﻿540 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [52] 
  

  

  The 
  air-bladder 
  became 
  perceptible 
  through 
  the 
  semi-transparent 
  

   bodies 
  of 
  the 
  young 
  on 
  the 
  tenth 
  day, 
  as 
  a 
  dorsal 
  outgrowth 
  of 
  the 
  back 
  

   part 
  of 
  the 
  oesophagus, 
  and 
  is 
  placed 
  far 
  forward, 
  a 
  little 
  above 
  and 
  

   behind 
  the 
  level 
  of 
  the 
  insertion 
  of 
  the 
  pectoral 
  fins, 
  and 
  as 
  it 
  grew 
  more 
  

   capacious 
  the 
  young 
  fish 
  commenced 
  to 
  swim 
  higher 
  in 
  the 
  aquarium. 
  

   When 
  first 
  hatched, 
  and 
  for 
  some 
  days 
  afterwards, 
  tbe 
  young 
  fish 
  ex- 
  

   hibited 
  a 
  great 
  tendency 
  to 
  gather 
  together 
  in 
  a 
  dense 
  school. 
  

  

  Of 
  the 
  development 
  of 
  the 
  viscera 
  I 
  shall 
  have 
  but 
  little 
  to 
  say 
  at 
  

   present. 
  The 
  intestine 
  is 
  not 
  prolonged 
  backwards 
  very 
  far 
  beyond 
  

   the 
  posterior 
  end 
  of 
  the 
  yelk-sack. 
  On 
  the 
  thirteenth 
  day 
  the 
  greenish 
  

   secretion 
  of 
  the 
  liver 
  can 
  be 
  seen 
  in 
  its 
  cavity. 
  

  

  The 
  liver 
  is 
  developed 
  on 
  the 
  ventral 
  side 
  of 
  the 
  intestine 
  and 
  very 
  

   soon 
  displaces, 
  more 
  or 
  less 
  extensively, 
  the 
  coarsely 
  granular 
  yelk 
  

   below 
  it. 
  It 
  is 
  crowded 
  into 
  the 
  anterior 
  end 
  of 
  the 
  yelk-sack 
  close 
  to 
  

   the 
  heart, 
  at 
  first 
  growing 
  downward 
  and 
  outward 
  on 
  the 
  left 
  side 
  as 
  a 
  

   rather 
  elongated 
  structure 
  lying 
  between 
  a 
  vertical 
  traversing 
  the 
  hinder 
  

   part 
  of 
  the 
  opercles 
  anteriorly 
  and 
  a 
  vertical 
  cutting 
  through 
  the 
  

   shoulder 
  girdle 
  posteriorly. 
  A 
  capillary 
  network 
  of 
  vessels 
  traverse 
  

   the 
  liver 
  and 
  pour 
  their 
  contents 
  directly 
  into 
  the 
  vitelline 
  or 
  portal 
  

   system 
  of 
  vessels 
  which 
  convey 
  the 
  blood 
  back 
  to 
  the 
  heart. 
  

  

  Behind 
  the 
  vent 
  a 
  distinct 
  urinary 
  duct 
  could 
  be 
  seen 
  by 
  the 
  sixth 
  

   day, 
  and 
  by 
  the 
  tenth 
  day 
  the 
  urinary 
  bladder 
  was 
  developed 
  in 
  the 
  

   usual 
  position 
  in 
  the 
  extreme 
  hinder 
  portion 
  of 
  the 
  body 
  cavity 
  and 
  

   just 
  behind 
  the 
  posterior 
  section 
  of 
  the 
  gut. 
  The 
  renal 
  apparatus 
  was 
  

   present 
  and 
  had 
  reached 
  an 
  advanced 
  stage 
  of 
  development 
  on 
  the 
  

   tenth 
  day, 
  urinary 
  tubules 
  and 
  glomeruli 
  being 
  found 
  in 
  advance 
  of 
  the 
  

   air-bladder, 
  and 
  also 
  behind 
  it. 
  

  

  In 
  the 
  upper 
  posterior 
  part 
  of 
  the 
  gill-cavity 
  of 
  either 
  side 
  a 
  large 
  

   glandular 
  organ 
  is 
  found 
  on 
  the 
  tenth 
  day, 
  which 
  is 
  undoubtedly 
  the 
  

   thymus 
  glaud 
  ; 
  it 
  is 
  embedded 
  only 
  in 
  the 
  posterior 
  part 
  of 
  the 
  upper 
  

   wall 
  of 
  the 
  gill-chamber. 
  

  

  The 
  air-bladder 
  is 
  formed 
  as 
  an 
  outgrowth 
  of 
  the 
  dorsal 
  wall 
  of 
  the 
  

   fore-gut. 
  The 
  saccular 
  diverticulum, 
  from 
  which 
  this 
  organ 
  is 
  formed, 
  

   acquires 
  a 
  lumen 
  about 
  the 
  fifth 
  day 
  after 
  the 
  commencement 
  of 
  devel- 
  

   opment, 
  and 
  on 
  the 
  tenth 
  day 
  the 
  organ 
  presents 
  the 
  form 
  of 
  a 
  depressed 
  

   oval 
  sack. 
  By 
  the 
  twentieth 
  day 
  the 
  hinder 
  end 
  of 
  the 
  air-bladder 
  be- 
  

   comes 
  emarginate 
  and 
  shows 
  traces 
  of 
  the 
  bilobed 
  character 
  which 
  it 
  

   presents 
  in 
  the 
  adult. 
  By 
  this 
  time 
  also 
  the 
  muscle 
  plates 
  overlying 
  its 
  

   exterior 
  right 
  and 
  left 
  aspects 
  have 
  aborted 
  more 
  or 
  less 
  completely, 
  so 
  

   that 
  its 
  walls 
  come 
  into 
  close 
  juxtaposition 
  with 
  the 
  integument 
  just 
  

   behind 
  the 
  shoulder 
  girdle. 
  

  

  The 
  cranium 
  of 
  Ictalurus 
  albidus 
  when 
  ten 
  days 
  old 
  I 
  have 
  figured 
  on 
  

   plate 
  xxx. 
  At 
  this 
  time 
  its 
  principal 
  elements 
  are 
  represented 
  by 
  car- 
  

   tilage, 
  though 
  the 
  membranous 
  representatives 
  of 
  parostoses 
  are 
  rap- 
  

   idly 
  developing 
  external 
  to 
  the 
  chondrified 
  parts. 
  None 
  of 
  these 
  have 
  

   been 
  represented 
  in 
  fig. 
  173. 
  This 
  drawing 
  was 
  made 
  from 
  a 
  series 
  of 
  

  

  