SPONGES  . The Sponges or Porifera See also:

• FORM (Lat. forma)

form a somewhat isolated phylum (or See also:

• PRINCIPAL

principal subdivision) of the See also:

• ANIMAL
• ANIMAL (Lat. animalis, from anima, breath, soul)

animal See also:

• KING
• KING (O. Eng. cyning, abbreviated into cyng, cing; cf. O. H. G. chun- kuning, chun- kunig, M.H.G. kiinic, kiinec, kiinc, Mod. Ger. Konig, O. Norse konungr, kongr, Swed. konung, kung)
• KING [OF OCKHAM], PETER KING, 1ST BARON (1669-1734)
• KING, CHARLES WILLIAM (1818-1888)
• KING, CLARENCE (1842–1901)
• KING, EDWARD (1612–1637)
• KING, EDWARD (1829–1910)
• KING, HENRY (1591-1669)
• KING, RUFUS (1755–1827)
• KING, THOMAS (1730–1805)
• KING, WILLIAM (1650-1729)
• KING, WILLIAM (1663–1712)

king-dom . This phylum includes an immense number of marine and fresh-See also:

• WATER

water organisms, all of which agree amongst them-selves in possessing a See also:

• COMBINATION (Lat. combinare, to combine)

combination of important structural characters which is not found in any other animals . Though the phylum is a very large one yet almost the only examples with which the name " sponge " is popularly associated are the See also:

• COMMON

common See also:

• BATH
• BATH, THOMAS THYNNE
• BATH, WILLIAM

bath sponges (See also:

• SPECIES

species of the genera Euspongia and Hippospongia), which are amongst the most highly organized and least typical members of the See also:

• GROUP

group . The See also:

• HISTORY

history of the group begins with See also:

• ARISTOTLE
• ARISTOTLE (384-322 B.C.)

Aristotle, who recognized several different kinds of sponge, some of which were used by the See also:

• GREEK
• GREEK, ETRUSCAN AND

Greek warriors for See also:

• PADDING

padding their helmets . Owing, however, to the permanently fixed See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character, irregular growth and feeble See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of See also:

• MOVEMENT

movement in the adult organism, it was not until the See also:

• ADVENT (Lat. Adventus, sc. Redemptoris, " the coming of the Saviour ")

advent of microscopical See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

research that it was definitely proved that the sponges are animals and not See also:

• PLANTS

plants . Indeed our scientific knowledge of the group can scarcely be said to begin much before the See also:

• MIDDLE

middle of the loth See also:

• CENTURY (from Lat. centuria, a division of a hundred men)

century, when the classical researches of R . E . See also:

• GRANT (from A.-Fr. graunter, O. Fr. greanter for creanter, popular Lat. creantare, for credentare, to entrust, Lat. credere, to believe, trust)
• GRANT, ANNE (1755-1838)
• GRANT, CHARLES (1746-1823)
• GRANT, GEORGE MONRO (1835–1902)
• GRANT, JAMES (1822–1887)
• GRANT, JAMES AUGUSTUS (1827–1892)
• GRANT, ROBERT (1814-1892)
• GRANT, SIR ALEXANDER
• GRANT, SIR FRANCIS (1803-1878)
• GRANT, SIR JAMES HOPE (1808–1895)
• GRANT, SIR PATRICK (1804-1895)
• GRANT, U
• GRANT, ULYSSES SIMPSON (1822-1885)

Grant, J . E . See also:

• GRAY
• GRAY (or GREY), WALTER DE (d. 1255)
• GRAY, ASA (1810-1888)
• GRAY, DAVID (1838-1861)
• GRAY, ELISHA (1835-1901)
• GRAY, HENRY PETERS (1819-18/7)
• GRAY, HORACE (1828–1902)
• GRAY, JOHN DE (d. 1214)
• GRAY, JOHN EDWARD (1800–1875)
• GRAY, PATRICK GRAY, 6TH BARON (d. 1612)
• GRAY, ROBERT (1809-1872)
• GRAY, SIR THOMAS (d. c. 1369)
• GRAY, THOMAS (1716-1771)

Gray, H . J .

See also:

• CARTER, ELIZABETH (1717-1806)

Carter and J . S . See also:

• BOWERBANK, JAMES SCOTT (1797-1877)

Bowerbank laid the See also:

• FOUNDATIONS

foundations of See also:

• MODERN

modern spongology . It very soon became evident that the group is one which illustrates with remarkable clearness and beauty those See also:

• LAWS

laws of organic See also:

• EVOLUTION

evolution which were beginning to attract so much See also:

• ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention from zoologists, a fact which found abundant recognition in See also:

• ERNST, HEINRICH WILHELM (1814–1865)

Ernst See also:

• HAECKEL, ERNST HEINRICH (1834- )

Haeckel's See also:

• EPOCH (Gr. E7roxij, holding in suspense, a pause, from E1rxav, to hold up, to stop)

epoch-making See also:

• WORK

work on the Calcareous Sponges published in 1872 . This was followed by a See also:

• SERIES (a Latin word from serere, to join)

series of remark-able researches by F . E . Schulze on the See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute See also:

• ANATOMY
• ANATOMY (Gr. avaroyil, from ava-silo c', to cut up)

anatomy, See also:

• HISTOLOGY
• HISTOLOGY (Gr. Ler6c, web, tissue, properly the web-beam of the loom, from iQravai, to make to stand)

histology and See also:

• EMBRYOLOGY

embryology of the group, which have served as a See also:

• PATTERN

pattern to all subsequent investigators . In more See also:

• RECENT

recent years our knowledge of the sponges has advanced very rapidly, especially as the result of the See also:

• GREAT

great series of scientific exploring expeditions inaugurated by the voyage of H.M.S . " Challenger." The large collection made by the " Challenger " expedition alone, necessitated a See also:

• COMPLETE

complete reorganization of our systematic knowledge of the phylum, and afforded the See also:

• FOUNDATION (Lat. fundatio, from fundare, to found)

foundation upon which our See also:

• PRESENT

present See also:

• SYSTEM

system of See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification has been built up . There is perhaps no great group of the animal See also:

• KINGDOM

kingdom in the study of which greater advance has been made in the last twenty years . It is impossible in the space at our disposal to do See also:

• JUSTICE (Lat. justitia)

justice to the numerous valuable See also:

• MEMOIRS

memoirs which have appeared during this See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period, but reference to the more important See also:

• WORKS

works of recent investigators will be found in the bibliography at the end of this See also:

• ARTICLE (from Lat. articulus, a joint)

article, while for a comprehensive See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account of the whole subject the reader should refer especially to See also:

• PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

Professor E . A .

