34 



THE FEATHERED TRIBES, 



site side — the one corresponding to the front, and the other to the back of the stem of 

 the future feather. 



It is in the interior of this C3'liudor that all the parts of the feather are constructed ; 

 their earliest rudiments being formed at the upper part of this organ, and the materials 

 of the several parts of the feather being successively deposited and fashioned into their 

 proper shapes in diflcrent places. For while the first lamina> are constructing in one 

 portion of the cylinder, the next are only just beginning to be formed in another. 

 While, too, the outer covering of the stem is growing in one membrane, the interior 

 spongy tissue is deposited in other places, in various stages of softness or consolidation. 

 Thus, the whole composes a system of operations, which, though they proceed on a micro- 

 scopic scale, ai-e, in fact, an extensive manufactory. 



Fig. 2 shows the mould laid open longituduiall}' : it is composed of a sheatli or capside, 

 and of a central pidpy mass called the bulh. The capsule consists of several membraneous 

 layers, which are more consolidated near the apex, and become gradually softer and 

 more delicate as they go towards the base, where their formation is only beginning. 



1. 



2. 



3. 



no. 25.— GKowTir OF a fkatuek. 



The laminsn and their fibrils, the assemblage of which constitulos the vane of the 

 fcatlicr, arc the parts which arc first formed. Their construction is efi'ected in the space 

 between the outer capsule, c, and the central b\db, b, in an exceedingly remarkable 

 manner. Instead of growing I'rom a base, like hairs, they arc cast in moulds, whero 

 they harden and acquire flic exact shape of tlic recipient cavities. 



These moidds are fonned of two membranes, tlie exterior one, e, en^•eIoping the oilier. 

 They are si-paratcd by a series of piii'lif ii>ns, which commence at tlie edges of (lie long 

 white band seen in fig. 1, and wind obliquely upwards till they reach the opposite 

 longitudinal hand aiieady (l(s( lilnd. Thus they leave between them narrow spaces, 

 whidi coTistitute so many coniparluK iils for tlie deposition, as in a iiimild, of tlic material 

 of each lamina. 



Tlic j)r(ip(r (illiic lil' ihr l)iiil), aTlcr il lias siipj)lir(l llic materials for llic linnialion 

 of tlio lamina', i.s to con>(ni<-1 llic siciii of the featlicr, and unite the lamina^ to 

 its sides, The anterior jiarl of (he bulb, during (lie process of filling up the stem, 

 exhibits a series ofconical-shaiicil hk mlnanes, as is seen in the section fig. -'i. The jjoints 

 of the cones are directed upwaids, and their intervals being occiqiied by the s2)ongy 

 .substance in diflcrent stages of consolidation, and ai'c more perfected in proportior. 

 ae they are Kituat«d nearer the apex of the stem. 



