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The marine fauna of Low Isles was surveyed by the Great Barrier Reef Expedition of 1928-9. A cyclone in 1950 caused damage to the island's coral, and an expedition visited Low Isles in 1954 with the prime objectives of assessing the extent of this damage, and of ascertaining the extent and nature of changes undergone by the island and its fauna and flora since 1929. It was found that the cyclone had caused great destruction to branching corals but that massive corals had, in most cases, survived. A heavy swell accompanying the cyclone had struck what is normally the lee side of the island, where a dense growth of fragile corals occurred. It is believed that the mechanical force exerted by breaking waves was the chief factor causing the destruction of corals. Coral rubble resulting from this destruction was being rolled about by waves on the seaward slopes of the island, and was hampering recolonization by hard corals. Soft corals, which appeared to have been unaffected by the cyclone, had spread, and appeared to be competing with hard corals for the available substratum. Alterations in the topography of habitats investigated by the 1928-9 expedition were observed. Some of the shingle ramparts had increased in size, and shingle was encroaching on many of the moats. The mangrove area had increased in extent. No marked changes in the faunistic composition of the fauna generally had occurred since 1929. However, direct comparison of the results of the 1928-9 expedition with those of the present survey proved difficult. In order to provide a basis for future surveys of the fauna, attempts were made to separate a large number of distinctive habitats, and to list the species found within each of these habitats. The relative abundance of each species found in each habitat was noted, and the general ecology and biogeography of the commoner animals investigated.

1. In the intact conscious dog, caerulein causes emesis and evacuation of the bowel. The mean effective dose by the intravenous route is 0.4-0.5 jig/kg, and by the subcutaneous route 3-4 jg/kg. 2. The gall bladder in situ or as an isolated preparation is highly sensitive to caerulein. A few ng/kg injected intravenously are sufficient to stimulate the gall bladder in situ and less than 1 ng/kg per min is effective when infused intravenously. The isolated gall bladder is contracted by caerulein in concentrations as low as 0.03-2 ng/ml. Krebs solution. There is no tachyphylaxis but, generally, a good dose-response relationship. Hence the gall bladder, especially that of the guinea-pig, appears to be very suitable for the bioassay of caerulein and related peptides. 3. In situ, the musculature of the gastrointestinal tract is also highly sensitive to caerulein. Doses as low as 1-5 ng/kg, administered intravenously, have a spasmogenic action on jejunal loops of the dog, and slightly larger doses contract the small intestine of the cat. The stomach and the large intestine seem to be somewhat less sensitive to the polypeptide. Caerulein has a considerable spasmogenic action on the rat pylorus but relaxes the sphincter of Oddi of the guinea-pig. 4. Isolated preparations of the gastrointestinal tract are relatively insensitive to caerulein and tachyphylaxis occurs readily.5. Blockade with atropine produces different effects in different intestinal segments and in different animal species. The spasmogenic action of caerulein on the gall bladder is atropine-resistant. 6. The effects of caerulein are -similar to those of cholecystokininpancreozymin in the organs tested in situ or as isolated preparations. Caerulein, however, is always more potent than cholecystokinin-pancreozymin, even on a molar basis. Compared with caerulein, human gastrin I has negligible activity. 7. The possible use of caerulein in cholecystography is discussed.In a preceding paper the actions of caerulein on the systemic arterial blood pressure of some common laboratory animals were reported