﻿360 
  R- 
  T. 
  Young, 
  

  

  while 
  others 
  have 
  both 
  membranes 
  and 
  "nucleoli". 
  In 
  some 
  nuclei 
  

   the 
  former 
  is 
  but 
  partly 
  formed, 
  in 
  others 
  apparently 
  complete. 
  

   These 
  nuclear 
  variations 
  have 
  been 
  discussed 
  by 
  me 
  at 
  length 
  in 
  

   two 
  preceding 
  papers 
  (Young, 
  1908, 
  1910) 
  to 
  which 
  discussion 
  I 
  

   have 
  nothing 
  further 
  to 
  add. 
  

  

  The 
  detailed 
  development 
  of 
  each 
  part 
  of 
  the 
  reproductive 
  

   system 
  will 
  now 
  be 
  considered 
  separately. 
  

  

  The 
  vagina 
  at 
  the 
  time 
  of 
  its 
  separation 
  from 
  the 
  vas 
  deferens 
  

   consists 
  of 
  a 
  narrow 
  cord 
  of 
  nuclei 
  three 
  or 
  four 
  rows 
  deep, 
  im- 
  

   bedded 
  in 
  a 
  fibrillar 
  cytoplasmic 
  network. 
  Soon 
  a 
  narrow 
  lumen 
  

   arises 
  by 
  a 
  splitting 
  at 
  the 
  center 
  of 
  this 
  mass 
  ^) 
  and 
  simultaneously 
  

   the 
  two 
  layers 
  of 
  the 
  wall 
  with 
  their 
  intervening 
  basement 
  mem- 
  

   brane 
  are 
  differentiated 
  (Figs. 
  10 
  and 
  12). 
  The 
  latter, 
  which 
  is 
  at 
  

   first 
  very 
  thin 
  and 
  indefinite, 
  appears 
  to 
  arise 
  directly 
  from 
  paren- 
  

   chyma 
  strands, 
  as 
  it 
  is 
  in 
  continuity 
  with 
  these. 
  It 
  soon 
  thickens 
  

   somewhat 
  and 
  becomes 
  much 
  more 
  distinct. 
  Whether 
  this 
  differen- 
  

   tiation 
  is 
  due 
  to 
  the 
  addition 
  of 
  parenchyma 
  strands 
  to 
  the 
  mem- 
  

   brane 
  or 
  by 
  growth 
  of 
  the 
  original 
  slight 
  layer 
  I 
  cannot 
  say. 
  

   Possibly 
  both 
  methods 
  play 
  a 
  part, 
  but 
  I 
  regard 
  the 
  latter 
  as 
  prob- 
  

   ably 
  the 
  more 
  important. 
  The 
  thickness 
  of 
  this 
  membrane 
  depends 
  

   of 
  course 
  on 
  the 
  amount 
  of 
  distension 
  of 
  the 
  duct. 
  It 
  is 
  typically 
  

   a 
  fairly 
  distinct 
  membrane, 
  becoming 
  in 
  later 
  stages 
  intimately 
  

   united 
  with 
  the 
  inner 
  layer. 
  The 
  inner 
  layer 
  of 
  the 
  syncytial 
  

   cord 
  arranges 
  itself 
  as 
  a 
  row^) 
  of 
  nuclei 
  imbedded 
  in 
  a 
  fibrillar 
  

   cytoplasmic 
  mass, 
  whose 
  meshes 
  give 
  the 
  impression 
  of 
  outlining 
  

   low 
  columnar 
  or 
  cubical 
  cells, 
  but 
  in 
  which 
  no 
  distinct 
  cell 
  outlines 
  

   are 
  discernible. 
  The 
  outer 
  layer 
  consists 
  also 
  of 
  a 
  single 
  row 
  of 
  

   nuclei 
  with 
  surrounding 
  cytoplasm, 
  the 
  meshes 
  of 
  which 
  are 
  so 
  

   arranged 
  as 
  to 
  give 
  the 
  impression 
  of 
  a 
  simple 
  or 
  pseudo-stratified 
  

   layer 
  of 
  cells 
  of 
  varying 
  height 
  and 
  less 
  regular 
  in 
  form 
  and 
  arrange- 
  

   ment 
  than 
  those 
  in 
  the 
  inner 
  layer. 
  But 
  here 
  too 
  distinct 
  cell 
  

   outlines 
  are 
  wanting 
  (Fig. 
  12).^) 
  

  

  The 
  lumen 
  meantime 
  enlarges 
  slightly 
  thruout 
  the 
  greater 
  part 
  

  

  1) 
  My 
  observations 
  agree 
  in 
  this 
  respect 
  with 
  the 
  statements 
  of 
  

   Braun 
  (1894—1900), 
  Lungavitz 
  (1895), 
  Gough 
  (1911) 
  etc., 
  and 
  differ 
  

   from 
  those 
  of 
  MONIEZ 
  (1881), 
  who 
  claims 
  that 
  the 
  lumen 
  arises 
  by 
  de- 
  

   generation 
  in 
  the 
  axial 
  cord 
  of 
  cells. 
  

  

  2) 
  Two 
  rows 
  in 
  the 
  seminal 
  receptacle. 
  

  

  3) 
  Contra 
  GoUGH 
  (1911) 
  who 
  finds 
  the 
  outlines 
  of 
  these 
  cells 
  very 
  

   distinct 
  in 
  Avitellina 
  centripiindata. 
  

  

  