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. — These 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 great deal of variation exists, as will be seen, within single 

 suborders or even families. Within the Ratitae there is an extreme 

 varia,tion from a total absence in the ostriches, rheas and Apteryx, 

 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 length 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 



