54 LIFE IN THE SEA [CH. 



seas within the Arctic and Antarctic Circles we should 

 find still greater dissimilarity. There would indeed 

 be a general kind of resemblance between the two 

 faunas and floras, but only in the cases of one or two 

 migratory birds and whales would the same species of 

 organism occur in both circumpolar areas. Speaking 

 quite generally, the further apart on the face of 

 the earth two sea areas are, the greater will be 

 the difference between their contained life, because 

 the further apart they are the greater, generally, 

 will be the- difference of physical conditions. Very 

 few animals or plants are truly cosmopolitan. 



It has been the province of systematic biology to 

 investigate and record the range of geographical 

 distribution of each species of animal and plant, and 

 so far the result has been the accumulation of a mass 

 of detail which possesses the very slightest interest, 

 and out of which it is not easy to extract general 

 laws or regularities. We may, however, try to indicate 

 a few prominent facts. Marine mammalia the 

 whales, seals, and some other species of warm-blooded 

 animals, are most abundant within the two Polar 

 Circles, and the larger sea-birds inhabit the cold and 

 temperate seas, and are least abundant within the 

 tropics. The marine and anadromous fishes of the 

 sub-polar and temperate seas are far more abundant, 

 and are generally larger than those of the tropics, 

 but the variety of species is not so great as in 



