14 



obstructed, but that descending to the stage 

 from above, the sheath became invisible 

 but the central column showed up like 

 phosphorus as a pale glimmering blue which 

 became opalescent with the varying quan- 

 tities of light admitted. Unsectioned feath- 

 ers 80 treated acted quite similarly, but the 

 parts of the column appearing in the tips of 

 the fall feathers, instead of betraying blue, 

 showed gleaming white effects. Under trans- 

 mitted light, as in ordinary examinations, 

 the effects of the pigments alone were seen. 



The massing of the granules of pigment 

 begins evenly upon each vane, from the 

 bottom of each barb and works towards the 

 tips, the barbules being filled, from the tips 

 first, as they are passed. The tips of the 

 distal barbs usually were the last to com- 

 pletely undergo this change. 



In both fall and spring feathers, the ob- 

 jective superstructure occupied the same 

 relative position, being confined to the cen- 

 ter of the barbs alone for almost their en- 

 tire lengths. 



Dr. Gadow, who has published results of 

 his investigations upon the nature of the 

 blue-producing structures in feathers, con- 

 cludes that the production of blue is, in a 

 measure, caused by the fine ridges of the 

 prismatic columns, and thinks that the 

 bodies of the columns and the transparent 

 sheaths of the barbs may exert an appreci- 

 able influence. He adds in consequence 

 ' ' the production of blue therefore in a 

 feather would be the result of a very com- 

 plicated process." 



As show^n in my feathers, however, the 

 blue appeared to be largely independent of 

 the envelope of the barbs, yet this might 

 concentrate light rays or so modify tliem 

 that the consequent would be helpful. One 



