Encyclopaedia Britannica, 11th Edition, "Echinoderma" to "Edward, prince of Wales"
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Title: Encyclopaedia Britannica, 11th Edition, "Echinoderma" to "Edward, prince of Wales"
Author: Various
Release date: January 17, 2011 [eBook #34992]
Most recently updated: January 7, 2021
Language: English
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Transcriber's notes:
(1) Numbers following letters (without space) like C2 were originally
printed in subscript. Letter subscripts are preceded by an
underscore, like C_n.
(2) Characters following a carat (^) were printed in superscript.
(3) Side-notes were relocated to function as titles of their respective
paragraphs.
(4) Macrons and breves above letters and dots below letters were not
inserted.
(5) [root] stands for the root symbol; [alpha], [beta], etc. for greek
letters.
(6) The letter 'Eth' is replaced by 'd'.
(7) The following typographical errors have been corrected:
ARTICLE ECHTERNACH: "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." 'an' amended from 'on'.
ARTICLE ECONOMIC ENTOMOLOGY: "Among the Coleoptera or beetles there
is a group of world-wide pests, the Elateridae or click beetles,
the adults of the various 'wireworms.'" 'beetles' amended from
'bettles'.
ARTICLE EDUCATION: "... laid down that the application of a
candidate might in no circumstances be rejected on any religious
ground, nor on the ground of social antecedents or the like." 'be'
amended from 'he'.
ARTICLE EDUCATION: "The public assistance afforded to secondary
education in Wales under the Intermediate Act is supplemented by
the grants of the Board of Education, and the Board's revised
Secondary School Regulations were applied to Wales in 1908."
'education' amended from 'educaton'.
ENCYCLOPAEDIA BRITANNICA
A DICTIONARY OF ARTS, SCIENCES, LITERATURE
AND GENERAL INFORMATION
ELEVENTH EDITION
VOLUME VIII, SLICE X
Echinoderma to Edward
ARTICLES IN THIS SLICE:
ECHINODERMA EDESSA (Macedonia)
ECHINUS EDESSA (Mesopotamia)
ECHIUROIDEA EDFU
ECHMIADZIN EDGAR (king of the English)
ECHO EDGAR (son of Edward)
ECHTERNACH EDGECUMBE
ECHUCA EDGE HILL
ECIJA EDGEWORTH, MARIA
ECK, JOHANN MAIER EDGEWORTH, RICHARD LOVELL
ECKERMANN, JOHANN PETER EDGEWORTH DE FIRMONT, HENRY ESSEX
ECKERNFORDE EDGREN-LEFFLER, ANNE CHARLOTTE
ECKERSBERG, KRISTOFFER EDHEM PASHA
ECKHART, JOHANNES EDICT
ECKHEL, JOSEPH HILARIUS EDINBURGH
ECKMUHL EDINBURGHSHIRE
ECLECTICISM EDISON, THOMAS ALVA
ECLIPSE EDMONTON (Alberta, Canada)
ECLIPTIC EDMONTON (England)
ECLOGITE EDMUND, SAINT
ECLOGUE EDMUND (king of East Anglia)
ECONOMIC ENTOMOLOGY EDMUND I.
ECONOMICS EDMUND (Ironside)
ECONOMY (Pennsylvania, U.S.A.) EDMUND (king of Sicily)
ECONOMY EDMUNDS, GEORGE FRANKLIN
ECSTASY EDOM
ECTOSPORA EDRED
ECUADOR EDRIC, STREONA
ECZEMA EDUCATION
EDAM EDWARD (The Elder)
EDDA EDWARD (The Martyr)
EDDIUS EDWARD (The Confessor)
EDELINCK, GERARD EDWARD I.
EDELWEISS EDWARD II.
EDEN, SIR ASHLEY EDWARD III.
EDEN EDWARD IV.
EDENBRIDGE EDWARD V.
EDEN HALL, LUCK OF EDWARD VI.
EDENKOBEN EDWARD VII.
EDENTATA EDWARD (prince of Wales)
EDENTON
ECHINODERMA.[1] The [Greek: echinoderma], 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 Muller (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 Muller.
