﻿MONGRELISATION 
  IN 
  LEPIDOPTERA. 
  41 
  

  

  ior 
  the 
  results 
  yet 
  obtained 
  by 
  crossing 
  one 
  of 
  such 
  forms 
  with 
  another, 
  

   is 
  that 
  they 
  may 
  possibly 
  throw 
  some 
  light 
  on 
  the 
  problems 
  of 
  heredity. 
  

   As 
  soon, 
  however, 
  as 
  a 
  form 
  becomes 
  permanently 
  associated 
  with 
  a 
  

   certain 
  condition, 
  or 
  conditions, 
  of 
  environment, 
  and 
  has, 
  possibly, 
  a 
  

   ■correspondingly 
  marked 
  variation 
  in 
  its 
  internal 
  structure 
  and 
  

   functions, 
  the 
  results 
  become 
  directly 
  connected 
  with 
  the 
  broad 
  

   problems 
  relating 
  to 
  hybrids 
  proper, 
  and 
  are 
  likely 
  to 
  throw 
  light 
  on 
  

   the 
  origin 
  of 
  the 
  peculiarities 
  which 
  so 
  many 
  hybrids 
  undoubtedly 
  

   present. 
  

  

  As 
  bearing 
  on 
  this 
  point, 
  Darwin 
  writes 
  (Origin 
  of 
  Species, 
  1884 
  

   <ed., 
  p. 
  263) 
  : 
  " 
  It 
  is 
  not 
  surprising 
  that 
  the 
  difficulty 
  in 
  crossing 
  any 
  

   two 
  species 
  and 
  the 
  sterility 
  of 
  their 
  hybrid 
  offspring, 
  should, 
  in 
  most 
  

   cases, 
  correspond, 
  even 
  if 
  due 
  to 
  distinct 
  causes, 
  for 
  both 
  depend 
  on 
  

   the 
  amount 
  of 
  difference 
  between 
  the 
  species 
  which 
  are 
  crossed. 
  Nor 
  

   is 
  it 
  surprising 
  that 
  the 
  facility 
  of 
  effecting 
  a 
  first 
  cross, 
  and 
  the 
  

   fertility 
  of 
  the 
  hybrids 
  thus 
  produced, 
  should 
  all 
  run, 
  to 
  a 
  certain 
  

   extent, 
  parallel 
  with 
  the 
  systematic 
  affinity 
  of 
  the 
  forms 
  subject 
  to 
  

   •experiment 
  ; 
  for 
  systematic 
  affinity 
  includes 
  resemblances 
  of 
  all 
  kinds. 
  

   First 
  crosses 
  between 
  forms 
  known 
  to 
  be 
  varieties, 
  or 
  sufficiently 
  alike 
  

   to 
  be 
  considered 
  as 
  varieties 
  and 
  their 
  mongrel 
  offspring, 
  are 
  very 
  

   generally, 
  but 
  not, 
  as 
  is 
  so 
  often 
  stated, 
  invariably, 
  fertile. 
  Nor 
  is 
  this 
  

   .almost 
  universal 
  and 
  perfect 
  fertility 
  surprising 
  when 
  it 
  is 
  remembered 
  

   how 
  liable 
  we 
  are 
  to 
  argue 
  in 
  a 
  circle 
  with 
  respect 
  to 
  varieties 
  in 
  a 
  state 
  

   •of 
  nature, 
  and 
  when 
  we 
  remember 
  that 
  the 
  greater 
  number 
  of 
  varieties 
  

   have 
  been 
  produced 
  under 
  domestication 
  by 
  the 
  selection 
  of 
  mere 
  

   •external 
  differences, 
  and 
  that 
  they 
  have 
  not 
  been 
  long 
  exposed 
  to 
  

   uniform 
  conditions 
  of 
  life. 
  It 
  should 
  also 
  be 
  especially 
  kept 
  in 
  mind, 
  

   .that 
  long-continued 
  domestication 
  tends 
  to 
  eliminate 
  sterility, 
  and 
  is, 
  

   therefore, 
  little 
  likely 
  to 
  induce 
  this 
  same 
  quality. 
  Independently 
  of 
  the 
  

   question 
  of 
  fertility, 
  in 
  all 
  other 
  respects 
  there 
  is 
  the 
  closest 
  general 
  

   resemblance 
  between 
  hybrids 
  and 
  mongrels 
  — 
  in 
  their 
  variability, 
  in 
  

   their 
  power 
  of 
  absorbing 
  each 
  other 
  by 
  repeated 
  crosses, 
  and 
  in 
  their 
  

   inheritance 
  of 
  characters 
  from 
  both 
  parent 
  forms. 
  Finally, 
  then, 
  

   although 
  we 
  are 
  ignorant 
  of 
  the 
  precise 
  cause 
  of 
  the 
  sterility 
  of 
  first 
  

   crosses 
  and 
  hybrids 
  .... 
  yet 
  the 
  facts 
  given 
  do 
  not 
  seem 
  to 
  be 
  

   opposed 
  to 
  the 
  belief 
  that 
  species 
  aboriginally 
  existed 
  as 
  varieties." 
  

  

  In 
  this, 
  without 
  expressly 
  stating 
  the 
  fact, 
  Darwin 
  recognised 
  that 
  

   domesticated 
  races 
  that 
  have 
  been 
  brought 
  about 
  first 
  of 
  all 
  by 
  selection 
  

   -of 
  casual 
  similar 
  aberrations, 
  and 
  weeding 
  out 
  from 
  the 
  progeny 
  all 
  

   but 
  those 
  possessing 
  the 
  superficial 
  characters 
  desired, 
  without 
  bring- 
  

   ing 
  into 
  play 
  any 
  selection 
  of 
  characters 
  essentially 
  functional, 
  are 
  

   distinctly 
  different 
  from 
  those 
  races 
  that 
  have 
  been 
  selected 
  by 
  nature, 
  

   not 
  only 
  as 
  presenting 
  some 
  superficial 
  external 
  character, 
  such 
  as 
  colour, 
  

   etc., 
  that 
  fits 
  each 
  one 
  better 
  for 
  its 
  environment, 
  but 
  as 
  also 
  having 
  

   undergone 
  some 
  functional 
  modification 
  with 
  regard 
  to 
  some 
  detailed 
  

   .specialisation, 
  e.g., 
  to 
  some 
  particular 
  foodplant, 
  which 
  has 
  separated 
  

   it 
  to 
  some 
  small 
  extent 
  functionally 
  as 
  well 
  as 
  superficially 
  from 
  the 
  

   parent 
  race. 
  

  

  The 
  broad 
  statement 
  that 
  we 
  have 
  made, 
  that 
  the 
  results 
  of 
  crossing 
  

   a 
  quite 
  sporadic 
  aberration 
  with 
  an 
  example 
  of 
  typical 
  form 
  may 
  

   possess 
  little 
  scientific 
  value, 
  appears 
  to 
  be 
  well 
  substantiated 
  by 
  the 
  

   -experiments 
  noted 
  later 
  with 
  Mimas 
  tiliae 
  and 
  its 
  obsoletely-banded 
  

   aberration 
  (Standfuss), 
  Abraxas 
  ulmata 
  and 
  its 
  ab. 
  sufusa 
  (Biding), 
  etc., 
  

  

  