﻿DEVELOPMENT 
  AND 
  METAMOEPHOSIS. 
  85 
  

  

  XII. 
  Development 
  and 
  Metamokphosis. 
  

  

  In 
  the 
  first 
  condition, 
  when 
  the 
  embryo 
  has 
  become 
  

   distinct 
  from 
  the 
  vitelline 
  sac, 
  the 
  head 
  is 
  large 
  and 
  

   distinct 
  from 
  the 
  elongate 
  body, 
  the 
  tail 
  absent 
  or 
  

   rudimentary. 
  The 
  head 
  is 
  usually 
  cleft 
  below 
  by 
  a 
  

   median 
  longitudinal 
  groove, 
  in 
  the 
  middle 
  of 
  which 
  a 
  

   transverse 
  or 
  rhomboidal 
  depression 
  represents 
  the 
  

   first 
  rudiments 
  of 
  the 
  mouth 
  ; 
  on 
  each 
  side, 
  in 
  front 
  

   of 
  the 
  mouth, 
  a 
  pit 
  indicates 
  the 
  nostril 
  ; 
  behind 
  it 
  is 
  

   a 
  grooved 
  fold, 
  the 
  cephalic 
  crescent, 
  which 
  develops 
  

   into 
  a 
  single 
  or 
  paired 
  prominence, 
  the 
  holder 
  — 
  

   "crochets 
  "of 
  Rusconi 
  — 
  acting 
  as 
  an 
  adhesive 
  apparatus 
  

   by 
  means 
  of 
  which 
  the 
  helpless 
  embryo 
  fixes 
  itself 
  at 
  

   first 
  to 
  the 
  outer 
  surface 
  of 
  the 
  mucilaginous 
  envelop 
  

   of 
  the 
  egg, 
  and 
  later 
  to 
  weeds 
  or 
  submerged 
  objects. 
  

   Eyes 
  are 
  absent. 
  A 
  small 
  bud-like 
  tubercle 
  on 
  each 
  

   side 
  of 
  the 
  posterior 
  border 
  of 
  the 
  head 
  is 
  the 
  rudi- 
  

   ment 
  of 
  the 
  externa] 
  gills, 
  and 
  vertical 
  grooves 
  in 
  

   front 
  and 
  behind 
  the 
  bud 
  represent 
  the 
  visceral 
  clefts, 
  

   the 
  intervals 
  between 
  which 
  will 
  later 
  become 
  converted 
  

   into 
  the 
  four 
  branchial 
  arches. 
  

  

  The 
  adhesive 
  apparatus 
  mentioned 
  above 
  varies 
  con- 
  

   siderably, 
  and 
  its 
  conformation 
  affords 
  the 
  means 
  of 
  

   distinguishing 
  genera 
  or 
  even 
  species 
  at 
  a 
  period 
  when 
  

   the 
  tadpole 
  characters 
  are 
  not 
  yet 
  developed. 
  It 
  is 
  

   mainly 
  through 
  the 
  observations 
  of 
  Heron 
  -Hoyer 
  and 
  

   the 
  more 
  scientific 
  researches 
  of 
  Thiele 
  that 
  we 
  have 
  

   become 
  acquainted 
  with 
  its 
  modifications 
  in 
  most 
  of 
  

   the 
  European 
  forms. 
  Thiele 
  has 
  shown 
  that 
  the 
  term 
  

   " 
  sucker," 
  which 
  has 
  been 
  bestowed 
  on 
  this 
  organ 
  by 
  

   various 
  authors, 
  is 
  a 
  misnomer. 
  There 
  is 
  no 
  muscular 
  

   suctorial 
  apparatus 
  developed 
  in 
  connection 
  with 
  it 
  ; 
  

   it 
  is 
  glandular 
  and 
  secretory, 
  producing 
  a 
  sticky 
  

   mucus 
  or 
  slime, 
  which 
  serves 
  to 
  fasten 
  the 
  larva 
  to 
  its 
  

   resting-place.* 
  The 
  mode 
  of 
  its 
  development 
  and 
  

  

  * 
  From 
  this 
  apparatus 
  the 
  ventral 
  adhesive 
  disk 
  of 
  certain 
  tadpoles 
  

   living 
  in 
  mountain 
  streams 
  of 
  the 
  Himalayas, 
  Burma, 
  and 
  the 
  Malay 
  

   Archipelago 
  is 
  no 
  doubt 
  developed. 
  

  

  