the principal respects,
My investigations lead me, thus, to maintain the view I have
previously stated, and I am now in a position to state it, as I
*) Leydig is, as before mentioned, the author with whom I can agree in
most respects.
2 ) 1. c. 1886.
3 ) 1. C..I886.
nope, with better and more complete expression. As will be seen
from the following description, the structure of the dotted sub-
stance is essentially the same in all the animals investigated. The
animal in which I have found it easiest to get a clear idea of the
structure is Homarus, the ventral ganglia of which give an excellent
material for investigations of this nature.
Komarus vulgaris.
Sections through the brain or the ventral ganglia of Homarus
exhibit, in their mesial part, a more or less minute reticulation; to
some extent this reticulation even passes over into masses which,
on a superficial examination, have a dotted appearance, for which
reason LEYDIG has also called it the dotted substance (Punkt-
substanz), without intending, however, that this designation should
be understood in its literal signification. On a more careful exa-
mination of good and successfully stained sections, even these masses
with the finest granular appearance exhibit a reticulation with very
minute but still distinct meshes; the granules are thickenings in the
reticulation. On examination of sections through a ventral ganglion
we will, indeed, find reticulations with meshes of all possible sizes,
from the transsected large nerve-tubes (dorsally situated and issuing
from the longitudinal commissures or from the peripheral nerves) down
to the extremely minute meshes in the dotted masses just mentioned,
which meshes are of about the same size as the transsected primi-
tive tubes in the sections of the nerve-tubes or even much smaller.
The substance forming this reticulation is rather uniformly
stained through the whole mass, and in a manner similar to that in
which the neuroglia-sheaths of the nerve-tubes are stained (vide
fig. 62). It is a distinct staining which is, consequently, different
from that of the spongioplasm in the nerve-tubes (vide fig. 62).
This makes me believe that it is not quite the same substance as
that which I have, previously, in this paper called spongioplasm, but
that it is rather the neuroglia-substance which forms this reticulation,
as I can, really, see no distinct difference between the neuroglia
enclosing the smaller or larger nerve-tubes and the substance form-
ing the smallest meshes.
Within the meshes a lightly stained, hyaline, substance occurs,
which is similar to the hyaloplasm of the nerve-tubes.
A question of great interest is now, whether these small meshes,
seen in sections, belong to a a real reticulation formed by fibrillce,
as almost all writers agree in describing it (some writers call it
I2 4
nervous retic. others call it partly retic. of connective-tissue ) or
whether they are transsected tubes similar to the meshes produced by
the transsection of the larger nerve-tubes with which we are already
acqvainted. In the former case, the hyaline substance seen within
the meshes should be interfibrillar substance, in the latter case it
must be a substance filling the tubes, probably hyaloplasm.
On careful examination of transverse sections w T e will immediately
receive a reply to this question. If the meshes are transsected tubes,
we may expect to find in a section through a mass consisting of a
plait of such slender tubes, not only transversally transsected tubes
but also longitudinal transsected ones. And that is, in fact, the
case. On a glance at fig. 62 (which represents a part of a trans-
verse section through a ventral ganglion of Neplirops norvegicus,
which is, however, so quite similar to Homarus, in this respect, that
we can indeed see no difference) we will, in the fine reticulation
(ds) be able to see transversally transsected tubes as well as longi-
tudinally transsected ones, the latter having the shape of more or
less oblong meshes.
On examination of spots where small parts of nerves originate
in similar masses of dotted substance, its composition of tubes
will be still more evident. Fig. 61 represents such a spot, highly
magnified, in the mesial part of the first ventral ganglion of Homa-
rus. That the meshes, tpt, are transsected tubes is, I think, dis-
tinctly seen; c is a tube partly longitudinally transsected; a is a
bundle of similar tubes issuing from various parts of this mass of dotted
substance and passing to the root of a nerve. Many similar proofs of
the tube-nature of the meshes, seen in the dotted substance, can be
found on examination of sections through the ganglia of Homarus, and
each of them speaks so clearly that I think it, really, to be a waste
of time to give further, circumstantial, description of it at present. 1 )
Having thus elucidated this question regarding the tube struc-
ture of the dotted substance, the next question of interest becomes
of what kind these tubes are, whether nerve-tubes or primitive
tubes, or what else?
