﻿Systematic 
  Atavism 
  631 
  

  

  as 
  for 
  instance 
  in 
  the 
  aroids 
  and 
  the 
  grasses. 
  

   Retrograde 
  evolution 
  is 
  also 
  typical 
  in 
  the 
  high- 
  

   est 
  and 
  most 
  highly 
  differentiated 
  family 
  of 
  the 
  

   monocotyledons, 
  the 
  orchids, 
  which 
  have 
  but 
  

   one 
  or 
  two 
  stamens. 
  In 
  the 
  second 
  place 
  I 
  have 
  

   had 
  occasion 
  more 
  than 
  once 
  to 
  assert 
  that 
  retro- 
  

   gression, 
  though 
  seemingly 
  consisting 
  in 
  the 
  

   disappearance 
  of 
  some 
  quality, 
  need 
  not, 
  as 
  a 
  

   rule, 
  be 
  considered 
  as 
  a 
  complete 
  loss. 
  Quite 
  on 
  

   the 
  contrary, 
  it 
  is 
  very 
  probable 
  that 
  real 
  losses 
  

   are 
  extremely 
  rare, 
  if 
  not 
  wholly 
  lacking. 
  Ordi- 
  

   narily 
  the 
  loss 
  is 
  only 
  apparent, 
  the 
  capacity 
  

   becomes 
  inactive 
  only, 
  but 
  is 
  not 
  destroyed. 
  The 
  

   character 
  has 
  become 
  latent, 
  as 
  it 
  is 
  commonly 
  

   stated, 
  and 
  therefore 
  may 
  return 
  to 
  activity 
  and 
  

   to 
  the 
  full 
  display 
  of 
  its 
  peculiarity, 
  whenever 
  

   occasion 
  offers. 
  

  

  Such 
  a 
  return 
  to 
  activity 
  was 
  formerly 
  called 
  

   atavism. 
  But 
  as 
  we 
  have 
  seen, 
  when 
  dealing 
  

   with 
  the 
  phenomena 
  of 
  latency 
  at 
  large, 
  sundry 
  

   cases 
  of 
  latency 
  are 
  to 
  be 
  distinguished, 
  in 
  order 
  

   to 
  get 
  a 
  clear 
  insight 
  into 
  these 
  difficult 
  proc- 
  

   esses. 
  

  

  So 
  it 
  is 
  with 
  atavism, 
  too. 
  If 
  any 
  plant 
  re- 
  

   verts 
  to 
  a 
  known 
  ancestor, 
  we 
  have 
  a 
  positive 
  

   and 
  simple 
  case. 
  But 
  ancestors 
  with 
  alternate 
  

   specific 
  marks 
  are 
  as 
  a 
  rule 
  neither 
  historically 
  

   nor 
  experimentally 
  manifest. 
  They 
  are 
  only 
  

   reputed 
  to 
  be 
  such, 
  and 
  the 
  presumption 
  rests 
  

  

  