XV. 



A COMPARISON OF THE ARCTIC AND 

 ANTARCTIC MARINE FLORAS. 



THE general similarity, and in many cases the identity, of species 

 of marine organisms in the Arctic and Antarctic regions have led to 

 a very interesting analysis of the facts, and an interpretation of them 

 by Dr. John Murray in the Summary of the Results of the Challenger 

 Expedition. His comparison is based mainly on the marine animals, 

 but he points out also, as confirming his argument, that the plankton 

 Algae are in many cases identical. ' Rhabdospheres are found only 

 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 Algae 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.' His 

 theoretical explanation of this remarkable fact in the distribution of 

 organisms is of the highest interest. Speaking of carboniferous times, 

 he holds that 'the surface temperature of the sea could not well have 

 been less than about 70 F., and the same temperature and the same 

 marine fauna prevailed from equator to poles, the temperature not being 



higher at the equator In early Mesozoic times cooling at the 



poles and differentiation into zones of climate appear to have commenced, 

 and temperature conditions did not afterwards admit of coral reefs in 

 the polar area, but the colder, and hence denser, water that in 

 consequence descended to the great depths of the ocean carried with 

 it a large supply of oxygen, and life in the deep sea became possible 

 for the first time. There have been many speculations as to how a 

 nearly uniform temperature could have been brought about in sea-water 

 over the whole surface of the earth in early geological ages, as uell as 



88 



