CORAL BUILDERS. 221 



Any one of these sea-anemones consists of a cylin- 

 drical body, or column, with a flattened base by 

 which it is attached to the rock, a flattened upper 

 surface or disk, surrounded by one or more rows of 

 tentacles, and a mouth or opening in the centre, 

 leading into the cavity of the body, or stomach, if you 

 will. They may vary in size, from an eighth of an inch 

 in diameter to more than a foot, but these general 

 features will apply to all. When fully expanded the 

 tentacles radiate from, and fringe the disk, like the 

 flower of a chrysanthemum. When retracted and 

 closed, the tentacles are hidden, and the whole 

 animal resembles a convex gelatinous button. The 

 number of tentacles is some multiple of six, which is 

 also a typical number in their internal organisation. 

 The mouth, in the centre of the disk, is usually a little 

 elevated at the margin or lips, and opens directly 

 into the stomach. This cavity is divided, in a radiate 

 manner, by fleshy partitions, or septa, into compart- 

 ments, the septa being in pairs, corresponding to some 

 multiple of six. The muscles of the body are the 

 means by which the animal contracts itself when 

 disturbed, and expands again when at rest ; during 

 the former process expelling forcibly a quantity of 

 water through its mouth, and in the latter imbibing 

 sufficient to inflate the tentacles and body. Food is 

 sometimes assisted in its passage through the mouth 

 into the stomach by the tentacles, as well as by the 



