OF THE KERGUELEN EEGION OF THE GREAT SOUTHERN OCEAN. 491 



York fauna with the fauna of the deep water of the Kerguelen Region, we find that the 

 same groups on the whole predominate in the deep sea as predominate in the shallow 

 water of the Kerguelen Region. If we compare the shallow- water fauna of the Kerguelen 

 area with the fauna procured in the tropics between 100 and 500 fathoms, we find that 

 the groups present in this deeper area of the tropics resemble much more the shallow- 

 water Kerguelen fauna than is the case with the shallow-water fauna of the tropics. A 

 very large percentage of the Foraminifera found at the mud-line oft" Kerguelen in 100 

 fothoms are found within the tropics and indeed all over the world in the mud at similar 

 or greater depths. 



The quantity of carbonate of lime secreted by marine organisms is determined by the 

 temjiprature of the water in which the animals live, and therefore chiefly by chemical 

 rather than by physiological conditions. When neutral ammonium carbonate is added to 

 sea-water at a temperature of 80° or 85° F., the lime salts present — other than carbonate 

 — are rapidly decomposed and thrown out of solution, giving down at once a precipitate 

 of carbonate of lime with the properties of aragonite. When a similar experiment is 

 carried out at a tem2:»erature of 40° or 45° F., the precipitate of carbonate of lime separates 

 out very slowly, and in doing so takes the form of calcite. The secretion of lime salts, 

 such as carbonate and phosphate, is eftected by the soluble salts of lime in the sea-water 

 forming insoluble compounds with the efiete products (principally ammonium carbonate) 

 set free by the metabolism of the organism. The warm waters of the tropics contain 

 ammoniacal salts in much greater abundance than the cold waters of the polar regions. 

 To this fact may be attributed the coral reefs, large shells, and other massive carbonate 

 of lime structures within the tropics, and the very feeble development of carbonate of 

 lime shells and skeletons in the cold waters of the Antarctic, Arctic, and deep sea. A 

 parallel condition of matters with reference to the secretion of cai-bonate of lime occurs 

 among pelagic organisms. In the tropics numerous species of Pteropods and other 

 Molluscs with carbonate of lime shells are present in the surface waters of the ocean. 

 These species gradually disappear as the cold waters of the polar regions are approached, 

 and in the Arctic and Antarctic are replaced by naked species and one species of minute 

 thin-shelled Limacina. The pelagic Foraminifera are represented in tropical waters by 

 about twenty species — some of them, like Pidvinulina and Sphceroidina, having very 

 thick shells. In the waters of the northern and southern temperate zones a lesser 

 number of species is present and the shells are not so massive. In the cold waters of the 

 Arctic and Antarctic only two small dwarfed species are present. A similar distribution 

 holds with respect to the unicellular Algte ; the calcareous Coccospheres and Rhabdo- 

 spheres, while abundant in the warm waters of the tropics, are absent from the surface 

 waters of the polar regions. 



It is well known that in Palaeozoic and even later geological times massive coral 

 reefs flourished within the Arctic circle, and even in Tertiary times massive shells were 

 formed in both the Arctic and Antarctic areas which could not have been secreted were 

 the waters of the polar regions as cold as they are at the present day. It has sometimes 



