VOL. III.] Recent Literature. 65 



theory to fact, but then a good and useful theory should not be too 

 lightly discarded. c. A. K. 



The North American Species of the Genus Colaptes, considered 

 -with Special Refererice to the Relationships of C. aurattis and 

 C. cafer. By J. A. Allen. Bull. Am. Mus. Nat. Hist., iv, 21-44. 

 In the present paper Mr. Allen has undertaken a most careful and 

 thorough investigation of the remarkable intergradation existing be- 

 tween Colaptes aiiratus and C. cafer. His report is based upon 

 the examination of 785 specimens of the genus from North Amer- 

 ica and the West Indies, representing all the known species and 

 varieties inhabiting this region. The relationship of the two 

 species under consideration is first discussed, and the characteristics 

 and distribution of the various races given. More detailed atten- 

 tion is then devoted to the intermediate birds, the conclusions ar- 

 rived at with regard to them being stated as follows: "The facts 

 elicited in the present investigation tend strongly to confirm Baird's 

 startling hypothesis of hybridization on a grand scale between 

 Colaptes auratics and C cafer, to account for the occurrence of birds 

 presenting ever-varying combinations of the characters of the two 

 species over the Plateau and Great Basin regions of the continent. 

 None of the other hypotheses thus far advanced so fully, or, in fact, 

 to any great extent, meet with the requirements of the case. In 

 no instance do we meet with stages or methods of geographical 

 variation at all comparable with what is seen in the case of C aura- 

 tus and C. cafer. The transition between geographic forms, how- 

 ever diverse, is gradual and symmetrical, affecting all parts of the 

 plumage equally and simultaneously, and is obviously correlated 

 with changes in the physical surroundings; also, the differences 

 between the most extreme forms are merely differences of degree. 

 In the case of Colaptes, the essential differences between auratus 

 and cafer a.ve radical; they are, in fact, contrasting characters, and 

 the intergradation is irregular, with all sorts of a symmetrical combi- 

 nations of the characters of the two forms, and no correlation be- 

 tween their intergradation and the conditions of environment." 



Mr. Allen has, in fact, practically demonstrated the habitual hy- 

 bridization of these two species, as Mr. Chapman has just succeeded 

 in doing for the grackles. The bearing of this demonstration upon 

 the infertility of crosses and the relation of color to sterility, as dis- 

 cussed by Wallace in " Darwinism," is very important, placing the 



