EXTERNAL FEATURES 



17 



QW 



the minute structural differences between feathers are 

 seldom adaptive, which -increases their taxonomic value. 

 As many a bird can be identified 

 from a single feather we need say 

 no more in regard to specificity. 



Structure of a Typical Feather. 

 — An ordinary contour feather or 

 penna shows the following parts : 

 (i) the cyhndrical hollow barrel 

 or calamus, the base of which is 

 embedded in a moat or follicle of 

 the skin ; (2) the main shaft or 

 rhachis, filled with white pith, 

 somewhat quadrangular in cross- 

 section, but convex externally and 

 with a longitudinal furrow along 

 its internal surface next the skin ; 

 (3) the vane, consisting of a 

 bilateral web, which in the case 

 of the pinions serves to strike 

 the air, and is built up of barbs, 

 barbules, and barbicels ; and (4), 

 it may be, an aftershaft or hypo- 

 rhachis, which arises to the inner 

 side at the little pit marking the 

 junction of calamus and rhachis, 

 and consists of a tuft of barbs 

 often with barbules. The basal 

 part of the vane is often downy. 

 The term " quill " should include 

 calamus and rhachis ; the minute 

 opening through which the pulp 

 of the dermis enters the base of Fig. i.— A typical feather r 



, , . , • r 1 rhachis; i.w., inner web of 



the calamus m the growmg feather vane; o.w., outer web of vane; 



is the inferior umbilicus ; the pit 

 at the junction of the calamus 

 and rhachis is called the superior 

 umbilicus ; the transparent partitions across the interior of 



C 



A.S., aftershaft ; c, calamus or 

 quill ; I.U., inferior umbilicus 

 where pulp enters. 



