ILLUSTRATIONS (7). CORAL ANIMALS. 255 



Ghauts of Malabar in the west, manifests itself in submarine, 

 symmetrical series of islands, on the one side in the Andaman 

 and Nicobar Islands, which are poor in corals, and on the 

 other in three long-extended archipelagos of Atolls the 

 Laccadives, the Maldives, and Chagos. The last, called by 

 mariners the Chagos Bank, forms a lagoon, belted by a 

 narrow, and already much broken coral-reef. The length of 

 this lagoon is 88, and its breadth 72 miles. Whilst the 

 enclosed lagoon is only from 17 to 40 fathoms deep, bottom, 

 was scarcely found at a depth of 210 fathoms at a small 

 distance from the outer margin of the coral wall, which 

 appears to be now sinking.* At the coral-lagoon, known as 

 Keeling-Atoll, south of Sumatra, Captain Fitz-Roy states, 

 that at only 2000 yards from the reef, no soundings were 

 found with 7200 feet of line. 



"The forms of coral, which in the Red Sea rise in thick wall- 

 like masses, are Maeandrinse, Astrseae, Favia, Madrepores 

 (Porites), Pocillopora (Hemprichii), Millepores, and Hetero- 

 pores. The latter are among the most massive, although they 

 are branched. The deepest coral trunks, which magnified by 

 the refraction of light, appear to the eye to resemble the dome 

 of a cathedral, belong, as far as could be determined, to Mrean- 

 drinre and Astra38e."f A distinction must be made between 

 single and in part free polyp-trunks, and those which form 

 wall-like rocks. 



If the accumulation of building polyp-trunks in some 

 regions is so striking, it is no less astonishing to observe the 

 perfect absence of these structures in other and often adjacent 

 regions. Their presence or absence must be determined by 

 certain, still uninvesti gated, relations of currents, by the par- 

 tial temperature of the water, and by the abundance or defi- 

 ciency of nutriment. That certain delicate-branched corals, 

 with less calcareous deposition on the side opposite to the 

 mouth, prefer the stillness of the interior lagoons, is not to 

 be denied; but this preference for still water must not, 

 as has too often happened,^; be regarded as a peculiarity of 

 the whole class of these animals. According to the expe- 

 riences of Ehrenberg and Chamisso in the Red Sea and in 



* Darwin, Structure of Coral Reefs, pp. 39, 111, and 183. 



t Ehrenberg's Manuscript Notes. 



$ Annales des Sciences naturdles, t. vi., 1825, p. 277. 



