﻿SOME 
  NEW 
  SPECIES 
  OF 
  THI<1 
  GENUS 
  PHREODRILUS. 
  291 
  

  

  Turning 
  now 
  to 
  the 
  sections 
  through 
  this 
  region. 
  The 
  

   figures 
  24, 
  26, 
  26 
  are 
  nearly 
  consecutive, 
  and 
  pass 
  through 
  

   the 
  ati'ium 
  where 
  it 
  traverses 
  the 
  penis. 
  

  

  The 
  first 
  figure 
  is 
  nearly 
  longitudiualj 
  as 
  it 
  cuts 
  the 
  atrium 
  

   at 
  a 
  curve 
  ; 
  on 
  the 
  right 
  side 
  of 
  the 
  figure, 
  at 
  y, 
  the 
  atrial 
  

   epithelium 
  appears 
  to 
  be 
  invaginated 
  into 
  the 
  cavity 
  of 
  the 
  

   tube. 
  As 
  a 
  matter 
  of 
  fact, 
  the 
  lining 
  of 
  the 
  tube 
  is 
  here 
  

   thrown 
  into 
  longitudinal 
  folds, 
  so 
  that 
  the 
  lumen 
  is 
  more 
  or 
  

   less 
  reduced. 
  The 
  next 
  section 
  (fig. 
  25) 
  is 
  the 
  fourth 
  from 
  

   the 
  preceding, 
  and 
  cuts 
  the 
  atrium 
  nearly 
  transversely. 
  The 
  

   atrial 
  sac 
  is 
  much 
  reduced 
  in 
  size, 
  and 
  the 
  atrial 
  wall 
  itself 
  

   is 
  folded 
  (at 
  y). 
  The 
  following 
  section 
  (fig. 
  26) 
  involves 
  the 
  

   very 
  tip 
  of 
  the 
  short 
  penis, 
  cutting 
  it 
  through 
  rather 
  obliquely. 
  

   The 
  penis 
  in 
  this 
  individual 
  is 
  less 
  prominent 
  than 
  in 
  the 
  

   individual 
  dissected 
  (compare 
  fig. 
  26 
  with 
  fig. 
  17), 
  for 
  in 
  it 
  

   the 
  penial 
  sac 
  was 
  protruded 
  and 
  the 
  penis 
  partially 
  so. 
  

   The 
  section 
  figured 
  at 
  fig. 
  26 
  is 
  taken 
  just 
  where 
  the 
  atrial 
  

   epithelium 
  is 
  being 
  reflected 
  so 
  as 
  to 
  approach 
  (and 
  on 
  the 
  

   right 
  side 
  has 
  reached) 
  the 
  inner 
  wall 
  of 
  the 
  atrial 
  sac. 
  

   In 
  the 
  centre 
  of 
  the 
  section 
  the 
  aperture 
  of 
  the 
  penis 
  is 
  

   shown. 
  

  

  The 
  epithelium 
  of 
  the 
  atrium 
  is 
  continuous 
  at 
  the 
  pore 
  

   with 
  that 
  covering 
  the 
  cervical 
  penis, 
  and 
  thus 
  with 
  the 
  

   lining 
  of 
  the 
  penial 
  sac, 
  and 
  this 
  epithelium 
  retains 
  practi- 
  

   cally 
  its 
  previous 
  character, 
  but 
  the 
  cytoplasm 
  appears 
  to 
  be 
  

   vertically 
  striated, 
  especially 
  at 
  the 
  outer 
  (basal) 
  sui-face, 
  

   where 
  minute 
  vacuoles 
  as 
  of 
  some 
  secretion 
  can 
  be 
  seen, 
  

   while 
  the 
  cuticle 
  is 
  thicker 
  than 
  before 
  (fig. 
  27). 
  

  

  There 
  is 
  here 
  no 
  circular 
  coat 
  of 
  muscle, 
  but 
  to 
  the 
  wall 
  is 
  

   attached 
  a 
  number 
  of 
  retractor 
  muscle-fibres 
  (as 
  in 
  figs. 
  17, 
  

   28), 
  and 
  outside 
  is 
  a 
  layer 
  of 
  flat 
  peritoneal 
  nuclei. 
  

  

  The 
  epithelium 
  of 
  this 
  penial 
  sac 
  passes 
  up 
  to 
  the 
  lip 
  of 
  

   the 
  external 
  pore, 
  and 
  is 
  here 
  continuous 
  of 
  course 
  with 
  the 
  

   epidermis; 
  but 
  there 
  is 
  a 
  sudden 
  change 
  (fig. 
  28), 
  no 
  transi- 
  

   tion 
  being 
  apparent, 
  the 
  epidermal 
  cells 
  having 
  flattened 
  

   oval 
  nuclei, 
  which 
  are 
  much 
  smaller 
  and 
  take 
  the 
  stain 
  very 
  

  

  