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UC-NRLF 


B    3    135 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


The  Structure  and  Combination 


of  the 


Histolomcal  Elements 


of  the  Central  Nervous  System. 


By 


F  r  i  d  tj  o  f  ^Njyi  sen, 

Curator  of  Bergen's  Museum 


Reprinted  from:    Bergens  Museums  Aarsberetning  for   1886. 


BERGEN. 

Printed  by  John  Grieg. 
1887. 


.. 

M*n4 


MsLAW 


The  Structure  and  Combination 

of  the 

Histological   Elements 

of  the  Central  Nervous  System. 


By 

Fridtjof  Nansen, 

Curator   of  Bergen's ;   Museum. 





Introduction. 

I.     History. 

The  progressive  history  of  our  knowledge  of  the  histology  of 
the  nervous  system  is  treated  of  so  often,  and  so  well,  by  previous 
writers  that  it  certainly,  to  some  extent,  entails  a  repetition  of  their 
words  to  refer  to  it  again. 

Still,  it  is  a  tradition  to  look  back  upon  the  works  and 
merits  of  our  predecessors  before  passing  to  our  own  work,  and 
I  do  not  think  it  right,  to  break  with  the  custom,  but  will, 
however,  confine  myself  as  much  as  possible  to  mentioning  the  most 
important  writers  of  modern  times  on  this  subject,  and  for  earlier 
literature  on  the  subject  refer  my  readers  to  the  many  sketches 
given  by  previous  writers. l)  As  it  is  especially  the  nervous  system 
of  the  evertebrates  which  is  about  to  be  treated  of  here,  I  will  restrict 
myself,  principally,  to  the  literature  on  that  subject,  all  the  more, 
as  in  a  separate  memoir  on  the  nervous  system  of  M yxine  glutinosa 
I  hope  to  obtain  an  opportunity  of  referring  to  the  literature  in  re- 
spect of  the  histology  of  the  vertebrate  nervous  system  more  circum- 
stantially. 


*)  The  literature  on  the  nervous  system  of  the  evertebrates  is  very  circum- 
stantially treated  of  by  Vignal.  His  reports  are,  however,  not  in  every  point  quite 
correct.  Very  good  reviews  of  the  literature  are  given  1882  by  Freud,  1879  by 
Hans  Schultze,  1875  by  Hermann  and  1872  by  Solbrig.  Of  course,  a  great  many 
other  writers  have  also  mentioned  the  previous  literature  more  or  less  circum- 
stantially. The  previous  literature  on  the  histology  of  the  nervous  system  of  the 
vertebrates  is  referred  to  in  Prof.  Golgis  last  work  on  this  subject.  Hans  Schultze 
has  given  a  very  good  review  of  the  literature  so  far  as  it  concerns  the  fibrillous 
structure  of  the  nervous  elements.  Besides  this  there  is  in  Kuhnt's  paper  a  very 
complete  review  of  the  literature  up  to  his  time. 


M373000 


—  30  — 
&}  The  structure  of  the  nerve-tubes.1) 

The  structure  of  the  nerve-tubes:  whether  it  is  fibrillous  or 
non-fib rillous,  has  been  very  much  disputed,  and  to  this  day  jthe 
point  must  be  considered  as  an  open  question.  Since  the  valuable 
and  important  works  of  REMAK,  there  have,  certainly,  always  been 
plenty  of  writers  to  defend  the  fibrillous  structure.  Amongst  these 
may  be  named  HANNOVER,2)  WILL,  LEBERT  and  ROBIN,  WALTER, 
WALDEYER,  LEYDIG  (only  to  a  certain  extent),  BOLL,  FLEMMING, 
HERMANN,  DIETL,  HANS  SCHULTZE,  FREUD,  VIGNAL  etc.  Especially 
have  HERMANN,  HANS  SCHULTZE  and  FREUD  expressed  themselves 
very  emphatically  and  distinctly  in  favour  of  the  fibrillous  structure. 
According  to  their  view  the  contents  of  the  nerve-tubes  consist  in 
»Primitivfibrillen«  suspended  or  swimming  in  an  homogeneous  semi- 
fluid » Interfibrillarsubstanz  « . 

At  the  same  time,  however,  there  have  also  been  others  who 
described  and  asserted  a  semi-fluid  (fest-weiche)  contents,  and  a 
homogeneous  structure  of  the  nerve-tubes  in  the  fresh  live  state 
(or,  also,  a  granulous  structure).  Amongst  those  are  HELMHOLTZ,3) 
H/ECKEL,4)  FAIVRE,5)  OWSJANNIKOW,6)  BUCHHOLZ,  LEMOINE,  SOL- 

*)  I  prefer  the  designation  nerve-tube  to  that  of  nerve-fibre,  because  I  think 
it  more  characteristic. 

2)  Hannover  states,   that  the  nervous  tubes  of  the  Mollusca  are  longitudinally 
striated,    whilst  those  of  A.stacus   have    a    granular,  nebulous  substance  in  a  mem 
branous  sheath. 

3)  Helmholtz  described  the  nervous  tubes  as   »zarthantige  Cylinder  mit  fliissi- 
gen  Inhalt«. 

4)  According   to  Hasckel  the  nervous  fibres  (»Primitivrohre)  have  the  form  of 
tubes.     »Die   Wand    der    Primitivrohre    oder    die    Nervenprimitivscheide    ist   an    den 
feinern  Cylindern  einfach,  an  den  starkeren  doppelt,  immer  aber  sharf  und  dunkel 
contourirt,    so    dass    sie  sehr    deuthlich    aus    dem   umhullenden  matten  Bindegewebe 
hervorschimmert.«      »Die    Inhalt   der   Nervenprimitivrohre    ist   wie    schon   Helmholtz 
erkannte  eine  dicke  Flussigkeit,  welche  ....  frish  ....  vollkommen  homogen,  wasser- 
klar,   und  leicht    glanzend    erscheint.*      Haeckel    has,    however,    also  found  Remak's 
»centrale  Faserbiindel*   and  agrees  with  him,  that  it  might  be  possible  that  such  a 
one  occurs  in  all  nervous  tubes. 

5)  According  to  Faivre  the  contents  of  the  nervous  tubes  are  granulous.     »Une 
tube  de  Sangsue  se  compose  de  deux  parties:    1'enveloppe  et  le  contenu.     L'enve- 
loppe    est  anhiste,    sans    structure    appreciable,    sans    noyaux,   —  le  contenu  des  tu- 
bes  est   forme    par   une    substance  finement   granuleuse  et  d'une  consistance  molle, 
meme  k  1'etat  frais.«     Under  high  powers  of  magnification  this  substance  is  seen  to 
consist  of  very  minute  granules   »agglutines  par  une  sorte  de  substance  intermediaire 
amorphe*. 

6)  Owsjannikow    supposes    the    fibrillous    appearance    of   the   tubes    to    be    a 
postmortem  product,  and  he  does  not  believe,  that  »les  tuyaux«  described  by  Stilling 
(in  the  nervous  fibres  of  vertebrates)  really  exist  in  living  nervous  fibres. 


BRIG,1)  YUNG,  KRIEGER,  and  lately  such  an  eminent  authority  as 
LEYDIG.  In  his  work  »Zelle  und  Gewebe«  (Bonn  1885)  this  veteran 
histologist  appears  to  have  changed  his  view  of  the  structure  of  the 
nervous  elements,  at  all  events  to  some  extent.2)  HANS  SCHULTZE, 
HERMANN  and  those  other  defenders  of  the  fibrillous  structure  are, 
he  says,  altogether  wrong.  »Bei  Aulocostomum  gewahren  unter 
Anwendung  der  gewohnlichen  Linsen  die  Nervenfasern  den  Ein- 
druck  einer  kornig  streifigen  Materie.  Die  jetzt  moglichen  Ver- 
grosserungen  lassen  aber  finden,  dass  das  »Streifige«  von  Langs- 
ziigen  eines  schwammigen  Geriistes  herriihrt  und  das  »K6rnige«  auf 
die  Knotenpunkte  eines  feineren  Zwischennetzes  zu  deuten  ist.  Die 
Haupt-  und  Langsziige  des  Maschenwerkesrufen  die  Abgrenzung  in 
»Fibrillen«3)  hervor,  aber  zwischendurch  zieht  ein  zartes  Schwam- 
gefiige,  in  dessen  Raumen  die  homogene,  eigentliche  Nervensubstanz 
enthalten  ist.« 

HANS  SCHULTZE'S  »Primitivfibrillen«  are,  consequently,  according 
to  LEYDIG,  only  parts  of,  or  longitudinal  fibres  in,  a,  usually,  rather 
spongy  supporting  substance  which  he  calls  ,,spongioplasm" ,  whilst 
SCHULTZE's  »Interfibrillarsubstanz«,  according  to  LEYDIG,  is  the  real 
nervous  substance,  diffused  in  the  cavities  of  the  spongioplasmatic 
reticulation;  he  calls  it  Jiyaloplasm" . 

I  think  this  is  enough  to  show  that  the  discussion  which  has, 
now,  for  40 — 50  years  been  going  on,  regarding  the  fibrillous  or  non- 
fibrillous  structure  of  the  nerve-tubes  is  not  yet  finished. 


J)  Buchholz  describes  the  cellprocesses  and  nervous  fibres  as  ribands  of  a 
homogeneous  substance  without  any  sheath;  they  are  to  be  considered  as  »nackte 
Axencylinder<r.  —  Solbrig's  description  is  very  like  that  ot  Buchholz:  »  Allen  Ner- 
venfasern der  von  mir  untersuchten  Gasteropoden  fehlt  eine  »Schwann'sche  Scheide*, 
und  sie  ercheinen  als  hiillenlose  Axenfasern  mit  scharf  begrenztem  Rande.*  .  .  . 
»Die  Nervenfasern  der  Mollusken  bestehen  aus  einer  festweichen,  elastischen,  ho- 
mogenen  Masse  von  schwach  glanzendem  Aussehen,  die  in  all  ihren  Eigenschaften 
mit  jener  eiweisartigen  grundsubstanz,  aus  der  sich  die  Ganglienzellen  aufbauen, 
iibereinstimmt.«  ....  »Durch  die  Annahme  der  Nichtexistenz  einer  Schwann'schen 
Scheide  muss  natiirlich  auch  die  altere  Ansicht,  dass  der  Inhalt  der  Nevenfasern 
aus  einer  fliissigen  Masse  bestehe,  fallen.  Denn  eine  fliissige  Substanz  ohne  um- 
hiillende  Membran  ist  geradezu  undenkbar.«  The  nerve-fibres  have  also  according 
to  Solbrig  a  flat  form  (»die  Form  von  Bandern  oder  wenigtens  von  plattgedriickten 
Cylinderna.) 

2)  This  work  I  have  already  mentioned  on  an  earlier  occasions,  vide:  Bidrag 
til  Myzostomernes  Anat.  og  Hist.  p.  32. 

3)  Hermann's  and  H.  Schultze's   »Fibrillen«f. 


—  32  — 

b)   The  structure  of  the  ganglion  ceils. 

Regarding  the  structure  of  the  ganglion  cells  there  has  been 
the  same  disagreement. 

A  great  many  writers  describe  a  fibrillous  structure,  whilst  othei 
stick  to  a  homogeneous  protoplasm. 

Amongst  the  adherents  of  a.  fibrillous  structure  REMAK  comes, 
also  here,  first.  He  describes  a  concentric  striation  in  the  proto- 
plasm occasioned  by  granular  fibres  circulating  round  the  nucleus. 
These  fibres  do  not,  however,  enter  into  the  processes. 

WILL  and  especially  WALTER  have  also  described  a  fibrillous 
structure.  LEYDIG  has  in  Gasteropodes  described  a  concentric  fibril- 
lous structure  of  the  protoplasm  of  the  ganglion  cells  and  a  stria- 
tion of  the  processes  (1865,  vide:  list  of  literature.  Taf.  XIX  fig.  3, 
Ganglienkugeln  des  Unterhirns  von  Helix  hortensis). 

Further,  SCHWALBE  can  also  be  named  as  an  adherent  of  the 
fibrillous  structure. 

BuCHHOLZ  supposes  the  protoplasm  of  the  ganglion  cells  to 
consist  of  two  substances,  of  which  the  one  can,  by  squeezing, 
easily  be  exuded  in  form  of  hyaline  pearls. 

This  hyaline  »Grundsubstanz«,  »in  welcher  gleichmassig  suspen- 
dirt  ein  anderer,  in  Form  feiner  Piinktchen  erscheinender  Korper  er- 
scheint«,  is  »in  alien  ihren  physikalischen  und  chemischen  Eigen- 
schaften  auf  das  Vollkommenste  iibereinstimmend  mit  derjenigen, 
welche  die  Zellenfortsatze  bildet,  sowie  auch  .  .  .  mit  derjenigen, 
welche  fibrillar  angeordnet  den  Inhalt  der  peripherischen  Nerven- 
stamme  bildet. « *) 


J)  It  is  really  astonishing  that  so  conscientious  a  writer,  as  Hans  Schultze 
seems  to  be,  can  so  seriously  misunderstand  another  author,  as  he  has  done,  when 
he  says  that  Buchholz  describes  »an  der  Ganglienzellen  zwei  Substanzen,  von  denen 
die  eine  leicht  durch  Druck  in  Form  hyaline  Tropfen  auspresbar,  die  zuruck- 
bleibende,  kornige  Masse  aber  durchaus  gleichwerthig  der  fibrillar  geordneten  In- 
haltsmasse  der  Nervenstamme  erschien.*"  As  will  be  seen,  that  is  quite  the  con- 
trary of  what  Buchholz,  has  really,  said.  That  and  similar  misunderstandings 
regarding  Buchholz  seem,  also,  to  have  descended  to  other  writers.  In  the  quite 
recently  published  paper  by  Rawitz  we  find  a  similar  confusion.  This  writer  com- 
pares »Buchholz's  hyaline  Grundsubstanze«  with  the  reticular  substance  described 
by  himself;  a  mistake  which  certainly  ought  to  have  been  very  difficult  if  Rawitz  had 
looked  a  little  more  carefully  at  the  description  of  *der  in  feinen  Piinktchen  er- 
scheinenden  Substanz  ...  in  der  hyalinen  Grundmasse  gleichmassig  vertheilt*  given 
by  Buchholz  in  his  excellent  paper  (p.  252).  In  reference  to  the  report  of  Buchholz's 
paper  given  by  Vignal,  there  is,  indeed,  little  else  to  say,  than  that  it  is  thoroughly 
misleading. 


-    33  — 

BOLL  (1869)  says:  »Die  Ganglienzellen  der  Mollusken  bestehen 
ebenso  wie  bei  den  Wirbelthieren  aus  zahlreichen  in  den  verschie- 
densten  Richtungen  verlaufenden  ausserst  feinen  Fibrillen  und  aus 
korniger  intern"  brillaerer  Substanz.  Eine  besondere  Membran  fehlt« 
(1.  c.  1869  p.  19).  »Die  Nervenfasern,  die  Fortsatze  der  Ganglien- 
zelle  gehen  stets  aus  der  Substanz  derselben  hervor  in  der  Art,  dass 
die  Fibrillen  an  den  Abgangsstellen  der  Fortsatze  eine  bestimmte 
parallele  Richtung  annehmen  und  sich  zu  mehr  oder  minder  feinen 
Strangen  zusammenlegend  von  dem  Zellenkorper  abtreten.« 

DiETL  (1877)  describes  a  concentric  striation  of  the  cell-proto- 
plasm, in  preparations  treated  with  osmic  acid.  This  striation  he  sup- 
poses, however,  also  to  exist  in  the  live-state.  The  striation  circulates 
round  the  nucleus  and  can  always  be  traced  directly  into  the  pro- 
cesses of  the  ganglion  cells.  In  the  brain  of  Tefhys  fimbria  he  des- 
cribes ganglion  cells  containing  a  peculiar  »protoplasmatisches  Balken- 
netz,  das  die  Verbindung  des  Zellkorpers  und  des  Fortsatzes  ver- 
mittelt*  (1.  c.  1878  p.  524). 

CADIAT  (1878)  does  not,  exactly,  tell  whether  he  supposes  the 
ganglion  cells  of  the  Crustaceans  to  have  a  fibrillar  structure  in  the 
live-state ;  their  protoplasm  is,  however,  in  his  opinion,  quite  identical 
with  the  contents  of  the  nerve-tubes,  and  in  the  latter  he  has 
occasionally  observed  fibrillae.  He  further  states  that,  on  application 
of  nitric  acid  he  has  seen  a  striation  in  the  nerve-tubes  and  »la  meme 
striation  se  voit  sur  les  cellules  et  leurs  prolongements  immediats.« 

The  author  who  has  most  distinctly  declared  himself  for  a 
fibrillar  structure,  and  who,  in  my  opinion,  has  made  the  closest  and 
most  convincing  investigations  on  this  subject  is  HANS  SCHULTZE 
(1879).  He  has  defined  the  point  in  debate,  and  has  concentrated 
his  investigations  upon  it,  but  neither  has  he  been  quite  successful. 

According  to  the  result  of  his  investigations,  the  protoplasm 
in  the  ganglion  cells,  as  well  as  in  their  processes  and  the  nerve- 
tubes,  consists  of  »Primitivfibrillen«  and  »Interfibrillar-Substanz«; 
everyone  of  the  fibrillae  is  surrounded  by  interfibrillar  substance, 
they  must,  consequently,  in  a  manner,  swim  in  it.  If  that, 
however,  is  correct,  why  then  has  Schultze,  as  well  as  everyone 
else,  succeeded  so  badly  in  isolating  these  freely  swimming  fibrillae? 
why  can  we  only  obtain  a  sort  of  isolation  of  them  in  the  ex- 
tremities of  teased  processes  or  tubes,  and  not  in  the  cell-protoplasm 
itself? 

To  this  question  Schultze  has  given  no  reply,  nor  has  any- 
body else,  so  far  as  I  know. 

3 


—  34  — 

FREUD'S  description  (1881)  of  the  structure  of  the  cell-processes 
is  very  similar  to  that  of  H.  SCHULTZE.  The  cell-protoplasm  has 
however,  according  to  his  opinion,  another  structure,  it  consists  of  a 
reticular  substance  and  a  homogeneous  one.  He  says  1.  c.  1881  p.  31 : 
»Die  Nervenzellen  im  Gehirn  und  in  der  Bauchganglienkette  bestehen 
aus  zwei  Substanzen  von  denen  die  eine,  netzformig  angeordnete, 
sich  in  die  Fibrillen  der  Nervenfasern,  die  andere,  homogene  in  die 
Zwischensubstanz  derselben  fortsetzt.« 

KoESTLER  (1883)  describes  the  ganglion  cells  of  the  frontal 
ganglion  etc.  of  Periplaneta  orientalis,  as  having  no  membranes:  »sie 
sind  nie  mit  einer  Hiille  versehen  und  erscheinen  als  membranlose, 
weiche  Ballen.«  Upon  treating  the  ganglion  cells  with  vapour  of 
osmic  acid,  and  examining  them  under  high  powers  of  the  microscope, 
he  has  been  able  to  observe  »eine  koncentrische  Lagerung  des  kor- 
nigen  Protoplasmas«,  »und  zwar  so,  dass  das  Protoplasma  in  Schich- 
ten  geordnet  erschien,  die  rosettenformig  den  Kern  umgeben«  (1.  c. 
p.  585).  Of  the  origin  and  structure  of  the  processes  he  says  1.  c. 
p.  586:  »Eigenthiimlich  erscheint  das  Verhalten  des  kornigen  Proto- 
plasmas  an  der  Ursprungsstelle  der  Nervenfasern,  Wahrend  sich 
diese  granulare  Zellsubstanz  sonst  in  Schichten  koncentrisch  um  den 
Kern  lagert  und  der  Zelle  ein  rosettenformiges  Aussehen  verleiht, 
gehen  die  aussersten  Ringe  am  Ursprunge  der  Nervenfasern,  ihre 
koncentrische  Schichtung  verlassend,  in  diese  iiber.  Es  ist  also 
dieser  Fortsatz  nur  als  eine  Fortsetzung  des  Zellinhaltes  aufzufassen, 
der  sogar  Anfangs  noch  etwas  kornig,  spater  erst  in  die  feinsten 
Fibrillen  zerlegbar  erscheint. « 

VEJDOVSKY  (1884)  has  not  succeeded  in  observing  a  fibrillar 
structure  in  the  protoplasm  of  the  ganglion  cells  of  the  Oligochcetes; 
»nur  die  aus  den  Zellen  austretenden  Stiele  zeigen  eine  deutliche 
Zusammensetzung  aus  den  feinsten  Nervenfibrillen«  (1.  c.  p.  90).  On 
another  occasion  he  says,  however,  of  the  ganglion  cells  that  »bereits 
altere  Forscher  eine  fibrillare  Anordnung  der  Plasmaelemente  sicher- 
gestellt  haben«  (1.  c.  p.  91.) 

Amongst  those  who  do  not  believe  in  a  fibrillar  structure  the 
following  authors  may,  here,  be  named1): 

*)  When  speaking  of  the  ganglion  cells  Faivre  says  »l'enveloppe  est  solide 
et  consistante ;  le  contenu  granuleux,  semi-fluide.«  Hceckel  says  of  the  ganglion 
cells  of  Astacus:  »Jede  von  ihnen  stellt  eine  mehr  oder  weniger  rundliche,  an- 
sehnliche  Blase  dar,  deren  zarte  Zellmembran,  oft  von  einer  dichten  Bindegewebs- 
kapsel  eingeschlossen  eine  triibe  kornige  Fliissigkeit  enthalt  in  der  ein  sehr  grosser 
mit  einem  Kernkorperchen  versehener  Kern  schwimmt.«  Waldeyer  denies  the 
existence  of  the  striation  of  the  cell-protoplasm  described  by  Walter.  Buchholz 
is  already  mentioned  above. 


—  35  — 

OWSJAXNIKOW  describes  the  ganglion  cells  of  the  lobster  (1.  c. 
1 86 1  p.  139)  as  having  »un  contenu  assez  liquide«  in  which  he  has 
observed  fibrillae,  »qui  semblent  penetrer  dans  le  milieu  de  la  cellule. « 
The  ganglion  cells  of  the  Mollusca  he  describes  as  having  a  semi- 
fluid protoplasm  which  »erst  nach  dem  Tode  fest  wird«  (1.  c.  1870 
p.  681).  Here,  he  mentions  no  fibrillae. 

CHERON  (1866)  describes  (in  Cephalopoda)  apolar,  uni-,  bi-  and 
multipolar  ganglion  cells  having  granular  or  homogeneous  contents. 
In  the  »ganglions  de  bras«  he  describes,  for  instance:  »des  cellules 
unipolaires  a  contenu  granuleux,  et  des  cellules  bipolaires  ou  tri- 
polaires  a  contenu  liquide  sans  granules. « 

CLAPAREDE  says  (I.e.  1869  p.  593):  »Die  Zellenkorper  bestehen 
aus  einem  kornigen  Protoplasma  ohne  erkennbare  Membran.« 

SOLBRIG'S  opinion  (1872)  was  that,  the  concentric  fibrillar  appear- 
ance was  a  postmortem  one  and  was,  partly,  artificially  produced 
by  folding  of  the  cell-surface  etc.  According  to  his  view,  the  proto- 
plasm of  the  cells,  as  well  as  of  the  processes,  is  a  homogeneous 
or  granular  »fest-weiche«  substance.  A  great  many  other  writers 
are,  also,  of  the  same  opinion. 

STIEDA  (1874)  says  in  his  description  of  the  Cephalopoda,  that 
the  protoplasm  of  the  ganglion  cells  have,  in  fresh  state,  an  extremely 
minute  granular  appearance ;  »an  den  Zellen  der  Schnittpraparate  lasst 
sich  eine  homogene  Grundsubstanz  erkennen,  in  welcher  ausserst 
feine  Kornchen  eingestreut  sind.«  The  processes  have  the  same 
appearance  (1.  c.  1874  p.  92). 

Even  HERMANN  (1875)  is  no  adherent  of  a  fibrillar  structure  of 
the  cell-protoplasm;  in  his  opinion  it  is  rather  granulous  or  homo- 
geneous.1) 

YUNG  (1878)  describes  the  protoplasm  of  the  ganglion  cells  as 
being  fluid,  and  homogeneous  or  granular. 

BELLONCI  (1878)  describes  the  protoplasm  of  the  large 
ganglion  cells  of  Sqiiilla,  as  having  »un  aspetto  finamente 


x)  According  to  Hermann  the  protoplasm  of  the  cells  consists  of  two  sub- 
stances: »Die  eine  umfasst  weitaus  seinen  grossten  Theil,  erscheint  gleichmassig 
homogen,  oder  in  einigen  Fallen  feingekornt,  nimmt  iiberall  die  ausseren  Schichten 
des  Zellkorpers  ein,  gibt  ihm  seine  Gestalt,  und  bildet  allein  den  Fortsatz.*  .... 
»Die  andere  Substanz  erscheint  als  aus  groberen  Kornern  bestehend  und  1st 
in  ungleich  grossen  Massen  um  den  Kern  herum  gelagert*  (1.  c.  1875  p.  30). 
The  processes  of  the  cells  have,  consequently,  in  Hermanns  opinion  a  homogeneous 
structure. 

3* 


-  36- 

granoso«.1)  Of  the  peripheral  cell-process  he  says:  that  it  >non 
presenta  alcuna  particolarita  strutturale« ;  in  Tav.  IX,  fig.  3  (1.  c. 
1878)  he  illustrates  a  ganglion  cell  with  a  peripheral  process  (»pro- 
lungamento  periferico«)  exhibiting  a  distinct  longitudinal  striation 
which  he  does  not,  however,  mention  in  the  text  so  far  as  I  have 
seen.  Some  large  fibres,  he  says,  have  a  fibrillar  appearance. 

NEWTON  (1879)  designates  the  cell-protoplasm  as  being  granular; 
he  says  that  »the  granular  cell  contents  may  be  seen  in  some  in- 
stance, extending  into  the  fibres «  (i.  e.  the  cell-processes). 

KRIEGER  (1880)  describes  a  granular  cell-protoplasm  and  a 
homogeneous  process. 

VlGNAL  (1883)  seems  to  have  taken  up  no  distinct  position  regard- 
ing the  fibrillar  or  non-fibrillar  structure  of  the  ganglion  cells.  About 
that  of  the  Mollusca  he  says:  »Elles  sont  formees  d'un  globe 
ganglionnaire  a  la  surface  et  dans  1'interieur  duquel  se  trouvent  de 
fines  fibrilles  qui  forment  le  ou  les  prolongements  de  la  cellule;  entre 
les  fibrilles  se  trouvent  de  fines  granulations  graisseuses,  quelque- 
fois  diversement  colorees  (1.  c.  p.  342).  Regarding  the  ganglion 
cells  of  the  Hirudinea  he  reports  in  somewhat  similar  terms.  »Elles 
sont  formees  d'un  globe  ganglionaire  a  la  surface  duquel  se  trouve 
un  noyau;  il  est  recouvert  par  de  fines  fibrilles  qui  en  constituent  le 
prolongement«  (1.  c.  p.  372). 

Regarding  the  ganglion  cells  ef  the  Crustaceans  and  Oligochcetes 
he  seems,  however,  to  be  of  quite  another  opinion.  About  those  of 
the  Crustaceans  he  says  e.g.:  »elles  sont  formees  presque  toutes  par 


J)  Of  the  large  ganglion  cells  he  says  (1.  c.  1878  p.  523):  »Esse  posseggono 
una  sottile  parete  e  sono  circondate  da  un  invoglio  di  tessuto  connettivo  nucleate. 
II  contenuto  ha  un  aspetto  finamente  granoso,  ma  al  polo  del  prolungamento  peri- 
ferico  i  granuli  sono  piu  fitti  e  formano  un  cono  distinto,  la  cui  base  e  la  corri- 
spondente  parete  del  nucleo  e  il  cui  vertice  fc  1'origine  del  cilindro  assile.*  In  the 
small  ganglion  cells  he  even  believes  to  have  seen  »il  cilindro  assile*  penetrate  into 
the  nucleus  and  terminate  »in  uno  spazio  chiaro  e  rotondo  che  si  trova  nel  centro 
di  questo.«  To  this  apparent  connection  of  the  peripheral  process  or,  as  I  call  it, 
nervous  process,  with  the  nucleus,  Bellonci  ascribes  great  importance,  it  shows,  in 
his  opinion,  that  the  nervous  impression  »si  propaga  al  centro  della  cellula  e  pro- 
priamente  al  nucleo,  il  quale  nella  cellula  nervosa,  come  in  tutte  le  altre,  e  il  vero 
centro  dell'allivita  vitale.*  We  will  return  to  this  subject,  and  to  my  view  of  it, 
at  the  conclusion  of  the  present  paper.  Of  great  interest  is,  that  Bellonci  expressly 
accentuates  that  each  ganglion  cell  has  only  one  real  nervous  process  (»cilindro 
assile*)  »destinato  a  formare  un  elemento  del  nervo,  tutti  gli  altri  non  sono  che 
prolungamenti  destinati  ad  unire  fra  di  loro  le  cellule  di  una  stessa  massa  cellulare.* 
In  the  latter  statement  I  do  not,  however,  agree  with  him  (vide  sequel). 


—  37  — 

une  substance  visqueuse,  epaisse,  granuleuse  et  tres  malleable. « 
About  the  Oligochastes  he  says:  »Les  cellules  nerveuses  ....  sont 
formees  par  une  substance  demi-liquide  visqueuse,  excessivement  mal- 
leable, peu  granuleuse.  Elles  contiennent  un  noyau  refringent  ho- 
mogene  et  granulations  graisseuses  situees  a  son  voisinage.« 

If  we  look  through  the  modern  literature  having  reference  to 
the  invertebrate  nervous  system,  and  compare  the  many  different 
views  of  the  structure  of  the  ganglion  cells,  we  meet  with  a  con- 
fusion on  the  subject  which  is  far  from  encouraging.  Some  writers 
distinguish  between  granulous  cells  and  homogeneous  ones,  other 
writers  believe  in  a  concentric  striation,  or  even  a  longitudinal 
striation  (ROHDE). l) 

Some  writers  distinguish  between  ganglion  cells  with  a  process 
originating  in  the  nucleolus  (^Kernkorperfortsatze«),  or  nucleus  and 
cells  with  a  process  originating  in  the  protoplasm  (»Protoplasmafort- 
satze«).  Others,  e.  g.  HALLER,  describe  cells  having  both  kinds 
of  processes.  A  great  many  writers  however  deny,  or  doubt,  any  exis- 
tence of  processes  originating  in  nucleoli  or  nuclei,  etc.  etc.  All  these 
distinctions  and  differences  of  opinion  exist,  although  we  certainly 
must  feel  inclined,  a  priori,  to  suppose  that  there  must  be  uniformity, 
to  some  extent,  through  the  whole  animal  kingdom  in  this  respect, 
and  that  the  differences  must  have  arisen  in  the  development  of  less 
complicated  structures  to  more  complicated  ones. 


*)  In  E.  Eohde's  paper  on  the  Nematodes  (1885)  we  meet  with  a  descrip- 
tion of  the  structure  of  the  ganglion  cells  which  is  of  a  somewhat  peculiar  kind. 
The  writer  describes  ganglion  cells  having  different  modes  of  striation,  a  radiate 
striation,  a  concentric  one,  and  a  longitudinal  one  (1.  c.  p.  16 — 17;  fig.  14 — 34.) 
As  I  have  not  examined  the  nervous  system  of  the  Nematodes  I  can  not,  of 
course,  deny  the  correctness  of  this  statement;  if  I  may  judge,  however,  from  the 
results  of  my  investigations  on  other  animals,  I  feel  inclined  to  believe  that  these 
descriptions  are  caused,  at  all  events  partly,  by  optical  illusion. 

It  may  here,  also,  be  mentioned  that  Tung  (1878)  describes  a  longitudinal 
striation  of  the  protoplasm  of  the  ganglion  cells  of  Astacus  as  being  a  post- 
mortem appearance  produced  by  the  influence  of  acids  (picric  or  nitric  acid  — 
1.  c.  1878,  p.  424 — 425).  In  the  fresh  state  he  describes  the  cells  as  having  »un 
contenu  liqttide  absolument  identiques  a  celui  des  tubes  nerveux  a  1'etat  frais.« 

The  American  scientist  Packard  gives  a  very  strange  description  of  the 
ganglion  cells  of  Asellus  (1884),  he  says  that  they  »have  not,  as  in  the  brain  of 
the  lobster,  a  simple  nucleus  and  nucleolus,  but  they  usually  have  numerous,  from 
10  to  20,  nuclei,  the  nucleolus  of  each  nucleus  readily  receiving  a  stain  and  forming 
a  distinct  dark  mass.*  How  this  description  is  to  be  explained  I  certainly  can  not 
tell;  he  does  not  mention  the  structure  of  the  cell-protoplasm. 


-  38  - 

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  Fibrillen1)  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«. 

STIEDA2)  (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, 
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  nanderen  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.  KENNEL2)  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.« 


_  56- 

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. 
1884  p.  14):  »C'est  d'elle  que  tous  les  nerfs  tirent  leur  origine, 
c'est  dans  elles  que  les  prolongements  des  cellules  ganglionnaires 
viennent  tous  se  jeter.  Ainsi  les  cellules  ne  peuvent  communiquez 
entre  elles,  les  nerfs  ne  peuvent  communiquez  avec  ces  memes 
cellules  que  par  1'intermediaire  de  la  substance  ponctuee. « 

BOHMIG  (1884)  has  himself  given  the  following  summary  of  the 
results  of  his  investigation  of  the  dotted  substance  etc.  of  the  G-astero- 
pods.  »Die  Markmasse  wird  von  einem  Punktsubstanzballen  gebildet. 
Unter  Punktsubstanz  hat  man  ein  inniges,  filzahnliches  Gewirr  von 
Primitivfibrillen,  aus  welchem  die  Zellfortsatze  gebildet  werden,  zu 
verstehen.  Aus  der  Punktsubstanz  gehen  die  Nerven  durch  eine 
parallele  Anordnung  der  erst  wirren  Primitivfibrillen  hervor.  Durch 
eindringende  Bindegewebssepten  werden  die  Fibrillen  zu  secundaren 
Biindeln  vereinigt.  Eine  directe  Uebergang  von  Zellfortsatzen  in  die 
Nerven,  also  ohne  vorherige  Auflosung  in  der  Punktsubstanz,  kommt 
vor;  und  zwar  fast  bei  alien  Nerven.  Jedoch  ist  diese  Erscheinung 
selten«  (1.  c.  p.  45).  As  will  be  seen,  this  view  is  somewhat  similar 
to  that  of  SOLBRIG;  the  nerve- fibres  may  have  a  direct  origin  as 
well  as  an  indirect  one. 

PACKARD  (1884)  makes,  in  my  opinion,  some  very  interesting 
statements  regarding  the  structure  of  the  brain  af  Asellns  communis. 
As  to  the  structure  and  importance  of  the  dotted  substance,  or 
»myeloid  substance«  as  he  calls  it,  he  does  not  think  himself  in 
a  position  to  say  anything  with  certainty.  He  says  of  it  (1.  c. 
1884  p.  6):  »This  latter  substance  does  not  exist  in  the  nervous 
system  of  the  vertebrates,  and  just  what  its  nature  and  function 
clearly  are  in  the  invertebrates  has  yet  to  be  worked  out.«  »His 
own  opinion  from  what  little  he  has  seen  is,  that  the  myeloid  sub- 
stance is  the  result  of  the  splitting  up  into  a  tangled  mass  of  very 
fine  fibrillae  of  certain  of  the  fibres  thrown  off  from  the  mono-polar 


—  57  — 

ganglion  cells,  i.  e.,  such  fibres  as  do  not  go  to  form  the  main 
longitudinal  commissures. «  As  to  the  origin  of  the  nerve-fibres,  and 
their  relation  to  the  dotted  substance  and  the  ganglion  cells,  it  will, 
already,  from  what  is  just  quoted,  be  seen  that  Packard  does  not 
quite  agree  with  Leydig;  1.  c.  p.  5  he  says  for  instance:  » there 
is  no  doubt  but  that  all  the  ganglion  cells  give  rise  to  fibres,  some 
of  which  at  least  pass  directly  through  or  above  or  around  the 
myeloid  substance  of  the  cerebral  lobes  and  form  the  commissures 
{i.  e.,  the  transverse  as  well  as  the  longitudinal  ones).  This  indepen- 
dence of  the  myeloid  substance  appears  to  be  more  general  in  the 
Assellidas,  at  least  this  we  would  infer  from  Leydig's  statements  previ- 
ously quoted. «  Packard  even  thinks  it  to  be  » little  doubt  but  that  in 
all  Arthropoda  certain  nerve-fibres  arising  in  the  pro  cerebral  lobes 
(from  ganglion  cells)  pass  uninterruptedly  to  the  last  ventral  ganglion* 
(i.  e.,  through  the  whole  central  nervous  system).1)  A  great  many 
peripheric  nerve-fibres,  he  supposes,  however,  to  originate  in  the  way 
which  Leydig  has  indicated;  he  says  that  in  the  » myeloid  substance « 
a  great  many  processes  from  ganglion  cells  become  » broken  up 
into  a  tangled  mass  of  fibrillae,  which  unite  finally  to  form  the  fibres 
constituting  the  nerves  of  the  appendages. «  Whether  he  supposes 
all  peripheric  nerve-fibres  to  originate  in  this  way,  or  not,  I  have  not 
understood  from  his  description. 

pRAIPONT  (1884)  affords  some  interesting  informations  regard- 
ing the  histology  of  the  nervous  system  of  the  Archeannelids. 
Judging  from  his  description,  I  think  there  is  no  doubt,  but  that 
the  central  nervous  system  of  these  primary  Annulates  has  a 
histological  structure  which  is,  principally,  of  quite  the  same  type 
as  that  of  the  central  nervous  system  of  higher  Annulates, 
Arthropods  and  other  invertebrates,  to  be  treated  of  in  this 
paper.  He  distinguishes  between  two  constituents,  an  external 
layer  of  ganglion  cells  and  a  central  fibrillar  mass;  for  the 
latter  he  uses  various  designations:  ^substance  fibro-nerveuses«, 
» substance  ponctuee«,  » substance  nerveuse  fibro-ponctuee«,  »mass 
finement  ponctuee  et  fibrillaire«  etc.  It  is  evident  that  he  sup- 
poses this  mass  to  consist  of  a  web  of  slender  fibrillae;  1.  c.  1884 
p.  267  he  says,  for  instance:  » Figure  5  (pi.  XI),  on  peut  voir  au 
milieu  des  cellules  ganglionnaires  les  sections  trausversales  ou  obliques 


')  As  will  be  seen  in  my  memoir  on  Myzostoma  (1885),  p.  35  &  75'  I 
have  expressed  myself  in  very  similar  terms  upon  this  subject,  and  have  said  that 
I  believed  similar  longitudinal  nerve-fibres  etc.  to  be  generally  present  in  Annelids 
and  Arthropods. 


-  58  — 

de  fibrilles  tres  minces  melees  a  une  substanse  fmement  ponctuee.« 
Whether  he  considers  these  fibrillae  to  spring  from  the  processes  of 
the  ganglion  cells,  he  does  not  distinctly  say,  though  I  suppose  this 
is  his  opinion.  The  ganglion  cells,  he  says,  generally  send  their 
processes  into  the  fibrillar  mass,  and  here  they  can  sometimes  be 
traced  only  for  a  short  distance,  sometimes  he  has  seen  them, 
even,  penetrate  the  whole  fibrillar  mass  of  the  ventral  nerve- 
cord  (»dans  toute  son  epaisseur«).  Whether  he  supposes  a  direct 
origin  of  the  nerve-tubes  in  ganglion  cells  or  an  indirect  one,  I  am 
not  quite  sure.  In  the  head  of  Polygordius  he  describes  two  masses 
of  ganglion  cells  in  which  Demerge  un  faisceau  de  fibrilles  nerveuses 
formant  un  gros  nerf  qui  constitue  1'axe  de  chaque  tentacule«  (1.  c. 
p.  263).  P.  270  he  says:  »Beaucoup  de  prolongements  de  ces 
cellules  penetrent  dans  la  masse  fibrillaire  et  contribuent  a  la  forma- 
tion du  faisceau  longitudinal;  d'autres  traversent  verticalement  la 
region  fibrillaire. «  Of  the  tentacular  nerves  ofProtodrilus  and  Sacco- 
cirrus  he  says,  however,  that  they  take  their  origin  »de  la  masse 
centrale  fibro-ponctuee  du  cerveau.«  The  same  he,  also,  says  of  the 
commissures. 

VEJDOVSKY,  in  his  Monograph  on  the  Oligochates  (1884),  gives 
us  no  distinct  description  of  our  subject  though  he  mentions  it  rather 
circumstantially.  The  fibrillar  »Punktsubstanz«  he  describes  as  con- 
sisting of  slender  nervous  fibrillae.  Of  the  fibrillar  mass  of  the  ventral 
nerve-cord  he  says,  for  instance,  that  it  »aus  feinen,  nur  in  derLangs- 
richtung  verlaufenden  und  dicht  neben  und  aneinander  liegenden 
Nervenfibrillen  besteht  die  bald  einen  gleichen  kaum  mehr  als  einen 
Bruchtheil  eines  Mikromillimeters  erreichenden  Durchmesser  haben, 
bald,  und  dies  in  der  grosseren  Anzahl  in  der  Mitte  mit  einer 
spindelformigen  Anhaufung  eines  feinkornigen  Plasmas  versehen  sind 
(Taf.  VIII,  fig.  2').  Weder  eine  besondere  Membrann,  noch  ein 
Kern  kommen  an  diesen,  wohl  den  letzten  nervosen  Formelementen 
zum  Vorschein;  indem  sie,  wie  wir  spater  unten  erkennen  .werden, 
dem  Zerfall  einiger  wenigen  urspriinglichen  Ganglienzellen  ihre  Ent- 
stehung  verdanken.«  *)  This  description  is  written  from  observations 
on  the  living  animal.  Vejdovsky  does  not  mention  any  interfibrillar 
substance  like  Hermann,  and  others,  it  is,  therefore,  very  difficult 
to  say  whether  he  has  seen  the  sheaths  of  the  nerve-tubes,  and 
described  them  as  fibrillae  like  most  writers,  or  if  he  has  really  seen 
the  nerve-tubes,  but  not  observed  their  sheaths.  I  feel  disposed  to 

])  l.  c   p.  91. 


—  59  — 

think  the  latter  supposition  to  be  the  right  one.  -  -  The  relation  of  this 
fibrillar  substance  to  the  ganglion  cells,  and  to  the  peripheric  nerves, 
as  also  the  origin  of  the  nerve-tubes,  Vejdovsky  defines  very 
indistinctly,  and  I  have  not,  indeed,  succeeded  in  getting  any  clear 
idea  of  his  real  opinion.  Once  he  says  that  in  Dendrobana  he  has 
observed  the  processes  of  the  ganglion  cells  penetrate  into  the 
fibrillar  substance  where  they  subdivide  »wiederholtenmalen  in  die 
feinsten  Fortsatze,  um  ein  merkwiirdiges  Fibrillennetz  zu  bewerk- 
stelligen«  (1.  c.  p.  90).  »Diese  Fibrillen  sind  jedoch  ganz  anderer 
Art  als  die  jenigen,  welche  in  der  Langsaxe  des  Bauchstranges  ver- 
laufen.  Sie  stellen  namlich  keine  selbstandigen  Elemente  vor,  sondern 
entspringen  aus  den  Ganglienzellen  in  denen  bereits  altere  Forscher 
eine  fibrillare  Anordnung  der  Plasmaelemente  sichergestellt  haben.« 

How  this  ought  to  be  understood,  and  what  the  importance  of 
»diese  Fibrillen «  is,  in  Vejdovsky's  opinion,  I  certainly  can  not  tell.1) 
Afterwards  he  tells  us,  that  in  other  species  of  Oligoclicetes  and 
especially  in  the  larger  ones,  he  has  observed  the  ganglion  cells 
send  their  processes  directly  into  the  fibrillar  substance  to  form 
»quer  und  schrag  verlaufende  Fibrillenbiindel«.  The  relation  of  these 
»Fibrillenbiindel«  to  the  nerves  he  does  not  mention,  neither  does  he 
say  anything  of  the  origin  of  the  nerves,  so  far  as  I  have  seen;  he 
only  tells  us  a  little  of  the  views  of  previous  writers,  especially  Will, 
Walter  and  Waldeyer,  and  it  really  looks  as  if  he  agrees  with  these 
old  authors. 

SCHIMKEWITSCH,  in  his  paper  on  »l'anatomie  de  l'epeire«  (1884), 
has  suplied  no  important  adition  to  the  knowledge  of  our  present 
subject.  Like  Viallanes,  he  refers  to  descriptions,  by  other  authors, 
of  the  structure  of  the  » substance  ponctuee«  the  significance  of 
which  he  states  to  be  very  difficult  to  understand.  He  supposes 
the  peripheric  nervefibres  to  originate  in  this  substance,  and,  thus, 
he  does  not  believe  in  a  direct  origin  of  the  fibres  in  ganglion  cells. 

REMY  SAINT-LOU?,  in  his  paper  on  »!' organisation  des  Hirudi- 
nees«  (1885),  agrees  with  Vignal  regarding  the  histology  of  the 
nervous  system  and  has  therefore  not  taken  up  this  subject  for  his 
own  investigations. 


7)  P.  92  he  says  that  of  these  fibrillre  »sich  offenbar  nur  ein  Theil  an  der 
Bildung  der  queren  und  schragen  Fibrillenbiindel  betheiligen.  Die  ubrigen  feinen 
Fibrillen  schlangeln  sich  zwischen  der  nbrilla'ren  Substanz  und  diirften  wohl  zur 
Entstehung  besonderer  Hohlraume  wesentlich  beitragen.*  These  »Hohlra'ume«  which 
he  describes  as  »meist  kreisformige,  farblose,  undeutlich  contourirte  Feldchen*  are 
evidently  nothing  but  transsected  nerve-tubes. 


—  6o  — 

Of  the  numerous  papers  on  the  invertebrate-nervous  system, 
which  have  appeared  in  recent  times,  we  will  only  refer  to  a  few. 
The  most  remarkable  work  in  the  latest  literature  on  this  subject  is 
LEYDIG'S  »Zelle  und  Gewebe«  (1885)  which  has  been  already  mentioned. 
There,  he  has  modified,  or  to  a  certain  extent  changed,  his  previous 
view  of  the  dotted  substance.  The  fibrillar  reticulation,  which  he  and 
others  have  described,  becomes  nothing  but  a  spongy  net-work  of 
supporting  substance,  spongioplasm,  in  the  cavities  of  which  the  homo- 
geneous, really  nervous  substance,  hyaloplasm,  is  diffused;  the  gang- 
lion cells  as  well  as  the  nerve-tubes  consist  of  the  same  substance. 
The  nerve-tubes  originate  in  this  way :  the  spongioplasm,  which  in  the 
central  mass  is  quite  diffusively  arranged,  unites  and  forms  longitudinal 
fibres  and  sheaths  which  envelope  the  hyaloplasm  like  tubes;  any 
isolation  of  nerve-tubes  or  fibrillae  in  the  central  dotted  substance 
can  thus,  as  a  rule,  not  arise.  It  will  be  seen  that  this  is  a  rather 
radical  revolution  in  the  views  of  most  histologists.  To  a  certain 
extent,  in  respect  of  the  supporting  substance  of  the  central  mass, 
it  certainly  reminds  somewhat  ofClaus;  in  all  other  respects,  however, 
Ley  dig  holds  a  view  quite  different  from  that  of  the  author  named. 

PRUVOT'S  view  (1885)  of  the  dotted  substance  or  »matiere 
ponctuee«  seems  to  be  of  a  somewhat  peculiar  kind;  he  has  not, 
indeed,  succeeded  in  finding  its  real  nature.  In  the  brain,  he  de- 
scribes it  in  the  following  way  (1.  c.  p.  232):  »C'est  une  matierc 
homogene,  refractaire  aux  colorations,  offrant  un  fin  pointille  qu'  un 
grossissement  suffisant  permet  de  resoudre  en  petites  granulations 
regulierement  espacees  et  traversee  seulement  par  quelques  rares 
fibres  anastomosees  qui  proviennent  de  la  substance  corticale.« 
What  these  » granulations «  and  » rares  fibres  anastomosees «  really 
are  in  Pruvot's  opinion,  I  dare  not  say,  I  think  it  is  evident  that  his 
powers  of  magnification  have  not  been  sufficiently  high. 

In  his  » conclusions  generale «  (1.  c.  p.  323)  he  gives  the  follow- 
ing summary  of  his  researches  on  this  subject:  »En  effet  tous  les 
elements  fibrillaires  nerveux  (prolongements  des  cellules,  fibres  des 
nerfs  et  des  connectifs)  traversent  sans  modifications  la  substance 
corticale,  mais  au  niveau  de  la  substanee  medullaire  se  fragmentent, 
se  resolvent  en  petites  granulations  d'abord  tres  rapprochees  et  dis- 
posees  en  series  lineaires,  qui  s'espacent  peu  a  peu  et  se  perdent 
au  milieu  des  granulations  voisines  pour  constituer  la  matiere  ponctuee. 
Cellesi  est  done  un  intermediaire  entre  la  cellule  et  la  fibre,  entre 
1'element  central  et  1'element  conducteur  .  .  .  .«  As  will  be  seen, 
this  is  no  very  distinct  description;  his  idea  of  the  dotted  substance 


-  61  - 

seems  to  be  somewhat  similar  to  that  of  Vignal,  and  also  to  the 
old  one  of  Leydig.  The  nef:ve-tubes  have  no  direct  origin  in  gang- 
lion cells,  but  always  in  the  dotted  substance.  »Ainsi  les  nerfs 
prennent  toujous  leur  origine  reelle  dans  la  matiere  ponctuee  et 
toutes  les  fois  qu'ils  semblent  partir  du  milieu  d'un  connectif,  qui  en 
est  depourvu  ainsi  que  de  cellules  nerveuses,  on  pent  etre  assure 
qu'il  n'y  a  la  qu'un  simple  accolement  de  leurs  fibres  et  qu'il  en 
faut  chercher  1'origine  dans  un  centre  superieur  ou  inferieur.« 

According  to  PRUVOT  the  nerves  have  two  roots.  He  says 
(1.  c.  p.  253):  »Chaque  cordon  (i.  e.  of  the  ventral  nerve-cord)  est 
luimeme  divise  en  deux  et  les  nerfs  de  la  chaine  y  prennent  leur 
origine  reelle  par  deux  racines,  une  anterieure  et  une  posterieure. 
Les  nerfs  pedieux  etant  chez  les  Annelides  incontestablement  mixtes 
par  leur  fonctions,  il  ne  serait  pas  impossible  que  Tune  en  representat 
la  racine  sensitive  et  1'autre  la  racine  motrice.« 

This  is  consequently  something  similar  to  what  HERMANN  and 
others  have  already  described  in  Annelids.  NEWPORT  has  already 
described  a  similar  arrangement  by  Insects  1834  (vide  1.  c.  1834). 

PoiRlER  (1885)  describes  and  illustrates  the  nerve-fibres  of 
the  Trematodes  as  being  tubes  with  a  granulous  non-fibrous  con- 
tents (containing  nuclei  and  bipolar  cells),  but  he  does  not  give 
any  distinct  description  of  the  dotted  substance  of  the  ganglia. 
He  calls  it  »une  substance  speciale  finement  granuleuse«.  In  his 
opinion,  it,  however,  includes  nerve-tubes  of  which  he  says:  »les 
tubes  nerveus  du  cerveau  et  de  sa  commissure  sont  remarquables  par 
le  pen  d'epaisseur  de  leurs  parois  et  le  faible  developpement  de  la 
substance  amorphe,  qui  reunit  ces  tubes  et  forme  leurs  parois. «  He 
seems,  thus,  to  have  partly  recognised  the  real,  nature  of  the  central 
mass  of  the  ganglia.  It  seems  as  if  he  supposes  the  nerve-tubes,  as  a 
rule,  to  originate  directly  in  the  ganglion  cells.  Of  the  cells  of  the  brain 
he  says:  »Les  prolongements  de  ces  cellules  nerveuses  se  continuent 
directement,  soit  dans  les  divers  nerfs  qui  partent  du  cerveau.  soit 
clans  la  large  commissure  transversale  qui  reunit  ses  deux  lobes,  et, 
de  la  apres  avoir  parcouru  une  partie  du  lobe  oppose  a  celui  dans 
lequel  ils  ont  pris  naissance,  ils  penetrent  dans  les  troncs  nerveux 
qui  en  partent«  (1.  c.  p.  605). 

BELA  HALLER,  who,  half  a  year  later  than  Leydig,  published  his 
paper  on  the  histology  of  the  nervous  system  of  the  Bhipidoglossa,  may, 
in  certain  respects,  be  quoted  as  a  contrast  to  Leydig.  According  to 
his  description,  the  dotted  substance  —  which  he  calls  »das  centrale 
Xervennetz«  —  consists  of  a  net-work  of  nervous  fibrillae,  which  by 


—   62   — 

infinite  anastomoses  form  minute  meshes;  these  nervous  fibrillae 
spring  from  cell-processes,  as  well  as  from  nerve-fibres.  If  Haller's 
illustrations  of  the  central  »Nervennetz«,  are  compared  with  Leydig's 
of  the  dotted  substance,  the  resemblance  must  certainly  strike  every- 
body. The  only  difference  is  that,  Leydig  calls  his  reticulation  a 
spongioplasmic  one,  in  the  cavities  of  which  the  real  nervous  sub- 
stance is  diffused,  whilst  Haller  calls  his  reticulation  a  nervous  one, 
the  fibrillae  of  which  are  surrounded  by  interfibrillar  substance.  It 
may  indeed  be  the  same  so  far,  because  in  both  cases  there  must 
be  a  quite  diffusive  distribution  of  the  nervous  substance  or  nervous 
reticulation  in  the  central  nervous  system.  The  cell-processes  which 
contribute  to  the  formation  of  this  reticulation  are,  according  to  Haller, 
those  which  do  not  directly  unite  with  other  cells,  and  which  do  not 
directly  form  peripheric  nerve-tubes;  the  latter  he  calls  »Stammfort- 
satze«.  He  even  illustrates  isolated  cells  with  processes  forming  a 
reticulation. 

The  nerve-tubes  have  two  modes  of  origin,  some  tubes  originate 
directly  in  ganglion  cells,  and  are  direct  continuations  of  »Stamm- 
fortsatze«,  other  tubes  originate  in  the  central  »Nervennetz«. 

No  previous  writer  has  so  decidedly  and  emphatically  maintained 
an  infinitely  anastomosing,  reticular,  character  in  the  central  dotted 
substance. 

At  about  the  same  time  as  Bela  Haller,  the  writer  of  this 
paper  published  a  Memoir  on  the  structure  of  the  Myzostoma  and, 
subsequently,  a  paper  on  the  nervous  system  of  the  Ascidia  and 
Myxine.  We  have  there  maintained  views  very  similar  to  those 
which  will  be  laid  forth  here,  and  will  therefore  now  refer  to  them 
somewhat  cursorily  only.  The  dotted  substance  is  no  anastomotic 
nervous  net-work,  but  a  complicated  web  or  plaiting  of  nervous 
fibrillae  or  tubes.  In  transverse  sections  a  reticulation  is  certainly 
seen,  it  is,  however,  to  a  great  extent  produced,  by  the  transsection 
of  the  sheaths  of  tube-shaped  fibres  traversing,  or  rather  forming,  the 
dotted  substance;  the  reticulation  is  thus  a  rather  apparent  one  and 
is  of  a  „ spongioplasmic"  nature.  It  is,  consequently,  the  same 
substance  which  Leydig  has  described  under  this  name,  but  it  has 
not,  in  the  writers  opinion,  the  reticular  structure  he  has  ascribed  to  it. 

Each  cell  has  only  one,  really  ^nervous  process",  if  the  cell 
has  several  processes,  then  the  other  ones  are  protoplasmic  pro- 
cesses with  a  nutritive  function.  The  » nervous  processes «  pass 
to  the  » dotted  substance «,  and,  there,  they  --  either  quite  lose 
their  individuality  and  sub-divide  into  fibrillae,  losing  themselves  in 


—  63  — 

the  fibrillar  plaiting  —  or  they  maintain  their  individuality,  and  pass 
through  the  dotted  substance  and  into  a  peripheral  nerve,  forming  a 
nerve-tube.  They  have,  however,  no  isolated  course,  and  give  off 
extremely  slender  fibrillar  branches  to  the  fibrillar  plaiting,  on  their 
way  through  the  dotted  substance.  The  nerve-tubes  have  tivo  modes 
of  origin,  they  -  -  either  spring  directly  from  ganglion  cells  (without 
isolated  course  as  above  mentioned)  -  -  or  indirectly,  from  the 
fibrillar  plaited  texture. 

FRANZ  VON  WAGNER  (1886)  who,  at  the  same  time  as  I  myself, 
has  described  the  nervous  system  of  Myzostoma1}  supposes  the 
nerve-fibres  or  nerves-}  to  have  only  an  indirect  origin;  i.  e.  in  the 
»Punktsubstanz«,  which  he  believes  to  be  »ein  dichtes  Geflecht 
feinster  Faserchen,  welche  aus  der  pinselformigen  Auflosung  der 
protoplasmatischen  Fortsatze  der  Ganglienzellen  hervorgehen.  Aus 
diesem  maschigen  Filz  treten  die  Nerven  heraus.«  »Das  schwammig- 
netzige  Gefiige«,  which  Ley  dig  describes,  in  »Zelle  und  Gewebe«, 
v.  Wagner  has  also  observed;  his  opinion  of  the  nature  of  this 
substance  he  does  not,  however,  give. 

Towards  the  close  of  last  year  another  paper  by  BELAHALLER 
appeared.  In  it  the  author  states  his  results  of  some  investigations 
on  the  structure  of  the  nervous  system  of  Annelids,  Arthropods 
(Tobanus  bovinus)  and  some  Vertebrates.  He  compares  these 
results  with  his  previous  description  of  the  nervous  system  of  the 
Ehipidoglossa.  In  the  dotted  substance  of  the  latter  he  found 
no  connective  tissue,  the  substance  consisted,  exclusively,  of  a  central 
nervous  reticulation  springing  from  the  processes  of  the  ganglion  cells. 
In  those  firstmentioned  animals  the  case  is  different.  In  their  nervous 
system  the  dotted  substance  is  formed  by  a  reticulation  of  connec- 
tive-tissue, as  well  as  by  a  real  nervous  one. 

This  is  a  description  very  similar  indeed  to  that  which  BELLONCI 
already,  some  years  ago,  on  several  occasions,  has  given  of  the  central 
nervous  system  of  Crustaceans  as  well  as  Vertebrates.  Haller 
seems  however  not  to  know  this  Italian  author. 

