﻿318 
  EEPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  muscle 
  is 
  cut 
  the 
  valves 
  separate 
  a 
  little, 
  and 
  the 
  right 
  valve 
  may 
  be 
  raised 
  up 
  and 
  

   broken 
  off 
  from 
  the 
  left, 
  thus 
  exposing 
  the 
  right 
  side 
  of 
  the 
  body. 
  The 
  surface 
  of 
  

   the 
  body 
  is 
  covered 
  by 
  the 
  mantle, 
  a 
  thin 
  membrane 
  which 
  is 
  attached 
  to 
  the 
  body 
  

   over 
  a 
  great 
  part 
  of 
  its 
  surface, 
  but 
  hangs 
  free 
  like 
  a 
  curtain 
  around 
  nearly 
  the 
  whole 
  

   circumference. 
  By 
  raising 
  its 
  edge, 
  or 
  gently 
  tearing 
  the 
  whole 
  right 
  half 
  away 
  

   from 
  the 
  body, 
  the 
  gills, 
  g, 
  will 
  be 
  exposed. 
  These 
  are 
  four 
  parallel 
  plates 
  which 
  

   occupy 
  the 
  ventral 
  half 
  of 
  the 
  mantle 
  cavity 
  and 
  extend 
  from 
  the 
  posterior 
  nearly 
  

   to 
  the 
  anterior 
  end 
  of 
  the 
  body. 
  Their 
  ventral 
  edges 
  are 
  free, 
  but 
  their 
  dorsal 
  edges 
  

   are 
  united 
  to 
  each 
  other, 
  to 
  the 
  mantle, 
  and 
  to 
  the 
  body. 
  The 
  space 
  above, 
  or 
  dorsal 
  

   to 
  the 
  posterior 
  ends 
  of 
  the 
  gills, 
  is 
  occupied 
  by 
  the 
  oval, 
  firm 
  adductor 
  muscle, 
  M, 
  

   the 
  so-called 
  "heart." 
  For 
  some 
  time 
  I 
  was 
  at 
  a 
  loss 
  to 
  know 
  how 
  the 
  muscle 
  came 
  

   to 
  be 
  called 
  the 
  "heart," 
  but 
  a 
  friend 
  told 
  me 
  that 
  he 
  had 
  always 
  supposed 
  that 
  this 
  

   ■was 
  the 
  heart, 
  since 
  the 
  oyster 
  dies 
  when 
  it 
  is 
  injured. 
  The 
  supposed 
  "death" 
  is 
  

   simply 
  the 
  opening 
  of 
  the 
  shell, 
  when 
  the 
  animal 
  loses 
  the 
  power 
  to 
  keep 
  it 
  shut. 
  

   Between 
  this 
  muscle 
  and 
  the 
  hinge 
  the 
  space 
  above 
  the 
  gills 
  is 
  occupied 
  by 
  the 
  body, 
  

   or 
  visceral 
  mass, 
  which 
  is 
  made 
  up 
  mainly 
  of 
  the 
  light-colored 
  reproductive 
  organs 
  

   and 
  the 
  dark-colored 
  digestive 
  organs, 
  packed 
  together 
  in 
  one 
  continuous 
  mass. 
  

  

  If 
  the 
  oyster 
  has 
  been 
  opened 
  very 
  carefully, 
  a 
  transparent, 
  crescent-shaped 
  space 
  

   will 
  be 
  seen 
  between 
  the 
  muscle 
  and 
  the 
  visceral 
  mass. 
  This 
  space 
  is 
  the 
  pericar- 
  

   dium, 
  and 
  if 
  the 
  delicate 
  membrane 
  which 
  forms 
  its 
  sides 
  be 
  carefully 
  cut 
  away, 
  the 
  

   heart, 
  ve 
  and 
  au, 
  may 
  be 
  found 
  without 
  any 
  difficulty 
  lying 
  in 
  this 
  cavity 
  and 
  pulsat- 
  

   ing 
  slowly. 
  If 
  the 
  oyster 
  has 
  been 
  opened 
  roughly, 
  or 
  if 
  it 
  has 
  been 
  out 
  of 
  water 
  for 
  

   some 
  time, 
  the 
  rate 
  of 
  beating 
  may 
  be 
  as 
  low 
  as 
  one 
  a 
  minute, 
  or 
  even 
  less, 
  so 
  the 
  heart 
  

   must 
  be 
  watched 
  attentively 
  for 
  some 
  time 
  in 
  order 
  to 
  see 
  one 
  of 
  the 
  contractions. 
  

