﻿182 
  M. 
  J. 
  ALLEN. 
  

  

  a 
  tliiu 
  layer 
  of 
  very 
  Hat 
  cells^ 
  but 
  the 
  existence 
  of 
  tliis 
  layer 
  is 
  

   not 
  easy 
  to 
  demonstrate 
  satisfactorily. 
  Strands 
  of 
  tissue 
  

   cross 
  the 
  blood-space 
  at 
  intervals, 
  having 
  the 
  appearance 
  of 
  

   prolongations 
  of 
  the 
  epithelial-lining-cells. 
  

  

  It 
  should 
  be 
  noted 
  that 
  in 
  the 
  walls 
  of 
  the 
  intestinal 
  

   pouches 
  no 
  nniscle-fibres 
  can 
  be 
  demonstrated 
  excepting 
  

   those 
  in 
  the 
  outer 
  wall 
  of 
  the 
  blood-sinus^ 
  and 
  the 
  con- 
  

   tractions 
  of 
  the 
  pouches 
  would 
  seem 
  to 
  be 
  brought 
  about 
  by 
  

   these 
  mnscles 
  (figs. 
  45 
  and 
  46). 
  

  

  The 
  Blood,— 
  The 
  blood 
  of 
  Posciloch 
  tetus 
  is 
  a 
  bright 
  

   scarlet 
  coloured, 
  homogeneous 
  fluid 
  without 
  corpuscles 
  of 
  any 
  

   kind. 
  Vei-y 
  occasionally 
  in 
  sections 
  an 
  isolated 
  cell, 
  having 
  a 
  

   similar 
  appearance 
  to 
  the 
  cells 
  of 
  the 
  epithelial 
  lining 
  of 
  the 
  

   blood-vessels, 
  is 
  seen 
  in 
  the 
  blood-space. 
  Such 
  cells 
  are 
  

   probably 
  only 
  cells 
  of 
  tliis 
  epithelium 
  which 
  have 
  become 
  

   detached. 
  

  

  The 
  change 
  of 
  colour 
  of 
  the 
  blood 
  caused 
  by 
  want 
  of 
  oxygen 
  

   has 
  already 
  been 
  described 
  (see 
  p. 
  120). 
  

  

  Nephridia 
  and 
  Nephromixia. 
  

  

  In 
  small 
  living 
  examples 
  of 
  Pceciloch^etus 
  viewed 
  from 
  

   the 
  ventral 
  surface 
  the 
  nephridial 
  organs 
  can 
  be 
  seen 
  as 
  short 
  

   greenish-brown 
  tubes, 
  one 
  pair 
  in 
  each 
  segment, 
  commencing 
  

   at 
  the 
  level 
  of 
  the 
  anterior 
  septum, 
  running 
  first 
  backwards 
  

   and 
  then 
  turning 
  outwards 
  and 
  forwards, 
  and 
  ending 
  on 
  the 
  

   antero-ventral 
  face 
  of 
  the 
  parapodium. 
  By 
  examining 
  the 
  

   more 
  transparent 
  segments 
  near 
  the 
  tnil 
  end 
  of 
  the 
  worm 
  with 
  

   a 
  moderately 
  higli 
  power 
  it 
  can 
  be 
  further 
  seen 
  that 
  anteriorly 
  

   the 
  nephridium 
  opens 
  in 
  a 
  large 
  ciliated 
  funnel, 
  and 
  that 
  the 
  

   whole 
  length 
  of 
  the 
  tube 
  from 
  the 
  anterior 
  internal 
  opening 
  

   to 
  the 
  external 
  opening 
  at 
  the 
  base 
  of 
  the 
  parapodium 
  is 
  

   strongly 
  ciliated. 
  

  

  Tiie 
  details 
  of 
  the 
  structure 
  of 
  these 
  organs 
  can 
  be 
  made 
  

   out 
  with 
  some 
  clearness 
  in 
  series 
  of 
  sections 
  of 
  specimens 
  

   preserved 
  in 
  Hermann's 
  fluid, 
  more 
  especially 
  in 
  longitudinal 
  

   vertical 
  (sagittal) 
  and 
  in 
  horizontal 
  sections 
  of 
  the 
  worm. 
  

  

  Adupting 
  the 
  nomenclature 
  of 
  Goodiich 
  (1*J00, 
  p. 
  742), 
  it 
  

  

  