Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/112

FEATHERS. tema of the cells of the pith of the feather is supplied by the nearest contiguous substance provided with vessels, that is, by the so-called matrix. In the young feathers of the hen, however, I found a layer of very small, extremely pale, round cells without nuclei,—a sort of imperfect epithelium,—between the matrix and the granulous cytoblastema, so that not even so much as an immediate contact exists between the latter and the organized substance.

The cortical substance of the shaft of the feather is a fibrous structure. Here the Cell-theory seems, at first sight, to fail; but we are soon taught otherwise, when we examine the generation of the fibres as exhibited in the incompletely formed portion of the cortical substance of a feather, which is in progress of formation within the capsule. The cortex is then seen to consist of large flat epithelium-cells, each having a beautiful nucleus, with one or sometimes two nucleoli. Some of these epithelial tables are long flat stripes, others are of an irregular rhomboidal form. They are very firmly connected together. Each cell generates several fibres, and the transitions may be readily observed at different parts of the same preparation. Plate II, fig. 13, represents them. The cells at first are flat tables, having a smooth margin, a slightly granulous aspect, and containing a very dis- tinct nucleus (fig. 13, a). Upon their margins and surfaces indistinct fibres gradually become visible, which project out insulated from the edges, but are connected together upon the surface by the substance of the tables (fig. 13, b). At this stage the fibres are pale, and the nucleus of the cell still quite visible. The fibres afterwards become more sharply and darkly defined; the insulated portions projecting from the edges are larger, the part of the table connecting them together becomes more indistinct, and the nucleus begins to wane, although it is still distinctly perceptible, and the nucleolus especially so (fig. 13, c). At length all traces of the original cell and the nucleus disappear, and we see only dark, stiff, thin fibres, which are closely connected together but may still be recognized as being insulated for a space, the length of the original table (fig. 13, d). These fibres, therefore, also originate from cells, and that not so much by an elongation of the cells, as by their division into several fibres. As the