1041 
or  more  micleoH,  bot  there  are  fewer  tlint  show  signs  of  division. 
I shall  discuss  at  greater  leiigth  below  some  of  the  literature 
conceniing  direct  post-embryonic  division  of  nerve-cells.  I will 
onlj  mention  here  that  Rodhe’)  describes  fonr  differents  types  of 
amitotic  division  of  the  ganglion  cells  in  fnll-grovvn  evei'tebrates. 
Paladino  States  that  direct  division  is  a very  common  way  for 
young  ganglion-cells  in  the  higher  vertebrates  to  increase. 
In  fig.  4a  1 reprodnce  a group  of  nerve-cells  from  a silver- 
impregnated  spiiial  ganglion  in  a sixty  days  old  pnppy.  In  it  the  cells 
are  packed  close  together  into  a formation  shaped  like  a string  of 
beads,  lying  within  the  same  capsule.  Between  the  cells  at  a few 
places  one  can  also  clearly  see  bridges  of  protoplasm,  which  connect 
cells  that  are  close  to  each  other.  The  sei-ies  of  sections  of  the 
spinal  ganglia  from  this  animal  show  nuraerous  examples  of  similar 
gronps  (Muller  E.)  of  cells  situated  within  the  same  capsule.  I have  ob- 
tained  the  impression,  however,  that  they  do  notoccur  in  equally  great 
numbers  in  all  the  spinal  ganglia  of  the  same  individual;  similar 
gronps  of  cells  have  been  observed  in  puppies  of  six  ajid  seventeen 
days  — but  they  were  not  so  nuraerous  as  in  the  sixty  days  old 
animal  ’).  In  the  3,5  j'ears  old  dog,  among  live  spinal  ganglia  that 
were  investigated,  I did  not  come  across  more  than  a few  of  these  groiips 
of  cells  and  in  the  tive  years  old  dog  among  a still  greater  amount 
of  rnaterial,  1 did  not  succeed  in  finding  such  a group  in  more  than 
a single  place.  It  is  thus  au  obvious  assumption  to  regard  these 
groups  of  cells  as  formations  belonging  to  the  post-euibryonic 
growth  of  the  spinal  ganglia  — forms  |)roduced  by  the  spinal 
ganglion  cells  during  the  post-erabryonic  increase  in  their  number. 
In  spite  of  the  considerable  number  of  works  that  have  been  publish- 
ed  on  spinal  ganglia  in  the  course  of  years,  the  information 
about  these  groups  of  cells  to  be  found  in  this  literature  is  exceed- 
ingly  small.  Before  1880,  however,  they  had  been  observed  by  a 
number  of  investigators  and  were  described  most  thoroughly  by 
P.  Mayer ’).  After  that  the  subject  seems  to  have  been  almost  forgotten, 
until  in  1889  and  1891  Müller  Erik  gave  more  thorough  and 
valuable  descriptions  of  similar  groups  of  S|)inal  ganglion  cells 
within  the  same  capsule.  Since  Müller’s  descrijition  of  these  groups 
of  nerve-cells  they  scem  to  have  been  uegiected  again  in  recent 
b Rodhe,  GangUenzellkern  and  Neuroglia.  Ein  Kapital  über  Verraehrung  and 
Wachslhum  der  Ganglienzelle.  Arch.  f.  mikr.  Anat.  Bd.  47. 
b The  sixty  days  old  dog  was  rachitic. 
®)  Mayer,  S.,  Arch.  f.  Psychiatrie,  Bd.  6.  187b. 
9 Muller,  E.,  L c. 
