Vol i9i8 XV ] Correspondence. 105 



CORRESPONDENCE. 



Editor of ' The Auk ' : 



In the notice of Lloyd-Jones's paper on feather pigments in the last 

 April number of ' The Auk ' (Vol. XXXIV, p. 232) there is one statement 

 which might be misleading, and I should accordingly like to put on record 

 a somewhat fuller statement of the point in question. Speaking of the 

 so-called blue color of domestic pigeons the review states that " blue as in 

 all birds is a structural color." It is true spectral blue in all birds is a 

 structural color, for as Lloyd-Jones says: " No blue pigment substance 

 has ever been discovered in the integument of higher vertebrates." The 

 point is, to quote further: " The color called ' blue ' in domestic pigeons 

 has very little claim to that name. It is not at all comparable to the blue 

 of the bluebird, jay or indigo bird, but resembes more the so-called blue 

 of the rabbit or maltese of the cat. In other words, the color belongs more 

 properly among the grays than among the blues. The ' gull-gray ' of 

 Ridgway ('12, plate 53) is a fair representation of the blue of the domesti- 

 cated pigeon. Typical spectrum blue, however, is found among tropical 

 members of the pigeon family," and there it is doubtless due to structural 

 causes. The ' blue ' of the domestic pigeon is then merely a neutral tint 

 such as might be produced by a layer of soot on snow, or by any intimate 

 mixture of black and white. In the pigeon " the blue effect is produced 

 by a layer of pigment-free material intervening between the eye [of the 

 observer] and the pigment mass " in the barbule cell of the feather. 



Sincerely, 



Leon J. Cole. 



University of Wisconsin, Nov. 1, 1917. 



