﻿372 
  ^- 
  T. 
  Young, 
  

  

  the 
  reproductive 
  ducts 
  may 
  be 
  postponed 
  to 
  the 
  discussion 
  of 
  

   results. 
  

  

  The 
  reproductive 
  glands. 
  There 
  is 
  comparatively 
  little 
  

   in 
  the 
  literature 
  regarding 
  the 
  development 
  of 
  sex 
  cells 
  and 
  j'olk 
  

   cells 
  in 
  cestodes. 
  Several 
  writers 
  mention 
  these 
  topics 
  but 
  their 
  

   observations 
  are 
  mostly 
  very 
  incomplete, 
  and 
  need 
  repetition 
  and 
  

   revision. 
  Of 
  recent 
  writers 
  Child 
  (1907, 
  I 
  — 
  V) 
  has 
  given 
  detailed 
  

   accounts 
  of 
  oogenesis 
  and 
  spermatogenesis 
  in 
  Moiiie^a, 
  Gough 
  (1909) 
  

   an 
  account 
  of 
  these 
  processes 
  in 
  Stilesia 
  centripunctata, 
  von 
  Janicki 
  

   (1907) 
  of 
  oogenesis 
  in 
  Taem'wserm^a 
  and 
  Richards 
  (1911) 
  of 
  oogenesis 
  

   in 
  Monie^ia}) 
  This 
  paucity 
  of 
  data 
  is 
  probably 
  due 
  to 
  the 
  fact 
  

   that 
  cestodes 
  are 
  less 
  favorable 
  for 
  cytological 
  study 
  than 
  other 
  

   forms. 
  The 
  sex 
  cells 
  are 
  comparatively 
  small 
  and 
  closely 
  packed 
  

   together 
  and 
  their 
  structures 
  lack 
  the 
  sharpness 
  of 
  definition 
  so 
  

   desirable 
  in 
  cytological 
  work, 
  rendering 
  the 
  determination 
  of 
  finer 
  

   details, 
  such 
  as 
  number 
  of 
  chromosomes, 
  their 
  plane 
  of 
  division, 
  

   structure 
  of 
  spermatozoa 
  etc. 
  very 
  difficult. 
  These 
  difficulties 
  are 
  

   not 
  however 
  a 
  sufficient 
  reason 
  for 
  avoiding 
  a 
  subject 
  which 
  is 
  of 
  

   especial 
  interest 
  because 
  gametogenesis 
  in 
  cestodes 
  differs 
  widely 
  

   from 
  that 
  in 
  other 
  animals. 
  

  

  The 
  testis 
  and 
  spermatogenesis. 
  At 
  about 
  the 
  time 
  

   that 
  the 
  uterus, 
  ovary 
  and 
  yolk 
  gland 
  appear 
  or 
  a 
  little 
  earlier, 
  

   the 
  testes 
  appear 
  as 
  small 
  groups 
  of 
  cells 
  scattered 
  thru 
  the 
  paren- 
  

   chyma 
  within 
  the 
  longitudinal 
  muscles 
  (Figs. 
  2—4). 
  These 
  cell 
  groups 
  

   are 
  formed 
  from 
  parenchyma 
  cells 
  which 
  are 
  at 
  first 
  indistinguish- 
  

   able 
  from 
  their 
  fellows 
  and 
  can 
  be 
  identified 
  with 
  certainty 
  only 
  

   after 
  testis 
  development 
  has 
  begun. 
  The 
  cells 
  actively 
  divide 
  and 
  

   the 
  testis 
  anläge 
  increases 
  correspondingly 
  in 
  size. 
  It 
  now 
  appears 
  

   as 
  a 
  spherical 
  or 
  ovoid 
  collection 
  of 
  cells 
  surrounded 
  b}^ 
  a 
  delicate 
  

   membrane. 
  The 
  cells 
  composing 
  this 
  group 
  are 
  themselves 
  generally 
  

   spherical 
  or 
  ovoid 
  in 
  shape 
  with 
  relatively 
  large 
  nuclei 
  and 
  small 
  

   amounts 
  of 
  cytoplasm.^) 
  The 
  nuclei 
  present 
  features 
  of 
  special 
  

   interest. 
  They 
  consist 
  of 
  irregular 
  masses 
  of 
  chromatin 
  gathered 
  in 
  

   groups 
  whose 
  general 
  form 
  is 
  that 
  of 
  the 
  containing 
  cell. 
  They 
  

  

  1) 
  Richards 
  (1909) 
  has 
  made 
  brief 
  reference 
  to 
  this 
  process 
  in 
  Taenia, 
  

   and 
  I 
  (1912a) 
  have 
  already' 
  given 
  a 
  preliminary 
  account 
  of 
  the 
  present 
  

   work. 
  

  

  2) 
  Cell 
  3,4 
  jLi, 
  nucleus 
  2,2 
  fi, 
  in 
  diameter. 
  Average 
  of 
  eight 
  measure- 
  

   ments. 
  

  

  