In  his  opinion  the  nervous  system  of  the  Mollusca  represents, 
thus,  a  very  primitive  state,  being  diffident  in  a  reticulation  of  con- 
nective tissue,  it  is  in  this  respect  like  that  of  Coelenterates.  In  inverte- 


1)  I    have    previously    mentioned    the    memoir    of  Wagner  in  a  paper  on    the 
nervous    system   of  Myzostoma,    which   will,    I    hope,    soon    appear    in    »Jenaische 
Zeitschr.   fur  Nat.«    1887. 

2)  v.  Wagner  does  not  believe  that  the  nerves  of  the  Myzostomes  are  really 
differentiated  into  fibres  (vide  1.  c.  p.  48.) 


-64- 

brates,    as   well   as   in   vertebrates,   he    describes  direct  anastomoses 
between  the  ganglion  cells. 

Haller  also  quotes  the  writer's  papers  on  Myzostoma  and 
Ascidians  etc.  As  they  are  mostly  written  in  Norwegian,  he  seems, 
however,  not  quite  to  have  understood  them.  —  As  will  be  shown 
in  this  paper,  Haller's  supposition  of  no  connective  tissue  in  the 
dotted  substance  of  the  nervous  system  of  the  lower  Molluscs  is 
incorrect. 


d)  The  combination  of  the  ganglion  cells  with  each  other. 

Regarding  the  combination  of  the  ganglion  cells,  two  opinions 
have  especially  been  prevalent.  Either,  a  direct  combination  by  di- 
rect anastomoses  is  described,  and  asserted  —  or  the  existence  of 
such  a  combination  is  denied,  the  latter  view  is,  strangely  enough, 
maintained  by  very  few  writers,  and  scarcely  by  any  modern  writer. 
The  former  view  is  especially  defended  by  WALTER  and  WALDEYER, 
and  is  certainly,  without  comparison,  the  most  prevalent  view  amongst 
histologists,  and  has  existed  from  a  very  early  period. 

Amongst  its  more  modern  adherents  are  HANS  SCHULTZE, 
BOHMIG,  BELLONCI  and  others;  a  very  zealous  adherent  is  BELA 
HALLER,  who  scarcely  illustrates  a  ganglion  cell  which  does  not 
anastomose  with  another.  According  to  this  view,  or  rather  theory 
of  a  direct  combination,  there  is  a  prominent  disposition  in  papers  on 
the  nervous  system  to  find  multipolar  cells  everywhere;  Bela  Haller 
even  says,  with  VlRCHOW,  that  the  more  closely  the  central  nervous 
system  is  investigated  the  less  numerous  will  the  unipolar  ganglion 
cells  be,  if  they  do  not  indeed  quite  disappear.  The  fact  is,  that 
multipolar  cells  and  direct  anastomoses  were  necessary  to  the  theory 
of  the  combination  of  the  nervous  elements  and  the  producing  of 
reflex-movements,  and  what  it  is  necessary  to  find  to  support  our 
theories  is  very  often  too  easily  seen.1)  As  a  consequense  of  this, 
there  are  very  few  writers  who  have  ventured  to  deny  direct 
combinations  or  anastomoses  between  the  ganglion  cells. 

Amongst  those  who  have  expressed  themselves  most  em- 
phatically as  to  their  non-existence,  we  may  rank  BuCHHOLZ  and 
SOLBRIG,  who  in  opposition  to  Walter  and  Waldeyer  quite  decidedly 
deny  any  direct  combination.  The  combination  between  the  cells  is 


J)  It  may  here  be  mentioned  that  the  »neuroglia-cells«  and  fibres,  which  are 
interposed  between  the  ganglion  cells,  have  certainly  assisted  a  great  many  writers 
to  see  anastomoses,  as  they  have  not  understood  the  real  nature  of  this  supporting 
tissue. 


-65  - 

according  to  both  writers  produced  by  the  »feinsten  Fasersysterru 
in  the  dotted  substance. 

CLAUS  (1879)  seems  not  disposed  to  believe  in  a  direct  com- 
bination, neither  VIALLANES,  F.  v.  WAGNER  and  others. 

The  writer  of  the  present  paper  has,  also,  on  several  previous 
occasions  firmly  denied  a  common  existence  of  direct  combinations 
between  the  cells,  not  having  found  any  case  of  indubitable  anasto- 
moses between  cell-processes. 


As  the  present  paper  is  just  about  to  be  completed,  a  memoir  by 
Dr.  BERNHARD  RAWITZ  on  »Das  centralen  Nervensystem  der  Ace- 
phalen«  appears  in  last  volume  of  »Jenaische  Zeitschrift*.  As  it 
treats  of  our  subject,  I  will  mention  it  here. 

First,  it  may  be  said  that  the  powers  of  magnification  used  by 
Rawitz  do  not  seem  to  have  been  high  enough,  which  he  also 
states  himself;  to  this  circumstance  may  perhaps  be  ascribed  some 
of  the  results  at  which  he  has  arrived. 

Regarding  the  structure  of  the  ganglion  cells,  Rawitz  supposes 
like  Buchholz,  Hermann,  Freud  and  others,  their  contents  to  con- 
sist of  two  substances,  »von  den  der  eine  eine  netzformig  angeord- 
neten  der  andere  eine  Zahe  unter  Umstande  olartige  Tropfen  bildende 
Substanz  ist,  die  in  den  Maschenraumen  der  ersteren  suspendirt 
ist.«  Rawitz's  mistake  regarding  Buchholz's  description  of  the 
protoplasm  of  the  ganglion  cells,  we  have  already  before  mentioned 
(note  on  p.  32).  He  is  not  sure  whether  the  reticulated  substance  is 
the  real  nervous  one  or,  »ob  man  nicht  vielmehr  die  in  Tropfen  aus- 
fliessende  Substanz  als  die  eigentlich  nervose,  die  netzformige  (Buch- 
holz's hyaline)  nur  als  Stiitzsubstanz  anzusehen  hat,  will  ich  defmi- 
tiv  nicht  entscheiden,  mb'chte  aber  die  letztere  Auffassung  der 
Buchholz'shen  vorziehen.«  As  mentioned  already,  this  comparison 
with  Buchholz  is  quite  misleading,  Rawitz  has  indeed  just  the 
same  view  as  Buchholz  regarding  the  hyaline  substance,  (»in 
Tropfen  ausfliessende  Substanze«,  Buchholz's  » hyaline  Grundsub- 
stanz«)  which  Buchholz  decidedly  supposes  to  be  the  really  nerv- 
ous one  (cfr.  my  report  of  Buchholz  p.  32).  As  will  be  seen  from 
my  description,  I  agree  with  Buchholz  and  Rawitz  in  this  respect. 

Rawitz  does  not  think  a  fibrillous  arrangement  in  the  cell  to 
be  very  probable. 

It  is   very   strange,   indeed,    that  Rawitz    seems   not  to   know 

5 


—  66  — 

LEYDIG's  work:  ,,Zelle  und  G-ewebe",  which  appeared,  at  least,  one 
and  a  half  year  previous  to  Rawitz's  paper,  and  is  mentioned 
by  Haller  in  his  paper  on  the  Rhipidoglossa;  a  paper  which  is 
quoted  by  Rawitz.  It  is  so  much  the  more  strange,  as  Leydig  in 
this  work  describes  the  protoplasm  of  the  ganglion  cells  quite  simil- 
arly to  Rawitz. 

Regarding  the  shape  of  the  ganglion  cells,  Rawitz  describes 
unipolar,  bipolar  and  multipolar  cells;  apolar  ganglion  cells  do  not 
exist;  neither  has  he  observed  cells  with  processes  originating  in  the 
nuclei  or  nucleoli.  The  largest  cells  of  all  the  three  kinds  occur  in 
the  visceral-ganglion,  and  are  motoric,  »homolog  und  analog  den 
Vorderhornzellen  im  Ruckenmark  der  Vertebraten.« 

»Unipolare  Zellen  im  Sinne  der  alten  Histologie«  do  exist,  as 
well  in  invertebrates  as  also  in  the  spinal  ganglia  of  vertebrates,  as 
previously  proved  by  the  same  author.  That  Leydig  (1865)  denies 
the  existence  of  such  cells  is  of  but  little  importance;  »denn  einmal 
hat  Leydig  in  der  citierten  Arbeit  (vide  list  of  literature  1865)  die 
Ganglien  nur  in  toto,  nicht  an  Schnittserien  studiert,  und  dann  leug- 
nen  die  Physiologen  uberhaupt  das  Vorkommen  von  nervosen  Zellen 
die  nicht  mit  anderen  Zellen  in  direlcter  Verbindung  stehen,  weil  dies 
mit  der  Theorie  nicht  in  Einklang  zu  bringen  ist.  Darauf  aber 
kommt  es  allein  an:  ob  es  wirklich  nervose  Zellen  giebt,  die  mit 
benachbarten  Zellen  nicht  in  direkter  Verbindung  stehen.  Ob  der 
Fortsatz  sich  weiterhin  teilt,  in  ein  Geflecht  feinster  Reiserchen  sich 
auflost,  ob  dieses  Geflecht  mit  ahnlichen  anderer  Zellfortsatze  eine 
netzformige  Verbindung  eingeht,  ist  vollstandig  irrevelant.  Es  sei 
denn,  dass  man  annimmt,  jede  einzelne  Fibrille  konnte  gleichzeitig 
zentrifugal  und  zentripetal  leiten.  -  -  Nun  giebt  is  aber  nicht  bloss 
soldi  unipolare  Zellen,  welche  nicht  mit  anderen  in  unmittelbarer 
Verbindung  stehen,  wahrend  der  Fortsatz  sich  in  feinste  Reiserchen 
zerspaltet,  sondern  es  giebt  auch  solche,  deren  Fortsatz  ungeteilt  in 
den  aus  dem  Ganglion  entspringenden  peripheren  Nervenstamm  uber- 
geht**)  In  another  place  (p.  410)  RAWITZ  also  says:  »Die  Phy- 
siologic mag  sich  strauben,  so  viel  sie  will,  sie  muss  mit  der  Existenz 
wirklich  unipolarer  Zellen  im  Sinne  der  alten  Histologie  rechnen.« 
How  much  my  view  differs  from  that  of  Rawitz  will,  I  suppose, 
become  evident  from  my  description  in  this  paper  (vide  sequel),  as 
also  from  my  previous  papers  on  Myzostoma,  Ascidians  etc.  What 
is  above  quoted  is,  I  think,  enough  to  show  into  how  many  dilemmas 


c.  p.  408 — 409. 


the  old  physiological  view  of  the  function  and  combination  of  the 
nervous  elements  has  brought  histologists. 

Rawitz  divides  the  ganglion'  cells  according  to  their  processes 
into  different  kinds,  as  this,  however,  in  my  opinion,  is  of  but  little 
importance  I  shall  pay  no  further  attention  to  it  here.  This  much  I 
shall  only  say,  that,  what  he  calls  »Schaltzellen«  -  -  which  are  mul- 
tipolar  cells  having  only  » protoplasmic  processes «  (cfr.  sequel)  and 
situated  only  in  the  central  »Nervennetz«  *)  --  are  in  my  opinion 
not  at  all  ganglion  cells,  but  cells  belonging  to  the  neuroglia. 

Rawitz  denies  the  presence  of  any  connective  tissue  inside  the 
outer  neurilem-sheath ;  this  is  the  more  surprising  as  on  the  one 
hand  neuroglia-cells,  according  to  my  investigations,  occur  in  great 
number  in  Molluscs,  and  on  the  other  hand  he  himself,  besides  the 
»Schaltzellen«  above  quoted,  describes  (p.  422)  and  illustrates  (fig.  79) 
some,  in  his  opinion,  remarkable  corpuscles  from  the  cerebral  gang- 
lia of  Unio  pictorum  and  Anodonta  anatina.  He  has  not  been  able 
to  understand  the  significance  of  these  corpuscles;  he  calls  them 
»geschwanzte  Kerne «.  I  do  not  think  there  can  be  much  doubt, 
but  that  they  are  the  cells  which  Buchholz  has  also  mentioned,  and 
which  I  describe  as  neuroglia-cells  in  the  » dotted  substance «.  They 
have,  certainly,  quite  the  same  appearance  and  shape. 

Rawitz  describes  numerous  direct  combinations  between  the 
ganglion  cells  of  different  kinds.  These  statements  are,  however,  of 
but  little  importance  to  me,  all  much  the  more  that  Rawitz  has  not 
employed  for  his  investigations  lenses  of  very  high  powers  or  ho- 
mogeneous immersion ;  his  observations  cannot  therefore  be  considered 
as  quite  reliable  in  all  respects,  and  especially  not  in  these,  where 
the  best  lenses  are  decidedly  quite  necessary,  if  you  are  to  obtain 
a  position  to  be  able  to  state  anything  with  certainty. 

The  processes  of  the  ganglion  cells  have,  according  to  Rawitz, 
numerous  »varikose  Anschwellungen«,  from  which  extremely  slender 
fibrillse  very  often  issue. 

The  cell-processes  he  divides  into  three  kinds  according  to 
their  course: 

1)  »Stammfortsatze",    »die  direkt  und  stets  ungetheilt  zum  peri- 
pheren  Nervenstamm  gehen.« 

2)  ,,Markfortsatze"   which   penetrate    into    the    »Marksubstanz«, 
and  are,  there,  broken  up  into  fine  fibrillae. 


*)   »In  welches  sie  eingeschaltet  sind,  um  es  in  seiner  Funktion  zu  verstarken, 
und  das  sie  mit  ihren  Fortsatzen  bilden  helfen.* 

5* 


—  68  — 

3)  »Protoplasmafortsatze"  which  produce  the  combination  of  the 
ganglion  cells  with  each  other.  They  have  the  same  appearance  as 
the  cell  protoplasm. 

The  »Stammfortsatze«  are  rare  and  only  occur  in  unipolar  cells. 
The  »Protoplasmafortsatze«  occur  in  bipolar  and  multipolar  cells  as 
well  as  also  in  the  smallest  unipolar  ones,  which  should,  conse- 
quently, completely  want  »Mark«-  or  »Stammfortsatze«. 

In  his  description  of  the  »Markfortsatze«  he  expresses  himselt 
somewhat  indistinctly.  »Markfortsatze«,  he  says  p.  416,  occur  in  all 
cells,  besides  those  which  have  a  »Stammfortsatz«,  and  this  he  says 
after  having  just  described  cells  wanting  »Mark«-  as  well  as  »Stamm- 
fortsatze«.  At  one  point  he  says:  »Die  geminipolen  Zellen  (conse- 
quently bipolar  cells)  haben  nur  Markfortsatze«.  Immediately  after- 
wards he  says:  »Keine  Zelle  hat  zwei  Markfortsatze,  sondern  immer 
nur  einen«  (1.  c.  p.  416).  How  this  is  to  be  understood  is  not,  I 
think,  very  easy  to  say. 

Immediately  afterwards  he  says,  again,  that  »die  oppositipolen 
Zellen  (consequently  bipolar  cells)  sind  diejenigen  Gebilde,  welche 
noch  am  ehesten  als  solche  betrachtet  werden  konnen,  welche  zwei 
Markforsatze  haben.  He  is,  however,  disposed  to  »auch  bei  Everte- 
braten  wie  bei  Vertebraten  (cmfr.  his  previous  paper  1883  Arch.  f. 
mikr.  Anat.  XXI)  die  oppositipolen  Zellen  als  Nervenzellen  sensu 
strictiori  nicht  anzuerkennen,  sondern  sie  nur  als  kern-  und  proto- 
plasm ahaltigen  Interpolationen  der  Nervenfortsatze  resp.  -fasern  zu 
erklaren.«  A  view  in  which  perhaps  I,  to  a  certain  extent,  can  agree 
with  him;  though  I  have  only  succeeded  in  finding  extremely  few 
similar  cells  or  formations. 

Rawitz  describes,  in  the  Acephales,  an  arrangement  of  the  cells 
somewhat  similar  to  what  I,  on  previous  occasions,  have  mentioned  in 
Ascidians  etc.  In  the  outer  layer,  unipolar  cells  exclusively  occur,  in 
the  middle  layer,  all  kinds  of  cells,  unipolar,  bipolar  and  multipolar  ones, 
and  in  the  inner  layer,  close  to  the  » dotted  substance «  multipolar 
cells  principally  occur.  This  is,  as  I  have  previously  declared,  in 
the  closest  relation  to  what  I  call  the  nutritive  function  of  the 
protoplasmic  processes,  and  it  has  not,  in  my  opinion,  the  significance 
which  Rawitz  ascribes  to  it. 

»Der  Markfortsatz  oder  Hauptfortsatz  der  multipolaren  Ganglien- 
zellen«,  of  the  Acephales  are,  according  to  Rawitz,  »das  Homologon 
des  Deiters'shen  Fortsatze  der  polyklonen  Ganglienzellen  im  Vorder- 
horn  des  Riickenmarkes  der  Vertebraten. «  And  he  believes  it  to 
be  »morphologisch  durchaus  nebensachlich,  ob,  wie  bei  dem  Axen- 


-69  - 

cylinderfortsatz  der  Wirbelthiere,  ein  direkter  Uebergang,  oder,  wie 
bei  dem  Markfortsatz  der  Acephalen,  ein  indirekter  Uebergang  zur 
Peripherie  durch  Vermittlung  eines  interponierten  Netzes  stattfindet. « 
He  believes,  thus,  the  unipolar,  »geminipolen«  and  »pseudobipolaren« 
cells  to  be  the  only  ones  from  which  »eine  nervose  Erregung  aus- 
gehen,  resp.  in  denen  sie  allein  perzipiert  werden  kann«,  whilst  the 
multipolar  cells  are  »Sammelorte  fiir  diese  Reize«  and  the  »oppositi- 
polen«  cells  must  be  considered  as  »Faseranschwellungen«  (vide  1.  c. 
p.  422). 

Regarding  the  structure  of  the  » dotted  substance  «,  he  arrives  at 
the  result,  after  having  mentioned  some  previous  writers:  »dass  nur 
HALLER  die  Struktur  der  Marksubstanz  erkannt  hat,  DlETL  dieselbe 
zu  ahnen  schien,  wahrend  alle  iibrigen  Autoren  sich  mit  Bemerkun- 
gen  wie  »Filz  feinster  Fasern«,  »Gewirr  feiner  Faserchen«  etc.  ab- 
finden.«  If  RAWITZ  had  known  works  such  as,  for  instance,  that  of 
HERMANN,  which  he  does  not  seem  to  know,  he  would  certainly 
have  aknowledged  that,  also,  other  writers  have  tried,  and  not  quite 
without  success,  to  penetrate  into  this  difficult  subject.  Rawitz's 
observations  are  even  in  some  respects  very  like  those  of  Hermann. 

RAWITZ  adopts  Dietl's  designation  » Marksubstanz «,  as  it  is,  in 
his  opinion,  more  characteristic  than  »Punktsubstanz«,  which  he  even 
declares  to  be  incorrect;  the  reason  why  he  does  not,  however, 
say.  Upon  the  whole,  I  think  it  a  very  doubtful  thing  to  give 
new  designations  where  an  old  and  well  known  one  is  present 
and  generally  used,  which  is  the  case  here.  I  think  it  the  more 
so  when  the  new  designation  can  scarcely  be  said  to  be  a  more 
characteristic  one  as  to  the  structure;  that  it  is  so  as  to  the  contents 
does  not  even  seem  to  me  to  be  quite  evident.  » Marksubstanz «  is 
not  used  for  the  same  reason  that  Dietl  uses  it,  viz.  because  it  is 
situated  in  the  »Mark«  or  centre  of  the  ganglia,  but  because  it, 
according  to  Rawitz,  contains  »eine  nervenmarkahnliche  Substanz, 
welche  unter  gevisse  Bedingungen  die  characteristischen  Erscheinun- 
gen  des  Myelin  darbietet.«  That  it  really  is  »Mark«  or  myeline 
Rawitz  has  observed,  I  do  not  think  is  at  all  proved  in  his  descrip- 
tion ;  why  may  it  not  be  a  substance  similar  to  the  hyalin  substance 
of  the  ganglion  cells,  and,  indeed,  I  suppose  it  to  be  the  same, 
though  one,  certainly,  a  priori,  may  feel  disposed  to  suppose 
myeline,  or  a  similar  substance,  also  to  be  present,  even,  if  not  in 
the  way  supposed  by  Rawitz,  i.  e.  diffusively  extended  in  the  meshes 
of  the  net-work  described  by  him  and  Haller. 

Of  the   structure   of  this   central   »Nervennetz«   he  gives   a  de- 


—  70  — 

scription  quite  similar  to  that  of  Haller.  It  is  a  anastomotic  net- 
work of  slender  fibrillae,  which  is  diffusively  extended  through  the 
whole  dotted  substance,  and  which  is  formed  by  the  »Markfortsatze« 
of  the  ganglion  cells,  as  also  by  the  »Schaltzellen«,  mentioned  above. 
The  only  difference  between  Rawitz's  and  Haller's  descriptions  is: 
that  Rawitz  ascribes  to  his  »Nervennetz«  numerous  »Varikositaten«, 
whilst  Haller  does  not  mention  anything  similar;  they  occur  at  the 
points  where  the  fibres  forming  the  meshes  unite;  they  appear  »im 
mikroskopischen  Bilde  als  dunkle  Punkte« ;  and  they  are  real  vari- 
oceles  and  not  merely  optic  products  (1.  c.  p.  429).  Besides  this 
»Nervennetz«  and  the  »nervenmarkahnliche  Substanz«  there  is,  in 
the  »Marksubstanz«,  a  third  constituent,  i.  e.  slender  fibrillae  which, 
in  macerated  preparations,  may  be  isolated  for  long  distances,  and 
which  are  also  varicose.  »Sie  sind  ausserordentlich  schmal  aber 

nicht  smaler  als  die  peripheren  Fibrillen Sie  stellen  das  Pro- 

dukt  des  centralen  Netzes  dar,  aus  dem  sie  sich  .  .  .  durch  Ver- 
schmelzung  von  2  oder  hochstens  3  Netzfibrillen  entwickeln.«  .  .  . 
»Die  Fasern  selber  treten  durch  die  Maschen  des  Netzes  hiridurch, 
um  vom  ihrem  Bildungsort  zur  Peripherie  zu  gelangen  und  werden 
wohl  durch  die  markahnliche  Substanz  von  den  Fibrillen  des  Netzes 
isolirt.«  Strange  to  say,  RAWITZ  supposes,  here,  the  importance 
of  this  substance  to  be  only  isolation,  whilst  the  substance  he 
found  in  the  ganglion  cells,  and  which  he  suposes  to  be  similar  to 
this  one,  ought,  in  his  opinion,  to  be  considered  as  the  real  nervous 
substance  strictly  speaking,  and  the  reticulation  in  the  cells  a  sup- 
porting substance;  that  is  consequently  quite  a  contrary  view. 

According  to  RAWITZ,  connective-tissue  occurs  neither  in  the 
central  nervous  system  of  the  Acephales  nor  in  their  nerves  inside 
the  outer  sheaths,  and  in  spite  of  this  statement  he  describes  cells, 
occuring  in  the  nerves  as  well  as  in  the  central  nervous  system,  so 
strikingly  similar  to  those  of  the  neuroglia,  or  inner  neurilem,  that 
I  do  not  think  there  can  be  much  doubt  about  their  identity  (e.  g. 
comfr.  his  »Schaltzellen«,  »geschwanzte  Kerne «,  round  nuclei  and 
oblong  nuclei  in  the  nerves  etc.). 

Regarding  the  structure  of  the  nerves  of  the  Acephales  he  says 
that  »die  Nervenfasern  einfach  ein  primares  Biindel  von  Axenfibrillen 
sind.«  This  is,  in  my  opinion,  a  mistake,  in  which  he,  however, 
agrees  with  HALLER  and  other  writers. 

Rawitz  wonders  that  HALLER  did  not  know  the  paper  by 
BELLONCI  on  the  »Tectum  opticum  der  Knochenfische«  (Zeitschr.  f. 


IJ  T        

wiss.  Zool.  Bd.  35)  but  at  the  same  time  he,  himself,  does  not  seem 
to  know  the  papers  by  Bellonci  on  the  nervous  system  of  inverte- 
brates, which  would  seem  to  be  of  even  higher  importance  to  his 
investigations. 

I  think  it  is,  indeed,  also  very  strange,  that  neither  Rawitz  nor 
Haller  (nor  most  modern  writers)  are  acquainted  with  the  exellent 
papers  on  the  central  nervous  system  of  vertebrates  by  GOLGI; 
they  quote  a  great  many  other  and  less  important  writers,  but  they 
do  not  seem  to  know  this  eminent  histologist  who,  in  my  opinion, 
has  really  introduced  a  new  epoch  in  our  researches  into  the  struc- 
ture of  the  nervous  system.1) 

If  we  look  back  at  this  review  of  the  literature  and  compare 
the  statements  of  the  various  authors  with  the  results  of  my  in- 
vestigations, it  will  be  seen  that  in  most  respects,  and  these  also  the 
principal  ones,  I  can  scarcely  agree  with  any  of  them ;  the  author  to 
whose  views  I  feel  most  related  is  LEYDIG.  As  to  the  nerve-tubes 
and  ganglion  cells,  we  have  seen  that  almost  all  writers,  except 
Leydig,  who  describe  a  fibrillar  structure  suppose  the  nerve-tubes 
to  consist  of  nervous  fibrillae  and  interfibrillar  substance,  and  in  the 
ganglion  cells  most  of  them  describe  a  similar  structure,  whilst  some 
writers  describe  a  reticulation.  Only  LEYDIG  has  decisively  expres- 
sed himself  in  favour  of  the  »interfibrillar  substance «,  hyaloplasm,  being 
the  real  nervous  substance,  whilst  the  fibrillae  should  belong  to  a  sup- 
porting substance,  spongioplasm.  As  to  the  dotted  substance,  we  have 
seen  that  most  writers  who  have  seen  a  reticulation  or  fibrillae  etc. 
in  it,  have  agreed  in  calling  the  reticulation  a  nervous  one,  and  the 
fibrillae  nerve-fibrillae.  Some  writers  have  certainly  described  a  nervous 
reticulation  as  well  as  a  reticulation  of  connective-tissue,  but  LEYDIG 
is  the  only  writer  who  has  decisively  said  that  the  whole  reticulation 
was  of  supporting  nature,  and  that  the  real  nervous  substance  was 
the  homogeneous  one  extended  in  the  cavities  of  the  reticulation. 
Though  I  do  not  agree  with  Leydig,  he  is,  however,  the  author  to 
whose  views  my  observations  are  most  related,  the  points  in  which 
we  essentially  differ  will  be  seen  in  the  description  of  my  investigations. 


*)  Haller  certainly  quotes  from  Unger  a  paper  by  Golgi,  this  is,  however, 
an  old  paper  (1872)  and  is  relatively  of  but  little  importance  when  compared  with 
Golgi's  later  publications. 


2.    The  material  examined. 

For  my  investigations  I  have  used  representatives  of  different 
groups  of  invertebrates  as  also  vertebrates,  I  have  chosen  classes  as 
little  related  to  each  other  as  possible,  partly,  in  order  that  if  I  found 
uniformity  in  these  classes  as  to  the  histological  structure,  the  ob- 
servations might  be  assumed  to  be  of  general  importance  to  the 
whole  animal  kingdom,  excluding  those  lower  classes  which  have 
not,  yet,  got  a  relatively  more  developed  nervous  system.  The 
Echinoderms  and  Coelenterates  I  will  pay  no  attention  to  in  this 
paper,  as  I  intend  to  keep  them  for  a  separate  paper. 

As  a  representative  of  the  lower  Molluscs  I  have  chosen  Patella 
vulgata,  it  being  a  large  species  which  I  could  obtain  in  abundance 
in  the  neighbourhood  of  Bergen. 

Of  Clicetopodes  I  have  examined  different  species  of  Nereis,  as 
well  as,  also,  species  of  other  families,  e.  g.  Leanira,  Nephtys  etc. 

Of  Oligochcetes  I  have  investigated  Lumbricus  agricola. 

Of  Crustaceans  I  have  particularly  investigated  the  Homarus  vul- 
garis,  as  also,  occasionally,  Nephrops  norvegicus  and  some  Amphipods. 

Of  Ascidians  I  have  had  for  my  investigations  specimens  of 
Phalusia  mentula,  Ph.  obliqua,  Ph.  venosa,  Ph.  pnmum,  Ascidia 
scabra,  Corella  parallelogramma,  Ciona  intestinalis  and  species  of 
Cynthia. 

Of  vertebrates,  it  is  especially  those  from  the  lowest  stage  of 
evolution,  viz.  Amphioxus  lanceolatus  and  Myxine  glutinosa  to  which 
I  have  paid  attention.  I  have,  however,  also,  examined  other 
vertebrates  e.  g.  Gadus  morrhua,  Tinea  vulgaris,  Hana  temporaria, 
Mus  musculus,  felix  domesticus,  Homo  sapiens  and  even  Balenoptera 
rostrata. 

As,  however,  I  intend  to  write  a  separate  paper  on  the  nervous 
system  of  the  vertebrates,  I  will  not  pay  much  attention  to  these 
investigations  on  higher  vertebrates  in  this  paper,  only  so  much  may 
he  said,  however,  that  I,  every  where,  have  found  the  most  beautiful 
uniformity  in  relation  to  most  of  the  observations  reported  in  this 
paper. 

As  to  the  vertebrates,  I  shall  confine  myself  to  mention  some 
observations  on  Amphioxus  and  Myxine.  I  got  Ampliioxus  in 
abundance  at  Naples  where,  by  Prof.  DOHRN'S  extraordinary  gen- 
erosity, I  was  allowed  to  study  at  the  zoological  station,  in  the 
spring  of  last  year  in  spite  of  Norway  having  no  working  table  at 
the  station.  Quite  recently  I  received  a  package  from  that  station 
containing  numerous  specimens  of  Amphioxus  most  exellently  pre- 


—  73  — 

served,  in  different  ways,  by  SALVATORE  Lo'BlANCO.  For  this,  and 
many  other  services,  it  is  a  pleasant  duty  to  return  Prof.  DoHRN 
my  most  sincere  and  grateful  thanks. 

Myxine  I  have  had   in   abundance   from   the  neighbourhood  of 
Bergen  (Alverstrommen). 


3.     Methods  of  Investigation. 

If  my  researches,  in  several  respects,  contribute  somewhat  to 
advance  our  knowledge  of  the  minute  structure  of  the  nervous  ele- 
ments, as  I  hope  they  will,  and  although  I,  in  several  respects,  have 
arrived  at  results  very  different  from  most  other  writers,  I  think 
that  must  principally  be  ascribed  to  my  methods  of  investigation,  and 
especially  to  the  methods  employed  for  fixing,  hardening,  and  staining. 

I  have  employed  fresh  isolated  preparations,  as  well  as  macera- 
tions and  sections. 

The  fresh  preparations  were,  usually,  either  examined  in  larger 
pieces  (commissures  or  nerves)  in  the  blood  of  the  animal  as  re- 
commended by  FREUD  (1882)  or  they  were  made  in  this  way; 
the  structures  (nerves  or  ganglia),  were  taken  as  rapidly  as  possible 
from  the  living  animal,  and  then  by  help  of  fine  needles l)  were 
teased  in  the  blood  of  the  animal,  and  afterwards  examined  as  quickly 
as  possible.  Very  often,  also,  I  took  as  thin  sections  as  possible 
from  the  fresh  animal,  examined  them  in  blood,  or  teased  and 
isolated  the  elements  from  them,  by  help  of  needles,  in  the  same 
fluid.  The  last  method  is  especially  to  be  recommended  for  such 
Molluscs,  e.  g.  Patella,  as  have  the  pedal  nerve-cords  and  nerves 
imbedded  in  the  strong  muscular  mass.  A  perfect  isolation  is, 
however,  as  a  rule,  not  possible  in  this  way,  and  therefore  macera- 
tion becomes  necessary. 

The  fluid  recommended  by  B.  HALLER  is  not  bad  for  the  purpose. 
It  consists  of  a  mixture,  acetic  acid  5  parts,  glycerin  5  parts,  Aqua  dest. 


a)  For  this  purpose  I  would  especially  recommend  glass-needles,  which  are, 
I  believe,  originally  recommended  by  Strieker.  They  are  cleaner,  smoother  and, 
in  several  respects,  better  than  any  metal-needles.  They  are,  certainly,  easily  broken, 
but  they  are,  also,  on  the  other  hand,  very  easily  made  from  a  glass-rod,  with  the 
aid  of  a  gas-jet.  If  the  hairlike  extremity  of  the  needle  is  passed  through  the 
flame  before  use, 'a  very  good  point  is  obtained,  blunt  enough  not  to  break  or  cut 
the  elements  when  cautiously  isolated,  but  still  very  fine  and  pointed,  allowing  the 
most  delicate  manipulation. 


—  74  — 

2O  parts.  I  treated  the  structures,  cut  into  as  small  pieces  as  possible 
with  this  fluid  for  one  or  several  hours  (sometimes  even  for  a 
whole  day),  then  teased  them  in  glycerin  (50  %)  and  examined; 
or  washed  out,  and  stained  with  ammonia- car  mine  or  pier  o- car  mine;  or 
diluted  htematoxylin  (DELAFIELD's  solution)  which  I,  for  many  purposes, 
can  specially  recommend,  as  it  gives  a  very  distinct  staining,  and 
the  isolation  is  not  very  difficult  afterwards. 

This  HALLER'S  maceration-method  is  very  convenient  in  many 
cases,  and  is  an  extremely  quick  one;  the  isolation  is  often  possible 
in  less  than  one  hour,  and  in  such  quickly  isolated  (or  stained  and 
isolated)  preparations  no  change  of  import  in  the  form  or  structure 
of  the  elements  was  perceptible. 

Another,  and  for  some  purposes  still  better,  method  is  with  a 
weak  solution  of  Alcohol.  I  tried  different  dilutions  from  RANVIER'S 
> Alcohol  au  tiers « »)  (30  %)  down  to  alcohol  of  25  °/0  or  20  °/o 
and  even  17  %  (as  recommended  by  SOLBRIG).  I  have  found  the 
weaker  solutions  especially  very  good.  The  structures  -  -  freshly 
cut  sections  or  pieces  (always  as  small  as  possible  however)  - 
were  macerated  for  one  or  several  days,  sometimes  even  weeks, 
then  stained  in  ammonia- car  mine  diluted  with  an  equal  quantity  of 
macerating  fluid,  for  24  hours,  and  teased  in  glycerin  of  50  %. 
Picro-carmin  and  DELAFIELD's  hcematoxylin  were  also  employed  as 
staining  agents,  the  latter  agent  gives,  also,  here,  when  employed 
for  a  short  time,  good  results. 

I  usually  stain  before  teasing  or  isolating,  because  I  think  it 
much  more  practical,  and  when  one  is  careful  not  to  employ  too 
strong  solutions,  and  to  dissolve  or  dilute  the  staining  colours  in  the 
macerating  fluid  when  possible,  it  does  not  at  all  disturb  the  facility 
of  isolation  in  any  notable  degree. 

After  having  teased  the  sections  or  small  macerated  pieces  in 
glycerin,  I  always  protect  them  with  coverglasses  on  wax-feet,  in 
order  that  I  may  improve  the  isolation,  if  not  sufficient,  by  careful 
knocking  on  the  coverglass  with  a  pencil,  or  a  needle. 

Besides  the   above  mentioned  methods  I  have,   of  course,    also 


*)  How  Rawitz  arrives  at  the  conclusion  he  mentions,  that  Ranvier's 
» Alcohol  au  tiers*,  which  consequently  is  about  30  °/0,  preserves  less  perfectly 
than  the  dilution  recommended  by  himself,  which  contains  about  25  °/o  alcohol 
or  less,  and  how  he,  in  the  latter  fluid,  can  keep  the  preparations  for  6  weeks 
withouth  any  deformation,  whilst  in  the  former  fluid  fungi  grew  after  a  few  days, 
I  really  do  not  understand.  In  my  opinion  it  ought  to  be  just  the  contrary,  if  any 
difference  is  to  be  perceived  in  that  respect. 


—  75  — 

employed  the  classical,  diluted  solution  of  potassium-bichromate 
(0.03 — o.i  %)•  Maceration  in  this  fluid  for  several  days,  and  stain- 
ing in  ammonia-carmine  diluted  with  or  dissolved  in  the  macerating 
fluid ')  gives  very  good  preparations.  A  shorter  staining  with  diluted 
licematoxylin  may  also  be  recommended.  Upon  the  whole,  macera- 
tion in  potassium-bichromate  is  a  method  which  cannot  possibly  be 
omitted,  if  the  most  delicate  structure  is  intended  to  be  disco- 
vered and  explored  with  good  results;  it  is  certainly  one  of  the 
oldest  methods  but  also  one  of  the  best. 

By  the  use  of  ammonium-bichromate,  in  very  diluted  solution 
(0.03 — o.i  %),  results  are,  I  think,  obtained  very  similar  to  those 
obtained  by  potassium-bichromate.  The  difference  is,  at  all  events, 
not  so  great  as  to  make  it  necessary  to  dwell  upon  it  here. 

A  maceration-fluid  which  is,  I  think,  for  many  purposes  very 
good,  is  that  originally  suggested  by  LANDOIS,  and  subsequently 
recommended  and  described  by  GlERKE.2)  It  consist  of  a  mixture 
of:  chromate  of  ammonium  (concentrated  solution  I  part),  phosphate 
of  potassium  (cone.  sol.  I  part),  sulphate  of  sodium  (cone.  sol.  I  part), 
Aqua  dest.  (20  parts). 

The  sections  or  small  pieces  are  macerated  for  one  or  several 
days,  then  stained  with  ammonia-carmine,  pier o- carmine  or  diluted 
hcematoxylin.  The  dilution  of  ammonia-carmine  with  this  macerating 
fluid,  as  recommended  by  GlERKE,  is,  according  to  my  experience, 
not  possible,  as  the  carmine  is  precipitated.  The  isolation  by  this 
method  is  a  very  perfect  one.  The  more  delicate  structures  are, 
however,  slightly  visible,  as  they  become  too  transparent. 

The  most  important  thing  in  researches  upon  the  histology  of 
the  nervous  elements  is,  beyond  comparison,  to  get  good  sections  from 
well  fixed  and  stained  preparations.  This  is,  no  doubt,  the  surest 
and  most  decisive  method.  A  very  careful  preparation  is,  here, 
however,  of  the  greatest  importance. 

A  splendid  fixing,  and  at  the  same  time  hardening,  agent  is  the 
chromo-aceto-osmic   acid   (FLEMMlNG's   strongest  formula),    which  for 
our  purpose  affords  really  excellent  results.     I  have  employed  both 
of  FLEMMlNG's  formulae  and  think  the  strongest  one  the  best.     It  is: 
Chromic  acid   .    .    I   °/0   15  parts 
Osmic  acid  .    .    .    2  °/o     4      » 
Acetic  acid  ...  I      »      or  less.3) 

')  As  recommended  by  Gierke  (1885,  Arch.  mikr.  Anat.  Bd.  XXV  p.  447). 

2)  1.   c.   1885   p.  446. 

•"')  Flemming :  Zeitschrift  f.  wiss.  Microscopic  Bd.  I.   1884  p.  349. 


_76- 

I  treat  as  small  pieces  as  possible  with  the  fluid  (in  not  too  small 
quantities)  for  1 2  to  24  hours,  or  sometimes  even  longer  (2 — 4  days), 
they  are  then  washed  and  may  now,  directly  enclosed  in  paraffin  (not 
imbedded),  easily  be  cut,  under  water  or  alcohol,  on  the  microtome ;  if 
necessary  the  pieces  may  also  be  hardened  in  alcohol.  If  cut  with 
a  sharp  knife,  one  obtains  in  this  way  really  brilliant  sections.  I 
have  even  got  sections  only  .005  mm.  thick.  The  sections  are 
stained  in  different  ways,  carmine,  hcematoxylin  (DELAFIELD's,  WEI- 
GERT'S  or  HEIDENHAIN'S  solutions)  or  coal-tar  colours  (eosin,  nigro- 
sin,  methylen-blue,  etc.),  or  combinations  of  these  different  staining 
methods  are  used. 

As  a,  for  many  purposes,  really  excellent  combination,  it  may 
be  recommended  first  to  stain)  the  sections  in  an  aqueous  solution  of 
haematpxylin  (l/2  %)  for  some  hours  or  longer,  then  wash  out  and 
treat  the  sections  for  a  day  (or  longer)  in  a  solution  of  potassium- 
bichromate  (.5 — i  %);  afterwards,  wash  out  again  (not  too  much) 
and  stain  in  DELAFIELD'S  haematoxylin ') ;  if  overstained,  decolour  in 
water  to  which  a  few  drops  of  acetic  acid  have  been  added.  The 
sections  are  examined  in  glycerin  (50 — 100  °/0)  or  in  Canada  bal- 
sam. The  preparations  obtained  in  this  way  are,  indeed,  in  many 
respects  superior  to  any  others. 

As  however  the  method  is  certainly  somewhat  complicated,  I 
prefer,  when  possible,  to  stain  in  toto.  This  affords  very  good  results 
when  the  pieces  are  sufficiently  small,  and  are  treated  carefully.  In 
this  case,  of  course,  a  longer  time  is  necessary  for  staining,  de- 
pending on  the  size  of  the  pieces.  DELAFIELD's  licematoxylin  I  generally 
employ  very  diluted,  for  staining  in  toto. 

Another  method,  which  affords  excellent  results  for  some  pur- 
poses, is  fixing  and  hardening  in  alcohol  gradatim.  Especially 
for  Annelids,  it  is  very  good  first  to  narcotise  the  animals,  by 
carefully  pouring  a  thin  layer  upon  the  surface  of  a  small  portion  of 
seawater  in  a  glass  in  which  they  live.  When  narcotised  they  are 
stretched  on  a  waxplate  and  hardened  in  alcohol  gradatim.  When 
sufficiently  hardened,  (not  too  much)  they  are  stained  in  a  watery 
solution  of  haematoxylin,  and  afterwards  treated  with  potassium- 
bichromate  as  originally  recommended  by  HEIDENHAIN.  For  some 
purposes  fixing  in  a  saturated  watery  solution  of  picric  acid  is  still 
better,  then  washing  out  in  diluted  alcohol  and  staining  as  above, 


])    As    will   be   seen   this    method    is  very  like  that  already  recommended  by 
Flemming,  for  staining  of  glands.     Zeitschr.  f.  wiss.  Microscopic  Bd.  II.  1885  p.  517. 


—  77  — 

—  or,  also,  fixing  in  LANG'S  fluid  (corrosive  sublimate  12  %  m  sea- 
water,  or  in  an  aqueous  solution  of  chloride  of  sodium  6  %  acetic 
acid  6  %,  alum  0.5  0/0)  then  washing  out,  hardening  a  little  in 
alcohol  gradatim  and  staining  with  HElDENHAIN's  haematoxylin 
as  above.  « 

All  these  methods  can  be  safely  recommended  for  trials;  every- 
one of  them  will,  I  think,  for  certain  purposes  afford  results  which 
certainly  are  obtained  by  none  of  the  methods  employed  before. 

My  list  of  methods  is  however  not  yet  finished.  For  some 
purposes  even  the  above  mentioned  ones  were  not  sufficient,  e.  g. 
in  Mollusca,  where  it  was  extremely  difficult  to  arrive  at  any  clear 
idea  of  the  most  minute  structure  of  the  nerves  and  LEYDIG'S  »Punkt- 
substanz«.  The  following  method  gave,  however,  excellent  results. 

The  pieces  for  examination,  cut  as  small  as  possible,  were 
treated  with  osmic  acid  (i  %)  for  48  hours,  then  washed  in  run- 
ning water,  and  cut  at  once  by  the  hand  or  in  the  microtome  or  they 
may  first  be  hardened  in  alcohol  and  then  cut.  The  sections,  transverse 
and  longitudinal,  were  stained  in  DELAFIELDs  hamatoxylin  (diluted), 
and  decoloured  in  water  containing  a  little  acetic  acid.  The  sections 
were  examined  in  glycerine  or  Canada  balsam.  In  this  way,  very 
distinct  preparations  of  the  fibrillar  substance  are  obtained;  the  sub- 
stance obtaining  a  distinct  blackish  staining. 

Finally,  I  shall  now  mention  a  method  whose  importance  for 
our  future  knowledge  of  the  nervous  system  can  scarcely  be  over- 
estimated, as  it  affords  really  quite  marvellous  preparations  and  far 
surpasses  every  method  hitherto  known. 

This  is  the  black  chroma-silver  method  of  Prof.  GoLGI  (at  Pavia). 
By  modifications  of  this  method  I  have  obtained  exellent  preparations, 
even  from  the  spinal  nerve-cord  of  Fishes,  in  which  nobody  before 
has  succeeded.  Dr.  FuSARI,  assistent  at  the  histological  laboratory 
in  Pavia,  told  me  that  he  had  worked  for  more  than  a  year  with 
the  nervous  system  of  fishes  without  getting  any  staining  by  this 
method  in  the  spinal  nerve-cord.  In  the  brain,  however,  the  method 
gave  excellent  results,  which  indeed  Dr.  FuSARl's  preparations  also 
richly  prove.  This  gentleman  is,  so  far  as  I  know,  the  only  one 
who,  besides  myself,  has  successfully  up  to  this  time  employed  the 
method  for  fishes.  I  am  largely  indebted  to  him  for  the  communi- 
cation of  his  experiences  obtained  in  a  lengthened  use  of  the  method. 

Besides  on  fishes  and  other  vertebrates,  I  have  also  tried  the 
method  on  several  invertebrates,  not  yet,  however,  with  so  much 


-  78  - 

success,  as  I  think  may,  ultimately,  probably  be  obtained.  Still,  I  have 
also  obtained  staining  here  in  several  groups  of  invertebrates  and, 
in  further  experiments,  it  may  probably  be  possible  to  find  a  modi- 
fication of  the  method,  by  which  it  would  succeed  on  a  larger  scale. 
In  Homanis  I  have  already  obtained  very  good  results;  as  com- 
municated a  year  ago J)  I  have  tried  it  on  Ascidians,  with  some 
success.  In  Mollusca,  I  have  also  seen  so  many  signs  of  a  be- 
ginning reaction  that  I  feel  convinced  that  it  is  possible  to  obtain 
good  staining,  if  only  the  most  suitable  modifications  are  employed. 
This  perhaps  a  near  future  may  enable  us  to  succeed  in. 

As  I  am  still  experimenting  on  this  subject,  I  shall,  for  the 
present,  only  quite  shortly  communicate  the  method  I  at  present 
employ  for  the  spinal  nerve-cord  of  Myxine  glutinosa. 

The  nerve-cord  is  cut  out  of  the  living  animal.  It  must  not  be 
isolated,  but  must,  necessarily,  be  taken  with  the  surrounding  sheaths, 
muscles  and  corda  spinalis  if  any  reaction  at  all  is  to  be  obtained. 
It  is,  however,  also  necessary  to  take  care  that  the  surrounding 
mass  is  not  too  thick,  because  in  that  case  the  hardening  agents 
will  penetrate  too  slowly;  the  half  thickness  of  the  corda  spinalis 
may,  therefore,  very  well  be  removed.  This  done,  it  is  desirable  to  cut 
the  preparation  into  short  pieces  (one  or  a  few  centimetres  long)  or,  if 
one  wishes  to  keep  it  in  longer  pieces,  then,  to  make,  in  these,  deep 
incisions  with  a  sharp  knife  at  short  intervals.  This  done,  the  pre- 
parations are  laid  in  a  solution  of  potassium  bichromate  (2 — 2.5  %) 
for  about  an  hour,  then  the  solution  is  changed  and  made  a  little 
stronger  (up  to  3  %  or  more).  Here  they  remain  for  about  24  hours ;  if 
there  is  plenty  of  solution  it  is  not  generally  necessary  to  change  it 
again.  After  24  hours  the  preparations  are  put  into  a  new  solution  con- 
sisting of  4  parts  of  3  °/0  solution  of  potassium-bichromate,  and  I  part 
osmic  acid  (i  °/o  sol.)  m  this  solution  they  remain  for  about  three  days 
(72  hours) ;  if  there  is  not  sufficient  solution,  it  is  necessary  to  change 
it  after  I  or  2  days.  Sometimes  I  have  also  employed  solutions  with 
more  osmic  acid  (i  part  osm.  ac.  [i  %]  and  3  parts  potass. -bichr.  [3  %j 
as  recommended  by  GOLGI)  sometimes  also  with  less  osmic  acid  ( I  part 
osm.  ac.  and  up  to  6  or  7  parts  potass. -bichr.)  The  good  results 
of  these  different  solutions  depend  much  upon  the  temperature 
maintained  in  the  rooms  where  the  preparations  are  kept.  After 
three  days,  or  about  that  time,  (the  duration  must  be  tested  by 
results)  the  preparations  are  directly  treated  with  silver-nitrate.  At 


l)  Nansen  1.  c.  1886. 


-  79  — 

first  it  is  well  to  wash  them  in  a  weaker  solution  (.5  %)  of  silver- 
nitrate  and  then  afterwards  place  them  in  stronger  solutions  (up  to 
I  %).  After  one  day  the  staining  is  generally  complete.  If  one 
wishes,  however,  to  keep  the  preparations  for  some  time  before  cutting 
them,  they  must  be  kept  in  a  clean  solution  of  silver-nitrate.  It  is 
best,  of  course,  to  keep  them  in  opaque  bottles;  kept  in  that  way 
they  are  not  destroyed  even  for  months.  If  we  wish  to  take  sec- 
tions we  may  cut  them,  directly  from  the  silver  solution,  with  a 
sharp  razor,  under  alcohol.  The  sections  need  not  be  very  thin; 
when  cut,  they  may  be,  preliminarily,  examined  at  once  in  glycerin, 
if  the  staining  proves  to  be  a  good  one  —  i.  e.  if  ganglion  cells  with 
all  their  processes,  and  nerve-tubes  with  their  ramifications,  appear 
quite  dark  or  black  on  a  transparent  field,  —  then  new  sections 
are  made  and  washed  well  in  alcohol  of  about  90  or  96  °/0. 

This  washing  I  have  usually  performed  in  the  following  way: 
the  inferior  end  of  a  funnel  with  a  rather  wide  tube  is  closed  with 
a  plug  of  cotton  so  as  to  form  a  kind  of  filter.  The  sections  are 
placed  upon  the  cotton,  then  the  tube  of  the  funnel  is  filled  with 
alcohol  and  another  plug  of  cotton  is  pushed  down  the  tube  to 
a  certain  distance  above  the  sections;  the  sections  are  thus  situated 
in  a  small  tube-chamber  filled  with  alcohol.  When  now,  however, 
the  body  of  the  funnel  is  filled  with  alcohol,  a  stream  will  slowly 
filter  through  this  chamber  and  thus  the  alcohol  in  it  will  be  con- 
stantly renewed.  By  putting  more  or  less  cotton  into  the  tube  one 
may  regulate  the  velocity  of  the  stream  through  the  chamber.  When 
the  sections  are  sufficiently  washed  (in  4—8  hours)  they  are  placed  in 
absolute  alcohol.  If  there  are  many  sections,  the  alcohol  is  changed 
once  or  twice.  Then  (after  some  hours)  the  sections  are  placed  for 
some  time  (some  hours  or  morek  even  a  day)  in  pure  turpentine  which 
has  to  be  changed  several  times.  Then  they  are  placed  on  the  slide 
in  dammar-resin  dissolved  in  turpentine  and  protected  ~by  no  coverglasses 
if  you  wish  to  keep  the  preparations  for  a  long  time.  The  dammar 
is  at  once  dried  in  a  warmbath  or  in  an  incubator,  where  the 
turpentine  is  very  rapidly  evaporated  and  the  dammar  becomes  quite 
hard  and  smooth;  a  coverglass  prevents  the  turpentine  and  other 
volatile  oils  evaporating.  If  the  dammar  is  not  quite  smooth  in 
some  places  after  drying,  a  little  more  dammar  is  added  to  these 
places,  and  the  drying  repeated.  A  very  good  method  of  mounting 
is,  of  course,  that  recommended  by  Prof.  GOLGI,  it  is,  however, 
a  little  more  complicated.  Prof.  GoLGI  mounts  the  sections,  in 
dammar,  on  coverglasses,  the  coverglasses  are  again  mounted  on 


—  8o  — 

wooden   slides,   in   the  middle  of  which  square  apertures  are  cut  to 
suit  the  glasses. 

This  is  an  exellent  method  and  admits  of  the  employment  of 
oil  immersions,  another  advantage  is,  also,  that  the  sections  can  be 
examined  from  both  sides,  which  is  often  of  great  importance  when 
the  sections  are  thick.  For  many  purposes  the  above  mode  of 
mounting  on  common  glass-slides  will  however  do.  The  preparations 
ought  to  be  kept  in  darkness  when  not  used.  Series  of  sections 
stained  by  this  silver  method  were  obtained  in  the  following  way. 

A  piece  of  the  spinal  nerve-cord  was  disected  out  from  a  stained 
preparation,  and  treated  quite  in  the  same  way  as  above  indi- 
cated for  the  sections:  washed  in  alcohol,  transferred  to  abs.  alcohol, 
then  to  turpentine.  The  only  difference  is  that,  I  let  the  stream  of 
alcohol  pass  quicker  over  it.  From  turpentine  it  is  transferred  to  a 
solution  of  paraffin  in  turpentine  which  is  placed  in  an  incubator  heated 
to  56°  C.  and  to  which  solution  paraffin  is  again  added,  then  into  pure 
paraffin  and  then  imbedded.  The  sections  are  now  made  at  once, 
then  fixed  on  the  slide  or  coverglass  by  collodion,  and  mounted  in 
dammar  in  the  above  indicated  ways.  This  method  may  be  recom- 
mended also  for  general  purposes,  even  where  no  series  are  required, 
as  it  is  much  quicker  and  more  convenient  than  the  other  method 
where  each  section  must  be  treated  and  mounted  separately,  though 
it  certainly  does  not  afford  sections  with  distinct  staining  of  such 
permanency. 

If  convenient,  the  sections  of  silver-stained  preparations  may  also 
be  stained  with  colours  dissolved  in  alcohol,  e.  g.  eosin,  safranin, 
methylen-blue  etc.  In  this  way  very  nice  looking  preparations  may 
be  obtained. 

There  are  probably  a  great  meny  ways  in  which  this  really 
exellent  method  of  GOLGI  may  still  be  improved,  and  I  would  re- 
commend it  to  every  histologist  of  the  nervous  system,  for  further 
experiments. 


Description  of  my  investigations. 

I.    The   structure    of  the    nerve-tubes    in    invertebrates. 

Homarus  vulgaris. 

The  nerve-tubes  of  the  lobster  (Homarus  vulgaris)  consist,  as  is 
well  known,  of  an  external  sheath,  with  nuclei,  and  a  viscous  con- 
tents. They  have  a  rather  homogeneous  and  refractive  appearance 
with  doubly  marked  outlines  when  they  are  examined  in  the  live-state 
under  low  powers  of  the  microscope.1)  On  application  of  higher 
powers,  a  longitudinal  striation,  not  very  prominent  but  still  quite 
distinct,  is  seen  to  form  an  axis  in  the  centre  of  some  large  nerve- 
tubes  (vide  PL  II,  fig.  12,  A  &  B).  This  striated  axis  is,  in  some 
tubes,  very  narrow  (fig.  12,  A)  and  in  the  rest  of  the  tube-contents 
no  striation  is  visible,  but  only  a  few  lines  close  to  the  axis.  In 
other  tubes  the  striated  axis  is  broader,  and  more  numerous  lines 
are  seen  in  the  contents  round  it.  In  some  tubes  the  striated  axis 
is  even  very  broad  (fig.  12,  B),  and  lines  are  visible  almost  through 
the  whole  contents  except  in  the  peripheral  layers ;  they  do  not  usually 
occur  there  or  are,  at  all  events,  very  rare.  Upon  a  careful  exa- 
mination of  several  preparations  it  is,  in  fact,  possible  to  find  every 
stage  of  striation,  from  tubes  with  a  striation  through  the  whole  mesial 
parts  of  their  contents,  to  tubes  with  a  very  narrow  striated  axis  in 
their  centre,  in  all  these  tubes  it  is,  however,  possible  to  observe  a 
concentration  of  the  striation  towards  the  centre  of  the  tubes,  in  such 


T)  For  examination  of  the  tubes  in  the  live-state,  I  think  it  is  best  to  take  long 
pieces  of  the  nerves  or  commissures  with  their  sheaths,  as  intact  as  possible,  and 
examine  them  quickly  in  the  blood  of  the  animal;  a  method  which  is  especially 
recommended  by  Freud  (1.  c.  1882).  The  oesophageal  commissures  I  found  to  be 
very  suitable  for  the  purpose  as  they  are  not  too  thick  and  can  be  very  quickly 
extricated.  I  have,  of  course,  also  isolated  the  tubes  in  the  blood  of  the  animal,, 
and  think  this  method  to  be  very  good,  for  some  purposes,  when  it  is  quickly 
performed. 

6 


—    82    — 

manner  that  the  intervals  between  the  lines  are  narrower  in  the 
centre  than  they  are  more  peripherically,  and  this  is  all  the  more 
prominent  the  narrower  the  axis  is. 

This  striation  in  some  large  nerve-tubes  is  already  observed  and 
described  by  REMAK,  and  subsequently  to  him  a  great  many  other 
writers  have  described  it,  even  H/ECKEL,  who  describes  the  tube- 
contents  as  being  homogeneous,  has  seen  it  (as  mentioned  p.  30 
foot  note  4)  in  some  tubes.  FREUD  assures  us,  however,  that  a 
similar  striation  is  visible  in  all  nerve-tubes  in  a  quite  fresh  state. 
In  spite  of  this  statement  of  FREUD'S  and  in  spite  of  the  application 
of  the  best  lenses  (Zeiss's  new  apochr.  lenses)  I  must  confess  that, 
I  have  found  it  extremely  difficult  to  observe  a  striation  in  a  great 
many  nerve-tubes.  In  the  greatest  number  of  the  slender  tubes 
and  tubes  of  middle  size,  and  even  in  some  large  tubes,  it  required, 
certainly,  a  predisposition  to  see  a  striation,  and  I  really  think  that 
an  uninterested  eye  would,  in  many  cases,  see  no  striation,  even 
when  the  nerves  or  commissures  were  instantly  taken  from  a  quite 
fresh  and  living  animal,  which  FREUD  states  to  be  a  quite  neces- 
sary condition  if  a  striation  is  to  be  seen  in  all  tubes.  I  have 
also,  in  some  rather  slender  tubes,  observed  a  but  little  prominent 
striation  (fig.  12,  &)  but  there  are  a  great  many  tubes  and,  as  men- 
tioned, even  large  ones  which  have  left  me  very  doubtful  as  to 
their  striation  in  the  fresh  state. 

