94 CORALS 



terminate in a swollen apex and are capitate. Sometimes 

 they are marked with white spots representing batteries of 

 nematocysts, sometimes these spots are not noticeable. In 

 retraction the tentacles may be introverted, but there is 

 not sufficient evidence to prove that this is always the 

 case. 



The number of mesenteries is nearly always twelve in a 

 full-grown polyp, and every polyp has two pairs of directive 

 mesenteries (Fig. 6, III, III, and IV, IV, p. ;^2). 



In some polyps additional mesenteries are formed in a 

 manner which seems to be peculiar to Madrepora, Porites, 

 and possibly some of their allies. Instead of being added in 

 unilateral pairs right and left of the directive mesenteries, 

 as they are in the Astraeidae, they are added in bilateral 

 pairs within the space between the two directives of a single 

 pair of directives (Figs. 9 and 10, p. 35). 



The colours of living Madrepores are so varied on different 

 reefs and on different places on the same reef that it is 

 difficult to make a general statement on the subject which 

 can be of any value for the collector. 



According to Duerden the colours of the Jamaican 

 Madreporas vary but little. Colonies as a w^hole are lighter 

 or darker shades of brown, becoming green, yellow, or orange. 

 According to Saville-Kent, the different varieties of Madre- 

 pora on the Great Barrier Reef exhibit almost every possible 

 colour variety from pale yellow through shades of green, 

 pink, and brown to lilac and blue. On the coral reefs of a 

 small island off the coast of Celebes, the Madrepores on one 

 side of the island, which was more exposed to the surf, 

 seemed to be uniformly brown, but in the calmer waters of 

 the other side of the island there was much greater variety, 

 the lilacs, bright greens, and yellows predominating. One 

 of the most striking colour features of these corals is the 

 brightness of the colours of the points of the branches. 

 When seen from a boat through the clear sea-water on a 

 bright, sunny day, these emerald green, pale yellow, lilac, or 

 sometimes white terminal branchlets produce a most fascinat- 

 ing and startling effect even in a background that is itself 

 a feast of brilliant colour schemes. When the tide falls, 



