﻿Eeproductive 
  organs 
  of 
  Taenia 
  pisiformis. 
  377 
  

  

  ance 
  of 
  distinct 
  skeins, 
  corresponding 
  to 
  the 
  close 
  skeins 
  of 
  an 
  

   ordinary 
  mitotic 
  prophase. 
  This 
  is 
  succeeded 
  by 
  a 
  loose 
  skein 
  

   stage. 
  Coincident 
  with 
  the 
  appearance 
  of 
  the 
  skeins 
  the 
  nuclei 
  of 
  

   the 
  spermatogonia 
  enlarge, 
  and 
  the 
  latter 
  fuse 
  to 
  form 
  a 
  cytophore 
  

   in 
  which 
  cell 
  walls 
  are 
  lacking, 
  the 
  nuclei 
  being 
  imbedded 
  directly 
  

   in 
  the 
  peripheral 
  cytoplasm 
  of 
  the 
  latter. 
  This 
  cytoplasm 
  is 
  similar 
  

   to 
  that 
  of 
  the 
  cytogenic 
  masses 
  described 
  by 
  me 
  elsewhere 
  (Young, 
  

   1908 
  and 
  1910). 
  With 
  the 
  formation 
  of 
  skeins 
  there 
  is 
  marked 
  in- 
  

   crease 
  of 
  chromatin. 
  Whether 
  this 
  is 
  due 
  to 
  enlargement 
  of 
  the 
  

   préexistent 
  chromatic 
  network, 
  or 
  whether 
  new 
  chromatin 
  is 
  added 
  

   de 
  novo 
  to 
  the 
  latter 
  from 
  the 
  cytoplasm, 
  or 
  whether 
  both 
  methods 
  

   play 
  a 
  part 
  is 
  impossible 
  to 
  say. 
  

  

  The 
  growth 
  period 
  here 
  is 
  not 
  pronounced, 
  the 
  increase 
  in 
  the 
  

   spermatogonial 
  nuclei 
  to 
  form 
  primary 
  spermatocytes^) 
  being 
  only 
  

   from 
  2,2 
  to 
  3,1 
  /«.-) 
  It 
  is 
  moreover 
  coincident 
  with 
  the 
  appearance 
  

   of 
  the 
  prophase 
  of 
  an 
  abortive 
  maturation 
  division. 
  A 
  similar 
  

   phenomenon 
  occurs 
  in 
  oogenesis 
  ^) 
  (Fig. 
  43). 
  

  

  The 
  cytophores 
  now 
  enlarge 
  by 
  the 
  formation 
  of 
  more 
  granulo- 
  

   fibrillar 
  cytoplasm, 
  but 
  the 
  spermatocytes 
  do 
  not 
  increase 
  in 
  size. 
  

   Karyokinetic 
  stages 
  later 
  than 
  the 
  prophase 
  I 
  have 
  observed 
  in 
  but 
  

   four 
  doubtful 
  instances.*) 
  The 
  skeins 
  now 
  break 
  down 
  and 
  are 
  

   distributed 
  thru 
  the 
  cytophore. 
  Evidence 
  of 
  this 
  is 
  found 
  in 
  the 
  

   presence 
  of 
  skein 
  fragments 
  in 
  the 
  cytophore 
  during 
  the 
  disappear- 
  

   ance 
  of 
  the 
  peripheral 
  skeins. 
  While 
  these 
  are 
  disappearing 
  and 
  

   the 
  cytophore 
  enlarging 
  new 
  nuclei 
  are 
  arising 
  in 
  the 
  latter, 
  which 
  

   I 
  shall 
  call 
  secondary 
  spermatocytes 
  (Figs. 
  44—46 
  and 
  49). 
  These 
  

   are 
  smaller 
  than 
  the 
  primary 
  and 
  contain 
  a 
  relatively 
  small 
  amount 
  

   of 
  chromatin, 
  which 
  is 
  usually 
  in 
  the 
  form 
  of 
  one 
  or 
  more 
  ''nucleoli" 
  

   and 
  a 
  few 
  secondary 
  granules 
  supported 
  by 
  a 
  delicate 
  linin 
  network. 
  

   In 
  many 
  cases 
  the 
  nuclear 
  membrane 
  is 
  apparently 
  complete, 
  but 
  in 
  

   some 
  it 
  is 
  obviously 
  not 
  so. 
  

  

  The 
  origin 
  of 
  the 
  secondary 
  spermatocytes 
  is 
  uncertain. 
  There 
  

   is 
  no 
  evidence 
  of 
  their 
  direct 
  origin 
  from 
  the 
  primary 
  spermatocytes, 
  

   nor 
  is 
  there 
  any 
  certain 
  evidence 
  of 
  their 
  de 
  novo 
  formation. 
  The 
  

  

  1) 
  Since 
  a 
  syncitium 
  is 
  formed 
  I 
  shall 
  henceforward 
  refer 
  to 
  the 
  

   nuclei 
  alone 
  in 
  mentioning 
  the 
  spermatogenic 
  elements. 
  

  

  2) 
  Average 
  of 
  eight 
  measurements. 
  

  

  3) 
  See 
  page 
  385. 
  

  

  4) 
  In 
  1900 
  nuclei 
  counted 
  I 
  found 
  one 
  doubtful 
  metaphase. 
  

  

  