The porifera and coelentera . al ectoderm. The anatomy of the soft parts of any Scleractinian resembles,in essential points, that of an Actinia. There are comi)lete andincomplete mesenteries arranged in cycles, the sequence of numbersbeing usually 12, 12, 24, 48, etc., as in Hexactiniae. Usually twocouples of directive mesenteries are present, but in a few forms(Mussa, Lophobelia, and Euphyllia) there are no directives. Fora detailed account of the anatomy of such corals as have beenstudied, the reader is referred to the works of von Koch (51, 57, 62 THE ANTHOZOA 58, 59, 63); von Heider (38);
The porifera and coelentera . al ectoderm. The anatomy of the soft parts of any Scleractinian resembles,in essential points, that of an Actinia. There are comi)lete andincomplete mesenteries arranged in cycles, the sequence of numbersbeing usually 12, 12, 24, 48, etc., as in Hexactiniae. Usually twocouples of directive mesenteries are present, but in a few forms(Mussa, Lophobelia, and Euphyllia) there are no directives. Fora detailed account of the anatomy of such corals as have beenstudied, the reader is referred to the works of von Koch (51, 57, 62 THE ANTHOZOA 58, 59, 63); von Heider (38); Fowler (23-26); Bourne (6 and 7);and Ogilvie (103). The relations of the zooid to the skeleton may be studied inFig. XXVIIL, which represents a diagrammatic longitudinal sectionthrough a Turbinolid coral. A quadrant is cut out on the leftside to further display the anatomy. In the skeleton of a typicalsolitary coral—the common Devonshire cup-coral, Caryophi/IliaSmithii, is a good example—the following parts are to be dis-. Ik;. XXVIII. Diagram illustrating the relation of the soft tissues to the corallum in a .solitary aporosacoral, ^it, stoniotiaeiun ; Sul, sulcus ; M, mesenteries; Th, theca ; 6, septa ; Col, columella ; Ep,epitheca; P, edge-zone. tinguishcd :—(1) The basal plate, between the zooid and thesurface of attachment. (2) The scpfa, radial calcareous laminaereaching from the periphery to near or quite to the centre of thecalycle. (3) The them or wall, which, in many corals, is not anindependent structure, but is formed by the conjoined peripheralends of the septa. (4) The cohimella, a structiue which occupiesthe axis of the corallite, and may be solid or trabeculate. If itarises from the base, it is termed essential; if formed by theunion of trabeculae from the septa, it is termed unessential. (5)The costae, longitudinal ribs or rows of spines on the outer surfaceof the theca. True costae always correspond to the septa, andare in fact the peripheral ends of the
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