sondern entspringen stets von einem Knotenpunkte* (1. c. p. 85).
On a careful examination of sections this is easily seen. Die vom
Zellvortsatz abzweigende Theil-Fibrille generally penetrates to the
middle of the fibrous mass of the ganglion. Here it unites with
Fasern anderer Herkunft in a Knotenpunkt, von dem aus erst
die Fibrille in die Bahn der Nervenwurzel, oft unmittelbar neben
dem Zellfortsatz, riicklaufig iibergeht.
2) from fibrils of the longitudinal commissures, in such manner
that a part of these in Knotenpunkten endet, von denen andere
Fibrillen entspringen, um zur Nervenwurzel zu ziehen.
3) and finally directly from fibrils of the longitudinal commissures,
without their passing through any Knotenpunkte. 1 )
In some cases Hermann has been able to detect a direct origin
of dorsal tubes of the longitudinal commissures in ganglion cells,
the mode in which these tubes terminate he has, however, not been
able to decide. Further, he has stated the mutual interpassage of
the processes of ganglion cells from one side into the nerves of
the other side etc.
Besides what is above quoted Hermann has described a great
many interesting particulars regarding the minute inner structure,
which, however, it would occupy too much space to mention here.
It seems, however, as if later writers have paid much too little
attention to these exellent investigations, which, indeed, contain an
amount of persevering accuracy, which can not be too highly
estimated, and which in my opinion a great many subsequent writ-
ers have rather failed in affording. 2 )
DlETL (1876, 77 and 78) describes the central mass which he
calls Marksubstanz as ein goberes oder feineres, unentwirrbares
Netzwerk feinster Fibrillen . The fibrillae principally originate in the
processes of the ganglion cells. Die Auslaufer der Ganglienzellen
(des Gehirns) tauchen in die Marksubstanz ein bilden hier eine reiche
Zerfaserung zum grossten Theile das Substrat derselben und schliess-
*) My view of Hermann's Knotenpunkte and fibrillae will be seen from the
description of my investigations on that subject.
2 ) The report of Hermann's memoir given by Vignal (1. c. p. 297 298) is,
in several respects, quite incorrect and misleading.
- 48 -
lich ordnen sich die Fibrillen neuerdings zu verschieden starken
Biindeln aus denen die peripheren Nervenstamme sich entwickeln
(1. c. 1877 p. 24). He does not, however, deny the possibility of a
direct origin of nerve-tubes existing. Ich habe aber unter gewohn-
lichen Verhaltnissen nur ein solches Verhalten nicht mit untriiglicher
Klarheit zur Anschauung bringen konnen (1. c. 1878 p. 487).
RABL-RUCKHARD (1875), in his paper on the brain of the ant,
has scarcely paid much attention to the histology of the brain. He
calls the dotted substance jener feinkornigen, homogenen, keine
Zellenstructur zeigenden Substanz, die so vielfach an der Bildung des
Centralnervensystems der Arthropoden betheiligt ist (1. c. p. 489),
and his mention of this subject almost confines itself to that.
FLOGER'S paper on the brain of Insects (1878) has scarcely any
more interest for our present researches as neither has he paid any
particular attention to the nervous elements. In the fibrillar parts ol
the brain, he distinguishes between masses of netzformig gestrickten
Substanz and masses of langsfaserigen Substanzc, of which he gives
no distinct description. The real structure he has not recognised;
he says for instance (1. c. p. 561) that the fibres of this langsfase-
rigen Substanz , transversally transsected, have the appearance of
points or dots (bei Horizontalschitten erscheint das Ganze aus zahl-
losen Punkten zusammengesetzt). As far as I have seen he does
not mention the relation of the nerve-tubes to the ganglion cells;
judging from his various descriptions I think, however, that he
supposes an indirect origin (i. e. in the central fibrillar substance) of
the tubes or fibres, as he would call them, to be the rule.
E. BERGER (1878) maintains a direct origin of the nerve-tubes
from ganglion cells; this he has been able to, especially, observe
in connection with the origin of the antennal nerve-tubes in Musca
vomitoria which he therefore recommends as a good subject for
examination to convince oneself of this mode of origin. He does
not, however, deny that an indirect origin may possibly occur, and
believes it, even, to be probable (1. c. p. 3).
