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 libei'ally sup;)lied 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. The Chemical K'ature of Feather Pigments. 



The researches of Bogdanow ('56, '57) 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 ('8^) designated the first group under the general terra 

 of lipochromes or fat pigments. The second group is included among 

 the widely distributed dark brown animal pigments known as melanins. 



The solubility of tlie 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 tlie 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 difterently 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 



