382 University of California Publications in Zoolog [Vox. 13° 
y gy 
the proximal barbules on the outer half of the barbs of the outer 
vane of the wing feathers undergo a rather sudden change. On 
the inner portion of the barbs, the proximal barbules have mod- 
erate bases and unusually broad pennula, but near the middle of 
the barb the base suddenly becomes greatly reduced and the pen- 
nulum elongated, the latter with a series of strong, hooked, ventral 
cilia which are very conspicuous (pl. 33, fig. 93a). Concomitant with 
this specialization of the proximal barbules, the distals deteriorate, 
the differentiation between base and pennulum being lost, the 
former being short and triangular, only about 0.1 mm. long to the 
point where it merges into the pennulum; no barbicels except a few 
rudimentary dorsal and ventral ones near tip. 
Although representatives of a very large number of passerine 
families have been examined, no further modifications worthy of 
special mention here have been found in the group, except in con- 
nection with color production or some other macroscopic effect, as 
in the ornamental plumes of birds of paradise and lyre birds. 
Plate 33, figure 95a shows the tip of a ‘‘wax-tipped”’ feather of 
Bombycilla garrula, showing the method of fusion of shaft with 
outer vane only. This ‘‘wax-tip’’ has usually been looked upon 
merely as the expanded terminal portion of the shaft. 
c) Down 
With the exception of its oceurrence also in the Trochilidae 
and all of the Pici except the Galbulidae, the down barbules of 
passerine birds have a constant and peculiar character in the pres- 
ence of lobate or fingerlike villi on the ventral edge or on the side 
of the base, as shown in plate 37, figure 115b, and also in figures 
114a and b, and 115a of the same plate. Down from over one 
hundred species of passerine birds has been examined, these being 
representatives of as diversified families as could be obtained, and 
this character has never been found missing on the barbules near 
the base of the well-developed downy barbs. It is never present, 
as far as I have observed, on the barbules on the more distal part 
of the barbs, nor in the aftershaft. 
The pennula of the downy barbules are of moderate length, 
ranging from about 1 mm. in most forms, e. g., Myiarchus and 
Turdus, to 5 mm. in Menura. With a few exceptions, as in Haema- 
toderus (Cotingidae), in the red shoulder patches of Agelaius phoeni- 
ceus, and in a few other cases, usually where the feathers are red, 
