﻿ANIMAL 
  BEHAVIOUR 
  191 
  

  

  words, 
  what 
  is 
  commonly 
  called 
  in 
  higher 
  animals 
  intelli- 
  

   gence 
  ' 
  (Jennings, 
  1906, 
  p. 
  241). 
  In 
  many 
  cases 
  we 
  have 
  

   to 
  do 
  with 
  l 
  chain 
  reflexes 
  ', 
  one 
  phase 
  leading 
  on 
  to 
  another, 
  

   but 
  the 
  fact 
  is 
  that 
  " 
  in 
  most 
  cases 
  the 
  succeeding 
  phase 
  is 
  

   not 
  invariably 
  and 
  irrevocably 
  called 
  up 
  by 
  the 
  preceding 
  

   one 
  ' 
  (Jennings, 
  p. 
  251), 
  the 
  present 
  action 
  depending 
  upon 
  

   the 
  entire 
  physiological 
  state 
  of 
  the 
  organism, 
  which, 
  again, 
  

   is 
  determined 
  by 
  various 
  factors. 
  

  

  i/ 
  

  

  One 
  of 
  the 
  clearest 
  results 
  of 
  the 
  modern 
  study 
  of 
  the 
  

   behaviour 
  of 
  the 
  lower 
  animals 
  is 
  that 
  the 
  kind 
  of 
  action 
  de- 
  

   pends 
  greatly 
  on 
  the 
  physiological 
  state 
  as 
  a 
  whole, 
  which, 
  

   again, 
  depends 
  in 
  part 
  on 
  history 
  and 
  experience. 
  That 
  ex- 
  

   perience 
  can 
  be 
  enregistered 
  in 
  organisms 
  with 
  the 
  simplest 
  

   of 
  nervous 
  systems 
  or 
  with 
  none 
  is 
  certain. 
  Two 
  individual 
  

   Planarias 
  (small 
  ciliated 
  fresh-water 
  worms) 
  often 
  react 
  in 
  

   opposite 
  ways 
  to 
  the 
  same 
  stimulus. 
  What 
  they 
  do 
  varies 
  

   with 
  their 
  appetite, 
  their 
  freshness 
  or 
  fatigue, 
  their 
  recent 
  

   stimulation 
  and 
  degree 
  of 
  excitement, 
  and 
  their 
  history. 
  

   After 
  long 
  study 
  of 
  Planaria, 
  Professor 
  Pearl 
  concludes 
  that 
  

   " 
  it 
  is 
  almost 
  an 
  absolute 
  necessity 
  that 
  a 
  person 
  should 
  be- 
  

   come 
  familiar, 
  or 
  perhaps 
  better, 
  intimate, 
  with 
  an 
  organ- 
  

   ism, 
  so 
  that 
  he 
  knows 
  it 
  in 
  something 
  the 
  same 
  way 
  that 
  

   he 
  knows 
  a 
  person, 
  before 
  he 
  can 
  hope 
  to 
  get 
  even 
  an 
  approxi- 
  

   mation 
  of 
  the 
  truth 
  regarding 
  its 
  behaviour' 
  (quoted 
  by 
  

   Jennings, 
  1906, 
  p. 
  254). 
  

  

  If 
  a 
  reflex 
  be 
  an 
  invariable 
  reaction 
  to 
  a 
  given 
  stimulus, 
  

   then 
  there 
  is 
  much 
  more 
  than 
  that 
  in 
  the 
  behaviour 
  of 
  lower 
  

   animals. 
  For 
  different 
  answers 
  to 
  the 
  same 
  stimulus 
  may 
  

   be 
  given 
  by 
  the 
  same 
  kind 
  of 
  creature 
  or 
  by 
  the 
  same 
  creature 
  

   at 
  different 
  times. 
  The 
  answer 
  depends 
  on 
  the 
  organismal 
  

   condition 
  as 
  a 
  whole. 
  Moreover, 
  the 
  fact 
  that 
  stands 
  out 
  most 
  

   clearly 
  in 
  the 
  behaviour 
  of 
  the 
  lower 
  organisms 
  is 
  this: 
  

  

  