18 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 



delicate fibres, which run in the direction of the length of the 

 cylinder. These are the primary muscular fibres ; together 

 they constitute a bundle, and this is the primary muscular 

 fasciculus, which is inclosed externally by a peculiar struc- 

 tureless wall the cell-membrane of the secondary muscular 

 cell. A process, in all respects analogous, occurs, according to 

 Meyen, in the cells of the liber, or inner bark of vegetables. 

 Here, too, simple cells arise, which arrange themselves in rows, 

 and by coalescing at the points where the cellular parietes are 

 in contact, subsequent absorption of the septa being produced, 

 change into a secondary cell, the wall of which increases in 

 thickness by means of secondary deposition ; the only thing 

 wanting in the resemblance is, that this thickening should 

 take place by means of longitudinal filaments. 



[ 55. " NERYE. The nerves appear to be formed after the 

 same manner as the muscles, viz. by the fusion of a number 

 of primary cells arranged in rows into a secondary cell. The 

 primary nervous cell, however, has not yet been seen with 

 perfect precision, by reason of the difficulty of distinguishing 

 nervous cells, whilst yet in their primary state, from the in- 

 different cells out of which entire organs are evolved. When 

 first a nerve can be distinguished as such, it presents itself as 

 a pale cord, with a coarse longitudinal fibrillation, and in this 

 cord a multitude of nuclei are apparent (fig. 7, a). It is easy 



to detach individual 

 dm l\ filaments from a cord 

 of this kind, as the 

 figure just referred to 

 shows, in the interiors 

 of which many nuclei 

 are included, similar to 

 those of the primitive 

 muscular fasciculus, 

 but at a greater dis- 

 tance from one an- 

 Fig. 7. Different stages in the development other. The filaments 

 of nerve ; a and b, of a very young fetal are pale, granulated, 

 sow ; c and d, nervous vagus, from the cranium anc [ ( as a ppears by 

 of a foetal calf. their f art i ier develop- 



ment) hollow. At this period, as in muscle, a secondary 

 deposit takes place upon the inner aspect of the walls of 



