MASCHA| ° STRUCTURE OF WING-FEATHERS 19 
the hook-fibers are longest. Here the proximal band-shaped part 
of the fibers measures on an average 250 in length, the terminal 
thread which is composed of about fifty cells, 1.77 mm. and the 
whole hook-fiber 2.02 mm. The terminal thread is about eight 
times as long as the proximal band-shaped part. Towards the middle 
of this vane the proximal part of the hook-fibers becomes longer, 
measuring 300 to 350m, and the terminal thread, here composed 
of only about 30 cells, shorter, measuring only 7op, so that the 
whole fiber is only 1.27 to 1.32 mm. long, and the terminal thread 
about three times as long as the proximal part. Near the tip of the 
feather we find hook-fibers, the proximal part of which measures 
200 » and the terminal thread, here composed of only 8 to Io cells, 
270m. Here the whole fiber is 470 long and the terminal thread 
only slightly longer than the band-shaped proximal part. The 
hook-fibers also, arising from the same secondary quill, are not all 
alike. The proximal band-shaped part remains fairly constant but 
the terminal thread varies considerably. Let us take a secondary 
quill of the middle of the above-mentioned feather vane: The 
proximal fiber portion on the whole length of the secondary quill is 
300 to 350 p long. 
The terminal thread is shortest and composed of fewest cells in 
the fibers arising proximally, nearest the main quill. Distally the 
terminal thread lengthens and the number of cells composing it in- 
creases until just beyond the middle of the secondary quill; further 
on toward the feather margin it again becomes a little shorter. 
In the anterior narrow vane of the same feather the hook-fibers 
are considerably shorter than in the broad inner vane. Measure- 
ment in the middle portion of the feather gives an average length 
of 600 » for the hook-fibers of the narrow vane as against 1.28 mm. 
for the hook-fibers in the corresponding part of the broad vane. 
The proximal band-shaped part is 300 long in the narrow vane, 
that is to say, just as long as the terminal thread. There are four 
or five hooks on the fibers of both vanes. 
In this place I may mention a few developments of hook-fibers 
characteristic of the feathers of owls. The cells forming the termi- 
nal thread bear one or two spines each, but whether one or two 
depends upon the position of the fiber. In the middle of the narrow 
outer vane of the distal hand-remiges the terminal threads of the 
hook-fibers are composed of about ten cells each, and provided with 
ventral spines only. In the middle of the broad inner vane the 
terminal threads of the hook-fibers arising from the proximal parts 
of the secondary quills are composed of cells which likewise bear 