Minchin's article in See also:

• SIR

Sir E . See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

Ray Lankester's See also:

• TREATISE

Treatise on See also:

• ZOOLOGY (from Gr. Nov, a living thing, and ?byos, theory)

Zoology . See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

General Characters of the Phylum.—The sponges are all aquatic organisms, and for the most See also:

• PART

part marine . They vary in See also:

• SIZE

size from minute solitary individuals, scarcely visible to the naked See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye, up to great See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

compound masses several feet in circumference, and in form from almost complete shapelessness to the most exquisite and perfect symmetry . The indefiniteness of shape and size which characterizes the vast See also:

• MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of the group is due to the power of budding, which is almost universal amongst them, whereby extremely complex colonies are built up in which it is usually impossible to determine the limits of the individual zooids or persons, while very frequently, by a See also:

• PROCESS

process of integration, individuals of a higher See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order are produced which again form colonies by budding (fig . 2) . The entire See also:

• BODY

body of the sponge is penetrated by a more or less complicated See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

canal-system, beginning with numerous inhalant pores, scattered over the general See also:

• SURFACE

surface or collected in See also:

• SPECIAL

special See also:

• PORE

pore-areas, and ending in one or several larger apertures, the vents or oscula, situated usually on the uppermost portions of the sponge (fig . 8) . If the living animal he kept underobservation it will be seen that a stream of water is ejected with considerable force from the vents, carrying with it minute particles in suspension . At the same See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time numerous smaller streams enter the canal system through the inhalant pores, bringing with them the minute particles of organic See also:

• MATTER

matter upon which the sponge feeds and the See also:

• OXYGEN (symbol 0, atomic weight 16)

oxygen which it requires for respiration . This stream of water may be temporarily interrupted by the See also:

• CLOSURE (Fr. clooture)

closure of the pores and vents, to be resumed apparently at will . It is maintained by the activity of certain cells, known as collared cells or choanocytes (fig .

35, g, fig . 36), which See also:

• LINE

line the walls of the canal system either throughout their entire extent or in certain regions only . These cells See also:

• BEAR
• BEAR, BLACK
• BEAR, BROWN
• BEAR, GRIZZLY
• BEAR, ISABELLINE
• BEAR, WHITE

bear an extraordinarily See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close resemblance to the choanoflagellate See also:

• PROTOZOA (Gr. 7rpwros, first, and i'woe, living thing)

Protozoa or collared Monads . Each is provided with a filmy protoplasmic See also:

• COLLAR

collar and a See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long See also:

• WHIP

whip-like flagellum, and the movements of the latter drive the water out of the canal-system through the vents and thus keep up the circulation . In all but the simplest sponges the collared cells are confined to certain portions cf the canal system known as flagellated See also:

• CHAMBERS (the Fr. chambre, from Lat. camera, a room)
• CHAMBERS, EPHRAIM (d. 1740)
• CHAMBERS, GEORGE (1803-1840)
• CHAMBERS, ROBERT (18oz-1871)
• CHAMBERS, SIR WILLIAM (1726-1796)

chambers (fig. o), the size, form and arrangement of which vary greatly in different types . That part of the canal-system which is not lined by collared cells is covered with a flattened See also:

• PAVEMENT (Lat. pavimentu;n, a floor beaten or rammed hard, from pavire, to beat)

pavement-epithelium (fig . 34, I), and so also is the See also:

• OUTER

outer surface of the sponge . The space between the various branches of the canal-system is occupied by a gelatinous ground-substance (mesogloea) in which amoeboid and connective-See also:

• TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue cells are em-bedded (fig . 34, 3, 4, 5; fig . 35, a), and in which in most cases a well-See also:

• DEVELOPED

developed See also:

• SKELETON

skeleton is secreted by special cells known as scleroblasts . This skeleton (See also:

• FIGS

figs . 24-32, &c.) supports the extremely soft tissues of which the body is composed, and consists either of See also:

• MINERAL

mineral spicules (carbonate of See also:

• LIME
• LIME (O. Eng. lim, Lat. limes, mud, from linere, to smear)

lime or See also:

• SILICA

silica) or of horny See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres (spongin), or of a combination of siliceous spicules with spongin .

In many cases the proper skeleton is more or less completely replaced by See also:

• SAND
• SAND, GEORGE (1804-1876)

sand . The question as to how far the See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell-layers of the sponge body correspond to the " germinal layers " usually recognizable in other multicellular animals is an extremely difficult one and not yet by any means settled . It has until recently been generally sup-posed that the flattened epithelium which covers the outer surface of the sponge, together with part of that which lines the canal-system, is ectodermal, while the collared cells and the See also:

• REMAINDER, REVERSION

remainder of the flattened epithelium lining the canal-system are endodermal, and the See also:

• TERM

term mesoderm has been frequently applied to the middle gelatinous layer . Recent embryological research, however, makes it extremely doubtful whether this view is justifiable, and whether indeed the germ-layers of typical Metazoa can be identified at all in the Porifera . Embryological research, moreover, tends to show that the See also:

• PRIMITIVE

primitive gastral epithelium (of collared cells) is in most sponges completely replaced, except in the flagellated chambers, by an invasion of the dermal epithelium (composed of See also:

• FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat pavement, cells) . Sexual See also:

• REPRODUCTION

reproduction, by means of ova and spermatozoa, is probably universal throughout the group . The segmentation of the ovum gives rise to the See also:

• FREE

free-See also:

• SWIMMING (from " swim," A.S. swimman, the root being common in Teutonic languages)

swimming ciliated larva (figs . 38, e, 39) in the form of a hollow " amphiblastula " or of a solid " parenchymula." This larva becomes attached and, by means of a more or less complex See also:

• METAMORPHOSIS

metamorphosis, gives rise to the See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

young sponge . During the metamorphosis the outer, ciliated or flagellated cells of the larva take up their position in the interior of the body and give rise to the collared cells of the adult; while the inner cells (of the parenchymula) migrate outwards and form the superficial epithelium, so that the position of the so-called " ectoderm " and " endoderm " is completely reversed in the adult as compared with the larva . A sexual reproduction is effected by budding, and the buds may either remain attached to the See also:

• PARENT, SIMON NAPOLEON (1855– )

parent and form colonies or become detached and form entirely See also:

• SEPARATE

separate individuals . Types of Structure.—We may illustrate our account of the general characters of the group by a brief description of the anatomy of three widely divergent types, selected as being fairly representative of the entire group, viz . Leucosolenia, Plakina and Euspongia .

