OF THE PARTS OF FEATHERS. 11 



the whole of the hooklets of each barbule thus grasp as many barbules of the following series as 

 are crossed by the hamuliferous barbule of the preceding series. An examination of the drawing 

 given in Plate I, fig. 2, will render this relation easily intelligible. It is seen, at once, that each 

 barbule of the anterior series crosses over eight or nine barbules of the posterior series of the 

 following barb, and when the enlarged figure of the hamuliferous barbule (fig. 4), is compared 

 with the equally magnified representation of the barbule destitute of hooklets (fig. 5), it will be 

 easily understood how a hooklet of one barbule must catch in each of the little pits visible in the 

 other (fig. 12). 1 It is to this peculiar and ingenious arrangement alone that we must ascribe 

 the faculty of the vanes of serving as an apparatus for flight. 2 



1 I give NITZSCH'S notion of this matter, although I do not believe that it is the correct one. In 

 the first place, these so-called "pits" are very often wanting in old barbules (fig. 5). But if the 

 curvature of the hooklets in the barbule correctly figured by me be compared with the position of the 

 pits in another barbule (fig. 12), it will easily be seen that the curvature is much too small to enable 

 them to reach down over the upper margin of the barbule to the pit. Nor do I believe that these 

 spots regarded by NITZSCH as pits are really depressed, but I consider them merely as the still existent 

 cavities of the primitive cells of which the barbule is composed. (See my observations on the genesis of 

 feathers, p. 4 et seq.) Lastly, I have noticed in all barbules a strongly thickened superior margin, which 

 is precisely of such a size that the hooklets can just grasp it. It is behind this margin, and not in the 

 pits, that the hooklets take hold, and thus fix the posterior barbules much more securely, because when 

 a pressure is applied to this connexion by the force of the air during flight, the hooklet need not let 

 go its hold of the margin, as must necessarily often occur if the hooklet was inserted into a pit 

 so wide, and situated so far below the upper margin, over which moreover the hooklets must extend 

 themselves. B. 



2 It is certainly remarkable, that the true relations of these barbules and barbs, which were well 

 indicated even by PERRALT and HOOKE (' Microgr. Rest./ p. 32, fig. 19), have remained quite unknown 

 to most writers of the present day, so that, in attempting to explain them, they put forward the most 

 preposterous notions, and do not take any notice of the hooklets. 



