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At many places corals formed thin reefs, as at Louisville, Kentucky, where the hardness of the reef rock is one of the causes of the Falls of the Ohio. Sponges, echinoderms, brachiopods, and mollusks were abundant. The cephalopods take a new departure.

Backbones are called by the Wise Men vertebrae; animals that have backbones are named Vertebrates; and animals that lack backbones are named Invertebrates." "Tell us the names of some Invertebrates, please, Doctor," said Rap. "Well, all sorts of insects are Invertebrates, and so are lobsters and crabs, oysters and clams, worms, starfishes, jelly-fishes, corals, and even sponges.

Moreover, in an atoll once breached on opposite sides, from the likelihood of the oceanic and tidal currents passing straight through the breaches, it is extremely improbable that the corals, especially during continued subsidence, would ever be able again to unite the rim; if they did not, as the whole sank downwards, one atoll would be divided into two or more.

Ah, what ugly, slimy things there are down in the bottom! What squalor and filth flung in from the houses, and covered over many a day by the waters! All that surface work will be drained off from the hearts of men. Shall we show slime and filth, or shall we show lovely corals and silver sands without a taint or a speck? These are the details of the life's aim of a Christian man.

She would sit very demurely on the after-deck, apparently absorbed in the shells and corals that lay spread before her; and by-and-by, it might be, Franci, who did not suffer from shyness, would venture on something more definite than admiring glances.

One more point in detail: as in the two neighbouring archipelagoes corals flourish in one and not in the other, and as so many conditions before enumerated must affect their existence, it would be an inexplicable fact if, during the changes to which earth, air, and water are subjected, the reef-building corals were to keep alive for perpetuity on any one spot or area.

A third and better theory was advanced by Chamisso, who thought that from the corals growing more vigorously where exposed to the open sea, as undoubtedly is the case, the outer edges would grow up from the general foundation before any other part, and that this would account for the ring or cup-shaped structure.

The coral mud, which occupies the bottom of the lagoon, and with which all the interstices of the coral skeletons which accumulate to form the reef are filled up, does not proceed from the washing action of the waves alone; innumerable fishes, and other creatures which prey upon the coral, add a very important contribution of finely-triturated calcareous matter; and the corals and mud becoming incorporated together, gradually harden and give rise to a sort of limestone rock, which may vary a good deal in texture.

On the contrary, the old shells, crustacea, corals, etc., represent types which have existed in all times with the same essential structural elements, but under different specific forms in the several geological periods. And here it may not be amiss to say something of what are called by naturalists representative types.

But now this cannot happen, and the inhabitants observe that the tide rises to a less height, during a high S.E. wind, at the head than at the mouth of the lagoon. The corals, which, under the former condition of things, had attained the utmost possible limit of upward growth, would thus occasionally be exposed for a short time to the sun, and be killed.