﻿400 
  R- 
  T. 
  Young, 
  

  

  with 
  which 
  it 
  is 
  confused 
  with 
  yolk 
  granules 
  which 
  are 
  similar 
  in 
  

   form 
  and 
  stain 
  similarlj^ 
  The 
  next 
  stage 
  readily 
  identified 
  is 
  shown 
  

   in 
  Fig. 
  85. 
  It 
  has 
  here 
  broken 
  up 
  into 
  several 
  chromosomes. 
  ^) 
  The 
  

   female 
  pronucleus 
  in 
  a 
  similar 
  condition 
  lies 
  nearby. 
  From 
  this 
  

   point 
  development 
  proceeds 
  differently 
  in 
  different 
  eggs. 
  In 
  some 
  

   the 
  pronuclei 
  pass 
  into 
  the 
  resting 
  condition, 
  (Fig. 
  86) 
  and 
  fuse 
  to 
  

   form 
  a 
  segmentation 
  nucleus 
  (Fig. 
  87). 
  This, 
  as 
  the 
  figure 
  shows^ 
  

   is 
  relatively 
  very 
  large 
  — 
  8,1 
  fi 
  in 
  diameter, 
  ^^g 
  diameter 
  11,6 
  yt* 
  -) 
  — 
  

   and 
  vesicular, 
  containing 
  a 
  loose 
  chromatin 
  network, 
  and 
  surrounded 
  

   by 
  a 
  very 
  incomplete 
  membrane. 
  In 
  the 
  other 
  process 
  resting 
  

   pronuclei 
  are 
  not 
  formed 
  and 
  cleavage 
  proceeds 
  precociously 
  as 
  is 
  

   shortly 
  to 
  be 
  described. 
  

  

  Cleavage. 
  It 
  is 
  not 
  my 
  intention 
  to 
  trace 
  in 
  detail 
  the 
  early 
  

   development 
  of 
  Taenia 
  pisiformis 
  as 
  has 
  already 
  been 
  done 
  for 
  

   several 
  species 
  by 
  Montez 
  (1881), 
  Van 
  Beneden 
  (1881), 
  St. 
  Eemy 
  (1901),. 
  

   and 
  V. 
  Janicki 
  (1907), 
  etc. 
  I 
  will 
  rather 
  restrict 
  myself 
  to 
  the 
  

   method 
  of 
  origin 
  of 
  the 
  cleavage 
  nuclei. 
  I 
  shall 
  first 
  describe 
  their 
  

   origin 
  in 
  those 
  eggs 
  in 
  which 
  a 
  fusion 
  nucleus 
  is 
  formed 
  and 
  then 
  

   in 
  those 
  in 
  which 
  cleavage 
  begins 
  while 
  the 
  pronuclei 
  are 
  still 
  in 
  

   the 
  active 
  condition. 
  

  

  In 
  the 
  former 
  type 
  of 
  cleavage 
  the 
  fusion 
  nucleus 
  appears 
  to 
  

   divide 
  amitotically 
  to 
  form 
  the 
  cleavage 
  nuclei, 
  without 
  however 
  

   simultaneous 
  division 
  of 
  the 
  cytoplasm. 
  Such 
  a 
  case 
  is 
  shown 
  in 
  

   Fig. 
  88. 
  It 
  is 
  of 
  course 
  impossible 
  to 
  be 
  absolutely 
  certain 
  here 
  

   as 
  to 
  whether 
  such 
  a 
  figure 
  represents 
  an 
  amitosis, 
  or 
  merely 
  a 
  

   lobulated 
  nucleus, 
  but 
  the 
  occurrence 
  of 
  eggs 
  showing 
  two 
  or 
  three 
  

   separate 
  nuclei^}, 
  whose 
  structure 
  resembles 
  in 
  every 
  way 
  save 
  

  

  1) 
  One 
  group 
  not 
  in 
  focus 
  in 
  the 
  figure, 
  I 
  cannot 
  be 
  certain 
  as 
  to 
  

   which 
  of 
  these 
  is 
  S 
  and 
  which 
  Ç. 
  The 
  smaller 
  denser 
  group 
  is 
  probably 
  

   $ 
  and 
  the 
  larger 
  looser 
  one 
  Ç. 
  

  

  2) 
  Average 
  of 
  10 
  eggs. 
  

  

  3) 
  Such 
  a 
  condition 
  has 
  been 
  figured 
  by 
  KiCHARDS 
  (1911) 
  (cf. 
  his 
  

   fig. 
  55 
  with 
  my 
  Fig. 
  88) 
  and 
  described 
  by 
  him 
  as 
  a 
  stage 
  in 
  the 
  recon- 
  

   struction 
  of 
  the 
  female 
  pronucleus. 
  He 
  says 
  (1. 
  c, 
  p. 
  152) 
  "These 
  stages 
  

   suggest 
  amitotic 
  division 
  of 
  the 
  ovum 
  — 
  some 
  more 
  than 
  that 
  figured 
  ; 
  their 
  

   true 
  nature, 
  however, 
  is 
  readily 
  ascertained." 
  In 
  Taenia 
  pisiformis 
  I 
  find 
  

   the 
  pronuclei 
  at 
  this 
  time 
  equal 
  in 
  size, 
  at 
  least 
  approximately, 
  whereas 
  

   in 
  Richards' 
  figures 
  the 
  male 
  is 
  much 
  smaller 
  than 
  the 
  female 
  pronucleus, 
  

   hence 
  I 
  seriously 
  doubt 
  his 
  interpretation. 
  

  

  In 
  a 
  comparison 
  of 
  Figs. 
  86 
  and 
  89 
  the 
  question 
  may 
  be 
  raised 
  as 
  

   to 
  what 
  evidence 
  there 
  is 
  that 
  the 
  former 
  represents 
  the 
  apposition 
  of 
  

  

  