﻿54 
  BRITISH 
  LEPIDOPTERA. 
  

  

  broods 
  there 
  are 
  some 
  obsoleta, 
  varying 
  from 
  a 
  few 
  to 
  as 
  many 
  as 
  

   intermediates 
  (Riding, 
  in 
  litt.). 
  

  

  8. 
  Zonosomabiobsoleta 
  J 
  x 
  biobsoleta 
  $ 
  . 
  — 
  One 
  small 
  brood 
  (parents 
  

   very 
  carefully 
  selected) 
  bred 
  true 
  this 
  year 
  (1904), 
  but 
  this 
  is 
  the 
  only 
  

   time 
  they 
  have 
  hitherto 
  done 
  so. 
  [I 
  often 
  have 
  difficulty 
  in 
  getting 
  

   the 
  desired 
  selections, 
  the 
  emergences 
  failing 
  to 
  suit, 
  and, 
  fearing 
  to 
  

   lose 
  the 
  race, 
  I 
  have 
  to 
  mate 
  with 
  intermediates. 
  I 
  have 
  not 
  crossed 
  

   wild 
  annulata 
  with 
  obsoleta 
  for 
  four 
  years, 
  so 
  there 
  has 
  been 
  no 
  new 
  

   blood 
  introduced 
  during 
  this 
  time 
  ; 
  the 
  imagines, 
  however, 
  keep 
  full 
  

   size, 
  indeed, 
  a 
  few 
  are 
  larger 
  than 
  any 
  I 
  have 
  taken 
  with 
  the 
  net 
  or 
  

   bred 
  from 
  fullgrown 
  larvas 
  beaten 
  from 
  maple.] 
  (Riding, 
  in 
  litt.). 
  

   III. 
  Crossing 
  of 
  typical 
  forms 
  with 
  aberrations 
  tending 
  to 
  develop 
  

  

  MELANOCHROIC 
  RACES. 
  

  

  Having 
  noted 
  the 
  recorded 
  results 
  of 
  inbreeding 
  Spilosow 
  a 
  lubricipeda 
  

   with 
  its 
  domesticated 
  races, 
  we 
  now 
  refer 
  to 
  a 
  certain 
  number 
  of 
  forms, 
  

   whose 
  varying 
  environmental 
  conditions 
  are 
  such 
  as 
  to 
  tend, 
  in 
  certain 
  

   districts, 
  to 
  the 
  development 
  of 
  a 
  melanic 
  race, 
  side 
  by 
  side 
  with, 
  

   or 
  gradually 
  supplanting, 
  the 
  type. 
  The 
  origin 
  of 
  melanic, 
  albinistic, 
  

   and 
  analogous 
  races, 
  is, 
  perhaps, 
  outside 
  the 
  scope 
  of 
  this 
  chapter, 
  

   yet, 
  without 
  considerable 
  knowledge 
  concerning 
  the 
  environment, 
  

   etc., 
  of 
  these, 
  the 
  bearing 
  of 
  experimental 
  work 
  in 
  the 
  direction 
  

   of 
  isolating 
  such 
  races, 
  or 
  having 
  for 
  its 
  object 
  the 
  study 
  of 
  their 
  

   development, 
  etc., 
  is 
  largely 
  missed, 
  and 
  the 
  experiments 
  them- 
  

   selves 
  rendered 
  to 
  a 
  certain 
  extent 
  purposeless. 
  This 
  view 
  we 
  have 
  

   already 
  discussed 
  at 
  length 
  [Melanism 
  and 
  Melanochroism 
  in 
  British 
  

   Lepidojitera), 
  and 
  simply 
  add 
  here 
  a 
  note 
  recently 
  penned 
  by 
  Bacot, 
  

   who 
  considers 
  it 
  a 
  point 
  of 
  some 
  importance 
  that 
  a 
  small 
  patch 
  of 
  pale 
  

   colour 
  on 
  the 
  upper 
  (costal) 
  margin 
  of 
  the 
  hindwing 
  occurs 
  in 
  many 
  

