﻿290 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.96 
  

  

  Plate 
  33 
  

  

  Urechis 
  caupo 
  Fisher 
  and 
  MacGinitie 
  

  

  1, 
  Dissection 
  of 
  contracted 
  specimen 
  from 
  above, 
  showing 
  the 
  intestine 
  in 
  hap- 
  

  

  hazard 
  convolutions. 
  The 
  principal 
  mesenterial 
  bands, 
  which 
  anchor 
  the 
  

   intestines 
  to 
  the 
  body 
  wall, 
  are 
  shown 
  but 
  not 
  lettered. 
  The 
  coelomic 
  aper- 
  

   tures 
  of 
  the 
  nephridia 
  are 
  recognizable 
  by 
  the 
  conspicuous 
  coiled 
  lips. 
  The 
  

   arrow 
  indicates 
  point 
  where 
  pharynx 
  becomes 
  esophagus. 
  The 
  figures 
  in 
  

   sequence 
  on 
  the 
  midgut 
  are 
  intended 
  to 
  aid 
  in 
  following 
  the 
  convolutions; 
  

   1 
  is 
  at 
  the 
  beginning 
  and 
  IS 
  near 
  the 
  end. 
  Beyond 
  13 
  the 
  slight 
  diverticulum 
  

   of 
  the 
  respiratory 
  gut 
  is 
  indicated. 
  

  

  2, 
  Pharynx 
  contracted 
  and 
  slit 
  open 
  along 
  ventral 
  side 
  to 
  show 
  the 
  straight 
  

  

  longitudinal 
  folds 
  of 
  lining, 
  continuous 
  with 
  those 
  of 
  the 
  proboscis. 
  Pos- 
  

   teriorly 
  is 
  shown 
  characteristic 
  lining 
  of 
  esophagus; 
  on 
  each 
  side 
  are 
  the 
  

   dorsal 
  mesenteries. 
  In 
  front 
  of 
  these 
  the 
  ventral 
  mesenteries 
  are 
  spread 
  

   laterally 
  since 
  pharynx 
  has 
  been 
  opened 
  ventrally 
  (see 
  pi. 
  34, 
  fig. 
  2, 
  14)- 
  

  

  3, 
  Ventral 
  surface 
  of 
  proboscis 
  and 
  anterior 
  end 
  of 
  body. 
  

  

  4, 
  Posterior 
  end 
  of 
  body 
  showing 
  eccentric 
  anus 
  and 
  circle 
  of 
  setae 
  ; 
  + 
  marks 
  the 
  

  

  midventral 
  line. 
  

  

  5, 
  Two 
  views 
  of 
  the 
  anterior 
  setae. 
  The 
  line 
  indicates 
  1 
  mm. 
  

  

  6, 
  An 
  anal 
  seta, 
  same 
  scale 
  as 
  figure 
  5, 
  with, 
  below, 
  a 
  tip 
  enlarged. 
  

  

  AS, 
  anterior 
  setae 
  (accessory 
  seta 
  shown 
  at 
  side; 
  muscles 
  not 
  drawn); 
  AV, 
  anal 
  

   vesicles; 
  Ci, 
  C2, 
  crops 
  1 
  and 
  2 
  of 
  Seitz, 
  subtended 
  by 
  muscular 
  bands 
  Mi 
  and 
  

   M2; 
  C2 
  is 
  the 
  stomach; 
  CL, 
  cloaca, 
  the 
  posterior 
  portion 
  lined 
  with 
  heavy 
  

   longitudinal 
  ridges 
  (arrows 
  mark 
  apertures 
  of 
  anal 
  vesicles) 
  ; 
  G, 
  gizzard, 
  a 
  

   portion 
  of 
  the 
  foregut 
  lying 
  between 
  Ci 
  and 
  C2, 
  characterized 
  by 
  thick 
  

   muscular 
  walls 
  and 
  circular 
  muscular 
  ridges 
  and 
  constrictions; 
  HG, 
  respira- 
  

   tory 
  gut, 
  specialized 
  posterior 
  segment 
  of 
  midgut; 
  Mi, 
  M2, 
  muscular 
  bands 
  

   of 
  crop 
  and 
  stomach 
  (C2) 
  ; 
  A'', 
  nephridium; 
  NC, 
  nerve 
  cord; 
  0, 
  esophagus, 
  

   anterior 
  limit 
  marked 
  by 
  an 
  arrow; 
  P, 
  pharynx; 
  PS, 
  posterior 
  or 
  anal 
  setae; 
  

   S, 
  siphon 
  or 
  accessory 
  intestine; 
  SI, 
  beginning 
  of 
  siphon 
  near 
  beginning 
  of 
  

   midgut; 
  S2, 
  end 
  of 
  siphon; 
  VM, 
  ventral 
  mesenteries 
  of 
  pharynx; 
  1-13, 
  these 
  

   figures 
  are 
  in 
  sequence 
  along 
  the 
  midgut 
  and 
  are 
  intended 
  to 
  aid 
  in 
  following 
  

   the 
  course; 
  13 
  is 
  near 
  the 
  junction 
  of 
  midgut 
  and 
  its 
  terminal 
  specialized 
  

   portion, 
  the 
  respiratory 
  gut. 
  

  

  Plate 
  34 
  

  

  Urechis 
  caupo 
  Fisher 
  and 
  MacGinitie 
  

  

  1, 
  Dissection 
  of 
  contracted 
  individual 
  showing 
  the 
  generically 
  characteristic 
  

  

  parts 
  of 
  alimentary 
  canal, 
  most 
  of 
  the 
  "small 
  intestine" 
  having 
  been 
  removed. 
  

   The 
  very 
  long 
  foregut 
  consists 
  of 
  pharynx 
  (anterior 
  to 
  P), 
  esophagus 
  (0), 
  

   crop 
  (C) 
  with 
  its 
  strong 
  muscular 
  mesentery, 
  gizzard 
  (G), 
  and 
  stomach 
  

   (C^) 
  anchored 
  posteriorly 
  by 
  a 
  strong 
  mesentery 
  here 
  shown 
  in 
  maximum 
  

   contraction. 
  Si 
  is 
  beginning 
  of 
  siphon 
  (pi. 
  35, 
  fig. 
  5). 
  Attachment 
  of 
  

   respiratory 
  gut 
  is 
  always 
  on 
  left 
  of 
  nerve 
  cord 
  (NC) 
  . 
  Along 
  its 
  dorsal 
  surface 
  

   _ 
  is 
  shown 
  the 
  muscle 
  strand 
  continued 
  from 
  the 
  small 
  intestines 
  and 
  serving 
  

  

  posteriorly 
  for 
  attachment 
  of 
  a 
  few 
  dorsolateral 
  mesenteries. 
  

  

  2, 
  Head 
  region 
  of 
  coelom 
  looking 
  forward 
  from 
  just 
  behind 
  first 
  pair 
  of 
  nephridia 
  

  

  {16) 
  showing 
  arrangement 
  of 
  muscular 
  mesenteries 
  of 
  pharynx: 
  1-7, 
  dorsal 
  

   and 
  dorsolateral; 
  8-12, 
  lateral 
  and 
  ventrolateral; 
  13, 
  the 
  dorsoventral 
  

   muscles 
  mentioned 
  in 
  text; 
  I4, 
  ventral 
  mesenteries 
  of 
  pharynx; 
  17, 
  nerve 
  

  

  