i, 

 FEATHERS OP BIRDS. 399 



and gradually folds it inwards till its sides meet at the mid- 

 dle groove along the back of the stem. The anterior part 

 of the bulb, during the process of fdling up the stem, exhi- 

 bibits a series of conical shaped membranes, as is seen in 

 the section, Fig. 231; the points of the cones being directed 

 upwards, and their intervals being occupied hy the spongy 

 substance in different stages of consolidation, and more per- 

 fected in proportion as they are situated nearer the apex of 

 the stem. 



While the construction of tlie feather, in Its different 

 stages, is thus advancing from below, those parts which 

 are completely formed, are rising above the surAice of the 

 skin, still enveloped in the capsule which originally protected 

 them, but the upper portions of which, from the action of 

 the air, and the obliteration of the vessels that nourished 

 them, now decaying, shrivel and fall off in shreds, allowing 

 the successive portions of the feather to come forth, and the 

 lamincE to unfold themselves as they rise and assume their 

 proper- shapes. This successive evolution proceeds until the 

 principal parts of the stem and of the vane are completed; 

 and then a different" kind of action takes place. The poste- 

 rior part of the bulb now contracts itself, and brino-ino; the 

 edges of that surf^ice of the stem closer toiiether, at lenirth 

 unites them at the superior orifice (o,) Fig. 22S; where the 

 laminae, which follow these lines, also terminate. Having 

 thus performed the office assigned to it, it ceases to be 

 nourished, and is incapable any longer of depositing a horny 

 covering to the feather: all that remains of its substance is a 

 thin membrane which adheres to the outside of the tubular 

 part or barrel of the quill, and which must be scraped off 

 before the latter can be used as a pen. The tubular part is 

 the product of the anterior part of the bulb, which now 

 ceases to deposite the spongy substance, but forms a transpa- 

 rent horny material over the whole of its external surface; 

 but as it retires towards the root, it leaves a succession of 

 very thin pellucid membranes, in the form of cones, which, 

 when dried, form what is termed the pith of the quill. The 



