Walther — Origin and Peopling of the Deep Sea. 55 



Art. VIII. — The Origin and Peopling of the Peep Sea / by 

 Prof. Dr. Johannes Walther.* 



The ocean covers two-thirds of the earth's surface. Five 

 continents and numberless islands rise out of it and divide the 

 ocean into separate parts, but nowhere is there to be found a 

 barrier which can permanently prevent the intermingling of 

 the waters. The ever-moving and restlessly intermingling sea 

 water shows therefore a very marked uniformity in its chemi- 

 cal composition. At Pole as at Equator, in the upper surface 

 as in the depth of the sea, the salt content amounts to about 

 3*5 per cent and the proportion of chloride, sulphate and car- 

 bonate remains on an average the same in brackish bays or at 

 the mouths of great rivers. 



It is known that the astronomical position of the earth with 

 relation to the sun causes marked climatic zones which are 

 arranged in almost parallel girdles perpendicular to the earth's 

 axis, and we notice on the mainland a steady decrease of 

 organic life the farther we proceed from the warm equatorial 

 region toward the cold polar circle. 



The surface of the sea is also girt about with climatic zones, 

 which, corresponding to the continental temperature belts, 

 reach from one coast to the other. In the equatorial region, 

 the water has a warmth of 30° (J.; toward the poles its tempera- 

 ture sinks, and since salt water first freezes at — 2*5° C, the 

 polar shores are laved by very cold water. One would then 

 believe that hand in hand with this decrease in temperature a 

 diminishing of the organic life in the sea would be noted, but 

 quite the opposite is the case. In the polar seas, the plankton 

 net is filled with a veritable jelly of floating plants and ani- 

 mals which serve as food for the numberless fish swarms and 

 the giant whales, and if the naturalist has drawn the dragnet 

 over the sea bottom, it is filled with a vast multitude of echino- 

 derins, mollusks and crabs. 



In order to understand this striking fact, we must keep 

 clearly in mind that almost all sea animals belong to cold- 

 blooded forms whose own warmth changes as the temperature 

 of their surroundings changes. Pecten islandicus thrives as 

 well in a sea temperature of zero centigrade as does Pecten 

 jacobceus in 10° C, or as the tropical Pecten sanguinolentus 

 in the water of the coral seas with a temperature of 25° C. 

 Consequently, the absolute degree of temperature is of no influ- 

 ence on the richness in forms of the sea fauna. 



We know that the climate of a continent undergoes very 



* Translated from the German (Naturwissenschaftliche Wochenschrift, 1904) 

 by Clara Mae LeVene, Peabody Museum, Yale University. 