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. Theel 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.
Loven ("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. Cuenot ("Etudes 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 Theel (in
_Festskrift for 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), Theel ("Echinocyamus," _Nov. Act. Soc. Sci. Upsala_,
1892), R. Semon ("Synapta," _Jena. Zeitschr._, 1888), and Loven (_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 _Systeme 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 _Paleontologie
francaise_, _Mem. Soc. paleontol. 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. Sturtz (see _Verhandl. nat. Vereins preuss. Rheinlande, Palaont.
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.
[Illustration: FIG. 1.--Diagram of a simple form of Crinoid, with five
arms, each forking once; the one nearest the observer is removed to
expose the tegmen of five orals. This crinoid has only two circlets of
plates in the cup, but the cup analysed in the adjoining diagram has in
addition infrabasals and a centrale C.]
[Illustration: FIG. 2.--An early stage in the development of _Antedon_,
showing the foot-plate or "dorso-central" _fp_ at the end of the stem
_col._ Some of the thecal plates, infrabasals _I B_, basals B, and orals
_O_ are forming around the body-cavities _r.pc_ and _l.pc_; _p_ is the
water-pore. (After Seeliger.)]
_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 Loven, 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.
[Illustration: FIG. 3.-Supposed calycinal systems of free-moving
Echinoderms. A, regular sea-urchin (_Cidaris_); B, sea-urchin with a
suranal plate (_Salenia_); C, developing ophiurid (_Amphiura_); D,
young starfish (_Zoroaster_).]
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. Loven 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.
[Illustration: FIG. 4.--The _Pentactula_ stage in the development of
_Synapta_.
T, The five interradial tentacles.
M, The water-pore, leading by the stone-canal stc to the water-ring,
from which hangs a Polian vesicle pb.
oc, Supposed otocysts.
m, Longitudinal muscles.
sk, Calcareous spicules.
st, Stomach.
(After Semon.)]
_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.
[Illustration: FIG. 5.--_Bothriocidaris globulus._ A, from the side;
B, the plates around the aboral pole. (After Jaekel.) The short spines
which were attached to the tubercles are not drawn.]
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.
[Illustration: FIG. 6.--Diagrammatic reconstruction of _Dipleurula_.
The creature is represented crawling on the sea-floor, but it may
equally well have been a floating animal. The ciliated bands are not
drawn.]
[Illustration: FIG. 7.--Diagrammatic reconstruction of primitive
Pelmatozoon, seen from the side. The plates of the test are not drawn;
their probable appearance may be gathered from fig. 8.]
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 Pelmatozoon (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).
[Illustration: FIG. 8.--_Aristocystis bohemicus_; side-view of the
theca. The internal structure may be gathered from fig. 7.]
[Illustration: FIG. 9.--_Fungocystis rarissima_, one of the
Diploporita, in which the thecal plates bordering the food-grooves are
not yet regularly arranged. The brachioles are not drawn.]
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.
[Illustration: FIG. 10.--_Chirocrinus-alter_, one of the Rhombifera,
showing the reduced number and regular arrangement of the thecal
plates, and the concentration of the brachioles. (Adapted from
Jaekel.)]
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.
[Illustration: FIG. 11.--_Edrioaster._ A, upper or oral surface of _E.
Bigsbyi_, with the covering-plates on the anterior and left posterior
food-grooves, but removed from the others, which show only the
flooring-plates, between which are pores; B, under surface of _E.
Buchianus_, with covering-plates on right posterior and right anterior
food-grooves (left hand in the drawing). The * denotes the position of
the anal interradius.]
[Illustration: FIG. 12.-Diagrammatic sections across the ambulacra of A,
C, PELMATOZOA, and B, D, ELEUTHEROZOA, placed in the same position for
comparison. _S_, Blood-spaces, of which the homology is still
uncertain.]
_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:--
/ Cystidea------Edrioasteroidea
| | |\
PELMATOZOA < | | \ Holothurioidea \
| | | |
| Blastoidea | > ELEUTHEROZOA
\ Crinoidea | |
Stelliformia |
Echinoidea /
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).
