﻿270 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  effectively 
  such 
  animals 
  may 
  be 
  camouflaged 
  in 
  other 
  respects, 
  unless 
  the 
  eye 
  re- 
  

   ceives 
  special 
  treatment, 
  it 
  will 
  prejudice 
  the 
  success 
  of 
  the 
  whole 
  color-scheme. 
  

   It 
  is 
  therefore 
  very 
  interesting, 
  though 
  not 
  surprising, 
  to 
  find 
  that 
  nature 
  — 
  the 
  

   supreme 
  camouflage 
  artist 
  — 
  has 
  dealt 
  in 
  great 
  detail 
  with 
  this 
  problem, 
  which 
  is 
  

   evidently 
  one 
  of 
  urgent 
  importance. 
  * 
  * 
  * 
  

  

  In 
  its 
  essentials, 
  the 
  method 
  * 
  * 
  * 
  invokes 
  the 
  optical 
  principle 
  of 
  coinci- 
  

   dent 
  disruptive 
  coloration. 
  * 
  * 
  * 
  If 
  an 
  eye, 
  and 
  particularly 
  its 
  staring 
  black 
  

   pupil, 
  can 
  be 
  made 
  to 
  appear 
  another 
  shape, 
  then 
  it 
  will 
  cease 
  to 
  resemble 
  an 
  eye. 
  

   In 
  theory, 
  such 
  an 
  illusion 
  could 
  be 
  created 
  by 
  covering 
  the 
  eye, 
  or 
  its 
  pupil, 
  with 
  

   a 
  black 
  mask 
  of 
  irregular 
  shape 
  — 
  so 
  designed 
  as 
  to 
  blend 
  with 
  and 
  seem 
  part 
  of 
  

   the 
  pattern 
  which 
  surrounds 
  it. 
  Now 
  that 
  is 
  essentially 
  the 
  system 
  devised 
  in 
  

   nature. 
  * 
  * 
  * 
  Animals 
  belonging 
  to 
  many 
  widely 
  separate 
  families 
  and 
  orders 
  

   have 
  the 
  eyes 
  camouflaged 
  in 
  precise 
  detail. 
  Although 
  the 
  underlying 
  principle 
  

   is 
  everywhere 
  the 
  same, 
  the 
  incidents 
  of 
  the 
  picture 
  vary 
  widely 
  in 
  different 
  

   cases. 
  Sometimes 
  an 
  irregular 
  dark 
  disruptive 
  area 
  includes 
  the 
  whole 
  orbit. 
  

   Sometimes 
  the 
  upper 
  margin 
  of 
  an 
  elongated 
  patch 
  of 
  dark 
  pigment 
  crosses 
  the 
  

   iris 
  exactly 
  on 
  a 
  level 
  with 
  the 
  top 
  of 
  the 
  pupil. 
  Or 
  conversely 
  it 
  may 
  extend 
  

   beneath 
  to 
  the 
  pupil's 
  lower 
  limit. 
  Or 
  again 
  the 
  eye 
  may 
  be 
  crossed 
  by 
  a 
  stripe 
  

   exactly 
  the 
  width 
  of 
  the 
  pupil 
  itself. 
  In 
  other 
  cases 
  similar 
  effects 
  are 
  produced 
  

   in 
  vertical 
  bars 
  instead 
  of 
  horizontal 
  stripes 
  ; 
  or 
  in 
  diagonal 
  markings 
  or 
  irregular 
  

   shapes 
  varying 
  greatly 
  in 
  size 
  and 
  distribution. 
  The 
  one 
  consistent 
  feature 
  in 
  all 
  

   this 
  diversity 
  is 
  the 
  significant 
  relation 
  between 
  that 
  unmitigated 
  black 
  spot 
  — 
  the 
  

   pupil 
  — 
  and 
  the 
  dark 
  element 
  which 
  serves 
  to 
  absorb 
  it. 
  

  

  Given 
  an 
  animal 
  with 
  any 
  or 
  all 
  of 
  the 
  types 
  of 
  concealing 
  color 
  

   pattern 
  already 
  discussed, 
  it 
  may 
  yet 
  be 
  concealed 
  in 
  vain 
  in 
  some 
  cases, 
  

   if 
  its 
  contour 
  or 
  bounding 
  margin 
  be 
  unaffected 
  by 
  the 
  camouflage. 
  

   Actually, 
  in 
  most 
  cases 
  of 
  disruptive 
  pattern 
  the 
  outlines 
  of 
  the 
  animal 
  

   are 
  affected 
  by 
  it, 
  and 
  further 
  marginal 
  disruption 
  is 
  unnecessary, 
  but 
  

   in 
  some 
  instances 
  the 
  peripheral 
  parts 
  — 
  tail, 
  limbs, 
  head 
  and 
  neck, 
  or 
  

   even 
  the 
  lateral 
  contour 
  margin 
  are 
  disruptively 
  marked. 
  

  

  CONCEALMENT 
  OF 
  THE 
  SHADOW 
  

  

  We 
  have 
  already 
  seen, 
  in 
  the 
  case 
  of 
  the 
  white 
  ptarmigan 
  against 
  a 
  

   snowy 
  background, 
  that 
  aside 
  from 
  the 
  bird's 
  lack 
  of 
  obliterative 
  

   shading 
  and 
  its 
  consequent 
  visual 
  solidity, 
  its 
  presence 
  is 
  revealed 
  by 
  

   the 
  shadow 
  it 
  casts 
  on 
  the 
  snow 
  at 
  its 
  feet. 
  In 
  case 
  of 
  danger 
  the 
  shadow 
  

   would 
  be 
  largely 
  done 
  away 
  with, 
  as 
  the 
  bird 
  would 
  squat 
  low 
  on 
  the 
  

   snow 
  and 
  actually 
  cover 
  a 
  good 
  part 
  of 
  its 
  shadow. 
  It 
  is 
  actually 
  no 
  ex- 
  

   aggeration 
  to 
  say 
  that 
  in 
  many 
  cases 
  of 
  animals 
  with 
  a 
  color 
  pattern 
  

   more 
  or 
  less 
  concealing 
  in 
  nature, 
  the 
  shadow 
  is 
  more 
  noticeable 
  than 
  

   the 
  animal 
  casting 
  it. 
  In 
  creatures 
  of 
  laterally 
  compressed 
  form 
  such 
  

   as 
  butterflies 
  that 
  rest 
  with 
  wings 
  closely 
  over 
  the 
  back, 
  we 
  find 
  two 
  

   definitely 
  established 
  orientation 
  habits 
  which 
  appear 
  to 
  be 
  related 
  

   to 
  the 
  matter 
  of 
  shadow 
  concealment 
  or 
  reduction. 
  A 
  number 
  of 
  

   species, 
  notable 
  among 
  which 
  is 
  the 
  green 
  hairstreak 
  butterfly 
  {Thecla 
  

   rubi) 
  , 
  tilt 
  the 
  wings 
  away 
  from 
  the 
  median 
  vertical 
  plane 
  toward 
  the 
  

   shadow, 
  thereby 
  hiding 
  a 
  large 
  part 
  of 
  it. 
  The 
  degree 
  of 
  tilting 
  is 
  said 
  

   to 
  be 
  constant 
  for 
  each 
  species, 
  and 
  numerous 
  independent 
  observers 
  

  

  