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in the cortex, and in some forms the spicules are cemented alcyonacea are founded upon the different architectural featuies those to form a hard supporting axis. There are four families of colonies produced by different modes of budding. A e recognize together of° Pseudaxonia—the Briareidce, Sderogorgidce, Melitodidce, and six orders—the Stolonifera, Alcyonacea, Pseudaxonia, Axi- Corallidce-. In the first-named the medulla is penetrated by solenia FERA, SXELECHOTOKEA, and OCENOTHECALIA.. forms an indistinct axis ; in the remainder the medulla is In the order Stolonifera the zooids spring at intervals from and of solenia, and in the Melitodidce and Corallidce it forms branching or lamellar stolons, and are usually free from one another, devoid dense axis, which in the Melitodidce consists of alternate calexcept at their bases, but in some cases horizontal solenia arising acareous and horny joints. The precious red coral of commerce. at various heights from the body-wall may place the more distal Corallium rubrum (Fig. 6), a member of the family Corallidce, portions of the zooids m communication with one is found at depths varying from 15 to 120 fathoms in the Mediteranother. In the genus ranean Sea, chiefly on the African coast. It owes its commercial Tubipora these hori- value to the beauty of its hard red calcareous axis, wdiich in life is zontal solenia unite to covered by a cortex in form a series of hori- which the proximal zontal platforms (Fig. 5). moieties of the zooids The order comprises the are imbedded. Coralfamilies Cornulariidaz, lium rubrum has been Syringoporidce, Tubipo- the subject of a beautiridce, and FavosUidce. fully - illustrated meIn the first-named the moir by de Lacaze zooids are united only Duthiers, which should by their bases and the be consulted for details skeleton consists of loose of anatomy. The Axifera comspicules. In the Tubiporidce the spicules of the prises those corals that proximal part of the have a horny or calcibody-wall are fused to- fied axis, which in posigether to form a firm tion corresponds to the tube, the corallite, into axis of the Pseudaxonia, which the distal part of but, unlike it, is never the zooid can be re- formed of fused spictracted. The corallites ules ; the most familiar are connected at inter- example is the pink Gorgonia CavoFio. 5.—A, Skeleton of a young colony of Tubi- val8 by horizontal plat- sea-fan, pora purpurea, st, stolon; p, platform. B, forms containing solenia, linii, which is found in Pig. 7.—The sea-fan (Gorgonia Cavolinii). Diagrammatic longitudinal section of a coral- J the level of each abundance in 10-25 lite, showing two platforms, p, and simple an( u f ] tf oav v 0 of water off the English coasts (Fig. 7). In this order the axis and cup-shaped tabula;, t. (After Hickson.) P/attoi m tne iscavity or fathoms is formed as an ingrowth of the ectoderm of the base of the mother the coralhte divided by a transverse calcareous partition, either flat or cup-shaped, called zooid of the colony, the cavity of the ingrowth being filled by a horny substance secreted a tabula. Formerly all corals in which tabuhe are present were by the ectoderm. In classed together as Tabulata, but Tubipora is an undoubted AlcyoGorgonia the axis renarian with a lamellar stolon, and the structure of the fossil genus mains horny throughout Syringopora, which has vertical corallites united by horizontal life, but in many forms solenia, clearly shows its affinity to Tubipora. The Favositidse, a it is further strengthened fossil family from the Silurian and Devonian, have a massive by a deposit of calcareous corallum composed of numerous polygonal corallites closely packed matter. In the family together. The cavities of adjacent corallites communicate by Isidince the axis consists means of numerous perforations, which appear to represent solenia, of alternate segments of and numerous transverse tabulae are also present. In Favosites horny and calcareous hemisphcerica a number of radial spines, projecting into the substance, the latter cavity of the corallite, give it the appearance of a madreporarian being amorphous. The coral. order contains six famiIn the order Alcyonacea the colony consists of bunches of lies — the Dasygorgida, elongate cylindrical zooids, whose proximal portions are united by Isidce, Primnoidce, Murisolenia and compacted, by fusion of their own walls and those of ceidce, Plexauridce, and the solenia, into a fleshy mass called the ccenenchyma. Thus the Gorgonidce. coenenchyma forms a stem, sometimes branched, from the surface In the order Steleof which the free portions of the zooids project. The skeleton of chotokea the colony the Alcyonacea consists of separate calcareous spicules, which are consists of a stem formed often, especially in the Nephthykke, so abundant and so closely by a greatly - elongated interlocked as to form a tolerably firm and hard armour. The mother zooid, and the order comprises the daughter zooids are families Xeniidce, Alborne as lateral buds on cyonidce, and Nephthyidce. Alcyonimn digithe stem. In the sectatum, a pink digitate tion Asiphonacea the form popularly known colonies are upright and branched, springing from as “dead men’s linmembranous or ramifygers,” is common in 10-20 fathoms of water ing stolons. They reoff the English coasts. semble and are closely In the order Pseudallied to certain families axonia the colonies are of the Cornulariidse, difupright and branched, fering from them only in consisting of a number mode of budding and in of short zooids whose the disposition of the proximal ends are imdaughter zooids round a bedded in a ccenencentral, much-elongated chyma containing Pig. 8.—A, Colony of Pennatula phosphorea from mother zooid. The seenumerous ramifying Fig. 6.—Portion of a colony of Corallium rubrum, the metarachidial aspect, p, the peduncle, tion contains two famiB, Section of the rachis bearing a single ][eS; the Telestidoe and qnlpnia and contracted zooids. In soienia ana snicules spicuies. showing the lowerexpanded part of theand figlire the cortex hag been pro- the Ccelogorgidce. The pinna, a, axis; b, metarachidial, I be ccenencbyma is cut away to show the axis, ax, and the longirachidial, d, pararachidial stem canals. further differentiated tudinal canals, lc, surrounding it. second section comprises into a medullary porthe Pennatulacea or sea-pens, which are remarkable from the tion and a cortex. The latter contains the proximal moieties of fact that the colony is not fixed by the base to a rock or the zooids and numerous but separate spicules. The medullary other object, but is imbedded in sand or mud by the proximal portion is densely crowded with spicules of different shape from portion of the stem known as the peduncle. In the typical
