﻿HYBRIDISATION 
  IN 
  LEPIDOPTERA. 
  

  

  of 
  two 
  species 
  {Tephrosia 
  crepuscidaria 
  and 
  T. 
  bistortata) 
  might 
  result 
  in 
  

   every 
  possible 
  intermediate 
  stage 
  of 
  fertility, 
  from 
  complete 
  sterility 
  to 
  

   the 
  production 
  of 
  the 
  full 
  number 
  of 
  fertilised 
  eggs. 
  These 
  extreme 
  

   results 
  may 
  even 
  happen 
  when 
  dealing 
  with 
  different 
  individuals 
  of 
  

   the 
  same 
  brood. 
  Failure, 
  therefore, 
  in 
  a 
  few 
  individual 
  cases 
  must 
  

   not 
  be 
  taken 
  as 
  proving 
  that 
  any 
  particular 
  cross 
  is 
  infertile, 
  and 
  it 
  

   is, 
  at 
  any 
  rate, 
  clear 
  from 
  this, 
  that 
  many 
  trials 
  are 
  necessary 
  

   before 
  it 
  can 
  be 
  assumed 
  that 
  any 
  cross 
  is 
  positively 
  infertile. 
  Standfuss 
  

   found 
  the 
  usual 
  range 
  of 
  fertility 
  in 
  Malacosowa 
  neustria 
  x 
  franconica 
  

   to 
  extend 
  from 
  to 
  50 
  per 
  cent, 
  of 
  the 
  eggs, 
  but 
  the 
  most 
  successful 
  

   pairing 
  produced 
  90 
  per 
  cent. 
  He 
  believes 
  that 
  absolute 
  impossibility 
  

   to 
  obtain 
  fertile 
  eggs 
  only 
  occurs 
  when 
  the 
  pairing 
  is 
  between 
  sexes 
  

   belonging 
  to 
  widely 
  different 
  genera, 
  e.g., 
  Smerinthus 
  and 
  Sphinx, 
  

   Syntomis* 
  and 
  Zyyaena 
  (Anthrocera), 
  Dimorpha 
  (Endromis) 
  and 
  Afjlia, 
  

   Af/lia 
  and 
  Saturnia. 
  In 
  such 
  cases 
  he 
  considers 
  failure 
  to 
  be 
  

   inevitable. 
  

  

  Failure 
  to 
  obtain 
  fertile 
  eggs 
  by 
  crossing 
  two 
  species 
  really 
  may 
  

   occur 
  between 
  very 
  closely 
  allied 
  species, 
  if 
  they 
  have 
  specialised 
  greatly 
  

   away 
  from 
  each 
  other 
  in 
  some 
  particular 
  character, 
  and 
  the 
  reason 
  for 
  

   failure 
  may 
  be 
  very 
  different 
  in 
  different 
  cases. 
  That 
  species 
  of 
  

   comparatively 
  distant 
  affinities 
  may 
  produce 
  fertile 
  ova 
  is 
  proved, 
  as 
  

   we 
  have 
  already 
  pointed 
  out, 
  by 
  Standfuss' 
  results 
  with 
  Saturnia 
  

   pavonia 
  $ 
  and 
  Graellsia 
  isabellae 
  $ 
  , 
  from 
  which 
  crossing 
  he 
  reared 
  

   larvFe 
  to 
  the 
  second 
  moult. 
  Some 
  of 
  the 
  reasons 
  for 
  failure 
  that 
  occur 
  

   to 
  us 
  are 
  : 
  (1) 
  Unsuitability 
  of 
  the 
  genital 
  organs 
  to 
  allow 
  effective 
  

   pairing. 
  (2) 
  The 
  failure 
  of 
  the 
  spermatozoa 
  to 
  be 
  deposited 
  in 
  the 
  

   receptacula 
  seminis. 
  (3) 
  The 
  inability 
  of 
  the 
  spermatozoa 
  to 
  enter 
  

   the 
  micropyle 
  of 
  the 
  egg. 
  (4) 
  The 
  unsuitability 
  of 
  the 
  protoplasmic 
  

   elements 
  (spermatozoa 
  and 
  germ) 
  to 
  combine 
  to 
  form 
  an 
  embryo. 
  

