1020 
the  tact  tliat  the  imnibers  for  these  animals  were  based  on  speci-  i 
mens  on  a few  investigations.  The  diffetence  between  the  nnmber  | 
of  nerve  tibres  in  the  dorsal  and  ventral  roots  is  comparativel}  j 
greater  in  old  than  in  yonng  animals  of  the  same  species.  I shall  I 
leave  a more  detailed  discussion  of  the  values  obtained  for  a tuture  | 
and  more  complete  account  of  the  questions  that  are  connected  with  ; 
this  problem  and  shall  pass  on  instead  to  an  attempt  to  answer  the  ' 
following  question : I 
Hoii'  does  a post-embri/onal  increase  in  the  nnmber  of  axons  in  the  i 
dorsal  and  ventral  roots  of  the  spinal  nerves  arise?  \ 
This  question  forces  itself  npon  our  attention  when  we  find  that  | 
the  nuraber  of  nerve  tibres  in  the  dorsal  and  ventral  roots  of  the  | 
spinal  nerves  increases  considerably  with  the  growth  ot  the  animal.  j 
There  may,  however,  be  different  opinions  as  to  the  manner  in  which 
this  increase  takes  place,  and  this  question  certainly  needs  to  be  , 
snbjected  to  a comprehensive  investigation.  There  are  really  two  j 
possibilities  to  be  taken  into  consideration.  dhe  increase  must  depend  i 
either  on  a T-  or  Y-formed  division  of  nerve  fibres,  or  on  an  outgrowth 
from  the  centre,  from  nerve  cells  (neuroblasts)  that  have  been  neivly  ! 
formed  or  are  lying  in  reserve.  There  is,  of  course,  a third  possibility  || 
which  is,  however,  not  very  probable,  namely,  that  one  nerve-cell  j 
has  discharged  two  axons  in  the  same  direction.  j 
Does  a division  of  the  nerve  fibres  exist  in  the  roots  of  the  spinal  ' 
nerves  f 1 
Most  obvious  is  of  course  the  supposition  that  we  have  here  a ! 
cleavage  {T-  or  F-division)  of  the  nerve  fibres  on  the  lines  of  the  , 
process,  of  which  such  fine  examples  may  be  seen  in  the  peripheral  i 
part  of  the  nerves  and  also  in  the  central  nerve  system.  A cleavage  , 
of  this  kind  may  be  exceedingly  frequent;  thus,  at  Prof.  Boeke’s  in  | 
Leyden  1 saw  a preparation  which  showed,  among  other  things, 
a nerve  fibre  that  was  divided  at  one  place  into  six  branches.  | 
Stefanelli')  describes  and  reproduces  a preparation  from  the  tongue  , 
of  the  chameleon,  in  which  a single  nerve  tibre  was  divided  into  | 
branches  terminating  in  uo  less  than  thirty-ti\'e  motory  plates.  During  , 
nerve  regeneration  after  a section  one  may  also  see  abundant  | 
examples  of  such  division.  See,  for  instance,  the  tigures  in  Cajal’) 
1)  Stefanelu,  A.  La  piastra  motrice  secondo  Ie  vecchie  e Ie  nuove  vedute. 
Annali  di  Neurologia  Fase.  IV  1912.  Quoted  by  Boeke  L.  c.  3. 
2)  Gajal,Ramon  Y.  Studiën  über  Nervenregeneralion  (J.  A.  Barth,  Leipzig)  19Ü8 
