﻿Shad, 
  Lake-Herring 
  and 
  White-fish 
  there 
  is 
  only 
  one 
  of 
  these 
  

   arteries. 
  In 
  the 
  Smelt 
  there 
  is 
  none 
  at 
  all, 
  since 
  the 
  yolk, 
  

   by 
  this 
  time, 
  is 
  entirely 
  absorbed, 
  undoubtedly 
  by 
  absorption 
  

   from 
  cell 
  to 
  cell, 
  without 
  any 
  assistance 
  from 
  the 
  blood-ves- 
  

   sels. 
  Fig. 
  4, 
  PL 
  V, 
  shows 
  the 
  yolk 
  nearly 
  absorbed, 
  with 
  

   the 
  liver 
  just 
  forming 
  at 
  its 
  posterior 
  dorsal 
  extremity. 
  

   There 
  is 
  no 
  blood 
  flowing 
  in 
  any 
  part 
  of 
  the 
  young 
  Smelt 
  at 
  

   this 
  time. 
  When 
  the 
  yolk 
  and 
  liver 
  become 
  as 
  shown 
  in 
  

   Figs. 
  6 
  and 
  T, 
  PL 
  V, 
  with 
  the 
  central 
  spherical 
  mass 
  of 
  the 
  yolk 
  

   ,of 
  a 
  decided 
  yellow 
  color, 
  and 
  so 
  as 
  to 
  be 
  barely 
  discernible 
  

   in 
  the 
  living 
  fish, 
  we 
  can 
  discover 
  the 
  1st 
  circulation 
  of 
  the 
  

   blood. 
  The 
  other 
  arteries 
  given 
  ofl' 
  from 
  the 
  aorta 
  are 
  dis- 
  

   tributed 
  alons; 
  the 
  entire 
  lenji^-th 
  of 
  the 
  bodv. 
  As 
  a 
  rule, 
  an 
  

   artery 
  is 
  given 
  oif 
  to 
  supply 
  each 
  vertebral 
  segment 
  of 
  the 
  

   body, 
  and 
  to 
  each 
  of 
  the 
  pectoral 
  fins. 
  In 
  the 
  tail, 
  the 
  aorta 
  

   is 
  at 
  first, 
  as 
  already 
  stated, 
  simply 
  folded 
  upon 
  itself; 
  soon, 
  

   however, 
  it 
  divides 
  into 
  three 
  branches, 
  or 
  more 
  properly, 
  a 
  

   connection 
  is 
  made 
  between 
  the 
  aorta 
  and 
  vena 
  cava, 
  at 
  a 
  

   short 
  distance 
  from 
  the 
  posterior 
  extremity 
  of 
  the 
  vessels, 
  

   thus 
  making 
  a 
  little 
  shorter 
  })assage 
  for 
  tlie 
  blood 
  ; 
  and 
  

   through 
  this 
  new 
  passage 
  most 
  of 
  the 
  blood 
  flows. 
  Where 
  

   this 
  connection 
  link 
  is 
  made 
  from 
  the 
  aorta, 
  a 
  third 
  ves- 
  

   sel 
  is 
  formed, 
  which 
  passes 
  upward 
  and 
  forward 
  around 
  

   the 
  notochord, 
  near 
  its 
  posterior 
  end. 
  Tlie 
  branch 
  which 
  

   was 
  the 
  original 
  end 
  fold 
  of 
  the 
  aorta, 
  still 
  persists 
  and 
  sup- 
  

   plies 
  blood 
  to 
  the 
  end 
  of 
  the 
  notochord. 
  The 
  connecting- 
  

   link 
  branch, 
  through 
  which 
  most 
  of 
  the 
  blood 
  now 
  returns 
  

   to 
  the 
  heart, 
  gradually 
  lengthens, 
  so 
  as 
  to 
  become 
  as 
  long- 
  

   as 
  the 
  primitive 
  branch, 
  is 
  divided 
  up 
  into 
  capillaries, 
  one 
  

   of 
  which 
  is 
  sent 
  to 
  each 
  ray 
  of 
  the 
  tail, 
  and 
  becomes, 
  iti 
  fact, 
  

   the 
  caudal 
  artery. 
  It 
  is 
  at 
  the 
  branching 
  of 
  these 
  three 
  arte- 
  

   ries 
  that 
  the 
  so 
  called 
  ''caudal 
  heart" 
  of 
  fishes 
  is 
  found. 
  

   It 
  is 
  no 
  heart 
  at 
  all, 
  and 
  there 
  are 
  no 
  pulsations 
  there, 
  

   except 
  such 
  as 
  are 
  seen 
  in 
  all 
  arteries, 
  and 
  due 
  to 
  the 
  same 
  

   cause. 
  It 
  is 
  true 
  there 
  is 
  a 
  slight 
  enlargement 
  at 
  this 
  point, 
  

   and 
  sometimes 
  the 
  enlargement 
  is 
  considerable, 
  but 
  it 
  is 
  due 
  

  

  