﻿386 
  Dr. 
  F. 
  A. 
  Dixey 
  on 
  

  

  surface 
  is 
  above, 
  the 
  condition 
  is 
  of 
  course 
  reversed, 
  and 
  

   the 
  accessory 
  disc 
  is 
  seen 
  through 
  the 
  superposed 
  lamina. 
  

   In 
  either 
  case, 
  the 
  termination 
  of 
  the 
  footstalk 
  in 
  the 
  disc 
  

   is 
  quite 
  abrupt, 
  and 
  is 
  in 
  apparent 
  connection 
  with 
  a 
  

   pecuhar 
  area 
  of 
  the 
  disc, 
  oval 
  in 
  outline 
  and 
  surrounded 
  

   by 
  a 
  chitinous 
  ring 
  which 
  seems 
  to 
  be 
  beaded. 
  This, 
  as 
  

   will 
  be 
  seen 
  later, 
  is 
  probably 
  an 
  aperture. 
  The 
  distal 
  

   end 
  of 
  the 
  footstalk, 
  at 
  its 
  junction 
  with 
  the 
  lamina, 
  is 
  

   laterally 
  expanded, 
  becoming 
  trumpet-shaped 
  in 
  outUne. 
  

   A 
  longitudinal 
  section 
  shows 
  that 
  the 
  lamina, 
  footstalk 
  

   and 
  disc 
  form 
  an 
  S-shaped 
  curve 
  ; 
  the 
  footstalk 
  being 
  

   directed 
  upwards 
  from 
  its 
  origin 
  in 
  the 
  disc, 
  bending 
  

   sharply 
  over 
  the 
  upper 
  margin 
  of 
  the 
  disc, 
  and 
  then 
  turn- 
  

   ing 
  downwards 
  to 
  reach 
  the 
  point 
  where 
  it 
  passes 
  into 
  the 
  

   lamina 
  (PI. 
  XVI, 
  fig. 
  1, 
  c; 
  fig. 
  4, 
  e, 
  a, 
  b). 
  Here 
  again 
  

   there 
  is 
  a 
  sharp 
  bend 
  (fig. 
  4, 
  h), 
  the 
  lamina 
  itself 
  being 
  

   parallel 
  with 
  this 
  distal 
  portion 
  of 
  the 
  footstalk. 
  

  

  Some 
  of 
  the 
  appearances 
  presented 
  by 
  lamina, 
  footstalk 
  

   and 
  disc 
  are 
  not 
  easily 
  interpreted 
  ; 
  I 
  think, 
  however, 
  

   that 
  there 
  is 
  little 
  doubt 
  that 
  the 
  footstalk 
  really 
  arises 
  

   from 
  that 
  surface 
  of 
  the 
  disc 
  which 
  lies 
  next 
  to 
  the 
  wing 
  

   membrane 
  ; 
  that 
  surface, 
  consequently, 
  which 
  in 
  the 
  

   normal 
  position 
  of 
  the 
  parts 
  is 
  furthest 
  from 
  the 
  lamina. 
  

   What 
  the 
  relation 
  may 
  be 
  between 
  the 
  origin 
  of 
  the 
  foot- 
  

   stalk 
  and 
  the 
  chitinous 
  oval 
  ring 
  mentioned 
  above 
  is 
  

   doubtful; 
  I 
  am 
  strongly 
  inchned, 
  however, 
  to 
  think 
  that 
  

   while 
  the 
  footstalk 
  arises 
  from 
  what 
  may 
  be 
  called 
  the 
  

   ventral 
  surface 
  of 
  the 
  disc, 
  i. 
  e. 
  the 
  surface 
  which 
  lies 
  next 
  

   to 
  the 
  wing-membrane, 
  the 
  chitinous 
  ring 
  bounds 
  an 
  

   aperture 
  belonging 
  to 
  the 
  other, 
  or 
  dorsal 
  surface. 
  In 
  

   Ganoris 
  rapae 
  Linn., 
  the 
  footstalk 
  has 
  a 
  marginal 
  origin 
  

   from 
  the 
  disc 
  ; 
  and 
  a 
  notch 
  or 
  aperture 
  is 
  visible, 
  indenting 
  

   the 
  margin 
  at 
  a 
  point 
  opposite 
  to 
  the 
  origin 
  of 
  the 
  foot- 
  

   stalk.* 
  If 
  the 
  disc 
  of 
  P. 
  liliana 
  really 
  possesses 
  an 
  aper- 
  

   ture 
  homologous 
  with 
  the 
  aperture 
  or 
  notch 
  in 
  G. 
  rapae, 
  

   we 
  must 
  suppose 
  that 
  the 
  disc 
  in 
  the 
  former 
  case 
  is 
  flattened 
  

   at 
  right 
  angles 
  to 
  the 
  plane 
  of 
  the 
  disc 
  in 
  the 
  latter. 
  With 
  

   respect 
  to 
  the 
  interpretation 
  of 
  these 
  appearances, 
  it 
  may 
  

   further 
  be 
  noted 
  that 
  in 
  many 
  Pierine 
  genera, 
  e. 
  g. 
  Nephe- 
  

   ronia, 
  Pieris 
  and 
  Appias, 
  the 
  accessory 
  disc 
  can 
  frequently 
  

   be 
  seen 
  to 
  carry 
  an 
  indentation 
  similar 
  to 
  that 
  in 
  G. 
  rapae, 
  

   and 
  like 
  that 
  feature, 
  suggesting 
  a 
  proximal 
  aperture. 
  

  

  * 
  See 
  Proc. 
  Ent. 
  Soc. 
  Lond., 
  1909, 
  PI. 
  D, 
  fig. 
  4. 
  

  

  