YUNG (1878) believes in a direct origin of the nerve-tubes
from ganglion cells. Les tubes, he says, ne sont bien en
realite que de simples prolongements cellulaires. Still it seems as
if he, to a certain extent, e. g. in the origin of the nervi optici,
supposes a kind of double origin (direct and indirect?) to exist,
this origin is not, however, definitely explained (p. 454)- His
view of the central fibrous substance seems to be of a some-
49
what peculiar kind; he describes it as une substance medulaire,
finement ponctuee, divisee en masses plus ou moins cubiques par
de fines lamelles conjonctives (1. c. p. 459). Altogether, his ex-
planations are certainly very indistinct, in another place (1. c. p. 453),
regarding the central masses of the brain (he calls it substance me-
dullaire a translation of DlETL's Marksubstanz) he says: ils re-
sultent, en effect, d'un complexus de fibres et de substance medul-
aires que dans ces derniers temps BELLONCI, qui les a retrouves et
descrits chez la Squilla mantis, a compare aux grands lobes du cer-
veau chez les animaux superieurs.
HANS SCHULTZE (1879) gives a view of the kornig fibrillare
Centralsubstanz somewhat similar to that of DlETL. It has a
reticular structure with anastomosing fibrillae; when speaking of
it, he uses expressions like anastomotischen centralen Fasernetz.
He has never succeeded in really observing a direct transition
of processes from the ganglion cells to nerve-tubes, but does,
however, not absolutely deny its existence. An indirect origin he
considers to be the rule, there even exist two kinds of indirect
origin: centralen Zellfortsdtze losen sie durch fortgesetzte Theilung
in die Jcornig-fibrillare netzformig-verziveigte Centralsubstanz auf, aus
dieser letzteren erst bilden sich direct Nervenfasern. Bei den Elato-
branchiaten habe ich iviederTiolt einen anderen Modus des sogenannten
indirecten Uebergangs beobachtet. Kleinen multipolaren Ganglienzel-
len sind in die Leitungsbahn zwisclien die grosseren Zellen und die
nervose, anastomotische Centralsubstanz eingeschaltet. Auch sah ich
bei G-asteropoden haufig intercellular e Commissuren."
This n anderen Modus'' is, consequently, somewhat similar to what
is maintained by WALTER and WALDEYER. As will be subsequently
described, these eingeschalteten kleinen Ganglienzellen are, in my
opinion, nothing but neuroglia- cells belonging to the inner connective*
tissue or inner neurilem of the nervous system.
CLAUS (1879) maintains a direct origin of the nerve-tubes
from the ganglion cells as being the only mode of origin exist-
ing in Phronimida. Die peripherischen Nerven wurzeln nicht in
der sog. Punktsubstanz, sondern beziehen ihre Fasern aus Gang-
lienzellen theils des entsprechenden Ganglions - und zwar sowohl
gekreuzt als ungekreuzt - - theils des vorausgehenden Ganglions,
theils vom Gehirne aus. Regarding the structure of der sogenannten
Punktsubstanz he is in doubt; die zarten, als protoplasmatische
zu bezeichnenden Ganglienfortsatze have probably the same relation
to this substance in the Arthropods, as they have in the Vertebrates.
4
50
Warscheinlich handelt es sich in der Punktmasse zum grosseren
Theile um eine bindegewebige der Neuroglia der Vertebraten ver-
gleichbare Substanz zu der die kleinen ovalen Kerne gehoren, welche
im Innern der Marklager auftreten.
NEWTON, in his paper on the brain of the cockroach (1879),
has not advanced much further than Floger in the knowledge of the
dotted substance. Under a high power of the microscope, he says
that, it exibits a fine reticulation the meshes of which are extremely
difficult to define . In another part of the brain (the peduncles), he
describes a similar network, but not quite so fine, and the meshes are
more elongated (fig. 14), especially towards the upper part, and it is
this which gives it a fibrous appearance. It is, in fact, a bundle of
fibres which freely anastomose with each other. From this descrip-
tion, and from the illustration, it is quite evident that the appearance
which Newton describes as anastomosing fibres is produced by the
sheaths of the slender nerve-tubes, they being transversally or semi-
longitudinally transsected. Newton says that the manner in which
these remarkable nervous structures are connected with the other
parts of the brain and nervous system has yet to be established.
Neither does he mention the origin of the nerve-tubes or their
relation to the ganglion cells. On another occasion, he also mentions
a network extending between the ganglion cells. He thinks it,
however, to be probable that connective tissue combines with
nervous tissue to produce the appearance presented by their sections.
MlCHELS (1880) has penetrated more closely, into the innet
minute structure of the brain and ventral nerve-cord of Oryctes. He
describes, very circumstantially, the course of the bundles of fibres
and cell-processes through the fibrous mass. Though he has not quite
understood the real nature of this substance he has, however, a view
of it which is more correct than that of many other writers. He calls it
Fasersubstanz instead of Punktsubstanz, weil ich nach Anfertigung
von Langs- und Querschnitten eine molekularen Punktmasse, wie Leydig
von den Nervencentren der Arthropoden beschreibt. nicht habe auf-
finden konnen, vielmehr immer nur mannigfach sich durchsetzende
Langs- und Querfaserziige wahrzuhnemen im Stande gewesen bin.
