﻿48 
  Dr. 
  H. 
  Eltringham 
  on 
  Butterfly 
  Vision. 
  

  

  side 
  of 
  a 
  small 
  bush. 
  We 
  observed 
  that 
  every 
  passing 
  

   euphrosyne 
  turned 
  aside, 
  even 
  from 
  positions 
  whence 
  the 
  

   pair 
  were 
  invisible, 
  and 
  seeking 
  them 
  out, 
  mobbed 
  them 
  

   furiously. 
  Even 
  after 
  the 
  pair 
  had 
  separated 
  and 
  flown 
  

   away, 
  other 
  passing 
  individuals 
  turned 
  aside 
  and 
  fluttered 
  

   round 
  the 
  place. 
  I 
  have 
  seen 
  similar 
  occurrences 
  in 
  con- 
  

   nection 
  with 
  C. 
  pamphilus, 
  and 
  I 
  have 
  recorded 
  an 
  example 
  

   observed 
  by 
  Lamborn 
  in 
  a 
  species 
  of 
  Planema. 
  The 
  

   remarks 
  there 
  made 
  apply 
  to 
  the 
  present 
  cases.* 
  

  

  I 
  have 
  already 
  explained 
  my 
  inability 
  to 
  continue 
  these 
  

   experiments 
  during 
  the 
  past 
  autumn. 
  I 
  hope 
  to 
  have 
  better 
  

   fortune 
  in 
  another 
  season. 
  So 
  far, 
  the 
  chief 
  results 
  of 
  my 
  

   researches 
  may 
  be 
  briefly 
  summarised 
  as 
  follows 
  : 
  — 
  

  

  The 
  pecuhar 
  refractive 
  body 
  at 
  the 
  base 
  of 
  the 
  omma- 
  

   tidium 
  in 
  the 
  butterfly 
  eye, 
  first 
  observed 
  in 
  one 
  species 
  by 
  

   Jonas, 
  is 
  commonly 
  found 
  in 
  other 
  species, 
  and 
  is 
  a 
  special 
  

   structure 
  of 
  the 
  trachaeal 
  apparatus, 
  varying 
  in 
  detail 
  in 
  

   the 
  examples 
  of 
  different 
  famihes 
  investigated. 
  

  

  The 
  periopticon 
  in 
  the 
  butterfly 
  eye 
  seems 
  to 
  preserve 
  

   in 
  its 
  structure 
  the 
  individuality 
  and 
  relative 
  position 
  of 
  the 
  

   nerve 
  fibres 
  relating 
  to 
  each 
  facet. 
  

  

  There 
  is 
  every 
  reason 
  to 
  suppose 
  that 
  the 
  retinula 
  cells 
  are 
  

   themselves 
  the 
  nerve 
  endings 
  of 
  the 
  receptive 
  layer 
  of 
  the 
  

   butterfly 
  eye, 
  and 
  that 
  the 
  alleged 
  existence 
  of 
  nerve 
  fibres 
  

   in 
  or 
  around 
  the 
  cone, 
  or 
  in 
  the 
  rhabdom, 
  is 
  an 
  error 
  due 
  

   to 
  incorrect 
  observation. 
  This 
  view 
  is 
  strongly 
  supported 
  

   by 
  the 
  recent 
  researches 
  of 
  Sanchez 
  on 
  the 
  pupal 
  eye. 
  

  

  The 
  eucone 
  eye, 
  as 
  found 
  in 
  butterflies, 
  gives 
  at 
  the 
  apex 
  

   of 
  each 
  cone 
  a 
  small 
  erect 
  image 
  made 
  up 
  of 
  parallel 
  rays 
  

   which, 
  proceeding 
  down 
  the 
  rhabdom, 
  stimulate 
  the 
  

   retinulae. 
  The 
  whole 
  field 
  of 
  view 
  is 
  reproduced 
  in 
  a 
  mosaic 
  

   of 
  correctly 
  correlated 
  elements 
  forming 
  a 
  continuous 
  and 
  

   complete 
  whole, 
  the 
  definition 
  of 
  which, 
  owing 
  to 
  the 
  com- 
  

   parative 
  paucity 
  of 
  retinal 
  elements 
  decreases 
  rapidly 
  as 
  

   the 
  distance 
  of 
  the 
  object 
  increases, 
  though 
  at 
  short 
  distances 
  

   the 
  sight 
  is 
  comparatively 
  acute. 
  

  

  The 
  behaviour 
  of 
  butterflies 
  under 
  certain 
  observed 
  

   conditions 
  lends 
  strong 
  support 
  to 
  the 
  view 
  that 
  they 
  can 
  

   distinguish 
  those 
  differences 
  of 
  light-wave 
  frequency 
  which 
  

   we 
  call 
  colour, 
  and 
  if 
  the 
  present 
  evidence 
  to 
  that 
  effect 
  is 
  

   not 
  entirely 
  conclusive, 
  the 
  testimony 
  to 
  the 
  contrary 
  is 
  

   totally 
  inadequate. 
  

  

  * 
  See 
  "Monograph 
  of 
  the 
  genus 
  Acraea,^' 
  Trans. 
  Ent. 
  Soc, 
  

   1912, 
  p. 
  8. 
  

  

  