﻿496 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [8J 
  

  

  pits. 
  The 
  same 
  would 
  also 
  be 
  inferred 
  from 
  another 
  figure 
  representing 
  

   an 
  advanced 
  larval 
  cod, 
  published 
  in 
  a 
  later 
  paper 
  26 
  by 
  the 
  writer. 
  

  

  The 
  true 
  state 
  of 
  the 
  case 
  is 
  as 
  follows, 
  as 
  may 
  be 
  gathered 
  from 
  figs. 
  

   1 
  and 
  2, 
  plate 
  i 
  : 
  The 
  true 
  median 
  dorsal 
  fin-fold 
  only 
  extends 
  as 
  such 
  

   forwards 
  as 
  far 
  as 
  to 
  about 
  or 
  slightly 
  behind 
  a 
  vertical 
  line 
  passing 
  

   through 
  the 
  base 
  of 
  the 
  pectoral. 
  The 
  larval 
  integument 
  continuous 
  with 
  

   the 
  median 
  dorsal 
  fin-fold 
  and 
  covering 
  the 
  brain 
  and 
  fore 
  part 
  of 
  the 
  

   spinal 
  cord 
  is 
  not 
  prolonged 
  forwards 
  as 
  a 
  flat 
  duplicature 
  or 
  fold, 
  but 
  

   is 
  distended 
  as 
  an 
  oblong 
  vesicle 
  and 
  filled 
  with 
  a 
  serous 
  fluid, 
  as 
  shown 
  

   from 
  the 
  side 
  m 
  fig. 
  1 
  and 
  from 
  the 
  front 
  in 
  fig. 
  2. 
  

  

  Immediately 
  after 
  hatching, 
  this 
  sinus 
  or 
  space 
  between 
  the 
  integu- 
  

   ment 
  and 
  the 
  brain 
  is 
  small, 
  as 
  may 
  be 
  observed 
  in 
  fig. 
  40, 
  plate 
  ix, 
  

   of 
  my 
  first 
  paper, 
  but 
  in 
  about 
  one 
  day 
  after 
  hatching 
  it 
  begins 
  to 
  be 
  

   obvious 
  that 
  the 
  integument, 
  over 
  the 
  brain 
  and 
  as 
  far 
  back 
  as 
  to 
  the 
  

   vertical 
  from 
  the 
  end 
  of 
  the 
  intestine, 
  is 
  being 
  lifted 
  up 
  and 
  becoming 
  

   filled 
  with 
  fluid. 
  This 
  proceeds 
  until 
  at 
  the 
  end 
  of 
  a 
  week 
  or 
  ten 
  days 
  

   the 
  larval 
  cod, 
  when 
  viewed 
  from 
  the 
  side 
  or 
  front, 
  presents 
  a 
  most 
  sin- 
  

   gular 
  resemblance 
  to 
  the 
  conventional 
  dolphins 
  of 
  the 
  ancient 
  sculptors. 
  

   The 
  rounded 
  and 
  swollen 
  front 
  and 
  top 
  of 
  the 
  head 
  is 
  in 
  marked 
  con- 
  

   trast 
  with 
  the 
  majority 
  of 
  pelagic 
  fish 
  larvae. 
  

  

  That 
  the 
  integument 
  is 
  actually 
  lifted 
  up 
  from 
  the 
  underlying 
  struct- 
  

   ures 
  is 
  shown 
  by 
  the 
  fact 
  that 
  the 
  long 
  efferent 
  branches 
  of 
  the 
  vagus 
  

   group 
  of 
  nerves 
  which 
  pass 
  outward 
  to 
  button-like 
  thickenings 
  of 
  the 
  

   epiblast 
  armed 
  externally 
  with 
  stiff 
  protoplasmic 
  hair-like 
  processes, 
  

   may 
  be 
  traced 
  through 
  the 
  wide 
  space 
  between 
  the 
  integument 
  and 
  the 
  

   brain 
  when 
  the 
  embryo 
  is 
  examined 
  by 
  transmitted 
  light. 
  Three 
  pairs 
  

   of 
  such 
  segmental 
  sense 
  organs 
  or 
  neuromasts 
  (Wright) 
  are 
  found 
  in 
  

   the 
  walls 
  of 
  the 
  large 
  integumentary 
  vesicle 
  overlying 
  the 
  head 
  and 
  

   body 
  of 
  the 
  young 
  cod. 
  These 
  organs 
  are 
  disposed 
  quite 
  symmetrically 
  

   on 
  the 
  fore 
  part 
  of 
  the 
  body, 
  but 
  posteriorly 
  they 
  are 
  not 
  symmetrically 
  

   disposed 
  on 
  the 
  sides 
  of 
  the 
  tail, 
  as 
  may 
  be 
  seen 
  by 
  referring 
  to 
  plate 
  

   x, 
  fig. 
  42, 
  Embryog., 
  Oss. 
  Fishes. 
  Agassiz 
  and 
  Whitman, 
  in 
  their 
  last 
  

   memoir 
  (Pelagic 
  stages 
  of 
  young 
  fishes), 
  also 
  figure 
  and 
  describe 
  larval 
  

   fishes 
  in 
  which 
  there 
  was 
  more 
  or 
  less 
  asymmetry 
  noticeable 
  in 
  the 
  ar- 
  

   rangement 
  of 
  the 
  caudal 
  neuromasts. 
  

  

  The 
  great 
  anterior 
  dorsal 
  integumentary 
  vesicle 
  of 
  the 
  larval 
  cod 
  is 
  

   gradually 
  developed 
  after 
  hatching, 
  and 
  appears 
  to 
  increase 
  in 
  size 
  as 
  

   the 
  yelk 
  sack 
  diminishes 
  and 
  becomes 
  empty. 
  I 
  first 
  noticed 
  and 
  

   described 
  what 
  is 
  obviously 
  homologous 
  with 
  this 
  vesicle, 
  which 
  is 
  

   so 
  exaggerated 
  in 
  dimensions 
  in 
  the 
  larval 
  cod, 
  in 
  1881, 
  in 
  the 
  Span- 
  

   ish 
  mackerel, 
  as 
  may 
  be 
  learned 
  if 
  the 
  reader 
  will 
  consult 
  plates 
  iii 
  

   and 
  iv, 
  figs. 
  14, 
  15, 
  16, 
  and 
  17, 
  illustrating 
  my 
  paper 
  on 
  the 
  develop- 
  

   ment 
  of 
  that 
  species 
  (Bull. 
  U. 
  S. 
  Fish 
  Com., 
  i, 
  1881, 
  p. 
  157), 
  where 
  it 
  is 
  

   also 
  stated 
  that 
  it 
  is 
  developed 
  after 
  hatching, 
  as 
  is 
  shown 
  by 
  the 
  con- 
  

  

  26 
  Ryder. 
  An 
  outline 
  of 
  a 
  theory 
  of 
  the 
  development 
  of 
  the 
  unpaired 
  fins 
  of 
  fishes, 
  

   Am. 
  Naturalist, 
  Jan., 
  1885, 
  pp, 
  90-97, 
  fig. 
  3. 
  

  

  