﻿10 
  INTEODUCTION. 
  

  

  nately 
  opening 
  and 
  closing 
  as 
  the 
  throat 
  is 
  drawn 
  in 
  

   and 
  swollen 
  out 
  during 
  respiration. 
  

  

  The 
  eye 
  is 
  large, 
  lateral 
  (Fig. 
  1, 
  a), 
  or 
  directed 
  

   upwards 
  and 
  outwards 
  (Fig. 
  1, 
  b), 
  and 
  protected 
  by 
  

   three 
  lids 
  : 
  the 
  upper 
  thick 
  and 
  coloured, 
  the 
  lower 
  

   rudimentary 
  and 
  immoveable, 
  and 
  the 
  nictitating 
  

   membrane, 
  transparent 
  or 
  partially 
  pigmented, 
  which 
  

   ascends 
  over 
  the 
  eyeball 
  to 
  meet 
  the 
  upper 
  lid. 
  The 
  

   eye 
  can 
  be 
  covered 
  without 
  the 
  vision 
  being 
  much 
  

   impaired 
  by 
  elevation 
  of 
  the 
  nictitating 
  lid, 
  as 
  when 
  

   the 
  frog 
  is 
  under 
  water, 
  or 
  completely 
  closed 
  when 
  

   the 
  eyeball 
  is 
  drawn 
  in 
  and 
  the 
  upper 
  eyelid 
  descends 
  

   to 
  meet 
  the 
  lower. 
  The 
  iris 
  is 
  brilliantly 
  coloured 
  

   with 
  metallic 
  pigment, 
  golden, 
  silvery, 
  or 
  bronzy, 
  

   with 
  or 
  without 
  an 
  admixture 
  of 
  red 
  or 
  black. 
  The 
  

   pupil 
  when 
  fully 
  distended 
  is 
  round 
  and 
  large, 
  but 
  

   when 
  contracted 
  affects 
  various 
  shapes, 
  which 
  afford 
  

   important 
  characters 
  for 
  the 
  distinction 
  of 
  the 
  genera. 
  

   Thus 
  the 
  contracted 
  pupil 
  of 
  Ba^ia, 
  Hyla, 
  and 
  Bufo 
  

   is 
  horizontal, 
  oval 
  with 
  an 
  angle 
  in 
  the 
  lower 
  border 
  

  

  Fig. 
  2. 
  

  

  A 
  

  

  C 
  D 
  E 
  

  

  Different 
  forms 
  of 
  pupils. 
  A. 
  Bomhinator 
  pachypus. 
  B. 
  Alytes 
  

   ohstetricans 
  . 
  c. 
  Pelohatesfuscus. 
  P. 
  Banaarvalis. 
  B. 
  Bufo 
  

   vulgaris. 
  

  

  in 
  Bana(Fig. 
  2, 
  d), 
  and 
  Bufo 
  viridis 
  and 
  calamita, 
  with 
  

   an 
  upper 
  and 
  lower 
  angle 
  in 
  Hyla 
  and 
  Bufo 
  vulgaris 
  

   (Fig. 
  2, 
  e). 
  That 
  of 
  Discoglossus 
  and 
  Bomhinator 
  may 
  

   be 
  described 
  as 
  roundish 
  or 
  subtriangular 
  according 
  

   to 
  specimens, 
  the 
  lower 
  angle 
  being 
  always 
  distinct, 
  

   but 
  the 
  upper 
  border 
  sometimes 
  convex, 
  when 
  the 
  

  

  