THE ENCYCLOPÆDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME VIII SLICE X
Echinoderma to Edward

Articles in This Slice

ECHINODERMA.[1] The ἐχινόδερμα, 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 [Coelentera]), 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., 1899), Théel (“Echinocyamus,” Nov. Act. Soc. Sci. Upsala, 1892), R. Semon (“Synapta,” Jena. Zeitschr., 1888), and Lovén (opp. citt.); and though the theories based thereon may have been fantastic and contradictory, we are now near the time when the results can be co-ordinated and some agreement reached. But the scattered details of comparative anatomy are capable of manifold arrangement, while the palimpsest of individual development is not merely fragmentary, but often has the fragments misplaced. The morphologist may propose classifications, and the embryologist may erect genealogical trees, but all schemes which do not agree with the direct evidence of fossils must be abandoned; and it is this evidence, above all, that gained enormously in volume and in value during the last quarter of the 19th century. The Silurian crinoids and cystids of Sweden have been illustrated in N.P. Angelin’s Iconographia crinoideorum (1878); the Palaeozoic crinoids and cystids of Bohemia are dealt with in J. Barrande’s Système silurien (1887 and 1899); P.H. Carpenter published important papers on fossil crinoids in the Journal of the Geological Society, on Cystidea in that of the Linnean Society, 1891, and, together with R. Etheridge, jun., compiled the large Catalogue of Blastoidea in the British Museum, 1886; O. Jaekel, in addition to valuable studies on crinoids and cystids appearing in the Zeitschrift of the German Geological Society, has published the first volume of Die Stammesgeschichte der Pelmatozoen (Berlin, 1899), a richly suggestive work; the Mesozoic Echinoderms of France, Switzerland and Portugal have been made known by P. de Loriol, G.H. Cotteau, J. Lambert, V. Gauthier and others (see Paléontologie française, Mém. Soc. paléontol. de la Suisse, Trabalhos Comm. Geol. Portugal, &c.); a beautiful and interesting Devonian fauna from Bundenbach has been described by O. Follmann, Jaekel, and especially B. Stürtz (see Verhandl. nat. Vereins preuss. Rheinlande, Paläont. Abhandl., and Palaeontographica); while the multitude of North American palaeozoic crinoids has been attacked by C. Wachsmuth and F. Springer in the Proceedings (1879, 1881, 1885, 1886), of the Philadelphia Academy and the Memoirs (1897) of the Harvard Museum.

The vast mass of material made known by these and many other distinguished writers has to be included in our classification, and that classification itself must be controlled by the story it reveals. Thus it is that a change, characteristic of modern systematic zoology, is affecting the subdivisions of the classes. It is not long since the main lines of division corresponded roughly to gaps in geological history: the orders were Palaeocrinoidea and Neocrinoidea, Palechinoidea and Euechinoidea, Palaeasteroidea and Euasteroidea, and so forth. Or divisions were based upon certain modifications of structure which, as we now see, affected assemblages of diverse affinity: thus both Blastoidea and Euechinoidea were divided into Regularia and Irregularia; the Holothuroidea into Pneumophora and Apneumona; and Crinoids were discussed under the heads “stalked” and “unstalked.” The barriers between these groups may be regarded as horizontal planes cutting across the branches of the ascending tree of life at levels determined chiefly by our ignorance; as knowledge increases, and as the conception of a genealogical classification gains acceptance, they are being replaced by vertical partitions which separate branch from branch. The changes may be appreciated by comparing the systematic synopses at the end of this article with the classification adopted in 1877 in the 9th edition of the Ency. Brit. (vol. vii.), or in any zoological text-book contemporary therewith. In the present stage of our knowledge these minor divisions are the really important ones. For, whereas to one brilliant suggestion of far-reaching homology another can always be opposed, by the detailed comparison of individual growth-stages in carefully selected series of fossils, and by the minute application to these of the principle that individual history repeats race history, it actually is possible to unfold lines of descent that do not admit of doubt. The gradual linking up of these will manifest the true genealogy of each class, and reconstruct its ancestral forms by proof instead of conjecture. The problem of the interrelations of the classes will thus be reduced to its simplest terms, and even questions as to the nature of the primitive Echinoderm and its affinity to the ancestors of other phyla may become more than exercises for the ingenuity of youth. Work has been and is being done by the laborious methods here alluded to, and though the diversity of opinion as to the broader groupings of classification is still restricted only by the number of writers, we can point to an ever-increasing body of assured knowledge on which all are agreed. Unfortunately such allusion to these disconnected certainties as alone might be introduced here would be too brief for comprehension, and we are forced to select a few of the broader hypotheses for a treatment that may seem dogmatic and prejudiced.

Calycinal Theory.—The theory which had most influence on the conceptions of Echinoderms in the two concluding decades of the 19th century was that of Lovén, elaborated by P.H. Carpenter, Sladen and others. This, which may be called the calycinal theory, will be appreciated by comparing the structure of a simple crinoid with that of some other types. A crinoid reduced to its simplest elements consists of three principal portions—(i.) a theca or test enclosing the viscera; (ii.) five arms stretching upwards or outwards from the theca, sometimes single, sometimes branching; (iii.) a stem stretching downwards from the theca and attaching it to the sea-floor (see fig. 1). That part of the theca below the origins of the free arms is called the “dorsal cup”; the ventral part above the origins of the arms, serving as cover to the cup, is known as the “tegmen.” All these parts are supported by plates or ossicles of crystalline carbonate of lime. The cup, in its simplest form, consists of two circlets of five plates. Each plate of the upper circlet supports an arm, and is called a “radial”; the plates of the lower circlet, the “basals,” rest on the stem and alternate with those of the upper circlet, i.e. are interradial in position. Some crinoids have yet another circlet below these, the constituent plates of which are called “infrabasals,” and are situated radially. The tegmen in most primitive forms, as well as in the embryonic stages of the living Antedon (fig. 2), consists of five large triangular plates, alternating with the radials, and called “orals,” because they roof over the mouth. In addition to these three or four circlets of plates, two other elements were once supposed essential to the ideal crinoid: the dorso-central and the oro-central. The former term was applied to a flattened plate observed in the embryonic stage of a single genus (Antedon) at that end of the stem attached to the sea-floor, and comparable to the foot of a wine-glass (fig. 2). In some crinoids which have no trace of a stem (e.g. Marsupites) a pentagonal plate is found at the bottom of the cup, where the stem would naturally have arisen (“centrale” in fig. 1); and since it was believed that the stem always grew by addition of ossicles immediately below the infrabasals, it was inferred that this pentagonal plate was the centro-dorsal in its primitive position, as though the wine-glass had been evolved from a tumbler by pulling the bottom out to form the foot. The oro-central was, it must be admitted, a theoretical conception due to a desire for symmetry, and was not confirmed by anything better than some erroneous observations on certain fossils, which were supposed to show a plate at the oral pole between the five orals; but this plate, so far as it exists at all, is now known to be nothing but an oral shifted in position. The theory was that all the plates just described, and more particularly those of the cup, which were termed “the calycinal system,” could be traced, not merely in all crinoids, but in all Echinoderms, whether fixed forms such as cystids and blastoids, or free forms such as ophiuroids and echinoids, even—with the eye of faith—in holothurians. It was admitted that these elements might atrophy, or be displaced, or be otherwise obscured; but their complete and symmetrical disposition was regarded as typical and original. Thus the genera exhibiting it were regarded as primitive, and those orders and classes in which it was least obscured were supposed to approach most nearly the ancestral Echinoderm. Every one knows that an “apical system,” composed of two circlets known as “genitals” or basals and “oculars” or radials, occurs round the aboral pole of echinoids (fig. 3, A), and that a few genera (e.g. Salenia, fig. 3, B) possess a sub-central plate (the “suranal”), which might be identified with the centro-dorsal. It is also the case that many asterids (fig. 3, D) and ophiurids (fig. 3, C) have a similar arrangement of plates on the dorsal (i.e. aboral) surface of the disk. Accepting the homology of these apical systems with the calycinal system, the theory would regard the aboral pole of a sea-urchin or starfish as corresponding in everything, except its relations to the sea-floor, with the aboral pole of a fixed echinoderm.

The theory has been vigorously opposed, notably by Semon (op. cit.), who saw in the holothurians a nearer approach to the ancestral form than was furnished by any calyculate echinoderm, and by the Sarasins, who derived the echinoids from the holothurians through forms with flexible tests (Echinothuridae, which, however, are now known to be specialized in this respect). The support that appeared to be given to the theory by the presence of supposed calycinal plates in the embryo of echinoids and asteroids has been, in the opinion of many, undermined by E.W. MacBride (op. cit.), who has insisted that in the fixed stage of the developing starfish, Asterina, the relations of these plates to the stem are quite different from those which they bear in the developing and adult crinoid. But, however correct the observations and the homologies of MacBride may be, they do not, as Bury (op. cit.) has well pointed out, afford sufficient grounds for his inference that the abactinal (i.e. aboral) poles of starfish and crinoids are not comparable with one another, and that all conclusions based on the supposed homology of the dorso-central of echinoids and asteroids with that of crinoids are incorrect. Bury himself, however, has inflicted a severe blow on the theory by his proof that the so-called oculars of Echinoidea, which were supposed to represent the radials, are homologous with the “terminals” (i.e. the plates at the tips of the rays) in Asteroidea and Ophiuroidea, and therefore not homologous with the radially disposed plates often seen around the aboral pole of those animals. For, if these radial constituents of the supposed apical system in an ophiurid have really some other origin, why can we not say the same of the supposed basals? Indeed, Bury is constrained to admit that the view of Semon and others may be correct, and that these so-called calycinal systems may not be heirlooms from a calyculate ancestor, but may have been independently developed in the various classes owing to the action of similar causes. That this view must be correct is urged by students of fossils. Palaeontology lends no support to the idea that the dorso-central is a primitive element; it exists in none of the early echinoids, and the suranal of Saleniidae arises from the minor plates around the anus. There is no reason to suppose that the central apical plate of certain free-swimming crinoids has any more to do with the distal foot-plate of the larval Antedon stem than has the so-called centro-dorsal of Antedon itself, which is nothing but the compressed proximal end of the stem. As for the supposed basals of Echinoidea, Asteroidea and Ophiuroidea, they are scarcely to be distinguished among the ten or more small plates that surround the anus of Bothriocidaris, which is the oldest and probably the most ancestral of fossil sea-urchins (fig. 5). A calycinal system may be quite apparent in the later Ophiuroidea and in a few Asteroidea, but there is no trace of it in the older Palaeozoic types, unless we are to transfer the appellation to the terminals. Those plates are perhaps constant throughout sea-urchins and starfish (though it would puzzle any one to detect them in certain Silurian echinoids), and they may be traced in some of the fixed echinoderms; but there is no proof that they represent the radials of a simple crinoid, and there are certainly many cystids in which no such plates existed. Lovén and M. Neumayr adduced the Triassic sea-urchin Tiarechinus, in which the apical system forms half of the test, as an argument for the origin of Echinoidea from an ancestor in which the apical system was of great importance; but a genus appearing so late in time, in an isolated sea, under conditions that dwarfed the other echinoid dwellers therein, cannot seriously be thought to elucidate the origin of pre-Silurian Echinoidea, and the recent discovery of an intermediate form suggests that we have here nothing but degenerate descendants of a well-known Palaeozoic family (Lepidocentridae). But to pursue the tale of isolated instances would be wearisome. The calycinal theory is not merely an assertion of certain homologies, a few of which might be disputed without affecting the rest: it governs our whole conception of the echinoderms, because it implies their descent from a calyculate ancestor—not a “crinoid-phantom,” that bogey of the Sarasins, but a form with definite plates subject to a quinqueradiate arrangement, with which its internal organs must likewise have been correlated. To this ingenious and plausible theory the revelations of the rocks are more and more believed to be opposed.

Pentactaea Theory.—In opposition to the calycinal theory has been the Pentactaea theory of R. Semon. There have always been many zoologists prepared to ascribe an ancestral character to the holothurians. The absence of an apical system of plates; the fact that radial symmetry has not affected the generative organs, as it has in all other recent classes; the well-developed muscles of the body-wall, supposed to be directly inherited from some worm-like ancestor; the presence on the inner walls of the body in the family Synaptidae of ciliated funnels, which have been rashly compared to the excretory organs (nephridia) of many worms; the outgrowth from the rectum in other genera of caeca (Cuvierian organs and respiratory trees), which recall the anal glands of the Gephyrean worms; the absence of podia (tube-feet) in many genera, and even of the radial water-vessels in Synaptidae; the absence of that peculiar structure known in other echinoderms by the names “axial organ,” “ovoid gland,” &c.; the simpler form of the larva—all these features have, for good reason or bad, been regarded as primitive. Some of the more striking of these features are confined to Synaptidae; in that family too the absence of the radial water-vessels from the adult is correlated with continuity of the circular muscle-layer, while the gut runs almost straight from the anterior mouth to the posterior anus. Early in the life-history of Synapta occurs a stage with five tentacles around the mouth, and into these pass canals from the water-ring, the radial canals to the body-wall making a subsequent, and only temporary, appearance (fig. 4). Semon called this stage the Pentactula, and supposed that, in its early history, the class had passed through a similar stage, which he called the Pentactaea, and regarded as the ancestor of all Echinoderms. It has since been proved that the five tentacles with their canals are interradial, so that one can scarcely look on the Pentactula as a primitive stage, while the apparent simplicity of the Synaptidae, at least as compared with other holothurians, is now believed to be the result of regressive changes. The Pentactaea, at all events as it sprang from the brain of Semon, must pass to the limbo of mythological ancestors.

Pelmatozoic Theory.—The rejection of the calycinal and Pentactaea theories need not scatter our conceptions of Echinoderm structure back into the chaos from which they seemed to have emerged. The idea of a calyculate ancestor, though by no means connoting fixation, turned men’s minds in the direction of the fixed forms, simply because in them the calyx was best developed. The Pentactaea again suggested a search for some primitive type in which quinqueradiate symmetry was exhibited in circumoral appendages, but had not affected the nervous, water-vascular, muscular or skeletal systems to any great extent, and the generative organs not at all. Study of the earliest larval stages has always led to the conclusion that the Echinoderms must have descended from some freely-moving form with a bilateral symmetry, and, connecting this with the ideas just mentioned, we reach the conception that this supposed bilateral ancestor (or Dipleurula) may have become fixed, and may have gradually acquired a radial symmetry in consequence of its sedentary mode of life. The different extent of quinqueradiate symmetry in the different classes would thus depend on the period at which they diverged from the sedentary stock. The tracing of this history, and the explanation of the general characters of Echinoderms and of the differentiating features of the classes in accordance therewith, constitutes the Pelmatozoic theory.

The word “Pelmatozoa” literally means “stalked animals,” but the name is now used to denote all Cystidea, Blastoidea, Crinoidea and Edrioasteroidea, as opposed to the other classes, which may be called Eleutherozoa. Many Pelmatozoa have, it is true, no stalk, while some are freely-moving, but all agree in the possession of certain characters obviously connected with a fixed mode of life. Thus, the mouth is central and turned away from the sea-floor; the animal does not seize its food by tentacles, limbs or jaws, neither does it move in search of it, but a series of ciliated grooves which radiate from the mouth sweep along currents of water, in the eddies of which minute food-particles are caught up and carried down into the gullet; the undigested food is driven out through an anus which is on the upper or oral side of the theca, but as far distant as practicable from the mouth and ciliated grooves. Such characters are found in any primitive, sedentary group. More peculiarly Echinoderm features, in which the Pelmatozoan nature is manifest, are the enclosing of the viscera in a calcified and plated theca, for protection against those enemies from which a fixed animal cannot flee; the development, at the aboral pole of this theca, of a motor nerve-centre giving off branches to the stroma connecting the various plates of the theca and of its brachial, anal, and columnar extensions, and thus co-ordinating the movements of the whole skeleton; the absence of suckers from the podia, which, when present, are respiratory, not locomotor, in function. There are other features of most, if not all, Pelmatozoa that appear to be due to a fixed existence; but those are also found in the Eleutherozoa. The Pelmatozoic theory thus regards the Pelmatozoa as the more ancestral forms, and the Pelmatozoan stage as one that must have been passed through by all Echinoderms during their evolution from the Dipleurula. It might be possible to prove the origin of all classes from Pelmatozoa, without thereby explaining the origin of such fundamental features as radial symmetry, the developmental metamorphosis, and the torsion that affects both gut and body-cavities during that process; but the acceptance of a Dipleurula as the common ancestor necessitates an explanation of these features. Such explanation is an integral part of the Pelmatozoic theory, but is provided by no other.

The evidence for the Pelmatozoic theory is supplied by palaeontology, embryology, the comparative anatomy of the classes, and a consideration of other phyla. Palaeontology, so far as it goes, is a sure guide, but some of the oldest fossiliferous rocks yield remains of distinctly differentiated crinoids, asteroids and echinoids, so that the problem is not solved merely by collecting fossils. Two lines of argument appear fruitful. First, a comparison of the relative numbers of the representatives of the various classes at different epochs; according to this they may be placed in the following order, with the oldest first: Cystidea, Crinoidea, Blastoidea, Asteroidea, Ophiuroidea, Echinoidea. As for Holothuroidea, the fossil evidence allows us to say no more than that the class existed in early Carboniferous times, if not before. The second method is to work out by slow and sure steps the lines of descent of the different families, orders, and classes, and so either to arrive at the ancestral form of each class, or to plot out the curve of evolution, which may then legitimately be projected into “the dark backward and abysm of time.” In this way the many highly modified orders of Cystidea may be traced back to a simple, many-plated ancestor with little or no radiate symmetry (see below). All the complicated structures of Blastoidea are evolved from a fairly simple type, which in its turn is linked on to one of the cystid orders. That the crinoids are all deducible from some such simple form as that above described under the head “calycinal theory,” is now generally admitted. Although, in the extreme correlation of the radial food-grooves, nerves, water-vessels, and so forth, with a radiate symmetry of the theca, such a type differs from the Cystidea, while in the possession of jointed processes from the radial plates, bearing the grooves and the various body-systems outwards from the theca, it differs from all other Echinoderms, nevertheless ancient forms are known which, if they are not themselves the actual links, suggest how the crinoid type may have been evolved from some of the more regular cystids. The fourth class of Pelmatozoa—the Edrioasteroidea—differs from the others in the structure of its ambulacra. As in all Pelmatozoa these seem to have borne ciliated food-grooves protected by movable covering-plates (fig. 11). Beneath each food-groove was a radial water-vessel and probably a nerve and blood-vessel, all which structures passed either between certain regularly arranged thecal plates, or along a furrow floored by those plates, which were then in two alternating series. The important and distinctive feature is the presence of pores between the flooring-plates, on either side of the groove; and these, we cannot doubt, served for the passage of podia. Thus in a highly developed edrioasteroid, such as Edrioaster itself (fig. 11), there was a true ambulacrum, apparently constructed like that of a starfish, but differing in the possession of a ciliated food-groove protected by covering-plates. The simpler forms of Edrioasteroidea, with their more sac-like body and undifferentiated plates, may well have been derived from early Cystidea of yet simpler structure, and there seems no reason to follow Jaekel in regarding the class as itself the more primitive. Turning to fossil Asteroidea, we find the earlier ophiurids scarcely distinguishable from the asterids, while in the alternation of the ambulacrals, which undoubtedly correspond to the flooring-plates of Edrioaster, both groups approach the Pelmatozoan type. These facts have been expressed by Sturtz in his names Encrinasteriae and Ophio-encrinasteriae. There is no difficulty in deducing the highly differentiated asterids and ophiurids of a later day from these simpler types. The evolution of the modern Echinoidea from their Palaeozoic ancestors is also well understood, but in this case the ancestral form to which the palaeontologist is led does not at first sight present many resemblances to the Pelmatozoa. It is, however, characterized by simplicity of structure, and a short description of it will serve to clear the problem from unnecessary difficulties. Bothriocidaris (fig. 5), a small echinoid from the Ordovician rocks of Esthonia, is in essential structure just the form demanded by comparative palaeontology to make a starting-point. It is spheroidal, with the mouth and anus at opposite poles; there are five ambulacra, and the ambulacral plates are large, simple and alternating, each being pierced by two podial pores which lie in a small oval depression; the ambulacrals next the mouth form a closed ring of ten plates; the interambulacrals lie in single columns between the ambulacra, and are separated from the mouth-area by the proximal ambulacrals just mentioned, and sometimes by the second set of ambulacrals also; the ambulacra end in the five oculars or terminals, which meet in a ring around the anal area and have no podial pores, but one of them serves as a madreporite; within this ring is a star-shaped area filled with minute irregular plates, none of which can safely be selected as the homologues of the so-called basals or genitals of later forms; within the ring of ambulacrals around the mouth are five somewhat pointed plates, which Jaekel regards as teeth, but which can scarcely be homologous with the interradially placed teeth of later echinoids, since they are radial in position; small spines are present, especially around the podial pores. The position of the pores near the centre of the ambulacrals in Bothriocidaris need not be regarded as primitive, since other early Palaeozoic genera, not to mention the young of living forms, show that the podia originally passed out between the plates, and were only gradually surrounded by their substance; thus the original structure of the echinoid ambulacra differed from that of the early asteroid in the position of the radial vessels and nerves, which here lie beneath the plates instead of outside them. To this point we shall recur; palaeontology, though it suggests a clue, does not furnish an actual link either between Echinoidea and Asteroidea, or between those classes and Pelmatozoa.

