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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  with 
  which 
  we 
  (or 
  its 
  enemies) 
  are 
  ordinarily 
  familiar. 
  Thus, 
  as 
  

   Cott 
  rightly 
  insists 
  — 
  

  

  * 
  * 
  * 
  for 
  effective 
  concealment, 
  it 
  is 
  essential 
  that 
  the 
  telltale 
  appearance 
  

   of 
  form 
  should 
  be 
  destroyed. 
  The 
  difficulty 
  of 
  doing 
  this 
  is 
  met, 
  often 
  with 
  

   extraordinary 
  success, 
  by 
  the 
  application 
  of 
  optical 
  principles 
  involving 
  the 
  use 
  

   of 
  pattern. 
  

  

  The 
  function 
  of 
  disruptive 
  coloration 
  (which 
  is 
  a 
  combination 
  of 
  color 
  

   and 
  pattern 
  tending 
  to 
  break 
  up 
  or 
  to 
  reduce 
  the 
  visible 
  outline 
  of 
  

   the 
  animal) 
  is 
  to 
  prevent 
  or 
  to 
  delay 
  the 
  quick 
  recognition 
  of 
  the 
  

   object 
  by 
  sight. 
  

  

  Its 
  success 
  depends 
  not 
  only 
  upon 
  optical 
  principles, 
  but 
  upon 
  a 
  psychological 
  

   factor. 
  When 
  the 
  surface 
  of 
  a 
  fish 
  * 
  * 
  * 
  is 
  covered 
  with 
  irregular 
  patches 
  

   of 
  contrasted 
  colours 
  and 
  tones, 
  these 
  patches 
  tend 
  to 
  catch 
  the 
  eye 
  of 
  the 
  

   observer 
  and 
  to 
  draw 
  his 
  attention 
  away 
  from 
  the 
  shape 
  which 
  bears 
  them. 
  

   The 
  patterns 
  themselves 
  may 
  be 
  conspicuous 
  enough, 
  but 
  since 
  they 
  contradict 
  

   the 
  form 
  on 
  which 
  they 
  are 
  superimposed, 
  they 
  concentrate 
  attention 
  upon 
  

   themselves, 
  and 
  pass 
  for 
  part 
  of 
  the 
  general 
  environment. 
  

  

  In 
  a 
  general 
  way 
  it 
  may 
  be 
  said 
  that 
  the 
  concealing 
  effect 
  of 
  a 
  dis- 
  

   ruptive 
  pattern 
  is 
  greater 
  if 
  parts 
  of 
  its 
  included 
  pattern 
  bear 
  a 
  good 
  

   color 
  resemblance 
  to 
  the 
  background 
  while 
  other 
  elements 
  are 
  strik- 
  

   ingly 
  distinct. 
  The 
  result 
  is 
  that 
  the 
  background 
  seems 
  to 
  be 
  seen 
  

   through 
  the 
  animal 
  in 
  places, 
  thus 
  breaking 
  up 
  its 
  visual 
  form. 
  Thus, 
  

   a 
  butterfly 
  with 
  a 
  brown 
  and 
  green 
  pattern 
  would 
  stand 
  out 
  as 
  a 
  

   butterfly 
  against 
  a 
  background 
  not 
  containing 
  either 
  of 
  these 
  colors, 
  

   but 
  against 
  a 
  brown 
  ground 
  it 
  would 
  look 
  like 
  an 
  aggregate 
  of 
  green 
  

   spots, 
  or, 
  against 
  a 
  green 
  ground, 
  like 
  a 
  bunch 
  of 
  brown 
  marks. 
  This 
  

   partial 
  matching 
  of 
  the 
  background 
  is 
  spoken 
  of 
  as 
  differential 
  

   blending. 
  The 
  effectiveness 
  of 
  this 
  disruptive 
  coloration 
  is 
  greatly 
  

   increased 
  if 
  the 
  adjacent 
  contrastingly 
  colored 
  markings 
  are 
  also 
  con- 
  

   trasting 
  in 
  tone 
  (lightness 
  or 
  darkness). 
  Cases 
  such 
  as 
  the 
  black 
  

   collar 
  bands 
  on 
  white 
  or 
  pale 
  sandy 
  plovers, 
  of 
  dark 
  lateral 
  longi- 
  

   tudinal 
  stripes 
  on 
  some 
  pale-colored 
  antelopes, 
  come 
  readily 
  to 
  mind 
  

   in 
  this 
  connection. 
  Everyone 
  who 
  has 
  watched 
  ring-necked 
  plovers 
  

   on 
  the 
  beach 
  is 
  aware 
  of 
  the 
  disruptive 
  effect 
  of 
  the 
  collar 
  at 
  a 
  

   significantly 
  short 
  distance. 
  

  

  CONSTRUCTIVE 
  SHADING 
  

  

  The 
  amount 
  of 
  difference 
  in 
  tone 
  and 
  color 
  of 
  immediately 
  adjacent 
  

   parts 
  of 
  the 
  pattern 
  has 
  an 
  important 
  bearing 
  not 
  only 
  on 
  the 
  degree 
  of 
  

   success 
  in 
  its 
  disruptive 
  illusion, 
  but 
  also 
  on 
  the 
  illusory 
  pictorial 
  relief 
  

   it 
  may 
  create 
  on 
  the 
  animal's 
  surface. 
  For 
  example, 
  if 
  between 
  the 
  

   darkest 
  and 
  the 
  lightest 
  elements 
  in 
  a 
  color 
  pattern 
  there 
  is 
  a 
  gradual 
  

   change 
  from 
  one 
  to 
  the 
  other, 
  the 
  optical 
  effect 
  is 
  that 
  of 
  a 
  rounded 
  sur- 
  

   face 
  (from 
  shade 
  to 
  light) 
  ; 
  if, 
  however, 
  the 
  darkest 
  and 
  the 
  lightest 
  

   elements 
  are 
  in 
  immediate 
  juxtaposition 
  the 
  effect 
  produced 
  is 
  one 
  of 
  

  

  