- 3 8 -

The latest important contribution to the literature on this sub-
ject is, so far as I know, to be found in LEYDIG'S Zelle und Ge-
webe. According to Ley dig's 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 Hauptziige 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 & 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 appears
to be. The spongioplasm extends, also, into the cell-processes
afnd 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 WAGNER'S 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 Leydig's dotted substance.

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, LEYDIG'S 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.



39

Regarding the combination of the ganglion cells with the
nerve-tubes, there are two various opinions which have especially
been prevalent. According to a great many writers, there is an
immediate combination of the cells with the tubes, these being di-
rect continuations of processes from the cells. Another opinion is
that, there does not exist any immediate combination between tubes
and cells but that the tubes have an indirect origin, i. e., in a fibrillar
mass.

The opinion of some authors is, that both modes of origin are
present.

A direct origin of the nerve-tubes in ganglion cells has long
ago been maintained by HELMHOLTZ.

Amongst the later adherents of this opinion the following may
be named : HANNOVER, WILL, BRUCH, WEDL, FAIVRE, OWSJANNIKOW, 1 )

BUCHHOLZ, CHERON, BRANDT, 2 ) STIEDA, BERGER, YUNG, CLAUS,
LANG, SPENGEL, MICHELS, FREUD, KOESTLER, ROHDE, POIRIER.
WALTER, SOLBRIG, BELLONCI, BOHMIG, HALLER and NANSEN^ have



T ) Owsjannikow states (1881) that in the Crustaceans the nerve-tubes
arise directly from ganglion cells. The large longitudinal nerve-tubes are formed
by the union of several processes from various cells; and they forment un systeme
particulier, etablissant la relation entre les cellules des noyaux de la chaine gang-
lionnaire et les cellules du cerveau (1. c. 1 86 1, p. 136). Of the combination of
cells, situated oposite to each other, he says: Les cellules nerveuse d'un cote sont
partout unies aux cellules de 1'autre par des commissures.* The nerve-tubes of the
Molluscs Owsjannikow also describes (1870), as arising directly from ganglion cells.
In most tubes he has, however, observed a division into two branches, the one of
which passes into a peripheric nerve, whilst the other one passes zu der ent-
gegengesetzten Halfte des Nervenknotens*. Es liisst sich aber auch ferner nach"
weisen, dass einzelne Gangliengruppen auf ebendieselbe Weise mit einander ver-
bunden sind. Of interest is, that Owsjannikow (like Buchholz) an manchen
primitiven Nervenfasern auch solche Nebenastchen entdeckt habe, die sich fast
plotzlich in eine sehr grosse Anzahl hochst feiner Astchen dritten und vierten
Ranges theilten und endlich so fein vurden, das'sie der starksten Vergrosserung
entgingen. Diese Astchen* he supposes to be similar to Deiter's protoplasmic
processes, in which supposition I do not, however, agree with him. It may also
be mentioned that Owsjannikow, like Walter, describes multipolare Nervenzellen*
situated an manchen primitiven Nervenasten*. These cells are, however, in my
opinion, not ganglion cells but neuroglia-cells.

2 ) Brandt (1870) designates the Punktsubstanz or Medullarsubstanz in the
ganglia of Lepas anatifera as consististing of feinen Kornchen. Its function or
importance he does not, however, mention. The nerve-fibres (welche den Achsen-
cylindern der markhaltigen Nervenfasern der Wirbelthiere und einiger Wirbellosen
entsprechen) are direct continuations of the processes of the ganglion cells.

3 ) Lately, a paper by Raicitz has appeared, where views are expressed very
like those of Haller. This paper will be referred to at the conclusion of the pre-
sent chapter.



40

described a direct origin of the tubes in cells, but at the same time
have also described an indirect origin as being present, WALTER,
SOLBRIG, BOHMIG and HALLER even suppose this to be the prevalent
mode.

WALTER desribes the indirect origin as being produced by
interposed multipolar cells, whilst the other writers presume a more
or less fibrous or reticular substance as being the interposing me-
dium ; this substance is principally formed by processes from the cells.

HALLER and HANS SCHULTZE (as will be mentioned later) de-
scribe both modes of indirect origin.

Upon several occasions I, myself, have described an indirect,
as well as a direct, origin of the nerve-tubes and supposed both
modes of origin to be present to a somewhat similar extent, as, in
my opinion, the nerve-tubes having a direct (never isolated as
most writers maintain) origin should be motoric ones, whilst those
with an indirect origin should be of a sensitive nature.