  

  In 
  front 
  of 
  the 
  gills, 
  that 
  is 
  between 
  them 
  and 
  the 
  hinge, 
  there 
  are 
  four 
  fleshy 
  

   flaps 
  — 
  the 
  lips, 
  p, 
  two 
  on 
  each 
  side 
  of 
  the 
  body. 
  They 
  are 
  much 
  like 
  the 
  gills 
  in 
  

   appearance, 
  and 
  they 
  are 
  connected 
  with 
  each 
  other 
  by 
  two 
  ridges, 
  which 
  run 
  across 
  

   the 
  middle 
  of 
  the 
  body 
  close 
  to 
  the 
  anterior 
  end, 
  and 
  between 
  these 
  folds 
  is 
  the 
  large 
  

   oval 
  mouth, 
  7n, 
  which 
  is 
  thus 
  seen 
  to 
  be 
  situated, 
  not 
  at 
  the 
  open 
  end 
  of 
  the 
  shell, 
  

   but 
  as 
  far 
  away 
  from 
  it 
  as 
  i^ossible. 
  As 
  the 
  oyster 
  is 
  immovably 
  fixed 
  upon 
  the 
  

   bottom, 
  and 
  has 
  no 
  arms 
  or 
  other 
  structures 
  for 
  seizing 
  food 
  and 
  carrying 
  it 
  to 
  the 
  

   mouth, 
  the 
  question 
  how 
  it 
  obtains 
  its 
  food 
  at 
  once 
  suggests 
  itself. 
  If 
  a 
  fragn.ient 
  of 
  

   one 
  of 
  the 
  gills 
  is 
  examined 
  with 
  a 
  microscope 
  it 
  will 
  be 
  found 
  to 
  be 
  covered 
  with 
  very 
  

   small 
  hairs, 
  or 
  cilia, 
  arranged 
  in 
  rows, 
  plate 
  ix, 
  fig. 
  3, 
  c. 
  Each 
  of 
  these 
  cilia 
  is 
  

   constantly 
  swinging 
  back 
  and 
  forth 
  with 
  a 
  motion 
  something 
  like 
  that 
  of 
  an 
  oar 
  in 
  

   rowing. 
  The 
  motion 
  is 
  quick 
  and 
  strong 
  in 
  one 
  direction 
  and 
  slower 
  in 
  the 
  other. 
  

   As 
  all 
  the 
  cilia 
  of 
  a 
  row 
  swing 
  together 
  they 
  act 
  like 
  a 
  line 
  of 
  oars, 
  only 
  they 
  are 
  

   fastened 
  to 
  the 
  gill, 
  and 
  as 
  this 
  is 
  immovable 
  they 
  do 
  not 
  move 
  forward 
  through 
  the 
  

   water, 
  but 
  produce 
  a 
  current 
  of 
  water 
  in 
  the 
  opposite 
  direction. 
  This 
  action 
  is 
  not 
  

   directed 
  by 
  the 
  animal, 
  for 
  it 
  can 
  be 
  observed 
  for 
  hours 
  in 
  a 
  fragment 
  cut 
  out 
  of 
  the 
  

   gill, 
  and 
  if 
  such 
  a 
  fragment 
  be 
  suj^plied 
  with 
  fresh 
  sea 
  water 
  the 
  motion 
  will 
  con- 
  

   tinue 
  until 
  it 
  begins 
  to 
  decay. 
  While 
  the 
  oyster 
  lies 
  undisturbed 
  on 
  the 
  bottom, 
  

   with 
  its 
  muscle 
  relaxed 
  and 
  its 
  shell 
  open, 
  the 
  sea 
  water 
  is 
  drawn 
  on 
  to 
  the 
  gills 
  by 
  

   the 
  action 
  of 
  the 
  cilia, 
  for 
  although 
  each 
  cilium 
  is 
  too 
  small 
  to 
  be 
  seen 
  without 
  a 
  

   microscope, 
  they 
  cover 
  the 
  gills 
  in 
  such 
  great 
  numbers 
  that 
  their 
  united 
  action 
  pro- 
  

   duces 
  quite 
  a 
  vigorous 
  stream 
  of 
  water, 
  which 
  is 
  drawn 
  through 
  the 
  shell 
  and 
  is 
  then 
  

   forced 
  through 
  very 
  small 
  openings 
  on 
  the 
  surfaces 
  of 
  the 
  gills 
  into 
  the 
  water 
  tubes 
  

   inside 
  the 
  gills, 
  and 
  through 
  these 
  tubes 
  into 
  the 
  cavity 
  above 
  them, 
  and 
  so 
  out 
  of 
  

   the 
  shell 
  again. 
  As 
  the 
  stream 
  of 
  water 
  passes 
  through 
  the 
  gills 
  the 
  blood 
  is 
  aerated 
  

   by 
  contact 
  with 
  it. 
  

  

  The 
  food 
  of 
  the 
  oyster 
  consists 
  entirely 
  of 
  minute 
  animal 
  and 
  vegetable 
  organisms 
  

   and 
  small 
  particles 
  of 
  organized 
  matter. 
  Ordinary 
  sea 
  water 
  contains 
  an 
  abundance 
  

   of 
  this 
  sort 
  of 
  food, 
  which 
  is 
  drawn 
  into 
  the 
  gills 
  with 
  the 
  water, 
  but 
  as 
  the 
  water 
  

  

  