382 University of California Puhlications in Zoology fVoL. 13 



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 (pi. 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 occurrence also in the Trochilidae 

 and all of the Pici except the G-albulidae, 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 115&, and also in figures 

 114a and &, 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 parii 

 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- 

 ceiis, and in a few other cases, usually where the feathers are red, 



