iR^^^l Chadbournk, Spyiiiff Plumage of the Boholink. 147 



Without a definite understanding on tliese points, any rational 

 discussion of the colors and color-changes in feathers, must of 

 necessity be both unprofitable and misleading. 



Supplementary Note. — It has been suggested that an outline 

 of the results of a more detailed study of the alterations on which 

 changes in color in the feather depend is needed to complete the 

 present paper. 



I. The mature feather (/. e., one which has reached full 

 functional development), is far from being " dead and dry," "a 

 foreign body no longer connected with the vital processes in the 

 rest of the organism," as has sometimes been asserted ; for during 

 its life it receives a constantly renewed supply of Huid from the 

 parts around it. In strong contrast to this is the really dead 

 feather, in which this fluid matter is deficient, as for example, the 

 majority of uninjured cast-off feathers. Some of the evidence in 

 support of these facts may be of interest: — (^a) The fatty or oil- 

 like droplets on the surface of the feather can be shown by 

 microchemical tests (staining, etc.), to be, some of them identical 

 with the oil from the so-called 'oil-gland' ; while others are totally 

 unlike that secretion, and these latter are alone found exuding 

 from the pores on the surface of the rami, radii, and shaft. The 

 pores, some with drops of varying size issuing from them, show 

 best at the distal ends of the segments of the downy rays, {b) 

 In the living bird the imported fluid can be colored, its progress 

 Hoied^ 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," "capillarity," 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 feather, {c) The 

 broken tips of the rays forming the vane are, when fresh, capped 

 by a mass of the Huid, which has escaped, leaving the part imme- 

 diately below the stump pale from the loss of the fiuid pigmented 

 matter. (^/) In museum skins this fluid matter gradually dries and 

 by its consequent increase in density, and that of the feather tissues, 

 the colors darken ; while the freshness and gloss of life disappear. 

 (<?) The 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 