Leucosolenia.—The genus Leucosolenia includes a number of calcareous sponges of very See also:

• SIMPLE

simple structure, and thus forms a suitable starting-point for our studies . Imagine a minute, thin-walled See also:

• SAC

sac (fig . I), attached at the See also:

• LOWER

lower end to some See also:

• ROCK
• ROCK (O.Fr. rake, Sp. rota, Ital. rocca; possibly from a Lat. form rupica, from rupes, rock)
• ROCK, DANIEL (1799–187t)

rock or seaweed, and enclosing a spacious cavity in its interior . This cavity is the gastral or See also:

• DIGESTIVE

digestive cavity, and it opens to the exterior 716 through a wide vent or osculum at the upper extremity of the sponge . The thin See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall is also pierced by numerous small inhalant pores or prosopyles . The inhalant pores, the gastral cavity and the vent constitute the canal-system, through which a stream of water can be kept flowing by the activity of the collared cells which line practically the whole of the gastral cavity . Each collared cell consists of an See also:

• OVAL (Lat. ovum, egg)

oval nucleated body surmounted by a filmy proto- plasmic collar, in the middle of which the whip-like flagellum projects into the water . They are placed close together, See also:

• SIDE
• SIDE (mod. Eski Adalia)

side by side, and thus form a continuous layer, extending almost up to the vent and interrupted only by the inhalant pores . The outer surface of the sponge is covered by a single layer of flattened pavement-epithelium or epidermis . Some of these cells, distinguished as porocytes, become perforated by the inhalant pores, around which they form contractile diaphragms capable of opening and closing, and thus regulating the See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply of water . Between the outer protective, dermal epithelium, and the inner gastral epithelium of collared cells, lies the mesogloea, a layer of gelatinous material containing cells of at least two kinds, amoebocytes and scleroblasts . The former closely resemble the amoeboid See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white See also:

• BLOOD

blood corpuscles, or leucocytes, of higher animals, and have the power of wandering about from See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place to place in the sponge-wall .

They probably serve to distribute See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

food material and carry away See also:

• WASTE (O. Fr. wast, guast, gast, gaste; Lat. vastus, vast, desolate)

waste products, and some of them undoubtedly give rise to the ova and spermatozoa . The scleroblasts are derived from cells of the dermal epithelium which migrate inwards into the See also:

• GELA

gela-(AfterHaeckel.) tinous ground-substance and there secrete the FIG . I.—Leucoso- spicules of which the skeleton is composed . lenia primordial is These spicules are composed of transparent (See also:

• OLYNTHUS

Olynthus form). crystalline carbonate of lime (See also:

• CALCITE

calcite), and may be of three fundamental forms: triradiate, quadriradiate and monaxon . It has been shown by E . A . Minchin, however, that the triradiate and quadriradiate types are not simple spicules but spicule-systems, each formed of three or four See also:

• PRIMARY

primary spicules, originating from as many See also:

• MOTHER

mother-cells and only secondarily See also:

• UNITED

united . In fig . I only triradiate spicules are represented, but very often all three kinds are present in the same sponge (cf. fig . 24) . The triradiates See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

lie in the mesogloea with their three rays extended in a See also:

• PLANE

plane parallel to the surfaces of the sponge-wall, and form a See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of loose scaffolding upon which the soft tissues are supported . The quadriradiates resemble the triradiates in form and position, but a See also:

• FOURTH

fourth ray is developed which projects through the layer of collared cells into the gastral cavity, where it serves as a See also:

• DEFENCE
• DEFENCE (Lat. defendere, to defend)

defence against See also:

• INTERNAL

internal parasites .

The monaxon spicules have one end embedded in the mesogloea while the other projects outwards and upwards and serves as a defence against See also:

• EXTERNAL

external foes . Although all species of the genus Leucosolenia agree essentially in structure, yet they exhibit very great diversity in external form . This is due to the See also:

• HABIT (through the French from Lat. habitus, from habere, to have, hold, or, in a reflective sense, to be in a certain condition; in many of the English senses the French use habitude, not habit)

habit of budding and See also:

• COLONY (Lat. colonia, from colonus, a cultivator)

colony formation . All start See also:

• LIFE

life after the metamorphosis of the larva in the simple sac-shaped See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition which we have just described, and to which the name " Olynthus-type " is sometimes applied . This is indeed the simplest type of sponge organization known to us and we must look upon the Olynthus as representing a primary sponge-individual or " See also:

• PERSON, OFFENCES AGAINST THE

person." By a simple process of budding, in which (After Minchin, from Lankester's Treatise on Zoology.) use, 'Osculum. plc, Sphincter of osculum . cl. osc, Closed osculum. diz, Diverticula . contr. osc, Closed oscula in See also:

• CON

con- osc. div, Diverticula from which tracted part of colony. new oscula arise.the buds all remain united together by their bases, we get a branched colony in which the persons or zooids are still easily recognizable, each with its own vent or osculum . Very frequently, however, the zooids become elongated into slender cylindrical tubes which See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch in an extremely complex manner and anastomose with one another in many places to form networks, in which it is no longer possible to recognize the component individuals (fig . 2) . This is known as the " Clathrina " type of structure, and we may look upon a Clathrina colony as an individual of a higher order, which may assume a definite external form and even acquire a secondary internal cavity (pseudogaster), opening to the exterior through a secondary vent (pseudosculum), while the outer tubes of the colony may give rise to a protective skin (pseudoderm), perforated by secondary inhalant pores (pseudopores) which are obviously quite distinct in nature from the primary inhalant pores or prosopyles of the Olynthus . Other types of colony-formation in the genus Leucosolenia will be discussed when we come to See also:

• DEAL

deal with the canal-system in general . Plakina.--The genus Plakina includes some of the simplest of the siliceous sponges .