I  do  not  think  this,  however,  to  be  decisive  as  to  the  fibrillar 
or  non-fibrillar  structure  of  these  tubes  in  the  live-state,  because,  a 
priori,  I  think  it  to  be  very  probable  that  if  there  are  two  sub- 
stances in  the  tubes,  their  refractive  difference  is  perhaps  so  small 
that,  when  one  of  the  substances  is  present  only  in  very  slender 
filaments  or  membranes,  the  whole  contents  look  as  a  homogeneous 
mass,  and  that  the  refractive  difference  must  be  altered  by  chemical 
(fixing)  agents  if  the  substances  are  to  become  easily  visible.  That 
such  is  the  case,  and  that  a  distinct  striation  becomes  visible  in  all 
nerve-tubes  when  treated  with  various  fixing  agents  (chromic  acid, 
osmic  acid,  picric  acid,  acetic  acid,  nitric  acid,  potassium-bichromate, 
etc.  etc.)  is  a  so  well-known  fact  that  it,  certainly,  need  not  be 
further  mentioned  here.  (PL  II,  fig.  15  &  16  epresents  some  smaller 
nerve-tubes;  macerated  for  some  hours  in  glycerine,  acetic  acid  and 
water;  a  striation  was  distinctly  visible.) 

Almost  all  writers  who  have  seen  a  striation  in  the  tubes  in 
the  live-state  have  agreed  in  declaring  the  darker  thin  lines  of  the 
striation  to  be  nervous  fibrillae  (»Primitivfibrillen«)  swimming  in  an 


-  83  - 

interfibrillar  substance,  this  also  explains  their  anxiety  to  find  a 
striation  in  all  tubes.  As  will  be  seen  from  my  present  paper,  I  do 
not  agree  with  any  of  those  writers,  and  when  the  further  results  of 
my  investigations  are  known  I  hope  we  shall  find  a  reliable  ex- 
planation of  the  reason  why  a  striation  is  not  more  generally  visible 
than  it  is. 

LEYDIG  forms  an  exception  to  most  other  writers  in  declaring 
the  dark  lines  of  the  striation  to  spring  from  a  structural  support, 
spongioplasm,  and  not  from  nervous  fibrillae  (vide  Leydig  1.  c.  1885, 
mentioned  before,  p.  31).  He  has  no  doubt  arrived  at  a  more 
correct  view  than  any  other  writer,  but  neither  is  he,  in  my  opinion, 
quite  correct,  as  will  shortly  be  seen. 

If  the  view  that  fibrillae  and  interfibrillar  substance  are  present 
in  the  tubes,  was  correct,  it  ought,  in  my  opinion,  to  be  easy 
to  isolate  these  fibrillae  by  splitting  the  tube-sheaths  longitudinally. 
This  is,  however,  very  far  from  being  the  case.  I  have  split  large 
and  small  nerve-tubes  in  the  fresh  state  longitudinally  and  no  fibrillae 
of  the  kind  were  visible,  I  have  teased  them  very  carefully  and 
some  thicker  or  thinner  filaments  became  visible  in  the  extremities 
of  the  tubes.  I  never  succeeded  in  obtaining,  in  spite  of  my  most 
persevering  care,  neither  fresh  preparations  nor  macerated  ones  with 
brushes  of  regular  fibrillae  in  the  extremities  of  the  tubes  similar  to 
those  illustrated  by  H.  SCHULTZE  in  Molluscs  and  Annelids.  The 
filaments  or  fibrillae  visible  at  the  extremities  of  the  nerve-tubes  had 
always  a  somewhat  irregular  appearance,  with  varying  thickness  and 
length,  and  they  certainly  looked  as  if  they  belonged  to  a  supporting 
substance  and  wrere  to  a-  certain  extent  artificially  produced. 

A  viscous  homogeneous  substance,  as  stated  by  SCHULTZE,  was 
certainly  also  visible  between  those  filaments.  This  substance  never 
occurs,  however,  in  such  a  way  that  I  can  say  it  formed  an  inter- 
fibrillar substance,  and  was  diffusively  extended  in  the  nerve-tube. 
At  the  extremities  of  the  nerve-tubes  it  always  appeared  on  pres- 
sure in  the  form  of  regular  small  pearls  issuing  from  the  tube-contents. 
I  never  saw  it  appear  in  large  pearls,  not  even  in  the  large  nerve- 
tubes  where  this  substance,  according  to  a  great  many  writers, 
forms  a  thick  layer  surrounding  a  central  bundle  of  fibrillae.  It  had, 
in  fact,  always  the  appearance  of  these  small  pearls  of  viscous 
substance  issuing  from  a  great  many  extremely  slender  tubes  or 
channels  contaning  the  substance,  situated  close  together  and 
forming  the  whole  contents  of  the  nerve-tubes,  and  this  we  shall 
see  is  really  the  case.  The  filaments  visible  at  the  extremities  of 

6* 


-  84  - 

the  nerve-tubes  gave  always  the  impression  that  they  could  have 
been  produced  by  the  sheaths  of  those  slender  tubes  being  split 
longitudinally  and  thus  forming  fibrillae.  The  viscous  substance  is 
certainly  very  often  seen  adhering  to  these  fibrillas,  but  if  we  look 
carefully  we  will  see  that  it  always  is  in  the  form  of  small  pearls 
adhering  to  the  sides  of  them;  I  have  never  observed  pearls  quite 
surrounding,  or  embracing,  a  filament,  which  certainly  ought  to  occur 
occasionally  if  the  filaments  were  round  fibrillae  swimming  in  an 
interfibrillar  substance  in  the  nerve-tubes. 

I  have  not  been  able  to  obtain  any  further  information  regard- 
ing the  structure  of  the  tube-contents  from  fresh  preparations. *) 

If  we  examine  macerated  preparations  we  will  not  become 
much  wiser,  and  neither  do  they  suffice  to  solve  the  riddle  as  to 
the  real  nature  of  the  fibrillar  structure. 

The  quickest  and  easiest  method  of  maceration  is  that  indicated 
by  BELA  HALLER  (cmfr.  p.  73 — 74).  In  that  way  an  isolation  of  the 
tubes  is  possible  even  after  a  lapse  of  one  or  two  hours;  the  tubes 
exhibit  a  distinct  sheath,  with  sheath-nuclei,  as  well  as  a  distinct  longi- 
tudinal striation  of  their  contents  (fig.  1 5) ;  a  staining  is  not  necessary. 
In  successful  preparations  you  may  find  nerve-tubes  with  extremities 
more  fibrillar  and  brush-like  than  any  of  those  obtained  in  fresh 
preparations.  With  a  good  will  and  skilful  hand  you  can,  by 
teasing  with  fine  needles,  even  improve  this  fibrillar  appearance, 
nay,  you  can  split  not  only  the  tube  contents  but  also  the  sheaths 
longitudinally  into  filaments  or  » fibrillae «.  This  shows,  however, 
that  these  fibrillae  can  be  artificially  produced,  because  most  writers 
agree  in  declaring  the  sheaths  to  be  homogeneous  membranes  of 
connective  substance  (neuroglia).  If  we  now  examine  the  fibrillae 
under  high  magnifying  powers  we  will  find  them  all  to  have  the 
same,  somewhat  irregular  appearance  both,  those  from  the  tube- 
contents  as  well  as  also  those  springing  from  the  tube-sheaths.  If 
we  try  other  maceration  fluids  (e.  g.  weak  sol.  of  alcohol,  amm, 
bichr.  0.03  %»  potass.-bichr.  o.i — 0.03  %,  LANGDOIS's  fluid  etc.)  we 
obtain  very  similar  results.  By  all  these  methods  we  arrive  at  the 


*)  In  PI.  II  fig.  13  an  appearance  of  the  nerve-tubes  is  illustrated  which  I 
have  often  noticed  in  the  fresh  state,  and  which  easily  could  give  rise  to  serious 
mistakes,  a,  a  are  the  hyaline-looking  contents  of  the  nerve-tubes  (belonging  to  a 
peripheral  nerve) ;  6,  b  are  the  sheaths  from  which  septa  (e,  C,  c')  aparently  issue 
and  penetrate  into  the  contents  of  the  tubes.  These  apparent  septa  are,  however, 
an  optic  illusion  only  artificially  produced  by  a  slight  bending  of  the  nerve  in 
which  the  nerve-tubes  are  situated. 


-  85  - 

conviction  that  a  fibrillar  structure  is  present  but  how  this  structure 
is  to  be  regarded,  that  is  the  point  respecting  which  we  remain 
in  uncertainty. 

There  remains  then  only  our  last  but  at  same  time  best  resource 
and  that  is  to  try  what  information  we  can  obtain  from  transverse 
and  longitudinal  sections  taken  from  preparations  fixed,  stained,  and 
hardened  in  the  best  way  our  present  histological  technology  can  afford. 

As  a  very  good  method,  for  this  purpose,  I  would  especially 
recommend  the  following :  the  nerves  or  commissures,  taken  directly 
from  the  living  animal,  are  treatod  with  FLEMMING's  fluid  (chromo- 
aceto-osmic  acid,  strongest  solution  cmfr.  p.  75 — 76)  for  12  to  24  hours, 
then  washed  for  some  hours  in  running  water,  and  stained  with  alum 
haematoxylin  (DELAFlELD's  formula),  or  in  an  aqueous  solution  of 
haematoxylin  (0.5  °  0),  and  afterwards  treated  with  a  solution  of 
potassium-bichromate  (0.5 — I  %)  as  recommend  by  HEYDENHAIN 
(vide  p.  76).  Now  the  structures  are  washed,  again  and  hardened, 
somewhat  quickly  in  alcohol  gradatim.  Preparations  treated  in  this 
way  can,  as  a  rule,  be  very  easily  cut  into  thin  sections,  directly 
enclosed  in  paraffin  only  (vide  p.  76).  Embedding  in  celloidin  or 
paraffin  can  of  course  also  be  employed;  this  can  not,  however,  be 
performed  with  too  great  care  as  we  have  here  to  deal  with  struc- 
tures of  the  most  delicate  nature. 

In  preparations  carefully  treated  in  this  way,  the  nerve-tubes, 
with  their  contents,  are  fixed  in  their  natural  position  and  state,  and 
no  visible  change  of  the  form  has  taken  place. 

If  we  now  examine  good  and  thin  longitudinal  sections,  it  will 
already,  under  low  powers  of  the  microscope,  be  easy  to  observe 
a  distinct  longitudinal  striation  in  the  larger  as  well  as  the  smaller 
nerve-tubes.  The  extremely  slender  longitudinal  lines  or  »fibrillae« 
have  got  a  distinct  blackish  staining,  and  are  situated  with  intervals 
between  them,  just  similar  to  what  we  have  found  in  the  fresh  state. 
The  substance  in  these  intervals  is  not  stained,  and  has  a  homogeneous 
or  rather  a  slightly  granular  appearance.  If  now,  however,  the 
stained  fibrillae  are  real  fibrillae  swimming  in  this  homogeneous  un- 
stained substance,  it  is  evident  that  they,  in  thin  transverse  sections 
of  nerve-tubes,  must  appear  as  minute  black  dots  or  points,  just 
similar  to  what,  VlGNAL  for  instance,  has  also  really  described  and 
illustrated. 

But  what  do  we  find?  --  Instead  of  black  dots,  ^ve  find  in  the 
sections  of  the  tubes  a  delicate  reticulation,  with  minute  circular 
meshes,  apparently  formed  by  extremely  slender  filaments  (fig.  2;  fig.  5>  t). 


—  86  — 

In  these  filaments  we  certainly  find  small  dark  granules  (fig.  6,  o) 
which,  occur  however,  only  in  the  point  or  knots  where  several 
filaments  unite;  they  never  occur  in  the  centres  of  the  meshes.  And 
the  same  reticulation  is  extended  through  the  whole  transverse  sec- 
tion of  every  nerve-tube,  and  fills  the  whole  space  inside  the 
tube-sheat. 

If  we,  now,  compare  the  impressions  which  transverse  sections  of 
the  nerve-tubes  give,  with  those  obtained  by  longitudinal  sections,  there 
can,  in  my  opinion,  be  no  doubt  left  but,  that  the  ,,fibrillce"  of  most 
writers  belong  to  a  substance,  spongioplasm,  forming  a  bundle  af 
slender,  cylindrical  tubes  or  channels  enclosed  in  the  neur  Hem- sheath 
of  each  nerve-tube.  These  primitive  tubes,  if  we  may  call  them  so, 
are  filled  with  the  homogeneous,  viscous  substance,  hyaloplasm,  which 
we  already  know  from  fresh  nerve-tubes.1}  The  granules  in  the  transverse 
sections  show  themselves  to  be  transsected  thicker  longitudinal  fibres 
of  spongioplasm  which,  occur  especially  along  the  longitudinal  edges 
where  several  tubes,  usually  three,  meet.  If  we  imagine  the  spongio- 
plasm as  forming  cylindrical  tubes  laid  or  pressed  together,  it  will 
be  evident,  that  the  spongioplasmic  walls  of  the  different  tubes  will 
unite  and  form  septa,  as  the  spongioplasm  cannot,  of  course,  be 
considered  as  a  quite  solid  and  unadherent  substance;  it  will  also  be 
evident  that,  in  the  corners  where  several  tubes  meet  the  spongio- 
plasmic walls  will  be  still  thicker.2) 

In  this  way,  I  think,  we  may  easily  understand  why  it  was  so 
extremely  difficult  to  isolate  and  get  a  clear  idea  of  SCHULTZE's 
»Primitivfibrillen«.  As  we  have  seen,  they  do  not  exist  in  the  way 
he  has  explained ;  what  he  called  fibrillae,  are  the  spongioplasmic  walls 
between  the  real  » primitive  fibrillae «  or  primitive  tubes  as  I  have 
called  them. 

The  above  description  refers  to  the  structure  of  nerve  tubes, 
which  are,  I  think,  in  the  most  primary  state. 

There  are,  however,  in  the  longitudinal  commissures,  as  well  as 
also  in  the  peripheral  nerves  a  great  many  tubes  exhibiting  a  kind  of 
concentration  towards  an  axis  in  their  centre.  —  As  described  p.  Si, 
a  more  or  less  concentrated  longitudinal  striation  was  visible  in  the 

a)  The  primitive  tubes  have  a  diameter  of  about  .0015 — .0017  Mm.;  their 
size  vary,  however,  and  is  very  difficult  to  measure. 

2)  There  occur,  however,  besides  these  granules  larger  dark  granules,  as  well 
in  transverse  sections  as  in  longitudinal  ones.  They  are  usually  very  sparingly  spread, 
especially  near  the  centres  of  the  nerve-tubes,  as  will  shortly  be  mentioned  and 
hey  are  always  situated  in  the  spongioplasmic  walls  of  the  primitive  tubes. 


-  8;  - 

centre  of  many  large  nerve-tubes.  If  we  now  examine  similar  nerve- 
tubes  in  transverse  and  longitudinal  sections  we  will  find  that,  their 
contents  consist  of  a  bundle  of  slender  cylindrical  primitive  tubes, 
quite  in  the  same  way  as  that  just  mentioned.  The  only  difference  is 
that,  their  central  primitive-tubes  have  a  smaller  diameter  and  thicker 
walls,  and  are  more  deeply  stained  than  the  peripheral  ones,  it 
seems,  indeed,  as  if  they  may  have  been  pressed  more  tightly 
together  and  thus  been  obliged  to  occupy  a  smaller  space,  as  they  have 
on  the  other  hand  got  a  firmer  consistency,  with  thicker  walls.  In 
this  axis,  and  in  its  neighbourhood,  larger  dark  granules,  as  mentioned 
above,  also  occur  more  frequently  than  anywhere  else,  which 
perhaps  contributes  somewhat  to  the  darker  staining.  In  some  nerve- 
tubes  this  concentration  and  forming  of  an  axis  is  so  far  developed 
that  it,  in  transverse  sections  (fig.  3),  appears  as  a,  by  osmic-acid 
and  haematoxylin,  deeply  stained  spot  in  the  centre  of  the  tube. 
In  this  spot  it  is  not  easy  to  distinguish  any  structure  or  primitive 
tubes,  but  in  extremely  thin  sections,  and  by  very  high  powers,  it 
is,  however  possible  to  see  slender  tubes  with  thick,  deeply  stained, 
walls  or  membranes  in  which  granules  occur.  In  longitudinal  sections 
a  longitudinal  striation  appears  as  in  fig.  4.  In  one  end  (fig.  4,  a)  this 
section  has  passed  through  the  periphery  of  the  axis  and,  here,  a 
striation  is  distinctly  visible;  in  the  other  end  (fig.  4,  a1)  the  section 
has,  however,  passed  more  through  the  centre  of  the  axis  and,  here, 
the  staining  is  so  deep  that  almost  no  striation  is  visible,  all  the  less 
from  the  section  being  somewhat  thick. 

Usually  however  this  concentration  is  not  so  distinctly  developed 
as  here.  Nay,  we  can  indeed  find  every  degree  of  development, 
from  the  primary  state  where  no  concentration  at  all  can  possibly 
be  traced  to  have  taken  place,  up  to  an  axis  as  described. 
Fig.  2,  t,  t',  t"  thus  represent  sections  of  fibres  with  different  degrees 
of  concentration,  from  a  very  slight  one  where  we  can  only  see 
that  the  primitive  tubes  are  somewhat  deeper  stained  in  this  central 
part  than  in  the  rest  of  the  tube  and  in  some  nervn-tubes  even  this 
is  not  visible  (£*). 

It  is  the  nerve-tubes  with  such  an  axis  that,  previous  writers 
have  called  myeloid  fibres;  with  what  right  we  will,  on  a  later 
occasion,  have  an  opportunity  of  examining. 

However  we  consider  this  formation  of  an  axis ;  in  one  thing 
we  cannot  be  in  doubt,  viz.,  that  the  whole  contents  of  the 
nerve-tubes,  wether  they  have  an  axis  or  not,  is  of  real  nervous 
nature,  because  the  constructing  element  in  the  ivhole  contents  through- 


—  88  — 

out  is,   as  we  have  seen,  the  primitive  tube";  that  is  the  thread  o 
which  the  whole  rope  is  woven. 

In  transverse  sections  of  some  nerve-tubes,  largish  vacuoli  or, 
as  it  were,  primitive  tubes,  can  be  seen  (fig.  5,  t\  t" ,  t"'\  fig.  2,  d). 
These  vacuoli  often  occur  in  a  peripheral  layer  just  inside  the 
sheath  of  the  nerve-tubes  (fig.  5,  t\  £").  I  suppose,  however,  this 
appearance  to  be  to  a  great  extent  artificially  produced.  In  some 
cases  the  whole  contents  of  the  nerve-tubes  has  the  same  appearance 
(fig.  5,  ^)  and  looks  as  if  it  were  principally  constituted  of  large  pri- 
mitive tubes,  amongst  which  only  some  few  primitive  tubes  of  the 
common  size  are  seen.  I  do  not  feel  disposed  to  suppose  this 
appearance  to  be  only  an  artificial  and  postmortem  product,  though 
I  cannot  with  certainty  account  for  its  nature  at  present. 

We  have,  hitherto,  only  mentioned  nerve-tubes  of  a  relatively 
large  diameter;  these  are  especially  numerous  in  the  longitudinal  and 
oesophageal  commissures,  as  will  be  seen  from  fig.  I,  which  re- 
presents a  transverse  section  of  an  oesophageal  commissure.  We 
find,  there,  transsected  nerve-tubes  of  very  varying  diameter. l)  In  a 
great  many  large  tubes  (t,  t\  #,)  a  deeply  stained  axis  is  visible;  in 
other  large  tubes  (£")  no  axis  is  visible,  n.t  represent  somewhat 
smaller  nerve-tubes  running  in  a  thick  bundle  along  the  centre  of 
the  commissure,  s.nt  represent  very  small  nerve-tubes  situated  more 
peripherically. 

Large  nerve-tubes,  usually  having  an  axis,  occur  very  frequently 
also  in  the  peripheral  nerves,  vide  fig.  7,  t\  they  have  generally,  as 
will  be  seen,  very  stout  sheaths,  and  are  prominent. 

On  the  other  hand  there  are,  especially  in  the  peripheral  nerves, 
a  great  multitude  of  extremely  slender  nerve-tubes;  indeed,  the 
peripheral  nerves  principally  consist  of  such  nerve-tubes  (fig.  7,  nt). 

These  nerve-tubes  have  so  small  a  diameter  that,  I  have,  usually, 
only  observed  some  few  primitive  tubes  inside  their  sheaths  (vide 
fig.  8,  nt)\  in  a  large  number  of  them  I  have  even  detected  no  pri- 
mitive tubes,  and  I  believe  they  are  partly  constructed  of  only  one 
primitive  tube,  the  sheath  of  which  is,  however,  much  stouter  than 
the  spongioplasmic  sheaths  inside  the  larger  nerve-tubes.2) 

These  slender  nerve-tubes  are,  in  most  nerves,  usually  arranged 
or  united  in  bundles,  and  are  enclosed  in  neurilem-sheaths,  larger 
fagots  of  these  primitive  bundles  are  again  enclosed  in  larger  and 

])  We  can  find  nerve-tubes  with  a  diameter  of  more  than  0.140  Mm. ;  and 
we  can  find  nerve-tubes  with  a  diameters  of  less  than  0.003  Mm. 

'*)  The  diameter  of  these  smallest  nerve-tubes  measures  about  .0017  Mm. 


stouter  neurilem-sheaths,  and  so  on,  concentrically,  untill  at  last  the 
whole  nerve  is  enclosed  in  one  common  external  neurilem-sheath.1) 
It  is,  indeed,  very  difficult  to  tell  here  where  the  separation  of  indi- 
vidual nerve-tubes  really  begins,  if  we  do  not,  as  I  have  done,  con- 
sider the  smallest  tubes  with  distinct  stout  sheaths  as  representing, 
^each  of  them,  a  nerve-tube,  consisting  of  some  few  primitive  tubes 
only,  or,  in  a  great  many  cases,  of  one  primitive  tube  only. 

When  we  examine  a  transverse  section  of  a  nerve,  we  will,  as 
a  rule,  observe  a  great  many  dark  granules  or  dots;  these  dots, 
appear,  however,  on  closer  examination,  to  be  thickenings  in  the 
tube-sheaths  along  the  longitudinal  edges  where  several  tubes  meet 
(vide  fig.  8,  p). 

The  sheaths  of  the  nerve-tubes.  —  Our  attention  has 
hitherto  been  directed  to  the  contents  of  the  nerve-tubes  only.  We 
will,  now,  before  we  leave  the  nerve-tubes  of  the  lobster,  pay  a 
little  attention  to  the  sheath  which  envelopes  the  contents.  This 
sheath  consists  of  a  connective  substance  which  is,  in  my  opinion, 
the  same  substance  as  the  neuroglia,  or  »connnctive-tissue«,  as  many 
authors  call  it,  which  extends  through  the  whole  central  nervous 
system  of  every  animal  I  have  had  under  investigation.  This 
sheath  of  connective  substance,  or  for  the  sake  of  brevity  we 
will  call  it  neuroglia- sheath,  has,  also,  a  great  resemblance  to  the 
spongioplasm  separating  the  primitive  tubes,  and  it  is,  in  fact,  very 
often,  extremely  difficult  to  distinguish  the  two  substances  from  each 
other  viz.  the  spongioplasm  occurring  inside  the  nerve-tubes  and  the 
ganglion  cells  —  as  will  subsequently  be  described  —  and  the 
neuroglia  enveloping  the  nerve-tubes  and  the  ganglion  cells  with 
sheaths  or  membranes;  the  two  substances  are  often  so  intimately 
united  that  it  is  really  impossible  to  decide  where  the  line  of  de- 
marcation can  be  drawn.  There  is  one  difference,  however,  viz.  that 
in  the  spongioplasm  no  nuclei  occur,  whilst  nuclei  occur  in  the 
neuroglia.  LEYDIG'S  view  that  it  is  the  same  substance,  spongioplasm, 
which  penetrates  from  whithout  into  the  nerve-system  and  even  into 
the  nervous  elements,  is,  in  my  opinion,  not  yet  sufficiently  well  sub- 
stantiated. If  I  had  to  choose,  I  would,  however,  much  prefer  that 
theory  to  VEJDOVSKY'S,  according  to  which  the  inner  connective 
substance  (i.  e.  neuroglia)  is  a  product  originating  in  the  ganglion 
cells;  I  really  do  not  understand  how,  in  that  case,  to  account  for 


T)  This  separation  into  bundles  and  fagots  is,  however,  les  prominent  or  not 
present  at  all  near  the  origin  of  the  nerves  in  the  central  nerve-system. 


—  90  — 

the  neuroglia-cells  and  nuclei,  and  how  they  can  be  produced  from 
ganglion  cells. 

In  my  opinion  there  can  be  no  doubt,  but  that  the  neuroglia  is 
a  separate  tissue  composed  of  cells  springing  from  the  ectoderm, 
just  as  the  ganglion  cells  spring  from  other  ectodermal  cells. 

The  doubly  marked  outlines  which  are  visible  in  nerve-tubes 
isolated  in  the  fresh  state,  but  which  are  specially  distinct  in  macerated 
nerve-tubes,  are  produced  by  the  sheath  which,  as  a  cylinder,  enve- 
lopes every  nerve-tube  and  forms  its  outer  isolating  layer.  It  con- 
sists of  one  or  several  concentric  layers  of  connective  substance  or, 
as  we  just  above  called  it,  neuroglia,  and  is  easily  seen  in  transverse 
as  well  as  in  longitudinal  sections;  the  sheaths  of  large  nerve-tubes 
are  especially  very  prominent  and  stout.  When  there  are  several 
layers;  which  is  generally  the  case  in  large  nerve-tubes,  especially 
those  of  the  peripheral  nerves;  then  the  innermost  layer  is  the 
strongest,  most  differentiated,  and  refractive  one  (vide  fig.  15).  These 
concentric  layers  of  the  tube-sheaths  are  seen,  in  fig.  7,  round  the 
large  nerve-tubes  (£),  and  in  some  peripheral  nerves  they  are  very 
prominent. 

In  the  sheaths,  nuclei  occur.  These  nuclei  are,  as  mentioned, 
quite  identical  with  the  usual  nuclei  of  the  neuroglia;  they  have  an 
oblong  form,  with  a  granular  appearance,  and  are  usually  situated  on 
the  outer  side  of  the  sheaths  (vide  fig.  2,  k\  fig.  5,  k\  fig.  8);  they 
occur,  however,  also  on  the  inside  of  the  sheath,  consequently  in 
the  tube  itself  (vide  fig.  4,  &;  fig.  5,  &';  fig.'  13,  &)• 

Nephrop  norvegicus. 

We  obtain  very  similar  results  as  to  the  structure  of  the  nerve- 
tubes  on  examining  Nephrops  norvegicus;  in  this  respect  Nephrops 
so  very  much  resembles  Homarus  that  it  is  really  unnecessary  to 
give  any  special  description  of  it.  We  can,  in  fact,  observe,  in  the 
large  nerve-tubes,  the  same  tendency  towards  a  concentration  of  a 
sort  of  axis  in  their  centre,  though  it  is  not  so  prominent  in  Nephrops 
as  in  Homarus,  and  neither  have  I  observed  so  narrow  and  deeply 
stained  axes  in  the  former  as  I  have  in  the  latter. 

In  the  transverse  sections  of  many  nerve-tubes,  I  have  observed 
similar  large  meshes  as  those.  I  have  mentioned  in  the  nerve-tubes 
of  Homarus  (cmfr.  fig.  5,  ^).  They  had  often  a  very  regular  ap- 
pearance and  looked  as  if  they  really  were  large  transsected  primi- 
tive tubes. 


In  the  Annelids  we  find  a  structure  of  the  nerve-tubes  very 
similar  to  what  is  described  in  Homarus. 

Polychsstes. 

As  representative  of  the  Polyclicetes  I  have  examined  several 
species  of  Nereis  (N.  virens,  N.  pelagica  and  others)  and  also, 
occasionally,  Neplitys,  Leanira  etc.  and  can  only  say  that,  in  them 
all,  I  have  found  the  same  structure  of  the  nerve-tubes  repeating  itself. 

In  the  Nereida,  to  which  I  have  especially  paid  attention,  we 
find  nerve-tubes  of  every  thickness,  ranging  from  the  two  gigantic 
nerve-tubes  running  along  the  centre  of  the  ventral  nerve-cord  (vide 
fig.  14  and  fig.  10)  down  to  nerve-tubes  consisting  of  only  one  pri- 
mitive tube,  like  what  is  described  in  Homarus.1) 

The  minute  structure  is,  of  course,  easiest  to  study  in  the  larger 
nerve-tubes.  If  we  examine  them  under  high  powers  of  the  micro- 
scope, in  good  preparations, 2)  we  find  that  quite  similar  primitive 
tubes  constitute  their  contents,  in  the  same  way  as  described  in  re- 
spect of  the  nerve-tubes  of  Homarus.  The  differentiation  in  primi- 
tive tubes  is,  however,  not  so  distinctly  marked  nor  so  easily  seen 
as  it  is  in  Homarus,  perhaps,  partly,  because  the  primitive  tubes 
have  a  smaller  diameter,3)  partly,  because  their  spongioplasmic 
sheaths  or  membranes  are  thinner  and  less  distinct.  In  fact,  it  often 
requires  the  best  lenses,  and  very  carefully  prepared  preparations, 
to  see  any  structure  in  the  contents,  and  this  is  evidently  the  reason 
why  so  many  authors  have  not  understood  these  structures,  and 
have  supposed  these  large  nervetubes  to  be  lymphoid  vessels  etc. 
Of  a  concentration  towards  an  axis,  there  are  only  very  slight  indi- 
cations in  some  rather  slender  nerve-tubes.  The  large  nerve-tubes 
(» gigantic  fibres «)  have  always  primitive  tubes,  only  slightly  marked, 
and  of  the  same  size  and  appearance  throughout.  Fig.  10  represents 
the  central  part  af  a  transverse  section  through  the  ventral  nerve- 
cord,  where  one  of  the  two  central  largest  nerve-tubes  (t)  (of  the 
other  only  a  small  part  is  seen),  also  some  more  ventrally  situated, 
not  so  large  nerve- tubes  (tlt  t2,  t$)  and  a  great  deal  of  the  surround- 
ing small  nerve-tubes  (nt)  are  seen.  Fig.  9,  b  represents  a  longi- 
tudinal section  of  one  of  the  largish  nerve-tubes  (cmfr.  fig.  10,  £2); 

T)    In   my    preparations    I    have    found    nerve-tubes   with    diameters    measuring 
from  .030  Mm.   down  to   .0018  Mm. 

2)  For  this  purpose  the  same  method  of  fixing  etc.  can  be  recommended  as 
we  have  recommended  for  the  neve-tubes  of  Homarus  (vide  p.  85). 

3)    In    my   preparations    I    have  generally  found  the  diameter  of  the  primitive 
tubes  to  be  about  .0012  Mm.   or  less. 


—  92  — 

nt  represents  smaller  surrounding  nerve-tubes.  As  will  be  seen, 
there  is,  in  these  tubes,  a  longitudinal  striation  quite  similar  to  what 
we  already  have  experienced  in  Homarus. 

The  nerve-tubes  of  the  peripheral  nerves  have  quite  a  similar 
structure  to  those  of  the  ventral  nerve-cord. 

The  sheaths  of  the  nerve-tubes  are  formed  by  the  neuroglia, 
in  the  same  way  as  they  are  in  Homarus  (cmfr.  fig.  10);  they  are, 
however,  not  so  stout,  and  nuclei  occur  very  sparingly  in  them. 

L.umbricu.8  agricola. 

In  Lumbricus,  the  nerve-tubes  in  the  ventral  nerve-cord  have  a 
more  uniform  and  relatively  smaller  size  (the  three  » gigantic  nerve- 
tubes «  excepted  [fig.  n,  t,  t,  *,])  than  they  have  in  the  ventral  nerve- 
cord  of  the  Polychaetes  examined;  the  nerve-tubes  have,  however, 
a  quite  similar  structure,  their  contents  being  composed  of  the  same 
elementary  constituents,  viz.  the  primitive  tubes,  which  certainly  have 
a  small  diameter,  but  are,  in  the  small  nerve-tubes,  only  present  in 
limited  number;  in  some  cases  nerve-tubes  consist  of  apparently 
only  one  primitive  tube;  it  is  consequently  somewhat  similar  to  what 
is  described  in  Nereis  and  Crustaceans. 

The  nerve-tubes  have  neuroglia-sheaths  which  are  very  prominent 
in  osmic-haematoxylin  preparations,  vide  fig.  n,  nt. 

The  nerve-tubes  of  the  peripheral  nerves  have  a  quite  similar 
structure  to  those  of  the  ventral  nerve-cord. 

In  the  ventral  nerve-cord  of  Lumbricus,  there  are,  as  is  well 
known,  three  large  tubes  running,  dorsally,  through  the  whole  length 
of  the  nerve-cord.  These  tubes,  which  are  generally  called  »CLAPA- 
REDE'S  gigantic  nerve-fib  res «,  have  given  rise  to  much  dispute  and  in 
the  views  of  the  various  writers  very  different  functions  have  been 
attributed  to  them.  Some  writers  have  called  them  supporting  rods, 
the  function  of  which  is  to  give  support  and  rigidity  to  the  ventral 
nerve-cord  under  the  many  movements  of  the  animal;  that  is,  for 
instance,  VEJDOVSKY'S  view;  other  writers,  again,  consider  them  as 
homologous  with  the  corda  spinalis  of  the  vertebrates;  some  writers 
call  them  vessels,  etc.  etc.,  and  finally  a  great  many  writers  call 
them  nerve-tubes.  Lately,  LEYDIG  has  published  a  paper  on  this 
subject  (1.  c.  1886)  in  which  he  very  emphatically  maintains  their 
exclusively  nervous  nature. 

After  having  examined  their  structure,  I  do  not  think  there  can 
be  any  doubt  that  LEYDIG  is  right,  and  that  VEJDOVSKY,  who  ex- 
presses himself  with  so  much  self-confidence,  is  entirely  wrong.  It 
was  indeed  to  be  hoped  that  those  organs  might  at  last  enjoy  that 


—  93  — 

rest  wich  they  so  well  deserved  and  that  they  might  now  be  left  in 
peace  in  the  rubric  of  nervous  elements. 

Seeing  that,  comparatively,  few  authors  have  been  in  doubt  as  to 
the  nervous  nature  of  the  large  nerve-tubes  of  the  Polychaetes,  it  is  really 
very  strange  that  there  has  been  so  much  dispute  about  these  organs 
in  Lumbricus.  —  If  we  examine  them  closely  under  high  powers  of 
the  microscope,  in  carefully  prepared  sections,  we  will,  instead  of  the 
homogeneous  contents  usually  described  in  them,  find  a  contents 
with  quite  the  same  structure  as  above  described  in  the  large  nerve- 
tubes  of  Nereis,  it  being  composed  of  a  large  bundle  of  primitive 
tubes,  the  spongioplasmic  sheaths  of  which  are,  however,  very  thin 
and  but  little  differentiated;  the  primitive  tubes  are  thus  extremely 
difficult  to  observe,  and  this  is  naturally  the  reason  why  no  author 
has  noticed  any  striation  in  these  large  tubes,  and  why  their  contents 
has  always  been  described  as  being  homogeneous. 

I  have  not  been  able  to  find  any  spongioplasmic  reticulation  or 
septa,  similar  to  what  LEYDIG  has  described  and  illustrated  (1.  c. 
1886  p.  594).  I  cannot  therefore  explain  their  absence  in  any  other 
way,  than  that  his  preparations  have  not  been  quite  succesful,  there 
may,  perhaps,  have  been  some  irregularities  in  them  produced  by 
shrinking  of  the  tube-contents,  which  indeed  very  often  happens, 
especially  in  those  thick  tubes.  From  my  own  sad  experience,  I  can 
testify  that  it  sometimes  happens  in  spite  of  an  apparently  very 
careful  preparation.  Judging  from  LEYDIG'S  illustration  I  should 
also  say  that  such  has  been  the  case. 

The  whole  contents  of  the  three  nerve-tubes  consist  of  primitive 
tubes,  having  the  same  size  and  diameter  throughout,  as  will  be  seen 
in  fig.  n,  and  no  concentration  towards  an  axis  is  visible  in  the 
centre  of  them.1) 

The  sheaths  of  the  nerve-tubes.  —  The  three  large  nerve- 
tubes  are  surrounded  by  very  thick  and  prominent  neuroglia-sheaths 
consisting  of  many  layers  or  membranes  of  connective  substance. 
When  LEYDIG  says  that  they  are  closely  surrounded  by  several 
slender  nerve-tubes,  he  is  scarcely  quite  correct.  I  have  certainly 
observed  nerve-tubes  between  them,  and  in  the  neuroglia  surround- 
ing them,  but  they  are  scarce,  and,  in  my  opinion,  the  three  large 
nerve-tubes  are  principally  surrounded  by  connective  substance,  or 
neuroglia,  forming  thick  sheaths  round  them.  This  neuroglia  does 
not,  however,  differ  from  the  neuroglia  of  the  rest  of  the  nervous 
system,  in  anything,  else  than  that  it  occurs  in  thicker  layers  than  is 

l)  In  my  preparations  the  diameter  of  the  primitive  tube  measured  about 
.0016  Mm. 


—  94  - 

generally  the  case,  and  is  more  sparingly  mixed  with  nervous  ele- 
ments. As  will  be  seen  in  fig.  n,  it  has,  also,  an  appearance  some- 
what different  from  the  rest  of  the  fibrillar  mass,  exhibiting,  as  it 
does,  a  prominent  disposition  to  form  concentric  layers  or  mem- 
branes round  the  tubes.  Between  the  tubes  may  also  be  seen  septa 
(fig.  n,s),  apparently  of  the  same  substance,  issuing  from,  or  rather 
adhering  to,  the  neurilem-slieatli  or  perineurium,  enveloping  the 
ventral  nerve-cord  inside  the  muscular  layer  (fig.  n,  m).  In  the 
neuroglia-mass  surrounding  the  three  large  nerve-tubes  nuclei  occur 
very  often  (fig.  n,  Jc),  they  are  oblong,  have  a  granular  appearance 
and  are  quite  similar  to  the  common  neuroglia-nuclei. 

The  Mollusca. 

Judging  from  the  latest  descriptions  of  the  nervous  system  ot 
the  Molluscs,  we  should  expect,  here,  to  find  very  extraordinary 
conditions.  HALLER  assures  us  that  there  exists  no  connective-tissue 
within  the  nervous  system  of  the  more  primary  Molluscs  (Chiton, 
Patella,  Rhipidoglossa  etc.)  and  that  there  really  exists  no  nerve-fibres 
or,  as  I  call  it,  nerve-tubes  only  »Primitivfibrillen«  which  unite  in 
large  bundles  to  form  the  peripheral  nerves.  The  same  statements 
are  quite  recently  made  by  RAWITZ  (as  mentioned  p.  70)  as  to  the 
nervous  system  of  the  Acephales;  this  latter  writer  seems,  however, 
in  these  as  well  as  other  respects,  to  walk  very  closely  in  the 
footsteps  of  HALLER. 

It  was  therefore  with  no  small  interest  that  I  began  the  investigation 
of  this  group.  I  chose  Patella  vulgata  for  my  purpose,  because  it 
was  on  the  one  hand  a  large  species,  and  a  rather  primary  mollusc, 
and  on  the  other  hand  I  could  get  plenty  of  it,  here,  in  Bergen. 

I  must  confess,  I  had  some  doubt  as  to  the  correctness  of  BELA 
HALLER's  statement  that  no  connective-tissue  (i.  e.  neuroglia)  existed, 
and  my  researches  have  not  at  all  diminished  my  doubts;  on  the  con- 
trary, I  found  a  well  developed  neuroglia,  with  neuroglia-nuclei  of  the 
typical  form,  and  sheaths  enclosing  nerve-tubes.  This  neuroglia  is, 
however,  not  so  well  developed  as  we  have  seen  it  in  Annelids  and 
Crustaceans.  It  took  me  some  time,  therefore,  to  come  to  a  full 
understanding  of  the  real  structure  of  the  nerves  and  the  nerve-tubes. 
Fresh  isolated  nerves,  as  well  as  nerves  macerated  in  different  ways, 
I  could,  usually,  though  always  with  some  difficulty,  split  up  into 
fibrillae,  which,  however,  varied  somewhat  in  size  (fig.  17).  In 
sections,  longitudinal  as  well  as  transverse,  I  came  to  similar  results, 
and  could  really  distinguish  longitudinally  running  darker  stained 
fibrillae,  of  somewhat  varying  size;  in  transverse  sections  they 


—  95  — 

appeared  as  dark  points;  in  longitudinal  srctions  as  dark  lines, 
and  in  oblique  sections  I  could  see  them  as  short  semi-erect  rods. 
There  could  be  no  doubt  that  real  fibrillae  of  some  kind  were  pre- 
sent, and  I  was  almost  disposed  to  consider  HALLER'S  description 
of  the  nerves,  as  consisting  of  bundles  of  » Primitivfibrillen « ,  to  be 
right.  Besides  these  fibriUae  I  could,  however,  in  transverse  sections 
see  a  reticulation,  as  if  produced  by  transsected  tubes;  in  this  re- 
ticulation the  transsected  fibrillae  were  always  situated  in  the  walls 
of  the  meshes,  and  especially  in  the  junctions  of  the  walls  of  several 
meshes  (i.  e.  nerve-tubes)  the  whole  had,  consequently,  somewhat 
of  a  resemblance  to  transverse  sections  of  nerves  of  Annelids  and 
Crustaceans.  I  could,  however,  in  preparations  obtained  in  my  usual 
ways  come  to  no  certain  results.  There  was,  besides,  also  another 
circumstance  which  made  me  certain  that  those  fibrillae  could  not 
be  real  nervous  fibrillae  as  HALLER  and  RAWITZ  suppose,  this  was 
their  staining,  which  was  quite  that  specially  pertaining  to  neuroglia. 

Finally,  I  succeeded  in  finding  a  method  of  preparing  the  nerves 
which  gave  a  quite  clear  idea  of  their  structure.  This  method  con- 
sists in  treating  pieces  of  Patella  (the  pedal  muscular  disc  in  which  the 
pedal  nervercords  are  imbedded)  for  about  48  hours  in  osmic  acid 
(i  %)  then  washing  them,  afterwards  cutting  them  and  staining  the 
sections  as  described  above  (p.  77). 

Examination  of  sections  obtained  in  this  way  left  no  doubt  as 
to  the  structure  of  the  nerves ;  they  contain  nerve-tubes  having  di- 
stinct neuroglia-sheaths,  in  which  thicker  longitudinally  running  fibres 
are  situated  (cmfr.  fig.  19). l)  These  neuroglia-fibres  are  the  »Primitiv- 
fibrillen«  of  HALLER  and  RAWITZ.  Besides  this,  there  occur  stouter 
neuroglia  septa  orriginating  in  the  outer  neurilem -sheath.  They 
ramify  and  divide  the  nerve-tubes  into  larger  or  smaller  bundles 
(fig.  19,  s,  s7).  Fig.  19,  Jc,  k  are  nuclei  occurring  in  these  neu- 
roglia-septa. 

The  nerve-tubes  are  of  somewhat  varying  size,  and  are  usually 
slender  and  seem  to  contain  but  few  primitive  tubes.  I  measured 
nerve-tubes  having  a  diameter  of  .002 — .006  Mm.  In  some  nerves 
the  nerve-tubes  are,  however,  much  smaller.  Fig.  20  is,  for  instance, 


])  A  glance  at  the  origin  of  the  small  lateral  nerves  a'  and  b'  (fig.  19)  gives 
a  very  clear  idea  of  the  structure  of  the  nerve-tubes,  s',  s'  are  the  neuroglia-septa 
which  separate  the  bundles  of  nerve-tubes,  forming  these  small  nerves,  from  the  rest 
of  the  great  nerve.  In  a  and  b  some  of  these  nerve-tubes  are  transversally  trans- 
sected in  a'  and  b'  they  are  longitudinally  transsected.  It  is  very  distinctly  see 
that  the  »fibrillge«  in  fact  belong  to  the  tube-sheaths. 


-96- 

an  illustration  of  a  longitudinally  transsected  nerve,  drawn  under 
higher  powers  than  fig.  19.  The  nerve-tubes  are,  however,  narrower 
in  fig.  20,  than  they  are  in  fig.  19  (cmfr.  a'  and  6').1) 

The  reason  why  the  longitudinal  neuroglia  fibres  in  the  nerves  and 
pedal  nerve-cords  are  isolated  in  macerated  preparations  is,  evidently, 
that  they  are  stouter  and  stronger  than  the  rest  of  the  tube-sheaths, 
and  thus  are  separated  from  them.  In  carefully  treated  macerated 
preparations  it  is,  however,  possible  to  see  the  nerve-tubes.  Fig.  17 
and  1 8  represent,  for  instance,  such  preparations,  where  nerve-tubes 
with  a  longitudinal  striation  are  distinctly  visible,  and  even  to  some 
extent  isolated ;  an  isolation  of  them  is,  however,  as  a  rule,  extremely 
difficult,  for  the  reason  just  indicated  above.  In  the  extremities  o 
these  nerve-tubes  we  can  see,  in  some  of  them,  isolated  fibrillse, 
which,  partly,  are  neuroglia  fibrillae,  partly,  spongioplasmic  fibrillae. 
Pearls  of  hyaloplasm  are  adherent  to  the  sides  of  them  (fig.  17,  a,  &,  d). 

The  Ascidians. 

Finally,  I  will  here  mention  a  group  of  invertebrates  which  some 
time  ago  were  the  subject  of  my  study,  the  results  of  which  I  have 
hitherto  only  given  in  a  preliminary  report  (1.  c.  1886).  This 
group  is  the  Ascidians.  The  peripheral  nerves  of  the  Ascidians 
have  a  structure  very  similar  to  what  is  described  of  the  peripheral 
nerves  of  Homarus  (cmfr.  fig.  7),  exept  as  regards  the  large  tubes; 
those  do  not  occur  in  the  Ascidian-nerves. 

The  whole  nerve  is,  in  the  Ascidians,  divided  by  the  neuroglia, 
or  inner  neurilem,  into  large  bundles,  these  are  again  divided  into 
smaller  and  these,  again,  into  still  smaller  bundles,  the  subdivision  being 
repeated  until  we  at  last  arrive  at  the  nerve-tubes,  which  are  very 
slender,  and  contain  but  few  primitive  tubes;  a  great  many  nerve- 
tubes  seem  to  consist,  even,  of  only  one  primitive  tube,  something 
similar  to  what  we  have  described  in  Homarus.  Very  often,  it  is 
even  very  difficult  to  decide  what  are  only  primitive  tubes,  and  what 
are  nerve-tubes,  and  again  what  are  bundles  of  nerve-tubes,  as  there 
is  often  seen,  in  transverse  sections,  a  subdivision  into  smaller  and 
smaller  tubes,  and,  the  higher  and  higher  we  employ  the  powers  of 
the  microscope  the  more  and  more  do  we  trace  out  minute  tubes. 
At  last,  however,  under  very  high  powers  we  are  able  to  observe 


a)  Sometimes  large  vacuoles  are  seen  in  transverse  section  of  nerves  (cmfr. 
fig-  19,  ci  d)]  whether  these  vacuoles  really  are  transsected  nerve-tubes  I  am  not 
in  a  position  to  decide  at  present. 


-  97  — 

some  very  slender  tubes  inside  which  no  subdivision  is  visible,  and 
these  we  must  supose  to  be  the  primitive  tubes,  a  small  bundle  of 
which  generally  forms  a  nerve-tube. 

Fig.  21,  which  represents  the  transverse  section  of  an  anterior 
nerve  of  Phallusia  venosa,  will,  I  hope,  give  easily,  at  a  glance,  a 
correct  idea  of  the  structure  of  the  peripheral  nerves  of  the  Ascidians. l) 
Fig.  22  represents  a  part  of  a  longitudinal  section  through  a  nerve, 
seen  under  high  powers  of  the  microscope;  the  primitive  tubes  are, 
here,  visible,  being  transsected  in  their  curved  course,  the  curvature 
in  which  arises  from  the  contraction  of  the  nerve,  ts,  is  are  the 
sheaths  of  the  nerve-tubes.  Some  of  them  (a  and  6)  are  stouter 
and  more  prominent  than  the  others ,  those  are  probably  transsected 
neuroglia-septa  enclosing  bundles  of  nerve-tubes.  In  one  of  these 
septa  is  seen  a  neuroglia-nucleus  (n). 

The  division  of  the  nerve-tubes  into  different  smaller  and  larger 
bundles  is,  in  the  Ascidians,  as  well  as  in  the  Molluscs,  Crustaceans 
etc.  less  prominent  near  the  origin  of  the  nerves;  close  to  the  nerve- 
roots  there  is,  in  the  Ascidians,  scarcely  any  division  visible,  and  a 
great  many  of  the  nerve-tubes  appear,  even,  to  be  broken  up  into 
nerve-tubes  of  a  much  smaller  diameter ;  the  reason  of  this  appearance 
we  will  in  a  later  chapter  have  an  opportunity  of  discussing. 

The  structure  of  the  nerves  of  the  Ascidians  reminds  much  of 
what  we  have  found  in  the  Molluscs.  The  nerve-tubes  are  separated 
by  only  very  thin  sheaths  (cmfr  fig.  22,  ts)  in  which  thickish  fibres 
are  situated,  especially  along  the  concreting  longitudinal  edges;  in 
transverse  sections  these  fibres,  when  transsected,  appear  as  darker 
dots,  situated  in  the  corners  of  the  meshes,  and  are  produced  by 
the  transsected  sheaths  of  the  nerve-tubes  (vide  fig.  21). 

Summary. 

The  results  of,  these,  our  researches  on  the  minute  structure  of 
the  nerve-tubes  of  various  invertebrates,  we  may,  I  think,  assume  to 
be  applicable  to  the  nerve-tubes  of  all  invertebrates  of  such  a  high 
organisation  as  to  posess  a  well  developed  nervous  system,  i.  e.  all 
invertebrated  bilaterates.  From  LANG'S  memoirs,  we  may  gather 
that  the  Polyclades  and  Trematodes  have  nerve-tubes  of  the  same 
type  described  in  this  chapter  (cmfr.  p.  52 — 54);  from  FRAIPONT's 


')    The  primitive  tubes  are  not  seen  in  this  illustration. 


—  98  — 

memoir  on  the  Archiannelids  we  may  gather  that  this  is  the  case 
also  in  those  animals  (cmfr.  p.  57),  etc.  etc.1) 

Of  the  results  of  our  researches  we  may  therefore  give  the 
following  summary: 

i)  The  nerve-tubes  of  the  invertebrated  bilaterates  consist  of  an 
external  consistent  sheath  with  a  viscous  contents. 

2]  The  sheaths  are  formed  by,  or  belong  to,  the  connective  sub- 
stance extending  through  the  whole  nervous  system,  and  which  I 
call  neuroglia.2)  In  these  sheaths  nuclei  (neuroglia-nuclei),  occur  more 
or  less  sparingly. 

3)  The   contents    of  the   nerve-tubes   consist  of  primitive  tubes, 
which    are    extremely    slender    tubes    or    cylinders,    separated  from 
each   other  or  rather   formed   by   membranes   or   sheaths  of  a  firm 
supporting  substance,   spongioplasm,  very  much  resembling  the  neu- 
roglia-substance ;   these   slender   cylinders  of  spongioplasm  contain  a 
hyaline,    viscous   substance,   hyaloplasm,   which   is   the   real    nervous 
substance,  and  which  very  often  is  exuded  from  fresh  isolated  nerve- 
tubes  in  form  of  small  hyaline  pearls. 

Fibrillae  and  fibres,  as  most  writers  describe  them,  do  not,  con- 
sequently, in  my  opinion,  exist. 

4)  A  concentration  towards  a  kind  of  axis  is  visible  in  a  great 
many  largish  nerve-tubes   of  Homarus  and  Nephrops;  this  axis  may 
be  more  or  less  narrow,  and  consists  of  a  bundle  of  central  primitive 
tubes  which  have  stouter  spongioplasmic  sheaths  and  smaller  diame- 
ters than  the  other  primitive  tubes.     A  similar  concentration   in  the 
centre   of  the   nerve-tubes   can,    as   a   rule,   not  be   observed  in  the 
other  animals   examined ;   only  a  slight  indication  of  it,  I  believe  to 
have  observed  in  some  nerve-tubes  of  Nereis. 


2.    The  structure  of  the  ganglion  cells,  and  their  processes, 
in  invertebrates. 

Homarus  vulgaris. 

The  contents  of  the  ganglion  cells  of  the  lobster  consist  of 
nucleus  and  protoplasm  enclosed  in  a  thicker  or  thinner  membrane 
or  sheath. 


a)    In  Myzostoma  I  have  previously  indicated  a  similar  structure. 
2)   In    my    memoir   on   Myzostoma    (1885)  I  have  called   it  »the  inner  neuri- 
lem«,  as  mentioned  before. 


—  99  — 

These  membranes  or  sheaths  of  the  ganglion  cells  have 
the  same  structure  as  the  sheaths  of  the  nerve-tubes,  and  are  formed 
of  the  same  substance,  viz.  the  neuroglia;  nuclei,  having  the  appear- 
ance of  common  neuroglia-nuclei,  occur  frequently  in  them,  and  are 
generally  adherent  to  their  outer  side;  I  have  seldom  observed  nuclei 
situated  on  the  inner  side  as  described  of  the  nerve-tubes.  The 
sheaths,  enveloping  the  cells,  very  often  consist  of  several  layers  or 
membranes,  similar  to  what  is  described  of  the  sheaths  of  the 
nerve-tubes. 

I  can  not  decide,  whether  inside  these  layers  of  neuroglia-sub- 
stance  there  also  occurs  a  thin  membrane,  spongioplasmic  membrane 
(different  from  the  neuroglia-sheath),  belonging  to  and  arising  from 
the  protoplasm  of  the  ganglion  cells.  It  would,  consequently,  be  a 
» cell-membrane «  as  many  writers  describe  it  to  be,  but  the  existence 
of  which  other  writers  deny.1)  The  importance  of  such  a  membrane 
existing,  or  not  existing,  is,  however,  in  my  opinion,  not  great  as 
may  be  seen  from  the  subsequent  description  of  the  structure  of 
the  cell-protoplasm. 

When  several  writers  deny  the  existence  of  a  cell-membrane, 
as  well  as  a  membrane  of  connective  substance,  I  think  that  must 
arise  from  their  examining  macerated  preparations,  and  imperfectly 
stained  sections.  In  macerated  preparations,  it  is  often  very  difficult 
to  distinguish  the  enveloping  membrane  from  the  cell-protoplasm,  it 
having  a  concentric  striation  which  is  very  similar  to  the  outer 
layers  of  the  protoplasm ;  neuroglia-nuclei  are,  however,  usually  ad- 
herent to  its  outer  side  and  indicate  its  real  neuroglia  nature 
(cmfr.  fig.  23,  ri). 

In  successfully  stained  sections,  e.  g.,  sections  stained  with 
HEIDENHAIN'S  haematoxylin-method  (vide  p.  76),  the  neuroglia  mem- 
branes are,  even  under  the  lower  powers  of  the  microscope,  distinctly 
visible  (fig.  24 — 29).  In  such  preparations,  these  membranes  also 
appear  to  be  intimately  connected  with  the  neuroglia-reticulation 
extending  between  the  ganglion  cells  (cmfr.  fig.  24),  and  they  look  as 
if  they  belonged  to  that  substance,  which,  in  my  opinion,  is  also 


*)  If  such  a  special  spongioplasmic  membrane  occurs,  which  is,  in  my 
opinion,  not  improbable,  it  would,  I  think,  be  so  intimately  connected  with  the 
surrounding  neuroglia-membranes  (cmfr.  my  subsequent  description  of  the  cell- 
protoplasm  and  its  reticulation)  and  have  an  appearance  so  perfectly  similar  to 
them  that,  I  cannot  understand  how  authors,  working  with  macerated  preparations, 
can  describe  special  cell-membranes  as  being  different  from  the  surrounding 
» connective-tissue*  membranes. 

7* 


—    100   — 

the  case,  as  will  also  be  subsequently  referred  to.  In  some  parts  of 
the  ganglia,  where  small  ganglion  cells  are  situated  closely  together, 
the  neuroglia-membranes  form  cavities  in  a  similar  way  as  the 
waxen-walls  in  a  honeycomb,  and  one  ganglion  cell  is  situated  in 
each  cavity  (vide  fig.  40). 

The  membranes  also  extend  into,  and  envelope,  the  processes 
of  the  ganglion  cells  (vide  fig.  26).  Round  the  processes  of  a  great 
many  cells,  sheaths  of  a  quite  peculiar  structure  occur,  these  sheaths 
will  be  mentioned  in  the  description  of  the  processes. 

The  protoplasm  of  the  ganglion  cells  of  the  lobster  has 
been  described  in  different  ways  by  the  many  authors  who  have 
treated  the  subject.  In  one  of  the  later  and  more  important  me- 
moirs on  this  subject,  viz.  that  by  FREUD  (1882),  it  is,  as  we  have 
seen  (p,  34),  described  as  consisting  of  two  substances,  a  reticulated 
substance,  and  a  hyaline  viscous  substance. 

FREUD  has  specially  examined  ganglion  cells  in  the  fresh  state. 
I  have  also  examined  them  in  the  fresh  state,  but  could  not  arrive 
at  a  lucid  conclusion  as  to  the  structure  of  their  protoplasm,  neither 
could  cells  isolated  by  maceration  afford  much  better  information 
in  this  respect. 

I  saw  a  kind  of  reticulation,  as  described  by  FREUD.  This  re- 
ticular  appearance  was  especially  distinct  in  macerated  preparations 
(cmfr.  fig.  23)  the  meshes  having  a  circular  shape  (they  have  be- 
come too  distinct  in  fig.  23;  the  illustration  not  being  a  successfull 
one) ;  I  could,  however,  not  convince  myself  whether  this  appearance 
was  really  produced  by  a  substance  having  a  reticular  structure  or 
not.  Besides  this  reticulation  I  could  generally  to  some  extent  trace 
out  a  concentric  striation  (cmfr.  fig.  23,  it  was,  however,  never  so 
distinct  as  it  appears  in  the  illustration). 

On  examination  of  carefully  prepared  sections l)  somewhat  more 
light  was,  however,  thrown  on  the  subject,  though  I  must  confess, 
that  there  are  several  points  in  which  I  could  still  wish  to  come 
to  more  clearness. 

Fig.  24  is  a  part  of  a  section  through  two  large  ganglion  cells 
in  an  abdominal  ganglion.  We  can  there  see  that  the  membranes 
(cm)  enclosing  the  cells  are  stout,  and  are  very  distinctly  marked, 


J)  The  best  preparation-method  for  this  purpose  I  found  to  be,  fixing  in 
chromo-aceto-osrnic  acid  and  staining  with  Heidenhain's  haematoxylin  (cmfr.  p.  j6\ 
or  fixing  in  Lang's  sublimate-solution  and  staining  in  Heidenhain's  haematoxylin 
(cmfr.  p.  77).  To  give  the  preparations,  afterwards,  a  nuclear  staining  by  Delafield's 
hsematoxylin  is  a  very  good  practice  (cmfr.  p.  76). 


