﻿Explanation 
  of 
  Plate 
  IV. 
  

  

  Fig. 
  1. 
  A 
  Tortoiseshell 
  butterfly 
  as 
  it 
  might 
  be 
  supposed 
  to 
  

   appear 
  to 
  another 
  of 
  the 
  same 
  species, 
  at 
  a 
  distance 
  

   of 
  twelve 
  inches, 
  on 
  the 
  assumption 
  that 
  each 
  facet 
  

   unit 
  gives 
  a 
  definite 
  but 
  inverted 
  image. 
  

   2. 
  Pliotograi^h, 
  taken 
  with 
  a 
  12 
  mm. 
  objective, 
  of 
  the 
  erect 
  

   image 
  in 
  the 
  eye 
  of 
  a 
  glow-worm, 
  Lmnjryris 
  noctiluca. 
  

   The 
  eye 
  was 
  mounted 
  on 
  a 
  cover 
  slip 
  with 
  a 
  drop 
  of 
  

   dilute 
  glj^cerine 
  and 
  a 
  transparency 
  of 
  the 
  portrait 
  

   placed 
  attout 
  two 
  inches 
  in 
  front 
  of 
  it. 
  The 
  actual 
  

   area 
  of 
  the 
  image 
  is 
  about 
  "15 
  sq. 
  mm. 
  The 
  definition 
  

   is 
  not 
  nearly 
  so 
  good 
  as 
  when 
  the 
  image 
  is 
  viewed 
  in 
  

   the 
  microscope 
  by 
  the 
  human 
  e,ye. 
  Also 
  it 
  has 
  lost 
  

   much 
  in 
  reproduction. 
  

  

  