﻿19 
  

  

  The 
  body 
  of 
  the 
  oyster, 
  like 
  that 
  of 
  all 
  animals, 
  except 
  the 
  

   Tery 
  simplest, 
  is 
  made 
  up 
  of 
  organs 
  such 
  as 
  the 
  heart, 
  diges- 
  

   tive 
  organs, 
  gills 
  and 
  reproductive 
  organs, 
  and 
  these 
  organs 
  

   are 
  at 
  some 
  period 
  in 
  the 
  life 
  of 
  the 
  oyster 
  made 
  up 
  of 
  mi- 
  

   <}roscopic 
  cells. 
  The 
  eggs 
  shown 
  in 
  Figures 
  49 
  and 
  53, 
  will 
  

   answer 
  to 
  illustrate 
  the 
  character 
  of 
  the 
  cells 
  which 
  compose 
  

   the 
  body 
  ; 
  each 
  of 
  these 
  consists 
  of 
  a 
  layer 
  of 
  protoplasm 
  

   around 
  a 
  central 
  nucleus, 
  which, 
  in 
  the 
  egg, 
  is 
  a 
  large, 
  cir- 
  

   cular, 
  transparent 
  body 
  known 
  as 
  the 
  germinative 
  vesicle. 
  

   Each 
  cell 
  of 
  the 
  body 
  is 
  able 
  to 
  absorb 
  food, 
  to 
  grow 
  and 
  to 
  

   multiply 
  by 
  division, 
  and 
  thus 
  to 
  contribute 
  to 
  the 
  growth 
  

   of 
  the 
  organ 
  of 
  wliich 
  it 
  forms 
  a 
  part. 
  The 
  ovarian 
  eggs 
  

   are 
  simply 
  the 
  cells 
  of 
  an 
  organ 
  of 
  the 
  body, 
  the 
  ovary, 
  

   and 
  they 
  differ 
  from 
  the 
  ordinary 
  cells 
  only 
  in 
  being 
  much 
  

   larger 
  and 
  more 
  distinct 
  from 
  each 
  other; 
  and 
  they 
  have 
  the 
  

   power, 
  when 
  detached 
  from 
  the 
  body, 
  of 
  growing 
  and 
  di- 
  

   viding 
  up 
  into 
  cells, 
  which 
  shall 
  shape 
  themselves 
  into 
  a 
  

   new 
  organism 
  like 
  tliat 
  from 
  whose 
  body 
  the 
  egg 
  came. 
  Most 
  

   of 
  the 
  steps 
  in 
  this 
  wonderful 
  process 
  may 
  be 
  watched 
  under 
  

   the 
  microscope, 
  and 
  owing 
  to 
  the 
  ease 
  with 
  which 
  the 
  eggs 
  

   of 
  the 
  oyster 
  may 
  be 
  obtained, 
  this 
  is 
  a 
  very 
  good 
  egg 
  

   to 
  study. 
  

  

  About 
  fifteen 
  minutes 
  after 
  the 
  eggs 
  are 
  fertilized, 
  they 
  

   "will 
  be 
  found 
  to 
  be 
  covered 
  with 
  male 
  cells, 
  as 
  shown 
  in 
  

   Figure 
  51. 
  In 
  about 
  an 
  hour 
  tlie 
  egg 
  will 
  be 
  found 
  to 
  have 
  

   changed 
  its 
  shape 
  and 
  appearance. 
  It 
  is 
  now 
  nearly 
  spheri- 
  

   cal, 
  as 
  shown 
  in 
  Figure 
  1, 
  and 
  the 
  germinative 
  vesicle 
  is 
  

   no 
  longer 
  visible. 
  The 
  male 
  cells 
  may 
  or 
  may 
  not 
  still 
  be 
  

   visible 
  upon 
  the 
  outer 
  surface. 
  In 
  a 
  short 
  time 
  a 
  little 
  trans- 
  

   parent 
  point 
  makes 
  its 
  appearance 
  on 
  the 
  surface 
  of 
  the 
  egg, 
  

   and 
  increases 
  in 
  size, 
  and 
  soon 
  forms 
  a 
  little 
  projecting 
  trans- 
  

   parent 
  knob 
  — 
  the 
  polar 
  globule 
  — 
  which 
  is 
  shown 
  in 
  Figure 
  

   -3, 
  and 
  in 
  succeeding 
  figures. 
  

  

  llecent 
  investigations 
  tend 
  to 
  show 
  that 
  while 
  these 
  changes 
  

   are 
  taking 
  place 
  one 
  of 
  the 
  male 
  cells 
  penetrates 
  the 
  proto- 
  

   plasm 
  of 
  the 
  egg 
  and 
  unites 
  with 
  the 
  germinative 
  vesicle, 
  

   which 
  does 
  not 
  disappear, 
  but 
  divides 
  into 
  two 
  parts, 
  one 
  of 
  

  

  