Amongst those who maintain an indirect origin of the nerve-
tubes from a granular-fibrous mass, and, as a rule, deny the existence
of a direct origin, the following writers may be specially named:
LEYDIG, WALDEYER, HERMANN, HANS SCHULTZE, KRIEGER, VIGNAL,
PRUVOT, VlALLANES, F. v. WAGNER Some of these, e. g. Leydig
and Waldeyer, admit a direct origin to occur quite exceptionally.

LEYDIG is the first writer who has given a somewhat detailed
description of the central mass of the ganglia. He calls it
Punktsubstanz and characterises it as a netzformig gestrickte
Gewirr feinster Faserchen. This Punktsubstanz receives on one
side the branching processes of the ganglion cells (these loose them-
selves into the fibrous substance) on the other side it gives origin to
the peripheric nerve-tubes.

This not very detailed description by Leydig has been supplemented
by very few scientists. Most writers seem to be satisfied with it,
they use the name without entering more closely upon this difficult
subject, and do not try to define the structure of the central mass
more exactly. WALDEYER characterises it as a Gewirr feinster Fa-
den , which should originate principally in the division of the cell-
processes.

BUCHHOLZ (1. c. 1863) calls this mass jenes feinste Fasersystem,
welches uberall innerhalb der Nervencentren verbreitet ist. He has, in
my opinion, in many respects, arrived at a very correct view, which is
scarcely surpassed by any other writer. The fibrillae of this Faser-
system are extremely slender. Die Ursprungsweise derselben ist
nun, wie angedeutet, eine doppelte ; einmal namlich gehen sie, wie



41

an den multipolaren Zellen zu bemerken ist, aus unmittelbar von
dem Ko'rper der Zelle entspringenden, urspriinglich breiten Zellen-
fortsatzen hervor, welche sich ganzlich in derartige feinste Fibrillen
auflosen, das andere Mai dagegen entspringen sie nicht unmittelbar
von den Ganglienzellen, sondern werden erst von den breiten Fort-
satzen abgegeben, wobei sie alsdann gewohnlich sogleich als sehr
feine Fasern sich darstellen, welche oftmals noch in ganz ausser-
ordentlicher Entfernung von der Zelle selbst entspringen; ohne dass
die breiten Axencylinder durch die Abgabe derartiger feinster
Reiserchen irgend merklich sich verschmalerten. - - Diese feinsten
Reiser entspringen sehr haufig mit einer sichtlichen plattenformigen
Verbreiterung von der breiten Stammfaser. These feinsten Reiser
generally subdivide so dass aus denselben eine ausserordentlich grosse
Anzahl unmessbar feiner Fasern hervorgeht, welche iiberall mannich-
fach sich durchkreuzend im Inneren der Nervencentren vorhanden
sind. 1 ) These unmessbar feinen Fasern are the smallest and
finest elements which Buchholz has been able to observe in the
fibrous mass, still, however, he is not sure whether they do not sub-
divide, or if they really are the ultimate branches by which the corre-
spondence between the ganglion cells is produced.

Regarding the appearance of these fibres he says: dass die-
selben je nach der Natur der Flussigkeit, in welcher dieselben iso-
lirt wurden, mehr oder minder deutlich unregelmassige Varicositaten
zu zeigen pflegen.

The fibres are, as he supposes, separated from each other durch
eine gewisse Menge seroser Flussigkeit , which in the preparations
have the appearance of einer fein granulirten Substanz*, the gra.
nular appearance is, however, probably artificially produced ; perhaps
it is, also, to some extent produced by destruction of some of the
nervous substance. And he says: bei dem volligen Mangel geformter
Bildungen zwischen der nervosen Elementen lasst sich daher fur die
Centraltheile ebenso wie fur die Nervenstamme als hochst wahr-
scheinlich annehmen, dass die geringen Zwischenraume, welche
zwischen den Gangliencellen und den Fasergebilden iibrig bleiben,
ebenfalls hier nur von einer des Ganglion durchtrankender Zwischen-
fliissigkeit erfiillt werden.

As to the origin of the nerve-tubes, he considers that all of
them originate directly in ganglion cells; but their course through
the fibrillar mass is, as mentioned, not an issolated one. Each

] ) l. c. p. 289.



cell has, generally, only one process forming nerve-tubes; as a rule
this process, however, sooner or later, divides dichotomically ; how
many divisions there may occur he has not ascertained. Doch
scheint zum mindesten eine dichotomische Theilung stets vorhanden
zu sein wenigstens sind mir in mehr bedeutender Lange erhaltene
Axenbander ohne jegliche Theilqng niemals begegnet (1. c. p. 283).

Thus, several tubes must be supposed to originate in each ganglion
cell, and really unipolar cells do not exist, according to his view,
or if existent they are very rare, and of a small size.

