368 



POLAR PROBLEMS 



0° C. many more successive generations of the same species must exist 

 contemporaneously than at io° or 20°. 



Such generaHzations are based upon very hmited but undoubtedly 

 sound data. Their extension offers a peculiarly fruitful field for re- 



Fig. I — Map of the fish regions of Antarctic and sub-Antarctic waters, after Regan (paper cited 

 above in footnote 2). Scale, about 1:120,000,000. 



The mean annual surface isotherms of 6° C. ( ) and 12° C. ( ) as calculated by G. 



Schott respectively represent the northern limits of the Antarctic and sub-Antarctic zones. The Ant- 

 arctic zone includes the Glacial district (G), whose northern boundary is the extreme limit of pack ice 

 (---'-" -^ -~ ), and the Kerguelen district (K), comprising, in addition to Kerguelen, the Marion, Crozet, 

 and Heard island groups. The sub-Antarctic zone includes the Magellan (M) and Antipodes (A) 

 districts. 



search of a type which might be readily conducted in the ship or shore 

 laboratories of a modern polar expedition. 



In tropical seas the predominating groups of marine invertebrates 

 are those which secrete large quantities of calcium carbonate, com- 

 prising such forms as corals, macrura, brachyura, anomura, lamelli- 

 branchs, gasteropods, etc. In the Antarctic seas these are largely 

 replaced by organisms containing little lime, among which may be 



