48 ON CORAL REEFS AND ISLANDS. 



which the coral animals may withdraw for concealment, any 

 more than the skeleton of a dog is its house or cell : for every 

 part of the coral of a polyp in most reef-making species is en- 

 closed within the polyp, where it was formed by the secreting 

 process.* 



It is important that this point should be thoroughly understood, 

 and fully appreciated. That error may no longer be perpetuated, 

 the words polypary and the like, have been rejected by the au- 

 thor in his volume on Zoophytes, and the more familiar term 

 corallum has been used instead.^ With this introductory expla- 

 nation, we proceed. 



a. Structure of Coral Animals or Polyps. — A. good idea of a 

 coral polyp may be had from comparison with the garden aster : 

 for the likeness in external form and delicacy of coloring is singu- 

 larly close. The aster consists of a tinted disk bordered with 

 one or more series of petals ; and in exact analogy, the polyp- 

 flower, in its most common form, has a disk often richly colored, 

 fringed around with petal-like organs called tentacles. Below 

 the disk, in contrast with the slender pedicel of the plant, there 

 is a stout cylindrical pedicel or body, often as broad as the disk 

 itself, and usually not much longer, which contains the stomach 

 and internal cavity of the polyp : and the mouth, which opens 

 into the stomach, is placed at the centre of the disk. Here, 

 then, the flower-animal and the garden-flower diverge in charac- 

 ter, the difference being required by the different modes of nu- 

 trition in the two kingdoms of nature. 



There are many species of polyps, which have all the exter- 

 nal and internal characters of coral polyps, yet secrete no lime 

 or coral. Our descriptions of structure may be best drawn from 

 them, and afterwards the single peculiarity of the coral-making 

 polyp — its secretion of coral — will come under consideration. 

 The species here referred to are called Actinia in science, in allu- 

 sion to the radiated or aster-like flower which forms the summit 

 of the animal. % There is the same allusion in the common ap- 

 pellation Sea-anemone. The richest anemones, daisies and tu- 

 lips of our gardens would not rival them in beauty, neither will 



* It is not, perhaps, "within the range of science to criticise the poet ; yet we 

 may say in this place, in view of the frequent use of the lines even by scientific 

 men, that more error in the same compass could scarcely be found than in the part 

 of Montgomery's Pelican Island, relating to coral formations. The poetry is beauti- 

 ful, the facts nearly all errors — if literature allows of such an incongruity. For 

 ourselves, we think the poet transcends his appropriate limits when false to nature. 



f See page 15, of the Report on Zoophytes. The term Corallium has been set 

 aside by authors because of its being used for a genus of corals. Corallum is an 

 old form of the same word, as particularly explained on the page just referred to, 

 and is not liable to this objection. The true nature of calcareous corals was first 

 pointed out by Milne Edwards and Ehrenberg. 



^ From axTiv, a ray of the sun. 



