1916] Chandler: Structure of Feathers 269 
ornamental plumes. In penguins and Colymbiformes they are indis- 
tinct. In a few birds, e. g., Menura, they are transformed into an 
ornament, although it is more frequently the upper tail coverts that 
are modified to produce an ornamental tail. In woodpeckers, swifts, 
and a number of other birds the rectrices have the plate undeveloped 
at the tip, and the bare shafts enlarged as stout spines to aid in 
climbing or bracing against a steep surface. Like the remiges, the 
rectrices never possess aftershafts. 
3. Unspecialized Contour Feathers 
Passing now to the coverts, we find that in them there is a com- 
plete transition from the remex type of structure to that found in 
the contour feathers of the trunk, the greater coverts being more 
like the former, some of the lesser ones very much like the latter. 
We may pass at once, therefore, to a discussion of the morphology 
of the trunk feathers. 
a) Aftershafts—tThese feathers in the majority of birds are char- 
acterized by the presence of an aftershaft, and the presence or ab- 
sence of this structure has been considered of considerable taxonomic 
importance. The condition of the aftershaft in the various groups 
of birds is given in the table on page 256. 
A evreat deal of variation exists, as will be seen, within single 
suborders or even families. Within the Ratitae there is an extreme 
variation from a total absence in the ostriches, rheas and Apteryz, 
to a maximum size, practically equivalent to the main shaft, in 
cassowaries and emus. Various types of aftershafts occur in carinate 
birds, the most common form being one with a very short shaft and 
long, spreading barbs, very similar in form to plumules. In many 
gallinaceous birds, e. g., in the Tetraonidae, the aftershaft reaches 
a very high degree of development, its shaft being frequently three- 
fourths of the leneth of the main shaft, with its vanes coherent and 
of even width throughout (fig. A). The usual type in passerine 
birds, on the other hand, is very different; the shaft is extremely 
short, with a few short rudimentary barbs near the base, followed 
by four to eight very long, free barbs, entirely disconnected from 
each other. The barbs and barbules of aftershafts are always of 
downy structure, the minute characteristics of the barbules being 
usually the same as those of the down of the main feather plate, 
but there are a number of exceptions to this, e. g., in the gallinaceous 
and passerine birds. In such cases the structure is less specialized 
