CENTRAL NERVE CELLS. 231 



tracts pass from the fibres over or under the bioplasm 

 (nucleus), without being connected with it, as has been 

 stated by some observers to be the case. (Proceedings of 

 the R.S., 1864.) 



One of the most beautiful forms of central nerve cells 

 known to me, is represented in fig. 3, PI. IX, and belongs to 

 the sympathetic nerve system of the little green tree frog 

 (Hyla viridis). These beautiful nerve cells are found in 

 great number in connection with some of the nerves in the 

 abdominal cavity of this animal, and they are to be met 

 with in all stages of development and growth. I have 

 described them fully in a memoir already referred to, and 

 published in the "Phil. Trans." for 1863. It will be re- 

 marked that from the body of the cell two fibres proceed, 

 i, a straight fibre, <z, prolonged from the central part of 

 the ovate body of the cell; and 2, a spiral fibre, #, con- 

 nected with its circumference. This is coiled spirally round 

 the lower part of the body of the cell and the straight 

 fibre extending from it. 



The fibres twist round one another as represented in the 

 drawing, and at a point about one five-hundredth of an inch 

 from the cell become much wider, expanding into well- 

 defined dark-bordered fibres which pursue opposite directions 

 in the nerve trunk, one passing towards the centre, the other 

 towards peripheral parts. In connection with these nerve 

 fibres are seen several minute bioplasts, from which, indeed, 

 the fibres grow, and thus increase in length as develop- 

 ment proceeds. The number of spiral coils round the 

 body is much greater in old cells than in young ones. At 

 an early period of the development of these cells there is 

 no coiling at all, but the two fibres which proceed from the 



