110 MADREPORES. 



trates the structure of the brain-stone, so called from 

 its outer surface resembling in its convolutions that 

 essential part of the human economy. Of the process 

 of forming this curious mass, a clear and correct idea 



SECTION OP MADREPORE. 



may easily be entertained. As in the sponge, 

 already described, the surface of the mass, and, of 

 course, all its sinuosities, were covered with a living 

 gelatinous film. When first deposited on the rock, 

 a minute nucleus was only thus covered ; but as the 

 creature grew, it went on building from its little 

 centre, depositing one stony particle after another, 

 and that as regularly and accurately as if it worked 

 by compasses and rule, until it attained the diameter 

 of one, two, or perhaps three feet. What wondrous 

 power has God conferred on the delicate tissue that 

 produces such fabrics ! 



But other marvels demand our attention. The 

 Pavonia lactuca, from the shores of the South Sea 