The argument from embryology leads further back. First, as already mentioned, it outlines the general features of the Dipleurula; secondly, it indicates the way in which this free-moving form became fixed, and how its internal organs were modified in consequence; but when we seek, thirdly, for light on the relations of the classes, we find the features of the adult coming in so rapidly that such intermediate stages as may have existed are either squeezed out or profoundly modified. The difficulty of rearing the larvae in an aquarium towards the close of the metamorphosis may account for the slight information available concerning the stages that immediately follow the embryonic. Another difficulty is due to the fact that the types studied, and especially the crinoid Antedon, are highly specialized, so that some of the embryonic features are not really primitive as regards the class, but only as regards each particular genus. Thus inferences from embryonic development need to be checked by palaeontology, and supplemented by comparison of the anatomy of other living genera.

Minute anatomical research has also aided to establish the Pelmatozoic theory by the gradual recognition in other classes of features formerly supposed to be confined to Pelmatozoa. Thus the elements of the Pelmatozoan ventral groove are now detected in so different a structure as the echinoid ambulacrum, while an aboral nervous system, the diminished representative of that in crinoids, has been traced in all Eleutherozoa except Holothurians. The broader theories of modern zoology might seem to have little bearing on the Echinoderma, for it is not long since the study of these animals was compared to a landlocked sea undisturbed by such storms as rage around the origin of the Vertebrata. This, however, is no more the case. The conception of the Dipleurula derives its chief weight from the fact that it is comparable to the early larval forms of other primitive coelomate animals, such as Balanoglossus, Phoronis, Chaetognatha, Brachiopoda and Bryozoa. So too the explanation of radial symmetry and torsion of organs as due to a Pelmatozoic mode of life finds confirmation in many other phyla. Instead of discussing all these questions separately, with the details necessary for an adequate presentation of the argument, we shall now sketch the history of the Echinoderms in accordance with the Pelmatozoic theory. Such a sketch must pass lightly over debatable ground, and must consist largely of suggestions still in need of confirmation; but if it serves as a frame into which more precise and more detailed statements may be fitted as they come to the ken of the reader, its object will be attained.

Evolution of the Echinoderms.—It is reasonable to suppose that the Coelomata—animals in which the body-cavity is divided into a gut passing from mouth to anus and a hollow (coelom) surrounding it—were derived from the simpler Coelentera, in which the primitive body-cavity (archenteron) is not so divided, and has only one aperture serving as both mouth and anus. We may, with Sedgwick, suppose the coelom to have originated by the enlargement and separation of pouches that pressed outwards from the archenteron into the thickened body-wall (such structures as the genital pouches of some Coelentera, not yet shut off from the rest of the cavity), and they would probably have been four in number and radially disposed about the central cavity. The evolution of this cavity into a gut is foreshadowed in some Coelentera by the elliptical shape of the aperture, and by the development at its ends of a ciliated channel along which food is swept; we have only to suppose the approximation of the sides of the ellipse and their eventual fusion, to complete the transformation of the radially symmetrical Coelenterate into a bilaterally symmetrical Coelomate with mouth and anus at opposite ends of the long axis. We further suppose that of the four coelomic pouches one was in front of the mouth, one behind the anus, and one on each side. Such an animal, if it ever existed, probably lived near the surface of the sea, and even here it may have changed its medusoid mode of locomotion for one in the direction of its mouth. Thus the bilateral symmetry would have been accentuated, and the organism shaped more definitely into three segments, namely (1) a preoral segment or lobe, containing the anterior coelomic cavity; (2) a middle segment, containing the gut, and the two middle coelomic cavities; (3) a posterior segment, containing the posterior coelomic cavity, which, however, owing to the backward prolongation of the anus, became divided into two—a right and left posterior coelom. Each of these cavities presumably excreted waste products to the exterior by a pore. There was probably a nervous area, with a tuft of cilia, at the anterior end; while, at all events in forms that remained pelagic, the ciliated nervous tracts of the rest of the body may be supposed to have become arranged in bands around the body-segments. Such a form as this is roughly represented to-day by the Actinotrocha larva of Phoronis, the importance of which has been brought out by Masterman. But only slight modifications are required to produce the Tornaria larva of the Enteropneusta and other larvae, including the special type that is inferred from the Dipleurula larval stages of recent forms to have characterized the ancestor of the Echinoderms. We cannot enter here into all the details of comparison between these larval forms; amid much that is hypothetical a few homologies are widely accepted, and the preceding account will show the kind of relation that the Echinoderms bear to other animals, including what are now usually regarded as the ancestors of the Chordata (to which back-boned animals belong), as well as the nature of the evidence that their study has been, or may be, made to yield. How the hypothetical Dipleurula became an Echinoderm, and how the primitive Echinoderms diverged in structure so as to form the various classes, are questions to which an answer is attempted in the following paragraphs:—

Confining our attention to that form of Dipleurula (fig. 6) which, it is supposed, gave rise to the Echinoderma, we infer from embryological data that its special features were as follow:—The anterior coelomic cavity was wholly or partially divided, and from each half a duct led to the exterior, opening at a pore near the middle line of the back. The middle cavities were smaller, and the ducts from them came to unite with those from the anterior cavities, and no longer opened directly to the exterior; whether these cavities were already specialized as water-sacs cannot be asserted, but they certainly had become so at a slightly later stage. The posterior cavities were the largest, but what had become of their original opening to the exterior is uncertain. The genital products were derived from the lining of the coelomic cavities, but it would not be safe to say that any particular region was as yet specialized for generation. The epithelium of the outer surface was probably ciliated, and a portion of it in the preoral lobe differentiated as a sense-organ, with longer cilia and underlying nerve-centre, from which two nerves ran back below the ventral surface. Into the space between the walls of the coelom and the outer body-wall, originally filled with jelly, definite cells now wandered, chiefly derived from the coelomic walls. Some of these cells produced muscles and connective tissue; others absorbed and removed waste products, iron salts, calcium carbonate and the like, and so were ready to be utilized for the deposition of pigment or of skeletal substance. In some of these respects the Dipleurula may have diverged from the ancestor of Enteropneusta and of other animals, but it could not as yet have been recognized as echinodermal by a zoologist, for it presented none of the structural peculiarities of the modern adult echinoderm.

Now ensued the great event that originated the phylum—the discovery of the sea-floor. This being apprehended by the sensory anterior end, it was by that end that the Dipleurula attached itself; not, however, by the pole, since that would have interfered at once with the sensory organ, but a little to one side, the right side being the one chosen for a reason we cannot now fathom; it may be that fixation was facilitated by the presence of the pore on that side, and by the utilization of the excretion from it as a cement. The first result was that which is always seen to follow in such cases—the passage of the mouth towards the upper surface (fig. 7). As it passed up along the left side, the gut caught hold of the left water-sac and pulled it upwards, curving it in the process; this being attached to the left duct from the anterior body-cavity, this structure with its water-pore was also pulled up, and the pore came to lie between mouth and anus. The forward portion of the anterior coelom shared in the constriction and elongation of the preoral lobe; but its hinder portion was dragged up along with the water-pore and formed a canal lying along the outer wall (the parietal canal). As the gut coiled, it pressed inwards the middle of the left posterior coelom of the Dipleurula, and drew the whole towards the mouth, while the corresponding cavity on the right was pressed down by the stomach towards the fixed end of the animal and became involved in the elongation of that region. These changes, which may still be traced in the development of Antedon, resulted in the primitive Pelmatozoön (fig. 7), represented in the rocks by such a genus as Aritocystis (fig. 8). The pear-shaped body is encased in a theca formed by a number of polygonal plates, and is attached by its narrow end. On the broad upper surface are four openings, that nearest the centre being the mouth, which is slit-like, and that nearest the periphery being the anus. The two other openings are minute, and placed between those two; one close to the mouth is almost certainly the water-pore, while that nearer the anus is regarded as a genital aperture. Which of the coelomic cavities this last is connected with is uncertain, for there is considerable doubt as to the origin of the genital glands in the embryonic development of recent echinoderms. It seems clear, however, that there was but a single duct and a single bunch of reproductive cells, as in the holothurians, though perhaps bifurcate, as in some of those animals. The line between mouth and anus, along which these openings are situate, corresponds with the plane of union between the two horns of the curved left posterior coelom, the united walls of which form the “dorsal mesentery.” Since this must have, on our theory, enclosed the parietal canal from the anterior coelom, it is possible that the genital products were developed from the lining cells of that cavity, and that the genital pore was nothing but its original pore not yet united with that from the water-sac. The concrescence of these pores can be traced in other cystids; but as the genital organs became affected by radial symmetry the original function of the duct was lost, and the reproductive elements escaped to the exterior in another way. Aristocystis may have had ciliated food-grooves leading to its mouth, but these have left no traces on the structure of the test. Traces, however, are perceptible in genera believed to be descended from such a simple type, and the majority may be grouped under two heads. One group includes those in which the grooves wander outwards from the mouth over the thecal plates, which gradually become arranged regularly on either side of the grooves, while further extensions ascend from the grooves on small jointed processes called “brachioles” (fig. 9). In the other group the grooves do not tend so much to stretch over the theca as to be raised away from it on relatively larger brachioles, arising close around the mouth (fig. 10).

These two types are, in the main, correlated with two gradual differentiations in the minute structure of the thecal plates. Originally the calcareous substance of the plates (stereom) was pierced by irregular canals, more or less vertical, and containing strands of the soft tissue (stroma) that deposited the stereom, as well as spaces filled with fluid. In the former group (fig. 9) these canals became connected in pairs (diplopores) still perpendicular to the surface, and this structure, combined with that of the grooves, characterizes the order—Diploporita. In the latter group (fig. 10) the canals, that is to say, the stroma-strands, came to lie parallel to the surface and to cross the sutures between the plates, which were thus more flexibly and more strongly united: since the canals crossing each suture naturally occupy a rhombic area, the order is called Rhombifera. At first the grooves were three, one proceeding from each end of the mouth-slit, and the third in a direction opposed to the anus; with reference to the Pelmatozoan structure, the anal side may be termed posterior, and this groove anterior. Eventually each lateral groove forked, so that there were five grooves. These gradually impressed themselves on the theca and influenced the arrangement of the internal organs: it is fairly safe to assume that nerves, blood-vessels and branches from the water-sac stretched out along with these grooves, each system starting from a ring around the gullet. At last a quinqueradiate symmetry influenced the plates of the theca, partly through the development of a plate at the end of each groove (terminal), partly through plates at the aboral pole of the theca (basals and infrabasals) arising in response to mechanical pressure, but soon intimately connected with the cords of an aboral nervous system. Before the latter plates arose, the stem had developed by the elongation and constriction of the fixed end of the theca, the gradual regularization of the plates involved, and their coalescence into rings. The crinoid type was differentiated by the extension of the food-grooves and associated organs along radial outgrowths from the theca itself. These constituted the arms (brachia), and five definite radial plates of the theca were specialized for their support. These radials may be homologous with the terminals already mentioned, but this is neither necessary nor certain. In this development of brachial extensions of the theca the genital organs were involved, and their ripe products formed at the ends of the brachia or in the branches therefrom. The remains of the original genital gland within the theca became the “axial organ” surrounded by the “axial sinus” derived from the anterior coelom, and this again by structures derived from the right posterior coelom, which, as explained above, had been depressed to the aboral pole. These last structures formed a nervous sheath around the axial sinus with its blood-vessels, and became divided into five lobes correlated with the five basals (the “chambered organ”) and forming the aboral nerve-centre. Before these changes were complete the Holothurioidea must have diverged, by the assumption of a crawling existence. Thus in them the mouth and anus reverted to opposite poles, and only the torsion of the gut and coelom, and the radial extensions of the nervous, water-vascular and blood-vascular systems, testified to their Pelmatozoan ancestry. The ciliated grooves, no longer needed for the collection of food, closed over, and are still traceable as ciliated canals overlying the radial nerves. At the same time the thecal plates degenerated into spicules. The Edrioasteroidea followed a different line from that of the cystids above mentioned and their descendants. The theca became sessile, and in its later developments much flattened (fig. 11). Mouth, water-pore and anus remained as in Aristocystis, but the five ciliated grooves radiated from the mouth between the thecal plates rather than over them, and were, as usual, protected by covering-plates. The important feature was the extension of radial canals from the water-sac along these grooves, with branches passing between the flooring-plates of the grooves (fig. 12, A). The resemblance of the flooring-plates to the ambulacral ossicles of a starfish is so exact that one can explain it only by supposing similar relations of the water-canals and their branches (podia). On the thinly plated under surface of well-preserved specimens of Edrioaster are seen five interradial swellings (fig. 11, B). These are likely to have been produced by the ripe genital glands, which may have extruded their products directly through the membranous integument of the under side. No other way out for them is apparent, and it is clear that Edrioaster was not permanently and solidly fixed to the sea-floor.

Now comes a great change, unfortunately difficult to follow whether in the fossils or in the modern embryos. We suppose some such form as Edrioaster, which appears to have lived near the shore, to have been repeatedly overturned by waves. Those that were able to accommodate themselves to this topsy-turvy existence, by taking food in directly through the mouth, survived, and their podia gradually specialized as sucking feet. Such a form as this, when once its covering-plates had atrophied, would be a starfish without more ado (fig. 12, B); but the sea-urchins present a more difficult problem, on which Bothriocidaris sheds no light. An Upper Silurian echinoid, however, Palaeodiscus, is believed by W.J. Sollas and W.K. Spencer to have had in its ambulacra an inner as well as an outer series of plates. If this be correct, the only change from Edrioaster, as regards the ambulacra, was that in Palaeodiscus the covering-plates could no longer open, but closed permanently over the whole groove, while the podia issued through slits between them. In more typical echinoids the covering-plates alone remained to form the ordinary ambulacral plates, while the flooring-plates disappeared, the canals and other organs remaining as before. In any case we have to admit a closure of the integument over the ciliated groove (fig. 12, D, e) just as in holothurians, since this is necessitated by anatomical evidence. The genital organs in both Asteroidea and Echinoidea would retain the interradial position they first assumed in Edrioaster; and in Echinoidea their primitive temporary openings to the exterior were converted into definite pores, correlated with five interradially placed plates at the aboral pole. The anus also naturally moved to this superior and aboral position. In the Echinoidea the water-canals and associated structures, ending in the terminal plates, stretched right up to these genital plates; but in the Asteroidea they never reached the aboral surface, so that the terminals have always been separated from the aboral pole by a number of plates.

Analysis of Echinoderm Characters.—Regarding the Echinoderms as a whole in the light of the foregoing account, we may give the following analytic summary of the characters that distinguish them from other coelomate animals:—

They live in salt or brackish water; a primitive bilateral symmetry is still manifest in the right and left divisions of the coelom; the middle coelomic cavities are primitively transformed into two hydrocoels communicating with the exterior indirectly through a duct or ducts of the anterior coelom; stereom, composed of crystalline carbonate of lime, is, with few exceptions, deposited by special amoebocytes in the meshes of a mesodermal stroma, chiefly in the integument; reproductive cells are derived from the endothelium, apparently of the anterior coelom; total segmentation of the ovum produces a coeloblastula and gastrula by invagination; mesenchyme is formed in the segmentation cavity by migration of cells, chiefly from the hypoblast. Known Echinoderms show the following features, imagined to be due to an ancestral pelmatozoic stage:—Increase in the coelomic cavities of the left side, and atrophy of those on the right; the dextral coil of the gut, recognizable in all classes, though often obscured; an incomplete secondary bilateralism about the plane including the main axis and the water-pore or its successor, the madreporite, often obscured by one or other of various tertiary bilateralisms; the change of the hydrocoel into a circumoral, arcuate or ring canal; development through a free-swimming, bilaterally symmetrical, ciliated larva, of which in many cases only a portion is transformed into the adult Echinoderm (where care of the brood has secondarily arisen, this larva is not developed). All living, and most extinct, Echinoderms show the following features, almost certainly due to an ancestral pelmatozoic stage:—An incomplete radial symmetry, of which five is usually the dominant number, is superimposed on the secondary bilateralism, owing to the outgrowth from the mouth region of one unpaired and two paired ciliated grooves; these have a floor of nervous epithelium, and are accompanied by subjacent radial canals from the water-ring, giving off lateral podia and thus forming ambulacra, and by a perihaemal system of canals apparently growing out from coelomic cavities. All living Echinoderms have a lacunar, haemal system of diverse origin; this, the ambulacral system, and the coelomic cavities, contain a fluid holding albumen in solution and carrying numerous amoebocytes, which are developed in special lymph-glands and are capable of wandering through all tissues. The Echinoderms may be divided into seven classes, whose probable relations are thus indicated:—

Brief systematic accounts of these classes follow:—

Grade A. PELMATOZOA.—Echinoderma with the viscera enclosed in a calcified and plated theca, of which the oral surface is uppermost, and which is usually attached, either temporarily or permanently, by the aboral surface. Food brought to the mouth by a subvective system of ciliated grooves, radiating from the mouth either between the plates of the theca (endothecal), or over the theca (epithecal), or along processes from the theca (exothecal: arms, pinnules, &c.), or, in part, and as a secondary development, below the theca (hypothecal). Anus usually in the upper or oral half of the theca, and never aboral. An aborally-placed motor nerve-centre gives off branches to the stroma connecting the various plates of the theca and of its brachial, anal and columnar extensions, and thus co-ordinates the movements of the whole skeleton. The circumoesophageal water-ring communicates indirectly with the exterior; the podia, when present, are respiratory, not locomotor, in function.

Class I. Cystidea.—Pelmatozoa in which radial polymeric symmetry of the theca is developed either not at all or not in complete correlation with the radial symmetry of the ambulacra (such as obtains in Blastoidea and Crinoidea); in which extensions of the food-grooves are exothecal or epithecal or both combined, but neither endothecal nor pierced by podia (as in some Edrioasteroidea) All Palaeozoic.

This class shows much greater diversity of organization than any other, and the classifications proposed by recent writers, such as E. Haeckel, O. Jaekel and F.A. Bather, start from such different points of view that no discussion of them can be attempted here. Following the narrative given above, we recognize a primitive group—Amphoridea—represented by Aristocystis (fig. 8). From this are derived the orders Diploporita (fig. 9) and Rhombifera (fig. 10) and the class Edrioasteroidea, all which have already been described as steps in the evolution of the phylum. But there were also side-branches leading nowhere, and therefore placed in separate orders—Aporita and Carpoidea.

Order 1. Amphoridea.—Radial symmetry has affected neither food-grooves nor thecal plates; nor, probably, nerves, ambulacral vessels, nor gonads. Canals or folds when present in the stereom are irregular. Families: Aristocystidae (fig. 8); Eocystidae.

Order 2. Carpoidea.—Theca compressed in the oro-anal plane and a bilateral symmetry thus induced, affecting the food-grooves and, usually, the thecal plates and stem. Food-grooves in part epithecal and may be continued on one or two exothecal processes. No pores or folds in the stereom. Families: Anomalocystidae, Dendrocystidae. These correspond to Jaekel’s Carpoidea Heterostelea; he also includes, as Eustelea, our Comarocystidae and Malocystidae.

Order 3. Rhombifera.—Radial symmetry affects the food-grooves and, in the more advanced families, the thecal plates; probably also the nerves and ambulacral vessels, but not the gonads. The food-grooves are exothecal, i.e. are stretched out from the theca on jointed skeletal processes (brachioles). These either are close to the mouth or are removed from it upon a series of ambulacral or sub-ambulacral plates not derived immediately from thecal plates, or are separated from the oral centre by hypothecal passages passing beneath terminal plates. The stereom and stroma become arranged in folds and strands at right angles to the sutures of the thecal plates; in higher forms the stereom-folds are in part specialized as pectini-rhombs. Families: Echinosphaeridae; Comarocystidae; Macrocystellidae; Tiaracrinidae; Malocystidae; Glyptocystidae, with sub-famm. Echinoencrininae, Callocystinae, Glyptocystinae, of which examples are Cheirocrinus (fig. 10) and Cystoblastus from which Jaekel deduces the blastoids; Caryocrinidae.

Order 4. Aporita.—Pentamerous symmetry affects the food-grooves and thecal plates; probably also the nerves and ambulacral vessels, but not the gonads. Food-grooves exothecal and circumoral. The stereom shows no trace of canals, folds, rhombs or diplopores. Family: Cryptocrinidae.

Order 5. Diploporita.—Radial symmetry affects the food-grooves, and by degrees the thecal plates connected therewith, but not the interradial thecal plates; probably also the nerves and ambulacral vessels, but not the gonads. The food-grooves are epithecal, i.e. are extended over the thecal plates themselves without intermediate flooring; they are also prolonged on exothecal brachioles, which line the epithecal grooves. The stereom of the thecal plates may be thrown into folds, but the mesostroma does not so much tend to lie in strands traversing the sutures, nor are pectini-rhombs or pore-rhombs developed; diplopores are always present in the mesostereom, but often restricted to definite tracts or plates, especially in higher forms. Families: Sphaeronidae; Glyptosphaeridae, e.g. Fungocystis (fig. 9); Protocrinidae; Mesocystidae; Gomphocystidae.

The Protocrinidae lead up to Proteroblastus, in which the theca is ovoid, sometimes prolonged into a stem, the plates differentiated into (a) smooth, irregular, depressed interambulacrals, (b) transversely elongate brachioliferous adambulacrals, to which the diplopores, which lie at right angles to the main food-groove, are confined. This leads almost without a break to the Protoblastoidea.

