Though the corallum appears to live within the zooid, it is morphologically external to it, as is best shown by its developmental history. The larvae of corals are free swimming ciliated forms known as planulae, and they do not acquire a corallum until they fix themselves. A ring-shaped plate of calcite, secreted by the ectoderm, is then formed, lying between the embryo and the surface of attachment. As the mesenteries are formed, the endoderm of the basal disk lying above the basal plate is raised up in the form of radiating folds. There may be six of these folds, one in each entocoele of the primary cycle of mesenteries, or there may be twelve, one in each exocoele and entocoele. The ectoderm beneath each fold becomes detached from the surface of the basal plate, and both it and the mesogloea are folded conformably with the endoderm. The cells forming the limbs of the ectodermic folds secrete nodules of calcite, and these, fusing together, give rise to six (or twelve) vertical radial plates or septa. As growth proceeds new septa are formed simultaneously with the new couples of secondary mesenteries. In some corals, in which all the septa are entocoelic, each new system is embraced by a mesenteric couple; in others, in which the septa are both entocoelic and exocoelic, three septa are formed in every chamber between two primary mesenterial couples, one in the entocoele of the newly formed mesenterial couple of the secondary cycle, and one in each exocoele between a primary and a secondary couple. These latter are in turn embraced by the couples of the tertiary cycle of mesenteries, and new septa are formed in the exocoeles on either side of them, and so forth.
Fig.17.—Transverse section through a zooid ofCladocora. The corallum shaded with dots, the mesogloea represented by a thick line. Thirty-two septa are present, six in the entocoeles of the primary cycle of mesenteries, I; six in the entocoeles of the secondary cycle of mesenteries, II; four in the entocoeles of the tertiary cycle of mesenteries, III, only four pairs of the latter being developed; and sixteen in the entocoeles between the mesenterial pairs.D, D, Directive mesenteries;st, stomodaeum. (After Duerden.)
It is evident from an inspection of figs. 16 and 17 that everyseptum is covered by a fold of endoderm, mesogloea, and ectoderm, and is in fact pushed into the cavity of the zooid from without. The zooid then is, as it were, moulded upon the corallum. When fully extended, the upper part of the zooid projects for some distance out of the calicle, and its wall is reflected for some distance over the lip of the latter, forming a fold of soft tissue extending to a greater or less distance over the theca, and containing in most cases a cavity continuous over the lip of the calicle with the coelenteron. This fold of tissue is known as theedge-zoneIn some corals the septa are solid imperforate plates of calcite, and their peripheral ends are either firmly welded together, or are united by interstitial pieces so as to form imperforate theca. In others the peripheral ends of the septa are united only by bars or trabeculae, so that the theca is perforate, and in many such perforate corals the septa themselves are pierced by numerous perforations. In the former, which have been called aporose corals, the only communication between the cavity of the edge-zone and the general cavity of the zooid is by way of the lip of the calicle; in the latter, or perforate corals, the theca is permeated by numerous branching and anastomosing canals lined by endoderm, which place the cavity of the edge-zone in communication with the general cavity of the zooid.
A, Schematic longitudinal section through a zooid and bud ofStylophora digitata. In A, B, and C the thick black lines represent the soft tissues; the corallum is dotted.s, Stomodaeum;c,c, coenosarc;col, columella,Ttabulae.
B, Similar section through a single zooid and bud ofAstroides calicularis.
C, Similar section through three corallites ofLophohelia prolifera.ez, Edge-zone.
D, Diagram illustrating the process of budding by unequal division.
E, Section through a dividing calicle ofMussa, showing the union of two septa in the plane of division and the origin of new septa at right angles to them.
(C original; the rest after von Koch.)
A large number of corals, both aporose and perforate, are colonial. The colonies are produced by either budding or division. In the former case the young daughter zooid, with its corallum, arises wholly outside the cavity of the parent zooid, and the component parts of the young corallum, septa, theca, columella, &c., are formed anew in every individual produced. In division a vertical constriction divides a zooid into two equal or unequal parts, and the several parts of the two corals thus produced are severally derived from the corresponding parts of the dividing corallum. In colonial corals a bud is always formed from the edge-zone, and this bud develops into a new zooid with its corallum. The cavity of the bud in an aporose coral (fig. 18, A, C) does not communicate directly with that of the parent form, but through the medium of the edge-zone. As growth proceeds, and parent and bud become separated farther from one another, the edge-zone forms a sheet of soft tissue, bridging over the space between the two, and resting upon projecting spines of the corallum. This sheet of tissue is called thecoenosarc. Its lower surface is clothed with a layer of calicoblasts which continue to secrete carbonate of lime, giving rise to a secondary deposit which more or less fills up the spaces between the individual coralla, and is distinguished ascoenenchyme. This coenenchyme may be scanty, or may be so abundant that the individual corallites produced by budding seem to be immersed in it. Budding takes place in an analogous manner in perforate corals (fig. 18, B), but the presence of the canal system in the perforate theca leads to a modification of the process. Buds arise from the edge-zone which already communicate with the cavity of the zooid by the canals. As the buds develop the canal system becomes much extended, and calcareous tissue is deposited between the network of canals, the confluent edge-zones of mother zooid and bud forming a coenosarc. As the process continues a number of calicles are formed, imbedded in a spongy tissue in which the canals ramify, and it is impossible to say where the theca of one corallite ends and that of another begins. In the formation of colonies by division a constriction at right angles to the long axis of the mouth involves first the mouth, then the peristome, and finally the calyx itself, so that the previously single corallite becomes divided into two (fig. 18, E). After division the corallites continue to grow upwards, and their zooids may remain united by a bridge of soft tissue or coenosarc. But in some cases, as they grow farther apart, this continuity is broken, each corallite has its own edge-zone, and internal continuity is also broken by the formation of dissepiments within each calicle, all organic connexion between the two zooids being eventually lost. Massive meandrine corals are produced by continual repetition of a process of incomplete division, involving the mouth and to some extent the peristome: the calyx, however, does not divide, but elongates to form a characteristic meandrine channel containing several zooid mouths.
