A. The Theory of the Net-like or Reticular Structure 

 of Protoplasm 



As is well known, the first observations upon the peculiar 

 structures in the protoplasm of certain cells were made at 

 a very early period. If we leave the muscle cells out of 

 consideration, as has been done throughout this work, 

 observations upon ganglion cells and the so-called axis- 

 cylinders were what first brought peculiar structures into- 

 notice. 



As far back as 1837 Eemak found (p. 39, footnote) that 

 the axis-cylinder of the medullated nerve fibres of vertebrates 

 (Eemak's so-called primitive band) appeared to be composed 

 of very minute fibres, which occasionally showed nodular 

 thickeniDgs in their course. In 1843 he discovered the 

 fibrillar structure of the axis-cylinder of the large nerve 

 fibres in the ventral nerve cords of Astacus fluviatilis, but 

 was not quite certain whether this fibrous strand was the 

 equivalent of the axis-cylinder of the vertebrate nerve fibre. 

 In 1844 he expressed himself more definitely upon this 

 homology, and at the same time demonstrated the fibrillar 

 nature of the ganglion cells of the crayfish, while Will in 

 the same year also observed a concentric striation in the 

 ganglion cells of Helix pomatia. 



Since it is not our intention to describe in detail the 

 further development of the question of the structure of 

 ganglion cells and nerve fibres, we will confine ourselves to 

 noting that, especially through the works of Eemak (1852), 

 Stilling (1856), Leydig (1862 and 1864), Walter (1863), 

 Deiters (1865), and above all, those of M. Schultze (1868 



