﻿103 
  

  

  enclosed 
  ; 
  the 
  proto-vcrtabr?G 
  numerous 
  and 
  distinct 
  ; 
  and 
  

   the 
  heart 
  tuLular, 
  and 
  beginning 
  to 
  pulsate. 
  At 
  thirty-eight 
  

   hours 
  tlio 
  cerebellic 
  fold 
  of 
  the 
  brain 
  is 
  ver}"- 
  distinct 
  ; 
  the 
  

   cjystalline 
  ions 
  lias 
  become 
  completely 
  enclosed, 
  but 
  the 
  eye, 
  

   as 
  yet, 
  has 
  acquired 
  no 
  pigment 
  granules 
  ; 
  the 
  ear 
  is 
  begin- 
  

   ninic 
  to 
  close 
  ; 
  and 
  the 
  branchial 
  fissures 
  are 
  forming. 
  At 
  

   sixty-two 
  hours 
  the 
  mouth 
  has 
  opened 
  ; 
  the 
  semi-circular 
  

   canals 
  of 
  the 
  ear 
  have 
  forjued, 
  and 
  the 
  ear 
  has 
  closed 
  exter- 
  

   nally 
  ; 
  and 
  the 
  pectoral 
  fins 
  liavo 
  formed 
  to 
  a 
  certain 
  extent 
  

   About 
  this 
  time, 
  or 
  during 
  the 
  third 
  day, 
  the 
  young 
  fry 
  

   begin 
  to 
  hatch 
  from 
  the 
  ova. 
  xVt 
  sixty-nine 
  hours 
  the 
  visce- 
  

   ral 
  arches 
  are 
  formed, 
  but 
  with 
  no 
  vessels 
  in 
  them 
  ; 
  the 
  oper- 
  

   culum 
  is 
  growing 
  backward, 
  toward 
  and 
  over 
  the 
  first 
  arch 
  ; 
  

   the 
  pectoral 
  fins 
  are 
  quite 
  prominent 
  ; 
  and 
  the 
  heart 
  has 
  

   become 
  abi-lobed 
  affair, 
  with 
  the 
  two 
  lobes 
  nearly 
  in 
  the 
  same 
  

   horizontal 
  plane, 
  the 
  auricle 
  on 
  the 
  left 
  side 
  of 
  the 
  embryo, 
  

   the 
  ventricle 
  on 
  the 
  right, 
  and 
  the 
  only 
  evidence 
  now 
  of 
  a 
  

   cavity 
  is 
  a 
  small 
  connecting 
  vacuole 
  in 
  the 
  centre 
  of 
  their 
  

   abutting 
  sides. 
  At 
  eighty-eight 
  hours 
  everything 
  is 
  more 
  

   mature 
  ; 
  the 
  yollc-sack 
  is 
  somewhat 
  absorbed 
  ; 
  and 
  the 
  heart 
  

   has 
  assumed 
  its 
  mature 
  position, 
  with 
  the 
  auricle 
  upon 
  the 
  

   dorsal 
  side 
  of 
  the 
  ventricle. 
  During 
  the 
  fourth 
  day 
  the 
  first 
  

   circulation, 
  through 
  the 
  first 
  and 
  second 
  branchial 
  aortte, 
  is 
  

   established 
  ; 
  and 
  during 
  the 
  fifth 
  day 
  vessels 
  are 
  formed, 
  and 
  

   blood 
  flows 
  througli 
  all 
  the 
  visceral 
  arches. 
  By 
  the 
  seventh 
  

   or 
  eighth 
  days 
  the 
  vessels 
  in 
  the 
  body 
  are 
  formed, 
  and 
  we 
  

   have 
  a 
  complete 
  systemic 
  circulation. 
  In 
  speaking 
  of 
  the 
  

   omjdialo-meseraic 
  arteries, 
  page 
  75, 
  I 
  mentioned 
  the 
  Shad 
  as 
  

   having 
  only 
  one. 
  This 
  is 
  perhaps 
  not 
  strictly 
  true, 
  since 
  the 
  

   large 
  artery 
  which 
  is 
  given 
  off 
  above 
  the 
  vitellus 
  passes 
  

   along 
  the 
  upper 
  bide 
  of 
  the 
  intestine, 
  returns 
  along 
  its 
  

   lower 
  side, 
  passes 
  along 
  the 
  dorsal 
  side 
  of 
  the 
  yolk, 
  without 
  

   giving 
  off 
  any 
  branches 
  to 
  it, 
  and 
  goes 
  directly 
  to 
  the 
  heart. 
  

   Although 
  it 
  is 
  not 
  what 
  an 
  omphalo-mcseraic 
  artery 
  is 
  gen- 
  

   erally 
  considered 
  to 
  be, 
  that 
  is, 
  one 
  which 
  sends 
  ramifying 
  

   branches 
  over 
  the 
  entire 
  surface 
  of 
  the 
  yolk, 
  yet 
  it, 
  without 
  

  

  