Class II. Blastoidea.—Pelmatozoa in which five (by atrophy four) epithecal ciliated grooves, lying on a lancet-shaped plate (? always), radiate from a central peristome between five interradial deltoid plates, and are edged by alternating side-plates bearing brachioles, to which side-branches pass from the grooves. Grooves and peristome protected by small plates, which can open over the grooves. The generative organs and coelom probably did not send extensions along the rays into the brachioles; but apparently nerves from the aboral centre, after passing through the thecal plates, met in a circumoral ring, from which branches passed into the plate under each main food-groove, and thence supplied the brachioles. The thecal plates, however irregular in some species, always show defined basals and a distinct plate (“radial”) at the end of each ambulacrum; they are in all cases so far affected by pentamerous symmetry that their sutures never cross the ambulacra. All Palaeozoic.

Division A. Protoblastoidea.—Blastoidea without interambulacral groups of hydrospire-folds hanging into the thecal cavity. Families: Asteroblastidae, Blastoidocrinidae. The former might be placed with Diploporita, were it not for a greater intimacy of correlation between ambulacral and thecal structures than is found in Cystidea as here defined. They form a link between the Protocrinidae and—

Division B. Eublastoidea.—Blastoidea in which the thecal plates have assumed a definite number and position in 3 circlets, as follows: 3 basals, 2 large and 1 small; 5 radials, often fork-shaped, forming a closed circlet; 5 deltoids, interradial in position, supported on the shoulders or processes of the radials, and often surrounding the peristome with their oral ends. The stereom of the radials and deltoids on each side of the ambulacra is thrown into folds, running across the radio-deltoid suture, and hanging down into the thecal cavity as respiratory organs (hydrospires).

These are the forms to which the name Blastoidea is usually restricted. They have been divided into Regulares and Irregulares, but it seems possible to group them according to three series or lines of descent, thus:—

Series a. Codonoblastida.—Families: Codasteridae, Pentremitidae (fig. 13).

Series b. Troostoblastida.—Families: Troostocrinidae, Eleutherocrinidae.

Series c. Granatoblastida.—Families: Nucleocrinidae, Orbitremitidae, Pentephyllidae, Zygocrinidae.

Class III. Crinoidea.—Pelmatozoa in which epithecal extensions of the food-grooves, ambulacrals, superficial oral nervous system, blood-vascular and water-vascular systems, coelom and genital system are continued exothecally upon jointed outgrowths of the abactinal thecal plates (brachia), carrying with them extensions of the abactinal nerve-system. The number of these processes is primitively and normally five, but may become less by atrophy. The brachia rise from a corresponding number of thecal plates, “radials (RR).” Below these is always a circlet, or traces of a circlet, of plates alternating with the radials, i.e. interradial, and called “basals (BB).” Through all modifications, which are numerous and vastly divergent, these elements persist. A circlet of radially situate infrabasals (IBB) may also be present. Below BB or IBB there follows a stem, which, however, may be atrophied or totally lost (see fig. 1).

The classification here adopted is that of F.A. Bather (1899), which departs from that of Wachsmuth and Springer mainly in the separation of forms with infrabasals or traces thereof from those in which basals only are present. These two series also differ from each other in the relations of the abactinal nerve-system. O. Jaekel (1894) has divided the crinoids into the orders Cladocrinoidea and Pentacrinoidea, the former being the Camerata of Wachsmuth and Springer (Monocyclica Camerata, Adunata and Dicyclica Camerata of the present classification), and the latter comprising all the rest, in which the arms are either free or only loosely incorporated in the dorsal cup. In minor points there is fair agreement between the American, German and British authors. The families are extinct, except when the contrary is stated.

Sub-class I. Monocyclica.—Crinoidea in which the base consists of BB only, the aboral prolongations of the chambered organ being interradial; new columnals are introduced at the extreme proximal end of the stem.

Order 1. Monocyclica Inadunata.—Monocyclica in which the dorsal cup is confined to the patina and occasional intercalated anals; such ambulacrals or interambulacrals as enter the tegmen remain supra-tegminal and not rigidly united. Families: Hybocrinidae, Stephanocrinidae, Heterocrinidae, Calceocrinidae, Pisocrinidae, Zophocrinidae, Haplocrinidae, Allagecrinidae, Symbathocrinidae, Belemnocrinidae, Plicatocrinidae, Hyocrinidae (recent), Saccocomidae.

Order 2. Adunata.—Monocyclica with dorsal cup primitively confined to the patina and an occasional single anal; tegmen solid; portions of the proximal brachials and their ambulacrals tend to be rigidly incorporated in the theca. Arms fork once to thrice, and bear pinnules on each or on every other brachial. BB fused to 3, 2 or 1. (Eucladocrinus and Acrocrinidae offer peculiar exceptions to this diagnosis.) Families: Platycrinidae, Hexacrinidae, Acrocrinidae.

Order 3. Monocyclica Camerata.—Monocyclica in which the first, and often the succeeding, orders of brachials are incorporated by interbrachials in the dorsal cup, while the corresponding ambulacrals are either incorporated in, or pressed below, the tegmen by interambulacrals; all thecal plates united by suture, somewhat loose in the earliest forms, but speedily becoming close, and producing a rigid theca; mouth and tegminal food-grooves closed; arms pinnulate.

Sub-order i. Melocrinoidea.—RR in contact all round; first brachial usually quadrangular. Families: Glyptocrinidae, Melocrinidae, Patelliocrinidae, Clonocrinidae, Eucalyptocrinidae, Dolatocrinidae.

Sub-order ii. Batocrinoidea.—RR separated by a heptagonal anal; first brachial usually quadrangular. Families: Tanaocrinidae, Xenocrinidae, Carpocrinidae, Barrandeocrinidae, Coelocrinidae, Batocrinidae, Periechocrinidae.

Sub-order iii. Actinocrinoidea.—RR separated by a hexagonal anal; first brachial usually hexagonal. Families: Actinocrinidae, Amphoracrinidae.

Sub-class II. Dicyclica.—Crinoidea in which the base consists of BB and IBB, the latter being liable to atrophy or fusion with the proximale, but the aboral prolongations of the chambered organ are always radial; new columnals may or may not be introduced at the proximal end of the stem.

Order 1. Dicyclica Inadunata.—Dicyclica in which the dorsal cup primitively is confined to the patina and occasional intercalated anals, and no other plates ever occur between RR (Grade: Distincta); Br may be incorporated in the cup, with or without iBr, but never rigidly, and their corresponding ambulacrals remain supra-tegminal (Grade: Articulata); new columnals are introduced at the extreme proximal end of the stem.

Sub-order i. Cyathocrinoidea.—Tegmen stout with conspicuous orals. Families: Carabocrinidae, Palaeocrinidae. Euspirocrinidae, Sphaerocrinidae, Cyathocrinidae, Petalocrinidae, Crotalocrinidae, Codiacrinidae, Cupressocrinidae, Gasterocomidae.

Sub-order ii. Dendrocrinoidea.—Tegmen thin, flexible, with inconspicuous orals. Families: Dendrocrinidae, Botryocrinidae, Lophocrinidae, Scaphiocrinidae, Scytalecrinidae, Graphiocrinidae, Cromyocrinidae, Encrinidae (preceding families are Distincta; the rest Articulata), Pentacrinidae, including the recent Isocrinus (fig. 14), Uintacrinidae, Marsupitidae, Bathycrinidae (recent).

Order 2. Flexibilia.—Dicyclica in which proximal brachials are incorporated in the dorsal cup, either by their own sides, or by interbrachials, or by a finely plated skin, but never rigidly; plates may occur between RR. Tegmen flexible, with distinct ambulacrals and numerous small interambulacrals; mouth and food-grooves remain supra-tegminal and open. Top columnal a persistent proximale, often fusing with IBB, which are frequently atrophied in the adult.

All the Palaeozoic representatives have non-pinnulate arms, while the Mesozoic and later forms have them pinnulate. There are other points of difference, so that it is not certain whether the latter really descended from the former. But assuming such a relationship we arrange them in two grades.

Grade a. Impinnata.—Families: Ichthyocrinidae, Sagenocrinidae, and Taxocrinidae, perhaps capable of further division.

Grade b. Pinnata.—Families: Apiocrinidae with the recent Calamocrinus, Bourgueticrinidae with recent Rhizocrinus, Antedonidae, Atelecrinidae, Actinometridae, Thaumatocrinidae (these four recent families include free-moving forms with atrophied stem, probably derived from different ancestors), Eugeniacrinidae, Holopodidae (recent), Eudesicrinidae.

Order 3. Dicyclica Camerata.—Dicyclica in which the first, and usually the second, orders of brachials are incorporated in the dorsal cup by interbrachials, at first loosely, but afterwards by close suture. IBB always the primitive 5. An anal plate always rests on the posterior basal; mouth and tegminal food-grooves closed; arms pinnulate. Families: Reteocrinidae, Dimerocrinidae, Lampterocrinidae, Rhodocrinidae, Cleiocrinidae.

Class IV. Edrioasteroidea.—Pelmatozoa in which the theca is composed of an indefinite number of irregular plates, some of which are variously differentiated in different genera; with no subvective skeletal appendages, but with central mouth, from which there radiate through the theca five unbranched ambulacra, composed of a double series of alternating plates (covering-plates), sometimes supported by an outer series of larger alternating plates (side-plates or flooring-plates). In some forms at least, pores between (not through) the ambulacral elements, or between them and the thecal plates, seem to have permitted the passage of extensions from the perradial water-vessels. Anus in posterior interradius, on oral surface, closed by valvular pyramid. Hydropore (usually, if not always, present) between mouth and anus. Families: Agelacrinidae, Cyathocystidae, Edrioasteridae, Steganoblastidae. All Palaeozoic. The structure and importance of Edrioaster have been discussed above (figs. 11, 12).

Grade B. ELEUTHEROZOA—Echinoderma in which the theca, which may be but slightly or not at all calcified, is not attached by any portion of its surface, but is usually placed with the oral surface downwards or in the direction of forward locomotion. Food is not conveyed by a subvective system of ciliated grooves, but is taken in directly by the mouth. The anus when present is typically aboral, and approaches the mouth only in a few specialized forms. The aboral nervous system, if indeed it be present at all, is very slightly developed. The circumoesophageal water-ring may lose its connexion with the exterior medium; the podia (absent only in some exceptional forms) may be locomotor, respiratory or sensory in function, but usually are locomotor tube-feet.

The classes of the Eleutherozoa probably arose independently from different branches of the Pelmatozoan stem. The precise relation is not clear, but the order in which they are here placed is believed to be from the more primitive to the more specialized.

Class I. Holothurioidea.—Eleutherozoa normally elongate along the oro-anal axis, which axis and the dorsal hydropore lie in the sagittal plane of a secondary bilateral symmetry. The calcareous skeleton, which may be entirely absent, is usually in the form of minute spicules, sometimes of small irregular plates with no trace of a calycinal or apical system; to these is added a ring of pieces radiately arranged round the oesophagus. Ambulacral appendages take the form of: (1) circumoral tentacles, (2) sucking-feet, (3) papillae; of these (1) alone is always present. The gonads are not radiately disposed.

The comparative anatomy of living forms, combined with the evolutionary hypothesis sketched above, suggests that the early holothurians possessed the following characters: subvective grooves entirely closed; 5 radial canals, proceeding from the water-ring, gave off branches furnished with ampullae to the podia on each side of them, the 10 anterior podia being changed into cylindrical tentacles; the transverse muscles of the body-wall formed a circular layer, probably interrupted at the radii (though Ludwig believes the contrary); longitudinal muscles as paired radial bands, without those special retractors for withdrawing the anterior part of the body which occur in many recent forms; a hydropore connected with the water-ring by a canal in the dorsal mesentery; a gonopore behind the hydropore connected by a single duct with a bunch of genital pouches on each side of the mesentery; gut dextrally coiled, with a simple blood-vascular system, and with an enlargement at the anus for respiration, this eventually producing branched caeca called “respiratory trees”; skeleton reduced to a ring of 5 radial and 5 interradial plates round the gullet, and small plates, with a hexagonally meshed network, dispersed through the integument. Such a form gave rise to descendants differing inter se as regards the suppression of the radial canals and of the podia, the form of the tentacles, and the development of respiratory trees. These anatomical facts are represented in the following classification by H. Ludwig:—

Order 1. Actinopoda.—Radial canals supplying tentacles and podia.

Order 2. Paractinopoda.—Neither radial canals nor podia. Tentacles supplied from circular canal. Fam. Synaptidae.

It is admitted, however, that this scheme does not represent the probable descent or relationship of the families. Consideration of the views of Ludwig himself, of H. Östergren, and especially of R. Perrier, suggests the following as a more natural if less obvious arrangement.

Order 1. Aspidochirota.—Tentacles more or less peltate; calcareous ring when present simple and radially symmetrical; no retractors; stone-canal often opens to exterior; genital tubes sometimes restricted to left side in consequence of altered position of gut (Fig. 15.) Families: Elpidiidae (deep-sea forms, with sub-famm. Synallactinae, Deimatinae, Elpidiinae, Psychropotinae), Holothuriidae (shallow water), Pelagothuriidae (pelagic).

Order 2. Dendrochirota.—Tentacles simple or branched, never peltate; calcareous ring well developed, often bilaterally symmetrical; retractor muscles usually present; stone-canal opens internally; genital tubes in right and left tufts.

Sub-order i. Apoda.—No tube-feet or papillae, but tentacular ampullae more or less developed. Mostly burrowers. Families: Synaptidae (sub-famm. Synaptinae, Chirodotinae, Myriotrochinae), Molpadiidae.

Sub-order ii. Eupoda.—Tube-feet present, but tentacular ampullae rudimentary or absent. Families: Cucumariidae (climbers and crawlers), Rhopalodinidae (burrowers).

Class II. Stelliformia (= Asteroidea sensu lato).—Eleutherozoa with a depressed stellate body composed of a central disk, whence radiate five or more rays; this radiate symmetry affects all the systems of organs, including the genital. The radial water-vessels lie in grooves on the ventral side of flooring-plates (usually called “ambulacrals”); they and their podia are limited to the oral surface of the body and their extremities are separated from the apical plates by a stretch of dorsal integument containing skeletal elements; the opening of the water-vascular system (madreporite) is not connected with a definite apical plate or system of plates.

The starfish, brittle-stars and their allies (see [Starfish]) have for the last fifty years usually been divided into two classes—Asteroidea and Ophiuroidea, each equivalent to the Holothurioidea or Echinoidea. Recently, however, some authors, e.g. Gregory, have attempted to show that these classes cannot be distinguished. It is true that some specialized forms, such as the Brisingidae among starfish, Astrophiura and Ophioteresis among ophiurans, contravene the usual diagnoses; but this neither obscures their systematic position, nor does it alter the fact that since early Palaeozoic times these two great groups of stellate echinoderms have evolved along separate lines. If then we place these groups in a single class, it is not on account of a few anomalous genera, but because the characters set forth above sharply distinguish them from all other echinoderms, and because we have good reason to believe that the ophiurans did not arise independently but have descended from primitive starfish. For that class Bell’s name Stelliformia is selected since it avoids both confusion and barbarism.

Sub-class I. Asterida.—Stelliformia in which the ambulacral groove always remains open and the podia serve as tube-feet (fig. 12, B); the rays as a rule pass gradually into the disk, and contain both genital glands and caecal extensions of the digestive system; an anus usually present; respiration is by tubular extensions from the body-cavity (papulae); skeletal appendages, in addition to small spines, are either small grasping organs (pedicellariae), or clumped spines (paxillae), or branched spines bearing a membrane.

No existing classification of the Asterida is satisfactory even for the recent forms, still less when the older fossils are considered. A separation of the latter as Palasterida, because of their alternating ambulacrals, from the recent Euasterida with opposite ambulacrals, is now discarded and an attempt made to arrange the Palasterida in divisions originally established for Euasterida. Those divisions fall under three schemes. C. Viguier has divided the starfish into: Astéries ambulacraires, with plates of ambulacral origin prominent in the mouth-skeleton, pedicellariae stalked, and straight or crossed, podial pores usually quadriserial; Astéries adambulacraires, with adambulacrals prominent in the mouth-skeleton, pedicellariae sessile, and forcipiform or valvular, podial pores usually biserial. Perrier, at first laying greater stress on the nature of the pedicellariae and afterwards on the form of the mouth-skeleton, has gradually perfected a scheme of five orders: (1) Forcipulata, with pedicellariae stalked, and straight or crossed; (2) Spinulosa, with pedicellariae sessile and forcipiform; (3) Velata, with membraniferous spines; (4) Paxillosa, pedicellariae represented by an ossicle of the test and the spines covering it, the whole forming a paxilla; (5) Valvata or Granulosa, with pedicellariae sessile and valvular or salt-cellar shaped. A more widely accepted scheme is that of W.P. Sladen, who divided the Euasterida into two orders; (1) Phanerozonia, with marginals large and highly developed, the supero-marginals and infero-marginals contiguous, with papulae confined to the dorsal surface, with ambulacrals well spaced and usually broad, adambulacrals prominent in the mouth-skeleton, with pedicellariae sessile; (2) Cryptozonia, with marginals inconspicuous and somewhat atrophied in the adult, the supero-marginals separated from the infero-marginals by intercalated plates, with papulae distributed over the whole body, with ambulacrals crowded and narrow, either ambulacrals or adambulacrals prominent in the mouth-skeleton, with pedicellariae stalked or sessile.

We give here a list of the families separated into Sladen’s orders and grouped under Perrier’s divisions, extinct families being marked †.

1. Phanerozonia.—Unclassed Famm., † Palaeasteridae, † Palasterinidae, † Taeniasteridae, † Aspidosomatidae. Paxillosa, Luidiidae, Astropectinidae (fig. 16), Archasteridae restr. Verrill, Porcellanasteridae, Chaetasteridae. Valvata, Benthopectinidae, Goniopectinidae, Plutonasteridae, Odontasteridae, Pentagonasteridae, Antheneidae, Pentacerotidae, Gymnasteriidae. Spinulosa, Poraniidae, Asterinidae.

2. Cryptozonia.—Unclassed Famm., † Sturtzasteridae (= Palaeocomidae Greg.), † Lepidasteridae, † Tropidasteridae. Valvata, Linckiidae restr. Perr. Spinulosa, Echinasteridae, Solasteridae (fig. 17), Korethrasteridae. Velata, † Palasteriscidae, Pterasteridae, Pythonasteridae, Myxasteridae. Forcipulata, Stichasteridae, Zoroasteridae (fig. 3, D), Heliasteridae, Pedicellasteridae, Asteriidae, Brisingidae.

Sub-class II. Ophiurida.—Stelliformia in which the ambulacral groove, though open in the oldest forms, soon becomes closed, while the podia cease to serve as tube-feet; the rays as a rule spring abruptly from the disk and contain neither genital glands nor digestive caeca; no anus; respiration may be through clefts at the bases of the rays, but not by papulae; skeletal appendages confined to spines, usually of simple structure.

There is as yet no satisfactory classification of the Ophiurida into orders expressing lines of descent; even as regards families, leading writers are at variance. The following scheme is based on the attempts of E. Haeckel, F.J. Bell, J.W. Gregory, B. Stürtz, J.O.E. Perrier, and A.E. Verrill. Extinct families marked †.

Grade A. Palophiurae.—Ambulacrals not yet forming complete vertebrae; plates of disk not yet specialized into mouth, radial or genital shields.

Stage a. Allostichia (= Lysophiurae).—Ambulacrals alternating and unfused, groove uncovered by ventral arm-plates. Families: † Protasteridae, † Protophiuridae.

Stage b. Zygostichia.—Ambulacrals opposite and, except in Ophiurinidae, fused; ventral arm-plates developed in some. Families: † Ophiurinidae, † Lapworthuridae, † Furcasteridae, † Palastropectinidae, † Eoluididae, † Palaeophiomyxidae.

Grade B. Colophiurae.—Ambulacral pairs fused to form vertebrae with definite articular surfaces; mouth, radial and genital shields developed, though not all need be present in any one form.

Order 1. Streptophiurae.—Rays simple and capable of coiling, since the vertebrae articulate by a ball-and-socket joint; arm-plates incompletely developed. Families: † Onychasteridae, Ophiohelidae, Ophioscolecidae, Ophiomyxidae, Hemieuryalidae, Astrophiuridae; unclassified genera, e.g. Ophioteresis, Ophiosciasma, Ophiogeron.

Order 2. Zygophiurae.—Rays simple and prevented from coiling by processes on the vertebral joints (fig. 18); dorsal, ventral and lateral arm-plates present.

Sub-order i. Brachyophiurae.—Spines short, simple, pointing towards the end of the arm. Families: Pectinuridae (= Ophiodermatidae), Ophiolepididae.

Sub-order ii. Nectophiurae.—Spines may be variously elaborated and are set more at right angles to the arm-axis. Families: Amphiuridae, Ophiacanthidae, Ophiocomidae, Ophiothrichidae.

Order 3. Cladophiurae (= Euryalae). Rays simple or branched, capable of coiling, since the vertebrae articulate by surfaces of hour-glass shape; ventral arm-plates, and often the others, much reduced; spines reduced or absent. Families: Euryalidae, Gorgonocephalidae, Astrochelidae, Astroschemidae, Astronycidae.

