﻿J 
  5° 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  free 
  and 
  predatory 
  condition. 
  Once 
  the 
  dependent 
  habit 
  is 
  es- 
  

   tablished 
  the 
  capacity 
  for 
  reaction 
  grows 
  weaker; 
  degenerative 
  

   adaptation 
  creeps 
  still 
  further 
  back 
  in 
  the 
  life 
  of 
  successive 
  genera- 
  

   tions 
  and 
  the 
  degradation 
  of 
  the 
  adult 
  state 
  becomes 
  more 
  pro- 
  

   found. 
  

  

  The 
  all 
  pervading 
  conditions 
  of 
  symbiosis 
  and 
  dependence 
  in 
  

   living 
  creatures 
  are 
  largely 
  beyond 
  the 
  reach 
  of 
  our 
  present 
  in- 
  

   quiry. 
  We 
  are 
  endeavoring 
  to 
  seek 
  some 
  clew 
  to 
  the 
  origin 
  of 
  

   dependent 
  life 
  from 
  its 
  earliest 
  and 
  simplest 
  expressions. 
  The 
  

   parasitic 
  conditions 
  of 
  the 
  present 
  organic 
  world 
  are 
  complicated 
  

   in 
  the 
  extreme 
  as 
  a 
  result 
  of 
  progressive 
  and 
  easy 
  adaptation; 
  

   often 
  two, 
  three 
  and 
  sometimes 
  four 
  hosts 
  are 
  necessary 
  to 
  the 
  full 
  

   life 
  course 
  of 
  the 
  dependent. 
  Usually 
  these 
  present 
  extreme 
  con- 
  

   ditions 
  are 
  expressed 
  only 
  by 
  soft-bodied 
  terrestrial 
  organisms. 
  

   The 
  evidences 
  of 
  dependent 
  life 
  presenting 
  themselves 
  to 
  . 
  the 
  

   paleontologist 
  must 
  be 
  chiefly 
  of 
  marine 
  origin 
  and 
  wholly 
  adapted 
  

   to 
  a 
  single 
  host; 
  they 
  must 
  moreover 
  be 
  wholly 
  simple 
  in 
  their 
  

   expression 
  or 
  may 
  be 
  easily 
  misconceived. 
  There 
  are 
  certain 
  of 
  

   these 
  simple 
  expressions 
  of 
  long 
  standing; 
  we 
  find 
  them 
  in 
  existing 
  

   nature 
  and 
  the 
  ancient 
  faunas 
  show 
  that 
  such 
  associations 
  began 
  

   far 
  back 
  in 
  the 
  history 
  of 
  life. 
  To 
  some 
  of 
  these 
  we 
  shall 
  make 
  

   special 
  reference. 
  Besides 
  these 
  a 
  multitude 
  of 
  illustrations 
  of 
  

   dependent 
  and 
  attached 
  forms 
  of 
  organisms 
  can 
  be 
  drawn 
  from 
  

   every 
  hand 
  in 
  the 
  ancient 
  as 
  well 
  as 
  the 
  recent 
  faunas. 
  They 
  call 
  

   for 
  no 
  special 
  illustration 
  but 
  they 
  nevertheless 
  enforce 
  our 
  con- 
  

   sideration 
  of 
  the 
  origin 
  of 
  this 
  condition. 
  

  

  So 
  far 
  as 
  our 
  facts 
  go 
  there 
  are 
  but 
  few 
  evidences 
  of 
  true 
  parasitic 
  

   conditions 
  in 
  the 
  Paleozoic 
  faunas. 
  The 
  oldest 
  and 
  clearest 
  is 
  the 
  

   well 
  known 
  case 
  of 
  the 
  coalition 
  of 
  the 
  limpetlike 
  snail 
  Platyceras 
  

   and 
  the 
  crinoids. 
  The 
  snail 
  settles 
  down 
  at 
  an 
  early 
  age 
  on 
  the 
  

   dome 
  of 
  the 
  crinoid, 
  placing 
  the 
  aperture 
  of 
  the 
  shell 
  over 
  the 
  anal 
  

   vent 
  of 
  its 
  host 
  and 
  remains 
  attached 
  for 
  an 
  indefinite 
  period 
  of 
  

   its 
  subsequent 
  life. 
  

  

  It 
  is 
  clear 
  that 
  the 
  snail 
  depends 
  for 
  its 
  food 
  on 
  the 
  waste 
  from 
  

   the 
  crinoid 
  and 
  the 
  fact 
  that 
  it 
  remains 
  attached 
  for 
  a 
  very 
  con- 
  

   siderable 
  period 
  of 
  its 
  existence 
  is 
  shown 
  by 
  specimens 
  of 
  the 
  

   crinoid 
  dome 
  bearing 
  successive 
  scars 
  made 
  by 
  the 
  enlarging 
  

   growth 
  of 
  the 
  mouth 
  of 
  the 
  snail 
  shell. 
  Though 
  this 
  is 
  the 
  most 
  

   extreme 
  expression 
  of 
  ancient 
  parasitism 
  known 
  to 
  us, 
  it 
  was 
  

   evidently 
  of 
  a 
  very 
  elastic 
  kind 
  and 
  by 
  no 
  means 
  affected 
  all 
  indi- 
  

  

  