﻿232 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.96 
  

  

  are 
  obviously 
  smaller, 
  and 
  there 
  is 
  a 
  suggestion 
  of 
  transverse 
  align- 
  

   ment. 
  The 
  appearance 
  of 
  the 
  skin 
  will 
  depend 
  a 
  good 
  deal 
  on 
  the 
  

   state 
  of 
  contraction 
  of 
  body 
  wall. 
  The 
  middle 
  portion 
  of 
  body 
  is 
  

   slightly 
  translucent, 
  not 
  transparent 
  in 
  places 
  as 
  in 
  Listriolobus 
  pelodes. 
  

  

  The 
  setae 
  have 
  a 
  stout 
  interbasal 
  muscle 
  connecting 
  the 
  inner 
  ends, 
  

   from 
  which 
  radiate 
  numerous 
  fan-shaped 
  sheets 
  of 
  muscle 
  which 
  

   attach 
  broadly 
  to 
  the 
  body 
  wall. 
  A 
  posterior 
  muscle 
  passes 
  over 
  the 
  

   first 
  nephridium 
  and 
  merges 
  with 
  the 
  body 
  wall 
  between 
  the 
  first 
  and 
  

   second 
  nephridia. 
  Setae 
  1.8 
  mm. 
  long 
  with 
  a 
  small 
  hook, 
  the 
  point 
  

   of 
  which 
  is 
  at 
  right 
  angles 
  to 
  the 
  shaft. 
  In 
  the 
  type 
  and 
  a 
  number 
  of 
  

   other 
  specimens 
  the 
  hook 
  is 
  worn 
  off. 
  

  

  Inner 
  layer 
  of 
  muscles 
  of 
  body 
  wall 
  smooth 
  except 
  in 
  front 
  of 
  

   anterior 
  nephridia 
  where 
  there 
  is 
  differentiation 
  into 
  about 
  a 
  dozen 
  

   bundles 
  passing 
  around 
  the 
  body. 
  The 
  middle 
  layer 
  is 
  undifferen- 
  

   tiated 
  as 
  in 
  other 
  species 
  of 
  the 
  restricted 
  genus 
  Thalassema. 
  

  

  The 
  four 
  nephridia 
  are 
  small 
  in 
  the 
  type, 
  which 
  is 
  probably 
  a 
  male. 
  

   In 
  the 
  specimen 
  from 
  station 
  2828 
  they 
  are 
  enormously 
  inflated 
  and 
  

   full 
  of 
  eggs. 
  In 
  the 
  type 
  the 
  ciliated 
  funnel 
  is 
  very 
  simple, 
  with 
  

   smooth 
  lips 
  forming 
  an 
  incomplete 
  circle. 
  In 
  the 
  female 
  the 
  funnel 
  is 
  

   flattened 
  and 
  pear-shaped 
  and 
  somewhat 
  distorted 
  by 
  pressure, 
  but 
  

   there 
  is 
  no 
  indication 
  of 
  elongation 
  into 
  spirals. 
  

  

  The 
  deflated 
  anal 
  vesicles 
  are 
  as 
  long 
  as 
  the 
  body 
  and 
  have 
  the 
  

   appearance 
  of 
  being 
  capable 
  of 
  inflation 
  to 
  a 
  great 
  size. 
  

  

  The 
  alimentary 
  canal 
  is 
  moderately 
  long 
  but 
  conspicuously 
  shorter 
  

   than 
  that 
  of 
  Listriolobus 
  pelodes. 
  The 
  contents 
  are 
  not 
  always 
  

   formed 
  into 
  pellets. 
  The 
  foregut 
  consists 
  of 
  a 
  pharynx-esophagus, 
  

   midway 
  along 
  which 
  is 
  a 
  sharp 
  bend. 
  Both 
  the 
  gizzard 
  and 
  stomach 
  

   are 
  unusually 
  short. 
  The 
  former 
  is 
  marked 
  by 
  ring 
  striations. 
  At 
  

   the 
  posterior 
  end 
  of 
  the 
  stomach 
  is 
  the 
  ring 
  blood 
  vessel 
  (5^) 
  marking 
  

   the 
  beginning 
  of 
  the 
  intestine, 
  on 
  the 
  lower 
  side 
  of 
  which 
  is 
  the 
  ciliated 
  

   groove. 
  At 
  a 
  distance 
  back 
  of 
  the 
  ring 
  vessel 
  equal 
  to 
  about 
  length 
  

   of 
  gizzard 
  and 
  stomach 
  the 
  siphon 
  begins 
  and 
  runs 
  for 
  about 
  half 
  

   length 
  of 
  intestine. 
  The 
  ciliated 
  groove 
  continues 
  to 
  the 
  intestinal 
  

   coecum 
  in 
  front 
  of 
  the 
  cloaca. 
  The 
  pharynx 
  has 
  a 
  conspicuous 
  

   ventral 
  mesentery, 
  and 
  all 
  along 
  the 
  canal 
  are 
  numerous 
  dorsal 
  

   mesenterial 
  strands. 
  Posterior 
  to 
  the 
  region 
  of 
  the 
  siphon 
  the 
  mesen- 
  

   teries 
  inclose, 
  or 
  hold, 
  conspicuous 
  yellowish-white 
  masses, 
  sometimes 
  

   subfusiform 
  or 
  in 
  irregular 
  sheets, 
  which 
  remind 
  one 
  of 
  the 
  suet 
  found 
  

   in 
  mammals. 
  A 
  squeeze 
  reveals 
  several 
  sorts 
  of 
  cells, 
  some 
  of 
  which 
  

   may 
  be 
  immature 
  sperm. 
  The 
  cloaca 
  is 
  small 
  and 
  thin-walled. 
  

  

  The 
  vascular 
  system 
  consists 
  of 
  the 
  dorsal 
  vessel 
  ending 
  posteriorly 
  

   in 
  the 
  ring 
  vessel, 
  from 
  which 
  the 
  neurointestinal 
  connective 
  passes 
  

   to 
  the 
  ventral 
  vessel, 
  forming 
  a 
  loop 
  enclosing 
  the 
  interbasal 
  muscle 
  

   of 
  setae. 
  The 
  ventral 
  vessel 
  ends 
  posteriorly 
  at 
  the 
  intestinal 
  coecum. 
  

   In 
  the 
  female 
  from 
  station 
  2828 
  the 
  vessels 
  are 
  the 
  same. 
  

  

  