ANTARCTIC ZOOGEOGRAPHY 367 



parts per million of water. The vast quantity of living substance in 

 the ocean is therefore built up from materials present in exceedingly 

 dilute solution, and the solution is dilute just because organisms 

 are incessantly using up the materials. But sea waters of low tem- 

 perature are favorable to a high gaseous content and are, moreover, 

 richer in the mineral nitrogenous compounds (ammonia, nitrites, and 

 nitrates) than are temperate or tropical waters. The waters of the 

 Antarctic, for example, contain on the average 0.5 per million of 

 nitrogen in the above forms, as compared with an average content of 

 0.15 per million in the North Atlantic and o.io in equatorial seas. 

 The plankton, and especially the phytoplankton, is therefore far 

 more abundant in polar than in warm oceans, and especially so in 

 shallow coastal waters of relatively low salinity. Owing to the angle 

 of incidence of a low sun and the dense screen of plankton, the photic 

 zone is thin. Growth is mostly restricted to the upper hundred 

 fathoms, with much reduced reproduction in the lower strata. The 

 microscopic plant forms, obtaining their food substances directly from 

 mineral sources, combine the simple nitrogenous salts with carbo- 

 hydrate resulting from the synthesis of water and carbonic acid under 

 the action of sunlight and produce proteids. This protophytic type 

 of growth is the basis of the existence of all animal organisms, from 

 tiny copepods to whales. 



But the abundance of nutritive substance in cold sea water, which 

 has been so greatly stressed by oceanographers, does not alone account 

 for the abundance of life. The crux of the matter lies in the vastly 

 larger number of coexisting generations. Loeb's^^ illuminating 

 experiments upon larval sea urchins demonstrate that the tempera- 

 ture coefficient of duration of life differs enormously from the tem- 

 perature coefficient of development. From this he concludes that 

 the chemical processes which determine development are altogether 

 different from those which cause old age and natural death. Accord- 

 ing to the formula deduced by Loeb, if the longevity of an echinoderm 

 larva at T° C. is equal to D, its length of life at a temperature of 

 T-n degrees will equal 2"^ D. In other words, a lowering of the tem- 

 perature n° C. multiplies the length of Hfe by 2^". When the tem- 

 perature coefficient of longevity at 10° C. equaled 1000, Loeb found 

 the coefficient of development to be only 2.8. With regard to the 

 extraordinarily rich plant and animal life in the surface waters of the 

 cooler seas, he applied the principle as follows: Within the range of 

 the experiments, reduction in temperature of 10° C. increases longevity 

 a thousandfold; reduction of 20° C. increases longevity a millionfold; 

 but the corresponding periods of development are multiplied by only 

 about three and nine, respectively. From this it follows that at 



32 Jacques Loeb: Uber den Temperaturkoeffizienten fiir die Lebensdauer kaltbliitiger Thiere und 

 iiber die Ursache des natiirlichen Todes, Pflugers Archiv filr die Gesammte Physiol., Vol. 124, 1908, 

 pp. 411-426. 



