STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 171 
field of numerous dark bodies a short distance above the inferior um- 
bilicus ; these are developing pigment cells. They soon become more 
conspicuous and pass abruptly into regularly arranged massive black 
rows, corresponding to the differentiating ridges. The whole inner sur- 
face from this point to the distal end appears almost continuously black, 
except for very narrow spaces between the ridges and the sparsely pig- 
mented region in the ventral side of the feather germ. If, however, we 
take a similar preparation from a dark brown feather of a dove, we find, 
instead of dense rows of pigment cells, a comparatively sparse and 
inconspicuous distribution of the latter along the ridges. A cross- 
section of a stage when the barbs are differentiated shows that the 
pigment cell. has given up all of its pigment to the feather funda- 
ment and that nothing remains of it except the nucleus (Plate 9, 
Fig. 42). 
In the nonpareil (Passerina ciris) there are enormous pigment cells 
which also give up all of their pigment contents to the barbules (cf. 
Fig. 40, Plate 8 and Fig. 41, Plate 9). Here is seen a heavy pigmen- 
tation of long barbules, which requires a large supply of pigment. 
Likewise, in the indigo bird (Passerina cyanea) all of the pigment 
formed is used by the feather. 
The persistence of a surplus of pigment in the main body of the 
pigment cell, which I have described for Sterna, seems to have been 
observed by Haecker (90) in the feather germ of Scolopax major. I 
have found the distal portions of barbs, with their barbules, which are 
developed on the ventral side of the feather germ to be unpigmented. 
Pigment cells occur in this region, however, making an almost complete 
circle of pigment cells about the pulp, as seen in cross-section. By 
this arrangement the series of pigment cells (Plate 1, Fig. 4, ers.) 
belonging to each ridge is continued to the distal end of the ridge 
on the ventral side of the feather germ. The pigment cells in the 
distal portions of the ridges, where the feather is not to be pigmented, 
are smaller, however, and less numerous ; and they do not branch nor 
give up any of their pigment. 
This development of pigment in excess of what is used by the feather 
fundament I am inclined to consider as of some phylogenetic importance, 
for it may indicate aneestors whose feathers were much more heavily 
pigmented. 
I have examined white feathers from the dove, and, like Post, have 
found no pigment. 
In the barbules of the completed feather, the rods of melanin are 