Nerve-tubes are, as previously mentioned, present in great plenty
in the dotted substance, as will be seen in fig. 62 65. These nerve-
tubes have all possible gradations from large, fig. 62,tnt y and tnt,
down to very small ones, of which we have, for instance, a trans-
sected bundle in fig. 62, s nt. The smallest meshes or tubes, ds,
1 ) In some parts of the dotted substance the tubes are somewhat loosely situ-
ated, and the intervals between them are then filled with a neuroglia sponge-ivork.
125
are, however, all of them, smaller than those small nerve-tubes, and
they have, to a certain extent, a rather uniform size, with their dia-
meter about the same as that of the common primitive tubes of
the nerve-tubes (vide in t nt'). There are, also, a great many ex-
tremely minute meshes or tubes which are even smaller than the
smallest primitive tubes I have been able to observe in the nerve-
tubes. These minute tubes will, subsequently, be more circum-
stantially described. The principal difference between the primitive
tubes of the nerve-tubes and the tubes of the dotted substance is
that, the latter have more distinct and deeper stained sheaths. Seeing
how nerves are formed by the union of these tubes, it is, therefore, in
my opinion, evident that they are primitive tubes with stouter sheaths
than they have in the nerve- tubes. These, the sheaths, in the
dotted substance, seem to be formed or, at all events, made stronger
by the same neuroglia which also envelopes the nerve-tubes; this
neuroglia does not seem, however, to be very distinctly distinguished
from the spongioplasm, as we have, also, previously seen in the
ganglion cells (cf. p. 100 102). Inside these primitive tubes, I have
been able to observe any structure, only the hyaline substance,
hyaloplasm, above mentioned. The granules which have given the
dotted substance its name, are, partly, thickenings in the sheaths of
the tubes, especially along their concreting edges; to some extent
they are extremely slender tubes traussected (vide sequel).
The meshes which are somewhat larger than those small meshes
in the dotted substance, are, I think, transsected small nerve-tubes
consisting of a few primitive tubes only.
We have thus, in the dotted substance in the ganglia of Ho-
marus, a complicated plaiting or web of primitive tubes, and partly
of nerve-tubes, of various sizes. On examination of longitudinal
sections we will find that, these tubes have in the dotted substance
of the ventral ganglia, to a certain extent, a tendency to follow a
longitudinal course; this is especially the case in the parts where the
nerve-tubes issuing from the longitudinal commissures are situated.
To some extent, we also find bundles of nerve-tubes running trans-
versally as commissures from one side of the central nerve-system
to the other, or also running to the peripheral nerves.
Smaller or larger distinctly defined masses, apparently consisting
exclusively of primitive tubes, are mesially situated in most ganglia;
they are, however, especially prominent in the first ventral ganglion
and in the brain; fig. 6 1 represents, as before mentioned, a part of
such a mass situated, mesially, in the first ventral (thoracic) ganglion.
- 126
The illustration is drawn under the camera lucida and very high
microscopical power.
As we can not undertake the very complicated topography of
the ganglia of Homarus in this paper, we will not enter upon the
topographical peculiarities here, which KRIEGER, YUNG, DlETL and
others have already to some extent previously described ; we must
confine ourselves to indicate the constituents of the various masses
of the fibrillar substance (dotted substance) filling the mesial parts
of the ganglia. The constituents of these we have found to be
primitive tubes, or also nerve-tubes, and neuroglia.
Though I have not, as mentioned, been able to observe any
structure inside the primitive tubes described there may perhaps be
a still smaller or more minute constituent in the dotted substance.
Such minuter constituent I have, however, not observed in common
preparations stained in haematoxylin, carmine etc.; it is only on
application of the chromo-silver method, mentioned p. 77 80,
and partly on staining by HElDENHAIN's haematoxlin method,
that it has been possible to observe such a constituent, and even
then only imperfectly. It consists of extremely slender fibrillae or
rather tubes, which run in all directions in the dotted substance
between the larger tubes, and whose diameters are much smaller
than any of the primitive tubes described. Such fibrillae or tubes
are seen in fig.s 63 65. Many of them are, here, seen to be given
off from larger nerve-tubes. Some of them have, at certain intervals,
varioceles (vide fig. 63, f; fig. 64, i, #/.), and resemble in their appear-
ance the varicose nerve-fib rillae I have found in the central nerve-
system of Myxine (and which will be subsequently described) and
the varicose nerve-fibrillae described by GOLGI in the central nerve-
system of the Mammalians, and, further, the nerve-fibrillae described
by BELLONCI in the tectum opticum etc. of fishes and birds, etc. etc.
