TEGUMENTARY ORGANS. 



developed from the subjacent periostium, like a large hair 

 from its follicle, or like the horny coverings of the papillae 

 on the plantar surface of the feet in carnivora ; and it exhi- 

 bits the same fibrous structure and filamentous mode of decay, 

 as in other epidermic parts composed of recti-lineal aggre- 

 gations of cytoblasts. In these various forms of epidermic 

 developments, the polyhedral form of the compressed cells, 

 their nuclei and fluid contents, and their lineal arrangements, 

 are most apparent in their primitive soft condition in the 

 foetus, or in the recently formed portions in the adult ; and in 

 their subsequent metamorphoses their internal fluid and nu- 

 clei disappear, the empty cells become elongated or flattened, 

 with their interior parietes contiguous, they are aggluti- 

 nated into laminae by the remains of the cytoblastema, and 

 their conformable stratified superposition is- rendered more 

 distinct. 



The feathers of birds, like the hairs of mammalia, are 

 epidermic developments contained in cutaneous follicles; they 

 are provided with their vascular secreting pulp, their hollow 

 bulbous base of increment, and their solid exposed shaft ; and 

 like them, they are composed of extravascular organized 

 independent cells, or cytoblasts, which were already figured 

 and described by Hooke, and by Leuwenhoek, as composing 

 the entire microscopic structure of the feather, Like other 

 epidermic structures, feathers are first formed and most 

 developed on those parts where they are first and most 

 required, and their horny composition and tubular structure 

 are those best adapted to combine strength with lightness. 

 The strong diaphanous tubular empty quill (147-A. o.) in 

 the adult bird, is deeply imbedded in the cutaneous pen- 

 niferous follicle, as the point of attachment and of nutriment 

 of the feather, and contains only a few dried remains of the 

 primitive secreting pulp-cells. The tapering light elastic 

 conical shaft (147. A../, b.) is occupied internally with white 

 dried aeriferous cytoblasts, which were described before the 

 time of Leuwenhoek, and gives a firm support to the two un- 

 equal sides of the vane (14?. A. c. d.). The vane is composed of 

 barbs (147. A. rf.) or laminae placed vertically to afford the 

 greatest resistance in flight, closely applied to each other, 

 continued from the sides of the shaft, and connected toge- 

 ther by barbules developed from each side of their dorsal or 



