356 Universitij of California Publications in Zoology [Vol. 11 



tip, each forming approximately half the length, which is 1.45 

 millimeters. 



The under tail coverts, consisting of three or four rows of 

 feathers back of the anus, are, in general appearance, very much 

 like the feathers of the belly and flank, but are always better 

 developed, possess filoplumes, and differ in some details of struc- 

 ture. The aftershaft is small, especially in the terminal row, 

 but the main shaft is comparatively heavy and stiff, nearly 

 round in cross-section, and with practically no groove on the 

 under surface. There is no noticeable difference in form or 

 structure in the feathers of the different rows, but thej^ increase 

 considerably in size from the anterior to the po.sterior row, 

 those of the former being about seven centimeters long, while the 

 po.sterior ones are twelve centimeters. Over half of the feather is 

 furnished with typical downy barbs, only the distal three-eighths 

 being provided with booklets and grooves, these, however, being 

 held together much more firmly than the belly feathers. 



On the more proximal portion of the feather there are as 

 many as thirty barbs per centimeter, and the filamentous bar- 

 bules, two to three millimeters long, are very dense, there being 

 about thirty-seven per millimeter on each side, thus producing a 

 cottony apearance, but the downy portion near the middle of the 

 feather, as in the case of the flank feathers, has a more open and 

 fragile appearance, due to a decrease in number of both barbs 

 and barbules. In the interlocking area, where there are twelve 

 or fourteen barbs per centimeter, the differentiated barbules are 

 of a higher type than those of the belly feathers. The distal 

 barbules, of which there are about eighteen per millimeter, have 

 bases 0.3 millimeter long, three well-formed booklets, and a series 

 of large curving ventral barbicels, the dorsal ones being small 

 and weak. The total length of the distal barbules is about 0.95 

 millimeter. The proximal barbules, which are from 0.95 to 

 1.00 millimeter long, have comparatively slender, tapering bases, 

 with a few weak, spinous ventral lobes, and a filamentous tip 

 which sometimes bears a few rudimentary barbicels. There 

 are about 14 of these barbules per millimeter. 



It is very noticeable that the ordinary contour feathers of the 

 trunk, which have no special function other than conservation of 



