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I do not think it necessary to discuss any further the many diffi- 
culties which would arise from such a theory; in my opinion, it is 
quite contrary to all known laws of evolution of the nervous-system. 
The longitudinal nerve-tubes have, in my opinion, another origin and 
significance, but this is not the place to enter into researches of 
this nature, we will defer this for a later occasion.^) 
^) Dr. E. Rohde describes »die Leydig'sche Punktsubstanz« of the Polychæ- 
tes in the following way: «Untersucht man das Gehirn der Polychæten auf feinen 
Schnitten, so erkennt man, das dieselbe aus sehr vielen und feinen Fåserchen be- 
steht, welche wirr durch einander ziehen und bald im Långsschnitt als Linien, bald 
im Querschnitt als Punkte erscheinen. Das Bauchmark hat im vvesentlichen die- 
selbe Structur, nur iiberwiegen hier langsverlaufende Fåserchen, welche aber zahl- 
reich von schiefen imd queren gekreuzt werden. Querschnitte und Långsschnitte 
zeigen im Gegenzatz zum Gehirn im Bauchstrang ein verschiedenes Bild, die Långs- 
schnitte mehr Linien, die Querschnitte mehr Punkte. « It will be seen that, this 
description by Bohde differs very much from mine. His «Fåserchen» are what I 
call sheaths of the nerve-tubes. It is strange, however, that he does not seem to 
have observed the reticulation which is produced in sections by the transsections 
of the nerve-tubes, and which is very prominent and distinct, lor instance, in trans- 
verse sections of the ventral nerve-cord ; he has perhaps applied unsuccessful 
staining-methods. In his description of the large nerve-tubes he mentions, however, 
fibrous sheaths enveloping them. Of one of the colossal nerve-fibres of Sthenelais, 
he says, that »it arises by a union of two nerve-fibres coming directly from two 
colossal ganglion cells in the brain, — and that it is enveloped by a fibrous 
sheath, which is at first closely applied to it, but in its further course separates 
from it and then encloses a cavity, which constantly becomes larger posteriorly 
and in the middle of the body attains an enormous diameter, k The nerve-fibre, 
which almost disappears in its wide sheath, gives off fine processes, traversing the 
whole cavity and apparently penetrating into the sheath. Towards the posterior 
extremity of the body the cavity becomes smaller, and conditions corresponding to 
those of the anterior extremity are reestablished. 
As I have not examined Sthenelais, I can have no opinion of the correct- 
ness of this statement; I have not met with any structure similar to it in the Poly- 
chætes I have examined. From Bohde^s own description it appears to me that 
there must have been some irregularities in his preparations. 
As to the origin of the large nerve-tubes, Bohde states that they spring di- 
rectly from ganglion eells. As to their terminations, his opinion is that they are 
generally broken up into »feine Fåserchen», wich in transverse sections are seen 
as minute dark points or dots. 
The processes of the ganglion cells (which are «ausnahmslos unipolar«) pass, 
in his opinion, to the dotted substance partly «begleitet von Subcuticularfasern, 
welche aber bald nach ihrem Eintritt verschwinden.« What is meant by «Sub- 
cuticularfasern» I do not exactly understand, perhaps it is the neuroglia-sheaths 
surrounding the processes. The smaller processes «gehen direct in die centralen 
Fåserchen iiber.» The larger processes are partly enveloped by a sheath, being a 
continuation of the sheath of the ganglion cells. He believes it to be probable 
«dass sie durch pinselformige Auflosung in die Fåserchensubstanz iibergehen.» 
