﻿Structure 
  of 
  Magelona. 
  451 
  

  

  VII. 
  The 
  Tentacles. 
  

  

  When 
  the 
  annelid 
  is 
  at 
  rest 
  amongst 
  the 
  sand 
  it 
  projects 
  

   its 
  extremely 
  elongated 
  tentacles 
  through 
  the 
  aperture 
  of 
  

   its 
  tube 
  into 
  the 
  surrounding 
  water, 
  in 
  which 
  they 
  are 
  

   jerked 
  to 
  and 
  fro, 
  stand 
  stiffly 
  out, 
  or 
  are 
  gracefully 
  curved 
  

   and 
  moved 
  in 
  a 
  serpentine 
  manner 
  here 
  and 
  there 
  over 
  the 
  

   sand 
  — 
  indeed, 
  when 
  many 
  are 
  confined 
  in 
  a 
  vessel 
  the 
  organs 
  

   resemble 
  independent 
  worms. 
  In 
  large 
  examples 
  they 
  measure, 
  

   when 
  gently 
  curved 
  from 
  the 
  aperture 
  in 
  the 
  sand, 
  about 
  an 
  

   inch 
  and 
  a 
  half 
  or 
  two 
  inches, 
  and 
  are 
  capable 
  of 
  much 
  greater 
  

   elongation. 
  In 
  the 
  extended 
  condition 
  of 
  the 
  organs 
  the 
  

   papillae 
  are 
  very 
  prominent 
  at 
  the 
  tip, 
  projecting 
  like 
  a 
  series 
  

   of 
  pinnae 
  along 
  the 
  inner 
  or 
  anterior 
  border, 
  and 
  susceptible 
  

   of 
  decided 
  and 
  independent 
  movements. 
  When 
  the 
  animal 
  

   lies 
  in 
  a 
  free 
  condition 
  on 
  the 
  surface 
  of 
  the 
  sand 
  the 
  tentacles 
  

   again 
  are 
  often 
  beautifully 
  coiled 
  in 
  a 
  spiral 
  manner 
  or 
  

   perform 
  various 
  independent 
  vermiform 
  movements. 
  During 
  

   the 
  process 
  of 
  boring 
  the 
  tentacles 
  are 
  trailed 
  behind 
  and 
  

   flatly 
  applied 
  to 
  the 
  body, 
  their 
  most 
  delicate 
  region 
  being 
  

   in 
  the 
  completed 
  channel, 
  while 
  the 
  stronger 
  smooth 
  part 
  

   only 
  meets 
  the 
  slight 
  pressure 
  of 
  the 
  sand 
  against 
  which 
  the 
  

   organs 
  are 
  thrust 
  by 
  the 
  advancing 
  snout. 
  When 
  reposing 
  

   within 
  its 
  tunnel 
  the 
  organs 
  are 
  stretched 
  in 
  a 
  parallel 
  con- 
  

   dition 
  in 
  front 
  of 
  it, 
  ready 
  to 
  be 
  protruded 
  on 
  the 
  return 
  of 
  

   the 
  tide. 
  

  

  Each 
  tentacle 
  forms 
  a 
  hollow 
  contractile 
  process, 
  furnished 
  

   with 
  a 
  series 
  of 
  papillae 
  along 
  the 
  anterior 
  border. 
  Ex- 
  

   ternally 
  it 
  is 
  invested 
  by 
  the 
  chitiuous 
  cuticle, 
  which 
  is 
  

   densest 
  at 
  the 
  basal 
  region 
  on 
  the 
  smooth 
  part 
  of 
  the 
  organ. 
  

   On 
  reaching 
  the 
  bases 
  of 
  the 
  papillae 
  this 
  coat 
  spreads 
  over 
  

   them 
  likewise, 
  but 
  is 
  extremely 
  attenuated 
  toward 
  the 
  tip. 
  

   The 
  subjacent 
  hypodermic 
  layer 
  is 
  largely 
  developed, 
  forming 
  

   at 
  the 
  base 
  of 
  the 
  tentacle 
  a 
  considerable 
  investment 
  through- 
  

   out 
  three-fourths 
  of 
  the 
  circumference, 
  while 
  the 
  remaining 
  

   anterior 
  region 
  is 
  greatly 
  thickened, 
  thus 
  foreshadowing 
  the 
  

   special 
  arrangement 
  further 
  outward. 
  It 
  is 
  more 
  finely 
  

   granular 
  than 
  the 
  hypoderm 
  of 
  the 
  body, 
  shows 
  the 
  usual 
  

   fibrous 
  or 
  connective-tissue 
  streaks, 
  and 
  likewise 
  contains 
  

   the 
  pigment. 
  Proceeding 
  outward, 
  the 
  thick 
  anterior 
  hypo- 
  

   dermic 
  area 
  by-aud-by 
  shows 
  numerous 
  low 
  pale 
  warts, 
  which 
  

   soon 
  attain 
  a 
  considerable 
  size. 
  In 
  the 
  living 
  specimen 
  each 
  

   papilla, 
  in 
  the 
  somewhat 
  contracted 
  condition 
  caused 
  by 
  

   slight 
  pressure, 
  has 
  a 
  rather 
  narrowed 
  base, 
  and 
  is 
  composed 
  

   of 
  a 
  continuation 
  of 
  the 
  hypoderm 
  and 
  cuticle, 
  as 
  formerly 
  

   noticed. 
  The 
  central 
  region 
  is 
  occupied 
  by 
  a 
  series 
  of 
  

  

  30* 
  

  

  