﻿370 
  -R. 
  T. 
  Young, 
  

  

  it 
  may 
  be 
  absent 
  — 
  viz., 
  Bothriocephalus 
  latus 
  (Moniez, 
  1881), 
  B. 
  

   pundatus 
  (Löxnbeeg, 
  1891), 
  etc. 
  

  

  The 
  yolk 
  duct 
  develops 
  similarly 
  to 
  the 
  oviduct. 
  The 
  main 
  

   trunk 
  is 
  differentiated 
  like 
  the 
  latter 
  out 
  of 
  the 
  common 
  anläge 
  

   already 
  described, 
  while 
  the 
  branches 
  arise 
  from 
  cords 
  of 
  cells, 
  whichy 
  

   like 
  the 
  oviduct 
  branches, 
  appear 
  to 
  arise 
  independently 
  in 
  the 
  

   parenchyma, 
  tho 
  precisely 
  to 
  what 
  extent 
  they 
  arise 
  independently 
  

   and 
  how 
  far 
  by 
  outgrowth 
  from 
  the 
  main 
  stem 
  1 
  cannot 
  say 
  (Figs. 
  18 
  

   and 
  19). 
  An 
  ampulla 
  or 
  enlargement 
  of 
  the 
  yolk 
  duct 
  as 
  described 
  

   by 
  Sommer 
  & 
  Landois 
  (1872) 
  in 
  Bothriocephalus 
  latus, 
  Lönxberg(1891) 
  

   in 
  B. 
  piDictatiis, 
  and 
  Balss 
  (1908) 
  in 
  Anoplocephala 
  magna 
  is 
  absent 
  

   here. 
  The 
  proximal 
  end 
  of 
  the 
  duct 
  may 
  however 
  be 
  greatly 
  

   distended 
  with 
  j'Olk 
  cells 
  giving 
  it 
  an 
  ampulla-like 
  enlargement, 
  

   when 
  the 
  wall 
  naturally 
  becomes 
  greatly 
  thinned 
  and 
  the 
  epithelium 
  

   much 
  flattened. 
  Muscles 
  however 
  are 
  lacking 
  and 
  hence 
  no 
  distinct 
  

   ampulla 
  or 
  "Schluckapparat" 
  occurs. 
  

  

  Similar 
  differences 
  regarding 
  the 
  structure 
  of 
  the 
  wall 
  of 
  the 
  

   yolk 
  duct 
  are 
  found 
  in 
  the 
  literature 
  as 
  those 
  relating 
  to 
  the 
  wall 
  

   of 
  the 
  oviduct, 
  and 
  may 
  I 
  believe 
  be 
  interpreted 
  similarly. 
  

  

  The 
  uterus 
  appears 
  shortly 
  after 
  the 
  growth 
  of 
  the 
  vagina 
  

   to 
  the 
  posterior 
  part 
  of 
  the 
  proglottid 
  as 
  a 
  slender 
  cord 
  of 
  cells 
  

   extending 
  thru 
  much 
  of 
  the 
  proglottid 
  in 
  a 
  longitudinal 
  direction 
  

   (Figs. 
  2 
  and 
  3). 
  Whether 
  this 
  cord 
  arises 
  as 
  an 
  outgrowth 
  of 
  the 
  mass 
  

   of 
  cells 
  at 
  the 
  posterior 
  end 
  of 
  the 
  vagina 
  or 
  independently 
  thereof 
  

   has 
  already 
  been 
  discussed. 
  The 
  differentiation 
  of 
  epithelium, 
  

   basement 
  membrane 
  and 
  outer 
  layer 
  of 
  the 
  uterus 
  wall 
  is 
  in 
  general 
  

   similar 
  to 
  that 
  of 
  the 
  ducts 
  already 
  described. 
  Here 
  however 
  the 
  

   basement 
  membrane 
  is 
  not 
  well 
  developed 
  and 
  the 
  two 
  laj^ers 
  are 
  

   consequently 
  not 
  as 
  sharply 
  separated 
  from 
  each 
  other 
  as 
  elsewhere. 
  

   The 
  outer 
  moreover 
  shows 
  a 
  less 
  regular 
  arrangement 
  than 
  is 
  present 
  

   at 
  first 
  in 
  most 
  of 
  the 
  ducts. 
  The 
  epithelium 
  at 
  first 
  consists 
  of 
  

   low 
  cuboidal 
  cells, 
  which 
  with 
  the 
  enlargement 
  of 
  the 
  uterus 
  undergo 
  

   extensive 
  separation 
  and 
  flattening, 
  finally 
  forming 
  isolated 
  flat 
  cells 
  

   lying 
  upon 
  the 
  thin 
  basement 
  membrane 
  which 
  ultimately 
  forms 
  the 
  

   main 
  part 
  of 
  the 
  uterus 
  wall. 
  The 
  cells 
  of 
  the 
  outer 
  layer 
  have 
  

   meantime 
  become 
  widely 
  separated 
  from 
  each 
  other 
  and 
  merged 
  

   with 
  the 
  parenchyma, 
  so 
  that 
  ultimately 
  a 
  definite 
  outer 
  layer 
  ceases 
  

   to 
  exist, 
  the 
  membrane 
  being 
  bounded 
  directly 
  by 
  the 
  parenchyma 
  

   (Figs. 
  16 
  and 
  24). 
  

  

  There 
  is 
  here 
  the 
  same 
  difference 
  of 
  opinion 
  regarding 
  the 
  

  

  