STRUCTURE AND GROWTH
remains of the cell-cavities also become filled with it at a subsequent period, and at the same time the stellated canaliculi 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 impor- 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 conclusion, viz. that these tissues originate from cells, which must be considered to correspond in 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 originates 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 acquainted with the signification of the individual parts of the animal 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 containing in its interior 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 observed the flattening of the cells agaist one another, the presence of intercellular substance between them in greater or less quantity, and lastly, the thickening of the cell-walls.