Regarding the form of the ganglion cells (the larger as well as
the smaller ones) so finden wir allerdings den unipolaren Habitus
durchaus vorwiegend. Really multipolar cells are, however, also
present; they are generally of a larger size. Die Fortsatze dieser
multipolaren Zellen zeigen nun, .... ein verschiedenes Verhalten an
derselben Zelle. Bald namlich theilen sie sich schon nach kurzem

Verlauf ganzlich in ungemein feine Fasern, 1 ) bald ver-

laufen sie in sehr grosser Lange, ohne sich aufzulosen mit ziemlich
gleich bleibender Breite fort, wobei sie nur hin und wieder vereinzelt
sehr feine Fibrillen 1 ) abgeben (1. c. p. 276). 2 )

According to BuCHHOLz, an indirect origin of the nerve-tubes,
as maintained by LEYDIG and WALTER, never occurs. Es kommt
nirgend vor, dass breite Primitivfasern von feinsten Fibrillen erst zu-
sammengesetzt werden, auch sind sie selbst als homogene Bander
und keinesveges selbst als Biindel feinster Fasern anzusehen (I.e. p. 305 j.
The function of jenes feinsten Fasersystem is, consequently, not to
form nerve-fibres withjndirect origin, but to produce correspondence
between the ganglion cells, which never have a direct connection
with each other as Walter and other writers maintained. So oft
ich aber auch einen derartigen Zusammenhang zwischen Zellen zu
sehen glaubte, habe ich mich doch immer wieder in jedem einzelnen
Falle davon tiberzeugt, dass dieser Anschein auf ganz bestimmt
nachweisbaren Tauschungen beruhte (1. c. p. 293).



') Cmfr. what is above mentioned regarding the origin of the slender fibrillse
of the fibrous mass.

2 ) According to Buchholz apolar ganglion cells do not exist. About this
he says: Es ist den vorangehenden Arbeiten zufolge kaum nothig hervorzuheben,
dass Ganglienzellen ohne Fortsatze gar nicht vorkommen.* Seeing that Buchholz
(and before him Owsjannikow) has already expressed himself so very decidedly on
that point, it is really very curious to find this phantom haunting the brains of,
even, quite recent writers. Regarding the non-existence of processes issuing from
nuclei or nucleoli Buchhoh, also, expresses himself very decidedly.



43

We will close this report of BuCHHOLZ's paper with a reference to
his description of some corpuscles occurring in the fibrous mass. About
these he says: Pnifen wir namlich die feinen Faserziige, welche neben
den breiten Axenbandern iiberall anzutreffen sind, so bemerken wir
an sehr zahlreichen dieser Fasern erhebliche Anschwellungen, welche
mit deutlichen ovalen Kernen versehen sind. Es sind fast immer
langgestreckt spindelformige Gebilde, welche nach beiden Seiten hin
in feinste Fasern unmittelbar sich fortsetzen, oder vielleicht richtiger
gesagt in den Verlauf derselben eingesehaltet sind. Die Kerne
enthalten einen oder mehrere sehr feine, punktformige Nucleoli.
The extremities of the fibres issuing from this Gebilde resemble
in ihrem ganzen Ansehen, sowie durch das Vorhandensein vielfacher
Yaricositaten auf das Vollkommenste den feinsten Verzweigungen
der Ganglienzellen. Besides these in reichlichster Anzahl vorhan-
denen regelmassig spindelformigen Faseranschwellungen giebt es aber
noch eine andere Art kernhaltiger, mit den feinsten nervosen Fasern
in Zusammenhange stehender Bildungen (1. c. p. 290 291).

These have generally a multipolar shape, and have nuclei of
quite the same appearance as those just mentioned. Buchholz does
not exactly know which nature he ought to ascribe to these cells,
I think, however, there can be no doubt but that these cells are
what I have described as neuroglia-cells (vide sequel). ! )

This report of Buchholz's paper is, perhaps, somewhat prolix.
I have, however, made it thus circumstantial, partly because I have
seen no correct report of the beautiful researches of this eminent
investigator, and also, partly, because I consider those researches to
be of the highest import, and it really seems as if they are far too
little known.

WALDEYER (1863) describes >>das molekulare mittlere Stratum
as eine Art Flechtwerk, welches eben der Feinheit der Faden we-
gen, aus denen es besteht, sehr schwer zu entwirren ist.. This
Flechtwerk , is formed of the three following elementary parts: feine
Auslaufer der grossen Zellen, kleine Zellen und deren feinste Aus-
laufer. Die kleinen Zellen liegen sehr dicht neben einander in the
central mass. This last description does not suit for my neuroglia-
cells, which in Mollusca (which Waldeyer has especially adopted



J ) It is indeed very strange that Rawitz has not observed Buchholz's descrip-
tion of those corpuscles, as he has described and figured quite similar ones (cmfr.
the subsequent report of R.'s paper). The multipolar cells of Holler, situated in
dem centralen Fasernetz, are also, undoubtedly, the same cells as those multipolar
Gebilde of Buchholz.



