﻿86 
  

  

  INTEODUCTION. 
  

  

  retrogression 
  

  

  is 
  shown 
  in 
  the 
  followinsr 
  series 
  of 
  

  

  figures 
  ol 
  Bufo 
  vulgaris 
  (after 
  Thiele). 
  

  

  Fig. 
  32. 
  

  

  Development 
  and 
  retrogression 
  of 
  the 
  subbuccal 
  apparatus 
  in 
  

  

  Bufo 
  vulgaris. 
  

  

  It 
  appears 
  as 
  a 
  crescentic 
  groove 
  very 
  early, 
  before 
  

   any 
  other 
  organ, 
  and 
  disappears, 
  after 
  having 
  under- 
  

   gone 
  various 
  changes, 
  in 
  the 
  beginning 
  of 
  the 
  tadpole 
  

   period. 
  Its 
  fullest 
  development 
  coincides 
  with 
  that 
  of 
  

   the 
  external 
  gills. 
  It 
  is 
  single 
  and 
  discoid, 
  with 
  a 
  

   crescentic 
  groove, 
  in 
  Discoglossus; 
  single 
  and 
  Y-shaped 
  

   in 
  Pelodytes 
  and 
  Pelohates 
  ; 
  single 
  and 
  V-shaped 
  or 
  

   crescentic 
  in 
  Bufo 
  ; 
  and 
  paired, 
  forming 
  two 
  small 
  

   disks, 
  in 
  Bomhinator, 
  Bana, 
  and 
  Hi/Ia. 
  These 
  disks 
  

   are 
  close 
  together 
  in 
  Bomhinator, 
  widely 
  separated 
  in 
  

   Hi/la 
  and 
  Bana 
  temporaria 
  and 
  agilis, 
  whilst 
  they 
  are 
  

   connected 
  by 
  a 
  fine 
  transverse 
  ridge 
  in 
  Bana 
  escu- 
  

   lenta, 
  which 
  thus 
  affords 
  a 
  link 
  between 
  the 
  single 
  and 
  

   paired 
  types 
  of 
  holders. 
  Eyla 
  differs 
  from 
  all 
  others 
  

   in 
  the 
  disks 
  shifting 
  forwards 
  so 
  as 
  to 
  be, 
  in 
  the 
  

   later 
  stages, 
  situated 
  on 
  a 
  level 
  with 
  the 
  mouth. 
  

   The 
  condition 
  in 
  Discoglossus 
  appears 
  to 
  be 
  the 
  most 
  

   primitive, 
  from 
  which 
  those 
  shown 
  by 
  Bomhinator, 
  

   Bana, 
  and 
  Syla 
  on 
  the 
  one 
  hand, 
  Belohates 
  and 
  Bufo 
  

   on 
  the 
  other 
  hand, 
  may 
  be 
  derived. 
  The 
  following 
  

  

  