—    101    — 

In  connection  with  these  membranes  we  find,  however,  a  very 
strange  structure.  In  B  it  has  the  appearance  as  if  a  series  of  deeply 
stained  oblong  corpuscles  were  situated  along  the  inner  side  of  the 
membrane.  Upon  closer  examination  we  will  see  that  these  cor- 
puscles are,  as  a  rule,  connected  with  the  membrane  by  very 
slender  filaments.  In  some  cases  these  filaments  are  even  very  thick 
and  the  dark  corpuscles  appear  thus  to  be  transsected  fibres  or  septa 
issuing  from  the  membrane  (cmfr.  fig.  24,  b).  On  the  other  side 
we  will,  on  close  examination,  find  slender  filaments  issuing  from 
the  inner  extremities  of  those  dark  corpuscles  or  fibres  and  pene- 
trating into  the  protoplasm  of  the  cells ;  indeed,  we  will  see  that 
they  anastomose  and  form  a  reticulation,  extending  through  the 
cell-protoplasm  and  distinctly  visible  in  its  outer  layers.  The 
meshes  of  this  reticulation  are  also  largest  in  the  outer  layers  near 
the  surrounding  membrane  (vide  fig.  24).  They  have,  here,  very 
often,  an  oblong  form,  going  in  a  radiate  direction  towards  the  centre 
of  the  cells,  and  having,  sometimes,  the  appearance  as  if  the  meshes 
were  formed  by  filaments  radiating  from  this  centre  to  the  surround- 
ing cell-sheaths;  in  fig.  24  B  such  an  arrangement  is  very  distinct. 
Within  these  large  meshes  smaller  meshes  are  generally  seen  (fig.  24). 
These  smaller  meshes  have,  however,  a  somewhat  different  appear- 
ance, they  being  not  so  distinctly  visible;  I  am  not  sure  whether 
they  are  formed  in  quite  the  same  way. 

Towards  the  inner  part  of  the  cell-protoplasm  (which  is  more 
deeply  stained)  the  meshes  of  the  first  mentioned  reticulation  be- 
come much  smaller  and  become  similar  to  the  small  meshes  just 
mentioned,  indeed,  they  cannot  be  distinguished  from  each  other. 
The  meshes  are  so  narrow  that  they  are  visible  only  under  the 
higher  powers  of  the  microscope,  and,  even  then,  not  very  distinctly ; 
in  small  cells  they  are  especially  very  difficult  to  observe. 

In  the  filaments  of  this  reticulation,  granules  and  thickenings 
occur,  giving  the  cell-protoplasm,  seen  under  lower  powers  of  the 
microscope,  a  granular  appearance.  These  thickenings  are,  especially 
in  the  large  ganglion  cells,  very  prominent  in  the  outer  layers  of 
the  protoplasm. 

In  the  small  meshes  of  this  reticulation,  a  hyaline  substance  is 
suspended,  very  similar  to  the  hyaloplasm  of  the  nerve-tubes. 

The  question  which  now,  as  regards  the  reticulation,  very  na- 
turally forces  itself  upon  us  is,  whether  is  it  a  real  spongy  reticulation 
extending  through  the  protoplasm  of  the  cells,  or  is  it  a  reticulation 
produced  by  a  transsection  of  tubes  in  the  same  way  as  we  have 


—    102   — 

seen  in  the  nerve-tubes.  My  opinion  upon  this  point  is,  that  this  reti- 
culation is,  to  some  extent,  a  real  one  having  partly  a  quite  spongy 
structure  without  the  formation  of  tubes;  to  some  extent  the  latter 
must,  however,  also  be  the  case,  as  we  shall  soon  see.  The  substance 
forming  the  reticulation  has,  as  mentioned,  a  great  resemblance  to 
the  sheaths  of  the  cells  as  regards  its  staining  etc.,  and  it  is,  in  my 
opinion,  the  same  substance  which  forms  the  sheaths  of  the  primi- 
tive tubes  in  the  nerve-tubes,  viz.  spongioplasm. 

Before  we  subject  the  significance  of  this  substance  to  a  further 
examination  I  think  it  will  be  well  to  look  somewhat  at  the  struc- 
ture of  the  processes  of  the  ganglion  cells  and  their  origin  in  the 
cell-protoplasm. 

The  contents  of  the  processes,  within  the  cell,  its 
structure  and  origin  in  the  cell-protoplasm.  -  -  The  ganglion 
cells  of  the  lobster  are,  as  a  rule,  unipolar;  if  they  have  several 
processes,  .there  is  always  one  of  the  process  which  has  a  special 
appearance,  and  which  is  the  real  nervous  process;  if  other  processes 
are  present  they  are,  as  I  call  them,  protoplasmic  processes,  and 
they  have,  in  my  opinion,  a  nutritive  function,  as  will  be  subse- 
quently mentioned.  At  present  we  will  only  consider  the  structure 
and  origin  of  the  nervous  process. !) 

In  well  prepared  sections,  a  distinct  longitudinal  striation  of  these 
processes  is  easily  observed.  On  observation  of  transversally  trans- 
sected  processes,  it  is  seen  that  this  striation  is  produced  by  primi- 
tive tubes  having  the  same  structure,  and  constituting  the  nervous 
processes  in  the  same  way,  as  described  of  the  nerve-tubes. 

As  regards  the  staining,  the  contents  of  the  nervous  processes 
differs  from  the  protoplasm  of  the  ganglion  cells;  the  latter  having 
generally  a  much  darker  staining.  This  difference  is,  for  instance, 
very  prominent  in  fig.  37  &  38,  where  the  contents  of  the  longitu- 
dinally transsected  processes  have  a  very  light  staining  and  a  distinct 
striation. 

The  origin  of  the  nervous  processes  differs  somewhat  in  the 
various  cells.  In  fig.  26  it  has  the  appearance,  as  if  the  contents  of 
the  nervous  process  arises  from  a  convergence  of  primitive  tubes  from 
the  whole  body  of  cell-protoplasm,  in  which  they  have  a  uniform 
extension,  and  to  which  they  generally  give,  to  some  extent,  a  con- 


a)  I  have  in  reality,  never  observed  a  multipolar  ganglion  cell  of  quite  in- 
dubitable multipolar  shape,  in  the  nervous  system  of  the  lobster.  I  am  afraid  that 
it  has  very  often  been  neuroglia-fibres  issuing  from  neuroglia-sheaths  which  have 
given  rise  to  descriptions  of  multipolar  ganglion  cells. 


—  103  — 

centric  striation.  Some  of  the  primitive  tubes  we  can  in  many  pre- 
parations even  trace,  for  some  distance,  in  their  course  through  the 
cell-protoplasm,  of  which  they  are  not,  as  we  have  previously  seen 
(cmfr.  reticulation  described  p.  101),  the  only  constituent,  but  of 
which  they  are,  however,  a  principal  part. l)  These  primitive  tubes 
have  the  same  structure  and  diameter  as  those  we  have  described 
in  the  nerve-tubes;  they  consist  of  hyaline  contents,  hyaloplasm, 
enveloped  in  sheaths  of  spongioplasm,  which  has  the  same  staining 
and  appearance,  and  is  evidently  the  same  substance,  as  that  pre- 
viously described  (vide  p.  101),  as  forming  the  reticulation  in  the 
cell-protoplasm.  In  fig.  27  and  28  it  is  very  distinctly  seen  that 
these  spongioplasmic  sheaths  ot  the  primitive  tubes  are  intimately 
connected  with  the  peculiar  peripherically  situated  fibres  (fig.  27,  & ; 
fig.  28,  6)  issuing  from  the  surrounding  neuroglia-membrane. 

In  a  great  many  ganglion  cells  these  primitive  tubes  have  not, 
however,  such  an  uniform  extension  through  the  protoplasm  as 
illustrated  in  fig.  26.  In  the  large  cells  they  are  generally  united 
to  bundles,  distinctly  distinguished  from  the  rest  of  the  protoplasm. 
In  successfully  stained  sections,2)  where  they  are  transversally  trans- 
sected,  they  are  distinctly  visible  as  larger  or  smaller  light  areas 
situated  in  the  deeply  stained  protoplasm.  Very  often,  when  the 
bundles  of  primitive  tubes  circulating  in  the  cell-protoplasm  are 
numerous  and  small,  we  get  sections  having  the  appearance  illustra- 
ted in  fig.  25  and  27. 

In  ganglion  cells  containing  such  bundles  of  primitive  tubes  circulat- 
ing in  the  protoplasm,  the  nervous  process  arises  in  such  manner  that 
the  bundles  unite  to  form  the  process,  as  illustrated  in  fig.  27  and  25. 
This  union  takes  place  generally  within  the  cell-protoplasm,  and  the 
contents  of  the  nervous  process  has  then,  for  some  distance,  an  un- 
divided course  through  the  cell- protoplasm,  and  can  be  traced  as  a 
large  light  area  through  a  series  of  transverse  sections  (cmfr.  fig. 
28  and  29).  It  is  surrounded  by  thicker  or  thinner  deeply  stained 
fibres  (fig.  28,  s  and  &;  fig.  29,  s  and  s')  of  the  same  substance  as  forms 
the  reticulation  of  the  protoplasm  (cmfr.  p.  101).  Some  of  these 


*)  That  it  really  is  primitive  tubes,  with  slightly  stained  hyaline  contents,  and 
not  »fibrillae«  which  circulate  in  the  protoplasm  of  the  ganglion  cells,  is  easily 
seen  in  preparations  deeply  stained  by  haematoxylin  (e.g.  fig.  37);  they  are  distinctly 
visible  as  light  concentric  lines  where  they  are  longitudinally  transsected  (cmfr. 
also  fig.  38). 

2)  The  fixing  method  and  staining  described  p.  76  and  p.  85  can  especially 
be  recommended  for  this  purpose. 


—   104  — 

fibres  are,  in  some  sections,  seen  issuing  from  the  sheath  of  the 
ganglion  cell.  Similar  fibres  can  also  be  traced  into  the  prosesses 
(fig.  27, 6)  where  they  have  a  longitudinal  course  (fig.  30,  sf,  sf").  Some- 
times, in  the  cells,  they  are  so  closely  situated  that  it  looks  as  if  they 
almost  formed  a  sheath  (cmfr.  fig.  28)  surrounding  the  process-contents 
for  some  distance  into  the  cell-protoplasm,  where  they  gradually 
disappear  and  obtain  the  same  appearance  as  the  reticulated  spongio- 
plasm,  which  spongioplasm  often  apparently  gives,  even  the  smaller 
bundles  of  primitive  tubes  in  the  protoplasm,  a  kind  of  relatively 
firmer  surrounding  layer  resembling  a  thin  membrane,  which  layer 
is  generally  more  deeply  stained  by  haematoxylin  than  the  surround- 
ing protoplasm  (vide  fig.  25,  27,  28,  v  and  29,  v,  v7). 

Sometimes  the  primitive  tubes  are  united  to  a  few  and  very 
large  masses  situated  peripherically  in  the  cell.1)  Fig.  38,  A  represents 
a  section  through  such  a  cell;  v  and  vf  are  the  transsected  masses 
of  primitive  tubes.  In  fig.  39,  which  represents  a  more  laterally 
running  section  through  the  same  cell,  it  is  seen  what  an  extensive 
distribution  these  masses  can  have  in  the  peripheral  parts  of  the  cell, 
the  section  passes  almost  exclusively  through  such  a  mass  of  primi- 
tive tubes.  If  we  examine  these  light  areas  under  high  powers  of 
the  microscope,  we  see  that  they  exhibit  the  same  reticulation  which 
we  know  from  transversally  transsected  nerve-tubes  and  nervous 
processes,  and  which  reticulation  evidently  arises  from  the  transsec- 
tion  of  primitive  tubes. 

In  many  ganglion  cells  we  find  similar  peripheral  masses,  which 
are  not,  however,  so  distinctly  defined  as  those  just  described.  We 
can,  indeed,  find  every  stage  of  transition,  from  cells  such  as  those 
illustrated  in  fig.  38,  A  to  cells  with  a  diffusive,  uniform  extension 
of  a  lightly  stained  mass  in  their  whole  peripheral  layers,  such  cells 
are,  for  instance,  illustrated  in  fig.  38,  B  and  fig.  37.  These  peri- 
pheral layers,  of  lightly  stained  mass,  can  have  a  more  or  less  di- 
stinct demarcation  from  the  mesial,  deeply  stained,  part  of  the  pro- 
toplasm, or  they  can  also  have  a  quite  successive  transition  into  it. 

In  the  protoplasm  of  most  ganglion  cells  we  will,  indeed,  find  a 


l)  In  macerated  preparations  these  masses  are  often  seen,  having  the  ap- 
pearance of  vacuoli  situated  especially  in  the  peripheral  layers  of  the  protoplasm 
of  the  cells  and  along  their  margins.  For  a  long  time  I  believed  this  appearance 
of  the  cells  to  be  of  artificial  nature,  produced  by  the  macerating  agents.  It  was 
first  on  examination  of  successfully  prepared  sections  that  I  learnt  their  real  nature. 
In  macerated  cells,  the  striated  process-contents  could  sometimes  be  traced  into  the 
cell-protoplasm,  it  having,  for  some  distance,  an  undivided  course  (vide  fig.  23,  A). 


—  105  — 

tendency  to  stain  most  deeply  in  their  mesial  part,  whilst  the 
peripheral  layers  are  generally  very  light  (cmfr.  fig.s  24,  26,  27,  37, 
38  B,  40).  The  reason  is  probably,  to  some  extent,  that  the  primi- 
tive tubes  occur  in  greater  plenty  in  the  peripheral  layers,  or  rather 
that  they  are  situated  closer  together,  and  that  they  are  not  to  such 
extent  separated  by  layers  of  the  substance  which  occurs  in  plenty 
in  the  mesial  parts  of  the  protoplasm  and  give  to  it  the  deep  staining 
(vide  sequel).  In  these  lightly  stained  layers,  a  spongioplasmic  reti- 
culation, described  above  (cmfr.  fig.  24),  is  generally  more  or  less 
visible,  in  fig.  37  it  is,  for  instance,  very  distinct,  and  thick  fibres 
also  occur  (vide  also  fig.  38,  B). 

In  other  cells  such  a  reticulation  is  but  slightly  visible,  and  we 
find  only  circular  meshes,  which  probably  are  transsected  pri- 
mitive tubes,  this  is  especially  the  case  in  cells  where  these  layers 
are  confined  to  masses  distinctly  defined  from  the  rest  of  the  pro- 
toplasm as,  for  instance,  in  fig.  38,  A.  Here,  only  a  few  such  fibres 
or  membranes  of  spongioplasm  are  visible  («'). l) 

In  ganglion  cells  with  such  peripheral  masses  of  primitive  tubes, 
the  nervous  processes  do  not  spring  directly  from  these  masses  but 
seem  to  get  their  whole  contents  from  the  mesial  deeply  stained 


J)  I  think'  it  must  have  been  ganglion  cells  with  similar  light  peripheral  masses 
which  Freud  mentions  1.  c.  1881  p.  29 — 30.  He  says:  »An  den  grossen  unipolaren 
Zellen  erscheint  eine  oft  sehr  breite,  einen  grosseren  oder  geringeren  Theil  der  Zell- 
peripherie  einnehmende  Zone,  welche  durchaus  homogen  und  dem  Kerninhalt  ahn- 
lich  ist.«  He  believes  »dass  diese  homogene  Zone  durch  den  als  »Zwischensub- 
stanz«  beschriebenen  Bestandtheil  des  Zellleibes  gebildet  wird,  aus  welcher  die 
netzformige,  dunklere  Substanz  sich  gegen  den  Kern  zuriickgezogen  hat.  Es  finden 
sich  auch  haufig  genug  Zellen,  an  denen  zwei  homogene  Randpartien  durch  einen 
diinnen  Strang  dunklerer,  genetzter  Substanz,  welcher  noch  an  der  Peripherie  fest- 
gehalten  ist,  getrennt  werden.«  Freud  supposes,  consequently,  those  »homogene 
Randpartien*  to  be  appearances  produced  on  the  death  of  the  cell.  In  the 
sympatic  ganglion  cells,  he  describes  somewhat  similar  masses  of  hyaline  substance, 
which  he,  however,  rather  believes  to  be  a  normal  appearance  belonging  to  the 
live-state  of  the  cells. 

It  may  here,  also  be  mentioned  that  Freud  describes  (1.  c.  1881  p.  26)  and 
illustrates  (fig.  I  &  5)  nervous  processes  having  a  peculiar  origin  in  the  ganglion 
cells.  He  says  of  them:  »In  manchen  Zellen  ist  ein  Ubergangsstiick  zwischen  Zell- 
leib  und  Nervenfaser  nicht  vorhanden;  die  Nervenfaser  entspringt  in  anderer,  sehr 
eigenthiimlicher  Weise.  Dieselbe  schmiegt  sich  nahmlich  in  Gestalt  eines  hellen 
Halbringes  der  Peripherie  der  Zelle  an,  um  dann  in's  Innere  des  Zellleibes  einzu- 
treten.«  Krieger  (in  his  dissert.  1879)  has  before  Freud  (as  Freud  himself  states) 
described  similar  appearances.  I  think  there  is  no  doubt  that  these  structures  are 
of  the  same  nature  as  those  described  above  respecting  the  origin  of  the  contents 
of  the  nervous  process  (vide  p.  103 — 104). 


-  106  - 

protoplasm.  This  is,  for  instance,  very  distinctly  visible  in  fig.  37, 
as  well  as  in  fig.  38,  A.  I  have  examined  a  great  many  cells  having 
quite  similar  appearance,  but  in  them  all  I  found  the  same  relation 
between  the  protoplasm  and  the  contents  of  the  nervous  process. 
Although  the  contents  of  the  process  is  often  surrounded  by  a  lightly 
stained  mass  at  its  entrance  into  the  cell,  it  can,  however,  be  seen 
passing  to  the  mesial  deeply  stained  protoplasm  (cmfr.  fig.  37  and  38), 
without  giving  off  tubes  to  the  light  mass,  it  having  an  undivided 
course  for  a  shorter  or  longer  distance  into  the  protoplasm.  In  this 
course  it  is,  as  described  above,  distinctly  visible,  and  is  surrounded 
by  thick  spongioplasmic  fibres  (fig.s  37,  sf ;  fig.  38,  sf).  At  some 
distance  from  the  entrance,  the  primitive  tubes  constituting  this 
process-contents  spread,  and  are  lost  in  the  protoplasm  of  the 
ganglion  cell;  generally,  I  could,  however,  trace  some  of  them  for 
some  distance  in  their  course  through  this  deeply  stained  protoplasm.1) 
To  explain  what  relation  there  may  be  between  the  primitive 
tubes  of  the  nervous  process  and  the  peripheral  masses  of  primitive 
tubes  in  these  cells  is,  of  course,  an  extremely  difficult  matter.  In 
fact,  I  have  not  been  able  to  trace  out  the  connection  between  them. 
We  have,  as  mentioned,  found  every  transition-form  of  ganglion 
cells,  from  cells  in  which  the  contents  of  the  process  is  spread  at 
once  on  its  entrance  into  the  cell  (fig.  26),  to  cells  where  the  contents 
of  the  process  passes  undivided,  and  distinctly  marked  for  a  longer 
or  shorter  distance  into  the  protoplasm  (fig.s  25,  28,  29,  37,  38)  and 
afterwards  is  uniformly  broken  up  and  spread  in  the  protoplasm  (fig.s 
37'  38)  or  is  to  a  greater  or  smaller  extent  broken  up  into  bundles  of 
primitive  tubes  (fig.s  25,  27).  We  have  also  found  every  transition- 
form,  from  ganglion  cells  having  a  protoplasm  which  is  uniformly 
deeply  stained  in  the  mesial  part,  and  the  staining  of  which  gradually 
passes  over  into  a  lighter  one  towards  the  peripheral  layers  (fig.  2.6), 
to  ganglion  cells  with  a  protoplasm  which  is  deeply  stained  in  the 

T)  Sections  similar  to  those  illustrated  in  fig.  37  or  fig.  38,  A,  can  certainly 
very  easily  give  rise  to  a  belief  in  nuclear  processes.  If  one  had  a  little  pre- 
disposition to  find  nuclear  processes,  one  could  easily,  for  instance,  in  fig.  38.  A 
combine  the  process  with  the  nucleus,  and  suppose  the  reason  why  this  connec- 
tion was  not  seen  in  the  section  was,  that  the  section  had  not  been  quite  successful. 
I  think,  therefore,  that  the  description  of  nuclear  processes  can  to  a  great  extent 
be  ascribed  to  processes  like  those  I  have  illustrated,  which  seen  in  isolated  cells 
can  of  course,  in  a  still  higher  degree,  give  the  appearance  of  being  connected 
with  the  nuclei.  Krieger  has  already  made  the  same  supposition  regarding  those 
peculiar  processes  described  by  him,  and  which  are,  in  my  opinion,  processes- 
originating  in  somewhat  similar  way  as  here  described  (cmfr.  fig.  23,  A  &  fig.  25). 


mesial  part,  but  has  distinctly  defined  light  masses  in  its  peripheral 
layers  (fig.  38,  A),  or  in  which  plenty  of  distinct,  lightly  stained 
bundles,  or  small  masses,  of  primitive  tubes  occur  (fig.  2$). 

There  is  evidently  a  great  variety  in  the  structure  of  the  proto- 
plasm, as  well  as  in  the  origin  of  the  nervous  process  in  the  ganglion 
cells.  I  do  not  think,  however,  that  this  difference  of  structure  can 
have  any  deep  physiological  significance,  because  we  find  every 
stage  of  transition  from  one  form  to  another.  The  peripheral  con- 
stituent of  the  protoplasm  in  all  cells,  is  evidently  the  primitive  tube. 
The  small  circular  meshes  which  are  found  in  sections,  every  where 
in  the  protoplasm,  in  the  deeply  stained  as  well  as  in  the  lightly 
stained  parts,  are  probably  only  transsected  primitive  tubes  which 
in  the  deeply  stained  parts  of  the  protoplasm  are  more  separated 
from  each  other  by  thicker  layers  of  a  deeply  stained  substance 
than  they  are  in  the  light  parts. 

Where,  and  how,  the  primitive  tubes  terminate,  or  rather  how 
they  originally  are  formed,  I  cannot  say. 

In  a  few  cases  I  have,  in  the  peripheral  parts  of  some  cells, 
believed  to  see  slender  tubes  pass  to  the  enveloping  neuroglia-sheath. 
This  appearance  can,  however,  also  be  occasioned  by  the  above 
mentioned  spongioplasmic  fibres  issuing  from  the  sheath.  If  such 
radiating  tubes  were  really  present  in  all  ganglion  cells,  we  could, 
perhaps,  easily  understand  the  statement  of  Dr.  RAWITZ  regarding 
the  ganglion  cells  of  the  Acephales;  viz.  that  hyaline  small  pearls 
were  exuded  from  the  cells  on  pressure.  These  pearls  consist,  I 
think,  of  hyaloplasm,  and  are  probably  exuded  from  primitive  tubes, 
which  must  either  terminate  in  the  envelope  of  the  cell  or  must 
have  been  broken  by  the  pressure. 

If  we  now  consider  what  we  have  learnt  of  the  protoplasm  of 
the  ganglion  cells,  we  may  sum  it  up  in  the  following  results: 

The  cell-protoplasm  is  composed  of  primitive  tubes  consisting  of 
liyaloplasmic  contents  and  spongioplasmic  envelope,  -  -  further,  of  a 
spongioplasmic  reticulation,  extending  through  the  protoplasm  and 
also  intimately  connected  with  the  surrounding  cell-sheath  —  and, 
finally,  of  a  hyaline  substance  having  much  resemblance  to  the  hyalo- 
plasm of  the  primitive  tubes. 

The  primitive  tubes  circulate,  as  we  have  seen,  in  the  proto- 
plasm, giving  it  often  a  concentrically  striated  appearance  (fig.  23). 
In  large  ganglion  cells  they  are  frequently  united  into  a  number 


—  loS  - 

of  thicker  or  thinner  bundles,  sometimes  these  even  grow  to  con- 
siderable masses,  generally  situated  peripherically  in  the  cells 
(cmfr.  fig.  30). 

If  we  try  to  explain  the  connection  and  relation  of  these  con- 
stituents of  the  protoplasm  to  each  other,  we  have  indeed  no  easy- 
task.  And  it  is,  especially  of  this,  I  could  wish  to  have  obtained 
more  light. 

That  a  principal  part  of  the  protoplasm  of  the  ganglion  cells 
consists  of  primitive  tubes,  I  think  must  be  evident  from  what  is 
already  described;  that  a  great  number  of  the  small  meshes,  seen 
in  sections  of  the  protoplasm  of  the  cells  (in  the  peripheral  part  as 
well  as  in  the  mesial  one)  are  transsected  primitive  tubes  is,  I  think, 
very  probable. 

There  must,  however,  in  the  protoplasm  of  the  ganglion  cells 
be  something  also  present,  besides  primitive  tubes,  because  the  pro- 
toplasm is  stained  by  haematoxylin  and  other  agents  in  a  manner 
very  different  from  the  contents  of  the  nerve-tubes,  which  exclusively 
consists  of  primitive  tubes.  By  haematoxylin,  the  protoplasm  is 
generally  stained  very  deeply,  except  those  bundles  or  masses  of 
primitive  tubes  which  get  a  similar  staining  as  the  contents  of  the 
nerve-tubes.  This  deep  staining  may,  certainly,  to  some  extent  be 
explained  by  a  rich  occurrence  of  spongioplasm  (cmfr.  the  spongio- 
plasmic  reticulation  described  above  p.  101).  I  feel,  however,  dis- 
posed to  think,  that  besides  this  spongioplasm  another  (myeloid?) 
substance  occurs,  perhaps  in  connection  with  it.  Spongioplasm  with 
this  fattish  substance l)  is,  T  suppose,  situated  in  thicker  or  thinner 
layers  between  the  primitive  tubes  running  through  the  protoplasm, 
and  separates  each  of  them  more  widely  than  is  the  case  in  the 
nerve-tubes.  Within  the  bundles  or  masses  of  primitive  tubes,  oc- 
curring in  large  ganglion  cells,  this  substance  is  not  present,  nor  is 
there  apparently  more  spongioplasm  than  is  generally  present  in  the 
nerve-tubes  or  the  nervous  processes. 

The  structure  of  the  nervous  processes  and  their 
sheaths,  in  their  course  outside  the  ganglion  cells.  —  The 
contents  of  the  nervous  processes  is,  as  already  mentioned,  composed 
of  primitive  tubes,  in  the  same  way  as  the  contents  of  the  nerve- 
tubes.  In  its  staining  it  is  differentiated  from  the  protoplasm  of  the 


J)  That  it  is  a  fattish  (myeloid?)  substance  is,  I  think,  probable  from  the 
dark  or  brownish  staining  of  the  cell-protoplasm  by  osmic  acid.  This  is,  however, 
also  the  case  with  the  common  spongioplasm. 


—  109  — 

ganglion  cell,  this  difference  being,  as  we  have  seen,  already  distinct 
within  the  cell  itself.  It  has,  in  preparations  often,  the  same  light 
staining  the  whole  way  from  the  origin  of  the  nervous  process  till  its 
entrance  into  the  dotted  substance  (fig.  35);  generally  it  is,  however, 
stained  in  a  quite  peculiar  manner  by  haematoxylin.  Fig.  30 — 33 
represents  various  sections  through  a  such  process;  it  is  the  same 
process  the  contents  of  which  is  also  seen  in  fig.  28  and  29.  At 
the  agress  from  the  ganglion  cell  (fig.  30),  the  contents  of  the 
nervous  process  has  the  same  light  staining  as  already  described. 
At  some  distance  from  the  cell  the  contents  begins,  however,  to  get 
a  darker,  more  black  staining,  especially  in  its  peripheral  layers  (fig.  31). 
At  the  same  time  the  diameter  becomes  also  diminished.  At  a 
greater  distance  from  the  cell  this  blacker  staining  increases,  and  the 
whole  contents  is  stained  quite  dark  or  black  (fig.  32),  the  diameter 
of  the  process  is  also  still  more  diminished.  In  fig.  33,  the  same 
process  is  seen  divided  into  two  branches  (a  and  &)  which  have  the 
same  black  staining  as  above.  This  black  staining  they  retain  till 
their  entrance  into  the  dotted  substance.  The  branchlets  issuing  from 
them  are  also  stained  in  the  same  manner.  It  is,  of  course,  very 
difficult  to  say  what  is  the  reason  of  this  dark  staining.  I  do  not 
think,  however,  that  it  is  of  qualitative  nature.  To  some  extent  it 
may,  perhaps,  be  explained  by  the  relatively  small  thickness  of  the 
processes,  and  by  their  situation  in  a  reticulated  neuroglia  through 
which  the  fixing  as  well  as  the  staining  agents  easily  find  their  way  to 
these  structures.  It  is,  however,  strange  that,  in  the  same  section, 
one  can  find  some  processes  with  dark  contents,  and  other  processes 
with  light  contents,  similar  to  the  contents  of  the  nerve-tubes  (cmfr. 
fig-  35  &  36).  The  branchlets  issuing  from  these  processes  have 
similar  lightly  stained  contents,  consisting  of  primitive  tubes  (cmfr. 
fig.  35,6r;  fig.  36,  6r,  6r?). 

Spongioplasmic  fibres  similar  to  those  surrounding  the  process- 
contents  within  the  ganglion  cell  (cmfr.  fig.  28  &  29,  also,  generally 
occur  in  the  process  itself.  They  have  a  longitudinal  course  along 
the  process,  inside  the  sheath  (vide  fig.  30,  sf,  sf)  and  can  often  be 
traced  to  a  considerable  distance  from  the  ganglion  cell  (vide 
fig-  35 >  sf)-  They  have  a  dark  staining;  sometimes  it  looks  as  if 
they  united  to  form  a  deeply  staining  peripheral  layer  round  the 
contents  of  the  process  inside  the  sheath  (fig.  36). 

The  sheaths  of  the  nervous  processes  are  formed  by  the 
neuroglia,  and  are  stained  in  the  same  manner  as  this  substance. 
They  have  generally  a  peculiar  structure,  and  consist  often  of  a  great 


—    110   — 

many  layers  or  membranes  aranged  concentrically  round  the  contents 
of  the  process;  only  the  innermost  layer  of  these  membranes  can, 
however,  be  considered  as  the  real  sheath.  What  a  great  extension 
these  structures  can  obtain  is,  for  instance,  seen  in  fig.  34,  where 
pc  is  the  contents  of  a  nervous  process,  br  is  a  branchlet  issuing 
from  the  process;  nm  the  surrounding  concentrically  arranged  neu- 
roglia-membra  n  es . 

The  nervous  pocesses  are  sometimes  provided  with  similar  con- 
centrically arranged  sheaths  quite  from  their  origin  in  the  ganglion 
cell  (fig.  25,  sh).  Generally,  the  sheaths  do  not,  however,  reach 
their  highest  thickness  before  some  distance  from  the  cell,  and  they 
do  not  consist  of  so  many  layers  near  their  origin. 

The  nuclei  of  the  ganglion  cells  are,  as  is  a  well-known 
fact,  enclosed  by  a  thin  membrane.  That  this  membrane  is  not 
seen  in  the  live-state  of  the  cell,  as  stated  by  FREUD,  is,  in  my 
opinion,  from  the  same  cause  as  makes  the  striation  of  the  nerve- 
tubes  so  slightly  visible  in  the  live-state.  The  refractive  difference 
between  the  protoplasm  of  the  ganglion  cell  and  the  substance  of 
which  this  membrane  consists  is  so  small,  that  this  difference  must 
necessarily  be  increased,  for  instance,  by  chemical  agents,  if  the 
membrane  should  become  distinctly  visible  (vide  fig.  23).  With  hae- 
matoxylin  this  membrane  gives  a  distinct  blackish  staining  (fig.s  37, 
38,  40,  42)  which  is  quite  similar  to  that  of  the  spongioplasmic  re- 
ticulation, and  to  the  sheath  of  the  cell.  In  my  opinion,  it  is  not 
improbable  that  this  membrane  is  also  formed  by  the  same  spongio- 
plasm  as  forms  the  reticulation  in  the  protoplasm  and  the  sheaths 
of  the  primitive  tubes. 

The  structure  of  the  nuclei  inside  this  membrane  varies  very  much. 
As  already  stated  by  FREUD,  there  appears  within  the  nucleus  a  great 
many  changes,  probably  connected  with  the  life  of  the  cell  and  the 
nucleus.  In  well  fixed  preparations  we  can,  in  fact,  also  find  nuclei 
exhibiting  the  greatest  variation  in  their  structure.  Fig.  41  and  42 
represent  nuclei  in  various  stages.  Generally,  each  nucleus  has  one 
nucleolus  situated  in  its  centre  or  also  near  its  membrane  (cmfr.  fig.  38). 
Sometimes  two  nuclei  are  present;  the  nucleus  has,  then  very  often, 
an  oblong  form,  and  one  nucleolus  is  situated  in  each  pole  (fig.  37); 
it  is,  however,  not  unusual  that  the  nucleus  has  a  circular  shape,  and 
that  nucleoli  are  situated  oposite  to  each  other,  near  the  membrane 
(fig.  41).  Sometimes  no  real  nuclei  are  present,  the  whole  nucleus 
exhibiting  a  peculiar  distinct  reticulation  with  dark  thickenings  in 
the  points  where  the  fibres  of  the  reticulation  unite  (fig.  42,  d). 
Sometime  fibres  are  seen  radiating  from  the  centre  of  the  nucleus, 


and  having  dark  thickenings  at  their  extremities,  near  the  membrane 
of  the  nucleus  (fig.  42,  /)  etc.  etc.  I  will,  however,  pay  no  more 
attention  to  these  structures,  here,  as  they  are  probably  only  pro- 
duced by  the  nuclei  being  fixed  in  different  stages  of  their  life;  in 
some  cases  we  have  even,  perhaps,  a  beginning  segmentation  of  the 
nucleus  (fig.  42,  e). 

Nephrops  norvegicus. 

In  Nephrops,  the  structure  of  the  ganglion  cells  is  quite  similar 
to  what  we  have  described  of  Homarus.  In  sections,  the  protoplasm 
of  the  large  cells  generally  exhibits  quite  similar  light  areas,  resemb- 
ling vacuoli,  and  arising  from  the  transsection  of  bundles  or  masses 
of  primitive  tubes.  The  contents  of  the  nervous  processes  originate 
in  the  same  manner;  a  similar  spongioplasmic  reticulation  is  present 
in  the  protoplasm,  it  being  especially  visible  near  the  sheaths  of  the 
cells  with  which  it  is  intimately  united.  We  can,  thus,  as  regards 
the  structure  of  the  ganglion  cells  of  Nephrops,  refer  the  reader  to 
our  description  of  the  ganglion  cells  of  Homarus. 

The  Polych6etes. 

Sections  of  the  large  ganglion  cells  of  the  Nereidce  (N.  virens  etc.) 
exibit,  generally,  a  prominent  granular  appearance  with  a  distinct 
reticulation  extending  between  and  uniting  the  granules  with  each 
other,  the  granules  being  generally  situated  at  the  points  where  the 
walls  of  the  meshes  unite  (fig.  43).  Some  of  the  granules  are  very 
large  and  prominent,  and  are  principally  situated  in  the  mesial  part  of 
the  protoplasm.  They  have,  in  my  preparations  treated  with  fluids 
containing  osmic  acid  and  stained  with  haematoxylin,  a  very  dark 
almost  black  staining,  and  they  consist,  I  think,  of  a  fattish  (myeloid?) 
substance.1) 

In  a  great  many  cells,  I  observed  a  differentiation  in  the  stain- 
ing of  the  protoplasm,  somewhat  similar  to  what  is  described  of  the 
cells  of  Homarus.  A  disposition  to  a  darker  staining  of  the  mesial 
part  of  the  protoplasm  is  very  often  observed;  besides  this  the 
larger  granules  are  also,  as  just  mentioned,  situated  especially  here 
which  contributes  somewhat  to  a  darker  appearance  (vide  fig.  44 


*)  Whether  the  substance  of  these  granules  is  the  same,  or  has  any  relation 
to  the  substance  which  gives  the  nervous  system  of  many  Polychaetes  the  well- 
known  reddish  or  yellowish  staining,  I  cannot  say,  as  I  have  not  yet  very  closely 
examined  the  ganglion  cells  of  the  Polychcetes  in  the  live-state. 


—    112   — 

and  45).  There  is  generally  no  distinct  demarcation  betvven  the 
deeply  stained  mesial  part  of  the  protoplasm  and  the  lighter  pe- 
ripheral layers;  sometimes,  however,  such  a  demarcation  is  present, 
the  lighter  stained  substance  being  peripherically  situated  in  various 
more  or  less  distinctly  defined  masses  (fig.  44).  Small  bundles  of 
primitive  tubes,  similar  to  those  which  are  often  present  in  the 
ganglion  cells  of  Homarus  and  Nephrops,  I  have  not  generally  ob- 
served in  the  ganglion  cells  of  Nereis.  The  contents  of  the  nervous 
process  seems  generally  to  originate  in  a  gradual  convergence  of 
primitive  tubes  in  the  protoplasm,  towards  the  pole  where  the  pro- 
cess originates  (cmfr.  fig.  43).  Sometimes,  I  believe  to  have  observed 
the  contents  of  the  nervous  process  passing  as  an  undivided,  lightly 
stained  bundle  for  some  distance  into  the  protoplasm ;  consequently, 
a  structure  somewhat  similar  to  what  is  above  described  in  the 
ganglion  cells  of  Homarus. 

A  spongioplasmic  reticulation  quite  similar  to  the  peculiar  re- 
ticulation in  the  ganglion  cells  of  Homarus  does  not  occur  in  Nereis, 
so  far  as  our  experience  goes,  at  all  events  not  to  such  an  extent.  In 
some  cells,  I  have,  however,  observed  spongioplasmic  fibres  issuing 
from  the  neuroglia-membrane  enveloping  the  cell  and  penetrating 
into  the  protoplasm  (vide  fig.  43,  sf  and  fig.  44,  sf}\  probably  con- 
tributing to  form  the  reticulation  already  described. 

A  question  of  great  interest  is,  whether  the  reticulation,  seen  in 
the  sections  of  the  cell-protoplasm  of  Nereis  is  a  real  reticulation 
or  only  an  appearance  produced  by  transsection  of  primitive  tubes  ? 
I  feel  most  disposed  to  believe  that  the  latter  is  the  case.  Strange 
to  say,  neither  longitudinally  transsected  primitive  tubes,  nor  a 
concentric  striation  are  as  often  seen  in  the  ganglion  cells  as  we 
could  expect  if  all  meshes  were  transsected  primitive  tubes;  some- 
times we  can,  however,  observe  longitudinally  transsected  tubes  in 
the  protoplasm,  and  the  reason  why  they  are  not  oftener  seen  is, 
perhaps,  because  they  have  a  very  curved  and  complicated  course. 

The  nuclei  of  the  ganglion  cells  have,  in  the  Nereidae,  a 
similar  structure  as  those  of  Homarus.  They  have  a  distinct  sur- 
rounding membrane,  inside  which  a  reticulation  is  extended;  in  this 
reticulation  dark  granules  are  situated,  generally  at  the  points  where 
the  fibres  forming  the  meshes  unite.  One  or  sometimes  two  nucleoli 
are  seen,  and  sometimes  no  distinct  nucleolus  is  present,  but  only 
largish  granules  are  spread  in  the  reticulation  (vide  fig.  43,  44,  45). 

The  situation  of  the  nuclei  in  the  protoplasm  is  generally  diffe- 
rent from  what  it  is  in  the  ganglion  cells  of  Homarus.  The  nuclei 


—  H3  — 

are  very  often  situated  in  one  side  of  the  cell,  near  the  surrounding 
sheath  (cf.  fig.  44  &  45)  and,  not  unusually,  towards  that  side  from 
which  the  nervous  process  issues  (cf.  fig.  43,  t).  They  are,  thus, 
very  frequently  situated  outside  the  mesial,  deeply  stained,  part 
of  the  protoplasm  (fig.  44  &  45).  In  the  small  cells  they  ate 
generally  situated  in  the  centre  of  the  cell,  and  are  proportionally 
very  large,  being  surrounded  by  a  thin  layer  of  protoplasm  only. 

The  processes  of  the  ganglion  cells.  -  -  The  ganglion  cells 
of  the  Nereidae  have  generally  a  unipolar  shape.  Quite  exeptionally, 
I  believe  to  have  observed,  in  sections,  cells  with  multipolar  shape; 
there  was  always,  however,  only  a  single  process  in  each  cell  capable 
of  being  traced  in  its  course  into  the  central  dotted  substance. 
The  other  processes  were  very  short,  immediately  tapering  off; 
they  were  directed  peripherically,  or  laterally,  (never  towards  the 
central  mass)  and  were  soon  lost  in  the  neuroglia.  I  could,  however, 
never  quite  convince  myself  of  the  real  existence  of  such  processes, 
and  it  is  only  in  a  very  few  cases  I  believe  to  have  seen  them  (fig. 
67).  I  think  that  it  is  the  issuing  of  neuroglia-fibres  from  the  sheath 
of  the  cells  that  has  generally  occasioned  the  descriptions  of  multi- 
polar  cells,  as  such  fibres  can  look  very  like  real  cell  processes 
(cf.  fig.  44). 

The  processes,  or,  as  I  call  them,  nervous  processes,  passing  to 
the  central  dotted  mass,  and  of  which  each  ganglion  cell  has  only 
one,  have  a  structure  similar  to  that  of  the  nerve-tubes.  They  are 
surrounded  by  a  neuroglia-sheath,  and  their  contents  consist  of 
primitive  tubes. 

In  other  forms  of  Polychaeta  the  ganglion  cells  have,  so  far  as 
my  investigations  go,  a  structure  similar,  principally,  to  what  is  here 
described. 

The  membranes  enveloping  the  ganglion  cells  are  formed 
by  the  neuroglia.  They  generally  consist  of  one,  or  of  a  few,  layers 
only.  In  the  small  cells  they  are  thin,  but  distinctly  marked;  in  the 
large  cells  they  are  often  thick  and  well  developed  (vide  fig.  44,  cm). 
Neuroglia-nuclei  adhering  to  them  do  not  occur  very  frequently.1) 


x)  Dr.  E.  Eohde  (1.  c.  1886  p.  785)  distinguishes  between  two  types  of 
ganglion  cells  in  the  central  nervous  system  of  the  Aphroditidce.  »Die  Ganglien- 
zellen  der  einen  Art  sind  sehr  schwach  granulirt,  deshalb  von  hellen  Aussehen  und 
meist  ziemlich  klein.  Ihr  Kern  enthalt  stets  mehrere  verschieden  grosse  Korperchen 
und  tritt  nach  Farbungen  in  der  durchsichtigen  Ganglienzelle  scharf  hervor.«  »Die 
Vetreter  des  zweiten  Typus  sind  sehr  grosse,  kugelige  Gebilde,  welche  durch  eine 
sehr  dunkele  Granulirung  sofort  in  die  Augen  fallen.  Sie  besitzen  einen  grossen, 


-   114  — 

Lumbricus  agriccla. 

The  ganglion  cells  of  Lumbricus  are,  in  their  structure,  somewhat 
similar  to  those  of  Nereis.  In  sections,  their  protoplasm  has  a  distinct, 
reticular,  grarmlous  appearance;  large  granules,  similar  to  those  found 
in  the  ganglion  cells  of  Nereis,  do  not,  however,  occur.  The  whole 
protoplasm  is,  in  preparations,  rather  deeply  stained ;  the  reticulation  is 
generally  very  distinct,  slight  thickenings  are  only  seen  in  the  points 
where  the  walls  of  the  meshes  unite.  The  meshes  are  generally 
very  large;  that  they  are,  at  all  events  to  a  great  extent,  really 
transsected  tubes  is,  I  think,  clearly  seen  in  fig.  47,  which  represents 
a  section  through  a  large  ganglion  cell,  and  which  is  drawn  under 
the  camera  lucida  as  exact  to  nature  as  possible  (very  highly  magni- 
fied). The  tubes  are,  in  this  illustration,  seen  transversally  as  well 
as  partly  longitudinally  transsected,  giving,  the  protoplasm  to  some 
extent,  a  concentric  appearance;  the  tubes  forming  the  nervous 
process  are  seen  to  be  quite  like  those  circulating  in  the  protoplasm.1) 

In  some  cells,  a  kind  of  higher  differentiation  seems  to  be  pre- 
sent in  the  protoplasm ;  such  a  cell  is  represented  in  fig.  46.  Lighter 


fein  granulirten  Kern  und  dieser  ein  einziges  grosses  K6rperchen.«  A  similar  dif- 
ference in  the  appearance  of  the  small  and  large  ganglion  cells  is,  certainly,  very 
prominent  also  in  the  nervous  system  of  Nereis;  but  as  I  have  found  transition  forms 
between  both  these  kinds  of  cells,  I  can  not  distinguish  between  two  types.  My 
experience  is  to  some  extent  that,  the  larger  the  cells  are,  the  more  and  more 
granular  become  their  protoplasm,  and  there  can  not  easily  be  drawn  any  line  of 
demarcation. 

As  to  the  sheaths  of  the  ganglion  cells  Rohde  says :  »Beide  Ganglienzellen- 
arten  .entbehren  einer  Zellenmembran  und  liegen  eingebettet  in  ein  Maschenwerk 
von  Fasern,  welche  tiberall  das  Nervensystem  begleiten  und,  wie  ich  glaube,  aus 
Subcuticularzellen  hervorgegangen  sind.«  As  may  be  seen  from  my  description  I 
agree  with  this  statement  of  Rohde;  his  »Fasern«  or  »Subcuticularfasern«  belong 
to  what  I  call  the  neuroglia. 

Of  the  protoplasm  of  the  largish  cells  Rohde  says:  »dass  die  ganze  Zelle 
nach  alien  Richtungen  von  veschieden  starken  Faserchen  durchzogen  wird,  welche 
auf  den  Zellfortsatz  iibergehen  und  diesem  eine  feine  Langsstreifung  verleien.  Aber 
nicht  nur  hier  verlassen  diese  Faserchen  die  Zelle,  sondern  man  ist  uberrascht  zu 
sehen,  wie  sie  theils  einzeln,  theils  zu  Biindeln  vereinigt  allenthalben  an  cler  Peri- 
pherie des  nackten  Zellkorpers  heraustreten  und  in  die  Subcuticularfaserhiille  ein- 
dringen.«  It  is  evident  that  Rohde  and  I  have  observed  the  same  structures;  his 
»Faserchen«  must  partly  be  what  in  my  opinion  are  the  spongioplasmic  sheaths  of 
the  primitive  tubes  (especially  those  which  pass  into  the  nervous  process),  and  the 
»Faserchen«  penetrating  in  the  Subcuticularfaserhiille «  must  be  the  spongioplasmic 
fibres  issuing  from  the  neuroglia-sheath  of  the  cell  (vide  fig.  44,  sf;  fig.  45,  sf;  fig  67). 
and  which  fibres  partly  form  a  spongioplasmic  reticulation  in  the  protoplasm  (coin- 
pare  my  description  of  Homarus  p.  101). 

T)    The  tubes  in  the  protoplasm  seem  to  be  of  different  size  in  the  various  cells. 


and  darker  parts  are  here  seen  in  the  protoplasm,  the  latter  ones 
forming  a  sort  of  reticulation  with  very  large  meshes,  in  which 
smaller  meshes  occur-  similar  to  those  mentioned  above.  This  is 
perhaps  an  appearance  produced  by  a  structure  somewhat  similar 
to  that  which  is  described  in  the  ganglion  cells  of  Homarus  (cf. 
fig.  25  &  27).  The  large  meshes,  or  lightly  stained  areas,  are  perhaps 
transsected  bundles  or  small  masses  of  primitive  tubes. 

Such  a  prominent  spongioplasmic  reticulation  as  we  have  found 
in  the  ganglion  cells  of  Homarus  is  not  present  in  the  ganglion  cells 
of  Lumbricus,  indeed,  it  is  very  difficult  to  detect  anything  similar  to  it. 

We  have  thus,  the  protoplasm  of  the  ganglion  cells  of  Lumbri- 
cus, according  to  my  investigations,  consisting  principally  of  primitive 
tubes,  with  distinctly  marked  spongioplasmic  sheaths;  besides  this 
there  must,  however,  also  be  another  subtance  present,  as  the  pro- 
toplasm is  more  deeply  stained  then  the  contents  of  the  nerve-tubes. 
This  protoplasm  has  therefore,  in  Lumbricus,  a  composition  which 
probably  is  very  similar  to  what  is  present  in  the  ganglion  cells  of 
Homarus. 

The  processes  of  the  ganglion  cells.  -  -  The  ganglion  cells 
are  unipolar  or  multipolar.  Each  cell  has,  however,  never  more  than 
one  nervous  process  passing  to  the  central  dotted  mass  of  the  nerve-cord. 
The  other  processes  are  very  short,  have  the  same  appearance  as  the 
protoplasm  of  the  cell,  and  are  lost  in  the  surrounding  reticular  neu- 
roglia,  or  can  be  traced  to  their  connection  with  the  neurilem-sheath 
or  perineurium  surrounding  the  ventral  nerve-cord  inside  the  mus- 
cular layer  (vide  fig.  68).  These  processes  I  call  protoplasmic  pro- 
cesses, and  their  function  is,  I  suppose,  of  nutritive  nature.  All 
ganglion  cells  are  thus,  in  reality,  of  unipolar  nature. 

The  structure  of  the  nervous  processes  is  similar  to  that  of  the 
nerve-tubes;  their  contents  consist  of  primitive  tubes,  and  they  are 
eveloped  by  a  neuroglia-sheath  which  is  a  direct  continuation  of  the 
membranes  or  sheaths  enclosing  the  ganglion  cells  from  which 
they  issue. 

The  nuclei  of  the  ganglion  cells  are  comparatively  large. 
They  have  the  same  appearance  as  described  above,  with  a  distinct 
surrounding  membrane  and  a  varying  inner  structure.  Their  situation 
in  the  cells  is  also  somewhat  variable;  they  are  very  often  situated 
towards  that  pole  from  which  the  nervous  process  issues;  this  is 
perhaps  the  most  common  situation  (fig.  46);  sometimes  they  are, 
however,  also  situated  towards  the  opposite  end  of  the  cell,  or  in 
its  mesial  part  (vide  fig.  47). 

8* 


—  n6  — 

The  membranes  enveloping  the  ganglion  cells  are 
formed  by  the  neuroglia;  they  are  generally  very  thin  and  only  little 
prominent.  Occasionally,  neuroglia-nuclei  are  seen  adhering  to  them. 
They  are  intimately  connected  with  the  reticulation  of  neuroglia 
extending  between  the  ganglion  cells  (vide  fig.  47  &  68). 

The  Molluscs. 

The  structure  of  the  ganglion  cells  af  Patella  vulgata  is  very 
similar  to  what  we  have  found  in  Lumbricus.  Their  protoplasm 
exhibits,  in  sections,  a  distinct  reticulation  with  rather  largish  meshes 
(vide  fig.  48,  49  and  50).  In  this  reticulation  small  granules  are 
seen,  situated  in  the  same  way  as  described  above,  viz.  in  the  points 
where  the  walls  of  the  meshes  unite.  The  meshes  are,  to  a  great 
extent,  transsected  tubes,  this  is  seen  in  several  cells  where  some 
tubes  are  longitudinally  transsected.1) 

In  macerated  preparations  plenty  of  large  yellow  granules  are 
generally  seen  in  the  protoplasm  of  the  ganglion  cells.  These  gra- 
nules have  a  variable  size,  and  no  regular  shape,  they  are  sometimes 
spherical,  sometimes  square  or  polyhedrical,  and  they  look  as  if  they 
were  produced  by  coagulation  of  a  homogeneous  yellow  substance. 
They  are  often  extended  through  the  whole  mass  of  the  protoplasm, 
very  frequently  they  are,  however,  concentrated  in  special  parts  of 
the  cells,  especially  in  the  neighbourhood  of  the  nucleus.  Plenty  of 
similar  smaller  or  larger  granules  generally  occur,  also,  outside  the  gan- 
glion cells,  in  macerated  preparations.  They  frequently  occur  in  such 
number  that  one,  for  a  time,  could  feel  disposed  to  believe  that 
they  belonged  to  a  substance  extended  through  the  whole  nervous 
system.  Sometimes  they  are  even  united  to  larger  homogeneous 
masses.  Upon  careful  examination  I  have,  however,  come  to  the 
conviction  that  they  are,  either  exuded  from  cells,  or  they  may  also 
spring  from  destroyed  cells.  I  have  sometimes  observed  such  a 
substance  exuded  from  the  protoplasm  of  cells. 

Fig.  52  represents  such  a  case.  The  substance  is  here  seen 
occurring  inside,  as  well  as  outside,  the  cell.  Inside  the  cell,  the  gra- 
nules are  concentrated  towards  the  part  of  the  surface  where  they 


*)  The  reticulation  which  H.awitz  describes,  in  the  ganglion  cells  of  the 
Acephales  (vide  p.  65)  is,  without  doubt,  the  same  appearance  as  here  described, 
and  it  is,  consequently,  in  my  opinion,  no  real  reticulation  but,  to  a  great  extent,  an 
appearance  produced  by  primitive  tubes,  which  are  seen  in  optic,  or  real  transverse, 
sections. 


are  probably  exuded ,  outside  the  cell  they  are  united  to  larger  pieces 
of  irregular  shape.  The  granules  are  not  only  situated  nearthe  surface 
of  the  cell,  but  also  occur  in  the  mesial  parts  of  the  protoplasm; 
this  can  easily  be  seen  by  changing  the  level  of  the  microscope. 

The  relations  of  the  substance  of  these  yellow  granules  in 
the  live-state  of  the  cells,  I  have  not  sufficiently  examined,  neither 
am  I  in  a  position  to  say  of  what  it  consists.  It  is  obviously  this 
substance  which  gives  the  nervous  system  of  Patella,  as  well  as 
other  Molluscs,  the  well-known  yellowish  collour,  and  which  RAWITZ, 
HALLER,  H.  SCHULTZE,  SOLBRIG,  BUCHHOLZ  and  others  have  de- 
scribed as  pigment.  I  think  it  is  most  probable  that  the  yellow 
colour  is  due  to  a  substance,  related  to,  or  similar  to  haemoglobin; 
the  substance  contains,  probably,  also  fat,  as  the  granules  are  deeply 
stained  by  osmic  acid.  Strange  to  say,  I  have,  as  a  rule,  not  been 
able  to  observe  quite  similar  granules  in  the  sections  of  the  cells. 
The  reason  why  I  do  not  exactly  know,  as  my  investigations  are 
still  too  imperfect  in  this  respect.1)  As  also  suggested  by  HALLER, 
I  think  it  is  very  probable  that  this  substance  is  principally  engaged 
in  the  nutrition  of  the  ganglion  cells.  I  suppose  that  the  correspond- 
ing substance  in  the  ganglion  cells  of  Homarus  is  the  fatty  substance, 
the  existence  of  which  we  have  above  (vide  p.  108)  indicated. 

In  the  sections  of  some  cells,  I  have  observed  a  slight  tendency 
to  a  differentiation  of  the  protoplasm  into  darker  and  lighter  stained 
parts  (vide  fig.  48).  This  tendency  is,  however,  never  very  promi- 
nent. Generally,  the  protoplasm  has  a  rather  uniform,  somewhat 
deep  staining,  which  -  possibly  indicates  the  extension  of  a  (myeloidr) 
substance,  connected  with  the  spongioplasm,  through  the  whole 
protoplasm  of  the  ganglion  cells,  as  before  mentioned  in  my  descrip- 
tion of  the  ganglion  cells  of  Homarus,  and  possibly  this  substance 
is  of  the  same  nature  as  that  which  forms  the  granules  (above 
mentioned)  in  macerated  preparations. 

The  processes  of  the  ganglion  cells.  —  The  ganglion  cells 
have  a  unipolar,  bipolar  or  multipolar  shape.  Whether  unipolar  or 
multipolar,  each  cell  has  one  nervous  process  only,  passing  into 
or  through  the  central  dotted  substance,  the  other,  protoplasmic 
processes,  if  they  are  present,  are  always  very  short,  and  have  an 
appearance  similar  to  the  protoplasm  of  the  cell.  They  are  immedi- 
ately lost  in  the  neuroglia-reticulation,  or  they  pass  to,  and  unite 
with  the  perineurium  surrounding  the  central  nervous  system. 

*)  In  a  great  many  sections  I  have  found  a  homogeneous  yellow  substance 
being  extended  in  the  protoplasm  of  the  ganglion  cells.  It  seems  to  be  the  same 
substance  which  forms  the  granules  in  isolated  cells. 


—  iiS  — 

system.  Their  function  is,  in  my  opinion,  of  nutritive  nature,  as 
mentioned  before. J) 

The  contents  of  the  nervous  processes  consists  of  primitive  tubes. 

The  nervous  processes  (as  well  as  the  protoplasmic  ones)  are 
enveloped  by  neuroglia-sheaths  adherent  to  which  neuroglia-nuclei 
may  be  seen. 

The  nuclei  of  the  ganglion  cells  have  a  structure  similar 
to  what  is  before  mentioned  as  regards  the  nuclei  of  the  cells  of 
Homarus  etc. 

They  are  generally  situated  in,  or  towards,  that  pole  of  the  cell 
from  which  the  nervous  process  issues.  Sometimes  they  are  also 
situated  in  the  mesial  part  of  the  cell  and  very  seldom  in  the  end 
opposite  to  the  nervous  process. 

They  have  a  relatively  large  size;  when  they  are  situated  near 
the  origin  of  the  nervous  process,  they  generally  fill  nearly  the 
whole  diameter  of  the  cell,  leaving  only  a  narrow  layer  of  proto- 
plasm, through  which  the  connection  of  the  nervous  process  with 
the  upper  principal  part  of  the  protoplasm  is  produced  (vide  fig.  53). 
Frequently  the  space  between  the  nucleus  and  the  membrane  en- 
veloping the  cell  is,  however,  so  extremely  narrow,  that  it  looks  as 
if  only  a  very  few  primitive  tubes  could  pass;  it  has,  indeed,  the 
appearance  as  if  the  protoplasm  of  the  ganglion  cell  was  almost 
divided  by  the  nucleus  into  two  separate  parts. 

In  one  case  I  have  seen  a  nucleus  sending  a  short  process  into 
the  nervous  process  (vide  fig.  54);  this  short  process  was  very 
distinct,  and  appeared  to  be  formed  by  the  nuclear  membrane;  it 
may  be  that  it  has  only  been  an  artificially  produced,  post-mortem, 
appearance. 

