﻿530 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [42] 
  

  

  stage, 
  while 
  the 
  anterior 
  end 
  of 
  the 
  notochord 
  has 
  become 
  more 
  com- 
  

   pletely 
  covered 
  by 
  the 
  parachordal 
  cartilages. 
  This 
  inclosure 
  of 
  the 
  

   anterior 
  extremity 
  of 
  the 
  chorda 
  by 
  the 
  parachordal 
  elements 
  pa 
  is 
  more 
  

   distinctly 
  displayed 
  in 
  figs. 
  146 
  and 
  147, 
  plate 
  xxi, 
  drawn 
  from 
  cross- 
  

   sections 
  of 
  the 
  same 
  stage 
  as 
  that 
  represented 
  by 
  fig. 
  142. 
  The 
  teg- 
  

   men 
  cranii 
  Tc, 
  fig. 
  142, 
  is 
  not 
  developed 
  during 
  the 
  earlier 
  stages, 
  shown 
  

   in 
  figs. 
  143 
  and 
  144. 
  The 
  palatopterygoid 
  is 
  not 
  present 
  until 
  the 
  stage 
  

   represented 
  by 
  fig. 
  142 
  is 
  attained, 
  or 
  perhaps 
  even 
  later. 
  An 
  element 
  

   which 
  I 
  identify 
  as 
  palatopterygoid 
  is 
  present 
  in 
  the 
  cross-section 
  rep- 
  

   resented 
  in 
  fig. 
  145, 
  and 
  has 
  been 
  cut 
  through 
  just 
  below 
  the 
  eye 
  atpt. 
  

   This 
  element, 
  at 
  any 
  rate, 
  seems 
  to 
  be 
  developed 
  quite 
  independently 
  

   of 
  any 
  connection 
  with 
  the 
  hyomandibular. 
  

  

  The 
  heart 
  at 
  the 
  time 
  of 
  hatching 
  opens 
  directly 
  into 
  the 
  cleavage 
  

   cavity 
  (= 
  body 
  cavity), 
  as 
  represented 
  in 
  fig. 
  144, 
  and 
  it 
  is 
  not 
  until 
  

   some 
  days 
  after 
  hatching 
  that 
  connection 
  is 
  established 
  between 
  its 
  

   venous 
  end 
  and 
  the 
  jugular 
  and 
  portal 
  veins 
  jf, 
  and 
  pv, 
  as 
  shown 
  in 
  

   fig. 
  152. 
  The 
  yelk 
  seems 
  to 
  be 
  absorbed 
  by 
  the 
  heart 
  and 
  portal 
  ves- 
  

   sels, 
  which 
  pass 
  above 
  it, 
  and 
  its 
  anterior 
  end 
  is 
  finally 
  drawn 
  out 
  into 
  

   a 
  pointed 
  process, 
  which 
  is 
  directed 
  toward 
  the 
  heart, 
  as 
  shown 
  in 
  fig. 
  

   152. 
  I 
  have 
  witnessed 
  the 
  budding 
  of 
  free 
  cells 
  from 
  the 
  periblast 
  p 
  

   in 
  the 
  stage 
  represented 
  in 
  fig. 
  144, 
  and 
  have, 
  also, 
  seen 
  such 
  cells 
  pass 
  

   directly 
  into 
  the 
  cavity 
  of 
  the 
  heart, 
  though 
  there 
  was, 
  as 
  yet, 
  no 
  com- 
  

   plete 
  circulation. 
  

  

  The 
  other 
  visceral 
  organs 
  are 
  differentiated 
  as 
  appendages 
  of 
  the 
  

   alimentary 
  canal. 
  The 
  first 
  and 
  most 
  conspicuously 
  developed 
  is 
  the 
  

   liver 
  L, 
  figs. 
  133, 
  148, 
  150 
  v 
  and 
  152, 
  it 
  being 
  formed 
  as 
  an 
  outgrowth 
  

   of 
  the 
  ventral 
  wall 
  of 
  the 
  intestine. 
  Just 
  a 
  little 
  distance 
  behind 
  the 
  

   posterior 
  extremity 
  of 
  the 
  liver, 
  the 
  alimentary 
  canal 
  is 
  constricted 
  at 
  

   py; 
  this 
  marks 
  the 
  point 
  just 
  behind 
  which 
  the 
  pyloric 
  appendages 
  will 
  

   grow 
  oat. 
  Just 
  in 
  advance 
  of 
  the 
  pyloric 
  constriction, 
  and 
  on 
  the 
  dor- 
  

   sal 
  side 
  of 
  the 
  oesophageal 
  portion 
  of 
  the 
  alimentary 
  canal, 
  the 
  air-blad- 
  

   der 
  grows 
  out 
  as 
  a 
  saccular 
  diverticulum 
  of 
  the 
  intestinal 
  wall 
  at 
  ab, 
  fig. 
  

   133. 
  The 
  first 
  traces 
  of 
  the 
  air-bladder 
  do 
  not 
  appear 
  until 
  some 
  days 
  

   after 
  hatching, 
  and 
  the 
  same 
  may 
  be 
  said 
  of 
  the 
  gall-bladder 
  Gb, 
  fig. 
  

   133, 
  which 
  is 
  formed 
  at 
  the 
  anterior 
  end 
  of 
  the 
  liver. 
  In 
  the 
  course 
  of 
  

   about 
  three 
  weeks 
  the 
  metamorphosis 
  of 
  the 
  visceral 
  organs 
  is 
  nearly 
  

   completed, 
  as 
  may 
  be 
  gathered 
  from 
  fig. 
  131, 
  as 
  this 
  figure 
  represents 
  

   the 
  pneumatic 
  duct 
  pn, 
  posterior 
  end 
  of 
  the 
  oesophagus 
  oe, 
  the 
  rudi- 
  

   mentary 
  stomach 
  st, 
  and 
  the 
  pylorus 
  py 
  of 
  a 
  young 
  shad 
  nearly 
  an 
  inch 
  

   long 
  and 
  three 
  weeks 
  old, 
  reared 
  in 
  confinement. 
  There 
  are 
  still 
  no 
  

   pyloric 
  cteca, 
  but 
  the 
  permanent 
  form 
  of 
  the 
  alimentary 
  tract 
  of 
  the 
  

   Clupeoids 
  is 
  already 
  very 
  clearly 
  apparent. 
  

  

  We 
  may 
  now 
  review 
  the 
  principal 
  and 
  most 
  striking 
  changes 
  in 
  ex- 
  

   ternal 
  form 
  which 
  the 
  young 
  shad 
  undergoes 
  within 
  the 
  egg. 
  Starting 
  

   with 
  the 
  phase 
  represented 
  in 
  figs. 
  137, 
  138, 
  139, 
  140, 
  and 
  141, 
  when 
  

   the 
  first 
  trace 
  of 
  the 
  embrvo 
  becomes 
  obvious 
  at 
  one 
  side 
  of 
  the 
  blasto- 
  

  

  