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 tiiis 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 tlie 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, crs.) 

 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 

 fiuidament I am inclined to consider as of some phylogenetic importance, 

 for it may indicate ancestors 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 



