﻿7B 
  

  

  At 
  8. 
  00 
  P. 
  M., 
  on 
  Mie 
  Otli, 
  or 
  two 
  days 
  and 
  nineteen 
  

   hours 
  after 
  fertilization, 
  owing 
  to 
  the 
  increased 
  amount 
  

   of 
  water 
  in 
  the 
  jar 
  (I 
  had 
  by 
  this 
  time 
  obtained 
  a 
  large 
  

   one,) 
  and 
  to 
  the 
  mortality 
  among 
  the 
  embryos, 
  I 
  found 
  it 
  

   very 
  difficult 
  to 
  find 
  any, 
  and 
  this 
  difficulty 
  was 
  a 
  con- 
  

   stantly 
  increasing 
  one 
  thence 
  forward. 
  Those 
  specimens 
  

   obtained 
  liad 
  well 
  develo]ied 
  shells, 
  and 
  the 
  digestive 
  

   tract 
  could 
  be 
  readily 
  distinguished, 
  as 
  coi.ild 
  the 
  cilia. 
  

   The 
  movements 
  of 
  the 
  embryo 
  were 
  so 
  rapid 
  and 
  erratic 
  

   that 
  T 
  found 
  great 
  difficulty 
  in 
  keei^ing 
  them 
  under 
  the 
  

   high 
  power 
  for 
  a 
  sufficient 
  time 
  to 
  decide 
  as 
  to 
  the 
  stage 
  

   they 
  had 
  reached, 
  but 
  those 
  least 
  advanced 
  appeared 
  as 
  

   figured 
  by 
  Brooks, 
  in 
  iSTo. 
  38, 
  while 
  the 
  older 
  embryos 
  

   presented 
  the 
  characteristics 
  of 
  tigs. 
  39 
  and 
  42. 
  

  

  At 
  11 
  P. 
  M., 
  on 
  the 
  10th, 
  or 
  four 
  days 
  and 
  three 
  hours 
  

   after 
  fertilization, 
  the 
  digestive 
  tract 
  and 
  shells 
  were 
  

   readily 
  distinguished, 
  especially 
  the 
  latter, 
  whu'li 
  were 
  

   very 
  apparent. 
  The 
  anus 
  was 
  ol)served 
  in 
  several 
  cases 
  

   and 
  the 
  course 
  (^f 
  the 
  intestine 
  fr'un 
  it 
  to 
  the 
  stomach 
  

   easily 
  traced. 
  The 
  cilia 
  of 
  the 
  velum 
  was 
  also 
  apparent, 
  

   even 
  with 
  the 
  low 
  power. 
  The 
  main 
  features 
  at 
  this 
  time 
  

   were 
  similar 
  to 
  those 
  of 
  tigs. 
  42 
  and 
  44. 
  

  

  At 
  11.00 
  P. 
  M., 
  cm 
  the 
  12th, 
  or 
  six 
  days 
  and 
  tliree 
  

   hour.^ 
  after 
  fertilization, 
  the 
  end)ryo 
  had 
  apparently 
  un- 
  

   dergone 
  little 
  or 
  no 
  change, 
  except 
  that 
  a 
  much 
  larger 
  

   number 
  had 
  i-eached 
  the 
  stage 
  shown 
  in 
  figure 
  44. 
  In 
  

   all. 
  tliH 
  shells 
  and 
  digestive 
  organs 
  were 
  well 
  developed 
  

   and 
  apparent, 
  and 
  the 
  movement 
  of 
  the 
  cilia 
  of 
  the 
  velum 
  

   regular 
  and 
  rapid, 
  though 
  the 
  cilia 
  appeared 
  to 
  have 
  

   decreased 
  in 
  size. 
  

  

  At 
  11.00 
  P. 
  M.. 
  on 
  the 
  13th, 
  seven 
  days 
  and 
  three 
  hours 
  

   after 
  fertilization, 
  there 
  was 
  no 
  apparent 
  change 
  in 
  those 
  

   em])ryos 
  that 
  could 
  be 
  found, 
  'i'hey 
  appeared 
  quite 
  

   healthy 
  and 
  were 
  rapid 
  in 
  their 
  movements. 
  The 
  diffi- 
  

   culty 
  of 
  ol^taining 
  si)ecimens, 
  however, 
  had 
  niuch 
  in- 
  

   creased. 
  

  

  At 
  11.00 
  P. 
  M., 
  on 
  the 
  14th. 
  eight 
  davs 
  and 
  three 
  hours 
  

  

  