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bryozoa which are remarkable lime-secreting organisms related more closely to the worms than to any other phylum of the animal kingdom.

This lithothamnion ridge thrives only where the breakers strike in full force upon its living barrier, and it serves as the chief protector of the island, breaking the force of every wave that approaches the windward shore.

Clustered in the tide pools of this lithothamnion ridge, with the waves dashing constantly over them one finds living corals which cling tenaciously to the shallow crevices and grow into thin encrusting forms instead of into dome-like shapes as in more protected waters; or their branches are remarkably short stump-like and gnarled and tend to bend inward toward the shore after the manner of the ragged trees that survive along a wind-swept coast.

At Maër Island, the lithothamnion ridge extends along the extreme outer edge of the southeastern reef between 1,800 and 2,200 feet from shore, and it forms a veritable dam which prevents the escape of the water from the basin of the reef-flat at the lowest tides, so that at the low tide of the springs, one finds here a great shallow marine lake about 1,700 feet wide, 2 miles long, and only about 18 inches deep.

About 3,600,000 coral heads grow upon the hard rocky bottom of this natural aquarium, and in the middle region of the reef-flat, 1,000 feet from shore, fully 50 per cent, of the bottom is covered with heads the dominant species being the delicate and profusely branched Seriatopora histrix which forms a veritable coral forest, growing so luxuriantly that no other species can thrive so well in this region as it does nearer shore or farther out upon the reef. It is evident that there is a struggle for existence between the different sorts of corals, and the Seriatopora