Corals have been divided intoAporosaandPerforata, according as the theca and septa are compact and solid, or are perforated by pores containing canals lined by endoderm. The division is in many respects convenient for descriptive purposes, but recent researches show that it does not accurately represent the relationships of the different families. Various attempts have been made to classify corals according to the arrangement of the septa, the characters of the theca, the microscopic structure of the corallum, and the anatomy of the soft parts. The last-named method has proved little more than that there is a remarkable similarity between the zooids of all recent corals, the differences which have been brought to light being for the most part secondary and valueless for classificatory purposes. On the other hand, the study of the anatomy and development of the zooids has thrown much light upon the manner in which the corallum is formed, and it is now possible to infer the structure of the soft parts from a microscopical examination of the septa, theca, &c., with the result that unexpected relationships have been shown to exist between corals previously supposed to stand far apart. This has been particularly the case with the group of Palaeozoic corals formerly classed together asRugosa. In many of these so-called rugose forms the septa have a characteristic arrangement, differing from that of recent corals chiefly in the fact that they show a tetrameral instead of a hexameral symmetry. Thus in the familyStauridaethere are four chief septa whose inner ends unite in the middle of the calicle to form a false columella, and in theZaphrentidaethere are many instances of an arrangement, such as that depicted in fig. 19, which represents the septal arrangement ofStreptelasma corniculumfrom the lower Silurian. In this coral the calicle is divided into quadrants by four principal septa, themain septum, counter septum, and twoalar septa. The remaining septa are so disposed that in the quadrants abutting on the chief septum they converge towards that septum, whilst in the other quadrants they converge towards the alar septa. The secondary septa show a regular gradation in size, and, assuming that the smallest were the most recently formed, it will be noticed that in the chief quadrants the youngest septa lie nearest to the main septum;in the other quadrants the youngest septa lie nearest to the alar septa. This arrangement, however, is by no means characteristic even of the Zaphrentidae, and in the familyCyathophyllidaemost of the genera exhibit a radial symmetry in which no trace of the bilateral arrangement described above is recognizable, and indeed in the genusCyathophyllumitself a radial arrangement is the rule. The connexion between the Cyathophyllidae and modern Astraeidae is shown byMoseleya latistellata, a living reef-building coral from Torres Strait. The general structure of this coral leaves no doubt that it is closely allied to the Astraeidae, but in the young calicles a tetrameral symmetry is indicated by the presence of four large septa placed at right angles to one another. Again, in the familyAmphiastraeidaethere is commonly a single septum much larger than the rest, and it has been shown that in the young calicles,e.g.ofThecidiosmilia, two septa, corresponding to the main- and counter-septa of Streptelasma, are first formed, then two alar septa, and afterwards the remaining septa, the latter taking on a generally radial arrangement, though the original bilaterality is marked by the preponderance of the main septum. As the microscopic character of the corallum of these extinct forms agrees with that of recent corals, it may be assumed that the anatomy of the soft parts also was similar, and the tetrameral arrangement, when present, may obviously be referred to a stage when only the first two pairs of Edwardsian mesenteries were present and septa were formed in the intervals between them.
Space forbids a discussion of the proposals to classify corals after the minute structure of their coralla, but it will suffice to say that it has been shown that the septa of all corals are built up of a number of curved bars called trabeculae, each of which is composed of a number of nodes. In many secondary corals (Cyclolites, Thamnastraea) the trabeculae are so far separate that the individual bars are easily recognizable, and each looks something like a bamboo owing to the thickening of the two ends of each node. The trabeculae are united together by these thickened internodes, and the result is a fenestrated septum, which in older septa may become solid and aporose by continual deposit of calcite in the fenestrae. Each node of a trabecula may be simple,i.e.have only one centre of calcification, or may be compound. The septa of modern perforate corals are shown to have a structure nearly identical with that of the secondary forms, but the trabeculae and their nodes are only apparent on microscopical examination. The aporose corals, too, have a practically identical structure, their compactness being due to the union of the trabeculae throughout their entire lengths instead of at intervals, as in the Perforata. Further, the trabeculae may be evenly spaced throughout the septum, or may be grouped together, and this feature is probably of value in estimating the affinities of corals. (For an account of coral formations seeCoral-Reefs.)
