362 DEVELOPMENT OF FEATHERS. 



capsule; and it often acquires a considerable length. From the 

 observations of M. Fred. Cuvier, it would appear, that the 

 capsule grows during the whole period of the development of the 

 feathers ; and that in proportion as its base lengthens, its extre- 

 mity dies, drying up as soon as it has formed the corresponding 

 portion of this appendix. Each capsule is composed of a cylin- 

 drical sheath, lined internally with two tunics united by oblique 

 partitions ; and of a central bulb. The substance of the feather 

 is deposited on the surface of the bulb ; and, to form the laminae, 

 it is moulded as it were in the spaces between the partitions. In 

 the portion corresponding to the stem, the bulb is in contact with 

 its lower surface; and after having deposited there a spongy 

 substance, it dries up and dies ; but where the trunk of the 

 feather is tubular, the plate of horny matter which the secreting 

 organ deposits, turns round it and completely envelopes it ; this 

 bulb, however, when it has fulfilled its functions, dries up, and 

 forms, in so doing, a series of membranous cones, imbedded in 

 one another, which fill the interior of the tube, and are sometimes 

 called the cores of the quill. 



324. The new feather is at first inclosed in the sheath of its 

 capsule, which often projects several inches beyond the stem, and 

 is gradually destroyed. The feather is then uncovered ; and its 

 laminae, at first rolled together, unfold laterally ; the extremity of 

 the tube remains imbedded in the skin, but in general can be 

 easily detached, and falls off at a certain period to give place to a 

 new feather. This removal of the feathers, which is called 

 moulting, generally takes place every year after the period of 

 incubation (the laying and hatching the eggs), and sometimes 

 twice in the same year, in spring and in autumn ; it is earlier in 

 old individuals than in young ones, and is a period of discomfort 

 to the bird, which loses its voice whilst it is going on. 



325. The form of these tegumentary appendages varies much ; 

 there are some which are destitute of laminae, and resemble por- 

 cupine's quills ; of these there are four or five in the wing of the 

 Cassowary. In others the laminae are stiff, and provided with 

 small barbs which hook together, so as to form an expanded 

 surface, which offers complete resistance to the air ; this is the 



