FEATHERS. 83 
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 occu- 
pied 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 be- 
tween 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 be- 
comes necessary to investigate whether each cell has its pecu- 
liar wall, and whether the course of development of each in- 
dividual cell be the same as in plants. There is no structure, 
however, in which it is easier to follow the process of develop- 
ment 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 ex- 
ternally 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 
