﻿HYBKIDISATION 
  IN 
  LEPIDOPTERA. 
  13 
  

  

  the 
  relative 
  phylogenetic 
  age 
  of 
  the 
  two 
  species 
  ; 
  the 
  older 
  being 
  able 
  to 
  transmit 
  

   its 
  properties, 
  whether 
  of 
  structure 
  or 
  habit, 
  better 
  than 
  the 
  younger. 
  

  

  With 
  regard 
  to 
  these, 
  Standfuss 
  shows 
  that, 
  in 
  crossing 
  Satumia 
  

   pavonia 
  $ 
  with 
  8. 
  pyri 
  ? 
  , 
  the 
  resulting 
  imago 
  is 
  by 
  more 
  than 
  two- 
  

   thirds 
  of 
  its 
  external 
  appearance 
  S. 
  pavonia, 
  and 
  by 
  less 
  than 
  one-third 
  

   S. 
  pyri. 
  Its 
  habits 
  and 
  functions 
  correspond 
  with 
  its 
  external 
  aspect. 
  

   It 
  prefers 
  to 
  fly 
  by 
  day, 
  like 
  S. 
  pavonia 
  $ 
  , 
  and 
  pairs 
  easily 
  with 
  the 
  

   2 
  of 
  that 
  species, 
  from 
  48 
  to 
  62 
  per 
  cent, 
  of 
  the 
  eggs 
  being 
  fertile. 
  

   On 
  the 
  other 
  hand, 
  it 
  does 
  not 
  pair 
  readily 
  with 
  S. 
  pyri, 
  and 
  the 
  

   resulting 
  eggs, 
  in 
  an 
  average 
  of 
  nine 
  cases, 
  gave 
  only 
  one 
  larva 
  out 
  of 
  

   180. 
  Similarly, 
  S. 
  pavonia 
  $ 
  , 
  when 
  paired 
  with 
  8. 
  spini 
  2 
  , 
  gives 
  a 
  

   form 
  of 
  which, 
  in 
  the 
  perfect 
  state, 
  about 
  two-thirds 
  of 
  the 
  external 
  

   aspect 
  belong 
  to 
  the 
  type 
  of 
  S. 
  spini. 
  The 
  $ 
  flies 
  by 
  night. 
  After 
  

   crossing 
  with 
  8. 
  pavonia 
  2 
  the 
  resulting 
  eggs 
  were 
  only 
  fertile 
  to 
  the 
  

   extent 
  of 
  16 
  to 
  22 
  per 
  cent., 
  while 
  the 
  crossing 
  with 
  8. 
  spini 
  2 
  , 
  

   though 
  not 
  easily 
  brought 
  about, 
  in 
  consequence 
  of 
  their 
  diverse 
  times 
  

   of 
  appearance, 
  yielded 
  eggs 
  of 
  which 
  from 
  94 
  to 
  98 
  per 
  cent, 
  were 
  fertile. 
  

   So 
  that 
  the 
  $ 
  8. 
  pavonia 
  (considered 
  the 
  middle 
  species 
  phylogeneti- 
  

   cally) 
  is 
  able 
  to 
  influence 
  the 
  issue 
  of 
  the 
  relatively 
  gigantic 
  S. 
  pyri 
  

   2 
  (considered 
  the 
  youngest 
  phylogenetically) 
  much 
  more 
  than 
  it 
  can 
  that 
  

   of 
  5. 
  spini 
  2 
  (considered 
  the 
  oldest 
  phylogenetically). 
  Again 
  the 
  issue 
  

   of 
  S. 
  spini 
  $ 
  x 
  S. 
  pavonia 
  2 
  is 
  much 
  nearer 
  S. 
  spini 
  than 
  is 
  that 
  of 
  

