352 



AVES. 



gradually proceeding from the apex downwards. 

 The capsule of the matrix (a a. Jig. 179) is 

 composed of several layers, the outermost of 

 which is of the nature of epidermis ; the inner 

 ones are more compact, but have no appear- 

 ance of organization. The sides of the cap- 

 sule which correspond to the outer and inner 

 sides of the growing feather within are indi- 

 cated by a white longitudinal line. 



The axis of the capsule is occupied by a 

 medulla or bulb, (e, Jig. 1 79,) also of a cy- 

 lindrical form, and of a soft fibrous texture, 

 adhering by its base to the parts beneath, and 

 there receiving numerous bloodvessels and a 

 nerve. 



Between the medulla and the capsule 

 there are two parallel membranes, one in- 

 ternal (d, Jig. 179); the other external, 

 (by jig. 179); from the latter membrane a 

 number of close-set parallel laminae extend 

 obliquely from one of the white longitudinal 

 lines above mentioned to the other on the 

 opposite side of the cylinder. The two mem- 

 branes seem to be united together by the 

 oblique septa. In the long and narrow spaces 

 between these septse, the matter of the vane 

 (c. Jig. 179) is deposited, and formed into 

 barbs and barbules, nearly in the same way as 

 the enamel of the teeth is formed between the 

 external membrane of the pulp, and the in- 

 ternal membrane of the capsule. The depo- 

 sition of the material of the barbs commences 

 at the apex of the bulb, and the stem is next 

 formed in the following manner. 



The external longitudinal line from which 

 the oblique laminae are continued, receives and 

 moulds on the inner surface of the external 

 capsule the horny covering of the back of the 

 feather, or that longitudinal band, to the two 

 sides of which the barbs are attached ; and on 

 the opposite surface of the internal membrane 

 are formed the pith or substance of the shaft, 

 and the horny pellicle which incloses it on the 

 inner surface. The internal longitudinal line 

 has no other use than to establish a solution 

 of continuity between the extremities of the 

 barbs of one side and those of the other, which 

 meet at that part, and thus curve round and 

 completely inclose the formative bulb. In 

 Jig. 180, the capsule of the matrix of a grow- 

 "ing feather has been laid open, and the nascent 

 barbs (c) which surrounded the bulb have been 

 unfolded, exposing that part at a b. A portion 

 of the barbs and stem have been completed 

 and protruded, and the bulb is beginning to 

 undergo a process of absorption at that part, 

 which will hereafter be described. The shaft 

 and barbs at the apex of the cylinder are the 

 first parts which acquire consistence, and the 

 molecules composing the remainder are less 

 compactly aggregated as they are situated 

 nearer the base of the matrix. As the gela- 

 tinous medulla increases at the base, the first- 

 formed shaft and barbs are protruded through 

 the extremity of the capsule, the bulb con- 

 tinuing to furnish the secretion whichis moulded 

 between the two striated membranes until the 

 entire feather is completed. If the striated 

 membrane inclosing the bulb be attempted to 



Fig. 180. 



Fig. 181. 



"" Structure of the Bulb. 



be reflected from below upwards, it will be 

 found to be connected with a series of mem- 

 branous cones (abed e,fg. 181,) ranged one 

 upon the other throughout the whole length of 

 the bulb, and connected together by a tube 

 running through its centre. In this figure 

 (181) the pulpy matter which occupied the 

 interspaces of the cones has been removed to 

 shew their central connecting tube. 



As the development of the feather advances, 

 the pulpy matter disappears from the summit 

 of the medulla, and only the membranous 

 funnel-shaped caps remain, which are pro- 

 truded from the theca and the centre of the 

 new-formed barbs, and fall off as these ex- 

 pand. The theca which incloses the whole 

 is of a firm texture where the new moulded 

 barbs are yet pulpy and tender, but it be- 

 comes thinner as these acquire consistency, 

 and lastly, dries and crumbles away after it 

 has been exposed to the action of the atmos- 

 phere. The bulb itself, when examined in a 

 half-formed quill-feather,* is composed of two 

 parts corresponding to the external and in- 

 ternal aspects of the feather. The internal 

 part represents a semi-cylinder or case, in- 



* The following description is taken from such a 

 feather in the goose. 



