STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 163 
A variation from the conditions described by Haecker for the pro- 
duction of blue is found in the blue feathers of the indigo bird. I have 
never seen any pigment in the medullary cells, but heavily pigmented 
barbules, occur and they are not reduced in size (Plate 5, Fig. 29). 
A section of a barb from the dark brown tertiaries of the “homer” 
pigeon shows little, if any, more pigment than is found in gray 
feathers of Sterna (cf, Plate 1, Fig. 9, and Plate 5, Fig. 24). The 
distal as well as the proximal barbules are liberally supplied with 
brown pigment, however; whereas in Sterna, only the more proximal 
portions of the distal barbules have an appreciable amount of pigment. 
The wing feathers of the juvenal plumage vary from plain gray to 
brownish gray. When the latter color occurs, there is a noticeable 
pigmentation of the proximal barbules. 
V. The Pigmentation of the Feather. 
A. Tue CuHemicaL NATURE OF FEATHER PIGMENTS. 
The researches of Bogdanow (56, 757) and Krukenberg (’81-’84) 
have shown that the pigments of birds’ feathers may be divided into 
two groups: (1) those soluble in alcohol and ether, — yellow, orange, 
and red pigments (also a single green pigment, turacoverdin) ; and 
(2) those soluble in acids and alkalies,—the dark brown to black 
pigments.. 
Krukenberg (’84) designated the first group under the general term 
of lipochromes or fat pigments. The second group is included among 
the widely distributed dark brown animal pigments known as melanins. 
The solubility of the lipochromes in alcohol and ether renders the 
study of their origin in the feather by ordinary histological technique 
impracticable. I have found, for instance, that yellow feather germs 
from the canary and from the nonpareil (Passerina ciris), though re- 
taining their color after fixation, lose it in all except the cornified 
portions during the process of hardening in alcohol. Various writers 
who have alluded to the origin of pigment in feathers have described a 
melanin pigment, but they usually fail to recognize that the melanins 
are not the only pigments present in feathers. 
The dissolving action of chemical re-agents on the melanins of differ- 
ent animals has been described differently by various authors, but, in 
general, a great resistance to acids and alkalies has been found. 
Alcohol, ether, chloroform, xylol, etc., seem to have no action whatever 
