190 THE OCEAN WORLD. 
stony, fixed, branched, or lobed, having a free surface covered with a 
great number of regular stars. 
In the TaBuLaTE Maprepores, the polypidom is essentially 
composed of a highly-developed mural system. The visceral cham- 
bers are divided into a series of stages or stories, by perfect diaphragms 
or plates placed transversely, the plates depending from the walls and 
forming perfect horizontal divisions, extending from one wall of the 
general cavity to the other. In order that the reader may form some 
idea of the Tabulate Madrepores, one of the commonest forms is 
here (Fig. 73) represented. The millepores were first separated from 
the madrepores by Linneus, along with a great number of species 
distinguished by the minuteness of their pores or polypiferous cells. 
Millepora moniliformis is a species which attaches itself to the 
branches of some of the Gorgonide, forming there a series of little 
rounded or lateral lobes. ‘The animal is unknown, the cells are very 
small, unequal, completely immersed, obsoletely radiate and scattered ; 
the polypidom is fixed, cellular within, finely porous and reticulated 
externally, extending into a palmated form. 
Of the TusuLous MapREpoRES, which consist almost entirely of 
fossil species chiefly belonging to the Silurian formation, we shall only 
note Aulopora repens as one of the best known species. 
The Rucose Maprepores.—Among these a highly developed 
sclérodermic skeleton occurs, each corallite being very distinct, and 
presenting, in many cases, both septa and tabulze. Most Rugosa 
belong to the large family Cyathophyllidee ; and all of them are wholly 
extinct, extending from the Silurian to the Cretaceous period. 
Cora IsLanps. 
There is no spectacle in Nature more extraordinary or more 
worthy of our admiration than that now under consideration. These 
corals, whose history we have investigated—beings gifted with a half- 
latent life only—these animals so small and so fragile—labour silently 
and incessantly in the bosom of the ocean, and, as they exist in 
innumerable aggregated masses, their cells and solid axes produce in 
the end enormous stony masses. These calcareous deposits increase 
and multiply with such incalculable rapidity, that they not only cover 
the submarine rocks as with a carpet, but they finish by forming reefs, 
and even entire islands, which rise above the surface of the ocean 
in a manner remarkable at once for their form and the regularity with 
which they repeat themselves. 
In noting the Indian and Pacific Oceans, navigators had long been 
