oIO THE MECHANICAL FUNCTIONS. 



tion, Fig. 231 ; the points of the cones being di- 

 rected upwards, and their intervals being occupied 

 by the spongy substance in different stages of con- 

 solidation, and more perfected in proportion as 

 they are situated nearer the apex of the stem. 



While the construction of the feather, in its dif- 

 ferent stages, is thus advancing from below, those 

 parts which are completely formed are rising above 

 the surface of the skin, still enveloped in the cap- 

 sule 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 oft' in shreds, allow- 

 ing the successive portions of the feather to come 

 forth, and the laminae to unfold themselves as they 

 rise and assume their proper shapes. This succes- 

 sive 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 

 posterior part of the bulb now contracts itself, and 

 bringing the edges of that surface of the stem 

 closer together, at length unites them at the supe- 

 rior orifice (o), Fig. 228 ; 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 deposit- 

 ing a horny covering to the feather : all that re- 

 mains of its substance is a thin membrane, which 

 adheres to the outside of the tubular part, or bar- 

 rel 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 deposit the spongy sub- 

 stance, but forms a transparent horny material 



