1916] Chandler: Structure of Feathers 271 



similar to that of the proximal vanules of the downy barbs of the 

 feather proper, in ease there is any special modification in the distal 

 vanules, as in gallinaceous birds. 



c) Pennaceous Barhules. — Concerning the pennaceous portion of 

 contour feathers of the trunk, all degrees of development of structure 

 can be found. In ratite birds, as is well known, there is never any 

 pennaceous structure developed, although the bases of the barbules 

 in Bhea (pi. 13, fig. la) are exceptionally well developed for down, 

 and seem to indicate a transition to or from a pennaceous type of 

 barbule. In typical trunk feathers there is no differentiation of 

 inner and outer vanes, and usually the structure is a mere simplifica- 

 tion of that found in the more highly specialized remiges. In the 

 contour feathers of the trunk, as would be expected, the distal bar- 

 bules are of the type of the outer vane of the remiges, and the proxi- 

 mal barbules of the type of the inner vane of the remiges, often in 

 very degenerate form, these types being the ones showing the lesser 

 degree of specialization. In the trunk feathers the conspicuous basal 

 dorsal cilia are seldom developed on distal barbules, and ventral cilia 

 seldom occur on the proximal barbules (pi. 20, figs. 20e and /). In a 

 great many birds these structures in trunk feathers are very much 

 simpler than they are in the remiges, all of the barbicels being very 

 much reduced or even absent. In distal barbules the cilia often 

 disappear entirely, the booklets are reduced to one or two very weak 

 ones, and the ventral teeth are represented only by a very small, 

 inconspicuous projection (pi. 33, fig. 92e) ; the proximal barbules 

 frequently lose the sharp differentiation between base and pennulum, 

 becoming evenly tapering all the way to the tip (pi. 33, fig. 92/). 

 Such modifications are always farther advanced on the breast and 

 belly feathers than on those of the back, the back feathers often 

 being intermediate between the remiges and coverts on the one hand, 

 and the breast and belly feathers on the other. 



In some birds the pennaceous barbules of trunk feathers have 

 special modifications of their own, and, as might be expected, these 

 are usually more conspicuous and better developed on breast than 

 on back feathers. The most peculiar structural modification charac- 

 teristic of trunk feathers only, and the only one which needs special 

 mention here, is the development of curved dorsal barbicels on the 

 base of both distal and proximal barbules (pi. 17, fig. lOe, 12a, 5). 

 Since these barbicels are not homologous with any other types of 



