The marriage of a strip of upper barbs to a correctly matching strip of lower barbs is quite easy if the face side of the upper strip is placed slightly behind the face side of the lower strip. If the strips are overlapped immediately above and below one another, or perhaps the upper strip is in front of the lower strip, due to their arrangement on the barbules, a complete interlocking of hooklets to flanges will not occur. If a strip is overlaid with another strip, but the matching strip is upside down, this arrangement of barbicels will not allow the strips to marry. If a right strip is overlaid with a left strip, even though the proximal to distal arrangement of the barbules is correct, no reliable marriage will occur, because the hooklets and flanges do not align.
Many feathers develop fault bars across the vane.
As feathers grow, a disruption in cell development may occur leaving distinct lines across the vane generally perpendicular to the shaft. These are due to stress, other abnormal conditions, or may be present under normal conditions. A fault bar's appearance is due to underdevelopment of barbules or total lack of barbules in the area of the disruption. Global Fly Fisher . All rights reserved.