﻿538 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [50] 
  

  

  gated 
  olfactory 
  depressions 
  begin 
  to 
  grow 
  toward 
  each 
  other 
  in 
  the 
  

   middle, 
  and 
  by 
  the 
  fifth 
  day 
  a 
  bridge 
  is 
  formed 
  across 
  the 
  nasal 
  sack, 
  

   so 
  that 
  an 
  anterior 
  and 
  posterior 
  opening 
  is 
  left, 
  corresponding 
  to 
  the 
  

   anterior 
  and 
  posterior 
  nostril 
  of 
  the 
  adult. 
  

  

  Hatching 
  occurs 
  on 
  the 
  sixth 
  day, 
  at 
  which 
  time 
  the 
  embryo 
  presents 
  

   the 
  appearance 
  shown 
  in 
  fig. 
  163, 
  when 
  viewed 
  as 
  a 
  transparent 
  object. 
  

   It 
  now 
  measures 
  9 
  mm 
  in 
  length, 
  or 
  somewhat 
  over 
  a 
  third 
  of 
  an 
  inch. 
  

   The 
  heart 
  is 
  now 
  prolonged 
  downward 
  over 
  the 
  anterior 
  pole 
  of 
  the 
  yelk. 
  

   The 
  branchial 
  arches 
  are 
  quite 
  hidden 
  by 
  the 
  downward 
  and 
  backward 
  

   extension 
  of 
  the 
  opercular 
  folds. 
  The 
  tail 
  has 
  also 
  become 
  decidedly 
  

   heterocercal, 
  and 
  distinct 
  indications 
  of 
  the 
  future 
  permanent 
  caudal 
  

   rays 
  are 
  developed. 
  The 
  anterior 
  dorsal 
  fin 
  is 
  also 
  becoming 
  evident, 
  

   just 
  behind 
  the 
  head, 
  where 
  mesoblast 
  has 
  begun 
  to 
  proliferate 
  into 
  the 
  

   median 
  dorsal 
  fin-fold. 
  

  

  On 
  the 
  seventh 
  day, 
  as 
  shown 
  in 
  fig. 
  164, 
  the 
  fins 
  have 
  undergone 
  

   still 
  farther 
  development. 
  The 
  pectoral 
  has 
  completed 
  its 
  rotation, 
  

   and 
  the 
  anterior 
  dorsal 
  and 
  the 
  anal 
  fins 
  are 
  outlined. 
  The 
  caudal 
  lobe 
  

   is 
  wider 
  and 
  its 
  rays 
  more 
  evident. 
  The 
  entire 
  set 
  of 
  four 
  pairs 
  of 
  bar- 
  

   bels 
  is 
  also 
  now 
  evident, 
  and 
  a 
  more 
  intricate 
  meshwork 
  of 
  vessels 
  

   traverses 
  the 
  surface 
  of 
  the 
  yelk. 
  

  

  On 
  the 
  eighth 
  day, 
  as 
  shown 
  in 
  fig. 
  165, 
  the 
  yelk 
  has 
  diminshed 
  

   somewhat 
  in 
  size. 
  The 
  anterior 
  dorsal 
  is 
  now 
  also 
  sharply 
  defined, 
  and 
  

   some 
  distance 
  behind 
  it 
  the 
  dorsal 
  fin-fold 
  is 
  widening 
  at 
  the 
  point 
  

   where 
  the 
  second 
  or 
  soft 
  dorsal 
  will 
  be 
  formed. 
  The 
  ventral 
  fins 
  have 
  

   also 
  appeared 
  as 
  a 
  low 
  horizontal 
  fold 
  at 
  the 
  ventral 
  side, 
  between 
  the 
  

   vent 
  and 
  the 
  yelk-sack. 
  The 
  rudiments 
  of 
  permanent 
  rays 
  are 
  also 
  evi- 
  

   dent 
  in 
  the 
  pectoral. 
  

  

  On 
  the 
  ninth 
  day, 
  as 
  shown 
  in 
  fig. 
  166, 
  the 
  ventral 
  is 
  a 
  more 
  pro- 
  

   nounced 
  lobe 
  than 
  on 
  the 
  preceding 
  day, 
  but 
  no 
  rays 
  have 
  yet 
  made 
  

   their 
  appearance. 
  The 
  upper 
  or 
  first 
  ray 
  of 
  the 
  pectoral 
  is 
  also 
  now 
  

   developed 
  as 
  a 
  spine, 
  and 
  the 
  position 
  of 
  the 
  soft 
  dorsal 
  is 
  indicated 
  by 
  

   a 
  decided 
  notch 
  at 
  its 
  posterior 
  extremity. 
  

  

  On 
  the 
  tenth 
  day 
  the 
  permanent 
  rays 
  of 
  the 
  dorsal 
  become 
  clearly 
  

   defined, 
  as 
  shown 
  in 
  fig. 
  167, 
  and 
  the 
  ventral 
  has 
  become 
  somewhat 
  

   more 
  prominent. 
  The 
  yelk 
  is 
  now 
  rapidly 
  disappearing, 
  and 
  by 
  the 
  

   eleventh 
  day 
  comparatively 
  little 
  is 
  left 
  to 
  distend 
  the 
  abdomen, 
  as 
  

   may 
  be 
  noted 
  in 
  fig. 
  168, 
  representing 
  a 
  young 
  Ictahirus 
  of 
  that 
  age. 
  

   At 
  this 
  stage 
  the 
  rays 
  of 
  the 
  ventral 
  begin 
  to 
  be 
  apparent, 
  while 
  those 
  

   of 
  the 
  pectoral, 
  dorsal, 
  anal, 
  and 
  caudal 
  are 
  clearly 
  differentiated; 
  acces- 
  

   sory 
  caudal 
  rays 
  are 
  also 
  beginning 
  to 
  be 
  formed, 
  and 
  the 
  nasal 
  bar- 
  

   bel 
  is 
  conspicuous. 
  

  

  Ou 
  the 
  fifteenth 
  day 
  all 
  of 
  the 
  fins 
  are 
  well 
  developed 
  and 
  permanently 
  

   outlined, 
  but 
  the 
  lower 
  lobe 
  of 
  the 
  caudal 
  is 
  still 
  shortest, 
  as 
  shown 
  in 
  

   fig. 
  169. 
  Five 
  days 
  later 
  the 
  lower 
  lobe 
  of 
  the 
  caudal 
  is 
  somewhat 
  

   longer, 
  as 
  shown 
  in 
  fig. 
  170. 
  The 
  anterior 
  spinous 
  ray 
  of 
  the 
  first 
  dor- 
  

   sal 
  and 
  of 
  the 
  pectoral 
  is 
  now 
  developed, 
  and 
  the 
  latter 
  has 
  assumed 
  a 
  

  

  