68 ON CORAL REEFS AND ISLANDS. 



accurately measured from month to month. Two such pins in 

 the surface of an Astraea, would in the same manner, by the en- 

 larging distance between, show the rate of increase in the cir- 

 cumference of the hemisphere; or if four were placed so as to 

 enclose an area, and the number of polyps counted, the numeri- 

 cal increase of polyps resulting from budding, might be ascer- 

 tained. It is to be hoped that some of the foreign residents at 

 the Sandwich, Society, Samoan or Peejee Islands will take this 

 subject in hand. There are also many parts of the West Indies, 

 where these investigations might be conveniently made. 



