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  ANIMAL 
  BEHAVIOUR 
  

  

  determined 
  by 
  its 
  momentum 
  and 
  the 
  circumstances, 
  but 
  

   there 
  is 
  a 
  spice 
  of 
  unpredictability 
  in 
  the 
  ways 
  of 
  most 
  

   living 
  creatures. 
  The 
  unexpected 
  often 
  happens. 
  There 
  are 
  

   indeed 
  uniformities 
  of 
  sequence 
  in 
  the 
  reactions 
  of 
  organisms, 
  

   otherwise 
  no 
  science 
  of 
  behaviour 
  were 
  possible, 
  but 
  there 
  

   is 
  an 
  undeniable 
  appearance 
  of 
  free 
  agency. 
  It 
  is 
  inter- 
  

   esting 
  to 
  watch 
  under 
  the 
  microscope 
  the 
  Brownian 
  move- 
  

   ment 
  seen 
  when 
  minute 
  granules 
  of 
  sepia 
  or 
  the 
  like 
  are 
  

   jostled 
  hither 
  and 
  thither, 
  probably 
  by 
  the 
  invisible 
  ions 
  

   which 
  abut 
  against 
  them, 
  but 
  the 
  scene 
  changes 
  in 
  character 
  

   when 
  we 
  put 
  in 
  a 
  vigorous 
  unicellular 
  organism. 
  It 
  does 
  

   not 
  ' 
  take 
  charge 
  ' 
  like 
  a 
  gun 
  torn 
  from 
  its 
  attachment 
  on 
  

   board 
  ship; 
  it 
  commands 
  its 
  course. 
  Only 
  in 
  the 
  realm 
  of 
  

   organisms 
  is 
  there 
  true 
  behaviour 
  in 
  which 
  the 
  creature 
  

   is 
  an 
  agent 
  and 
  exhibits 
  a 
  correlated 
  or 
  concatenated 
  series 
  

   of 
  acts, 
  effective 
  towards 
  some 
  definite 
  result, 
  favourable 
  to 
  

   the 
  continuance 
  and 
  harmony 
  of 
  vital 
  processes. 
  

  

  There 
  are 
  two 
  master-activities 
  in 
  the 
  animal 
  organism 
  

   for 
  the 
  sake 
  of 
  which 
  life 
  is 
  worth 
  living 
  movement 
  and 
  

   feeling, 
  contractility 
  and 
  irritability, 
  the 
  functions 
  in 
  most 
  

   cases 
  of 
  the 
  muscular 
  and 
  nervous 
  systems 
  respectively. 
  

   These 
  master-activities 
  are 
  kept 
  agoing, 
  the 
  relevant 
  struc- 
  

   tures 
  are 
  kept 
  in 
  working 
  order, 
  by 
  the 
  other 
  everyday 
  func- 
  

   tions 
  of 
  nutrition, 
  circulation, 
  respiration, 
  excretion, 
  and 
  so 
  

   on 
  ; 
  never 
  forgetting, 
  in 
  connection 
  with 
  Vertebrates 
  at 
  least, 
  

   the 
  fundamental 
  trigger-pulling 
  and 
  regulative 
  function 
  of 
  

   the 
  organs 
  of 
  internal 
  secretion. 
  These 
  everyday 
  functions 
  

   are 
  the 
  pre-conditions 
  of 
  behaviour 
  ; 
  and 
  growth 
  and 
  maturity 
  

   may 
  also 
  condition 
  behaviour. 
  But 
  behaviour 
  itself 
  is 
  much 
  

   more, 
  it 
  means 
  that 
  the 
  organism 
  is 
  an 
  agent 
  and 
  that 
  it 
  

   exhibits 
  a 
  correlated 
  or 
  concatenated 
  series 
  of 
  actions. 
  

  

  