[Illustration: FIG. 13.--A Eublastoid, _Pentremites_.]
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.
[Illustration: FIG. 14.--A living Pentacrinid, _Isocrinus asteria_;
the first specimen found, after Guettard's figure published in 1761.]
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.
A. With respiratory trees.
/Fam. 1, Holothuriidae.
(a) With podia < Fam. 4, Cucumariidae.
\Fam. 5, Molpadiidae.
(b) Without podia
B. Without respiratory trees.
(a) With podia Fam. 2, Elpidiidae.
(b) Without podia Fam. 3, Pelagothuriidae.
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. Ostergren, and especially of R.
Perrier, suggests the following as a more natural if less obvious
arrangement.
[Illustration: FIG. 15.--An Aspidochirote Holothurian of the family
_Holothuriidae_, showing the mouth surrounded by tentacles, the anus
at the other end of the body, and three of the rows of podia.]
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:
_Asteries ambulacraires_, with plates of ambulacral origin prominent
in the mouth-skeleton, pedicellariae stalked, and straight or crossed,
podial pores usually quadriserial; _Asteries 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 [+].
[Illustration: FIG. 16.--Section across the arm-skeleton of a
Phanerozonate Asterid, _Astropecten_.
a, Ambulacral plates.
b, Adambulacral plates.
c and d, Inferior and superior lateral plates.
e, Dorsal plates with paxillae. Certain supra-ambulacral plates,
which also exist, are not shown.]
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.
[Illustration: FIG. 17.--A Cryptozonate Asterid, _Solaster papposus_,
from the upper or dorsal surface.]
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. Sturtz, 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.
[Illustration: FIG. 18.--A vertebral arm-ossicle (fused ambulacrals)
of a Zygophiuran, _Ophiolepis_.
A, Proximal joint-face.
B, Distal joint-face.
c, Ventral groove, where lies the water-vessel, from which branches
pass through the ossicle, emerging as podia at e and e.]
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.
[Illustration: 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.
_
Cambrian |
|
|
Ordovician BOTHRIOCIDAROIDA (jaws unknown) |
/ \ |
/ \ columns
Silurian MELONITOIDEA \ unfixed
# CYSTO- \ in
## CIDAR- \ number
### OIDA \ |
Devonian ### CIDAROIDA |
### # |
### # |
Carboniferous ### ##\ _|
## ## \
## ## \ _
Permian # ## \ |
## \ |
Trias ## DIADEMOIDA columns
## # \ 20
Jurassic ## ## \ HOLECTYPOIDA |
## ### / # \ SPATANGOIDEA |
Cretacious ## ### CLYPEASTROIDEA # \ # |
## ### # ## ## |
Tertiary ## ### ## ## ### |
## ### ### # ### |
Recent ## ### ### # #### _|
|----------jaws lofty--------| jaws flat-reduced ---- lost
|------abranchiate-----| |-----branchiate-----| |-lipobranchiate-|
|----no sphaeridia-----| |--------------sphaeridia---------------|
|-------endocyclic---------| |------------exocyclic--------------|
[Illustration: FIG. 20.]
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. Herouard, _Traite de zoologie concrete,
iii., Echinodermes_ (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 Stamme des Tierreiches_
(Wien, 1889); P.B. and C.F. Sarasin, "Uber 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 ... Palaozoologie_, i. pp. 308-560 (Munchen,
1879); also Grundzuge, 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.)
FOOTNOTE:
[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. [Greek: echis], adder, and [Greek: oura], 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.
[Illustration: FIG. 1.--A, _Bonellia viridis_, Rol., [female]; B, B.
_fuliginosa_. Both natural size. a, grooved proboscis; b, mouth; c,
ventral hooks; d, anus.]
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.
[Illustration: FIG. 2.--Female _Bonellia viridis_, Rol. Opened along the
left 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.
