174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



fluid can be colored, its progress noted, and the feather stained intra 

 vitam. Soon after death this becomes no longer possible. To see the 

 stain the microscope is usually necessary. Call this ' osmosis,' ' capil- 

 larity,' or what you please, it is none the less a vital process in that it 

 ceases soon after death, and must be studied in the fresh featlier. 

 (c) The broken tips of the rays forming the vanes are, when ficsh, 

 capped by a mass of the fluid, which has escaped, leaving tlic part 

 immediately below the stump pale from the loss of the fluid pigmented 

 matter, (d) In museum skins this fluid matter gradually dries and by 

 its consequent increase in density, and that of the feather tissue, tlie 

 colors darken : while the freshness and gloss of life disappear, (e) 'I'lie 

 evanescent tints of some species, — notably the fading of the rosy 

 ' blush ' of some of the Terns, soon after life is extinct, is due to the 

 drying up or escape of this fluid, while the lost tint was due to the 

 physical effect of structure, the shrivelling and change of form would 

 act on the light rays and the former colors would be lost in conse- 

 quence. Comparisons of specimens of Sterna paradisea, S. dougalli, 

 and other Terns in my collection, showed that examples having the 

 'blush ' most marked are those in which the feathers are least drj'." 



Cliadbourne ('97 °) has described the case of a canary ^ which was sup- 

 posed to have changed under the influence of being fed with red pepper 

 to the reddish yellow color which, as is well known, may be pro- 

 duced at the time of molting. It was clearly demonstrated by Sauer- 

 mann ('89), however, that in the birds experimented on by him the 

 color is not altered unless the special feeding is carried on while the 

 feathers are in process of development. This I have found to be also 

 the testimony of bird fanciers. 



Though it is probable that the oil supplied by the uropygeal gland is 

 a factor in the production of color effbcts^ especially in giving gloss or 

 lustre, it is unreasonable to suppose that the feather itself produces or 

 gives forth any of the oil found upon it. Although the feather struc- 

 ture is slightly permeable by liquids, as Fatio observed, it does not fol- 

 low that the pigment imbedded or diff'used in its horny substance is able 

 to flow about. 



There is no satisfactory evidence of the occurrence of repigmentation. 



1 Dr. Chaflbourne has explained to me tliat tliere was a misunderstanding in 

 the case of the canaries he mentioned. They were not kept by him, but were in 

 the possession of tlie janitor of the Harvard Medical School, wlio tells me that the 

 changes mentioned by Dr. Cliadbourne were produced only by feeding at the time 

 when the feathers were developing. 



