1031 
steps  of  division  under  eertaiii  forms  of  stimiilation,  as  lias  been 
obsei’ved  by  some  investigators ; bnt  in  the  normal  state  the  centro- 
some in  an  adult  cell  presenis  slight  morphologioal  differences  froni 
tliat  of  the  embryonic  cell,  which  we  interpret  as  the  beginning  of 
degeneration”.  Hatai  comes  finally  to  the  concliision  ihat  the  only 
way  to  tind  out  whetlier  there  is  generally  a division  of  ganglion 
cells  in  the  spinal  ganglion  is  to  connt  the  nuinber  of  ganglion  cells 
in  oorresponding  ganglia  in  animals  of  different  ages.  Hatai  counted 
the  ganglion  cells  in  6' VII,  77*  IV  and  Lil  in  fonr  specimens  of 
Mus  norwegic'us  alhinus  weighing  10,3,  24,5,  68,5  and  167  grammes 
respectively.  I have  given  a synopsis  of  the  resnlts  of  his  calculations 
in  Table  h above.  At  the  ontset  I wish  to  make  this  criticism 
on  his  calculations,  naraely,  thal  he  has  contented  himself  with 
counting  the  number  of  ganglion  cells  in  only  one  spinal  nerve  in 
each  of  the  cervical,  thoracal  and  lumbal  regions.  Great  variation 
may  exist  in  these,  as  1 ha\  e had  abundant  opportnnities  of  observing 
during  my  counting  of  axons.  These  variations  may  be  so  great  that, 
in  a species  in  which  the  total  increase  of  the  number  of  nerve  fibres 
in  the  dorsal  roots  dui-ing  post-embryonal  growth  is,  let  us  say, 
100  per  cent.,  certain  nerves  in  the  few  days’  old  individual 
may,  in  spite  of  this,  contain  more  nerve  fibres  than  the  corresponding 
nerves  in  the  full-grown  animal.')  My  continued  investigations  have 
also  shown  that  a similar  variation  may  be  found  in  the  number 
of  ganglion  cells  in  the  spinal  ganglion.  In  this  case  one  has  to 
investigate  a rather  large  number  of  spinal  ganglia  in  order  to 
obtain  reliable  information  by  the  method  used  by  Hatai.  On  account 
of  the  values  obtained  by  counting  (Table  h)  H.  concludes  that  “the 
total  number  of  the  spinal  ganglion  cells  remains  approximately 
constant  bet  ween  10,3  and  167  grams,  though  individual  variations 
in  the  numbers  of  the  cells  in  corresponding  ganglia  exist.  It  can 
therefore  be  stated  that  this  number  does  not  increase  or  decrease 
with  age.”  We  must,  however,  note  that  the  number  of  ganglion 
cells  was  throughout  larger  in  the  older  specimens  (Table  (6),  although 
the  excess  in  the  numbers  was  not  so  great.  Hatai  puts  these  larger 
numbers  of  cells  in  the  older  individual  within  the  limits  of  the 
variations.  It  seems  as  if  he  cannot  admit  the  possi bility  that  a 
division  of  cells  in  a spinal  ganglion  might  occur.  Hatai  reveals  this 
especially  in  his  criticism  of  Bühi.er’s’)  observations.  Bühler  writes : 
,,Es  kommt  wie  ich  niich  bei  Frosch  und  Kröte  und  auch  beim 
b Further  details  about  this  will  be  given  in  the  more  complete  account. 
“**)|Bühler,  A.  Untersuchungen  über  den  Bau  der  Nervenzellen.  Verh.  d.  Phys 
med.  Ges.  Würzburg.  N.  T.  Bd  39,  1898  Git.  nach  Hatai  (1902). 
