﻿170 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  i03 
  

  

  changeable. 
  In 
  specimens 
  that 
  were 
  fixed 
  in 
  a 
  well-extended 
  condi- 
  

   tion, 
  the 
  bulb 
  appears 
  spherical 
  and 
  the 
  papilla 
  has 
  a 
  conical 
  shape. 
  

   The 
  bulb 
  contains 
  a 
  spacious, 
  irregularly 
  lobed 
  cavity, 
  the 
  seminal 
  

   vesicle 
  (vs). 
  Numerous 
  gland 
  ducts 
  empty 
  into 
  the 
  lumen 
  of 
  the 
  

   bulb 
  after 
  entering 
  the 
  bulb, 
  particularly 
  from 
  its 
  anterior 
  surface, 
  

   and 
  penetrating 
  between 
  its 
  muscle 
  fibers. 
  The 
  ducts 
  are 
  filled 
  

   with 
  a 
  granular, 
  slightly 
  eosinophilic 
  secretion. 
  The 
  two 
  vasa 
  

   deferentia 
  (vd) 
  open 
  into 
  the 
  seminal 
  vesicle 
  separately 
  from 
  the 
  

   anterolateral 
  sides. 
  

  

  The 
  penis 
  papUla 
  is 
  conical 
  or 
  finger-shaped 
  when 
  well 
  extended. 
  It 
  

   is 
  covered 
  with 
  a 
  cubical 
  epithelium 
  below 
  which 
  there 
  are 
  two 
  rather 
  

   feebly 
  developed 
  muscle 
  layers, 
  tapering 
  in 
  thickness 
  toward 
  the 
  tip 
  

   of 
  the 
  papilla: 
  a 
  layer 
  of 
  circular 
  fibers 
  adjoining 
  the 
  epithelium 
  and 
  

   a 
  thinner 
  layer 
  of 
  longitudinal 
  ifibers. 
  The 
  absence 
  of 
  a 
  strong 
  mus- 
  

   cular 
  wall 
  probably 
  accounts 
  for 
  the 
  great 
  variation 
  in 
  the 
  shape 
  of 
  

   the 
  penis 
  papilla 
  observed 
  in 
  the 
  material. 
  The 
  lumen 
  of 
  the 
  seminal 
  

   vesicle 
  continues 
  into 
  the 
  papilla 
  as 
  a 
  wide 
  canal 
  (de), 
  opening 
  at 
  or 
  

   near 
  (ventrally 
  to) 
  the 
  tip 
  of 
  the 
  papUla. 
  The 
  canal 
  is 
  lined 
  with 
  an 
  

   epithelium 
  of 
  cubical 
  cells 
  and 
  lacks 
  the 
  gland 
  openings 
  character- 
  

   istic 
  of 
  the 
  seminal 
  vesicle. 
  It 
  corresponds 
  to 
  an 
  ejaculatory 
  duct 
  

   but 
  it 
  apparently 
  has 
  no 
  distinct 
  muscle 
  coat. 
  

  

  The 
  two 
  oviducts, 
  riuming 
  posteriorly 
  along 
  the 
  ventral 
  nerve 
  

   cords, 
  bend 
  dorsally 
  and 
  medially 
  at 
  the 
  level 
  of 
  the 
  copulatory 
  

   organs. 
  The 
  left 
  one 
  passes 
  through 
  the 
  space 
  between 
  the 
  atrium 
  

   and 
  the 
  bursa 
  duct 
  and 
  unites 
  with 
  the 
  oviduct 
  of 
  the 
  right 
  side 
  

   dorsally 
  to 
  the 
  atrium. 
  The 
  common 
  oviduct 
  {ode) 
  runs 
  ventrally 
  

   and 
  opens 
  into 
  the 
  posterior 
  part 
  of 
  the 
  atrial 
  cavity. 
  The 
  terminal 
  

   sections 
  of 
  the 
  paired 
  oviducts 
  and 
  a 
  section 
  of 
  the 
  common 
  oviduct 
  

   are 
  equipped 
  with 
  strongly 
  eosinophilic 
  shell 
  glands. 
  

  

  The 
  copulatory 
  bursa 
  (6) 
  is 
  a 
  large 
  sac 
  with 
  a 
  lobed 
  outline. 
  It 
  

   connects 
  posteriorly 
  with 
  a 
  duct 
  of 
  almost 
  uniformly 
  wide 
  diameter, 
  

   the 
  bursa 
  stalk 
  (bd). 
  The 
  duct 
  runs 
  first 
  posteriorly, 
  to 
  the 
  left 
  of 
  

   the 
  penis 
  bulb, 
  then 
  curves 
  ventrally 
  and 
  opens, 
  from 
  the 
  dorsal 
  side, 
  

   into 
  the 
  narrow 
  terminal 
  portion 
  of 
  the 
  atrium, 
  close 
  to 
  the 
  genital 
  

   pore. 
  The 
  bursa 
  stalk 
  has 
  a 
  strong 
  coat 
  of 
  intermingled 
  circular 
  and 
  

   longitudinal 
  muscle 
  fibers. 
  There 
  is 
  no 
  histological 
  differentiation 
  

   into 
  anterior 
  and 
  posterior 
  sections 
  of 
  the 
  bursa 
  stalk. 
  

  

  Taxonomic 
  position. 
  — 
  Polycelis 
  borealis 
  is 
  the 
  second 
  species 
  of 
  the 
  

   genus 
  Polycelis 
  to 
  be 
  found 
  on 
  the 
  North 
  American 
  continent. 
  The 
  

   other 
  species, 
  P. 
  coronata 
  (Girard), 
  reported 
  from 
  Wyoming 
  and 
  South 
  

   Dakota 
  (Hyman, 
  1931), 
  resembles 
  it 
  closely 
  in 
  external 
  appearance 
  

   and 
  probably 
  cannot 
  be 
  distinguished 
  from 
  it 
  in 
  life. 
  In 
  both 
  species, 
  

   the 
  shape 
  of 
  the 
  anterior 
  end 
  is 
  very 
  similar. 
  The 
  auricles 
  of 
  P. 
  

   borealis 
  are 
  perhaps 
  a 
  trifle 
  longer 
  and 
  more 
  pointed 
  than 
  those 
  of 
  P. 
  

  

  