690 OCEANOGRAPHY 



starch which prevail in terrestrial vegetation. This is doubtless the 

 original source of the oil which appears in marine fishes, birds, and 

 mammals in such abundance. 



Many interesting physiological problems are suggested by the 

 study of oceanography. In the ocean there are very few warm- 

 blooded and air-breathing animals, and we have to deal chiefly 

 with cold-blooded animals, the temperature of whose blood and 

 bodies rises and falls with that of the water in which they live. In 

 the tropics marine animals for instance, a Copepod or Amphipod, 

 pass all their lives in water with a temperature of 80 to 90 F. 

 In the polar seas a quite similar animal passes the whole of its life 

 in water below the freezing-point. In these cases it is evident that 

 the metabolism of the warm-water animal is much more rapid than 

 that of the cold-water one; it reproduces its kind much more fre- 

 quently, and its individual life is shorter than in the case of the cold- 

 water animal. All chemical and all physiological changes take 

 place much more rapidly in warm than in cold water. In cold sea- 

 water there is much albuminoid ammonia, in warm water regions 

 much saline ammonia, which fact points to more rapid change in the 

 warm water of the ocean. By remembering these conditions we may 

 account for the fact that genera and species are much more numer- 

 ous in the warm water, while on the other hand the species are few, 

 but the individuals of a species are enormously greater, in the 

 cold water. The animals in a tow-net from the tropics are most 

 probably not more than a few weeks old, whereas a similar tow-net in 

 the polar waters captures animals, some a few weeks old, and others, 

 it may be, years of age. It seems certain that the warm tropical 

 waters are the most favorable for vigorous life and rapid change, 

 and here the struggle for life is most severe, and the evolution of 

 new species much more frequent, than in the cold waters of the 

 poles or the deep sea. In this direction we must look for an explana- 

 tion of the so-called bipolarity in the distribution of marine organisms. 



A great characteristic of organisms in warm tropical waters is 

 the very large quantity of carbonate of lime they secrete from the 

 ocean. This is evident, not only in the massive coral reefs, but also 

 in the abundance of calcareous organisms in the plankton of the 

 tropics like coccospheres, Globigerinae, and mollusks. All these 

 lime-secreting organisms become less abundant as we approach the 

 poles, or descend into the deep sea. In the warm water the carbon- 

 ate of lime is deposited in shells and skeletons as aragonite, but in 

 the cold water it is deposited much more slowly, and in the form 

 of calcite. This shows that when we find a limestone rock with 

 abundance of fossil-shells we may assume that it was laid down in 

 a warm sea where the temperature approached 70 or 80 F. It 

 may be safely asserted that at the present time lime is being ac- 



