﻿A 
  Further 
  Study 
  of 
  Chromosome 
  Dimensions. 
  163 
  

  

  The 
  evidence 
  that 
  we 
  have 
  now 
  considered 
  is 
  remarkable. 
  We 
  have 
  

   observed 
  that 
  the 
  total 
  volume 
  of 
  the 
  chromatin 
  on 
  the 
  spindles 
  maybe 
  

   much 
  smaller 
  in 
  a 
  mammal 
  and 
  a 
  bird 
  than 
  in 
  a 
  grasshopper 
  ; 
  while 
  a 
  very 
  

   great 
  difference 
  was 
  seen 
  between 
  a 
  grasshopper, 
  on 
  the 
  one 
  hand, 
  and 
  >a 
  

   moth 
  and 
  a 
  butterfly 
  on 
  the 
  other 
  — 
  animals 
  that 
  not 
  only 
  belong 
  to, 
  but 
  

   have 
  been 
  shown 
  to 
  be 
  typical 
  of 
  closely 
  allied 
  divisions 
  of 
  the 
  animal 
  

   kingdom. 
  And 
  the 
  same 
  results 
  have 
  been 
  obtained 
  in 
  the 
  case 
  of 
  

   the 
  chromosome 
  diameter. 
  The 
  animals 
  dealt 
  with 
  belong 
  to 
  various 
  

   divisions 
  of 
  the 
  Arthropoda, 
  Mollusca, 
  and 
  Vertebrata 
  ; 
  but 
  a 
  comparison 
  of 
  

   the 
  photo-micrographs 
  given 
  in 
  the 
  Plate 
  completely 
  fails 
  to 
  show 
  corre- 
  

   pondence 
  between 
  our 
  systematic 
  classification 
  and 
  a 
  classification 
  based 
  upon 
  

   either 
  chromatin 
  volume 
  or 
  chromosome 
  diameter. 
  In 
  the 
  circumstances, 
  

   we 
  must 
  realise 
  that 
  the 
  tendencies 
  observed 
  in 
  our 
  earlier 
  data 
  for 
  the 
  

   chromatin 
  volume 
  and 
  chromosome 
  diameter 
  to 
  increase 
  as 
  we 
  passed 
  from 
  

   simple 
  to 
  complex 
  animals 
  must 
  have 
  been 
  fortuitous. 
  The 
  evidence 
  now 
  

   before 
  us 
  proves 
  conclusively 
  that 
  the 
  suggestions 
  embodied 
  in 
  my 
  third 
  

   generalisation 
  and 
  in 
  my 
  fourth 
  in 
  its 
  amended 
  form 
  must 
  be 
  abandoned. 
  

  

  Conclusion. 
  

  

  The 
  evidence 
  produced 
  in 
  my 
  first 
  paper 
  proved 
  two 
  negative 
  generalisa- 
  

   tions, 
  viz., 
  that 
  the 
  degree 
  of 
  somatic 
  complexity 
  of 
  an 
  animal 
  cannot 
  be 
  

   correlated 
  with 
  either 
  the 
  lengths 
  or 
  the 
  number 
  of 
  the 
  chromosomes 
  com- 
  

   posing 
  its 
  complex. 
  Our 
  new 
  evidence 
  has 
  proved 
  two 
  more 
  negative 
  

   generalisations, 
  viz., 
  that 
  the 
  degree 
  of 
  somatic 
  complexity 
  of 
  an 
  animal 
  cannot 
  

   be 
  correlated 
  with 
  either 
  the 
  total 
  volume 
  or 
  the 
  diameters 
  of 
  the 
  chromo- 
  

   somes 
  composing 
  its 
  complex. 
  Cytometrical 
  investigations 
  have 
  failed 
  so 
  

   far 
  to 
  give 
  a 
  positive 
  generalisation 
  concerning 
  these 
  phenomena. 
  But 
  the 
  

   work 
  done 
  has 
  been 
  justified 
  ; 
  for 
  many 
  facts 
  have 
  been 
  discovered, 
  and 
  the 
  

   establishment 
  of 
  these 
  four 
  negative 
  generalisations 
  must 
  reduce 
  the 
  number 
  

   of 
  possible 
  explanations. 
  

  

  If 
  now 
  we 
  consider 
  the 
  hypothesis 
  that 
  I 
  put 
  forward, 
  we 
  find 
  that 
  the 
  

   new 
  evidence 
  necessitates 
  the 
  elimination 
  from 
  it 
  of 
  all 
  reference 
  to 
  con- 
  

   nection 
  between 
  increase 
  of 
  somatic 
  differentiation, 
  resulting 
  from 
  evolu- 
  

   tionary 
  development, 
  and 
  increase 
  of 
  chromatin 
  volume 
  and 
  chromosome 
  

   diameter. 
  The 
  hypothesis 
  thus 
  becomes 
  nothing 
  more 
  than 
  a 
  suggested 
  

   explanation 
  of 
  the 
  process 
  by 
  which 
  increase 
  in 
  chromosome 
  length 
  and 
  

   diameter 
  is 
  effected. 
  But 
  the 
  discovery 
  of 
  many 
  different 
  chromosome 
  

   diameters 
  removes 
  the 
  grounds 
  for 
  suggesting 
  that 
  increase 
  in 
  diameter 
  is 
  

   discontinuous 
  and 
  is 
  effected 
  by 
  conjugation 
  of 
  units, 
  while 
  increase 
  in 
  

   length 
  is 
  continuous 
  and 
  is 
  effected 
  by 
  growth. 
  These 
  increases 
  may 
  occur 
  

  

  