﻿INTEGUMENT. 
  25 
  

  

  of 
  Merkel, 
  formed 
  by 
  tlie 
  grouping 
  together 
  of 
  

   terminal 
  ganglion-cells. 
  These 
  sense-organs 
  are 
  found 
  

   principally 
  on 
  the 
  limbs 
  and 
  flanks 
  of 
  Eana 
  esculenta^ 
  

   more 
  developed 
  in 
  males 
  than 
  in 
  females 
  ; 
  the 
  small 
  

   warts 
  on 
  the 
  fore 
  limbs 
  of 
  Pelohates, 
  which 
  have 
  by 
  

   some 
  been 
  compared 
  with 
  the 
  nuptial 
  horny 
  excres- 
  

   cences, 
  seem 
  to 
  be 
  of 
  the 
  same 
  nature. 
  Very 
  similar 
  

   productions 
  appear 
  during 
  the 
  breeding 
  season 
  in 
  the 
  

   females 
  of 
  Bana 
  teinporaria 
  and 
  R. 
  arvalis, 
  but 
  are 
  of 
  a 
  

   merely 
  temporary 
  character, 
  and 
  will 
  be 
  noticed 
  in 
  

   the 
  chapter 
  on 
  Pairing 
  and 
  Oviposition, 
  together 
  with 
  

   the 
  horny 
  excrescences 
  which 
  arm 
  the 
  digits 
  or 
  other 
  

   parts 
  in 
  the 
  males 
  at 
  the 
  same 
  period, 
  and 
  assist 
  them 
  

   in 
  maintaining 
  their 
  hold 
  whilst 
  pairing. 
  

  

  Pigment, 
  usually 
  confined 
  to 
  the 
  cutis, 
  sometimes 
  

   occurs 
  in 
  small 
  quantity 
  in 
  the 
  epidermis. 
  As 
  Leydig 
  

   has 
  shown, 
  five 
  kinds 
  of 
  special 
  cells 
  may 
  be 
  pre- 
  

   sent 
  in 
  the 
  cutis 
  — 
  black, 
  yellow, 
  red, 
  white, 
  and 
  

   metallic 
  or 
  iridescent, 
  the 
  last 
  being 
  the 
  so-called 
  

   guanin- 
  cells 
  or 
  iridocytes. 
  The 
  yellow 
  and 
  black 
  pig- 
  

   ments 
  combine 
  to 
  produce 
  the 
  bright 
  green 
  colour, 
  as 
  

   in 
  normal 
  specimens 
  of 
  Bana 
  esculenta 
  typica 
  and 
  

   Hyla 
  arhorea 
  : 
  if 
  the 
  yellow 
  pigment 
  be 
  absent, 
  as 
  in 
  the 
  

   Grerman 
  specimens 
  of 
  Bana 
  esculenta, 
  var. 
  ridihunda, 
  

   the 
  black 
  and 
  gold 
  produce 
  the 
  dull 
  green 
  or 
  olive 
  hue; 
  

   if 
  both 
  yellow 
  and 
  gold 
  pigments 
  are 
  absent, 
  the 
  black 
  

   below 
  the 
  cloudy 
  medium 
  of 
  connective 
  tissue 
  and 
  

   epidermis 
  produces 
  blue, 
  as 
  in 
  the 
  sky-blue 
  specimens 
  

   of 
  Bana 
  esculenta 
  and 
  Hijla 
  arhorea. 
  In 
  the 
  play 
  of 
  

   the 
  special 
  pigment-cells 
  or 
  chromatophores, 
  which 
  

   contract 
  or 
  expand 
  and 
  radiate, 
  we 
  find 
  the 
  explana- 
  

   tion 
  of 
  the 
  changes 
  of 
  colour 
  which 
  some 
  specimens 
  

   undergo 
  with 
  so 
  great 
  rapidity. 
  A 
  tree-frog 
  will 
  turn 
  

   from 
  yellow 
  to 
  green 
  and 
  black 
  in 
  less 
  than 
  an 
  hour, 
  

   yellow 
  when 
  the 
  black 
  pigment 
  contracts, 
  black 
  in 
  the 
  

   opposite 
  process. 
  

  

  That 
  these 
  rapid 
  changes 
  of 
  colour 
  harmonise, 
  

   within 
  certain 
  limits, 
  with 
  the 
  surroundings 
  is 
  well 
  

   known. 
  The 
  researches 
  of 
  Dutartro 
  on 
  Bana 
  escu- 
  

  

  