I could study now the madreporal system, to which are due the islands in this ocean.
Madrepores (which must not be mistaken for corals) have a tissue lined with a calcareous crust, and the modifications of its structure have induced M.Milne Edwards, my worthy master, to class them into five sections.

The animalcule that the marine polypus secretes live by millions at the bottom of their cells.

Their calcareous deposits become rocks, reefs, and large and small islands.

Here they form a ring, surrounding a little inland lake, that communicates with the sea by means of gaps.

There they make barriers of reefs like those on the coasts of New Caledonia and the various Pomoton islands.