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 his mathematics to the drama; no writer excels him in artful construction, in the arrangement of dramatic scenes, in mere theatrical technique, in the focusing of attention on his chief personages. These are valuable gifts in their way, and Echegaray has, moreover, a powerful, gloomy imagination, which is momentarily impressive. In the drawing of character, in the invention of felicitous phrase, in the contrivance of verbal music, he is deficient. He alternates between the use of verse and prose; and his hesitancy in choosing a medium of expression is amply justified, for the writer’s prose is not more distinguished than his verse. These serious shortcomings may explain the diminution of his vogue in Spain; they will certainly tell against him in the estimate of posterity.

 ÉCHELON (Fr. from échelle, ladder), in military tactics, a formation of troops in which each body of troops is retired on, but not behind, the flank of the next in front, the position of the whole thus resembling the steps of a staircase. To form échelon from line, the parts of the line move off, each direct to its front, in succession, so that when the formation is completed the rightmost body, for example, is farthest advanced, the one originally next on its left is to the left rear, a third is to the left rear of the second, and so on. The word is also used more loosely to express successive lines, irrespective of distances and relative positions, e.g. the “second échelon of ammunition supply,” which is fully a day’s march behind the first.  ECHIDNA, or (Echidna aculeata), one of the few species of Monotremata, the lowest subclass of Mammalia, forming the family Echidnidae. It is a native of Australia, where it chiefly abounds in New South Wales, inhabiting rocky and mountainous districts, where it burrows among the loose sand, or hides itself in crevices of rocks. In size and appearance it bears a considerable resemblance to the hedgehog, its upper surface being covered over with strong spines directed backwards, and on the back inwards, so as to cross each other on the middle line. The spines in the neighbourhood of the tail form a tuft sufficient to hide that almost rudimentary organ. The head is produced into a long tubular snout, covered with skin for the greater part of its length. The opening of the mouth is small, and from it the echidna puts forth its long slender tongue, lubricated with a viscous secretion, by means of which it seizes the ants and other insects on which it feeds. It has no teeth. Its legs are short and strong, and form, with its broad feet and large solid nails, powerful burrowing organs. In common with the other monotremes, the male echidna has its heel provided with a sharp hollow spur, connected with a secreting gland, and with muscles capable of pressing the secretion from the gland into the spur. It is a nocturnal or crepuscular animal, generally sleeping during the day, but showing considerable activity by night. When attacked it seeks to escape either by rolling itself into a ball, its erect spines proving a formidable barrier to its capture, or by burrowing into the sand, which its powerful limbs enable it to do with great celerity. “The only mode of carrying the creature,” writes G. Bennett (Gatherings of a Naturalist in Australasia), “is by one of the hind legs; its powerful resistance and the sharpness of the spines will soon oblige the captor, attempting to seize it by any other part of the body, to relinquish his hold.” In a younger stage of their development, however, the young are carried in a temporary abdominal pouch, to which they are transferred after hatching, and into which open the mammary glands. The echidnas are exceedingly restless in confinement, and constantly endeavour by burrowing to effect their escape. From the quantity of sand and mud always found in the alimentary canal of these animals, it is supposed that these ingredients must be necessary to the proper digestion of their insect food.

