554 DR. F. W. JONES ON OROWTH-FORMS [JlUie 18, 



continued, for all those corals tha,t live in rock-pooLs are immune 

 to the influence of the fresh water accumulated during a heavy- 

 downpour at low tide. When the tide is low and the rainfall is 

 heavy, the rock-pools undergo a remarkable degree of freshening, 

 and so too does the lagoon if the weather is calm and the rainfall 

 is a sudden one. 



In the lagoon the surface specific gravity may fall to 1021, but 

 I have never found it lower, and the perpetual churning 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 Feb. 13th, 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. 



On Feb. 24th, after -5 of an inch of rain had fallen in half an 

 hour, the sp. gr. was 1023, and the temperature was 82°-7. 



On Jan. 4th, after 7-4 inches had fallen in the passed 12 hours, 

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



The sui-face 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 lise 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 coinci- 

 dence 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 ranked amongst the enemies of corals, 

 and Darwin classed some fish and the myriad Holothuridse 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 factors in atoll formation is great, but 

 it is not as destroyers of living coral that they fulfil their r61e, 

 for the coral that they took in at their mouths was ali-eady dead. 



From the study of the life of the colony in different sur- 

 roundings, and from the repair of injury, and death, in unsuitable 

 habitats, I think it will be seen that the number of the true 