In the varioceles extremely slender branches are probably given off,
these have, however, only in a few places been stained. The varioceles
exepted, the fibrillae are smooth and have a deep reddish-black
staining. As will be seen from the illustrations, their thickness is
very variable; they subdivide and at each subdivision they grow
thinner.
Whether the structure of those fibrillae is that of tubes with
sheaths and semi-fluid contents, as we have previously described the
primitive tubes to have, is of course extremely difficult to decide.
We know, at present, so very little of the nature of the chromo-
silver staining, that it can only give us little instruction in this
respect. The reason why these fibrillae, and also small nerve-tubes,
are so distinctly and deeply stained, whilst the sheaths of the larger
nerve-tubes only get a light reddish staining is, for instance, very
difficult to explain. Seing, however, that it is only the sheaths of
the larger nerve-tubes or a layer just inside the sheaths which be-
comes stained, we may perhaps conclude that this is also the case
with the smallest nerve-tubes; indeed, we can, to some extent,
observe it in transverse sections of them, though their contents
also appear to be somewhat stained. Seeing that it is the case
with the smallest nerve-tubes from which these fibrillae issue, and
which they quite resemble in their staining, it is, in my opinion,
most probable that they also have an external layer which is the
essential staining part of them, notwithstanding that the contents are
also stained. That it is principally the external layers of the fibrillae
which are stained, can sometimes be observed, especially in the
thicker fibrillse, or in their varicose thickenings. To speak more
distinctly I will say that I do not think it is the external part of
the neuroglia-sheaths, but that it is either their internal parts or rather
a layer inside them which is specially staining in these slender tubes.
Judging from chromo-silver preparations I think therefore that
it is probable these fibrillae are tubes, the smallest of which must
consequently have an almost infinitesimal diameter. On examination
of preparations stained with HEIDENHAIN'S haematoxylin method we
arrive at very similar results; indeed, the tube-structure of these
slender fibrillae (which are also partly stained by this method) is
still more evident. Fig. 65 represents a part of a section through
such a preparation of the dotted substance (drawn under the cam.
luc. and very high powers of the microscope). The slender fibrillae,
which are deeply stained, are seen longitudinally or transversally trans-
sected in this very thin section. Transversally transsected they
appear, partly, as extremely minute meshes, which we have before
mentioned. Longitudinally transsected they, partly, exhibit very
distinct longitudinal outlines and a lighter contents. Frequently they
are, however, so slender, that no such structure can be distinguished,
neither in transverse sections nor in longitudinal ones. Of the tube-
structure of these smallest fibrillae I must, therefore, once more ex-
pressly say that we do not yet know anything with certainty.
Another question is, whether are those fibrillae or tubes only very
thin primitive tubes which by subdivision etc. have become so thin,
or are they a special constituent contained in the primitive tubes?
Seeing that they issue from nerve-tubes, I think it is evident that the
former, or the latter must be the case, tertmm non datum. That they
128
are of real nervous nature, and are not simply fibres belonging to the
connective substance, neuroglia, is not, I think, open to argument.
To decide the above question is not easy. As before mentioned,
it has not been possible to detect any structure inside the sheaths
of the primitive tubes, neither in the nerve-tubes nor in the dotted
substance. In spite of this a structure may of course be present;
the primitive tubes are already so very minute that even our present
powers of the microscope, though high, would not readily suffice to
exhibit such a structure of small tubes or fibrillae inside them. We,
therefore, at present, stand, here, before a terra incognita, and must
content ourselves with suppositions, which we will, however, leave
the reader to form for himself. What we know is that, these
fibrillas spring from subdivisions of nerve-tubes or primitive tubes
or they are given off, from them, in form of slender lateral
branchlets, and it is then, perhaps, most reasonable to assume that
they arise only by a subdivision of primitive tubes.
