130 SOME WONDERS OF THE SEA. 



Many of the common Madrepores look very much as 

 if a vast number of the Mushroom Madrephylles had 

 been moulded into a convex mass, very much diminished 

 in size, and viewed through the pseudoscope, so that each 

 individual appears concave instead of convex.' 



Those, however, which are the most conspicuously 

 apparent in their submarine office are the beautiful 

 species which are here represented by the Plantain Mad- 

 repore (Madrepora plantaginea), so common in drawing- 

 room ornaments. These are the formers of the so-called 

 Coral Islands, and in spite of the small size of the living 

 polypes, and the minuteness of the calcareous particles 

 which they deposit, they actually alter the surface of the 

 globe so rapidly that important changes are made 

 within the compass of a single human lifetime, and the 

 physical geography of enormous tracts is entirely 

 transformed. 



In the first place, it must be understood that not even 

 the apparently inorganic film of the Madrephylles can 

 exist at any great depth of water, a certain amount of 

 light and warmth being necessary for them. When we 

 come to the better organised beings which produce the 

 true Madrepores, we find that a larger supply of light 

 and warmth is required, and that in consequence they 

 are brought more within the scope of personal observa- 

 tion. Moreover, the water is so translucent in such 

 localities that objects are clearly discernible at a depth of 

 forty or fifty feet. 



The whole surface of the Madrepore is covered with 



