FROM THE SIDES OF THE NECK OF THE DOMESTIC PIGEON. 277 



Fig. 14. A lateral sectional view of a non-metallic-colored barbule from the proximal end of a barb. X540. 



Fig. 15. Diagrammatic sectional view of the apparatus used in measuring color ranges, a, mirror; 6, slit in wall 

 of dark chamber; c, position of feather; d, axis; e, protractor; /, indicator of inclination of feather; 

 g, indicator for position of eye. 



Figs. 16-21. Diagrams indicating relative positions of the observer's eye and the feather with respect to parallel 

 rays of sunlight, for metallic colors. The line AB represents the plane of the feather. The arrows indi- 

 cate the direction of the light from its source to the feather (incident rays) and thence to the eye 

 (reflected rays). The source of light is always on the right side. (See pp. 270-272.) 



