INTRODUCTORY 7 



into the skin. Tubular in shape and semi-transparent, it en- 

 closes a series of hollow, oblong cells fitting one into the other. 

 During the growth of the feathers these cells contained the 

 pulp, or nutrient matter out of which the feather is built up. 

 The shrivelled end of the last of these cells projects from a 

 small aperture — the upper umbilicus — at the point where the 

 quill passes into the " rhachis " or shaft. This is formed by 

 a process of continuous growth of the dorsal surface of the 

 calamus, and the resultant lateral edges of this projecting out- 

 growth ultimately curl inwards, meeting in the middle line of 

 the under surface of the feather and leaving a fine groove to 

 mark the junction. The enclosed cavity is simultaneously 

 filled with a closely packed mass of " pith "-cells, recalling 

 " elder-pith," giving stability and elasticity to this region of the 

 axis. Along each side of this rhachis, which has a quadrangular 

 section, there runs, from the region of the upper umbilicus to 

 the tip of the feather, a closely planted series of flattened 

 laminae, terminating in a point, and these in turn support a 

 double row of smaller laminae. The former are known as 

 the rami or " barbs," the latter as the " radii " or barbules. The 

 whole form the remarkably elastic fringe which runs along each 

 side of the shaft, and which together form the " vane " or 

 " vexillum " of the feather. 



This fringe must be more closely examined. On a super- 

 ficial inspection it presents a homogeneous surface, but grooved 

 withal by a number of fine, parallel lines. If an attempt be 

 made to stretch this web in the direction of the long axis of the 

 feather, it will be found that though at first resisting, it will 

 eventually split, when, by drawing the fringe through the fingers 

 the original unity will be restored. If a lens be now brought to 

 bear on this surface, it will be found that the grooved or ribbed 

 appearance of this vane is caused by the interspaces between 

 the rami just described ; interspaces which are more or less 

 perfectly filled by the series of barbules which intercross. 

 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 out- 

 wards, into a number of long, hooked filaments, while those 



