pene | CHADBOURNE, Spring Plumage of the Bobolink. 147 
Without a definite understanding on these points, any rational 
discussion of the colors and color-changes in feathers, must of 
necessity be both unprofitable and misleading. 
SUPPLEMENTARY Norte. — 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. 
1. Zhe mature feather (t. 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 fluid 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. (0) 
In the living bird the imported fluid can be colored, z¢s 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,” “capillarity,” or what 
you please, it is none the less a wtal 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 fluid, which has escaped, leaving the part imme- 
diately 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 tissues, 
the colors darken; while the freshness and gloss of life disappear. 
(e) 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 