In the present state of our knowledge the Zoantharia in which a primary cycle of six couples of mesenteries is (or may be inferred to be) completed by the addition of two pairs to the eight Edwardsian mesenteries, and succeeding cycles are formed in the exocoeles of the pre-existing mesenterial cycles, may be classed in an orderActiniidea, and this may be divided into the subordersMalacactiniae, comprising the soft-bodied Actinians, such asActinia, Sagartia, Bunodes, &c., and theScleractiniae, comprising the corals. The Scleractiniae may best be divided into groups of families which appear to be most closely related to one another, but it should not be forgotten that there is great reason to believe that many if not most of the extinct corals must have differed from modern Actiniidea in mesenterial characters, and may have only possessed Edwardsian mesenteries, or even have possessed only four mesenteries, in this respect showing close affinities to the Stauromedusae. Moreover, there are some modern corals in which the secondary cycle of mesenteries departs from the Actinian plan. For example, J.E. Duerden has shown that inPoritesthe ordinary zooids possess only six couples of mesenteries arranged on the Actinian plan. But some zooids grow to a larger size and develop a number of additional mesenteries, which arise either in the sulcar or the sulcular entocoele, much in the same manner as in Cerianthus. Bearing this in mind, the following arrangement may be taken to represent the most recent knowledge of coral structure:—
Group A.Family I.Zaphrentidae.—Solitary Palaeozoic corals with an epithecal wall. Septa numerous, arranged pinnately with regard to four principal septa. Tabulae present. One or more pits or fossulae present in the calicle. Typical genera—Zaphrentis, Raf.Amplexus, M. Edw. and H.Streptelasma, Hall.Omphyma, Raf.Family 2.Turbinolidae.—Solitary, rarely colonial corals, with radially arranged septa and without tabulae. Typical genera—Flabellum, Lesson.Turbinolia, M. Edw. and H.Caryophyllia, Lamarck.Sphenotrochus, Moseley, &c.Family 3.Amphiastraeidae.—Mainly colonial, rarely solitary corals, with radial septa, but bilateral arrangement indicated by persistence of a main septum. Typical genera—Amphiastraea, Étallon.Thecidiosmilia.Family 4.Stylinidae.—Colonial corals allied to the Amphiastraeidae, but with radially symmetrical septa arranged in cycles. Typical genera—Stylina, Lamarck (Jurassic).Convexastraea, D’Orb. (Jurassic).Isastraea, M. Edw. and H.(Jurassic). Ogilvie refers the modern genusGalaxeato this family.Group B.Family 5.Oculinidae.—Branching or massive aporose corals, the calices projecting above the level of a compact coenenchyme formed from the coenosarc which covers the exterior of the corallum. Typical genera—Lophohelia, M. Edw. and H.Oculina, M. Edw. and H.Family 6.Pocilloporidae.—Colonial branching aporose corals, with small calices sunk in the coenenchyme. Tabulae present, and two larger septa, an axial and abaxial, are always present, with traces of ten smaller septa. Typical genera—Pocillopora, Lamarck.Seriatopora, Lamarck.Family 7.Madreporidae.—Colonial branching or palmate perforate corals, with abundant trabecular coenenchyme. Theca porous; septa compact and reduced in number. Typical genera—Madrepora, Linn.Turbinaria, Oken.Montipora, Quoy and G.Family 8.Poritidae.—Incrusting or massive colonial perforate corals; calices usually in contact by their edges, sometimes disjunct and immersed in coenenchyme. Theca and septa perforate. Typical genera—Porites, M. Edw. and H.Goniopora, Quoy and G.Rhodaraea, M. Edw. and H.Group C.Family 9.Cyathophyllidae.—Solitary and colonial aporose corals. Tabulae and vesicular endotheca present. Septa numerous, generally radial, seldom pinnate. Typical genera—Cyathophyllum, Goldfuss (Devonian and Carboniferous).Moseleya, Quelch (recent).Family 10.Astraeidae.—Aporpse, mainly colonial corals, massive, branching, or maeandroid. Septa radial; dissepiments present; an epitheca surrounds the base of massive or maeandroid forms, but only surrounds individual corallites in simple or branching forms. Typical genera—Goniastraea, M. Edw. and H.Heliastraea, M. Edw. and H.Maeandrina, Lam.Coeloria, M. Edw. and H.Favia, Oken.Family 11.Fungidae.—Solitary and colonial corals, with numerous radial septa united by synapticulae. Typical genera—Lophoseris, M. Edw. and H.Thamnastraea, Le Sauvage.Leptophyllia, Reuss (Jurassic and Cretaceous).Fungia, Dana.Siderastraea, Blainv.Group D.Family 12.Eupsammidae.—Solitary or colonial perforate corals, branching, massive, or encrusting. Septa radial; the primary septa usually compact, the remainder perforate. Theca perforate. Synapticula present in some genera. Typical genera—Stephanophyllia, Michelin.Eupsammia, M. Edw. and H.Astroides, Blainv.Rhodopsammia, M. Edw. and H.Dendrophyllia, M. Edw. and H.Group E.Family 13.Cystiphyllidae.—Solitary corals with rudimentary septa, and the calicle filled with vesicular endotheca. Genera—Cystiphyllum,Lonsdale (Silurian and Devonian).Goniophyllum, M. Edw. and H. (In this Silurian genus the calyx is provided with a movable operculum, consisting of four paired triangular pieces, the bases of each being attached to the sides of the calyx, and their apices meeting in the middle when the operculum is closed).Calcecla, Lam. (In this Devonian genus there is a single semicircular operculum furnished with a stout median septum and numerous feebly developed secondary septa. The calyx is triangular in section, pointed below, and the operculum is attached to it by hinge-like teeth.)Authorities.—The following list contains only the names of the more important and more general works on the structure and classification of corals and on coral reefs. For a fuller bibliography the works marked with an asterisk should be consulted: * A. Andres,Fauna und Flora des Golfes von Neapel, ix. (1884); H.M. Bernard, “Catalogue of Madreporarian Corals†in Brit. Museum, ii. (1896), iii. (1897); * G.C. Bourne, “Anthozoa,†in E. Ray Lankester’sTreatise on Zoology, vol. ii. (London, 1900); G. Brook, “ChallengerReports,â€Zoology, xxxii. (1899) (Antipatharia); “Cat. Madrep. Corals,†Brit. Museum, i. (1893); D.C. Danielssen, “Report Norwegian North Atlantic Exploring Expedition,â€Zoology, xix. (1890); J.E. Duerden, “Some Results on the Morphology and Development of Recent and Fossil Corals,â€Rep. Brit. Association, 1903, pp. 684-685; “The Morphology of the Madreporaria,â€Biol. Bullet, vii. pp. 79-104; P.M. Duncan,Journ. Linnean Soc.xviii. (1885); P.H. Gosse,Actinologia britannica(London, 1860); O. and R. Hertwig,Die Actinien(Jena, 1879); R. Hertwig, “ChallengerReports,â€Zoology, vi. (1882) and xxvi. (1888); * C.B. Klunzinger,Die Korallthiere des Rothen Meeres(Berlin, 1877); * G. von Koch,Fauna und Flora des Golfes van Neapel, xv. (1887);Mitth. Zool. Stat. Neapel, ii. (1882) and xii. (1897);Palaeontographica, xxix. (1883); (also many papers in theMorphol. Jahrbuchfrom 1878 to 1898); F. Koby, “Polypiers jurassiques de la Suisse,â€Mem. Soc. Palaeont. Suisse, vii.-xvi. (1880-1889); A. von Kölliker, “Die Pennatuliden,â€Abh. d. Senck. Naturf. Gesell. vii.; * “ChallengerReports,â€Zoology, i.Pennatulidae(1880); Koren and Danielssen,Norske Nordhaus Exped., Alcyonida(1887); H. de Lacaze-Duthiers,Hist. nat. du corail(Paris, 1864); H. Milne-Edwards and J. Haime,Hist. nat. des coralliaires(Paris, 1857); H.N. Moseley, “ChallengerReports,â€Zoology, ii. (1881); H.A. Nicholson,Palaeozoic Tabulate Corals(Edinburgh, 1879); M.M. Ogilvie,Phil. Transactions, clxxxvii. (1896); E. Pratz,Palaeontographica, xxix. (1882); J.J. Quelch, “ChallengerReports,â€Zoology, xvi. (1886); * P.S. Wright and Th. Studer, “ChallengerReports,â€Zoology, xxxi. (1889).