The  neuroglia-membranes  enveloping  the  ganglion  cells 
are  thin  and  but  slightly  prominent.  Neuroglia-nuclei,  adherent  to 
them,  are  occasionally  seen.  They  are  intimately  connected  with  the 
neuroglia  reticulation  extending  between  the  ganglion  cells  (fig. 
48 — 50,  nur).  When  HALLER  and  RAWITZ  seem  to  deny  to  some 
extent  the  existence  of  such  membranes,  I  think  that  it  is  owing 


J)  In  the  peripheral  layers,  almost  all  cells  have  unipolar  shape,  in  the  inner 
layers  (towards  and  in  the  dotted  substance),  the  bipolar  or  multipolar  shape  is  more 
common;  as  will  later,  in  a  separate  chapter,  be  treated  of,  this  also  indicates  the 
nutritive  significance  of  the  protoplasmic  processes.  Real  anastomoses  of  proto- 
plasmic processes  from  the  same  cell,  or  from  various  cells,  I  have  never  been  able 
to  observe,  and  do  not  believe  either  in  their  existence  or  in  the  significance 
which  Hatter  and  most  writers  attribute  to  those  processes  (vide  sequel). 


—  119  — 

to  imperfect   staining.     As  above  mentioned,   these  membranes  also 
envelope  the  processes  issuing  from  the  cells. 

The  Aecidians. 

The  protoplasm  of  the  ganglion  cells  of  the  Ascidians 
has,  in  isolated,  macerated  preparations,  a  reticular  appearance  (vide 
fig-  55 — 56),  quite  similar  to  what  is  before  described  in  Mollnsca, 
Ltimbricits  etc.,  and  which  appearance  is,  I  suppose,  to  a  certain 
extent,  produced  by  primitive  tubes,  which  in  a  complicated  way 
are  woven  between  each  other  and  are,  in  the  preparations,  partly 
seen  in  optic  diameter.  It  is  remarkable  that  a  concentric  arrange 
ment  in  the  protoplasm  round  the  nucleus  can,  only  very  seldom,  be 
traced  out.  The  .shape  of  a  great  many  cells,  and  the  situation  of 
the  nuclei  is,  perhaps,  to  some  extent,  the  cause  of  this.  In  sections, 
the  protoplasm  of  the  cells  exhibits  a  reticulation  similar  to  what  is 
observed  in  isolated  cells.  At  the  points  where  the  walls  of  the 
small  meshes  unite,  small  thickenings  or  granules  occur,  giving  the 
protoplasm  a  slightly  granular  appearance. 

I  have  never  observed  in  or  outside  the  ganglion  cells  of  the 
Ascidians,  yellow  granules,  similar  to  those  just  described  in  the 
ganglion  cells  of  Patella,  neither  in  macerated  preparations  nor  in 
sections. 

In  sections  of  some  large  cells,  I  have  observed  a  tendency  to 
differentiation  into  small  lighter  stained  areas,  similar  to  what  is  de- 
scribed in  the  ganglion  cells  of  Homarus.  This  differentiation  is 
not,  however,  very  prominent  (vide  fig.  58,  a). 

In  preparations  treated  with  osmic  acid,  or  fluids  containing  this 
agent,  the  whole  protoplasm  of  the  ganglion  cells  is  also  very 
deeply  stained  by  carmine  colours  (picro-carmine). !)  This  indicates 
perhaps  the  presence  of  a  special  substance  (compare  what  is  said 
of  this  above.) 

The  nuclei  of  the  ganglion  cells  have  a  distinct  thin  mem- 
brane, and  an  inner  structure  which  has  a  varying  appearance,  similar 
to  what  is  above  mentioned  in  respect  of  the  ganglion  cells  of 
Homarus  etc.  A  distinct  nucleolus  is  generally  seen.  The  nuclei 
are  relatively  large;  they  are  situated  in  the  mesial  parts  of  the  cells, 


])  A  method  which  in  my  experience  is  very  good  for  the  nervous  system 
of  the  Ascidians,  is  treating  with  osmic  acid  (^ — I  °/o)  f°r  i — T  nour,  or  even 
longer,  then  sufficient  washing  in  running  water  and  staining  in  good  picro- 
carmine  (i  °/0)  for  24  hours  or  longer. 


—    120    — 

or  also  sometimes  near  the  pole  from  which  the  nervous  process 
issues  or  in  the  opposite  side. 

The  processes  of  the  ganglion  cells.  —  The  most  common 
shape  of  the  ganglion  cells  is  the  unipolar  one ;  the  large,  peripheric- 
ally  situated  cells,  especially,  are  of  this  shape  (fig.s  55,  56,  58).  In 
the  inner  layers  and  in  the  dotted  substance,  cells  with  bipolar,  tri- 
polar  or  multipolar  shape  occur  (fig.  57).  Each  cell  has  only  one 
nervous  process,  the  other  processes  are  protoplasmic,  and  their 
function  is  of  nutritive  nature.  That  is  also,  in  my  opinion,  the 
reason  why  they  principally  occur  in  connection  with  cells  situated 
in  the  inner  layers,  and  are  directed  towards  the  external  sheath 
(perineurium)  enveloping  the  brain. 

The  nervous  processes  exhibit  a  longitudinal  striation,  and  their 
contents  consist  of  primitive  tubes.  They  are,  in  macerated  prepra- 
tions,  only  lightly  stained,  and  have  an  appearance  different  from  that 
of  trie  protoplasm  of  the  cells.  The  protoplasmic  processes  resemble, 
in  their  appearance,  the  protoplasm  of  the  cells. 

The  neuroglia-membranes  enveloping  the  ganglion 
cells  are  very  thin  and  but  slightly  prominent.  The  neuroglia  is 
but  little  developed,  and  occurs  very  sparingly  between  the  gang- 
lion cells  in  the  brain  of  the  Ascidians. 


Summary. 

If  the  reader  has  followed  me  in  these  researches  on  the  struc- 
ture of  the  ganglion  cells  of  various  types  of  invertebrates,  he  will 
have  gathered  that  there  are  some  principal  features  in  the  structure 
which  seem  to  be  common  to  all  the  types  investigated ;  and,  if  it  is  so, 
we  may  conclude  as  above,  in  respect  of  the  structure  of  the  nerve- 
tubes,  that  those  features  in  the  structure  of  the  ganglion  cells  are 
common  to  all  invertebrated  bilaterates.  We  may  thus  give  the 
following  summary  of  our  results: 

1)  The  ganglion   cells   of  all  invertebrated  bilaterates  consist  of 
a  nucleus  with  distinct  membrane,  and  a  varying  inner  structure,  and 
also  of  a  protoplasm  with  various  constituents ;  the  cells  are  enclosed 
by  a  membrane  of  neuroglia-substance. 

2)  The  principal  constituents  of  the  protoplasm  are  primitive  tubes, 
having  the  same  structure  as  those  in  the  nerve-tubes  (they  contain 
hyaloplasm   enclosed  in   spongioplasm}.     The   course,   and   origin   (or 
termination)  in  the  cell,  of  these  primitive  tubes  I  am  not  in  a  posi- 
tion to  describe  particularly;  some  of  them  very  frequently  circulate 


—    121    — 

for  some  distance,  concentrically,  round  the  nucleus,  giving  the 
ganglion  cells  a  concentrically  striated  appearance. 

In  some  ganglion  cells,  especially  those  of  Homarus  and  Neplirops, 
primitive  tubes  are  partly  united  in  bundles,  or  to  smaller  or  larger 
masses  situated  in  the  protoplasm,  and  which  are  distinctly  lighter 
staining  than  the  rest  of  the  protoplasm,  in  which,  however,  also, 
plenty  of  primitive  tubes  occur  (fig.  38). 

In  a  great  many,  or  possibly  in  all,  ganglion  cells  a  spongioplas- 
mic reticulation  is  present,  extending  from  the  enclosing  neuroglia- 
membrane  into  the  protoplasm,  between  the  primitive  tubes,  and 
intimately  connected  with  the  spongioplasmic  sheaths  of  the  latter. 
This  reticulation  is  very  prominent,  especially  in  the  ganglion  cells, 
of  Homarus  and  Nephrops,  where  thick  spongioplasmic  fibres  af  a 
peculiar  appearance,  and  connected  with  the  reticulation  often  occur 
in  the  peripheral  layers  of  the  protoplasm,  penetrating  from  the 
neuroglia-membrane  into  the  protoplasm  (fig.  24). 

Besides  this  reticulation,  there  is,  probably,  also  a  special,  partly 
fatty  (myeloid?)  substance  present  in  all  ganglion  cells  of  inverte- 
brated  bilaterates,  which  substance  does  not  generally  occur  in  the 
nerve-tubes.  This  substance  possibly  occurs  to  some  extent,  in 
connection  with  the  spongioplasmic  reticulation,  and  extends  between 
the  primitive  tubes  of  the  protoplasm,  giving  the  latter,  in  preparations, 
the  deep  staining  which  is  generally  prominently  different  from  the 
staining  of  the  contents  of  the  nervous  processes  and  nerve-tubes 
where  primitive  tubes  only  occur. 

Whether  it  is  the  same  substance  which,  in  the  ganglion  cells 
of  a  great  many  animals  (cf.  Polychseta,  Mollusca  etc.),  is  connected 
with  a  pigment  (haemoglobin?)  and  gives  the  nervous  system  its 
special  colour,  I  am  not  in  a  position  to  decide,  although  I  think  it 
not  improbable. 

3)  The  processes  of  the  ganglion  cells  are  of  two  kinds;  viz. 
nervous  processes  and  protoplasmic  processes. 

Of  nervous  processes  each  ganglion  cell  in  the  central  nervous 
system  has  always  one  and  never  more.  The  nervous  processes  are 
generally  directed,  centrally,  towards  the  dotted  substance. 

When  the  ganglion  cells  are  multipolar  (the  unipolar  cell  is, 
however,  the  most  common  type  in  invertebrated  bilaterates)  the 
other  processes  are  protoplasmic  ones,  and  they  are  generally  short 
and  directed  peripherically,  they  having  a  nutritive  function  and 
being  united  with  the  neuroglia.  As  regards  structure  and  appear- 
ance, they  are  quite  similar  to  the  protoplasm  of  ganglion  cells. 


—    122   — 

4)  The  contents  of  the  nervous  processes  consists  of  primitive 
tubes  which  spring  from  the  protoplasm  of  the  ganglion  cells, 
generally  in  such  manner  that  they  converge  uniformly  from  the 
whole  protoplasm,  towards  the  pole  where  the  nervous  process 
issues;  here  they  unite,  and  constitute  the  contents  of  the  latter 
(ng.s  26,  43—58). 

In  some  ganglion  cells  (observed  in  Homarus  and  Nephrops) 
the  contents  arises  from  a  union  of  bundles  of  primitive  tubes.  The 
contents  of  the  nervous  process  may  also  be  formed,  in  this  or  the 
common  manner,  within  the  protoplasm  of  the  cell  for  a  shorter  or 
longer  distance  from  the  place  where  the  process  issues,  the  process- 
contents  has  thus,  to  some  extent,  an  undivided  course  through  the 
protoplasm  within  the  cell  itself  (fig.s  37,  38  A,  59,  60).  These  latter 
modes  of  origin  I  have  observed  especially  in  Homarus  and  Nephrops. 


3.     The  structure  of  Leydig's  dotted  substance. 

The  nature  of  the  so-called  LEYDIG'S  dotted  substance  (»Punkt- 
substanz«),  which  is  centrally  situated  in  the  nervous  ganglia  or  the 
central '  nerve-system  of  all  invertebrated  bilaterates,  has  been  very 
much  discussed,  and  has  been  described  in  very  different  ways  by 
the  many  previous  authors  on  this  subject,  as  is  already  mentioned 
in  the  historical  introduction  to  this  paper. 

Where  so  many  prominent  scientists  have  given  their  opinion, 
it  is,  of  course,  a  serious  matter  to  suggest  a  new  view  which  is 
contrary  to  almost  all  previous  views. l)  It  was  therefore  not  with- 
out some  hesitation  and  only  after  careful  investigations  that  I 
entered  upon  the  description  of  the  dotted  substance  in  the  nerve- 
system  of  the  Myzostomes**)  and  subsequently  upon  the  dotted  sub- 
stance in  the  brain  of  the  Ascidians.*)  Since  that  time  I  have 
extended  my  investigations  to  a  great  many  animals  of  various 
classes,  and  have  always  found  my  previous  results  confirmed  in 
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 


—    I24   — 

» 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  wTe  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,tnty  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). 


—    I29  — 

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, 
such  a  nerve-tube,  seen  in  a  section  stained  by  the  chromo-silver 
method;  in  the  section  a  few  lateral  branchlets  only  were  stained* 
but  I  think  it  probable  that  there  were  more.  The  nerve-tubes 
spring  from  ganglion  cells  which  are  situated  either  on  the  same 
side  as  the  peripheral  nerve  to  which  the  nerve-tubes  belong,  or  on 
the  opposite  side  of  the  ganglion. 

Other  nerve-tubes  do  not  spring  directly  from  ganglion  cells,  but 
arise  from  the  dotted  substance  by  a  wnion  of  slender  primitivv 
tubes  and  fibrilla,  which  unite  to  form  thicker  and  thicker  tubes. 
I  have  never  succeeded  in  tracing  a  nerve-tube  with  such  an  origin 
to  its  finest  branches;  this  is  owing  to  the  very  complicated  course 
of  those  nerve-tubes;  they  often  originate  on  the  same  side  as  the 
peripheral  nerve  to  which  they  belong,  but  most  frequently  they 
originate  on  the  opposite  side.  They  then  pass  united  to  bundles,, 
or  transverse  commissures,  from  one  side  of  the  ganglion  to  the 
other.  Though  I  have  not  been  able  to  trace  such  nerve-tubes 
through  the  whole  extent  of  their  course,  I  have,  however,  seen 
their  origin  in  portions  and  believe  I  am  entitled  to  say  that  it  is 
as  just  described. 

When  we  now  gather  what  will  be  the  constituents  of  the 
dotted  substance  according  to  the  above  given  investigations  we  will 
have  the  following. 

1)  The  branches  of  those  nervous  processes  which  lose  their 
individuality  and  are  entirely  broken  up  into  fine  branches. 

2)  The   side-branchlets   of  those   nervous   processes    which   di- 
rectly become  nerve-tubes   and   do  not  lose  their  individuality   (but 
which  on  their   course   through  the  dotted  substance  give  off  side- 
branchlets). 

3)  The   branches   of  those   nerve-tubes   which   come   from  the 
longitudinal   commissures,   and  which  in  the    dotted  substance   are- 
entirely  broken  up  into  slender  branches. 

4)  The  side-branchlets  given  off  from  those  nerve-tubes  of  the 
longitudinal    commissures    which    pass   entirely  through  the   ventral 
ganglia,  only  giving  off  branchlets  to  the  dotted  substance. 

5)  The  side-branchlets  joining  those  nerve-tubes  of  the  longi- 
tudinal commissures  which  spring  directly  from  ganglion  cells.    These 
branchlets  are  partly  the  same  as  those  mentioned  in  2. 

6)  The   primitive  tubes  and  branchlets,  or  fibrillae,  which  unite 


-  133  - 

to  constitute  those  peripheral  nerve-tubes  which  entirely  spring  from 
the  dotted  substance. 

7)  The  side-branchlets  joining  those  peripheral  nerve-tubes  which 
.are  direct  continuations  of  nervous  processes  from  ganglion  cells. 
These  side-branchlets  are,  consequently,  partly  the  same  as  those 
mentioned  in  2. 

We  have  thus  seen  that  the  constituents  of  the  dotted  sub- 
stance are  tubes,  and  that  these  tubes  have  a  rather  variable  origin. 
What  the  significance  of  the  dotted  substance  is,  we  will  in  subse- 
quent chapters  have  the  oportunity  to  examine. 

Nephrops  norvegicus. 

In  Nephrops  the  structure  and  relations  of  the  dotted  substance 
is  so  quite  similar  to  what  they  are  in  Homarus,  that  the  above 
•given  description  will  suit  in  all  particulars  for  both  Homarus  and 
Nephrops. 

The  Nereidae. 

Amongst  the  Polychaetes,  it  is  chiefly  the  Nereidae  (especially 
Nereis  virens)  that  I  have  examined  in  respect  of  the  structure  of 
the  dotted  substance;  I  shall  therefore  in  this  chapter  mention  those 
animals  only. 

As  the  dotted  substance  of  the  ventral  nerve-cord  is  the 
simplest,  and  easiest  to  investigate,  we  will  confine  ourselves  to  it. 

In  the  ventral  nerve-cord  of  Nereis  the  dotted  substance  has,  as 
is  well  known,  a  situation  and  extension  very  different  from  what  is  the 
case  in  the  ventral  nerve-cord  of  Homarus.  There  are  no  distinct 
•ganglia,  and  no  distinctly  separated  longitudinal  commissures,  the  dot- 
ted substance  has,  thus,  a  more  uniform  extension  in  two  longitudinal 
rods  along  the  whole  nerve-cord.  Its  composition  of  tubes  is,  if 
possible,  still  more  evident  than  it  is  in  Homarus.  In  transverse 
•sections  of  the  nerve-cord  we  find,  as  before  mentioned  (vide  fig.  14), 
a  reticulation  with  small  and  large  meshes.  In  longitudinal  sections 
we  find  a  longitudinal  striation,  which  shows  that  the  meshes  of  the 
reticulation,  seen  in  transverse  sections,  are  transsected  thick  and  thin 
longitudinal  nerve-tubes.  The  whole  so-called  dotted  substance  of 
the  ventral  nerve-cord  of  Nereis  consists,  thus,  principally  of  longi- 
tudinally running  tubes. 

On  close  examination  of  sections  under  high  powers  of  the 
•microscope  it  will,  however,  be  seen  that  slender  tubes  pass  in 
all  directions  between  these  longitudinal  tubes;  this  is  very  pro- 


—  134  — 

minent  in  some  small  masses,  which  are  especially  ventrally  situated 
on  each  side  of  the  nerve-cord,  and  which  have  a  more  minute  and 
granular  appearance  than  the  rest  of  the  dotted  substance. 

In  longitudinal  section  such  masses  will  be  found  to  occur 
especially  near  places  where  peripheral  nerves  issue.  Fig.  66  represents 
such  a  place  taken  from  a  longitudinal  section,  a  a  are  parts  of 
the  central  longitudinal  septum,  dividing  the  ventral  nerve-cord  longi- 
tudinally into  two  lateral  cords  (cf.  fig.  10,  a).  Smaller  and  larger 
nerve-tubes  (#",  tt\  tt)  are  seen  passing  the  septum,  from  one  side 
of  the  nerve-cord  to  the  other,  a  great  many  of  these  small  nerve- 
tubes  (tf")  seem  to  pass  to  the  origin  of  the  peripheral  nerve, 
which  origin  lies  to  the  left  of  the  illustration.  Some  large  nerve- 
tubes  (pt,  pt)  pass  to  the  same  peripheral  nerve.  Amongst  the 
longitudinal  nerve-tubes  smallish  (t)  as  well  as  largish  (It)  tubes  may 
be  seen.  The  nerve-tubes  running  transversally  between  these 
longitudinal  nerve-tubes  are,  also,  of  different  sizes.  Besides  nerve- 
tubes,  neuroglia-fibres  with  transverse  courses  also  occur,  and  they 
are  often  difficult  to  distinguish  from  nerve-tubes.  Such  transverse 
neuroglia-fibres  may,  for  instance,  be  distinctly  seen  in  the  dotted 
substance  on  the  left  hand  side  of  fig.  67. 

Neuroglia-nuclei  occur  somewhat  sparingly  in  the  dotted  sub- 
stance of  the  ventral  nerve-cord  of  Nereis.  They  are  oblong,  have 
a  granular  appearance,  and  are  generally  longitudinally  situated  in 
the  sheaths  of  the  longitudinal  nerve-tubes  (vide  fig.  66,  n).  They 
are,  however,  also  transversally  situated  in  the  sheaths  of  transverse 
nerve-tubes  (vide  fig.  66,  n1). 

To  find  the  origin  and  course  of  the  various  tubes  constituting  the 
dotted  substance  has  been  very  difficult,  as  I  have  not  yet  succeeded 
in  obtaining  any  staining  by  the  chromo-silver  method  in  the  nervous 
system  of  these  animals.  As  far  as  I  have  been  able  to  penetrate 
by  help  of  the  common  staining  with  haematoxylin  etc.  (which  has 
before  been  described)  I  believe,  however,  to  have  found  that  the 
constituents  of  the  dotted  substance  have  chiefly  (if  not  wholly)  the 
same  origin  in  these  animals  as  they  have  in  Homarus. 

I  have  found  ganglion  cells  with  nervous  processes  wich  were 
directly  transformed  into  nerve-tubes,  but  from  which  side-branchlets 
were  given  off  (vide  fig.  44).  I  have,  however,  not  been  able  to 
trace  such  nerve-tubes  (direct  continuations  of  nervous  processes) 
into  peripheral  nerves;  those  which  I  have  observed,  have  partly 
had  a  longitudinal  course  in  the  nerve-cord. 

I  have  also  found  ganglion  cells  with  nervous  processes,  which 


—  135  — 

subdivided  in  the  clotted  substance,  and  seemed  to  be  entirely  broken 
up  into  slender  branches. 

I  have  observed  longitudinal  nerve-tubes  which  seemed  to  sub- 
divide and  be  broken  up  into  branches,  similar  to  those  longitudinal 
nerve-tubes  I  have  observed  in  the  ventral  ganglia  of  Homarus. 

I  have  also  observed  side-branchlets  to  be  given  off  from  longi- 
tudinal nerve-tubes  passing  along  the  nerve-cord. 

Finally,  I  have  observed  peripheral  nerve-tubes  springing  from 
the  dotted  substance,  being  apparently  formed  by  a  union  of 
slender  tubes. 

Peripheral  nerve-tubes  springing  directly  from  ganglion  cells,  I 
have,  as  above  mentioned,  not  been  able  to  trace  out,  but  I  have 
been  able  to  trace  peripheral  nerve -tubes  for  considerable  distances 
through  the  dotted  substance  passing  frequently  over  to  the  other 
side  of  the  ventral  nerve-cord,  and  I  believe  that  they  often  spring 
directly  from  ganglion  cells. 

From  the  little  we  have  seen,  we  may  therefore  conclude,  that 
the  constituents  of  the  central  mass,  or  dotted  substance,  of  the 
ventral  nerve-cord  of  Nereis  are  chiefly  the  same  as  those  we  have 
found  in  Homarus;  the  principal  constituent  is,  however,  in  Nereis 
longitudinally  running  nerve-tubes,  and  the  other  constituents  are 
comparatively  sparingly  present.  Masses  of  a  complicated  web  or 
plaiting  of  extremely  slender  tubes,  similar  to  that  which  is  de- 
scribed in  the  ganglia  of  Homarus,  do  not  occur  in  Nereis. 

Upon  the  whole,  the  dotted  substance  of  Nereis  is  very  simple 
in  its  structure,  and  represents  a  primary  state. 

The  suggestion  of  E.  RoHDE  ')  that  the  ventral  nerve-cord  of 
the  Polychaetes  are  only  developed  peripheral  nerves  because  of 
the  longitudinally  running  nerve-tubes,  which  should  indicate  the 
nerve-origin,  is  I  think  not  very  well  founded.  If  that  is  right,  the 
ventral  nerve-cord  of  all  invertebrated  bilaterates  which  have  a  nerve- 
cord,  must  also  spring  from  peripheral  nerves  only,  because  in  all 
of  them  there  are,  according  to  my  investigations,  a  great  many 
longitudinal  nerve-tubes ,  indeed  the  spinal  nerve-cord  of  the  verte- 
brates must  also  have  the  same  origin.  I  do  not  know  if  this  is 
ROHBE'S  opinion?  According  to  this  view  the  primary  state  of  the 
nerve-system  must  be  a  central  brain  from  which  nerves  only  issue. 
Some  of  these  nerves  must  then  at  a  later  stage,  by  an  emigration 
from  the  brain,  or  in  some  other  manner,  have  got  ganglion  cells. 


i.  c.  1886. 


-  136- 

I  do  not  think  it  necessary  to  discuss  any  further  the  many  diffi- 
culties which  would  arise  from  such  a  theory;  in  my  opinion,  it  is 
quite  contrary  to  all  known  laws  of  evolution  of  the  nervous-system. 
The  longitudinal  nerve-tubes  have,  in  my  opinion,  another  origin  and 
significance,  but  this  is  not  the  place  to  enter  into  researches  of 
this  nature,  we  will  defer  this  for  a  later  occasion.1) 


l)  Dr.  E.  Rohde  describes  »die  Leydig'sche  Punktsubstanz*  of  the  Polychee- 
tes  in  the  following  way:  »Untersucht  man  das  Gehirn  der  Polychaeten  auf  feinen 
Schnitten,  so  erkennt  man,  das  dieselbe  aus  sehr  vielen  und  feinen  Faserchen  be- 
steht,  welche  wirr  durch  einander  ziehen  und  bald  im  Langsschnitt  als  Linien,  bald 
im  Querschnitt  als  Punkte  erscheinen.  Das  Bauchmark  hat  im  wesentlichen  die- 
selbe Structur,  nur  iiberwiegen  hier  langsverlaufende  Faserchen,  welche  aber  zahl- 
reich  von  schiefen  und  queren  gekreuzt  werden.  Querschnitte  und  Langsschnitte 
zeigen  im  Gegenzatz  zum  Gehirn  im  Bauchstrang  ein  verschiedenes  Bild,  die  Langs- 
schnitte mehr  Linien,  die  Querschnitte  mehr  Punkte. «  It  will  be  seen  that,  this 
description  by  Rohde  differs  very  much  from  mine.  His  »Faserchen«  are  what  I 
call  sheaths  of  the  nerve-tubes.  It  is  strange,  however,  that  he  does  not  seem  to 
have  observed  the  reticulation  which  is  produced  in  sections  by  the  transsections 
of  the  nerve-tubes,  and  which  is  very  prominent  and  distinct,  for  instance,  in  trans- 
verse sections  of  the  ventral  nerve-cord ;  he  has  perhaps  applied  unsuccessful 
staining-methods.  In  his  description  of  the  large  nerve-tubes  he  mentions,  however, 
fibrous  sheaths  enveloping  them.  Of  one  of  the  colossal  nerve-fibres  of  Sthenelais, 
he  says,  that  »it  arises  by  a  union  of  two  nerve-fibres  coming  directly  from  two 
colossal  ganglion  cells  in  the  brain,  —  and  that  it  is  enveloped  by  a  fibrous 
sheath,  which  is  at  first  closely  applied  to  it,  but  in  its  further  course  separates 
from  it  and  then  encloses  a  cavity,  which  constantly  becomes  larger  posteriorly 
and  in  the  middle  of  the  body  attains  an  enormous  diameter.*  The  nerve-fibre, 
which  almost  disappears  in  its  wide  sheath,  gives  off  fine  processes,  traversing  the 
whole  cavity  and  apparently  penetrating  into  the  sheath.  Towards  the  posterior 
extremity  of  the  body  the  cavity  becomes  smaller,  and  conditions  corresponding  to 
those  of  the  anterior  extremity  are  reestablished. 

As  I  have  not  examined  Sthenelais,  I  can  have  no  opinion  of  the  correct- 
ness of  this  statement;  I  have  not  met  with  any  structure  similar  to  it  in  the  Poly- 
chsetes  I  have  examined.  From  Rohde's  own  description  it  appears  to  me  that 
there  must  have  been  some  irregularities  in  his  preparations. 

As  to  the  origin  of  the  large  nerve-tubes,  Rohde  states  that  they  spring  di- 
rectly from  ganglion  cells.  As  to  their  terminations,  his  opinion  is  that  they  are 
generally  broken  up  into  »feine  Faserchen«,  wich  in  transverse  sections  are  seen 
as  minute  dark  points  or  dots. 

The  processes  of  the  ganglion  cells  (which  are  »ausnahmslos  unipolar^)  pass, 
in  his  opinion,  to  the  dotted  substance  partly  »begleitet  von  Subcuticularfasern, 
welche  aber  bald  nach  ihrem  Eintritt  verschwinden.«  What  is  meant  by  »Sub- 
cuticularfasern«  I  do  not  exactly  understand,  perhaps  it  is  the  neuroglia-sheaths 
surrounding  the  processes.  The  smaller  processes  »gehen  direct  in  die  centralen 
Faserchen  liber. «  The  larger  processes  are  partly  enveloped  by  a  sheath,  being  a 
continuation  of  the  sheath  of  the  ganglion  cells.  He  believes  it  to  be  probable 
»dass  sie  durch  pinselformige  Auflosung  in  die  Faserchensubstanz  iibergehen.« 


—  137  — 

Lumbricus  agricola. 

In  Lumbricus,  the  dotted  substance  of  the  central  nervous  system 
represents  a  more  developed  state  than  it  does  in  Nereis,  it  having  a 
much  more  complicated  structure ;  this  is  at  once  prominently  apparent 
in  transverse  and  longitudinal  sections.  The  substance  consists  of 
tubes,  and  exhibits  in  sections  a  minute  reticular  appearance,  the 
tubes  being  generally  very  slender;  they  vary  a  great  deal  as  to 
their  diameter,  some  are  extremely  slender,  others  are  thicker  but 
their  average  size  is  small.  The  tubes  have,  in  the  ventral  nerve- 
•cord,  a  longitudinal  course,  principally  as  may  be  seen  in  longitudinal 
sections.  Between  the  longitudinal  tubes,  slender  tubes  are,  however, 
interwoven,  running  in  all  directions,  and  forming  a  complicated  web 
or  plaiting.  This  plaiting  is  present  to  a  much  greater  extent  than 
is  the  case  in  Nereis,  and  at  the  same  time  the  diameters  of  the 
tubes  are  generally  much  smaller  than  they  are  there. 

As  is  well  known  there  are  no  ganglia  in  the  ventral  nerve-cord 
of  Lumbricus,  and  thus  the  dotted  substance  is  uniformly  extended 
along  the  whole  nerve-cord. 

The  fibrillae  described  by  many  previous  authors,  e.  g.  CLAPA- 
REDE,  are,  in  my  opinion,  as  before  mentioned,  only  the  transsected 
sheaths  of  the  tubes  which  are  the  real  constituents  of  the  dotted 
.substance. 

In  respect  of  the  origin  of  these  tubes  forming  the  constituents 
of  the  dotted  substance,  it  may  be  said  so  far  as  my  experience 
;goes,  that  their  origin  is  quite  similar  to  what  is  found  in  Nereis 
and  Homarus. 

As  to  the  nervous  processes  of  the  ganglion  cells,  I  have  ob- 
served the  same  two  types  as  are  described  in  Homarus,  viz. 
i)  nervous  processes  retaining  their  individuality  and  directly  becom- 
ing nerve-tubes  (either  of  a  peripheral  nerve  or  running  longitudinally 
in  the  ventral  nerve-cord  [fig.  84])  but  which  give  off  side-branchlets 
to  the  dotted  substance  (fig.  /I,/,  g),  and  2)  nervous  processes  which 
lose  their  individuality  and  are,  by  subdivisions,  entirely  broken  up 
into  slender  tubes  losing  themselves  in  the  dotted  substance 
-(fig.  71,  a,  d,  h  and  fig.  72). 

As  to  the  course  of  the  longitudinal  nerve-tubes  of  the  dotted 
substance,  and  the  double  origin  of  the  peripheral  nerve-tubes,  I  have 
•observed  conditions  very  similar  to  those  stated  of  Homarus,  but 
my  observations  have  been  rather  imperfect,  as  I  have  not  obtained 
.such  staining  in  Lumbricus  as  I  have  in  Homarus. 


-  138  - 

Neuroglia-nuclei  occur  sparingly  in  the  dotted  substance  of 
Lumbricus  (fig.  ii,A;  fig.  7i,w,  nj). 

The  Molluscs. 

In  Patella  we  find  the  dotted  substance  to  have  an  appearance 
rather  different  from  that  of  the  animals  before  described.  The 
elements  of  the  dotted  substance  are,  here,  much  smaller,  and  more 
difficult  to  trace  out  than  those  we  have  hitherto  examined. 

On  a  careful  examination  of  successfully  stained  transverse  sec- 
tions through  the  pedal  nerve-cord  of  Patella,,  it  is  possible  to  ob- 
serve a  minute  reticulation  with  very  small  but  distinct  meshes.  It 
is  this  reticulation  which  HALLER  in  the  Rliipidoglossa,  and  RAWITZ 
in  the  Acephales,  describe  as  nervous  reticulation.  Besides  the  meshes 
which  have  extremely  slender  walls,  a  great  many  dark  dots  are  also 
seen.  These  dots  are  situated  in  the  walls  of  the  meshes,  and 
chiefly  in  their  corners  where  several  walls  of  various  meshes  meet. 
It  is  these  dots  which  RAWITZ  has  described  as  varicose  thickenings 
in  the  nervous  fibrillae  which  he  supposes  to  form  this  reticulation 
in  the  Aoephales. 

On  examination  of  longitudinal  sections  through  the  pedal  nerve- 
cord,  it  is  seen  that  the  dotted  substance  has,  here,  a  somewhat 
different  appearance.  The  reticulation  seen  in  transverse  sections 
is  not  present  to  such  extent,  on  the  other  hand  longitudinally 
running  distinctly  stained  fibrillae  are  very  prevalent.  These  fibrillae 
are  extremely  slender,  and  are  stained  in  the  same  way  as  the 
reticulation  in  transverse  sections.  The  intervals  between  those 
fibrillae  are  very  small  and  are  of  about  the  same  size  as  the  dia- 
meters of  the  meshes  of  the  reticulation.  This  indicates  that  the 
meshes  are  transsected  tubes,  and  that  the  longitudinal  fibrillae  are 
partly  the  transsected  sheaths  of  these  tubes.  It  is  consequently,  in 
so  far,  a  structure  somewhat  similar  to  what  we  have  found  in 
Lumbricus  and  Nereis.  In  longitudinal  sections,  but  especially  in 
oblique  ones,  it  is  seen  that  the  dark  dots  visible  in  transverse  sec- 
tions are  transsected  fibrillae,  chiefly  running  along  the  concreting 
edges  of  the  tubes.  The  question  is,  now,  whether  these  fibrillae 
belong  to  the  neuroglia,  and  are  only  thickenings  in  the  fibrous  sheaths 
of  the  nerve-tubes,  or  whether  they  are  real  nerve-fibrillae  ?  To  decide 
this  question,  I  have  examined  fresh  preparations  as  well  as  macerated 
ones,  but  I  must  admit,  that  in  this  respect  I  have  not  till  yet  succeeded 
in  getting  a  clear  idea  of  the  real  relations  in  the  structure  of  the 
dotted  substance  of  Patella.  In  fresh  isolated  preparations  of  the 


—  139  — 

dotted  substance  plenty  of  fibres  of  various  sizes  are  seen.  The 
greater  part  of  them  are  extremely  slender.  In  fig.  85  some  of  these 
fibres  from  fresh  preparations  are  illustrated.  They  are  present  in 
every  preparation  to  unlimited  extent,  and  do  not  seem  to  be  formed 
in  any  artificial  way,  but  only  to  be  just  isolated.  In  macerated 
preparations  they  are  still  more  prominent  (fig.  86).  They  may, 
here,  be  isolated,  and  traced  for  long  distances  through  the  dotted 
substance;  to  some  extent,  they  are  of  a  rather  uniform  size  with  a 
small  diameter;  they  have  a  smooth  aspect  but  may  sometimes, 
though  seldom,  be  seen  to  give  off  extremely  fine  lateral-fibrillae  (vide 
fig.  85,  b,  e;  86,  a,  6);  where  such  fibrillae  issue  small  varicose  thicken- 
ings are  generally  present.  In  thicker  fibriHae  subdivisions  occasionally 
happen  (vide  fig.  85,  d).  It  is  obvious  that  a  great  deal  of  the  thickish 
fibres  found  in  macerated  preparations  are  real  nerve-tubes,  as  they 
may  be  seen  to  be  direct  continuations  of  nervous  processes  from 
ganglion  cells;  these  fibres  have  also,  to  a  certain  extent,  an  aspect 
like  what  is  characteristic  for  nerve-tubes.  To  decide  the  nature  of 
the  extremely  slender  fibrillae,  which  occur  in  such  abundance,  is,  how- 
ever, much  more  difficult;  their  aspect  is  undeniably  very  like  that  of 
common  neuroglia-fibres  or  connective-tissue  fibres ;  a  great  many  of 
them  are  so  thin  that  they,  even  under  the  highest  powers  of  the 
microscope,  appear  like  lines.  As,  however,  we  may  find  fibrillae  of 
every  transition-stage  from  those  finest  ones  up  to  these  largish 
fibres,  which  unquestionally  are  nerve-tubes,  and  as  we  may  see 
such  fine  fibrillae  to  be  given  off  from  these  nerve-tubes  as  side- 
branches,  or  being  formed  as  a  final-product  by  the  breaking  up 
of  the  latter,  we  feel  ourselves  forced  to  define  these  fibrillae  as 
being  to  a  great  extent  real  nerve-fibrillas.  These  nerve-fibrillae  or 
tubes,  as  we  should  more  properly  call  them,  are  certainly  of  a 
much  smaller  size  than  most  of  the  tubes  we  have  hitherto  found 
in  the  dotted  substance  of  other  animals;  this  may,  however,  be 
accounted  for  from  the  smallness  of  all  the  nervous  elements  in 
Patella. 

On  the  other  hand,  it  is  obvious  that  a  great  many  fibriHae  seen 
in  fresh  and  macerated  preparations  belong  to  the  neuroglia.  Such 
fibrillae  may  often  be  seen  to  issue  directly  from  neuroglia-cells,  or 
united  with  neuroglia-nuclei  (vide  fig.  79 — 81 ;  73,  nn\  &2,nc;  83,  n,  nc; 
86,  nc)  which  occur  abundantly  in  the  dotted  substance. l)  These 


*)  The  reason  why  Hatter  and  Rawitz  deny  the  occurence  of  neuroglia- 
nuclei  is,  I  think,  that  they  have  not  recognized  their  real  nature  and  describe  them 
as  »Schaltzellen«  which  they  believe  to  be  multipolar  ganglion  cells.  H.  Sclmltze, 
Walter,  and  others  have  given  somewhat  similar  descriptions. 


—  140  — 

neuroglia-fibrillae  resemble  in  their  aspect  the  fine  nerve-fibrillse,  so 
very  much,  that  I  am  not  at  present  in  a  position  to  point  out  any 
distinct  difference  between  them.1) 

As  to  an  interfibrillar  substance,  which  many  authors  describe,  it 
may  be  stated  that,  in  fresh  preparations,  I  have  occasionally  observed 
hyaline  pearls  adhering  to  the  sides  of  the  fibrillae  (vide  fig.  85,  6).  In 
my  opinion  these  pearls  do  not,  however,  spring  from  an  interfibrillar 
substance,  but  are  pearls  of  hyaloplasm,  springing  from  destroyed 
nerve-tubes. 

The  origin  of  the  constituents,  forming  the  dotted  substance,  we 
will  find  to  be  quite  correspondent  to  what  is  found  in  Homarus. 
All  the  nervous  processes  of  the  ganglion  cells  are,  as  already 
mentioned,  directed  towards,  and  penetrate  into,  the  dotted  substance. 

As  in  Homarus,  and  the  other  animals  examined,  it  may  be 
seen  that  some  nervous  processes  (vide  fig.  73,  Jc,  m"'t  74,  a,  c,  d,  /;  75  ; 
76;  78;  82,  a\  83,  a)  retain  their  individuality,  in  their  course  through 
the  dotted  subsance,  and  as  far  as  they  can  be  traced  are  not  seen 
to  subdivide;  at  intervals,  however,  they  give  off  some  few  fine  side- 
branchlets,  at  the  origin  of  which  small  varicose  thickenings  frequently 
occur  (fig.  74,  a,  f\  fig.  75,  76). 

Other  nervous  processes   (vide   fig.  73,  &, /*;   fig.  74, 7&,  £;   fig.  77) 

•  lose  their  individuality;  they  subdivide  and  are  broken  up  into  slender 
nerve-fibrilla. 

We  have  thus  two  types  of  nervous  processes,  like  what  is 
found  in  Homarus  etc. 

As  to  the  course  and  termination  of  the  many  longitudinal 
nerve-tubes,  which  form  such  a  material  part  of  the  dotted  sub- 
stance of  the  pedal  nerve-cord,  little  can  be  said  at  present.  In 
some  of  them  I  have  observed  side-branchlets  to  be  given  off,  in 

•  others  I  have  occasionally  seen  subdivisions;  but  upon  the  whole  my 
present  methods  of  investigation  have  been  insufficient  to  trace  out 
these  very  slender  structures.     A  great  many  of  them  are,  however, 
easily  seen  to  pass  into  peripheral  nerves,  forming  peripheral  nerve- 
:  tubes. 

As  to  the  origin  of  the  peripheral  nerve-tubes,  my  investigations 
are  also  in  that  respect  very  imperfect.  I  have  observed  nerve-tubes 
which,  probably,  come  directly  from  ganglion  cells,  as  they  could  be 
•traced  for  long  distances  in  their  course  through  the  dotted  substance 
•without  subdividing,  only  giving  off  some  few  side-branchlets; 


Vide  also  my  description  of  the  nerve-tubes  of  the  Mollusca  p.  94 — 96. 


they  were  often  directed  towards  groups  of  ganglion  cells ;  I  have 
not,  however,  succeeded  in  observing  any  direct  combination  with 
the  latter.  Other  peripheral  nerve-tubes  could  be  seen  to  subdivide 
soon  after  their  entrance  into  the  dotted  substance. 

A  significant  relation  is  that,  a  great  many  nerve-tubes  of  the 
peripheral  nerves  are  considerably  larger  in  the  peripheral  parts  of  the 
latter,  than  they  are  near  their  origin  in  the  pedal  nerve-cord,  and  in  the 
latter  itself.  As  to  the  size  of  the  nerve-tubes;  the  pedal  nerve-cord 
and  the  first  parts  of  the  peripheral  nerves  are  very  much  alike,  and 
it  is  presumably  the  same  substance,  viz.  dotted  substance,  that  forms 
both.  To  make  this  correspondence  quite  complete,  a  great  many 
ganglion  cells  also  occur  in  the  first  parts  of  the  peripheral  nerves, 
especially  in  the  larger  ones  (e.  g.  vide  fig.  20,  gc).  Thus,  it  really 
looks  as  if  the  first  parts  of  the  larger  peripheral  nerves,  issuing  from 
the  pedal  nerve-cord  of  Patella,  also  belong  to  the  central  nervous 
system. 

The  fact  that  the  nerve-tubes  in  the  peripheral  parts  of  the 
nerves  have  generally  a  larger  diameter  than  the  nerve-tubes  near 
the  origin  of  the  nerves,  can  not,  in  my  opinion,  be  explained  in  any 
•other  way  than  that  the  former  to  a  great  extent  arises  by  a  union 
of  the  latter.  In  other  words,  the  roots  of  the  nerves  contains, 
to  a  great  extent,  only  the  elements  of  the  peripheral  nerve-tubes, 
and  the  formation  of  the  latter  does  not  take  place  in  the  pedal 
nerve-cord  or  the  central  nervous  system  only  but  also  in  the 
peripheral  nerves  themselves. 

The  Ascidians. 

I  have  already,  in  a  previous  paper,  given  a  preliminary  report 
of  the  results  of  my  investigations  on  the  dotted  substance  of  the 
Ascidia  (vide  1.  c.  1886),  and  my  present  description  will  partly  be,. 
only  a  confirmation  of  what  is  there  stated. 

In  well  prepared  transverse  sections  of  the  brain,  the  dotted 
substance  exhibits  a  distinct  reticulation  with  minute  round  meshes 
(vide  fig.  87).  These  meshes  are  comparatively  larger,  and  more 
distinct,  than  those  we  found  in  the  dotted  substance  of  Patella; 
their  walls  are  distinct  and  rather  uniform.  Upon  close  examination 
of  transverse  as  well  as  longitudinal  sections,  they  may  be  seen  to 
be  produced  by  a  transsection  of  nerve-tubes,  and  the  walls  of  the 
meshes  in  the  reticulation  are  only  the  transsected  sheaths  of  the 
tubes.  This  may  partly  be  seen  in  longitudinal  sections  where  a 
great  many  nerve-tubes  are  longitudinally  transsected  and  show 


—  142  — 

a  longitudinal  course;  it  is  especially  prominent  near  the  anterior 
and  posterior  extremities  of  the  brain  where  the  large  anterior  and 
posterior  nerves  issue,  and  where,  consequently,  a  great  many  nerve- 
tubes  converge  towards  their  roots,  causing  longitudinal  sections  to  have 
a  longitudinal  striation  (fig.  88),  whilst  transverse  sections  of  the  same 
parts  exhibit  a  distinct  reticulation  with  meshes  of  about  the  same 
diameter  as  the  intervals  between  the  longitudinal  lines  of  the  longi- 
tudinal sections.  In  the  mesial  parts  of  the  brain,  the  nerve-tubes 
run  in  more  diversified  directions,  and  thus  longitudinal  as  well  as 
transverse  sections  exhibit  a  reticulation,  as  tubes  are  transversally 
transsected  in  both;  some  tubes  are,  however,  obliquely,  or  partly 
longitudinally  transsected  and  appear  then,  in  the  sections,  as  oblong 
or  elongated  meshes.  As  the  nerve-tubes  forming  the  dotted  sub- 
stance vary  in  diameter,  the  meshes  are  consequently  also  of 
various  sizes. 

In  the  walls  between  the  meshes,  slender  fibrillae  are  seen  to 
run  in  all  directions,  forming  an  intricate  web  or  plaiting  between 
the  tubes,  but  neither  these  fibrillae  nor  the  larger  nerve-tubes  can 
be  seen  to  anastomose  with  each  other,  and  thus  no  real  reticulation 
is  formed  by  either  of  them ;  the  dotted  substance  consists  of  a  web 
or  plaiting  of  nerve-tubes  and  fibrillce J),  and  it  is  only  the  transsection 
of  the  tubes  which,  in  section,  gives  the  substance  the  appearance  of 
containing  a  reticulation. 

In  macerated  preparations  of  the  dotted  substance,  a  great  many 
tubes  and  fibrillae  are  easily  isolated.  Fig.  89  represents  such  a 
preparation.  It  is  here  distinctly  seen  that,  no  reticulation  and  no 
anastomoses  are  present.  From  some  tubes  side-branches  are 
given  off. 

On  examination  of  the  origin  of  these  nerve-tubes  and  fibrillae 
it  will  be  seen  that  they  have  the  very  same  origin  as  they  have  in 
the  animals  previously  examined.  A  great  many  come  from  ganglion 
cells,  and  a  great  many  pass  on  to  constitute  the  peripheral  nerves, 
and  from  both  fibrillae  and  side-branches  are  given  off. 

The  nervous  processes  issuing  from   the  ganglion   cells  are   of 


*)  These  fibrillae  are  partly  nerve-fibrillse,  partly  neuroglia-fibrillae.  The  nerve- 
fibrillse  have,  probably  all  of  them,  a  tube-structure  like  the  larger  nerve-tubes ; 
i.  e.  an  external  sheath  enclosing  a  semi-fluid  hyaline  contents,  hyaloplasm.  In 
nerve-fibrillae  which  are  not  too  slender,  this  tube-structure  may  be  seen  on  close 
examination.  The  neuroglia-fibrillae  are  often  seen  issuing  from  neuroglia-cells 
which  frequently  occur  in  the  dotted  substance.  I  am  not  in  a  position  to  say 
anything  with  certainty  about  their  structure  at  present. 


—  143  — 

the  same  two  types  previously  described.  Some  processes  retain 
their  individuality,  and  pass  directly  to  form  nerve-tubes,  whilst  giving 
of  slender  side-branches  (fig.  55 — 57;  87,  e;  89,  gc),  other  processes 
lose  their  individuality  and  are  broken  up  into  slender  branches  losing 
themselves  in  the  plaiting  of  the  dotted  substance  (fig.  87,  a,  I,  d,  e\ 
I  have  been  able  to  trace  both  these  types  of  processes,  only  for 
comparatively  short  distances  through  the  dotted  substance,  but 
still  the  difference  between  them  is  generally  possible  to  distinguish.1) 

As  before  said,  a  great  many  of  the  nerve-tubes  of  the  dotted 
substance  go  to  constitute  the  peripheral  nerves.  Many  of  these 
nerve-tubes  are,  consequently,  direct  continuations  of  the  nervous 
processes  from  ganglion  cells  of  the  one  type;  these  nerve-tubes 
probably  form  peripheral  nerve-tubes  directly.  A  great  many 
of  the  other  nerve-tubes  and  fibrillae,  constituting  the  nerves, 
are  either  continuations  of  the  slender  branches  arising  from  the 
subdivisions  of  the  nervous  processes  of  the  other  type  (these 
fibrillae  are  extremely  slender,  and  in  the  roots  of  the  nerves  they 
unite  to  form  thicker  tubes),  or  they  spring  from  a  union  of  similar 
fibrillae  or  branches;  perhaps  the  side-branches  given  off  from  the 
nervous  processes  of  the  first  type  also  contribute  to  the  forming  of 
these  nerve-tubes. 

As  constituents  of  the  peripheral  nerves,  present  in  their  roots, 
we  have  thus  elements  of  two  kinds;  viz.  i)  nerve-tubes  which  are 
direct  continuations  of  nervous  processes,  but  which,  however,  are 
partly  strengthened  by  the  junctions  of  slender  side-branches,  and 
2)  nerve-tubes  arising  from  a  union  of  slender  tubes  or  fibrillae.2) 


T)  As  is  mentioned  in  my  previous  paper  on  the  nervous  system  of  the 
Ascidia  (1.  c.  1886),  small  ganglion  cells  occur  in  the  dotted  substance  (vide 
ng-  87, /",  9}-  Those  cells  have  generally  a  trip olar  or  multipolar  form  (bipolar  cells 
also  occur).  Fig.  57  represents  such  a  cell,  isolated,  in  a  macerated  preparation. 
The  protoplasmic  processes  of  these  cells  are,  generally,  directed  peripherically 
towards  the  external  layers  of  the  brain,  whilst  the  nervous  process  has  very  often 
a  longitudinal  course  through  the  dotted  substance.  I  have  often,  both  in  macerated 
preparations  and  in  sections,  been  able  to  trace  such  nervous  processes  for  some 
distance  of  their  course  through  the  brain,  but  have  rarely  observed  any  sub- 
division of  them.  I  think  it  therefore  probable  that  they,  to  a  certain  extent,  are 
directly  continued  into  peripheral  nerve  tubes;  some  of  them  are,  however,  broken 
up  into  branches  losing  themselves  in  the  dotted  substance. 

2)  It  may  here  be  mentioned  that,  I  have  vbserved  ganglion  cells  situated  in 
the  roots  of  the  nerves  and  sending  their  nervous  processes  directly  into  the  nerve. 
In  fig.  88,  which  represents  a  part  of  a  longitudinal  section  through  the  anterior 
end  of  the  brain  of  a  Coretta,  such  a  ganglion  cell  (gc)  is  seen  situated  at  the 
root  of  one  of  the  anterior  nerves.  I  am  not  in  a  position  to  state  whether  the 
nervous  processes  of  these  cells  send  off  side-branches. 


—   144  — 

Neuroglia-nuclei  are  scattered  through  the  dotted  substance  of 
the  Ascidia ;  they  distinguish  themselves  from  the  nuclei  of  the  before 
mentioned  ganglion  cells,  also  occurring  in  the  dotted  substance, 
by  a -darker  staining,  a  more  oblong  form,  and  a  more  granular 
appearance ;  they  are  also  generally  of  a  smaller  size  than  the  latter, 
As  before  said,  neuroglia-fibres  are  very  often  seen  in  connection 
with  these  neuroglia-nuclei.  Sometimes  neuroglia-nuclei  are  seen 
adhering  to  the  nervous  processes  issuing  from  the  ganglion  cells 
(vide  fig.  87). 

Summary. 

If  we  now  gather  together  the  results  of  our  previous  researches 
on  the  structure  of  the  dotted  substance,  and  if  we  assume  them 
to  be  applicable  to  the  dotted  substance  of  all  invertebrated  bi- 
laterates  —  which  we  may  probably  do,  seeing  the  correspondence 
between  the  principal  characteritics  in  the  structure  of  the  various 
groups  investigated  —  we  may  give  the  following  summary  of  our 
investigations : 

The  dotted  substance  of  all  invertebrated  bilaterates  consists 
chiefly  of  nerve-tubes,  and  primitive-tubes  (and  nerve-fibrillae  which 
are  only  small  primitive-tubes);  these  tubes  consist  of  a  neuroglia- 
sheath,  and  a  semi-fluid  contents  (hyaloplasm),  they  have  conse- 
quently a  structure  similar  to  the  primitive-tubes  of  the  nerve-tubes,, 
only  that  their  sheaths  are  stronger  than  the  spongioplasmic  ones 
of  the  latter. 

The  tubes  and  fibrittce  forming  the  dotted  substance  do  not 
anastomose  with  each  other,  but  form,  only,  a  more  or  less  intricate 
web  or  plaiting.  The  reticulation  seen  in  sections,  and  described  by 
various  authors  as  a  real  nervous  reticulation,  is  no  reticulation, 
but  is  produced  by  the  transsection  of  the  tubes  forming  the  dotted 
substance,  and  the  meshes  of  the  reticulation  are  only  the  transsected 
sheaths  of  these  tubes.  The  })interftbriUar  substance",  described  by 
various  authors,  is  the  hyaline  hyaloplasm,  which  forms  the  contents 
of  the  tubes,  and  is  the  real  nervous  substance.1) 


*)  I  think  it  probable  that  it  is  the  same  substance  which  Rawitz  describes 
as  myeloid  substance.  Hermann's  »Zwischensubstanz«  (cf.  p.  46)  is  evidently 
hyaloplasm.  The  »Knotenpunkte«,  described  by  Hermann,  are,  I  suppose,  thicke- 
nings in  the  sheaths  of  the  tubes,  they  can  not  be  neuroglia-nuclei,  as  they  seem 
to  occur  in  too  great  abundance. 


—  145  — 

The  origin  of  the  nerve-tubes  and  nerve-fibrillae  (primitive  tubes) 
of  which  the  dotted  substance  consists  is  the  following: 

1)  The   branches   of  those   nervous   processes  which  lose  their 
individuality  and  are  entirely  broken  up  into  slender  branches. 

2)  The  side-branches  of  those  nervous  processes   which  do  not 
lose  their  individuality  but  directly  become  nerve-tubes  whilst  giving 
off  side-branches  on  their  course  through  the  dotted  substance. 

3)  Those  longitudinal  nerve-tubes  which  run  along,  through  the 
dotted   substance,    especially   of  the   ventral   nerve-cord,    and  which 
partly  pass  into  peripheral  nerves. 

4)  The  side-branches  given  off  from  those  nerve-tubes. 

5)  The   branches   of  those   longitudinal    nerve-tubes   which   are 
entirely   broken  up   into   slender  branches  losing  themselves   in  the 
dotted  substance. 

6)  The   slender   tubes   or  fibrillae   which    unite    to    form    those 
peripheral    nerve-tubes    which    exclusively    spring    from    the    dotted 
substance. 

7)  The  side-branches  joining  those  peripheral  nerve-tubes  which 
spring  directly  from  ganglion   cells,   i.  e.  which  are   direct  continua- 
tions of  nervous  processes  from  ganglion  cells.     These  side-branches 
are  consequently  partly  the  same  as  those  mentioned  in  2. 

Besides  nerve-tubes  and  fibrillae,  neuroglia- cells  and  fibres  are 
also  present  in  the  dotted  substance  of  all  invertebrated  bilaterates. 
The  neuroglia-nuclei  have  generally  an  oblong  shape  with  a  granular 
appearance. 


4,    The  combination  of  the  ganglion  cells  with  each  other, 
and  the  function  of  the  protoplasmic  processes. 

In  the  historical  introduction  to  this  paper  it  is  pointed  out  that 
two  views  as  to  the  combination  of  the  ganglion  cells  have  especially 
been  prevalent  amongst  the  previous  authors  (vide  p.  64—65). 
We  will  now  examine  the  conclusions  in  this  respect  our  present 
researches  must  lead  us  to. 

A  direct  combination  between  the  ganglion  cells  is,  as  we  have 
seen,  not  acceptable.  In  spite  of  the  most  persevering  investigations 
I  have  not  been  able  to  find  any  direct  anastomosis  of  indubitable 
nature  between  the  processes  of  the  ganglion  cells.  Where  I  thought 
to  have  found  an  anastomosis  it  always  on  application  of  the  strongest 

10 


—   1 46  — 

lenses  resolved  itself  into  an  optical  illusion.  In  a  few  cases  I  have 
certainly  observed  short  bridges  extending  between  neighbouring 
cells,  these  bridges  have,  however,  in  my  opinion,  evidently  been 
remnants  of  cell-divisions,  and  are  therefore  of  but  little  interest 
to  our  present  subject;  they  had  not  the  appearance  of  common 
processes. 

If  a  direct  combination  is  the  common  mode  of  combination 
between  the  cells,  as  most  authors  suppose,  direct  anastomoses 
between  their  processes  ought,  of  course,  to  be  quite  common. 
When  one  has  examined  so  many  preparations  (stained  by  the 
most  perfect  methods)  as  I  have,  without  finding  one  anastomosis 
of  indubitable  nature,  I  think  one  must  be  entitled  to  say,  that 
direct  anastomosis  between  the  processes  of  the  ganglion  cells  does  not 
exist,  as  a  rule.  What  previous  writers  have  supposed  to  be 
anastomoses  is,  in  my  opinion,  probably  the  neuroglia-reticulation 
generally  extending  between  the  ganglion  cells,  and  the  fibres  of 
which  are  often  difficult  to  distinguish  from  the  processes  of  the  latter. 

