Strong. — Development of Color in Feathers. 



PLATE 3. 



Figs. 15-18. Transverse sections of feather germs of Sterna liirundo. x49o. 

 Fig. 15. Section at level 15 in Figure 1. 

 Fig. 16. Section at level 16, Figure 1. 

 Fig. 17. Section at level 17, Figure 1. 



Fig. 18. Section at level 18, Figure 1. pre' A pigment-cell process apparently 

 not entirely filled with pigment granules. 



