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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  quent 
  in 
  nature. 
  In 
  many 
  cases 
  the 
  seasonal 
  changes 
  in 
  coloration 
  

   are 
  not 
  such 
  as 
  make 
  for 
  greater 
  concealment. 
  

  

  All 
  the 
  examples 
  of 
  color 
  resemblance 
  hitherto 
  mentioned 
  are 
  fixed 
  

   for 
  their 
  durations, 
  whether 
  they 
  be 
  for 
  life 
  or 
  for 
  a 
  season 
  only. 
  

   There 
  are 
  a 
  number 
  of 
  types 
  of 
  color 
  resemblance 
  in 
  animals 
  which 
  are 
  

   variable 
  and 
  depend 
  on 
  changing 
  environmental 
  conditions. 
  Some 
  

   are 
  built 
  up 
  gradually 
  over 
  a 
  considerable 
  period 
  of 
  time, 
  while 
  others 
  

   are 
  very 
  rapidly 
  brought 
  about. 
  In 
  a 
  sense, 
  the 
  seasonal 
  changes 
  al- 
  

   ready 
  alluded 
  to 
  are 
  a 
  connecting 
  type 
  of 
  color 
  resemblance 
  between 
  

   definitely 
  fixed 
  and 
  purely 
  variable 
  resemblances, 
  but 
  their 
  period 
  of 
  

   effectiveness 
  is 
  long 
  enough 
  to 
  warrant 
  our 
  considering 
  them 
  with 
  the 
  

   fixed 
  types. 
  In 
  the 
  lives 
  of 
  many 
  kinds 
  of 
  animals, 
  especially 
  the 
  more 
  

   active 
  ones 
  — 
  that 
  is, 
  not 
  sessile 
  or 
  parasitic 
  forms 
  — 
  individuals 
  are 
  con- 
  

   stantly 
  coming 
  into 
  contact 
  with 
  differing 
  variations 
  of 
  their 
  im- 
  

   mediate 
  surroundings. 
  In 
  many 
  cases 
  when 
  danger 
  is 
  sensed 
  these 
  

   creatures 
  tend 
  to 
  get 
  back 
  as 
  rapidly 
  as 
  they 
  can 
  to 
  their 
  optimum 
  

   backgrounds, 
  but 
  others 
  have 
  the 
  ability 
  to 
  meet 
  the 
  changed 
  condi- 
  

   tions 
  with 
  variable 
  coloration. 
  Probably 
  the 
  best-known 
  case 
  of 
  

   rapid 
  change 
  in 
  color 
  is 
  that 
  of 
  the 
  chameleon, 
  a 
  small 
  lizard 
  which 
  

   in 
  the 
  course 
  of 
  a 
  few 
  minutes 
  can 
  change 
  its 
  color 
  through 
  a 
  sur- 
  

   prising 
  range 
  of 
  browns, 
  reds, 
  and 
  greens, 
  and 
  darks 
  and 
  lights. 
  

   Other 
  lizards, 
  such 
  as 
  some 
  iguanas 
  and 
  geckos, 
  are 
  also 
  known 
  to 
  

   possess 
  the 
  ability 
  to 
  alter 
  their 
  color 
  rapidly. 
  All 
  are 
  essentially 
  

   arboreal 
  dwellers 
  and 
  rely 
  on 
  concealment 
  more 
  than 
  on 
  speed 
  for 
  their 
  

   safety. 
  Terrestrial 
  forms 
  rely, 
  in 
  many 
  cases, 
  on 
  speed 
  first, 
  and 
  then 
  

   on 
  concealment. 
  

  

  Fishes 
  also 
  possess 
  amazing 
  ability 
  to 
  change 
  their 
  color 
  in 
  keeping 
  

   with 
  changes 
  in 
  the 
  background 
  against 
  which 
  they 
  find 
  themselves. 
  

   A 
  notable 
  series 
  of 
  experiments 
  on 
  the 
  flounder 
  was 
  conducted 
  by 
  Mast 
  

   (Changes 
  in 
  Shape, 
  Color, 
  and 
  Pattern 
  in 
  Fishes 
  and 
  Their 
  Bearing 
  

   on 
  the 
  Problems 
  of 
  Adaption 
  and 
  Behavior, 
  with 
  Special 
  Reference 
  

   to 
  the 
  Flounders, 
  Paralichthys 
  and 
  Ancylopsetta. 
  Bull. 
  U. 
  S. 
  Bureau 
  

   Fisheries, 
  vol. 
  34, 
  pp. 
  173-238, 
  1916). 
  The 
  flounders, 
  ordinarily 
  gray- 
  

   ish 
  brown 
  or 
  grayish 
  olive 
  in 
  color, 
  speckled 
  with 
  darker 
  brown, 
  not 
  

   only 
  can 
  and 
  do 
  respond 
  to 
  altered 
  backgrounds 
  by 
  changing 
  from 
  pale 
  

   sandy 
  yellow 
  to 
  dark 
  blackish 
  brown, 
  but 
  even 
  alter 
  the 
  fineness 
  or 
  

   coarseness 
  of 
  their 
  pattern 
  in 
  keeping 
  with 
  that 
  of 
  the 
  background, 
  

   simulating 
  to 
  an 
  astonishing 
  degree 
  the 
  texture 
  and 
  pattern 
  of 
  the 
  

   bottom 
  on 
  which 
  they 
  are 
  resting. 
  When 
  lying 
  on 
  a 
  uniform 
  muddy 
  

   background, 
  they 
  tend 
  to 
  be 
  uniformly 
  colored, 
  the 
  speckling 
  being 
  

   much 
  reduced 
  in 
  size 
  and 
  number 
  of 
  specks 
  and 
  in 
  any 
  difference 
  in 
  

   color 
  from 
  that 
  of 
  the 
  rest 
  of 
  the 
  fish 
  ; 
  when 
  placed 
  on 
  coarse 
  gravel 
  

   they 
  become 
  coarsely 
  flecked 
  and 
  speckled. 
  The 
  mechanism 
  by 
  which 
  

   the 
  chromatophores 
  in 
  the 
  skin 
  are 
  caused 
  to 
  effectuate 
  the 
  resulting 
  

   changes 
  is 
  only 
  partly 
  understood 
  and 
  is 
  out 
  of 
  our 
  province 
  in 
  this 
  

  

  