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  Atavism 
  191 
  

  

  bility. 
  ' 
  ' 
  And 
  to 
  avoid 
  the 
  repetition 
  of 
  the 
  lat- 
  

   ter 
  word 
  it 
  is 
  called 
  " 
  fluctuation." 
  In 
  con- 
  

   trast 
  to 
  these 
  fluctuations 
  are 
  the 
  so-called 
  

   sports 
  or 
  single 
  varieties, 
  not 
  rarely 
  denomi- 
  

   nated 
  spontaneous 
  variations, 
  and 
  for 
  which 
  I 
  

   propose 
  to 
  use 
  the 
  term 
  " 
  mutations.' 
  They 
  

   are 
  of 
  very 
  rare 
  occurrence 
  and 
  are 
  to 
  be 
  con- 
  

   sidered 
  as 
  sudden 
  and 
  definite 
  steps. 
  

  

  Lastly, 
  we 
  have 
  to 
  consider 
  those 
  varieties, 
  

   which 
  vary 
  in 
  a 
  much 
  wider 
  range 
  than 
  the 
  

   ordinary 
  ones, 
  and 
  seem 
  to 
  fluctuate 
  between 
  

   two 
  opposite 
  extremes, 
  as 
  for 
  instance 
  varie- 
  

   gated 
  leaves, 
  cultivated 
  varieties 
  with 
  va- 
  

   riegated 
  or 
  striped 
  flowers, 
  double 
  flowers 
  

   and 
  some 
  other 
  anomalies. 
  They 
  are 
  ever- 
  

   sporting 
  and 
  ever-returning 
  from 
  one 
  type 
  to 
  

   the 
  other. 
  If 
  however, 
  we 
  take 
  the 
  group 
  of 
  

   these 
  extremes 
  and 
  their 
  intermediates 
  as 
  a 
  

   whole, 
  this 
  group 
  remains 
  constant 
  during 
  the 
  

   succeeding 
  generations. 
  Here 
  we 
  find 
  once 
  

   more 
  an 
  instance 
  of 
  the 
  seemingly 
  contradictory 
  

   combination 
  of 
  high 
  variability 
  and 
  absolute 
  

   constancy. 
  It 
  means 
  that 
  the 
  range 
  of 
  varia- 
  

   bility 
  has 
  quite 
  definite 
  limits, 
  which 
  in 
  the 
  com- 
  

   mon 
  course 
  of 
  things, 
  are 
  never 
  transgressed. 
  

  

  We 
  may 
  infer 
  therefore 
  that 
  the 
  word 
  varia- 
  

   bility 
  has 
  such 
  a 
  wide 
  range 
  of 
  meanings 
  that 
  

   it 
  ought 
  never 
  be 
  used 
  without 
  explanation. 
  

  

  