334 CORAL REEFS. 



Polype they remain permanently attached to the bottom 

 Thus one generation establishes the basis whereon the next 

 fixes its habitation, which is destined to form the foundation 

 of a farther and continual succession of similar constructions, 

 until the mass, being at length raised to the surface of the 

 sea, a limit is thereby put to its farther accumulation. 

 ■ The tendency of Polypes to multiply in the waters of 

 warm climates is so great, that the bottom of our tropical 

 seas swarms with countless myriads of these little creatures, 

 ever actively engaged in constructing their small but 

 enduring habitations. Almost every submarine rock, and 

 submarine volcanic cone, and ridge, within these latitudes, 

 has become the nucleus and foundation of a colony of 

 Polypes, chiefly belonging to the genera Madrepora, Astrea. 

 Caryophyllia, meandrina, and Millepora. The calcareous 

 secretion of these Polypes are accumulated into enormous 

 banks or I'eefs of coral, sometimes extending to a length of 

 many hundred miles ; these continually rising to the surface 

 in spots where they were unknown before, endanger the 

 navigation of many parts of the tropical seas.* 



If we look to the office these Polypes perform in the 

 present economy of nature, we find them acting as scaven- 

 gers of the lowest class, perpetually employed in cleansing 

 the waters of the sea from the impurities which escape 

 even the smaller Crustacea ; in the same manner as the 

 Insect Tribes, in their various stages, are destined to find 

 their food by devouring impurities caused by dead animal 

 and vegetable matter upon the land.f The same system 



* Interesting accounts of tlie extent and mode of formation of these Coral 

 Reefs may be found in the voyages of Peron, Flinders, Kotzcbue. and 

 Becchy ; and an admirable application of the facts connected with modern 

 Corals to the illustration of geological phenomena has been made by Dr. 

 Kidd in his Geological Essay, and by Mr. Lyell in his Principles of Geo- 

 logy, 3d edit. vol. iii, 



t Mr. De la Bcchc observed that the Polypes of the Caryophyllia 

 Smithii CPl- 54, Figs. 9, 10, 11,) devoured portions of the flesh of 



