OF CARTILAGE.
nous plants,) or whether the little corpuscle, which presents itself on the inner surface of some young cells, is the nucleus which grows with the cell, as it is observed to do in some other animal cells; or whether the nucleus in the young cells is invisible in consequence of its translucency, since even fully-developed cells are met with, in which, although certainly present, it is, in consequence of its transparency, barely visible.
2. Cartilage.
The accordance of the structure of cartilage with the tissue of plants is of more importance in reference to animal organization. We have here to do not only with a more widely extended animal tissue, but also with one which, at least, in its subsequent stages of development, contains vessels, and therefore bears more decidedly the character of an animal tissue. The simplest form of cartilage is exhibited in the cartilages of the branchial rays of fishes. If, for example, a branchial ray of Cyprinus erythrophthalmus be loosened from the branchial arch, and the mucous membrane be removed by gentle scraping, the cartilage remaining presents the appearance of a little rod, which diminishes from the point of its insertion on the branchial arch towards its free end, its sides being somewhat compressed, and exhibiting on their margins some blunt prominences. The structure of this cartilage is very simple. At the point it perfectly resembles, in its whole appearance, the parenchymatous cellular tissue of plants. (See pl. I, fig. 5, from the above-mentioned Cyp. eryth.) Little polyhedral cell-cavities with rounded corners are seen lying closely together. The cell-cavities are separated from each other by extremely thin partition walls. The cell-contents are transparent, and a small pale round nucleus (a) may be seen in some cells when in the recent state, in others only after the action of water upon them. The structure of the lateral prominences of the cartilage is similar to that at the point, only that the cells are somewhat extended in length. Advancing from that point towards the middle, or still better from the point towards the root of the branchial ray, the partition walls of the cell-cavities are observed to become gradually thicker ; and the cavities are here somewhat smaller. (Pl. I, fig. 6.) On the thickened cell-walls it may now also be seen