   (5) 
  The 
  inability 
  of 
  the 
  embryonic 
  structures 
  to 
  blend, 
  owing 
  to 
  the 
  

   great 
  difference 
  in 
  the 
  structures. 
  (6) 
  A 
  want 
  of 
  synchronism 
  in 
  the 
  

   sequence 
  of 
  time 
  at 
  which 
  the 
  various 
  embryonic 
  changes 
  in 
  develop- 
  

   ment 
  occur. 
  Or, 
  as 
  Standfuss 
  summarises 
  the 
  reasons 
  of 
  failure, 
  they 
  

   must 
  be 
  sought 
  in 
  (1) 
  External 
  morphological 
  or 
  anatomical 
  con- 
  

   ditions, 
  (2) 
  Microscopic 
  histological 
  structure, 
  (3) 
  Molecular 
  

   differences. 
  

  

  When 
  the 
  greater 
  part 
  of 
  a 
  batch 
  of 
  eggs 
  is 
  fertilised 
  by 
  the 
  

   spermatozoa 
  of 
  another 
  species, 
  and 
  the 
  eggs 
  undergo 
  a 
  certain 
  amount 
  

   of 
  development, 
  it 
  follows 
  that 
  the 
  failure 
  to 
  produce 
  a 
  living 
  larva 
  does 
  

   not 
  lie 
  in 
  the 
  functional 
  inability 
  of 
  the 
  spermatozoa, 
  but 
  to 
  some 
  one 
  

   or 
  other 
  of 
  the 
  other 
  causes 
  noted. 
  In 
  some 
  cases, 
  the 
  embryonic 
  

   development 
  ceases 
  in 
  the 
  early 
  stages 
  of 
  growth, 
  in 
  others, 
  it 
  goes 
  on 
  

   and 
  the 
  embryo 
  is 
  developed 
  into 
  a 
  larva, 
  and 
  yet 
  none, 
  or 
  only 
  a 
  few, 
  of 
  

   the 
  latter 
  may 
  hatch. 
  This 
  imperfect 
  development 
  appears. 
  o( 
  course, 
  

   to 
  be 
  primarily 
  due 
  to 
  the 
  fact 
  that 
  the 
  conditions 
  o( 
  the 
  egg 
  are 
  

   unsuitable 
  to 
  the 
  development 
  of 
  the 
  embryo, 
  which 
  lias 
  only 
  one-half 
  

   tlu* 
  constitution 
  and 
  nature 
  of 
  the 
  $? 
  parent 
  (that 
  laid 
  the 
  Qgg), 
  that 
  

   of 
  the 
  c? 
  parent 
  being 
  possibly 
  entirely 
  different, 
  and 
  hence 
  leading 
  to 
  

   the 
  early 
  death 
  of 
  the 
  embryo. 
  In 
  the 
  case 
  of 
  the 
  larva 
  becoming 
  

   fullyformed 
  in 
  the 
  egg, 
  failure 
  to 
  hatch 
  may 
  he 
  due 
  to 
  [\) 
  The 
  embryo 
  

  

  * 
  Syntomis 
  and 
  Anthrocera, 
  in 
  spite 
  of 
  the 
  similarity 
  of 
  wing-markings, 
  are 
  

   exceedingly 
  distant 
  from 
  one 
  another. 
  The 
  former 
  belongs 
  to 
  our 
  Noctuo-Hepialid 
  

   (" 
  upright-egged 
  ") 
  stirps, 
  the 
  latter 
  to 
  the 
  Sphingo-Mioropterygid 
  (" 
  flat 
  egged 
  '") 
  

  

  stirps. 
  

  

  