Just as in the Calcarea the most primitive " person " or individual is represented by the Olynthus type, so in the non-calcareous sponges we may recognize a primitive or (A ter See also:

• KELLER, ALBERT (1845- )
• KELLER, GOTTFRIED (1819-1890)
• KELLER, HELEN ADAMS (188o- )

Keller.) fundamental form of individual to which the name "Rhagon " has been applied . This is the first See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage reached after the See also:

• META

meta-morphosis of the larva in certain species, and the little sponge consists of a See also:

• CUSHION (from O. Fr. coisson, coussin; according to the New English Dict., from Lat. coxa, a hip; others say from Lat. culcita, a quilt)

cushion-shaped sac, attached below by a broad flattened See also:

• BASE

base and terminating above in a single vent or osculum (fig . 3) . There is a large gastral cavity lined by pavement-epithelium and surrounded by a number of more or less spherical " flagellated chambers," lined by collared cells . These chambers open into the gastral cavity by wide mouths (apopyles) and communicate with the exterior by smaller inhalant pores . The entire outer surface of the sponge is covered with pavement-epithelium and there is a well-developed mesogloea which may contain spicules . This Rhagon may be compared to an Olynthus which has become flattened out from above downwards and from which a number of small buds (the flagellated chambers) have been given off all See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round, except from the attached basal portion; so that the whole forms a small colony, in which the collared cells have become restricted to the buds . We may, therefore, perhaps, look upon the Rhagon as an individual or person of a higher order than the Olynthus . Like the Olynthus the Rhagon occurs as a transient stage in the development of certain sponges, but we do not know any non-calcareous sponge which remains in such a simple condition through-out life . In Plakina monolopha, for example, the entire *all of the Rhagon becomes thrown into folds (fig . 4) so that a system of inhalant and exhalant canals is formed between the folds, through which the water has to pass on its way to and from the chambers . The inhalant canals See also:

• LEAD
• LEAD (pronounced iced)

lead down between the folds from the outer surface of the aponge .

In P. monolopha they are wide and See also:

• ILL

ill defined . In another species, Plakina dilopha, they become constricted to form perfectly definite, narrow canals, by the development of a thick layer of mesogloea (and pavement-epithelium) which covers the outer surface of the sponge in such a manner that the folded character is no longer visible externally . The external openings of the inhalant canals now form definite dermal pores . In such a sponge as this the folded chamber-toyer of the sponge-wall is sometimes called the choanosome, while the external layer of mesogloea and pavement-epithelium is called the ectosome . In a third species, Plakina trilopha, further folding of the " choanosomal lamella " takes place and we thus get a still more complex canal-system . In Plakina the spicules are composed of colloidal silica . The fundamental spicule form is the primitive tetract or calthrops, consisting of four See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

sharp-pointed rays diverging at equal angles from a common centre (fig . 5, a–e) . Modifications of this form occur in two directions: in the first place some of the tetracts, by branching of one ray, give rise to " candelabra," while others, by suppression of rays, give rise to forms with three or even two rays only, triacts and diacts, the latter sometimes termed oxeate (fig . 5, f–l) . The arrangement of the spicules is very irregular; the candelabra alone are definitely arranged (at the surface of the sponge). the other forms are thickly scattered without any sort of order throughout the mesogloea . Euspongia.—The genus Euspongia, to which belong all the finer bath sponges, is a typical example of the true " horny " sponges or Euceratosa, characterized especially by the fact that the skeleton is not composed of spicules but of so called horny fibres, A living Pf ' c .

(After F . E . Schulze . From a coloured See also:

• PLATE

plate in Zeits. See also:

• FUR (connected with O. Fr. forre, a sheath or case; so " an outer covering ")

fur Wissen . Zoologie. by permission of Wilhelm Engelmann.) p.f, Primary fibre of skeleton. i.c, Inhalant canals . s.f, Secondary fibres. e.c, Exhalant canals . d.p, Dermal pores (inhalant). f.c, Flagellated chambers. fibres, connect the primaries in all directions and themselves branch and anastomose freely . The primary fibres contain particles of sand or See also:

• FOREIGN

foreign spicules which are taken in by their growing SPONGES 717 bath sponge appears as a dark-coloured, irregular or sometimes I speak of under the name " sponge." It consists of a very close See also:

• CUP (in O.E. cuppe; generally taken to be from Late Lat. cuppa, a variant of Lat. cupa, a cask, cf. Gr. KuaeXXov)

cup-shaped See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass attached by the under surface to the See also:

• SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain)
• SEA, COMMAND OF THE

sea-bottom. network of spongin fibres (closely resembling See also:

• SILK

silk in chemical The outer surface is covered by a skin or dermal membrane, elevated See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition), some of which, known as primaries, run towards the in innumerable minute conuli by the growing apices of the primary surface at fairly See also:

• REGULAR

regular intervals, while others, known as secondary a, Ciliated embryo (the central e, Rhagon stage, viewed as a transparent See also:

• OBJECT

object, showing the inhalant pores on the surface and the flagellated chambers in the interior; the osculum is not shown . Part of See also:

• VERTICAL (from Lat. vertex, highest point)

vertical See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section through adult sponge, showing the folded choanosomal lamella or spongophare . embryo. ov, Ova. bl, Embryo . skeleton fibres . This skin is pierced by a vast number of inhalant dermal pores of microscopic size, and by a much smaller number of comparatively large vents or oscula .

When the sponge is removed from the water the soft tissues rapidly decay and leave behind only the elastic " horny " skeleten, which is what we usually (After F . E . Schulze . From a plate in Zeitschrift fur Wissen . Zoologie, by permission of Wilhelm Engelmann.) Spicules, a—e, tetracts or calthrops; f—k, triacts or triradiates; i—t, diacts, showing how the monaxon form (I) may be derived from the primitive tetract (a) by suppression of actines.See also:

• CAR (Late Lat. carra)

car (After F . E . Schulze . From Lankester's Treatise on Zoology.) surrounded by spongoblasts . sp.f, Spongin fibre; sp.bl, Spongoblasts . See also:

• COLL

Coll, Collencytes . apices at the surface of the sponge, and the presence of which may greatly injure the quality of the sponge . The connecting fibres are only about 0.035 mm. in See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter, or even less, and the primaries are a little thicker, while the meshes between the fibres are so narrow as to permit of the soaking up of water by capillary attraction, (After F .

E . Schulze.) Flo . 8.—Euspongia officinalis (bath sponge) . See also:

• DIAGRAM

Diagram of the arrangement of the canal-system as seen in vertical sections of two young individuals . d.p, Dermal pores; o, Oscula; r, Rock to which the sponges are attached . part should be shaded) . b, Part of section of ciliated embryo . See also:

• COL
• COL (Fr. for " neck," Lat. collum)

col, Inner cell-mass . ec, External, columnar cells. fl, Flagella . c, Attached embryo, viewed from above, with the gastral cavity appearing in the interior . d, Vertical section of attached f, the See also:

• PROPERTY

property upon which the economic value of the bath sponge depends . In the living sponge the fibres are embedded in the mesogloea, where they are secreted by special cells known as spongo- blasts, which are often found thickly clustering around them (fig .

