THE BIOLOGY OF THE FUNAFUTI ATOLL AND EEEF FORMATION. 139 



ebb. By this means the coral has been enabled to grow to a greater height above 

 low water than was observed anywhere else on the atoll. Great care was exercised to 

 determine the exact height of this coral growth, since it would seem to offer an 

 explanation for the occurrence in situ of dead Ileliopora considerably above low- water 

 mark in the Mangrove Swamp and in other localities on the main Island of Funafuti. 



(6) The Millepores. — Of these, the species M. alclcornis helps to forms the founda- 

 tions of shoals and additions to the platform in the same manner as Hdiopora ccendea. 

 In doing this it is greatly aided by its enormous rapidity of growth in comparison with 

 that of the corals, as well as by its habit of growth, for (1) when two branches meet 

 they join, whereby an irregular reticulating mass is produced ; (2) it is capable of 

 encrusting any object with which it comes in contact. 



M, complanata differs widely in its habits. It is capable, where washed by 

 successive waves, of growing in situations above low- water spring tide, so the surface 

 of the water does not, as in the case of the Tleliojjora ccervlea and M. alcicornis, 

 constitute a definite limiting plane to its upward increase. It grows in irregular 

 ridge-like masses, which, as already mentioned in connection with the ocean slope, 

 attain to considerable dimensions in certain localities, such as Pava. In no instance 

 was it seen to be attacked by the Lithothamnion , but it is doubtful whether this was 

 a purely accidental circumstance, or whether this genus is in reality proof against the 

 encroachment of the Lithothamnion. 



(c) The Porites family require special notice on account of the important part they 

 play in contributing to the upward extension of the lagoon platforms. When growing 

 in deeper water the Porites do not differ in their habits from other corals ; they neither 

 assume large dimensions nor play a more prominent part in the reef formation 

 than the rest. On the lagoon platforms, however, they undergo very characteristic 

 changes. They become pancake-shaped, reaching a maximum of 6 feet in diameter 

 and about 1 foot in thickness. The smallest lie loose on the platform ; the larger 

 ones are fixed down, but are easily detached ; whereas those of the largest dimensions 

 are firmly cemented down. Some of these last, having by growth come into contact 

 with their neighbours, unite with them to form a continuous, perfectly level surface 

 several inches above the level of low- water spring tide. The whole, neither of these 

 surfaces, nor of the surfaces of the individual corallum, is not actually growing ; the 

 central portions to within a few inches of the periphery being killed by a calcareous 

 incrustation, which is Lithothamnion growth, although its nature is obscured on' 

 account of its growth being greatly interfered with, no doubt, by the fortnightly 

 exposure to the sun's rays during spring tides. 



The above description applies particularly to a patch of Porites on the lagoon plat- 

 form close to the village. A similar area exists near the edge of the platform in the 

 same locality. The latter consists of innumerable coralla of very small dimensions, 

 from' 2 to 3 inches in diameter, all united by growth to their neighbours and thus 

 forming a solid living crust on the dead platform. 



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