The Silurian genera Eucladia and Euthemon have the rays greatly reduced and merged in the disk, so that the ambulacrals are unseen. There are a few large dorsal, lateral and ventral arm-plates, and at the angles of the latter emerge huge podia with a granular or plated skin. There are five prominent mouth-shields and a separate madreporite on the ventral surface. These genera attained the Colophiuran grade in respect of external plating, but it is unlikely that they or their ancestors had acquired even the Streptophiuran type of vertebra. Sollas has separated them as an order Ophiocistia.

Class III. Echinoidea.—Eleutherozoa with a test of roughly circular, subpentagonal or elliptical outline, spheroidal, domed or flattened, of primary pentameric symmetry affecting all systems of organs except the gut. The radial water-vessels lie within the test through which their podia pass (fig. 12, D); the ambulacra thus formed are continuous from the peristome to the apical system of plates; the hydropore is connected with a definite plate of that system, and thus marks a secondary bilateral symmetry. An anus is present either within the apical system (endocyclic, fig. 3, A and B), or outside it in an interradius (exocyclic, fig. 19, 7), thus initiating yet another bilateral symmetry. Skeletal appendages are spines (radioles), pedicellariae, and, in some forms, minute sense-organs called sphaeridia.

The echinoids or sea-archins (see [Sea-Urchin]) may be grouped under the following orders, here named in the sequence of their appearance in the rocks.

Order 1. Bothriocidaroida.—Ambulacrals simple, each with two pores vertically superposed, 2 columns to each ambulacrum; interambulacrals multi-tuberculate, in 1 column, none passing on to or resorbed by the peristome; mouth central, jaws unknown, no external gills or sphaeridia; anus aboral, endocyclic. Sole genus Bothriocidaris (fig. 5), Ordovician.

Order 2. Melonitoida.—Ambulacrals simple, each with two pores horizontally juxtaposed, in 2 to 18 columns; interambulacrals granulate with occasional tubercles, in 3 to 11 columns, not more than one row passing on to the peristome; mouth central, with jaws, no external gills or sphaeridia; anus aboral, endocyclic. Families: Palechinidae (fig. 19, 1), Melonitidae and Lepidesthidae, Silurian to Carboniferous.

Order 3. Cystocidaroida.—Ambulacrals simple, each with one or two pores, which sometimes pass between rather than through the plates, in 2 columns; interambulacrals, uni- or multi-tuberculate, in numerous (say 10 or more) columns, none passing on to peristome; mouth central with jaws, no external gills or sphaeridia; position of anus doubtful, acyclic, i.e. no apical system so far as known. Include only Echinocystis, Palaeodiscus and (?) Myriastiches, all Upper Silurian.

Order 4. Cidaroida.—Ambulacrals simple, each with two pores horizontally juxtaposed, in 2 columns; interambulacrals unituberculate, in 2 to 11 columns, some rows may pass on to the peristome; mouth central, with jaws, no external gills or sphaeridia; anus aboral, endocyclic. Families: Lepidocentridae and Archaeocidaridae (fig. 19, 2), Devonian and Carboniferous; Cidaridae (fig. 19, 3, 4). Permian to present; Diplocidaridae and Tiarechinidae, Mesozoic.

Order 5. Diademoida.—Ambulacrals generally compound, with two pores obliquely juxtaposed, in 2 columns as in all subsequent orders; interambulacrals usually with large radioles surrounded by smaller ones, as in Cidaroida, in 2 columns as in all subsequent orders, only one plate resorbed; mouth central, with jaws and external gills, sphaeridia present; anus aboral endocyclic. J.W. Gregory divides this into four suborders, each representing a distinct evolutionary series; i. Calycina, Saleniidae (fig. 19, 5) and Acrosaleniidae; ii. Arbacina, Hemicidaridae and Arbaciidae; iii. Diademina, Orthopsidae, Diadematidae, Diplopodiidae, Pedinidae, Cyphosomatidae, and Echinothuridae; iv. Echinina, Temnopleuridae, Triplechinidae, Strongylocentrotidae and Echinometridae. The order is Triassic to Recent.

Fig. 19.—Denuded tests of some fossil Echinoids.
1, Palaeechinus; Carboniferous. 2, A plate and radiole of Archaeocidaris; Carboniferous. 3, A radiole of Cidaris; Jurassic. 4, Hemicidaris; Mid. Jurassic.	5, Salenia; Cretaceous. 6, Dysaster; Jurassic. 7, Enallaster: Cretaceous. 8, Catopygus; Cretaceous.

Order 6. Holectypoida.—Ambulacrals sometimes compound, with one or two pores to a plate, some dorsal podia begin to assume respiratory function; interambulacrals multi-tuberculate, none resorbed; mouth central, with jaws weak or wanting, with external gills and sphaeridia; anus exocyclic. Families: Pygasteridae, Discoidiidae, Galeritidae, Conoclypeidae; Jurassic to Recent.

Order 7. Spatangoida.—Ambulacrals simple, with two pores juxtaposed, dorsal podia respiratory; interambulacrals bearing numerous small spines, none resorbed; mouth central or shifted forwards, with no jaws or external gills, sphaeridia numerous; anus exocyclic. As the mouth moves forward and the anus downward, the posterior interambulacrals between them are enlarged and strengthened so as to form a sternum. The order may therefore be divided into: (i.) Asternata, Famm. Echinoneidae, Nucleolitidae and Cassidulidae (fig. 19, 8); (ii.) Sternata, Famm. Collyritidae (fig. 19, 6), Echinocorytidae, Spatangidae (fig. 19, 7), Palaeostomidae, and Pourtalesiidae; Jurassic to Recent.

Order 8. Clypeastroida.—Ambulacrals simple or compound, with two pores juxtaposed, dorsal podia respiratory; interambulacrals multi-tuberculate, none resorbed; mouth central with flattened unequal jaws, reduced external gills, and few sphaeridia; anus exocyclic. Families: Fibulariidae, Laganidae, Scutellidae, Clypeastridae; Cretaceous to Recent.

The probable relationship of these orders is shown in the annexed table. Here the Cystocidaroida occupy an isolated position. It is, however, quite possible that Echinocystis may some day be referred to the Cidaroida, and Palaeodiscus to the Melonitoida. This would leave the Echinoid scheme remarkably simple, with the Melonitoida and Cidaroida as divergent branches from an ancestor like Bothriocidaris; but while the former branch soon decayed, the latter continues to flourish at the present day. To take the Echinoidea now living, and to divide them into Endocyclica and Exocyclica, Branchiate and Abranchiate, Gnathostomata and Atelostomata, is easy and convenient; or again to distinguish as Palechinoidea those pre-Jurassic genera which do not conform to the fixed type of twenty vertical columns found in the later Euechinoidea, is to express an interesting fact; but all such divisions obscure the true relationships, and the corresponding terms should be recognized as descriptive rather than classificatory.

Authorities.—In addition to the works referred to at the beginning of the article, the following deal with the general subject: Bather, Gregory and Goodrich, “Echinoderma,” in Lankester’s Treatise on Zoology (London, 1900); F.J. Bell, Catalogue of the British Echinoderms in the British Museum (London, 1892); P.H. Carpenter, “Notes on Echinoderm Morphology,” Quart. Journ. Micr. Sci., 1878-1887; Y. Delage and E. Hérouard, Traité de zoologie concrète, iii., Échinodermes (Paris, 1904); A. Lang, Text-Book of Comparative Anatomy, transl., part ii. (London, 1896); Ludwig and Hamann, “Echinodermen,” in Bronn’s Klassen und Ordnungen des Tierreichs (Leipzig, 1889), in progress; M. Neumayr, Die Stämme des Tierreiches (Wien, 1889); P.B. and C.F. Sarasin, “Über die Anatomie der Echinothuriden und die Phylogenie der Echinodermen,” Ergebnisse naturw. Forsch. auf Ceylon, Bd. i Heft 3 (Wiesbaden, 1888); R. Semon, “Die Homologien innerhalb des Echinodermenstammes,” Morph. Jahrb. (1889); W.P. Sladen, “Homologies of the Primary Larval Plates in the Test of Brachiate Echinoderms,” Quart. Journ. Micr. Sci., 1884; K.A. v. Zittel, Handbuch der ... Paläozoologie, i. pp. 308-560 (München, 1879); also Grundzüge, translated and revised by C.R. Eastman as Text-Book of Palaeontology (New York and London, 1899). The larger treatises here mentioned contain very full bibliographies, and a complete analytical index to the annual literature of the Echinoderma has for many years been published in the Zoological Record (London).

(F. A. B.)

[1] Sometimes called “Echinodermata,” a Greek name meaning “sea-urchin-skins,” which was invented by J.T. Klein (1734) to denote the tests of the Echini or sea-urchins; its later use for the animals themselves, or for the whole phylum, was an error in both history and etymology.

ECHINUS (Gr. for “hedge-hog” or “sea-urchin”), in architecture, the convex moulding which supports the abacus of the Doric column. The term is sometimes given to the ovolo of the Ionic capital, especially when curved with the egg-and-tongue enrichment. The origin of this use of the word in architecture, which comes down from ancient times, is uncertain.

ECHIUROIDEA (Gr. ἔχις, adder, and οὐρά, tail), the zoological name for a small group of marine animals which show in their larval life-history a certain degree of segmentation, and are therefore grouped by some authorities as Annelids. Formerly, together with the Sipunculoidea and Priapuloidea, they made up the class Gephyrea, but on the ground that they retain in the adult a large preoral lobe (the proboscis), that they have anal vesicles, that their anus is terminal, that setae are found, and finally that they are segmented in the larval stage, they have been removed from the class, which by the proposed further separation of the Priapuloidea on account of their unique renal and reproductive organs, has practically ceased to exist.

Echiuroids are animals of moderate size, varying roughly from one to six or seven centimetres in length, exclusive of the proboscis. This organ is capable of very considerable extension, and may attain a length in Bonellia viridis of about a metre and a half (fig. 1). It is grooved ventrally and ciliated. At its attachment to the body the groove sinks into the mouth. In Bonellia the proboscis is forked at its free end, but in the other genera it is short and unforked. The body is somewhat sausage-shaped, with the anus at the posterior extremity, surrounded in Echiurus by a single or double ring of setae. The skin is usually wrinkled, and in B. viridis, Thalassema lankesteri, Th. baronii, Hamingia arctica, and in the larva of many species, is of a lively green colour. A pair of curved bristles, formed in true setal sacs as in Chaetopoda, project from the body a short distance behind the mouth, and are moved by special muscles; they are of use in helping the animal to move slowly about, and they take a large share in the burrowing movements (C.B. Wilson, Biol. Bull., 1900), for some species tunnel in the mud and sand and form more or less permanent burrows, the walls of which are strengthened by mucus secreted from the skin. The openings of the burrows become silted up, leaving, however, a small aperture through which the proboscis is extruded. This organ carefully searches the neighbourhood for particles of food. When these are found the grooved proboscis folds its walls inwards, and the cilia pass the particles down the tube thus formed to the mouth. Echiuroids also move by extending the proboscis, which takes hold of some fixed object, and, then contracting, draws the body forwards. Recently it has been shown that Echiurus swims freely at night-time, using for locomotion both the proboscis and the contraction of the muscles of its body-wall. The motion is described as “gyratory,” and the anterior end is always carried foremost. Those species which do not burrow usually conceal themselves in crevices of the rocks or under stones, or at times in empty Mollusc or Echinid shells. They are occasionally used by fishermen for bait.

Fig. 2.—Female Bonellia viridis, Rol. Opened along theleft side.
a, Proboscis cut short. b, Bristle passing through the mouth into the pharynx. c, Coiled intestine. d, Anal tufts or vesicles. e, Ventral nerve cord.	f, Ovary borne on ventral vessel running parallel with e. g, Position of anus. h, Position of external opening of nephridium. i, Nephridium—the line points towards, but does not reach,the internal opening.

Anatomy (fig. 2).—A thin cuticle covers the epidermis, which contains mucus-secreting glands. Beneath the epidermis is a layer of circular muscles, then a layer of longitudinal, and finally in some cases a layer of oblique muscle-fibres. The inner face of this muscular skin is lined by a layer of epithelium. The coelomic body-cavity is spacious. It does not extend into the proboscis, which is a solid organ traversed by the nervous and vascular rings, but otherwise largely built up of muscle fibres and connective tissue. Many sense-cells lie in the epidermis. The ciliated ventral groove of the proboscis leads at its base into the simple mouth, which gives access to the thin-walled alimentary canal. This is longer than the body, and to tuck it away it is looped from side to side. The loops are supported by strands of connective tissue, which in some species are united so as to form a dorsal mesentery, whilst traces of a ventral mesentery are met with anteriorly and posteriorly (H.L. Jameson, Zool. Jahrb. Anat., 1899). The alimentary canal is divisible into fore-gut, mid-gut and hind-gut, and the first-named can be further divided into pharynx, oesophagus, gizzard and crop, mainly on histological grounds. The mid-gut is characterized by the presence of a ciliated groove, from which arises the collateral intestine or siphon, a second tube which rejoins the alimentary canal lower down. Similar collateral intestines are familiar in the Echinids and certain Polychaets (Capitellidae). The rectum receives the openings of a pair of very characteristic organs, the anal vesicles. Each consists of a branching tube, the tips of whose twigs terminate in minute ciliated funnels. The anal vesicles are thought to be excretory; whether this be so or not, they undoubtedly have some influence on the amount of fluid found in the coelom. The coelomic fluid contains as a rule both amoeboid and rounded corpuscles, and, when ripe, the products of the gonads. A closed system of vessels, usually called the vascular system, is present. There are, however, no capillaries connected with this, and it is confined to certain portions of the body. It can possess few of the functions usually associated with a vascular system, and its main use is probably to assist in the expansion of the proboscis. The system consists of the following parts:—A dorsal vessel applied to the alimentary canal is continued anteriorly into a median vessel, which traverses the proboscis to its tip. Here the vessel splits, and each half returns along the lateral edge of the proboscis; they reunite around the oesophagus and form a single ventral vessel, which lies above the ventral nerve-cord. The ventral vessel, which ends solidly behind, sends off a branch which forms a ring around the intestine and opens into the posterior extremity of the dorsal vessel. In Echiurus and Thalassema the same vessel forms a ring round a stout muscle, which connects the bases of the two ventral setae before passing to surround the intestine. Amoeboid corpuscles float in the fluid contents. The nephridia vary in number from a single one in Bonellia to three pairs in many species of Thalassema. Their external openings are ventral, and on the same level as the ciliated funnel-shaped nephrostomes. The posterior wall of the organ is produced into a long blind sac, which is lined by secretory cells. The nervous system is a single ventral cord, which starts from a circumoesophageal ring. This ring is involved in the growth of the proboscis, and is drawn out with it. Thus there is a lateral nerve near each edge of the proboscis which unites with its fellow dorsally above the oesophagus at the tip of the proboscis, and ventrally beneath the oesophagus, where they fuse to form the ventral nerve-cord. There are no specialized ganglia, but ganglion-cells are scattered uniformly along the nerve-cords. The ventral cord gives off rings, which run into the skin at regular intervals. The reproductive cells are modified coelomic cells, which lie on the ventral vessel. They escape into the coelomic fluid and there develop. When mature they leave the body through the nephridia. Bonellia and Hamingia are very interesting examples of sexual dimorphism. The female has the normal Echiuroid structure, but the male is reduced to a minute, flattened, planarian-like organism, which passes its life usually in the company of two or three others in a special recess of the nephridia of the female. Its structure may be gathered by a reference to fig. 3.

Larva.—The larva is a typical trochosphere, which, although of a temporary character, shows a distinct segmentation of the mesoblast, of the nervous system, and of the ciliated and pigmented structures in the skin, resembling that of Chaetopods. The preoral lobe persists as the proboscis. The sexes of the larvae are not determinable in the early stages, but when a certain growth has been reached in Bonellia the males seek the proboscis of the adult females, and passing into the mouth undergo there the transformation into the planarian-like parasite which is the fully-formed male. This now creeps along the body of the female and takes up its home in her nephridia.

Classification and Distribution.—The Echiuroidea consists of the following genera:—(1) Bonellia (Rol.), with four species, widely distributed, but inhabiting the temperate and warmer waters of each hemisphere. (2) Echiurus (Guérin-Méneville), with four species. This genus reaches from the Arctic waters of both hemispheres into the cooler temperate regions. (3) Hamingia (Kor. and Dan.), with one species, which has been taken in the Arctic Sea and the Hardanger Fjord. (4) Saccosoma (Kor. and Dan.) was described from a single specimen dredged about half-way between Iceland and Norway. (5) Thalassema (Gaertner, Lamarck), with twenty-one species. This genus is in the main a denizen of the warmer waters of the globe. Sixteen species are found only in tropical or subtropical seas, three species are Mediterranean (Mt. Stat. Neapel, 1899), whilst three species are from the eastern Atlantic, where the temperature is modified by the Gulf Stream (Shipley; see Willey’s Zoological Results, part iii. 1899; Proc. Zool. Soc. Lond., 1898, 1899; and Cambridge Natural History, ii.). The following are found in the British area:—E. pallasii (Guérin-Méneville), Th. neptuni (Gaertner), and Th. lankesteri (Herdman, Q.J.M.S., 1898).

Affinities.—The occurrence of trochosphere larva and the temporary segmentation of the body have led to the belief that the Echiuroids are more nearly allied to the Annelids than to any other phylum. This view is strengthened by certain anatomical and histological resemblances to the genus Sternaspis, which in one species, S. spinosa, is said to carry a bifid proboscis resembling that of the Echiuroids.

(A. E. S.)

ECHMIADZIN, or Itsmiadsin, a monastery of Russian Transcaucasia, in the government of Erivan, the seat of the Catholicus or primate of the Armenian church. It is situated close to the village of Vagarshapat, in the plain of the Aras, 2840 ft. above the sea, 12 m. W. of Erivan and 40 N. of Mount Ararat. The monastery comprises a pretty extensive complex of buildings, and is surrounded by brick walls 30 ft. high, which with their loopholes and towers present the appearance of a fortress. Its architectural character has been considerably impaired by additions and alterations in modern Russian style. On the western side of the quadrangle is the residence of the primate, on the south the refectory (1730-1735), on the east the lodgings for the monks, and on the north the cells. The cathedral is a small but fine cruciform building with a Byzantine cupola at the intersection. Its foundation is ascribed to St Gregory the Illuminator in 302. Of special interest is the porch, built of red porphyry, and profusely adorned with sculptured designs somewhat of a Gothic character. The interior is decorated with Persian frescoes of flowers, birds and scroll-work. It is here that the Catholicus confers episcopal consecration by the sacred hand (relic) of St Gregory; and here every seven years he prepares with great solemnity the holy oil which is to be used throughout the churches of the Armenian communion. Outside of the main entrance are the alabaster tombs of the primates Alexander I. (1714), Alexander II. (1755), Daniel (1806) and Narses (1857), and a white marble monument, erected by the English East India Company to mark the resting-place of Sir John Macdonald Kinneir, who died at Tabriz in 1830, while on an embassy to the Persian court. The library of the monastery is a rich storehouse of Armenian literature (see Brosset’s Catalogue de la bibliothèque d’Etchmiadzin, St Petersburg, 1840). Among the more remarkable manuscripts are a copy of the gospels dating from the 10th or 11th century, and three bibles of the 13th century. A type-foundry, a printing-press and a bookbinding establishment are maintained by the monks who supply religious and educational works for their co-religionists.

To the east of the monastery is a modern college and seminary. Half a mile to the east stand the churches of St Ripsime and St Gaiana, two of the early martyrs of Armenian Christianity; the latter is the burial-place of those primates who are not deemed worthy of interment beside the cathedral. From a distance the three churches form a fairly striking group, and accordingly the Turkish name for Echmiadzin is Uch-Kilissi, or the Three Churches. The town of Vagarshapat dates from the 6th century B.C.; it takes its name from King Vagarsh (Vologaeses), who in the 2nd century A.D. chose it as his residence and surrounded it with walls. Here the apostle of Armenia, St Gregory the Illuminator, erected a church in 309 and with it the primacy was associated. In 344 Vagarshapat ceased to be the Armenian capital, and in the 5th century the patriarchal seat was removed to Dvin, and then to Ani. The monastery was founded by Narses II., who ruled 524-533; and a restoration was effected in 618. The present name of the monastery was adopted instead of Vagarshapat in the 10th century. At length in 1441 the primate George brought back the see to the original site.

(P. A. K.; J. T. Be.)

ECHO (Gr. ἠχώ), in Greek mythology, one of the Oreades or mountain nymphs, the personification of the acoustical phenomenon known by this name. She was beloved by Pan, but rejected his advances. Thereupon the angry god drove the shepherds of the district mad; they tore Echo in pieces, and scattered her limbs broadcast, which still retained the gift of song (Longus iii. 23). According to Ovid (Metam. iii. 356-401), Echo by her incessant talking having prevented Juno from surprising Jupiter with the Nymphs, Juno changed her into an “echo”—a being who could not speak till she was spoken to, and then could only repeat the last words of the speaker. While in this condition she fell in love with Narcissus, and in grief at her unrequited affection wasted away until nothing remained but her voice and bones, which were changed into rocks. The legends of Echo are of late, probably Alexandrian, origin, and she is first personified in Euripides.

In acoustics an “echo” is a return of sound from a reflecting surface (see [Sound]: Reflection).