The greatest part of these Faserzuge especially the Querfaser-
ziige spring, in his opinion, from the processes of the ganglion
cells; his opinion evidently is also that most peripheral nerve-tubes
spring directly from sucli processes. He describes numerous Ouer-
faserbiindel, die, aus den Ganglienzellen der einen Seite ent-
stehend, den peripheren Nerven der anderen Seite bilden, jedoch
zusammen mit einem Biindel, das in den Einschniirungen von
den jedwede Bauchmarkshalfte durchziehenden drei Langsziigen ab-
tritt. These Langsziigen do not, however, originate in einer
peripheren Ganglienmasse nor in einer centralen Punktsubstanz,
sondern sind bloss Fortsetzungen jener nach hinten an Dicke ab-
nehmenden Langsfaserziige, die sich durch die Schlundringskommis-
suren bis zum Gehirn verfolgen lassen. They run through the
whole length of the ventral nerve-cord.
An interesting view of the central mass is, in my opinion, found
in KRIEGER'S paper (1880) on the nervous system of Astacus. He
prefers LEYDIG'S name Punktsubstanz to DlETL's Marksubstanz,
finding the former one characteristic, whilst the latter one is mislead-
ing. Die Punktsubstanz ist (he says 1. c. p. 540) ein Netzwerk
oder vielleicht richtiger ein Filz von feinsten Fasern. This is easily
seen by help of high powers of magnification, in thin transverse
sections taken from ganglia treated with osmic acid, it can also be
seen in macerated preparations (obtained by maceration in o.oi %
ammonium-bichromate). In such, carefully treated, preparations wird
man deutlich wahrnehmen dass die Punktsubstanz aus ausserst feinen
einander durchflechtenden Faserchen besteht. Regarding a direct
transition of cell-processes into nerve-tubes, he does not deny its
existence in Astacus, but has, however, not succeeded in really
observing it. He supposes an indirect origin of the tubes to be the
most common mode. Die Ganglienauslaufer losen sich, indem sie
sich in immer feinere Aeste theilen, in der Punktsubstanz auf oder sie
bilden vielmehr dieselbe, indem die durch ihre Theilungen entstan-
denen feinsten Fasern sich auf die verschiedenste Weise durchflech-
ten, und anderseits kommen die peripherischen Nervenfasern aus den
Punktsubstanzballen hervor, nachdem sie sich durch die Vereinigung
verschiedener solcher feinster Fasern constituirt haben. The division
is not produced in such a way that shon vorher getrennt neben ein-
ander herlaufende Elemente (Primitivfibrillen), nur ihren gemeinsamen
Verlauf aufgeben, sondern der vorher gemeinsame Inhalt einer Faser
theilt sich in mehrere Aeste wie sich das Wasser in den Rohren
einer Wasserleitung theilt, die die verschiedenen Hauser einer Stadt
zu versorgen hat und in ahnlicher Weise verschmilzt der Inhalt der
einzelnen Faserchen die zu einer peripherischen Nervenfaser zusam-
mentreten, nach meiner Auffassung ebenso zu einer gemeinsamen
Masse, wie sich das Wasser verschiedener Bache zu einem Flusse
vereinigt.
J. BELLONCI (1878, 80, 81 and 83) has supplied several beautiful
4*
52
contributions to our knowledge of the central fibrous mass of different
invertebrates (Squilla, Sphaeroma, Nephrops), as well as vertebrates.
He has, very correctly, described it as consisting of connective tissue
and nerve-fibres, he has, however, not succeeded in finding the
real relation between these two substances: Selon moi, la sub-
stance grenue-reticulee est formee d'un stroma conjonctif et d'un
reseau nerveux. Le stroma conjonctif reticule est excessivement fin
dans les parties centrales du cerveau ; an contraire, dans la peripherie
des ganglions il est plus grossier et ne differe pas beaucoup de celui
dont se composent les capsules cellulaires (1. c. 1881 p. 178). Through
this reticulation of connective-tissue, extremely slender nervous fibrillce
run in all directions, anastomosing with each other and forming another
reticulation of nervous nature. These fibrilloe are partly derived from
processes of ganglion cells, and, partly, they are constituents of peri-
pherie nerve-tubes. He says of them: ils proviennent des nerfs
peripheriques et des cellules nerveuses et se ramifient en une foule de
branches grandes et petites qui, les reliant entre eux, forment un
veritables reseau. Besides an indirect origin of the nerve-tubes in
this reseau , there exists, however, also a direct origin from gang-
lion cells: cependant il est certain que beaucoup de fibres peri-
pheriques proviennent directement du corps des cellules centrales et,
dans les plus grandes cellules j'ai remarque deux prolongements qui
partent du meme pole; 1'un forme directement une fibre nerveuse
peripherique, 1'autre se resout dans le reseau de la substance grenue.
