of the Arctic and the Ant irctic Faun ><>. 3()3 



contains, may be Jivideil vertically into the three following 

 regions : — 



First: the surface-water, — the warmest of all the vertical 

 zones, with variations in warmth, with movement of the 

 water, with the inHuence of li^lit, and therefore with plant- 

 growth, with a terrigenous floor consisting of rock, gravel, 

 and sand. This region reaches, according to the locality, 

 from the surface to a depth of from 50-150 fathoms. The 

 expressions "surface-water" and "surface-fauna" are here 

 used as practically equivalent to " littoral z me "and "littoral 

 fauna." 



Second : the subsurface-water, — cool, without variations in 

 warmth, without light, without plant-growth; its Hoor lies 

 on the slope of the continents and is covered with terrigenous 

 mud. According to locality, this region reaches to a depth 

 of 600-1000 fathoms; its fauna consists only of the mud- 

 eaters, and is therefore economically dependent on supplies 

 from other regions, particularly on the assimilating flora and 

 fauna of the adjoining surface-water. The fauna of this region 

 resembles the fauna of the surface-water of higher latitudes. 

 Third : the deep water, the deep sea, — resembling the sub- 

 surface zone in its lack of variations of warmth, of ligtit, of 

 plant-growth, and water-movement ; its tloor is the bottom 

 of the ocean, and is covered with fine slimy ooze or clay of 

 pelagic origin ; its fauna is economically independent of that 

 of the coasts, because of the great distance between them, 

 but, on the other hand, it is depi^ndent on the pelagic 

 animals, whose dead bodies form its food-supply. Apart 

 from archaic or highly specialized forms, the fauna of this 

 region has an arctic character ; that is, it resembles the 

 surface-fauna of the highest latitudes. 



Disregarding for the present the nature of the ocean-floor, 

 and considering the water with reference to its temperature 

 alone, we have, first, a tropical warm water occurring only 

 as the surface-water of the tro[)ical zone ; second, a cool 

 subsurface-water, which, in the higher temperate Dues, 

 gradually passes over into the surface-water of a similar 

 temperature; third, a cold, deep water, which covers the 

 whole ocean-floor, and within the polar zones passes over 

 into equally cold surface-water. Tlius the cold water has a 

 universal spatial distribution over the whole earth, the cool 

 water an almost universal distribution over the torrid and 

 temperate zones, while the warm water occurs solely as the 

 surface-water of the tropics. 



Corresponding to this there is, first, a warm-water fauna, 

 which is developed only in the surface-water of the tropics; 



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