﻿Retrograde 
  Varieties 
  141 
  

  

  present 
  in 
  allied 
  species. 
  There 
  are 
  a 
  great 
  

   many 
  cases 
  however, 
  in 
  which 
  the 
  morpho- 
  

   logic 
  cause 
  of 
  the 
  dissimilarity 
  is 
  not 
  so 
  easily 
  

   discerned. 
  But 
  there 
  is 
  no 
  reason 
  to 
  doubt 
  that 
  

   most 
  of 
  them 
  will 
  be 
  found 
  to 
  conform 
  to 
  the 
  

   rule 
  on 
  closer 
  investigation. 
  Therefore 
  we 
  can 
  

   consider 
  the 
  following 
  as 
  the 
  principal 
  differ- 
  

   ence 
  between 
  elementary 
  species 
  and 
  varieties 
  ; 
  

   that 
  the 
  first 
  arise 
  by 
  the 
  acquisition 
  of 
  entirely 
  

   new 
  characters, 
  and 
  the 
  latter 
  by 
  the 
  loss 
  of 
  

   existing 
  qualities 
  or 
  by 
  the 
  gain 
  of 
  such 
  pecul- 
  

   iarities 
  as 
  may 
  already 
  be 
  seen 
  in 
  other 
  allied 
  

   species. 
  

  

  If 
  we 
  suppose 
  elementary 
  species 
  and 
  varie- 
  

   ties 
  originated 
  by 
  sudden 
  leaps 
  or 
  mutations, 
  

   then 
  the 
  elementary 
  species 
  have 
  mutated 
  in 
  the 
  

   line 
  of 
  progression, 
  some 
  varieties 
  have 
  

   mutated 
  in 
  the 
  line 
  of 
  retrogression, 
  while 
  others 
  

   have 
  diverged 
  from 
  their 
  parental 
  types 
  in 
  a 
  

   line 
  of 
  degression, 
  or 
  in 
  the 
  way 
  of 
  repetition. 
  

   This 
  conception 
  agrees 
  quite 
  well 
  with 
  the 
  cur- 
  

   rent 
  idea 
  that 
  in 
  the 
  building 
  up 
  of 
  the 
  vegeta- 
  

   ble 
  kingdom 
  according 
  to 
  the 
  theory 
  of 
  descent, 
  

   it 
  is 
  species 
  that 
  form 
  the 
  links 
  of 
  the 
  chain 
  

   from 
  the 
  lower 
  forms 
  to 
  the 
  more 
  highly 
  organ- 
  

   ized 
  later 
  derivatives. 
  Otherwise 
  expressed, 
  

   the 
  system 
  is 
  built 
  up 
  of 
  species, 
  and 
  varieties 
  

   are 
  only 
  local 
  and 
  lateral, 
  but 
  never 
  of 
  real 
  

   importance 
  for 
  the 
  whole 
  structure. 
  

  

  