TEGUMENTARY ORGANS. 651 



mic capsule (147. B.) embracing in its axis two concentric 

 striated membranes, (147. B. b. d.), and a highly vascular, se- 

 creting, formative pulp (147. B. d. e.), and contained in a deep 

 penniferous follicle. This exterior epidermic capsule, perfo- 

 rated below by the vessels and nerves of the organized pulp, 

 elongates, opens above, and allows the newly formed parts of 

 the feather to escape from the opening of the cutaneous follicle. 

 This general extra- vascular enveloping capsule, (147- C. c.), 

 is entirely composed of strata of large flattened cytoblasts, 

 which grow by their independent vitality, are united by their 

 cytoblastema, and give a necessary brittleness to the texture 

 of this deciduous membrane. On cutting open the exterior 

 capsule of the young feather, the two more delicate tonics 

 are seen investing the pulp, and connected together by nu- 

 merous septa ; the soft, newly formed barbs, (147. B. c. c.) 

 moulded between these septa, are thus found folded around 

 the central organized matrix, being developed in a polythala- 

 mous cavity filled with the granular secretion of the vas- 

 cular pulp. The pulp developes a series of superimposed 

 conical capsules, and traverses their axis in a continuous 

 canal, as seen in the annexed figures from F. Cuvier (147. E. 

 F. G.). The dense tubular elastic quill is formed by the 

 meeting of the edges of the exterior horny dorsal lamina of 

 the shaft, after the completion and convergence of the two 

 sides of the vane ; and an exterior opening, or upper um- 

 bilicus, is left at this point for the admission of air to the 

 interior and cells of the quill and the shaft. The membranous 

 cells (147. K. L.), disengaged from the distal extremity of 

 the organized pulp, and occupying at first the cylindrical 

 cavity of the folded barbs, are successively detached, ex- 

 posed, and lost by the unfolding of the barbs, and the rest 

 are confined and retained, dried, and collapsed, within the 

 closed tubular quill, after the shaft is completed. 



The large polyhedral pith- cells of the growing shaft con- 

 tain, at first, a fluid substance ; they are provided each with a 

 distinct nucleus adhering to its inside, and within the nuclei 

 are seen one or two comparatively large nucleoli ; the cells 

 are easily separable from each other ; they have firm exterior 

 parietes, and in the adult state, like the few large ceUs of the 

 quill, they contain only air, and have nearly lost all traces of 

 their nuclei. As the internal constituent cytoblasts of the shaft- 



