1 055 
cells  iii  the  ependyma  and  that  iii  the  spiiial  gaiiglia  from  imdiffe- 
rentiated  eells  among  the  eapsular  cells.  These  cells  iiicrease  duriiig 
their  ditferentiation  into  ganglion  cells,  ainong  others,  partij  by  ineans 
of  mitotic  division  and  as  far  as  1 can  see  froin  iny  preparations 
also  partly  by  means  of  ainitotic  division.  This  post-enibryonic 
increase  in  the  nuinber  of  the  cell-matei-ial  is  greater  dniing  the 
first  inonth  of  post-embryonic  life,  bnt  seeins  to  continue  afterwards 
as  well.  It  is  only  dnring  the  first  month  of  the  post-einbryonal 
life  of  the  individual  that  one  sees  mitoses  in  these  cells,  bnt  even 
diiring  its  continued  life  cell-division  seenis  to  oecnr;  it  then  takes 
place  amitotically.  These  new  ganglion  eells  that  have  arisen  by 
mitotic  or  araitotic  division  seem  to  develop  into  neurones,  which 
not  only  replace  older  neurones  that  have  been  destroyed  by 
degeneration  (Paladino),  bnt  also  help  to  increase  the  absolute  nmnber 
of  neurones. 
Figures  of  growth  for  the  axons  have  been  shown  inorphologically 
in  the  dorsal  and  ventral  roots  of  the  lunibar  nerves  of  a 17  days 
old  dog  ').  These  figures  of  growth  have  been,  among  varioiis  other 
shapes,  claviforni  — Ihus  under  completely  physiological  conditions 
the  saine  shape  is  found  for  the  tignres  of  growth  of  the  axons  as 
is  usually  found  in  experimenlally  produced  regeneration  of  periphe- 
ral  nerves. 
Addendum. 
It  seems  as  if  the  post  embryonal  increase  in  the  neurones  can 
be  effected  by  external  influences.  Thus,  for  instance,  it  has  ap[)eared 
that  in  growing  animals  (among  others  Mns  nmsculus  var. 
albus)  the  increase  in  the  niimber  of  axons  can  be  intensified 
by  suitably  adapted  and  gradnally  increased  training.  If,  on  the 
other  hand,  the  training  has  been  made  too  intense,  quite  a 
contrary  result  is  obtained  — the  niimber  of  axons  has  been  found 
to  be  relatively  less  in  these  animals  than  in  the  controlling  animals. 
Dnring  my  continued  investigations  of  this  problem  1 have  succeeded 
in  showing,  in,  among  other  animals,  a 3,5  year  old  dog,  niimeroiis 
transitional  stages  from  indifferent  cells  — as  large  as  small  eapsular. 
cells  — to  fully  developed  ganglion  cells.  These  different  transitional 
stages  have  been  examined  with  regard  to  the  position,  size,  off- 
shoots  and  neiiro-fibrillar  structnre  of  the  cells.  These  qnestions  will 
be  dealt  with  more  fully  in  a later  and  more  complete  account. 
b This  is  the  oldest  animal  that  I have  investigated  so  far  with  regard  to  this. 
