POLYPS. 65 



Polyps have their being. It is a covering which, like a dermal 

 skeleton 1 , may become horny or calcareous. 



The hard, stone-like Polypstocks which form coral-banks, are 

 particularly deserving of notice. But the part they play in altering 

 the earth's surface has been much exaggerated by FORSTER, PERON, 

 and other voyagers. The numerous coral islands of the southern 

 Pacific having an annular form with banks steep on the outside 

 and shelving gently down to the trough or the included water, are 

 clearly of volcanic origin. They are covered with Corals, but do 

 not consist of Corals. Polyps cannot live at great depths, but the 

 Corals rest on shallows or on mountain-ridges in the sea, similar to 

 the rocks parallel to the coast of the Red Sea. Hence Corals may 

 contribute to the formation of islands, or may prevent the washing 

 away of the shores of islands already formed, just as plants that 

 grow on sandy coasts protect the hillocks from being blown away 2 . 



After these general remarks on Polyps and Polypstocks, we must 

 dwell for a little on the particulars of structure of the different 

 animals that belong to this class. It would be a defective and 

 erroneous idea, to suppose that TREMBLE Y'S fresh-water Polyps are 

 to be considered as the Type of the class. That we drew the atten- 

 tion of our readers, in the first instance, to the fresh-water Polyp, is 

 merely to be attributed to the historic form which, in introducing 

 this class, we thought useful for the right understanding of it. The 

 animals which live in Polyparies have in several respects a much 



1 See MILNE EDWARDS, Observations sur la nature el le mode de croissance des Poly- 

 piers, Ann. des Sc. Natur, Seconde Se'rie, Tom. x. 1838. Zoologie, pp. 321 334. 



LAMARCK appears to me in some degree to contradict himself, when in one place he 

 calls the polypary a common body possessing an independent life, and producing new 

 individuals upon its surface, which die and are again replaced by new ones, and con- 

 tinuing its life almost unobserved as long as it is surrounded by water alone (Hist. Nat. 

 des Anim. sans Vert. I. p. 63, new edition) ; and in another place denies to the poly- 

 pary all life, and compares it with the shells of molluscs, ibid. II. pp. 86 99. Before 

 this, LINN.&US, PALLAS and others had recognised in the polypary a proper life, but of 

 late years this opinion, on the authority of LAMARCK, has been almost generally 

 relinquished. 



3 Comp. J. B. FORSTER, Bemerkungen auf seine Reise urn die WeU, Wien. 1787. 

 8vo. s. 120, 121 ; A. VON KOTZEBUE, EnldecTcungs-reise in die Sudsee, in. Weimar 1821, 

 s. 187 ; QUOY et GAIMARD, Memoire sur I'accroisement des Polypes considere geolo- 

 giquement, Ann. des Sc. Nat. vi. 1825. pp. 273 290 ; EHRENBERG, Ueber die Natur und 

 Bildungdcr Corallenbdnke des rothen Meeres, Physik. Abhandlungen der Akad. der Wis- 

 sensch. zu Berlin. 1833. s. 381 438. 



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