298 



SCIENCE. 



[N. S. Vol. XI. No. 269. 



titles of light admitted. Unsectioned feath- 

 ers so treated acted quite similarlj^, 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 shown 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 them 

 that the consequent would be helpful. One 

 thing appears certain, that to the presence 

 of quantities of granular black-like matter 

 is due no small share of the ultimate pro- 

 duction of blue. 



The causes of the differences in the shade 

 of the blue feathers from violet to greenish, 

 according to their position on the bird, ap- 

 peared to be very slight microscopically, and 

 I could detect no constant characters with 

 the facilities at my disposal. 



As to the causes of the activity necessary 

 to produce a color change, we may only 

 infer. As proved by dissection my bird was 

 not undergoing any prominent sexual 

 change, and the theory that the temperature 

 of the atmosphere might be responsible 

 would not be applicable to most cage birds 

 which are kept in warm rooms. There can 

 be no doubt, however, but that the fall 

 change of plumage is one of protective ten- 

 dency, and it is highly possible that until 

 changed in the spring, the feathers, in a 

 certain sense, are immature. In the case 

 of the double j'ellow-headed parrot before 

 mentioned, the color change was of a retro- 

 grade nature, but in the present example 

 the process is synthetic rather than other- 

 wise. 



Numerous theories have been published 

 which endeavor to account for the dichro- 

 matic fall change of many birds, but it 

 would be irrelevant to discuss them here. 

 One thing appears certain, that the process 

 is deeply involved in the vital system of 

 the organism. Professor Beddard cites an 

 example noticed by Professor Weber of a 

 chaflSnch which was so colored that one-half 

 of the bird was in the male plumage and 

 the other portion in the female. Dissection 

 proved the bird to be a Hermaphrodite, i. e., 

 the side sustaining the male plumage was 

 found to contain a testicle, while the opposite 

 portion of the body possessed an ovary, and 

 Professor Beddard writes that this curious 

 abnormality had been noticed before. 



As no vascular connection appeared to be 

 present in the perfect feathers of my bird, 

 the change appears to be one of internal 

 activity in the feathers themselves, and the 

 simile before mentioned, of the autumn leaf; 

 appears to be still more strongly consistent. 

 The change is none the less vital, however, 

 and ceases with the death of the organism. 

 No tests delicate enough were applied to 

 determine if new matter was formed di- 

 rectly in the feather. It appeared prob- 



