﻿20 
  

  

  H. 
  S. 
  Pratt, 
  

  

  is 
  a 
  continuation 
  of 
  the 
  median 
  indentation 
  of 
  the 
  posterior 
  (dorsalj 
  

   lip 
  of 
  the 
  vulva 
  mentioned 
  above 
  and 
  a 
  sagittal 
  section 
  of 
  the 
  vagina, 
  

   which 
  would 
  pass 
  through 
  this 
  groove 
  its 
  entire 
  length, 
  would 
  repre- 
  

   sent 
  the 
  dorsal 
  vaginal 
  wall 
  as 
  becoming 
  rapidly 
  higher 
  anteriad 
  as 
  

   far 
  as 
  the 
  beginning 
  of 
  the 
  uterus 
  (PL 
  II, 
  Fig. 
  3 
  vag). 
  A 
  comparison 
  

   of 
  this 
  section, 
  however, 
  with 
  the 
  cross-section 
  (Fig. 
  5) 
  shows 
  at 
  once 
  

   that 
  the 
  portions 
  of 
  the 
  dorsal 
  vaginal 
  wall 
  to 
  the 
  right 
  and 
  left 
  of 
  the 
  

   median 
  line 
  do 
  not 
  thus 
  increase 
  in 
  height. 
  The 
  two 
  lateral 
  grooves 
  

   of 
  the 
  dorsal 
  vaginal 
  wall 
  (Fig. 
  5) 
  are 
  continuations 
  of 
  the 
  grooves 
  

   mentioned 
  above 
  (Fig. 
  6 
  gr) 
  which 
  bound 
  the 
  plate 
  (Fig. 
  1 
  ch.pl) 
  forni- 
  

   ing 
  the 
  posterior 
  lip 
  of 
  the 
  vulva. 
  The 
  cuticula 
  of 
  the 
  dorsal 
  wall 
  

   is 
  hard 
  and 
  yellow 
  like 
  that 
  of 
  the 
  outside 
  of 
  the 
  body 
  and 
  is 
  

   studded 
  with 
  small, 
  chitinous 
  bristles, 
  deflected 
  towards 
  the 
  vulva. 
  

   The 
  cuticula 
  of 
  the 
  ventral 
  wall 
  is 
  thicker 
  than 
  that 
  of 
  the 
  dorsal 
  

   wall 
  but 
  is 
  not 
  hard 
  and 
  yellow 
  and 
  contains 
  no 
  spines. 
  

  

  The 
  vagina 
  is 
  very 
  evidently 
  an 
  infolding 
  of 
  the 
  outer 
  body- 
  

   wall. 
  Its 
  cuticula 
  and 
  hypodermis 
  are 
  identical 
  with 
  those 
  of 
  the 
  

   body-wall 
  and 
  a 
  direct 
  continuation 
  of 
  them, 
  and 
  its 
  muscles 
  

   undoubtedly 
  also 
  belong 
  to 
  it. 
  These 
  muscles 
  form 
  several 
  distinct 
  

   groups 
  of 
  fibres 
  and 
  the 
  function 
  of 
  all 
  of 
  them 
  is 
  to 
  increase 
  the 
  

   capacity 
  of 
  the 
  vagina 
  during 
  the 
  growth 
  of 
  the 
  larva 
  and 
  at 
  the 
  time 
  

   of 
  a 
  birth. 
  The 
  most 
  important 
  of 
  them 
  is, 
  perhaps, 
  a 
  paired 
  group 
  

   of 
  fibres 
  which 
  connects 
  the 
  dorsal 
  vaginal 
  wall 
  and 
  the 
  posterior 
  

   (dorsal) 
  lip 
  of 
  the 
  vulva 
  with 
  a 
  broad 
  ingrowth 
  of 
  the 
  body-wall 
  

   situated 
  directly 
  dorsad 
  of 
  the 
  anus 
  (PL 
  II, 
  Fig. 
  3 
  p.R). 
  These 
  muscles 
  

   appear 
  fan-shaped 
  in 
  longitudinal 
  section 
  (PL 
  II, 
  Fig. 
  3 
  d.vag.mus); 
  

   they 
  Surround 
  the 
  end-intestine, 
  which 
  runs 
  through 
  them 
  and 
  divides 
  

   them 
  into 
  two 
  equal 
  divisions. 
  Laterad 
  of 
  this 
  group 
  of 
  fibres 
  on 
  

   each 
  side 
  are 
  muscles-fibres 
  which 
  connect 
  the 
  lateral 
  portions 
  of 
  

   the 
  dorsal 
  wall 
  of 
  the 
  vagina 
  with 
  the 
  dorsal 
  body-wall 
  (PL 
  II, 
  

   Fig. 
  5 
  and 
  6). 
  

  

  The 
  significance 
  of 
  the 
  folds 
  of 
  the 
  dorsal 
  vaginal 
  wall 
  will 
  be 
  

   clearly 
  seen 
  from 
  their 
  relation 
  to 
  these 
  muscles. 
  When 
  the 
  latter 
  

   are 
  contracted 
  the 
  folds 
  are 
  lifted 
  and 
  the 
  capacity 
  of 
  the 
  vagina 
  

   thereby 
  very 
  largely 
  increased. 
  This 
  takes 
  place 
  not 
  only 
  during 
  

   birth 
  but 
  also 
  during 
  the 
  growth 
  of 
  the 
  young 
  larva 
  in 
  the 
  uterus. 
  

   The 
  spiracles 
  of 
  the 
  larva, 
  as 
  is 
  so 
  common 
  among 
  Diptera, 
  are 
  on 
  

   the 
  hinder 
  end 
  of 
  the 
  body. 
  They 
  are 
  thus 
  directed 
  towards 
  the 
  

   maternal 
  vagina 
  (PL 
  II, 
  Fig. 
  4 
  lar.sp), 
  and 
  the 
  air 
  necessary 
  for 
  the 
  

   respiration 
  of 
  the 
  larva 
  must 
  come 
  fthrough 
  that 
  organ. 
  The 
  figure 
  

  

  