[Illustration: FIG. 3.--Adult male, _Bonellia viridis_, Rol. The
original was 1.5 mm. long. The nervous system is not shown. (After
Selenka.)
a, Generative pore with spermatozoa coming out.
b, Anterior blind end of intestine attached to the parenchymatous
tissue by muscular strands.
c, Green wandering cells containing chlorophyll.
d, Parenchymatous connective tissue.
e, Epidermis.
i, Intestine.
j, Vas deferens.
l, Internal opening of vas deferens.
m, The left anal vesicle.
n, Spermatozoa in the body-cavity.]
_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_ (Guerin-Meneville), 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_ (Guerin-Meneville), _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 bibliotheque 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. [Greek: echo]), 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 antiquites_.
ECHTERNACH, a town in the grand duchy of Luxemburg, on the Sure, 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 Hotel-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 Sure, 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.
ECIJA, 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 Ecija 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.
Ecija, 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 Tubingen, 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 Gottingen, 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 _Beitrage
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 _Gesprache 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
_Beitrage 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).
ECKERNFORDE, 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. Eckernforde 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 Junger_ (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
Buttner (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. Grundzuge 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 speculatif en Allemagne au XIV^e siecle_ (Paris, 1900); E.
Kramm, _Meister Eckhart im Lichte der Denifleschen Funde_ (Bonn,
1889); R. Langenberg, _Uber die Verhaltnisse Meister Eckharts zur
niederdeutschen Mystik_ (Gottingen, 1896); W. Schopff, _Meister
Eckhart_ (Leipzig, 1889); A. Jundt, _Hist. du pantheisme populaire au
moyen age_ (Paris, 1875); art. in Herzog-Hauck, _Realencyklopadie_
(S.M. Deutsch); R.M. Jones, _Mystical Religion_ (1909).
FOOTNOTE:
[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 Steinbuchel from
Eckhel's papers after his death, was published in 1826. Among his other
works are--_Choix de pierres gravees du Cabinet Imperial 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.
ECKMUHL, or EGGMUHL, 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. [Greek: eklego], 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, Theodore Jouffroy, J.P.
Damiron, Barthelemy St Hilaire, C.F.M. de Remusat, 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 Laromiguiere, 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. [Greek: ekleipsis], 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.
[Illustration: FIG. 1.]
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.
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
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
Konigsberg. 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 deg. 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
H[alpha] 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:--
+--------------------------------------+---------+---------+---------+
| | August | January | December|
| | 1886. | 1889. | 1889. |
+--------------------------------------+---------+---------+---------+
| Intrinsic actinic brilliancy of the | | | |
| brightest parts of the corona | 0.031 | 0.079 | 0.029 |
| Do. of the polar rays | . . | 0.053 | 0.016 |
| Do. of the sky near the sun | 0.0007 | 0.0050 | 0.0009 |
| Ratio of intrinsic brilliancy of the | | | |
| brightest parts of the corona to | | | |
| that of the sky (actinic) | 44 to 1 | 16 to 1 | 32 to 1 |
| Magnitude of the faintest star | | | |
| shown on the eclipse negatives | . . | 2.3 | . . |
+--------------------------------------+---------+---------+---------+
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. (Angstrom) 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 deg. 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 3-1/2
minutes of totality, and in Sumatra with 6-1/2 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 3-1/2 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.
Trepied 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.
Eclipse seasons.
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 deg. of one of the nodes of
the moon's orbit. The eclipse can be total only within about 11 deg. of
the node. An eclipse of the moon can occur only when the line
sun-moon-earth makes an angle less than about 11 deg. with the line of
nodes; and the eclipse can be total only within about 8 deg. of the
node, the average limiting distances varying 1 deg. or 2 deg. 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 deg. 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 deg. there will probably be an eclipse of the sun, which
may be central if the angle is less than 11 deg. Let the next new moon
take place in the line ES2 a month later. The mean value of the angle
S1ES2 is about 29 deg.; but as the node N has moved towards S1 about 1.4
deg. during the interval, the sum of the angles NES1 and NES2 will be
somewhat greater than S1ES2 by about 1.6 deg. 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.
[Illustration: FIG. 4.]
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 deg. and the distance of the
moon from its perigee has changed less than 3 deg. 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
deg. 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
deg. in a period, the eclipses will vary from total to annular, but at
the end of 3 periods the perigee is only 7.1 deg. 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._
Notable eclipses.
