190 THE OCEAN WORLD. 



Stony, fixed, branclied, or lobed, having a free surface covered with a 

 great number of regular stars. 



In the Tabulate Madrepores, 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 sonje 

 idea of the Tabulate Madrepores, one of the commonest forms is 

 here (Fig. 73) represented. The millepores were first separated from 

 the madrepores by Linnseus, along with a great number of species 

 distinguished by the minuteness of their pores or polypiferous cells. 



Millepora moni/iformis is a species which attaches itself to the 

 branches of some of the Gorgonidae, 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 TuBULOUS Madrepores, which consist almost entirely of 

 fossil species chiefly belonging to the Silurian formation, we shall only 

 note Aulopora rcpens as one of the best known species. 



The Rugose Madrepores. — Among these a highly developed 

 sclerodermic skeleton occurs, each corallite being very distinct, and 

 presenting, in many cases, both septa and tabulae. Most Rugosa 

 belong to the large family Cyathophyllidse ; and all of them are wholly 

 extinct, extending from the Silurian to the Cretaceous period. 



Coral Islands. 



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 



