STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 1509 
The common condition of asymmetry in the vane, with the barbs on 
one side of the rhachis longer than those of the other side, causes the 
point where the distal ends of the ridges meet to be more or less at 
one side of the median plane of the feather-germ (Plate 9, Fig. 41, dst’.). 
A conspicuous out-curving of the two sides of the feather funda- 
ment at this point is seen in a wing-feather from the dove (Plate 9, 
Fig. 42, dst.). 
The cylinder-cell layer, which forms a continuous sheet of cells 
covering the ridge completely on the pulp side and between adjacent 
ridges, takes no direct part in the formation of barb or barbule. These 
’ which constitute 
the greater portion of the ridge. These intermediate cells become 
are formed exclusively from the “ intermediate cells,’ 
differentiated into three parallel structures, an axial plate, longer in a 
radial than in a tangential direction, and two lateral plates. <A large 
portion of the cells forming the axial plate are ultimately metamorphosed, 
or fused together, to form the barb; the cells which compose the lateral 
plates of the ridge, and which are separated from the furrows by the 
cylinder-cells, are to be connected into barbules, whose attachment to 
the barb will be near the inner or pulp margin of the axial plate. In 
each ridge one lateral plate will form the distal barbules and the other 
the proximal barbules of a single barb. 
Davies (89, Taf. 24, Fig. 19) described and figured clefts or spaces, 
which he found occurring between the plates of barbule cells and the 
cells forming the axial plate. He called these spaces “ Langsfurchen,”’ 
a term which seems inappropriate for a fissure-like space, and especially 
so in this case, because he uses the same word for the spaces that he 
found between successive ridges. The latter could with some reason 
be called furrows, but the spaces between the barbule rows and the 
axial plate are nothing but artificial clefts. I have never found them 
except in preparations that had experienced shrinkage in fixation. In 
osmic material these clefts are altogether wanting, as are also the wide 
V-shaped furrows which he described and figured as occurring between 
ridges (Davies, ’89, pp. 574-5; Figs. 17-19). 
The growth of the cells comprising the feather fundament and the 
proliferation of cells at its basal, or proximal, end brings about a lon- 
gitudinal growth of the feather germ, the sheath preventing lateral 
expansion. 
Davies described this extension of the feather germ as due exclusively 
to cell proliferation at the base, ignoring the growth of the cells asa 
factor. This is partly explained by his conception that there were 
