16 ELEMENTARY STRUCTURE OE ORGANIZED BODIES. 



Cb 



cellular tissue contains blood-vessels, the evolution of new 

 cells also proceeds through the entire substance of the tissue. 

 The cells grow, but scarcely attain to twice the diameter of 

 the nuclei they enclose ; at a very early period, however, they 



begin to length- 

 en out in two 

 opposite direc- 

 tions into fibres 

 (figure 5 b). 

 The fibres then 

 stretch on either 

 hand into seve- 

 ral branches (c, 

 d), and these, 

 in their turn, di- 

 vide into still 

 smaller fibres. 

 This fibrillation 

 of the branch- 

 es, however, by 

 and by proceeds 

 Fig. 5. Various stages in the evolution of the eel- backwards, to- 

 lular tissue of the fetus of the sow; the stages are in -yy ar( J s the stem 

 the order of the letters of reference; c and d are f > /-i 



mere varieties. 



ing immediately 



from the body of the cell ; so that at a later period, instead of 

 a single fibre, a bundle of isolated fibres is seen proceeding from 

 either side of the body of the cell (fig. 5 e). Finally, the body 

 of the cell itself also splits into fibres, and then, instead of a 

 cell, we have a bundle of separate fibres, to which the nucleus 

 of the former cell still continues attached. This process con- 

 sists, therefore, in a kind of splitting up of a single cell into 

 a multitude of hollow fibres. At a subsequent period, the 

 nucleus is taken away, so that the fibres alone remain, and 

 compose the filaments of the cellular tissue, as we find them 

 in adults. It would appear, however, that they must suffer a 

 chemical change, in addition to the changes in form, inasmuch 

 as the cellular tissue at first affords no proper gelatine. 



[ 54. " MUSCLE. The researches of Valentin have shown 

 that the muscles are composed of globules arranged in rows, 

 like strings of beads, which then unite into a fibre, the pri- 



