1456 
THE VOYAGE OF H.M.S. CHALLENGER 
Rklagic 
Fi>RAl(IMrKnA. 
Pki.aoic 
Moi.i.usca. 
M!< OK 
J'uidoxate ok 
I.iw» 
of the ocean. At the present day these Algae are the primary source of food for 
the majority of pelagic and deep-sea animals. Rhabdospheres are only found in the 
warmer waters of the ocean, but the Coccospheres abound in the northern and 
southern temperate zones ; in the Arctic and Antarctic zones these calcareous unicellular 
.\lgaj are replaced by species of Protococci which are identical in the two polar regions. 
.Many pelagic Diatoms of the Arctic and Antarctic are likewise identical. 
The pelagic Foraminifera are represented in the surface-waters of the tropics by 
about twenty species. These are replaced in the waters of the northern temperate 
and southern temperate regions by a lesser number of species possessing less massive 
shells ; only two dwarfed but identical species, Glohigemna dutertrei and Globigerina 
injlata, extend to the waters about the Arctic and Antarctic circles. 
Again there are numerous sjDecies of Pteropods in the tropical regions provided with 
calcareous shells of large size. These species gradually disappear from the surface as we 
approach the Arctic and Antarctic regions till the group is represented either by naked 
species or by nearly identical species of the minute thin-shelled Limacina in both the 
polar areas. Numerous other examples might be cited from other groups showing the 
close resemblance between the surface organisms of high northern and high southern 
latitudes. 
The above instances of the very slight development of carbonate of lime shells and other 
carbonate of lime structures in the cold waters of the polar regions are instructive 
when recalled in connection with the massive coral reefs constructed in the polar 
regions in Palaeozoic and even later geological times. The waters of these ancient 
oceans must have had a temperature of 65° or 70° F. at the poles, for it has 
been shown that the deposition of carbonate of lime is due to the secretion of 
carbonate of ammonia, one of the effete or waste products of marine animals, which, 
decomposing the soluble sulphate of lime in sea-water, produces insoluble carbonate of 
lime to form shells, its precipitation taking place with great difficulty and very slowly 
in cold water, but easily and very rapidly within the organism in water of a high 
temperature,' hence in the cold polar and deep-sea waters of our day no massive 
carbonate of lime shells or other structures are secreted by organisms. 
'I’he vegetation of the coal period implies over the whole globe an almost complete 
cfpiality in the distribution of light and heat at that epoch. Marine species indicate 
the same uniformity. The Arctic Ocean was a coral sea in carboniferous times. A massive 
conil — Lithostrotion — is common to Europe, the United States, and the Arctic regions. 
Pi'oductus sendreticulatus and Productus longispinus are found in the Andes of Bolivia 
' Murray and Irvine, On Coral Reefs and oilier Carlionate of Lime formations in Modern Seas, Proc. Roy. Hoc. 
pAiin., voL xvii. p. 90, 1889 ; see also Proc. Roy. Hoc. Edin., 1895, for paper on the Influence of Temperature on the 
Depoaition of Carbonate of Lime. 
