﻿FOURTH 
  REPORT 
  OF 
  THE 
  DIRECTOR 
  I907 
  ' 
  1 
  59 
  

  

  illustrations 
  of 
  a 
  worm 
  from 
  the 
  Hamilton 
  group 
  described 
  by 
  Hall 
  

   as 
  Spirorbis 
  angulatus 
  from 
  closely 
  attached 
  examples 
  

   showing 
  but 
  one 
  or 
  two 
  entirely 
  horizontal 
  volutions. 
  These 
  silica 
  

   etchings 
  show 
  how 
  quickly 
  in 
  later 
  growth 
  the 
  tube 
  departs 
  from 
  

   the 
  horizontal 
  position 
  and 
  draws 
  out 
  into 
  a 
  loose 
  spiral 
  even 
  when 
  

   not 
  confronted 
  by 
  the 
  necessity 
  of 
  keeping 
  its 
  feeding 
  end 
  on 
  a 
  level 
  

   with 
  that 
  of 
  some 
  companion 
  organism 
  [pi. 
  2, 
  fig. 
  8-1 
  1]. 
  

  

  The 
  third 
  of 
  these 
  combinations 
  is 
  illustrated 
  by 
  a 
  specimen 
  for 
  

   which 
  I 
  am 
  again 
  indebted 
  to 
  Professor 
  Calvin. 
  A 
  little 
  colony 
  of 
  

   Favosites 
  has 
  had 
  its 
  tentacular 
  surface 
  entirely 
  overgrown 
  with 
  a 
  

   Stromatopora. 
  Within 
  the 
  substance 
  of 
  the 
  Stromatopora 
  is 
  a 
  

   multitude 
  of 
  spiral 
  worm 
  tubes 
  not 
  stretched 
  out 
  into 
  loose 
  volu- 
  

   tions 
  as 
  in 
  the 
  other 
  instances 
  mentioned, 
  but 
  keeping 
  their 
  two 
  or 
  

   three 
  volutions 
  in 
  close 
  contact 
  and 
  resembling 
  an 
  Autodetus 
  with- 
  

   out 
  its 
  external 
  smoothly 
  sloping 
  surface. 
  The 
  edges 
  of 
  these 
  

   tubes 
  are 
  apparently 
  always 
  angular. 
  These 
  little 
  worms 
  have 
  

   started 
  growth 
  anywhere 
  on 
  the 
  substance 
  of 
  the 
  Stromatopora 
  

   and 
  instead 
  of 
  growing 
  like 
  a 
  Spirorbis 
  with 
  whorls 
  broadly 
  

   attached 
  for 
  a 
  turn 
  or 
  two, 
  have 
  coiled 
  closely 
  upward 
  and 
  ceased 
  

   growth 
  in 
  every 
  case 
  very 
  abruptly. 
  This 
  case 
  is 
  singularly 
  in- 
  

   structive 
  as 
  showing 
  that 
  the 
  worm 
  failed 
  to 
  keep 
  pace 
  in 
  growth 
  

   with 
  the 
  coral 
  and 
  confessed 
  its 
  natural 
  limitations 
  of 
  growth, 
  while 
  

   in 
  the 
  other 
  cases 
  cited 
  the 
  worm 
  apparently 
  has 
  had 
  the 
  ability 
  to 
  

   adapt 
  itself 
  to 
  this 
  upward 
  growth 
  by 
  stretching 
  out 
  its 
  tube 
  into 
  

   loose 
  curves 
  and 
  keeping 
  its 
  aperture 
  always 
  clear 
  at 
  the 
  surface. 
  

   The 
  little 
  Streptindytes 
  compactus 
  however 
  was 
  not 
  equal 
  

   to 
  this 
  struggle 
  for 
  existence 
  except 
  as 
  it 
  planted 
  its 
  successors 
  in- 
  

  

  d 
  

  

  ^z/E&f 
  

  

  Stromatopora 
  with 
  embedded 
  spiral 
  annelid 
  tubes. 
  Streptindytes 
  compactus, 
  

   located 
  at 
  various 
  stages 
  of 
  the 
  growth 
  of 
  the 
  coral. 
  The 
  character 
  of 
  the 
  annelid 
  tube 
  is 
  

   shown 
  in 
  the 
  enlargement 
  at 
  the 
  right 
  (x 
  5). 
  The 
  Stromatopora 
  has 
  entirely 
  overgrown 
  a 
  

   small 
  Favosite* 
  colony. 
  Middle 
  Pevonic. 
  Iowa 
  

  

  