﻿THE 
  ANAT0;\1Y 
  OF 
  PO^.PH.Orff^.TTTS, 
  nf,APAi;EPE. 
  133 
  

  

  may 
  be 
  stated 
  that 
  both 
  nephridia 
  and 
  nephromixia 
  are 
  found 
  

   in 
  PoecilocliaUns. 
  Nephridia, 
  opeiiino- 
  by 
  nephridiostoiiies 
  

   into 
  the 
  next 
  set>'inent 
  in 
  fi'ont, 
  are 
  fonnd 
  in 
  the 
  anterior 
  

   segments 
  (4 
  to 
  IG), 
  whilst 
  compound 
  organs 
  (nepliromixia), 
  

   consisting 
  of 
  nephridia 
  with 
  large 
  genital 
  funnels 
  (gono- 
  

   stomes) 
  attached 
  to 
  the 
  nephridiostomes, 
  are 
  fonnd 
  in 
  the 
  

   genital 
  segments 
  from 
  segment 
  17 
  backwards. 
  

  

  In 
  the 
  two 
  anterior 
  body 
  segments 
  (1 
  and 
  2) 
  no 
  trace 
  of 
  a 
  

   nephridium 
  has 
  been 
  detected. 
  In 
  segment 
  8 
  the 
  nejihridio- 
  

   stomes 
  of 
  the 
  organs 
  of 
  the 
  following 
  segment 
  nre 
  well 
  

   developed, 
  and 
  they, 
  as 
  well 
  as 
  the 
  organs 
  to 
  whicli 
  they 
  

   belong, 
  have 
  the 
  strncture 
  about 
  to 
  be 
  described, 
  which 
  is 
  

   t^'pical 
  of 
  that 
  in 
  all 
  the 
  segments 
  from 
  4 
  to 
  16. 
  'J'he 
  

   nephridia! 
  tubes 
  in 
  each 
  of 
  these 
  segments 
  are 
  simple 
  and 
  

   J-shaped 
  (cf. 
  fig. 
  58), 
  running 
  from 
  the 
  anterior 
  septum 
  of 
  

   the 
  segment 
  straight 
  backwards, 
  then 
  tni-ning 
  outwards 
  and 
  

   forwards 
  to 
  the 
  external 
  opening 
  on 
  the 
  parapodium, 
  as 
  

   already 
  described. 
  The 
  cells 
  lining 
  the 
  tubes 
  ai-e 
  low, 
  

   elongated, 
  ciliated 
  cells, 
  which 
  contain 
  large 
  numbers 
  of 
  

   excretory 
  granules. 
  The 
  lips 
  of 
  the 
  nephridiostomes, 
  which 
  

   lie 
  close 
  to 
  the 
  posterior 
  septum 
  of 
  the 
  segment 
  next 
  in 
  front, 
  

   form 
  a 
  strncture 
  of 
  considerable 
  size, 
  Avith 
  a 
  small 
  ciliated 
  

   aperture 
  which 
  puts 
  the 
  lumen 
  of 
  the 
  nephridial 
  canal 
  into 
  

   communication 
  with 
  the 
  body-cavity 
  of 
  the 
  latter 
  segment. 
  

   Fig. 
  55 
  (PI. 
  12) 
  represents 
  a 
  transverse 
  section 
  through 
  a 
  

   nephridiostome 
  of 
  one 
  of 
  these 
  segments, 
  and 
  fio-. 
  54 
  a 
  

   sagittal 
  section. 
  The 
  lips 
  {Ip.nst.) 
  form 
  masses 
  of 
  swollen 
  

   cells 
  filled 
  with 
  vacuoles 
  and 
  granules. 
  These 
  masses 
  of 
  cells 
  

   are 
  attached 
  to 
  the 
  posterior 
  septum 
  of 
  the 
  segment 
  along 
  a 
  

   somewhat 
  narrow 
  border^ 
  and 
  protrude 
  for 
  some 
  little 
  distance 
  

   into 
  the 
  cavity 
  of 
  the 
  segment 
  (cf. 
  fig. 
  47). 
  The 
  nephridio- 
  

   stome 
  itself 
  [nst.) 
  lies 
  near 
  the 
  lateral 
  wall 
  of 
  the 
  body, 
  but 
  

   the 
  swollen 
  masses 
  of 
  cells 
  forming 
  its 
  lips 
  run 
  inwards 
  almost 
  

   to 
  the 
  median 
  line 
  of 
  the 
  body. 
  This 
  inward 
  extension 
  of 
  the 
  

   lips 
  is 
  seen 
  in 
  the 
  transverse 
  section 
  (fig. 
  55)/ 
  and 
  is 
  also 
  well 
  

   shown 
  in 
  horizontal 
  sections. 
  Externally 
  the 
  lips 
  are 
  covered 
  

   by 
  a 
  layer 
  of 
  ccelomic 
  epithelium 
  (fig. 
  54). 
  

  

  