ON POLYPS. 



crusted over by thick masses of madrepore, has been suddenly 

 heaved up by one of those stupendous convulsions of nature, pro- 

 bably produced by the sea finding its way into some sub-marine 

 volcano ; and rocks and corals, raised from their beds by the tre- 

 mendous explosion so produced, give birth to islands and elevated 

 tracts of country, such as are met with in the South Seas. 



CORALLID.E. The Corallidse are compound polyps of appa- 

 rently more perfect organization than those forming the last family. 

 The polypary or central axis, which supports the external or living 

 crust, is solid, without cells, and variously branched ; the larger 

 species resembling shrubs of great beauty, frequently coloured with 

 lovely hues, and studded over their whole surface with living 

 flowers, for such the polyps which nourish them were long consi- 

 dered even by scientific observers. The central stem of these 

 zoophytes differs much in its composition in different families ; 

 sometimes being of stony hardness, in other cases it is soft and 

 flexible, resembling horn ; and not unfrequently it is formed of both 

 kinds of material : it is however always produced by the living 

 cortex, which secretes it in concentric layers, the external being 

 the last deposited. 



The example which we shall select for special description is the 

 Coral of commerce, Corallium rubrum, (Jig. 6.) from which we 

 derive the material so much prized in Fi S- 6 - 



the manufacture of ornaments. 



(44.) The red coral is principally 

 obtained in the Mediterranean. When 

 growing at the bottom of the sea, it 

 consists of small branched stems, en- 

 crusted with a soft living investment, 

 by which the central axis is secreted, 

 and studded at intervals with polyps 

 possessing eight fringed arms, and 

 capable of being contracted into 

 cells contained in the fleshy covering, 

 but not penetrating the stem itself. 



The skeleton or polypary of the coral is of extreme hardness, and 

 susceptible of a high polish ; a circumstance to which the estima- 

 tion in which it is held is principally owing. But in other 

 genera of this family, the central axis, instead of being con- 

 structed of calcareous matter, is formed of concrete albumen, and 

 resembles horn both in appearance and flexibility ; such are the 