See F. Wieseler, Die Nymphe Echo (1854), and Narkissos (1856); P. Decharme in Daremberg and Saglio’s Dictionnaire des antiquités.

ECHTERNACH, a town in the grand duchy of Luxemburg, on the Sûre, close to the Prussian frontier. Pop. (1905) 3484. It is the oldest town in Luxemburg, and was the centre from which the English Saint Willibrord converted the people to Christianity in the 7th century. There are the Benedictine abbey, the hospital almshouse, which is said to be the oldest hospital in Europe except the Hôtel-Dieu in Paris, and the church of St Peter and St Paul. The Benedictine abbey has been greatly shorn of its original dimensions, but the basilica remains a fair monument of Romano-Gothic art. The church of St Peter and St Paul stands on an isolated mound, and for the ascent sixty steps have been built in the side, and these are well worn by the tread of numerous pilgrims who come in each succeeding year. The interior of the church is curious more than imposing, and is specially noteworthy only for its gloom. Under the altar, and below a white marble effigy of himself, lies Saint Willibrord.

Echternach is famous, however, in particular for the dancing procession held on Whit-Tuesday every year. The origin of this festival is uncertain, but it dates at least from the 13th century and was probably instituted during an outbreak of cholera. Nowadays it is an occasion of pilgrimage, among Germans and Belgians as well as Luxemburgers, for all sick persons, but especially for the epileptic and those suffering from St Vitus’ dance. The ceremony is interesting, and the Roman Catholic Church lends all its ritual to make it more imposing. The archbishop of Trier attends to represent Germany, and the bishop of Luxemburg figures for the grand duchy. There is a religious ceremony on the Prussian side of the bridge over the Sûre, and when it is over the congregation cross into the duchy to join the procession, partly religious, partly popular, through the streets of the town. The religious procession, carrying cross and banners and attended by three hundred singers, comes first, chanting St Willibrord’s hymn. Next comes a band of miscellaneous instruments playing as a rule the old German air “Adam had seven sons,” and then follow the dancers. Many of these are young and full of life and health and dance for amusement, but many others are old or feeble and dance in the hope of recovery or of escaping from some trouble, but on all alike the conditions of the dance are incumbent. There are three steps forward and two back; five steps are thus taken to make one in advance. This becomes especially trying at the flight of steps mounting to the little church where the procession ends in front of the shrine of the great saint. There are sixty steps, but it takes three hundred to reach the top for the final time. It is said that those who fall from age or weariness have to be dragged out of the way by onlookers or they would be trampled to death by the succeeding waves of dancers. The procession, although it covers a distance of less than a mile, is said to take as much as five hours in its accomplishment. In olden days the abbey was the goal of the procession, and King William I. of the Netherlands—great-grandfather of Queen Wilhelmina—changed the day from Tuesday to Sunday so that a working day should not be lost. This reform did not answer, and the ancient order was restored. Some critics see in the dancing procession of Echternach merely the survival of the spring dance of the heathen races, but at any rate it invests the little town with an interest and importance that would otherwise be lacking.

ECHUCA, a borough of the county of Rodney, Victoria, Australia, 156 m. by rail N. of Melbourne. Pop. (1901) 4075. It is situated on the river Murray, across which it is connected by bridge with Moama, on the New South Wales side, whence a railway runs to Deniliquin. The town is the terminus of the Murray River railway and the entrepot of the overland intercolonial trade; it has large wool stores, saw-mills, coach factories, breweries and soap-works. The rich agricultural district is noted for its vineyards.

ÉCIJA, a town of southern Spain, in the province of Seville; on the Cadiz-Cordova railway and the left bank of the river Genil. Pop. (1900) 24,372. The river, thus far navigable, is here crossed by a fine old bridge; and the antiquity of the town betrays itself by the irregularity of its arrangement, by its walls and gateways, and by its numerous inscriptions and other relics. Its chief buildings include no fewer than twenty convents, mostly secularized. The principal square is surrounded with pillared porticoes, and has a fountain in the centre; and along the river bank there runs a fine promenade, planted with poplar trees and adorned with statues. From an early period the shoemakers of Écija have been in high repute throughout Spain; woollen cloth, flannel, linen and silks are also manufactured. The vicinity is fertile in corn and wine, and cotton is cultivated. The heat is so great that the spot has acquired the sobriquet of El Sarten, or the “Frying-pan” of Andalusia. Écija, called Estija by the Arabs, is the ancient Astigis, which was raised to the rank of a Roman colony with the title of Augusta Firma. According to Pliny and Pomponius Mela, who both wrote in the 1st century A.D., it was the rival of Cordova and Seville. If local tradition may be believed, it was visited by the apostle Paul, who converted his hostess Santa Xantippa; and, according to one version of his life, it was the see of the famous St Crispin (q.v.) in the 3rd century.

ECK, JOHANN MAIER (1486-1543), German theologian, the most indefatigable and important opponent of Martin Luther, was born on the 13th of November 1486 at Eck in Swabia, from which place he derived his additional surname, which he himself, after 1505, always modified into Eckius or Eccius, i.e. “of Eck.” His father, Michael Maier, was a peasant and bailiff (Amtmann) of the village. The boy’s education was undertaken by his uncle Martin Maier, parish priest at Rothenburg on the Neckar, who sent him at the age of twelve to the university of Heidelberg, and subsequently to those of Tübingen, Cologne and Freiburg in the Breisgau. His academic career was so rapidly successful that at the age of twenty-four he was already doctor and professor of theology. During this period he was distinguished for his opposition to the scholastic philosophy; and, though he did not go to all lengths with the “modernists” (Moderni) of his day, his first work—Logices exercitamenta (1507)—was distinctly on their side. This attitude brought him into conflict with the senate of the university, a conflict which Eck’s masterful temper, increased by an extreme self-confidence perhaps natural in one so young and so successful, did not serve to allay. His position in Freiburg becoming intolerable, he accepted in 1510 an invitation from the duke of Bavaria to fill the theological chair at Ingolstadt, where he was destined for thirty years to exercise a profound influence as teacher and vice-chancellor (Prokanzler).

A ducal commission, appointed to find a means for ending the interminable strife between the rival academic parties, entrusted Eck with the preparation of fresh commentaries on Aristotle and Petrus Hispanus. He had a marvellous capacity for work, and between 1516 and 1520, in addition to all his other duties, he published commentaries on the Summulae of Petrus Hispanus, and on the Dialectics, Physics and lesser scientific works of Aristotle, which became the text-books of the university. During these early years Eck was still reckoned among the “modernists,” and his commentaries are inspired with much of the scientific spirit of the New Learning. His aim, however, had been to find a via media between the old and new; his temper was essentially conservative, his imagination held captive by the splendid traditions of the medieval church, and he had no sympathy with the revolutionary attitude of the Reformers. Personal ambition, too, a desire to be conspicuous in the great world of affairs, may have helped to throw him into public opposition to Luther. He had won laurels in a public disputation at Augsburg in 1514, when he had defended the lawfulness of putting out capital at interest; again at Bologna in 1515, on the same subject and on the question of predestination; and these triumphs had been repeated at Vienna in 1516. By these successes he gained the patronage of the Fuggers, and found himself fairly launched as the recognized apologist of the established order in church and state. Distinguished humanists might sneer at him as “a garrulous sophist”; but from this time his ambition was not only to be the greatest scientific authority in Germany but also the champion of the papacy and of the traditional church order. The first-fruits of this new resolve were a quite gratuitous attack on his old friend, the distinguished humanist and jurist Ulrich Zasius (1461-1536), for a doctrine proclaimed ten years before, and a simultaneous assault on Erasmus’s Annotationes in Novum Testamentum.

It is, however, by his controversy with Luther and the other reformers that Eck is best remembered. Luther, who had some personal acquaintance with Eck, sent him in 1517 copies of his celebrated 95 theses. Eck made no public reply; but in 1518 he circulated, privately at first, his Obelisci, in which Luther was branded as a Hussite. Luther entrusted his defence to Carlstadt, who, besides answering the insinuations of Eck in 400 distinct theses, declared his readiness to meet him in a public disputation. The challenge was accepted, and the disputation took place at Leipzig in June and July 1519. On June 27 and 28 and on July 1 and 3 Eck disputed with Carlstadt on the subjects of grace, free will and good works, ably defending the Roman Semipelagian standpoint. From July 4 to 14 he engaged with Luther on the absolute supremacy of the papacy, purgatory, penance, &c., showing a brilliant display of patristic and conciliar learning against the reformer’s appeals to Scripture. The arbitrators declined to give a verdict, but the general impression was that victory rested with Eck. He did, indeed, succeed in making Luther admit that there was some truth in the Hussite opinions and declare himself against the pope, but this success only embittered his animosity against his opponents, and from that time his whole efforts were devoted to Luther’s overthrow. He induced the universities of Cologne and Louvain to condemn the reformer’s writings, but failed to enlist the German princes, and in January 1520 went to Rome to obtain strict regulations against those whom he called “Lutherans.” He was created a protonotary apostolic, and in July returned to Germany, as papal nuncio, with the celebrated bull Exsurge Domine directed against Luther’s writings. He now believed himself in a position to crush not only the Lutheran heretics, but also his humanist critics. The effect of the publication of the bull, however, soon undeceived him. Bishops, universities and humanists were at one in denunciation of the outrage; and as for the attitude of the people, Eck was glad to escape from Saxony with a whole skin. In his wrath he appealed to force, and his Epistola ad Carolum V. (February 18, 1521) called on the emperor to take measures against Luther, a demand soon to be responded to in the edict of Worms. In 1521 and 1522 Eck was again in Rome, reporting on the results of his nunciature. On his return from his second visit he was the prime mover in the promulgation of the Bavarian religious edict of 1522, which practically established the senate of the university of Ingolstadt as a tribunal of the Inquisition, and led to years of persecution. In return for this action of the duke, who had at first been opposed to the policy of repression, Eck obtained for him, during a third visit to Rome in 1523, valuable ecclesiastical concessions. Meanwhile he continued unabated in his zeal against the reformers, publishing eight considerable works between 1522 and 1526.

His controversial ardour was, indeed, somewhat damped by Luther’s refusal to answer his arguments, and with a view to earning fresh laurels he turned his attention to Switzerland and the Zwinglians. At Baden-in-Aargau in May and June 1526 a public disputation on the doctrine of transubstantiation was held, in which Eck and Thomas Murner were pitted against Johann Oecolampadius. Though Eck claimed the victory in argument, the only result was to strengthen the Swiss in their memorial view of the Lord’s Supper, and so to diverge them further from Luther. At the Augsburg diet in 1530 Eck was charged by Charles V. to draw up, in concert with twenty other theologians, the refutation of the Protestant Confession, but was obliged to rewrite it five times before it suited the emperor. He was at the colloquy of Worms in 1540 and at the diet of Regensburg (Ratisbon) in 1541. At Worms he showed some signs of a willingness to compromise, but at Regensburg his old violence reasserted itself in opposing all efforts at reconciliation and persuading the Catholic princes to reject the Interim.

Eck died at Ingolstadt on the 10th of February 1543, fighting to the last and worn out before his time. He was undoubtedly the most conspicuous champion produced by the old religion in the age of the Reformation, but his great gifts were marred by greater faults. His vast learning was the result of a powerful memory and unwearied industry, and he lacked the creative imagination necessary to mould this material into new forms. He was a powerful debater, but his victories were those of a dialectician rather than a convincing reasoner, and in him depth of insight and conviction were ill replaced by the controversial violence characteristic of the age. Moreover, even after discounting the bias of his enemies, there is evidence to prove that his championship of the Church was not the outcome of his zeal for Christianity; for he was notoriously drunken, unchaste, avaricious and almost insanely ambitious. His chief work was De primatu Petri (1519); his Enchiridion locorum communium adversus Lutherum ran through 46 editions between 1525 and 1576. In 1530-1535 he published a collection of his writings against Luther, Opera contra Ludderum, in 4 vols.

See T. Wiedemann, Dr Johann Eck (Regensburg, 1865).

ECKERMANN, JOHANN PETER (1792-1854), German poet and author, best known owing to his association with Goethe, was born at Winsen in Hanover on the 21st of September 1792, of humble parentage, and was brought up in penury and privation. After serving as a volunteer in the War of Liberation (1813-1814), he obtained a secretarial appointment under the war department at Hanover. In 1817, although twenty-five years of age, he was enabled to attend the gymnasium of Hanover and afterwards the university of Göttingen, which, however, after one year’s residence as a student of law, he left in 1822. His acquaintance with Goethe began in the following year, when he sent to him the manuscript of his Beiträge zur Poesie (1823). Soon afterwards he went to Weimar, where he supported himself as a private tutor. For several years he also instructed the son of the grand duke. In 1830 he travelled in Italy with Goethe’s son. In 1838 he was given the title of grand-ducal councillor and appointed librarian to the grand-duchess. Eckermann is chiefly remembered for his important contributions to the knowledge of the great poet contained in his Conversations with Goethe (1836-1848). To Eckermann Goethe entrusted the publication of his Nachgelassene Schriften (posthumous works) (1832-1833). He was also joint-editor with Friedrich Wilhelm Riemer (1774-1845) of the complete edition of Goethe’s works in 40 vols. (1839-1840). He died at Weimar on the 3rd of December 1854.

Eckermann’s Gespräche mit Goethe (vols. i. and ii. 1836; vol. iii. 1848; 7th ed., Leipzig, 1899; best edition by L. Geiger, Leipzig, 1902) have been translated into almost all the European languages, not excepting Turkish. (English translations by Margaret Fuller, Boston, 1839, and John Oxenford, London, 1850.) Besides this work and the Beiträge zur Poesie, Eckermann published a volume of poems (Gedichte, 1838), which are of little value. See J.P. Eckermanns Nachlass, herausgegeben von F. Tewes, vol. i. (1905), and an article by R.M. Meyer in the Goethe-Jahrbuch, xvii. (1896).

ECKERNFÖRDE, a town of Germany, in the Prussian province of Schleswig-Holstein, on a fjord of the Baltic, 20 m. by rail N.W. from Kiel. Pop. (1905) 7088. It has a good harbour, fishing, trade in agricultural products, and manufactures of tobacco, salt and iron goods. There are a technical school of building and a Protestant teachers’ seminary. Eckernförde is mentioned as far back as 1197. It was taken by Christian IV. of Denmark in 1628 from the Imperial troops. In 1813 the Danes were defeated here, while in 1849 the harbour was the scene of the blowing up of the Danish line-of-battle ship “Christian VIII.” and of the surrender of the frigate “Gefion” after an engagement with the German shore batteries. The place lost most of its trade after the union with Germany in 1864, and suffered severely from a sea-flood in 1872. In the immediate neighbourhood is the village of Borby, much frequented for sea-bathing.

ECKERSBERG, KRISTOFFER (1783-1853), Danish painter, was born in south Jutland. He became successively the pupil of Nikolaj Abildgaard and of J.L. David. From 1810 to 1813 he lived at Paris under the direction of the latter, and then proceeded, as an independent artist, to Rome, where he worked until 1816 in close fellowship with Thorwaldsen. His paintings from this period—“The Spartan Boy,” “Bacchus and Ariadne” and “Ulysses”—testify to the influence of the great sculptor over the art of Eckersberg. Returning to Copenhagen, he found himself easily able to take the first place among the Danish painters of his time, and his portraits especially were in extreme popularity. It is claimed for Eckersberg by the native critics that “he created a Danish colour,” that is to say, he was the first painter who threw off conventional tones and the pseudo-classical landscape, in exchange for the clear atmosphere and natural outlines of Danish scenery. But Denmark has no heroic landscape, and Eckersberg in losing the golden commonplaces scarcely succeeds in being delightful. His landscapes, however, are pure and true, while in his figure-pieces he is almost invariably conventional and old-fashioned. He was president of the Danish Academy of Fine Arts in Charlottenburg.

ECKHART,[1] JOHANNES [”Meister Eckhart”] (?1260-?1327), German philosopher, the first of the great speculative mystics. Extremely little is known of his life; the date and place of his birth are equally uncertain. According to some accounts, he was a native of Strassburg, with which he was afterwards closely connected; according to others, he was born in Saxony, or at Hochheim near Gotha. Trithemius, one of the best authorities, speaks of him merely as “Teutonicus.” 1260 has frequently been given as the date of his birth; it was in all probability some years earlier, for we know that he was advanced in age at the time of his death, about 1327. He appears to have entered the Dominican order, and to have acted for some time as professor at one of the colleges in Paris. His reputation for learning was very high, and in 1302 he was summoned to Rome by Boniface VIII., to assist in the controversy then being carried on with Philip of France. From Boniface he received the degree of doctor. In 1304 he became provincial of his order for Saxony, and in 1307 was vicar-general for Bohemia. In both provinces he was distinguished for his practical reforms and for his power in preaching. Towards 1325 we hear of him as preaching with great effect at Cologne, where he gathered round him a numerous band of followers. Before this time, and in all probability at Strassburg, where he appears to have been for some years, he had come in contact with the Beghards (see [Beguines]) and Brethren of the Free Spirit, whose fundamental notions he may, indeed, be said to have systematized and expounded in the highest form to which they could attain. In 1327 the opponents of the Beghards laid hold of certain propositions contained in Eckhart’s works, and he was summoned before the Inquisition at Cologne. The history of this accusation is by no means clear. Eckhart appears, however, to have made a conditional recantation—that is, he professed to disavow whatever in his writings could be shown to be erroneous. Further appeal, perhaps at his own request, was made to Pope John XXII., and in 1329 a bill was published condemning certain propositions extracted from Eckhart’s works. But before its publication Eckhart was dead. The exact date of his death is unknown. Of his writings, several of which are enumerated by Trithemius, there remain only the sermons and a few tractates. Till the middle of the 19th century the majority of these were attributed to Johann Tauler, and it is only from Pfeiffer’s careful edition (Deutsche Mystiker d. XIV. Jahrhunderts, vol. ii., 1857) that one has been able to gather a true idea of Eckhart’s activity. From his works it is evident that he was deeply learned in all the philosophy of the time. He was a thorough Aristotelian, but by preference appears to have been drawn towards the mystical writings of the Neoplatonists and the pseudo-Dionysius. His style is unsystematic, brief and abounding in symbolical expression. His manner of thinking is clear, calm and logical, and he has certainly given the most complete exposition of what may be called Christian pantheism.

Eckhart has been called the first of the speculative mystics. In his theories the element of mystical speculation for the first time comes to the front as all-important. By its means the church doctrines are made intelligible to the many, and from it the church dogmas receive their true significance. It was but natural that he should diverge more and more widely from the traditional doctrine, so that at length the relation between his teaching and that of the church appeared to be one of opposition rather than of reconciliation. Eckhart is in truth the first who attempted with perfect freedom and logical consistency to give a speculative basis to religious doctrines. The two most important points in his, as in all mystical theories, are first, his doctrine of the divine nature, and second, his explanation of the relation between God and human thought. (See [Mysticism].)

For the German writings of Eckhart see F. Pfeiffer, Deutsche Mystiker, vol. ii. (Leipzig, 1857), and F. Jostes, Meister Eckhart und seine Jünger (Freiburg, 1895); for the Latin works, H. Denifle in Archiv f. Litt- und Kirchengeschichte d. Mittelalters, ii. (1886), pp. 417-652, and v. (1889), pp. 349-364; German translations by G. Landauer, Meister Eckarts mystische Schriften (Berlin, 1903), and Büttner (Leipzig, 1903 foll.). See also A. Lasson, Meister Eckhart der Mystiker (1868); H.L. Martensen, Meister Eckhart (1842); J. Bach, Meister Eckhart der Vater der deutschen Speculation (1864); C. Ullmann, Reformatoren vor der Reformation (1842); W. Preger, Geschichte d. deutschen Mystik, i. (1874); and “Ein neuer Traktat M. Eckharts und d. Grundzüge der Eckhartischen Theosophie” in Zeitschr. f. hist. Phil. (1864), pp. 163 foll.; A. Bullinger, Das Christenthum im Lichte der deutschen Philos. (Dillingen, 1895); H. Delacroix, Le Mysticisme spéculatif en Allemagne au XIVe siècle (Paris, 1900); E. Kramm, Meister Eckhart im Lichte der Denifleschen Funde (Bonn, 1889); R. Langenberg, Über die Verhältnisse Meister Eckharts zur niederdeutschen Mystik (Göttingen, 1896); W. Schopff, Meister Eckhart (Leipzig, 1889); A. Jundt, Hist. du panthéisme populaire au moyen âge (Paris, 1875); art. in Herzog-Hauck, Realencyklopädie (S.M. Deutsch); R.M. Jones, Mystical Religion (1909).

[1] The name is variously spelled: Eckehart, Eckart, Eckhard.

