26 



a series of capsules fitted one upon the other and united together by 

 a central pedicel. This is termed the pith by some authors, and is 

 the remains of the pulp, which is seen as a highly vascular body in a 

 young feather. The shaft is always more or less of a square form, 

 tapering gradually from the point where it is connected to the barrel 

 to its free extremity or apex, and is more or less curved. The outer 

 side of the shaft is convex and horny, the inner is divided into two 

 parts by a median groove, proceeding from the upper umbilicus ; this 

 also is horny, and the two inclose a white, elastic material, which is 

 termed the pith. On minute examination, this is found to be com- 

 posed of a cellular tissue very much resembling that of plants. From 

 the two other sides of the shaft the vane arises ; it is composed of a 

 double set of horny filaments, termed barbs. These are given off at 

 acute angles and are of a flattened figure, the flat sides being towards 

 each other and the edges in the direction of the outer and inner side 

 of the vane. From these edges another set of very minute filaments 

 arises, which are termed barbules, and these barbules are often simple, 

 but sometimes they have other little barbules arising from them, which, 

 for the sake of distinction, I have named barbulettes. The barbules 

 which arise from the upper margin of the barbs, or that nearest the 

 free extremity of the quill, are curved towards the inner surface of the 

 vane, whilst those which arise from the under margin of the same barb 

 are curved upwards, so that the two hook nicely one into the other 

 and keep the respective barbs in firm apposition.* We have now at 

 least six elements entering into the composition of a single feather, 

 viz., primarily, the quill, the shaft and the vane, and secondarily, the 

 barbs, the barbules and the barbulettes. 



This brief explanation of the parts entering into the formation of a 

 perfect feather is quite essential to the understanding of certain pecu- 

 liarities in the structure of the vane, which are to be found only in 

 particular birds. 



If the fingers be passed along the vane in a direction from the quill 

 towards the apex, the individual barbs will be only forced more com- 

 pactly together, but if the operation be performed in the opposite di- 

 rection, the barbs, in some cases, will separate every here and there, 

 but by far the greater number of them will be found so adherent one 

 to the other, that some little difficulty will be experienced in getting 

 them apart. If this be done before the light of a window or of a can- 



* This locking together of the barbs was known to Hooke, and was figured by him 

 nearly two centuries ago, in his ' Micrographia.' 



