EXTERNAL FEATURES 19 



the calamus, marking the retreat of the pulp, may be called 

 the " caps " ; the barbs are also known as rami, the bar- 

 bules as radii. The barbicels or cilia are outgrowths of 

 the barbules, and some bear microscopic booklets or hamuli 

 which are linked to the barbule next in front. 



" Under a high magnification of the microscope these 

 barbules will be found to consist of two very distinct kinds, 

 ranged one on either side of the barb. Those on the side 

 of the barb pointing to the tip of the feather have the 

 appearance — when examined separately — of flattened plates, 

 cut up, from the middle outwards, into a number of long, 

 hooked filaments, while those of the opposite side of the 

 barb take the shape of long scrolls, whereof the upper edge 

 is the more deeply curled. When in situ the two series are 

 so arranged that the booklets are thrust down between the 

 scrolls so that their curled edges are caught thereby " 

 (Pycraft, 1910, p. 7). 



Professor Newton notes that on one of the primary 

 feathers of a crane he found 650 barbs on the inner web, 

 that each of these barbs bore about 600 pairs of barbules, 

 making 780,000 barbules for the inner web alone, and 

 therefore far over a million for the whole feather. And 

 then there are the barbicels ! 



Kinds of Feathers. — There are three chief kinds of 

 feathers — {a) the ordinary contour feathers or pennse, 

 whether covering the body as a whole or specialised as 

 pinions (remiges) and tail-feathers (rectrices) ; {b) the 

 down feathers or plumules, whether confined to nestlings 

 or persisting throughout life ; and (c) the hair-like filo- 

 plumes, which are hardly seen until the others have been 

 plucked off. 



Some of the peculiar feathers, such as bristles about 

 the gape, eyelashes, and ornamental plumes, may be derived 

 from contour feathers. Others, like powder-down and 

 oil-gland feathers, may be referred to the plumule type. 

 It need hardly be said that filoplumes, bristles, eyelashes, 

 and the like, show no real approach to mammalian hairs 

 except in shape. 



