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MASCHA] STRUCTURE OF WING—FEATHERS 17 
do not extend downward but raise themselves and point toward the 
margin of the feather. 
The spines of adjacent hook-fibers therefore cross each other at 
an angle of about go°, and thus form a system of rectangularly 
crossing threads similar to that formed by the hook and curved 
fibers. It is this peculiar structure of the distal portion of the hook- 
fibers which gives to the remiges of owls their great softness. 
If one reflects that the distance between the secondary quills 
amounts only to 250 to 300m while the hook-fibers reach a length 
of 2 mm., it becomes clear that the hook-fibers attached to one 
secondary quill project a good distance beyond the next one, and 
often reach the second, or even the third or the fourth secondary quill. 
The many long terminal threads of the hook-fibers thus forming 
several overlapping layers, together with their numerous rectangu- 
larly crossing spines, form a dense, felt-like mass on the dorsal 
side of the feather. The constituent parts of this mass are prevented 
from becoming deranged through exterior mechanical influences 
by an extremely interesting arrangement. If one cuts through the 
proximal portion of the feather vane parallel to the direction of the 
hook-fibers and slightly magnifies the section thus exposed, it is 
seen that the proximal band-shaped portion of the fiber les almost 
horizontal and that the distal part rises abruptly up at an angle of 
aon, 40. (figs: 12, 32). 
The hook-fibers of the Caprimulgi are very similar (fig. 13) to 
those of the owls, but the proximal band-shaped part of the hook- 
fibers of their remiges is relatively short and the terminal threads 
considerably lengthened. There are three to five rather narrow 
hooks, the distal ones being considerably longer than the proximal. 
The limits of the cells forming the fiber are often clearly recognizable 
in the hook region on account of their being somewhat raised and 
also on account of their color. As the hook-fibers of the remiges 
of the owls, so also those of the remiges of the Caprimulgi are dis- 
tinguished from the hook-fibers of other birds by the peculiar de- 
velopment of their thread-like, distal part. In the hook-fibers of the 
first hand-remiges of Podargus humeralis, the proximal, band- 
shaped part is 200 », the terminal thread 2.3 mm. long, that is, more 
than eleven times as much. While, however, the terminal threads 
of the hook-fibers of the Striges bear a great number of spines dor- 
sally and ventrally, such processes are entirely absent on the terminal 
part of the Caprimulgus hook-fibers. There are indeed immediately 
beyond the hooks one or two dorsal spines and four or five ventral 
the first remex. In the lower proximal third of this vane 
