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always some multiple of six. These tentacles increase in 

 number by the introduction of new ones between those first 

 formed, in a very regular way and according to very beauti- 

 ful laws. The common Sea Anemones, or Actinias, belong 

 to this order, but they never produce corals. Those kinds, 

 by which the corals that are porous and consist of limestone, 

 are formed, resemble the Actinias very much, but deposit 

 limy matter in their sides and internal membranes and only 

 the upper parts of their bodies and their tentacles remain 

 soft and flexible. The coral itself is a complete internal 

 skeleton of the polyp that forms it. 



These polyps may be very minute or they may be several 

 inches or even a foot in diameter. Some, like the Fungi a, 

 remain always simple and free, but others adhere to rocks 

 or other solid substances. Other kinds develop buds upon 

 their sides or other parts, and these buds soon become per- 

 fect individuals, but generally remain connected with the 

 parent polyps so as to form clumps or masses. The star- 

 corals (Astrea) and the common branching corals (Madre- 

 pora) are formed in this way. Again, some species, when 

 they have reached a certain size, begin to widen and finally 

 divide in the centre, so as to form two distinct individuals 

 with two mouths, two stomachs and two sets of tentacles, 

 from what was before one individual. In some cases the 

 separation remains incomplete, and the polyps are united in 

 long series. Corals of this kind generally lorm large solid 

 masses and are among the most important of the reef-build- 

 ing species. The common Brain Coral (Meandrina) is a 

 good example of this kind. 



The next order, called Halcyonoid Polyps or Alcyonaria, 

 have always eight tentacles and these are always compound 

 or lobed along the sides. These also may be soft and pro- 

 duce no coral or they may form corals, but never such ones 

 as are produced by the Actinoids. Some of them produce 

 solid calcareous corals without pores or cells, but such corals 

 serve merely as a support for the polyps which are situated in a 

 soft external crust and secrete the solid coral from their 

 inner membranes. The well known Red Coral is formed in 

 this way. Other kinds, such as the Gorgonise or " Sea Fans" 

 and " Sea Plumes" form solid interior corals resembling 

 horn, and are generally dark colored, but the crust that 

 covers them and in which the polyps are situated is gener- 



