﻿FOURTH 
  REPORT 
  OF 
  THE 
  DIRECTOR 
  I907 
  1 
  57 
  

  

  they 
  have 
  been 
  buried 
  in 
  the 
  later 
  accumulations 
  of 
  stereom. 
  

   There 
  are 
  long 
  tubular 
  passages 
  between 
  the 
  corallites 
  in 
  early 
  

   growth 
  stages 
  which 
  have 
  not 
  been 
  described 
  in 
  the 
  structure 
  of 
  

   this 
  coral 
  genus 
  and 
  in 
  sections 
  these 
  are 
  confounded 
  with 
  worm 
  

   tubes 
  but 
  in 
  etched 
  specimens 
  such 
  as 
  have 
  here 
  principally 
  served 
  

   for 
  illustration, 
  their 
  nature 
  is 
  clear. 
  

  

  In 
  this 
  interesting 
  combination 
  there 
  is 
  still 
  another 
  member 
  — 
  a 
  

   small 
  calcareous 
  sponge. 
  It 
  has 
  come 
  to 
  my 
  notice 
  several 
  times. 
  

   The 
  one 
  here 
  figured 
  was 
  taken 
  from 
  the 
  tube 
  of 
  the 
  worm 
  but 
  

   whether 
  that 
  is 
  its 
  usual 
  position 
  or 
  whether 
  it 
  may 
  seat 
  itself 
  in 
  

   one 
  of 
  the 
  coral 
  calyces 
  or 
  whether 
  indeed 
  it 
  is 
  a 
  usual 
  member 
  of 
  

   the 
  consociation 
  can 
  not 
  clearly 
  be 
  regarded 
  as 
  established. 
  

  

  I 
  have 
  given 
  (pi. 
  4) 
  some 
  illustrations 
  which 
  show 
  how 
  readily 
  

   the 
  dead 
  parts 
  of 
  these 
  organisms 
  become 
  incrusted 
  with 
  serpulid 
  

   worms. 
  Figure 
  8 
  is 
  the 
  surface 
  of 
  a 
  part 
  of 
  a 
  dead 
  Loxonema 
  to 
  

   which 
  a 
  Pleurodictyum 
  had 
  grown 
  and 
  figure 
  7 
  shows 
  the 
  inside 
  

   of 
  an 
  old 
  tube 
  of 
  the 
  commensal 
  worm 
  Hicetes 
  innexus, 
  

   itself 
  incrusted 
  with 
  minute 
  worm 
  tubes. 
  

  

  Interesting 
  as 
  is 
  this 
  instance 
  of 
  commensalism, 
  its 
  most 
  extra- 
  

   ordinary 
  feature 
  is 
  the 
  amazing 
  evidence 
  of 
  selection 
  by 
  the 
  larval 
  

   coral 
  of 
  the 
  body 
  to 
  serve 
  as 
  the 
  base 
  on 
  which 
  it 
  is 
  to 
  grow. 
  I 
  have 
  

   stated 
  above 
  that 
  a 
  very 
  evident 
  majority 
  of 
  the 
  colonies 
  of 
  this 
  coral 
  

   Pleurodictyum 
  as 
  it 
  occurs 
  in 
  the 
  Hamilton 
  shales 
  are 
  attached 
  to 
  

   an 
  organic 
  object 
  and 
  that 
  this 
  organic 
  base 
  in 
  approximately 
  80 
  

   per 
  cent 
  of 
  the 
  cases 
  is 
  a 
  shell 
  of 
  Loxonema 
  hamiltoniae. 
  

   Occasionally 
  the 
  shell 
  may 
  be 
  a 
  Pleurotomaria 
  of 
  one 
  or 
  another 
  

   species, 
  I 
  have 
  no 
  record 
  of 
  its 
  being 
  any 
  other 
  than 
  one 
  of 
  these 
  

   gastropods. 
  On 
  the 
  other 
  hand 
  the 
  German 
  Pleurodictyum 
  

   problematicum 
  fixes 
  itself 
  by 
  decided 
  preference 
  to 
  the 
  brachi- 
  

   opod 
  Chonetes 
  sarcinulatus 
  Schlotheim. 
  I 
  have 
  ex- 
  

   amined 
  a 
  considerable 
  number 
  of 
  specimens 
  of 
  this 
  Coblentzian 
  

   species 
  but 
  have 
  seen 
  no 
  other 
  shell 
  used 
  for 
  attachment 
  nor 
  have 
  I 
  

   found 
  record 
  of 
  any 
  other. 
  Though 
  I 
  can 
  not 
  use 
  percentages 
  with 
  

   reference 
  to 
  the 
  frequency 
  of 
  this 
  occurrence, 
  this 
  palpable 
  fact 
  remains 
  

   that 
  as 
  between 
  these 
  two 
  closely 
  allied 
  if 
  not 
  identical 
  corals, 
  one 
  

   selects 
  a 
  gastropod, 
  the 
  other 
  a 
  brachiopod 
  as 
  its 
  base 
  of 
  attachment. 
  

   Emphasis 
  is 
  to 
  be 
  put 
  on 
  the 
  word 
  "selects" 
  for 
  among 
  the 
  brilliant 
  

   examples 
  of 
  selective 
  adaptation 
  none 
  could 
  be 
  more 
  striking 
  than 
  

   this. 
  The 
  floor 
  of 
  the 
  New 
  York 
  ocean 
  was 
  covered 
  with 
  Chonetes 
  

   and 
  of 
  the 
  German 
  ocean 
  with 
  gastropods 
  during 
  the 
  life 
  of 
  this 
  

   coral. 
  Were 
  either 
  wanting 
  in 
  the 
  other 
  fauna, 
  hundreds 
  of 
  other 
  

   species 
  of 
  organisms 
  lined 
  the 
  sea 
  bottom. 
  The 
  coral 
  was 
  not 
  de- 
  

   prived 
  of 
  its 
  choice. 
  

  

  