FEATHERS 7 



NITZSCH, and among recent writers more especially by 

 WE AY. 1 A typical feather consists of the stern or rhachis, 

 of which the lower ' quill ' region is termed the calamus. 

 From the rhachis above the calamus spring a series of lateral 

 branches, the rarni or barbs, which in turn give rise to 

 barbules, and they to minute, often hooked, processes, the 

 barbicels. At the junction of the calamus with the barb- 

 beariiig rhachis arises in many feathers an aftershaft (fig. 

 4), which has the character of a second smaller feather 

 arising from the shaft of the first ; but in the cassowary, 

 emu, and the extinct Dinornis this aftershaft is as large as 

 the main feather from which it arises. The barbicels with 

 their terminal hamuli give the stiffness to the feather which 

 is caused by the interlocking of these processes. The bar- 

 bules are of two sorts, those nearest to the root of the barb 

 being different from those nearest to its tip. The former 

 are shaped something like a knife blade ; they are thickened 

 above and bent in the middle, gradually tapering away to 

 a fine point ; just in the middle, where the bend is, are 

 two or three small teeth on the upper margin. It is by 

 means of these teeth that successive barbules are locked 

 together. The remaining set of barbules are frayed out 

 towards the end into a series of branchlets which are 

 hooked at first, but the more distal set are merely fine- 

 pointed branchlets ; these arise obliquely, so that a given 

 barbule comes into relation with four or five other barbules. 



All feathers, however, have not so complicated a structure. 

 The strong wing feathers of the cassowary consist of the 

 stem alone. Filoplumes have but few radii, consisting 

 almost alone of the calamus and rhachis; 



Down feathers are as a rule without the hamuli ; often 

 the radii spring at once from the calamus, there being 

 no rhachis. 2 A peculiar form of these feathers, called 



1 ' On the Structure of the Barbs, Barbules, and Barbicels of a Typical 

 Pennaceous Feather,' Ibis, 1887, p. 420. 



- The term neossoptiles has been applied to the down covering the newly 

 hatched young of many birds, in contradistinction to telcoptiles, the feathers 

 (down or contour) of the adult bird. 



