240 



FEA THERS 



the inner web of one of the primaries of a Crane (Gh'us), 38 cm. 



long, I found about 650. 



(5) The radii or harhules are attached in two opposite rows to the 



thick upper rim of the 

 rami, and like them point 

 toward the tip of the 

 feather. Each radius is a 

 thin lamella, about 1 mm. 

 in length, the upper sur- 

 face of which is not, how- 

 ever, thickened like that 

 of the rami, but doubled 

 up. Their number is 

 enormous : every ramus 

 of the Crane's feather just 

 mentioned bore about 

 600 pairs — making nearly 

 800,000 radii for the 

 inner web alone, and cer- 

 tainly moi'e than a million 

 for the whole feather. 



(6) The cilia or harhicels 

 with their hamuli or hoolcs 

 are outgrowths of the radii. 

 The hamuli are of the 

 greatest importance in 

 regard to the faculty of 

 Flight, because by their 

 means alone the radii, and 

 consequent^ the rami, 

 are connected to form a 

 coherent almost air-tight 

 surface. The hamuli grow 

 only on the distal rows of 

 the radii, that is, the rows 

 which look toward the tip 

 of the feather, and those 

 of one radius reach over 

 and hook on to thedoubled- 

 up margin of the radii 

 (themselves bookless) of 

 the proximal row of the 



next ramus, as she^vn in the opposite figures. Cilia which are not 



Contour-Peathee, with Afteeshaft. 

 Part of the barrel has been cut away to shew the 

 series of homy cups (p) continued (as p') through the 

 umbilicifonii pit, whence arises the Aftershaft. D, 

 downy portion of the web. 



furnished Avith hooks frequently have shapes which may possibly 

 })rove to be characteristic of different groups of birds. 



From their varying forms feathers are usually divided into 



