THE BIOLOGY OF THE FUNAFUTI ATOLL AND REEF FORMATION. 141 



The same portion of the platform, and specially its slope oceanwards, is rendered 

 pitted and uneven by innumerable cavities, the homes of echinoids ; these animals 

 having apparently made the excavations for their dwellings. To what extent 

 destruction of the reef rock by these agencies is going on was not ascertained, but in 

 course of time it must be considerable. Indeed, were it not for the Lithothamnion, 

 localities such as the ocean platform of the Island of Funafuti, where there is so little 

 other growth, would be undergoing decided diminution. 



In view of the fact that Darwin and others bring certain fishes and tlie Holothuroidea 

 under the category of coral destroyers and mud-producers, some attention was given 

 to these animals, although there exists nowhere on the atoll a sand fine enough to be 

 even compared with inud. In regard to the fishes, no conclusive evidence for or against 

 their coral- eating habits was obtained beyond the fact that although a large number 

 of kinds were watched in the neighbourhood of coral, in no instance were they seen to *V^_ 



browse on it. Numerous small scratches, however, on the Lithothamnion, rendered 

 visible by the removal of the crimson surface layer and consequent baring of the white 

 calcareous substance below, were thought to have been caused by teeth of fish feeding 

 on this calcareous alga. In the case of the Holothuroidea, investigation proved that 

 these animals do not live on coral or on either calcareous or any other seaweed, unless 

 the latter be microscopic. Certain species of them were always found in large 

 numbers in the shallow pools of the platforms, which were entirely destitute of any 

 living organisms visible to the naked eye. They were, however, continually feeding 

 on the coarse sand, which, as was seen from the sausage -shaped excrements, left them 

 (so far as could be ascertained by the naked eye examination) in the same condition 

 as that in which it entered. It is then evident that purely microscopic organic 

 particles, contained in the sand, furnish their food supply. The very large specimens, 

 up to 2 feet in length, which were procured by spearing, invariably ejected the 

 greater part of their alimentary tract when brought into the canoe. It was always 

 observed that this tract contained the ordinary fine gravel of the lagoon bottom. 



The only true destroyer of coral, and its great competitor, is the Lithothamnion. 

 It kills by smothering. This destruction of the coral, however, does not mean the 

 destruction of the reef, but quite the reverse ; for before the coral can enter into 

 the formation of the reef rock, it must be killed. In its living state and by itself the 

 coral cannot form a solid mass ; dead, however, its skeleton supplies valuable material 

 which the Lithothamnion unites together with remains of other calcareous organisms " 



to form the reef rock. 



(6) Experiments on the Rate of Growth of Coral, Lithothamnion and Halimeda. 



The difi&culties which present themselves in regard to these experiments, especially 

 to one who attempts them for the first time, are, to say the least, disheartening. 

 They are due not only to the lack of experience, but also to the want of suitable 



