1914] Chandler: Fcathfvs of Circus hudsonius 345 



Greater Under Coverts 



The greater under coverts are peculiar in that they lie in the 

 same position as do the remigas, thus exposing their under 

 surface instead of the upper, as do all the other feathers of the 

 body. They have very short calami, their chief function being, 

 apparently, to cover the bare calami of the remiges. Their 

 shafts are tlat, straight, and very tiexible, with an inconspicuous 

 groove running a short distance out from the umbilicus. The 

 vanes are practically equal. The barbs, of which there are about 

 twenty-five per centimeter on the inner vane, and twenty-three 

 on the outer, and whose rami are only 0.12 millimeter deep at 

 the base, are furnished with the normal type of proximal barbule, 

 the filamentous tip being long and very slender. The distal 

 barbules have a rather short base, with two or three weak hook- 

 lets, but an extremely long tip with a double row of weak, 

 scattered barbieels. 



There is a very considerable decrease from base to tip in 

 the number of barbules per unit of distance. On the barbs near 

 the base of the feather the number of barbules per millimeter 

 decreases from about forty-five distals and thirty-three proximals 

 at the base of the barb to thirty-one distals and twenty-four 

 proximals near the outer limit of the differentiated portion, the 

 average for these basal barbs being about forty di.stals and thirty 

 proximals per millimeter. The downy barbules on the outer 

 portion of the barbs are in turn more numerous than the 

 differentiated barbules immediately preceding them, there being 

 twenty-nine per millimeter on the proximal side, and thirty-five 

 on the distal side. The uneven distribution of these barbules on 

 the two sides is interesting, since there can be no functional 

 reason for .such an arrangement of undifferentiated barbules. 

 In the differentiated types, on the other hand, the proximal 

 barbules must be spaced to accommodate the booklets of the 

 distal barbules, and there is therefore a correlation between the 

 distance apart of the proximal barbules, modified by their angle 

 with the ramus, and the intervals between the booklets of the 

 distal barbules. At the tip of these under coverts, the number 

 of barbules ranges from twenty-nine distals and twenty proximals 

 at the base of the barbs, to twenty-six distals and seventeen 



