34 STRUCTURE AND GROWTH 
remains of the cell-cavities also become filled with it at a 
subsequent period, and at the same time the stellated canali- 
culi issuing from them make their appearance. The formation 
of these canaliculi probably takes place by the transformation 
of round cartilage-cells into a stellated form, after the manner 
of the pigment-cells at plate II, figs. 8 and 9. 
The above detailed investigation of the chorda dorsalis and 
cartilage, has conducted us to this result,—that the most mmpor- 
tant phenomena of their structure and development accord with 
corresponding processes in plants, that some anomalies and 
differences may indeed still remain unexplained, but that 
they are not of sufficient importance to disturb the main con- 
clusion, viz. that these tissues originate from cells, which 
must be considered to correspond im every respect to the 
elementary cells of vegetables. Thus then are we furnished 
with the first of the proofs required in the Introduction ; that 
is to say, we have shown with regard to a certain tissue, that 
it not only origimates from cells, but that these cells in the 
process of their development manifest phenomena analogous to 
those of the cells of plants. We have now thrown down a 
grand barrier of separation between the animal and vegetable 
kingdoms, viz. diversity of structure. We have become ac- 
quainted with the signification of the individual parts of the ani- 
mal tissues as compared with the vegetable cells, and know that 
cells, cell-membrane, cell-contents, nuclei, and nucleoli in the 
former are in every respect analogous to the parts having 
similar names in the cells of plants. We have already observed 
several modifications both of the nucleus and cell. The former 
presented itself as a corpuscle having either an oval or circular 
outline, spherical in figure, or very much flattened, sometimes 
hollow, and often scarcely perceptible, in consequence of its 
transparency, but generally granulous and yellowish, and con- 
taining in its imterior from one to three nucleoli. This 
nucleus lay within, and fast adhering to the wall of the cell, 
but never in its centre. The fundamental form of the cell 
appeared to be that of a round vesicle, but we have also ob- 
served the flattening of the cells agaimst one another, the 
presence of intercellular substance between them in greater 
or less quantity, and lastly, the thickening of the cell-walls. 
