﻿F. 
  FLUCTUATION 
  

   LECTURE 
  XXV 
  

  

  GENERAL 
  LAWS 
  OF 
  FLUCTUATION 
  

  

  The 
  principle 
  of 
  unit-characters 
  and 
  of 
  ele- 
  

   mentary 
  species 
  leads 
  at 
  once 
  to 
  the 
  recognition 
  

   of 
  two 
  kinds 
  of 
  variability. 
  The 
  changes 
  of 
  

   wider 
  amplitude 
  consist 
  of 
  the 
  acquisition 
  of 
  

   new 
  units, 
  or 
  the 
  loss 
  of 
  already 
  existing 
  ones. 
  

   The 
  lesser 
  variations 
  are 
  due 
  to 
  the 
  degree 
  of 
  

   activity 
  of 
  the 
  units 
  themselves. 
  

  

  Facts 
  illustrative 
  of 
  these 
  distinctions 
  were 
  

   almost 
  wholly 
  lacking 
  at 
  the 
  time 
  of 
  the 
  first 
  

  

  +j 
  ^^ 
  

  

  publication 
  of 
  Darwin's 
  theories. 
  It 
  was 
  a 
  bold 
  

   conception 
  to 
  point 
  out 
  the 
  necessity 
  for 
  such 
  

   distinction 
  on 
  purely 
  theoretical 
  grounds. 
  Of 
  

   course 
  some 
  sports 
  were 
  well 
  known 
  and 
  fluc- 
  

   tuations 
  were 
  evident, 
  but 
  no 
  exact 
  analysis 
  of 
  

   the 
  details 
  was 
  possible, 
  a 
  fact 
  that 
  was 
  of 
  great 
  

   importance 
  in 
  the 
  demonstration 
  of 
  the 
  theory 
  

   of 
  descent. 
  The 
  lack 
  of 
  more 
  definite 
  knowl- 
  

   edge 
  upon 
  this 
  matter 
  was 
  keenly 
  felt 
  by 
  Dar- 
  

  

  715 
  

  

  