CORAL-REEFS. 21 



violence, although the day was quite calm and the tide low, 

 the polypifers in the uppermost cells were all dead, but 

 between three and four inches lower down on its side they 

 were living, and formed a projecting border round the upper 

 and dead surface. The coral being thus checked in its 

 upward growth, extends laterally, and hence most of the 

 masses, especially those a little further inwards, had broad 

 flat dead summits. On the other hand I could see, during 

 the recoil of the breakers, that a few yards further seaward, 

 the whole convex surface of the Porites was alive ; so that 

 the point where we were standing was almost on the exact 

 upward and shoreward limit of existence of those corals 

 which form the outer margin of the reef. We shall presently 

 see that there are other organic productions, fitted to bear a 

 somewhat longer exposure to the air and sun. 



Next, but much inferior in importance to the Porites, 

 is the Millepora comftlanata. 1 It grows in thick vertical 

 plates, intersecting each other at various angles, and forms 

 an exceedingly strong honeycombed mass, which generally 

 affects a circular form, the marginal plates alone being 

 alive. Between these plates and in the protected crevices 

 on the reef, a multitude of branching zoophytes and other 

 productions flourish, but the Porites and Millepora alone 

 seem able to resist the fury of the breakers on its upper 

 and outer edge : at the depth of a few fathoms other kinds 

 of stony corals live. Mr. Liesk, who was intimately 

 acquainted with every part of this reef, and likewise with 

 that of North Keeling atoll, assured me that these corals 

 invariably compose the outer margin. The lagoon is 

 inhabited by quite a distinct set of corals, generally brittle 



1 This Millepora (Palmipora of Blainville), as well as the M. 

 alctcornis, possesses the singular property of stinging the skin where 

 it is delicate, as on the face and arm. 



