ANNOTATIONS AND ADDITIONS. 271 



among the most massive, although they are somewhat 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 were enabled to judge, to 

 Meandrina and Astrsea." (Ehrenberg, manuscript notices.) It is 

 necessary to distinguish between separate and in part free and de- 

 tached polypifers, and those which form wall-like structures and 

 rocks. 



If we are struck with the great accumulation of building polypi- 

 fers in some regions of the globe, it is not less surprising to remark 

 the entire absence of their structures in other and often nearly ad- 

 joining 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 ap- 

 propriate food. That certain thin-branched corals, with less deposit 

 of lime on the side opposite to the opening of the mouth, prefer the 

 r epose 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 re- 

 garded 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 ob- 

 servations of Captain Bird Allen in the West Indies, and those of 

 Captain Moresby in the Maldives, living Madrepores, Millepores, 

 and species of Astrsea 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 reefe, 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 



