08 



ANTHOZOA. 



any power. The circumference of the islet is perpetually augmented by 

 the same agency : sea-weeds and vegetable substances cast upon it, by 

 their decay cover its top with vegetable mould ; and if its proximity to 

 other land permit the united action of winds and currents to bring the 

 germs of vegetation from neighbouring coasts, they take root in the 

 fresh soil, and soon clothe with verdure a domain thus rescued from 

 the ocean. 



(147.) CORALLID^;. The Corallidae 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 re- 

 sembling 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 considered even by scientific ob- 

 servers. The central stem of these 

 zoophytes differs much in its com- 

 position in different families, some- 

 times being of stony hardness ; in 

 other cases it is soft and flexible, 

 resembling horn; and not unfre- 

 quently it is formed of both kinds of 

 material : it is, however, always pro- 

 duced by the living cortex, which se- 

 cretes it in concentric layers, the ex- 

 ternal being the last deposited. 



(148.) The example which we 

 shall select for special description is 

 the coral of commerce, Corallium 

 rubrum (fig. 29), from which we de- 

 rive the material so much prized in 

 the manufacture of ornaments. 



(149.) The red coral is principally obtained in the Mediterranean. 

 When growing at the bottom of the sea, it consists of small branched 

 stems, incrusted 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 estimation in which it is held is 

 principally owing. But in other genera of this family, the central 

 axis, instead of being constructed of calcareous matter, is formed of 

 concrete albumen, and resembles horn both in appearance and flexi- 

 bility ; such are the Gorgonia3 of the Indian Ocean. In the Isis "hip- 

 puris (fig. 30, B) the central axis is alternately composed of both these 

 substances, exhibiting calcareous masses united at intervals by a flexible 



Corallium rubrum. 



