INFLUENCE OF EXTENT OF RANGE 133 



The comparison of the New Zealand fauna with that of the East 

 Indies shows that the extent of the area concerned is the deciding 

 factor only when other factors are similar or comparable. The West 

 Indian islands, likewise, are comparable only with one another. 



A somewhat similar result though with equally necessary exceptions 

 is exhibited by the numbers of species of fishes in the faunae of the 

 larger river basins.* In similar climatic zones the larger stream tends 

 to have the larger fish fauna. The greater extent of the oceans in the 

 southern hemisphere similarly reacts favorably on the evolution of 

 genuinely pelagic animals. These seas have larger numbers of whales. 

 The same relation appears among the plankton. 41 Chun 42 characterizes 

 the Antarctic pelagic fauna as in general richer in comparison with 

 that of the Arctic; even among the bottom-dwelling forms the 

 Antarctic fauna is the richer, as among echinoderms 43 or pycnogonids 

 which have 82 Antarctic species as compared with 62 in the Arctic. 44 



Large areas with uniform conditions like great stretches of forest, 

 prairies, steppes, and extended mountain ranges are especially favor- 

 able to the development of specifically adapted forms, since they 

 afford residence and perpetuation to large numbers of individuals, and 

 the prosperity of a species, its further development and progressive 

 adaptation, are in general more favored by wealth of individuals. 

 Regions with a wide variation in habitat conditions contrast with 

 such uniform areas, and these favor the existence of numerous species 

 and subspecies, since they afford conditions adapted to needs of varied 

 animals. The great uniformity in Africa south of the Sahara in climate 

 and flora conditions a certain uniformity of the African fauna, and 

 south, west, and east resemble each other more here than in any other 

 continent; 45 the wealth of species in South America, in contrast, is 

 much greater. The subdivision into varied situations of the sea bottom 

 of the Sagami Bay near Tokyo has its share in conditioning the 

 surprising wealth of species in this area. 46 The Norwegian coastal 

 herrings show much more variation and division into races than the 

 herrings of the open Atlantic and of the North Sea, 47 on account of 

 the great variation of physical conditions on the coast. The variety of 

 conditions in the littoral affords habitat to a greater number of 

 gorgonians than the deep sea, but the littoral species have much more 

 circumscribed ranges than the deep-sea forms. 48 The broken and varied 

 east coast of the Adriatic affords a greater variety of habitat than the 

 more uniform west coast; of 143 species of decapods in the Adriatic, 

 116 are found on the east coast and only 65 on the west, while on the 



* For details, see Hesse, 1924. 



