﻿ECHIUROID 
  WORMS 
  OF 
  NORTH 
  PACIFIC 
  — 
  FISHER 
  253 
  

  

  with 
  eggs 
  its 
  tlistal 
  oiul 
  is 
  usually 
  iuvaginatt'd, 
  coiicoaliiig 
  the 
  iicpliro- 
  

   stomo 
  (pi. 
  27, 
  fig. 
  1). 
  The 
  mucosa 
  is 
  thrown 
  into 
  shallow 
  longitudinal 
  

   folds, 
  most 
  pronounced 
  at 
  proximal 
  end. 
  

  

  The 
  two 
  anal 
  vesicles 
  have 
  the 
  relative 
  size 
  and 
  general 
  form 
  in- 
  

   dicated 
  in 
  plate 
  26, 
  figure 
  1, 
  where 
  only 
  one 
  is 
  shown. 
  Each 
  opens 
  

   by 
  a 
  small 
  pore 
  into 
  the 
  cloaca. 
  The 
  primary 
  branches 
  of 
  the 
  vesicle 
  

   vary 
  in 
  number. 
  In 
  plate 
  2G, 
  figure 
  2, 
  is 
  shown 
  the 
  tip 
  of 
  one 
  of 
  the 
  

   major 
  subdivisions 
  including 
  two 
  of 
  the 
  smaller 
  secondary 
  branches, 
  

   each 
  of 
  which 
  bears 
  several 
  fumiels. 
  

  

  Ali.ment.\ky 
  c.\nal. 
  As 
  contrasted 
  with 
  Bonellia 
  viridis 
  the 
  ali- 
  

   mentary 
  canal 
  differs 
  in 
  having 
  a 
  much 
  shorter 
  forcgut, 
  especially 
  the 
  

   portion 
  between 
  the 
  gizzard 
  and 
  the 
  intestine, 
  corresponding 
  in 
  general 
  

   to 
  the 
  "stomach" 
  of 
  Thalassema 
  and 
  allies. 
  The 
  abruptly 
  enlarged 
  

   intestine 
  is 
  produced 
  forward 
  into 
  a 
  coecum 
  where 
  the 
  dorsal 
  blood 
  

   vessel 
  envelops 
  the 
  intestinal 
  wall. 
  In 
  the 
  specimen 
  of 
  B. 
  viridis 
  that 
  

   I 
  dissected 
  this 
  was 
  not 
  differentiated 
  (fig. 
  15). 
  

  

  The 
  pharynx 
  is 
  connected 
  with 
  the 
  body 
  wall 
  by 
  nmnerous 
  radiating 
  

   muscular 
  frenula 
  of 
  which 
  only 
  a 
  few 
  are 
  indicated 
  in 
  the 
  figures. 
  

   The 
  mucosa 
  is 
  thick, 
  verrucose, 
  and 
  not 
  very 
  different 
  from 
  that 
  of 
  

   the 
  esophagus. 
  The 
  gizzard 
  has 
  stronger 
  ring 
  muscles 
  than 
  the 
  

   esophagus 
  (which 
  shows 
  a 
  ringed 
  structure), 
  and 
  the 
  mucosa 
  is 
  

   thrown 
  into 
  consecutive 
  ring 
  folds. 
  \Vhen 
  spread 
  out 
  these 
  ring 
  

   folds 
  subdivide 
  into 
  eight 
  longitudinal 
  divisions. 
  Behind 
  the 
  gizzard 
  

   the 
  mucosa 
  becomes 
  al)ruptly 
  tiiinncr, 
  and 
  between 
  the 
  gizzard 
  and 
  

   this 
  elongated 
  stomach 
  there 
  is 
  a 
  sort 
  of 
  pjdoric 
  constriction, 
  with 
  a 
  

   very 
  narrow 
  passage. 
  The 
  opening, 
  on 
  the 
  stomach 
  side, 
  is 
  surrounded 
  

   by 
  a 
  fiange 
  of 
  tissue. 
  There 
  is 
  no 
  presiphonal 
  ciliated 
  groove, 
  but 
  a 
  

   postsiphonal 
  one 
  runs 
  along 
  the 
  intestine 
  to 
  the 
  point 
  where 
  the 
  

   ventral 
  blood 
  vessel 
  and 
  genital 
  stolon 
  join 
  the 
  hind-gut. 
  The 
  

   fecal 
  pellets 
  are 
  slender 
  blunt 
  ellipsoids 
  2.5 
  mm. 
  long. 
  In 
  one 
  I 
  found 
  

   an 
  ostracod 
  and 
  a 
  small 
  Balanus. 
  

  

  Mesenteries. 
  The 
  mesenteries 
  are 
  continuous, 
  very 
  thin 
  sheets, 
  

   even 
  in 
  the 
  postsiphonal 
  region 
  of 
  the 
  intestine. 
  In 
  plate 
  27, 
  figure 
  2, 
  

   an 
  attempt 
  has 
  been 
  made 
  to 
  show 
  the 
  principal 
  mesenteries 
  of 
  the 
  

   foregut, 
  which 
  are 
  voluminous 
  and 
  folded 
  when 
  the 
  animal 
  is 
  contracted. 
  

   In 
  this 
  sernidiagrammatic 
  drawing 
  the 
  left 
  half 
  of 
  the 
  animal 
  only 
  is 
  

   slunvn. 
  Wliat 
  is 
  probably 
  the 
  ventral 
  mesentery 
  (VAf) 
  is 
  attachcnl 
  

   to 
  body 
  wall 
  over 
  a 
  sinuous 
  and 
  not 
  so 
  smoothly 
  regular 
  course 
  as 
  

   shown 
  in 
  figure. 
  It 
  is 
  fastened 
  to 
  the 
  l(>ft 
  sid(> 
  of 
  pharynx-esophagus, 
  

   passing 
  gradually 
  to 
  the 
  side 
  of 
  the 
  intestine 
  oj)posite 
  the 
  siphon. 
  

   The 
  posterior 
  part 
  of 
  dorsal 
  blood 
  vessel 
  (/?') 
  is 
  attached 
  to, 
  or 
  in- 
  

   volved 
  in, 
  this 
  mesentery. 
  The 
  dorsal 
  mesentery 
  (DAf) 
  is 
  attached 
  

   to 
  the 
  body 
  wall 
  in 
  a 
  long 
  spiral 
  passing 
  from 
  right 
  siile 
  (dot 
  and 
  dash 
  

   line) 
  over 
  to 
  left 
  side. 
  Posteriorly 
  it 
  merges 
  with 
  the 
  ventral 
  mescn- 
  

  

  