﻿88 
  

  

  INTEODUCTION. 
  

  

  Fig. 
  34. 
  

  

  bcb 
  

  

  -sp 
  

  

  unbranched 
  or 
  bifid 
  in 
  Biifo 
  viridis 
  and 
  calamita 
  and 
  in 
  

  

  Hyla 
  arhorea. 
  

  

  In 
  Alytes, 
  within 
  the 
  egg, 
  the 
  external 
  gills 
  are 
  

  

  extremely 
  developed, 
  but 
  single; 
  and 
  the 
  very 
  long 
  

  

  and 
  slender 
  branches 
  are 
  confined 
  to 
  the 
  ventral 
  side, 
  

  

  as 
  in 
  other 
  tailless 
  Batrachians. 
  

  

  On 
  entering 
  the 
  second 
  period, 
  

   or 
  true 
  tadpole 
  stage, 
  the 
  external 
  

   characters 
  of 
  which 
  will 
  be 
  more 
  

   fully 
  described 
  in 
  the 
  following 
  

   chapter, 
  an 
  opercular 
  fold 
  covers 
  

   the 
  external 
  gills 
  (the 
  right 
  some 
  

   time 
  before 
  the 
  left 
  in 
  the 
  forms 
  

   with 
  lateral 
  spiraculum), 
  which 
  

   atrophy 
  and 
  are 
  replaced 
  by 
  in- 
  

   ternal 
  ones, 
  small 
  branched 
  fila- 
  

   ments 
  disposed 
  along 
  four 
  cartila- 
  

   ginous 
  arches. 
  The 
  anal 
  tube 
  is 
  

   developed 
  ; 
  the 
  mouth 
  acquires 
  

   horny 
  mandibles 
  and 
  the 
  lips 
  

   horny 
  teeth 
  ; 
  the 
  nostrils 
  assume 
  

   a 
  more 
  dorsal 
  position 
  ; 
  the 
  sub- 
  

   buccal 
  adhesive 
  organ 
  disappears; 
  

   and 
  the 
  opercular 
  fold 
  having 
  fused 
  

   with 
  the 
  skin 
  above 
  the 
  gill-arches, 
  

   the 
  head 
  becomes 
  confluent 
  with 
  

   the 
  globular 
  swollen 
  belly, 
  in 
  which 
  

  

  Young 
  tadpole 
  of 
  Hyla 
  

   arhorea, 
  seen 
  from 
  

   below, 
  sliowing 
  the 
  

  

  branchial 
  arclies 
  (6a), 
  the 
  extremely 
  elongate 
  intestine 
  

  

  the 
  heart 
  (c), 
  and 
  the 
  

   coiled-up 
  intestine 
  

  

  the 
  heart 
  (c), 
  and 
  the 
  ^j^qws 
  through 
  the 
  transparent 
  

  

  (i). 
  X 
  3. 
  

  

  up 
  

  

  abdominal 
  membrane, 
  coiled 
  

   like 
  a 
  watch-spring 
  (Fig. 
  34). 
  

   In 
  the 
  third 
  period 
  the 
  hind 
  limbs 
  appear 
  as 
  buds 
  

   at 
  the 
  base 
  of 
  the 
  tail, 
  and 
  gradually 
  attain 
  their 
  full 
  

   development 
  during 
  the 
  tadpole 
  life. 
  The 
  fore 
  limbs 
  

   grow 
  simultaneously, 
  and 
  even 
  more 
  rapidly, 
  but 
  

   remain 
  concealed 
  within 
  a 
  diverticulum 
  of 
  the 
  bran- 
  

   chial 
  chambers 
  until 
  fully 
  formed, 
  when 
  they 
  burst 
  

   through 
  the 
  skin 
  (unless 
  the 
  left 
  spiraculum 
  be 
  utilised 
  

   for 
  the 
  egress 
  of 
  the 
  corresponding 
  limb), 
  leaving 
  in 
  

  

  