1916] Chandler: Structure of Feathers 297 



dorsal surface as in other birds. Barhs very numerous, about 30 or 

 40 per centimeter on each side, thus in some measure making up for 

 weakness of structure by strengthening vanes. More or less of inner 

 portion of barbs, usually about one-half, furnished with primitive 

 pennaceous barbules ; outer portion downy, compactness of vanes 

 being maintained only by stiffness of rami. Terminal portion of 

 feather devoid of barbules, rami becoming cylindrical and bristly. 

 Inner and outer vanes similar. Distal barbules of pennaceous 

 portion (pi. 15, figs. 6a, 6b) with poorly developed base. Pennulum 

 with a series of ventral barbicels extending to tip, not differentiated 

 into ventral teeth, booklets, and cilia. Usually all of them much 

 curved and hooklike, but not hooked merely at tip as in other 

 birds. Proximal barbules (pi. 15, figs. 6c, 6d) with no bend or 

 sharp differentiation between base and pennulum, the latter dis- 

 tinguishable only by presence of outward-curAdng, dorsal and ventral 

 barbicels, which hardly differ in form from prongs of down barbules, 

 though usually longer. Distal barbules reaching length of about 

 0.35 mm., the proximals about 0.6 mm., the base in each case 

 occupying about half total length. 



2. Down 



Transition from pennaceous to down barbules simple and easy, 

 the hooked form of barbicels of distal barbules being lost and size 

 of those of proximal barbules reduced. Typical down barbules (pi. 15, 

 fig. 6e, and pi. 34, fig. 96) characterized by unusual shortness, not 

 exceeding 0.8 mm. in length, and usually considerably less. Base 

 very narrow and poorly differentiated from pennulum. The latter 

 naked and filamentous basally, but furnished with comparatively 

 long and conspicuous prongs towards tip. As usual in typical 

 down, barbules inserted in four instead of two rows, those of either 

 side alternately projecting in different directions (pi. 15, fig. 6e). 

 Counting all four rows, there are about 60 barbules per millimeter. 



b) Other Types 



The dark feathers of Eudyptes chrysocome are very familiar, differ- 

 ing chiefly in having longer pennaceous barbules (pi. 15, figs, la, lb), 

 which have a dark pigment segregated into transverse bands, as in the 

 feathers of gulls and some pigeons. This probably accounts for the 

 bluish tinge which the feathers of this species have. In Spheniscus 

 mendicidatus the distal barbules are relatively short, while the proxi- 

 mals are long, with a well-developed series of ventral baricels; they 

 are about 0.25 mm. and 0.68 mm. long respectively. 



The stiff, spinelike rectrices of the latter species have a broad, 

 shallow concavity on the ventral side of the shaft, although in the 

 body feathers the shaft is very thin and almost perfectly flat both 

 above and below. 



