— 55 — 
dotted substance in Polyclades as in Trematodes, and also in MoUiiscs, 
Annelids etc. 
Spengel (i 88 i) describes in Oligognatlius large ganglion cells 
with processes directly forming large ner\^e-tubes. Leydig's and 
ClaparÉDE's gigantic nerve-tubes, he supposes to be similar cell- 
processes. These nerve-tubes have sheaths of connective-tissue, being 
continuations of the connective-tissue enveloping the ganglion cells. 
Spengel gives no description of the dotted substance; he supposes, 
however, the observations just quoted to be of importance for 
our understanding of this substance. (»Aber auch flir die Frage 
nach dem Wesen der sog. Punktsubstanz werden diese Elemente 
eine Bedeutung gewinnen miissen.«) I suppose his opinion is, that 
it is also probably formed by »Nervenrohre« with sheaths — at all 
events to some extent — and here he is, in my opinion, quite right. 
Freud (1882) does not seem to have paid any special attention 
to the structure of the dotted substance. The relation of the gang- 
lion cells to the nerve-tubes, he supposes to be the same in inverte- 
brates as in vertehrates, and he believes, to a certain extent at all 
events, in a direct origin. He expresses himself, however, very in- 
distinctly on this subject. 
ViGNAL (1883) believes only in an indirect connection of the 
ganglion cells with the nerve-tubes by means of a granular fibrous 
mass. In his description of the Crustaceans, he says, for instance 
(1. c. p. 325): »Le centre des ganglions est formé par des fibres 
nerveuses d'un coté, des prolongements cellulaires de lautre; ces 
fibres et ces prolongements se melent intimement et forment un 
plexus d'ou partent les nerfs.« 
Koestler, in his paper on >^das Eingeweidenervensystem von 
Periplaneta« (1883), mentions the structure of the »Stirnganglion« 
(Ganglion frontale). Of the minute structure of the fibrillar substance, 
he says nothing, but that it exhibits reinen netz- oder gefiechtartig 
gestrickten Charakter.« His opinion of the importance of this 
substance he does not give ; he seems to suppose the direct origin 
of the nerve-tubes in the ganglion cells to be the rule when he says: 
»Ganz deutlich ist der Ursprung der Nervenfasern aus den Ganglien- 
kugeln zu beobachten.« The ganglion cells are, in his opinion, all of 
them, unipolar. Their relation to each other he does not mention, 
he only says that from them »ausgehenden 'Nervenfasern gehen 
nach der Punktsubstanz hin und fast regelmåssig so, dass sich die 
von mehreren Ganglienkugeln ausgehenden Fasern vereinigen und 
dann gemeinschaftlich in die Punktsubstanz eintreten.« 
