6 A HISTORY OF BIRDS 



A typical contour feather consists of a central axis, and a 

 vane or vexillum. The axis is divisible into two portions : (a) 



III. I. — Diagrams Illustrating the Structure of a Feather 



I. A contour feather showing the calamus or quill (C), the rhachis or shaft 

 (R), and the web or vane (V) attached thereto. On the right-hand side of the 

 vane is a portion showing the appearance presented under a low magnifying 

 power, B = barb and Bs = barbule. 



II. A section cut across two barbs parallel with the barbules of the anterior 

 series to show the method of interlocking. 



III. Shows a barbule of the anterior series (A) with its booklets, and two 

 barbules of the posterior series (B). 



a hollow " calamus," and i^) a solid rhachis or shaft. The calamus 

 forms the lower portion of the axis and is inserted by its base 



