1044 
If  now  we  summarize  the  observations  that  have  been  made  and 
given  above  on  tliese  colonies  of  cells  and  the  processes  of  the  cells 
that  belong  to  them,  it  seems  to  be  clearly  shown  that  some  at  least 
of  the  apolar  cells  in  these  colonies  grow  out  to  nero  neurones  during 
the  postembrgonic  growth  of  the  anima l.  On  the  other  hand  it  does 
not  seem  to  me  so  easy  to  decide  hovv  these  colonies  of  cells  arise. 
The  waj  is  perhaps  that  small  cells  from  the  capsule  cells  which 
have  been  developed  mitotically,  or  are  at  least  situated  within  the 
capsule,  grow  out  into  new  ganglion  cells,  which  are  added  to  other 
ganglion  cells  alreadj’  existing  within  the  saaie  capsule.  Might  not  a 
relativelj  large  ganglion  cell,  which  in  some  respects  is  at  an  earlier 
stage  of  development  — for  instance,  apolar  — increase  in  number 
and  become  one  of  these  colonies  of  cells  by  means  of  amitotic 
divisions.  1 have  not  been  able  to  decide  with  certainty  whether 
one  or  other  or  both  of  these  melhods  of  formations  occur.  though, 
as  a matter  of  fact,  there  are  signs  in  my  preparations  to  support 
the  idea  that  both  these  methods  of  formation  may  occur, 
If,  as  seems  to  be  shown  above,  a new  formation  of  neurones  in 
the  spinal  ganglion  really  occurs  post-ernbryonall} , one  would  and 
might,  of  course,  also  expect  to  tind,  during  post-embryonic  life, 
figures  of  growing  axons  in  the  [leripheral  nerves.  I have  examples 
of  such  claviform  figures,  which  are  quite  evident  in  silver-impi'eg- 
nated  preparations  of,  for  instance,  the  dorsal  and  ventral  roots  of 
young  dogs.  More  details  of  this  will,  however,  be  given  below. 
1 consider  that  I have  now  shown  that  the  cells  in  the  spinal 
ganglia  sufficiently  explain  the  origin  of  the  actually  existing  and 
fairly  considerable  post-embryonic  numeric  growth  of  axons  in  the 
dorsal  roots  of  the  spinal  nerves.  I shall  now  pass  on  to  examine 
to  some  extent  in  connection  with  those  matters  the 
Medulla  spinalis. 
There  is  but  exceedingly  scanty  information  aboiit  post-embryonic 
divisions  of  the  ganglion  cells  of  the  central  nervous  systern  to  be 
found  in  literature,  and  the  existing  accounts  are  not  generally 
admitted  to  be  correct.  These  accounts,  however,  take  two  directions. 
Some  investigators  maintain  that  the  cells  in  this  region  divide  by 
means  of  mitoses,  others  say  that  the  usual  method  of  increase  in 
this  case  is  that  of  amitotic  cell  di\’ision. 
Mitoses. 
Alt, RN States  that  in  the  spinal  cord  of  an  “albino  rat”  twelve 
Allen,  Ezra.  The  cessation  of  mitosis  in  the  central  nervous  systern  of  the 
Albino  rat;  J.  Gomp.  Neurol.  Vol.  22,  pp.  547—568,  1912. 
