CORAL REEFS, ETC. 



inon forms of this coral are hemispherical or dome-shaped 

 masses, some of which are twenty feet in diameter ; 

 and the polyps themselves are often an inch in diam- 

 eter. Most of them, however, are very much smaller. 

 One beautiful little Astnean (Dana's Astrangia) has its 

 home in Long Island Sound, where it occurs in little 

 clusters upon the stones and shells. In the Oculinas, the 

 coral when young spreads so as to form a broad base ; 

 later beautiful tufts and tree-like branches arise from this 

 base. In one of the groups of the Madreporaria the 

 corals are broad and flat, resembling the fungi of the 

 vegetable kingdom; hence they are called Fungoid Corals. 

 The polvps which secrete 



t/ IT FIG 731 



this coral have short lobed 

 tentacles in multiples of 

 six. The broad flat spe- 

 cimens are from two to 



twelve inches in diaiu- Fungoid Coral 



eter each the skeleton 

 of a single polyp. 



Hundreds of islands and reefs are made of coral the 

 skeletons of Polyps. 



These islands and reefs are most abundant in the Pacific and Indian 

 Oceans ; but the islands which skirt the coast of Florida the Keys- 

 are also of coral formation ; and, according to Agassiz, a large part 

 of Florida itself is composed of coral. Some reefs are small, and 

 have made only a little progress upward towards the surface of tin- 

 water ; others are miles in length and breadth, and come so near the 

 surface that it is dangerous for vessels to sail over them ; and others 

 rise above the surface of the water, forming islands which, in some 

 cases, are covered with coral sand, and in others with a more or less 

 luxuriant growth of tropical vegetation. 



Coral reefs stretch north and south near New Caledonia for the dis- 

 tance of four hundred miles ; and along the north-eastern coast of 

 Australia for a thousand miles. 

 21 