Another  objection  against  a  direct  combination,  and  which  does 
not  seem  to  have  been  thought  of  by  a  great  many  authors,  is  the 
existence  of  unipolar  ganglion  cells.  How  is  it  possible  to  explain 
an  existence  of  unipolar  cells,  when  we  believe  in  a  direct  combina- 
tion by  anastomosing  processes?  Certainly  we  will  be  obliged  to 
say  with  VlRCHOW,  and  others,  that  -  -  the  closer  we  examine  the 
nervous  systems  —  the  fewer  unipolar  cells  do  we  find;  in  other 
words  we  can  not  believe  in  the  usual  existence  of  unipolar  cells.1) 


1)  A  good  instance  of  the  results  to  which  the  common  theory  of  the  func- 
tion and  combination  of  the  ganglion  cells  must  bring  us  is  a  recent  paper  by 
Fritsch  (op.  cit.  Arch.  mikr.  Anat.  1886).  This  author  says,  that  the  apolar  gang- 
lion cells  have  »lange  genug  in  unserer  Litteratur  gespukt.*  Improved  methods  of 
investigations  have  taught  us  that  they  were  creation  of  our  imagination.  And  he 
continues  (1.  c.  p.  24):  »Wenn  ich  jelzt  nach  reiflicher  Ueberlegung  erklare,  dass 
die  unipolaren  Ganglienzellen  denselben  Weg  wie  die  apolaren  wandern  warden, 
so  muss  ich  fiirchten,  augenblichlich  noch  dem  energichsten  Wiederspruch  zu  be- 
gegnen.«  I  agree  with  the  author  in  the  latter  point,  he  will  certainly  meet 
opposition.  Further  on  in  the  same  paper  he  says  (p.  29):  »dass  es  der  Natur  der 
Ganglienzellen  iiberhaupt  wiederspricht,  als  einzelnes  Element  nur  eine  Verbindung 
mit  der  Peripherie  zu  haben.«  And:  »Eine  wirchlich  unipolare  Zelle  ist  fur  den 
Organismus  nicht  viel  mehr  werth  als  eine  apolare  Zelle. «  This  is  in  my  opinion  a 
quite  logic  conclusion  if  we  suppose  that  the  common  view  of  the  nature  of  the  gang- 
lion cells  is  correct.  When  now,  however,  unipolar  ganglion  cells  actually  exist, 
can  that  easily  be  supposed  to  be  the  fault  of  the  ganglion  cells?  or  is  there  not 
a  possibility  that  our  view  of  the  nature  of  the  ganglion  cells  is  incorrect?  We 
can  not  change  the  the  reality  according  to  our  ideas  but  we  can  change  our  ideas 


-  147  - 

But  we  must  believe  in  it.  We  need,  for  instance,  only  go  to  the 
nervous  systems  of  the  lobster,  and  we  shall  be  quite  convinced  of 
the  existence  of  real  unipolar  cells.  If  those  large  ganglion  cells  of 
the  lobster  have  several  processes,  it  is  strange  that  we  should  not 
be  able  to  observe  one  of  them  by  our  present  modes  of  investigation. 

We  are  thus  obliged  to  reckon  with  real  unipolar  cells,  indeed 
we  are  obliged  to  reckon  with  nervous  systems  containing  almost 
entirely  unipolar  ganglion  cells,  and  how  could  direct  combination 
between  the  cells  be  present  where  there  are  no  processes  to  pro- 
duce the  combination.  We  thus  see  that  also  for  that  reason  we 
are  obliged  to  abandon  the  theory  of  the  direct  combination  between 
the  ganglion  cells. 

Two  questions  which  will  now  present  themselves  are : 

How  is  the  combination  between  the  ganglion  cells  produced? 
and  what  is  the  function  of  those  processes  which  were  previously 
thought  to  produce  the  direct  combination  between  the  cells? 

We  will  first  examine  the  latter  question.  As  before  described, 
the  processes  of  the  ganglion  cells  are  of  two  kinds:  nervous  pro- 
cesses and  protoplasmic  processes.  Of  nervous  processes  each  cell 
(unipolar  or  multipolar)  has  always  one  and  never  more;  the  nervous 
processes  are  always  directed  towards  the  dotted  substance,  or  in 
a  few  cases  they  may  pass  directly  into  peripheral  nerves  (cf.  p.  143, 
note  i).  It  was  not,  however,  these  processes  which  were  gener- 
ally supposed  to  produce  the  combination  between  the  cells,  but  it 
was  the  protoplasmic  processes. 

The  protoplasmic  processes.  —  When  a  ganglion  cell  is 
bipolar  or  multipolar,  then  the  processes  it  posesses,  besides  the 
nervous  process,  are  protoplasmic  processes.  These  protoplasmic 
processes  are  not  directed  towards  the  dotted  substance,  but  gener- 
ally have  a  peripheral  direction  towards  the  external  layers  of  the 
central  nervous  system.  In  a  great  many  cases  I  have  been  able 
to  trace  such  processes  just  to  their  communication  with  the  peri- 


according  to  the  reality,  some  people  can,  at  all  events ;  as  the  mountain  would 
not  walk  to  Muhamed,  Muhamed  had  to  walk  to  the  mountain.  In  chapter  7  we 
will  have  an  opportunity  to  discuss  this  subject  somewhat  more  circumstantially. 

(Regarding  unipolar  cells  etc.  vide  also  my  quotation  from  Rawitz's  paper 
p.  66.) 

As  subsequently  may  be  seen,  it  is,  in  my  opinion,  of  no  importance  as  to 
the  combination  of  the  cells  whether  they  are  unipolar  or  not.  I  do  not  at  all 
doubt  the  existence  of  the  slender  processes  Fritsdl  describes  in  his  ganglion 
cells  from  the  ganglion  gasseri  of  Lophius,  but  I  suppose  them  to  be  proto- 
plasmic processes,  i.  e.  nutritive  processes. 


-  148  - 

neurium  enveloping  the  nervous  system  (e.  g.  vide  fig.  50,  ppr). 
In  Patella  I  have  even  found  ganglion  cells  with  similar  processes 
in  peripheral  nerves  (e.  g.  vide  fig.  20,  gc,  the  nervous  process 
of  this  cell  is  not  distinctly  seen  in  the  illustration),  Whether  the 
protoplasmic  processes,  as  a  rule,  extend  to  the  perineurium,  like 
what  is  the  case  in  the  spinal  cord  of  Myxine  (as  will  be  sub- 
sequently described)  I  do  not  know,  as  they  are  generally  lost  in 
the  neuroglia  reticulation  extending  between  the  ganglion  cells  (e.  g. 
vide  fig.  47,  50,  71,  73).  In  the  brain  of  the  Ascidia,  as  well  as  in 
the  nervous  system  of  Patella,  I  have  found  bipolar  and  multipolar 
ganglion  cells  situated  in  the  dotted  substance,  and  sending  their 
protoplasmic  processes  towards  the  periphery  of  the  nervous  system 

Like  Prof.  GOLGI  I  belive  the  function  of  the  protoplasmic  pro- 
cesses to  be  a  nutritive  one;  when  the  ganglion  cells  can  not  get 
sufficient  nutrition  in  their  neigbourhood,  they  have  to  send  processes 
towards  the  periphery  of  the  nervous  system,  or  out  into  the  loose 
neuroglia  reticulation,  where  there  is  sufficient  nutritive  fluid  for  the 
processes  to  absorb.1)  This  is  the  reason  why  the  protoplasmic  pro- 
cesses have  generally  a  peripheral  direction,  and  why  they  chiefly 
occur  in  cells  which  are  somewhat  deeply  situated  in  the  nervous 
system,  i.  e.  at  some  distance  from  the  periphery.  The  ganglion 
cells  situated  near  the  periphery  do  not  need  any  special  organs  to 
absorb  their  nutrition  from  the  fluid  surrounding  them,  neither  do 
the  ganglion  cells  situated  in  a  loose  neuroglia-reticulation  need  any 
(compare  the  ganglion  cells  of  the  lobster). 

Though  we  have  of  course  no  proof  of  the  real  function  of 
the  protoplasmic  processes,  I  think  this  theory  of  their  nutritive 
function  is  very  probable,  and  explains  a  great  deal  which,  else, 
may  seem  inexplicable.  What  other  function  could  we  suppose  them 
to  have  when  they  terminate  under  the  perineurium,  what  they 
actually  do,  at  all  events,  in  a  great  many  cases?  -  -  Indeed,  I  do 
not,  at  present,  see  any  acceptable  explanation  besides  this  one 
suggested  by  GOLGI.  Subsequently,  we  will  have  an  opportunity  to 
state  some  other  facts  which  will  still  further  add  to  its  probability. 

The  combination  of  the  ganglion  cells.  --  Having  thus 
elucidated  that  no  combination  between  the  cells  can  be  produced 
by  the  protoplasmic  processes,  and  as  it  is  very  improbable  that 
any  combination  between  them  can  be  produced  by  the  neuro- 
glia, I  suppose  it  to  be  most  probable,  if  not  certain,  that  if  any 


J)  Where  there  are  blood-vessels  in  the  central  nerve-system  (e.  g.  in  the 
Vertebrata)  the  protoplasmic  processes  can  often  be  seen  to  be  directed  towards 
the  connective  tissue  surrounding  the  blood-vessels. 


—  149  — 

combination  upon  the  whole  exists  between  the  ganglion  cells,  then 
this  combination  must  be  produced  by  the  nervous  processes.  That 
such  a  combination  can  exist,  with  the  dotted  substance  as  a  medium, 
we  will  easily  understand  wrhen  we  think  of  the  course  of  the  nervous 
processes.  As  is  previously  mentioned,  there  may  be  drawn  a 
distinction  between  two  types  of  ganglion  cells  in  respect  of  the 
course  of  their  nervous  processes;  viz.  i)  ganglion  cells  with  nervous 
processes  which  directly  become  nerve-tubes  and  thus  do  not  lose 
their  individuality,  though  they  have  no  isolated  course  but  give  off 
side-branches  to  the  dotted  substance;  2)  ganglion  cells  with  nervous 
processes  which  lose  their  individuality  and  by  subdivisions  are 
entirely  broken  up  into  slender  branches,  losing  themselves  in  the 
dotted  substance. 

We  have,  thus,  slender  branches  given  off  to  the  dotted  sub- 
stance, by  both  kinds  of  nervous  processes.  What  is  to  prevent 
these  branches  standing  in  communication  with  each  other,  seeing 
that  they  are  so  intimately  intermixed.  Certainly,  I  have  not  been 
able  to  observe  such  a  communication,  but  seeing  how  very  intricate 
these  structures  are,  we  need  scarcely  at  present  expect  to  do  so. 
In  fact,  I  do  not  see  any  objection  which  can  justly  be  made  to  a 
combination  existing  between  the  ganglion  cells  by  help  of  the  nervous 
processes  and  their  branches.  Still,  I  do  not  lay  much  stress  upon 
such  a  combination  existing,  or  not  existing,  as  in  a  subsequent 
chapter  will  be  explained;  the  principal  question,  in  my  opinion,  is, 
how  is  the  combination  between  the  nerve-tubes  produced. 


5.     The  nervous  elements  of  Amphioxus  and  Myxine. 

Though  I  propose  to  reserve  the  nervous  systems  of  Amphioxus 
and  Myxine  for  a  future  special  memoir,  I  will,  here,  for  the  sake 
of  comparison,  make  some  remarks  on  the  structure  of  their  nervous 
elements. 

Amphioxus  lanceolatus. 

As  is  known  from  the  descriptions  of  previous  writers *)  the 
spinal  cord  of  Amphioxus  has,  along  the  centre,  a  groove  or 
canal  extending  from  the  dorsal  side  and  surrounded  by  and  epi- 

J)  Owsjannikow  (1.  c.  1868)  and  Stieda  (I.e.  1873)  may  especially  be  men- 
tioned. I  regret  to  say  that  I  have  had  no  access  to  Stieda'?,  paper;  I  only  know 
it  therefore  from  the  abstract  of  it  in  Hofmann's  and  Schwalbe's  Jahresb.  d. 
Anat.  u.  Phys.  Bd.  2.  1875. 


thelium  of  cylindrical  cells,  and  outside  this  epithelium  a  limited 
number  of  ganglion  cells  (vide  fig.  90).  The  rest  of  the  spinal  cord 
consists  of  white  substance. 

The  wliite  substance  and  the  nerve-tubes.  —  As  is  easily 
seen  in  transverse  sections,  the  white  substance  of  Amphioxus  con- 
sists, chiefly,  of  longitudinal  (partly  also  transverse)  nerve-tubes,  which 
in  transverse  sections  are  transsected  and  give  the  section  the  ap- 
pearance of  containing  a  reticulation  (vide  fig.  90).  Some  of  the 
longitudinal  nerve-tubes  are  very  large,  and  very  much  resemble,  in 
their  appearance,  the  large  nerve-tubes  which  are,  for  instance, 
present  in  the  ventral  nerve-cord  of  Nereis.  They  are  especially 
situated  in  the  lateral  ventral  parts  of  the  white  substance  (vide  fig.  90). 
The  large  tubes,  which  OwsjANNlKOW  has  described  as  blood-vessels, 
are  colossal  nerve-tubes.  There  is  one  colossal  nerve-tube  running 
on  the  ventral  side  of  the  nerve-cord,  just  under  the  central  canal 
(fig.  90,  vnt).  One  colossal  nerve-tube  generally  runs,  laterally,  in 
each  side  of  the  spinal  cord  (fig.  90,  Int).  These  three  nerve-tubes, 
especially  the  ventral  one,  are  so  far  as  my  experiece  goes,  the 
largest  ones  existing  in  the  nervous  system  of  Amphioxus. 

The  small  nerve-tubes  vary  very  much  in  size,  and  some  of 
them  have  an  extremely  small  diameter. 

There  are  no  blood-vessels  present  in  the  spinal  nerve-cord. 

The  white  substance  is  traversed  by  a  great  many  radiating 
fibres,  issuing  from  the  cylindrical  cells  of  the  epithelium  investing 
the  central  groove,  and  passing  to  the  sheath  enveloping  the  spinal 
cord,  with  which  sheath  they  unite. 

The  structure  of  the  nerve-tubes.  —  The  nerve-tubes  have 
a  structure,  quite  similar  to  what  is  found  in  the  invertebrates  we 
have  before  examined.  They  consist  of  a  rather  deeply  staining 
sheath  and  a  less  staining  contents.  The  sheaths  are  generally  very 
thin.  The  contents  consist  of  primitive  tubes,  quite  similar  to  those 
which  are,  for  instance,  present  in  the  nerve-tubes  of  Homarus. 
The  primitive  tubes  may  easily  be  seen  in  the  large  nerve-tubes 
(vide  fig.  91);  the  spongioplasmic  walls  separating  the  tubes  contain- 
ing hyaloplasm  are  here  very  distinct. 

The  ganglion  cells.  -  -  The  ganglion  cells  occur  rather  spar- 
ingly. They  are  situated  on  both  sides  of  the  central  groove  outside 
the  epithelium.  Some  ganglion  cells  are  very  large  (vide  fig.  90,  gc) 
but  generally  they  have  a  moderate  size.  They  are  usually  multi- 
polar,  have  always  only  a  single  nervous  process,  the  other  processes 
are  protoplasmic  ones.  The  protoplasmic  processes  seem  generally 


to  traverse  the  white  substance  and  to  extend  to  the  envelope 
of  the  spinal  cord.  In  a  great  many  cases,  I  have  been  able  to  trace 
them  to  the  external  layers  of  the  white  substance  (vide  fig.  90,  pp ; 
92,  pp}.  In  some  cases  I  even  believe  to  have  observed  cells  which  send 
protoplasmic  processes  to  the  envelope  on  both  sides  of  the  spinal 
cord;  fig.  90,  gc  represents  such  a  case;  though  there  is  not  quite 
complete  continuation  of  the  process  in  this  section,  it  seems,  how- 
ever, to  be  the  same  process  which  crosses  the  central  canal,  sub- 
dividing and  sending  its  branches  just  to  the  external  envelope  on 
the  other  side.  The  relations  of  the  protoplasmic  processes  seem, 
thus,  to  be  the  same  in  Amphioxus  as  are  found  in  the  other  animals, 
examined,  where  such  processes  were  present ;  viz.  they  are  peripheric- 
ally  directed  (here  traversing  the  white  substance).  If  we  assume  that 
they  have  a  nutritive  function  this  is  easily  understood,  because  as 
there  are  no  blood  vessels  present  within  the  nerve-cord,  the  pro- 
cesses must  penetrate  to  the  external  layers  to  absorb  nutrition. 

I  have  not  yet  had  sufficient  opportunity  to  investigate  the 
course  of  the  nervous  processes,  and  will  therefore  reserve  them 
entirely  for  the  future  memoir. 

The  protoplasm  of  the  ganglion  cells  has,  in  sections,  a 
reticular  appearance,  produced,  as  I  suppose,  principally  by  a  trans- 
section  of  primitive  tubes,  composing  the  chief  constituents  of  the 
protoplasm  (vide  fig.  92,  gc).  These  tubes  penetrate  into  both  the 
protoplasmic  and  the  nervous  processes  and  form  their  contents, 
whilst  giving  them  a  longitudinal  striation.  The  protoplasmic  pro- 
cesses have,  however,  a  more  granular  appearance  than  the  nervous 
processes. 

The  cylindrical  cells  of  the  epithelium  investing  the 
central  groove  (or  canal)  have,  in  their  external  extremities,  pro- 
cesses which  traverse  the  white  substance,  and  unite  with  the  enve- 
lope of  the  nerve-cord,  as  already  mentioned.  These  fibres  are  partly 
united  into  bundles  (vide  fig.  90),  which  apparently  divide  the  longi- 
tudinal nerve-tubes  into  various  columns.  This  division  into  columns 
is,  however,  only  partial  as  the  bundles  do  not  form  any  continuous 
septa;  they  are  only  seen  in  some  sections,  whilst  in  other  sections 
bundles  of  similar  fibres  may  occur  on  other  places.  There  are, 
however,  some  definite  places  where  such  bundles  of  fibres  especi- 
ally occur;  as  some  of  the  most  prominent  of  these,  two  places, 
one  on  each  side  of  the  ventral  colossal  nerve-tube,  may  be  men- 
tioned (fig.  90,  ns,  ns). 

I   have  often   observed  very  strong  fibres   or   even   bundles  of 


-    152   — 

fibres  of  this  kind  directed  towards  the  nerve-roots,  especially  the 
dorsal  ones,  and  penetrating  into  the  nerves. 

It  is  obvious  that  the  fibres,  radiating  from  the  epithelial  cells 
of  the  central  groove,  and  running  between  the  longitudinal  nerve- 
cord,  have  just  the  same  significance  as  the  neuroglia-fibres  issuing 
from  the  neuroglia-cells  of  higher  vertebrates.  No  such  neuroglia- 
cells  are  found  in  Amphioxus  as  are,  for  instance,  found  in  Myxine 
(vide  sequel).  We  may,  therefore,  assume  that,  these  epithelial  cells 
are  the  real  neuroglia-cells  of  Amphioxus,  and  that  this  neuroglia 
represent  the  most  primary  state  found  amongst  the  Vertebrata.  In 
the  description  of  the  neuroglia  of  Myxine  we  will  have  an  oppor- 
tunity to  return  to  this  subject. 

Fibres  are  often  seen  crossing  the  central  groove;  these  fibres 
seem  partly  to  be  neuroglia-fibres,  partly  nerve-tubes  and,  as  we 
have  seen,  partly  also  processes  from  ganglion  cells. 

As  to  the  origin  of  the  nerve-tubes  of  the  ventral  and  dorsal 
nerve-roots,  my  investigations  are  yet  in  this  respect  very  incomplete, 
and  must  be  reserved  for  the  furture  paper. 

Myxine  glutinosa. 

It  is  only  the  nervous  elements  of  the  spinal  cord  we  will,  here, 
describe. 

The  white  substance.  --On  examination  of  transverse  and 
longitudinal  sections  of  the  spinal  nerve-cord  of  Myxine  it  is  easily 
seen  that  the  white  substance  chiefly  consists  of  longitudinal  nerve- 
tubes,  which  vary  a  great  deal  in  size.  The  large  tubes,  the  so- 
called  »MULLER's  nerve-fib  res «,  are  especially  situated  on  the  ventral 
side.  Between  the  large  and  largish  tubes  and  through  the  whole 
white  substance  a  multitude  of  very  slender  longitudinal  nerve-tubes 
occur;  the  white  substance  has  thus  in  well  preserved  transverse 
sections  a  reticular  appearance  (vide  fig.  100)  quite  similar  to  that  of 
a  section  through  the  dotted  substance  of  the  ventral  nerve-cord  of 
an  invertebrate  (e.  g.  Homarus  and  Nereis).  Between  each  of  these 
tubes  a  multitude  of  extremely  slender  tubes  (neuroglia-fibres  and 
branches  from  the  protoplasmic  processes  of  the  ganglion  cells)  run 
transversally.  These  transverse  fibres  are  not  very  distinctly  seen 
in  so  well  preserved  sections  as  fig.  100;  they  are,  however,  very 
conspicuous  in  sections  of  preparations  where  the  contents  of  the 
longitudinal  tubes  have  shrunk  in  so  much  that  the  transsected  tubes 
have  the  appearance  of  empty  vacuoles,  the  white  substance  has 
here  become  very  transparent  (vide  fig.  101).  They  run  from  the 


—  153  — 

grey  substance  and  just  to  the  periphery  of  the  white  substance 
(to  the  sheath  of  connective  tissue).  They  seem  to  compose  a  signi- 
ficant constituant  of  the  white  substance.  Subsequently  they  will  be 
more  circumstantially  described. 

The  structure  of  the  nerve-tubes  is  the  same,  in  Myxine, 
as  in  the  other  animals  examined.  The  nerve-tubes  consist  of  a 
distinct  external  sheath,  and  a  contents  containing  spongioplasm  and 
hyaloplasm.  The  external  sheaths  are  rather  thin  (vide  fig.  100). 

The  contents  of  the  nerve-tubes  consist  of  primitive  tubes.  In 
the  large  nerve-tubes  (MULLER's  nerve-tubes),  the  primitive  tubes  are 
very  distinctly  seen  (vide  fig.  100,  Int).1)  Upon  the  whole,  it  is  striking 
how  very  much  these  MULLER's  nerve-tubes  resemble  the  large  nerve- 
tubes  of  the  lobster;  in  Myxine  I  have  even  observed  a  tendency 
to  the  formation  of  an  axis  along  the  centre  of  some  larg  tubes 
(vide  fig.  100,  Inf)  somewhat  similar  to  what  is  described  of  the  large 
nerve-tubes  of  the  lobster  (vide  p.  87). 

Medullated  nerve-tubes  are  not  observed  in  the  spinal  cord 
of  Myxine. 

The  ganglion  cells  are  situated  in  the  grey  substance;  they 
are,  as  a  rule,  multipolar,  have  always  one  nervous  process  each, 
and  generally  several  protoplasmic  ones. 

The  protoplasm  of  the  ganglion  cells  has,  in  sections,  always  a 
minute  reticular  appearance,  with  spongioplasmic  meshes  containing 
a  less-staining  substance;  the  meshes  are,  to  a  great  extent,  produ- 


*)  I  think  it  is  very  strange  that  previous  authors  have  not  seen  the  compo- 
sition of  primitive  tubes  in  the  large  nerve-tubes  of  the  spinal  cord  of  the  fishes. 
In  his  description  of  the  large  nerve-tubes  in  medulla  oblongata  of  Lophius, 
Fritsch  says  (1.  c.  1886,  p.  22):  »Der  Faserlangsschnitt  zeigt,  dass  die  Fibrillen 
nicht  regelmassig  parallel  angeordnet  sind,  sondern  sich  vielfach  durchflechten  .  .  .  .« 
It  is  obvious,  in  my  opin.on,  that  Fritsch  has  seen  the  spongioplasmic  walls  of 
the  transsected  primitive  tubes  and  has  called  them  »Fibrillen«. 

Stilling  has  long  time  ago  (1.  c.  1855)  decribed  the  contents  of  the  nerve- 
tubes  of  the  Vertebrata  as  consisting  of  slender  tubes;  he  said  himself  in  his 
paper  that  there  would  likely  go  a  long  time  before  anybody  could  state  the  cor- 
rectness of  his  observations,  as  it  was  only  by  help  of  new  and  very  high  powers 
of  the  microscope  he  had  been  able  to  obtain  his  results.  Indeed,  there  has  gone 
a  long  time ;  no  other  writer  has  since  been  able  to  see  Stilling's  »Elementar- 
nervenrorchen«.  His  observations  were  made  too  early.  They  were  of  cource, 
imperfect,  as  he  had  not  the  same  lenses  and  modes  of  investigation  as  we 
have  at  precent;  a  great  deal  of  what  he  has  seen,  has  been  artificial  products 
(e.  g.  his  description  of  the  myeline  of  the  medullated  nerve-tubes)  but  he  has 
said  that  the  cylinder-axis  consist  of  slender  nElementarrorchen"  and  in  this 
point  I  do  entirely  agree  with  him. 


—  154  — 

ced  by  a  transsections  of  the  primitive  tubes  of  which  the  proto- 
plasm chiefly  consists.  These  primitive  tubes  extend  into  the  pro- 
cesses and  give  them  a  longitudinally  striated  appearance,  the  dark 
lines  of  the  striation  being  the  spongioplasmic  walls  of  the  primi- 
tive tubes. 

In  sections  of  a  great  many,  especially  large,  ganglion  cells, 
there  are  in  the  protoplasm  circular  or  oblong  lightly  staining  areas 
resembling  vacuoles  (vide  fig.  96,  v)  which  are  very  similar  to 
those,  previously  mentioned,  in  the  ganglion  cells  of  Homarus 
(cf.  p.  103  &  fig.  25,  27).  These  areas  are  transsected  tubes  of  a 
lightly  staining  substance,  probably  bundles  of  primitive  tubes,  which 
circulate  in  the  protoplasm  and  run  into  the  processes.  They  are 
often  obliquely  or  longitudinally  transsected  and  produce  then 
areas  of  an  elongated  shape  (vide  fig.  96,  #').  I  have  observed  very 
similar  tubes  or  bundles  in  the  cells  of  the  spinal  ganglia  of  Myxine, 
as  will  be  subsequently  described,  and  I  have  also  observed  similar 
structures  in  the  ganglion  cells  of  higher  vertebrates  (Mammalia). 
It  seems  thus  to  be  a  relation  of  rather  general  nature,  and  it  is 
therefore,  in  my  opinion,  strange  that  it  has  not  previously  been 
described.  We  know  of  course  yet  too  little  of  these  structures  to 
attempt  to  say  anything  of  their  significance. 

The  sheath  enveloping  the  ganglion  cells.  -  -  The  gang- 
lion cells  are  always  enveloped  by  a  membran  or  sheath  (vide  fig. 
96,  cm),  which  also  extends  into  the  process  and  forms  their  sheaths 
(cf.  fig.  96).  This  sheath  is,  I  think,  a  product  of  the  neuroglia,  or 
has,  at  all  events,  the  same  origin  as  the  latter.  I  have  not,  how- 
ever, hitherto  been  able  to  observe  any  nuclei  situated  in  the  sheath 
or  adhering  to  it.  Between  this  sheath  and  the  protoplasm  of  the 
ganglion  cells  there  is,  generally,  a  cavity *}  (fig.  96,  «)  filled  with  a 
loose,  apparently  reticular  substance,  which  is  extremy  lightly  stain- 
ing; this  substance  is  somewhat  delicate,  and  is  seen  in  well  pre- 
served sections  only. 

The  protoplasmic  processes  of  the  ganglion  cells  have  al- 
ways a  more  or  less  peripheral  direction;  they  subdivide,  generally 
dichotomically  a  great  many  times,  and  the  numerous  extremely 
slender,  branches  resulting  from  these  divisions  run,  between  the 
longitudinal  nerve-tubes  of  the  white  substance,  towards  the  peri- 
phery of  the  spinal  cord,  where  they  terminate  in  small  thickenings, 


!)  It  is  probably  the  same  cavities  which  are  described  by  Key  and  Eetzius 
(1.  c.    1876)  and  which  these  authors  supposes  to  be  filled  with  lymphoid  fluid. 


—  155  — 

or  plates,  just  inside  the  sheath.  The  only  methods  which  affords 
satisfactory  staining  of  these  processes  is  the  chromo-silver  method, 
but  by  its  use  I  have  been  able  to  trace  them  to  their  extreme 
terminations  (vide  fig.  94,  ppr\  104 — 105).  I  have,  however,  also  in 
preparations  stained  with  borax-carmine  (fig.  93)  or  stained  according 
to  HEIDENHAIN'S  hasmatoxylin  method  (fig.  95)  been  able  to  trace 
the  protoplasmic  processes  with  their  branches  through  the  white 
substance  and  very  close  towards  its  periphery  if  not  entirely  to 
the  external  sheath. 

The  same  ganglion  cell  may  have  protoplasmic  processes,  the 
various  branches  of  which  penetrate  to  the  periphery,  both  on  the 
ventral  side  and  on  the  dorsal  side  of  the  nerve-cord  (vide  fig.  93, 
95,  105,  1 06). 

The  slender  protoplasmic  processes  and  their  branches  resemble 
the  processes  of  the  neuroglia-cells  very  much  in  their  aspect  and 
it  is  indeed  extremely  difficult  to  draw  any  distinction  between  them, 
Both  have  the  same  appearance,  both  come  from  the  grey  substance, 
and  both  traverse  the  white  substance  towards  the  periphery  where  both 
as  a  rule  terminate  under  the  sheath  enveloping  the  spinal  cord.  In  fig. 
109,  a  protoplasmic  processes  issues  from  the  small  ganglion  cell  gc,  but 
this  process  can  not  be  distinguished  from  the  many  neuroglia-fibres,  ft 
in  any  respect  but  that  it  issues  from  a  ganglion  cell.1)  A  difference  is 
sometimes  that  the  neuroglia-fibres  have  a  straighter  course  more 
directly  towards  the  periphery  of  the  white  substance  than  the  pro- 
toplasmic processes  have.  I  have  found  no  constant  and  reliable 
difference  in  the  chromo-silver  staining  of  these  processes  similar  to 
what  GoLGI  has  stated  as  regards  the  neuroglia  cells  and  proto- 
plasmic processes  of  the  Mammalia,  and  what  I  also  have  had 
opportunity  to  observe  myself  in  higher  Vertebrata.  Sometimes 
there  was,  however,  also  in  Myxine  a  tendency  towards  a  more  red- 
dish staining  of  the  processes  of  the  neuroglia  cells. 

The  branches  of  the  protoplasmic  processes  of  one  cell  do  not 
anastomose,  neither  do  the  processes  from  various  cells  anastomose. 
Though  I  have  examined  a  considerable  number  of  preparations, 
and  although  they  have  been  most  perfectly  stained,  in  this  respect, 
I  have  not  yet  observed  a  single  case  of  indubitable  anastomosis 
between  protoplasmic  processes.2)  I  believe,  thus,  that  I  am  entitled 


M  Vide  also  fig.  93,  #C2. 

2)  In  my  previous  paper  on  Myxine  (1.  c.  1886)  I  have  mentioned  one 
case  from  the  brain  where  I  was  in  doubt  whether  there  was  an  anastomosis  or 
not.  The  more  I  have  examined  this  preparation,  the  more  do  I  doubt  that  an 


-  i56- 

to  affirm  that  a  direct  combination  between  the  ganglion  cells,  by  direct 
anastomosis  of  the  protoplasmic  processes  does  not  exist. 

A  thing  which  I  take  to  be  rather  puzzling  is,  that  processes 
which  in  their  aspect  can  not  be  distinguished  from  common  pro- 
toplasmic processes,  are  often  seen  to  pass  towards  the  periphery 
of  the  nerve-cord ;  arrived  there,  they  do  not,  however,  terminate, 
but  run  along  the  periphery  and  partly  back  into  the  white  sub- 
stance (vide  fig.  1 02,  pr,  6r2)  I  have  not  found  the  terminations  of  such 
processes.  Some  other  processes,  with  quite  similar  aspect,  may 
be  traced  for  very  long  distances,  even  crossing  the  ventral  com- 
missures and  passing  over  into  the  other  side  of  the  spinal  nerve- 
cord  (vide  fig.  1 02,  6r4).  A  great  many  processes  which  I  have 
observed  to  have  a  similar  course  are,  near  their  origin  in  the  cell, 
very  thick  and  large,  and  they  give  off  branches  which  terminate 
in  the  periphery,  under  the  sheath,  quite  in  the  same  way  as 
common  protoplasmic  processes,  whilst  at  the  same  time,  the  main 
stem  of  the  process  runs  along,  and  takes  a  course  as  above  de- 
scribed (vide  fig.  93,  mp  and  94,  mp).  It  has  been  possible  to  trace 
similar  processes  not  only  in  chromo-silver  stained  preparations  but 
I  have  also  traced  them  for  considerable  distances  in  preparations 
stained  with  carmine  or  HEIDENHAIN'S  haematoxylin  only  (vide  fig. 
93  and  95).  If,  now,  these  processes  are  protoplasmic  processes, 
and  if  the  protoplasmic  processes  have  a  nutritive  function,  which 
makes  it  necessary  for  them  to  terminate  under  the  sheath  enve- 
loping the  spinal  cord,  it  is,  indeed,  very  difficult  to  understand  why 
they  pass  through  the  nervous  system  for  so  long  distances  without 
terminating;  why  they  pass  to  the  other  side;  and  why  they  do  not 
terminate,  but  return  again,  when  they  are  in  the  periphery?  These 
are  questions  of  so  serious  a  nature  that  they  oblige  us  to  assume 
that  either  these  processes  are  not  wholly  protoplasmic  processes 
though  they  have  their  aspect,  or  that  the  function  of  the  proto- 
plasmic processes  is  not  only  a  nutritive  one.  I  will  not  decide 
between  these  alternatives  at  present,  though  I  find  the  former  one 
most  probable.  It  can  not  be  doubted,  in  my  opinion,  that  some 


anastomosis  is  really  present.  If  there  is  an  anastomosis,  however,  it  may  be  ac- 
counted for  as  a  remnant  of  a  cell-division  not  yet  finished,  as  the  bridge  between 
the  cells  is  very  thick  and  short. 

Mr.  W.  S.  Colman  (1.  c.  1884)  has  actually  observed  anastomoses  of  ganglion 
cells  in  the  spinal  cord  of  a  human  foetus;  but  there  is,  in  my  opinion,  little  doubt 
but  that  they  are  results  cf  divisions  of  ganglion  cells;  in  two  of  the  cells  there 
were  even  two  nuclei,  what  obviously  indicates  that  the  cells  are  dividing. 


—  157  — 

of  the  branches  given  off  from  these  processes  are  protoplasmic 
branches,  as  they  have  the  same  appearance  and  course  and  actually 
terminate  under  the  external  sheath  in  a  way  entirely  similar  to  that  of 
common  protoplasmic  processes  (as  also  neuroglia-fibres,  vide  sequel). 
Could  it  be  possible  that  these  processes  are  mixed  protoplasmic 
nervous  processes?  GoLGI  has  described  and  illustrated  nervous 
processes  issuing  from  protoplasmic  processes  near  their  origin  in 
the  cell  (vide  1.  c.  1885).  It  may  be,  that  these  structures  in  Myxine 
are  processes  of  a  still  more  mixed  nature.  More  complete  observa- 
tions on  the  course  and  termination  of  the  main  branch  of  these 
processes  are  necessary  to  decide  in  this  question.  I  can  not  omit 
to  state  that  it  has  not  been  possible  to  find  any  other  processes 
which  looked  like  nervous  processes  and  which  issued  from  the 
same  cells  as  the  » mixed  processes «,  described  above. 

The  nervous  processes.  —  My  observations  on  the  nervous 
processes  are  yet  very  scanty.  The  chromo-silver  staining  is  the 
only  one  which  can  tell  us  anything,  with  certainty  about  the 
course  of  these  processes,  and  upto  this  time  it  has  been  exceedingly 
difficult  to  get  any  perfect  staining  of  them.  They  have  a  smooth 
and  less  granular  aspect  than  the  protoplasmic  process.  The  slender 
branches  have  generally  at  certain  intervals  varioceles  (vide  fig.  103,  104). 

From  what  little  I  have  seen  it  is  probable  that  in  Myxine 
there  are  also  two  forms  of  nervous  processes,  viz. : 

1)  Nervous  processes,  which  do  not  lose  their  individuality,  as 
they  are  directly  transformed  into  nerve-tubes;  they  have,  however, 
no  isolated  course,  as  they  give  off  slender  side-branches.     Fig.  103,  gc, 
represents  a  ganglion  cell  with  such  a  nervous  process.     The  process 
has   often   varicose   thickenings   at   the   origin   of  the   side-branches. 
Processes  which  have  no  side-branches,  but  sometimes  varicose  thicken- 
ings at  certain  distances,  are  also  seen  (vide  fig.  94,  gc^ ,  gc.2\  I  think, 
however,  that  the  absence  of  side- branches  issuing  from  the  thicke- 
nings  is   only   owing  to  imperfect  staining.      Nervous   processes   of 
this   kind   are   often   seen   to   pass   through  one  of  the  commissures 
and  over  into  the  other  side  of  the  spinal  cord  (fig.  94). !) 

2)  Nervous  processes  which  lose  their  individuality  and  are  en- 
tirely broken  up  into  slender  branches.     Fig.  103,  gcz  and  104  represent 
ganglion  cells  with  such  processes.     In  their  slender  parts  the  branches 


1)  In  fig.  103,  <7C2  is  seen  a  ganglion  cell  with  a  process  which  crosses  the 
commissure  and  which  could  be  traced  for  some  distance  over  into  the  other  side; 
this  process  had  the  aspect  characteristic  for  protoplasmic  processes,  but  judging 
from  its  course  I  think  it  is  a  nervous  process.  At  a  a  branch  was  given  off. 


-  i58  - 

of  these  processes  have,  generally,  varicose  thickenings  at  each  places 
where  they  subdivide.  They  have,  generally,  also  a  great  many 
varioceles  where  no  side-branches  are  seen,  I  suppose,  however,  this 
is  only  owing  to  an  imperfect  staining,  and  that  side-branches  are 
given  off  at  each  variocele. 

The  branches  of  the  nervous  processes  do  not  anasto- 
mose.—  They  contribute  to  form  a  reticulation,  or  rather  interlacing 
of  nervous  fibrillse  which  extends  through  the  grey  substance,  and 
which  also  seems  to  extend  into  the  white  substance. 

The  origin  of  the  peripheral  nerve-tubes.  —  In  horisontal 
sections  of  successfull  chromo-silver  stained  preparations  of  the 
spinal  cord,  it  is  easy  to  observe  that,  the  nerve-tubes  of  the 
dorsal  (posterior)  nerve-roots ')  subdivide  dicliotomically,  just  after 
their  entrance  into  the  spinal  cord;  some  of  them  subdivide  even 
before  they  have  reached  the  cord  (vide  fig.  in,  a). 
As  far  as  my  experience  goes  I  dare  to  say  that  all  nerve-tubes 
subdivide,  it  has  in  my  opinion  therefore,  only  been  optical  illusions 
which  have  occasioned  previous  outhors  (e.  g.  RANSOM  &  THOMPSON 
[1.  c.  1886]  and  others)  to  state  that,  they  have  observed  some  of 
these  nerve-tubes  to  originate  directly  from  ganglion  cells;  these 
authors  will,  I  hope,  forgive  me  this  denial  of  their  statements,  when 
I  tell  them  that  such  an  illusion  has  once  deceived  myself,  before 
I  obtained  perfect  chromo-silver  stained  prepations  (cf.  my  previous 
paper  1.  c.  1886).  The  fibres  which  I  at  that  time  observed  (and 
which  probably  the  other  authors  have  also  seen)  were  neuroglia- 
fibres  issuing  from  neuroglia-cells  in  the  grey  substance  and  inter- 
mixing with  the  nerve-tubes  of  the  dorsal  nerve-roots  (vide  fig.  93,  flt) 

The  two  branches  resulting  from  the  dichotomical  subdivi- 
sions of  the  nerve-tubes  separate,  and  run  in  opposite  directions, 
longitudinally,  along  the  spinal  cord.  I  have  been  able  to  trace 
these  branches  for  considerable  distances  along  the  cord  but,  as 
a  rule,  I  have  found  no  new  subdivisions;  neither  have  I  seen 
them  passing  over  to  the  other  side  of  the  spinal  cord.  In  a  very 
few  cases,  I  belive  to  have  seen  very  slender  side-branches  to  be 
given  off  (vide  fig.  112,  br).  My  investigations  on  this  subject  are  very 
far  from  being  finished,  and  I  hope  yet  to  be  able  to  make  im- 
portant observations  in  this  respect.  From  what  is  already  observed, 


1)  It  may  be  noticed  that  in  my  previous  paper  (1.  c.  1886)  there  is  in  the 
English  translation  (Ann.  mag.  nat.  hist.  1 886)  printed  » dorsal  nerve-rods«  and 
»ventral  nerve-rods«  instead  of  dorsal  nerve-roots  and  ventral  nerve-roots. 


—  159  — 

I  am,  however,  at  all  events,  entitled  to  say  that,  the  nerve-tubes 
of  the  dorsal  (posterior)  nerve-roots  have  no  direct  origin  from  gang- 
lion cells. 

The  nerve-tubes  of  the  ventral  (anterior)  nerve-roots 
do  not  subdivide  after  they  have  entered  the  spinal  nerve- 
cord,  according  to  my  observations.  I  have  been  able  lo  trace 
them  for  considerable  distances  into  the  nerve-cord,  in  chromo-silver 
stained  preparations  (vide  fig.  105)  as  well  as  in  carmine  and 
hnematoxylin  preparations  (vide  fig.  93  and  95)  but  no  subdivisions 
have  been  discovered,  though  the  tubes  are  thick  and  easy  to  ob- 
serve; slender  side- bran  dies  are,  however,  given  off  (vide  fig.  93,  nbr] 
105,  sbr). 

In  a  few  cases  only  have  I  been  able  to  trace  their  direct  com- 
bination with  ganglion  cells  (vide  fig.  106)  and  the  tubes  which  in 
these  cases  had  a  direct  combination  were  comparatively  very  thin. 

From  what  is  seen,  there  can,  however,  be  no  objection  to  the 
assumption,  that  all  the  nerve-tubes  of  the  ventral  nerve-roots  are 
directly  connected  with  ganglion  cells,  indeed,  I  think  this  is  all  but 
certain,  seeing  that  these  tubes  have  no  subdivisions;  but  it  is  pro- 
bable that  the  thick  ones  pass  for  some  distance  through  the  white 
and  grey  substance  before  they  united  with  the  cells.  A  great 
many  of  them  seem  to  pass  over  into  the  other  side  of  the  spinal 
cord  crossing  the  ventral  transverse  commissure. 

I  will  not  omit  to  mention  a  section  which  I  once  obtained 
of  a  chromo-silver  stained  preparation.  A  part  of  this  section  is 
illustrated  in  fig.  102  which  is  drawn  under  the  camera  lucida  and 
is  an  exact  representation  of  what  was  seen  in  the  preparation. 
The  nervous  process  (mpr-^  or  perhaps  » mixed  process «  (cf.  above) 
issuing  from  the  ganglion  cell  gc,  is  seen  to  give  off  a  thick  branch 
(6r,),  which  passes  towards  the  ventral  (anterior)  nerve-root  (vnr). 
This  branch  becomes  very  thin  towards  the  periphery  of  the  white 
substance  and  can  not  be  traced  entirely  into  the  ventral  nerve-root, 
though  there  only  wants  an  extremely  short  distance.  Whether 
this  branch  was  really  connected  with  the  ventral  nerve-root  (was 
transformed  into  a  peripheral  nerve-tube),  and  it  was  only  owing  to 
an  incomplete  staining  that  it  could  not  be  traced  into  the  nerve- 
root  was  very  difficult  to  decide.  In  its  whole  appearance  this  branch 
was  not  at  all  like  common  protoplasmic  branches,  which  I  certainly 
very  often  have  observed  to  be  directed  towards  the  nerve-roots 
(vide  fig.  105, ppr\  iog,ppr]  93,  gcj,  but  it  had  that  smooth  and  black 
staining  which  is  caracteristic  for  nervous  processes.  What  is  strange 


-  160  - 

is,  that  in  the  same  section  (which  was  somewhat  thick)  I  observed 
two  similar  processes  (consequently  from  other  cells)  running  parallel 
to  this  one,  situated  one  over  the  other  and  giving  oft"  quite  similar 
processes  at  the  same  place  and  towards  the  same  nerve-root.  I  have 
drawn  only  one  of  these  processes  (flijtff)  in  the  illustrations  in  order 
not  to  make  it  too  complicated.  These  3  processes  were  thus 
situated  that  they  quite  covered  each  other  vertically ;  in  the  illustra- 
tion I  was  obliged,  of  course,  to  draw  them  running  beside  each 
other.  Similar  instances  of  processes  running  quite  the  same  way 
one  over  the  other  on  the  border  between  the  grey  and  the  white 
substance  and  giving  off  branches  at  certain  places  are  not  rare  in 
the  spinal  cord  of  Myxine. 

The    longitudinal   nerve-tubes    of   the    spinal   cord.   -  -  I 
have   observed   side-branches  to   be  given    off   from    many    of  the 
nerve-tubes     running    longitudinally    in    the    spinal    cord    (vide    fig 
in,lnt';  H2,lnt^.     Some  longitudinal  nerve-tubes  are  also,  by  sub 
divisions,  broken  up  into  slender  fibrillae  (vide  fig.  intsnt\   112,  snt] 
whether  these  tubes  are  nerve-tubes  coming  from  other  parts  of  the 
central    nervous   system,    or  they   are   only   branches    coming   from 
some  dorsal  nerve-roots,  I  can  not  decide.     In  some  instances  I  saw 
them  cross  the  transverse  commissure  and  pass  over  into  the  other 
side  of  the  nerve-cord  (vide  fig.   in,snt?). 

The  neuroglia.  —  Neuroglia-cells  are  situated  in  great  abun- 
dance in  the  grey  substance  of  Myxine.  Their  nuclei  are  smaller 
than  those  of  the  ganglion  cells,  have  a  circular  or  ovate  form,  and  a 
somewhat  granular  appearance.  The  neuroglia  cells  have  often  many 
processes  (fig.  103,  nuc{,  nuc?).1)  These  processes  do  not  subdivide  much 
but,  like  the  protoplasmic  processes,  the  traverse  the  white  substance  to 
its  periphery,  and  terminate  there  under  sheath  enveloping  the 
spinal  cord  (vide  fig.  95,/).  The  course  of  the  processes  is  parti- 
cularly easy  to  study,  in  successful  chromo-silver  stained  sections 
where  they  are  seen  in  great  abundance  as  black,  or  reddish  black, 
fibres,  passing  from  the  grey  substance  to  the  periphery,  everywhere, 
through  the  white  substance.  The  same  neuroglia  cells  sends  often, 
at  the  same  time,  processes  to  the  dorsal  side  as  well  as  to  the 
ventral  side  of  the  spinal  cord  (fig.  103,  nuclf  /wc2).  The  processes 
of  the  neuroglia  cells  can,  however,  easily  be  traced  also  in  section 


7)  It  may  be  that  in  nucl  and  WMC2  several  neuroglia-cells,  situated  close 
together,  have  been  stained  in  one  body;  seeing,  however,  that  the  many  processes 
issue  from  so  comparatively  very  small  spaces  I  think  it  to  be  not  improbable  that 
we  have  here  single  cells  (at  all  events  in  nuc^. 


-  161  — 

stained  with  carmine  or  haematoxylin ')  (HElDENHAIN's  haematoxylin- 
staining  can  especially  be  recommended).  Fig.  101  will  probably 
give  a  good  impression  of  in  what  multitudes  they  occur  in  the 
white  substance. 

The  processes  of  the  neuroglia  cells  do  not  anastomose, 
neither  those  from  the  same  cells,  nor  those  from  different  cells. 
Though  I  have,  for  instance,  seen  so  many  processes  issuing  close 
to  each  other  as  is  illustrated  in  fig.  io82)  yet  I  have  not  found  a 
single  anastomosis.  In  sections,  stained,  for  instance,  with  HElDEN- 
HAIN's haematoxylin  (fig.  101),  it  is  seen,  as,  above  mentioned,  that  there, 
between  the  longitudinal  nerve-tubes  of  the  white  substance,  runs  a 
multitude  of  slender  fibres  in  every  direction,  but  neither,  here,  are 
anastomoses  found.  The  chief  part  of  these  fibres,  running  between 
the  nerve-tubes,  are  neuroglia  fibres  coming  from  the  neuroglia  cells 
and  penetrating  to  the  periphery,  but  some  of  them  are,  also,  as 
we  have  seen,  branches  of  protoplasmic  processes  coming  from  the 
ganglion  cells,  and  finally  some  fibres  are  branches  from  the  nervous 
processes.  It  is,  generally,  in  sections,  stained  in  the  common  way 
(i.  e.  carmine,  haematoxylin  etc.),  exceedingly  difficult  to  draw  any 
distinction  between  these  various  kinds  of  fibres  or  tubes. 

The  cells  of  the  epithelium  surrounding  the  central 
canal  resemble,  in  their  appearance,  very  much,  the  neuroglia  cells, 
their  nuclei  have,  to  some  extent,  the  form  and  appearance  of  common 
neuroglia  nuclei.  At  their  exterior  extremities,  these  cells  have  pro- 
cesses which  penetrate,  at  all  events  to  a  great  extent,  to  the  periphery 
of  the  spinal  cord  on  the  dorsal  side,  as  well  as  on  the  ventral  one 
(vide  fig.  93,  95,  103);  these  processes  are,  consequently,  quite  like 
those  of  the  neuroglia  cells.  Some  processes  from  these  cells  have  a 
more  lateral  direction  into  the  grey  substance  (vide  fig.  94,  cec;  102, pec) 
I  have  not  been  able  to  trace  these  processes  to  their  extremitie . 3) 


*)  Vide  what  is  said  of  that  p.   152. 

2)  In  this  preparation  \  think  it  is  probable  that  some  cells  have  been  stained 
at  one  and  same  time  and  have  acquired  an  appearance  as  if  they  were  one  cell. 
The  illustration  is  drawn  to  nature  as  exactly  as  possible,  arid  it  may  be  seen  that 
there  are  several  irregularities  in  the  staining  of  the  mesial  part.  Similar  prepara- 
tions are  very  often  obtained. 

3)  In  the  spinal  cord  of  higher  fishes  (Teleostii),  I  have  also  by  chromo-silver 
staining  been  able  to  trace  the  processes  of  the  epithelial  cells  of  the  ventral  canal 
through  the  white  substance  and  just  to  its  periphery  where  they  terminate  or  unite 
with  the  sheath.  As  regards  the  processes  of  these  central  epithelial  cells  in  higher 
Vertebrata  I  will  refer  the  reader  to  Golgi's  observations  (JSulla  fma  etc.,  vide  list  of 
Literature  1885)  he  has  in  the  spinal  cord  of  the  chicken  observed  similar  processes 

II 


-    162   - 

The  cells  situated  in  the  grey  substance  just  outside  the  epi- 
thelial cells,  are  quite  like  the  latter.  They  are  elongated  at  their 
interior  extremities,  and .  penetrate  between  the  epithelial  cells  to 
the  central  canal  (if  they  cary  cillia,  like  the  latter,  I  can  not 
decide);  at  their  exterior  extremities  they  have  processes  wich  pe- 
netrate to  the  surface  of  the  spinal  cord,  like  those  from  the  epi- 
thelial cells.  These  cells  represent,  consequently,  a  kind  of  tran- 
sition-stage between  the  common  neuroglia  cells  and  the  epithelial 
cells  surrounding  the  central  canal;  indeed,  in  the  many  layers  of 
such  cells  surrounding  the  epithelium  of  the  canal,  we  can  find 
all  possible  transition-stages.  When  we,  now,  consider  that  in 
Amphioxus  the  neuroglia  principally  consists  of  epithelial  cells  (we  do 
not,  here,  refer  to  the  sheaths  surrounding  the  nerve-tubes  etc.)  and 
there  is  every  reason  to  believe  that  this  is  a  primary  state  from 
which  the  conditions  found  in  Myxine  are  developed,  I  think  we 
are  fully  entitled  to  say,  that  the  neuroglia  cells  have  an  ectodermal 
origin,  and  spring  from  the  epithelial  cells  of  the  central  canal  or  we 
may  rather  say  the  central  groove.1) 

The  nerve-cells  of  the  spinal  ganglia.  —  Before  we  leave 
the  nervous  system  of  Myxine  I  will  make  some  remarks  on  the 
structure  of  the  spinal  ganglion  cells,  as  I  think,  they  exhibit  relations 
which  in  several  respects  are  of  great  interest  for  the  subjects  treated 
of  in  this  paper.  Upon  the  whole  the  spinal  ganglion  cells  reminds 
in  their  structure  very  much  of  the  ganglion  cells  of  the  central 
nervous  system  of  many  invertebrates,  and,  amongst  those  we  have 
here  examined,  especialy  the  large  unipolar  cells  of  Homarus  vulgar  is. 
They  represent  obviously  a  less  developed  stage  than  that  of  the 
ganglion  cells  of  the  spinal  cord. 


traversing  the  white  substance  (vide  1.  c.  p.  179).  Regarding  these  processes 
in  higher  Vertebrata  I  vill  also  refer  the  reader  to  the  various  memoirs  by  Ainslie 
Hollis  (1.  c.  1883),  Ley  dig  (Zelle  und  Gewebe  1885  P-  189),  Eabl-Eilckhard 
(1.  c.  1883),  Eeissner  (1.  c.  1864),  John  Dean  tl.  c.  1863^  and  others. 

1)  I  think  it  is  most  probable  that  the  neuroglia  cells  of  the  invertebrates 
have,  also,  an  ectodermal  origin.  This  may,  for  instance,  easily  be  seen  in  Nereis, 
where  the  ventral  nerve-cord  is  not  yet  fully  separated  from  the  ectoderm.  It  is, 
here,  even  difficult  to  see  any  difference  between  the  neuroglia  and  the  ectodermal 
cells,  and  it  is  in  many  cases  impossible  to  draw  any  distinct  line  between  the 
cells  enveloping  the  nerve-cord,  and  the  ectodermal  cells  situated  outside  them 
(vide  fig.  14).  I  have,  here,  only  considered  what  we  may  infer  from  the  nervous 
system  of  full  grown  specimens.  In  examination  of  the  embryological  development 
of  the  nervous  system,  the  ectodermal  origin  of  the  neuroglia  will  be  still  more 
evident;  on  that  subject  the  reader  may  be  referred  to  the  recent  paper  by  Klein  en- 
berg  on  the  embryologie  of  the  Annelides  (Zeitschr.  f.  wiss.  Zool.  1886). 


-  i63  - 

Fig-  97,  98  and  99  represent  sections  through  various  spinal 
nerve-cells  stained  with  carmine.  Their  slieatlis  are  in  sections  rather 
conspicuous,  and  there  is,  generally,  several  nuclei  situated  inside 
(and  also  outside)  them  (vide  fig.  97,  n\  98,  n\  99,  n).  These  sheaths 
and  their  nuclei  resemble  very  much  the  sheaths  and  nuclei  of  the 
ganglion  cells  of  Homarus.  The  nuclei  are  not,  however,  present  in 
such  number  in  the  latter  as  the  sometimes  are  in  the  spinal  cells. 

The  structure  of  the  protoplasm  of  the  spinal  nerve-cells  is 
very  similar  to  that  of  the  protoplasm  of  the  common  ganglion  cells. 
The  lightly  staining  areas  (transsected  tubes)  are  also  present  in 
sections  of  this  protoplasm,  but  they  are  perhaps  still  more  distinctly 
prominent  and  frequently  arranged  in  defined  groups.  Sometimes 
they  are,  in  sections,  present  on  two  sides  of  the  nuclei  in  the 
elongated  cells  (fig.  97),  somitimes  they  are  present  only  in  one  side 
of  the  cells  (fig.  98,  99).  On  careful  examination  of  successful  sections 
it  becomes  quite  evident  that  these  lightly  staining  areas  are  trans- 
sected tubes,  or  perhaps  bundles  of  primitive  tubes.  These  tubes  or 
bundles  have  generally,  when  the  cells  are  bipolar  or  elongated,  a 
longitudinal  course  through  the  protoplasm  of  the  cells,  and  they 
are  often  logitudinally  transsected  (fig.  98,  v).  What  these  tubes  or 
bundles  are  is  not  easy  to  say,  my  observations  are  still  too  imper- 
fect. In  sections  of  cells  where  the  processes  are  longitudinally  trans- 
sected in  their  origin,  it  is,  however,  frequently  seen  that  these 
tubes  or  bundles  run  towards  the  origin  of  the  processes  (vide  fig.  98). 
I  think  it  is  probable  that  they  constitute  the  process  in  a  way  si- 
milar to  what  the  bundles  of  primitive  tubes  do  in  the  ganglion  cells 
of  Homarus  (cf.  p.  103).  In  the  bipolar  cells  it  is  possible  that  the 
contents  of  the  nerve-tube,  entering  a  cell  at  one  end,  is  broken  up 
into  such  bundles  of  primitive  tubes  which  traverse  the  protoplasm 
longitudinally  and  re-unite  at  the  other  end  to  form  the  peripheral 
nerve-tube  quitting  the  cell  here.  As  is  already  known  from  FREUD'S 
paper  (1.  c.  1878)  there  exist  unipolar  and  bipolar  ganglion  cells  in 
the  spinal  ganglion  of  Petromyzom,  and  in  this  respect  as  in  others 
they  resemble  those  of  Myxine. 

In  the  nerve-cells  of  the  spinal  ganglia  of  the  frog,  M.  V. 
LENHOSSEK  has  described  »eine  seichte,  aber  breite  durch  sharfe 
Rander  begrenzte,  tellerformige  Vertiefung,  whelche  durch  2 — 3 
rundliche,  bisher  unbekannte  Zellen  beinahe  vollstandig  ausgefiillt  wird« 
(1.  c.  1886  p.  450).  This  »Vertiefung«  was  situated  in  the  surface 
of  the  cells  near  the  origin  of  their  processes.  In  some  spinal  cells  of 
I  have  observed  structures  which  seem  to  be  very  like  these. 


-  164  - 

Fig.  99  represents  a  cell  with  a  such  structure.  The  light  circular 
area  x  is  very  distinctly  defined.  There  is  a  very  long  nucleus  (N), 
with  some  protuberances,  situated  in  one  side  of  this  area,  in  the 
centre  there  is  another  somewhat  lighter  corpuscle  (N1)  which  is  perhaps 
also  a  nucleus.  I  could,  however,  see  no  cells  in  this  area,  and 
whether  it  is  one  cell  or  contains  several  cells  or  what  it  is,  I  can 
not  decide. 

The  nuclei  of  the  spinal  nerve-cells  are  large  and  exhibit  gener- 
ally a  distinct  chromatin  reticulation. 

On  comparing  the  main  characters  in  the  structure  of  the 
nervous  elements  of  these  two  vertebrates  (Amphioxus  and  Myxine) 
with  what  is  previously  described  in  this  paper,  we  will  see  that  there  is 
the  most  perfect  correspondence  in  this  respect  between  the  inverte- 
brated  bilaterates  and  these  inferior  vertebrates.  But  as  we  can 
not  easily  suppose  that  their  is  any  principal  difference  between 
them  and  higher  vertebrata  in  these  respects,  we  may  thus  assume 
that  the  principal  results  arrived  at  in  this  paper  are  applicable  to 
all  bilaterates.  In  a  future  paper  I  hope  to  be  able  to  pay  a  more 
special  attention  to  the  nervous  elements  of  the  vertebrata. 


6.    The  combination  of  the  nerve-tubes  with  each  other. 

A  question  of  much  interest  arises,  viz.  how  is  the  combination, 
between  the  nerve-tubes  produced,  or  rather  how  is  the  impression 
received  by  a  sensitive  nerve-tube  conveyed  to  a  motoric  one.  To 
express  it  in  another  way  me  may  say,  which  elements  has  an 
irritation  of  a  sensitive  nerve-tube  to  pass,  to  produce  a  reflex- 
movement? 

