PLUMAGE OF BIRDS. 



239 



115 



116 



k 



a, 



^$X^ 



which incloses it on the inner surface. The internal lono-itudinal 

 line has no other use than to establish a solution of continuity 

 betAveen the extremities of the barbs of one side and those of the 

 other, which meet at that part, and thus curve round and com- 

 pletely inclose the formative bulb. In fig. 115, the capsule of the 

 matrix of a growing feather, 

 c, has been laid open, and the 

 nascent barbs, d, d, which sur- 

 rounded the bulb, have been 

 unfolded, exposing that part 

 at «, b. A portion of the 

 barbs and stem have been 

 completed and protruded, and 

 the bulb is beo-inninoc to un- 

 dergo a process of absorption 

 at that part, which will here- 

 after be described. The shaft 

 and barbs at the apex of the 

 cylinder are the first parts 

 which acquire consistence, and 

 the molecules composing the 

 remainder are less compactly 

 aggregated as they are situ- 

 ated nearer the base of the 

 matrix. As the gelatinous 

 medulla increases at the base, 

 the first-formed shaft and 

 barbs are protruded through 

 the extremity of the capsule, 

 the bulb continuing to furnish 

 the secretion which is mould- 

 ed between the two striated 

 membranes until the entire 

 feather is completed. If the 

 striated membrane inclosing 

 the bulb be attempted to be 

 reflected from below upward, it will be found to be connected with 

 a series of membranous cones, a, b, <?, d, e, fig. 116, ranged one 

 upon the other throughout the whole length of the bulb, and con- 

 nected together by a tube running through its centre. In this 

 figure the pulpy matter which occupied the interspaces of the 

 cones has been removed to show their central connecting tube. 

 As the developement of the feather advances, the pulpy matter 



Growing feather, li*. 



Structure of tlic bulb. 



