THE BXTBENAl STEIJOTrEB OT BIEDS. 1 39 



Feathers may be considered as very complex hairs of a conical 

 ■form, which split up according to a definite pattern. Each is at 

 first a little, soft, vascular process or papilla, curiously grooved. 

 On one side is a central vertical groove, broadest at the base, 

 and vanishing towards the apex of the papilla. Other less deep 

 grooves, closely set, go out, nearly at right angles, from either 

 side of this vertical groove. They extend almost all round the 

 papilla, only vanishing towards the middle of the opposite side 

 to that which bears the vertical groove. Grooves smaller still 

 and much shorter are given off again nearly at right angles 

 from the grooves encircling the papilla, and sometimes others 

 again from these. . A horny secretion is deposited on the 

 papilla, and is, of course, thickest where the grooves are deepest, 

 and thinnest where there are no grooves at all — i. «., on the 

 interspaces of the grooves. With the progress of growth, this 

 whole horny investment splits up along the interspaces, where 

 the deposit is thinnest. The part which was the main vertical 

 groove is thickest of all, and becomes the shaft of the feather, 

 the parts in the secondary grooves become the " barbs," those 

 on the still smaller ones the " barbules," and those in the occa- 

 sionally present yet smaller ones, the " barbulets." Sometimes 

 a papilla wiU have a vertical groove on either side, and then the 

 feather vidll have two shafts (one an aftershaft) — as in the 

 Cassowary. The vane is the part of the case of the papilla 

 which thus splits. The quill is that part of the case which does 

 not split at all. At the upper end of the quill there must 

 be a small perforation which marks just that spot where the 

 feather ceases to open and flatten itself, and begins to remain 

 curled round and continuous, as it all was at first. The space 

 where it thus begins to remain curled round is the wmbilwus 

 superior before mentioned. The papilla persists as the " pulp " 

 which ascends through the umbilicus inferior. 



Feathers are developed with great rapidity, sometimes attain- 

 ing a length of two feet or more in a few days. They are also 

 almost all renewed every year, and in many species twice a yeas*. 

 When we think of the serious effects of teething in mankind 

 we cannot but be struck with the great vital energy of birds, 

 and with the critical character of their process of moulting 

 (ecdysis), which is, indeed, not unfrequently a fatal one. • 



The annual moult commonly begins just after the close of 

 the breeding-season, and it takes place in all Birds, from the 

 Wren to the Ostrich. Such a process is obviously a necessary 



