﻿ECHIUROID 
  WORMS 
  OF 
  NORTH 
  PACIFIC 
  — 
  FISHER 
  

  

  273 
  

  

  tumiels 
  ill 
  the 
  mud 
  tiiul 
  conduct 
  a 
  more 
  or 
  less 
  permanent 
  manage. 
  

   The 
  mud 
  teems 
  with 
  amiehds 
  such 
  as 
  Lumbrinireis, 
  and 
  there 
  are 
  

   hterally 
  acres 
  that 
  have 
  a 
  greenish 
  tinge 
  from 
  the 
  tentacles 
  of 
  Phoro- 
  

   nopsi^ 
  rirulis 
  Hilton. 
  Zostera 
  grows 
  in 
  jiermanent 
  patches 
  and 
  sup- 
  

   ports 
  a 
  characteristic 
  association 
  of 
  animals. 
  At 
  favorable 
  times 
  wide 
  

   expanses 
  support 
  a 
  growth 
  of 
  green 
  Enteromorpha 
  which, 
  either 
  fresh 
  

   or 
  decayed, 
  is 
  an 
  important 
  food 
  element, 
  shice 
  the 
  bulk 
  of 
  animal 
  

   life 
  consists 
  of 
  detritus 
  feeders. 
  

  

  At 
  low 
  water 
  broad 
  areas 
  are 
  left 
  bare, 
  but 
  Urechis 
  usually 
  excavates 
  

   its 
  home 
  where 
  the 
  entrances 
  are 
  not 
  exposed 
  at 
  lowest 
  tide. 
  A 
  few 
  

   places 
  were 
  found 
  where 
  they 
  are 
  exposed 
  at 
  lowest 
  tide. 
  

  

  Figure 
  19. 
  — 
  A, 
  Urechis 
  caupo 
  Fisher 
  and 
  MacGinitie, 
  in 
  resting 
  posture. 
  B, 
  Position 
  

   assumed 
  while 
  dig^'ing 
  with 
  anal 
  setae. 
  C, 
  Plan 
  of 
  Urechis 
  tunnel, 
  the 
  worm 
  in 
  situ 
  

   pumping 
  water 
  through 
  the 
  slime-tube. 
  Water 
  enters 
  at 
  C, 
  where 
  there 
  are 
  two 
  Cleve- 
  

   landia 
  ios 
  (one 
  outside); 
  at 
  a, 
  Hespernoe 
  lies 
  in 
  wait 
  to 
  feed 
  on 
  tube 
  when 
  it 
  shall 
  be 
  swal- 
  

   lowed; 
  b, 
  the 
  tiny 
  clam 
  Cryptomya 
  californica; 
  c, 
  Scleroplax; 
  d, 
  Clevelandia 
  creating 
  

   disturbance; 
  e, 
  eruption 
  of 
  mud 
  cloud 
  on 
  ventilating 
  current; 
  castings 
  around 
  exit. 
  

  

  The 
  tunnel 
  (fig. 
  19, 
  C), 
  never 
  carried 
  very 
  deep, 
  has 
  two 
  entrances 
  

   and 
  is 
  in 
  the 
  form 
  of 
  a 
  widely 
  expanded 
  U, 
  of 
  which 
  the 
  uprights 
  are 
  

   nearly 
  perpendicular 
  and 
  the 
  bottom 
  horizontal. 
  The 
  apertures 
  are 
  

   small, 
  being 
  about 
  one-third 
  the 
  diameter 
  of 
  the 
  tunnel 
  itself. 
  Around 
  

   one 
  of 
  the 
  openijigs 
  there 
  is 
  a 
  considerable 
  cjuantity 
  of 
  castings. 
  The 
  

   greatest 
  distance 
  between 
  entrances 
  measured 
  38 
  inches, 
  the 
  shortest 
  

   16 
  ii\ches. 
  Twenty-seven 
  was 
  the 
  average 
  for 
  many 
  measurements. 
  

   The 
  distance 
  apart 
  of 
  the 
  two 
  entrances 
  depends 
  upon 
  the 
  size 
  of 
  the 
  

   animal 
  but 
  not 
  proportionately 
  so, 
  for 
  small 
  specimens 
  have 
  more 
  

   extensive 
  burrows 
  for 
  their 
  size 
  than 
  larger 
  ones. 
  The 
  largest 
  speci- 
  

   men 
  obtained 
  was 
  19.5 
  ijiches 
  long 
  when 
  relaxed 
  in 
  anesthesia, 
  and 
  

   the 
  smallest 
  was 
  1 
  inch. 
  

  

  The 
  burrows 
  have 
  a 
  permanent 
  aspect 
  and 
  none 
  of 
  those 
  contijiutiily 
  

   observed 
  was 
  found 
  changed 
  except 
  that 
  occasionally 
  one 
  had 
  a 
  Jiew 
  

   entrance. 
  The 
  animals 
  grow 
  very 
  slowly, 
  and 
  so 
  the 
  enlargements 
  need 
  

  

  