Group A.
Family I.Zaphrentidae.—Solitary Palaeozoic corals with an epithecal wall. Septa numerous, arranged pinnately with regard to four principal septa. Tabulae present. One or more pits or fossulae present in the calicle. Typical genera—Zaphrentis, Raf.Amplexus, M. Edw. and H.Streptelasma, Hall.Omphyma, Raf.
Family 2.Turbinolidae.—Solitary, rarely colonial corals, with radially arranged septa and without tabulae. Typical genera—Flabellum, Lesson.Turbinolia, M. Edw. and H.Caryophyllia, Lamarck.Sphenotrochus, Moseley, &c.
Family 3.Amphiastraeidae.—Mainly colonial, rarely solitary corals, with radial septa, but bilateral arrangement indicated by persistence of a main septum. Typical genera—Amphiastraea, Étallon.Thecidiosmilia.
Family 4.Stylinidae.—Colonial corals allied to the Amphiastraeidae, but with radially symmetrical septa arranged in cycles. Typical genera—Stylina, Lamarck (Jurassic).Convexastraea, D’Orb. (Jurassic).Isastraea, M. Edw. and H.(Jurassic). Ogilvie refers the modern genusGalaxeato this family.
Group B.
Family 5.Oculinidae.—Branching or massive aporose corals, the calices projecting above the level of a compact coenenchyme formed from the coenosarc which covers the exterior of the corallum. Typical genera—Lophohelia, M. Edw. and H.Oculina, M. Edw. and H.
Family 6.Pocilloporidae.—Colonial branching aporose corals, with small calices sunk in the coenenchyme. Tabulae present, and two larger septa, an axial and abaxial, are always present, with traces of ten smaller septa. Typical genera—Pocillopora, Lamarck.Seriatopora, Lamarck.
Family 7.Madreporidae.—Colonial branching or palmate perforate corals, with abundant trabecular coenenchyme. Theca porous; septa compact and reduced in number. Typical genera—Madrepora, Linn.Turbinaria, Oken.Montipora, Quoy and G.
Family 8.Poritidae.—Incrusting or massive colonial perforate corals; calices usually in contact by their edges, sometimes disjunct and immersed in coenenchyme. Theca and septa perforate. Typical genera—Porites, M. Edw. and H.Goniopora, Quoy and G.Rhodaraea, M. Edw. and H.
Group C.
Family 9.Cyathophyllidae.—Solitary and colonial aporose corals. Tabulae and vesicular endotheca present. Septa numerous, generally radial, seldom pinnate. Typical genera—Cyathophyllum, Goldfuss (Devonian and Carboniferous).Moseleya, Quelch (recent).
Family 10.Astraeidae.—Aporpse, mainly colonial corals, massive, branching, or maeandroid. Septa radial; dissepiments present; an epitheca surrounds the base of massive or maeandroid forms, but only surrounds individual corallites in simple or branching forms. Typical genera—Goniastraea, M. Edw. and H.Heliastraea, M. Edw. and H.Maeandrina, Lam.Coeloria, M. Edw. and H.Favia, Oken.
Family 11.Fungidae.—Solitary and colonial corals, with numerous radial septa united by synapticulae. Typical genera—Lophoseris, M. Edw. and H.Thamnastraea, Le Sauvage.Leptophyllia, Reuss (Jurassic and Cretaceous).Fungia, Dana.Siderastraea, Blainv.
Group D.
Family 12.Eupsammidae.—Solitary or colonial perforate corals, branching, massive, or encrusting. Septa radial; the primary septa usually compact, the remainder perforate. Theca perforate. Synapticula present in some genera. Typical genera—Stephanophyllia, Michelin.Eupsammia, M. Edw. and H.Astroides, Blainv.Rhodopsammia, M. Edw. and H.Dendrophyllia, M. Edw. and H.
Group E.
Family 13.Cystiphyllidae.—Solitary corals with rudimentary septa, and the calicle filled with vesicular endotheca. Genera—Cystiphyllum,Lonsdale (Silurian and Devonian).Goniophyllum, M. Edw. and H. (In this Silurian genus the calyx is provided with a movable operculum, consisting of four paired triangular pieces, the bases of each being attached to the sides of the calyx, and their apices meeting in the middle when the operculum is closed).Calcecla, Lam. (In this Devonian genus there is a single semicircular operculum furnished with a stout median septum and numerous feebly developed secondary septa. The calyx is triangular in section, pointed below, and the operculum is attached to it by hinge-like teeth.)