A  very  common  theory  is,  as  is  well-known,  that  an  irritation 
of  a  sensitive  nerve- tube  passes  to  a  » sensitive «  ganglion  cell,  then, 
from  this  cell,  through  a  protoplasmic  process  to  a  motoric  ganglion 
cell,  and  from  that  cell  it  passes  into  a  motoric  nerve-tube  to 
produce  a  reflex-movement.  In  a  previous  chapter  (ch.  4,  p.  148), 
it  is,  I  hope,  suficiently  proved,  that  in  the  invertebrated  bilaterates 
there  is  no  direct  combination  between  the  ganglion  cells  through 
the  protoplasmic  processes,  neither  is  there  in  Myxine  (as  we  have 
seen  in  the  previous  chapter);  the  above  quoted  theory  of  the 


-  i65  - 

course  of  an  irritation  producing  a  reflex-movement  is  therefore  for 
this  reason  alone  not  maintainable. 

Before  we  enter  into  the  inquiry  of  how  a  combination  between 
the  nerve-tubes  is  produced,  we  will  examine  if  there  is  any  mor- 
phological difference  to  be  observed  between  motoric  nerve-tubes 
and  sensitive  nerve-tubes. 

As  is  above  stated  the  nerve-tubes  of  the  dorsal  (posterior) 
nerve-roots  of  the  spinal  cord  of  Myxine  subdivide,  immediately 
after  their  entrance  into  the  nerve-cord  and  thus  lose  their  individu- 
ality, whilst  the  nerve-tubes  of  the  ventral  (anterior)  nerve-roots 
retain  their  individuality  and  seem  to  spring  directly  from  ganglion 
cells,  whilst  giving  off  slender  side-branches. 

I  have  also  observed  similar  conditions  in  the  spinal  cord  of 
higher  vertebrata.  I  have  even  been  able  to  obtain  here  more 
complete  observations  on  the  subdivisions  of  the  nerve-tubes  of  the 
posterior  nerve-roots. 

My  observations  fully  agree  therefore  with  those  of  Prof.  C. 
GOLGI  in  this  respect;  and  as  GoLGI  says,  I  think  we  are  entitled 
to  assume  that,  in  the  spinal  nerve-cord,  the  sensitive  nerve-tubes 
arise  from  a  junction  of  slender  nervous  fibrillce,  whilst  the  motoric 
nerve-tubes  are  direct  continuations  of  nervous  processes  (from  gang- 
lion cells)  which  however  give  off  slender  side-branches.  If  this  is 
correct  the  opposite  conclusion  seems,  also,  to  be  admissible,  at 
all  events  to  a  certain  extent,  viz.  that  nerve-tubes  arising  from  a 
junction  of  nervous  fibrillae  are  sensitive  nerve-tubes,  whilst  nerve- 
tubes  springing  directly  from  ganglion  cells  are  motoric  nerve-tubes. 
In  the  brain  of  the  vertebrata,  we  find  nerve-tubes  originating  in 
both  ways,  and  hence,  I  think,  there,  is  every  reason  to  believe 
that  the  same  morphological  differences  between  motoric  and  sensi- 
tive nerve-tubes  are  there  present. 

Having  now  settled  what  morphological  difference  there  appears 
between  the  origin  of  sensitive  and  motoric  nerve-tubes  in  verte- 
brata, and  seeing  that  in  invertebrata  quite  a  similar  difference  is 
present  in  the  modes  of  origin  of  two  kinds  of  nerve-tubes,  I  think 
we  are  entitled  to  conclude  further:  that  in  the  nervous  system  of 
the  invertebrated  bilaterata  there  is  the  same  morphological  diffe- 
rence between  the  origin  of  the  sensitive  and  the  motoric  nerve- 
tubes,  as  is  found  in  vertebrata;  viz.  the  sensitive  nerve-tubes  arise 
from  a  junction  of  nervous  fibrillae,  whilst  the  motoric  nerve-tubes 
spring  directly  from  ganglion  cells. 

Arrived  at  this  conclusion,  we  will  now  consider   the   question, 


—  1 66  - 

how  is  an  impression,  probably,  conweyed  from  a*  sensitive  nerve- 
tube,  to  a  motoric  one?  As  it  is  chiefly  the  invertebrated  bilaterata 
which  have  been  treated  of  in  this  paper,  we  will  also  in  the  present 
inqiury  principally  confine  our  remarks  to  the  consideration  of  their 
nervous  system  only. 

As  is  above  seen,  the  sensitive  nerve-tube  probably  subdivides, 
and  is  broken  up  into  slender  branches,  after  its  entrance  into  the 
dotted  substance,  it  is,  thus,  not  very  probable,  that  an  irritation  of 
such  a  nerve-tube  should  be  conweyed  to  one  ganglion  cell  only, 
it  would  then  be  necessary  that  all  the  branches  of  a  sensitive 
nerve-tube  should  unite  again  to  form  the  nervous  process  of  a 
ganglion  cell  (sensitive  ganglion  cell). 

According  to  what  is  before  stated  of  the  combination  of  the 
ganglion  cells  it  will  be  obvious  that:  to  be  forwarded  to  a  motoric 
cell,  the  irritation  would  necessarily  after  its  arrival  in  the  sensitive 
ganglion  cell  have  to  return  through  the  same  nervous  process,  to 
pass  over  through  some  other  branches  of  the  process  into  the 
nervous  process  of  a  motoric  cell;  arrived  in  the  motoric  cell  it 
had  then  to  return  through  the  same  process  and  finally  pass  into 
the  centrifugal  nerve-tube,  to  produce  the  reflex  movement.  It 
needs  no  further  discussion  to  see  that  this  would  be  a  highly 
artificial  and  complicated  explanation  of  the  course  of  an  irritation, 
from  a  centripetal  to  a  centrifugal  nerve-tube.  For  one  thing,  it  is 
not,  in  my  opinion,  admissible  to  assume  that  all  the  branches 
arising  from  the  subdivisions  of  a  sensitive  tube  should  re-unite  to 
constitute  the  nervous  process  of  a  sensitive  ganglion  cell;  why 
then  does  the  subdivision  of  the  nerve-tube  exist,  why  does  not  the 
nerve-tube  pass  undivided  to  the  cell?  For  another  thing,  I  do  not 
think  it  admissible  that  the  same  irritation  should  pass  and  return 
through  the  same  nervous  processes. 

In  my  opinion,  it  is  a  much  more  probable  assumption  that 
the  irritation  does  not  at  all  pass  through  any  ganglion  cells,  but  that 
after  its  arrival  in  the  dotted  substance,  through  subdivisions  of 
the  centripetal  nerve-tube,  it  is  at  once  carried  on,  into  one  or  several 
centrifugal  nerve-tubes  by  the  slender  side-branches  or  fibrillce  joining 
them.  How  the  combination  between  the  branches  of  the  centri- 
petal nerve-tubes  and  the  side-branches  of  the  centrifugal  nerve-tubes 
is  produced  in  the  dotted  substance,  can  not  at  present  be  defined; 
I  can  not,  however,  see  any  objection  to  the  assumption  that  it 
does  exist. 


-  i67  - 

According  to  the  above  conclusion,  we  may  thus  illustrate  a 
reflex-curve  (i.  e.  the  way  an  irritation  of  a  centripetal  nerve-tube 
has  to  pass  to  arrive  in  a  centrifugal  nerve-tube  and  produce  a 
reflex-movement)  as  in  the  diagrame  fig.  113,  the  large  arrows  indicate 
the  course  of  an  irritation  producing  a  reflex-movement.  The 
reflex-curve  is,  consequently,  composed  of  the  following  constituents: 
i)  centripetal  (sensitive)  nerve-tube,  2)  the  central  web  or  interlacing 
of  nervous  fibrillce  or  tubes  (fig.  113,  cf) ;  3)  the  centrifugal  (motoric) 
nerve- tube 

This  theory  will  necessarily  give  a  new  view  of  the  functions 
of  the  central  element;  but  it  will,  I  think,  explain  a  great  many 
relations  which  have  been  rather  difficult  to  understand.  The  dotted 
substance  (the  interlacing  of  nervous  fibrillae)  must  be  a  principal  seat 
of  the  nervous  activity,  through  this  substance  or  interlacing  is  the  re- 
flex-actions etc.  communicated  to  the  consciousness,  which  even  pos- 
sibly has  its  seat  in  this  substance  itself  (especially  that  of  the  brain). 
According  to  this  view  there  can  of  course,  to  some  extent,  be  a 
localisation  in  the  central  nerve-system  but  no  isolation.  This  view  will 
also  I  think  possibly  be  able  to  explain  the  fact  that  other  parts  of 
the  brain  can  take  up  the  function  of  lost  parts.  This  is  not,  how- 
ever, the  place  to  enter  into  such  physiological  details,  we  have 
especially  taken  up  the  histological  side  of  the  question  and  in  this 
respect  we  can  state,  as  a  fact,  that  a  plaiting  or  interlacing  (not 
reticulation)  of  nervous  fibrillae  extends  through  the  whole  central 
nervous  system  of  all  animals  (which  posses  a  central  nervous  sy- 
stem) and  that  probably  all  peripheral  nerve-tubes,  entering  into  or 
issuing  from  the  central  nervous  svstem,  are  connected  with  this 
central  fibrillar  interlacing  by  branches.  We  will  then  ask  the  phy- 
siologists if  it  is  not  probable  that  it  is  this  interlacing  of  nervous 
fibrillae  (or  tubes)  which  especially  produces  the  feeling  of  unity  in 
the  nervous  system,  in  other  words  that  it  is  the  principal  seat  of 
self-consciousness  ? 


7.     The  function  of  the  ganglion  cells. 

A  great  many  physiologists  will  probably  object,  that  if  this  is 
correct,  what  functions  have,  then,  the  ganglion  cells? 

I  have  thought  of  this,  and  am  fully  aware  that  if  the  proposed 
theory  of  the  elements  of  the  reflex-curve  is  approved,  it  will  cause 
the  common  theory  of  the  function  of  the  ganglion  cells  to  totter. 


-  i68  - 

The  reflex-actions  are,  as  is  well  known,  probably,  the  primary 
state  or  the  starting  point  of  a  great  many,  if  not  all,  actions  (volun- 
tary or  unvoluntary.) 

And  if  reflex  movements  are  produced  without  direct  help  of 
the  ganglion  cells,  then  there  are  certainly  a  great  many  actions 
which  can  be  produced  without  any  direct  assistance  from  these  cells. 

In  the  same  way  as  above,  me  may  also  assume  that  an 
impression  or  irritation  is  conweyed  from  one  part  of  the  central 
nervous  system  to  another,  e.  g.  from  the  ventral  (or  spinal)  nerve- 
cord  to  the  brain,  or  vice  versa,  without  any  passage  through 
ganglion  cells;  an  irritation  producing  a  voluntary  action  may,  thus, 
be  conweyed  from  the  brain  and  into  the  centrifugal  nerve-tubes, 
passing  to  the  active  limb,  without  passing  any  ganglion  cells  on  the 
way,  or  without  any  direct  action  of  the  ganglion  cells  of  the  ven- 
tral (or  spinal)  nerve-cord,  or  of  the  motoric  centre  of  the  limb. 
It  is  not  in  our  present  state  of  knowledge  possible  to  predict  the 
extent  of  the  influence  this  theory,  if  approved,  will  have  an  our 
ideas  about  the  function  of  the  nervous  system.  I  will,  therefore, 
by  no  means  attempt  to  trace  it  here,  but  will  subsepuently  return 
to  the  ganglion  cells,  and  examine  what  functions  there  may  be 
left  for  them,  for  certainly  we  cannot  one  moment  doubt  that  they 
are  of  great  importance  to  the  nervous  system. 

A  function  which  I  suppose  they  have,  and  which  certainly  is 
a  very  important  one,  is  to  serve  as  nutritive  centres  of  this  nerve- 
tubes  and  fibriHae  originating  in  them.  We  have,  before,  seen,  that 
the  protoplasmic  processes  have  probably  a  nutritive  function  and 
absorb  nutrition,  for  the  cell,  in  the  periphery  of  the  ganglia  (or  nerve- 
cords)  or  near  the  walls  of  the  blood-vessels ;  now,  I  think  it  is  probable 
that  this  nutrition  is  not  meant  to  be  for  the  cell  only,  but  that  it  is 
assimilated  by  the  protoplasm  of  the  cell  (the  nucleus  has  probably 
an  important  function  in  this  respect)  and  is,  in  a  suitable  form, 
carried  on  into  the  primitive  tubes  of  the  nervous  processes;  in 
other  words,  the  ganglion  cells  are  the  nutritive  centres  of  the  ner- 
vous processes,  and  then  probably  also  of  the  branches  and  nerve- 
tubes  arising  from  these  processes.1)  We  know  of  what  great  impor- 
tance nutrition  is  for  the  nervous  system;  it  is  very  peculiar,  in 


*)  Those  ganglion  cells,  from  which  the  motoric  nerve-tubes  directly  issue, 
are  the  nutritive  centres  of  these  tubes;  whilst  those  ganglion  cells,  the  nervous 
process  of  which  are  entirely  broken  up  into  slender  branches,  are  the  nutritive 
centres  of  these  branches  (which  contribute  to  the  formation  of  the  dotted  substance). 


—  169  -- 

this  respect,  and  it  is  well  known  that  a  few  moments  want  of  nutrition 
for  the  brain  is  enough  to  disorder  the  nerve-system  and  produce 
unconsciousness  in  man.  The  nutrition  is  certainly  not  a  function  of 
too  insufficient  importance  to  explain  the  extension  the  ganglion 
cells  have  in  the  central  nervous  system. 

That  the  ganglion  cells  of  the  spinal  yanglia  have  a 
nutritive  function  is  in  my  opinion  vere  probable.  As  the  nerve- 
tubes  of  the  dorsal  (posterior)  nerve-roots  have  got  no  special  nu- 
tritive centres  in  the  central  nerve-system  (as  they  do  not  originate 
directly  from  cells)  they  have  got  them  in  special  ganglia  outside 
the  central  nerve-system.  In  Myxine  the  spinal  nerve-cells  are  uni- 
polar or  bipolar.  The  processes  of  the  unipolar  cells  subdivide  di- 
chotomically  in  a  T  and  send  one  branch  peripherally  and  one 
centrally  (cf.  FREUD'S  investigations  1.  c.  1878).  In  my  opinion  the 
cell  is  the  nutritive  centre  of  both  these  branches,  but  is  of  no  di- 
rect importance  for  their  sensitive  function ;  the  irritation  of  the  peri- 
pheral branch  can  not  pass  through  the  cell  (as  it  then  must  pass 
and  return  through  the  same  process)  but  passes  directly  into  the 
centripetal  branch  at  the  subdivision  in  T  of  the  process.  In  the 
bipolar  cells  the  irritation  of  the  peripheral  part  of  the  nerve-tube 
must  certainly  pass  through  the  cell  to  come  into  the  centripetal  part; 
in  so  far  it  is  no  objection  that  the  bipolar  cell  may  be  of  direct 
importance  for  the  sesitive  function  of  the  nerve-tubes.  But  the  fact 
only  that  in  the  same  ganglion,  unipolar  cells  are  present  and  are 
united  with  quite  similar  nerve-tubes  must  be  enough  to  make  us 
doubtful  in  this  respect.  If  the  unipolar  cells  have  a  nutritive  func- 
tion only,  it  must  be  probable  that  the  bipolar  cells  have  the  same 
function;  indeed,  seeing  that  in  higher  verterbrata  the  spinal  ganglia 
consist  exclusively  of  unipolar  cells  (notwithstanding  the  slender 
protoplasmic  processes  described  by  FRITSCH  (1.  c.  1886)  which 
processes  I  suppose  to  be  nutritive  processes,  cf.  above  p.  146, 
note  i),  I  think  that  this  must  be  quite  certain.  There  are  also  ap- 
pearances in  the  structure  of  the  bipolar  cells,  which,  as  we  have 
before  seen,  indicates  that  the  contents  of  the  processes  to  some 
extent  pass  through  the  protoplasm  of  the  cells  without  intermixing 
with  it  (compare  the  description  of  the  protoplasm  of  these  cells 
p.  163). 

We  arrive  thus  at  the  conclusion  that  all  the  nerve-cells  of  the 
spinal  ganglia  have  a  nutritive  function  only.  They  are  probaly  of 
a  similar  importance  for  the  sensitive  (centripetal)  nerve-tubes  as  the 
»motoric«  ganglion  cells  (i.  e.  the  cells  from  which  the  motoric 


—  1 70  — 

nerve-tubes  spring)  are  for  the  motoric  (centrifugal)  nerve-tubes,  the 
difference  is  that  the  former  are  situated  outside  the  central  nervous 
system  and  have  got  a  simple  shape  without  many  prosesses,  pro- 
bably because  they  can  easily  get  their  nutrition  without  special 
organs;  whilst  the  latter  are  situated  in  the  central  nervous  system 
and  need  generally  many  and  long  processes  to  reach  the  blood- 
vessels or  the  periphery  of  the  nervous  organs  and  there  obtain 
sufficient  nutrition  for  the  cell  and  its  nervous  process. 

From  the  recent  works  by  my  much  estimated  friend  ADOLF 
D.  ONODI  (1.  c.  1884,  1885,  1886)  (cf.  also  the  previous  papers  by 
MARSHALL,  1.  c.  1877;  BALFOUR,  1.  c.  1876  &  1877;  HENSEN,  1.  c. 
1876;  SCHENK,  1.  c.  1876)  we  have  learnt  that  the  spinal  ganglia 
spring  from  the  spinal  cord.  We  are  thus  entitled  to  say  there  is 
no  principal  difference  between  the  ganglion  cells  of  the  nervous 
system  and  those  of  the  spinal  ganglia,  they  have  the  same  origin 
and  the  same  function  but  they  have  got  a  different  situation  and 
differ  therefore  also  in  shape,  some  are  unipolar  whilst  other  are  bi- 
polar, and  even  multipolar,  which,  however,  does  not  make  any  diffe- 
rence in  their  function. 

I  have  not  yet  had  opportunity  to  examine  in  invertebrates  how 
the  relations  are  as  to  the  nutritive  centres  of  those  nerve-tubes 
which  spring  from  the  dotted  substance  by  a  union  of  slender  tubes. 
Whether  the  ganglion  cells  which  I  have  found  in  the  peripheral 
nerves  of  various  animals  (cf.  my  paper  on  Mysostoma  1885  p.  31 
&  74  and  this  paper  p.  141  &  143,  note  2)  are  of  importance  in 
this  respect  I  can  not  decide  at  present,  it  is,  at  all  events,  not 
impossible.  In  the  peripheral  nerves  of  Patella  I  have,  as  mentioned 
p.  141  found  ganglion  cells  which  had  even  protoplas-mic  processes 
(cf.  fig.  2O,  gc). 

Whether  the  ganglion  cells  of  the  central  nerve-system  have 
any  functions  besides  being  nutritive  centres  is,  of  course,  extremely 
difficult  to  decide. 

It  is  not  imposisble  that  they  may  be  the  seat  of  memory. 
A  small  part  of  each  irritation  producing  a  reflex  action,  may  on 
its  way  through  the  dotted  substance  be  absorbed  by  some  branches 
of  the  nervous  processes  of  the  ganglion  cells,  and  can  possibly  in 
one  way  or  another  be  stored  up  in  the  latter.  Howsoever  that 
may  be,  and  whatever  the  function  of  the  ganglion  cells  is,  this 
new  theory  of  the  combination  between  the  centripetal  and  the 
centrifugal  nerve-tubes  gives,  if  approved,  a  quite  new  view  of 
the  importance  of  the  dotted  substance  (or  the  interlacing  of  nerv- 


ous  fibrillae  of  the  vertebrates)  and  will,  in  my  opinion,  explain 
many  facts  as  to  its  occurrence.  If  the  theory  is  correct,  then,  the 
dotted  substance  must  be  a  principal  seat  of  the  nervous  activity, 
and  —  the  higher  an  animal  is  mentally  developed  -  -  the  more 
complicated  and  extensive  '  must  we  expect  to  find  its  dotted  sub- 
stance ;  this  is  in  the  fullest  harmony  with  the  facts  already  known. 
We  need  only  refer  the  reader  to  the  ant,  or  the  bee,  to  compare 
the  extremely  complicated  and  highly  developed  dotted  substance 
of  these  small  inteligent  animals,  with  the  dotted  substancs  of  less 
developed  insects,  or  to  compare  the  dotted  substance  of  the  insects 
or  Crustacea  with  that  of  annelides,  etc.  etc.  I  am  sure  that  my 
readers  will  very  soon  arrive  at  the  conclusion,  that  the  more  com- 
plicated the  structure  of  dotted  substance  is  -  -  the  more  highly  is 
the  animal  mentally  developed;  in  other  words,  we  may  conclude 
that  the  more  the  inteligence  of  an  animal  is  developed  -  -  the  more 
intricate  becomes  the  web  or  plaiting  of  nerve-tubes  and  fibrillce  in 
its  dotted  substance;  the  protoplasmic  processes  etc.  of  the  ganglion 
cells  are  of  no  great  importance  in  this  respect.  In  this  manner  we 
can  explain  how,  it  is,  that  unipolar  cells  occur  in  the  nervous 
system  of  animals  (e.  g.  insects  and  Crustacea)  which  are  mentally 
even  highly  developed;  these  animals  have  an  extremely  intricate 
web  of  nerve-tubes  in  their  dotted  substance,  and  this  web  is  pro- 
bably the  principal  seat  of  inteligence. 


List  of  the  principal  Literature 

having  reference  to  the  subjects  treated  of  in  this  memoir. 

(There    is    also   referred    to    a    few    papers    to    which    I   have  had  no  access  as  we 

have    not    got    them    in    the    library    of  Bergen's    Museum,    and  which  I  only  know 

from  the  reports  by  other  authors.) 

1804.     Mangili.     Nuove   richerche    zootomiche  sopra  alcune  specie  di  Conchiglie 

bivalvi.     Milano. 
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An  abstract  in  Reil's  Archiv.     Bd.  X.      1811   p.  467. 

1819.  —     Osservazioni  microscopiche  etc.  .  .  Seconda  edizione  aggiunte.    Napoli. 
—     Translated    in    German:     (Beobachtungen    u'ber    das    Gehirn    etc.)    by 

Dr.  J.  J.  Albrecht  v.   Schonberg.     Wurzburg   1829. 

1820.  Treviranus.      Vermischte     Schriften    anat.    und    phys.    Inhalts.      Bd.    III. 

Untersuchungen  tiber  den  Bau  und  die  Funktionen  des  Gehirns  der 
Nerven  und  der  Sinneswerkzeuge  in  den  verschiedenen  Klassen  und 
Familien  des  Thierreiches.  Gottingen. 

1824.  Serres.     Anatomic   comparee  du  cerveau. 

1825.  Roth.     De  animalium  invertebratorum  systemate  nervoso.      Disertatio  inau 

gural  Wiceburgi. 
de  Blainville.     Manuel  de  Malacologie. 

1828.  Milne  Edwards.     Recherches    anatomiques    sur    le    systeme    nerveux  des 

Crustaces.     Ann.  d.  sci.  nat.     T.  XIII  p.    113 — 123. 

Johannes  M  tiller.  Ueber  ein  eigenthiimliches,  dem  Nervus  sympathicus 
analoges  Nervensystem  der  Eingeweide  bei  dem  Insekten.  Nova  acta 
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1829.  Morren.     Histoire  du  Lombric  terrestre.     Bruxelles. 

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morphoses of  the  insect.  Phil,  trans,  of  the  Royal  Soc.  London 
1832  p.  383. 


—  173  — 

1833-  Christian  Gottfried  Ehrenberg.     Ueber  die  Structur  des  Gehirns  und 

der  Nerven.     Froriep's  Notizen.     XXXVII. 

—  Nothwendigkeit    einer    feineren    mechanischen    Zerlegung    des    Gehirns 
und    der   Nerven    vor  der  chemischen,  dargestellt  aus  Beobachtungen. 
Poggendorfs  Annalen  der  Phys.     Bd.  XXVIII  p.  449 — 472. 

1834-  —     Bemerktmgen    zum    vorhergehenden    Aufsatz.      (Bemerkungen  u'ber  die 

feinsten  Nervenfasern,  von  Krause.)  ibid. 

—  Beobachtungen     einer    bisher    unbekannten    auffallenden    Structur    des 
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G.G.Valentin.  Ueber  die  Dicke  der  varikosen  Fa'den  in  dem  Gehirn 
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les  animaux  invertebres.  Ann.  des  sci.  nat.  Ser.  2  T.  V.  p.  81 — no. 
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Gabr.  Gust.  Valentin.  Ueber  den  Verlauf  und  die  letzten  Enden  der 
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541—543- 
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(Prag)   1837   p.   177—178. 
—     Ueber  die  gangliosen  Korperchen  in  verschiedenen  Theilen  des  Gehirns. 

ibid.  p.   179. 


-  174  - 

1838.  Johann  es  Miiller.     Vergleichende  Anatomic  der  Myxinoiden.    Neurologic. 

Abhandl.   d.  konigl.  Akad.  d.  Wiss.  zu  Berlin   1838. 
Robert  Remak.    Observationes  anatomicae   et  microsc.   de  systematis  ner- 

vosi  structura.     Diss  Berolini. 
Volkmann.     Ueber  die  Faserung  des  Riickenmarkes  und  des  sympatischen 

Nerven  in  Rana  esculenta.     Miiller's  Arch.  f.  Anat.  u.  Phys.      1838. 

1839.  Carpenter.     Dissertation    on   the    physiological    inference,    to    be  deduced 

from  the  structure  of  the  nervous  system  in  the  invertebrated  classes 
of  animals.  Edinburgh. 

Georg  Newport.  Insects.  Todds  Cyclopaedia  of  Anatomy  and  Physio- 
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Anderson.  Nervous  system.  Todds  Cyclopaedia  of  Anatomy  and  Phy- 
siology vol.  III.  London. 

Gabr.  Gust.  Valentin.  Ueber  die  Scheiden  der  Ganglienkugeln  und 
deren  Fortsetzungen.  Miiller's  Arch.  f.  Anat.  u.  Phys.  1839  p.  139 
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—  Zuv   Entwickelung  der  Gewebe  des  Muskel-,  Blut-  und  Nervensystems 
ibid.  p.   194. 

—  De    functionibus    nervorum    cerebralium    et    nervi    sympathici.     Bernse 
Liv.  I. 

Rosenthal.     De  formatione  granulosa  in  nervis  etc.     Vratislaviae. 

1841.  Robert  Garner.      On  the  anatomy   of  the   Lamellibranchiate    Conchifera. 

Trans,  of  the  Zool.     Soc.  of  London.     Vol  II  p.  87. 
Grant     Outlines  of  Comparative  Anatomy  p.   185 — 204. 

1842.  Milne  Edwards.     Sur  la  structure  et  les  fonctions  de  quelques  zoophytes. 

mollusques    et    crustaces    des  cotes  de  la  France.      Ann.  des  sci.  nat. 

Ser.  2  T.  XVIII.     Nerv.syst  p.  326—329. 

Helmholtz.     De  fabrica  systematis   nervosi    evertebratorum.  Diss.    inaug. 

Berolini  (vide  also  reference  in    Siebold   &   Reichert.      Arch.   f.    Anat. 

u.  Phys.   1843  p.   ii   &  CXCVII). 

Hannover.     Mikroskopiske  Undersogelser  af  Nervesystemet.  Kjobenhavn. 

1843.  A.  de  Quatrefages.      Memoire    stir   1'Eolidine    paradoxale.  Ann.    d.    sc. 

nat.  Ser.  2.  T.  XIX  p.  293 — 300. 

Robert  Remak.1)  Uber  die  Inhalt  der  Nervenprimitivrohren.  Miiller's 
Arch.  f.  Anat.  u.  Phys.  1843  p.  197—201. 

1844.  —     Neurologische    Erlanterungen.      Miiller's    Arch.    f.    Anat.  u.  Phys.   1844 

p.  463—473. 
Hannover.     Recherches  microscopiques  sur   le    systeme  nerveux.     Copen- 

hague,  Paris,  Leipzig. 
Friedrich  Will.     Vorlaufige  Mittheilungen  iiber  die  Structur  der  Ganglien, 

und    den   Unsprung   der  Nerven    bei    Wirbellosen    Thieren.       Miiller's 

Arch.  f.  Anat.  u.  Phys.      1844  p.  76 — 94. 


Vide  also  Remak.     Carper's  med.  Wochenschrift  1839. 

Ammon's  Zeitschr.  f.  Med.  etc.     Bd.  III.     Hft.  3.     1840. 
Med.  Vereins-Zeitung.      1840  No.  2. 


1844.  A.  W.  Volkmann.     Ueber    Nervenfasern    und    deren    Messung    mit    Hiilfe 

der  Schrauben-  und  Glasmikrometer.  Miiller's  Arch.  f.  Anat.  u.  Phys. 
1844  p.  9—26. 

Julius  Budge.  Ueber  den  Verlauf  der  Nervenfasern  im  Riickenmarke 
des  Frosches,  ibid.  1844  p.  160 — 190. 

G.  Valentin.  Erwiderung  anf  .  .  .  Volkmann'schen  Aufsatz  iiber  Ner- 
venfasern etc.  ibid  1844  p.  395 — 404. 

F.  Bidder  und  A.  W.  Volkmann.  Die  Selbstandigkeit  des  sympathi- 
schen  Nervensystems  durch  anatomische  Untersuchungen  nachgewiesen. 

F.  Bidder.  Erfahrungen  u'ber  die  functionelle  Selbstandigkeit  des  sympathi- 
schen  Nervensystems,  aits  brieflichen  Mittheilungen  von  F.  Bidder  an 
A.  W.  Volkmann.  Miiller's  Arch.  f.  Anat.  u.  Fhys.  1844  p.  358—381. 

1845.  A.  de  Quatrefage.     Sur   le    systeme    nerveux    et    sur    1'histologie    du    Bra- 

chiostome  on  Amphioxus.  Ann.  d.  sci.  nat.  Ser.  3.  T.  IV  p.  214 — 229. 
Emile  Blanchard.  Recherches  anatomiques  et  geologiques  sur  1' organi- 
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mier partierles  Coleopteres.  Comptes  Rendus.  Paris.  XXI  p.  752 — 754, 
963—964. 

—  Observations  sur  le  systeme  nerveux    des   Mollusques   testaces    ou   La- 
mellibranches.     Ann.   d.  sc.  nat.     Ser.   3.     T.  Ill  p.  321 — 340. 

(vide  also  Froriep  Notizen  XXXIV   1845.     Comptes  rendus.    Paris 
XX  1845  P-  496—489-) 

—  Recherches  sur  le  systeme  nerveux  des  Mollusques  gasteropodes.     Extr. 
proces-verbaux  de  la  Soc.  philom.     Paris.      1845  p.  25 — 27. 

1846.  —     Du  systeme  nerveux  des  insectes.   Memoire  sur  les  Coleopteres.     Ann. 

d.  sc.  nat.     Ser.  3.     T.  V  p.  273 — 379. 
Harless.     Briefl.  Mittheilung  iiber    die  Ganglienkugeln   von   Torpedo    Gal- 

vanii.     Miiller's  Arch.  f.  Anat.  u.  Phys.    1846  p.  283. 
H.  Lebert  und  Ch.  Robin.     Kurze  Notiz    iiber   allgemeine    vergleichende 

Anatomic  niederer  Thiere.      Miiller's    Arch.    f.    Anat.  u.  Phys.   1846  p. 

128 — 129. 

1847.  Rudolph  Wagner.     Ueber   den  feinen  Bau  des  elektrischen    Organes    im 

Zitterrochen. 

—  Neue  Untersuchungen  iiber  die  Elemente  der  Nervensubstauz. 
Bidder.     Zur  Lehre  von  dem  Verhaltnisse  der  Ganglienkorper  ztt  den  Ner- 
venfasern.    Leipzig. 

Axmann.     De  gangliorum  structura  penitiori  ciusque  functionibus. 
Ch.  Robin.     Sur   la  structure  des  ganglions  nerveux  des  Vertebres.     Extr. 
proces-verbaux  de  la  Soc.  philomatique.     Paris.      1847,  p.  23 — 30. 

—  Sur    la    structure    des    ganglions    nerveux    des    Raies.  ibid.  p.  68 — 71 ; 
Froriep  Notizen  II  &  III.      1847. 

1848.  Emile  Blanchard.     Du  systeme  nerveux  chez  les  Invertebres  (Mollusque 

et   Anneles)    dans  ses  rapportes  avec  la  classification   de  ces  animaux. 
Comptes  rendus.     Paris.     XXVII  p.  623 — 625. 


1849.  Lieberkiihn.     De  structura  gangliorum  penitiori.     Berolini. 

Franz  Ley  dig.  Zur  Anatomie  von  Piscicola  geometrica  mit  theilweiser 
Vergleichung  anderer  einheimischer  Hirudineen.  Zeits.  f.  wiss.  ZooL 
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A.  Kolliker.  Neurologische  Bemerkungen.  Zeits.  f.  wiss.  Zool.  Bd.  I 
p.  135—163. 

Carl  Bruch.  Ueber  das  Nervensystem  des  Blutegels.  Zeits.  f.  wiss.  Zool. 
Bd.  I.  p.  164 — 175. 

Hermann  Stannius.  Das  peripherische  Nervensystem  der  Fische.  Ro- 
stock. 

1850.  Rudolph    Wagner.      Neurologische    Untersuchungen.      Nachrichten  v.  d. 

Georg-Augusts    Universitat    u.    d.    K.    Gesellsch.    d.  Wiss.      Gdttingen. 

1850    p.    41 — 56;   1851   p.   185 — 196;   1853    p.   59 — 72.      Abstract   in: 

Ann.  d.  sci.  nat.  Ser.  3.  T.  XIX  p.  370 — 379.      1853. 
Johann  Czermdk.     Verastelungen  der  Primitivfasern  des  Nervus  acusticus. 

Zeits.  f.  wiss.  Zool.     Bd.  II  p.   105 — 109. 
Felix  Dujardin.     Memoire  sur  le  susteme  nerveux  des   Insectes.     Ann.  d. 

sci.  nat.     Ser.  3.     T.  XIV  p.   195—206. 
A.  de  Qtiatref  ages.     Memoire  sur  le  systeme  nerveux  des  Annelides.    Ann. 

d.  sc.  nat.     Ser.  3.  T.  XIV  p.  329 — 398. 
Clarke.     Researches    into    the    structure    of  the    spinal    cord.      Phil,    trans. 

of  the  Royal.    Soc.  of  London  for   1851   (read  Decbr.   5   1850). 

1851.  Franz  Leydig.     Ueber    Artemia    salina   und   Branchipus   stagnalis.      Zeits. 

f.  wiss.  Zool.     Bd.  Ill  p.  290 — 295. 

—  Anatomische  Bemerkungen  iiber  Carinaria,  Firda  und  Amphicora,  ibid. 
Bd.  Ill  p.  32S—332. 

1852.  —     Anatomisches  und  Histologisches  iiber  die  Larve  von  Corethra  plumi- 

cornis,  ibid.  Bd.  Ill  p.  438 — 442. 

—  Zur    Anatomie    und    Entwickelungsgeschichte    der   Lacinularia    socialis, 
ibid.  Bd.  Ill  p.  457—460. 

A.  d e  Q uatr ef ages.1)     Memoires  sur  le  systeme  nerveux,    les    affmites  et 

les  analogies  des  Lombrics  et  des  Sangsues.     Ann.  d.  sc.  nat.    Ser.  3. 

T.  XVIII  p.   167—179. 
Leon  Dufour.     Apergu  anatomiques  sur  les  Insectes  lepidopteres.     Compte 

rendus.     Paris   1852  p.  749. 
Johann    Marcusen.       Zur    Histologie    des    Nervensy stems.      Bull.    acad. 

imp.  d.  sci.     St.  Petersb.  X.  p.   187 — 192. 

G.  Schilling.     De  medullae  spinalis  textura,  Diis.  inaug.  Dorpat. 
(vide  Miiller's  Arch.  f.  Anat.  u.  Phys.    1853  p.   66). 

1853.  HeinrichMuller.     Ban  der  Cephalopoden.     Zeits.  f.  wiss.  Zool.   Bd.  IV 

P-  344- 

Axmann.  Beitrage  zur  mikroskopischen  Anatomie  und  Physiologic  des 
Ganglien-Nervensystems.  Berlin. 


*)    Vide  also  Quatrefages :  Regne  animal.  Annelides  Atlas  Anatomie  PI.   I  d  &  I  c. 


—  177  - 

185 3-     Franz  Leydig.     Zur  Anatomic    von    Coccus    hesperidum.      Zeits.   f.    wiss. 
Zool.  Bd.  V   1853  p.   5—8. 

1854.  —     Ueber  den  Bau  und  die  systematische  Stellung   der   Raderthiere,    ibid. 

Bd.  VI  p.  83—87. 
R.    Remak.      Ueber    multipolare    Ganglienzellen.      Ber.    ii.  Verhandl.  d.  k. 

preuss.  Akad.     Berlin   1854  p.  29. 
R.  Wagner.     Neurologische  Untersuchungen. 
P.  Owsjannikow.     Disquisitiones  microscopicse  de  medullae   spinalis   tex- 

tura  imprimis  in  Piscibus  factitatse.    Dorpat. 
Georg    Meissner.     Beitrage    zur    Anatomic    und  Physiologic  von    Mermis 

albicans.     Zeits.  f.  wiss.  Zool.  Bd.  V  p.  220 — 236. 

1855.  —     Beitrage  zur  Anatomic  und  Physiologic  der  Gordiaceen.     Zeits.  f.  wiss. 

Zool.  Bd.  VII  p.  20—28  &  93—103. 

Leconte  et  Faivre.  Etudes  sur  la  constitution  chemique  du  systeme  ner- 
veux  de  la  Sangsue.  Gazette  medical  No  45  1855  p.  709. 

Wedl.  Untersuchungen  iiber  das  Nervensystem  der  Nematoden.  Ber. 
Akad.  Wiss.  Wien.  Bd.  XVII. 

Franz  Leydig.  Zum  feineren  Bau  der  Arthropoden.  Arch.  f.  Anat.  u. 
Phys.  1855  p.  398. 

Metzler.     De  medullae  spinalis  avium  textura.     Diss.  inaugur.     Dorpat. 

Jakubowitsch  und  Owsjannikow.  Mikroskopische  Untersuchungen  iiber 
die  Nervenursprunge  im  Gehirn.  Melanges  biologiques  T.  II.  St.  Pe- 
tersburg 1858  p.  333 — 335.  (Bull,  phisico — math.  d.  1'Acad.  imp.  d. 
sci.  St.  Petersb.  T.  XIV  No.  12.) 

E.  Faivre.  Observations  histologiques  sur  le  grand  sympathique  de  la 
Sangsue  medicinale.  Ann.  d.  sc.  nat.,  Ser.  4,  T.  IV  p.  249 — 261. 

1856.  —     Etudes  sur  1'histologie    comparee    du    systeme   nerveux    chez    quelques 

Annelides.  Ann.  d.  sc.  nat.  Ser.  4,  T.  V  p.  337—374;  T.  VI  1856  p. 
16—82. 

Jakubowitsch.  Microskopische  Untersuchungen  iiber  die  Nervenursprunge 
im  Riickenmarke  und  verlangertem  Marke,  iiber  die  Empfindungszellen 
und  sympatischen  Zellen  in  denselben  und  iiber  die  Structur  der 
Primitivnervenzellen,  Nervenfasern  und  der  Nerven  iiberhaupt.  Melan- 
ges biologiques.  Bulletin  de  1'academie  imp.  des  Sciences  de  St.  Pe- 
tersbourg  Tom  II  p.  374—387. 

Benedict  Stilling.  Ueber  den  feinern  Bau  der  Nervenprimitivfaser  und 
der  Nervenzelle.  Frankfurt  a.  M. 

Ernst  Hack  el.     De  telis  quibusdam  astaci  fluviatilis.     Diss.  Berolini  1856. 

1857.  —     Ueber  das  Gewebe  des  Flusskrebses.      Arch.    f.    Anat.    u.    Phys.    1857 

p.  469-486  &  532—541- 
Lockhart-Clarke.     On  the  nervous  system  of  Lumbricus  terrestris.    Proc. 

of  the  Royal  Soc.     London.     Vol.  VII  1856 — 1857  p.  343. 
Jakubowitch.     Mittheillungen   iiber    den    feinern    Bau    des  Gehirns    und 

Riickenmarks.     Breslau  1857. 

12 


1857-     Franz  Leydig.     Lehrbuch  der  Histologie  des  Menschen  und  der  Thiere. 
Frankfurt  a.  M. 

1858.  Jakubo  wits  ch.    Recherches  comparatives  sur  le  systeme  nerveux.    Comptes 

rendus.     Paris.      XLXII.  p.    290 — 294,    380 — 383    (vide    also    Berliner 

»Medic.  Centralzeitung«   1858  3  Novbr.  88  Stuck). 
G.  Wagener.     Ueber    den   Zusammenhang    der    Kernes    und    Kernkorpers 

der    Ganglienzellen    mit    dem    Nervenfaden.      Zeitschr.    f.    wiss.    Zool. 

Bd.  VIII  1857  p.  455—457- 
J.  Gerlach.     Mikroskopische  Studien  aus  dem    Gebiete    der   menschlichen 

Morphologic.      Erlangen. 
Emile  Blanchard.     Du    grand   sympatiques    chez    les    animaux    articules. 

Ann.  d.  sci.   nat.    Ser.    4,    T.    X    p.    5 — 10.     (Comptes    rendus    XL VII 

p.  992—995    1858.) 
—     L'organisation  du  regne  animal.      Classe  des  acephales,    nerv.  syst.  p. 

23.     Classe  des  Arachnides,  nerv.  syst.  p.  39,   no,   149,   186. 

1859.  Max  Schultze.     Observationes  de  retinae  structura  penitiori.     Bonn. 
Benedict  Stilling.      Neue    Untersuchungen    ueber  den  Ban  des  Riicken- 

marks.     Cassel   1859  p.  701 — 775. 

A.  K 6 Hiker.     Handbuch  der  Gewebelehre.     3  Aufl. 
Jakubowitsch.      Etudes    sur    la    structures    iutime    du    cerveau    et  de  la 

moelle  epiniere.     Ann.  d.  sci.  nat.  T.  XII.  p.   189 — 245. 

1860.  Philip  p    Owsjannikow.      Recherches    microscopiques    sur   les    lobes  ol- 

factifs  des  Mammiferes.    Comptes  rendus.    Paris.    L.    1860,  p.  428 — 434. 

Reichert's  Arch.   1860  p.  469 — 477. 
Reissner.     Beitrage    zur   Kenntniss    vom    Ban  des  Riickenmarkes  von  Pe- 

tromyzon  fluviatilis.     Arch.  f.  Anat.  u.  Phys.     1860. 
Henry  S.  Wilson.     The  nervous  system  of  the  Asteridae.     Transact.  Lin - 

nean  Society.    London.     Vol.  XXIII  Part  the  first  p.   107.      1860. 
Mauthner.       Beitrage    zur    na'hern    Kenntniss     der    morphologischen    Ele- 

rnente  des  Nervensystems.     Sitzb.  d.  kais.  Akad.  Wiss.     Wien.      1860. 
John    Dean.      Microscopic    anatomy    of    the    lumbar    enlargement    of  the 

spinal  cord.    American  Academy  of  Arts  and  Sciences   1860. 
Franz  Leydig.     Naturgeschichte  der  Daphniden. 
Owsjannikow.      Ueber   die    feinere    Structur    der  Lobi  olfact.  der  Sauge- 

thiere.     Arch.  f.  Anat.  u.  Phys.    1860. 

1 86 1.  —     Sur    la    structure    intime   du   systeme    nerveux    du    Homard.      Comptes 

rendus.    LIT  1861    p.  378 — 381. 
S  tie  da.     Riickenmark    und    einzelne    Theile  des    Gehirns   von   Esox   lucius 

Dorpat. 
Owsjannikow.     Recherches    sur    la    structure    intime    du  systeme  nerveu> 

des  Crustaces  et    principalement  du  Homard.     Ann.    d.  sc.  nat.  Ser.  4 

T.  XV  p.   128—141. 
M.  Schultze.      Die    kolbenformigen  Gebilde  in  der  Haut  von  Petromyzor 

etc.     Arch.  f.  Anat.  u.  Phys.    1 86 1   p.  285. 


—  179  — 

1 862.  M.  Schultze.      Bau    der    Geruchsschleimhaut.     Aus    dem    yten    Bande   der 

Abhandlungen  der  naturforsch.   Ges.  zu  Halle.    1862  p.  65  u.  66  Ann. 

J.  L.  Clarke.  Ueber  den  Bau  des  Bulbus  olfactorius  und  der  Geruchs- 
schleimhaut. Zeitschr.  f.  wiss.  Zool.  Bd.  XI  p.  31 — 42. 

Franz  Leydig.  Uber  das  Nervensystem  der  Anneliden.  Arch.  f.  Anat. 
u.  Phys.  1862  p.  90. 

1863.  R.  Buchholz.      Bemerkungen    iiber    den   histologischen    Bau    des    Central- 

ncrvensystems     der     Siisswassermollusken.       Arch.     f.     Anat.    u.   Phys. 

1863. 
Walter.     Mikroscopische  Studien  iiber  das  Centralnervensystem  wirbelloser 

Thiere.     Bonn. 
Waldeyer.      Untersuchungen    iiber    den    Ursprung    und    den    Verlauf    des 

Achsencylinders    bei     Wirbellosen    und    Wirbelthieren.       Henle  und 

Pfeufer's  Zeitschr.    fur   ration.  Medizin.     3  Reihe.      Bd.  XX,  p.   193 

-256. 
ames  Rorie.     On   the  Anatomy  of  the  nervous  system  in  Lumbricus  ter- 

restris.     Quart.  Journ.  of  Micr.  Sci.    Ser.  2.     Vol.  Ill,  p.   106 — 109. 
Ph.  O  wsj  annikow.     Ueber  die  feinere  Structur  des  Kopfganglions  bei  den 

Krebsen,    besonders    beim    Palinurus    locust  a.      Mem.  Acad.   imp. 

d.  sci.    St.  Petersbourg.     VI.  No.   10.     1863. 

—  Ueber    die    Inauguraldissertation    des  Herrn  Dr.  Kutschin  das  Riicken- 
mark    der   Neunauge    betreffend,  nebst  einigen  eigenen  Beobachtungen 
iiber  das  Riickenmark  der  Knochenfische  und  anderer  Thiere.    Novemb. 
1863.     Melanges    biologiques    T.    IV    St.    Petersb.    1865  p.   527 — 538. 
(Bull.  Acad.  imp.  sci.  St.  Petersb.  T.  VII  p.   137 — 145.) 

—  Ueber  die  feine  Structur  des  Kleinhirns  der  Fische.    Dec.  1863.    Melang. 
biolog.    T.    IV.    p.    551 — 562.      (Bull.    Acad.    imp.    sc.  St.  Petersb.  T. 
VII  p.   157—166.) 

A.  K 6 Hiker.  Handbuch  der  Gewebelehre  des  Menschen.  4  Aufl.  .Leip- 
zig. 15  Aufl.  1867.) 

John  Dean.  The  gray  substance  of  the  medulla  oblongata  and  trapezium. 
Smithsonian  contributions  to  knowledge.  1863. 

Lionel  Smith  Beale.  On  the  structure  and  formation  of  the  so-called 
apolar,  unipolar,  and  bipolar  nerve-cells  of  the  Frog.  Philos.  trans. 
Royal.  Soc.  London.  1863.  Vol.  153,  p.  543— 571.  (Abstract  in  Quart. 
Journ.  micr.  sci.  Ser.  2.  Vol.  Ill  p.  302 — 307.) 

1864.  Johann  Marcusen.     Sur  1'anatomie  et  1'histologie  du    Branchiostoma    lu- 

bricum,    Costa    (Amphioxus    lanceolatus,  Yarrell).      Comptes  rendus  de 

1'Acad.    d.  sc.    de    Paris.    LVIII   p.    479 — 483;    LIX    1864   p.    89 — 90. 

(Ann.  Mag.  Nat.  Hist.  XIV  1864  p.   151  —  154,  319—320.) 
Benedict  Stilling.     Untersuchungen  iiber  den  Bau  des  kleinen  Gehirns 

des  Menschen.     Heft.   I.     Cassel. 
Schramm.       Neue     Untersuchungen     iiber     den     Bau    der    Spinalganglie  n 

Wiirzburg. 

12* 


—  i8o  - 

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visceral   nerves    of   Cyclostomata.      Zool.  Anzeiger.     IX  Jahrg.,  p.  421 

—426.      1886. 
Nicolaus   Kleinenberg.      Die    Entstehung    des  Annelids  aus  der  Larve 

von  Lopadorhynchus.     Zeits.  f.  wiss.  Zool.     Bd.  XLIV.     Neuromuske- 

system  p.   58 — 151. 
Emil  Rohde.     Histologische    Untersuchungen  iiber    das  Nervensystem  der 

Chaetopoden.      Sitzber.  d.  k.  pr.  Akadem.  der  Wiss.     Berlin.    XXXIX 

p.   781 — 786.     Juli   1886.     Translated  in:  Ann.  mag.  nat.  hist.     Ser.  5. 

Vol.  XVIII  p.  311—316.      1886. 
Michael   v.    Lenhossek.      Untersuchungen    iiber    die  Spinalganglien  des 

Fsosches.     Arch.  f.  mikr.  Anat.     Bd.  XXVI,  p.  370 — 453; 
G.  Fritsch.     Uebersicht    der   Ergebnisse  einer  anatomischen  Untersuchung 

iiber     den     Zitterwels     (Malopterus     electricus).       Sitzungsber,    der    k. 

preus.      Akad.    der   Wissensch.    Berlin.      XLlX.    L.    2  Decemb.    i886r 

p.   1137—1140. 
F.    Ley  dig.      Die  riesigen  Nervenrohren  im  Bauchmark  der  Ringelwurmer. 

Zool.  Anzeiger  No.  234.      1886. 
Romeo  Fusari.      Richerche    intorno  alia  fina  anatomia  dell'  encefalo  del 

Teleostei.     Nota  preventiva.     Bollettino  scientifico  N.  2,  Giugno  1886. 

Pavia. 
1887.     Bela   Halle r.      Ueber  die  sogenannte  Leydig'sche  Punktsubstanz  im  Cen- 

tralnervensystem.     Morph.  Jahresbuch.     Bd.  XII.      1887.     p.  325 — 332. 

During  the  printing  of  the  present  memoir  the  following  papers    of   interest 
to  our  subject  have  appeared: 
1887.     Bernhard  Rawitz.     Das  centrale  Nervensystem  der  Acephalen.    Jenaische 

Zeitschr.  f.  Naturwissenschaft.     Bd.  20,  p.  386—461. 
Julius    Waldschmidt.      Zur   Anatomic    des    Nervensystems    der  Gymno- 

phionen.      Jenaische    Zeitschr.    f.    Naturwiss.      Bd.    20,    p.    461 — 476. 

1887. 
L.  Edinger.      Vergleichend-entwicklungsgeschichtliche  Studien  im  Bereich 

der    Gehirn-Anatomie.      Anatom.  Anzeiger.     Bd.  II.     No.  6,  p.   145 — 

143.     (Marz   1887.) 
H.    Viallanes.     Etudes  hist.  etc.     Quatrieme  memoire.    Le  cerveau  de  la 

Guepe    (Vespa  crabro    et   V.  vulgaris).     Ann.  sci.  nat.     Ser.  7.     T.  2. 
Alfred    Sanders.      Contributions    to    the  anatomy  of  the  central  nervous 

system    in     vertebrate     animals     (Plagiostomata).       Phil,    trans.    Royal. 

Soc.     London.     Vol.    177.     Part    II,  p.   733 — 766.    (Read.  Jan.   1886.) 
A.    A.    W.   Hubrecht.      Report    on    the    Nemertea    collected  by  H.  M.  S. 

Challenger  during  the  years   1873 — 76.     Zool.  Chall.  Exp.     Part.  LIV. 

1886  vol.  XIX.     Nerv.syst.  p.   73 — 90. 
W.  Bechterew.     Le  cerveau  de  I'homme  dans  ses  rapports  et  connexions 

intimes.      Arch,    slaves    cle    biologic.      T.    Ill,    Fasc.    3,    p.  293 — 321 

(Mai);  T.  IV,  Fasc.   I,  p.   1—30  (Juillet). 


—  193  — 

1887.     Willy  Kiikenthal.     Ueber  das  Nervensystem  der  Opheliaceen.     Jenaische 

Zeits.  f.  Naturwiss.     Bd.  XX,  p.   511 — 580. 
Michael    v.    Lenhossek.      Beobachtungen    am    Gehirn    des    Menschen. 

Anat.  Anzeiger.     Bd.  II.     No.  14,  p.  450 — 461.     Juni. 
A.  Koelliker.     Die  Untersuchungen  von  Golgi  iiber  den  feineren  Bau  des 

zentralen   Nervensystems.      Anat.    Anzeiger.      Bd.  II.     No.   15,    p.  480 

-483  (Juli). 
Charles  Julin.     Le  systeme  nerveux  grand  sympathique  de  l'Ammocoetes 

(Petromyzon  Planeri).     Communication  prelimiuaire.     Anat.  Anzeiger  II 

Jahrg.     Nr.   7,  p.   192 — 201.     1887. 
Romeo  Fusari.     Untersuchungen  tiber  die  feinere  Anatomic  des  Gehirnes 

der  Teleostier.     Intern.  Monatschr.  f.  Anat.  u.  Phys.      Bd.  IV,  p.  275 

-300.1) 


J)  Last  winter  I  wrote  a  paper:  Uber  das  Nervensystem  der  Myzostomen, 
which  was  going  to  be  published  in  Jenaische  Zeitschr.  f.  Naturwiss.  but  which  is 
not  yet  appeared  as  far  as  I  know.  As  that  paper  was  written  before  the  investigations, 
above  described,  had  been  finished,  there  are  some  remarks  on  the  nervous  system 
of  various  animals  which  do  not  quite  agree  with  the  results  we  have  here  obtained. 


Explanation  of  the  plates. 

Plate   I. 

The  illustrations  are  drawn  under  the  camera  lucida,  from  the 
microscope  directly  upon  the  stone.  The  preparations  (exept  fig.  5  &  6) 
were'  fixed  i  chromo-aceto-osmic  acid  and  stained  with  haematoxylin. 
Fig.  I.  Homarus  vulgaris.  (Magnified  60  diameters ;  Zeiss  AA,  2.) 
Transverse  sections  of  an  oesophageal  commissure,  a  Ex- 
ternal sheath,  b  Layer  of  connective  tissue  inside  the 
ext.  sheath,  c  Inner  layer  or  sheath  of  connective-tissue 
closely  applied  to  the  contents  of  nerve-tubes  (compare 
fig-  5.'  «)•  t,  ^>  ti  Large  nerve-tubes  with  more  or  less 
concentrated  axes,  f  Large  nerve-tubes  with  no  axis. 
nt  Central  bundle  of  largish  nerve-tubes,  snt  Masses  of 
small  nerve-tubes,  more  peripherically  situated. 
»  2.  Homarus  vulgaris.  (Magnified  950  diameters;  Zeiss.  Horn, 
im.  V18,  i.)  A  part  of  fig.  i,  representing  some  smallish 
nerve-tubes  of  various  sizes,  more  highly  magnified.  The 
transsected  primitive  tubes,  of  which  the  contents  of  the 
nerve-tubes  are  composed,  are  distinctly  visible  as  round 
meshes.  I,  t  Largish  nerve-tubes  in  which  a  concentration  to- 
wards an  axis  is  visible,  t',  f  Small  nerve-tubes ;  in  one  of  them 
a  slight  concentration  towards  an  axis  is  visible,  j"  Small 
nerve-tube  in  which  no  concentration  towards  an  axis  is 
visible,  a  Vacuoles.  b  Neuroglia-substance.  c  The  sheath 
of  a  large  nerve-tube  which  is  illustrated  in  fig.  i,  ^. 
d  Vacuoles  in  some  nerve-tubes,  probably  artificially  pro- 
duced, k  Neuroglia-nuclei. 

»  3.  Homarus  vulgaris.  (Magnified  950  diameters;  Zeiss.  Horn, 
im.  Vis*  I-)  Transverse  section  of  a  large  nerve-tube 
with  axis  (it  is  the  same  tube  which  is  illustrated  in 
fig.  i,  t1).  a  Neuroglia-sheath.  b  Sheath  of  another  large 
nerve-tube. 


—  195  — 

Fig.  4.  Homarus  vulgar  is  (Magnified  950  diameters;  Zeiss.  Horn, 
im.  Vis*  x)-  Longitudinal  section  of  the  same  nerve -tube 
as  is  illustrated  in  fig.  3  (of  the  same  piece  of  an  oeso- 
phageal  commissure  was  first  taken  transverse  sections, 
and  subsequently  longitudinal  sections,  a,  a?  Deeply  staining 
axis,  b  Externel  layers  of  primitive  tubes  which  are 
samewhat  obliquely  transsected.  c  &  d  Neroglia-sheath  of 
the  nerve-tube,  which  on  one  side  (c)  is  considerably 
thicker  than  on  the  other.  Jc  Neuroglia-nucleus  situated 
inside  the  sheath. 

»  5.  Neplirops  norvegicus.  (Magnified  950  diameters;  Zeiss. 
Horn.  im.  Vis*  I-)  Transverse  section  of  nerve-tubes, 
from  an  oesophageal  commissure,  a  Inner  layer  of  the 
connective-tissue  surrounding  the  bundle  of  nerve-tubes 
of  the  commissure  (compare  fig.  i,  c).  b  Outer  layer  of 
the  same  connective-tissue  (compare  fig.  I,  &).  t,  t  Trans- 
sected nerve-tubes;  in  the  right  one  is  a  very  slight 
concentration  towards  a  deeply  staining  axis  visible. 
t',  t",  t1"  Nerve-tubes  with  vacuoles,  which  possibly,  to 
some  extent,  are  transsected  tubes.  t{  Nerve-tubes  con- 
taining solely  large  meshes,  which  possibly  are  transsected 
tubes,  c  Vacuoles.  Jc,  #,,  Jc',  Jc",  k1"  Neurogla-nuclei  and 
nuclei  of  the  connective-tissue,  k'  Neuroglia-nucleus  situated 
inside  the  sheath  of  a  nerve-tube.  The  preparation  was 
fixed  in  Lang's  fluid  (corrossive  sublimat  1 2  %)  and  stained 
with  hcemotoxylin. 

»      6.      Nephrops    norvegicus.     (Magnified    1700  diameters;    Zeiss. 
Horn.  im.   y,8,  3-)     ?art  of  the  contents  of  a  nerve-tube 
highly  magnified  to  show  the  walls  of  the  primitive  tubes. 
a  Thickenings   in   these  walls  along  the  concreting  edges 
of  the  tubes.     From  the  same  preparations  as  fig.   5. 

»  7.  Homarm  vulgar  is.  (Magnified  190  diameters;  Zeiss  CC,  2). 
Transverse  section  of  a  small  peripheral  nerve  containing 
large  and  small  nerve-tubes,  t  Large  nerve-tubes;  their 
sheaths  are  very  thick  and  consist  of  several  layers. 
n  t  Small  nerve-tubes,  s  Septa,  dividing  the  small  nerve- 
tubes  into  bundles.  Jc  Neuroglia-  and  connective-tissue- 
nuclei. 

