﻿130 
  E. 
  J. 
  ALLEN. 
  

  

  dorsal 
  vessel 
  and 
  the 
  network 
  of 
  bloodvessels 
  which 
  sur- 
  

   rounded 
  the 
  oesophagus 
  and 
  pharynx, 
  have 
  as 
  it 
  were 
  run 
  

   together 
  to 
  form 
  oue 
  large 
  sinus, 
  which 
  completely 
  surrounds 
  

   the 
  intestine 
  (figs. 
  45 
  and 
  59, 
  i. 
  hi. 
  -s.). 
  The 
  circulation 
  of 
  

   the 
  blood 
  is 
  now 
  brought 
  about, 
  not 
  by 
  the 
  contraction 
  of 
  a 
  

   blood-vessel 
  with 
  highly 
  muscular 
  walls, 
  but 
  by 
  the 
  contrac- 
  

   tion 
  and 
  expansion 
  of 
  the 
  segmental 
  pouches 
  of 
  the 
  intestine. 
  

  

  The 
  intestinal 
  sinus 
  communicates 
  with 
  the 
  ventral 
  vessel 
  

   by 
  short, 
  vertical 
  branches, 
  and 
  it 
  also 
  gives 
  off 
  in 
  each 
  

   segment, 
  from 
  the 
  region 
  of 
  the 
  narrowed 
  portion 
  of 
  the 
  

   intestine 
  behind 
  the 
  intestinal 
  pouches, 
  the 
  lateral 
  blood- 
  

   vessels. 
  Each 
  lateral 
  blood-vessel 
  runs 
  in 
  the 
  posterior 
  

   septum 
  of 
  the 
  segment, 
  at 
  first 
  upwards 
  and 
  outwards, 
  then 
  

   outwards 
  and 
  downwards, 
  to 
  the 
  base 
  of 
  the 
  gills 
  on 
  the 
  

   notopodium. 
  It 
  enters 
  the 
  first 
  gill 
  filament, 
  to 
  the 
  tip 
  of 
  

   which 
  it 
  runs 
  ; 
  it 
  there 
  turns 
  sharply 
  on 
  itself 
  and 
  comes 
  

   back 
  again 
  to 
  the 
  base 
  of 
  the 
  gill, 
  thus 
  forming 
  a 
  single, 
  

   simple 
  loop, 
  which 
  occupies 
  the 
  whole 
  of 
  the 
  interior 
  of 
  the 
  

   gill 
  filaments 
  (PI. 
  10, 
  fig. 
  31). 
  After 
  having 
  formed 
  a 
  similar 
  

   loop 
  in 
  all 
  the 
  other 
  gill 
  filaments 
  the 
  blood-vessel 
  again 
  runs 
  

   in 
  the 
  posterior 
  septum 
  of 
  the 
  segment, 
  its 
  course 
  being 
  

   inwards 
  and 
  downwards 
  to 
  the 
  ventral 
  vessel, 
  which 
  it 
  joins. 
  

   During 
  this 
  latter 
  part 
  of 
  its 
  course 
  the 
  vessel 
  sends 
  back 
  a 
  

   branch 
  along 
  the 
  tube 
  of 
  the 
  nephridium 
  into 
  the 
  segment 
  

   behind, 
  which 
  appears 
  to 
  supply 
  not 
  only 
  the 
  nephridium, 
  

   but 
  also 
  the 
  genital 
  organs, 
  which 
  lie 
  along 
  the 
  tube 
  of 
  the 
  

   nephridium 
  (PL 
  12, 
  figs. 
  52 
  and 
  60, 
  b. 
  lat. 
  v.). 
  Th-ere 
  is, 
  how- 
  

   ever, 
  no 
  obvious 
  formation 
  of 
  a 
  cluster 
  of 
  blind, 
  finger- 
  

   shaped 
  processes 
  such 
  as 
  was 
  met 
  with 
  in 
  the 
  anterior 
  seg- 
  

   ments 
  of 
  the 
  worm. 
  

  

  One 
  point 
  of 
  interest 
  in 
  connection 
  with 
  the 
  lateral 
  vessels 
  

   remains 
  to 
  be 
  noticed. 
  In 
  describing 
  the 
  course 
  of 
  the 
  

   lateral 
  vessels 
  of 
  the 
  anterior 
  segments, 
  it 
  was 
  statetl 
  that 
  

   each 
  vessel, 
  before 
  sending 
  back 
  its 
  branch 
  to 
  the 
  finger- 
  

   shaped 
  processes 
  in 
  the 
  segment 
  behind, 
  ran 
  forwards 
  and 
  

   formed 
  a 
  simple 
  loop 
  at 
  the 
  base 
  of 
  the 
  parapodium. 
  It 
  will 
  

   be 
  remembered 
  that 
  the 
  parapodiaof 
  these 
  anterior 
  segments 
  

  

  