172 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
arranged parallel with the axis of the barbule (Plate 5, Figs. 26, 27), 
a condition for which I have no explanation. 
The variations in pattern exhibited by a single feather, in the form 
of bars, spots, etc., are easily correlated with variations in the distri- 
bution of pigment in the corresponding regions of the feather germ. 
That the distribution of lipochrome pigments to the feather funda- 
ment takes place at about the same stages in the development of the 
feather as that of the melanins, seems certain. The germs of yellow 
feathers from the canary and the nonpareil show a yellow color which 
corresponds in position to the dark color of feather germs pigmented 
with melanin. 
VI. Change of Color without Molt. 
The changes in color claimed by many writers to occur without molt 
may be grouped under two heads: (1) the destructive, and (2) the con- 
structive. Under destructive changes are included the results of 
abrasion and physical disintegration. Constructive changes include 
supposed regeneration. and rearrangement of pigment. 
For a review of the general literature of change of color without molt, 
the reader is referred to Allen (96). More recently Meerwarth (’98) 
has claimed that change of color without molt occurs in the tail- 
feathers of certain Brazilian Raptores. He describes variations in color 
pattern that he has observed in material consisting mostly of skins. 
His paper gives no satisfying evidence that the changes alleged may 
not have taken place through irregular molting. Furthermore, he does 
not offer any explanation of the process of change. 
Descriptions of repigmentation have been mostly pure speculation. 
Within a few years the following remarkable explanation of the pig- 
mentation of the feather has been given by Keeler (’93): “ Pigment is 
a definite chemical substance which travels through the various branches 
of the feather, advancing farthest and most rapidly along the lines of 
least resistance and accumulating in masses where the resistance is 
greatest. Now the pigment cells must reach the various parts of the 
feather by way of the shaft, and we should a priort expect to find that 
the resistance would be least down the shaft. It might spread out a 
very short distance on the barbs, but the main tendency would be 
towards the tip. This would produce a streaked feather as the most 
primitive form.” 
Still more recently Birtwell (:00), in arguing for change of color with- 
