Fig. 34.—Mushroom coral; a single polyp (Ctenactis), one fourth natural size.
Such is the history of an ordinary coral island, built up, not by corals alone, but by countless animals. Even to-day some writers describe this coral animal as an "insect," but it is an entirely different animal, being a polyp, so closely related to the anemones that very few can distinguish between them. For the purpose of examination we may consider a coral animal as a sea anemone possessing the faculty of taking lime from the sea water and secreting it in the little rooms which we have found existing in the anemones (Fig. 32), there forming a little platform, then partitions or cells, as the case may be. In Figure 33 is shown a section of branch coral. The starlike spots are the polyps with their tentacles outspread as in feeding. They may be considered so many anemones, each resting in a little cell, and all connected by a common brown or olive-hued tissue. This is a many-celled coral, while that shown in Figure 34 is an example of a single-celled coral, a huge anemone with a framework of lime. These single-celled corals are often found in very deep water.
Fig. 35.—A single polyp coral (Caryophyllia).
In the vicinity of Garden Key on the Florida Reef there are six or seven keys, each almost surrounded by a deep-blue channel. On the east a long fringing reef is forming which some day may form an atoll (Fig. 36). In this lagoon are acres of beautiful branch coral, rising two or three feet from the bottom in a mass of points almost bare at low tide, and at the very lowest tides becoming exposed and dying. At certain places on the edges of channels are vast heads of coral (Fig. 37), some being four feet high and six or seven feet across. Many of these are hollowed out into great vases and filled with beautiful sea fans, the Gorgonias, in yellow, lavender, and brown, while in and out swim fishes of beautiful colors. The surface of these heads is often dotted with objects which resemble flowers of gorgeous hues, red, blue, white, and spotted. At the slightest alarm or jar these disappear, showing themselves merely worms, which have bored into the coral, the flowerlike petals being the breathing organs. Along the sides of the channels the groves of branch coral (Fig. 33) dip down, and thirty feet below the surface the growth is much more vigorous, the branches often being three or even four feet in length, and resembling the antlers of the elk.
Fig. 36.—An atoll.
Wishing to see how deep the coral descended, I had a boat held on the edge of the channel, and taking a heavy stone in my hands allowed myself to sink. The stone carried me down rapidly for perhaps twenty feet, until the water was perceptibly colder and the light very dim, yet as far below me as I could see, the almost perpendicular wall of coral extended, being in all probability sixty feet in height and almost vertical. As I swam upward not four feet from the jagged points, I could plainly see the beautiful coral with parrot fishes garbed in brilliant tints, poising among the great branches.
The coral on this reef grows or flourishes more or less in communities. The great heads are found in groups, the branch coral in plantations, if the word can be used, in the center of the lagoon and on the edge of the deep channels. On a shallow point, growing among seaweeds, I found small heads five or six inches long.
