1914] Chandler: Feathers of Circus huclsoiiius 337 



umbilicus there is a decided bend in the entire feather in the 

 direction of the inner vane, and there is an even curve toward 

 the under surface, somewhat increased at the tip, where the 

 vanes are also somewhat rotated on their axis to comply with 

 the different physical forces which come into play at the tip of 

 the wing, and to permit the free passage of the air during its 

 up-stroke. 



The points of origin of the rami of both vanes have a common 

 beginning on the lower surface at the superior umbilicus, and 

 proceed in an even curve toward the dorsal surface, coming to 

 the plane of the upper surface of the shaft at about the 

 proximal fourth of the vanes. 



The shaft is quadrangular in cross-section, becoming so 

 immediately on the under surface, but remaining rounded ou 

 the upper surface to the point where the origin of the barbs 

 reaches the dorsal surface. At this point the shaft measures 

 2.8 millimeters on the under surface, 1.86 millimeters on the 

 upper surface, and approximately 3 millimeters in depth, taper- 

 ing evenly from here to the tip. The under side is grooved in 

 the middle for almost its entire length. 



As is usual with birds having highly developed flight, the 

 vanes of some of the primaries are incised, i.e., abruptly nar- 

 rowed toward the tip. On the inner vane of the feather this 

 involves no change except the shortening of the barbs, and a 

 slight decrease in the angle made with the shaft, but in the outer 

 vane the character of the barbs is considerably changed beyond 

 the point of incision. The angle made with the shaft is reduced 

 from over 40 degrees to about 7 degrees, the intervals between 

 origins on the shaft being thereby much increased, so that 

 whereas about eighteen or twenty barbs per centimeter spring 

 from the shaft on each side proximad to the incision, distad to 

 it there are only four per centimeter. In addition to this, the 

 ramus is increased in depth, and correspondingly in strength, to 

 such an extent that while the dorsal .surface of the barb is in 

 the same plane with the dorsal surface of the shaft, the ventral 

 surface, at the point of origin, is in the same plane as the 

 ventral surface of the shaft. The barbs of the outer vane are 

 thus rendered very stiff and elastic, and hold their place, even 



