﻿NO. 
  1959. 
  SIPUNCULID8 
  OF 
  EASTERN 
  NORTH 
  AMERICA— 
  GEROULD. 
  399 
  

  

  ventrad 
  and 
  cephalad 
  (pi. 
  59, 
  fig. 
  6). 
  About 
  three 
  rows 
  of 
  delicate, 
  

   recurved 
  hooks 
  lie 
  in 
  the 
  zone 
  immediately 
  behind 
  the 
  tentacles. 
  

   The 
  wall 
  of 
  the 
  introvert 
  is 
  

   thinner 
  and 
  more 
  translu- 
  

   cent 
  than 
  that 
  of 
  the 
  trunk. 
  

   The 
  circular 
  muscle 
  fibers 
  in 
  

   this 
  region 
  are 
  coarse 
  and 
  

   so 
  promment 
  as 
  to 
  cause 
  in 
  

   certain 
  places 
  slight 
  circular 
  

   elevations 
  of 
  the 
  epidermis. 
  

   They 
  are 
  separated 
  from 
  one 
  

   another 
  by 
  rather 
  wide 
  inter- 
  

   vals, 
  whereas 
  the 
  underlying 
  

   longitudinal 
  muscle 
  fibers, 
  

   which 
  are 
  much 
  finer 
  than 
  the 
  

   circular 
  fibers, 
  form 
  a 
  con- 
  

   tinuous 
  layer. 
  The 
  action 
  

   of 
  the 
  strong, 
  isolated 
  circu- 
  

   lar 
  muscle 
  fibers 
  is 
  evident 
  

   in 
  the 
  trunk 
  by 
  numerous 
  

   constrictions 
  that 
  occur 
  in 
  

   the 
  extended 
  specimen 
  and 
  

   by 
  the 
  tendency 
  of 
  the 
  

   body 
  wall 
  to 
  become 
  torn 
  

   transverseh^ 
  Parallel 
  longi- 
  

   tudinal 
  ridges 
  appear 
  promi- 
  

   nently 
  in 
  the 
  epidermis 
  of 
  

   the 
  contracted 
  trunk. 
  

  

  Conspicuous 
  oval 
  papUlae 
  

   occur 
  near 
  the 
  posterior 
  ex- 
  

   tremity. 
  At 
  the 
  extreme 
  

   tip 
  of 
  the 
  body, 
  however, 
  

   the 
  papillse 
  are 
  exceedingly 
  

   small, 
  gradually 
  but 
  rapidly 
  

   increasing 
  to 
  the 
  maximum 
  

   size 
  from 
  behind 
  forward. 
  

   Inconspicuous 
  papillae 
  are 
  

   scattered 
  over 
  the 
  entire 
  

   trunk 
  and 
  introvert. 
  They 
  

   are 
  largest 
  and 
  most 
  numer- 
  

   ous 
  immediate^ 
  behind 
  the 
  

   base 
  of 
  the 
  introvert, 
  and 
  

   exceedingly 
  small 
  in 
  the 
  middle 
  of 
  the 
  trunk 
  and 
  upon 
  the 
  introvert. 
  

  

  The 
  two 
  specimens 
  differ 
  in 
  color. 
  That 
  which 
  occurs 
  w-ith 
  Ph. 
  

   procerum 
  is, 
  like 
  that 
  species, 
  gray; 
  the 
  other 
  is 
  grayish-brown, 
  but 
  

  

  Fig. 
  8.— 
  Dissection 
  of 
  Phascolosoma 
  cinctum, 
  

   STATION 
  2084. 
  X 
  13 
  J. 
  an, 
  anus; 
  m. 
  col, 
  collar 
  

   muscle; 
  m.rtr, 
  retractor 
  muscle; 
  nph, 
  nephki- 
  

   dium; 
  n. 
  v, 
  ventral 
  nerve 
  coed; 
  os, 
  esophagus. 
  

  

  