﻿6 
  Dr. 
  H. 
  Eltringham 
  on 
  Butterfiy 
  Vision. 
  

  

  in 
  the 
  eye 
  several 
  series 
  of 
  cells 
  containing 
  pigment 
  

   granules. 
  Their 
  precise 
  number 
  and 
  arrangement 
  varies 
  

   greatly 
  in 
  different 
  eyes. 
  In 
  F. 
  vrticae 
  there 
  are 
  two 
  very 
  

   conspicuous 
  cells 
  occupying 
  the 
  space 
  between 
  the 
  apex 
  

   of 
  the 
  cone 
  and 
  the 
  outer 
  ends 
  of 
  the 
  retinulae 
  ; 
  they 
  form 
  

   a 
  dense 
  black 
  collar 
  round 
  the 
  cone 
  apex 
  and 
  the 
  distal 
  

   end 
  of 
  the 
  rhabdom. 
  Between 
  the 
  cones 
  there 
  are 
  series 
  of 
  

   secondary 
  pigment 
  cells 
  which 
  extend 
  processes 
  towards 
  the 
  

   basal 
  membrane, 
  these 
  meeting 
  similar 
  processes 
  from 
  

   pigment 
  cells 
  attached 
  to, 
  or 
  extending 
  from, 
  the 
  basal 
  

   membrane. 
  There 
  are 
  also 
  pigment 
  granules 
  in 
  the 
  

   retinulae 
  cells, 
  and 
  in 
  or 
  around 
  the 
  nerves 
  and 
  nerve 
  cells 
  

   beneath 
  the 
  basal 
  membrane. 
  

  

  It 
  has 
  already 
  been 
  stated 
  that 
  the 
  retinulae 
  cells 
  extend 
  

   backwards 
  to 
  the 
  basal 
  membrane. 
  The 
  latter 
  is 
  perforated, 
  

   and 
  through 
  the 
  openings 
  there 
  pass 
  eight 
  nerve 
  fibres, 
  one 
  

   to 
  each 
  retinula 
  (PI. 
  II, 
  fig. 
  1, 
  n.). 
  Below 
  the 
  basal 
  mem- 
  

   brane 
  these 
  nerve 
  fibres 
  (PI. 
  II. 
  fig. 
  4, 
  n.) 
  are 
  arranged 
  more 
  

   or 
  less 
  symmetrically 
  round 
  a 
  large 
  nucleated 
  cell 
  through 
  

   the 
  centre 
  of 
  which 
  passes 
  a 
  small 
  tracheal 
  tube 
  (PI. 
  II, 
  fig. 
  

   4, 
  t.). 
  Passing 
  backwards 
  into 
  the 
  head, 
  these 
  nerve 
  fibres 
  

   are 
  seen 
  to 
  occur 
  in 
  bundles, 
  each 
  bundle 
  containing 
  fibres 
  

   appertaining 
  to 
  more 
  than 
  one 
  set 
  of 
  retinulae. 
  The 
  bundles 
  

   are 
  separated 
  by 
  what 
  appear 
  to 
  be 
  large 
  spaces. 
  These 
  

   are 
  the 
  lumina 
  of 
  a 
  tracheal 
  network 
  lying 
  horizontally 
  in 
  

   this 
  part 
  of 
  the 
  eye. 
  Below 
  this 
  layer 
  are 
  several 
  well- 
  

   marked 
  strata 
  of 
  nerve 
  tissue, 
  notably 
  three 
  ganglionic 
  

   bodies 
  named 
  by 
  Hickson 
  (Quart. 
  Jour. 
  Micr. 
  Sci. 
  p. 
  215, 
  

   etc., 
  1885), 
  counting 
  from 
  within 
  outwards, 
  the 
  " 
  opticon," 
  

   the 
  " 
  epi-opticon," 
  and 
  the 
  " 
  peri-opticon." 
  In 
  the 
  peri- 
  

   opticon 
  the 
  individuality 
  of 
  the 
  ommatidia 
  seems 
  to 
  be 
  

   preserved, 
  since 
  transverse 
  sections 
  show 
  a 
  more 
  or 
  less 
  

   regular 
  geometrical 
  arrangement. 
  (See 
  PI. 
  II, 
  fig. 
  3). 
  One 
  

   might 
  fancifully 
  compare 
  it 
  with 
  a 
  telephone 
  switch-board 
  

   in 
  which 
  all 
  wires 
  or 
  nerves 
  arrive 
  at 
  their 
  proper 
  sockets, 
  

   though 
  traversing 
  the 
  intervening 
  space, 
  the 
  tracheal 
  area, 
  

   in 
  apparently 
  haphazard 
  bundles. 
  

  

  Beyond 
  this 
  area 
  I 
  have 
  not 
  so 
  far 
  attempted 
  to 
  trace 
  

   the 
  course 
  of 
  the 
  fibres, 
  since 
  in 
  the 
  depths 
  of 
  the 
  brain 
  or 
  

   gangha 
  the 
  phenomena 
  of 
  sense 
  transmission 
  and 
  percep- 
  

   tion 
  constitute 
  more 
  of 
  a 
  psychological 
  than 
  a 
  physiological 
  

   problem, 
  and 
  a 
  study 
  of 
  the 
  inner 
  ganglia 
  is 
  not 
  calculated 
  

   to 
  throw 
  much 
  light 
  on 
  the 
  visual 
  capacity 
  of 
  the 
  insect. 
  

  

  I 
  have 
  already 
  spoken 
  of 
  a 
  highly 
  refractive 
  body 
  lying 
  

  

  