﻿ANIMAL 
  BEHAVIOUR 
  213 
  

  

  brainless, 
  ganglionless 
  starfish 
  already 
  referred 
  to. 
  And 
  our 
  

   inclination 
  to 
  be 
  parsimonious 
  in 
  our 
  interpretation 
  is 
  of 
  

   course 
  strengthened 
  by 
  the 
  fact 
  that 
  the 
  hermit-crab 
  belongs 
  

   to 
  the 
  i 
  little 
  brain 
  ' 
  type 
  of 
  organisation 
  on 
  quite 
  a 
  different 
  

   line 
  of 
  evolution 
  from 
  Vertebrates. 
  Many 
  spiders 
  are 
  read- 
  

   ily 
  deceived 
  if 
  a 
  vibrating 
  timing 
  fork 
  is 
  brought 
  near 
  their 
  

   web. 
  They 
  rush 
  out 
  to 
  deal 
  with 
  the 
  situation 
  responding 
  

   to 
  the 
  familiar 
  tremor 
  stimulus. 
  They 
  may 
  be 
  cheated 
  over 
  

   and 
  over 
  again. 
  In 
  one 
  case, 
  however, 
  after 
  a 
  tantalising 
  

   deception 
  extending 
  over 
  fifteen 
  days, 
  the 
  spider 
  ceased 
  to 
  

   give 
  any 
  attention 
  to 
  the 
  tuning 
  fork. 
  The 
  question 
  is 
  

   whether 
  we 
  must 
  in 
  such 
  a 
  case 
  postulate 
  memory 
  and 
  per- 
  

   ceptual 
  inference, 
  or 
  whether 
  some 
  purely 
  physiological 
  in- 
  

   terpretation 
  is 
  adequate. 
  Thus 
  the 
  ( 
  getting 
  used 
  to 
  ' 
  a 
  stim- 
  

   ulus 
  may 
  be 
  in 
  some 
  cases 
  due 
  to 
  fatigue, 
  in 
  the 
  wide 
  sense, 
  

   including 
  dulled 
  sensation. 
  Our 
  inclination 
  to 
  a 
  parsimoni- 
  

   ous 
  interpretation 
  in 
  such 
  a 
  case 
  as 
  this 
  is 
  strengthened 
  by 
  

   the 
  fact 
  that 
  even 
  brainless 
  and 
  ganglionless 
  animals 
  illus- 
  

   trate 
  a 
  modification 
  of 
  activity 
  by 
  individual 
  experience. 
  

   Repeated 
  stimulation 
  alters 
  ' 
  the 
  physiological 
  condition 
  ' 
  of 
  

   an 
  animal 
  so 
  that 
  it 
  gives 
  an 
  intensified 
  reaction 
  to 
  a 
  mod- 
  

   erate 
  stimulus, 
  as 
  in 
  the 
  case 
  of 
  an 
  earthworm 
  that 
  has 
  been 
  

   teased 
  a 
  little. 
  Contrariwise, 
  repeated 
  stimulation 
  that 
  leads 
  

   to 
  nothing 
  may 
  result 
  in 
  the 
  suppression 
  of 
  a 
  reaction, 
  as 
  in 
  

   sea-urchins 
  that 
  soon 
  stop 
  answering 
  back 
  to 
  fruitless 
  changes 
  

   in 
  light 
  and 
  shade, 
  or 
  in 
  sea-anemones 
  that 
  cease 
  to 
  respond 
  

   to 
  the 
  touch 
  of 
  false 
  food. 
  Even 
  the 
  carnivorous 
  plant, 
  

   Venus's 
  Fly 
  Trap, 
  refuses 
  to 
  be 
  duped 
  many 
  times 
  in 
  suc- 
  

   cession. 
  

  

  One 
  of 
  the 
  marks 
  of 
  intelligence 
  is 
  profiting 
  by 
  experience 
  

   learning. 
  At 
  a 
  lower 
  level 
  there 
  is 
  temporary 
  modification 
  

   of 
  behaviour, 
  and 
  this 
  passes, 
  insensibly 
  -we 
  think, 
  into 
  last- 
  

  

  