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 cuticular extensions for this purpose (fig. 7, a, b). Asplanchnaceae, plankton, dwellers in small pools, are, however, ovoid, and Trochosphaera is spherical and must owe its floating powers to the low density of the liquid in its enormously dilated body-cavity. Lacinularia racemovata and Conochilus form free floating aggregates, the eggs, as laid, hatching and the young settling among the approximated gelatinous tubes of the parents. Some species only frequent the clearest waters; but the lovely transparent Hydatina senta (fig. 2, 3) likes water contaminated by the visits of cattle or the trainings of manure. Drilophagus and Albertia are parasitic on the surface or within the gut of Naid Oligochaete worms: Seisonaceae are ectoparasitic on the Crustacean Nebalia, Proales werneckii forms galls within the Conferva Vaucheria, and P. parasita infests the central jelly of the Phytoflagellate Volvox; P. pelromyzon is a frequent commensal in the gill cavity of some Cladoceran Crustacean Eurycereus lamellatus.

The geographical distribution is cosmopolitan, as is the case with Protozoa and Protophyta of similar habits. A curious fact is that when a new and striking form is found first in one place it is shortly after collected from widely separated areas. In the case of one genus, Gastroschiza, this led to the creation of no less than six generic names.

History and Bibliography.—As rotifers are common in ponds, the first workers with the microscope observed them repeatedly, the first record being that of John Harris in 1696, who found a Bdelloid in a gallipot that had been standing in his window. Leeuwenhoek found and described some tubicolous species; and during the 18th century a fair number of species were observed, figured and described with names. During this time the illusion of a wheel or wheels produced by the ciliary action of the disk had puzzled all observers. C. E. Ehrenberg included the Rotifers in his Infusionsthiere, and described and figured with fair precision many of the genera and species. Dujardin gave a less detailed but more accurate account under the name of Zoophytes Systolides. The next full work was a valuable compilation by W. C. Williamson (best known as a botanist) in Pritchard's Infusoria, in 1861. Much work was done with the gradual introduction of improved methods during the last forty years of the century. The discovery and recognition of the males was made, however, at the close of the fifties. P. H. Gosse collected and described many species, and elucidated the structure of the mastax in 1856. Zoologists of the standing of Huxley, Claus and Leydig added to our knowledge of the anatomy and to the theory of their relations. But the monumental monograph of C. T. Hudson and Gosse containing a new classification, an illustrated description of all the then known species and much information on habits and structure, provided students with an easy access to the domain and stimulated many to work hard at the group. Of these new-comers we may cite C. F. Rousselet, who has found many new species and many unknown males of known species, elucidated habits and faithfully kept record of the publications on the class in the Journal of the Royal Microscopical Society. He has moreover elaborated a method for preserving Rotifera for microscopic observation, so that the types of each observer are now as readily available for comparison as the plant-specimens of the botanist's herbarium. C. Zelinka has given us the most detailed anatomical accounts we possess for several Bdelloidaceae, and was the first to utilize modern methods of microscopic technique on a complete scale.

C. G. Ehrenberg, Die Infusionsthiere als vollkommenere Organismen (1838); F. Dujardin, Histoire naturelle des zoophytes (1841); T. H. Huxley, “Lacinularia socialis,” ''Trans. Micr. Soc.'' i. (1853); P. H. Gosse, “Manducatory Organs in Class Rotifera,” ''Phil. Trans.'' (1856); W. C. Williamson, “The Rotifera” in A. Pritchard's History of the Infusoria (1861); C. T. Hudson and P. H. Gosse, The Rotifera (1886), and supplement (1889); Marcus Hartog, “Rotifera,” in Cambridge Natural History, vol. ii., reprinted 1901; H. S. Jennings, Synopses of North American Invertebrates, xvii., “The Rotifera,” ''Amer. Nat.'' xxxv. (1901); C. F. Rousselet, numerous papers in ''Journ. Micr. Soc. and Journ. Quekett Club; C. Wesenberg-Lund, “Danmarks Rotifera,” in Vid. Meddel. Nat. For.'' Kjöbenhavn (1899); C. Zelinka, “Studien über Rotiferen,” in Zeit. ''Wiss. Zool.'' xliv. (1886), xlvii. (1888), liii. (1891).
 * (Author:Marcus Manuel Hartog)

 ROTORUA, a town of Rotorua county, North Island, New Zealand. It lies in the midst of a remarkable volcanic district generally known as the Hot Spring district, or fancifully as the Wonderland, which covers an area of 660 sq. m. and extends 160 m. from N.E. to S.W. from White Island, an active volcanic cone in the Bay of Plenty to the mountains of Tongariro, Ngaruhoe and Ruapehu in the interior of the island, S.W. of lake Taupo. Rotorua attracts many visitors on account of the beauty and scientific interest of the locality and the bathing

in its various medicinal springs. It is a scattered township lying on the south-western shore of lake Rotorua, amid hills reaching 2600 ft. in the immediate neighbourhood, and much of the volcanic soil supports a rich growth of forest or “bush.”

