﻿276 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.96 
  

  

  posterior 
  portion 
  of 
  the 
  body 
  a 
  new 
  one 
  begins 
  at 
  the 
  anterior 
  end, 
  

   Urechis 
  is 
  normally 
  always 
  in 
  control 
  of 
  the 
  water 
  and 
  senses 
  any- 
  

   thing 
  which 
  may 
  attempt 
  to 
  pass 
  through 
  the 
  burrow. 
  

  

  Feeding. 
  — 
  The 
  unique 
  method 
  employed 
  by 
  Urechis 
  to 
  gather 
  

   nourishment 
  is 
  generic 
  and 
  furnishes 
  a 
  striking 
  example 
  of 
  the 
  coordi- 
  

   nation 
  of 
  adaptive 
  structure 
  and 
  behavior. 
  

  

  A 
  short 
  distance 
  back 
  of 
  the 
  oral 
  setae 
  is 
  a 
  zone 
  of 
  compound 
  

   mucous 
  glands, 
  which 
  form 
  a 
  sort 
  of 
  clitellum 
  very 
  faintly 
  differen- 
  

   tiated 
  externally 
  by 
  the 
  ringlike 
  arrangement 
  of 
  the 
  low 
  rugosities 
  of 
  

   the 
  skin. 
  These 
  glands 
  are 
  specializations 
  of 
  the 
  simpler 
  and 
  more 
  

   numerous 
  multicellular 
  flask-form 
  mucous 
  glands 
  of 
  the 
  integument. 
  

   The 
  slime-net 
  or 
  girdle 
  glands, 
  as 
  they 
  have 
  been 
  called, 
  secrete 
  a 
  

   fairly 
  long 
  transparent 
  mucous 
  tube, 
  or 
  funnel, 
  whose 
  upper, 
  open 
  

   end 
  is 
  fastened 
  near 
  the 
  mouth 
  of 
  the 
  tunnel 
  while 
  the 
  lower 
  remains 
  

   attached 
  to 
  the 
  clitellum. 
  This 
  strains 
  from 
  the 
  ventilating, 
  or 
  respir- 
  

   atory 
  currents, 
  all 
  minute 
  particles 
  as 
  the 
  water 
  flows 
  through 
  and 
  

   when 
  sufficiently 
  loaded 
  the 
  tube 
  is 
  swaUowed. 
  The 
  process 
  is 
  

   repeated 
  as 
  long 
  as 
  the 
  animal 
  feeds. 
  Urechis 
  readily 
  adopts 
  a 
  glass 
  

   substitute 
  for 
  its 
  normal 
  burrow 
  so 
  that 
  feeding 
  reactions 
  can 
  be 
  closely 
  

   followed 
  (pi. 
  37, 
  flg. 
  1). 
  

  

  Just 
  before 
  starting 
  a 
  tube, 
  the 
  body 
  is 
  constricted 
  at 
  the 
  clitellum. 
  

   This 
  region 
  is 
  then 
  expanded 
  until 
  it 
  presses 
  firmly 
  against 
  the 
  sides 
  

   of 
  the 
  burrow 
  (usually 
  near 
  the 
  mouth, 
  but 
  sometimes 
  in 
  the 
  hori- 
  

   zontal 
  portion) 
  with 
  which 
  it 
  remains 
  in 
  contact 
  for 
  about 
  2 
  seconds. 
  

   During 
  the 
  spinning 
  process, 
  which 
  occupies 
  only 
  a 
  few 
  minutes, 
  the 
  

   constricted 
  portion 
  of 
  the 
  body 
  anterior 
  to 
  the 
  clitellum 
  (whence 
  the 
  

   slime 
  is 
  issuing) 
  undergoes 
  a 
  curious 
  spiral 
  peristalsis 
  (pi. 
  37, 
  fig. 
  5) 
  

   easily 
  detected 
  by 
  watching 
  the 
  nerve 
  cord, 
  which 
  shows 
  through 
  the 
  

   pink 
  body 
  wall, 
  while 
  back 
  of 
  the 
  clitellum 
  the 
  normal 
  respiratory, 
  or 
  

   pumping, 
  peristalsis 
  is 
  taking 
  place. 
  

  

  The 
  tubes 
  vary 
  in 
  length 
  from 
  about 
  2 
  to 
  8 
  inches 
  without 
  apparent 
  

   reason. 
  As 
  the 
  tube 
  lengthens 
  Urechis 
  backs 
  down 
  the 
  tunnel, 
  and 
  on 
  

   completion 
  the 
  spiral 
  peristalsis 
  anterior 
  to 
  the 
  clitellum 
  ceases, 
  being 
  

   replaced 
  by 
  a 
  faint 
  normal 
  peristalsis, 
  the 
  main 
  wave 
  starting 
  just 
  back 
  

   of 
  the 
  attachment 
  of 
  slime 
  tube 
  to 
  the 
  body. 
  These 
  normal 
  ventilating 
  

   reactions 
  are 
  kept 
  up 
  until 
  the 
  animal, 
  apparently 
  sensing 
  the 
  blocking 
  

   of 
  the 
  water 
  current 
  by 
  the 
  clogging 
  of 
  the 
  mucus 
  with 
  detritus, 
  slips 
  

   the 
  tube 
  forward 
  "over 
  its 
  head." 
  In 
  doing 
  this 
  it 
  deftly 
  catches 
  the 
  

   hind 
  edge 
  of 
  the 
  tube 
  by 
  expanding 
  the 
  proboscis 
  and 
  bending 
  it 
  back- 
  

   ward, 
  collarwise, 
  against 
  the 
  inflated 
  nuchal 
  region, 
  until 
  the 
  muscular 
  

   pharynx 
  is 
  able 
  to 
  pick 
  up 
  and 
  suck 
  in 
  a 
  portion 
  of 
  the 
  margin 
  (pi. 
  37, 
  

   fig. 
  7). 
  When 
  diatom 
  culture 
  or 
  detritus 
  is 
  introduced 
  with 
  a 
  pipette 
  

   the 
  slime 
  tube 
  is 
  soon 
  swallowed; 
  but 
  if 
  unmolested, 
  Urechis 
  may 
  

   continue 
  pumping 
  for 
  an 
  hour 
  before 
  the 
  tube 
  is 
  clogged. 
  

  

  