1916] Chandler: Structure of Feathers 387 
which are of high value from a taxonomic point of view, namely, the 
number and size relative to the proximal barbules, the form and gen- 
eral character of the base, the general size and form of the pennulum 
relative to the base, the number, size, shape, and general characters of 
the various kinds of barbicels, especially the ventral teeth, ventral 
cilia, and basal dorsal cilia, and finally, the differences between the 
distal barbules of inner and outer vane. 
The proximal barbules are far less variable than the distal barb- 
ules, and as a rule are of much less taxonomic value. Their chief 
phylogenetic modifications are in the following: size of base relative 
to distal barbules, and relation of width to length; number, form, and 
conspicuousness of ventral teeth; form of pennulum, and length rela- 
tive to base; and condition of ventral cilia in barbules near the tip 
of barbs in the outer vane. 
The chief value of the body feathers lies in the degree and man- 
ner of simplification of the barbules from the remex types, and the 
presence or absence, and form, if present, of flexules. 
The down barbules from the region of the superior umbilicus of 
remiges and large coverts, and from the less developed portions of 
barbs of other feathers, e. g., at the tip of the barb, are not always of 
taxonomic value, but the typical down barbules from a portion of the 
feather where they reach their highest development, as for instance 
near the base of the distal vanule of a well-developed downy barb, 
are of very great value from a phylogenetic point of view; in fact, 
it is frequently possible by means of the down alone to identify the 
group to which a bird belongs and unquestionably to determine its 
relationship to other groups. The characters which are of value are 
the length, the size and form of the base (of value only in the case of 
some Coraciiformes and Passeriformes), the character and frequency 
of the nodes, and the presence or absence of prongs. 
Methods of color production are of more or less taxonomic value 
in certain cases. For instance, the iridescent colors of ducks and 
other water-birds are produced differently than in gallinaceous birds, 
and in both of these differently than in Coraciiform birds. 
3. Relationships of Groups Suggested or Corroborated 
The morphology of feathers, as presented in the preceding pages, 
adds one more basis for comparison of different groups of birds, and 
seems to throw new light on the relationship of certain groups to 
others. A classification which even comes near to expressing true 
