CHAPTER II. 



ISLAND AND REEF BUILDERS. 



T!)ASSING from the comparatively simple one- 

 A celled animals we have been considering in the 

 last chapter, the Corals next attract our attention as 

 individually small, but extremely expert, builders and 

 architects, producing the most graceful and varied 

 structures, some frail and almost lacelike in appear- 

 ance, others extraordinarily massive, yet covered with 

 exquisite tracery. 



The temperature of the sea round the shores oi 

 Great Britain to-day is not sufficiently high to sup- 

 port the life of the reef-building corals, although from 

 the fossil remains preserved in various strata there 

 is abundant evidence to prove that in a past epoch 

 our shores were lapped by the waves of a tropical sea 

 beneath whose surface coral life luxuriated. The reef- 

 forming corals can only flourish in a warm sea, the 

 temperature of which never falls below 68 Fahrenheit 

 and may rise to 86, and which is highly aerated, free 

 from sediments, and containing an abundance of minute 

 living organisms which constitute the food of the coral 

 animals, or polyps. Also the reef-builders do not appear 

 to be able to live at such great depths as their simple 

 solitary relations, probably because the temperature of 



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