182 FUNCTIONS AND INSTINCTS. 



means of still increasing its coral palace, and 

 thus it goes on till it has formed a habitation, 

 not for itself, but, as I said, for man, in the 

 midst of the world of waters. 



One of their most celebrated historians, Amou- 

 reux, thus expresses himself upon this part of their 

 history. " Some, by their union or aggregation, 

 form a long narrow ridge or reef, which extends 

 uninterruptedly several degrees, opposing an im- 

 movable rampart to the great currents of the sea, 

 which it often traverses, the solidity and magni- 

 tude of which increases daily. Sometimes this line 

 of madreporic rocks assumes a circular form ; the 

 polypes that inhabit it gradually elevate their 

 rocky dwelling to the surface of the sea, working 

 then in a sheltered basin, they by little and little 

 fill up its voids, taking the precaution, however, 

 to leave in the upper part of this impenetrable 

 wall openings by which the water can enter and 

 retire, so as to renew itself, and furnish them 

 with a constant supply of their aliment, and of 

 the material with which they erect their habi- 

 tation." 



They do not always elevate their polyparies 

 from the depths of the waters to their surface, 

 some extend themselves horizontally upon the 

 bottom of the sea, following its curvatures, decli- 

 vities, and anfractuosities, and cover the soil of 

 old ocean with an enamelled carpet of various and 

 brilliant colours, sometimes of a single colour as 



