8o ADDENDUM TO THE ANTHOZOA 



attached to the spicule sheath. The inorganic constituents of the 

 spicule show a complex, fibro- crystalline structure, the component 

 crystalline fibres always being oriented in a definite manner with 

 regard to the organic threads. In Hdioiwra the skeleton is not spicular 

 but lamellar, resembling in structure that of the Scleractinian corals. It 

 is not formed of a number of fused spicules, but is secreted by a special 

 layer of cells derived from the ectoderm and called calicoblasts. The 

 calicoblasts are separated from the corallum by a fine membrane. At 

 intervals in the layer of calicoblasts and lying among them are peculiar 

 structures which will be called desmocytes. These are wedge-shaped 

 bodies, with their narrower ends attached to the mesogloea, their broader 

 ends attached to the corallum. They exhibit a faint but distinct 

 longitudinal striation, which is not due to the presence of needles of 

 carbonate of lime. The desmocytes are most abundant in the older parts 

 of the colony, and are absent or only represented by early stages ot 

 development in those parts where coral growth is most active. There 

 can be no doubt that the desmocytes of Heliopora are homologous with 

 the similar structures in Scleractinian corals, discovered by von Heider 

 and called by him calicoblasts. After examination of a large number of 

 Scleractiniae the present writer found that (1) the corallum is everywhere 

 clothed by a layer of cells either rounded, columnar, or fused together, 

 which form the true calicoblastic layer ; (2) that the calicoblastic layer is 

 sei)arated from the corallum by a fine membrane ; (3) that desmocytes (von 

 Heider's calicoblasts) occur at widely separated intervals in the calicoblastic 

 layer, except along the lines of insertion of the mesenteries, where they are 

 numerous and closely crowded together ; (4) that each desmocyte is the 

 product of a single cell; (5) that the striationa of the desmocytes are not 

 due to the presence of spicules of carbonate of lime as von Ileider 

 supposed, since they give none of the optical effects of crystals ; (6) that 

 desmocytes do not occur in the regions of most active coral growth. The 

 conclusion arrived at is that the desmocytes, both in Hdiopora and the 

 Scleractiniae, have no share in coral' formation, but serve, as Fowler 

 suggested, to attach the soft tissues to the corallum. A study of the 

 costal spines of Madrepora rosacea showed that the carbonate of lime 

 secreted by the calicoblasts is deposited in the form of minute crystals on 

 the far side of the limiting membrane which separates the calicoblasts 

 from the corallum. These minute crystals are oriented conformably to 

 the crystalline structure of the previously existing corallum, and eventually 

 become merged into its structure. Thus von Koch's view that the corallum 

 is secreted by the calicoblastic layer derived from the ectoderm is shown 

 to be correct (see Quart. Jour. Micro. Sci. vol. xli. 1899, p. 449). 



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