PERIPHERAL NERVE FIBRES. 



nerve cells, these two classes of nerve cells could not 

 have been distinguished from one another at an early 

 period of development. I have described the struc- 

 ture and mode of formation of these elementary parts, 

 or units of nerve in my paper in the " Phil. Trans." 

 for 1863.* In PL XXXVIII, fig. 29, I have given 

 a representation of a dark-bordered nerve fibre at an 

 early period of development, and later when the nerve was 

 so far fully formed as to be active. A nerve fibre at an 

 early period of development consists of a number of oval 

 masses of bioplasm formed by division and lineally 

 arranged. These are afterwards seen to be connected by 

 a small quantity of formed material, the future nerve fibre. 

 As development proceeds, the bioplasts become separated 

 farther and farther from one another, and the non-living 

 tissue which is thus spun off as they become separated, 

 the nerve fibre, increases in length. (PL IX, fig. i.) 



The quantity of formed matter in proportion to the 

 bioplasm of nerve, increases as the tissue advances in age. 

 This holds good, I believe as regards all tissues, in all 

 animals from the lowest to the highest. Many observers 

 now speak of the axis cylinder of a nerve as if it was alive, 

 and assert that it consists of "protoplasm;" but observation 

 leads me to the conclusion that this special nerve structure is 

 really composed of formed material. Unquestionably the 

 axis cylinder of a nerve is not made of the living matter 

 which I have termed bioplasm. 



Very delicate peripheral nerve fibres are represented 

 under a very high power, in fig. 2, PL IX. These very fine 



* " On the Structure and Formation of the so-called Apolar, Uni- 

 polar, and Bipolar Nerve-cells of the Frog." " Phil. Trans.," 1863. 



