THE IMPENETRABLE SEA 



The coral polyp's building patterns are manifold. 

 About 2,500 living, and 5,000 fossil, species are known. 

 It secretes lime under its base, around its sides, and in 

 radial ridges. Living polyps can withdraw themselves 

 almost completely into the connected chambers formed 

 by these ridges. It might be said of the creature, when it 

 is inside, that it is living in all the rooms of its house at 

 once. The shapes of the structures give the polyps their 

 various names, and are self-explanatory : star coral, rose 

 coral, organ-pipe coral, mushroom coral, and brain coral 

 are some of them. 



In most corals the sexes are separate, and even the 

 reef growths may have areas entirely male or female. 

 Hermaphrodites may occur, and there are even corals 

 which have male and female branches in the individual. 

 Semper says that there is at least one species in which 

 the sex changes from male to female in alternate genera- 

 tions. 



The richest and most impressive areas of the world's 

 seas are the coral reefs, and of these the chain of shoals, 

 shelves and islands along Australia's north-east coast, 

 which forms the world's greatest coral structure and is 

 known as the Great Barrier Reef, is our planet's finest 

 ''show-case" of the wonders of the sea. 



Captain James Cook, whose ship was beached and 

 damaged on a submerged reef one night in June 1770, 

 at a place now known as Cooktown, was too anxious to 

 repair his ship and sail on to Batavia, to appreciate the 

 beauties of the island shores. 



Even today the vast labyrinth of coral formations 

 remains almost entirely undisturbed by man's explora- 

 tions. Over five hundred of the Great Barrier Reef's 

 sand-banks and islands remain unpeopled, while hun- 

 dreds of thousands of coral grottoes have never been 

 approached by divers. Because the visible surfaces of the 

 mighty Reef are generally flat, they never drain dry 

 between tides. Under skies of brilliant blue, untold multi- 



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