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LEFT DIDELPHIA 356 DIDYMIUM tise on the Sublime"; the "Institutiones of Quintilian," etc.; but the term is more exclusively applied to all poetical writ- ings devoted to the communication of in- struction on a particular subject, or of a reflective or ethical character, thence called didactic poetry. Among the most celebrated poems of this species may be reckoned in ancient times, that of Lu- cretius, ''De Rerum Natura;" Vergil's "Georgics"; and Horace's "Art of Poetry"; in more recent times, Pope's "Essay on Criticism," and "Essay on Man"; Du Fresnoy's "Art of Painting"; Vida and Boileau's "Art of Poetry." DIDELPHIA, one of the three primary divisions into which the class Mavimalia is divided, when the structure of the reproductive organs is taken as a basis for classification; the other two being the OrmthodeJphia (Monotremata) and the Monodelphia. Didelphia comprises the Marsupialia or those non-placental mammals in which the uterine dilations of the oviducts continue distinct through- out life, opening into two separate vaginse, which in turn open into a uro- genital canal, distinct from the rectum, though embraced by the same sphincter muscle. The young of this subclass are born imperfect, or, as it were, prema- turely, and are carried in the pouch or second womb till perfect. DIDEROT, DENIS (de-dro'), a French philosopher, foremost of the "Encyclopaedists"; born in Langres, Oct. 5, 1713. "Philosophic Reflections"— burned by the hangman and therefore widely circulated — and "A Skeptic's Walk" (1747), were part of a warfare against the church. In the compilation of the "Encyclopjedia" Diderot bore the main burden. He wrote all the articles on technology and industries, on points of philosophy, and even on physics and chemistry. He wrote admirable reports (1765-1767) of the art expositions at the Paris Academy, and some plays. His novel, "The Nun," and his dramatic dia- logue, "Rameau's Nephew," are won- derfully effective pictures of the cor- rupt society of the time. His little sketches "Little Papers" show kindly humor and wit. He died July 31, 1784. DIDIER, CHABLES (ded-ya'), a French poet and novelist (1805-1864); born in Geneva. He wrote some novels designed to awaken patriotic sentiment in Italy, and to make known the strug- gles of the carbonari and other revolu- tionists against Austrian and papal dominion. Among these novels were: "Underground Rome" (2 vols. 1833) ; "The Roman Campagna" (1842) ; and "Fifty Years in the Wilderness" (1857). His lyric poems, "Melodies" (1827), are unimportant. DIDIER, EUGENE LEMOINE, an American prose-writer; born in Balti- more, Md., Dec. 22, 1838. Many of his wrritings have appeared over the signa- ture "Lemoine" and "Timon." He pub- lished the "Life of Edgar A. Poe" (1876); "Life and Letters of Madame Bonaparte" (1879), republished in Lon- don and translated into French and Italian; a "Primer of Criticism" 1883); etc. D I D I TJ S SALVIUS JULIANTJS, MARCUS, a Roman emperor, bom about A. D. 133. Having filled the offices of questor, asdile, and praetor, he was ap- pointed commander of a legion in Ger- many, and subsequently governor of Belgica. For his services against the Catti, he was made governor of Dal- matica, and next of lower Germany. Having distinguished himself in Africa and Asia Minor, he returned to Rome, and, on the assassination of Pertinax, made himself emperor by bribing the praetorian guards. He now assumed the name of Marcus Didius Commodus Sev- erus Julianus; but, after a short reign of two months, was killed in his palace by a common soldier, a. d. 193. DIDO, or ELISSA, the reputed founder of Carthage. She was the daughter of a king of Tyre, and after her father's death her brother Pygmalion murdered her husband Sicharbas, or as Vergil calls him Sichaeus, with the view of obtaining his wealth; but Dido, accompanied by many Tyrians of her party, fled with all the treasure over sea, and landing on the coast of Africa founded Carthage about 860 B. C. The story is told by Vergil with many inventions of his own in the "jEneid" (books i and ii). DIDONCEPHALUS, a monster with a double range of teeth, or a double jaw. DIDUNCULID.ffi, a family of Colum- bacei (pigeons), which some authorities connect with the extinct dodo. DIDUNCULUS, the typical genus of the family Didunculidse. D. stHffirostris inhabits the Navigator Islands. DIDYMIUM, a metallic triad element, symbol Di'", atomic weight 144. It occurs along with cerium and lantha- num in the mineral cerite. It is sepa- rated from cerium by igniting the oxa- late, and treating the resulting oxides with very dilute nitric acid, which does not dissolve the cerium oxide. The fil- tered solution is mixed with sulphuric acid, concentrated by evaporation, and, then a hot solution of potassium sul- phate' is added, which precipitates the