﻿8 
  Dr. 
  H. 
  Eltringham 
  on 
  Butterfly 
  Vision. 
  

  

  long 
  and 
  proj&tless 
  reading. 
  Thousands 
  of 
  preparations 
  

   have 
  been 
  made, 
  and 
  various 
  processes 
  which 
  seemed 
  

   to 
  be 
  indicated 
  have 
  been 
  tried 
  in 
  vain, 
  and 
  I 
  am 
  forced 
  

   to 
  the 
  conclusion 
  that 
  the 
  nerve 
  does 
  not 
  continue 
  as 
  

   fibrils 
  into 
  the 
  body 
  of 
  the 
  ommatidium, 
  but 
  that 
  the 
  

   retinulae 
  are 
  themselves 
  merely 
  large 
  elongated 
  nerve- 
  

   end 
  cells. 
  Workers 
  on 
  the 
  Crustacea 
  claim 
  in 
  certain 
  

   cases 
  to 
  have 
  observed 
  nerve 
  fibrils 
  passing 
  from 
  the 
  

   retinulae 
  horizontally 
  into 
  the 
  rhabdom. 
  So 
  far 
  as 
  my 
  

   researches 
  go 
  no 
  such 
  structure 
  can 
  be 
  seen 
  in 
  the 
  eyes 
  of 
  

   butterflies, 
  nor 
  in 
  those 
  of 
  many 
  other 
  insects 
  which 
  I 
  have 
  

   examined. 
  It 
  will 
  be 
  seen 
  later 
  that 
  certain 
  other 
  workers 
  

   claim 
  to 
  have 
  seen 
  nerve 
  fibres 
  in 
  various 
  positions, 
  such 
  as 
  

   the 
  rhabdom 
  and 
  in 
  and 
  around 
  the 
  cones. 
  I 
  have 
  repeated 
  

   their 
  methods 
  and 
  experimented 
  with 
  many 
  others, 
  but 
  

   I 
  have 
  never 
  succeeded 
  in 
  tracing 
  the 
  nerves 
  as 
  recognisable 
  

   fibres 
  further 
  than 
  a 
  short 
  distance 
  beyond 
  the 
  basal 
  

   membrane. 
  That 
  they 
  do 
  undoubtedly 
  pass 
  through 
  that 
  

   membrane 
  there 
  is 
  no 
  question 
  whatever, 
  and 
  this 
  fact 
  

   should 
  be 
  remembered 
  in 
  connection 
  with 
  Lowne's 
  theory 
  

   to 
  be 
  mentioned 
  later. 
  

  

  Some 
  time 
  after 
  I 
  had 
  arrived 
  at 
  these 
  conclusions 
  in 
  

   regard 
  to 
  the 
  nature 
  of 
  the 
  retinulae 
  they 
  received 
  apparent 
  

   confirmation 
  by 
  the 
  work 
  of 
  Domingo 
  Sanchez 
  on 
  the 
  

   development 
  of 
  the 
  retinal 
  elements 
  in 
  G. 
  brassicae 
  (Trab. 
  

   del 
  Lab. 
  de 
  Investig. 
  Biol, 
  de 
  Madrid, 
  1916-17). 
  

  

  My 
  attention 
  was 
  called 
  to 
  this 
  work 
  by 
  my 
  friend 
  Mr. 
  

   J. 
  Bronte 
  Gatenby 
  of 
  the 
  Department 
  of 
  Physiology 
  at 
  

   Oxford. 
  Sanchez 
  worked 
  on 
  the 
  pupa 
  of 
  G. 
  brassicae 
  and 
  

   succeeded, 
  apparently 
  by 
  Cajal's 
  modification 
  of 
  Golgi's 
  

   silver 
  chromate 
  impregnation, 
  in 
  demonstrating 
  the 
  purely 
  

   nervous 
  nature 
  of 
  the 
  retinulae 
  cells. 
  The 
  process 
  is 
  very 
  

   capricious 
  in 
  its 
  action, 
  and 
  though 
  I 
  had 
  already 
  tried 
  it 
  

   without 
  result, 
  I 
  made 
  still 
  further 
  efforts, 
  and 
  after 
  a 
  time 
  

   succeeded 
  in 
  obtaining 
  a 
  differentiation 
  of 
  the 
  retinulae 
  cells 
  

   indicating 
  their 
  nervous 
  nature. 
  

  

  The 
  optical 
  and 
  primarily 
  receptive 
  layers 
  are 
  evidently 
  

   to 
  be 
  sought 
  between 
  the 
  basal 
  membrane 
  and 
  the 
  corneal 
  

   layer, 
  and 
  having 
  noted 
  the 
  general 
  structure 
  of 
  the 
  eye, 
  

   we 
  may 
  now 
  proceed 
  shortly 
  to 
  review 
  some 
  of 
  the 
  theories 
  

   which 
  have 
  been 
  advanced 
  in 
  regard 
  to 
  the 
  method 
  and 
  

   quahty 
  of 
  vision 
  of 
  which 
  such 
  an 
  eye 
  may 
  be 
  deemed 
  

   capable. 
  

  

  The 
  theory 
  which 
  is 
  at 
  the 
  same 
  time 
  the 
  oldest 
  and 
  

  

  