﻿522 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [34] 
  

  

  been 
  derived 
  directly 
  from 
  the 
  cleavage 
  cavity. 
  By 
  this 
  time 
  the 
  pig- 
  

   ment 
  cells 
  on 
  the 
  body 
  and 
  tail 
  have 
  begun 
  to 
  aggregate 
  in 
  definite 
  

   groups, 
  as 
  shown 
  in 
  fig. 
  63, 
  and 
  the 
  majority 
  have 
  also 
  become 
  dis- 
  

   tinctly 
  stellate. 
  

  

  Fig. 
  64 
  represents 
  the 
  recently-hatched 
  moonfish. 
  The 
  body 
  cavity 
  

   sc, 
  formerly 
  the 
  cleavage 
  cavity, 
  is 
  already 
  very 
  spacious, 
  as 
  the 
  yelk 
  is 
  

   being 
  absorbed 
  more 
  rapidly 
  than 
  the 
  outer 
  somatopleural 
  envelope 
  of 
  

   the 
  yelk 
  is 
  collapsing. 
  This 
  outer 
  somatopleural 
  covering 
  of 
  the 
  yelk 
  

   in 
  this 
  species, 
  as 
  in 
  all 
  youug 
  fishes, 
  even 
  Elasmobranchs, 
  is 
  quite 
  free 
  

   and 
  is 
  not 
  fused 
  with 
  the 
  periblast-splanchnopleure 
  beneath 
  it. 
  The 
  

   oil-drop, 
  it 
  will 
  also 
  be 
  noticed, 
  is 
  now 
  invested 
  by 
  distinct 
  cells 
  of 
  peri- 
  

   blastic 
  origin, 
  which 
  have 
  well-defined 
  borders, 
  and 
  are 
  more 
  or 
  less 
  

   stellate. 
  It 
  also 
  bulges 
  outward, 
  more 
  or 
  less 
  distinctly, 
  but 
  it 
  is 
  easy 
  

   to 
  see 
  that 
  it 
  is 
  still 
  invested 
  by 
  the 
  yelk. 
  The 
  pectoral 
  fin-fold 
  appears 
  

   far 
  behind 
  the 
  auditory 
  involution 
  in 
  the 
  stage 
  represented 
  by 
  fig. 
  64; 
  

   it 
  is 
  somewhat 
  more 
  developed 
  in 
  the 
  more 
  advanced 
  stage 
  represented 
  

   by 
  fig. 
  G3. 
  The 
  ventral 
  fins 
  appear 
  quite 
  late, 
  as 
  they 
  were 
  absent 
  in 
  

   the 
  oldest 
  stages 
  observed 
  by 
  me. 
  

  

  Twenty-eight 
  hours 
  after 
  hatching, 
  the 
  youug 
  moonfish 
  measures 
  

   3.5 
  mm 
  in 
  length, 
  and 
  presents 
  the 
  appearance 
  shown 
  in 
  fig. 
  65. 
  Em- 
  

   bryonic 
  fin-rays 
  have 
  by 
  this 
  time 
  made 
  their 
  appearance 
  at 
  the 
  end 
  

   of 
  the 
  tail; 
  the 
  pectoral 
  fin 
  is 
  well 
  developed, 
  and 
  the 
  intestine 
  is 
  

   longer 
  and 
  the 
  urinary 
  bladder 
  is 
  larger. 
  The 
  yelk 
  has 
  also 
  diminished 
  

   greatly 
  in 
  size, 
  and 
  the 
  mouth 
  will 
  soon 
  be 
  open. 
  There 
  is 
  still 
  no 
  com- 
  

   plete 
  circulation, 
  though 
  all 
  the 
  principal 
  subdivisions 
  of 
  the 
  heart 
  are 
  

   developed 
  and 
  that 
  organ 
  is 
  pulsating 
  vigorously. 
  By 
  this 
  time 
  traces 
  

   of 
  a 
  reddish 
  pigment 
  begin 
  to 
  appear 
  on 
  the 
  upper 
  and 
  lateral 
  portions 
  

   of 
  the 
  abdomen. 
  

  

  Fifty-three 
  hours 
  after 
  hatching 
  the 
  young 
  moonfish 
  has 
  grown 
  

   mainly 
  in 
  height 
  of 
  the 
  body, 
  as 
  shown 
  in 
  fig. 
  66. 
  The 
  snout 
  is 
  very 
  

   blunt 
  and 
  declivous 
  and 
  foreshadows 
  the 
  form 
  of 
  the 
  blunt, 
  rounded 
  

   profile 
  of 
  the 
  parent 
  fish. 
  The 
  yelk 
  is 
  nearly 
  absorbed 
  and 
  over 
  the 
  

   abdominal 
  walls 
  there 
  is 
  now 
  developed 
  a 
  strongly-marked 
  group 
  of 
  

   stellate 
  red 
  pigment 
  cells. 
  A 
  flexure 
  of 
  the 
  intestine 
  is 
  also 
  developed 
  

   and 
  the 
  urinary 
  bladder 
  is 
  very 
  large 
  and 
  distinct. 
  The 
  pectoral 
  is 
  

   strongly 
  developed 
  and 
  a 
  complete 
  circulation 
  is 
  apparent, 
  though 
  the 
  

   aorta 
  bends 
  upon 
  itself 
  and 
  is 
  continued 
  forward 
  against 
  the 
  caudal 
  

   vein 
  at 
  a 
  point 
  less 
  than 
  half 
  the 
  distance 
  becweeu 
  the 
  vertical 
  from 
  the 
  

   vent 
  and 
  the 
  end 
  of 
  the 
  tail. 
  The 
  pigment 
  cells 
  have 
  also 
  by 
  this 
  time 
  

   been 
  more 
  definitely 
  aggregated 
  into 
  a 
  definite 
  band 
  on 
  the 
  tail 
  and 
  on 
  

   the 
  integument 
  above 
  the 
  pectoral. 
  The 
  young 
  fish 
  by 
  this 
  time 
  meas- 
  

   ures 
  nearly 
  4 
  mm 
  in 
  length. 
  

  

  I 
  have 
  seen 
  some 
  of 
  the 
  post-larval 
  stages 
  of 
  the 
  young 
  of 
  this 
  species 
  

   in 
  Chesapeake 
  Bay 
  measuring 
  from 
  one-half 
  to 
  one 
  inch 
  and 
  a 
  quarter 
  

   in 
  length. 
  In 
  these 
  the 
  transverse 
  dusky 
  bands 
  seen 
  in 
  the 
  adult 
  are 
  

   intensely 
  bluish-black 
  in 
  color. 
  It 
  is, 
  therefore, 
  obvious 
  that 
  the 
  color- 
  

  

  