Strong. — Development of Color in Feathers. 



PLATE 4. 



Figs. 19-21. Transverse sections of feather germ of Sterna liirundo. X 495. 



Fig. 19. Section at level 19, Figure 1. 



Fig. 20. Section at level 20, Figure 1. 



Fig. 21. Section at level 21, Fig. 1. cl. pig. Unused pigment. 



Fig. 22. Section of feather germ of body covert of Passerina cyanea, showing 

 pigmentation of blue portion of feather and also the witlidrawal of 

 the feather elements from the surrounding tissue. X 496. 



