18 CLASSIFICATION AND ADAPTATION 



Bateson describes several particular cases which 

 show how impossible it is to find any relation at all 

 between the diagnostic characters of certain species 

 or local forms and their mode of life. One of these 

 cases is that of the species of Colaptes, a genus of 

 Woodpeckers in North America, of which a detailed 

 study was published in the Bull. Am. Mus. Nat. 

 Hist., 1892. The two forms specially considered 

 are named C. auratus and C. cafer, and they differ in 

 the following seven characters : 



C. auratus. C. cafer. 



1. Quills yellow. 1. Quills red. 



2. Male with black cheek 2. Male with red cheek 



stripe. stripe. 



3. Adult female with no 3. Adult female with 



cheek stripe. usually brown cheek 



stripe. 



4. A scarlet nuchal cres- 4. No nuchal crescent in 



cent in both sexes. either sex. 



5. Throat and fore-neck 5. Throat and fore-neck 



brown. grey. 



6. Top of head and hind- 6. Top of head and hind- 



neck grey. neck brown. 



7. General tone of plum- 7. General tone of plum- 



age olivaceous. age rufescent. 



C. auratus occurs all over Canada, and the United 

 States, from the north to Galveston ; westwards it 

 extends to Alaska and the Pacific coast to the 

 northern border of British Columbia. C. cafer in 

 comparatively pure form occupies Mexico, Arizona, 

 California, part of Nevada, Utah, Oregon, and is 

 bounded on the east by a line drawn from the Pacific 

 south of Washington State, south and eastward 



