Birds. 3667 



tube is inserted in the hide, on a papilla perforated in its centre by the 

 umbilical vessel of the former, which, if torn away, is followed by 

 bleeding. Within the sheath is contained a softish mucous follicle, 

 of an ashy colour, with bloody spots ; but although it seems to con- 

 sist of fibres longitudinally arranged, there is really no organic struc- 

 ture but the umbilical vessel which runs through it lengthwise. From 

 the sides of the follicle, about its base, little black plumules arise, and 

 from its tip some white ones, from which hairs stretch out, and the tip 

 of the sheath opening as the growth proceeds, the extremities of these 

 plumules with their conjoined hairs burst forth, and the sheath being 

 further opened, the follicle appears, forming the stem, dried at its tip, 

 and divided into empty membranous chambers, whilst its remaining 

 or lower part is softish, and gives origin laterally to the plumules with 

 the hairs, which, when the sheath is torn off, are withdrawn with it, 

 and the whole extent of the stem, from the tip to the bottom of the 

 follicle, is seen : the follicle, as an uterine placenta, providing the 

 growing material of the feather, presenting first the upper, subse- 

 quently the lower part of the stem, and finally the barrel of the fea- 

 ther. The follicle is a cylindrical tube, formed of delicate membrane, 

 inclosing a series of utricles of different sizes, proportionate to the 

 quantity of fluid contained, which is gradually absorbed in the growth 

 of the feather ; thus where the fluid is actively propelled, the cham- 

 bers are conical, as may be observed when vegetation first commences 

 about the stem, the apex of which is first gradually lengthened ; to 

 this succeeds the production of the barrel, when the chambers again 

 elongate towards its apex, but as they descend, the resistance of the 

 cartilaginous tube compels a change of form, and the conical shape 

 being lost, the chambers assume the appearance of numerous valves 

 piled on each other. When the generation of the feather is perfected, 

 the barrel or elongated tubular part of the feather becomes solid. The 

 barrel is a cartilaginous substance, by which probably the whole stem 

 is covered, and being folded externally, forms the plumules, and 

 finally hollowing itself into a tube forms the barrel. At the part where 

 the stem ends in the hide, the shrivelled follicle bursts forth, but the 

 rest is contained within the barrel, the external membrane of which, 

 so closely connected at the middle that it can scarcely be separated, 

 is obtained from the sheath, but the upper part subsides into scales. 

 If the barrel be opened prior to its solidification, the contained folli- 

 cle is found loaded with fluid, and externally its thick investment is 

 overspread with blood-vessels. When the growth is completed, and 

 the feather becomes solid, plumules are produced from the cartilagi- 



