MASCHA] STRUCTURE OF WING-FEATHERS 21 
the hook-fibers, but appears involuted (fig. 28, R). Klee (1886, 
p. 18) was the first to show that the dorsal margin of the curved 
fiber is not thickened but involuted to form a groove in which the 
hooks of the hook-fibers are inserted. As before-mentioned these 
fibers are transversely bent in the shape of a groove. The concavity 
lies towards the secondary quill from which the fiber arises. It is 
most pronounced above and flattens out below, the section being an 
evolvent (fig. 27, .). Perhaps one may consider the slight thicken- 
ing of the upper margin in the proximal part of the hook-fiber a 
formation corresponding to the involution of the curved fiber (fig. 
26, Wit). The sections show that the fiber is thickest at the dorsal 
involuted margin, decreases in thickness downward and thins out 
to a fine membranous lamella below. This lower lamellate portion 
has not the same curvature as the upper part but displays toward its 
margin an inclination to bend in an opposite direction so that the 
transverse section becomes slightly S-shaped. The curved fibers 
like the hook fibers consist of a single row of cells lying one behind 
the other. A row of nuclei extending obliquely upward and out- 
ward is clearly visible (fig. 27, K), and one can also make out the 
cell limits. 
The ventral margin of the proximal part of the fiber is continuous 
up to the bend, or only interrupted by shallow incisions so as to 
appear-somewhat wavy. The dorsal involuted margin retains its 
direction, the diminution of the fiber in width toward the end is 
caused only by the falling back of the ventral margin. In the region 
of the bend three or four tooth-like projections are observed at the 
upper, here less strongly involuted margin of the fiber. These teeth 
are turned backward and pointed. The middle ones are usually best 
developed (fig. 27, Zf), and correspond to a certain extent with the 
hooks on the hook-fibers. In cases where the hooks are broad, 
the teeth also are large, while in the case of birds whose hooks are 
long and thin, the teeth are often very small and hardly discernible. 
The first case is exemplified by the Psittaci, Columba and Anseres, 
the second by Diomedea and the Striges. It is remarkable that 
these tooth-like projections, which are not particularly difficult to 
see, have hitherto been mentioned in only a single description of 
feathers (Wray, 1887, p. 421, pl. x, fig. 2). They have either 
quite escaped the other observers, or have appeared to them not 
worthy of notice. I believe that their function is far from unim- 
portant. 
In and beyond this region the ventral margin is divided by sev- 
eral deep incisions into a number of processes. These processes are 
