248 CALIFORNIA ACADEMY OF SCIENCES. 



rule is traceable over large portions, at least, of the Old 

 World." 



One of the very best illustrations of the influence of 

 climate upon color is illustrated in Plate XIII. The song 

 sparrow ( Melospiza fasciata) is a resident of all the tem- 

 perate j)ortions of the North American continent. The 

 plate shows the general color effect of the back of each 

 of the various forms into which it divides in the various 

 portions of its range. In the Eastern States the color is 

 normal, being neither excessively dark nor light. In the 

 arid regions of the great plains and Rocky Mountains it is 

 pale (M. fasciata montana), while in the Colorado desert 

 region of Arizona it is very small, and the colors pecu- 

 liarly light (M. fasciata fallax). Coming to the Pacific 

 Coast, the darkest forms are found, M. fasciata samuelis 

 and heermanni in California, the dark rusty form M. 

 fasciata guttata in Oregon and Washington, and the 

 darkest of all, M, fasciata rufina, along the northwest 

 coast of British America. It will be noted that these 

 various races coincide perfectly with the regions of 

 greatest and least rainfall, the palest forms being found 

 on the hot arid deserts and the darkest in the region of 

 most constant rains. It may be thought a singular con- 

 tradiction that in the genus Sphyrapicus the bird of the 

 Rocky Mountain district is darker than the eastern form, 

 while in the genus Melospiza, the variety inhabiting this 

 district is paler. This may be understood, I think, by 

 taking into account the diflference in habits of the two 

 species. Sphyrapicus inhabits the forests exclusively, 

 and in the mountainous districts would resort to the 

 groves of pine, etc. Melospiza, on the contrary, is con- 

 fined to underbrush, and in the Rocky Mountain district 

 would most frequently live in the sagebrush country, 

 which is dry and comparatively exposed to the sun's 

 rays. 



