Strone. — Development of Color in Feathers. 
PLATE 38. 
Figs. 15-18. Transverse sections of feather germs of Sterna hirundo. 495. 
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. prc.’ A pigment-cell process apparently 
not entirely filled with pigment granules. 