;) . The canal-system (figs . 6, 8) is very complex and shows but little indication of its origin from a folded rhagon . The in- halant pores lead each into a See also:

• SHORT, FRANCIS JOB (1857– )

short, narrow, inhalant canal; these unite in roomy subdermal cavities lying in the ectosome, and from these in turn the See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main inhalant canals come off . The latter See also:

• DIVIDE

divide and subdivide, and thus ramify through the deeper parts of the sponge amongst the flagellated chambers, to each of which a small number of slender canaliculi are ultimately given off (fig . 9) . The chambers themselves, lined by the usual collared cells, are small and approximately spherical, and each one discharges its water through a short and narrow exhalant canali- culus (g . 9) . The openings of the inhalant canaliculi into the chambers, of which there are several, correspond to the prosopyles of an Olynthus, while the single exhalant opening, or apopyle, may possibly (After F . E . Schulze . From a plate correspond to an Olynthus osculum. in Zeits.far Nissen. zoologie, by per .

The exhalant canaliculi unite to-See also:

• MISSION

mission of Wilhelm Engelmaun.) gether to form larger and larger parts of the canal-system, contains cells of various kinds, embedded in a very granular See also:

• MATRIX

matrix . See also:

• COMPARATIVE

Comparative Anatomy . external Characters.—Amongst the simpler calcareous sponges, which are all of comparatively small size, the external form is usually symmetrical and is evidently a kind of outward expression of the arrangement of the canal-system . This is well seen in the simplest form of all, the sac-shaped Olynthus, and also in its simpler Syconoid and Leuconoid derivatives (described later on), which may be regarded either as individuals of a higher order or as colonies of Olynthus persons grouped around a central individual whose large gastral cavity opens to the exterior through the single osculum . In the more complex Leuconoids, however, the process of colony formation becomes very irregular and may give rise to great compound masses, with many vents . In these masses we may perhaps recognize the presence of individuals of three orders: (1) the primitive Olynthus persons, represented by the individual flagellated chambers; (2) the Leuconoid persons, indicated each by its osculum; and (3) the entire colony formed by the See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union of many such Leuconoid persons in an irregular manner . It is, however, very doubtful how far the flagellated chambers in such forms as this can be regarded as morphologically See also:

• EQUIVALENT

equivalent to Olynthus persons . In the non-calcareous sponges we are always dealing with individuals of a high order, which usually form complex aggre- See also:

• GATES, HORATIO (1728-1806)

gates (colonies) of large size and very various shape . As a general See also:

• RULE

rule the form of those non-calcareous sponges which grow in shallow water is extremely irregular and variable while at great ocean depths the shape is usually defi- nite, See also:

• CONSTANT, BENJAMIN (1845-1902)

constant and often exquisitely symmetrical, a fact which may perhaps (After See also:

• RIDLEY, NICHOLAS (c. 1500-1555)

Ridley and Dendy . From be accounted for in part by the See also:

• ABSENCE (Lat. absentia)

absence a plate in .. Challenger" Reports, of disturbing influences such as are met xx., by permission of the Controller with in shallow water . Perhaps the of H.M .

See also:

• STATIONERY

Stationery See also:

• OFFICE (from Lat. officium, " duty," " service," a shortened form of opifacium, from facere, " to do," and either the stem of opes, " wealth," " aid," or opus, " work ")

Office.) most extraordinary external form yet (After Ridley and Dendy . From "Challenger" Reports, xx., by permission of the Controller of H . M . Stationery Office.) as an See also:

• ADAPTATION (from Lat. adaptare. to fit to)

adaptation to the special exigencies of the environment . Thus, for example, many species are provided with long stalks which lift up the body of the sponge out of the soft See also:

• OOZE (O. Eng. wdse, cognate with an obsolete waise, mud; cf. O. Nor. veisa, muddy pool)

ooze in which it would otherwise be smothered, while the bottom of the stalk is frequently extended in See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root-like processes which serve to attach it to some solid object (e.g . Stylocordyla) . In other cases the sponge supports itself on the surface of the ooze by long stiff processes, formed of bundles of spicules which radiate from the central, cap-shaped body ; this is known as the " Crinorhiza form," and is met with in several distinct genera (fig . II) . Amongst the Hexactinellida, which are essentially a deep-water group, many very beautiful external forms are met with, the best known, perhaps, being the so-called See also:

• VENUS

Venus's See also:

• FLOWER (Lat. flos, floris; Fr. fleur)
• FLOWER, SIB

flower See also:

• BASKET

basket (Euplectella, fig . 12) . Flabellate (or See also:

• FAN (Lat. vannus; Fr. eventail)

fan-shaped) and cup-shaped forms are frequently met with even amongst shallow-water sponges, and in widely separated genera, such as Poterion (the great See also:

• NEPTUNE
• NEPTUNE (Lat. NEPTUNUS)

Neptune's cup sponge) and Reniera testudinaria . In Phyllospongia the flabellate and cup-shaped forms pass insensibly into one another, the cup being apparently merely a folded lamella .

Slender branching forms are also not uncommon in shallow water, as seen in the common Chalina oculata of the See also:

• BRITISH

British See also:

• COAST (from Lat. costa, a rib, side)

coast . Spherical forms, such as Tethya, likewise occur . By far the greater number of shallow-water sponges, however, are quite irregular in shape and either form crusts of varying thickness on the surface of rocks and sea-See also:

• WEED, THURLOW (1797—1882)

weed, or large and massive aggregates which may rise to a consider-able height above the substratum . In the See also:

• BORING

boring sponges (See also:

• FAMILY

Family Clionidae) the sponge occupies an elaborate system of chambers and passages which it excavates for itself in the shells of See also:

• MOLLUSCA

Mollusca and other calcareous organisms . The common British Cliona celata begins (After F . E . Schulze . From a plate in "Challenger" Reports, xxi., by permission of the Controller of H.M . Stationery Office.) life in this way, but soon outgrows the See also:

• HOUSING

housing capacity of its See also:

• HOST

host, whose See also:

• SHELL
• SHELL (O. Eng. scell, scyll, cf. Du. sceel, shell, Goth. skalja, tile; the word means originally a thin flake,. cf. Swed. skalja, to peel off; it is allied to " scale " and " skill," from a root meaning to cleave, divide, separate)

shell then serves merely as a base of See also:

• ATTACHMENT

attachment for the large See also:

• INDEPENDENT

independent sponge-colony . One of the most striking features of living sponges is their See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour, which is often very brilliant . Yellow, red, See also:

• ORANGE
• ORANGE (Citrus Aurantium)
• ORANGE, HOUSE OF

orange, See also:

• PURPLE

purple, See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown, See also:

• BLACK
• BLACK, ADAM (1784-1874)
• BLACK, JEREMIAH SULLIVAN (1810–1883)
• BLACK, WILLIAM (1841-1898)

black, See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green and See also:

• BLUE (common in different forms to most European languages)

blue are all met with, in varying degrees of purity and intensity, amongst the commoner Non-calcarea; whilst the calcareous sponges are usually white . It appears probable that the colour is more or less constant for each species, and may therefore afford a useful See also:

• GUIDE (in Mid. Eng. gyde, from the Fr. guide; the earlier French form was guie, English " guy," the d was due to the Italian form guida; the ultimate origin is probably Teutonic, the word being connected with the base seen in O. Eng. witan, to know)

guide to specific See also:

• IDENTIFICATION (Lat. idem, the same)

identification .

