1054 
fibres  witli  a winding  course  were  to  be  fonnd  in  my  preparatious, 
althongli  I could  not  ünd  the  free  end  of  all  of  them.  Of  these 
figures  of  growth  at  least  those  that  form  the  basis  of  figs.  22,  25, 
and  26  niaj  be  eonsidered  as  being  absolntely  reliable.  Tliese  figures 
resemble,  of  conrse,  those  usually  fonnd  in  preparations  of  nerves 
engaged  in  regeneration  (in  the  regeneration  of  a peripheral  end 
of  a nerve,  being  produced  experiinentaliy),  Boeke,  Ramon  y Cajal, 
etc.  We  thus  arrivé  at  the  interesting  fact  tliat  in  tiie  roots  of  the 
segmental  nerves  of  fiilly  intact  aninials  as  old  as  those  we  are 
dealing  with  there  really  exist  neurites  engaged  in  growth,  and  also 
a new  formation  of  neurones  — a phenomenon  that  mnst  be  con- 
sidered  of  fnndamental  iinportance  for  a coinprehension  of  the  post- 
embryonal  gi’owlh  of  the  whole  individual. 
Résumé  and  conclusions. 
0 
The  investigations  of  the  material  in  question  have  shown  that  ‘ft 
the  post-embryonic  growth  of  tlie  peripheral  nerves  is  not  due  | i 
— as  far  as  the  axons  are  concerned  — solely  to  an  advancing  || 
myelinisation  (Donaldson,  etc.)  and  an  increase  in  the  thickness  of 
the  separate  axons,  biit  is  also  dne  to  an  increase  in  the  number  if 
of  axons.  This  increase  in  the  number  of  axons  is,  however,  relatively  1 
larger  during  the  earlier  tlian  dnring  the  later  post-embryonic  period  | (- 
of  the  animal’s  development.  It  is  of  special  interest  to  note  that  the  j(< 
results  of  counting  the  axons  show  that  the  increase  in  the  number  l«: 
of  axons  goes  on  for  a considerable  iength  of  time  during  the  post- 
embiyonic  life  of  the  individual  (see  the  table).  This  post-embryonic  | i 
period  during  which  an  increase  in  the  number  of  nerve  fibres  in  j 
the  roots  of,  the  spinal  nerves  takes  place  is  many  times  longer  ; i 
than  that  during  which  mitoses  can  be  shown  in  the  spinal  ganglia  | 
and  the  spinal  cord.  j 
Investigations  carried  out  with  the  object  of  explaining  the  method  i I 
in  which  such  a post-embryonal  increase  in  the  number  of  axons  j .i 
arises  have  shown  that  it  can  not  be  explained  by  means  of  T-  or  i i 
J^-division  of  the  nerve  fibres  or  by  assuraing  that  the  same  nerve  | ' 
cell  sends  off  more  than  one  axon,  but  that  the  explanation  must  i 
be  sought  in  a real  increase  in  the  number  of  the  neurones.  This  | 
increase  in  the  neurones  seems  to  a great  extent  to  be  due  to  the  j 
fact  that  from  young  cells  lying  in  reserve  processes  are  developed,  j 
among  which  the  so-called  axons  grow  out  in,  among  other  regions,  \ 
the  roots  of  the  nerves  and  the  peripheral  nerves.  Probably  the  j 
young  cell  material  in  the  spinal  cord  comes  from  undifferentiated  I 
