130 CORAL AND ATOLLS 



of the waves prevents any marked evidences of freshening being 

 observable near shore. Outside, in the ocean itself, there is 

 such complete mixing of the waters at the surf-beaten barrier 

 edge that it is not likely that the influence of the rain could 

 be recognised. 



On February 13, 1906, when "28 of an inch of rain fell 

 in ten minutes, the sp. gr. of the surface of the lagoon 

 dropped from 1027 to 1021, and the temperature was 77°*5 

 Fahr. 



On February 24, after -5 of an inch of rain had fallen in 

 half an hour, the sp. gr. was 1023, and the temperature 

 82°- 7 Fahr. 



On January 4, after 7 '4 inches had fallen in twelve 

 hours, the sp. gr. was 1021, with a temperature of 78° 

 Fahr, 



The surface of the fish-pond, which is a pit about 15 feet 

 square, will show a reading as low as 1015 three days after a 

 downfall of 5 inches in twelve hours, although its waters rise 

 and fall with the tides, and the outside ocean shows no change 

 after the downpour. 



It is therefore mainly wave-action that obliterates the 

 effects of tropical showers in freshening the salt water, and 

 the coincidence of great rainfall and dead calm must be very 

 complete, and very lasting, before anything approaching a 

 general destruction of corals could result. 



Many animals have been ]-anked amongst the enemies of 

 corals, and Darwin classed some fish and the myriad Holo- 

 thuridse as causes of coral death. In this atoll Dr. H. 0. Forbes 

 has described the '' Scarus feeding in the surf on the living 

 coral," and has asserted that the Kakatua and other lagoon 

 fish actually eat the living polyps. The observation has been 

 several times doubted, and, so far as this atoll is concerned, it 

 is certainly an error. There are no fish and no Holothurids in 

 Cocos-Keeling lagoon, or on the barrier, that eat coral when it 

 is living, though many different classes of animals contain great 

 quantities of dead coral in their alimentary canals. The 

 importance of the coral-haunting fish and the Holothurids as 