Authorities.—The following list contains only the names of the more important and more general works on the structure and classification of corals and on coral reefs. For a fuller bibliography the works marked with an asterisk should be consulted: * A. Andres,Fauna und Flora des Golfes von Neapel, ix. (1884); H.M. Bernard, “Catalogue of Madreporarian Corals†in Brit. Museum, ii. (1896), iii. (1897); * G.C. Bourne, “Anthozoa,†in E. Ray Lankester’sTreatise on Zoology, vol. ii. (London, 1900); G. Brook, “ChallengerReports,â€Zoology, xxxii. (1899) (Antipatharia); “Cat. Madrep. Corals,†Brit. Museum, i. (1893); D.C. Danielssen, “Report Norwegian North Atlantic Exploring Expedition,â€Zoology, xix. (1890); J.E. Duerden, “Some Results on the Morphology and Development of Recent and Fossil Corals,â€Rep. Brit. Association, 1903, pp. 684-685; “The Morphology of the Madreporaria,â€Biol. Bullet, vii. pp. 79-104; P.M. Duncan,Journ. Linnean Soc.xviii. (1885); P.H. Gosse,Actinologia britannica(London, 1860); O. and R. Hertwig,Die Actinien(Jena, 1879); R. Hertwig, “ChallengerReports,â€Zoology, vi. (1882) and xxvi. (1888); * C.B. Klunzinger,Die Korallthiere des Rothen Meeres(Berlin, 1877); * G. von Koch,Fauna und Flora des Golfes van Neapel, xv. (1887);Mitth. Zool. Stat. Neapel, ii. (1882) and xii. (1897);Palaeontographica, xxix. (1883); (also many papers in theMorphol. Jahrbuchfrom 1878 to 1898); F. Koby, “Polypiers jurassiques de la Suisse,â€Mem. Soc. Palaeont. Suisse, vii.-xvi. (1880-1889); A. von Kölliker, “Die Pennatuliden,â€Abh. d. Senck. Naturf. Gesell. vii.; * “ChallengerReports,â€Zoology, i.Pennatulidae(1880); Koren and Danielssen,Norske Nordhaus Exped., Alcyonida(1887); H. de Lacaze-Duthiers,Hist. nat. du corail(Paris, 1864); H. Milne-Edwards and J. Haime,Hist. nat. des coralliaires(Paris, 1857); H.N. Moseley, “ChallengerReports,â€Zoology, ii. (1881); H.A. Nicholson,Palaeozoic Tabulate Corals(Edinburgh, 1879); M.M. Ogilvie,Phil. Transactions, clxxxvii. (1896); E. Pratz,Palaeontographica, xxix. (1882); J.J. Quelch, “ChallengerReports,â€Zoology, xvi. (1886); * P.S. Wright and Th. Studer, “ChallengerReports,â€Zoology, xxxi. (1889).
(G. C. B.)
ANTHRACENE(from the GreekἄνθÏαξ, coal), C14H10, a hydrocarbon obtained from the fraction of the coal-tar distillate boiling between 270° and 400° C. This high boiling fraction is allowed to stand for some days, when it partially solidifies. It is then separated in a centrifugal machine, the low melting-point impurities are removed by means of hot water, and the residue is finally hot-pressed. The crude anthracene cake is purified by treatment with the higher pyridine bases, the operation being carried out in large steam-jacketed boilers. The whole mass dissolves on heating, and the anthracene crystallizes out on cooling. The crystallized anthracene is then removed by a centrifugal separator and the process of solution in the pyridine bases is repeated. Finally the anthracene is purified by sublimation.
Many synthetical processes for the preparation of anthracene and its derivatives are known. It is formed by the condensation of acetylene tetrabromide with benzene in the presence of aluminium chloride:—
and similarly from methylene dibromide and benzene, and also when benzyl chloride is heated with aluminium chloride to 200° C. By condensing ortho-brombenzyl bromide with sodium, C.L. Jackson and J.F. White (Ber., 1879, 12, p. 1965) obtained dihydro-anthracene
Anthracene has also been obtained by heating ortho-tolylphenyl ketone with zinc dust
Anthracene crystallizes in colourless monoclinic tables which show a fine blue fluorescence. It melts at 213° C. and boils at 351° C. It is insoluble in water, sparingly soluble in alcohol and ether, but readily soluble in hot benzene. It unites with picric acid to form a picrate, C14H10·C6H2(NO2)3·OH, which crystallizes in needles, melting at 138° C. On exposure to sunlight a solution of anthracene in benzene or xylene deposits para-anthracene (C14H10)2, which melts at 244° C. and passes back into the ordinary form. Chlorine and bromine form both addition and substitution products with anthracene; the addition product, anthracene dichloride, C14H10Cl2, being formed when chlorine is passed into a cold solution of anthracene in carbon bisulphide. On treatment with potash, it forms the substitution product, monochlor-anthracene, C14H9Cl. Nitro-anthracenes are not as yet known. The mono-oxyanthracenes (anthrols), C14H9OH or(α) and (β) resemble the phenols, whilst(γ) (anthranol) is a reduction product of anthraquinone. β-anthrol and anthranol give the corresponding amino compounds (anthramines) when heated with ammonia.
Numerous sulphonic acids of anthracene are known, a monosulphonic acid being obtained with dilute sulphuric acid, whilst concentrated sulphuric acid produces mixtures of the anthracene disulphonic acids. By the action of sodium amalgam on an alcoholic solution of anthracene, an anthracene dihydride, C14H12, is obtained, whilst by the use of stronger reducing agents, such as hydriodic acid and amorphous phosphorus, hydrides of composition C14H16and C14H24are produced.
Methyl and phenyl anthracenes are known; phenyl anthranol (phthalidin) being somewhat closely related to the phenolphthaleins (q.v.). Oxidizing agents convert anthracene into anthraquinone (q.v.); the production of this substance by oxidizing anthracene in glacial acetic acid solution, with chromic acid, is the usual method employed for the estimation of anthracene.
ANTHRACITE(Gr.ἄνθÏαξ, coal), a term applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition; or, in other words, which burn with a smokeless and nearly non-luminous flame. Other terms having the same meaning are, “stone coal†(not to be confounded with the GermanSteinkohle) or “blind coal†in Scotland, and “Kilkenny coal†in Ireland. The imperfect anthracite of north Devon, which however is only used as a pigment, is known asculm, the same term being used in geological classification to distinguish the strata in which it is found, and similar strata in the Rhenish hill countries which are known as the Culm Measures. In America, culm is used as an equivalent for waste or slack in anthracite mining.
