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 transluccncy, 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 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 pi. 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 