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 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:--
A.D. 538, February 15, C. (partial). | A.D. 878, October 29, C.
540, June 12, C. (partial). | 885, June 15.
594, July 23. | 1023, January 24.
603, August 12. | 1133, August 1, C.
639, September 3. | 1140, March 20, C.
664, May 1, C. | 1185, May 1, C.
733, August 14 (annular). | 1191, June 23, C. (annular).
764, June 4 (annular). | 1330, July 16.
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.
+----------------+--------------+---------------+---------+------+-------+------------------------------------------------------------+
| | Point where |Greenwich M.T. |Duration | | | |
| Date at | Central at |of conjunction | of | | | |
| Noon-Point. | Noon. | in Longitude. |Totality.| Node |Series.| Regions Swept by Shadow. |
| +------+-------+---------------+---------+ | | |
| | Lat. | Long. | d. h. m. | m. | | | |
+----------------+------+-------+---------------+---------+------+-------+------------------------------------------------------------+
| 1803, Feb. 21 | 11 S.| 136 W.| 21 9 20 | 4.2 | Asc. | 1 | Pacific Ocean, Mexico. |
| 1804, Aug. 5 | 38 S.| 66 W.| 5 4 6 | 1.2 | Desc.| 2 | Pacific Ocean, Chile, Argentina. |
| 1806, June 16 | 42 N.| 66 W.| 16 4 22 | 4.6 | Desc.| 3 | New England, Atlantic, Africa. |
| 1807, Nov. 29 | 11 N.| 2 E.| 28 23 48 | 1.4 | Asc. | 4 | Central Africa, Areolia. |
| 1810, April 4 | 12 N.| 154 E.| 3 13 41 | Ann. | Desc.| 5 | Pacific Ocean, Borneo. |
| 1811, Mar, 24 | 39 S.| 26 W.| 24 2 19 | 3.4 | Desc.| 6 | South Atlantic to and across South Africa. |
| 1814, July 17 | 31 N.| 84 E.| 16 18 33 | 6.6 | Asc. | 7 | Africa, Central Asia, China. |
| 1815, July 6 | 88 N.| 175 W.| 6 11 52 | 3.2 | Asc. | 8 | Polar Regions, Western Siberia. |
| 1816, Nov. 19 | 43 N.| 30 E.| 18 22 9 | 1.8 | Desc.| 9 | Eastern Europe, Central Asia. |
| 1817, Nov. 9 | 7 S.| 149 E.| 8 13 53 | 4.7 | Desc.| 10 | Burma, Pacific Ocean. |
| 1821, Mar. 4 | 8 S.| 96 E.| 3 17 50 | 4.3 | Asc. | 1 | Indian and Pacific Oceans. |
| 1822, Aug. 16 | 36 S.| 176 W.| 16 11 22 | 1.4 | Desc.| 2 | Australia, Pacific Ocean. |
| 1824, June 26 | 47 N.| 175 W.| 26 11 43 | 4.4 | Desc.| 3 | Pacific Ocean, Japan, China. |
| 1825, Dec. 9 | 9 N.| 127 W.| 9 8 27 | 1.5 | Asc. | 4 | Pacific Ocean, Mexico. |
| 1828, April 14 | 18 N.| 39 E.| 13 21 18 | 0.3 | Desc.| 5 | Northern Africa, India. |
| 1829, April 3 | 32 S.| 149 W.| 3 10 24 | 4.1 | Desc.| 6 | South Pacific Ocean. |
| 1832, July 27 | 24 N.| 28 W.| 27 2 2 | 6.8 | Asc. | 7 | West Indies and across Central Africa. |
| 1833, July 17 | 78 N.| 76 E.| 16 19 16 | 3.5 | Asc. | 8 | North-eastern Asia and Polar Regions. |
| 1834, Nov. 30 | 40 N.| 101 W.| 30 6 48 | 1.9 | Desc.| 9 | Southern and Western United States. |
| 1835, Nov. 20 | 10 S.| 20 E.| 19 22 31 | 4.6 | Desc.| 10 | Central Africa, Madaga
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