Stbono. — Development of Color in Feathers. 



PLATE 5. 



All Figures are from feathers of Sterna hirundo except Fig. 29. 



Fig. 23. Transverse section of feather germ at level 23 in Fig. 1. X 495. 

 Note, — By an oversight tlie proximal and distal barbules are lettered brb. instead 

 of hrbl. 



Fig. 24. Transverse section of wing-covert, showing withdrawal of barbs from the 

 surrounding tissue preceding the unfolding of the feather. X -lOS- 



Fig. 25. A proximal barbule from wing-feather. X 117. 



Fig. 26. A distal barbule from wing-feather. X 117. 



Fig. 27. Middle portion of a barbule from wing-feather showing distribution of 

 pigment, the form of the cells composing the barbule, and the forma- 

 tion of barbicels. Cornification is not yet complete. X 495. 



Fig. 28. Distal portion of barbule siiown in Figure 27. X 495. 



Fig. 29. Transverse section of barb from blue portion of a body-covert of Pas- 

 serina cyanea with portions of barbules on either side. X 495. 