Physically, anthracite differs from ordinary bituminous coal by its greater hardness, higher density, 1.3-1.4, and lustre, the latter being often semi-metallic with a somewhat brownish reflection. It is also free from included soft or fibrous notches and does not soil the fingers when rubbed. Structurally it shows some alteration by the development of secondary divisional planes and fissures so that the original stratification lines are not always easily seen. The thermal conductivity is also higher, a lump of anthracite feeling perceptibly colder when held in the warm hand than a similar lump of bituminous coal at the same temperature. The chemical composition of some typical anthracites is given in the articleCoal.
Anthracite may be considered to be a transition stage between ordinary bituminous coal and graphite, produced by the more or less complete elimination of the volatile constituents of the former; and it is found most abundantly in areas that have been subjected to considerable earth-movements, such as the flanks of great mountain ranges. The largest and most important anthracite region, that of the north-eastern portion of the Pennsylvania coal-field, is a good example of this; the highly contorted strata of the Appalachian region produce anthracite exclusively, while in the western portion of the same basin on the Ohio and its tributaries, where the strata are undisturbed, free-burning and coking coals, rich in volatile matter, prevail. In the same way the anthracite region of South Wales is confined to the contorted portion west of Swansea and Llanelly, thecentral and eastern portions producing steam, coking and house coals.
Anthracites of newer, tertiary or cretaceous age, are found in the Crow’s Nest part of the Rocky Mountains in Canada, and at various points in the Andes in Peru.
The principal use of anthracite is as a smokeless fuel. In the eastern United States, it is largely employed as domestic fuel, usually in close stoves or furnaces, as well as for steam purposes, since, unlike that from South Wales, it does not decrepitate when heated, or at least not to the same extent. For proper use, however, it is necessary that the fuel should be supplied in pieces as nearly uniform in size as possible, a condition that has led to the development of the breaker which is so characteristic a feature in American anthracite mining (seeCoal). The large coal as raised from the mine is passed through breakers with toothed rolls to reduce the lumps to smaller pieces, which are separated into different sizes by a system of graduated sieves, placed in descending order. Each size can be perfectly well burnt alone on an appropriate grate, if kept free from larger or smaller admixtures. The common American classification is as follows:—
Lump, steamboat, egg and stove coals, the latter in two or three sizes, all three being above 1½ in. size on round-hole screens.
From the pea size downwards the principal use is for steam purposes. In South Wales a less elaborate classification is adopted; but great care is exercised in hand-picking and cleaning the coal from included particles of pyrites in the higher qualities known as best malting coals, which are used for kiln-drying malt and hops.
Formerly, anthracite was largely used, both in America and South Wales, as blast-furnace fuel for iron smelting, but for this purpose it has been largely superseded by coke in the former country and entirely in the latter. An important application has, however, been developed in the extended use of internal combustion motors driven by the so-called “mixed,†“poor,†“semi-water†or “Dowson gas†produced by the gasification of anthracite with air and a small proportion of steam. This is probably the most economical method of obtaining power known; with an engine as small as 15 horse-power the expenditure of fuel is at the rate of only 1 ℔ per horse-power hour, and with larger engines it is proportionately less. Large quantities of anthracite for power purposes are now exported from South Wales to France, Switzerland and parts of Germany.
(H. B.)
ANTHRACOTHERIUM(“coal-animal,†so called from the fact of the remains first described having been obtained from the Tertiary lignite-beds of Europe), a genus of extinct artiodactyle ungulate mammals, characterized by having 44 teeth, with five semi-crescentic cusps on the crowns of the upper molars. In many respects, especially the form of the lower jaw,Anthracotherium, which is of Oligocene and Miocene age in Europe, and typifies the familyAnthracotheriidae, is allied to the hippopotamus, of which it is probably an ancestral form. The EuropeanA. magnumwas as large as the last-mentioned animal, but there were several smaller species and the genus also occurs in Egypt, India and North America. (SeeArtiodactyla.)
ANTHRAQUINONE,C14H8O2, an important derivative of anthracene, first prepared in 1834 by A. Laurent. It is prepared commercially from anthracene by stirring a sludge of anthracene and water in horizontal cylinders with a mixture of sodium bichromate and caustic soda. This suspension is then run through a conical mill in order to remove all grit, the cones of the mill fitting so tightly that water cannot pass through unless the mill is running; the speed of the mill when working is about 3000 revolutions per minute. After this treatment, the mixture is run into lead-lined vats and treated with sulphuric acid, steam is blown through the mixture in order to bring it to the boil, and the anthracene is rapidly oxidized to anthraquinone. When the oxidation is complete, the anthraquinone is separated in a filter press, washed and heated to 120° C. with commercial oil of vitriol, using about 2½ parts of vitriol to 1 of anthraquinone. It is then removed to lead-lined tanks and again washed with water and dried; the product obtained contains about 95% of anthraquinone. It may be purified by sublimation. Various synthetic processes have been used for the preparation of anthraquinone. A. Behr and W.A. v. Dorp (Ber., 1874, 7, p. 578) obtained orthobenzoyl benzoic acid by heating phthalic anhydride with benzene in the presence of aluminium chloride. This compound on heating with phosphoric anhydride loses water and yields anthraquinone,
It may be prepared in a similar manner by heating phthalyl chloride with benzene in the presence of aluminium chloride. Dioxy- and tetraoxy-anthraquinones are obtained when meta-oxy- and dimeta-dioxy-benzoic acids are heated with concentrated sulphuric acid.
Anthraquinone crystallizes in yellow needles or prisms, which melt at 277° C. It is soluble in hot benzene, sublimes easily, and is very stable towards oxidizing agents. On the other hand, it is readily attacked by reducing agents. With zinc dust in presence of caustic soda it yields the secondary alcohol oxan-thranol, C6H4: CO·CHOH : C6H4, with tin and hydrochloric acid, the phenolic compound anthranol, C6H4: CO·C(OH) : C6H4; and with hydriodic acid at 150° C. or on distillation with zinc dust, the hydrocarbon anthracene, C14H10. When fused with caustic potash, it gives benzoic acid. It behaves more as a ketone than as a quinone, since with hydroxylamine it yields an oxime, and on reduction with zinc dust and caustic soda it yields a secondary alcohol, whilst it cannot be reduced by means of sulphurous acid. Various sulphonic acids of anthraquinone are known, as well as oxy-derivatives, for the preparation and properties of which seeAlizarin.