As a rule the colour is lost is spirit-preserved or dry specimens, but a noteworthy exception is found in the brilliant purple Suberites wilsoni of See also:

• PORT

Port See also:

• PHILLIP, JOHN (1817-1867)

Phillip, in which the colour, though soluble in water, is permanent in dry specimens and in See also:

• ALCOHOL

alcohol . The colouring matter is some-times lodged in special pigment cells belonging to the sponge itself, and sometimes in symbiotic See also:

• ALGAE

algae, with which the mesogloea is frequently filled . Canal-system.—Whether we start with the primitive Olynthus form of the Calcarea or with the more advanced Rhagon of many Non-calcarea, it is evident that further advance in the complication of the canal-system is arrived at either by budding or folding, or by a combination of these processes . As, however, the canal-systems of the calcareous and of the main types of non-calcareous sponges have been evolved along perfectly independent lines it will be well to consider them separately . In the genus Leucosolenia (Calcarea Homocoela) the primitive Olynthus form may, as we have already seen, give rise, by branching and anastomosing, to complex reticulate colonies of the Clathrina type, in which a pseudoderm, pierced by inhalant pores, may See also:

• COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover over a system of inhalant canals which are simply the inter-spaces between the branching tubes of which the colony is made up, while at the same time a centrally placed pseudogaster, which is simply a space enclosed by upgrowth of the colony around it, may form the main exhalant canal and open to the exterior through a well-defined vent or pseudosculum . In this direction perhaps the most remarkable modification arrived at is that of Leucosolenia cavata, in which the Clathrina tubes, lined by collared cells, widen out into large irregular spaces, while the inhalant interspaces become constricted into narrow canals lined by collared cells on the outside . We have here a kind of See also:

• INVERSION (Lat. invertere, to turn about)

inversion of the See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary Clathrina canal-system, but a perfectly See also:

• GRADUAL (Med. Lat. gradualis, of or belonging to steps or degrees; gradus, step)

gradual transition from the ordinary to the inverted condition is seen as we pass from the older to the younger parts of the colony . In Leucosolenia (Dendya) tripodifera (fig . 13) we find a totally different type of colony formation, which is of great importance as indicating in its canal-system the possible starting-point of a line of evolution which culminates in the highest Calcarea . I-Iere a large central individual, whose spacious gastral cavity is lined by collared. cells, gives off radial buds from all sides, which branch slightly and terminate in See also:

• BLIND, MATHILDE (1841—1896)

blind ends in contact with one another, so that the entire colony has an approximately even surface . The inhalant canals are represented by the interspaces between the radial tubes, between the blind extremities of which the water finds its way in from the outside . There is only a single vent, situate at the extremity of the central cavity .

This cavity must be regarded as the See also:

• ORIGINAL

original gastral cavity of a parent Olynthus, from which the radial tubes have been produced by budding . (After Dendy . Simplified from a coloured We have next, amongst the plate in Trans . See also:

• ROY, WILLIAM (1726-1790)

Roy . See also:

• SOC

Soc. of See also:

• VICTORIA
• VICTORIA (or VITTORIA), TOMMASSO LUDOVICO DA (C. I540-C. 1613)
• VICTORIA [ALEXANDRINA VICTORIA]

Victoria, Calcarea Heterocoela, the Sycon elboume, vol. in. pt . I.) Olynthus . In the simplest Syconoid forms (Sycetta) the radial chambers remain perfectly straight and unbranched . They do not See also:

• TOUCH (derived through Fr. toucher from a common Teutonic and Indo-Germanic root, cf. " tug," " tuck," O. H. Ger. zucchen, to twitch or draw)

touch one another at all and there is no trace of an ectosome or dermal cortex, and hence there are no true inhalant canals, and the water circulates without interruption between the chambers . In the genus Sycon (fig . 14) the walls of adjacent chambers come into contact with one another and fuse together and thus give rise to more or less well-defined inhalant " inter-canals." The chambers themselves may branch, and in some species of Sycon a thin, pore-bearing dermal membrane connects together their distal extremities and covers over the entrances to the inhalant canals . The canal-system now exhibits all the different parts found in the most highly-organized sponges: viz. dermal pores, inhalant canals, flagellated chambers, exhalant canal and osculum . In the genus Grantia and its See also:

• ALLIES, THOMAS WILLIAM (1813-1903)

allies (e.g .

See also:

• UTE
• UTE, or UTAH

Ute, fig . 15) pros, the thin dermal membrane c.g.c, of Sycon is converted into a i.c, well-developed cortex, cover- g.See also:

• COR

cor, big the extremities of both g.q the inhalant canals and the radial chambers, and some- s.g.s, times containing a system of special cortical inhalant canals . We may now distinguish between an ectosome t.ox, (the dermal cortex), which contains no flagellate cham- bers, and a choanosome in which chambers are present . The next stage has probably been arrived at by a kind of folding of the choanosome, for we find the chambers arranged (After Polejaeff.) radially, not around the central gastral cavity but around diverticula of the latter which form special exhalant canals . This condition, sometimes called the " sylleibid " type, is not characteristic of any particular genus 'or family, but occurs in a few isolated species, such as Leucilla connexiva (fig . 16) . A somewhat similar condition may be arrived at by branching of the radial flagellated chambers, as in Heteropegma (fig. i7) . The next stage is marked by great reduction in the size of the chambers, which may become almost spherical, and by further folding cf the choanosome, so that in a section of the sponge-wall we see the small chambers scattered irregularly in the mesogloea between the numerous branches of complicated inhalant and exhalant canals . Each (From Dendy, in Quart . Journ . Micro . Sc., new series, See also:

• XXXV

xxxv., by permission of J. and A .

