in] THE FACTORS OF DISTRIBUTION 57 



been such extensive and ruthless destruction of 

 mammalian life as among the whales and seals of 

 Arctic and Antarctic seas. The account of every 

 Antarctic voyage contains striking pictures of the 

 enormous wealth of bird life in the penguin rookeries, 

 and among the petrels and gulls; and also of the 

 incredible abundance of diatoms, which visibly dis- 

 colour the sea- water and clog the nets used for fishing. 

 All plankton investigation bears witness to the paucity 

 of microscopic life in the tropical seas and to its 

 abundance in the north temperate and sub-polar 

 waters. The German exploring ship ' National' 

 obtained the richest plankton catches in the sea off 

 the south of Greenland, and the poorest in the warm 

 Sargasso Sea; and this has been the experience of 

 most investigators. 



We see that there are some general facts of 

 distribution. The variety of species is greatest in 

 tropical seas, and least in the temperate and polar 

 seas; and it is greatest near the land, and least in 

 the oceanic areas far away from the influence of the 

 land: generally the density of both benthos, nektic 

 and planktonic life decreases as we pass out from 

 shallow into deep water. In the middle of the 

 greatest oceans planktonic life is scarcest, and at the 

 bottom of the oceans, in the abyssal regions, the benthos 

 is also scarcest. Perhaps no part of the ocean bed is 

 actually devoid of animal life, but the nearest approach 