ANTHRAX(the Greek for “coal,†or “carbuncle,†so called by the ancients because they regarded it as burning like coal; cf. the French equivalentcharbon; also known asfièvre charbonneuse, Milzbrand, splenic fever, and malignant pustule), an acute, specific, infectious, virulent disease, caused by theBacillus anthracis, in animals, chiefly cattle, sheep and horses, and frequently occurring in workers in the wool or hair, as well as in those handling the hides or carcases, of beasts which have been affected.
Animals.—As affecting wild as well as domesticated animals and man, anthrax has been widely diffused in one or more of its forms, over the surface of the globe. It at times decimates the reindeer herds in Lapland and the Polar regions, and is only too well known in the tropics and in temperate latitudes. It has been observed and described in Russia, Siberia, Central Asia, China, Cochin-China, Egypt, West Indies, Peru, Paraguay, Brazil, Mexico, and other parts of North and South America, in Australia, and on different parts of the African continent, while for other European countries the writings which have been published with regard to its nature, its peculiar characteristics, and the injury it inflicts are innumerable. Countries in which are extensive marshes, or the subsoil of which is tenacious or impermeable, are usually those most frequently and seriously visited. Thus there have been regions notorious for its prevalence, such as the marshes of Sologne, Dombes and Bresse in France; certain parts of Germany, Hungary and Poland; in Spain the half-submerged valleys and the maritime coasts of Catalonia, as well as the Romagna and other marshy districts of Italy; while it is epizootic, and even panzootic, in the swampy regions of Esthonia, Livonia, Courland, and especially of Siberia, where it is known as theSibirskaja jaswa(Siberian boil-plague). The records of anthrax go back to a very ancient date. It is supposed to be the murrain of Exodus. Classical writers allude to anthrax as if it were the only cattle disease worthy of mention (see Virgil,Georg.iii.). It figures largely in the history of the early and middle ages as a devastating pestilence attacking animals, and through them mankind; the oldest Anglo-Saxon manuscripts contain many fantastic recipes, leechdoms,charms and incantations for the prevention or cure of the “blacan blezene†(black blain) and the relief of the “elfshot†creatures. In the 18th and 19th centuries it sometimes spread like an epizootic over the whole of Europe, from Siberia to France. It was in this malady that disease-producing germs (bacteria) were first discovered, in 1840, by Pollender of Wipperfürth, and, independently, by veterinary surgeon Brauell of Dorpat, and their real character afterwards verified by C.J. Davaine (1812-1882) of Alfort in 1863; and it was in their experiments with this disease that Toussaint, Pasteur and J.B. Chauveau first showed how to make the morbific poison its own antidote. (SeeVivisection.)
The symptoms vary with the species of animal, the mode of infection, and the seat of the primary lesion, internal or external. In all its forms anthrax is an inoculable disease, transmission being surely and promptly effected by this means, and it may be conveyed to nearly all animals by inoculation of a wound of the skin or through the digestive organs. Cattle, sheep and horses nearly always owe their infection to spores or bacilli ingested with their food or water, and pigs usually contract the disease by eating the flesh of animals dead of anthrax.
Internal anthrax, of cattle and sheep, exhibits no premonitory symptoms that can be relied on. Generally the first indication of an outbreak is the sudden death of one or more of the herd or flock. Animals which do not die at once may be noticed to stagger and tremble; the breathing becomes hurried and the pulse very rapid, while the heart beats violently; the internal temperature of the body is high, 104° to 106° F.; blood oozes from the nose, mouth and anus, the visible mucous membranes are dusky or almost black. The animal becomes weak and listless, the temperature falls and death supervenes in a few hours, being immediately preceded by delirium, convulsions or coma. While death is usually rapid or sudden when the malady is general, constituting what is designated splenic apoplexy, internal anthrax in cattle is not invariably fatal. In some cases the animal rallies from a first attack and gradually recovers.
In the external or localized form, marked by the formation of carbuncles before general infection takes place, death may not occur for several days. The carbuncles may appear in any part of the body, being preceded or accompanied by fever. They are developed in the subcutaneous connective tissue where this is loose and plentiful, in the interstices of the muscles, lymphatic glands, in the mucous membranes of the mouth and tongue (glossanthrax of cattle), pharynx and larynx (anthrax anginaof horses and pigs), and the rectum. They begin as small circumscribed swellings which are warm, slightly painful and oedematous. In from two to eight hours they attain a considerable size, are cold, painless and gangrenous, and when they are incised a quantity of a blood-stained gelatinous exudate escapes. When the swellings have attained certain proportions symptoms of general infection appear, and, running their course with great rapidity, cause death in a few hours. Anthrax of the horse usually begins as an affection of the throat or bowel. In the former there is rapid obstructive oedema of the mucous membrane of the pharynx and larynx with swelling of the throat and neck, fever, salivation, difficulty in swallowing, noisy breathing, frothy discharge from the nose and threatening suffocation. General invasion soon ensues, and the horse may die in from four to sixteen hours. The intestinal form is marked by high temperature, great prostration, small thready pulse, tumultuous action of the heart, laboured breathing and symptoms of abdominal pain with straining and diarrhoea. When moved the horse staggers and trembles. Profuse sweating, a falling temperature and cyanotic mucous membranes indicate the approach of a fatal termination.
