CORAL AND CORAL REEFS. 13 



depths of water, and which also form islands, on which the 

 usual plants and animals exist. The shapes of these coral 

 formations are various flat, tubular, oval, and irregularly 

 rounded at their circumference and are almost invariably 

 supported by an under-water elevation, such as extinct vol- 

 canoes or underlying rock. It is thought that these aggrega- 

 tions are stratified rocks of limestone, and that all calcareous 

 formations have proceeded from the putrid bodies of fish. 



Polyparia are composed of two separate parts : an external 

 living fleshy envelope bearing and containing polypi, and an 

 internal firm, solid, and inorganic axis. The base of the 

 attachment is large, the stem fixed, the branches subdivided, 

 calcareous, and mostly jointed. The animals inhabit the con- 

 cretions in minute cells, and draw their nourishment through 

 an aperture. 



The formation of the coral-reefs consists of the shells of 

 myriads of these little beings, resembling plants without leaves. 

 Coral itself is, in fact, an animal growing in plant-like form, 

 and seems to be a connecting link between the animal and 

 vegetable kingdoms. 



The sea is found to be deficient in lime-salts near the islands 

 of the South Pacific. Chemically the common reef corals con- 

 sist almost wholly of carbonate of lime, the same substance, in 

 fact, which constitutes ordinary limestone. The currents of 

 the Pacific are constantly bringing new supplies of sea-water 

 (on which the tiny insects live) over the growing coral beds, 

 and the whole ocean is thus engaged in contributing to their 

 nutriment. 



The coral-reefs around the islands are guardians of the low 

 lands against the incursions of the sea. In Fiji they are often 

 miles from the shore, the water inside the reef being usually 

 calm, while that without, if there be anything like a breeze, is 



