480 Mr Gardiner, The Coral Reefs of [Mar. 7, 



then drawn by Murray that "when coral plantations build up 

 from submarine banks, they assume an atoll form owing to the 

 more abundant supply of food to the outer margins and the 

 removal of dead coral rock from the interior portions by currents 

 and the action of the carbonic acid dissolved in the water." With 

 the latter statement we are not at present concerned, but that the 

 more abundant supply of food to the outer margins causes these to 

 grow up quicker, I am inclined to doubt. I have already stated that 

 I do not consider that the Madreporaria, together with Heliopora 

 and Millepora, are the chief factors in the formation of coral reefs 

 within shallow depths, as Murray seems to infer, but at the same 

 time I do not deny to them a very considerable influence. 



At Funafuti I did not have many opportunities of examining 

 the " auftrieb " outside the reef, and none in the early morning, 

 when it is always most abundant near the surface. On the few 

 occasions that I used my nets outside the atoll I found that the 

 deeper I sank them into the water, up to 50 fathoms, the greater 

 were the quantity and variety of pelagic animals obtained. IN' ear 

 the surface and down to 25 fathoms the nets were useless, and on 

 no occasion did I find, even at 50 fathoms, a luxuriant pelagic 

 fauna. This proves nothing, but it indicates that, at any rate 

 during the daytime, the fauna must sink down to very considerable 

 depths ; unfortunately I had neither the time nor the opportunity 

 to investigate depths below 50 fathoms. In the lagoon, the 

 surface fauna, before daybreak, is generally very rich in the 

 pelagic larvae of Crustacea (especially the Phyllosoma), pelagic 

 Crustacea and Sagitta. There are usually found in addition 

 veliger and trochosphere larvae of the Mollusca, and larvae of 

 Tunicata, Chaetopoda, fishes and Echinodermata. Pteropoda, 

 especially of the genus Greseis, are occasionally very abundant, 

 while the remainder of the ' auftrieb " is almost entirely made up 

 of bits of green seaweed, dirt, etc. Before dawn, nets at 10, 15, 

 and 20 fathoms in the lagoon give only a few Sagitta, but a large 

 amount of sand, with bits of weed, etc. in suspension. After 

 dawn, the fauna for an hour can be followed down, as it sinks 

 from the surface, and is obtained progressively in the deeper 

 nets. At midday, even the deepest nets in the lagoon almost 

 failed to obtain any animals ; the whole fauna seemed to sink 

 until it lies in the layer of water which immediately covers the 

 bottom, as it was found, when a net was accidentally scraped 

 along the bottom, that with the dirt brought up there was a 

 decidedly rich fauna. Generally outside the atoll the fauna was 

 the same, but unicellular algae and Radiolaria are at times very 

 common. At Rotuma I fixed my " auftrieb " nets in the passages 

 of the reef to find out what animals were driven over the reef to 

 form the food of the corals on the reef-flat and in the boat 



