INFLUENCE OF EXTENT OF RANGE 



127 



(cosmopolitan) range is the maximum possible, and stands in contrast 

 with geographic specialization. 



Extended ranges. — An animal is said to be cosmopolitan when it 

 occurs in all the places that afford it suitable habitat conditions; 

 cosmopolitanism does not mean that it occurs alike in salt and fresh 

 water and on land. An animal that is found to inhabit a wide variety 

 of unlike habitats is said to be ubiquitous. The term cosmopolitan 

 distribution is used in the geographic, and ubiquitous occurrence in 

 the ecologic, sense. Cosmopolitan species may accordingly be marine 

 animals occurring in all oceans or air-breathers occurring in all the 

 zoogeographic regions, although the polar regions are often omitted 

 from consideration in this connection. The widest distribution in both 



Fig. 10. — Cyphoderia ampulla. After Schulze. 



the geographic and ecologic sense is probably to be found among 

 Protozoa, especially among the rhizopods. Thus Cyphoderia ampulla 

 (Fig. 10) lives in the ocean, in salt-water marshes, in fresh water, in 

 the sand of the seashore, in the springs and glacial lakes of mountains, 

 and in the warm ponds of the lowlands. In addition to central Europe, 

 this protozoan is recorded from the coast of the Arctic Ocean, from 

 Russian Lapland, from the Rocky Mountains, and from Argentina and 

 Paraguay. The thistle butterfly (Pyrameis cardui) is an example of a 

 widely distributed metazoan. It is known from all parts of the world 

 with the exception of some small islands and of South America, ranging 

 from the tropics to the arctic regions and from the plains to the snow 

 line in the mountains. Animals found in all seas are the edible mussel 

 (Mytilus edulis) and the thresher shark {Alopias vulpes) . 



The importance of wide distribution is graded according to the 

 gradations of the groups concerned. A wide range is much commoner 

 for genera than for species; it is still more common for families and 

 orders. The families of myriapods and scorpions, and very many 

 families of insects, are cosmopolitan. Fresh-water fishes, amphibians, 