As will be seen, these observations are, in several respects, very
similar to mine on the nervous system of Myzostoma and of the
Assidians etc. and, also, to many of those, on various nervous systems,
which will be described in this paper. Bellonci has found the same
substance grenue-reticulee in the nervous system of the various
animals examined by him.
ARNOLD LANG has, in his various papers (1879, 1881, 1884),
afforded some valuable additions to our knowledge of the histology
of the nervous system of the Polyclades, Trematodes etc. In my
opinion, he has formed a very correct idea of the structure of the
fibrillar substance in the nerves and ganglia. Of the nerves he says,
for instance (1. c. 1884 p. 190): Das spongiose Aussehen auf dem
Ouerschnitt kommt dadurch zu Stande, dass der Nerv aus lauter
kleinen Balkchen zu bestehen scheint, welche alle miteinandef ver-
bunden sind und welche zahlreiche rundliche, verschieden grosse
Liicken umschliessen Auf guten Praparaten aber sind sie
(i. e. die Liicken) angefiillt von einer feinkornigen blassen Substanz,
53
die an einzelnen Stellen Zellen und Kernen Platz macht ....
die blasse, zarte, feinkornige Substanz ist nichts anderes, als em
Querschitt einer Nervenfaser. Das spongiose Balkennetz er-
weist sich also als ein Stiitsgewebe der Nervenfasern. Auf Langs-
schnitten der Nerven ist naturlich von einem spongiosen Bau des
Stiitzgewebes nichts zu sehen, da die Balken derselben in der Richt-
ung der Nervenfaser ausgezogen sind. In jedem Nerven bildet das
Stutzgewebe deshalb mehr oder wenige zahlreiche, miteinander ver-
schmolzenen Rohren, von denen jede eine Nervenfaser umschliesst. l )
Of the central mass (dotted substance) of the brain he says, after-
wards (p. 190): Ich glaubte friiher, dass sich das Stutzgewebe der
Nerven bei den Polycladen nicht ins Innere der Gehirnkapsel fort-
setze, habe mich aber, nachdem v. KENNEL 2 ) die entgegengesetzte,
Behauptung ausgesprochen hat, davon iiberzeugt dass dieser Forscher
imRechtist. Lang's opinion must, consequently, be that the spongy
looking reticulation in the dotted substance of the brain, as also
in the nerves, is produced by a Stutzgewebe or, as I call it, neu-
roglia, which in reality forms tubes; an opinion in which I do quite
agree with him, as will be seen from my subsequent description
and also from my previous papers.
In his description of the brain of the Trematodes, he even ex-
presses himself quite unmistakably in favour of this view. He
says: Vergleicht man Schnitte durch das Gehirn mit Schnitten
durch einen der starken Langsnerven, so ist man iiberrascht von
den Ahnlichkeit der Bilder. Auch im Gehirn treffen wir, wie
TASCHENBERG 3 ) richtig bemerkt, auf Schnitten, die in der Langs-
1 ) These nerve-tubes, he describes, at first, as anastomosing with each other.
Die Nerven bestehen aus ausserst zarten, mit einander anastomosirenden ....
Fasern (1. c. 1879 p. 485). Later, in his Monograph (1884), he uses just the same
words, dropping only the expression mit einander anastomosirenden. From this
it seems as if Lang has, probably, partly changed his view regarding the anastom-
osing of the fibres, and if so, he is, I suppose, right if I may judge from my in-
vestigations on the nervous system of other animals.
In his description of the nerves of the Trematodes he says (1. c. 1881 p. 37):
In Folge fortgesetzter Theilung solcher Lumina durch neue Scheidewande kommen
die kleineren Hohlungen der spongiosen Strange zu Stande. Es darf uns deshalb-
nicht verwundern, dass wir in den feinsten peripherischen Nervenastchen nicht mehr
das Bild des spongiosen Stranges sondern bloss das einer unregelmiissig punktirten
Flache erhalten ; denn hier sind durch wiederholte Theilung der sehr fein gewor-
denen Faserscheiden die Lumina auf eine ausserordentlich geringe Grosse reducirt.
