﻿10 
  Dr. 
  H. 
  Eltringham 
  on 
  Butterfly 
  Vision. 
  

  

  within 
  the 
  facet's 
  field 
  of 
  view. 
  Hence 
  an 
  erect 
  image 
  will 
  

   be 
  formed 
  made 
  up 
  of 
  such 
  spots 
  of 
  light 
  in 
  the 
  form 
  of 
  a 
  

   mosaic. 
  Miiller 
  was 
  of 
  course 
  mistaken 
  in 
  stating 
  that 
  the 
  

   facets 
  could 
  not 
  form 
  an 
  image. 
  

  

  The 
  first 
  to 
  throw 
  doubt 
  on 
  Muller's 
  theory 
  was 
  R. 
  Wag- 
  

   ner 
  (Archiv. 
  f. 
  Naturgesch. 
  p. 
  372, 
  1835), 
  who 
  considered 
  

   the 
  sheath 
  of 
  the 
  cone 
  as 
  the 
  true 
  nerve 
  expansion. 
  Will 
  

   (Leipzig, 
  1840) 
  regarded 
  the 
  compound 
  eye 
  as 
  an 
  aggregate 
  

   of 
  simple 
  eyes. 
  Gottsche 
  (Beit, 
  sur 
  Anat. 
  u. 
  Physiolog., 
  

   etc., 
  Muller's 
  Archiv. 
  p. 
  483-92, 
  1852) 
  reobserved 
  the 
  images 
  

   formed 
  by 
  the 
  facets 
  of 
  an 
  insect's 
  eye 
  with 
  the 
  inside 
  

   removed, 
  and 
  calculated 
  the 
  focal 
  distance 
  of 
  the 
  image. 
  

   He 
  considered 
  that 
  his 
  work 
  disproved 
  Miiller's 
  theory, 
  

   and 
  certainly 
  it 
  was 
  the 
  cause 
  of 
  its 
  temporary 
  displace- 
  

   ment. 
  Leydig 
  in 
  various 
  papers 
  expressed 
  the 
  view 
  that 
  

   the 
  cones 
  were 
  the 
  nervous 
  elements, 
  forming 
  with 
  their 
  

   thread-hke 
  continuations 
  a 
  perceptive 
  element 
  comparable 
  

   with 
  the 
  retina 
  of 
  vertebrates. 
  He 
  thought 
  all 
  the 
  small 
  

   images 
  were 
  in 
  some 
  way 
  conveyed 
  to 
  the 
  brain 
  and 
  com- 
  

   bined 
  into 
  one 
  large 
  picture. 
  Claparede 
  (Zur 
  Morph. 
  

   der 
  Zusamm. 
  Augen, 
  etc., 
  Zeit. 
  Wiss. 
  Zool. 
  p. 
  191, 
  1859) 
  

   points 
  out 
  that 
  Miiller's 
  theory 
  makes 
  the 
  definition 
  of 
  

   the 
  object 
  dependant 
  on 
  the 
  number 
  of 
  the 
  facets 
  and 
  

   states 
  that 
  bees 
  can 
  see 
  the 
  hive 
  entrance 
  at 
  great 
  distances. 
  

   It 
  hardly 
  requires 
  Grenacher's 
  refutation 
  to 
  remind 
  us 
  

   that 
  there 
  is 
  no 
  proof 
  that 
  bees 
  can 
  see 
  the 
  hive 
  any 
  more 
  

   than 
  that 
  carrier 
  pigeons 
  can 
  see 
  their 
  pigeon 
  -house, 
  and 
  

   indeed 
  we 
  know 
  from 
  many 
  experiments 
  that 
  bees 
  do 
  not 
  

   return 
  to 
  the 
  hive 
  door 
  by 
  sight, 
  since 
  they 
  will 
  return 
  

   infalhbly 
  to 
  the 
  place 
  where 
  the 
  door 
  was 
  if 
  the 
  hive 
  be 
  

   turned 
  round. 
  Claparede 
  suggests 
  that 
  each 
  facet 
  sees 
  a 
  

   definite 
  image 
  and 
  the 
  view 
  is 
  made 
  up 
  of 
  the 
  sum 
  of 
  these 
  

   images, 
  the 
  physiological 
  difficulty 
  of 
  multiple 
  inverted 
  

   images 
  being 
  in 
  his 
  opinion 
  no 
  greater 
  than 
  in 
  the 
  case 
  of 
  

   several 
  simple 
  eyes. 
  He 
  regarded 
  the 
  cone 
  as 
  an 
  optical 
  

   and 
  percipient 
  element 
  combined. 
  

  

  Ruete 
  (1861) 
  thought 
  that 
  not 
  only 
  the 
  axial 
  rays 
  

   affected 
  the 
  nerve 
  elements 
  but 
  many 
  rays 
  affected 
  many 
  

   neighbouring 
  elements. 
  Here 
  we 
  seem 
  to 
  have 
  an 
  antici- 
  

   pation 
  of 
  Exner's 
  "superposition 
  image." 
  Dor 
  (1861), 
  

   examining 
  the 
  subject 
  from 
  an 
  optical 
  point 
  of 
  view, 
  made 
  

   out 
  that 
  the 
  image 
  was 
  formed 
  at 
  the 
  hinder 
  end 
  of 
  the 
  

   cone 
  and 
  condemned 
  Leydig's 
  theory 
  of 
  the 
  nervous 
  

   constitution 
  of 
  that 
  body. 
  He 
  regarded 
  the 
  cone 
  sheath 
  

  

  