- 38 - 
The latest important contribution to the literature on this sub- 
ject is, so far as I know, to be found in Leydigs »Zelle und Ge- 
webe«. According to Leydigs description, the contents of the cells 
consist, also, of the same two substances spongioplasm and hyalo- 
plasm, which are mentioned in respect of the nerve-tubes. As in 
the nerve-tubes the striation — the concentric one in the gang- 
lion cells, and the longitudinal one in their processes — is a rather 
apparent one, occasioned by »Hauptzuge« in the otherwise reticular 
spongy spongioplasm, through which the hyaloplasm is diffused. On 
a previous occasion he has expressed himself in somewhat similar 
terms (vide 1. c. 1883, p. 56). 
In my memoir on the Myzostoma (1885 p. 30 — 31 %l p. 74) I 
describe the protoplasm of the ganglion cells in a somewhat similar 
way. It consists of the same two substances: spongioplasm and 
hyaloplasm; the spongioplasm I am, however, »inclined to regard, 
more, as isolating the hyaloplasm into fibres, than Leydig appeårs 
to be.« »The spongioplasm extends, also, into the cell-processes 
and there, I believe, partly isolates the hyaloplasm into small tubes. « 
This is, as will be seen, a description very similar to that of Freud, 
but our opinions regarding the nature of the two substances are 
quite opposed to each other. ^ 
In Franz von Wagners work on the nervous system of Myzo- 
stoma (which appeared at about the same time as my own paper) the 
author describes the ganglion cells as having a granular protoplasm 
or also a homogeneous one. 
That is, generally speaking, our present state of knowledge 
regarding the structure of the invertebrate ganglion cells. As will 
be seen, there are, still, almost as many^views as there are writers. ^) 
c) The structure of ]aeydig's dotted sulDStance. 
We have mentioned in the foregoing, the history of the nerve- 
tubes and the ganglion cells of the invertebrates; but there yet 
remains the most difficult point in debate, viz. the combination of 
the ganglion cells with each other and with the nerve-tubes, and 
the real structure of the interposing mass, Leydigs »Punktsubstanz«. 
In the present review of the literature my attention has been especially directed 
to the statements regarding the structure of the protoplasm of the ganglion cells, 
as I take this to be the most important point for my present researches. As to 
the various statements regarding the existence or non-existence of a cell-membrane 
etc. and regarding the structure of the nucleus etc. I will, if necessary, refer to 
them during the description of my own investigations. 
