28 CORALS 



p. ;^^). The number and arrangement of the mesenteries 

 are important characters in classification. 



The fleshy substance of which the polyp is composed is 

 translucent and of a faint fawn colour, with a broad band 

 of brown colour on the disc surrounding the mouth, and red 

 or brown patches on the tentacles. 



But, as in the sea-anemone, and, indeed, in most of the 

 Madreporaria, the colours of the living polyps are so variable 

 that the detailed descriptions of no two specimens from the 

 same locality would agree. De Lacaze-Duthiers, in his 

 description of some specimens from the coast of Brittany, 

 states that in one of his specimens there was a circle of 

 bright Veronese green at the margin of the disc, and in others 

 the walls were of brown or burnt sienna colour. In all 

 varieties, however, the colour scheme is of exquisite beauty 

 and of such delicacy of tone that it is almost impossible to 

 interpret it justly by art. 



As an example of a colonial and imperforate coral Loplw- 

 helia prolifera (Fig. 5) may be taken. This coral, which is 

 found in deep water in many localities off the western coasts 

 of Europe, forms large tree-like growths with spreading 

 and sometimes anastomosing branches. On each of these 

 branches a number of cup-like prominences are arranged 

 alternately right and left, which show a series of radiating 

 septa like those of Caryophyllia. The prominences are 

 called the " Calices," and the common substance which 

 supports them is called the " Coenosteum." ^ A transverse 

 section of the coenosteum shows a thick imperforate wall 

 and an axial cavity divided into a number of chambers by 

 radiating bands of coral substance which meet at a hub 

 in the centre. Further investigations would show that 

 these radiating bands are continuous with the septa of the 

 calyx immediately above the section of the branch that has 

 been examined, and that the branch has been formed by 

 a process of budding and subsequent growth of a new 



^ Many writers on corals use the term " Coenenchym." This is 

 etymologically and historically inaccurate. The word coenenchym was 

 introduced by Milne- Edwards and Haime for the fleshy substance between 

 the polyps in Alcyonaria (Hisloire natuyelle des coralliaires, 1S37, vol. i. 

 p. 29). 



