OF THE PARTS OF FEATHERS. 9 



stem. It resembles the main shaft, and like it emits two series of barbs, thus forming along with the 

 shaft an apparently double feather. It is found on the feathers of very many birds, but is always 

 deficient on the remiges and rectrices. It is largest in the two Cassowaries, in which it attains 

 the same length as the main shaft, and is exceedingly similar to the latter in the general form of 

 the vane. In other birds, it is shorter, and merely supports downy barbs. This is especially the 

 case in the gallinaceous birds, 1 the structure of the feathers in which may be learnt from the 

 figure of a dorsal feather of Argus gigantem, shown in Plate I, fig. 1. I find it similar in the 

 Swifts (Cypselus). It is smaller in the diurnal rapacious birds, with the exception of the genus 

 Pandion ; and also in Caprimulgus, Prodotes (Indicator, Aucrr.), Musophaga, Psittacus, most 

 Wading birds, and amongst the Natatores in the Longipennes, the Nasuta or Tubinares (but 

 with the exception of Diomeded), and the Pygopodes. I find a small, soft, and very weak after- 

 shaft in most passerine birds (in some of which, indeed, it seems to be wanting), and in the 

 genus Picus. There are, however, a great many birds in which it is deficient, and in its place a 

 few isolated barbs occur, amongst these, are the genus Pandion, the nocturnal rapacious birds, 

 the genera Cuculus, Centropus, Coracias, Merops, Upupa, Alcedo, Rhamphastus, Columba, and 

 Pterocles, some species of Crypturus, and the natatorial families of the Unguirostres and 

 Steganopodes? 



more unequal, and more angular. During this process their nucleus continues visible, and the larger 

 the cell is, the more distinctly can we recognise in its nucleus one or two nuclear corpuscles or cavities. 

 In its form each barb, like the barbules, is a lamella, terminating above and below in a sharp edge. 

 (Fig. 3 a shows the section of six barbs from the outer half of the vane of the primary of a goose.) The 

 lower margin of the barb is thinner and more delicate, and finally quite membranous without cellular 

 contents, and is therefore certainly produced like the barbule, by one-sided extension of the walls of the 

 last series of cells. The upper margin, on the contrary, has an oblique terminal surface, which bears 

 the anterior, booklet-bearing series of barbules near its upper edge, and the posterior, hookless series near 

 its lower one. (These conditions are shown very distinctly in the section of six barbs, with their 

 barbules, in fig. 3.) This upper margin, which might more correctly be called the upper surface, 

 undergoes a change in its texture ; that is to say, the cell-structure disappears in it, and in its place 

 a very distinct longitudinal striation, a sort of fibrillation, makes its appearance. This is likewise 

 caused by a modification of the cells originally situated here, and appears to be produced by each cell 

 becoming elongated and fusiform, and amalgamated by its pointed extremities with the cells placed 

 before and behind it. The cells then also form filaments inflated into knots, as is shown in fig. 16 

 magnified 500 diameters, and still exhibit the cell-nuclei very distinctly in their knots as the origin of 

 the cells. The same structure is visible distinctly enough, although on a smaller scale in fig. 6, both 

 in the shaft and in the barbs issuing from it. I have not detected any other fibrification of the cells 

 except this, but indeed I have not sought for it, so that it is quite possible that the formation of fibres 

 described and figured by SCHWANN (' Mikroskospische Untersuchungen/ Berlin, 1839, p. 87, tab. ii, 

 fig. 13), as detected by him in the uppermost cells of the main shaft of a raven's feather, may be a 

 peculiarity of the solid horny substance of the shaft and tube. 



These are my observations on the formation of feathers ; they appear to me to explain the genesis 

 and metamorphosis of these interesting structures quite sufficiently for our purpose. B. 



1 In the limitation and arrangement of the families I follow the system, founded mainly upon 

 anatomical characters, proposed in my memoir De Avium Arteria Carotide (Halse, 1829, 4to). 



2 In Anas clangula and A. fuligula there is an aftershaft, which, although small, is still rigid. 

 Does it occur in all Plunging Ducks (Hydrobates, TKMM.)? 



2 