This is a description which, in my opinion, is also quite suitable for the dotted
substance.
2 ) Vide Kennel 1. c. 1879 p. 153.
3 ) Vide Taschenberg 1. c. 1879 p. 19.
54
richtung der Thiere gefiihrt sind, dasselbe spongiose Gewebe, wie
in den Nerven auf Querschnitten. Bel beiden sehen wir auf Flachen-
schnitten dasselbe System mit einander verbundener Rohren und
in diesen Rohren liegen bei beiden gleichartige Ganglienzellen.* 1 )
In the Stiitzgewebe Lang even describes what he calls:
,,Faserlcerne" (vide 1. c. 1879 p. 485 and Taf. XV, fig. 5 and Tat
XVI, fig. 7, fk.) ; they have completely the appearance of neuroglia-
cells. Although Lang does not say anything regarding his view of
the nature of these nuclei, I do not think there can be any doubt
of their real neuroglia-nature (vide also Monograph 1884, Taf. 32,
fig. 9, d, e, f, g, and also Taf. 31, fig. 6, g z 3, g z 4). Lang even
describes small nuclei adhering to the processes of the ganglion cells,
(Auch der kleinen, den Auslaufern der Ganglienzellen anliegenden
Kerne miissen wir, als allgemein vorkommend, Erwahnung thun.
Mon. 1884 p. 183, Taf. 32, fig. 9, a). These nuclei have, also, quite
the appearance of those belonging to the neuroglia, as will be seen
from Lang's illustrations. It is, consequently, a situating of neuroglia-
cells quite similar to what I have previously described in Myzostoma,
and to what will be described, particularly of Molluscs, in this paper.
In the Trematodes there must, in his opinion, be a direct origin
of the nerve-tubes from ganglion cells, so far as I understand him. In
his description of their brain he says, for instance: Auf liickenlosen
Serien von Quer-, Langs- und Flachenschnitten ist es moglich, alle
Einzelheiten des Faserverlaufs zu erkennen und die Fortsatze wenigstens
der grossern Ganglienzellen bis in die Nerven hinein zu verfolgen. 2 )
Whether the nerve-tubes of the Polyclades have a direct origin in
ganglion cells of the central nervous system, or an origin in the
central fibrillar substance, he does not mention, and neither does
he give any distinct description of the dotted substance in these
animals besides what is above quoted (vide p. 53). The central
part of the brain, he says, consists aus einer sich sehr schwach
farbenden, ausserordentlich feinfaserigen Substanz, in deren Inneren
weder Kerne noch Ganglienzellen vorkommen. From this descrip-
tion it is, however, evident that we have a similar structure of the
1 ) Regarding these cells situated in the nerve-tubes, vide foot note 2.
2 ) In the peripheral nerves, he describes nerve-tubes wich are direct processes
of ganglion cells situated in the nerves. The nerves of the Trematodes, he says,
(1. c. 1881 p. 37) consist zweitens aus der Nervenfaser, die, in diesen Rohren ein-
geschlossen, die Fortsatze der ebenfalls in ihnen liegenden Ganglienzellen darstellt.
As I have not examined the Trematodes, I can, of course, form no opinion of
the correctness of this statement.
55
dotted substance in Polyclades as in Trematodes, and also in Molluscs,
Annelids etc.
SPENGEL (1881) describes in Oligognatlius large ganglion cells
with processes directly forming large nerve-tubes. LEYDIG'S and
CLAPAREDE'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 fur 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 vertebrates, and he believes, to a certain extent at all
events, in a direct origin. He expresses himself, however, very in-
distinctly on this subject.
VlGNAL (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 forme par des fibres
nerveuses d'un cote, des prolongements cellulaires de 1'autre; 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 einen netz- oder geflechtartig
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-
kugelnzubeobachten. 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 regelmassig so, dass sich die
von mehreren Ganglienkugeln ausgehenden Fasern vereinigen und
dann gemeinschaftlich in die Punktsubstanz eintreten.
_ 5 6-
VlALLANES's voluminous papers (1884, 1885, 1887) on the nervous
system of Atlieropods have not much interest for our present re-
searches, as he has paid no special attention to the minute structure
of the nervous elements. Regarding the structure of the dotted
substance, he only quotes the general opinions of other authors,
and seems, especially, to believe in the descriptions and views
afforded by Krieger and Vignal. The nerve-fibres (he distinguishes
between three kinds : tubes nerveux, fibres fibrilloides and fibres
filiformes) have no direct origin in ganglion cells, neither have
the ganglion cells any direct combination with each other. Of
the dotted substance (substance ponctuee) he says for instance (1. c.