﻿RAN 
  A. 
  269 
  

  

  the 
  sac 
  actually 
  developed, 
  although 
  smaller 
  than 
  in 
  

   the 
  males. 
  

  

  Fig. 
  99. 
  

  

  4 
  K 
  

  

  Lower 
  view 
  of 
  head 
  of 
  male, 
  showing 
  

   inflated 
  vocal 
  sacs. 
  

  

  Variations. 
  — 
  It 
  is 
  a 
  well-known 
  fact 
  that 
  the 
  edible 
  

   frog 
  presents 
  a 
  greater 
  amount 
  of 
  variation, 
  both 
  as 
  

   regards 
  structure 
  and 
  coloration, 
  than 
  perhaps 
  any 
  

   other 
  species 
  of 
  Batrachians. 
  No 
  herpetologist 
  having 
  

   before 
  him 
  the 
  Japanese 
  and 
  Spanish 
  frogs, 
  without 
  

   a 
  knowledge 
  of 
  the 
  intermediate 
  forms, 
  would 
  hesi- 
  

   tate 
  to 
  pronounce 
  them 
  as 
  representing 
  different 
  

   species 
  ; 
  they 
  have, 
  in 
  fact, 
  been 
  referred 
  to 
  distinct 
  

   genera 
  by 
  such 
  experienced 
  workers 
  as 
  Peters 
  and 
  

   Cope. 
  But 
  if 
  we 
  pursue 
  our 
  investigations 
  over 
  the 
  

   wide 
  area 
  occupied 
  by 
  this 
  frog, 
  viz. 
  the 
  whole 
  of 
  the 
  

   Palaearctic 
  region, 
  we 
  soon 
  find 
  all 
  the 
  differences 
  by 
  

   which 
  we 
  were 
  at 
  first 
  struck 
  to 
  blend 
  through 
  such 
  

   a 
  number 
  of 
  intermediate 
  forms 
  as 
  to 
  leave 
  no 
  other 
  

   course 
  open 
  but 
  to 
  maintain 
  intact 
  the 
  Linnean 
  species. 
  

   However, 
  a 
  great 
  difficulty 
  still 
  remains 
  to 
  be 
  dealt 
  

   with 
  : 
  the 
  principal 
  of 
  the 
  differences 
  ascertained 
  are 
  

   not 
  merely 
  individual 
  ; 
  nor 
  are 
  they 
  entirely 
  dependent 
  

   on 
  locality 
  or 
  climate, 
  as 
  almost 
  identical 
  specimens 
  

   are 
  met 
  with 
  at 
  such 
  distant 
  points 
  as 
  North 
  Germany, 
  

   the 
  Sahara, 
  and 
  Baluchistan. 
  And, 
  what 
  is 
  more 
  

   striking 
  still, 
  in 
  the 
  case 
  of 
  two 
  forms 
  occurring 
  in 
  

   the 
  same 
  locality 
  they 
  may 
  be 
  perfectly 
  separable 
  

   and 
  not 
  interbreed, 
  as 
  has 
  been 
  shown 
  to 
  be 
  the 
  case 
  

  

  