﻿CAMOUFLAGE 
  — 
  FRIEDMANN 
  263 
  

  

  slightly 
  countershaded. 
  In 
  them, 
  the 
  degree 
  of 
  countershading 
  shows 
  

   a 
  relation 
  to 
  the 
  body 
  form. 
  (Examples 
  are 
  some 
  of 
  the 
  ilarchid, 
  

   scatophagid, 
  and 
  cichlid 
  fishes, 
  which, 
  unfortunately, 
  have 
  no 
  com- 
  

   mon 
  names.) 
  Other 
  animals 
  living 
  in 
  dim 
  light, 
  where 
  shading 
  

   would 
  be 
  less 
  extreme, 
  reveal 
  in 
  the 
  slightness 
  of 
  their 
  countershading 
  

   a 
  relation 
  to 
  this 
  environmental 
  factor. 
  Likewise, 
  animals 
  living 
  on 
  

   open 
  plains 
  in 
  bright 
  sunlight, 
  such 
  as 
  many 
  antelopes, 
  deer, 
  larks, 
  

   etc., 
  are 
  strongly 
  countershaded. 
  In 
  the 
  case 
  of 
  the 
  shark 
  sucker, 
  a 
  

   fish 
  that 
  has 
  the 
  habit 
  of 
  attaching 
  itself 
  by 
  a 
  sucker 
  on 
  its 
  head 
  to 
  

   different 
  parts 
  of 
  sharks, 
  no 
  countershading 
  is 
  present. 
  However, 
  

   since 
  it 
  may 
  have 
  any 
  side 
  uppermost, 
  the 
  lack 
  of 
  countershading 
  may 
  

   be 
  considered 
  in 
  relation 
  to 
  this 
  habit, 
  as 
  the 
  fish 
  maintains 
  no 
  con- 
  

   stant 
  position 
  with 
  reference 
  to 
  the 
  source 
  of 
  light. 
  In 
  some 
  cater- 
  

   pillars, 
  the 
  normal 
  resting 
  position 
  is 
  inverted; 
  i. 
  e., 
  the 
  back 
  is 
  down 
  

   and 
  belly 
  up 
  (example, 
  the 
  larva 
  of 
  the 
  eyed 
  hawk-moth, 
  'Smerinthus 
  

   ocellatus), 
  and 
  it 
  is 
  indeed 
  suggestive 
  that 
  in 
  these 
  creatures 
  the 
  coun- 
  

   tershading 
  is 
  reversed 
  being 
  darker 
  on 
  the 
  underparts 
  and 
  paler 
  on 
  

   the 
  back. 
  

  

  The 
  simplest 
  form 
  of 
  countershading 
  is 
  merely 
  an 
  even, 
  gradual 
  

   transition 
  from 
  darkest 
  on 
  the 
  parts 
  receiving 
  the 
  most 
  light 
  to 
  lightest 
  

   on 
  the 
  parts 
  most 
  in 
  shade. 
  However, 
  the 
  same 
  effect 
  may 
  be, 
  and 
  in 
  

   nature 
  often 
  is, 
  effected 
  by 
  patterns 
  which 
  blend 
  at 
  rather 
  short 
  dis- 
  

   tance. 
  For 
  example, 
  the 
  spots 
  in 
  many 
  spotted 
  animals 
  are 
  larger 
  on 
  

   the 
  back 
  and 
  become 
  smaller 
  on 
  the 
  sides 
  and 
  disappear 
  on 
  the 
  under- 
  

   parts. 
  If 
  these 
  spots 
  are 
  fairly 
  close 
  together, 
  at 
  a 
  distance 
  they 
  tend 
  

   to 
  blend, 
  forming 
  a 
  graded 
  countershading. 
  The 
  body 
  stripes 
  of 
  

   zebras, 
  for 
  example, 
  are 
  very 
  broad 
  on 
  the 
  back 
  and 
  taper 
  very 
  ap- 
  

   preciably 
  on 
  the 
  sides, 
  giving 
  again 
  something 
  of 
  the 
  effect 
  of 
  counter- 
  

   shading. 
  Mottram 
  (Proc. 
  Zool. 
  Soc. 
  London, 
  1915, 
  pp. 
  679-692) 
  ex- 
  

   pounded 
  this 
  idea 
  that 
  certain 
  patterns 
  found 
  on 
  animals 
  become 
  

   blended 
  with 
  distance 
  and 
  result 
  in 
  obliterative 
  shading. 
  This 
  depends 
  

   on 
  the 
  fact 
  that 
  if 
  a 
  pattern 
  composed 
  of 
  alternating 
  dark 
  and 
  pale 
  

   markings, 
  regardless 
  of 
  shape 
  (they 
  may 
  be 
  bars, 
  stripes, 
  spots, 
  etc.), 
  is 
  

   looked 
  at 
  from 
  successively 
  increasing 
  distances, 
  a 
  point 
  will 
  be 
  reached 
  

   from 
  which 
  the 
  separate 
  markings 
  are 
  lost 
  in 
  a 
  blended 
  effect, 
  pro- 
  

   ducing 
  a 
  tone 
  depending 
  on 
  the 
  relative 
  amounts 
  of 
  dark 
  and 
  pale. 
  It 
  

   may 
  be 
  pointed 
  out 
  that 
  this 
  type 
  of 
  countershading 
  is 
  effective 
  only 
  at 
  

   a 
  distance 
  and 
  would 
  be 
  of 
  little 
  value 
  to 
  an 
  animal 
  in 
  the 
  last 
  

   crucial 
  seconds 
  when 
  it 
  is 
  about 
  to 
  catch 
  or 
  to 
  be 
  caught, 
  but 
  it 
  might 
  

   help 
  prevent 
  the 
  situation 
  from 
  arising. 
  However, 
  the 
  picture 
  is 
  not 
  

   as 
  simple 
  as 
  it 
  has 
  been 
  presented 
  so 
  far 
  in 
  this 
  paper. 
  In 
  the 
  majority 
  

   of 
  cases, 
  the 
  immediate 
  background 
  against 
  which 
  even 
  the 
  most 
  per- 
  

   fectly 
  countershaded 
  animal 
  is 
  to 
  become 
  invisible 
  is 
  not 
  an 
  even 
  tone 
  

   of 
  one 
  color 
  without 
  breaks 
  of 
  any 
  kind. 
  If 
  there 
  is 
  a 
  background 
  of 
  

  

  