44

for his investigations) occur somewhat sparingly , in spite of this, I
do not doubt, however, that what Waldeyer has called kleine Zel-
len (kleine bi- und multipolare Zellen) is what I describe as
neuroglia-cells.

Of the results of his investigations liber den Ursprung der den
Axencylindern gleichwerthigen Axenfibrillen der Wirbellosen Wal-
deyer, himself, gives us the following summary: Stellenwir . . . .
das Endresultat zusammen, so ergiebt sich: dass dieselben (i. e.
Axenfibrillen der Wirbellosen) in den von mir untersuchten Fal-
len direct aus feinen Auslaufern kleiner bi- und multipolarer Zellen ')
ihren Ursprung nehmen, entweder aus einem solchen Zellenauslaufer
ohne Weiters, oder so, dass erst Theilaste desselben die Axenfibril-
len sind. Niemals aber gehen direct Auslaufer der grossen unipo-
laren Nervenzellen, welche die Randpartien des Ganglion constituiren,
in periphere Nerven iiber.

Thus Waldeyer denies the existence of what we would call a
direct origin of the nerve-tubes from ganglion cells.

According to CHERON (1866) the nerve-tubes of the Cephalopoda
have, as a rule, a direct origin from ganglion cells, usually in such
manner that several processes of small cells unite to form one large
nerve-tube. In some cases he supposes that one large ganglion cell
alone fournit directement un tube (vide 1. c. 1866 p. 94). The
nerve-tubes of the systeme stomatogastrique have another (in-
direct?) mode of origin. Of the central mass of the ganglia he
seems to have no distinct view; he describes it as une matiere
finement granuleuse, absolument amorphe.

CLAPAREDE (1869) quite agrees with LEYDIG in his description
of the dotted substance. Die Zentralmasse des Bauchstranges von
Lumbricus hat Leydig ganz richtig als eine sehr feine Punktsubstanz
mit darin gelegenen diinnen Faserchen beschrieben. Andere Nerven-
fasern giebt es nicht, weder im eigentlichen Nervenmark noch in
den Nerven selbst. Diese meist geschlangelten Faserchen verlaufen
in den verschiedensten Richtungen die Mehrzahl jedoch der Lange
nach; die von den Nerven stammenden strahlen nach alien Seiten
in das Bauchmark hinein. 2 ) It is quite evident that Claparede's
Faserchen , which he believes to be the real nerve-fibres , are the
sheaths of the nerve-tubes, which, transsected longitudinally, very
often have the geschlangelte appearance which he mentions. In



x ) As mentioned above, it is these cells which I call neuroglia-cells.
2 ) 1. c. 1869 p. 593.



45

his description of a connective tissue, or VlRCHOW's Neuroglia ver-
gleichbare Stiitsubstanz in the nervous system, he says, even, that he
has not been able to distinguish the fibres of this Stutzsubstanz"
von denjenigen der centralen, fibrillaren Punktsubstanz .... auch
scheinen sie in dieselben unmittelbar uberzugehen. Ueber die ner-
vose Natur der letzteren kann aber kein Zweifel obwalten. ! ) The
mode of origin of these nerve-fibres Claparede scarcely mentions,
and it seems as if he agrees with LEYDIG, also, in regard to it.

In his last memoir on the Annelids (1873) he gives a descrip-
tion very similar to what is above quoted.

SOLBRIG (1872) describes the Punktsubstanz as a granular
fibrous mass which, in a successfully isolated preparation, may be seen
traversed by einem merkwiirdig feinen Fasersystem, dessen Fibril -
len an dem Rande des Praparates oft auf weite Strecken hin isoliert
verfolgt verden konnen. He compares this Fasersystem with
the capillary reticulation of the vascular system, and supposes that a
part of its function is to produce the correspondence of the unipolar
ganglion cells with each other. Besides a direct origin of the
nerve-tubes from ganglion cells, Solbrig also distinctly maintains an
indirect origin from this kornig-faserigen Masse , the latter mode
being the most common one. In this case the nerve-tubes are
formed by the union of several Fibrillen des feinen Fasersystems.

