﻿MONGRELISATION 
  IN 
  LEPIDOPTEEA. 
  55 
  

  

  forms 
  without 
  the 
  co-operation 
  of 
  additional 
  moisture, 
  or 
  some 
  factor 
  

   antagonistic 
  to 
  the 
  growth 
  of 
  lichens. 
  Granted 
  favourable 
  conditions 
  

   on 
  the 
  lines 
  above 
  indicated, 
  and 
  the 
  evolution 
  of 
  a 
  stirps 
  of 
  a 
  species 
  

   showing 
  dimorphic 
  or 
  polymorphic 
  conditions 
  is 
  only 
  what 
  might 
  be 
  

   expected. 
  The 
  apparent 
  discontinuity, 
  due 
  to 
  the 
  absence 
  or 
  extreme 
  

   rarity 
  of 
  intermediate 
  forms, 
  would 
  be 
  accounted 
  for 
  by 
  the 
  period 
  of 
  

   change 
  being 
  too 
  brief, 
  in 
  comparison 
  with 
  the 
  long 
  periods 
  of 
  

   approximate 
  stability 
  that 
  follow, 
  to 
  allow 
  of 
  heredity 
  fixing 
  the 
  

   intermediate 
  stages 
  with 
  any 
  degree 
  of 
  firmness 
  in 
  the 
  architecture 
  of 
  

   the 
  germinal 
  material. 
  The 
  present 
  appearance 
  and 
  rapid 
  spread 
  of 
  

   dark 
  forms, 
  must, 
  on 
  this 
  hypothesis, 
  be 
  explained 
  by 
  (a) 
  the 
  recur- 
  

   rence 
  of 
  conditions 
  favourable 
  to 
  the 
  melanic 
  race, 
  putting 
  an 
  

   enormous 
  premium 
  on 
  the 
  few 
  dark 
  forms 
  that 
  would 
  appear 
  from 
  

   time 
  to 
  time, 
  (b) 
  the 
  desire 
  of 
  entomologists 
  to 
  possess 
  the 
  dark 
  forms 
  

   leading 
  to 
  extensive 
  artificial 
  selection 
  and 
  rearing 
  from 
  dark 
  stock, 
  

   and 
  the 
  escape 
  of 
  surplus 
  imagines 
  and 
  young 
  larvae 
  (Bacot). 
  Such 
  a 
  

   view 
  as 
  this 
  would 
  necessarily 
  tend 
  to 
  the 
  rejection 
  of 
  the 
  opinions 
  of 
  

   Standfuss, 
  concerning 
  Lymantria 
  monacha 
  and 
  its 
  dark 
  form 
  eremita 
  

   (infra), 
  and 
  postulate, 
  for 
  such 
  forms, 
  an 
  origin 
  by 
  slow 
  

   response 
  to 
  changed 
  environmental 
  conditions, 
  excluding 
  largely 
  the 
  

   theory 
  of 
  sudden 
  development 
  by 
  discontinuous 
  variation. 
  Our 
  view 
  

   is 
  distinctly 
  in 
  favour 
  of 
  the 
  former, 
  and 
  against 
  the 
  latter 
  explanation 
  

   of 
  the 
  origin 
  of 
  such 
  forms. 
  One 
  suspects 
  that 
  all 
  these 
  races 
  are 
  

   atavistic, 
  and 
  have 
  the 
  potentialities 
  of 
  producing 
  melanic 
  races 
  (by 
  

   selection) 
  within 
  the 
  ordinary 
  variational 
  limits 
  of 
  the 
  species. 
  The 
  

   inbreeding 
  of 
  these 
  aberrations, 
  however, 
  has 
  not 
  been 
  carried 
  out 
  in 
  a 
  

   sufficient 
  number 
  of 
  experiments 
  to 
  give 
  any 
  sound 
  or 
  reliable 
  data. 
  

