Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/109

FEATHERS. time are surrounded by a dense capsule, which is composed, throughout its entire thickness, of gigantic tabular epithelium. The feather is so placed in this capsule, that the shaft and vane are folded together to form a hollow cylinder, which is occupied by the so-called organized matrix of the feather (see an article on this subject by Fr. Cuvier, in Froriep’s ‘ Notizen,’ No. 317). According to Cuvier, a membrane lines the inner surface of the vane, and gives off septa, which penetrate between its separate barbs. This membrane, however, as well as the septa, is composed of epithelium.

The shaft of the feather consists of a loose medullary sub- stance (the pith), surrounded by a firm cortex. On making thin transverse or longitudinal sections of the pith, it is seen to be composed of beautiful polyhedral cells, which perfectly resemble the parenchymatous cellular tissue of plants,—as the substance of cork for example. (See plate II, fig. 10.) The cell-cavities which have moderately thick, dark partition-walls, are at first filled with a transparent fluid, but subsequently become dry, and in that state contain air. Notwithstanding, however, that this pith so precisely resembles vegetable tissue in its general appearance, it may be questioned whether these cells be actually cells in that sense of the word in which we receive it here, viz. elementary cells of organic structure, and whether they correspond to vegetable cells. It therefore becomes necessary to investigate whether each cell has its peculiar wall, and whether the course of development of each individual cell be the same as in plants. There is no structure, however, in which it is easier to follow the process of development than in the one before us, chiefly because the cells, even from the first, have no connexion with the organized so-called matrix, but remain attached to the fully-developed cells of the shaft, when the matrix, which terminates externally with a smooth surface, is taken away. The following description is taken from the large wing-feather of a raven: it applies however equally well to the feathers of the young chicken.

The pith, when in progress of formation, is soft and friable. When a small portion of it is examined, after the component particles have been separated asunder, it is found to consist of cells, in various stages of development. Those which