ECKHEL, JOSEPH HILARIUS (1737-1798), Austrian numismatist, was born at Enzersfeld in lower Austria, 1737. His father was farm-steward to Count Zinzendorf, and he received his early education at the Jesuits’ College, Vienna, where at the age of fourteen he was admitted into the order. He devoted himself to antiquities and numismatics. After being engaged as professor of poetry and rhetoric, first at Steyer and afterwards at Vienna, he was appointed in 1772 keeper of the cabinet of coins at the Jesuits’ College, and in the same year he went to Italy for the purpose of personal inspection and study of antiquities and coins. At Florence he was employed to arrange the collection of the grand duke of Tuscany; and the first-fruits of his study of this and other collections appeared in his Numi veteres anecdoti, published in 1775. On the dissolution of the order of Jesuits in 1773, Eckhel was appointed by the empress Maria Theresa professor of antiquities and numismatics at the university of Vienna, and this post he held for twenty-four years. He was in the following year made keeper of the imperial cabinet of coins, and in 1779 appeared his Catalogus Vindobonensis numorum veterum. Eckhel’s great work is the Doctrina numorum veterum, in 8 vols., the first of which was published in 1792, and the last in 1798. The author’s rich learning, comprehensive grasp of his subject, admirable order and precision of statement in this masterpiece drew from Heyne enthusiastic praise, and the acknowledgment that Eckhel, as the Coryphaeus of numismatists, had, out of the mass of previously loose and confused facts, constituted a true science. A volume of Addenda, prepared by Steinbüchel from Eckhel’s papers after his death, was published in 1826. Among his other works are—Choix de pierres gravées du Cabinet Impérial des Antiques (1788), a useful school-book on coins entitled Kurzgefasste Anfangsgrunde zur alten Numismatik (1787), of which a French version enlarged by Jacob appeared in 1825, &c. Eckhel died at Vienna on the 16th of May 1798.

ECKMÜHL, or Eggmühl, a village of Germany, in the kingdom of Bavaria, on the Grosse Laaber, 13 m. S.E. of Regensburg by the railway to Munich. It is famous as the scene of a battle fought here on the 22nd of April 1809, between the French, Bavarians and Wurttembergers under Napoleon, and the Austrians under the Archduke Charles, which resulted in the defeat of the latter. Napoleon, in recognition of Marshal Davout’s great share in the victory, conferred on him the title of prince of Eckmuhl. For an account of this action and those of Abensberg and Landshut see [Napoleonic Campaigns].

ECLECTICISM (from Gr. ἐκλέγω, I select), a term used specially in philosophy and theology for a composite system of thought made up of views borrowed from various other systems. Where the characteristic doctrines of a philosophy are not thus merely adopted, but are the modified products of a blending of the systems from which it takes its rise, the philosophy is not properly eclectic. Eclecticism always tends to spring up after a period of vigorous constructive speculation, especially in the later stages of a controversy between thinkers of pre-eminent ability. Their respective followers, and more especially cultured laymen, lacking the capacity for original work, seeking for a solution in some kind of compromise, and possibly failing to grasp the essentials of the controversy, take refuge in a combination of those elements in the opposing systems which seem to afford a sound practical theory. Since these combinations have often been as illogical as facile, “eclecticism” has generally acquired a somewhat contemptuous significance. At the same time, the essence of eclecticism is the refusal to follow blindly one set of formulae and conventions, coupled with a determination to recognize and select from all sources those elements which are good or true in the abstract, or in practical affairs most useful ad hoc. Theoretically, therefore, eclecticism is a perfectly sound method, and the contemptuous significance which the word has acquired is due partly to the fact that many eclectics have been intellectual trimmers, sceptics or dilettanti, and partly to mere partisanship. On the other hand, eclecticism in the sphere of abstract thought is open to this main objection that, in so far as every philosophic system is, at least in theory, an integral whole, the combination of principles from hostile theories must result in an incoherent patchwork. Thus it might be argued that there can be no logical combination of elements from Christian ethics, with its divine sanction, and purely intuitional or evolutionary ethical theories, where the sanction is essentially different in quality. It is in practical affairs that the eclectic or undogmatic spirit is most valuable, and also least dangerous.

In the 2nd century B.C. a remarkable tendency toward eclecticism began to manifest itself. The longing to arrive at the one explanation of all things, which had inspired the older philosophers, became less earnest; the belief, indeed, that any such explanation was attainable began to fail. Thus men came to adopt from all systems the doctrines which best pleased them. In Panaetius we find one of the earliest examples of the modification of Stoicism by the eclectic spirit; about the same time the same spirit displayed itself among the Peripatetics. In Rome philosophy never became more than a secondary pursuit; naturally, therefore, the Roman thinkers were for the most part eclectic. Of this tendency Cicero is the most striking illustration—his philosophical works consisting of an aggregation, with little or no blending, of doctrines borrowed from Stoicism, Peripateticism, and the scepticism of the Middle Academy.

In the last stage of Greek philosophy the eclectic spirit produced remarkable results outside the philosophies of those properly called eclectics. Thinkers chose their doctrines from many sources—from the venerated teaching of Aristotle and Plato, from that of the Pythagoreans and of the Stoics, from the old Greek mythology, and from the Jewish and other Oriental systems. Yet it must be observed that Neoplatonism, Gnosticism, and the other systems which are grouped under the name Alexandrian, were not truly eclectic, consisting, as they did, not of a mere syncretism of Greek and Oriental thought, but of a mutual modification of the two. It is true that several of the Neoplatonists professed to accept all the teaching both of Plato and of Aristotle, whereas, in fact, they arbitrarily interpreted Aristotle so as to make him agree with Plato, and Plato so as to make his teachings consistent with the Oriental doctrines which they had adopted, in the same manner as the schoolmen attempted to reconcile Aristotle with the doctrines of the church. Among the early Christians, Clement of Alexandria, Origen and Synesius were eclectics in philosophy.

The eclectics of modern philosophy are too numerous to name. Of Italian philosophers the eclectics form a large proportion. Among the German we may mention Wolf and his followers, as well as Mendelssohn, J.A. Eberhard, Ernst Platner, and to some extent Schelling, whom, however, it would be incorrect to describe as merely an eclectic. In the first place, his speculations were largely original; and in the second place, it is not so much that his views of any time were borrowed from a number of philosophers, as that his thinking was influenced first by one philosopher, then by another.

In the 19th century the term “eclectic” came to be applied specially to a number of French philosophers who differed considerably from one another. Of these the earliest were Pierre Paul Royer-Collard, who was mainly a follower of Thomas Reid, and Maine de Biran; but the name is still more appropriately given to the school of which the most distinguished members are Victor Cousin, Théodore Jouffroy, J.P. Damiron, Barthélemy St Hilaire, C.F.M. de Rémusat, Adolphe Garnier and Ravaisson-Mollien. Cousin, whose views varied considerably at different periods of his life, not only adopted freely what pleased him in the doctrines of Pierre Laromiguière, Royer-Collard and Maine de Biran, of Kant, Schelling and Hegel, and of the ancient philosophies, but expressly maintained that the eclectic is the only method now open to the philosopher, whose function thus resolves itself into critical selection and nothing more. “Each system,” he asserted, “is not false, but incomplete, and in reuniting all incomplete systems, we should have a complete philosophy, adequate to the totality of consciousness.” This assumes that every philosophical truth is already contained somewhere in the existing systems. If, however, as it would surely be rash to deny, there still remains philosophical truth undiscovered, but discoverable by human intelligence, it is evident that eclecticism is not the only philosophy. Eclecticism gained great popularity, and, partly owing to Cousin’s position as minister of public instruction, became the authorized system in the chief seats of learning in France, where it has given a most remarkable impulse to the study of the history of philosophy.

ECLIPSE (Gr. ἔκλειψις, falling out of place, failing), the complete or partial obscuration of one heavenly body by the shadow of another, or of the disk of the sun by the interposition of the moon; then called an eclipse of the sun. Eclipses are of three classes: those of the sun, as just defined; those of the moon, produced by its passage through the shadow of the earth, and those of the satellites of other planets, produced by their passage through the shadow of their primary. Jupiter (q.v.) is the only planet of whose satellites the eclipses can be observed, unless under very rare circumstances.

The geometrical conditions of an eclipse of the sun or moon are shown in fig. 1, which represents the earth E as casting its shadow towards C, and the moon M between the earth and sun as throwing its shadow towards some part of the earth and eclipsing the sun. The dark conical regions are those within which the sun is entirely hidden from sight. This portion of the shadow is called the umbra. Around the umbra is an enveloping shaded cone with its vertices directly towards the sun. To an observer within this region the sun is partly hidden from view. As the apparent path of the moon may pass to the north or south of the line joining the earth and sun, the axis of its shadow may pass to the north or south of the earth, and not meet it at all. An eclipse of the sun is called central when the shadow axis strikes any part of the earth; partial when only the penumbra falls upon the earth. It is evident that an eclipse can be seen as central only at those points of the earth’s surface over which the axis of the shadow passes.

A central eclipse is total when the umbra actually reaches the earth; annular when it does not. These two cases are shown in figs. 2 and 3. In the first of these the sun is entirely hidden within the region uu′. In fig. 3 within the region aa’ the apparent diameter of the sun is slightly greater than that of the moon, and at the moment of greatest eclipse a narrow ring of sunlight is seen surrounding the dark body of the moon.

We shall treat the subject in the following sections:—

I. Phenomena of Eclipses of the Sun and conclusions derived from their observation.

II. Eclipses of the Moon.

III. The Laws and Cycles of recurrences of Eclipses of the Sun and Moon.

IV. Chronological list of remarkable eclipses of the Sun, past and future, to the end of the 20th century.

V. Description of the methods of computing eclipses.

I. Phenomena of Eclipses of the Sun.

While an eclipse of the sun, whether partial, annular or total, is in progress, no striking phenomena are to be noted until, in the case of total eclipses, the moment of the total phase approaches. It will, however, be noticed that as the moon advances on the solar disk the sharply defined and ragged edge of the moon’s disk contrasts strongly with the soft and uniform outline of the sun’s limb. As the total phase approaches, the phenomenon known as shadow bands may sometimes be seen. These consist of seeming vague and rapidly moving wave-like alternations of light and shade flitting over any white surface illuminated by the sun’s rays immediately before and after the total phase. They are probably due to a flickering of the light from the thin crescent, produced by the undulations of the air, in the same way that the twinkling of the stars is produced. The rapid progressive motion sometimes assigned to them may be regarded as the natural result of an optical illusion. A few seconds before the commencement of the total phase the red light of the chromosphere becomes visible, and will be seen most distinctly as continuations of the solar crescent at its two ends. Owing to the inequalities of the lunar surface, the diminution of the solar crescent does not go on with perfect uniformity, but, just before the last moment, what remains of it is generally broken up into separate portions of light, which, magnified and diffused by the irradiation of the telescope, present the phenomenon long celebrated under the name of “Baily’s beads.” These were so called because minutely and vividly described by Francis Baily as he observed them during the annular eclipse of May 15, 1836, when he compared them to a string of bright beads, irregular in size and distance from each other. The disappearance of the last bead is commonly taken as the beginning of totality. An arc of the chromosphere will then be visible for a few seconds at and on each side of the point of disappearance, the length and duration of which will depend on the apparent diameter of the moon as compared with that of the sun, being greater in length and longer seen as the excess of diameter of the moon is less. The red prominences may now generally be seen here and there around the whole disk of the moon, while the effulgence of soft light called the corona surrounds it on all sides. Before the invention of the spectroscope, observers of total eclipses could do little more than describe in detail the varying phenomena presented by the prominences and the corona. Drawings of the latter showed it to have the appearance of rays surrounding the dark disk of the moon, quite similar to the glory depicted by the old painters around the head of a saint. The discrepancies between the outlines as thus pictured, not only at different times, but by different observers at the same time and place, are such as to show that little reliance can be placed on the details represented by hand drawings.

During the eclipse of July 8, 1842, the shadow of the moon passed from Perpignan, France, through Milan and Vienna, over Russia and Central Asia, to the Pacific Ocean. Very detailed physical observations were made, but none which need be specially mentioned in the present connexion.

The eclipse of July 28, 1851, was total in Scandinavia and Russia. It was observed in the former region by many astronomers, among them Sir George B. Airy and W.R. Dawes. It was specially noteworthy for the first attempt to photograph such a phenomenon. A daguerreotype clearly showing the protuberances was taken by Berkowski at the Observatory of Königsberg. An attempt by G.A. Majocchi to daguerreotype the corona was a failure. Photographs of the eclipse of July 18, 1860, were taken by Padre Angelo Secchi and Warren De La Rue, which showed the prominences well, and proved that they were progressively obscured by the edge of the advancing moon. It was thus shown that they were solar appendages, and did not belong to the moon, as had sometimes been supposed. The corona was barely visible on De La Rue’s plates, but those of Secchi showed it, with its rifts and the bases of the tall coronal wings, to about 15’ from the sun’s limb. The sketches taken at this eclipse proved that the corona extended in some regions 1° from the sun’s limb. As the sensitiveness of photographic plates has increased, they have gradually been wholly relied upon for information respecting the corona, so that at the present time naked-eye descriptions are regarded as of little or no scientific value. Owing to the great contrast between the brilliancy of the coronal light at its base and its increasing faintness as it extends farther from the sun, no one photograph will bring out all the corona. An exposure of one or two seconds is ample to show the details of inner corona to the best advantage, while longer exposures give greater extent of the brighter portions. The most extended streamers are very little brighter than the sky, and must be photographed with long exposures.

The first application of the spectroscope to the phenomenon was made during the total solar eclipse of August 18, 1868, by P.J.C. Janssen and other observers in India. By them was made the capital discovery that the red solar prominences give a spectrum of bright lines, and are therefore immense masses of incandescent gases, chiefly hydrogen and the vapours of calcium and helium. Janssen also found that this bright-line spectrum could be followed after the eclipse was over, and, in fact, could be observed at any time when the air was sufficiently transparent. By one of those remarkable coincidences which frequently occur in the history of science, this last discovery was made independently by Sir Norman Lockyer in England before the news of Janssen’s success had reached him. It was afterwards found that, by giving great dispersing power to the spectroscope, the prominences could be observed in a wide slit, in their true form. At this eclipse the spectrum of the corona was also observed, and was supposed to be continuous, while polariscopic observation by Lieutenant Campbell showed it polarized in planes passing through the sun’s centre. The conclusion from these two observations was that the light was composed, at least in great part, of reflected sunlight.

At the total eclipse of August 7, 1869, it was independently found by Professors C.A. Young of Princeton and W. Harkness of Washington that the continuous spectrum of the corona was crossed by a bright line in the green, which was long supposed to be coincident with 1474 of Kirchhoff’s scale. This coincidence is, however, now found not to be real, and the line cannot be identified with that of any terrestrial substance. The name “coronium” has therefore been given to the supposed gas which forms it. It is now known that 1474 is a double line, one component of which is produced by iron, while the other is of unknown origin. The wave-length of the principal component is 5317, while that of the coronal line was found at the eclipses of 1896 and 1898 to be 5303.

The eclipse of December 28, 1870, passed over the south-western corner of Spain, Gibraltar, Oran and Sicily. It is memorable for the discovery by Young of the “reversing layer” of the solar atmosphere. This term is now applied to a shallow stratum resting immediately upon the photosphere, the absorption of which produces the principal dark lines of the solar spectrum, but which, being incandescent, gives a spectrum of bright lines by its own light when the light of the sun is cut off. This layer is much thinner than the chromosphere, and may be considered to form the base of the latter. Owing to its thinness, the phenomenon of the reversed bright lines is almost instantaneous in its nature, and can be observed for a period exceeding one or two seconds only near the edge of the shadow-path, where the moon advances but little beyond the solar limb. Near the central line it is little more than a flash, thus giving rise to the term “flash-spectrum.” Young also at this eclipse saw bright hydrogen lines when his spectroscope was directed to the centre of the dark disk of the moon. This can only be attributed to the reflection of the light of the prominences and chromosphere from the atmosphere between us and the moon. The coronal light as observed in the spectroscope may thus be regarded as a mixture of true coronal light with chromospheric light reflected from the air, and it is therefore probable that the H and K (calcium) lines of the coronal spectrum are not true coronal lines, but chromospheric.

At the eclipse of December 12, 1871, visible in India and Australia, Janssen observed, as he supposed, some of the dark lines of the solar spectrum in the continuous spectrum of the corona, especially D, b and G. This would show that an important part of the coronal light is due to reflected sunshine. This feature of the spectrum, however, is doubtful in the most recent photographs under the best conditions. At this eclipse the remarkable observation was also made by Colonel John Herschel and Colonel J.F. Tennant that the characteristic line of the coronal spectrum is as bright in the dark rifts of the corona as elsewhere. This would show that the gas coronium does not form the streamers of the corona, but is spherical in form and distributed uniformly about the sun. Photographs were also taken on wet plates by a party in Java and by the parties of Lord Lindsay (at Baikul, India) and of Colonel Tennant (at Dodabetta). The Baikul and Dodabetta photographs were of small size (moon’s diameter = 3⁄10 in.), but of excellent definition. A searching study was made of them by A. C Ranyard and W.H. Wesley (Memoirs R.A.S. vol. xli., 1879), and for the first time a satisfactory representation of the corona was obtained. The drawings in the volume quoted show its polar rays, wings, interlacing filaments and rifts as they are now known to be, as well as the forms and details of the prominences.

The eclipse of April 16, 1874, was observed in South Africa by E.J. Stone, H.M. astronomer at the Cape, who traced the coronal line about 30’ (430,000 m.) from the sun’s limb. The visual corona was seen to extend in places some 90′ from the limb.

The eclipse of April 6, 1875, was observed in Siam by Sir J. Norman Lockyer and Professor Arthur Schuster. Their photographs showed the calcium and hydrogen lines in the prominence spectrum.

The eclipse of July 29, 1878, was observed by many astronomers in the United States along a line extending from Wyoming to Texas. A number of the stations were at high altitudes (up to 14,000 ft.), and the sky was generally very clear. The visible corona extended on both sides of the sun along the ecliptic for immense distances—at least twelve lunar diameters, about eleven million miles. Photographs taken by the parties of Professors A. Hall and W. Harkness gave the details of the inner corona and of the polar rays, showing the filamentous character of the corona, especially at its base in the polar regions. A photograph taken by the party of Professor E.S. Holden showed the outer corona to a distance of 50′ from the moon’s limb. The bright-line spectrum of the corona was excessively faint and, as the solar activity (measured by sun-spot frequency) was near a minimum, it was concluded that the brilliancy of the coronium line varied in the sun-spot period, a conclusion which subsequent eclipse observations seem to have verified. It is not yet certain that the other coronal spectrum lines vary in the same way.

The eclipse of May 17, 1882, was observed in Egypt. On the photographs of the corona the image of a bright comet was found, the first instance of the sort. (A faint comet was found on the plates of the Lick Observatory eclipse expedition to Chile in 1893.) The slitless spectroscope showed the green line (coronium) and D3 (helium) in the coronal spectrum.

The eclipse of May 6, 1883, was observed from a small coral atoll in the South Pacific Ocean by parties from America, England, France, Austria and Italy. A thorough search was made by Holden (with a 6 in. telescope) for an intra-Mercurial planet, without success, during an unusually long totality (5 m. 23 s.). J. Palisa also searched for such a planet. Janssen again reported the presence of dark lines in the coronal spectrum. “White” prominences were seen by P. Tacchini.

The eclipse of August 29, 1886, was observed in the West Indies. The English photographs of the corona, taken with a slitless spectroscope, show the hydrogen lines as well as K and f. Tacchini devoted his attention to the spectra of the prominences, and showed that their upper portions contained no hydrogen lines, but only the H and K lines of calcium. He also observed a very extensive “white” prominence. It was shown on the photographs of the corona, but could not be seen in the Hα line with the spectroscope. It has been suggested by Professor G.E. Hale that the colour of a “white” prominence may be due to the fact that the H and K lines (calcium) are of their normal intensity, while the less refrangible prominence lines are, from some unknown cause, comparatively faint. It is known that the intensity of such lines does, in fact, vary, though it is not yet certain that the “white” prominences are produced in this way. The subject is one demanding further observation. High prominences are generally “white” at their summits, “red” at their bases. The Harvard College Observatory photographs show the corona out to 90′ from the moon’s limb, though no detail is visible beyond 60′. W.H. Pickering made a series of photographic photometric measures of the corona, some of which are given below, together with results deduced by Holden from the eclipses of January and December 1889:—

The results in the first and third columns are derived from plates taken in a very humid climate, and are not very different.

The eclipse of August 19, 1887, was total in Japan and Russia, but cloudy weather prevented successful observations except in Siberia and eastern Russia.

The eclipse of January 1, 1889, was observed in California and Nevada by many American astronomers. The photographs of the corona, especially those by Charoppin and E.E. Barnard, show a wealth of detail. Those of Barnard, of the Lick Observatory party, were studied by Holden, and exhibited the fact that rays, like the “polar-rays,” extended all round the sun, instead of being confined to the polar regions only. The outer corona was registered out to 100′ from the moon’s limb on Charoppin’s negatives, to 130′ on those of Lowden and Ireland. On other plates the outline of the moon is visible projected on the corona before totality began. The spectrum of the corona showed few bright lines besides those of coronium and hydrogen.

The eclipse of December 22, 1889, was observed in Cayenne, S. America, by a party from the Lick Observatory under rather unfavourable conditions. Expeditions sent to Africa were baffled by cloudy weather. Father Stephen Joseph Perry observed at Salute Islands, French Guiana, and obtained some photographs of value. The effort cost him his life, for he died of malarial fever five days after the eclipse.