STIEDA 2 ) (1874) supposes the nerve-tubes of the Cephalopoda
to be direct continuations of the processes of the ganglion cells.
Such a relation, he has been able to observe in some few cases.
Ein anderweitiger Faserursprung lasst sich mh Sicherheit nicht de-
monstriren. He mentions some feinsten Nervenfasern, kaum mess-
bare Faden, welche ein im Centrum des Knoten befindliches schwer
zur entwirrendes Netz bilden. His view of the import or function
of this Netz he does not, however, give.

The writer who has paid most attention to, and has made the
most minute investigations upon, the central fibrous mass of the inverte-
brate nervous system is, in my opinion, HERMANN (1875). This eminent
investigator has, in his really classical memoir, given a very circum-
stantial description of this substance, describing it as being granular-
fibrillous, and in which he very particularly indicates the course and
origin of the fibres (1. c. p. 84 etc.).



1) 1. c. p. 595.

2 ) I regret to say that to Trinchese's memoir on the nervous system of the
Cephalopoda (1. c. 1868) I have had no access, as we do not posess it in the
library of Bergen's Museum.



46 -

The extremely slender fibrillae of the mass spring, partly from
cell-processes, partly from peripheral nerve-tubes, and partly from
the longitudinally and transversally running fibres of the commissures.
The fibrillae unite in Knotenpunkte not in such a way, however, as
to form a real reticulation.

Der Zusammentritt zweier Fibrillen verschiedener Herkunft von
denen die eine z. B. von den Zellen entspringt, die andere den
Commissuren angehort, geschieht in der Weise, dass die eine Fibrille

- in Folge der Verlaufsrichtung unter nahezu rechtem Winkel -
in die andere unmittelbar iibergeht. Nur eine kleine Verdickung
die ich oben Knotenpunkt genannt habe, ist an der Verbindungs-
stelle zu bemerken. Tritt an denselben Knotenpunkt noch eine
dritte oder vierte Faser, so verwischt sich allerdings das charakteri-
stische Bild und es ensteht der einer multipolaren Zelle ahnliche
Korper, iiber den ich bereits meine Ansicht mitgetheilt habe. *)
Sorgfaltigst angefertigte Zupfpraparate bringen jene Knotenpunkte
besonders dann gut zur Anschauung, wenn sie nicht zu feinen Durch-
chnitten entnommen sind. Doch zeigen auch frische Praparate diese
Verhaltnisse, wobei jedoch die Untersuchung einmal durch die un-
gemeine Blasse der Fibrillen erschwert ist, ferner dadurch, dass alle
nicht vollstandig zerzupften und so durch die Mannigfaltigkeit der
Verbindungen netzformig erscheinenden Theile in den Liicken zwischen
Fibrillen und Knotenpunkten eine helle, nahezu halbfliissige Zwischen-
substanz erkennen lassen, welche durch ihren Reichtum an Kb'rnchen
die Deutlichkeit des Bildes beeintrachtigt (1. c. p. 84 85).

This is quoted, thus circumstantially, because I propose to refer
to it in describing my own investigations. From what is quoted, i
will be seen that Hermann supposes the central mass to be formed
by fibrillae, and by a granulous, viscous, Zwischensubstanz.

a ) Although Hermann has never observed nuclei in these multipolar corpuscles,
nor in the usual Knotenpunkte, he says of the former (1. c. p. 36): Ich kann
diese kleincn Verbindungskorper den iibrigen Ganglienzellen zwar nicht gleichstellen,
halte fur sie aber doch den Werth multipolarer Zellen aufrecht, insoferne, als
ich sie als Uebergangselemente betrachte, welche die Verbindung zwischen den zur
Peripherie ziehenden Fibrillen und den im Obigen beschriebenen grossen Ganglien-
korpern, seien es die unipolaren, oder die multipolaren , vermitteln. Whether
these Hermann's Verbindungskorper are identical with the interposed multipolar
cells which Walter describes, I can not positively deny, but am, however, not dis-
posed to think so. Walter's cells are, I think, identical with Haller's Schalt-
zellen*, which I call neuroglia- cells, whilst Hermann's Verbindungsk6rper and
Knotenpunkte* are, I think, thickenings of the neuroglia-filaments which are
also perhaps, to a certain extent, artificially produced by teasing or splitting of the
slender tube-sheaths. Their diameter is, he says, .0005 .0006 Mm.



47

Regarding the origin of the nerve-tubes, Hermann's opinion is,
that a direct origin from ganglion cells is very rare, as a rule they
have an indirect origin, and are formed of fibrillae originating in 3
different ways:

1) from ganglion cells. Diese Fibrillen sind aber nicht, wie
etwa vermuthet werden konte, direJcte Auslaufer der Ganglienzellen,