The royal natural history . in vastcolonies. It is the accumulation of alltheir little contributions of coral which,in the process of time, build up islands oreven continents. In regarding coralanimals as reef-builders, we may leaveout of account, as unimportant, thosewhich form hard spicules within theirbodies, and consider only those whichperform most of the work. Imagine acrowd of small animals like sea-anemonesfixed to a rock, each one secreting a layerof carbonate of lime between itself andthe rock, and this layer becoming thickerand thicker till each polyp rises on alittle pedestal. Ther
The royal natural history . in vastcolonies. It is the accumulation of alltheir little contributions of coral which,in the process of time, build up islands oreven continents. In regarding coralanimals as reef-builders, we may leaveout of account, as unimportant, thosewhich form hard spicules within theirbodies, and consider only those whichperform most of the work. Imagine acrowd of small animals like sea-anemonesfixed to a rock, each one secreting a layerof carbonate of lime between itself andthe rock, and this layer becoming thickerand thicker till each polyp rises on alittle pedestal. There is probably a racebetween them, as there is among trees in a forest, which shall reach the highestto get most of the food as it passes by on the currents in the water. Now, it isobvious that a crowded colony of polyps like this would in a short time add athick layer of solid carbonate of lime to the rock on which they first settled, andthis is, in brief, the principle of reef-building. As a matter of fact, however, it is. Monoxenia darivini (magnified). Longitudinal section, on the left, through one of theinterseptal cavities, on the right through one of thepartition walls ; M, Transverse section through theline m n; N, Transverse section through the lines b t; O, The eight-lipped mouth-aperture, with thebases of the arms ; a b c o, Principal axis ; p,Pharyngeal cavity ; g, Digestive cavity ; k, Divisionsof the digestive cavity; w, Radial septa or wallsdividing up the digestive cavity ; e, Masses of eggs ;w, Mesenterial filaments ; /, Masses of muscle andconnective tissue. SEA-ANEMONES AND CORALS. 499 not quite so simple. The layer each polyp secretes is not a smooth flat disc., evenlysecreted by the whole surface of its foot. Some parts of the foot secrete morethan others, hence those parts rise up as spines, walls, and rings, which protrudeinto the body of the polyp without, however, breaking through the skin. Theseprobably help to fasten the polyp to its pedestal, and prev
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
