io6 ELEMENTARY ZOOLOGY 



and thus render the whole mass more compact. At the 

 same time larger fragments are broken and rolled about 

 by the waves and are eventually washed up into banks 

 upon the coral plantation, so that the island now appears 

 slightly elevated above the tides. This may be called a 

 first stage in the development of a coral island. It is, 

 however, little more than a low ridge of worn fragments 

 of coral washed by the high tides and swept by the larger 

 waves a low, narrow island resting on a large submarine 

 bank." 



When the coral island rises thus a little above the sur- 

 face of the water, the waves break up some of the coral 

 into fine sand, which fills in the interstices, and offers a 

 sort of soil in which may germinate seeds brought in the 

 dried mud on the feet of ocean birds or carried by the 

 ocean currents. With the beginning of vegetable growth 

 the soil is more firmly held, is fertilized and ready for the 

 seeds of plants which need a better soil than lime sand. 

 Flying insects find their way to the island, especially if 

 it be near the mainland, birds begin to nest on it, and 

 soon it may be the seat of a luxuriant plant and animal 

 life. 



For an account of coral islands see Darwin's "The 

 Structure and Distribution of Coral Reefs." 

 I There are over 2000 kinds of coral polyp known, and 

 / their skeletons vary much in appearance. Because of the 

 appearance of the skeleton certain corals have received 

 common names, as the organ-pipe coral, brain coral, etc. 

 The red coral, of which jewelry is made, grows chiefly in 

 the Mediterranean. It is gathered especially on the 

 western coast of Italy, and on the coasts of Sicily and 

 Sardinia. Most of this coral is sent to Naples, where it is 

 cut into ornaments. 



There are other interesting members of the class 

 f Actinozoa like the beautiful sea-pens, sea-feathers and 



