1916] Chandler: Structure of Feathers 245 
paper, since it was believed that the comparative morphology of 
feathers would almost certainly be of some taxonomic value in estab- 
lishing the relationships of various groups of birds. 
Since feathers are external and in constant contact with the 
environment, they would naturally be expected to be among the first 
structures of the body to feel the influence of environmental changes 
and shocks, and would still be as liable to change by hybridization, 
orthogenesis or any other method of evolution, as any of the other 
structures. 
There are numerous groups of birds, the taxonomic position and 
phylogenetic relationships of which have been in very great doubt. 
As far as possible the feathers of these groups have been studied with 
the hope that the structure of the feathers would reveal relationships 
that the structure of the other organs would not, on account of 
parallel adaptations in the latter. Instances in which the morphology 
of feathers has been found in this study to throw light on doubtful 
relationships are numerous, for example, in the case of the Phoeni- 
copteri, Tinamidae, and Pici. 
Provided that birds were found to possess constant and peculiar 
characters in the structure of their feathers, the results of such 
work would be of high economic importance in the identification of 
feathers used commercially, and for the confiscation of feathers 
illegally used in commerce. This belief, in the course of the work, 
has been amply justified, and already successful diagnoses of 
unknown feathers have been made for the United States Customs 
officers in the port of San Francisco. 
Before undertaking a study of the phylogenetic modifications in 
feathers, a careful study was made of the structural modifications 
of feathers in the different parts of the plumage of a single repre- 
sentative bird, namely, Circus hudsonius (Chandler, 1914). It was 
discovered that certain general modifications found in this bird in 
the structure, not only of different feathers, but of different parts 
of the same feather, occur almost uniformly throughout the class. 
A diseussion of the typical structure of various kinds of feathers, 
with a consideration of the more important modifications of struc- 
ture correlated with color production, constitutes the first part of 
this paper, while the second part deals with special group characters, 
modifications and peculiarities, arranged in systematic order. No 
attempt has been made to make a systematic study of the morphology 
of any feathers except those of adult birds—i. e., of teleoptiles. 
