In fig. 2 of the plate, you may see some of these animals showing their rich rosettes on a piece of branch coral, such as is represented in the first wood cut, page 204.
There is another sort of branch coral, where the animal always lives at the end of the branch, the whole of which it has to itself, and will then spread out its tentacula in a star on the extremity, as you may see in figs. 3 and 4.
In fig. 5, you may see one of the animals which construct the sort of coral represented in the cut, page 205.
Since these little creatures can lay down their tentacula in the openings of their stony houses, when they are not hungry, or when they are alarmed by the approach of anything that would hurt them, they do not want the tough skin with which the Actinia is covered, but have bodies of a very soft and yielding texture.
As I have now introduced to you, as well as I can by means of description and pictures, the inhabitants of these wonderful submarine continents, I shall now tell you something of the form in which they arrange their habitations. Those that I saw about the Society and Friendly Islands, were mostly in three different conditions. One kind forms a nearly circular reef, sometimes with an opening in it. It is a part of the common design of the Polypes always to make this opening on the Leeward side, when the place is one in which any particular wind blows during a great part of the year. I cannot tell you why this is, but it is constantly observed wherever coral reefs are found. This peculiarity makes the enclosed spaces of water, (which are called Lagoons,) capital harbours for ships to anchor in, for they are nearly always smooth, the windward side of the reef acting as a breakwater. Here is a map of three reefs of this form, in a part of the ocean where the prevailing wind is South East, and you will see all the openings are towards the North West.
Another sort have an island of which the foundation is coral, in the middle of a ring like the above; and a third sort are merely the same kind of rings round large islands, composed of other sorts of rocks and earth. A very great number of the islands hereabouts,--perhaps most of them, are surrounded in this manner.