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94 thus an uninterrupted passage from one cell-cavity into the other is produced. I am not certain as to whether a similar process does not take place in some fibres of the crystalline lens.

The transformations which the cells undergo are not, however, restricted to those already mentioned. A completely opposite process occurs in the cortical substance of the shaft of feathers, viz. a division of the cells into fibres. By this process, out of a single cell several fibres are generated, which, in the first instance, are united together by the rest of the substance of the cell, but at a later period of development may be insulated to a considerable extent. An elongation of the cells into these fibres takes place, indeed, at the same time, but the major portion of each fibre is formed by the division of the bodies of the cells.

With respect to the formation of the cells of this class, we find it to be a constant rule, that their size increases in proportion with their age, a fact which Henle has already pointed out with. regard to the epithelium. We have seen in the different tissues, that the nucleus is first present, that the cell is then formed around it, the nucleus, therefore, being the true cytoblast, and that it holds the same position in these cells that it does in those of plants, being fixed eccentrically upon the internal surface of the wall. Cell and nucleus advance in growth for a time, the former, however, much more vigorously than the latter. The nucleus is generally absorbed after the formation of the cell is completed. The generation and growth of the cells and all the phenomena connected with the nucleus resemble those of the vegetable cells, and we may unhesitatingly draw a parallel between them. In no class is the quantity of the cytoblastema smaller than in this. In the immature state the walls of the cells lie close together, with at the most, but a minimum of intercellular, substance between them at points where three cells are in contact, and it is only between those nuclei, around which no cells have as yet formed, that a somewhat larger quantity of cytoblastema is present.

The class of cells now treated of, and the teeth which will be examined in the following class, have been comprised under the term unorganized tissues, and their growth represented as