FEATHERS. 421 



feather. The barbs are narrow elastic laminae which, project 

 obliquely on each side from the rhachis. The barbules are also 

 set obliquely on each side of the barb, in such a way that those 

 on the distal side of a barb, i.e. those pointing towards the apex 

 of the feather, cross several of the barbules on the proximal side 

 of the next barb, i.e. on the side of the barb turned towards the 

 quill end of the feather. The distal barbules possess on their 

 lower face, i.e. on the face turned towards the body of the animal, 

 a number of minute processes (barbicels or cilia) with hooked 

 terminations (kamuli). The upper edges of the proximal 

 barbules are folded over so as to form a flange with 

 which the hamuli of the distal barbules of the adjacent 

 barbs interlock. In this way the barbs on each side of 

 the rhachis are closely connected together into an almost 

 air-tight web. The hyporhachis or after shaft is a second shaft 

 arising from the calamus just proximally to the superior um- 

 bilicus. In the cassowary it is as large as the main shaft, but 

 in other birds it is much smaller, and is sometimes absent. It 

 possesses barbs and barbules, but not barbicels. In the de- 

 veloping feather the vascular pulp of the quill extends through 

 the superior umbilicus along the ventral side of the rhachis. The 

 two rows of barbs converge at the proximal end of the rhachis 

 so as to run into one another proximally to the superior umbi- 

 licus. 



According to the nature of the rhachis and barbs, the 

 following kinds of feathers may be distinguished : Contour 

 feathers (pennae) with stig^jhaft and firm vexillum ; down 

 feathers (plumulae) with soft shaft and v ane, and without hooks ; 

 filoplumes with slender hair-like shaft with few or no barbs. 

 The contour feathers appear on the surface and attain their 

 greatest development as the remiges (wing- quills) in the wing 

 and the rectrices (tail -quills) in the tail ; they usually possess 

 hamuli. The down feathers fonn the deep layer of the plumage 

 and are covered by the contour feathers ; they serve for the re- 

 tention of warmth, and in some cases are without a shaft, the 

 barbs arising in a tuft from the end of the quill. The filoplumes 

 are distributed among the contour feathers and arise near their 

 base. There are many forms of feather intermediate between 

 these principal forms. Powder -downs are down feathers the 

 ends of which break off into a fine dust ; they occur in patches 



