﻿206 
  E. 
  lUY 
  I.ANKESTEK. 
  

  

  fonns 
  of 
  animals 
  (or 
  of 
  plants) 
  to 
  one 
  another 
  is 
  that 
  of 
  the 
  

   ultimate 
  twigs 
  of 
  a 
  much-branching 
  genealogical 
  tree. 
  

   Secondly, 
  identity 
  of 
  structui'e 
  in 
  two 
  organisms 
  does 
  not 
  

   necessarily 
  indicate 
  that 
  the 
  identical 
  structure 
  has 
  been 
  

   inherited 
  from 
  an 
  ancestor 
  common 
  to 
  the 
  two 
  organisms 
  

   compared 
  (homogeny), 
  but 
  may 
  be 
  due 
  to 
  independent 
  de- 
  

   velopment 
  of 
  a 
  like 
  structure 
  in 
  two 
  different 
  lines 
  of 
  descent 
  

   (homoplasy). 
  Thirdly, 
  those 
  members 
  of 
  a 
  group 
  which, 
  

   whilst 
  exhibiting 
  undoubted 
  structural 
  characters 
  indicative 
  

   of 
  their 
  proper 
  assignment 
  to 
  that 
  group, 
  yet 
  are 
  simpler 
  than 
  

   and 
  inferior 
  in 
  elaboration 
  of 
  their 
  organisation 
  to 
  other 
  

   members 
  of 
  the 
  group, 
  are 
  not 
  necessarily 
  representatives 
  of 
  

   the 
  earlier 
  and 
  primitive 
  phases 
  in 
  the 
  development 
  of 
  the 
  

   group, 
  but 
  are 
  very 
  often 
  examples 
  of 
  retrogressive 
  change 
  

   or 
  degeneration. 
  The 
  second 
  and 
  third 
  implements 
  of 
  analy- 
  

   sis 
  above 
  cited 
  are 
  of 
  the 
  nature 
  of 
  cautions 
  or 
  checks. 
  

   Agreements 
  are 
  not 
  necessarily 
  due 
  to 
  common 
  inherit- 
  

   ance; 
  simplicity 
  is 
  not 
  necessarily 
  primitive 
  and 
  ancestral. 
  

   On 
  the 
  other 
  hand, 
  we 
  must 
  not 
  rashly 
  set 
  down 
  agree- 
  

   ments 
  as 
  due 
  to 
  "homoplasy" 
  or 
  "convergence 
  of 
  develop- 
  

   ment" 
  if 
  we 
  find 
  two 
  or 
  three 
  or 
  more 
  concurrent 
  agreements. 
  

   The 
  probability 
  is 
  against 
  agreement 
  being 
  due 
  to 
  homoplasy 
  

   when 
  the 
  agreement 
  involves 
  a 
  number 
  of 
  really 
  separate 
  

   (not 
  correlated) 
  coincidences. 
  Whilst 
  the 
  chances 
  are 
  in 
  

   favour 
  of 
  some 
  one 
  homoplastic 
  coincidence 
  or 
  structural 
  

   agreement 
  occurring 
  between 
  some 
  member 
  or 
  other 
  of 
  a 
  

   large 
  group 
  a, 
  and 
  some 
  member 
  or 
  other 
  of 
  a 
  large 
  group 
  h, 
  

   the 
  matter 
  is 
  very 
  different 
  when 
  by 
  such 
  au 
  initial 
  coinci- 
  

   dence 
  the 
  two 
  members 
  have 
  been 
  particularised. 
  The 
  chances 
  

   aoainst 
  these 
  two 
  selected 
  members 
  exhibiting 
  another 
  really 
  

   independent 
  homoplastic 
  agreement 
  are 
  enormous 
  ; 
  let 
  us 
  

   say 
  10,000 
  to 
  1. 
  The 
  chances 
  against 
  yet 
  another 
  coincidence 
  

   are 
  a 
  hundred 
  million 
  to 
  one, 
  and 
  against 
  yet 
  one 
  more 
  

   " 
  coincidence 
  " 
  they 
  are 
  the 
  square 
  of 
  a 
  hundred 
  million 
  to 
  

   one. 
  Homoplasy 
  can 
  only 
  be 
  assumed 
  where 
  the 
  coincidence 
  

   is 
  of 
  a 
  simple 
  nature, 
  and 
  is 
  such 
  as 
  may 
  be 
  reasonably 
  

   supposed 
  to 
  have 
  arisen 
  by 
  the 
  action 
  of 
  like 
  selective 
  

  

  