The eclipse of April 16, 1893, was observed by British and French parties in Africa and Brazil, and by Professor J.M. Schaeberle of the Lick Observatory in Chile. The Chile photographs of the corona were taken with a lens of 40 ft. focus, and are extremely fine. They show a faint comet near the sun. No great extensions to the corona were shown on any of the negatives, or seen visually, though they were specially looked for by British parties. The neighbourhood of the sun was carefully examined by G. Bigourdan without finding any planet. The spectrum of the corona was the usual one. The following lines were photographed in slitless spectroscopes, and undoubtedly belong to the corona: W. L. 3987; 4086; 4217; 4231; 4240; 4280; 4486; 5303 (the last number is the wave-length of the green coronium line). All of these have been seen in slit spectroscopes also. It is possible that two lines observed by Young in 1869, namely, W. L. (Ångstrom) 5450 and 5570, should be added to the list of undoubted coronal lines. It is not likely that helium or hydrogen or calcium vapour forms part of the corona. The wave-lengths of some 700 lines belonging to the chromosphere and prominences were determined by the British parties.

The eclipse of August 9, 1896, was total in Norway, Novaya Zemlya and Japan. The day was very unfavourable as to weather, but good photographs of the corona were obtained by Russian parties in Siberia and Lapland. Shackelton, in Novaya Zemlya, with a prismatic camera obtained a photograph of the reversing-layer at the beginning of totality. This photograph completely confirms Young’s discovery, and shows the prominent Fraunhofer lines bright, the bright lines of the chromosphere spectrum being especially conspicuous.

At the solar eclipse of January 22, 1898, the shadow of the moon traversed India from the western coast to the Himalaya. The duration of totality was about 2 m. The eclipse was very fully observed, more than 100 negatives of the corona being secured. The equatorial extension of the visible corona was short and faint, and the invisible (spectroscopic) corona was also very faint. The spectrum of the reversing-layer was successfully photographed; one set of negatives shows the polarization of one of the longest streamers of the corona, and proves the presence of dust particles reflecting solar light. The bright-line spectrum of hydrogen in the chromosphere was followed to the thirtieth point of the series, and the wave-lengths were shown to agree closely with Balmer’s formula (see [Spectroscopy]). The wave-length of coronium was found to be 5303 (not 5317 as previously supposed), and the brightness of the corona was measured. E.W. Maunder made the curious observation of coronal matter enveloping a prominence in the form of a hood.

Observations of the eclipse of May 28, 1900, were favoured in a remarkable degree by the absence of clouds. The photographs of the corona obtained by W.W. Campbell extended four diameters of the sun on the west side. The sun’s edge was photographed with an objective-prism spectrograph composed of two 60° prisms in front of a telescope of 2 in. aperture and 60 in. focus. A fine photograph, 6 in. long, of the bright- and dark-line spectra of the sun’s edge at the end of totality was thus obtained. It shows 600 bright lines sharply in focus besides the dark-line spectrum, to which the bright lines gave way as the sun reappeared. The coronal material radiating the green light was found to be markedly heaped up in the sun-spot regions. No dark lines were found in the spectrum of the inner corona. G.E. Hale and E.B. Frost also photographed the combined bright- and dark-line spectra of the solar cusps at the instants before and after totality. On one photograph showing no dark lines 70 bright lines could be measured between 4070 and 4340. On another were 70 bright lines between Hb and Hs. On a third were 266 bright lines between 4026 and 4381, and some dark lines. These lines show a marked dissimilarity from the solar spectrum.

(S. N.)

The eclipse of May 18, 1901, was observable in Mauritius with 3½ minutes of totality, and in Sumatra with 6½ minutes. Unfortunately there was cloudy weather in Sumatra, which at some stations prevented observations entirely and at others neutralized the advantages promised by the long duration of totality. Thus spectroscopic observations for the detection of motion of the corona, for which the long totality gave a special opportunity, failed owing to cloud; and the search for intra-Mercurial planets had only a negative result, though stars down to magnitude 8.8 were photographed on the plates. But though no particular step in advance was taken, successful records of the eclipse were obtained, which will enable comparison to be made with other eclipses and will contribute their share to the discussion of the whole series. These include photographs of the corona, showing that it was of the sun-spot minimum type, and available for measures of its brightness; photographs of the spectra of the chromosphere and corona which are of the same general character as those obtained at previous eclipses; photographs showing the polarization of the corona, available for quantitative measures of polarization at different points. Photographs of the spectrum of the outer corona taken by the Lick Observatory party show a strong Fraunhofer dark-line spectrum, consistent with the view that the light is reflected sunlight. At Mauritius there was no cloud, but the definition was poor. Successful photographs of the corona were obtained for comparison with those taken in Sumatra one and a half hours later, but nothing of great interest was revealed by the comparison.

The eclipse of August 30, 1905, offered a duration of 3½ minutes in Spain, the track running from Labrador through Spain to North Africa, and affording excellent opportunities for observers, who flocked to the central line in great numbers. Unfortunately it was cloudy in Labrador, so that the special advantages of the long line of possible stations were lost. Exceptionally good weather conditions were enjoyed in Algeria and Tunisia, and full advantage was taken of them by H.F. Newall, C. Trépied and others at Guelma, by the party from Greenwich and G. Bigourdan at Sfax. That G. Newall’s spectroscopic photographs for rotation of the corona again gave no result is a clear indication of the faintness of the corona at 3′ from the limb; but F.W. Dyson at Sfax obtained two new lines at 5536 and 5117 in the spectrum of the corona; and a very large number of photographs of the corona (including many in polarized light on several different plans), of its spectrum, and of the spectrum of the chromosphere, were obtained by the various parties, which will afford copious material for discussion. Newall also obtained a polarized spectrum of the corona. Altogether no less than eighty stations were occupied. There were English, American, Russian and German observers in Egypt; English and French in Algeria and Tunisia; English in Majorca; observers of almost all nationalities in Spain; and English and American in Labrador. In Egypt the weather was bright, though the sun was low; in Majorca and Spain there were local clouds. Consequently many observations, in addition to those in Labrador, were lost, notably the special spectroscopic observations undertaken by Evershed on the northern limit of totality, and the observations of radiation undertaken by H.L. Callendar. A search for intra-Mercurial planets was conducted on an elaborate plan, with similar batteries of telescopes, in Egypt, Spain and Labrador, by three parties from the Lick Observatory, but the examination of the plates showed nothing noteworthy. Pending discussion of the greater part of the material, some interesting preliminary results were published in 1906 by the French observers. C.E.H. Bourget and Montangerand conclude that there is a marked division of the chromosphere into two regions or shells, a lower or “reversing-layer,” extending only 1″ from the limb, and a chromospheric layer extending to 3″ or 4″; and that the coronal light contains less blue and violet, but more green and yellow, than sunlight; while Fabry, by visual methods, obtained measures of the total and intrinsic intensity of the light from the corona closely confirming recent photographic observations, finding the total brightness about equal to that of the full moon, and the intrinsic brightness at 5′ from the limb about one quarter of that of the full moon.

(H. H. T.)

II. Eclipses of the Moon.

The physical phenomena attending eclipses of the moon are no longer of a high order of interest either to the layman or scientific observer. A brief statement of them and their causes will therefore be sufficient. An observer watching such an eclipse from the moon would see the earth, which has nearly four times the apparent diameter of the sun, impinging on the sun’s disk and slowly hiding it. The phenomenon would be quite similar to that of an eclipse of the sun seen from the earth, until the sun was completely covered. During the progress of this partial eclipse the moon would be passing into the earth’s penumbra. As the moment of total obscuration approached, a red band of light would rapidly form in the neighbourhood of the disappearing limb of the sun, and gradually extend around the earth. This would arise from the refraction of the sun’s light by the earth’s atmosphere, and the absorption of its blue rays. When the light of the sun was completely hidden, a reddish ring of great brilliancy would, owing to this cause, surround the entire dark body of the earth during the period of the total eclipse.

The aspect of the moon, as seen from the earth, corresponds to this view from the moon. The fading of the moon’s light, due to its entrance into the penumbra, is scarcely noticeable without direct photometric determination until near the beginning of the total phase. Then, as the limb of the moon approaches the earth’s shadow, it begins to darken. When only a small portion has entered into the shadow, that portion is completely hidden. But, as the total phase approaches, the part of the moon’s disk immersed in the penumbra becomes visible by a reddish coppery light—that of the sun refracted through the lower parts of the earth’s atmosphere. The brightness of this illumination is different in different eclipses, a circumstance which may be attributed to the greater or less degree of cloudiness in those regions of the earth’s atmosphere through which the light of the sun passes in order to reach the moon. Its colour is due to absorption in passing through the earth’s atmosphere.

III. Laws and Cycles of Recurrences of Eclipses of the Sun and Moon.

It has been known since remote antiquity that eclipses occur in cycles. These cycles are known now to be determined principally by the motion of the moon’s node and the relations between the revolutions of the earth round the sun and the moon round the earth.

Owing to the inclination of the moon’s orbit to the plane of the ecliptic, an eclipse of the sun can occur only when the conjunction of the sun and moon takes place within about 16° of one of the nodes of the moon’s orbit. The Eclipse seasons. eclipse can be total only within about 11° of the node. An eclipse of the moon can occur only when the line sun-moon-earth makes an angle less than about 11° with the line of nodes; and the eclipse can be total only within about 8° of the node, the average limiting distances varying 1° or 2° according to the circumstances. These conditions being understood, the cycles of recurrence of eclipses of either kind can be worked out geometrically from the mean motions of the sun, moon, node and perigee by the aid of geometric conceptions shown in their simplest form in fig. 4. Here E is the earth, at the centre of a circle representing the mean orbit of the moon around it. MN is the line of nodes which is moving in the retrograde direction from N towards S1, at a rate of about 19.3° in a year, making a complete revolution in 18.6 years. Let the sun at the moment of some new moon be in the line ES1, continued. If the angle NES1 is less than 16° there will probably be an eclipse of the sun, which may be central if the angle is less than 11°. Let the next new moon take place in the line ES2 a month later. The mean value of the angle S1ES2 is about 29°; but as the node N has moved towards S1 about 1.4° during the interval, the sum of the angles NES1 and NES2 will be somewhat greater than S1ES2 by about 1.6°. The result is that if these two angles are nearly equal there may be two small partial eclipses of the sun, after which no more can occur until, by the annual revolution of the earth, the direction of the sun approaches the opposite line of nodes EM, nearly six months later. The result is that there are in the course of any one year two “eclipse seasons” each of about one month in duration, in which at least one eclipse of the sun, or possibly two small partial eclipses, may occur. One eclipse of the moon will generally, but not always, occur during a season.

Owing to the retrograde motion of the node the direction ES of the sun returns to the node at the end of about 347 days, so that a third eclipse season may commence before the end of a year. In this way there is a possible but very rare maximum of five eclipses of the sun in a year. Owing to the motion of the line of nodes each eclipse season occurs about 19 days earlier in the year than it did the year before. Another conclusion from the greater eclipse limit for the sun than for the moon is that in the long run eclipses of the sun, as regards the earth generally, occur oftener than those of the moon. But as any eclipse of the sun is visible only from a limited region of the earth’s surface, while one of the moon may be seen from an entire hemisphere, more eclipses of the moon are visible at any one place than of the sun.

If, starting with a conjunction along some line ES1, we mark by radial lines from E the successive conjunctions year after year, we shall find that at the end of 18 years and about 11 days the 223rd conjunction will fall once more very near the line ES1, the angle NES1 being about 24′ greater than before. Successive eclipses will then occur very nearly in the same order as they did 18 years and 11 days before. This period of recurrence has been known from remote antiquity and is called the Saros. What is most remarkable in this period is that in addition to the distance from the node being nearly the same as before, the longitude of the sun increases by only 11° and the distance of the moon from its perigee has changed less than 3°. The result of this approach to coincidence is that the recurring eclipse will generally be of the same kind—total, annular or partial—through a number of successive periods.

To see the law of recurrence of corresponding eclipses in the successive periods let us suppose the line of conjunction ES1 to be that at which there is a very small eclipse, visible only in high northern or southern latitudes. At the end of 18 years 11 days a second eclipse will occur along a line nearly half a degree nearer EN, the line of nodes. The successive eclipses will occur at the same interval through about ten periods, or 180 years, when the line of conjunction will pass within 11° of EN. Then the eclipse will be central, whether annular or total depending on circumstances: in the first one the central lines will pass only over the polar regions; but in successive eclipses of the series it will pass nearer and nearer to the equator until the conjunction line coincides with the node. The path of centrality will then cross in the equatorial region. During 22 or 23 more recurrences the path will continually approach to the opposite pole and finally leave the earth entirely. The entire number of central eclipses in any one series will generally be about forty-five. Then a series of continually diminishing partial eclipses will go on for about ten periods more. The whole series of eclipses will therefore extend through about sixty-five periods; and interval of time of about twelve hundred years.

Another remarkable eclipse period recurs at the end of 358 lunations. At the end of this period the line of mean conjunction ES1 falls so near its former position relative to the node that we find each central eclipse visible in our time to be one of an unbroken series extending from the earliest historic times to the present, at intervals equal to the length of the period. The recurring eclipses in this period do not, however, have the remarkable similarity of those belonging to the Saros, but may differ to any extent, owing to the different positions of the line of conjunction with respect to the moon’s perigee. Moreover, they recur alternately at the ascending and descending node. The length of the period is 10,571.95 days, or 29 Julian years less 20.3 days. Hence 18 periods make 521 years, so that at the end of this time each eclipse recurs on or about the same day of the year. As an example of this series, starting from the eclipse of Nineveh, June 15, 763 B.C., recorded on the Assyrian tablets, we find eclipses on May 27, 734 B.C., May 7, 705 B.C., and so on in an unbroken series to 1843, 1872 and 1901, the last being the 93rd of the series. Those at the ends of the 521-year intervals occurred on June 15, O.S., of each of the years 763, 242 B.C., A.D. 280, 801, 1322 and 1843. As the lunar perigee moves through 242.4° in a period, the eclipses will vary from total to annular, but at the end of 3 periods the perigee is only 7.1° in advance of its original position relative to the node. Hence in a series including every third eclipse the eclipses will be of the same character through a thousand years or more. Thus the eclipses of 1467, 1554, 1640, 1727, 1814, 1901, 1988, &c., are total.

IV. Chronological Lists of Eclipses of the Sun.

The following is a brief chronological enumeration of those total eclipses of the sun which are of interest, either from their historic celebrity or the nature of the conclusions Notable eclipses. derived from them. In numbering the years before the Christian era the astronomical nomenclature is used, in which the number of the year is one less than that used by the chronologists. The Chinese eclipses are passed over, owing to the generally doubtful character of the records pertaining to them.

—1069 June 20 and —1062 July 31; total eclipses recorded at Babylon.

—762, June 14; a total eclipse recorded at Nineveh. Computation from the modern tables shows that the path of totality passed about 100 m. or more north of Nineveh.

—647, April 6; total eclipse at or near Thasos, mentioned by Archilochus.

—584, May 28; the celebrated eclipse of Thales. For an account of this eclipse see [Thales].

—556, May 19, the eclipse of Larissa. The modern tables show that the eclipse was not total at Larissa, and the connexion of the classical record with the eclipse is doubtful.

—430, August 3; eclipse mentioned by Thucydides, but not total by the tables.

—399, June 21; eclipse of Ennius. Totality occurred immediately after sunset at Rome. The identity of this eclipse is doubtful.

—309, August 14; eclipse of Agathocles. This eclipse would be one of the most valuable for testing the tables of the moon, but for an uncertainty as to the location of Agathocles, who, at the time of the occurrence, was at sea on a voyage from Syracuse to Carthage.

F.K. Ginzel (Spezieller Kanon der Finsternisse) has collected a great number of passages from classical authors supposed to refer to eclipses of the sun or moon, but the difficulty of identifying the phenomenon is frequently such as to justify great doubt as to the conclusions. In a few cases no eclipse corresponding to the description can be found by our modern table to have occurred, and in others the latitude of interpretation and the uncertainty of the date are so wide that the eclipse cannot be identified.

Of medieval eclipses we mention only the dates of those visible in England, referring for details to the works mentioned in the bibliography. The letter C following a date shows that the eclipse is mentioned in the Anglo-Saxon Chronicles. The dates in question are:—

Besides these, the tables show that the shadow of the moon passed over some part of the British Islands on 1424, June 26; 1433, June 17; 1598, March 6; 1652, April 8; 1715, May 2; 1724, May 22. Of these the eclipse of 1715 is notable for the careful observations made in England, and published by Halley in the Philosophical Transactions. The next dates are 1927, June 29, when a barely total eclipse will be seen soon after sunrise in the northern counties near the Scottish border, and 1999, August 11, when the moon’s shadow will graze England at Land’s End.

We give below, in tabular form, a list of the principal total eclipses during the 19th and 20th centuries, omitting a few visible only in the extreme polar regions, and some others of which the duration is very short. The first column gives the civil date of the point on the earth’s surface at which the eclipse is central at noon. The next two columns give the position of this point to the nearest degree. The fourth column shows the Greenwich astronomical time of conjunction in longitude. The next column gives the duration of the total phase at the noon-point; this is sometimes 0.1′ less than the absolutely greatest duration at any point. Next is given the node near which the eclipse occurs; and then the number in the Saros. Corresponding eclipses at intervals of 18 y. 11 d. have the same number, and occur near the same node of the noon, which is indicated in the next column.

Recurrence of Remarkable Eclipses.

From the property of the Saros it follows that eclipses remarkable for their duration, or other circumstances depending on the relative positions of the sun and moon, occur at intervals of one saros (18 y. 11 d.). Of interest in this connexion is the recurrence of total eclipses remarkable for their duration. The absolute maximum duration of a total eclipse is about 7′ 30″; but no actual eclipse can be expected to reach this duration. Those which will come nearest to the maximum during the next 500 years belong to the series numbered 4 and 6 and in the list which precedes. These occurring in the years 1937, 1955, &c., will ultimately fall little more than 20″ below the maximum. But the series 4, though not now remarkable in this respect, will become so in the future, reaching in the eclipse of June 25, 2150, a duration of about 7′ 15″ and on July 5, 2168, a duration of 7′ 28″, the longest in human history. The first of these will pass over the Pacific Ocean; the second over the southern part of the Indian Ocean near Madras.

All the national annual Ephemerides contain elements of the eclipses of the sun occurring during the year. Those of England, America and France also give maps showing the path of the central line, if any, over the earth’s surface; the lines of eclipse beginning and ending at sunrise, &c., and the outlines of the shadow from hour to hour. By the aid of the latter the time at which an eclipse begins or ends at any point can be determined by inspection or measurement within a few minutes.

V. Methods of computing Eclipses of the Sun.

The complete computation of the circumstances of an eclipse ab initio requires three distinct processes. The geocentric positions of the sun and moon have first to be computed from the tables of the motions of those bodies. The second Elements of eclipses. step is to compute certain elements of the eclipse from these geocentric positions. The third step is from these elements to compute the circumstances of the eclipse for the earth generally or for any given place on its surface. The national Astronomical Ephemerides, or “Nautical Almanacs,” give in full the geocentric positions of the sun and moon from at least the early part of the 19th century to an epoch three years in advance of the date of publication. It is therefore unnecessary to undertake the first part of the computation except for dates outside the limits of the published ephemerides, and for many years to come even this computation will be unnecessary, because tables giving the elements of eclipses from the earliest historic periods up to the 22nd century have been published by T. Ritter von Oppolzer and by Simon Newcomb. We shall therefore confine ourselves to a statement of the eclipse problem and of the principles on which such tables rest.

Two systems of eclipse elements are now adopted in the ephemerides and tables; the one, that of F.W. Bessel, is used in the English, American and French ephemerides, the other—P. A. Hansen’s—in the German and in the eclipse tables of T. Ritter von Oppolzer. The two have in common certain geometric constructions. The fundamental axis of reference in both systems is the line passing through the centres of the sun and moon; this is the common axis of the shadow cones, which envelop simultaneously the sun and moon as shown in figs. 1, 2, 3. The surface of one of these cones, that of the umbra, is tangent to both bodies externally. This cone comes to a point at a distance from the moon nearly equal to that of the earth. Within it the sun is wholly hidden by the moon. Outside the umbral cone is that of the penumbra, within which the sun is partially hidden by the moon. The geometric condition that the two bodies shall appear in contact, or that the eclipse shall begin or end at a certain moment, is that the surface of one of these cones shall pass through the place of the observer at that moment. Let a plane, which we call the fundamental plane, pass through the centre of the earth perpendicular to the shadow axis. On this plane the centre of the earth is taken as an origin of rectangular co-ordinates. The axis of Z is perpendicular to the plane, and therefore parallel to the shadow axis; that of Y and X lie in the plane. In these fundamental constructions the two methods coincide. They differ in the direction of the axis of Y and X in the fundamental plane. In Bessel’s method, which we shall first describe, the intersection of the plane of the earth’s equator with the fundamental plane is taken as the axis of X. The axis of Y is perpendicular to it, the positive direction being towards the north. The Besselian elements of an eclipse are then:—x, y, the co-ordinates of the shadow axis on the fundamental plane; d, the declination of that point in which the shadow axis intersects the celestial sphere; μ, the Greenwich hour angle of this point; l, the radius of the circle, in which the penumbral or outer cone intersects the fundamental plane; and l’, the radius of the circle, in which the inner or umbral cone intersects this plane, taken positively when the vertex of the cone does not reach the plane, so that the axis must be produced, and negatively when the vertex is beyond the plane.