There are two varieties of this species, the Port Moresby echidna and the hairy echidna. The last-mentioned is found in south-eastern New Guinea, Australia and Tasmania. In all the spines are mixed with hair; in the Tasmanian race they are nearly hidden by the long harsh fur. Of the three-clawed echidnas (Proechidna) confined to New Guinea there are two species, Bruijn’s echidna (P. bruijnii), discovered in 1877 in the mountains on the north-east coast at an elevation of 3500 ft., and the black-spined echidna (P. nigroaculeata) of larger size—the type specimen measuring 31 in., as against 24 in.—with shorter claws.  ECHINODERMA. The , or “urchin-skinned” animals, have long been a favourite subject of study with the collectors of sea-animals or of fossils, since the lime deposited in their skins forms hard tests or shells readily preserved in the cabinet. These were described during the 18th and first half of the 19th centuries by many eminent naturalists, such as J. T. Klein, J. H. Linck, C. Linnaeus, N. G. Leske, J. S. Miller, L. v. Buch, E. Desor and L. Agassiz; but it was the researches of Johannes Müller (1840–1850) that formed the groundwork of scientific conceptions of the group, proving it one of the great phyla of the animal kingdom. The anatomists and embryologists of the next quarter of a century confirmed rather than expanded the views of Müller. Thus, about 1875, the distinction of Echinoderms from such radiate animals as jelly-fish and corals (see ), by their possession of a body-cavity (“coelom”) distinct from the gut, was fully realized; while their severance from the worms (especially Gephyrea), with which some Echinoderrns were long confused, had been necessitated by the recognition in all of a radial symmetry, impressed on the original bilateral symmetry of the larva through the growth of a special division of the coelom, known as the “hydrocoel,” and giving rise to a set of water-bearing canals—the water-vascular or ambulacral system. There was also sufficient comprehension of the differences between the main classes of Echinoderms—the sea-urchins or Echinoidea, the starfish or Asteroidea, the brittle-stars and their allies known as Ophiuroidea, the worm-like Holothurians, the feather-stars and sea-lilies called Crinoidea, with their extinct relatives the sac-like Cystidea, the bud-formed Blastoidea, and the flattened Edrioasteroidea—while within the larger of these classes, such as Echinoidea and Crinoidea, fair working classifications had been established. But the study that should elucidate the fundamental similarities or homologies between the several classes, and should suggest the relations of the Echinoderma to other phyla, had scarcely begun. Indeed, the time was not ripe for such discussions, still less for the tracing of lines of descent and their embodiment in a genealogical classification. Since then exploring expeditions have made known a host of new genera, often exhibiting unfamiliar types of structure.

Among these the abyssal starfish and holothurians described by W. P. Sladen and H. Théel respectively, in the Report of the “Challenger” Expedition, are most notable. The sea-urchins, ophiuroids and crinoids also have yielded many important novelties to A. Agassiz (“Challenger,” “Blake,” and “Albatross” Expeditions), T. Lyman (“Challenger”), Sladen (“Astrophiura,” Ann. Mag. Nat. Hist., 1879), F. J. Bell (numerous papers in Ann. Mag. Nat. Hist. and in Proc. Zool. Soc.), E. Perrier (“Travailleur” and “Talisman,” Cape Horn and Monaco Expeditions), P. H. Carpenter “Challenger” Reports), and others. The anatomical researches of these authors, as well as those of S. Lovén (“On Pourtalesia” and “Echinologica,” published by the Swedish Academy of Science), H. Ludwig (Morphologische Studien, Leipzig, 1877–1882), O. Hamann (Histologie der Echinodermen, Jena, 1883–1889), L. Cuénot (“Études morphologiques,” ''Arch. Biol., 1891, and papers therein referred to), P. M. Duncan (“Revision of the Echinoidea,” Journ. Linn. Soc., 1890), H. Prouho (“Sur Dorocidaris,” Arch. Zool. Exper., 1888), and many more, need only be mentioned to recall the great advance that has been made. In physiology may be instanced W. B. Carpenter’s proof of the nervous nature of the chambered organ and axial cords of crinoids (Proc. Roy. Soc., 1884), the researches of H. Durham (Quart. Journ. Micr. Sci., 1891) and others into the wandering cells of the body-cavity, and the study of the deposition of the skeletal substance (“stereom”) by Théel (in Festskrift för Lilljeborg, 1896). Knowledge of the development has been enormously extended by numerous embryologists, e.g. Ludwig (op. cit.), E. W. MacBride (“Asterina gibbosa,” Quart. Journ. Micr. Sci., 1896), H. Bury (Quart. Journ. Micr. Sci., 1889, 1895), Seeliger (on “Antedon,” Zool. Jahrb., 1893), S. Goto (“Asterias pallida,” Journ. Coll. Sci. Japan, 1896), C. Grave (“Ophiura,” Mem. Johns Hopkins Univ.'',