   Ampliidasysdh.doubledayaria, 
  this 
  portion 
  being 
  covered 
  by 
  the 
  forewings 
  

   in 
  the 
  normal 
  resting-position 
  of 
  the 
  moth. 
  It 
  suggests 
  that 
  the 
  dark 
  

   form 
  was 
  evolved 
  later 
  than 
  the 
  type, 
  and 
  strongly 
  hints 
  that 
  the 
  dark 
  

   coloration 
  is 
  not 
  due 
  to 
  any 
  sudden 
  discontinuous 
  change 
  or 
  darkening 
  

   of 
  the 
  wing-pigment 
  as 
  a 
  whole, 
  but 
  is 
  the 
  outcome 
  of 
  a 
  long 
  course 
  of 
  

   evolution 
  in 
  the 
  history 
  of 
  the 
  species, 
  during 
  which 
  the 
  death-roll 
  of 
  

   individuals 
  showing 
  minute 
  variations 
  in 
  the 
  direction 
  of 
  darkening 
  was 
  

   lower 
  than 
  in 
  the 
  typical 
  form, 
  i.e., 
  the 
  colour 
  is 
  due 
  to 
  an 
  adjustment 
  to 
  

   a 
  gradual 
  darkening 
  of 
  the 
  resting-surface 
  over 
  at 
  least 
  a 
  portion 
  of 
  the 
  

   range 
  of 
  the 
  species. 
  Such 
  a 
  change 
  may 
  have 
  originated 
  in 
  a 
  greater 
  

   humidity 
  of 
  the 
  atmosphere 
  and 
  denser 
  forests, 
  or, 
  possibly, 
  in 
  part, 
  to 
  

   a 
  successive 
  change 
  in 
  the 
  trees, 
  of 
  which 
  the 
  forests 
  themselves 
  were 
  

   composed, 
  e.g., 
  pine 
  replaced 
  by 
  oak, 
  oak 
  by 
  beech, 
  beech 
  by 
  birch, 
  etc. 
  

   Such 
  a 
  succession 
  alone 
  would 
  probably 
  cause 
  considerable 
  change 
  in 
  

   the 
  facies 
  of 
  a 
  species 
  without 
  a 
  change 
  in 
  atmospheric 
  conditions, 
  

   which, 
  in 
  all 
  probability, 
  however, 
  would 
  be 
  associated 
  with 
  the 
  change, 
  

   e.g., 
  if 
  it 
  be 
  allowed 
  that 
  A. 
  betularia 
  started 
  on 
  its 
  career 
  during 
  the 
  

   oak 
  dynasty, 
  the 
  comparative 
  open 
  nature 
  of 
  the 
  wood 
  and 
  the 
  fact 
  

   that 
  the 
  trees 
  would 
  hardly 
  be 
  in 
  full 
  foliage 
  at 
  the 
  time 
  of 
  the 
  

   emergence 
  of 
  the 
  moths, 
  would 
  be 
  favourable 
  to 
  the 
  development 
  of 
  

   the 
  " 
  pepper 
  and 
  salt 
  " 
  pattern. 
  The 
  succeeding 
  beech 
  period 
  would 
  

   give 
  a 
  denser 
  foliage, 
  and, 
  as 
  the 
  trees 
  break 
  into 
  leaf 
  earlier, 
  a 
  much 
  

   darker 
  forest 
  results 
  at 
  the 
  period 
  when 
  the 
  moths 
  are 
  at 
  large, 
  while 
  

   the 
  replacement 
  of 
  beech 
  by 
  birch 
  would 
  again 
  bring 
  in 
  lighter 
  

   conditions, 
  accompanied 
  by 
  a 
  paler 
  resting 
  surface. 
  It 
  is 
  probable, 
  

   however, 
  that 
  such 
  a 
  series 
  of 
  changes 
  could 
  not 
  produce 
  the 
  extreme 
  

  

  