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SMITHSONIAN MISCELLANEOUS COLLECTIONS [voL. 48 
triangular, pointed distally and sometimes slightly curved hook-like 
at the end (figs. 27, 28, wnL,). Ahlborn (1896, p. 20) mentions 
these processes in his description of the curved fibers and calls them 
“the finest saw-toothlets.” Strong (1902, fig. 25, pl. 5) has rep- 
resented them in his figure of a curved fiber. These processes of the 
curved fibers seem to correspond to and be homologous with the 
hooks of the hook-fibers. They are most highly developed in 
Diomedea where they are extremely narrow and terminate in long, 
fine points. In this region, where on the dorsal margin the teeth, 
and on the ventral the processes appear, the curved fiber is already 
considerably narrowed and it continues to grow narrower distally 
till it finally terminates in a long, fine thread (fig. 28, F). The 
point of transition of the band-shaped proximal portion into this 
terminal thread coincides with the completion of the bend. The 
ventral processes take no part in this bend and retain the direction 
of the basal part of the fiber unchanged. 
We will now consider again the series of transverse sections. We 
have seen that in the proximal parts the upper margin of the fibers 
is involuted spirally and that the curvature decreases toward the 
lower margin, the concave band gradually unrolling itself, as it 
were, toward the latter. Toward the middle of the length of the 
fiber there is a change. The portion of the transverse section lying 
midway between the upper and the lower margins, which before 
was considerably curved first flattens itself out and then forms an 
obtuse angle the reverse way, so that here the section attains the 
shape of a 3 (fig. 27, X). At the same time the whole fiber is 
spirally twisted so that the axis of the transverse section assumes 
first a vertical position and then inclines above toward the secondary 
quill. 
The distal termination of the curved fibers is very similar to the 
long, thin terminal thread of such hook-fibers as those of the Capri- 
mulgi. While in most cases the thread in which the curved fiber 
terminates appears as a simple filament without any differentiation, 
sometimes slight thickenings appear in it at about equal distances, 
which apparently correspond to the nuclei of the cells arranged one 
behind the other, which compose this portion of the fiber (fig. 27, 
V-). The terminal threads of the successive curved fibers are parallel 
with each other and lie close together (figs. 19, 21). 
The curved fibers spring from that side of the secondary quill 
which is turned toward the feather base. Their points of origin lie 
lower than those of the hook-fibers (figs. 3, 4). 
In length the curved fibers surpass the hook-fibers, particularly in 
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