Mr W. Macgillivray on the Covering of Birds. S59 



but when the anterior barb is pulled downwards, or the posterior 

 barb upwards, there is found to be no cohesion at all. The 

 curved form of the barbules is distinctly seen by the naked eye, 

 in the tail-feathers of Buceros galeatus. 



The barbules themselves frequently present an appearance 

 similar to that of barbs, giving off laterally two series of fila- 

 ments, which may be termed barbicels, barhiceUa. These fi- 

 laments are much more sparse than those of the barbs, but their 

 object appears to be the same, namely that of connecting the 

 barbules, and retaining them in apposition. They are very dis- 

 tinctly seen, with the aid of a small magnifying power, in the 

 quills of Falco fulvus^ Diomedea exulans, and Buceros galea- 

 tus. 



It may here be remarked, that, while what has been assumed, 

 for the purpose of general description, as a perfect feather, is, 

 what is termed in botany, supra-decompound, there is yet in 

 feathers the following gradation in respect to division : 



1,9^, A feather may have only a tube and a shaft, without any 

 other part ; for example, the quill of the cassowary. 



9.d, There are feathers which have a tube, a shaft, and barbs 

 destitute of barbules; as in the crest-feathers of the golden 

 pheasant. 



3 J, Feathers consisting of tube, shaft, barbs, and bai'bules ; 

 as in most birds. 



^thy Feathers composed of tube, shaft, barbs, barbules and 

 barbicels, as in the examples mentioned above. 



A barb also may have barbules in one part, and be simple 

 toward its extremity, which is a case of very frequent occur- 

 rence ; but these, and similar modifications, will be more proper- 

 ly treated of, when we come to the varieties of form and struc- 

 ture exhibited in the plumage. 



Feathers, then, in general, consist of three parts, — the tube, 

 the shaft, and the webs; or they may be primarily divided into 

 two parts, the tube and the vane, the latter of which consists of 

 the shaft and webs. The webs consist of barbs furnished with 

 barbules. 



With respect to the immediate consequences of their mecha- 

 nical structure, it may be remarked of feathers in general, that, 

 from being convex above, they resist flexion or fracture more 



r2 



