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MASCHA | STRUCTURE OF WING—FEATHERS 23 
the terminal threads of the former which are always longer than 
those of the latter in the same part of the feather. In Nyctea nivea, 
for instance, the proximal portion of the hook-fibers is on an aver- 
age only 300 to 350, those of the curved fibers, g00 long. The 
shape of the curved fibers is very constant. With the exception of 
a few isolated cases, such as Diomedea, in which the ventral mem- 
branous processes display a peculiar structure, they are entirely 
similar in all birds, differing only in respect to their size, which 
is proportional to that of the whole feather. The number of the 
curved fibers is somewhat less than that of the hook-fibers. The 
reason for this is that they are 30 to 40» apart, which is a little 
greater than the distance between the hook-fibers. 
6. The Formation of the Feather-Plate 
The two kinds of tertiary fibers described above together form 
the greater part of the plate represented by the feather. As 
Schroeder (1880, p. 3) tells us in the historical part of his work, 
Marcellus Malpighi, the first investigator who occupied himself 
with the study of the feather, could only speak of an interweaving 
(amplicatio) of its smaller elements. Subsequent investigators de- 
clared that these elements were too small for exact study. Nitzsch 
(1840, pp. 14, 15) was the first to try to solve the problem. He 
pointed out that the hooks of the upper “ rays” (hook-fibers) were 
designed to grip the lower fibers. This they do by inserting them- 
selves into small depressions in the sides of the latter. These “ de- 
pressions ’ of Nitzsch’s are however not depressions at all but the 
nuclei of the cells composing the curved fibers. Burmeister in a 
note pointed out this error (Nitzsch, 1840, p. 15), and stated that 
the hooks were too short to reach these “* depressions ”’ of the curved 
fibers. According to him the hooks are intended to grip the upper 
margin of these fibers, which he considers thickened and which he 
says they just reach and actually grasp. Schroeder (1880, p. 10), 
and Klee (1880, p. 18) discovered that the upper margin of the 
lower (curved) fibers is not thickened, as Burmeister had thought, 
but involuted to form a groove, which makes the impression of a 
thickened edge in surface views of the feather magnified with the 
microscope. This involuted margin is grasped by the hooks of the 
hook-fibers, which can glide backward and forward beneath it with- 
out relaxing their grip. Wray (1887, p. 422) and Ahlborn (1896, 
p. 20) also describe the formation of the feather-plate. According 
to them the hooks of the hook-fibers penetrate into the layer of 
underlying curved fibers and take hold of the membranous ventral 
