1914] Chandler: Feathers of Circus hudsonius 353 



five to thirty per millimeter on each side, reaehiug a length of 

 3.5 millimeters. The line of demarcation between the differen- 

 tiated barbules and the downy ones runs out farther and farther 

 from the shaft, the distal half of the feather having no downy 

 barbules. The distal barbules of the differentiated portion of 

 the feather are in general very slender and weak, varying in 

 length from 0.95 millimeter on the basal fifth of the feather, to 

 1.25 at the middle, and decreasing again to about 0.85 near the 

 tip. A tjT)ieal distal barbule from near the middle of the feather 

 (pi. 18, fig. 10) has a base about 0.35 millimeter long, followed 

 by a single lobe, and then from two to four small, weak hooklets. 

 The long, slender tip is armed with a single series of fairly long, 

 curved barbicels on the ventral side of the barbule, those of the 

 dorsal side being rudimentary or absent. The proximal barbules 

 (pi. 18, fig. 11) are of almost exactly the same length as the distal 

 barbules opposite them, but the base is miich longer, being over 

 0.6 millimeters, though only about 0.04 millimeters in width. 

 At the bend, which is sharply defined only in the more basal 

 barbules, there are three or four sharp spines, the barbule mean- 

 while tapering to a threadlike tip. Toward the tip of the barb, 

 the bases of the proximal barbules taper gradually into the tips, 

 which are filamentous and bear a double series of weak, rudi- 

 mentary barbicels. 



The feathers of the upper back, as compared with those of 

 the middle back, have more barbs per centimeter on the shaft, 

 there being twenty-two and twenty-six on the inner and outer 

 vanes respectively, and the downy portion is considerably in- 

 creased. The feathers are inserted at nearly 90 degrees to the 

 body of the bird, and stand closer together, the shaft being, 

 therefore, very sharply curved in order to bring the interlocking 

 terminal portion of the feather to lie flat on the bird. The 

 barbules are less numerous, there being eleven proximals and 

 sixteen distals per millimeter. 



The feathers of the nape are in general more elongate and 

 narrow. They have an average of twenty-four and twenty-eight 

 barbs per centimeter on the outer and inner vanes respectively, 

 and have the same wide spacing of the barbules exhibited by the 

 upper back feathers. 



