Jones — Nestling Feathers. 



PLATE I. 



Figures i, 6, 7, 8, 9, from the chick embryo. Figures 4 and 5, from 

 embryo of Sterna hirundo. Figures 2 and 3, semidiagrammatic from feathers 

 of Larus atricilla. 

 Fig. I, Longitudinal section of developing down and cross section of skin 



from 14-day embryo, x 28. 

 Fig. 2. Diagram showing the relation of the down to the first definitive 



feather when each down barb is continuous with one or more first defin- 

 itive feather barbs. 

 Fig. 3. Diagram showing the relation of the down to the first definitive 



feather when a so-called quill occurs between them. 

 Fig. 4. Semidiagrammatic cross section of down, x 141. 

 Fig. 5. Semidiagrammatic cross section of a definitive feather, x 103. 

 Fig. 6. Portion of a down papilla from 8-day embryo, longitudinal section 



of the papilla, x 618. 

 Fig. 7. A portion of a cross section of down at 7 in Figure i. x 618. 

 Fig. 8. A portion of a cross section of down at 8 in Figure i. x 618. 

 Fig. 9. A portion of a cross section of down at 9 in Figure i. x 618. 



Figures 7, 8, and 9 represent three stages in the development of the 

 down at the time when the insinking of the base begins. 



