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Show ANNOTATIONS AND ADDITIONS. 271 among the most mass~ve, although they are somewh~t branched. The corals which lie deepest below the surface of the water in this locality, and which, being magnified by the refraction of the rays of light, appear to the eye like the domes or cupolas of a cathedral or other large building, belong, so far as we are enabled to judge, to Meandrina and Astrrea." (Ehrenberg, manuscript notices.) It is necessary to distinguish between separate and in part free and detached polypifers, and those which form wall-like structures and rocks. If we are struck with the great accumulation of building polypifers in some regions of the globe, it is not less surprising to remark the entire absence of their structures in other and often nearly adJOlmng regions. These differences must be determined by causes which have not yet been thoroughly investigated; such as currents, local temperature of the water, and abundance or deficiency of appropriate food. That certain thin-branched corals, with less deposit of lime on the side opposite to the opening of the mouth, prefer the repose of the interior of the lagoon, is not to be denied; but this preference for the unagitated water must not, as has too often been done (Annales des Sciences Naturelles, 1825, t. vi. p. 277), be regarded as a property belonging to the entire class. According to Ehrenberg's experience in the Red Sea, that of Chamisso in the Atolls of the Marshall Islands east of the Caroline group, the observations of Captain Bird Allen in the West Indies, and those of Captain Moresby in the Maldives, living Madrepores, Millepores, and species of Astrrea and of Meandrina, can support the most violent action of the waves-" a tremendous surf" -(Darwin, Coral Reefs, pp. 63-65,) and even appear to prefer the most stormy exposure. The living organic forces or powers regulating the cellular structure, which with age acquires the hardness of rock, resist with wonderful success the mechanical forces acting in the shock of the agitated water. In the Pacific, the Galapagos Islands, and the whole Western Coast of America, are entirely without coral reefs, although so near to the many Atolls of the Low Islands, and the Archipelago of the Marquesas. This absence of corals might perhaps be ascribed to the presence of colder water, since we know that the coasts of Chili |