»  8.  Homarus  vulgaris.  (Magnified  1150  diameters;  Zeiss. 
Horn.  im.  !/18,  2.)  Transsected  nerve-tubes  from  a  peri- 
pheral nerve,  nt  Small  nerve-tubes  containing  some  few 

13* 


-  196  - 

primitive  tubes  only.  p,p  Thickenings  along  the  concret- 
ing edges  of  the  sheaths  of  the  small  nerve-tubes,  t  Large 
nerve-tubes  outside  the  scheath  of  which  a  neuroerlia- 

o 

nucleus  is  situated. 

Fig.  9.  Nereis  virens.  (Magnified  950  diameters;  Zeiss  1/16,  i.) 
Longitudinal  section  of  a  large  nerve-tube  (b)  and  some 
small  nerve-tubes  (nt)  from  the  ventral  nerve-cord,  a  Sheath 
of  the  large  nerve-tube  (&).  The  spongioplasmic  walls 
of  the  primitive  tubes  of  the  nerve-tubes  are  distinctly 
seen  longitudinal  transsected. 

»  10.  Nereis  vifens.  (Magnified  950  diameters;  Zeiss  Vis»  l-) 
Transverse  sections  of  some  large  nerve-tubes  running 
centrally  along  the  ventral  nerve-cord  (compare  fig.  14). 
a  Central  fibrous  septum  dividing  the  nerve-cord  longi- 
tudinally into  two  lateral  cords  (cf.  fig.  14).  6  &  b'  Trans- 
verse bundles  of  neuroglia-fibres ;  subdividing  into  branches 
(c,  c).  t,  t  Large  central  nerve-tubes.  tlt  t2  tz  Somewhat 
smaller  nerve-tubes,  more  ventrally  situated,  nt  Small 
nerve-tubes,  nt1  Small  nerve-tubes  situated  between  the 
large  central  nerve-tubes  (t)  and  the  central  septum  (and 
the  transverse  bundles  of  fibres  [b]).  k  Neuroglia-nucleus 
situated  in  the  ventral,  reticular  part  (B)  of  the  central 
septum  (a). 

»  ii.  Lumbricus  agricota.  (Magnified  500  diameters;  Seibert 
Vs,  Zeiss  2.)  Transverse  section  of  the  three  colossal 
nerve-tubes  (£,,  t,  t)  and  a  part  of  the  dotted  sub- 
stance (c).  a  Connective-tissue  outside  the  perineu- 
riuin.  6  Perineurium  (Vignal's  gaine  troisieme),  outside 
which  the  layer  of  muscles  (m,  m)  is  situated,  d  Neu- 
roglia  extending  inside  the  perineurium,  between  the  three 
colossal  nerve-tubes,  s,  s,  s  Septa  or  very  thick  fibres 
occurring  in  this  neuroglia  and  connected  with  the  peri- 
neurium. c  Dotted  substance,  exhibiting  a  reticulation 
produced  by  a  transsection  of  tubes,  nt  Transsected 
nerve-tubes,  k  Neuroglia-nuclei. 

Plate   II. 

Fig.  12.  Homarus  vulgar  is.  (Magnified  330  diameters;  Zeiss.  Apochr. 
4,0,  —  0,45,  I.  Cam.  luc.)  Large  nerve-tubes  from  an  oeso- 
phageal  commissure,  seen  in  the  live  state  in  the  commissure. 


—  197  - 

A&B  Large  nerve-tubes  with  striated  axes  (c,  d).  a,  a  Neu- 
roglia  layers  between  the  nerve-tubes.  I  Small  nerve- 
tube  with  a  visible  longitudinal  striation.  e,  e  Small  nerve- 
tubes  without  visible  striation. 

Fig.  13.  Homarus  vulgaris.  (Magnified  950  diameters;  Zeiss.  Horn, 
im.  Vis*  J-  Cam.  luc.)  Large  nerve-tubes  (a,  a)  from  a 
peripheral,  abdominal  nerve,  and  seen  in  the  nerve  in  the 
live  state ;  no  striation  is  visible,  ft  Sheaths  of  the  nerve- 
tubes,  c,  c,  c1  Apparent  septa,  optic  illusions  produced 
by  a  slight  bending  of  the  nerve-tubes  and  their  sheaths. 
k  Neuroglia-nucleus  situated  inside  the  sheath  of  the 
one  nerve-tube. 

»  14.  Nereis  virens.  (Magnified  190  diameters;  Zeiss.  CC,  2. 
Cam.  luc.  direct  upon  the  stone.)  Transverse  section  of 
the  ventral  nerve-cord,  cu  External  cuticulum.  ep  Thick 
ectodermal  epithelium,  outside  the  ventral  nerve-cord. 
k  Nuclei  of  the  high  cylindrical  cells  of  this  ectoderm. 
ep{  The  common  ectoderm  of  the  body.  k>  The  nuclei 
of  this  ectoderm,  n,  sh  »Connective«  or  neuroglia  tissue 
surrounding  and  enveloping  the  ventral  nerve-cord,  k'  k" 
Nuclei  of  this  tissue.  &,  Similar  nuclei,  situated  more 
ventrally,  towards  the  ectodermal  epithelium,  from  the 
nuclei  of  which  they  are  not  easily  distinguished. 
gc  &  gcy  Ganglion  cells,  m,  m  Membrane  separating  the 
ectoderm  and  the  ventral  nerve-cord  from  the  inner  layers 
of  the  body.  (From  a  preparation  fixed  in  Flemming's 
chromo-aceto-osmic  acid  and  stained  with  Delafield's 
haematoxylin.) 

»  15.  Homarus  vulgaris.  (Magnified  620  diameters;  Zeiss  F,  i. 
Cam.  luc.)  Isolated,  largish  nerve-tubes  from  an  oeso- 
phageal  commissure,  macerated  in  acetic  acid  (i),  glyce- 
rin (i)  and  aqua  dest.  (5). 

»  16.  Homarus  vulgaris.  (Magnified  620  diameters ;  Zeiss  F,  I. 
Cam.  luc.)  Isolated  smallish  nerve-tubes  from  an  oeso- 
phageal  commissure,  macerated  in  the  same  way  as  in 
fig.  15. 

»  17.  Patella  vulgata.  (Magnified  620  diameters;  Zeiss  F,  I. 
Cam.  luc.  direct  in  the  stone.)  Nerve-tubes  from  a  pedal 
nerve-cord  and  a  peripheral  nerve,  macerated  as  above. 

»  1 8.  Patella  vulgata.  (Magnified  620  diameters;  Zeiss  F,  i. 
Cam.  luc.)  Nerve-tubes  macerated  as  above,  stained  with 
picro-carmine. 


—  198  — 

Fig.  19.  Patella  vulgata.  (Magnified  620  diameters;  Zeiss  F,  I. 
Cam.  luc.  direct  upon  the  stone.)  Transverse  section  of 
a  nerve,  from  which  two  smaller  nerves  (a  and  &)  later- 
ally issue,  v  Vental  side  of  the  nerve,  a  &  6  Trans- 
versally  transsected  nerve-tubes  of  the  small  lateral  nerves, 
a'  &  b'  Longitudinally  transsected  nerve-tubes  of  the  same 
nerves,  c  &  d  Large  nerve-tubes,  transversally  transsected 
s,  s  Septa  dividing  the  nerve  into  bundles  of  nerve-tubes. 
s',  s'  Septa  separating  the  nerve-tubes  of  the  two  small 
lateral  nerves  from  the  rest  of  the  large  nerve.  /  Neu- 
roglia-cell  with  nucleus  situated  inside  the  neurilem -sheath 
k  Neuroglia-nuclei.  (From  a  preparation  treated  with 
osmic  acid  (i  %)  f°r  4&  hours,  stained  with  Delafield's 
haematoxylin  and  decoloured  in  water  to  wich  some  drops 
of  acetic  acid  had  been  added ;  the  section  was  taken  directly 
with  a  razor  without  imbedding.) 

»  19  A.  A  part  of  the  section,  illustration  in  fig.  19,  highly  mag- 
nified to  show  the  structure  of  the  walls  between  the 
nerve-tubes. 

>  20.  Patella  vulgata.  (Magnified  750  diameters;  Zeiss  F,  2. 
Cam.  luc.  direct  upon  the  stone.)  Longitudinal  section 
of  a  peripheral  nerve  near  its  origin  in  the  pedal  nerve- 
cord,  gc  A  ganglion  cell  sending  a  protoplasmic  process  (jp) 
towards  the  neurilem-sheath  (sh}\  the  nervous  process 
which  runs  longitudinally  was  not  distinctly  visible  in 
this  section.  k,  k',  k"  Circular  and  oblong,  deeply 
staining  neuroglia-nuclei.  n,  nn,  nn',  nnr' ',  nn'"  Ovoid,  less 
staining  and,  generally,  larger  neuroglia-nuclei.  (The  pre- 
paration was  fixed  in  chromo-aceto-osmic  acid  and  stained 
with  Delafield's  haematoxylin.) 

»  21.  Phallusia  obliqua.  (Magnified  350  diameters;  Zeiss  CC,  4. 
Cam.  luc.  direct  upon  the  stone.)  Transverse  section  of 
a  peripheral  nerve,  sh  External  neurilem-sheath.  (From 
a  preparation  fixed  and  hardened  in  Miiller's  fluid,  stained 
with  acid  fuchsin  dissolved  in  turpentine  with  a  little 
abs.  alcohol  added.) 

»  22.  Phallusia  obliqua.  (Magnified  750  diameters;  Zeiss  F,  2. 
Cam.  luc. ;  drawn  directly  upon  the  stone.)  Longitudinal 
section  of  a  part  of  a  peripheral  nerve,  a  &  &  Septa 
(longitudinally  transsected)  between  bundles  of  nerve-tubes. 
n  Neuroglia-nucleus  situated  in  one  septum  (a),  ts  Sheaths 


—  199  — 

of  the  nerve-tubes.  The  spongioplasmic  walls  of  the  pri- 
mitive tubes  are  distinctly  seen  in  the  nerve-tubes.  (From 
a  preparation  treated  as  above.) 

Plate   IIL 

The  illustrations  of  this  plate  are  drawn  under  the  camera 
lucida,  from  the  microscope  directly  upon  the  stone  (except  fig.  23). 
The  preparations  (exept  fig.  23)  are  fixed  in  chromo-aceto-osmic  acid, 
stained  according  to  Heidenhain's  haematoxylin  method  (except  fig.  24) 
and  some  of  them  afterwards  with  Delafield's  haematoxylin.  All  the 
illustrations  are  taken  from  ganglion  cells  of 

Homarus  vulgaris. 

Fig.  23.  (Magnified  620  diameters;  Zeiss  F,  i.  Camera  lucida.) 
A  &  B  Ganglion  cells  (from  a  ventral  ganglion)  isolated 
in  acetic  acid  (i),  glycerin  (i),  and  aqua  dest.  (5),  and 
stained  with  picro-carmine.  a  Space  surrounding  the 
central  bundle  of  primitive  tubes  (b)  of  the  process,  and 
in  which  no  structure  is  visible,  n,  n  Neuroglia  nuclei 
situated  outside  the  sheath  of  the  cell  and  the  process. 

24.  (Magnified  620  diameters;   Zeiss  F,  i.)     Part  of  a  section 
through  two  ganglion  cells  (A  &  B)  and  the  neuroglia  (nu) 
situated  between  them.     A  &  B   Parts   of  the  protoplasm 
of  the  two  ganglion  cells,   in  which  a  spongioplasmic  re- 
ticulation is   distinctly  visible,      cm,  cm    Neuroglia-sheaths 
of  the  cells,     a  Transsected,  spongioplasmic  fibres  pene- 
trating,   from    the    sheaths    into    the    protoplasm    of  the 
ganglion    cells.     &   Such   a  fibre  seen  in  connection  with 
the   sheath,     sp   Similar  fibre  subdividing  and  forming  a 
reticulation,     nu  Neuroglia.     n  Neuroglia-nuclei. 

25.  (Magnified  350  diameters;  Zeiss  CC,   4.)     Section  through 
a  large  ganglion  cell  (of  an  abdominal  ganglion)   and  the 
root  of  its  process ;  the  lightly  staining  contents  of  which 
partly  originates  from  bundles  of  primitive  tubes,     s,  s  Fi- 
bres penetrating  from  the  neuoglia-sheath  into  the  proto- 
plasm of  the  cell,     a  Similar  fibres  transsected. 

26.  (Magnified  750  diameters;  Zeiss  F,  2.)     Section  through  a 
ganglion  cell  and  a  part   of  its   prosess,   the   contents   of 
which  arises   equally   from   the  whole  protoplasm   of  the 
cell  by  a  convergence  af  primitive  tubes,      nu  Neuroglia, 
cm  Sheath  of  a  ganglion  cell. 


—    200   — 

Fig.  27.  (Magnified  620  diameters;  Zeiss  F,  i.)  Section  through 
a  large  ganglion  cell  and  the  root  of  its  process,  the 
lightly  staining  contets  (a)  of  which  arises  from  a  union 
of  bundles  of  primitive  tubes.  6  Transsected  spongio- 
plasmic  fibres,  with  which  the  spongioplasmic  walls  separat- 
ing the  primitive  tubes,  unite,  cm  Sheath  of  a  ganglion  cell. 
»  28  &  29.  (Magnified  620  diameter;  Zeiss  F.  i.)  Parts  of  suc- 
cessive sections  through  the  same  ganglion  cell,  selected 
from  a  series  of  sections  to  show  how  the  lightly  stain- 
ing contents  (p,  p)  of  the  process  penetrates  into  the 
protoplasm  of  the  eels  surrounded  for  some  distance  by 
deeply  staining  fibres  (s,  s').  b  Such  fibres  transsected. 
a  &  s"  Similar  fibres  penetrating  into  the  protoplam  of 
the  cell,  cm  Sheath  of  the  cell,  v,  v  Transsected  bundles 
or  small  masses  of  primitive  tubes,  nv  Cavities  in  the 
sheath  of  the  cell  into  which  cavities  the  protoplasm  of 
the  cell  partly  extends. 

Plate   IV. 

The  illustrations  are  drawn  under  camera  lucida  from  the  mi- 
croscope directly  upon  the  stone.  The  preparations  (exept  fig.  41) 
are  fixed  and  stained  in  the  same  way  as  in  Plate  III.  All  the 
illustrations  are  taken  from  ventral  ganglia  of 

Homarus  vulgar  is. 

Fig.  30 — 33.  (Magnified  350  diameter;  Zeiss  CC,  4.)  Successive 
sections  through  the  process  of  a  ganglion  cell,  selected 
from  a  series  of  transverse  sections  through  an  abdominal 
ganglion.  In  fig.  30  the  process  is  seen  quitting  the  cell 
in  fig.  33  it  is  divided  into  two  branches  (a  &  6).  p,  c  Con- 
tents of  the  process;  near  the  cell  (fig.  30)  this  contents 
is  lightly  stained,  in  a  greater  distance  from  the  cell  (fig.  31) 
it  becomes  more  deeply  stained  until  it,  at  a  certain  distance 
(fig.  32),  becomes  quite  dark,  pr  Protoplasm  of  the  ganglion 
cell,  sf  Spongioplasmic  fibres,  penetrating  into  the  proto- 
plasm of  the  cell  and  (sf")  into  the  contents  of  the  pro- 
cess, s/"  Similar  spongioplasmic  fibres  occurring  in  the 
external  layers  of  the  contents  of  the  process,  cm  Neu- 
roglia-sheath  of  the  ganglion  cell,  is  Inner  neuroglia-sheath 
enveloping  the  process,  nm  Concentric  layers  of  neu- 
roglia  surrounding  the  process. 


—   2OI    — 

Fig.  34.  (Magnified  350  diameters;  Zeiss  CC,  4).  Transverse  sec- 
tion through  the  process  of  a  ganglion  cell,  exhibiting 
the  concentric  layers  of  neuroglia  (nm)  surrounding  the 
contents  of  the  process  (pc].  br  Transsected  side-branch, 
issuing  from  the  process  the  process. 

»  35  &  36.  (Magnified  620  diameters;  Zeiss  F,  I.)  Two  trans- 
verse sections  through  the  same  process  of  a  ganglion 
cell;  selected  from  a  series  of  sections,  pc  Contents  of 
the  process,  in  which  the  transsected  primitive  tubes  are 
distinctly  seen,  sf  Transsected  spongioplasmic  fibres 
ocurring  in  the  external  layers  of  the  contents.  br,  brj  Trans- 
sected branches  issuing  from  the  process,  nm  Concentric 
layers  of  neuroglia.  n  Neuroglia-nucleus.  b  &  c  Similar 
nuclei  deeply  stained. 

»  37.  (Magnified  350  diameters;  Zeiss  CC,  4.)  Section  through 
a  ganglion  cell,  a  External,  lightly  stained,  layer  of  the 
protoplasm.  b  Mesial  deeply  stained  part  of  the  proto- 
plasm, sf  Spongioplasmic  fibres,  s/'&s/"  Similar  spon- 
gioplasmic fibres  surounding  the  lightly  stained  contents  of 
the  process,  in  the  prototoplasm  of  the  cell,  br,  br  Branches 
of  the  process. 

»  38.  (Magnified  620  diameters;  Zeiss  F,  i.)  Section  through 
three  ganglion  cells  (A,  B,  C)  from  an  abdominal  ganglion. 
v,  v'  Transsected  masses  of  primitive  tubes,  situated  peri- 
pherically  in  the  protoplasm  of  the  cell.  vj  Similar 
masses  situated  on  the  sides  of  the  bundle  of  primitive 
tubes  forming  the  contents  of  the  process,  sf  Spongio- 
plasmic fibres  surrounding  this  bundle  of  primitive  tubes. 
s  Septa  or  fibres,  partly  separating  the  masses  of  primi- 
tive tubes.  sr  Small  septa  and  fibres  penetrating  these 
masses,  n  Neuroglia-uncleus.  a,  a  Lightly  stained  parts 
of  protoplasm  situated  round  the  bundle  of  primitive 
tubes  forming  the  contents  of  the  process.  b  External 
lightly  staining  layer  of  the  protoplasm,  p  Process  of 
the  ganglion  cell  (C).  cm  Sheath  of  a  ganglion  cell. 

»  39.  (Magnified  620  diameters;  Zeiss  F,  I.)  Lateral  section 
through  the  same  cell  as  is  illustrated  in  fig.  38,  A,  In 
this  section  lightly  staining  masses  of  primitive  tubes  are 
almost  solely  transsected.  a  Deeply  staining  protoplasm. 
b  Place  where  the  section  has  passed  just  on  the  border 
between  the  deeply  staining  protoplasm  and  the  lightly 


—   202   — 

staining  mass  of  primitive  tubes,  ss  Spongioplasmic  septa 
and  fibres  occurring  in  the  lightly  staining  mass.  ssj  Si- 
milar septum  with  a  little  deeply  staining  protoplasm. 
v,  v'  Small  lightly  staining  masses,  cm  Sheath  of  the  cell. 
nm  Neuroglia. 

Fig.  40.  (Magnified  350  diameters;  Zeiss  CC,  4.)  Section  through 
a  group  of  smallish  ganglion  cells  in  a  thoracal  ganglion. 
a  Transsected  processes  issuing  from  the  cells,  n  sh  Peri- 
neurium  enveloping  the  ganglion,  nm  Neuroglia  occur- 
ring inside  the  perineurium. 

»  41.  (Magnified  750  diameters;  Zeiss  F,  2.)  Section  of  the 
nucleus  of  a  ganglion  cell  stained  with  borax-carmine. 
The  nucleus  has  two  nucleoli  (a  &  6).  c  Thickenings  in 
the  chromatine-structure.  n  Membrane  of  the  nucleus. 

»  42.  (Magnified  750  diameters;  Zeiss  F,  2.)  Sections  of  nuclei 
of  ganglion  cells. 

Plate    V. 

All  the  illustrations  of  this  plate  are  drawn  under  the  camera 
lucida  and  from  the  microscope  directly  upon  the  stone.  They  are 
all  taken  from  preparations  fixed  in  chromo.-aceto-osmic  acid,  and 
stained  with  Delafield's  haematoxylin  (and  partly  also  with  eosin  or 
picric  acid  in  turpentine). 

Fig.  43.  Nereis  virens.  (Magnified  1 1 50  diameters ;  Zeiss.  Horn.  im. 
Vi8)  2-)  Ganglion  cells,  from  a  transverse  section  of  the 
ventral  nerve-cord.  I — 5  ganglion  cells  in  three  of  which 
processes  (pr)  are  transsected.  2  Part  of  a  ganglion  cell. 
a  Transsected  nerve-tubes  of  the  dotted  substance.  b  Lightly 
stained  part  of  the  protoplasm  of  the  cell  I.  cm,  cm  Sheaths 
of  the  ganglion  cells.  nu  Neuroglia.  n  m  Neuroglia- 
septum  penetrating  between  the  ganglion  cells,  and  some- 
times dividing  them  into  groups.  lg  Large  dark  granules 
in  the  protoplasm. 

»  44  &  45.  Nereis  virens.  (Magnified  1150  diameters;  Zeiss. 
Horn.  im.  V18,  2.)  Ganglion  cells,  from  horizontal  sec- 
tions of  the  ventral  nerve-cord,  a  Mesial,  deeply  stain- 
ing part  of  the  protoplasm,  b  Peripheral,  lightly  staining 
layers  of  the  protoplasm,  sf  Spongioplasmic  fibres,  pe- 
netrating into  the  protoplasm,  cm,  cmj  Neuroglia-sheaths 
enveloping  the  ganglion  cells,  nu  Neuroglia.  nm  Thick 
neuroglia-septum. 


—  203  — 

Fig.  46  &  47.  Lumbricus  agricola.  (Magnified  2070  diameters; 
Zeiss.  Horn.  im.  1/IB,  4.)  Sections  of  ganglion  cells  of  the 
ventral  nerve-cord,  a  Lightly  staining  parts  of  the  proto- 
plasm, npr  Nervous  processes.  br,  br'  Side-branches, 
given  off  from  the  nervous  process,  ppr  Protoplasmic 
processes,  cm  Neuroglia-sheath  of  the  ganglion  cells. 
nu  Neuroglia.  nur  Neuroglia  retuculatation.  n  Nouroglia- 
nucleus. 

»  48.  Patella  vulgata.  (Magnified  2070  diameters;  Zeiss.  Horn, 
im.  Vi8>  4-)  Section  of  a  ganglion  cell  of  the  pedal  nerve- 
cord,  npr  Nervous  process,  nur  Neuroglia-reticulation. 

*  49  &  50.  Patella  vulgata.  (Magnified  1150  diameters;  Zeiss 
Horn.  im.  Vis*  20  Sections  of  ganglion  cells;  taken  from 
transverse  sections  of  the  pedal  nerve-cord,  npr  Nervous 
processes,  npr'  Roots  of  nervous  processes,  br  Branches 
given  off  from  the  nervous  process,  ppr  Protoplasmic 
process  terminating  under  the  perineurium.  pe  Perineu- 
rium.  n,  n'  Neuroglia-nuclei.  n"  Nucleus  situated  outside 
the  perineurium  and  belonging  to  it.  nur  Neuroglia- 
reticulation. 


Plate    VI. 

All  the  illustrations  of  this  plate  are  drawn  from  the  microscope 
directly  upon  the  stone  under  the  camera  lucida. 

51 — 54-  Patella  vulgata.  (Magnified  1350  diameters;  Zeiss 
F,  4.)  Isolated  ganglion  cells  of  the  pedal  nerve-cord. 
npr  Nervous  process,  gr  Yellow  granules  (containing 
haemoglobin?)  occurring  in  the  protoplasm  of  the  cells. 
gr1  Simular  granules  exuded  from  the  cells,  a  (fig.  52). 
Large  granule  of  yellow  substance,  being  formed  on  a 
place  where  such  substance  is  exuded  from  the  cell. 
b  Side-branches,  given  off  from  the  nervous  processes. 
ppr  Protoplasmic  process.  a  (fig.  54)  Short  process  or 
prolongation  of  the  nucleus  of  the  ganglion  cell.  (The 
cells  were  isolated  in  acet.  ac.  (ij,  glycerin  (i),  aqua 
dest.  (5)  or  in  weak  solution  of  alcohol  and  stained  with 
ammonia-carmine). 

55 — 57-  Phallusia  venosa.  (Magnified  1350  diameters;  Zeiss 
F,  4)  Isolated  ganglion  cells  from  the  brain.  Fig.  55  & 
56  Peripheral  cells.  Fig.  57  Tripolar  cell  situated  in  the 


—    2O4   — 

dotted  substance,      npr  Nervous   process.      a,  a\  ~b   Side-] 
branches  given  of  from  the  nervous  processes,    ppr  Pro- 
toplasmic   processes.      (The    cells    were  isolated  in  weak  i 
solution  of  alcohol  or  in  potassium-bichromate  (0.003  °/o))-  I 
Cor ellaparallelo gramma.     (Magnified  1350  diameters;  Zeiss 
F.  4.)     Section   of  a   ganglion   cell  situated  peripherically  j 
in   the   brain,     n  pr  Nervous  process,     a  Lightly  staining 
parts   of  the   protoplasm.     (Fixed    in    osmic    acid    (i   °/0) 
and  stained  with  picro-carmine.) 

59.  Homarus  vulgaris.     (Magnified  350  diameters;  Zeiss  CC,  4.) 
Isolated  ganglion  cell  of  a  ventral  ganglion,     a  &  b  Lightly 
staining  masses  of  primitive  tubes,     c  Bundle  of  primitive! 
tubes  forming  the  contents  of  the  nervous  process  (npr).  i 
6r  Side-branches  given  off  from  the  process.     (Macerated! 
in  acetic  acid  (i),  glycerin  (i),  aqua  dest.  (5)  and  stained) 
with  ammonia-carmine.) 

60.  Homarus  vulgaris.     (Magnified  750  diameters;  Zeiss  F,  2.) 
Isolated  ganglion  cell  from  a  ventral  ganglion,     n  Neuro-j 
glia-nucleus  situated  in  the  sheath  of  the  cell,     npr  Nervous! 
proceses.     (Macerated  in  acetic  acid  (i),  glycerin  (i),  aquaj 
dest.  (5)  and  stained  with  picro-carmine.) 

61.  Homarus  vulgaris.     (Magnified  1350  diameters;  Zeiss  F,  4.) 
Part    of  a    section    through    the    dotted    substance    of  a 
thoracal  ganglion,  exhibiting  the  origin  of  a  bundle  (a)  of 
nerve-tubes   or   rather   primitive  tubes  in  the  dotted  sub- 
stance,    a  Bundle  of  primitive  tubes,  longitudinally  trans- 
sected.    b  Longitudinally  transsected  primitive  tube,    c  Ob. 
liquely  transsected  primitive  tube,     tpt  Trans versally  trans- 
sected  primitive   tubes,      n   Neuroglia-nucleus.     (Fixed   in 
chromo-aceto-osmic    acid,     stained     with    neutral    borax-j 
carmine.) 

62.  Homarus  vulgaris.     (Magnified  620  diameters;  Zeiss  F,   i. 
Part  of  a  section  through  the  dotted  substance  of  an 
dominal   ganglion,    exhibiting   the   mixture    of   large    and 
small  tubes  in  the  dotted  substance      ds  The  real  dotted) 
substance  consisting  of  very  small  tubes,  which  are  trans-: 
versally,  or  obliquely,  or  partly  longitudinally  transsected. 
tnt,  tnf  Transversally  transsected  large  nerve-tubes,     a&b 
Bundle  of  nerve-tubes  longitudinally  transsected.     nt  Large 
nerve-tube,     nt'  Large  nerve-tubes,  subdividing  dichotom- 
ously.    nu  Neuroglia.    n,  ri,  n"  Neuroglia-nuclei.    x  Large 
nucleus. 


—  205  — 

Plate    VII. 

The  illustrations   of  this   plate   are  drawn  from  the  microscope 

directly  upon  the  stone,  under  the  camera  lucida. 

Fig.  63  &  64.  Homarus  vulgaris.  (Magnified  350  diameters;  Zeiss 
CC,  4.)  Parts  of  a  transverse  (tig.  63)  and  a  longitudinal 
(fig.  64)  section  through  ventral  ganglia.  a— g  Nervous 
processes  from  ganglion  cells  or  branches  springing  from 
such  processes.  h  Subdividing  part  of  a  nerve-tube. 
i  Varicose  nervous  fibril.  vf  Varicose  nervous  fibril. 
I — 12  Parts  of  longitudinal  nerve-tubes  belonging  to  the 
longitudinal  commissures.  sf,  sf  Slender  nerve-tubes 
partly  given  off  from  these  longitudinal  large  nerve-tubes. 
(From  chromo-silver  stained  preparations.) 

»  65.  Homarus  vulgaris.  (Magnified  1150  diameters;  Zeiss. 
Horn.  im.  '/18,  I.)  Part  of  a  transverse  section  through 
the  dotted  substance  of  an  abdiminal  ganglion,  a — /  Nerve- 
tubes,  some  of  which  are  seen  to  subdivide.  (Fixed  in 
chromo-aceto-osmic  acid;  stained  in  accordance  with  Hei- 
denhain's  haematoxylin  method.) 

»  66.  Nereis  virens.  (Magnified  950  diameters ;  Zeiss.  Horn.  im. 
Vis,  !•)  Part  of  a  horizontal,  longit.  section  through  the 
dotted  substance  of  the  ventral  nerve-cord,  a  The  central 
vertical  septum,  dividing  the  nerve-cord  longitudinally 
(compare  fig.  10,  a  &  fig.  14).  tt,  it\  tt"  Transverse,  small 
and  large,  nerve-tubes  crossing  this  septum,  tt111  Trans- 
verse nerve-tubes  passing  to  the  root  of  a  peripheral 
nerve,  pt  Large  nerve-tubes  passing  to  the  root  of  the 
same  nerve,  t  Small  longitudinal  nerve-rubes.  It  Large 
longitudinal  nerve-tubes,  n,  n'  Neuroglia-nuclei,  situated 
longitudinally  (n)  or  transversally  (V)  in  the  dotted  sub- 
stance. (Fixed  in  chromo-aceto-osmic  acid,  stained  with 
Delafield's  haematoxylin.) 

Plate   VIIL 

Fig.  67.  Nereis  virens.  (Magnifid  •  620  diameters;  Zeiss  F,  I. 
Cam.  luc.  from  the  microscope  direct  upon  the  stone.) 
Part  of  a  horizontal,  longitudinal,  section  through  the 
ventral  part  of  the  ventral  nerve-cord,  ds,  ds  The  dotted 
substance  on  each  side  of  the  central  mass  of  ganglion 


—    206  — 

cells  etc.  a  Neuroglia  forming  the  central,  vertical  sep- 
tum dividing  the  nerve-cord  longitudinally  (compare  fig. 
10,  a  &  fig.  14).  Igc  Large  ganglion  cells  with  deeply 
staining  protoplasm,  with  spongioplasmic  fibres  issuing  from 
the  sheaths  of  the  cells,  and  with  small  lightly  staining  masses 
of  primitive  tubes  (?).  np  Nervous  process,  gc,  gc'  Large 
ganglion  cells  with  deeply  staining  protoplasm,  sgc  Small 
ganglion  cells  with  lightly  staining  protoplasm,  sgc1  Gan- 
glion cell  of  mesial  size  with  a  small  mass  of  deeply 
staining  protoplasm,  nf,  nf  Neuroglia-fibres  and  longitu- 
dinally transsected  tube-sheaths  uniting  with  the  sheaths 
of  the  ganglion  cells.  (Fixed  and  stained  as  fig,  66.) 
Fig.  68.  Homarus  vulgaris  (Magnified  100  diameters.)  Ganglion 
cell  from  an  abdominal  ganglion ;  constructed  from  a  series 
of  transverse  sections,  partly  by  help  of  the  cam.  luc. 
(Fixed  in  chromo-aceto-osmic  acid,  stained  in  accordance 
with  Heidenhains  haemotoxylin  method. 

»  69.  Homarus  vulgaris.  (Magnified  132  diameters;  Zeiss  A  A,  4. 
Cam.  luc.)  Ganglioncell  from  a  thoracal  ganglion,  observed 
in  a  transverse  section  (chromo-silver  staining);  the  proces 
could  be  traced  directly  into  a  peripheral  nerve. 

»  70.  Homarus  vulgaris  (Magnified  350  diameters;  Zeiss  CC,  4. 
Cam.  luc.)  Unipolar  ganglion  cell  from  a  chromo-silver 
stained  section  of  a  thoracal  ganglion.  The  nervous  pro- 
cess subdivides  and  is  broken  up  into  slender  branches. 
The  slender  fibres  issuing  from  the  body  of  the  cell  are 
neuroglia-fibres  issuing  from  its  sheath. 

»  71.  Lum~bricus  agricola  (Magnified  620  diameters;  Zeiss  F.  I. 
Cam.  luc.  from  the  microscope  directly  upon  the  stone.) 
Lateral  part  of  a  transverse  section  of  the  ventral  nerve- 
cord,  a — h  Ganglion  cells,  c  Ganglion  cell  containing 
two  nuclei,  pe  Perineurium.  m  Muscles,  ct  Septa  and 
fibres  of  comective  tissue  issuing  from  the  perineurium. 
nu  Neuroglia.  ds  Dotted  substance,  nt,  nt\  n^1  Transsected 
nerve-tubes  of  various  sizes.  Its,  Us1  Sheaths  of  two  of 
the  three  colossal  nerve-tubes,  n,  n}  Neuroglia-nuclei. 
(Fixed  in  chromo-aceto-osmic  acid,  stained  with  Dela- 
field's  haemotoxylin). 

»  72.  Lumlricus  agricola.  (Magnified  750  diameters;  Zeiss  F,  2. 
Cam.  luc.)  Ganglion  cell  from  a  transverse  section  of 
the  ventral  nerve-cord. 


-  207  • 

Fig.  73-  Patella  vulgata.  (Magnified  750  diameters;  Zeiss  F,  2.) 
Part  of  a  transverse  section  through  a  pedal  nerve-cord. 
a — m,  o  Ganglion  cells,  n  Neuroglia-nuclei.  nn  Similar 
nuclei  or  cells  from  which  fibres  issue,  en  Large  ovoid 
or  circular  neuroglia-nuclei,  more  lightly  staining  than  the 
smaller  nuclei.  en  Similar  nuclei  situated  close  to  the 
nervous  processes  of  ganglion  cells,  ds  Dotted  substance. 
p  Perineurium,  enveloping  the  pedal  nerve-cord,  nu  Neu- 
roglia-reticulation  extending  inside  this  perineurium.  af  Fi- 
bres, neuroglia-fibres  and  protoplasmic  processes,  running 
from  the  ganglion  cells  a&a'  towards  the  perineurium. 
cct  Cells  adhering  externally  to  the  perineurium.  (Fixed 
in  chromo-aceto-osmic  acid,  stained  with  Delafield's  hae- 
motoxylin). 

»  74  Patella  vulgata.  (Magnified  1 1 50  diameters ;  Zeiss.  Horn, 
im.  Vis*  2-)  Part  °f  a  transverse  section  through  a  pedal 
nerve-cord,  a — i  Ganglion  cells,  ds  Dotted  substance. 
nu  Neuroglia  reticulation,  n  Neuroglia-nuclei.  n'  Neu- 
roglia-nuclei, adhering  to  the  sheath  of  a  ganglion  cell. 
(Preparation  the  same  as  fig.  73). 

»  75 — 78.  Patella  vulgata.  (Magnified  750  diameters;  Zeiss  F,  2.) 
Ganglion  cells  with  their  processes,  n  Neuroglia  nuclei. 
(Fig.  75  and  76  are  isolated  in  glycerin  (i),  acetic  acid(i), 
aqua  dest.  (5) ;  fig.  77  and  78  are  taken  from  in  sections). 

»  79 — 81.  Patella  vulgata.  (Magnified  750  diameters;  Zeiss  F,  2.) 
Isolated  neuroglia-cells. 

Plate   IX. 

The  illustrations  of  this  plate  (exept  fig.  83 — 85)  are  drawn 
under  the  camera  lucida,  from  the  microscope  directly  upon  the 
stone. 

Fig.  82.  Patella  vulgata,  (Magnified  750  diameters;  Zeiss  F,  2.) 
Ganglion  cells  and  their  processes  from  a  transverse  section 
of  a  pedal  nerve-cord,  gc  Ganglion  cells,  a  Ganglion 
cell,  the  nervous  process  of  which  can  be  traced  for  some 
distance  through  the  dotted  substance,  n1  Neuroglia- 
nucleus  adhering  to  the  sheath  of  this  process,  n  Neu- 
roglia-nuclei. nc  Larger  less  staining  neuroglia-nuclei. 
(Fixed  in  chromo-aceto-osmic  'acid,  stained  with  Delafield's 
haemotoxyline.  The  section  was  stained  with  picric  acid 


—    208    — 

dissolved  in  turpentine  to  which  was  added    a   little   abs. 
alcohol). 

Fig.  83.  Patella  vulgata.  (Magnified  570  diameters).  Part  of  a 
transverse  section  through  a  pedal  nerve-cord,  gc  Ganglion 
cell,  a  Ganglion  cell,  n"  Neuroglia  nuclei  adhering  to 
the  sheath  of  this  cell  and  its  nervous  pracess.  n"'  Three 
similar  nuclei  situated  close  together,  n  Neuroglia-nuclei. 
Quite  similar  nuclei  (n)  are  also  situated  in  the  connective 
tissue  outside  the  perineurium  (sh).  n'  Larger,  circular 
or  ovoid,  less  staining  nuclei  situated  in  the  same  con- 
nective-tissue, nc,  nc'  Neuroglia-cells.  nc"'  Large,  ovoid 
neuroglia-cell.  nf  Nerve-tubes  or  nervous  processes.  (Pre- 
paration the  same  as  in  fig.  82). 

»  84.  Lumbricus  agricola.  (Magnified  950  diameters;  Zeiss. 
Horn,  im  '/18,  I.)  Ganglion  cells  (gc)  the  nervous  pro- 
cesses of  which  pass  into  the  dotted  substance  (ds)  and 
run  longitudinally  along  the  ventral  nerve-cord.  Taken 
from  a  horisontal  longitudinal  section  of  the  ventral 
nerve-cord. 

»  85.  Patella  vulgata.  (Magnified  1 150  diametars;  Zeiss.  Horn, 
im.  '/i8>  2>)  Slender  nerve-tubes  and  nervous  fibrillae, 
from  a  pedal  nerve-cord,  isolated  in  fresh  state. 

»  86.  Patella  vulgata.  (Magnified  750  diameters;  Zeiss  F,  2.) 
Nerve-tubes  and  fibrillae  from  a  pedal  nerve-cord,  ma- 
cerated in  glycerin  (i),  acet.  acid  (i),  aqua  dest.  (5). 
a  &  b  Thick  nerve-tubes  giving  off  side-branches,  nc  Neu- 
roglia cells. 

»  87.  Corella  parallelo gramma.  (Magnified  1150  diameters; 
Zeiss.  Horn.  im.  l/lt,  20  Part  °f  a  longitudinal  section 
through  the  brain.  a — g  Ganglion  cells,  n  Neuroglia- 
nuclei.  n  Similar  nucleus  adhering  to  the  sheath  of  a 
nervous  process.  (Fixed  in  osmic  acid  (i  °/0),  stained 
with  pier 'O- carmine) 

•»  88.  Corella  parallelo gramma.  (Magnified  620  diameters;  Zeiss 
F,  i.)  Anterior  part  of  a  horizontal  longitudinal  section 
of  the  brain,  c  Ganglion  cells,  gc  Ganglion  cell  situated 
in  one  of  the  anterior  nerves,  n  Nuclei  adhering  to  the 
inside  of  the  perineurium.  n1  Neuroglia-nuclei  situated  in 
the  sheaths  of  the  nerve-tubes.  (Fixed  in  osmic  acid  (i  %), 
stained  with  pier  o- car  mine). 


—   2O9   - 

Fig.  89.  Phallusia  venosa.  (Magnified  750  diameters;  Zeiss  F,  2.) 
Nerve-tubes  and  ganglion  cells  (gc)  from  a  brain,  ma- 
cerated in  weak  solution  of  alcohol.  a  Nervous  process 
from  which  side-branches  are  given  off.  6 — e  Nerve-tubes 
from  which  side-branches  are  given  off. 

»  90.  Ampluoxus  lanceolatus.  (Magnified  350  diameters;  Zeiss 
CC,  4.)  Transverse  section  of  the  spinal  cord,  gc,  gc* 
Ganglion  cells,  pp  Protoplasmic  process,  vnt  Ven- 
tral colossal  nerve-tube.  Int  Lateral  colossal  aerve- 
tubes.  eg  Central  groove  (or  canal).  /  Fibres  crossing 
the  grove,  nf  Fibres  issuing  from  the  epithelial  cells  sur- 
rounding the  central  groove  and  penetrating  to  the  sheath, 
enveloping  the  spinal  cord,  ns  Similar,  thick  fibres,  united 
to  strong  bundles,  one  on  each  side  of  ventral,  colossal 
nerve-tube,  p  Pigment,  nt  Slender  nervetubes  running 
transversally  in  the  white  substance.  (Fixed  in  chromo-aceto- 
osmic  acid,  stained  according  to  Heidenhain's  haematoxy- 
lin  method  and  afterwards  with  Delafields  haematoxylin). 

91 .  Amphioxus  lanceolatus.  (Magnified  7  50  diameters ;  Zeiss  F,  2.) 
Transsected  large   nerve-tubes  from  the  a  transverse  sec- 
tion of  the  spinal  cord.     (Preparation  same  as  in  fig.  90). 

92.  Amphioxus  lanceolatus.      (Magnified   620  diameters;  Zeiss 
F,   i.)     Ganglion   cell   (gc)   from    a   transverse    section    of 
the  spinal  cord,     pp  Protoplasmic  process  penetrating  to 
the  sheath  (a)  enveloping  the  spinal  cord,    pp'  Protoplasmic 
process,  which  possibly   crosses   the   central   groove,    and 
which  in  this  section   is   transsected.      eg  Bottom   of  the 
central   groove   (or   canal),      c  Epithelium,      ec  Epithelial 
cell,     p  Pigment   occurring  at  the  bottom  of  the  central 
groove,      ns  Fibres  issuing  from   the   epithelial   cells   and 
in    which   some   pigment  is   deposited.      (Fixed    in   osmic 
acid  (i  °/0),  stained  with  ammonia- car  mine). 

Plate   X. 

The  illustrations  of  this  plate  are  drawn  under  the  camera  lucida, 
from  the  microscope  directly  upon  the  stone.  They  are  all  taken 
from  sections  of  the  spinal  cord  of 

Myxine  glutinosa. 

Fig.  93.  (Magnified  132  diameters;  Zeiss  AA,  4.)  Transverse 
section  of  the  spinal  cord.  (To  some  extent  composed 
from  several  sections  of  series  of  transverse  sections, 


—   2IO  — 

but  each  part  is  drawn  under  the  cam.  luc.)     gc  Ganglion 
cells.     Igc^  Igc2  Large  ganglion  cells,     mp  Mixed  process 
(or  nervous  process?).      br  Branches   given   off  from   the 
mixed  process,     pbr  Branches    of  the   protoplasmic   pro- 
cesses.     vnrlt  vnr.2,  vnr%,  vnr4  Ventral   nerve-roots,    which 
are  not  transsected   in   the   same   section,   but  which  are 
drawn  here  to  show  their  possition.     ribr  Side  branch  given 
off  from  a  nerve-tube,  of  the  ventral  nerve-root,     nf  Nerve- 
tubes,      tnt  Transsected  nerve-tubes,      v  Vacuoles   which 
possibly   also   are   transsected  nerve-tubes.     .  Mnt  Miillers 
nerve-tubes  transsected;  those  in  the  one  half  of  the  spinal 
cord   are   only  illustrated,      nc   Neuroglia   cell,      nn  Neu- 
roglia  nuclei,  situated  in  the  grey  substance.      flt  /2  Neu- 
roglia fibres.      eplt  ep^  ep$  Processes  from   the   cells    sur- 
rounding the  central  canal,      n  Nuclei  of  the   sheath   en- 
veloping the  nerve-tubes  of  the  dorsal  nerve-root. 
Fig.  93.  A.     The    transsected  spinal    ganglion,    through    which    the 
nerve-tubes    of    the    dorsal    nerve-root    pass.      At  a   the 
nerve  is  somwhat  shortened   on   account    of  the    limited 
space  of  the  plate,     sh  Wall  of  connective  tissue  surround- 
ing   the    cavity    in    which    the    spinal    cord    is    situated. 
sgc  Transsected  ganglion  cells,     n"  Nuclei  situated  in  the 
sheaths  of  the  ganglion   cells,      vr  Ventral   ramus  issuing 
from   the   ganglion.      dr  Dorsal  ramus   issuing   from    the 
ganglion,     n1  Nuclei  situated  in  the  sheaths  of  the  nerve- 
tubes  of  the   latter  ramus.,     (Hardened   in   Potassium   bi- 
chromate (2 — 3  %),  stained  with  neutral  borax-carmine). 
»      94.      (Magnified  154  diameters;  Zeiss  CC,   I.)     Part  of  a  trans- 
verse section  through  the  spinal  cord,     mp  Mixed  process 
of  a  ganglion  cell   (which  was   not,    hower,    seen    in    the 
section),    pbr  Protoplasmic  branches  given   off  from  this 
process.     gcl)  gc2  Ganglion  cells,     npr  Nervous  processes. 
ppr  Protoplasmic    processes,      nf,  nfa,  nfa  Nerve-tubes    or 
fibrillae  some  of  which  (nflt  nf2)  have  varicose  thickenings 
and  give  off  branches,      cec   Cell   of  the   epithelium    sur- 
rounding the  central  canal,     grs  Border  of  the  grey  sub- 
stance.    (Stained  according  to  the  chromo  silver  method, 
vide  p.  77). 

»  95.  (Magnified  132  diameters;  Zeiss  AA,  4.)  Part  of  a  trans- 
verse section  of  the  spinal  cord.  The  letters  have  the 
same  signification  as  in  fig.  93.  grs  Border  of  the  grey  sub- 


i 


—   211    — 

stance.  cec  Epithelium  surrounding  the  central  canal. 
npr  Nervous  process,  ribr  Siciebranch  of  the  nervous 
process.  mbr  Main  branch  of  the  mixed  process  from 
Igc.  brlf  br2  Branches  given  off  from  the  same  process. 
nt  Obliquely  transsected  nerve-tube  from  the  ventral 
nerve-root  (twy),  (Fixed  in  saturated  aquous  solution  of 
picric  acid,  stained  according  to  Heidenhain's  haemo- 
toxylin  method). 

Fig.  96.  (Magnified  950  diameters;  Zeiss.  Horn.  im.  '/i8»  i).  The 
ganglion  cell  Igc  of  fig.  95,  more  lighly  magnified,  mp  Mixed 
process,  pp  Protoplasmic  process,  v,  vj  Transsected, 
lightly  staining  tubes  (probably  bundles  of  primitive  tubes). 
cm  Sheath  enveloping  the  cell.  a  Cavity,  filled  with  a 
lightly  staining,  reticular  substance,  between  the  sheath 
and  the  protoplam  of  the  cell. 

97 — 99.  (Magnified  950  diameters;  Zeiss.  Horn,  im  J/i8>  r-) 
Transsected  ganglion  cells  of  a  spinal  ganglion,  n,  n*  Nuclei 
situated,  generally,  inside  the  sheath  enveloping  the  cell. 
Nucleus  situated  in  the  sheath  of  a  process,  gr  Dark 
granules,  occurring  inside  the  sheaths  (possibly  artifical 
products  in  the  sections),  v  Transected,  lightly  staining 
tubes  (probably  bundles  of  primitive  tubes),  x  Hyaline 
organ  (or  cell?)  situated  in  the  surface  of  the  cell. 
N  Elongated  nucleus  situated  in  this  organ.  N1  Another 
nucleus  (?)  situated  in  the  same  organ,  pr  Process  issuing 
from  a  cell;  at  a  the  sheath  of  this  process  is  only 
transsected,  we  do  not,  therefore,  see  the  origin  of  the 
process-contents  in  the  protoplasm  of  the  ganglion  cell. 
pn  Nucleus  situated  in  the  sheath  of  the  process,  nt  Nerve- 
tube,  tn  Nucleus  .situated  in  the  sheath  of  the  nerve-tube. 
(Hardened  in  potassium  bicromate  (2 — 3  %)  stained  with 
neutral  borax-carmine). 

100.  (Magnified  1150  diameters;  Zeiss.  Horn.  im.  Vis»  2-) 
Transsected  nerve-tubes  from  a  transverse  section  of  the 
white  substance.  Int  Large  nerve- tubes  (Miiller's  nerve- 
tubes)  Inf  Such  tubes  in  which  a  slight  concentration 
towards  a  deeply  staining  axis  is  visible,  nt  Transsected  small 
nerve-tubes,  t  Tubes  or  cell-processes  running  transversally 
between  the  longitudinal  nerve-tubes.  /  Neuroglia  fibres, 
which  are,  however,  .slightly  visible  in  this  section.  (Fixed 
in  saturated  aqvous  solution  of  picric  acid,  stained  ac- 
cording to  Heidenhain's  haematoxylin  method). 

14* 


—    212    — 

Fig.  101.  (Magnified  620  diameters;  Zeiss.  F,  i.)  Part  of  a  trans- 
.  verse  section  through  the  white  substance  (of  the  ventral 
side  of  the  spinal  cord.  The  neuroglia  fibres  (/)  running 
transversally  between  the  transsected  nerve-tubes  are 
here  very  distinctly  visible,  a  External  layer  where  these 
unite  with  the  sheath  (pm),  enveloping  the  spinal  cord. 
Int  Transsected  large  nerve  tubes,  where  the  contents  (c) 
has  skrunk  into  one  side  and  is  deeple  stained,  c'  Contents 
(skrunk  in  the  same  way)  of  the  small  longitudinal  nerve- 
tubes,  nf  Slender  nerve-tubes  running  in  the  external 
layers  of  the  white  substance.  (Hardened  in  alcohol, 
stained  according  to  Heidenhains's  haemotoxylin  method). 

Plate   XL 

The  illustrations  of  this  plate  (exept  fig.   109  &  113)  are  taken 
from   chromo-silver   stained   sections   of  the   spinal   cord    of  Myxine 
glutinosa.     They  are  drawn  under  the  camera  lucida. 
Fig.  102.     (Magnified  154  diameters;  Zeiss  CC,   I.)     Part  of  a  trans- 
verse section  through  the  spinal  cord  of  Myxine.     gc  Gang- 
lion cell,     mpr  Mixed  process.      l>rl,  br$,  6r3  ,br4  Branches 
given  off  from  this  process,    pr  Protoplasmic  (?)  process, 
which,  however,  seem  to  return  into  the  white  substance. 
mpr2  Mixed  process  of  a  cell  which   is   not  seen    in    the 
section,    ppr'  Protoplasmic  process  of  a  cell  which  is  not 
seen  in  the  section,     nf,  nf",  nf"  Nerve-tubes   or  fibrillas, 
running  transversally,   in   various    directions    in    the    grey 
and  white  substance,     vnr  Ventral  nerve-root,     v  Vacuole, 
possibly  transsected  nerve-tube,    pec  Epithelial    cell   with 
process,    stained    for    considerable    distance    through    the 
grey  tubstance.     grs  Border  of  the  grey  substance. 
>      103.     (Magnified    150    diameters;    Zeiss    CC,    i.)      Part    of    a 
transverse  section    through    the    spinal    cord    of 


ffCit  gc%,  gc3  Ganglion  cells,  np  Nervous  processes,  ppr  Pro- 
toplasmic processes,  a  Place  where  a  branch  is  given  off 
from  the  nervous  process  np'.  nuc^,nuc^  Neuroglia  cells. 
nf,  nf,  nf"  Nerve-tubes,  ec  Epethelial  cells  surrounding 
the  central  canal,  grs  Border  of  the  grey  substance. 
dnr  Dorsal  nerve-root. 

104.     (Magnified  200  diameters).      Ganglion   cell,   from  a  trans- 
verse section  of  the   spinal   cord   of   Myxine.      sh  Sheath 


enveloping  the  spinal  cord,  grs  Border  of  the  grey  sub- 
stance, np  Nervous  process,  ppr  Protoplasmic  process. 
IO5-  (Magnified  130  diameters).  Ganglion  cell,  from  a  trans- 
verse section  of  the  spinal  cord  of  Myxine.  np  Nervous 
process  or  mixed  process,  ppr  Protoplasmic  process. 
vnr  Nerve-tube  of  the  ventral  nerve-root,  sh  sheath  enve- 
loping the  spinal  cord. 

106.  (Magnified  130  diameters).      Ganglion  cell,  from  at  trans- 
verse section  of  the  spinal  cord  of  Myxine.      vnr  Nerve- 
tube  (of  the   ventral    nerve-root)    springing    directly    from 
the  ganglion  cell,     sh  Sheath  enveloping  the  spinal  cord. 

107.  (Magnified    130   diameters).      Mesial   part   of  a  transverse 
section  through   the   spinal   cord    of   Myxine.      Plenty    of 
nerve-tubes   (nt)    are    seen    in    the    section    crossing    the 
transverse   commissures.      cc  Central  canal,      v  Vacuoles. 
cec  Central  epithelial  cells  with  stained  processes,     sh  Sheath 
enveloping  the  spinal  cord. 

108.  (Magnified    200    diameters).      Neuroglia    cells    with    their 
processes  from  a  transverse   section    of  the    spinal    cord. 
The  black  body  in  the  centre  is  probably  produced  arti- 
ficially   by    the    staining    of    several    cells    situated    close 
together,     sh  Sheath  enveloping  the  spinal  cord. 

109.  (Magnified  500  diameters).      Part  of  a  transverse  section 
through  the  white  substance  of  the  spinal  cord,   showing 
how    neuroglia   fibres    gather    round    the    nerve-tubes    of 
the  ventral  nerve-roots,    p  Ventral  periphery  of  the  spinal 
cord,     grs  Border  of  the  grey  substance,     vnr  Nerve-tube 
of  the  ventral  nerve-root,     br  Side-branch   given  off  from 
this   nerve-tube,      f  Neuroglia-fibres.      nc    Neuroglia-cells. 
gc  Ganglion  cell,      ppr  Protoplasmic  process.      (Fixed  in 
saturated  aqveous  solution  of  picric  acid,  stained  in  accor- 
dance with  Heidenhain's  haematoxylin  method). 

110.  (Magnified  500  diameters).     Neuroglia-fibres  running  trans- 
versally  between   the   large   nerve-tubes    (Miiller's   nerve- 
tubes)  in  the  white  substance ;  from  a  chromo-silver  stained 
transverse  section  of  the  spinal  cord  of  Myxine.     nuf  Neu- 
roglia-fibres,    Mnt  Miiller's  nerve-tubes,    pe  Ventral  peri- 
phery of  the  white  substance. 

in.  (Magnified  80  diameters.)  Part  of  a  chromo-silver  stained 
horisontal  section  of  the  spinal  cord  of  Myxine;  exhibiting 
the  dichotomous  subdivisions  of  the  nerve-tubes  of  the 


—  214  — 

nerve-root,  dnr  Dorsal  nerve-root,  a  Nerve-tube  subdi- 
viding outside  the  spinal  cord,  pe  Periphery  of  the  spi- 
nal cord,  cc  Central  canal.  Int  Longitudinal  nerve-tubes. 
Int  Longitudinal  nerve-tubes  giving  oft  side-branches,  snt 
Subdividing  nerve-tube,  snt'  Subdividing  nerve-tube  cros- 
sing the  central  canal. 

Fig.  112.  (Magnified  1 60  diameters.)  Part  of  a  chromo-silver  stained 
horisontal  section  of  the  spinal  cord.  The  letters  have 
the  same  signification  as  in  rig.  in.  br  Slender  branches 
given  off  from  the  nerve-tubes  of  the  dorsal  nerve-root. 
»  113.  Diagrame  of  the  reflex-curve  The  large  arrows  indicate 
the  way  the  irritation  of  a  sensitive  nerve-tube  has  to 
pass  to  produce  a  reflex-movement.  SN  Centripetal  (sen- 
sitive) nerve-tube,  dd  Dotted  substance  or  interlacing  of 
nervous  fibrillae  in  the  central  nerve-system.  MN  Centri- 
fugal (motoric)  nerve-tube. 

The  small  arrows  indicate  the  way  small  parts  of  the* 
irritation  of  the  centripetal  (sensitive)  nerve-tube  pass  to 
arrive  in  other  parts  of  the  central  nerve-system.  I  Nerve- 
tube  passing  to  the  brain.  2  Longitudinal  nerve-tube 
running  along  the  spinal  cord,  whilst  giving  off  side-branches. 
snc  The  nutritive  centre  of  the  centripetal  nerve-tube 
(i.  e.  spinal  ganglion  cell),  cnc  The  nutritive  centre  of  a 
part  of  the  fibrillae  forming  the  dotted  substance  or  inter- 
lacing of  nervous  fibrillae  (i.  e.  ganglion  cell  of  the  central 
nerve-system),  mnc  The  nutritive  centre  of  the  centrifugal 
nerve-tube  (i.  e.  ganglion  cell  of  the  central  nerve-system ). 
ppr  Nutritive  (i.  e.  protoplasmic)  processes  sometimes 
issuing  from  the  nutritive  centres,  and  penetrating  towards 
the  periphery  of  the  central  nerve-system  or  towards 
blood-vessels  to  absorb  nutrition,  a •  &  b  Periphery  of  the 
central  nerve-system. 


Contents. 


Introduction:  Pag. 

1.  History 29 

a)  The  structure  of  the  nerve-tubes \ 30 

b)  The  structure  of  the  ganglion  cells 32 

c)  The  structure  of  Leydig's  dotted  substance 38 

d)  The  combination  of  the  ganglion  cells  with  each  other 64 

Dr.  B.  Rawitz's  paper  on  the  central  nerve-system  of  the  Acephala.    .    .  65 

2.  The  material  examined •  .    .  72 

3.  Methods  of  investigation 73 

Description  of  my  investigations: 

1.  The  structure  of  the  nerve-tubes  in  invertebrates 81 

Summary 97 

2.  The  structure  of  the  ganglion  cells,  and  their  processes,  in  invertebrates  .  98 
Summary 120 

3.  The  structure  of  Leydig's  dotted  substae 122 

Summary 144 

4.  The  combination   of  the  ganglion  cells  with  each  other,  and  the  function 

of  the  protoplasmic  processes 145 

5.  The  nervous  elements  of  Amphioxus  and  Myxine 149 

6.  The  combination  of  the  nerve-tubes  with  each  other 164 

7.  The  function  of  the  ganglion  cells 167 

List  of  the  principal  Literature 172 

Explanation  of  the  plates 194 


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