i8o THE GREAT BARRIER REEF. 



Taken collectively, the tints of the living coralla and polyps of the species of Madrepora are 

 among the most brilliant in the coral class, and they abound with remarkable combinations. It is 

 further noteworthy that local colony-stocks of the same species may be of conspicuously distinct 

 tints. Finally, it has fallen within the writer's experience that the same colony-stock may undergo 

 a distinct change in colour of both its corallum and polyps, within a more or less brief interval 

 of time. The following was observed of a luxuriant patch of Madrepora hcbcs growing in a coral 

 reef pool in Vivien Point, Thursday Island, utilised by the author for experimental cultiva- 

 tion of the mother-of-pearl shell, Mclcagrina margaritifera. When first noted, in the month of 

 September, 1889, the corallum was of a pinkish-brown hue, with greenish-white growing apices ; 

 while all the polyps, with the associated tentacles, were a light emerald-green. The coloured 

 sketch then made of a branch is reproduced in Chromo plate IX., Fig. 15, with a magnified 

 view of the extended polj'ps. No particular notice was taken of this coral colony on revisiting the 

 locality in the subsequent year, excepting that it was observed that its growth appeared to have 

 been greatly retarded. On re-examining it, however, in August, 1891, it was found that the 

 corallum was of a clear seal-brown hue, with white, and in some instances pale lilac-blue, tips, 

 while all the polyps were a clear red-brown, with greenish-white tips only to the extremities of 

 the tentacles. All the emerald-green tints that so conspicuously distinguished the extended polyps 

 two years previously had entirely disappeared. The phenomenon above recorded suffices to 

 prove that colour cannot be accepted as yielding a reliable diagnostic character for the specific 

 distinction of closely allied coral types. As here demonstrated, it is not only subject to varia- 

 tion among separate colony-stocks of the same species, but it may vary at different epochs in 

 the same colony. The variety, Madrepora hcbcs, now under consideration, belongs, as will be 

 recognised by the illustration already named, to that series in which one (the lowermost) tentacle 

 is abnormally prolonged. In the larger, terminal, or growing, corallites of the same species, it 

 was observed that the polyps did not exhibit the same radial symmetry of their tentacles that 

 characterised the adjacent individuals, two or three abnormally elongate tentacles only being 

 exserted from the calicinal orifices. A similar structural peculiarity has been observed by 

 the author in several other species of the same genus. 



An enumeration of the more remarkable colour variations of the living coralla and 

 the associated polyps of the Barrier Reef Madreporas, may now be proceeded with. The 

 Stags'-horn variety, Madrepora liebes, already referred to, while most commonly dark-brown 

 with white extremities, may, in some instances, including both the corallum and polyps, be 

 entirely a vivid grass-green. This green variety may have white or bright lilac extremities 

 to all the branchlets, as shown in Chromo plate IX., Fig. 13 ; or the corallum may be 

 bright lilac throughout. A typical illustration of the luxuriant growth of this Madrepora in 

 certain localities is afforded by the photographic reef-view reproduced in Plate XII., wherein 

 this single species, chiefly the brown, white-tipped, variety, monopolises almost the entire 



