STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 175 



The number of supposed cases was greatly reduced when it was discov- 

 ered that more than one molt may take place in a year, and the recent 

 researches of Chapman ('96), Dwight (:00, :00 '), and Stone ('96 and 

 -.00), which I can corroborate from my own observations on caged birds, 

 have shown that partial molts may take place at various times during 

 the vear. Changes due to such partial molts seem sufficient to account 

 for all forms of color change hitherto attributed to a process of repig- 

 mentation. 



I iiave found no good record of actual solution by natural causes of 

 pigments contained in the feather except in the case of the pigment 

 turacin. In the great majority of cases, artificial solution is accom- 

 plished by chemical reagents with great difficulty. Even if pigments 

 were dissolved in the feather, it is inconceivable that they should be re- 

 distributed to form the exceedingly constant and often complex patterns 

 characteristic of bird feathers. 



Pigmentation takes place, as has been shown, at a very early stage in 

 the differentiation of the feather, when the cells composing its funda- 

 ment are in an active condition and in intimate relation with sources of 

 nutrition. In the case of melanin pigments, there are bj-anched pig- 

 ment cells which supply pigment in the form of rod-shaped granules 

 directly to the feather fundament. The contention for a flow of pig- 

 ment from the barbs into the barbules, etc. (Keeler), is at once made 

 absurd by the fact that the barbules are pigmented before the barbs are 

 differentiated. 



Variations in color patterns are easily correlated with variations in 

 the distribution of pigment in the early stages of the feather's develop- 

 ment. When completed, the feather is composed of cells which have 

 been entirely metamorphosed into a firm horny substance and its 

 pigment is imbedded in that lifeless matter. The cells composing a bar- 

 bale are fused into a solid, more or less homogeneous structure. The 

 pigment of one portion of the barbule is as effectually isolated from that 

 of another as is the coloring of various parts of a piece of agate. Like- 

 wise in the barb and rhachis, pigment is definitely and permanently 

 located either in the solid cortex or in effectually separated cells of the 

 medulla; and there are no pores large enough to admit the passage of 

 melanin granules. The characteristic longitudinal arrangement of 

 melanin granules, which one finds at the close of cornification of the 

 feather, is permanent. 



The case cited by Krukenberg of a regeneration of the pigment tura- 

 cin was unfortunately not described. It seems to me probable that the 