See also:

• CHURCHILL (MISSINNIPPI or ENGLISH)
• CHURCHILL, CHARLES (1731-1764)
• CHURCHILL, LORD RANDOLPH HENRY SPENCER (1849-1895)

Churchill.) fl.ch, Flagellated chamber . ex.op, Its exhalant opening or apopyle . Prosopyle . Central gastral cavity . Inhalant canal . Gastral cortex . Gastral quadriradiate spicule . Subgastral sagittal triradiate spicules, forming the first See also:

• JOINT (through Fr. from Lat. junctum, jungere, to join)

joint of the articulate tubar skeleton . Tufts of monaxon spicules at the ends of the chambers . chamber still has several prosopyles, through which it receives water from the ultimate branches of the inhalant canals, while it opens into a relatively large exhalant canal by a wide apopyle . This is the highest type of canal-system met with amongst the Calcarea . It is sometimes known as the Leucon type and is seen in most species of the genus Leucandra, as well as in many others .

(After Polejaeff.) It is almost identical with one of the types commonly found in non-calcareous sponges (e.g . Plakina, fig . 4), but has of course been evolved independently . The various types of canal-system met with in the Calcarea are connected together by numerous intermediate forms, thus forming a very interesting evolutionary series, while both the Sylleibid and Leuconoid types appear to have been in-dependently evolved several times, thus affording excellent examples of the phenomenon of convergence, a phenomenon which is very frequently me,; with amongst sponges . (After Polejaeff.) In describing the anatomy of Plakina as a type of non-calcareous sponge, we have traced the development of a fairly complex canal-system from the so-called Rhagon form . We can, however, hardly regard the Rhagon as representing a fundamental type of canal-system common to all the Nen-calcarea, for in some of the Myxospongida, which are the most primitive of all, and again in the Hexactineliida, we find a type characterized by the presence of elongated sac-shaped flagellated chambers resembling those of the Syron type amongst the Calcarea, and these chambers are arranged radially around the exhalant canals (Halisarca, Hexactinellida) . The first recognizable stage in the evolution of the canal-system of the Non-calcarea would thus appear to be a condition not unlike that of Sycon, with a number of elongated chambers arranged radially around a central gastrzl cavity and having their blind outer extremities covered over by a dermal membrane . This stage is very nearly reproduced in the young form of a Hexactinellid sponge, Lanuginella pupa . From some such form the Rhagon type may perhaps be derived by flattening out of the lower end of the sponge into a broad base of attachment, and by reduction in the size of the flagellated chambers, accompanied by a more irregular arrangement . Starting from the primitive Myxosponge ancestor, with large sac-shaped chambers, radially arranged, the Non-calcarea have apparently developed along four main lines, giving rise to the existing Myxospongida, the Hexactinellida (Triaxonida), the Tetraxonida "Sc . (After F . E .

Schulze . From Lankester's Treatise on Zoology.) specimen (spicules omitted) . d.m, Dermal membrane. g.rrt, Gastral membrane. sd.tr, Subdermaltrabecularlayer . G.C, Gastral cavity . fl.c, Flagellated chamber. osc, Region of future osculum. sg.tr, Subgastral trabecular layer . and the Euceratosa . The Myxospongida have retained the large size of the chambers in certain forms (Halisarca, Bajalus), but have lost this primitive character in the more advanced members of the group (Oscarella) . The Hexactinellida have retained the large size and radial arrangement of the flagellated chambers throughout their entire series . The chamber layer, however, tends to become more or less folded (fig . 19), and always lies between two layers of !Lc OR o t1 (After Schulze . From Lankester's Treatise on Zoology.) ex.c, Exhalant canals. sg.tr, Subgastral trabecular layer . d.m, Dermal membrane. g.m, Gastral membrane. sd.tr, Subdermaltrabecularlayer .

G.C, Gastral cavity. fl.c, Flagellated chambers . loose trabecular tissue in which the canals are represented by irregular spaces . The Tetraxonida appear to have suffered reduction in the size of the flagellated chambers at a very See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

early date, and it is of this group especially that the Rhagon type is characteristic (e.g . Plakina, fig . 4) . The Euceratosa exhibit a beautiful series, Q0 0 10t 'h) O \- o a ) set in 0 or 00 OQ Q6 00 0 04 beginning with forms (Aplysillidae) having large sac-shaped chambers To this type (fig . 4, f) the name " eurypylous " has been given, and like those of Hexactinellids and ending with forms (Spongiidae, we may include in it cases where there is only a single prosopyle, and Euspongia, figs . 6, 8, 9) having small spherical chambers . Along all four lines of descent it is probable that folding of the choanosome, or chamber-bearing layer of the sponge-wall, has played a very important part in the evolution of the canal-system . This folding is very clearly seen in the Hexactinellida and in such forms as Oscarella (l\/Iyxospongida) and Plakina (Tetraxonida) . By this process inhalant and exhalant canal-systems have been formed, and then the ends of the inhalant canals have in most cases been closed in by development of an ectoseme, as in Plakina trilopha and Stelletta phrissens (fig . 20) .

In the majority of cases (e.g . (After Sollas.) Euspongia) the folding has become so complex that it is no longer recognizable as such, and the origin of the now well-defined inhalant and exhalant canals is completely disguised. in many cases the principal exhalant canals may be surrounded by a layer of tissue of considerable thickness in which there are no flagellated chambers at all, known as the endosome, so that the folded choanosome may be sandwiched in between ectosome' on the outside and endosome on the inside . The manner in which the flagellated chambers communicate with their respective branches of the inhalant and exhalant canal- (After Sollas.) system varies considerably in different forms, and the following types are recognizable, though by no means sharply distinguished from one another . In the more primitive forms (e.g . Hexactinellida, Aplysillidae, Spongeliidae) each chamber is provided with several prosopyles and receives its water supply See also:

• DIRECT

direct from relatively large inhalant canals or even lacunae, discharging it again through a wide mouth (apopyle) into a relatively large exhalant canal or lacuna which also receives water directly from other chambers . perhaps even a short, narrow inhalant canal . In more advanced forms the water is discharged from each chamber through a narrow exhalant canaliculus (aphodus) See also:

• PECULIAR

peculiar to itself, and thence into wider canals . This is known as the "aphodal " type (e.g . Cydonium, fig . 21) . In the " diplodal " type there is a special inhalant canaliculus (prosodus) as well as a special aphodus to each chamber, with usually, at any See also:

• RATE

rate, oniy a single prosopyle (e.g . Corticium, fig .

