﻿NO. 
  1959. 
  SIPUNCULIDIS 
  OF 
  EASTERN 
  NORTH 
  AMERICA— 
  GEROULD. 
  401 
  

  

  being 
  uttached 
  to 
  the 
  body 
  wall 
  by 
  two 
  roots, 
  the 
  gonad 
  crosses 
  the 
  

   right 
  root. 
  

  

  The 
  intestine 
  has 
  six 
  characteristic 
  loops, 
  the 
  first, 
  third, 
  and 
  fifth 
  

   extending 
  forward, 
  the 
  second, 
  fourth, 
  and 
  sixth 
  backward; 
  the 
  

   fifth 
  hangs 
  free, 
  but 
  the 
  others 
  are 
  bound 
  to 
  the 
  body 
  wall 
  by 
  muscle 
  

   strands. 
  

  

  The 
  opinion 
  advanced 
  by 
  Selenka 
  (1883) 
  that 
  the 
  various 
  species 
  

   of 
  Phascolion 
  have 
  arisen 
  from 
  PTiascolosoma 
  appears 
  to 
  be 
  well 
  

   founded. 
  Such 
  a 
  change 
  would 
  have 
  involved 
  the 
  almost 
  complete 
  

   fusion 
  of 
  the 
  two 
  dorsal 
  and 
  likewise 
  of 
  the 
  two 
  ventral 
  retractor 
  

   muscles 
  to 
  form 
  in 
  each 
  case 
  one. 
  Selenka 
  also 
  expressed 
  the 
  belief 
  

   that 
  Phascolion 
  has 
  arisen 
  by 
  several 
  distinct 
  stems. 
  However 
  that 
  

   ma}- 
  be, 
  the 
  individuals 
  of 
  the 
  North 
  American 
  coast 
  form 
  a 
  fairly 
  

   homogeneous, 
  though 
  variable, 
  group. 
  

  

  With 
  the 
  possible 
  exception 
  of 
  Phascolion 
  alberti 
  Sluiter, 
  all 
  of 
  these 
  

   eastern 
  forms 
  will 
  be 
  most 
  satisfactorily 
  considered 
  as 
  forming 
  a 
  single 
  

   species, 
  formerly 
  known 
  as 
  Ph. 
  cxmentarium 
  (Quatref 
  ages) 
  , 
  but 
  which 
  

   is 
  identical 
  with 
  the 
  widespread 
  Ph. 
  strombi 
  of 
  Europe, 
  as 
  I 
  have 
  

   determined 
  by 
  comparing 
  specimens 
  from 
  the 
  west 
  coast 
  of 
  Sweden 
  

   with 
  those 
  from 
  the 
  eastern 
  coast 
  of 
  North 
  America. 
  

  

  Ph. 
  strombi 
  in 
  America, 
  as 
  elsewhere, 
  shows 
  a 
  remarkable 
  varia- 
  

   bility 
  in 
  size, 
  color, 
  thickness 
  of 
  the 
  body 
  wall, 
  size 
  of 
  the 
  papillae 
  and 
  

   holdfasts, 
  and 
  hence 
  in 
  the 
  smoothness 
  or 
  roughness 
  of 
  the 
  skin. 
  

   The 
  internal 
  organization 
  is 
  more 
  stable, 
  though 
  the 
  eggs 
  vary 
  in 
  shape, 
  

   in 
  the 
  thickness 
  of 
  the 
  yolk 
  membrane 
  and 
  in 
  the 
  amount 
  of 
  yolk. 
  In 
  

   certain 
  localities 
  off 
  Halifax 
  the 
  dorsal 
  retractor 
  shows 
  a 
  tendency 
  to 
  

   a 
  division 
  at 
  the 
  base 
  into 
  two 
  roots, 
  but 
  this 
  in 
  no 
  region 
  is 
  a 
  con- 
  

   stant 
  character. 
  

  

  The 
  extraordinary 
  plasticity 
  of 
  the 
  external 
  characteristics 
  of 
  Ph. 
  

   strombi 
  make 
  it 
  a 
  favorable 
  animal 
  upon 
  which 
  to 
  study 
  experimen- 
  

   tally 
  the 
  effect 
  of 
  the 
  environment 
  upon 
  form. 
  According 
  to 
  Theel 
  

   (1875), 
  moreover, 
  it 
  is 
  remarkably 
  tenacious 
  of 
  life, 
  and 
  is 
  readily 
  

   kept 
  alive 
  for 
  more 
  than 
  a 
  month 
  in 
  ordinary 
  aquaria, 
  so 
  that 
  it 
  would 
  

   no 
  doubt 
  live 
  well 
  under 
  such 
  modification 
  of 
  external 
  conditions 
  as 
  

   such 
  experiments 
  would 
  demand. 
  

  

  A 
  study 
  of 
  the 
  very 
  large 
  number 
  of 
  specimens 
  of 
  this 
  species 
  in 
  

   the 
  U. 
  S. 
  National 
  Museum 
  has 
  convinced 
  me 
  that 
  the 
  most 
  striking 
  

   variations 
  in 
  the 
  external 
  features 
  are 
  due 
  in 
  large 
  measure 
  to 
  the 
  

   environment. 
  Thus 
  the 
  introvert 
  is 
  relatively 
  short 
  in 
  individuals 
  

   that 
  have 
  adapted 
  themselves 
  to 
  the 
  narrow 
  tubes 
  of 
  Protula, 
  Hyali- 
  

   noscia, 
  or 
  Pectinaria, 
  in 
  comparison 
  with 
  the 
  trunk 
  which 
  is 
  greatly 
  

   elongated 
  by 
  compression 
  within 
  the 
  slender 
  tube. 
  Such 
  individuals 
  

   also 
  have 
  a 
  smooth 
  and 
  often 
  lustrous 
  skin, 
  especially 
  in 
  the 
  region 
  

   of 
  the 
  holdfast 
  near 
  the 
  posterior 
  end 
  of 
  the 
  body. 
  Furthermore, 
  

   they 
  show 
  no 
  external 
  signs 
  of 
  a 
  spiral 
  twist, 
  whereas 
  those 
  which 
  

   69077°— 
  Proc.X.M.voI.44— 
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  26 
  

  

  