1898.] Funafuti, Rotuma and Fiji. 487 



water can be passed on by diffusion, or in some other way, from 

 polyp to polyp. At spring tides at Rotuma, parts of the Heliopora 

 and Millepora clumps in the boat channel were exposed for four 

 hours. I examined them when they were thus exposed, and also 

 on my return from the reef after the tide had turned, when they 

 were just covered, and found that all the polyps of the Heliopora 

 were expanded fully and those of the Millepora partially so. I 

 found, too, that true corals also tended to partially expand on 

 being immersed again. 



The effect of rivers is due more to the sediment which they 

 carry down in suspension, than to the freshness of their water. 

 Yet at the chief mouth of the River Rewa, the bottom is hard 

 from the edge of the reef for some distance up the river, and 

 corals are absent from the whole of the inner part of this area. 

 The streams on the east of Taviuni vary enormously in size and 

 very quickly rim down ; the reef outside, where it exists, is well 

 formed and covered entirely above the low water level by Litho- 

 thamnion. The fresh water, being lighter, must spread out in a 

 sheet, when it meets the ocean, and yet the reefs, in the neigh- 

 bourhood of the Rewa, Navua, Penang and Lambasa Rivers, are 

 all well developed and awash at low tide. 



SECTION V. 



The Rate of Growth of Corals. 



I had an opportunity of assisting in cleaning the chain of a 

 buoy, which had been down in Levuka Harbour, Fiji, for one year 

 and ten months. The first, or upper, fathom of chain had no 

 corals, but was covered completely with Tunicata, bivalve Mollusca 

 and sponges. In the next two fathoms I obtained six different 

 coral growths which with their weights were as follows : — 



1. Turbinaria 45 grains. 



2. Pocillopora 41 and 13 grams. 

 1. Heliastraea 34 grams. 



1. Madrepora 20 grams. 



1. Galaxea Two corallites weighing nearly 1 gram. 



A rusty iron chain is not likely to be a good foundation for 

 the corals to fix themselves on, so that these growths in this space 

 of time are most remarkable. 



