent; transverse flagellum coiled round base of longitudinal. Exuviaeella (Cienk.) (fig. 2, 3); Prorocentrum (Ehrb.) (fig. 2, 4).

3. Peridiniaceae (Schütt); body with a shell of plates, a girdle band along the transverse groove, in which the transverse flagellum lies. Genera, Peridinium (Ehrb.) (fig. 1), fresh-water and marine; Ceratium (Schrank) (fig. 2, 5, 6), fresh-water and marine; Citharistes (Stein); Ornithoceras (Claparède and Lachmann) (fig. 2, 1).

—R. S. Bergh, “Der Organismusder Cilioflagellaten,” ''Morphol. Jahrbuch'', vii. (1881); F. von Stein, Organismus der Infusionsthiere, Abth. 3, 2. Hälfte; Die Naturgeschichte der arthrodelen Flagellaten (1883); Bütschli, “Mastigophora” (in Bronn’s Thierreich, i. Abth. 2), 1881–1887; G. Pouchet, various observations on Dinoflagellates, Journal de l’anatomie et de la physiologie (1885, 1887, 1891); F. Schütt, “Die Peridineen der Plankton Expedition” (Ergebnisse d. Pl. Exed. i. Th. vol. iv. 1895); and “Peridiniales” in Engler and Prantl’s Pflanzenfamilien, vol. i. Abt. 2 b. (1896); Zederbauer, Berichte d. deutschen botanischen Gesellschaft, vol. xx. (1900); Delage and Hérouard, Traité de zoologie concrète, vol. i. La Cellule et les protozoaires (1896).

 DINOTHERIUM, an extinct mammal, fossil remains of which occur in the Miocene beds of France, Germany, Greece and Northern India. These consist chiefly of teeth and the bones of the head. An entire skull, obtained from the Lower Pliocene beds of Eppelsheim, Hesse-Darmstadt, in 1836, measured 4 ft. in length and 3 ft. in breadth, and indicates an animal exceeding the elephant in size. The upper jaw is apparently destitute of incisor and canine teeth, but possesses five molars on each side, with a corresponding number in the jaw beneath. The most remarkable feature, however, consists in the front part of the lower jaw being bent downwards and bearing two tusk-like incisors also directed downwards and backwards. Dinotherium is a member of the group Proboscidea, of the line of descent of the elephants.

 DINWIDDIE, ROBERT (1693–1770), English colonial governor of Virginia, was born near Glasgow, Scotland, in 1693. From the position of customs clerk in Bermuda, which he held in 1727–1738, he was promoted to be surveyor-general of the customs “of the southern ports of the continent of America,” as a reward for having exposed the corruption in the West Indian customs service. In 1743 he was commissioned to examine into the customs service in the Barbadoes and exposed similar corruption there. In 1751–1758 he was lieutenant-governor of Virginia, first as the deputy of Lord Albemarle and then, from July 1756 to January 1758, as deputy for Lord Loudon. He was energetic in the discharge of his duties, but aroused much animosity among the colonists by his zeal in looking after the royal quit-rents, and by exacting heavy fees for the issue of land-patents. It was his chief concern to prevent the French from building in the Ohio Valley a chain of forts connecting their settlements in the north with those on the Gulf of Mexico; and in the autumn of 1753 he sent George Washington to Fort Le Bœuf, a newly established French post at what is now Waterford, Pennsylvania, with a message demanding the withdrawal of the French from English territory. As the French refused to comply, Dinwiddie secured from the reluctant Virginia assembly a grant of £10,000 and in the spring of 1754 he sent Washington with an armed force toward the forks of the Ohio river “to prevent the intentions of the French in settling those lands.” In the latter part of May Washington encountered a French force at a spot called Great Meadows, near the Youghiogheny river, in what is now south-western Pennsylvania, and a skirmish followed which precipitated the French and Indian War. Dinwiddie was especially active at this time in urging the co-operation of the colonies against the French in the Ohio Valley; but none of the other governors, except William Shirley of Massachusetts, was then much concerned about the western frontier, and he could accomplish very little. His appeals to the home government, however, resulted in the sending of General Edward Braddock to Virginia with two regiments of regular troops; and at Braddock’s call Dinwiddie and the governors of Massachusetts, New York, Pennsylvania and Maryland met at Alexandria, Virginia, in April 1755, and planned the initial operations of the war. Dinwiddie’s administration was marked by a constant wrangle with the assembly over money matters; and its obstinate resistance to military appropriations caused him in 1754 and 1755 to urge the home government to secure an act of parliament compelling the colonies to raise money for their protection. In January 1758 he left Virginia and lived in England until his death on the 27th of July 1770 at Clifton, Bristol.

 DIO CASSIUS (more correctly ), (c.  150–235), Roman historian, was born at Nicaea in Bithynia. His father was Cassius Apronianus, governor of Dalmatia and Cilicia under Marcus Aurelius, and on his mother’s side he was the grandson of Dio Chrysostom, who had assumed the surname of Cocceianus in honour of his patron the emperor Cocceius Nerva. After his father’s death, Dio Cassius left Cilicia for Rome (180) and became a member of the senate. During the reign of Commodus, Dio practised as an advocate at the Roman bar, and held the offices of aedile and quaestor. He was raised to the praetorship by Pertinax (193), but did not assume office till the reign of Septimius Severus, with whom he was for a long time on the most intimate footing. By Macrinus he was entrusted with the administration of Pergamum and Smyrna; and on his return to Rome he was raised to the consulship about 220. After this he obtained the proconsulship of Africa, and again on his return was sent as legate successively to Dalmatia and Pannonia. He was raised a second time to the consulship by Alexander Severus, in 229; but on the plea of ill health soon afterwards retired to Nicaea, where he died. Before writing his history of Rome ( or  ), Dio Cassius had dedicated to the emperor Severus an account of various dreams and prodigies which had presaged his elevation to the throne (perhaps the  attributed to Dio by Suidas), and had also written a biography of his fellow-countryman Arrian. The history of Rome, which