1914] Chandler: Feathers of Circus hudsonius 343 



The distal barbules (pi. 17, fig. 6) are short, being about 

 0.6 millimeter in length, and are characterized by unusually long 

 barbieels on the ventral side, but mere rudiments on the dorsal 

 side. The barbules of the barbs distal to the incision do not 

 differ materially from those proximal to it. 



The minute structure of all the primaries is very similar, 

 the tenth, for example, differing from the third only in the 

 greater length and consequent slenderness of both kinds of 

 barbules. The proximal barbules of the inner vane of the tenth 

 primary are about 1.2 millimeters long with a 0.65 millimeter 

 base, while the distal ones are 1.35 millimeters long with only 

 a 0.23 millimeter base, which is somewhat shorter than in the 

 second primar.y. 



The secondaries differ from the primaries microscopically only 

 in very minor details. The inner vane is precisely similar to 

 that of the innermost primaries in the details of its finer struc- 

 ture, except in the .slightly narrower rami, but the outer vane 

 differs in a few details. The distal barbules, of which there are 

 about twenty-six to twenty-eight per millimeter on each side, 

 differ from those previously described in having a proportion- 

 ately longer base, and a stouter tip with slightly longer and 

 le.ss spreading barbieels. The proximal barbules are of the same 

 barbicelled type as in the outer vane of the primaries, the only 

 noticeable differences being in the sharper points of the sawlike 

 teeth on the ventral side of the bend, and the somewhat better 

 developed dorsal barbieels on the terminal portion. 



As stated before, the remiges are the most important and 

 most highly specialized feathers of the body, and, as shown here, 

 possess a great many adaptive modifications. The elongation 

 of the third and fourth primaries, and the large number of 

 secondaries, are responsible for the long, moderately pointed 

 shape of the wing, which is so well suited for the manner of 

 flight employed by Circus hudsonius. The incision of the outer 

 primaries, their inward and downward bend, the rotation of the 

 vanes on their axis toward the tips of the feathers, the stiff, 

 narrow outer vanes, and broad, flexible inner vanes, and the 

 increasing flexibility of the more proximal .secondaries, are all 

 mechanical adjustments to meet the varying physical forces 



