POLYPS. 65 
Polyps have their being. It is a covering which, like a dermal 
skeleton!, may become horny or calcareous. 
The hard, stone-like Polypstocks which form coral-banks, are 
particularly deserving of notice. But the part they play im 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”. 
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 TREMBLEY’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 MitnE Epwarbs, Observations sur la nature et le mode de croissance des Poly- 
piers, Ann, des Sc. Natur. Seconde Série, Tom. x. 1838. Zoologie, pp. 32I—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. 1. p. 63, new edition) ; and in another place denies to the poly- 
pary all life, and compares it with the shells of molluscs, ibid. 11. 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. 
2 Comp. J. B. Forster, Bemerkungen auf seine Reise wm die Welt, Wien. 1787. 
8vo. s. 120, 121; A. VON KoTzEBuE, Entdeckungs-reise in die Siidsee, 111. Weimar 1821, 
s. 187; Quoy et GaImaRD, Mémoire sur laccroisement des Polypes considéré géolo- 
giquement, Ann. des Sc. Nat. VI. 1825. pp. 273—290 ; EHRENBERG, Ueber die Natur und 
Bildung der Corallenbdnke des rothen Meeres, Physik. Abhandlungen der Akad. der Wis- 
sensch. zu Berlin. 1832. s. 381—438. 
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