INTROUL'CTION. Ill 



merely barbless feathers is shewn by their being shed and 

 renewed along with the otlier feathers. 



Tiie quill is fixed in a tube formed by a fold of skin. 

 A reproduction of feathers tnkes place annually at the 

 so-ctilled moult. The new feather is formed in a vesicle 

 which perforates the skin as a horny case or sheath, and 

 finally gives passage to the vane of the new feather, the 

 part first formed. As the development of the feathers 

 goes on, the sheath is resolved into scales or plates which 

 fall oif, or are removed by the bird. The shaft is origi- 

 nally double, hence the groove we see, and is formed 

 after the quill. The shrivelled-up membrane in the quill 

 is the remnant of the fluid in which the feather was 

 formed. Some incomplete downy feathers secrete a 

 powdery substance, the remains of the unfinished shaft, 

 as in Herons, some Birds of prey, and Parrots, and this is 

 usualh' either white or yellow. This is, of course, develop- 

 ed in greatest quantity at the time of the moult. 



The moult of birds appears, like the shedding of the 

 horns of Stags, to have some connection with the sexual 

 functions. Most birds renew their plumage once a year 

 only, in autumn, afrer the season of pairing and incuba- 

 tion. Certain families and tribes have a second or spring 

 moult, which takes place just before the pairing, and is, in 

 almost all cases, a change to a more gaudy or showy 

 plumage, and in many cases an addition of ornamental 

 tufts or plumes takes place at this season. The bill of 

 some Herons, and of a few others also, undergoes a change 

 of colour at this time. Some birds, in spring, undergo an 

 actual chanjre of color in certain of the feathers, unac- 

 companied by any moult, and, in others, a change of color 

 takes place simply by the terminal portion of the feather 

 being cast or worn off, and showing the brighter tint of 