   Some 
  of 
  the 
  crossings, 
  however, 
  that 
  have 
  been 
  recorded 
  are 
  as 
  

   follows 
  : 
  — 
  ■ 
  

  

  1. 
  Grammesia 
  trigrammica 
  $ 
  x 
  bilinea 
  £ 
  • 
  — 
  Standfuss 
  records 
  

   (Handbuch, 
  etc., 
  p. 
  313) 
  a 
  cross 
  of 
  this 
  supposed 
  parentage, 
  but 
  $ 
  

   really 
  unknown 
  ; 
  67 
  perfect 
  insects 
  resulted, 
  38 
  being 
  triyrammica 
  and 
  

   29 
  bilinea, 
  there 
  being 
  no 
  intermediates. 
  One 
  of 
  the 
  latter 
  be 
  figures 
  

   (pi. 
  viii., 
  fig. 
  10). 
  

  

  2. 
  Polia 
  olivacea 
  $ 
  x 
  olivacea 
  $ 
  . 
  — 
  Eggs 
  laid 
  September, 
  1891, 
  

   hatched 
  May, 
  1892 
  ; 
  larvae 
  did 
  well 
  till 
  half 
  -grown, 
  when 
  many 
  died. 
  

   Those 
  that 
  pupated 
  and 
  resulted 
  in 
  imagines 
  produced 
  in 
  every 
  ease 
  

   olivacea. 
  [Two 
  typical 
  old 
  $ 
  s 
  taken 
  in 
  same 
  locality 
  and 
  J 
  s 
  un- 
  

   known, 
  produced 
  in 
  each 
  case 
  75 
  percent, 
  chi 
  and 
  25 
  percent, 
  olicacea,] 
  

   (Maddison, 
  Ent. 
  Rec, 
  iv., 
  p. 
  3). 
  

  

  3. 
  Lymantria 
  monacha 
  $ 
  x 
  eremita 
  ? 
  . 
  — 
  Standfuss, 
  in 
  1893. 
  

   reared 
  a 
  brood 
  from 
  a 
  pair 
  of 
  normal 
  monacha, 
  from 
  near 
  Breslau, 
  in 
  

   Silesia. 
  This 
  brood 
  contained 
  one 
  £ 
  eremita, 
  which 
  was 
  paired 
  with 
  a 
  

   normal 
  monacha 
  $ 
  , 
  from 
  Zurich. 
  The 
  issue 
  consisted 
  of 
  22 
  typical 
  

   monacha, 
  2 
  $ 
  s 
  and 
  20 
  $ 
  s 
  ; 
  23 
  eremita, 
  18 
  J 
  s 
  and 
  5 
  $ 
  s, 
  and 
  6 
  

   intermediates, 
  5 
  ^ 
  s 
  and 
  1 
  $ 
  , 
  in 
  which 
  the 
  characters 
  of 
  the 
  two 
  wore 
  

   asymmetrically 
  mixed, 
  but 
  with 
  no 
  apparent 
  tendency 
  to 
  gynandro- 
  

   morphism. 
  One 
  of 
  these 
  is 
  figured 
  by 
  Standfuss 
  (Handbuch, 
  etc.. 
  

   pi. 
  iv., 
  fig. 
  4). 
  

  

  4. 
  Lymantria 
  eremita 
  <$ 
  x 
  monacha 
  £ 
  . 
  — 
  Standfuss 
  found, 
  in 
  L888, 
  

   near 
  Liegnitz, 
  in 
  Silesia, 
  a 
  $ 
  eremita 
  paired 
  with 
  a 
  J 
  monacha. 
  The 
  

   result 
  was 
  entirely 
  different 
  from 
  that 
  of 
  the 
  reciprocal 
  crossing 
  noted 
  

   (supra), 
  for 
  the 
  issue 
  contained 
  every 
  kind 
  of 
  transition 
  between 
  

   the 
  two 
  parent 
  forms, 
  whilst 
  a 
  few 
  wore 
  even 
  darker 
  than 
  the 
  " 
  

  

  