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 coating has apertures through which the polyps protrude in order to feed when no danger is near (Fig. 46). The red "corals" used for jewelry are bits of stalks of corallines. The corallines (Figs. 47, 48) are not so abundant nor so important as the coral polyps (Figs. 45, 49).

with crust and polyps (eight tentacles).

(a coralline).

Colonies of coral polyps grow in countless numbers in the tropical seas. The coral formed by successive colonies of polyps accumulates and builds up many islands and important additions to continents. The Florida "keys," or islands, and the southern part of the mainland of Florida were so formed.

"Coral" (a coralline).