128 FIBRE-CELLS, ETC. 
or to the minimum of cytoblastema between the epithelium- 
cells ; or, lastly, to the fluid, in which the cells of the first 
class are formed. In this way one can also readily understand 
how fibro-cartilage forms a gradual transition between true 
cartilage and fibrous tissue ; it only requires that the cartilage- 
cells pass through the same transformations as the elementary 
cells of areolar tissue. 
As the present class was based upon the alteration in form 
which the cells comprised in it undergo, it necessarily could not 
present many modifications in the shape of the cells, and accord- 
ingly exhibits throughout merely an elongation of nucleated 
cells into fasciculi of fibres, and a subsequent splitting of the 
bodies into fibres. We have already seen the types of these 
changes in the second class, where the pigment-cells and those of 
the crystalline lens, &c., became elongated by a more vigorous 
growth of the cell-membrane at different spots ; and the class 
now before us merely affords us an instance of the same pro- 
cess in a higher degree, since here, one side of one of these 
more highly developed fibre-cells gives origin to a great num- 
ber, or even a whole fasciculus, of fibres. The cells of the 
cortex of the feather also furnished us with an example in the 
same class of the division of the body of the cells into fibres. 
Inasmuch as the prolongations of the pigment-cells remain 
hollow, however minutely they may ramify, one may suppose the 
same to be the case with regard to the fibres of the tissues 
now under consideration. The decision of this poimt would, 
as we shall subsequently see, be of great importance for 
the theory of nutrition; but it is quite impossible to deter- 
mine it by observation, in consequence of the cells of this class 
not possessing any characteristic contents like those of pigment. 
An observation by Purkinje and Raiischel was quoted, however, 
in favour of these cells being hollow. If the hollowness of the 
fibres of areolar tissue, &c., could be proved, there would 
then be a division of a single cell into many cells at each 
transformation of a fibre-cell, and thus the fibrous tissues would 
not lose their cellular character. 
The fibre-cells undergo chemical changes during their 
growth and gradual transformation into the fibres of areolar 
tissue, since that tissue, when boiled, even long after the forma- 
tion of fibres has commenced, yields no gelatinizing gelatine. 
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