November 24; ]905.] 



SCIENCE. 



665 



eastern North America are compared with 

 each other, or either of these with the 

 Rocky Mountain forms, and these again 

 with the northwest coast and southern 

 California birds. 



The eastern flickers {Colaptes auratus), 

 the western flickers (C cafer), and the 

 eastern pileated woodpecker (Ceoplmus 

 pileatus), have also been divided into sub- 

 species, mainly on the difi^erence in size 

 between the northern and southern repre- 

 sentatives of the species. The bob-white 

 (Colinus virginianus) has in the east its 

 northern and southern forms, differing 

 markedly in size and coloration, with an- 

 other pallid form in Texas, which passes 

 into a group of very diverse forms in dif- 

 ferent parts of Mexico, some of them hav- 

 ing black instead of white throats, uniform 

 chestnut instead of barred black and white 

 underparts, and others with various other 

 combinations of characters, yet all retaining 

 their characteristic hob-white call, and so 

 blending with each other and the northern 

 forms as to be found to be specifically in- 

 separable, though they have usually been 

 accorded the status of species. 



The horned larks (Otocoris alpestris 

 group), ranging from the Arctic regions 

 to northern South America, and embracing 

 nearly a score of forms, some of them ex- 

 tremely diverse, are found to completely 

 intergrade, though the various forms have 

 special breeding areas, and have obviously 

 attained their differentiations under the 

 most diverse climatic conditions. Yet they 

 are separated by no appreciable barriers, 

 and contiguous forms completely inter- 

 grade, forming an unbroken jchain from 

 one extreme of the series to the other. 



The almost hackneyed case (at least to 

 ornithologists) of the song sparrows {Melo- 

 spiza cinerea group), nearly continental in 

 dispersal and differentiated into about 

 twenty recognized forms, may well close 



this series of illustrations. Many of the 

 forms of this group are so different that, 

 when compared without the connecting 

 links, they seem like remotely related spe- 

 cies, almost different enough for subgen- 

 eric separation. Between the great gray 

 song sparrow of the Aleutian Islands and 

 the little song sparrow (pusillula) of the 

 San Francisco salt marshes the difference 

 in size is enormous, the length of the wing 

 being 85 mm. in the Alaska bird and 56 

 mm. in the San Francisco bird, the north- 

 ern bird having probably more than twice 

 the bulk of the southern one. Between 

 them are some eight Pacific coast forms, 

 by means of which there is continuous 

 gradation between these extremes. Be- 

 tween the desert forms of the interior and 

 the coast form at Sitka, there is much less 

 difference in size, but the former is a pale 

 gray bird, while the latter is deep intense 

 rufous. 



The recognized Pacific coast forms, from 

 Lower California to the Aleutian Islands, 

 excluding several insular phases, are nine 

 in number, between which there is no ab- 

 rupt barrier, either climatic or geographic, 

 and consequently we find the successive 

 and gradual mergence of all; but if a few 

 of the links were dropped out, the remain- 

 ing forms might readily be taken for dis- 

 tinct, fully segregated species, so much do 

 they mutually differ. 



Almost numberless similar illustrations 

 might be cited among North American 

 mammals. In general, the geographic 

 ranges of conspecific groups in mammals 

 are less extended, but they are of suffi- 

 ciently wide range to include a great va- 

 riety of environmental conditions, which 

 result in marked modifications of size, color 

 and structure. 



Indeed, mammals being sedentary, they 

 are even more susceptible to climatic modi- 

 fication than birds. Some of the more 