As to their course in the dotted substance, I will expressly
say that, I have never succeeded in observing these fibrilla to form
a reticulation with real meshes, neither have I seen them anastomose
with each other. They frequently exhibit, in sections, an extremely
complicated course with a great many subdivisions and branches,
but in my preparations they always avoid union with each other.
They form, consequently, a kind of loose plaiting or web and not a
reticulation as most authors describe. They pass along the walls
between the thicker tubes of the dotted substance.
What previous authors have described as nervous reticulation
in Homarus, as well as other invertebrates, is, as mentioned above,
the transsected tubes, primitive tubes and nerve-tubes, forming the
dotted substance, the sheaths of which tubes, in sections, give the
appearance of a reticulation. LEYDIG describes, as mentioned p. 60,
a sponge- work (Schwammwerk, Balkenwerk) in the dotted sub-
stance, which sponge-work he supposes to be of the nature of a
support; the real nervous substance, hyaloplasm, is diffusively ex-
tended in the cavities of this sponge-work. l ) As may be seen from
J ) Leydiy does not exactly state what he supposes to be the origin of this
reticulation. In Zelle und Gewebe* 1885 p. 173 174 he only speaks of the
dotted substance as containing a protoplasmatisches Netz- oder richtiger Schwamm-
werk*. Of this Schwammwerk or Balkenwerk he says: wo nun Nervenur-
sprunge gesetzt sind ordnet sich das Balkenwerk zu Langsstreifen, die zwischen
sich die homogene Grundsubstanz ebenso aufnehmen, als es in dem sich durch-
kreuzenden Maschemverk geschehen war. In another place he says, however, that
the dotted substance entsteht durch fortgesetzte Theilung und netzige Auflosung
der Fortzatze der Ganglienkugeln, genauer gesagt, ihres Spongiplasma (I.e. p. 187).
I2 9
my description, above, I agree principally with LEYDIG, as to the
nature of the two substances, but we do not agree as to their
structure. LEYDIG calls the substance of his reticulation spongio-
plasm; as I have tried to distinguish between spongioplasm and neu-
roglia, I have called the same substance neuroglia, which, however,
in my opinion, forms tubes (enveloping primitive tubes or nerve-tubes)
and not a sponge-work in the dotted substance. LEYDIG does not
draw any line of demarcation between spongioplasm and neuroglia.
His opinion is that, what he calls spongioplasm is a reticulated sub-
stance which is present in the ganglion cells, as well as in the cells
of the neuroglia, or the connective-tissue as he calls it; and that
there is, in the nerve-system of the vertebrates, an intimate connec-
tion between the spongioplasm of both kinds of cells (cf. op. cit.
p. 187 189). In a future paper on the structure of the neu-
roglia, the writer will have an opportunity to treat of this subject
more circumstantially.
The origin of the primitive tubes and filrillce of the
dotted substance. Having described what the constituents of
the dotted substance are, as far as our ability goes, we will now
advance to examine from whence these constituents come. To do this,
we must try to learn the course of the nervous processes, issuing
from the ganglion cells, and the nerve-tubes in the dotted substance.
We have, already, said that the nervous processes of the ganglion
cells occasionally subdivide, and give off branches, on their course
from the ganglion cells to the dotted substance. On a closer
examination we will find that they do the same, in a higher degree,
on their course through the dotted substance.
This subdivision and branching of the nervous processes cannot
easily be traced, without staining by the chromo-silver method
(cf. p. 78). In successful preparations, stained in this way, I have
occasionally been able to trace the nervous processes, to some ex-
tent, on their course through the dotted substance. When a nervous
process was visible for some distance along its course dichotomous
subdivisions, or finer side-branches given off from it, were always
observed; I have never observed a nervous process which, for any
considerable length, had an isolated course through the dotted sub-
stance.
On comparison of the course of the various nervous processes,
I have found that they essentially differ, and that there must be two
kinds or types of them, which behave in two different ways on
their course through the dotted substance.
