﻿Reproductive 
  organs 
  of 
  Taenia 
  pisiformis. 
  401 
  

  

  size 
  the 
  larger 
  ones 
  (Fig. 
  89), 
  renders 
  the 
  former 
  view 
  very 
  probable. 
  

   In 
  a 
  few 
  cases 
  the 
  cleavage 
  nuclei 
  appear 
  to 
  arise 
  from 
  the 
  fusion 
  

   nucleus 
  by 
  endogenous 
  division, 
  as 
  chromatin 
  granules 
  are 
  seen 
  

   collecting 
  at 
  various 
  points 
  on 
  the 
  periphery 
  of 
  the 
  latter 
  and 
  

   surrounding 
  themselves 
  with 
  indefinite 
  membranes 
  (Fig. 
  82). 
  Some 
  

   of 
  these 
  may 
  be 
  extruded 
  into 
  the 
  cytoplasm, 
  there 
  to 
  form 
  the 
  

   cleavage 
  nuclei. 
  

  

  In 
  those 
  eggs 
  in 
  which 
  cleavage 
  begins 
  precociously, 
  at 
  the 
  time 
  

   when 
  the 
  two 
  pronuclei, 
  each 
  consisting 
  of 
  a 
  group 
  of 
  chromosomes 
  

   which 
  are 
  probably 
  inconstant 
  in 
  number 
  in 
  both 
  male 
  and 
  female 
  ^), 
  

   are 
  lying 
  near 
  one 
  another 
  (Fig. 
  85), 
  one 
  may 
  see 
  scattered 
  thru 
  

   the 
  cytoplasm 
  several 
  small 
  granules 
  of 
  varying 
  size. 
  About 
  som^e 
  

   of 
  these, 
  delicate 
  membranes 
  are 
  forming 
  (Figs. 
  90 
  and 
  91). 
  They 
  

   are 
  the 
  anlagen 
  of 
  cleavage 
  nuclei. 
  It 
  is 
  impossible 
  in 
  all 
  cases 
  

   to 
  distinguish 
  between 
  nuclear 
  and 
  yolk 
  granules 
  in 
  the 
  eggs 
  as 
  

   both 
  have 
  much 
  the 
  same 
  form 
  and 
  stain 
  similarly. 
  When 
  however 
  

   a 
  membrane 
  is 
  formed 
  about 
  a 
  nuclear 
  granule 
  or 
  "nucleolus" 
  its 
  

   identity 
  is 
  readily 
  established. 
  The 
  two 
  pronuclei 
  now 
  give 
  place 
  

   to 
  the 
  newly 
  formed 
  cleavage 
  nuclei. 
  Whether 
  they 
  degenerate 
  and 
  

   are 
  absorbed 
  by 
  the 
  cytoplasm, 
  which 
  gives 
  rise 
  simultaneously 
  to 
  

   new 
  chromatin 
  material 
  in 
  the 
  cleavage 
  nuclei, 
  or 
  whether 
  some 
  

   of 
  these 
  latter 
  arise 
  directly 
  from 
  the 
  former 
  by 
  the 
  development 
  

   of 
  membranes 
  about 
  one 
  or 
  more 
  of 
  their 
  chromosomes 
  is 
  difficult 
  to 
  

   say. 
  The 
  occurrence 
  of 
  groups 
  of 
  chromosomes 
  exactly 
  resembling 
  

   those 
  of 
  the 
  male 
  and 
  female 
  pronuclei, 
  about 
  which 
  incomplete 
  

   membranes 
  may 
  be 
  seen, 
  and 
  of 
  immature 
  nuclei 
  containing 
  much 
  

   smaller 
  chromatin 
  granules 
  inclines 
  me 
  to 
  believe 
  that 
  both 
  these 
  

   processes 
  occur. 
  

  

  In 
  the 
  earlier 
  stages 
  of 
  cleavage 
  I 
  have 
  practically 
  no 
  evidence 
  

   of 
  mitosis; 
  in 
  later 
  stages 
  on 
  the 
  contrary 
  it 
  is 
  of 
  fairly 
  common 
  

   occurrence. 
  To 
  obtain 
  an 
  idea 
  of 
  the 
  relative 
  frequence 
  of 
  mitosis 
  

   at 
  these 
  stages 
  I 
  have 
  made 
  the 
  following 
  counts 
  ^) 
  : 
  

  

  the 
  pronuclei, 
  while 
  the 
  latter 
  represents 
  two 
  cleavage 
  nuclei. 
  Fig. 
  86 
  

   was 
  taken 
  from 
  an 
  egg 
  in 
  a 
  proglottid 
  showing 
  numerous 
  cases 
  of 
  pronuclear 
  

   fusion, 
  one 
  of 
  which 
  is 
  shown 
  in 
  Fig. 
  87. 
  Furthermore 
  the 
  egg 
  from 
  

   which 
  this 
  figure 
  was 
  taken 
  showed 
  only 
  two 
  nuclei, 
  while 
  that 
  from 
  

   which 
  Fig. 
  89 
  was 
  taken 
  contained 
  more 
  than 
  two, 
  and 
  was 
  surrounded 
  

   by 
  eggs 
  in 
  various 
  stages 
  of 
  cleavage. 
  

  

  1) 
  I 
  cannot 
  speak 
  with 
  certainty 
  on 
  this 
  point. 
  

  

  2) 
  The 
  total 
  number 
  of 
  embryos 
  studied, 
  especially 
  in 
  early 
  stages, 
  

  

  