NERVE TISSUE. 



201 



ture of the cells (Fig. 177). From the interior of its rounded, 

 or pear and kidney-shaped body passes a straight axis-cylin- 

 der process (c), which subse- 

 quently acquires a medullary 

 sheath. 



From the surface of the cell 

 arises, singly or doubly, with 

 close spiral convolutions, an- 

 other filament, which surrounds 

 the straight axis cylinder with 

 wider turns ; it may also run 

 alongside of the latter (d), and 

 subsequently leave it (/), pass- 

 ing further in a straight form. 

 Whether these spiral fibres are 

 elastic or — which we regard as 

 more probable — are actually of 

 a nervous nature, is still unde- 

 cided. Subsequent German in- 

 vestigations have, unfortunately, 

 not determined this. 



Finally, the fine, fibrillated 

 formations, such as are pre- 

 sented by the axis cylinder (p. 

 196), have also been most re- 

 cently observed, continuing into the interior of the cell body, 

 and more especially in the cortical portion of the latter. The 

 finest fibrillae which stream in from the protoplasma, as well 

 as the axis-cylinder process, run sometimes divergently, some- 

 times crossing each other. 



Fig. 177. — Ganglion cell from the sym- 

 pathetic of the hyla or green tree-frog ; a, 

 cell body ; b, sheath ; c, straight nerve 

 fibre : and d, spiral fibre ; continuation of 

 the former, e ; and of the latter, f. 