The springs are principally alkaline, alkaline and siliceous, acidic, or acidic and hepatic (sulphurous). The township includes the Maori village of Ohinemutu, an interesting collection of native dwellings, whose inmates constantly use the numerous rudely excavated baths which are fed by springs varying in temperature from 60&deg; F. to the boiling-point, and are in some cases used for cooking. In the vicinity, on the lake-shore, is the government sanatorium. Two miles south of Rotorua is another native village, Whakarewarewa, where there are geysers as well as hot springs. Four miles from Rotorua, near the centre of the lake, the island of Mokoia rises to 1518 ft. It is partly under grass and partly wooded, and is inhabited by Maoris, by whom it is regarded as holy ground. A short channel connects lake Rotorua with lake Rotoiti to the N.E. At the eastern end steep cliffs rise from the water, and luxuriant vegetation covers the hills. Both this lake and the smaller ones to the east, Rotoehu and Rotoma, have deeply indented shores, and are set in exquisite scenery. The group is known collectively as the Cold Lakes. The waters of Rotoma are of a particularly vivid blue. To the south of Rotoiti is Tikitere, a sombre valley abounding in mud volcanoes, springs and other active volcanic phenomena. Mount Tarawera (16 m. S.E. of Rotorua) is noted for the eruption of June 1886, which changed the outline of several lakes, destroyed the famous Pink and White terraces on the adjoining lake Tarawera, and converted a region of great beauty into a desolate wilderness. A fissure was formed extending nearly 9 m. along the axis of the disturbance, and the mission station of Wairoa (8 m. from Rotorua) on the western shore of the lake was overwhelmed. A line of craters is seen to the south-west. The large lakes Okataina, Kahahi and Rerewhakaitu lie respectively N., W. and S.E. of lake Tarawera.  ROTROU, JEAN DE (1609-1650), French tragic poet, was born on the 19th or 20th of August 1609, at Dreux in Normandy. Rotrou studied at Dreux and at Paris, and, though three years younger than Corneille, began play-writing before him. In 1632 he became playwright to the actors of the Hôtel de Bourgogne. With few exceptions, the only events recorded of his life are the successive appearances of his plays and his enrolment in 1635 in the band of five poets who had the duty of turning Richelieu's dramatic ideas into shape. Rotrou's own first piece, L'Hypocondriaque (pr. 1631), dedicated to the Comte de Soissons, seigneur of Dreux, appeared when he was only eighteen. In the same year he published a collection of Œuvres poetiques, including elegies, epistles and religious verse. His second piece, La Bague de l'oubli (pr. 1635), an adaptation in part from the Sortija del Olvido of Lope de Vega, was much more characteristic. It is the first of several plays in which Rotrou endeavoured to naturalize in France the romantic comedy which had flourished in Spain and England instead of the classical tragedy of Seneca and the classical comedy of Terence. Corneille had leanings in the same direction. Rotrou's brilliant but hasty and unequal work showed throughout marks of a stronger adhesion to the Spanish model. In 1634, when he printed Cleagénor et Doristée (acted 1630), he said he was already the author of thirty pieces; but this applies no doubt to adaptations. Diane (acted 1630; pr. 1633), Les Occasions perdues (acted 1631; pr. 1635), which won for him the favour of Richelieu, and L'Heureuse Constance (acted 1631; pr. 1635), which was praised by Anne of Austria, succeeded each other rapidly, and were all in the Spanish manner. In 1631 Rotrou imitated Plautus in Les Menechmes (pr. 1636), and in 1634 Seneca in his Hercule mourant (pr. 1636). Comedies and tragi-comedies followed. Documents exist showing the sale of four pieces to Antoine de Sommarille for 750 livres tournois in 1636, and in the next year he sold ten to the same bookseller. He spent much time at Le Mans with his patron, M. de Belin, who was one of the opponents of Corneille in the quarrel of the Cid. It has been generally assumed, partly because of a forged letter long accepted as Corneille's, that Rotrou was his generous defender in this matter. He appears to have been no more than neutral, but is credited with an attempt at reconciliation between the parties in a pamphlet printed in 1637, L'Incognu et véritable amy de messieurs de Seudéry et Corneille. M. de Belin died in 1637,