284 



GENERAL BIOLOGY 



tion of the species from each other and from the com- 



mon original stock. 



Fig. 170. Diagram of the distribution of the common 

 song sparrows of North America. Shaded areas in- 

 dicate the range, a of the eastern song sparrow; b, of 

 the Rocky Mountain song sparrow; c, of the gray 

 song sparrow; d, of Samuel's song sparrow; e, of Heer- 

 mann's song sparrow; /, of the Oregon song sparrow, 

 and g, of the rusty song sparrow. 



This is segrega- 

 tion of the most 

 obvious sort. 

 Many a wide 

 ranging species 

 has varieties or 

 sub-species for 

 every distinct 

 f aunal area with- 

 in its range. 

 The accompany- 

 ing map illus- 

 trates the geo- 

 graphic distri- 

 bution of the 

 races of the 

 common song 



sparrow. 



AVhate\'er the means employed, nature has practiced 

 segregation on a large scale, even isolating more or less the 

 larger groups of organisms — the palms in the tropics of 

 the world, the marsupials in the Australian region, etc., etc. 

 This is a subject of great biological interest and importance, 

 but it falls outside the scope of our practical studies and 

 therefore, the sttident; is referred for fuller statement to 

 general works on the geographic distribution of plants and 

 animals. 



2) Climatic and meteorological conditions. — Tempera- 

 ture and altitude, rainfall and winds, and other similar 

 influences differentiate desert and plain, meadow and 

 forest, and all the host of animal and plant forms that accom- 

 pany them. This is so familiar a matter, that any one who 



