386 University of California Publications in Zoology  |Vou. 18 
scales of reptiles and on the hair of mammals shows promise of 
bringing out facts concerning them also, which will be of taxonomic 
value. But in all of these the range of possible or probable modi- 
fiability is very slight as compared with that of feathers, on account 
of the much greater complexity and minute structural units of the 
latter, and therefore the morphology of feathers is of greater value 
than lepidology or any other branch of epiphyology from a taxo- 
nomic point of view. 
2. Principal Modifications of Structure Useful in Taxonomy 
There are a great many different parts of feathers and plumage 
which show phylogenetic modifications, among which some are of 
great value and can almost certainly be depended upon to be of 
importance in showing relationships, while others are as plainly of 
very doubtful value. From the foregoing systematic study of the 
different groups of birds, the relative value of the different structures 
and arrangements of different parts of feathers has made itself 
apparent, and the following general conclusions may be drawn. 
The distribution of plwmules is a character which, in itself, is of 
little value, on account of its great variability, in a few cases, within 
a single group, and on account of the adaptive value of the plumules, 
as shown by their presence in all the lower orders of water-birds and 
their recurrence in kingfishers amongst a group in which there is 
elsewhere a tendency for plumules to be reduced or entirely lost. 
However, in conjunction with the condition of other structures, the 
distribution of plumules is of some phylogenetic importance. 
The aftershaft is of more importance, and its presence or absence, 
and form if present, may be depended upon to a considerable extent 
as showing phylogenetic tendencies. 
The quill, even of the remiges, is too variable within groups to be 
of any great value except in a few cases, as, for instance, in the 
Anseres, where the disproportionate length of the calamus is of diag- 
nostic value. The condition of the ventral groove and of the stria- 
tions on the sides are of little value except in a few cases. 
The rami have a number of characters which are significant, 
namely, the thickness of the pithy portion, whether of one or more 
layers of cells (see Mascha, 1904), the width relative to the shafc, 
the relative size and form of the ventral ridge, and the presence or 
absence of villi on its ventral edge in the outer vane. 
The distal barbules of the remiges have a number of characters 
