CORAL 



69 



body cavity is subdivided by many partitions which in- 

 crease the digesting and absorbing surface. The sea- 

 anemone reproduces by eggs and sperms. 



The resulting embryo is free at first, but later becomes 

 fixed to some object and develops into the sea-anemone. 

 There is no medusa stage. 



54. Coral. — Geographies tell us of the many coral islands 

 and reefs built up by the coral animals. These animals 

 are coelenterates, most 

 of them closely allied 

 to the sea-anemone, 

 but the coral animal 

 secretes about the body 

 and along the parti- 

 tions calcareous (kal- 

 ka/ re-us, limy) skele- 

 tons which form the 

 stone-like masses of the 

 coral rock. The upper 

 portion of the coral 

 rocks is alive with 

 these coral animals. 

 The lower portion is made up of skeletons only. Suc- 

 ceeding generations build upon the work of their ancestors. 



Corals reproduce much as trees grow branches, but at 

 certain periods eggs and sperms are produced as in the 

 sea-anemone. Then the embryo settles down, secretes its 

 own skeleton, and this is added to the work of other 

 corals. 



Sea-fans and sea-plumes are coelenterates which have the 

 forms suggested by their names. A dried specimen of 

 either looks as if a branch had been dipped in a solution 

 and coated. The interior is of a horny substance. The 

 exterior is covered with a limy secretion. 



Figure 70. — Some Common Corals. 