   S. 
  pavonia 
  $ 
  x 
  S. 
  spini 
  2 
  , 
  which 
  shows 
  that 
  the 
  older-established 
  species 
  

   (spini) 
  is 
  more 
  effective 
  than 
  the 
  younger 
  (pavonia), 
  and 
  the 
  sexual 
  

   prepotency 
  of 
  the 
  $ 
  8. 
  pavonia 
  counts 
  far 
  less 
  than 
  the 
  specific 
  pre- 
  

   potency 
  of 
  the 
  2 
  S. 
  spini. 
  The 
  greatest 
  effect 
  is 
  produced 
  when 
  the 
  

   two 
  influences 
  concur, 
  as 
  in 
  the 
  hybrid 
  S. 
  spini 
  $ 
  x 
  8. 
  pavonia 
  2 
  , 
  

   the 
  male 
  parent 
  being 
  also 
  the 
  oldest 
  phylogenetically. 
  This 
  rule 
  as 
  

   to 
  the 
  prepotency 
  of 
  the 
  phylogenetically 
  older 
  species 
  is, 
  as 
  Dixey 
  

   says, 
  probably 
  only 
  another 
  expression 
  of 
  the 
  fact 
  so 
  clearly 
  established 
  

   by 
  Darwin 
  (Animals 
  and 
  Plants 
  under 
  Domestication, 
  1868, 
  ii., 
  p. 
  254) 
  

   that 
  hybridisation 
  frequently 
  leads 
  to 
  reversion. 
  It 
  is 
  significant 
  that 
  

   Standfuss 
  considers 
  the 
  hybrid 
  form 
  8. 
  hybr. 
  emiliae 
  (pavonia 
  x 
  pyri) 
  

   as 
  partly 
  reproducing 
  an 
  ancestral 
  stage 
  in 
  the 
  history 
  of 
  S. 
  pavonia 
  

   rather 
  than 
  the 
  form 
  of 
  that 
  species 
  now 
  existing. 
  Kaye 
  also 
  observes 
  

   (Proc. 
  8th. 
  Land. 
  Ent. 
  Soc, 
  1902, 
  p. 
  117) 
  that, 
  in 
  Amorpha 
  hybr. 
  metis 
  

   and 
  Smerinthus 
  hybr. 
  hybridus, 
  the 
  prepotency 
  of 
  the 
  $ 
  was 
  noticeable. 
  

   Detailed 
  observation 
  on 
  a 
  larger 
  number 
  of 
  specimens 
  is, 
  however, 
  

   desirable. 
  

  

  Some 
  of 
  the 
  Tephrosiid 
  hybrids 
  (Trans. 
  E?it. 
  Soc. 
  Pond., 
  1898, 
  pp. 
  

   17 
  ct 
  seq.) 
  did 
  not 
  altogether 
  appear 
  to 
  bear 
  out 
  the 
  first 
  of 
  these 
  

   rules, 
  but 
  this 
  may 
  have 
  possibly 
  been 
  due 
  to 
  the 
  disturbing 
  

   influence 
  of 
  using 
  an 
  aberrative 
  form 
  (delamerensis) 
  instead 
  of 
  

   the 
  more 
  stable 
  typical 
  form 
  of 
  crepusculavia 
  (biundularia). 
  On 
  

   the 
  other 
  hand, 
  those 
  reciprocal 
  broods, 
  in 
  which 
  this 
  disturbing 
  

   influence 
  was 
  eliminated, 
  viz., 
  '/'. 
  bistortata 
  x 
  crepuscularia 
  and 
  7'. 
  

   crepusculavia 
  xhistovtata 
  showed 
  distinctly 
  in 
  the 
  first 
  cross 
  a 
  great 
  

   tendency 
  to 
  the 
  bistortata 
  form. 
  ami. 
  in 
  the 
  second, 
  a 
  less 
  distinct 
  

   tendency 
  in 
  the 
  same 
  direction, 
  thus 
  bearing 
  out 
  Standfuss' 
  further 
  

   suggestion 
  that 
  bistortata, 
  assumed 
  on 
  various 
  grounds 
  to 
  be 
  the 
  

   phylogenetically 
  older 
  spries, 
  is 
  more 
  dominant 
  in 
  stamping 
  its 
  

   characters 
  on 
  thv 
  progeny. 
  It 
  may 
  be, 
  oi 
  course, 
  that 
  /'. 
  bist<>rtt;; 
  

   merely 
  a, 
  predominant 
  species, 
  mow 
  active 
  in 
  its 
  vital 
  functions, 
  and 
  

  

  