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interfibrillar substance, this also explains their anxiety to find a 
striation in all tubes. As will be seen from my present paper, I do 
not agree with any of those writers, and when the further results of 
my investigations are known I hope we shall find a reliable ex- 
planation of the reason why a striation is not more generally visible 
than it is. 
Leydig forms an exception to most other writers in declaring 
the dark lines of the striation to spring from a structural support, 
spongioplasm, and not from nervous fibrillæ (vide Leydig 1. c. 1885, 
mentioned before, p. 31). He has no doubt arrived at a more 
correct view than any other writer, but neither is he, in my opinion, 
quite correct, as will shortly be seen. 
If the view that fibrillæ and interfibrillar substance are present 
in the tubes, was correct, it ought, in my opinion, to be easy 
to isolate these fibrillæ by splitting the tube-sheaths longitudinally. 
This is, however, very far from being the case. I have split large 
and small nerve-tubes in the fresh state longitudinally and no fibrillæ 
of the kind were visible, I have teased them very carefully and 
some thicker or thinner filaments became visible in the exlremities 
of the tubes. I never succeeded in obtaining, in spite of my most 
persevering care, neither fresh preparations nor macerated ones with 
brushes of regular fibrillæ in the extremities of the tubes similar to 
those illustrated by H. SCHULTZE in Molluscs and Annelids. The 
filaments or fibrillæ visible at the extremities of the nerve-tubes had 
always a somewhat irregular appearance, with varying thickness and 
length, and they certainly looked as if they belonged to a supporting 
substance and were to a certain extent artificially produced. 
A viscous homogeneous substance, as stated by SCHULTZE, was 
certainly also visible between those filaments. This substance never 
occurs, however, in such a way that I can say it formed an inter- 
fibrillar substance, and was diffusively extended in the nerve-tubc. 
At the extremities of the nerve-tubes it always appeared on pres- 
sure in the form of regular small pearls issuing from the tube-contents. 
I never saw it appear in large pearls, not even in the large nerve- 
tubes where this substance, according to a great many writers, 
forms a thick layer surrounding a central bundle of fibrillæ. It had, 
in fact, always the appearance of these small pearls of viscous 
substance issuing from a great many extremely slender tubes or 
channels contaning the substance, situated close together and 
forming the whole contents of the nerve-tubes, and this we shall 
see is really the case. The filaments visible at the extremities of 
6* 