Hansen’s method differs from that of Bessel in that the ecliptic is taken as the fundamental plane instead of the equator. The axis of X on the fundamental plane is parallel to the plane of the ecliptic; that of Y perpendicular to it. The other elements are nearly the same in the two theories. As to their relative advantages, it may be remarked that Hansen’s co-ordinates follow most simply from the data of the tables, and are necessarily used in eclipse tables, but that the subsequent computation is simpler by Bessel’s method.

Several problems are involved in the complete computation of an eclipse from the elements. First, from the values of the latter at a given moment to determine the point, if any, at which the shadow-axis intersects the surface of the earth, and the respective outlines of the umbra and penumbra on that surface. Within the umbral curve the eclipse is annular or total; outside of it and within the penumbral curve the eclipse is partial at the given moment. The penumbral line is marked from hour to hour on the maps given annually in the American Ephemeris. Second, a series of positions of the central point through the course of an eclipse gives us the path of the central point along the surface of the earth, and the envelopes of the penumbral and umbral curves just described are boundaries within which a total, annular or partial eclipse will be visible. In particular, we have a certain definite point on the earth’s surface on which the edge of the shadow first impinges; this impingement necessarily takes place at sunrise. Then passing from this point, we have a series of points on the surface at which the elements of the shadow-cone are in succession tangent to the earth’s surface. At all these points the eclipse begins at sunrise until a certain limit is reached, after which, following the successive elements, it ends at sunrise. At the limiting point the rim of the moon merely grazes that of the sun at sunrise, so that we may say that the eclipse both begins and ends at that time. Of course the points we have described are also found at the ending of the eclipse. There is a certain moment at which the shadow-axis leaves the earth at a certain point, and a series of moments when, the elements of the penumbral cone being tangent to the earth’s surface, the eclipse is ending at sunset. Three cases may arise in studying the passage of the outlines of the shadow over the earth. It may be that all the elements of the penumbral cone intersect the earth. In this case we shall have both a northern and a southern limit of partial eclipse. In the second case there will be no limit on the one side except that of the eclipse beginning or ending at sunrise or sunset. Or it may happen, as the third case, that the shadow-axis does not intersect the earth at all; the eclipse will then not be central at any point, but at most only partial.

The third problem is, from the same data, to find the circumstances of an eclipse at a given place—especially the times of beginning and ending, or the relative positions of the sun and moon at a given moment. Reference to the formulae for all these problems will be given in the bibliography of the subject.

Authorities.—The richest mine of information respecting eclipses of the sun and moon is T.R. von Oppolzer’s “Kanon der Finsternisse,” published by the Vienna Academy of Sciences in the 52nd volume of its Denkschriften (Vienna, 1887). It contains elements of all eclipses both of the sun and moon, from 1207 B.C. to A.D. 2161, a period of more than thirty centuries. Appended to the tables is a series of charts showing the paths of all central eclipses visible in the northern hemisphere during the period covered by the table. The points of the path at which the eclipse occurs, at sunrise, noon and sunset, are laid down with precision, but the intermediate points are frequently in error by several hundred miles, as they were not calculated, but projected simply by drawing a circle through the three points just mentioned. For this reason we cannot infer from them that an eclipse was total at any given place. The correct path can, however, be readily computed from the tables given in the work. Eduard Mahler’s memoir, “Die centralen Sonnenfinsternisse des 20. Jahrhunderts” (Denkschriften, Vienna Academy, vol. xlix.), gives more exact paths of the central eclipses of the 20th century, but no maps. General tables for computing eclipses are Oppolzer’s “Syzygientafeln für den Mond” (Publications of the Astronomische Gesellschaft, xvi.), and Newcomb’s, in Publications of the American Ephemeris, vol. i. part i. Of these, Oppolzer’s are constructed with greater numerical accuracy and detail, while Newcomb’s are founded on more recent astronomical data, and are preferable for computing ancient eclipses. F.K. Ginzel’s Spezieller Kanon der Sonnen- und Mondfinsternisse (Berlin, 1899) contains, besides the historical researches already mentioned, maps of the paths of central eclipses visible in the lands of classical antiquity from 900 B.C. to A.D. 500, but computed with imperfect astronomical data. Maguire, “Monthly Notices,” R.A.S. xlv. and xlvi., has mapped the total solar eclipses visible in the British Islands from 878 to 1724. General papers of interest on the same subject have been published by Rev. S.J. Johnson. A résumé of all the observations on the physical phenomena of total solar eclipses up to 1878, by A.C. Ranyard, is to be found in Memoirs of the Royal Astronomical Society, vol. xli. A very copious development of the computation of eclipses by Bessel’s method is found in W. Chauvenet’s Spherical and Practical Astronomy, vol. i. The Theory of Eclipses, by R. Buchanan (Philadelphia, 1904), treats the subject yet more fully. Hansen’s method is developed in the Abhandlungen of the Leipzig Academy of Sciences, vol. vi. (Math.-Phys. Classe, vol. iv.). The formulae of computation by this method are found in the introductions to Oppolzer’s two works cited above.

(S. N.)

ECLIPTIC, in astronomy. The plane of the ecliptic is that plane in or near which the centre of gravity of the earth and moon revolves round the sun. The ecliptic itself is the great circle in which this plane meets the celestial sphere. It is also defined, but not with absolute rigour, as the apparent path described by the sun around the celestial sphere as the earth performs its annual revolution. Owing to the action of the moon on the earth, as it performs its monthly revolution in an orbit slightly inclined to the ecliptic, the centre of the earth itself deviates from the plane of the ecliptic in a period equal to that of the nodal revolution of the moon. The deviation is extremely slight, its maximum amount ranging between 0.5′ and 0.6″. Owing to the action of the planets, especially Venus and Jupiter, on the earth, the centre of gravity of the earth and moon deviates by a yet minuter amount, generally one or two tenths of a second, from the plane of the ecliptic proper. Owing to the action of the planets, the position of the ecliptic is subject to a slow secular variation amounting, during our time, to nearly 47″ per century. The rate of this motion is slowly diminishing.

The obliquity of the ecliptic is the angle which its plane makes with that of the equator. Its mean value is now about 23° 27′. The motion of the ecliptic produces a secular variation in the obliquity which is now diminishing by an amount nearly equal to the entire motion of the ecliptic itself. The laws of motion of the ecliptic and equator are stated in the article [Precession of the Equinoxes].

Attempts have been made by Laplace and his successors to fix certain limits within which the obliquity of the ecliptic shall always be confined. The results thus derived are, however, based on imperfect formulae. When the problem is considered in a rigorous form, it is found that no absolute limits can be set. It can, however, be shown that the obliquity cannot vary more than two or three degrees within a million of years of our epoch.

The formula for the obliquity of the ecliptic, as derived from the laws of motion of it and of the equator, may be developed in a series proceeding according to the ascending powers of the time as follows: we put T, the time from 1900, reckoned in solar centuries as a unit. Then,

Obliquity = 23° 27′ 31.68″ − 46.837″ T − 0.0085″ T² + 0.0017″ T³.

From this expression is derived the value of the obliquity at various epochs given in the following table. The left-hand portion of this table gives the values for intervals of 500 years from 2000 B.C. to A.D. 2500 as computed from modern data. For dates more than three or four centuries before or after 1850 the result is necessarily uncertain by one or more tenths of a minute, and is therefore only given to 0.1′.

(S. N.)

ECLOGITE (from Gr. ἐκλογή, a selection), in petrology, a typical member of a small group of metamorphic rocks of special interest on account of the variety of minerals they contain and their microscopic structures and geological relationships. Typically they consist of pale green or nearly colourless augite (omphacite), green hornblende and pink garnet. Quartz also is usually present in these rocks, but felspar is rare. The augite is mostly a variety of diopside and is only occasionally idiomorphic. The garnet sometimes forms good dodecahedra, but may occur as rounded grains, and encloses quartz, rutile, kyanite, and other minerals very frequently. The hornblende is usually pale green and feebly dichroic, but, in some eclogites which are allied to garnet-amphibolites, it is of dark brown colour. Among the commoner accessory minerals are kyanite (of blue or greyish-blue tints), rutile, biotite, epidote and zoisite, sphene, iron oxides, and pyrites. The rutile is invariably in small brown prisms; the kyanite forms bladed crystals, with perfect cleavage; felspar, if present, belongs to basic varieties rich in lime. Other minerals which have been found in eclogites are bronzite, olivine and glaucophane. The last mentioned is a bright blue variety of hornblende with striking pleochroism. The eclogites in their chemical composition show close affinities to gabbros; they often exhibit relationships in the field which show that they were primarily intrusive rocks of igneous origin, and occasionally contact alteration can be traced in the adjacent schists. Examples are known in Saxony, Bavaria, Carinthia, Austria, Norway. A few eclogites also occur in the north-west highlands of Scotland. Glaucophane-eclogites have been met with in Italy and the Pennine Alps. Specimens of rock allied to eclogite have been found in the diamantiferous peridotite breccias of South Africa (the so-called “blue ground”), and this has given rise to the theory that these are the parent masses from which the Kimberley diamonds have come.

(J. S. F.)

ECLOGUE, a short pastoral dialogue in verse. The word is conjectured to be derived from the Greek verb ἐκλέγειν, to choose. An eclogue, perhaps, in its primary signification was a selected piece. Another more fantastic derivation traces it to αἴξ, goat, and λόγος, speech, and makes it a conversation of shepherds. The idea of dialogue, however, is not necessary for an eclogue, which is often not to be distinguished from the idyll. The grammarians, in giving this title to Virgil’s pastoral conversations (Bucolica), tended to make the term “eclogue” apply exclusively to dialogue, and this has in fact been the result of the success of Virgil’s work. Latin eclogues were also written by Calpurnius Siculus and by Nemesianus. In modern literature the term has lost any distinctive character which it may have possessed among the Romans; it is merged in the general notion of pastoral poetry. The French “Églogues” of J.R. de Segrais (1624-1701) were long famous, and those of the Spanish poet Garcilasso de La Vega (1503-1536) are still admired.

See also [Bucolics]; [Pastoral].

ECONOMIC ENTOMOLOGY, the name given to the study of insects based on their relation to man, his domestic animals and his crops, and, in the case of those that are injurious, of the practical methods by which they can be prevented from doing harm, or be destroyed when present. In Great Britain little attention is paid to this important branch of agricultural science, but in America and the British colonies the case is different. Nearly every state in America has its official economic entomologists, and nearly every one of the British crown colonies is provided with one or more able men who help the agricultural community to battle against the insect pests. Most, if not all, of the important knowledge of remedies comes from America, where this subject reaches the highest perfection; even the life-histories of some of the British pests have been traced out in the United States and British colonies more completely than at home, from the creatures that have been introduced from Europe.

Some idea of the importance of this subject may be gained from the following figures. The estimated loss by the vine Phylloxera in the Gironde alone was £32,000,000; for all the French wine districts £100,000,000 would not cover the damage. It has been stated on good evidence that a loss of £7,000,000 per annum was caused by the attack of the ox warble fly on cattle in England alone. In a single season Aberdeenshire suffered nearly £90,000 worth of damage owing to the ravages of the diamond back moth on the root crops; in New York state the codling moth caused a loss of $3,000,000 to apple-growers. Yet these figures are nothing compared to the losses due to scale insects, locusts and other pests.

The most able exponent of this subject in Great Britain was John Curtis, whose treatise on Farm Insects, published in 1860, is still the standard British work dealing with the insect foes of corn, roots, grass and stored corn. The most important works dealing with fruit and other pests come from the pens of Saunders, Lintner, Riley, Slingerland and others in America and Canada, from Taschenberg, Lampa, Reuter and Kollar in Europe, and from French, Froggatt and Tryon in Australia. It was not until the last quarter of the 19th century that any real advance was made in the study of economic entomology. Among the early writings, besides the book of Curtis, there may also be mentioned a still useful little publication by Pohl and Kollar, entitled Insects Injurious to Gardeners, Foresters and Farmers, published in 1837, and Taschenberg’s Praktische Insecktenkunde. American literature began as far back as 1788, when a report on the Hessian fly was issued by Sir Joseph Banks; in 1817 Say began his writings; while in 1856 Asa Fitch started his report on the “Noxious Insects of New York.” Since that date the literature has largely increased. Among the most important reports, &c., may be mentioned those of C.V. Riley, published by the U.S. Department of Agriculture, extending from 1878 to his death, in which is embodied an enormous amount of valuable matter. At his death the work fell to Professor L.O. Howard, who constantly issues brochures of equal value in the form of Bulletins of the U.S. Department of Agriculture. The chief writings of J.A. Lintner extend from 1882 to 1898, in yearly parts, under the title of Reports on the Injurious Insects of the State of New York. Another author whose writings rank high on this subject is M.V. Slingerland, whose investigations are published by Cornell University. Among other Americans who have largely increased the literature and knowledge must be mentioned F.M. Webster and E.P. Felt. In 1883 appeared a work on fruit pests by William Saunders, which mainly applies to the American continent; and another small book on the same subject was published in 1898 by Miss Ormerod, dealing with the British pests. In Australia Tryon published a work on the Insect and Fungus Enemies of Queensland in 1889. Many other papers and reports are being issued from Australia, notably by Froggatt in New South Wales. At the Cape excellent works and papers are prepared and issued by the government entomologist, Dr Lounsbury, under the auspices of the Agricultural Department; while from India we have Cotes’s Notes on Economic Entomology, published by the Indian Museum in 1888, and other works, especially on tea pests.

Injurious insects occur among the following orders: Coleoptera, Hymenoptera, Lepidoptera, Diptera, Hemiptera (both heteroptera and homoptera), Orthoptera, Neuroptera and Thysanoptera. The order Aptera also contains a few injurious species.

Among the Coleoptera or beetles there is a group of world-wide pests, the Elateridae or click beetles, the adults of the various “wireworms.” The insects in the larval or wireworm stage attack the roots of plants, eating them away below the ground. The eggs deposited by the beetle in the ground develop into yellowish-brown wire-like grubs with six legs on the first three segments and a ventral prominence on the anal segment. The life of these subterranean pests differs in the various species; some undoubtedly (Agriotes lineatum) live for three or four years, during the greater part of which time they gnaw away at the roots of plants, carrying wholesale destruction before them. When mature they pass deep into the ground and pupate, appearing after a few months as the click beetles (fig. 1). Most crops are attacked by them, but they are particularly destructive to wheat and other cereals. With such subterranean pests little can be done beyond rolling the land to keep it firm, and thus preventing them from moving rapidly from plant to plant. A few crops, such as mustard, seem deleterious to them. By growing mustard and ploughing it in green the ground is made obnoxious to the wireworms, and may even be cleared of them. For root-feeders, bisulphide of carbon injected into the soil is of particular value. One ounce injected about 2 ft. from an apple tree on two sides has been found to destroy all the ground form of the woolly aphis. In garden cultivation it is most useful for wireworm, used at the rate of 1 ounce to every 4 sq. yds. It kills all root pests.

In Great Britain the flea beetles (Halticidae) are one of the most serious enemies; one of these, the turnip flea (Phyllotreta nemorum), has in some years, notably 1881, caused more than £500,000 loss in England and Scotland alone by eating the young seedling turnips, cabbage and other Cruciferae. In some years three or four sowings have to be made before a “plant” is produced, enormous loss in labour and cost of seed alone being thus involved. These beetles, characterized by their skipping movements and enlarged hind femora, also attack the hop (Haltica concinna), the vine in America (Graptodera chalybea, Illig.), and numerous other species of plants, being specially harmful to seedlings and young growth. Soaking the seed in strong-smelling substances, such as paraffin and turpentine, has been found efficacious, and in some districts paraffin sprayed over the seedlings has been practised with decided success. This oil generally acts as an excellent preventive of this and other insect attacks.

In all climates fruit and forest trees suffer from weevils or Curculionidae. The plum curculio (Conotrachelus nenuphar, Herbst) in America causes endless harm in plum orchards; curculios in Australia ravage the vines and fruit trees (Orthorrhinus klugii, Schon, and Leptops hopei, Bohm, &c.). In Europe a number of “long-snouted” beetles, such as the raspberry weevils (Otiorhynchus picipes), the apple blossom weevil (Anthonomus pomorum), attack fruit; others, as the “corn weevils” (Calandra oryzae and C. granaria), attack stored rice and corn; while others produce swollen patches on roots (Ceutorhynchus sulcicollis), &c. All these Curculionidae are very timid creatures, falling to the ground at the least shock. This habit can be used as a means of killing them, by placing boards or sacks covered with tar below the trees, which are then gently shaken. As many of these beetles are nocturnal, this trapping should take place at night. Larval “weevils” mostly feed on the roots of plants, but some, such as the nut weevil (Balaninus nucum), live as larvae inside fruit. Seeds of various plants are also attacked by weevils of the family Bruchidae, especially beans and peas. These seed-feeders may be killed in the seeds by subjecting them to the fumes of bisulphide of carbon. The corn weevils (Calandra granaria and C. oryzae) are now found all over the world, in many cases rendering whole cargoes of corn useless.

The most important Hymenopterous pests are the sawflies or Tenthredinidae, which in their larval stage attack almost all vegetation. The larvae of these are usually spoken of as “false caterpillars,” on account of their resemblance to the larvae of a moth. They are most ravenous feeders, stripping bushes and trees completely of their foliage, and even fruit. Sawfly larvae can at once be recognized by the curious positions they assume, and by the number of pro-legs, which exceeds ten. The female lays her eggs in a slit made by means of her “saw-like” ovipositor in the leaf or fruit of a tree. The pupae in most of these pests are found in an earthen cocoon beneath the ground, or in some cases above ground (Lophyrus pini). One species, the slugworm (Eriocampa limacina), is common to Europe and America; the larva is a curious slug-like creature, found on the upper surface of the leaves of the pear and cherry, which secretes a slimy coating from its skin. Currant and gooseberry are also attacked by sawfly larvae (Nematus ribesii and N. ventricosus) both in Europe and America. Other species attack the stalks of grasses and corn (Cephus pygmaeus). Forest trees also suffer from their ravages, especially the conifers (Lophyrus pini). Another group of Hymenoptera occasionally causes much harm in fir plantations, namely, the Siricidae or wood-wasps, whose larvae burrow into the trunks of the trees and thus kill them. For all exposed sawfly larvae hellebore washes are most fatal, but they must not be used over ripe or ripening fruit, as the hellebore is poisonous.

The order Diptera contains a host of serious pests. These two-winged insects attack all kinds of plants, and also animals in their larval stage. Many of the adults are bloodsuckers (Tabanidae, Culicidae, &c.); others are parasitic in their larval stage (Oestridae, &c.). The best-known dipterous pests are the Hessian fly (Cecidomyia destructor), the pear midge (Diplosis pyrivora), the fruit flies (Tephritis Tyroni of Queensland and Halterophora capitata or the Mediterranean fruit fly), the onion fly (Phorbia cepetorum), and numerous corn pests, such as the gout fly (Chloropstaeniopus) and the frit fly (Oscinis frit). Animals suffer from the ravages of bot flies (Oestridae) and gad flies (Tabanidae); while the tsetse disease is due to the tsetse fly (Glossina morsitans), carrying the protozoa that cause the disease from one horse to another. Other flies act as disease-carriers, including the mosquitoes (Anopheles), which not only carry malarial germs, but also form a secondary host for these parasites. Hundreds of acres of wheat are lost annually in America by the ravages of the Hessian fly; the fruit flies of Australia and South Africa cause much loss to orange and citron growers, often making it necessary to cover the trees in muslin tents for protection. Of animal pests the ox warbles (Hypoderma lineata and H. bovis) are the most important (see fig. 2). The “bots” or larvae of these flies live under the skin of cattle, producing large swollen lumps—“warbles”—in which the “bots” mature (fig. 2). These parasites damage the hide, set up inflammation, and cause immense loss to farmers, herdsmen and butchers. The universal attack that has been made upon this pest has, however, largely decreased its numbers. In America cattle suffer much from the horn fly (Haematobia serrata). The dipterous garden pests, such as the onion fly, carrot fly and celery fly, can best be kept in check by the use of paraffin emulsions and the treatment of the soil with gas-lime after the crop is lifted. Cereal pests can only be treated by general cleanliness and good farming, and of course they are largely kept down by the rotation of crops.

Lepidopterous enemies are numerous all over the world. Fruit suffers much from the larvae of the Geometridae, the so-called “looper-larvae” or “canker-worms.” Of these geometers the winter moth (Cheimatobia brumata) is one of the chief culprits in Europe (fig. 3). The females in this moth and in others allied to it are wingless. These insects pass the pupal stage in the ground, and reach the boughs to lay their eggs by crawling up the trunks of the trees. To check them, “grease-banding” round the trees has been adopted; but as many other pests eat the leafage, it is best to kill all at once by spraying with arsenical poisons. Among other notable Lepidopterous pests are the “surface larvae” or cutworms (Agrotis spp.), the caterpillars of various Noctuae; the codling moth (Carpocapsa pomonella), which causes the maggot in apples, has now become a universal pest, having spread from Europe to America and to most of the British Colonies. In many years quite half the apple crop is lost in England owing to the larvae destroying the fruit. Sugar-canes suffer from the sugar-cane borer (Diatioca sacchari) in the West Indies; tobacco from the larvae of hawk moths (Sphingidae) in America; corn and grass from various Lepidopterous pests all over the world. Nor are stored goods exempt, for much loss annually takes place in corn and flour from the presence of the larvae of the Mediterranean flour moth (Ephestia kuniella); while furs and clothes are often ruined by the clothes moth (Tinea trapezella).