148 CHADBOURNE, Spring Plumage of the Bobolink. Anti 
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 consequence. Comparison of specimens of Sverna 
paradisea, S. dougalli and other Terns in my collection, shows 
that examples having the ‘blush’ most marked are those in 
which the feathers are the least dry. Absolutely fresh specimens 
are hardly obtainable, owing to the destruction of these birds for 
the demands of fashion. It is probable that the same explanation 
will be found to be true in the fading of other species. (/) 
Other substances than red pepper (¢. Auk, XIV, 1896, p. 33) 
_when given with the food, also produce changes in the color of 
the feather and in its composition, recognizable by proper tests. 
This applies to other species than the Canary. 
2. Change of color in the individual feather after maturity. — 
How the colors of feathers can change; the modus operandi of the 
process, has long been an ornithological stumbling block, but the 
explanation is, I believe, neither incredible, nor complicated, and 
in fact most simple and easily accounted for by well known physi- 
ological laws. It may be briefly summarized as follows : —(a) 
As the result of retrograde or other activity within the cells, and 
with or without the action of the imported fluid, new pigmented 
products are formed, which may be solid matter or may be in 
solution, but are unlike those previously present. (0) Vital con- 
ditions within the organism determine the composition of the fluid 
supplied to the feather, as well as the amount of the supply ; and 
hence indirectly regulate the character of the new compounds in 
the feather, into which the fluid enters or which depend upon its 
influence. Thus at the mating season there would be an alteration 
in the amount and character of the fluid received by the feather, 
and a freshening and often a color-change quite distinct from a 
more or less complete feather-change, and in some cases without 
which would be a separate process, 
any associated ‘ moulting,’ 
even if present. 
EXPLANATION OF PLATE la. 
(Nore: —Figs. 1, 2, 4, and 5 were first photographed, and the prints 
from the negatives then colored from the original specimens ; thus insur- 
ing absolute accuracy in outlines. They are about twice the natural 
size. Fig. 3 was outlined with a camera lucida to secure exactness, and 
