310 University of California PiiblicationH in Zoology I Vol. ] 3 



all of the cells clearly marked off by ridges. The barbules are set 

 fairly close together, the distals being about 30 and the proximalfj 

 18 per millimeter. 



In the outer vane of the secondaries are to be found the most 

 unusual types of barbules in the whole avian class. The portion 

 of the vane which possesses a beautiful silvery grey color owes this 

 entirely to the pennula of the distal barbules (pi. 18, fig. 13c). The 

 bases are similar to those of the inner vane, but the pennula are 

 profoundly transformed into thick, clumsy, inflated, sacklike ex- 

 pansions, filled with opaque air bubbles which, when the barbules 

 are immersed in balsam, become infiltrated and rendered transparent, 

 leaving the round nuclei appearing like eyelike spots. There are 

 no dorsal cilia whatever, the booklets are only three or four in num- 

 ber, short and heavy, and the ventral cilia are produced into extremely 

 long, filamentous processes, lying closely appressed to each other, and 

 extending far beyond the tip of the expanded portion of the pennulum. 

 There are nine or ten short cells in the pennulum beyond the 

 booklet region, each with a long ventral barbieel, so that there is 

 a dense brush of these. The deep black pigment of these barbules 

 has a peculiar distribution, being dense in the base and in the 

 hooklet cells and first two cilia cells of the pennulum, but absent 

 in the terminal part of the pennulum. Distal to the silvery area, 

 the pennula lose their inflated form and long cilia, then resembling 

 those of the inner vane, but with no dorsal spinelike cilia. The 

 proximals of the outer vane (pi. 18, fig. 13c?) are hardly distin- 

 guishable from those of the inner vane, except that the pennulum 

 is slightly shorter, and the recurved dorsal spines more prominent. 



The back feathers of Plotus are modifications of the same type. 

 The proximals (pi. 18, fig. ISg) have a similar short, relatively 

 broad base, and the pennulum with recurved spines, but it is pro- 

 duced into a long, slender filament, and ultimately the whole bar- 

 bule is transformed into down on the more basal barbs. On the 

 more distal barbs the pennula become elongated and lose their 

 broad character, at the same time developing a few very weak and 

 minute ventral cilia, but the typical form of the whole barbule is 

 then soon lost and it becomes merely rodlike in form with a few 

 ventral barbicels. The distal barbules also ultimately assume this 

 form at the tip of the barbs. On the black portion of the feather 

 the distal barbules (pi. 18, fig. 13/) have long, slender bases with 

 small but typical ventral teeth, no hump on dorsal contour between 



