EXPLANATION OF PLATES. 



PLATE I. 



Pigs. 1, 2, 3. Three outer tail feathers of Dri/obaies pubescens, showing 

 individual variation in color marks. 



Figs. 4, 5. Feathers from the back of Dryobates villosus and D. scalaris, 

 respectively, illustrating the striped and barred pattern. 



Pig. 6. Frontal feather of Oeothlypis trichas occidenialis in winter plum- 

 age, illustrating acraptosis. The dark edge wears off in spring, leaving 

 the yellow base exposed. Four times natural size. 



Fig. 7. Feather from back of head of Dendroica occidenialis in winter 

 plumage. The dark edge wears off in spring, exposing the yellow beneath. 

 Three times natural size. 



Fig. 8. Feather from breast of Scolecophagus caroUnus in winter plum- 

 age. The light rusty edge wears off in spring, leaving the black exposed. 

 Natural size. 



Fig. 9. Feather from the back of Plectrophenax nivalis in spring plum- 

 age, the white having worn down and left the black base remaining. 



Fig. 10. Feather from the back of Plectrophenax hyperboreus in spring 

 plumage, the white tip remaining unworn. 



Fig. 11. Feather from the throat of Icterus cucullatus nelsoni, changing 

 from yellow to black by the accession of pigment without moult. Twice 

 natural size. 



Fig. 12. Feather from the back of the head of Icterus bullocki, showing 

 the change from yellow to black by the accession of black pigment. Twice 

 natural size. 



PLATE II. 



Feathers illustrating the stages of transition to a completely black mode 

 of pigmentation. Natural size. 



Figs. 1-6, inclusive. Changes from a streaked plumage. From the 

 under parts of Melanerpes formicivorus bairdi. 



Figs. 7-13, inclusive. Changes from a streaked to a barred, and from a 

 barred to a completely black feather. From the under parts of Sphyra- 

 picus varius. 



Figs. 14-17, inclusive. Changes from a barred to a black stage. From 

 the edge of the throat-patch of the female Sphyrapicus thyroideus. 



