﻿26 
  INTEODUCTION. 
  

  

  lenta 
  have 
  shown 
  that 
  the 
  changes 
  are 
  controlled 
  

   by 
  the 
  animal, 
  the 
  contraction 
  or 
  expansion 
  of 
  the 
  

   chromatophores 
  not 
  being 
  due 
  entirely 
  to 
  the 
  direct 
  

   action 
  of 
  light 
  and 
  moisture 
  upon 
  the 
  skin, 
  but 
  also 
  to 
  

   a 
  reflex 
  action 
  of 
  the 
  sympathetic 
  nervous 
  system 
  

   brought 
  about 
  by 
  the 
  visual 
  impression. 
  Comparative 
  

   experiments 
  conducted 
  on 
  frogs 
  possessed 
  or 
  deprived 
  

   of 
  the 
  sense 
  of 
  sight, 
  and 
  placed 
  in 
  different 
  conditions 
  

   of 
  light, 
  show 
  the 
  blind 
  individuals 
  to 
  change 
  colour 
  

   much 
  less 
  rapidly. 
  

  

  The 
  changes 
  which 
  we 
  observe 
  in 
  Hyla, 
  Rana, 
  and 
  

   Bafo 
  are 
  not 
  limited 
  to 
  the 
  ground 
  colour, 
  but 
  also 
  

   extend 
  to 
  the 
  markings. 
  The 
  tree-frog, 
  normally 
  

   uniform, 
  may 
  become 
  covered 
  with 
  lighter 
  or 
  darker 
  

   dots 
  or 
  spots, 
  sometimes 
  disposed 
  with 
  great 
  regu- 
  

   larity 
  and 
  even 
  assuming 
  the 
  form 
  of 
  cross-bars 
  on 
  

   the 
  limbs. 
  An 
  edible 
  frog, 
  of 
  a 
  fine 
  grass-green 
  with 
  

   few 
  black 
  spots 
  above 
  and 
  with 
  a 
  pure 
  white 
  belly 
  

   when 
  captured, 
  may 
  shortly 
  after, 
  w^hen 
  transferred 
  to 
  

   an 
  aquarium, 
  appear 
  largely 
  marbled 
  with 
  black 
  both 
  

   above 
  and 
  beneath. 
  

  

  F. 
  Werner 
  has 
  proposed 
  to 
  group 
  the 
  European 
  

   Batrachians, 
  w^ith 
  respect 
  to 
  this 
  peculiarity, 
  into 
  

   such 
  as 
  actually 
  change 
  colour 
  {Alytes, 
  Hyla, 
  Bufo, 
  

   Rana), 
  and 
  such 
  as 
  only 
  lighten 
  or 
  darken 
  their 
  shade 
  

   (Discoglossus, 
  Pelodytes, 
  Pelohates). 
  He 
  considers 
  

   Bonibinator 
  as 
  representing 
  a 
  tlaird 
  category, 
  no 
  

   changes 
  of 
  any 
  kind 
  taking 
  place 
  ; 
  but 
  I 
  cannot 
  agree 
  

   with 
  him 
  in 
  this, 
  as 
  I 
  have 
  seen 
  B. 
  ijachypiis 
  pass 
  

   from 
  yellowish 
  to 
  a 
  very 
  dark 
  brown, 
  and 
  also 
  vary 
  in 
  

   the 
  i^resence, 
  absence, 
  or 
  distinctness 
  of 
  the 
  light 
  and 
  

   dark 
  markings. 
  

  

  In 
  a 
  recent 
  work 
  on 
  East 
  African 
  Reptiles 
  and 
  

   Batrachians 
  G. 
  Tornier 
  endeavours 
  to 
  show 
  that 
  the 
  

   yellow 
  and 
  red 
  pigments 
  do 
  not 
  exist 
  as 
  chemical 
  

   entities, 
  but 
  are 
  only 
  degenerations 
  of 
  the 
  brown 
  

   pigment 
  or 
  " 
  melanin." 
  And 
  as 
  a 
  first 
  " 
  simple 
  and 
  

   sure 
  " 
  proof 
  of 
  his 
  contention 
  he 
  adduces 
  the 
  example 
  

   of 
  Pelohates 
  fascus 
  larvae, 
  which 
  according 
  to 
  him 
  are 
  

  

  