In a book entitled _Problems of Genetics_, 1913, 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 stripe. 2. Male with red cheek stripe. 3. Adult female with no 3. Adult female with usually cheek stripe. brown cheek stripe. 4. A scarlet nuchal crescent 4. No nuchal crescent in in both sexes. either sex. 5. Throat and fore-neck brown. 5. Throat and fore-neck grey. 6. Top of head and hind-neck grey. 6. Top of head and hind-neck brown. 7. General tone of plumage 7. General tone of plumage olivaceous. 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 through Colorado to the mouth of the Rio Grande on the Gulf of Mexico. Between the two areas thus roughly defined is a tract of country about 300 to 400 miles wide, which contains some normal birds of each type, but chiefly birds exhibiting irregular mixtures of the characters of both. Bateson remarks that some naturalists may be disposed once more to appeal to our ignorance, and suggest that if we only knew more we should find that the yellow quills, the black 'moustache,' and the red nuchal crescent specially adapt _auratus_ to the conditions of the northern and eastern region, while the red quills, red moustache, and absence of crescent fit _cafer_ to the conditions of the more southern and western territory. But, as the author we are quoting points out, when we think of the wide range of conditions in the country occupied by _auratus_, extending from Florida to the Arctic, it is impossible to believe that there is any common element in the conditions which demands a scarlet nuchal patch in _auratus_, while the equally varied conditions in the _cafer_ area do not require that character. It may be added that the same objection is equally valid whether we apply it to the utility of such a character or to the supposition that the character has been caused by external conditions; in other words, whether we attempt to explain the