28 4 



GENERAL BIOLOGY 



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

 mon original stock. 



This is segrega- 

 tion of the most 

 obvious sort. 

 Many a wide 

 ranging species 

 has varieties or 

 sub-species for 

 every distinct 

 faunal area with- 

 in its range. 

 The accompany- 

 ing map illus- 

 trates the geo- 

 graphic distri- 

 bution of the 

 races of the 

 common song 

 sparrow. 



Whatever 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 student 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 



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. 



