Eevieivs—Tlte Atoll of Funafuti. 223 



1 inclies which killed the Zithoth amnion, then living in the zone now 

 marked as 'dead' Zithothamnion (0.3). At the same time the 

 Hurricane beaches were pushed further back. 



In the future, probably, the lagoon will be filled up by the 

 .growth of Halimeda, and the islets will be gradually levelled by 

 marine denudation. Against this destruction may be set a present 

 upward movement of the land, as well as a very slowly widening 

 rim of Zithothamnion. But another levelling factor is the subaerial 

 <lenudation caused by the torrential tropical rains. 



The biology of the reef-forming organisms, by Alfred E. Finckh, 

 forms the subject of the next section. 



Three main marine biological zones are noted, namely : (a) that 

 of living Lithothamnion ; (b) a zone of less active growth between 

 the former zone and that line which marks the limit of the waves at 

 low-water spring-tides; (c) the lagoon in which occur all forms 

 found outside and in addition Ifeliopora ccerulea. The bottom of 

 the lagoon is formed mainly of Halimeda sand. 



The organisms of the reef now forming, in the order of their 

 importance, are as follows : (a) Zithothamnion, [h) Halimeda, 

 (c) Foraminifera, (d) Corals and Hydrocorallines. Zithothamnion 

 occurs in three forms, two encrusting and one frondose. Halimeda 

 is the most important organism in the lagoon. The chief use of 

 the corals and hydrocorallines in reef-building is to form a base- 

 work on which Lithothamnion can grow. There are five main 

 groups of corals and hydrocorallines occurring as follows in order 

 of importance in reef-building : (a) Heliopora cmndea, (6) the 

 Millepores, (c) the Porites family, [d) Bladrepora, (e) Pocillopora. 



Mention is made in this section of the enemies of the reef-formers. 

 Excluding Zithothamnion, which, by its cementing action, constructs 

 the reef more than it destroys it by its swamping effects on the other 

 reef-forming organisms, the chief enemies are two Gephyrean 

 worms, one of which is a Sipuuculoid (As2ndosi2Jhon) . Holothuroids, 

 supposed by Darwin to be destructive to the reef- formers, are 

 acquitted of this charge, for it was found that their food was entirely 

 composed of microscopic organisms. 



A series of experiments are next described, carried out to ascertain, 

 if possible, the rate of growth of the reef-forming organisms. The 

 lack of experience in such experiments, their novel character, and 

 the consequent absence of suitable apparatus caused the results to be 

 somewhat vague. The situation of the camp precluded experiments 

 upon the branching form of Zithothamnion and upon Heliopora. 

 Four methods were employed, namely, weighing at intervals, 

 measuring at intervals ai-eas marked out on the coral by glass pins, 

 measuring the distance of approaching portions of a coral and noting 

 how long they took to meet, and causing the organism to grow 

 through a hole in a board. Many of these specimens are now 

 exhibited in the Geological Department of the British Museum, 

 South Kensington. Experiments were also made on the amount of 

 exposure to the sun needed to kill the various reef-formers. Less 

 than two hours sufficed in the case of all except Porites. 



