156 PROTOPLASM 



which run in the matrix, filling the supposed framework of the 

 axis-cylinder, to be quite untenable, the more so as he never 

 convinced himself of the existence of such fibrillse. To enter 

 into the dispute as to whether the substance of the framework 

 of the protoplasmic axis-cylinder, or the enchylema itself, is the 

 true nervous substance, seems to me quite superfluous in this 

 place. 



Although Leydig (1885) speaks occasionally of a spongy 

 structure in the nerve fibres (especially in Aulastomum and 

 Lumbricus), he yet openly defends the view that the axis-cylinder 

 of the fibres of vertebrates is structureless, that is to say, that it 

 consists of structureless so-called hyaloplasm ( = enchylema), which 

 collects in the centre of the medullated fibres, while the reticular 

 spongioplasm forms the medullary sheath round the axis- 

 cylinder. 



A passage in Dietl (1878, p. 95) may well be taken to indicate 

 that he had seen the net-like connections of the so-called nerve 

 fibrillae in invertebrates, while denying their existence in verte- 

 brates. It is difficult, however, to become quite clear on this point, 

 yet I consider this interpretation of Dietl's statements as correct. 



Heitzmann also (1883, p. 296) speaks of a "delicate net-like 

 structure " in the axis-cylinder of vertebrates, but apparently 

 has not paid sufficient attention to these relations, since in 

 opposition to Schultze and others he denies the longitudinal 

 fibrillar structure. He therefore cannot raise any claim to be 

 considered seriously in this question, the less so also as he gives 

 no figures. 



