OF CARTILAGE. 15 
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 in- 
visible in consequence of its translucency, since even fully-deve- 
loped 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 erythroph- 
thalmus be loosened from the branchial arch, and the mucous 
membrane be removed by gentle scraping, the cartilage remain- 
ing presents the appearance of a little rod, which diminishes 
from the point of its imsertion 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. (PI. I, 
fig. 6.) On the thickened cell-walls it may now also be seen 
