﻿ECHIUROID 
  WORMS 
  OF 
  NORTH 
  PACIFIC 
  — 
  FISHER 
  277 
  

  

  Usually 
  only 
  a 
  few 
  minutes 
  are 
  required 
  for 
  swallowing 
  the 
  tube, 
  

   but 
  the 
  time 
  depends 
  upon 
  length 
  of 
  tube 
  and 
  the 
  amount 
  of 
  detritus 
  

   intercepted. 
  ^Yhen 
  the 
  tube 
  has 
  been 
  swallowed 
  up 
  to 
  the 
  point 
  of 
  

   attachment 
  the 
  animal 
  makes 
  a 
  movement 
  to 
  release 
  it 
  from 
  the 
  

   sides 
  of 
  the 
  burrow 
  similar 
  to 
  the 
  reaction 
  while 
  digging 
  with 
  oral 
  setae. 
  

  

  The 
  food 
  funnel 
  is 
  porous 
  to 
  liquid 
  but 
  will 
  intercept 
  the 
  smallest 
  

   particles. 
  Phenol 
  red 
  passes 
  through 
  everywhere, 
  but 
  no 
  carmine 
  

   particles 
  ever 
  do. 
  Under 
  the 
  microscope 
  no 
  openings 
  can 
  be 
  detected, 
  

   but 
  particles 
  approaching 
  a 
  micron 
  in 
  diameter 
  are 
  lodged 
  in 
  the 
  

   nmcus. 
  

  

  When 
  first 
  secreted 
  the 
  tube 
  is 
  perfectly 
  transparent, 
  but 
  as 
  it 
  

   collects 
  detritus 
  it 
  becomes 
  gray 
  and 
  its 
  outlmes 
  are 
  easily 
  seen. 
  

   Peristalsis 
  becomes 
  more 
  energetic 
  as 
  the 
  tube-wall 
  fills. 
  

  

  When 
  spuming 
  the 
  tube 
  or 
  lying 
  at 
  its 
  lower 
  end 
  pumping 
  water 
  

   through 
  it, 
  Urechis 
  is 
  very 
  sensitive 
  to 
  disturbances. 
  If 
  water 
  is 
  in- 
  

   jected 
  into 
  the 
  mouth 
  of 
  the 
  tunnel, 
  the 
  animal 
  immediately 
  ceases 
  

   movement 
  and 
  remains 
  perfectly 
  still 
  for 
  a 
  minute, 
  then 
  slowly 
  

   resumes 
  peristalsis. 
  If 
  the 
  disturbance 
  is 
  too 
  great, 
  it 
  will 
  drop 
  out 
  of 
  

   the 
  tube 
  and 
  retreat 
  toward 
  the 
  center 
  of 
  the 
  burrow, 
  returning 
  later 
  

   to 
  eat 
  the 
  slime 
  tube. 
  While 
  it 
  is 
  lying 
  at 
  the 
  end 
  of 
  a 
  completed 
  slime 
  

   tube 
  any 
  sUght 
  disturbance 
  such 
  as 
  the 
  introduction 
  of 
  a 
  little 
  mud 
  or 
  

   fresh 
  clean 
  meat 
  will 
  cause 
  Urechis 
  at 
  once 
  to 
  pass 
  the 
  tube 
  forward 
  and 
  

   begin 
  swallowing. 
  No 
  large 
  particles 
  are 
  ingested. 
  They 
  are 
  rejected 
  

   as 
  the 
  tube 
  is 
  being 
  swallowed. 
  

  

  Urechis 
  feeds 
  to 
  some 
  extent, 
  although 
  not 
  very 
  efficiently, 
  when 
  

   lying 
  without 
  its 
  burrow 
  in 
  an 
  aquarium. 
  In 
  such 
  a 
  position 
  it 
  will 
  

   swallow 
  sediment 
  from 
  the 
  bottom 
  of 
  the 
  aquarium 
  gathering 
  it 
  with 
  

   the 
  proboscis. 
  

  

  Resting. 
  — 
  After 
  a 
  period 
  of 
  feeding 
  Urechis 
  goes 
  to 
  the 
  horizontal 
  

   portion 
  of 
  the 
  burrow, 
  contracts 
  its 
  body 
  so 
  that 
  it 
  fits 
  the 
  tunnel 
  

   snugly, 
  and 
  lies 
  in 
  a 
  state 
  of 
  suspended 
  activity 
  during 
  which 
  even 
  

   respiration 
  ceases. 
  These 
  rests 
  may 
  last 
  for 
  an 
  hour 
  or 
  more, 
  but 
  the 
  

   long 
  rests 
  are 
  always 
  preceded 
  by 
  one 
  or 
  more 
  short 
  rests, 
  which 
  last 
  4 
  

   to 
  8 
  minutes, 
  and 
  between 
  which 
  respiratoiy 
  water 
  is 
  expclh'd 
  and 
  

   more 
  taken 
  in 
  (fig. 
  19, 
  A). 
  

  

  Commensals 
  (pi. 
  37, 
  figs. 
  1-3). 
  — 
  Urechis 
  has 
  three 
  pcrmaiK'nt 
  

   commensals: 
  A 
  polynoid 
  annelid, 
  IIes])er()ii<>c 
  adirnior 
  (Skogsberg), 
  

   and 
  2 
  pinnotherid 
  crabs, 
  ScleropUiT. 
  (franv/uta 
  Katlibun 
  and 
  Piniiixa 
  

   Jranciscana 
  Rathbun. 
  Sometimes 
  all 
  three 
  are 
  found 
  in 
  (he 
  same 
  

   burrow, 
  but 
  usually 
  only 
  a 
  Ilesperotioe 
  and 
  either 
  a 
  ScleropUix 
  or 
  a 
  

   Pinnixa. 
  In 
  addition, 
  the 
  litth; 
  Cryptomya 
  californica 
  (Conrad) 
  

   projects 
  its 
  siphons 
  into 
  the 
  burrow 
  to 
  make 
  use 
  of 
  the 
  water 
  in 
  the 
  

   burrow 
  for 
  its 
  source 
  of 
  food 
  and 
  oxygen. 
  The 
  goby 
  Clevelnmlia 
  ios 
  

   (Jordan 
  and 
  Clilbcrt) 
  uses 
  the 
  burrow 
  as 
  a 
  retreat 
  rather 
  than 
  a 
  resi- 
  

   dence, 
  as 
  the 
  little 
  fish 
  freely 
  forages 
  outside, 
  returning 
  when 
  alarmed 
  

  

  