Strono. — Development of Color in Feathars. 



PLATE 1. 



All Figures except 7-9 are of Sterna hirundo. 



Fig. 1. Diagrammatic longitudinal section. X15. Figures 12-21 and 23 were 



drawn from sections taken at the points indicated by the dotted 



lines 12, 13, 14, etc. 

 Fig. 2. Semi-diagrammatic cross-section, indicating by an asterisk (*) the region 



chosen for illustration in Figures 12-21 and 23. 

 A portion of a barb and its barbules seen from the dorsal side. Xll7. 

 A " primary " feather having been split dorso-ventrally and the pulp 



removed, the inner or pulp, surface of the proximal portion of one 



half of the feather fundament is here shown. X16. 

 External view of definitive feather germ. The dotted line 23 corresponds 



in position to the line 23 in Fig. 1. 

 Diagram, to show position of barbules with reference to the barb, while 



still enclosed in the feather sheath. 

 Transverse section of barb from blue body-covert of Sialia sialis. X495. 



as'. Ventral ridge of cortex of barb. 

 Transverse section of barb from blue wing-covert of Cyanocitta cristata. 



X495. 

 Transverse section of barb from brown wing-covert of the "homer" 



pigeon. X4y5. 



