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  its 
  walls 
  are 
  made 
  up 
  of 
  a 
  delicate 
  meshwork 
  of 
  muscu- 
  

   lar 
  libers 
  so 
  interlaced 
  as 
  to 
  be 
  altogether 
  untraceable 
  ; 
  

   by 
  its 
  contractions 
  it 
  forces 
  the 
  Oxygenated 
  blood 
  fresh 
  

   from 
  the 
  gills 
  to 
  all 
  parts 
  of 
  the 
  body 
  through 
  two 
  large 
  

   vessels, 
  or 
  x>roperly, 
  aortae, 
  the 
  first, 
  ao, 
  supplying 
  the 
  

   forepart 
  of 
  the 
  body, 
  and 
  ao' 
  the 
  hinder 
  portion. 
  These 
  

   larger 
  vessels 
  divide 
  into 
  smaller 
  ones 
  which 
  effect 
  the 
  

   distribution 
  of 
  the 
  blood 
  towards 
  the 
  head, 
  and 
  through 
  

   the 
  viscera, 
  where, 
  as 
  in 
  other 
  parts 
  of 
  the 
  body, 
  a 
  net- 
  

   work 
  of 
  fine 
  capillary 
  vessels 
  exists. 
  The 
  blood 
  accumu- 
  

   lates 
  perhaps 
  in 
  sinuses, 
  one 
  of 
  which 
  is 
  the 
  pericardial 
  

   space, 
  and 
  there 
  are 
  besides 
  probably 
  a 
  pair 
  of 
  rudimen- 
  

   tary 
  ones 
  in 
  the 
  oyster, 
  the 
  vestibule 
  of 
  a 
  rudimentary 
  

   organ 
  of 
  Bojanus, 
  from 
  these, 
  through 
  the 
  venous 
  sys- 
  

   tem 
  of 
  vessels, 
  the 
  blood 
  is 
  carried 
  back 
  to 
  the 
  gills 
  to 
  

   be 
  aerated, 
  and 
  returned 
  through 
  the 
  vessels 
  wiiich 
  carry 
  

   the 
  blood 
  from 
  the 
  gills 
  to 
  the 
  auricles, 
  the 
  branchio- 
  

   cardiac 
  vessels 
  be. 
  Of 
  the 
  last, 
  there 
  are 
  three 
  on 
  each 
  

   side 
  of 
  the 
  oyster, 
  two 
  pairs 
  of 
  which 
  collect 
  the 
  blood 
  

   from 
  the 
  forepart 
  of 
  the 
  gills, 
  and 
  one 
  pair 
  of 
  which 
  

   gather 
  the 
  blood 
  from 
  the 
  jiosteriar 
  portion 
  of 
  the 
  gills 
  

   to 
  be 
  carried 
  to 
  the 
  auricles, 
  from 
  whence 
  it 
  enters 
  the 
  

   ventricle, 
  having 
  completed 
  its 
  circulation 
  through 
  the 
  

   whole 
  vascular 
  system. 
  

  

  It 
  is 
  frequently 
  noticed 
  that 
  the 
  edges 
  or 
  a 
  consider- 
  

   able 
  part 
  of 
  the 
  mantle 
  of 
  the 
  oyster 
  is 
  very 
  much 
  swol- 
  

   len 
  and 
  nearly 
  transparent, 
  as 
  though 
  greatlj^ 
  distended 
  

   with 
  water 
  ; 
  this 
  is 
  due 
  to 
  a 
  peculiar 
  arrangement 
  of 
  ca- 
  

   pillary 
  vessels 
  connected 
  with 
  the 
  blood-system 
  which 
  

   causes 
  the 
  blood 
  to 
  be 
  held 
  in 
  these 
  places 
  until 
  turges- 
  

   cence 
  is 
  produced 
  as 
  in 
  erectile 
  tissues. 
  The 
  i)resence 
  

   of 
  an 
  unusual 
  amount 
  of 
  water 
  in 
  the 
  blood 
  no 
  doubt 
  

   sometimes 
  helps 
  to 
  produce 
  this 
  last 
  effect, 
  since 
  the 
  

   blood-system 
  is 
  probably 
  in 
  communication 
  with 
  the 
  

   water 
  outside, 
  through 
  the 
  openings 
  from 
  without 
  into 
  

   the 
  organ 
  of 
  Bojanus. 
  a 
  part 
  which 
  answers 
  to 
  the 
  kid- 
  

   ney 
  in 
  other 
  bivalve 
  mollusks, 
  but 
  which 
  seems 
  to 
  be 
  

  

  