ALCYONARIAN CORALS 113 



" stolon," as it is called, a number of tubes arise, which are 

 bound together by a horizontal platform at a distance of a 

 few millimetres from the base. Every tube passes through 

 the platform, and at a distance of another few millimetres 

 passes with its fellows through a second platform, and so on, 

 through several platforms, until the surface is reached. 



If two or three of these primary tubes springing from the 

 base are traced through their whole length, it is found that 

 they are not quite parallel, but spread out fan-wise in all 

 directions, and from each of the platforms secondary tubes 

 arise which fill up the spaces between the primary tubes, 

 and thus in each series the number of tubes increases. By 

 this manner of growth great dome-shaped masses of coral 

 are formed which may reach the size of a man's head, but 

 the time comes when the weight of the mass is too great for 

 the support given by the few primary tubes that have 

 sprung from the stolon, and then it is broken off by wave 

 action, is rolled by the breakers, and eventually cast up on 

 the beach. 



On making an anatomical examination of a preserved 

 specimen, it is found that the soft lining tissues of the polyps 

 do not extend below the level of the second platform from 

 the surface. The inner parts of the mass, therefore, are 

 nothing but a skeletal structure for the support of the living 

 surface ; but the shelter they afford attracts many interest- 

 ing examples of the aquatic fauna and flora, such as worms, 

 mollusca, crabs, and other Crustacea, encrusting sponges, 

 polyzoa and algae, so that it becomes a miniature museum 

 of strange creatures. Some of these organisms assist in the 

 destruction of the inner tubes, and thereby hasten the time 

 when the coral meets its fate by becoming detached from 

 its base. 



The polyps are all of one kind, and have the typical 

 Alcyonarian structure. The mouth, at the distal extremity, 

 is surrounded by eight pinnate tentacles, and the short 

 throat or stomodaeum into which the mouth opens is con- 

 nected with the body wall by eight mesenteries. 



\Mien the polyp is fully extended the body wall is con- 

 tinuous with the extremity of one of the red tubes. In 



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