22) . The progress from the eurypylous to the diplodal condition is accompanied by a corresponding increase in the development of the mesogloea, whereby the canals are greatly .Y restricted in diameter, and at the same time the mesogloea (After F . E . Schulze.) tends to lose its transparent FIG . 22.-Part of a section of gelatinous character and to Corticium See also:

• CANDELABRUM (from Lat. candela, a taper or candle)

candelabrum, O.S., show-become compact and granular. See also:

• ING

ing diplodal type of canal-system . With the growth of the ectc- The canal shown on the See also:

• LEFT

left is some we necessarily get a inhalant and that on the right (e) corresponding development of exhalant . the proximal portion of the inhalant canal-system . At first the ectosome is merely a thin membrane, the dermal membrane, pierced by the inhalant pores, which are usually arranged in See also:

• GROUPS
• GROUPS, THEORY

groups . Beneath the groups of pores (pore-areas) lie spacious sub-dermal cavities which form the commencement of the inhalant canal-system in the choanosome . In more advanced types the ectosome becomes greatly thickened and may be specially strengthened in a variety of ways to form a cortex . The inhalant pores now no longer lead directly into the subdermal cavities, but first into a series of cavities lying in the cortex and known as chones, which may be separated from the underlying subdermal cavities (sub-cortical crypts) by definite sphincters (Cydonium, fig . 23) .

The arrangement of the oscula and pores on the surface of the sponge varies greatly in different types, and sometimes gives rise to very striking modifications of the external form . The oscula or vents are usually relatively large openings situated on the more prominent parts of the sponge, often on special elevations . Occasionally they are replaced by See also:

• SIEVE (O.E. sife, older sibi, cf. Dutch zeef, Ger. Sieb; from the subst. comes O.E. siftan, to sift)

sieve-like oscular areas (e.g . Geodia perarmata), a modification which doubtless serves to prevent foreign bodies from entering the wide exhalant canals . The inhalant pores may be irregularly scattered over the surface of the sponge or collected in more or less well-defined pore-areas . In cup-shaped sponges the pores are usually confined to the outer and the oscula to the inner surface . In flabellate sponges we find pores on one side and oscula on the other . In Tedania actinii{ormis, a deep-sea form. the pores are restricted to a narrow See also:

• BAND

band surrounding the columnar body of the sponge just beneath the flattened See also:

• TOP (cf. Dan. top, Ger. Topf, also meaning pot)

top, which bears the vents; thus they are kept from being choked up by the soft ooze on which the sponge lies . In Xenospongia, a flattened discoid form, they are confined to narrow grooves on the upper surface, the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief of which run round the margin of the disk . In Esperella murrayi the pores are also confined to special grooves on the surface of the sponge, and in both these cases the grooves can apparently be opened and closed by special bands of muscle-fibres, and the supply of water thus regulated . In some species of Latrunculia we find the surface of the sponge covered with (After Sullas.) conspicuous projections of two kinds, some conical and bearing each a single vent, others truncated at the top and bearing the inhalant pores . Skeleton.—The original ancestral form (Protolynthus) from which all the Porifera are supposed to be descended, probably possessed no proper skeleton at all, and this condition has been retained in the existing Myxospongida, although these sponges have made considerable progress in the evolution of their canal-system .

There appears to be little doubt that the Myxospongida are primitively devoid of skeleton, and in this respect they must becarefullydistinguishedfrom thegenusChondrosia, in which the skeleton has been secondarily suppressed, as well as from numerous and See also:

• DIVERS

divers species in which the proper skeleton has been more or less completely replaced by grains of sand or other foreign bodies . The Calcarea, Triaxonida, Tetraxonida and Euceratosa, except in cases of extreme degeneration, all possess a well-developed proper skeleton . As this skeleton has been independently evolved in each of these great groups it is necessary to deal with it separately in each See also:

• CASE
• CASE, JOHN (d. 1600)

case . Calcarea.—The skeleton in this group is composed of spicules of crystalline carbonate of lime (usually calcite), developed within special mother-cells or scleroblasts . Each spicule is enclosed in a delicate membranous spicule-sheath and contains an axial See also:

• THREAD (0. Eng. praed, literally, that which is twisted, prawan, to twist, to throw, cf. " throwster," a silk-winder, Ger. drehen, to twist, turn, Du. draad, Ger. Draht, thread, wire)

thread of organic matter . Three main types of calcareous spicule are met with, triradiate, quadriradiate and monaxon (fig . 24) . The triradiates and quadriradiates, however, are not simple spicules, but spiculesystems formed of three or four rays each originating independently from its own scleroblast (actinoblast) and all uniting together secondarily . There is See also:

• REASON (Lat. ratio, through French raison)

reason to believe that this may also sometimes be the case with the monaxon or oxeate spicules . In the most primitive triradiate spicules all three rays lie in thequadriradiate spicules . These may be sagittal, in which case the oral rays are turned towards the osculum while the basal ray is directed downwards . If there is an apical ray it projects into the gastral cavity .

The walls of the radial chambers are supported by a special " tubar " skeleton (cf. fig . 14), consisting exclusively of triradiates with their basal rays directed towards the distal end of each chamber . The oral rays are spread out at right angles to the length of the chamber, and as several spicules generally lie at the same level the tubar skeleton forms a series of more or less definite See also:

• JOINTS

joints and is said to be " articulate." This type of skeleton is almost invariably associated with the Syconoid type of canal-system . In the genus Sycon itself we find the distal ends of the chambers specially protected by tufts of monaxon spicules (fig . 14), but the next great advance in the evolution of the skeleton is brought about by the development of a dermal cortex, in which a special dermal skeleton is developed . This is well seen in the genus Ute (fig. i5) . After this the skeleton of the chamber layer in the sponge-wall begins to undergo modifications, some of which are obviously correlated with the gradual See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change of the canal-system from the Syconoid to the Leuconoid condition (cf. figs . 16 and 17) . Finally all trace of the articulate tubar skeleton is lost, and we get a " parenchymal " skeleton of scattered radiate spicules in the chamber layer . The skeleton of the chamber layer, no matter what the type of canal-system, may be supplefnented by large subdermal sagittal triradiates or subdermal quadriradiates (fig . 17), whose basal or apical rays project inwards from the dermal cortex (Heteropidae and Amphoriscidae) . Very generally a special " oscular " skeleton is developed in the form of a fringe of long monaxon spicules around the vent .

Various aberrant types of skeleton are met with in the group . In the genus Lelapia we find a partly fibrous skeleton, in wjtich the fibres are composed of bundles of triradiates shaped like tuning-forks (fig . 24, o), and in Petrostoma the main skeleton is formed of calcareous spicules actually fused together . In Astrosclera (fig . 25) a very anomalous type of calcareous skeleton is found, consisting of spherical masses of arragonite, each originating in a special scleroblast and having a radiate structure, recalling that of a siliceous (After W . J . Sollas.) FfG . 26.—Typical Siliceous Megascleres . a, Diactinal monaxon (oxeate). g, b, See also:

• STYLE
• STYLE (from Gr. a-6'1ms, a column; a different word from that used in literature, see below)

Style . c, Triact . d, Primitive tetraxon (calthrops) . e, Hexact .