﻿47 
  

  

  'cleus. 
  The 
  disappearance 
  of 
  the 
  large 
  chamber 
  by 
  a 
  sudden 
  

   contraction, 
  and 
  the 
  diffusion 
  of 
  its 
  contents 
  through 
  radiat- 
  

   ing 
  channels, 
  are 
  phenomena 
  which 
  are 
  as 
  unmistakable 
  as 
  the 
  

   •somewhat 
  similar 
  changes 
  of 
  the 
  contractile 
  vacuole 
  of 
  an 
  

   infusorian, 
  although, 
  like 
  the 
  latter, 
  they 
  are 
  somewhat 
  diffi- 
  

   cult 
  to 
  discover, 
  and 
  can 
  only 
  be 
  seen 
  by 
  keeping 
  the 
  egg 
  

   under 
  constant 
  observation. 
  

  

  In 
  some 
  instances, 
  I 
  was 
  able 
  to 
  actually 
  observe 
  the 
  disap- 
  

   pearance 
  of 
  the 
  germinative 
  vesicle 
  of 
  the 
  oyster 
  egg. 
  In 
  

   many 
  Lamellibranchs 
  this 
  body 
  has 
  considerable 
  elasticity, 
  

   and 
  in 
  Anodonta 
  it 
  may 
  be 
  forced 
  by 
  pressure 
  through 
  a 
  small 
  

   fissure 
  in 
  the 
  ruptured 
  egg-shell, 
  and 
  it 
  will 
  regain 
  its 
  original 
  

   shape 
  and 
  size 
  after 
  it 
  has 
  escaped 
  from 
  the 
  egg. 
  This 
  is 
  not 
  

   the 
  case 
  in 
  the 
  oyster, 
  and 
  in 
  the 
  ripe 
  egg 
  the 
  vesicle 
  seems 
  to 
  

   be 
  almost 
  as 
  fluid 
  as 
  water, 
  and 
  cannot 
  be 
  pressed 
  out 
  of 
  the 
  

   ,yolk. 
  Like 
  all 
  the 
  changes 
  in 
  the 
  oyster-egg, 
  the 
  disappear- 
  

   ance 
  of 
  the 
  germinative 
  vesicle 
  takes 
  place 
  with 
  great 
  rapid- 
  

   ity, 
  and 
  the 
  manner 
  of 
  disappearance 
  is 
  identical 
  with 
  that 
  

   which 
  I 
  have 
  just 
  described 
  in 
  the 
  case 
  of 
  the 
  segmentation 
  nu- 
  

   cleus. 
  It 
  becomes 
  irregular 
  ; 
  radiating 
  channels 
  run 
  off 
  from 
  

   it 
  into 
  the 
  yolk 
  ; 
  the 
  central 
  chamber 
  vanishes, 
  and 
  the 
  chan- 
  

   nels 
  are 
  visible 
  for 
  an 
  instant 
  longer, 
  and 
  then 
  disappear. 
  

   The 
  yolk 
  is 
  so 
  opaque 
  that 
  I 
  was 
  not 
  able 
  to 
  see 
  that 
  any 
  part 
  

   of 
  the 
  vesicle 
  was 
  left 
  behind 
  as 
  a 
  pronucleus, 
  but 
  this 
  is 
  pro- 
  

   bably 
  the 
  case. 
  

  

  It 
  is 
  useless 
  to 
  speculate 
  at 
  present 
  upon 
  the 
  significance 
  of 
  

   these 
  highly 
  suggestive 
  changes, 
  but 
  they 
  certainly 
  show 
  that 
  

   we 
  may 
  hope 
  for 
  very 
  interesting 
  results 
  from 
  the 
  minute 
  his- 
  

   tological 
  study 
  of 
  the 
  eggs 
  of 
  marine 
  Lamellibranchs. 
  

  

  In 
  this 
  connection, 
  I 
  may 
  call 
  attention 
  to 
  a 
  point 
  in 
  the 
  

   history 
  of 
  the 
  "Auerbach's 
  figures." 
  It 
  is 
  not 
  generaly 
  known 
  

   that 
  these 
  were 
  first 
  figured 
  by 
  Carus, 
  more 
  than 
  fifty 
  years 
  

   ago, 
  in 
  the 
  egg 
  of 
  a 
  Lamellibranch. 
  His 
  figures 
  of 
  the 
  seg- 
  

   menting 
  egg 
  of 
  Unio 
  (Neue 
  Untersuchungen 
  iiber 
  die 
  Ent- 
  

   wickelungsgeschichte 
  unserer 
  Flussmuschel. 
  Yon 
  Dr. 
  J. 
  G. 
  

   Cams. 
  Nova 
  Acta, 
  1832, 
  8, 
  1), 
  show 
  these 
  structures 
  about 
  

   •as 
  they 
  are 
  represented 
  by 
  Flemming, 
  but 
  he 
  regards 
  them 
  

  

  