9
130
In the course of some processes dichotomous subdivisions are
very common, and the branches of the process subdivide, again, into
smaller and smaller branches, this seems to continue until the whole
process is broken up into a great many fine primitive tubes or
fibrillse, and its individuality is, consequently, quite lost. I have not,
yet, been able to trace any process to its division into the finest
tubes, but from the little I have seen, however, I believe that I
am entitled to conclude that such must be the case. Fig. 63, a
and b represent pieces of such processes, which are drawn under
the camera lucida direct upon the stone; fig. 70 represents a gang-
lion cell with such a process.
A great many processes have quite another character. I have
been able to trace them for long distances through the ganglia,
in one case even directly into the root of a nerve, without seing
any subdivision. They have, however, no isolated course; at
certain intervals they give off slender side-branchlets which often
subdivide in the dotted substance. At the places where such
branchlets issue, the nervous processes have generally small thicken-
ings or varioceles. I think that all the nervous processes of this
type pass to a commissure or peripheral nerve, and become a com-
missural or peripheral nerve-tube. We may thus say, of these
nervous processes, that they keep their individuality, but have no
isolated course. Fig. 64, a, b, c, d represent nervous processes of
this kind; fig. 68 and 69 represent ganglion cells with such processes.
We may thus establish two types of nervous processes viz.
i) nervous processes which lose their individuality and are entirely
broken up into slender primitive tubes and fibrillce, and 2) nervous pro-
cesses which keep their individuality and pass through the dotted
substance of the ganglia, forming a nerve-tube, but which have no
isolated course, side-branchlets being given off on the way through
the dotted substance.
We have, before, said that the nervous processes subdivide, and
give off branchlets also before the reach they dotted substance. The
branches and branchlets which arise in this way seem, however,
chiefly, if not wholly, to penetrate into the dotted substance; they
frequently enter into this substance together with the thicker nervous
processes, as will be seen in fig. 64, e, f, where several such branches
are represented. It seems, thus, not to be of any essential import
whether the nervous processes subdivide in or outside the dotted
substance, as in both cases the branches penetrate into it and be-
come one of its constituents.
It is, however, not only the nervous processes which subdivide
or give off branches to the dotted substance and thus contributes
to its formation ; the nerve-tubes coming from the longitudinal com-
missures and from the peripheral nerves also do the same.
That the largish nerve-tubes of the longitudinal commissures sub-
divide to some extent in the ganglia, may already be concluded
from the fact that, in a transverse section through the central
part of a ventral ganglion, only a very small number of trans-
sected large nerve-tubes is seen. The many largish nerve- tubes of
the commissures must, therefore, either have passed to the peripheral
nerves, or they must have subdivided, or have become diminished
by giving off lateral branchlets, or finally they may originate in
ganglion cells. On examination of longitudinal sections stained
with haematoxylin etc. it may be seen that these longitudinally
running nerve-tubes subdivide, in the ganglia, to a great extent.
The contents of the longitudinal commissures radiate into the dotted
substance of the ganglia, and are to some extent lost in it owing to
the subdivisions of the nerve-tubes.
On examination of longitudinal sections of preparations success-
fully stained by the chromo-silver method this is of course seen
much more distinctly. In such sections, I have seen longitudinal
nerve-tubes which were broken up by subdivisions into fine primitive
tubes and fibrillae (vide fig. 64, lt 3 , 11 ).
I have, however, also seen longitudinal nerve-tubes passing
undivided through the ventral ganglia and into the commissures
quitting them at the other side. Sometimes I have observed such
nerve-tubes to give off side-branchlets to the dotted substance of
the ganglia through which they pass (cf. fig. 64, 2 , e> s> 9' 10)-
I believe that some of the longitudinal nerve-tubes pass to ganglion
cells, and are connected witht their nervous processes, or, in other
words, that they are direct continuations of the nervous processes.
I have certainly in no preparation succeeded in really observing such
a direct connection; I have, however, seen so many indications of
its probable existence that I do not think there can be much doubt
about it. These nerve-tubes do not, however, have any isolated
course, they give off side-branchlets to the dotted substance.
The nerve-tubes of the peripheral nerves originate in the
ganglia in two, or rather three, ways.
Some nerve-tubes spring directly from ganglion cells, being di-
rect continuations of nervous processes, as before mentioned. These
9*
132
nerve-tubes, or nervous, processes give off side-branchlets on their
way through the dotted substance, vide fig. 69, which represents,