In splenic fever or splenic apoplexy, the most marked alterations observed after death are—the effects of rapid decomposition, evidenced by the foul odour, disengagement of gas beneath the skin and in the tissues and cavities of the body, yellow or yellowish-red gelatinous exudation into and between the muscles, effusion of citron or rust-coloured fluid in various cavities, extravasations of blood and local congestions throughout the body, the blood in the vessels generally being very dark and tar-like. The most notable feature, however, in the majority of cases is the enormous enlargement of the spleen, which is engorged with blood to such an extent that it often ruptures, while its tissue is changed into a violet or black fluid mass.
The bacillus of anthrax, under certain conditions, retains its vitality for a long time, and rapidly grows when it finds a suitable field in which to develop, its mode of multiplication being by scission and the formation of spores, and depending, to a great extent at least, on the presence of oxygen. The morbid action of the bacillus is indeed said to be due to its affinity for oxygen; by depriving the red corpuscles of the blood of that most essential gas, it renders the vital fluid unfit to sustain life. Albert Hoffa and others assert that the fatal lesions are produced by the poisonous action of the toxins formed by the bacilli and not by the blocking up of the minute blood-vessels, or the abstraction of oxygen from the blood by the bacilli.
It was by the cultivation of this micro-organism, or attenuation of the virus, that Pasteur was enabled to produce a prophylactic remedy for anthrax. His discovery was first made with regard to the cholera of fowls, a most destructive disorder which annually carries off great numbers of poultry. Pasteur produced his inoculation material by the cultivation of the bacilli at a temperature of 42° C. in oxygen. Two vaccines are required. The first or weak vaccine is obtained by incubating a bouillon culture for twenty-four days at 42° C., and the second or less attenuated vaccine by incubating a bouillon culture, at the same temperature, for twelve days. Pasteur’s method of protective inoculation comprises two inoculations with an interval of twelve days between them. Immunity, established in about fifteen days after the injection of the second vaccine, lasts from nine months to a year.
Toussaint had, previous to Pasteur, attenuated the virus of anthrax by the action of heat; and Chauveau subsequently corroborated by numerous experiments the value of Toussaint’s method, demonstrating that, according to the degree of heat to which the virus is subjected, so is its inocuousness when transferred to a healthy creature. In outbreaks of anthrax on farms where many animals are exposed to infection immediate temporary protection can be conferred by the injection of anthrax serum.
Human Beings.—For many years cases of sudden death had been observed to occur from time to time among healthy men engaged in woollen manufactories, particularly in the work of sorting or combing wool. In some instances death appeared to be due to the direct inoculation of some poisonous material into the body, for a form of malignant pustule was observed upon the skin; but, on the other hand, in not a few cases without any external manifestation, symptoms of blood-poisoning, often proving rapidly fatal, suggested the probability of other channels for the introduction of the disease. In 1880 the occurrence of several such cases among woolsorters at Bradford, reported by Dr J.H. Bell of that town, led to an official inquiry in England by the Local Government Board, and an elaborate investigation into the pathology of what was then called “woolsorters’ disease†was at the same time conducted at the Brown Institution, London, by Professor W.S. Greenfield. Among the results of this inquiry it was ascertained: (1) that the disease appeared to be identical with that occurring among sheep and cattle; (2) that in the blood and tissues of the body was found in abundance, as in the disease in animals, theBacillus anthracis, and (3) that the skins, hair, wool, &c., of animals dying of anthrax retain this infecting organism, which, under certain conditions, finds ready access to the bodies of the workers.
Two well-marked forms of this disease in man are recognized, “external anthrax†and “internal anthrax.†In external anthrax the infecting agent is accidentally inoculated into some portion of skin, the seat of a slight abrasion, often the hand, arm or face. A minute swelling soon appears at the part, and develops into a vesicle containing serum or bloody matter, and varying in size, but seldom larger than a shilling. This vesicle speedily bursts and leaves an ulcerated or sloughingsurface, round about which are numerous smaller vesicles which undergo similar changes, and the whole affected part becomes hard and tender, while the surrounding surface participates in the inflammatory action, and the neighbouring lymphatic glands are also inflamed. This condition, termed “malignant pustule,†is frequently accompanied with severe constitutional disturbance, in the form of fever, delirium, perspirations, together with great prostration and a tendency to death from septicaemia, although on the other hand recovery is not uncommon. It was repeatedly found that the matter taken from the vesicle during the progress of the disease, as well as the blood in the body after death, contained theBacillus anthracis, and when inoculated into small animals produced rapid death, with all the symptoms and post-mortem appearances characteristic of che disease as known to affect them.
In internal anthrax there is no visible local manifestation of the disease, and the spores or bacilli appear to gain access to the system from the air charged with them, as in rooms where the contaminated wool or hair is unpacked, or again during the process of sorting. The symptoms usually observed are those of rapid physical prostration, with a small pulse, somewhat lowered temperature (rarely fever), and quickened breathing. Examination of the chest reveals inflammation of the lungs and pleura. In some cases death takes place by collapse in less than one day, while in others the fatal issue is postponed for three or four days, and is preceded by symptoms of blood-poisoning, including rigors, perspirations, extreme exhaustion, &c. In some cases of internal anthrax the symptoms are more intestinal than pulmonary, and consist in severe exhausting diarrhoea, with vomiting and rapid sinking. Recovery from the internal variety, although not unknown, is more rare than from the external, and its most striking phenomena are its sudden onset in the midst of apparent health, the rapid development of physical prostration, and its tendency to a fatal termination despite treatment. The post-mortem appearances in internal anthrax are such as are usually observed in septicaemia, but in addition evidence of extensive inflammation of the lungs, pleura and bronchial glands has in most cases been met with. The blood and other fluids and the diseased tissues are found loaded with theBacillus anthracis.
Treatment in this disease appears to be of but little avail, except as regards the external form, where the malignant pustule may be excised or dealt with early by strong caustics to destroy the affected textures. For the relief of the general constitutional symptoms, quinine, stimulants and strong nourishment appear to be the only available means. An anti-anthrax serum has also been tried. As preventive measures in woollen manufactories, the disinfection of suspicious material, or the wetting of it before handling, is recommended as lessening the risk to the workers.