﻿85 
  

  

  I 
  did 
  not 
  succeed 
  in 
  following 
  the 
  development 
  farther 
  

   than 
  to 
  the 
  formation 
  of 
  a 
  gastrula, 
  and 
  was 
  not 
  able 
  to 
  

   time 
  the 
  changes 
  which 
  were 
  observed, 
  owing 
  to 
  the 
  fact 
  

   that 
  my 
  watch 
  was 
  broken. 
  I 
  still 
  hope 
  to 
  be 
  able 
  to 
  

   make 
  a 
  series 
  of 
  observations 
  which 
  will 
  include 
  the 
  later 
  

   stages. 
  

  

  Fig. 
  

  

  1 
  shows 
  an 
  egg 
  which 
  has 
  been 
  re- 
  

  

  Figure 
  1. 
  

  

  moved 
  for 
  some 
  time 
  from 
  the 
  ovary 
  ; 
  the 
  

   vitellus 
  composed 
  of 
  minute 
  corpuscles 
  or 
  

   ' 
  spherules 
  has 
  assumed 
  a 
  rounded 
  form, 
  a 
  

   nucleus 
  is 
  still 
  visible 
  as 
  well 
  as 
  a 
  clear 
  

   nucleolus 
  within 
  it 
  ; 
  the 
  vitelline 
  mem- 
  

   brane 
  has 
  become 
  defined, 
  while 
  the 
  deli- 
  

   cate 
  thin 
  membrane 
  which 
  held 
  the 
  eggs 
  

   fast 
  to 
  the 
  wall 
  of 
  the 
  ovarian 
  follicle 
  re- 
  

   mains 
  attached 
  as 
  a 
  transparent 
  structure- 
  

   less 
  lilm. 
  It 
  is 
  the 
  supposition, 
  based 
  upon 
  the 
  conclu- 
  

   sions 
  of 
  other 
  observers, 
  that 
  at 
  this 
  stage 
  impregnation 
  

   has 
  not 
  yet 
  been 
  effected. 
  This 
  is 
  effected 
  by 
  the 
  en- 
  

   trance 
  of 
  a 
  single 
  spormatozoan 
  or 
  male 
  cell 
  into 
  the 
  '?^%^ 
  

   through 
  the 
  vitelline 
  membrane, 
  but 
  as 
  I 
  have 
  not 
  noted 
  

   a 
  micropyle, 
  eithei' 
  in 
  the 
  eggs 
  of 
  this 
  animal 
  or 
  that 
  of 
  

   the 
  oyster, 
  it 
  is 
  very 
  probable 
  that 
  the 
  male 
  cell 
  finds 
  its 
  

   way 
  into 
  the 
  vitellus 
  through 
  an 
  opening 
  in 
  the 
  vitelline 
  

   membrane 
  extemporized 
  for 
  its 
  passage. 
  We 
  are, 
  at 
  any 
  

   rate, 
  not 
  yet 
  ready 
  for 
  a 
  general 
  conclusion 
  as 
  to 
  the 
  

   presence 
  or 
  absence 
  of 
  a 
  micropyle 
  in 
  the 
  Lamellibranch- 
  

   iate 
  ovum, 
  to 
  which 
  Balfour 
  in 
  his 
  Comparative 
  Em- 
  

   bryology, 
  Vol. 
  I., 
  p. 
  31, 
  commits 
  himself. 
  The 
  histology 
  

   of 
  the 
  ovaries 
  of 
  more 
  forms 
  must 
  be 
  studied 
  before 
  we 
  

   can 
  decide, 
  and 
  no 
  more 
  promising 
  field 
  is 
  open 
  before 
  us 
  

   than 
  the 
  investigation 
  of 
  the 
  ovogenesis 
  of 
  the 
  oyster 
  and 
  

   clam, 
  both 
  of 
  which 
  are 
  still 
  unstudied 
  in 
  relation 
  to 
  this 
  

   point. 
  

  

  