Stbono. — Development of Color in Feathers. 



PLATE 6. 



All Figures are from feather germs of Sterna hirundo. 



Fig. 30. Transverse section showing first appearance of pigment granules in the 



cytoplasm of the pigment cell. X 1500. 

 Figs. 31-34. Successive stages in development of pigment cells. Figures 31 and 



32 represent about the same stage. X 1500. 

 Fig. 35. Pulp edge, or apex, of a ridge of the fi-atlier fundament, showing three 



pigment cells with granules crowded into an opaque mass and with 



processes beginning to be formed. X 1500. 

 Fig. 36. A somewhat later stage, showing pigment granules or rods entering 



barbule cells (compare Plate 3, Fig. 17). X 1500. 



