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  which 
  will 
  allow 
  little 
  else 
  than 
  the 
  eggs 
  to 
  pass 
  through 
  

   its 
  meshes. 
  The 
  spermaries 
  of 
  the 
  ripe 
  males 
  are 
  treated 
  

   in 
  the 
  same 
  way 
  in 
  another 
  saucer, 
  after 
  which 
  the 
  male 
  

   cells 
  mixed 
  with 
  sea- 
  water 
  may 
  be 
  poured 
  into 
  the 
  dish 
  

   containing 
  the 
  eggs. 
  In 
  two 
  or 
  three 
  hours 
  after 
  the 
  

   water 
  containing 
  the 
  male 
  cells 
  has 
  been 
  x^oured 
  over 
  the 
  

   eggs, 
  development 
  will 
  have 
  begun. 
  The 
  Avater 
  should 
  

   now 
  be 
  removed 
  from 
  time 
  to 
  time 
  by 
  pouring 
  it 
  out 
  of 
  

   the 
  dish 
  or 
  tumbler, 
  taking 
  care 
  not 
  to 
  stir 
  up 
  the 
  eggs 
  

   which 
  have 
  settled 
  to 
  the 
  bottom. 
  Soon, 
  however, 
  the 
  

   embryos 
  will 
  begin 
  to 
  swim, 
  when 
  it 
  will 
  be 
  necessary 
  to 
  

   remove 
  the 
  water 
  in 
  another 
  way, 
  or 
  with 
  the 
  siphon. 
  

  

  The 
  changes 
  Avhicli 
  occur 
  in 
  the 
  eggs 
  during 
  develop- 
  

   ment, 
  succeed 
  each 
  other 
  with 
  considerable 
  rapidity, 
  

   and, 
  as 
  in 
  the 
  development 
  of 
  the 
  oyster, 
  there 
  are 
  very 
  

   well-marked 
  periods 
  of 
  active 
  change 
  of 
  form, 
  Avhich 
  

   alternate 
  with 
  periods 
  of 
  repose, 
  while 
  there 
  is 
  a 
  bilateral 
  

   symmetry 
  which 
  is 
  just 
  as 
  well 
  marked 
  as 
  in 
  the 
  latter 
  

   and 
  Unio. 
  A 
  power 
  of 
  250 
  diameters 
  enlarges 
  the 
  eggs 
  

   satisfactorily 
  ; 
  shows 
  the 
  freshly 
  impregnated 
  eggs 
  as 
  

   spheres 
  measuring 
  i 
  inch 
  in 
  ai:)parent 
  diameter, 
  a 
  proof 
  

   that 
  the 
  actual 
  diameter 
  of 
  the 
  eggs 
  is 
  very 
  nearly 
  l-500th 
  

   of 
  an 
  inch. 
  The 
  eggs 
  are 
  not 
  spherical 
  when 
  first 
  re- 
  

   moved 
  from 
  tile 
  ovary, 
  but 
  are 
  usually 
  irregular 
  in 
  form 
  

   with 
  a 
  more 
  or 
  less 
  well 
  pronounced 
  conical 
  extremity, 
  

   by 
  which 
  they 
  were 
  atta^ched 
  to 
  the 
  walls 
  of 
  the 
  ovarian 
  

   follicles. 
  The 
  other 
  end 
  is 
  more 
  or 
  less 
  irregularly 
  

   rounded. 
  A 
  nucleus 
  is 
  plainly 
  visible 
  during 
  this 
  irreg- 
  

   ular 
  stage, 
  but 
  no 
  well 
  defined 
  egg-membrane 
  is 
  apparent. 
  

  

  The 
  early 
  stages 
  which 
  I 
  was 
  enabled 
  to 
  figure 
  may 
  

   not 
  entirely 
  cover 
  the 
  different 
  phases 
  through 
  which 
  the 
  

   embryos 
  pass 
  at 
  that 
  time, 
  but 
  in 
  view 
  of 
  the 
  circumstance 
  

   that 
  there 
  is 
  but 
  little 
  known 
  of 
  the 
  development 
  of 
  La- 
  

   mellibranchiate 
  or 
  bivalvemollusks, 
  and 
  that 
  little 
  relates 
  

   to 
  but 
  few 
  forms, 
  I 
  feel 
  justified 
  in 
  offering 
  the 
  results 
  

   obtained 
  from 
  a 
  study 
  of 
  the 
  embryonic 
  development 
  of 
  

   the 
  Clam, 
  which 
  has 
  not 
  been 
  studied 
  hitherto. 
  Though 
  

  

  