ANTARCTIC ZOOGEOGRAPHY 359 



On the northern continents, the winter is rendered excessively cold by the radia- 

 tion from a large area of land into a clear sky, nor is it moderated by the warmth- 

 bringing currents of the sea; the short summer, on the other hand, is hot. In the 

 Southern Ocean the winter is not so excessively cold, but the summer is far less 

 hot, for the clouded sky seldom allows the sun to warm the ocean, itself a bad ab- 

 sorbent of heat ; and hence the mean temperature of the year, which regulates the 

 zone of perpetually congealed under-soil, is lowJ 



From this characterization and the preceding sketch of climatic 

 environment, it will be seen that there is nothing in the south to com- 

 pare with the highly diversified terrestrial flora and fauna of the north 

 polar regions. Lacking are the equivalents of the Arctic tundra 

 plants, the flowers which bespangle moist, snow-free meadows during 

 the short but warm summer. Lacking, too, are the myriads of ephem- 

 eral insects, the land birds, the reindeer, musk oxen, polar carnivora 

 and rodents, which penetrate to the northernmost land projections 

 of the globe. 



Another contrast is apparent in the relationships of the respective 

 higher faunas of the two areas. In the Arctic most elements of the 

 vertebrate life are, as might be expected, closely related to forms 

 found within the adjacent temperate belt; but the greater proportion 

 of the higher animal life in the far south gives the impression of strong 

 endemism. The penguins, which have no counterpart in northern 

 regions, the four extremely well-marked genera of truly Antarctic 

 seals, the one genus, and perhaps more species, of cetaceans which 

 are said to be peculiar, well exemplify this distinctive character. 



Theory of Bipolarity 



Any consideration of Antarctic zoogeography could hardly omit 

 at least a brief review of the time-honored theory of bipolarity, 

 originally suggested by Theel in discussing some of the deep-sea 

 invertebrates of the Challenger expedition. The hypothesis was re- 

 stricted to the marine faunas of extratropical regions and particu- 

 larly to those of the Arctic and Antarctic. It took into account not 

 so much an admitted general resemblance between the two polar faunas 

 as an alleged identity involving large numbers of marine organisms 

 occurring in both polar areas and not found in the intervening tropics, 

 even though in deep water the temperature conditions remain the same. 



Pfefifer,^ who with Sir John Murray,^ strongly advocated the 

 essential truth of the theory, interpreted the evidence to mean that 

 numerous species occurring in the higher latitudes of both hemi- 



' Charles Darwin : Journal of Researches into the Natural History and Geology of the Countries 

 Visited During the Voyage of H. M. S. Beagle round the World, London, i860, p. 249. 



* Georg Pfeffer: Uber die gegenseitigen Beziehungen der arktischen und antarktischen Fauna, 

 Verhandl. Deuisch. Zool. Gesell., Vol. 9, 1899, pp. 266-287. 



9 John Murray: On the Deep and Shallow-Water Marine Fauna of the Kerguelen Region of the 

 Great Southern Ocean, Trans. Royal Soc. of Edinburgh, Vol. 38, 1896, pp. 343-500. 



