THE ANIMAL KINGDOM. 75 



the bed of the sea. Volcanic action l^egins the work, and 

 the Polypi finish it; they bring the construction ^^p to the 

 level of the waves. These islands always display a pecu- 

 liar configuration; they are nearly all circular, and there 

 is a crater-like depression in the middle. This peculiarity 

 seems to be owing to the fact, that the little workmen 

 can support their vital energies better where the water, 

 being agitated brings them a more ample supply of nour- 

 ishment. The animals in the centre, placed under different 

 conditions, wasted and languishing, can only raise their 

 living rampart more slowly. 



In the Pacific Ocean, where a tolerably large number of 

 those islands are seen, the polypidoms reach the level of 

 the low tides, and after that the great surges raise the 

 middle part, by casting back upon it incessantly the frag- 

 ments which they tear away from the circumference. 

 When in the lapse of years the island rises above water, 

 the detritus of marine plants liaises it still more, and the 

 virgin soil is speedily fecundated by seeds which the winds, 

 birds, and currents carry thither. Soon after man comes 

 to cro^\Ti the handiwork of nature by raising dwellings on 

 the ruins of those of myriads of unseen beings. Then a 

 king arrives, who sits proudly upon his throne, amidst this 

 mass of skeletons of Polypi abandoned by the sea. 



Two of the most celebrated travellers of our epoch, 

 Forster and Pdron, think that these madrepore reefs and 

 islands are formed with extraordinary rapidity, and that a 

 few years suffice to materially change the depths of the 

 sea, and strew Avith dangerous rocks and impassable barriers 

 tracts of the ocean in which, but a little while previously, 

 navigators sailed in safety. These new lands sometimes 

 spring up with such celerity as to baffle all nautical science. 

 One of the straits in the approaches to Australia, Avliich a 



